Mineral is defined as a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not have a specific chemical composition. Mineral resources of India are sufficiently rich and varied to provide the country with strong industrial base. The country is particularly rich in metallic minerals of the ferrous group such as iron ores, manganese etc. It has the world largest reserves in mica and bauxite. In the field of extractive metallurgy, mineral processing, also known as mineral dressing or ore dressing, is the process of separating commercially valuable minerals from their ores. Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body; the term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, limestone, etc. There are three methods of mining; conventional or manual mining, semi mechanised mining and mechanised mining. Geopolymerisation is the processes which can transfer large scale alumina silicate wastes into value added geopolymeric products with sound mechanical strength and high acid, fire and bacterial resistance. One of many useful applications of geopolymerisation is the immobilization of heavy metals and radioactive elements. The production of non ferrous metals from natural mineral ores is, in general, highly energy intensive. Some of the non ferrous mineral sources are bauxite, granite, magnesite, limonite etc. Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO3). Limestone processing includes several steps; primary crushing (jaw crusher, gyratory crusher, impact breaker), secondary crushing (cone crusher), fine grinding and pulverization, conveying, screening, washing, heavy media separation, optical mineral sorters, drying and storage. The non metallic mineral mining and quarrying industry segment covers a wide range of mineral extraction. Most of these minerals are found in abundance close to the surface, so underground mining is uncommon in this industry segment. Mineral resources of India are sufficiently rich and varied to provide the country with strong industrial base. The country is particularly rich in metallic minerals of the ferrous group such as iron ores, manganese etc. It has the world largest reserves in mica and bauxite.
This book basically deals with methods of mining, mining machineries, geopolymerisation of mineral products and waste, industrial and scientific aspects of non ferrous metals production, processing of alumina rich Indian iron ore slimes, limestone processing, limestone exploration and extraction, the mineralogy of asbestos, the use of asbestos and asbestos free substitutes in buildings, flotation column ;a novel technique in mineral processing, applications of thermal plasma in the synthesis of covalent carbides, nitrogenous fertilizers, manufacture of ammonium bicarbonate etc.
This book is designed to describe the details of mining and processing of different minerals like alumina rich iron ore slimes, conversion of waste to a high valued product, lime stone, asbestos, coal beneficiation, gravity concentration processes to recover values from coal and ore fines and many more. The book is meant for everyone who wants to study about the subject or wants to venture into the field of mineral processing.
Production of blocks of large
sizes and weight is a special feature of granite mining. As such the
quarrying for granite as well as equipments used for the purpose differ
considerably from those applied in normal mining of other ore deposits.
means which cause fragmentation and irregular shape of mined out
for the sake of higher recovery will be miserable.
Granite mining is essentially
by open cast quarrying. Efforts are made to select a deposit showing
features concerning hardness, colour shades and textures preferably
spaced vertical and horizontal joints. These favourable features make
granite simpler and easier. In few countries it is customary to mine
and then split them into sizeable blocks as per size requirement of the
Normally deposits with little
or no over burden are preferred. In case over burden covers a potential
it has first to be removed by drilling 30 to 60 cm deep holes of 5 cm
followed by blasting. Boulders which can yield marketable blocks, if
over burden, are transported and dumped separately for sizing and
other boulders are removed and thrown in the waste dump. The exposed
carefully examined for its suitability to produce large blocks.
portion is drilled to a depth of 30 to 60 cms, blasted and removed to
yard. The in situ rocks mass found suitable is marked for splitting
blocks. If joints are present holes are drilled into joint to a
usually controlled by horizontal joints and charged to an optimum level
blasted. In case no joints are present, series of holes are drilled
chosen line of splitting at interval of 15 to 20 cms upto 30 cms depth.
Feathers and wedges are inserted into the holes and carefully hammered
calculated sequence so that the block splits along the line.
The horizontal joint – planes
help in dislodging the block at its base. The splitting of blocks is
done by taking advantage of the rift and grain. The block is then
dressing yard where it is dressed to required size and shape.
In respect of mining of the black
granite, a greater
precision and careful examination of the rock has to be made. In course
dressing of the block sometime careful examination reveals that the
hair cracks and other defects like presence of white lines, etc. As
blocks are rejected leading to poor recovery of desired sizeable blocks
total mined volume.
The opening of the quarry is done
by cutting first a
trench across its face towards the inner body. Another trench is cut at
angle to the first one and thus two long free faces are developed as
in plate No. IV. The first range of blocks is to be recovered from
trenches. After this preliminary operation, the blocks are mined by
regular holes along chosen lines as stated above and splitting of them
these lines. The purpose of this drilling system is to relieve the
hard toil, ensuring the best straight alignment of the range of holes,
splitting the blocks becomes easier with sharply reduced use of
consequently lower rate of granite wastage.
Granite quarrying as stated above
involves removal of over burden and waste rock from quarry, drilling,
splitting, lifting transportation and dressing of the blocks. These
require certain amount of mechanization at some stage or the other.
machines like compressor with jack hammer for drilling, cranes for
lifting and loading the heavy blocks, shovel for loading of waste dump,
dumpers/dump trucks for transportation, diamond wire saw for recovery
shaped blocks from in situ rock body are required for good output from
mine. Failure to invest adequately in equipments often leads many mines
to poor returns or even losses.
The nature and quantity of
machinery required for mining of granite blocks will depend on the
capacity of the mine, determined while planning and preparing the
report. For example, to have a limited number of blocks for meeting the
domestic requirement of a small processing plant (generally a tile
manufacturing plant) a compressor with jack hammer drills having
for line drilling coupled with few sets of pegs and feathers, chisels
crowbars will be sufficient. For the purpose of lifting and loading of
block, provision may be made for a chain pulley block having 10 tonne
On the other hand, for a medium to large size quarry producing sizeable
mainly for export, various kinds of equipments will be required to be
various stages of mining operation.
The major stages involved in
granite quarrying and the machinery used for the same are as follows
of mining faces This is done by using shovel and
bulldozers, which remove the over burden
or weathered rocks covering the deposit. For preparing the two long
at right angle to each other flame jet burner is used to make two
slots some 10 cms wide.
Compressor (12 cu. mt/min. air delivery) and jack hammers with
line drilling are required to make holes at the interval of 15 to 20
chosen lines. Pegs and feathers are inserted in these holes and
hammered in a
calculated sequence for splitting of the blocks. After cracks are
hydraulic jacks are used to push the bigger blocks away from their
mass, whereas a dragging winch is used to pull the blocks away from
faces. To prevent air pollution, dust collectors are used at the time
drilling the holes. Recently diamond wire saws have been developed to
blocks from insitu rock mass.
Chain pulley blocks (10 to 15 ton capacity) or more commonly fixed or
cranes (20 to 30 ton capacity), are used for tilting, lifting and
the blocks. These cranes also remove the rejected blocks or mine wastes
quarry faces. To effect this operation rejects are loaded on a wire mat
strong loops on four corners which are put into the dragging hook of
attached with the boom for throwing the quarry waste away from mining
or dressing of blocks After the blocks are detached
from their mother rocks, they are shifted from quarry faces to dressing
Commonly dressing is done to have well shaped blocks free from
depressions by making use of pitcher hammers (Fig. 5), and chisels of
sizes. In well equipped mines squarring of the blocks is done by using
plants to have perfect flat walls of the blocks.
Transportation To transport the blocks from
mine site to processing plant, lorries and trucks are utilized. For
blocks are put into the containers placed on the lorries and are
with containers by shipping.
Methods of Mining
1. Conventional or Manual
Linear vertical drilling along
chosen lines and wedge
splitting by manual method is the most common procedure of granite
Rocks having desired quality are selected from among the rock
Overburden, if any, is removed and fresh rock are exposed and checked
suitability. Drilling and channelling are done by hand using chisels
hammers. Blocks as well as slabs of desired sizes are then cut from
faces. Vertical joints if well spaced, rifts and grains. If any, are
for splitting the blocks. Horizontal joints, which are called
used for dislodging the blocks at their base.
In course of quarrying the grey or
pink granite the
rock is at times heated by burning wood, charcoal or dry grass along a
particular line. The heat generated splits the rock along that line and
workers job easier. To avoid development of cracks in unwanted
generally very little blasting is done. To dislodge the bigger blocks,
charging of linear holes with gun powder and controlled blasting using
is done in the few quarries. The granite blocks recovered from the
is lifted manually with levers and taken to the dressing yards by
same on wooden logs by using crow bars as lever.
The recovery of black granite
blocks from a quarry
varies from 10 to 15% whereas those of grey or pink, granite from 30
Recovery depends mostly on the nature of the deposit and technique of
Semi mechanized Method
The manual method of granite mining
is labour intensive
resulting into high production cost. The recovery of material in
may be enhanced with aided equipments like air compressor and jack
high capacity derick cranes. For transportation of quarry wastes away
mine, a couple of trucks or dumpers may be provided in which loading
unloading can be done by manual means. The same trucks or dumpers can
utilized for carrying the finished blocks from mine to processing
blocks dislodged from the parent rock can be manually dressed to
and sizes. Provision of a quarry bar will facilitate rock cutting in a
line and at right angle avoiding a lot of wastage obtained by drilling
manually held jackhammers.
As stated on the foregoing
chapters, for a granite
quarry having capacity production of 1500 and 2000 m3 per
annum, mechanization will be
required at various stages of activities like face development,
wedge splitting, handling, squaring or dressing of sizeable blocks etc.
Involvements and utilization of various kinds of equipments for
mining of dimensional blocks of granite have already been described in
Para. In some of the countries complete range of machineries for
handling of granite blocks are manufactured and supplied to quarries
accelerated production of desired blocks. An illustration of such
and procedures with the help of which well selected and well shaped
blocks of export quality are extracted is attached as Plate I.
After overburden lying on the
deposit is removed with
the help of proclain, dozer or pay loader, two long free faces are
faces are vertical and situated at right angle to each other. Thus if
deposit occurs above ground level, more than one mining benches can be
prepared. Preparation of such mining benches will involve drilling,
and throwing away of superfluous materials part of which may also
smaller size granite blocks. The vertical faces having flat walls can
developed either by jet flame channeling (Mch. 3) or by drilling series
holes along selected lines at the interval of 15 or 20 cms with the
help of of
pneumatic drills (Mch 3) followed by splitting of the peripheral blocks
the help of pegs and feathers (Mch. 2) and also by controlled blasting
powder. After the faces are ready series of holes are drilled along
lines and bigger blocks are detatched by wedge hammering in a
sequence. After the cracks are formed, hydraulic jacks are used to push
blocks on a kind of cushion made of smaller fragments of quarry wastes.
bigger blocks are then dragged away from mining face with the help of
winch and further split up into sizeable blocks of the size
quoted by the buyers. Such blocks are then dressed by skilled cutters
commonly by bush hammering and flaming machines and shifted by cranes
yards for final checking and dispatch.
According to the latest technique
of granite mining,
modern methods like jet channeling, flame cutting and various
diamond saws, etc., are being used in few countries for their quarries
high production capacity. Through these latest techniques of mining,
of the desired granite blocks is remarkably higher, the wastage of
being considerably low. On the other hand, well shaped blocks are
produced in a
shorter time to ensure better margin of profit.
Mining of other decorative Stones
Other stones, which are extensively
construction and decorative purpose, are marbles, sand stones, slates,
calcsilicates, limestones, etc. of various shades and colours. Most of
flaggy in nature and are quarried mostly by manual means. Except
are generally massive and compact, the mining techniques for all other
stones are almost similar. In respect of marbles the mining methods
similar to those used for granite.
A case history related to mining of
Rajasthan highlights the quarrying procedures applicable to all other
A cushion bed with 1 to 1.5 m
thickness is left
between over burden and productive (splitable) zone to avoid any damage
layers due to deep hole blasting. This cushion bed is broken manually
handled manually. Where it is too compact, it is shattered by small
Mining of productive bed is totally
manual and stones
of desired sizes are extracted with the help of chisels, hammers and
Slabs are split up along cleavage planes and are dressed into regular
dimensions. Channels/recess to a depth of 8 cms are cut manually to
edges from where the layers can be splitted.
The wastes recovered in course of
mining are loaded
into trucks or dumpers and thrown into the dump yards. The useful
stacked as per size and thickness into stock yard or directly sent to
siding or polishing units for further dressing, polishing or edge
recovery from production zone varies from 40 50%.
The annual production from 55
mining leases stands at
about 10 million m3 engaging
about 20,000 labourers in mining, polishing,
transportation and dispatch of Kotastone, Rajasthan.
Before opening a
mining face the layer chart is prepared precisely to decide upon the
ratio and thereby the profitability.
Conservation and Safety
Like other minerals, decorative
stones are also a non
renewable commodity. Good black granites in particularly have very
reserve. As such the following steps should be taken to conserve them
Adoption of modern method of mining
permitting higher recovery and lower wastage of the material.
Utilization of smaller blocks for tile
manufacture. In many of the South Indian States smaller blocks are
as mine wastes.
Use of even second grade material to
meet the domestic requirements.
Taking up R & D work indigenously
to evolve a solution, which can treat the hair cracks on account of
blocks are rejected and thrown away as mine waste. In Italy cementing
are used to join the cracks.
There is a general practice to work
for only such deposits, which are occurring above ground. This permits
profitability for the mine owner because working below ground and below
table involves higher cost of production. Rigid implementation of
legislative measures for working below ground, will go a long way to
this valuable scarce natural resource.
The provisions of the M.M.R.D. Act,
the Indian mines
Act and the Rules & Regulations made therein apply to the mines
Proper attention has to be paid to the following
Mining benches be prepared in such a
that it takes care of fundamental safety requirements.
use of wedges for splitting the blocks may injure the worker due to
course of hammering. As such the wedges should be tied to each other
wire or linear holes after insertion of wedges be filled up with sand
dust to avoid jumping of the wedges.
workers driving the wedges into the holes should never stand on the
being split. If a large block is being reduced to smaller size blocks
former be stabilized before a worker mounts on it.
driving the wedges, neighbouring workers should maintain a safe
avoid injury by flying rock splinters, goggles with shatter proof glass
safety shield between adjacent workers be provided to minimize the
worker should be allowed to push away the separate block from mother
blasting the rock with light gun powder all safety rules should be
The cranes and all other
machineries deployed at
quarry must be operated in accordance with the relevant safety
For safe handling of the large blocks the crane should never be loaded
excess of its rated capacity or its stability limit.
or other decorative stones attain their importance and beauty only
processing. Carving and processing of stones in India and abroad are in
practice since the dawn of civilization. Some of the most spectacular
of architecture have been oriented with stones. The great wall of
pyramids and leaning Tower of Pisa, statue of Gomteshwar, Vidhan Sabha
Bangalore and stone chariot at Humpy, Karnataka, Vivekanand rock
Kumari, etc. are the significant examples. Our ancestors have developed
unique style and pattern of chiseling, carving and polishing to give
to lifeless stones. However, the ancient processing of stones was crude
of sophisticated machineries for sawing, polishing and edge cutting
processing of granite slabs of large sizes and mirror finish, the stone
industries have attained a new height in recent past creating a boom in
international as well as domestic market.
recovered from a mine are sawn into various sizes, shapes and
suit the requirement of the users. With the help of diamond saw it is
possible to cut thinner slabs and tiles with mirror finish for the
wall cladding and such others uses.
Processing of granites broadly
involves four phases of
activities, viz. (i) final dressing of the block, (ii) sawing or
polishing and finally (iv) edge cutting and polishing of edges. These
activities were in the past carried out mostly by manual methods. But
methods are more prevalent.
In the early years cutting and
dressing of granite
block used to be mostly manual or sometimes with the help of wire saws.
Grinding and polishing was also manual, which used to be done by
specially, trained for the purpose. The process used to be very slow
consuming. Subsequently the process was replaced by crude form of
machineries operated manually or partly manually. The abrasives used
The crude block or slab received
from the quarry site
is dressed with chisels and hammers. Such blocks are generally 2 to 5
oversize of the net volume for which prices are paid to quarry owners.
material lost in course of finely dressing to get almost a perfect
block is well compensated for by higher value. Polishing is done either
of the six faces or all the faces according to the requirements of a
In the former case only the face to be polished is first dressed and
to polishing. In the latter case, all the faces are finely dressed and
subjected to polishing. After flat surface is obtained by rough
face is made more even and uniform by fine chiseling which is a
of minutes equispaced and dense depressions almost of equal size caused
light strokes from a chisel point. The face is now ready for grinding.
worker takes 10 to 12 hours to dress one square foot area.
Manual polishing is done by rubbing
the stone with
rough surfaced iron plates with polishing media like steel shots,
powder and tin oxide. Fragmented steel shots are employed in initial
followed by carborundum powder of diminishing grit sizes starting from
At the end tin oxide is used to get a mirror like finish. Polishing of
sq. ft. granite surface requires about 14 hours to obtain glazed
this method of manual polishing is obsolete. Only sides of slabs are
Engraving of pictures and
inscribing letters on polished
surface is done even now by skilled craftsman by using pneumatic
or by applying sand blasting techniques. (Sand blasting film – cutting
required pattern on the film and then exposing the pattern to a sand
method the entire processing inclusive of sawing, polishing, edge
chamfering is done by machines of different designs and capacities.
dressing or squaring of the granite block before it is subjected to
done by block dressing machine, which increases sawing capacity upto
reduces the cost of slicing irregular materials over the undressed
the block. The Process flow sheet for cutting and polishing of granite
Sawing or slicing is a
process by which granite blocks are reduced to monument, slabs and
varying thicknesses suiting the requirement of the buyers. In size it
from a small tile slicing plant to a giant monument or slabs sawing
various kinds of sawing machines are described as under
Wire saw This has a continuous length
of wire running over pulleys which is used as a cutting tool. Silicon
or steel shots mixed with water are used as cutting media. Wire saws
although cheaper are not capable of yielding a high rate of production.
advantage to wire sawing is that it produces a smooth cut which
subsequent dressing cost. However, its disadvantages are low rate of
production, increasing cost of loose abrasives and frequent changing of
Diamond wire saw is improved
version of the usual wire saw machine. In this case the loop of wire is
with diamond bound steel beads to provide accelerated cutting action.
pulleys provide proper wire contact length with the drive wheel and
vibration of the wire while cutting the stone.
The Italian Diamantfil
manufactured by Pellegrini which is a fixed plant for squaring and
the blocks of granite and other similar type of stones with diamond
wire, has the
same device of wire sawing. The rigidity of structure together with the
feed control system and the absence of vibration allows the machine to
surfaces of the maximum precision and planarity. Once cutting has been
the machine can work without an operator since the down feed control is
automatic while a series of safety devices stop the machine in the case
insufficient water supply, a break in the wire or the completion of the
Gang saws there are various types of
gang saws with oscillating motion for slicing the granite blocks in
abroad. The gang saws of Carl Meyer, West Germany being used by TAMIN
Nadu Mineral Corporation) and MML (Mysore Mineral Limited) can take 30
blades. Steel grit circulated with a slurry of lime water acts as
media. The rate of down feed is 4 cms/hr and power requirement is met
with by a
10 HP motor. A few of the Italian gang saws have provision for 100
which requires main motor of 30 HP and auxiliary motor of 8.75 HP.
with 80 blades is operated by a 25 HP main motor. The main advantage of
is higher production and the fact that it can saw larger granite blocks
produce large monuments and slabs to fetch higher value. Further, to
saw the slabs
of 20 mm thickness, steel shot gang saw is found to be most economical.
Circular saws Circular saws are by far the
most commonly used equipments for sawing of granite or marble blocks.
the depth of cutting, circular saws with variable diameter are in use.
A typical circular sawing
machine consists of a stable heavy machine gantry which moves
vertically on two
robust machine columns. On the gantry guide, the circular saw is fixed
vertically so as to slide from one end to the other. The machine is
computerized control panel which helps automatic monitoring of the
stages of sawing. Depending on the hardness of the rock, required
the slabs/tiles and the size of the block, various parameters of sawing
speed of horizontal movement of the saw, the RPM of the circular blade
down feed etc. are to be adjusted. All these parameters can be fed to
system in advance through the control panel for automatic control and
of sawing. Lifting of the blade and positioning of the block for the
is also achieved by programming through the control panel. Water of
pressure is used as coolant and is supplied to the machine with a pump.
The granite blocks are placed
on the block carriage cemented firmly to the carriage trolley with
Paris moved on rails underneath the blade and positioned suitably. For
life of the blade, peripheral RPM of the blade and the rate of down
feed are to
be controlled properly. Higher rate of cutting may be had at the cost
life of the blade. Circular block saw are mainly used for slab cutting.
Depending on the nature of the rock the rate of cutting varies from 0.9
sq meter per hour.
Yet another type of machine
manufactured indigenously by Shah Granite, Bombay, saws the blocks
with half of the block sawn from one side and another half from the
The machine has a total power requirement of 110 HP. Each saw has a
1.35 m. Since the horizontal slicing machine requires much smaller saws
thinner diamond segments, the tool cost and material wastage is
lower than the vertical block saw required to cut the same size granite
Further, since sawing is effected from two opposite sides
production rate is also higher. However, the main drawback with such
machine is the step caused by the deviation of the saw. However, as
by the manufacturer of this type of machine, the deviation of the saws
sawing of a hard stone like granite is inevitable, irrespective of the
whether slicing is done by horizontal saw, vertical block saw or steel
gang saw. The basic reason for the deviation of the blade is the
normal load (bucking load) on the saw, which tends to bend the saw. In
a horizontal slicing machine this deviation results in a slight stop in
center, which can be removed easily. In case of a vertical block saw
deviation of the blade does occur. However, instead of leaving a step
center, it results in a taper or in other words non uniform thickness
slab. In the case of a steel shot gang saw, the blade also deviates
in unequal thickness as well as an adulating surface. As such deviation
the sawing of hard granites cannot be completely eliminated but at best
be reduced to an acceptable level by using a good sturdy machine, good
and efficient operation of machine.
One of the Automatic block
sawing machine (fixed and portable type) manufactured by Fickert
Winterling, West Germany, has the following description.
The machine consists of the
bridge on which the saw carriage runs with rise and fall rest. The
the fixed type is mounted on two lateral foundation walls. The machine
with a portable block carriage. The bridge of the portable type runs on
The sturdy steel bridge is designed
in such a way in
order to reduce self induced vibrations. The inverted V guides are
hardened stainless steel strips. These strips are wear resistant and
The bridge of the portable type is
movable by sturdy
cast iron travelling devices on precision rollers. The bridge runs on
beams being equally covered with stainless steel strips. The
exact guidance of the bridge is effected by rack and pinion drive on
sides. A brake prevents the bridge from being shifted during the cut.
The saw carriage is made of cast
iron and runs in the
inverted V guides of the bridge on hardened, adjustable precision
feed of the saw carriage is effected by a special lead screw, driven by
infinitely variable D.C. motor with speed reducer.
and fall rest
The rise and fall rest runs in
amply dimensioned dove
tail ways with hydraulic control and self adjustment. Strong and
released disc springs warrant a connection between the saw carriage and
rise and fall rest absolutely free from play. This kind of vertical
is sturdy and insensitive. Its advantage in comparison with the
adjusting mechanism by lead screw and nut consists in the very poor
allows both a very sensitive and a rapid adjustment. Moreover, the rise
fall rest is equipped with a scale and easily adjustable stop dogs for
switches limiting the upper and lower position of the saw blade.
The work spindle runs in
precision ball and roller bearings. It is driven by a three phase A.C.
with speed reducer. The gears of the speed reducer are ground or shaved
in oil bath.
A variable speed drive unit
would have the disadvantage that an over dimensioned motor with an
current demand would be required for the low speed of the sawing
The complete electrical control
units including the
control buttons for the machine, is incorporated into the control desk
one of the machine foundations.
In order to allow the
operator to be close to the block when setting, an additional pendant
The machine may be equipped with a
very sturdy block
carriage, made of steel. With its four sturdy rollers running in roller
bearings, the carriage runs on rails.
With the fixed type, the lateral
displacement of the
block carriage within the machine can also be effected by self braking
driven gear and rack and pinion on both sides. For the exact
positioning of the
block carriage, the automatic displacement is effected by quick and
approach. The block carriage is clamped in its respective working
The machine may be equipped with an
sequence control of cuts. The required width of each plate, even of
size may be pre selected. After each cut, the saw blade moves upwards
the block, and the block carriage is displaced by the pre selected
After the last cut, the machine is
protection of the main motor by under voltage relay.
protection of the saw blade by contact ammeter. When the saw blade is
overloaded, e.g. by a faulty set, rate of cutting depth or rate of
rise and fall rest moves upwards until the overload will disappear.
against undue idle run by contact ammeter. In case of idle run of the
of about 10 minutes, due to a trouble of the automatic control, the
against falling off in speed (jamming protection). When the speed falls
below ca. 50% of the lower spindle speed, the machine is stopped.
against the interruption of the water supply by a control pressure
stops the machine as soon as the water pressure falls below the
The original colour and pattern of
a natural stone
become apparent only after polishing. The sawn surface of stone is
manually or mechanically in stages by making use of various grinding
polishing media. Steel shots/grits or rough carborundum powder is used
rough polishing, which is followed, by medium and fine carborundum
silicon carbide. Emery powders are used in the next stage and finally
finish is obtained by using tin oxide. The last stage of operation is
known as buffing. A series of polishing heads arranged in a straight
the rigid beds make up the nonstop polishing machine. Polishing discs
mild steel copper or lead are common. Segments or bricks, of abrasive
are often used in sophisticated polishing machines.
The consumption of polishing
media and time involvement will depend on the area to be polished as
extent of required finish of course, operational techniques and
observed during the same together with quality of polishing media
different degree of finish in different types of stone also play
The types of polishing
machines, which are commonly in use, are single head polishing machine,
polishing machine and hand polishing machine.
Single Head Polishing Machine The machine generally used for
polishing of monuments consists of a cross bar which moves horizontally
paralleled toothed rails on side walls. The cross bar carries the
could slide perpendicular to and simultaneously with the horizontal
the cross bar. Depending on the stages of grinding or polishing
of grinding or polishing heads are fixed to the head of the spindle.
movements of the cross bars and the spindle are pre adjusted with the
electric motors provided for the purpose. The system can work in
semi automatic mode. Electric switches and censors monitor control
activities of the system. Water is used as coolant to minimize the wear
tear of the polishing head as well as to achieve the even polishing of
surface. Generally the length of tract is about 5 m and effective
width is about 2 m depending on the nature of the rock, rate of
polishing varies from 1.5 to 1.75 sq m per hour.
Line Polishing Machine This machine is used for slab
polishing in big processing plant. This consists of 6 to 8, sometimes
spindles arranged in a line. Spindles are mounted in pairs on separate
and slide along the cross bars in opposite direction from side to side.
the single head polishing machine the cross bars containing spindles do
The slabs to be polished are
placed on a continuous conveyer belt, which moves below the row of the
with approximate rate of 0.1 to 0.5 m per minute. The stages like rough
smooth grinding, rough polishing, fine polishing, buffing, etc. are
from one end to other by using polishing heads containing different
grinding and polishing media. Every pair of spindles is controlled by a
separate control board and the entire process, i.e. feeding the slabs
polishing is fully automatic. Roller conveyers are provided at input
ends to facilitate proper loading and unloading of slabs. The grinding
ranges from 1.6 m to 1.8 m. The thickness of slabs to be processed
minimum 20 mm to maximum 250 mm. The production capacity is about 20 sq
Hand polishing machine In this machine the
polishing arm having the spindle carriage and the grinding wheel
attached to it
is moved manually over the surface to be polished. The spindle head
means of electric power. This machine is generally used for polishing
blocks, which cannot be polished in the single head automatic machines.
polishing machine, grinding head can be raised to required height. Thus
blocks of any height, which cannot be accommodated in single head
machine, can easily be polished by hand polishing machine. Blocks
up to 5.5 meters and width of 2.5 to 3 meters can be polished with this
machine. It is a versatile machine, which can do a lot of work, which
expensive to do on the automatic machine. The quality of polish depends
skill of the operator. Since the machine has only one polishing head
operated manually the production is limited.
different types of polishing discs which are in
use, are made of cast iron mild steel copper and lead. The diameters of
discs reduce with stages of polishing from coarse to fine. For initial
grinding and polishing keeping steel shots as grinding media generally
iron or mild steel discs having diameters from 15 to 30 cms are used.
subsequent stages discs having diameters from 12.5 to 10 cm are used.
polishing copper discs with 7.5 to 20 cm diameter are utilized. In the
polishing stage lead discs having diameter from 7.5 to 12.5 cm and
from 3 mm to 6 mm are used. Out of all the polishing head the most
satellite head, which is also known as planetary head. The second one
rocking head, which is also known as fickert type oscillating head.
these have their advantages and disadvantages. The planetary type
rapidly and also gives well polished surfaces. However, since it is
grinding head it needs frequent maintenance. On the other hand rocking
simpler and cheaper to maintain. Most of the stone processors prefer
There is yet another device to
grind the granite
surface which is known as diamond grinding plates which grinds the
granite very rapidly. However, they are used when larger production is
to justify higher fixed cost. Further the diamond grinding plates are
to use. Further the diamond grinding plates are costlier to use, and it
required when surface of the sawn slab is not flat.
Polishing media The quality of
polishing as well as
time taken for the same depends to a large extent on the abrasives
The abrasives for stone industry consists mostly of silicon carbide
a magnesite bound. The abrasives are apparently very easy to
manufacture. It is
for this reason that a large number of stone processors in India
their own abrasives. A good abrasive will grind faster and will give
quality of polish. In Europe, there are firms specializing in the
of abrasives and rarely does a granite processor make his own abrasive.
GEOPOLYMERISATION OF MINERAL PRODUCTS AND WASTE
PRINCIPLES OF GEOPOLYMERISATION
Since 1978 Joseph Davidovits has
to semi crystalline three dimensional alumino silicate materials, which
called geopolymers (mineral polymers resulting from geochemistry).
Geopolymerisation involves a chemical reaction between various alumino
oxides (Al3+ in
IV V fold coordination) with silicates
under highly alkaline conditions, yielding polymeric Si O Al O bonds,
be presented schematically as follows
The above two reaction paths
indicate that any Si Al
materials might become sources of geopolymerisation. According to
geopolymeric binders are the amorphous analogues of zeolites and
similar hydrothermal synthesis conditions. Reaction times, however, are
substantially shorter, which results in amorphous to semi crystalline
compared with the highly crystalline and regular zeolitic structures.
electron diffraction analysis conducted by Van Jaarsveld, Van Deventer
Schwartzman showed that the structure of geopolymers is amorphous to
The exact mechanism by which geopolymer setting and hardening occur is
The formation of geopolymeric
materials follows much
the same route as that for most zeolites, i.e. the three main steps are.
Dissolution, with the formation of
precursors through the complexing action of hydroxide ions
Partial orientation of mobile
well as the partial internal restructuring of the alkali polysilicates
Reprecipitation where the whole
to form an inorganic polymeric structure.
As shown by Figure 1. the main
zeolite formation and geopolymerisation is the solid to liquid ratio in
initial reaction mixture. It is thought that for a solid to liquid
greater than 0.1 the mobility of species within the reaction mixture is
impaired. Consequently, the Si and Al containing species described by
Davidovits are unable to successfully form on ordered crystal structure
(indicative of zeolite formation) before hardening of the mixture
REACTION MECHANISMS AND MATERIAL PROPERTIES
It appears that an alkali metal
salt and/or hydroxide
is required for dissolution of silica and alumina to proceed, as well
the catalysis of the condensation reaction. In alumino silicate
silicon is always 4 co ordinated, while aluminium can be 4 or 6 co
It is possible that the coordination number of aluminium in the
materials will have an effect on its eventual bonding in the matrix. A
reactive intermediate gel phase is believed to form by co
individual alumino and silicate species. Little is known about the
this gel phase and the extent to which the nature of the starting
the actual concentrations in solution are affecting the formation and
of this gel phase. A major experimental problem is that the gel phase
frozen and then analysed to observe the evolution of its composition
texture. Moreover, the dissolution step that takes place under highly
concentrated conditions cannot be isolated in order to study this
the absence of a shifting equilibrium due to gel setting.
In order to enhance the
understanding of dissolution
mechanisms of Al Si minerals in highly alkaline environments. Xu and
Deventer performed ab initio Restricted Hartree Fock calculations on
geometries of a five membered aluminosilicate framework rings cluster.
dissolution mechanism of the five membered Al Si framework rings model
highly alkaline solution has been revealed to consist of an ion pairing
reaction and an interaction between the remaining broken ring cluster
MOH, where T represents Al or Si and M represents Na+ or
K+. The sodium cation gives a
stronger ion paring effect, which results in
a higher exothermal dissolution energy when the five membered rings
dissolves in NaOH compared with KOH solution. As a result, the sodium
stabilize the remaining broken ring structure better than the potassium
Consequently, in geopolymerisation NaOH solution is expected to give a
extent of dissolution of Al Si minerals with a five membered ring
to supply a better initialization as well as faster gel formation.
It is well known that geopolymers
mechanical properties, fire resistance and acid resistance. These
make geopolymers a potential construction material, which has attracted
deal of attention internationally in the past twenty year. Geopolymers
been used in products such as bricks, high strength tools, high acid
moulds, ultra high efficiency filters, high temperature resistance
materials, protective coating materials, water and fire resistance
materials and lightweight thermal insulation materials. Although
applications of geopolymers are limited at present, a recent increase
research and development activity could facilitate the wider acceptance
In previous papers many Al Si
containing source materials such as building residues, flyash, furnace
pozzolan and some pure Al Si minerals and clays (kaolinite and
have been studied. In fact, some research results have already been
successfully in industry to substitute traditional cement. These
not consider the mineralogy or paragenesis of the individual minerals.
subsequent study, Xu and Van Deventer (2000b) determined the solubility
selected Al Si minerals in alkaline medium and their propensity to
geopolymerise. It was shown that the interrelationship between
reactivity of individual minerals is extremely complex, and that
research is required. More than 65% of the crust of the earth consists
of Al Si
materials, so that it is most useful to understand how individual Al Si
minerals geopolymerise. Such information will enhance the
this promising new technology.
It is not required to use
large quantities of calcined material as reactants in geopolymers, so
geopolymer technology gives substantially reduced carbon dioxide
compared with conventional Portland cement. Davidovits stated that for
tonne of cement produced there is 0.55 tonne of chemically bound carbon
released from calcining of limestone, together with 0.40 tonne of
dioxide from the combustion of fossil fuel. Davidovits estimated that
cement production contributed to 5% of world carbon dioxide emissions,
increased construction in developing countries like China this is
reach 17% in 2015. Even if some calcined metakaolinite is used in
there is still a significant environmental incentive to replace
Typical FTIR and MAS NMR spectra
obtained for a
geopolymer are presented in Figure 2 and Figure 3 respectively. The
feature of all FTIR spectra of geopolymeric materials is a central peak
1010 cm 1 and
1040 cm 1 that
is attributed to the Si O Si and Al O Si
asymmetric stretching mode.
A shift in the location of the peak
is a result of
heavy metals contained within the geopolymer. In Figure 2, this peak is
approximately 1025 cm 1. This central peak is a
major fingerprint for the geopolymer matrix. The peak at 559 cm 1 originates
from double ring
structures formed by Al and Si tetrahedra. The peak at 467 cm 1 is
assigned to in plane bending
of Al O and Si O linkages found inside the basic aluminosilicate
It is important to note that the location of this peak may vary between
450 cm 1
and 480 cm 1.
The Si MAS NMR spectrum
exhibits two main shifts at –87.3 ppm and –91.9 ppm, indicating an
Si atoms connected in 4 direction via oxygen linkages to 4 Al atoms or
to 1 Si
atom and 3 Al atoms, the so called Si(4Al) and Si(3Al) sites
spectrum is in good agreement with the classical model of a geopolymer
by Davidovits which theoretically contains mainly Si (4Al) sites. In
the Al MAS
NMR spectrum, the peak shifts of 58.5 ppm and 2.2 ppm indicate a
mixture of 4
and 6 coordinated Al. It is worth noting that different alkali and
ions do not seem to influence either the Si or Al spectra.
It is possible that the
coordination number of aluminium in the starting materials will have an
on its eventual bonding in the matrix. A highly reactive intermediate
is believed to form by copolymerisation of individual alumino and
species. Little is known about the behaviour of this gel phase and the
to which the nature of the starting materials and the actual
solution are affecting the formation and setting of this gel phase. A
experimental problem is that the gel phase cannot be frozen and then
to observe the evolution of its composition and texture.
Recent work by phair, van
Deventer and Smith used zirconia as an inert reference to examine the
of a non aluminosilicate source on the chemical and physical properties
geopolymer matrix. Zirconia was chosen as a filler material because it
defined physical characteristics (homogeneity, stability at high
and chemical properties such as high purity and it is relatively
water. Furthermore, the high structural resilience of zirconia to
makes it an ideal additive to increase the capacity and efficiency of
geopolymers in encapsulating radioactive wastes. It was demonstrated
inclusion of only a small quantity of zirconia (3% by mass) imparts a
substantial increase in the compressive strength of geopolymers derived
fly ash. It was postulated that the observed increase in compressive
is due to the formation of specific zirconia associated 3 dimensional
polysialate species, which reduce the mobility of sodium while
charge balance and structural stability of the matrix.
Lee and Van Deventer showed that
inorganic salts can
act as a setting accelerator which promotes the geopolymer to set
acquire faster gaining of strength. It can also work as a setting
having the opposite effect of that of an accelerator. It was found that
the cation and the anion of inorganic salts affect the setting
geopolymers. The cation may have a greater effect on the orientation
the geopolymeric precursor species, which are negatively charged,
attraction. By influencing the accessibility of the reacting species to
other, the cation may promote bond formation and thus give different
behaviour than the base geopolymer. The anion, due to its bulky spatial
distribution and electrostatic repulsion to the reacting species, may
affect the bond formation and setting behaviour. The electrostatic
introduced by the addition of inorganic salt to a geopolymer may have a
significant effect on the viscosity of the reaction mixture. The more
the mixture, the less freely the reaction precursors can move, thus
faster setting geopolymer.
Generally, geopolymerisation takes
place in an
ambient environment if the reactants are pozzolanic materials. A
setting and hardening with temperature ranging from 30°C to 70°C is
most cases when the reactants are naturally occurring aluminosilicate
(Xu and Van Deventer, 2000b). Kaolinite, feldspar, mica and many other
aluminosilicate minerals have been studied for their potential to
geopolymerisation with the positive results showing that natural Al Si
could be the largest source for a geopolymer industry.
Figures 4 to 7 depict the
compressive strength of
geopolymer synthesized from alkali feldspar and kaolinite in either
NaOH or KOH
solution. The compressive strength of 24.5MPa and 25 MPa are achieved
when Na feldspar
and K feldspar are respectively geopolymerised in KOH and NaOH
should be noted that these strengths are for the gel and unreacted
only and significantly higher strengths are achieved when suitable
are added. With the right combination of reactants it is not difficult
obtain compressive strengths exceeding 90 MPa after 7 days. By
composition and particle size of reactants, percentage of aggregates
reaction conditions, the strength of produced geopolymers, both early
and long term
strength can be optimized. For instance, a geopolymer synthesized from
metakaolinite in NaOH and Na2 SiO2 solutions reached a
compressive strength of 48MPa and 52MPa after one hour and 24 hours
65°C, respectively. In Russia, a twenty floor building constructed from
geopolymerised slag twenty years ago using the technology of Prof.
of Kiev, Ukraine, is another excellent example of the long term
extraordinary durability of this material. Prof Kryvenko has
samples of more than 40 years old that show no sign of degradation or
At present the geopolymer research group at the University of Melbourne
studying these old samples from Prof Kryvenko in an attempt to explain
scientifically the excellent durability of geopolymeric matrices.
Immobilisation of heavy metals and radioactive elements
of many useful applications of geopolymerisation is the immobilization
metals and radioactive elements. Since geopolymers possess high
strength, and high acid, water and fire resistance, they have excellent
stability and a higher durability compared with traditional Portland
concrete. These advantages make geopolymers potentially useful for land
well. Table 1 lists the percentage of metals immobilized and not
under aggressive conditions for geopolymers synthesized from
ash and kaolinite/fly ash matrices. It is noted that not only can the
metals Cu and Pb be successfully immobilized in the metakaolinite or
kaolinite/fly, ash based geopolymers, by a high mechanical strength can
achieved in the resulting geopolymers.
A laboratory and pilot scale
study was conducted by Hermann et. al. to solidify
residues in Germany by geopolymerisation with an emphasis on long term
stability. The treated sludges containing radioactive residues and
could be characterized by the parameters listed in Table 2. The
used to solidify the sludges were synthesized from reactive clay, slag
potassium silicate. The results of solidification are summarized in
Encouragingly, the solidification of the radioactive sludges by
geopolymerisation was found to be successful, and the formed
demonstrated a sufficiently high compressive strength of 20 25 MPa.
freeze thaw and wet dry tests indicated that these geopolymers are
and water durable materials which are suitable for landfill. Extensive
testing by the group of Prof Pavlo Kryvenko in Kiev has also
geopolymeric materials have excellent durability for cold climate
By using geopolymer technology based on the early patents of Joseph
Hermann et. al have now commercialized a landfill
for radioactive waste
material at Schlema Alberoda in Germany. Other researchers have also
that geopolymers can effectively immobilized heavy metals, radioactive
and certain organic waste, with the resulting solids revealing
excellent long term
stability and contaminant retention. In addition, this technology is
apply and requires basically the same equipment as conventional cement
methods. It fills the gap between concrete based solidification methods
do not satisfy the requirements of long term structural stability, and
vitrification which is too expensive for most cases in which larger
sludges have to be treated.
Encapsulation of organic residue
A successful example of the
encapsulation of used
solvent distillation residue by means of geopolymerisation was given by
and Osterbacka. The treated residues consisted of 50% organic material,
inorganic binders and heavy metal pigments. The geopolymer was
situ by mixing large amounts of coal fly ash with silica fume and blast
slag. Approximately 8,000 drums of distillation residues from spent
distillation were encapsulated. The whole project consisted of several
Firstly, a 20 cm layer pumpable geopolymer was spread over an area of
1,000 m2. Secondly, a drainage layer
was placed on top of the geopolymer layer. Another 40 cm thick layer of
geopolymer was applied on the top of the drainage materials.
drums with solvent residues were placed together with soil on top of
geopolymer layer. Then the pumpable geopolymeric paste was poured into
between drums to encapsulate the waste. Again another 40 cm layer of
was applied on top of the layer of drums followed by another drainage
and finally soil was placed on top of the completed structure. This
completed in Marttila, Finland, serves as another successful landfill
Stabilisation of mine tailings
mine tailings is another example of the use of geopolymers in the
industry. Van Jaarsveld et al. Investigated the
potential use of geopolymers
as capping materials for Kaltails tailings in Western Australia. The
samples were collected from four sites at a depth of 40 cm and 120 cm,
respectively. The geochemistry of the Kaltails tailings and the total
soluble content are listed in Tables 4 and 5. A series of PVC columns
dimension of 650 mm in height and 300 mm in diameter were used to cap
Kaltails tailings. Fly ash based geopolymeric pastes were tested in the
with addition of 65 to 70% (mass percentage) of tailings. Each
geopolymer hardpan remained in each column for seven months before they
removed. The increasing hardness was monitored with some of data listed
Table 6. The geopolymers formed from fly ash, clay additives as well as
tailings were found to demonstrate some strength, low water
high stability, and could be used potentially to stabilize mine
INDUSTRIAL AND SCIENTIFIC ASPECTS OF NON FERROUS METALS
nonferrous metals imply all metals other than iron. This Classification
too wide and scientifically ill defined. Within this group there can be
subgroups and, therefore, there are many terminologies, which are in
use. Names of some such subgroups, which often overlap, are common
common metals, noble metals, reactive metals, reactor or nuclear
metals, rare metals etc. Some of these can have further classification
properties, applications or other criteria. Table 1 shows, as an
classification of rare metals.
metals (e.g. Mn, Cr, V, Mo, Si, Ti etc.) are often produced as
therefore, generally discussed in ferrous metallurgy. Metals can be
on the basis of different scientific criteria but these are not useful
industry concerned with utility, abundance, price, properties etc.
principles, however, from a common basis, in processing of ores,
refining methods. In this sense even ferrous and nonferrous metallurgy
common features. This article mainly discusses some scientific
relevant in winning of nonferrous metals, in general, and also
newer developments possible in the future with advancement of science
RESOURCES IN INDIA
resources from the basis of indigenous commercial activity. If
abundant and not strategic then they can be exported. Yet, processing
addition is always a more favourable option. Ongoing industrial
R&D create a knowledge base that generate capabilities to set
based on imported resources and/or to export know how.
production figures for some important minerals and the share of public
private sectors. From production point of view, there are two groups,
the developed (Cu, Pb, Zn and Al) and the developing (Ni, Co, Ti, W,
India has a strong nuclear energy programme under which are metals are
to meet indigenous needs. For all metals production one or more of the
following aspects need increasing attention improved characterization
available resources, upgradation/beneficiation of resources by modern
scientific techniques, increased productivity in plants through
control of operational parameters and use of up to date technology,
stringent quality parameters for products, minimization of energy
stricter environmental control and better waste recycline and/or
and finally, exploration for and exploration of newer resources.
resources one can make mention of multimetal sulphides available in
locations in the country, various indigenous and imported secondary
polymetallic ocean floor nodules etc. Trillions of tonnes of nodules
scattered across the ocean floor. These nodules whose principal
are Mn, Ni, Fe, Cu, Co and siliceous ocean floor silt are collectively
as manganese nodules. They are also potential sources of Ni and Co.
shows percentages of some major constituents and compares their
land and ocean floor. It should be noted that the seas contain in
state nearly all metals but generally metal extraction is not
scientific basis, metals can be grouped in terms of reactivity based on
thermodynamic criterion such as hydrogen electrode potential. Table 5
chemical properties can be understood on this basis. It should be
however, that commercial activities ultimately depend on economic and
THE DEVELOPED METALS INDUSTRY
there is significant production of Zn, Cu, Pb and Al, although each
faces stiff global competition and numerous economic uncertainties.
now modern technology and experts examine the position periodically to
progress and future requirements. With about 0.6 mt/year of production,
is self sufficient in Al. However, there are short falls in Zn (about
against a demand of about 250,000 t/year) and Pb (about 40% against a
about 90,000t/year). The situation is worse for copper where annual
demand of about
250,000t is met 75% by imports. The industry has latest technology but
for newer processes and intermediate technologies must continue. There
for recycling and environmental control. Experts have identified the
needs as development of newer agents, application bacterial leaching,
newer hydrometallurgical routes employing ion exchange and solvent
extraction of trace, minor and precious metals, development of newer
use of mathematical models in processes, R&D on ocean floor
minimization, enhancement of productivity and recovery, simplification
flowsheets, and treatment of secondaries.
play an increasingly important role in the Indian industry. The
vitality of the
industry will only be sustained if plants become more efficient and
competitive and more environment friendly. Areas identified for
R&D attention have been discussed elsewhere both the Bayers
process and the
Hall Heroults process need further improvements. Table 6 lists the
alumina quality projections. Constant attempts to improve things are
Welch, in a
recent review, mentions that the energy consumption has been reduced in
plants to around 13 kWh/kg with current efficiency in excess of 96%.
are directed towards constructing wettable cathode surfaces which
and developing non consumable anodes, better cell design and process
optimization etc. Unfortunately, alternative paths to aluminium, e.g.
reduction of Al2 O3, carbochlorination, electrolysis of AlCl3 in
etc. have not yet been economically viable. The scientific aspects of
thermodynamics and kinetics associated with the aluminium electrolysis.
industry enjoys much scope for diversification, for example, there is
need of various special grade alumina alone for various applications.
LIFE CYCLE ASSESSMENT (LCA)
ingredients and systems which are major contributors to environmental
are now a days identified by making use of LCA which also serves as a
cooperation between the technical specialists and environmentalists of
components, viz. (1) life cycle inventory analysis which considers
production emissions and pollutants throughout life cycle, (2) life
impact analysis which can be qualitative or quantitative, and (3) life
improvement analysis which aims at minimizing the adverse effects. In
quantitative evaluations are made of the resources and energy used and
released to the environment during the entire life (cradle go grave)
the product, package or process. As an example, consider production of
a 50 kW
electric pump, which would need about half a tonne of coal for
generation and half a tonne of metal. The CO2
emitted is about 2
tonnes. Assuming a life of 20 years, the pump would consume some 1000
coal emitting 400 tonne of CO2 and consume 9000
MWh of electricity.
Thus, the impact of the pump on the environment in terms of CO2
emission above is 2000 times than required for its production. Various
of impact of the non ferrous metals industry on the environment have
discussed more in detail in the present monograph by other experts. It
be noted; however, there are remedial measures now technologically
Table 7 lists some principal wastes of the aluminium industry and
METALS FOR SECONDARY SOURCES THE ENERGY ASPECT
quantities of scrap and now being processed for increased production of
In North America and Japan, more than a third of the output now comes
scrap. There is great deal of recycling in the case of other metals too
which the figures may be approximately as follows Pb, 40 Au, 40 Ni, 20
ferrous, 15 stainless steel, 80 and Zn, 5. In addition to the
protection such as recycling leads to substantial energy saving. Table
some figures for energy requirement for production of metals from their
concentrates in theory and practice.
As is seen,
process efficiencies as usually low. Although there are scientific and
technological reasons for such wide gaps between theory and practice,
possible to effect substantial energy savings by use of correct science
technology. Recovery from secondary sources plays an important role
energy consumption is often substantial lower as indicated in Table 9.
and minerals industry is
most energy intensive. In advanced countries, it may amount to only 10
the total volume of manufactured output, but it consumes 50% or more of
delivered energy, the metal sector accounting for about two third of
energy intensive values of some important processes are indicated in
which compares actual fuel consumption with theoretical minimum values
(approximate figures). The Table also indicates potential energy saving
on todays technology.
energy requirement for a
process is based and understood in terms of a parameter called Process
Use of PFE
eliminates many misconceptions. An aluminothermic process is not
attractive from energy point of view because of exothermicity because
itself consumes energy in its production. Similarly, in theory use of
metal also is not necessarily attractive unless it is available as a
energy source. Sponge iron produced as an alternative to scrap iron
necessarily lead to overall energy economy during steelmaking.
have the misconception that because of the high temperatures involved,
pyrometallurgy, in general, is more energy intensive. This is often not
because many high temperature steps, such as roasting of sulphides
exothermic heat and hot flue gases also allow waste heat recovery.
handling of large volumes of liquors, drying, evaporation and other
operations and, particularly, electrolytes and electro refining require
significant energy in hydro and
electrometallurgy. Table 11 lists some energy requirement values
pyro and hydro and
EXTRACTION AS A SEPARATION PROCESS
processes involve separation of a desired phase from an input source.
pyrometallurgy, this often achieved through a slag metal reaction. At
temperatures, there is often closer approach to equilibrium and,
is often possible to apply thermodynamics directly. We can compare an
extraction step to some common methods of separation as summarized in
extraction, there can be three basic approaches (a) produce a bulk
then refine. (B) produce and simultaneously purify, and (c) produce a
compound to then produce a pure metal. Common bulk metals are generally
by (a) and (b) whereas for rare metals often adopt method (c). In
pyrometallurgy, the usual steps are drying, crushing, grinding,
agglomeration, roasting, reduction, smelting, refining etc. The usual
steps in hydro
and electrometallurgy are leaching, solid/liquid separation, ion
solvent extraction, precipitation, electrolysis, electrorefining etc.
be special techniques such as bioprocessing, vapour transport
processing, vacuum melting/refining, sublimation, arc/beam melting,
refining etc. The final steps in any refining process become
difficult because the purified material tends to absorb impurities from
environment readily. Thermodynamic considerations show that a metal is
stable when it is impure. Therefore, often one has to strike a balance
quantity and quality, and purification is based on carried out in
stages and in
a selective manner eliminating impurities in order of priority,
principles and kinetic theory can be of great advantage. It explains
achieved by a great deal of trial and error. It can be used in guiding
altogether eliminating trial and error. Many extraction methods,
those for rare metals, have been based on theoretical and bench scale
alone. The fundamental concept is described now. Essentially, in all
and refining processes, a desired metallic value is transferred from
to another. This is made possible by the presence of an activity or
gradient at metal/slag separation, solid/gas separation, solid/liquid
separation, liquid/liquid separation or whatever considers some simple
examples, ferroalloys are produced with relative ease because the
element being at lower activity in solution allows easier reduction of
oxide. Consider extension of the idea to beryl, BeO which is a very
content, lower is aBe and more teasible is the reaction to the right.
It is another
matter that Be is often used as Be Cu alloy just as Mn, Si, Ti, V, Ni
often used more as ferroalloys a for deoxidation and or alloying rather
simple example. One may want to have nickel impurities in the slag
copper the metallurgy so that nickel can be subsequently recovered from
treatment of slag. Many years ago, the author imported some data on
and solubility of different oxides such as NiO, FeO, CoO, Cu2O etc. in
standard solvent (eutectic Na2O. SiO2 K2O. SiO2). At all imperatures
distinctive low solubility values. Assuming similar results in other
system, one can say that during copper smelting and converting, nickel
rather go to the copper metal phase rather than the slag phase.
involved in rare metal extraction are different from conventional
smelting and refining processes familiarly adopted for common metals.
for this which are discussed elsewhere make it imperative that they be
first in the form of a pure compound in which pure metal is extracted.
new developments which
created initial excitement have not proved commercial viability
Mention may be made of the ALCOA process based on AlCl3 electrolysis
chloride solvent) using bipolar electrodes and continuous copper
(WORCRA process. NORANDA Process). However, many of the ideas generated
found applications in other sectors.
THE IMPORTANCE OF USING A MULTIDISCIPLINARY APPROACH IN THE
AMMONIA LEACHING BEHAVIOUR OF MULTIMINERAL SULPHIDES
challenge to hydrometallurgical research centres upon effective
raw materials that are not amenable to pyrometallurgical processing.
example, a leaching operation is ideally suited for processing of lean
complex sulphide ores and concentrates for extraction of nonferrous as
precious metals. Selective leaching aims at dissolving only the readily
metal species and not the sulphide sulphur. Any detailed investigation
partial or total dissolution of metal values from complex sulphide ores
important theoretically, as well as for application to flotation,
that need to be considered critically include the overall aim of
studies, raw material characteristics, analysis of leach solution and
and experimental options and limitations. These are discussed briefly
reference to multimineral sulphides.
Overall Aim of Leaching
to be specific with regard to the development of a leaching process for
recovering a particular metal or all metal values present in the Cu Zn
concentrate. One is interested in knowing what is the minimum recovery
and what is the product mix required, because this information helps
penalties imposed on concentrates for processing in smelters. If it is
that the ultimate aim is to maximize the recovery of all metal values,
should carry out leaching studies in terms of sulphur dissolution
undissolved sulphur value in the leach residue. It is also necessary to
the priorities when leaching various sulphide fractions, e.g. Pb Cu, Zn
assuming that industrially it is still not possible to produce
sulphides of a multimineral sulphide ore techno economically and, at
bulk concentrates can be produced with good recoveries.
minerals are not always stable compounds. Mining, comminution and
alter their characteristics and compositions in an uncertain manner.
these sulphide concentrates are moist (3 10% moisture) and have fine
size and, therefore, are susceptible to atmospheric oxidation during
It is also noted that composition is likely to change with size
storage time etc. This means that the raw material has to be
thoroughly. A convenient way to characterize the raw material would be
techniques such as ore microscopy, thermal analysis, X ray diffraction,
chemical phase analysis etc. Any process flow sheet developed would
used for a specific input material only.
Analysis of Feed Material,
Leach Solution and Residues
analysis of a multimineral system interference amongst different metals
introduces errors. In the absence of accurate chemical phase analysis
an unusual situation arises where the entire leaching data become
Many procedures have been recommended in the literature by earlier
to minimise analytical errors.
Leaching as a process
involving Parallel Reactions
number of sulphides dissolving simultaneously (congruent leaching) the
of individual reactions are likely to be influenced by several factors
(a) the leaching of other sulphides (thermodynamic interference) and
presence of reaction products of other sulphides (kinetic factors).
many important commercial sulphide minerals possess semiconducting
Experimental Options and
Limitations during Laboratory Studies
In order to
uncertainties, it is possible in laboratory studies to modify the
control regime by suitable adjustment of the experimental conditions.
in an industrial operation there are practical limitations and
control may still prevail. Thus, pulp density may be high enough to
reagent starvation, stirring may not be sufficiently vigorous to
liquid phase mass transfer resistance, and the system may be operated
region where changes in oxygen and ammonia concentrations influence the
Analysis of Kinetic Data in
Terms of Models
too much emphasis in the literature on fitting of kinetic models and
kinetic parameters for leaching of both individual and multimineral
Due to the uncertainties cited earlier, fitting a model may not be of
significance. Many of the reported data have been explained in terms of
interface controlled models. The basic premise is rather restrictive
not be valid for the following reasons the polydisperse nature of the
uncertain shape and mineralogical composition, changes in density,
pore size, and variations in magnetic susceptibility, electrical
7. Selection of Experimental
Conditions for Oxidative
Ammonia Leaching of Multimetal Sulphides
need to be fixed in certain ranges, and this cannot be done
to selecting experimental conditions or variables, it is always
evaluate critically the literature and the experimental facilities
the laboratory. Certain guidelines are too followed considering the
used in a laboratory, for example autoclaves for leaching of
sulphides. These aspects are now discussed.
working volume of the unit is
very important. This is to be determined from factors such as the
length of the
agitator shaft, type of impeller used, etc. that contribute to the
hydrodynamics of the system under study. Another important aspect
temperature pressure relationship of water in a closed vessel and how
pressure increases exponentially above a certain temperature. The
allowable water loading in any sealed bomb or pressure vessel is given
(bomb volume)/ volume multiplier at maximum given temperature. Such a
relationship available in the literature indicates that the increase in
of water is small for temperatures up to 200°C. However, as the
raised to higher levels, the fluid expands to fill 150% of its original
at 321°C, and to more than 3 times its original volume at the 374°C
point. This has to be borne in mind and a pressure vessel should not be
overfilled to ensure safety. Necessary precautions are to be taken to
or minimize common hazards and thereby accidents. One ought to have
outlook for process chemistry, risk and general safety, design aspects
autoclave components, operation and maintenance of autoclaves, safety
standards etc. as described elsewhere.
more autoclaves are available
for experimentation, one has to consider their type
length/diameter ratio), volume capacity, type of agitator and impeller
speed, heating medium (electrical/thermal oil type) etc. and their
the leaching data generated. It is to be noted that mass transfer
depend on factors such as the geometry of the system, the viscosity and
density of the lixiviant, the diffusivity of the species and the
any reaction system, one must
also consider the concept of zeroth time that concerns initiation of
particular reaction at the desired temperature. Not many researchers
the importance of this induction period. It is possible to investigate
dissolution of partially oxidized sulphide mineral species present in
starting feed material. The information obtained during the zeroth hour
be taken into account while interpreting the actual leaching data.
guidelines and a critical review of literature, one can now arrive at
criteria for various factors that effect leaching with emphasis on
experimental conditions and their control for specific results. For
methodology used for selection of 9 experimental variables
agitation, time, ammonia concentration, ammonium sulphate addition, pH
measurements, oxygen partial pressure, pulp density and particle size)
recently discussed. This has led to a judicious selection of
variables and their ranges, hereafter known as standard leaching
These are as follows
ambient temperature (25°C) to 135°C
1080 min 1
time, 0 to 2 h
concentration, 60 gpl (3.34 mole/l)
sulphate when added, 45 gpl (0.34 mole (1)
11.2 with liquor ammonia, (d) as above, 10.1 with (e) as above
partial pressure, 150 kPa
concentration, 1%, and 10% of bulk concentrate solids
size, 200+300 mesh (63+43 µm for 1% solid concentration of pure
minerals and actual bulk concentrates, and, 10% solids of single
concentrates and –140+500 mesh (106+22.5 µm) for studies with 10% solid
concentration of actual bulk concentrates.
standard conditions, the ammonia leaching of bulk concentrates with
mineralogical composition results in high extraction rates
(>90%) of copper
from chalcopyrite, zinc from sphalerite, and lead from galena. An
interdisciplinary approach involving various experimental techniques,
microscopy, X ray diffraction, thermal analysis, chemical phase
surface area measurements, and electrochemical measurements (galvanic
interactions), in support of a leaching study on multimetal sulphides
PROCESSING OF ALUMINA RICH INDIAN IRON ORE SLIMES
India is endowed with rich
resources of iron ores in
the form of hematite and magnetite ore deposits. Hematite reserves,
primarily in the states of Bihar, Orissa and Madhya Pradesh, are
be 11.9 billion tonnes with an average grade around 62% Fe. Total
reserves, estimated at around 5 billion tonnes with an average grade of
Fe are found in the states of Karnataka, Goa, Andhra Pradesh and
total iron ore production in India (sixth largest producer of iron ore
world) is currently around 73 million tonnes. Approximately 50% of this
production is exported in the form of raw ore, ore concentrates,
iron oxide powder.
Indian hematite ores are typically
rich in iron but
contain unusually high alumina (as high as 7%). The current practice of
ore washing in India results in three products, namely coarse ore
directly charged to blast furnace, the classifier fines, (3.5% alumina)
with or without beneficiation are fed to sintering plants and the
slimes (6 10%
alumina) which are currently discarded as waste.
It is a well recognized fact that
in order to enhance
the competitive edge of Indian iron and steel industry, and efficient
removal technology for Indian iron ores is absolutely essential. It is
noting the following facts in this context
The alumina content in iron
ore fines used in sinter making all over the world is less than 1%. In
contrast, iron ore fines in India assay as high as 3.0 5.5%. The sinter
produced from such alumina rich ore fines, is thus much poorer. The
effect of alumina on sinter strength productivity and its reduction –
degradation characteristics (RDI) are well documented and conclusively
Whether in the form of
alumina rich lumps or sinter, the blast furnace productivity is
affected due to the presence of alumina in the feed. High alumina slag,
is highly viscious, requires larger quantity of flux (10% MgO) and
larger slag volumes resulting in an increases in coke consumption and a
decrease in blast furnace productivity. According to one estimate, a
in alumina content in the sinter from 3.1 to 2.5% will improve the RDI
least six points, lower blast furnace coke rate by 14 kg per tonne of
and increase its productivity by about 30% under Indian operating
The generation of iron ore
slimes in India is estimated to be 10 25% by weight of the total iron
– the iron ore values are lost to the tune of 15 20 million tonnes
In addition, these slimes stored in massive water ponds pose enormous
environmental hazard. SAIL alone has more than 40 million tonnes of
accumulated over the years. Considering the fact that iron ore
rise to at least 100 million tonnes soon, finding means of safe
disposal/utilization of slimes is indeed urgent.
MOTIVATION FOR THE BENEFICIATION OF INDIAN IRON ORES
Iron ores are being beneficiated
all around the world
including at Kudremukh in India. Several techniques such as jigs, multi
separator, low and high intensity magnetic separator, conventional as
column flotation, selective dispersion – flocculation are all part of
industrial practice. Recent advances include packed flotation column,
column jigs and centrifugal concentrators like Falcon concentrator,
jigs, Knelson concentrator for the beneficiation of iron ore slimes.
of hematitic ores in India at present, however, does not involve any
beneficiation except for whatever rejection of silica (and to some
alumina) occurs during washing and classification of crushed ores.
commendable efforts have been made by Tata Steel to come up with an
economically viable beneficiation flowsheet for processing classifier
A comprehensive technology
needed to delineate the appropriate beneficiation/utilization strategy
Indian iron ore deposits must include (1) the nature of occurrence,
and liberation characteristics of the alumina containing minerals (2) a
comparison of the separation efficiency of various unit operations for
hematite goethite/kaolinite/gibbsite separation in terms of recovery
plots (separation characteristics) and as a function of particle size
preliminary techno economic assessment of the various technology
options for a
typical iron ore mine in the country. A schematic diagram showing the
technological elements of an integrated strategy to utilize alumina
ore deposits in the country is presented in Figure 1.
BENEFICIATION STRATEGIES FOR INDIAN IRON ORE SLIMES
Considering the present magnitude
of the iron ore
slimes generation annually, the quantities of slimes accumulated over
years, the fact that these slimes are available in already ground form
assaying reasonably high% Fe, it is obvious that if properly
these slimes can be considered a national resource rather than a waste
The alumina content of the slimes,
if brought to less
than 2% Al2O3 in the beneficiated product will (a) lead to better
of national resources (b) achieve higher mine output (enhanced
not much additional costs (c) reduce environmental hazards associated
storage and disposal of slimes and (d) result in higher blast furnace
sinter plant productivity.
A number of research groups in the
explored the possibility of reducing alumina in iron ore slurries. A
review of the earlier R&D investigations, as presented and
greater detail in our earlier publications. Clearly indicates the need
out a comprehensive study targeted to establish an integrated strategy
utilization of Indian iron ore slimes. It must address the following
A quantitative and definitive
assessment of the extent of alumina reduction possible with state of
A conclusive evaluation of
the state of the art agglomeration (sintering/pelletization/
can successfully convert the beneficiated slimes into a product
blast furnace without adversely affecting its productivity.
A techno economic assessment
of the various options available to utilize the residual waste product
could be as high as 50%) containing high amount of alumina and iron
oxide – for
example, in the production of iron rich cements, recycling of iron rich
by thermal treatment including conversion into metallic iron and in the
production of glass ceramic materials from iron rich waste.
A comprehensive eco friendly
and safe technology (for example, semi dry disposal technology) to
conventional practice of storing iron ore slimes in tailings ponds.
One of the more important findings
investigations is that alumina in Indian iron ore slimes occurs in the
two distinct mineral constituents namely, gibbsite (hydrated aluminium
and kaolinite (and other clay minerals in minor quantities). Even
adequately quantified, the liberation studies also indicate that a
portion of alumina is present in the liberated form and hence amenable
separation by physical means.
The work conducted by Tata Steel on
Noamundi iron ore
slimes is by far the most comprehensive study available at present.
their data, Pradip compared the efficiencies of different unit
including wet high intensity magnetic separation (WHIMS) and multi
separator (MGS). As illustrated in Figure 2, it was possible to produce
concentrates at least on a laboratory scale, assaying less than 2%
an overall yield of around 50% from a slimes feed analysing 7 8%
Another noteworthy observation is that the separation achieved in MGS
remarkably close to the theoretical yield predicted based on the sink
tests done on the same sample of slimes. The availability of high
units is currently a serious limitation. Based on the published
the beneficiation of Indian iron ore slimes, it is not possible to
reasons why the yield is limited to 50% only. Is it because of
and/or because of lack of a suitable separation device? Any future work
topic must address this question.
Separation processes based on the
differences between iron and alumina containing minerals, for example,
flotation and selective dispersion flocculation are also promising but
investigated adequately. The availability of selective reagents capable
achieving the desired separation efficiencies is a serious limitation.
been addressed by us in our work on iron ore slimes. A brief summary of
investigations is presented in the following section.
SELECTIVE DISPERSION FLOCCULATION STUDIES ON IRON ORE SLIMES
Pradip and co workers have
the possibility of achieving selective separation amongst hematite
montmorillonite minerals, the mineral constituents representative of
iron ore slimes.
Two classes of commercially
namely starch based natural polymers and polyacrylamide (PAM)
(PAA) family of synthetic polymers were extensively tested.
designed experiments were conducted in order to compare the
efficiencies of the
two polymers namely starch and PAA for selective separation of hematite
kaolinite. As illustrated in Figure 3. Starch at pH 10 is found to be a
more selective reagent for this separation.
Pradip et al. have also established
that as compared
to the commonly used dispersant, sodium silicate, low molecular weight
synthetic polymers such as polyethylene oxide (PEO) and polyvinyl
(PVP) are more selective dispersants for hematite kaolinite separation
as a flocculant. It is interesting to note that this effect of various
on selectivity is not observed in case starch is used as a flocculent.
We also modified starch as well as
incorporating more selective functional groups. Modified
containing iron chelating groups such as hydroxamates, (PAMX) were, for
found to be much more selective than PAA or PAM. The representative
the separation efficiency of PAMX in hematite kaolinite separation are
presented in Table 1.
The deleterious effect of the
presence of montmorillonite
in the system was also studied in detail. Flocculation experiments
the synthetic mixtures of hematite/kaolinite/monimorillonite indicated
little as 5% of montorillonite when introduced in hematite kaolinite
could lead to a marked deterioration in the separation efficiency due
relatively less flocculation of hematite in presence of
Kaolinite flocculation remained largely unaffected. This deleterious
montmorillonite could be partially mitigated by the use of modified
containing more selective functional groups. As illustrated in Figure
selectivity could be partially restored when modified starch mercaptan
was used as a flocculant instead of conventional maize starch (MS). The
beneficial effect of a more selective flocculant like starch mercaptan
observed with synthetic dispersants as well.
An interesting finding of our work
is that starch,
modified starches (MMS) and modified polyacrylamides (PAMX), which were
to be excellent flocculants for selective separation of hematite from
and even montmorillonite, turned out to be disastrous in
separation. In fact, we established that starch flocculated both
(gibbsite) and hematite (iron oxide) – equally well. It is well known
oxide and alumina have identical crystal structures. The results for
(iron oxide)– kaolinite and hematite – alumina separation using starch
shown in Figure 6 for illustration.
We also proposed a molecular
underlying starch interaction with iron oxide and alumina, which
Various research groups including
ours have reported
on the lack of any worthwhile success in the beneficiation of natural
slimes using commonly used dispersant flocculant combinations. Based on
systematic work on delineating the reasons for this observation, we
it to the remarkable similarities in the crystal structure as well as
surface chemical properties of the two constituent minerals of iron ore
namely hematite (iron oxide) and gibbsite (alumina).
While kaolinite separation is
possible with certain
modified flocculants synthesized by us, even in presence of minor
montmorillonite, it is not enough to reduce alumina to the desired
the concentrate because gibbsite remains with hematite. The key to
problem of iron ore slimes thus lies in developing selective reagents
(flocculants, dispersants and flotation collectors) for iron oxide –
breakthroughs on this front, in the authors opinion will have far
impact on the techno economics of processing alumina rich iron ore
These reagents are not only essential for solving the problem of
iron ore slimes but those will also have a significant impact on the
beneficiation of iron rich bauxite deposits in India. Processing of
muds, rich in alumina and iron oxide will also become economically more
attractive with the availability of reagents capable of iron oxide
separation. A sustained and systematic interdisciplinary effort by
researches in this direction is therefore highly recommended.
CONVERSION OF A WASTE TO A HIGH VALUED PRODUCT
A large quantity of rice husk
is generated as a byproduct
of rice milling. At present, the rice husk is considered as an
waste. Burning has been the primary means of disposal. Not only does
create pollution problems but the extremely fine silica ash is also
thus constitutes a health hazard. Even careful incineration procedures
completely eliminate this airborne silica. Thus, burning with its
problems of air pollution and ash disposal has proven to be an
solution. Fortunately, rice husk contains the necessary carbon and
provide a nearly ideal source material for production of silicon
article describes a process for converting a waste such as rice husk to
crystalline SiC (a high valued product).
Silicon carbide (SiC) is
bestowed with many
attractive properties it is extremely hard it can withstand
1000°C without undergoing significant changes in its properties it has
degree of thermal and chemical stability it is resistant to wear and
a semiconductor it could operate at high temperatures and high
well as in radiation environments. All these properties make Sic a top
candidate material for a host of traditional as well as sophisticated
Commercial production of SiC
by Acheson process,
involves high temperatures reaction of silica and carbon (generally low
petroleum coke). This methods requires long reaction time and produces
agglomerates with varying crystal structure and purity. The lack of
over structure and purity of SiC obtained by the above process
use for many advanced engineering applications. Components intended for
applications are usually made by high temperatures sintering of powder
as SiC does not melt. To have improved sintering properties, the SiC
required to be sub micron particle size Obviously, SiC produced by
process is not suitable for making dense sintered bodies unless it is
ultrafine size. Therefore, in recent years increasing attention has
for production ultrafine SiC powders.
A finer fraction of the semi
ground raw rice husk
was cleaned, oven dried and treated at 550°C for 2 h ambient nitrogen.
resultant product was in the far of fine powders. The inflight
heat treated fine powder was then carried out in a 20 kW r.f. plasma
The details of the reactor assembly and the operating conditions are
elsewhere. Argon was used as both plasma generating gas and carrier
coating was observed at the inner wall of the double walled, water
cylindrical quartz chamber. The powder could be easily scrapped off for
detailed characterization. The plasma produced powder was then treated
at 700°C in a tube furnace using nature convection to remove excess
removal excess silica was affected by treatment with HF.
The plasma synthesized SiC
powder was doped with
platinum (1%) and tested as a catalyst support material. The details
RESULTS AND DISCUSSIONS
composed of silica in hydrate amorphous form and cellulose. Proper heat
treatment such husk results in a product that is primarily an
mixture of silica and carbon with very high surface area. When such a
is further heated in the 1400 1800°C range, a reaction occurs between
and carbon resulting in the formation of SiC. The possible reaction of
process was given by Lee and Cutler as
(amorphous) + 3C (amorphous) SiC
The reaction time can be
greatly reduced by
increasing the temperature. The effect of Co from the reaction may be
sufficiently significant to decrease the reaction rate. Thus, CO needs
constantly flushed away. Both of the above processes can easily be
a thermal plasma reactor. Moreover, the very high temperature (104 K),
temperature gradients (106 km 1) and high quench rates (106 Ks 1)
with thermal plasmas can be a unique route for the preparation of
from rice husk.
DEFINITIONS AND PROPERTIES OF LIMES
Before delineating the
physical and chemical
characteristics of lime, it is appropriate at the outset to define some
different types of lime, the first derivative, manufactured product of
limestone. Many of the following definitions are repetitious and
these terms are widely employed in the industry and among its consumers
Agricultural hydrate is a
unrefined form of hydrated lime that is mainly used for neutralizing
acidity and for purposes where high purity and uniformity are
Air slaked lime contains
various proportions of the
oxides, hydroxides, and carbonates of calcium and magnesium resulting
excessive exposure of quicklime to air, which vitiates its quality. It
partially or largely decomposed quicklime that has become hydrated and
Autoclaved lime is a special
form of highly hydrated
dolomitic lime, largely utilized for structural purposes, that has been
under pressure in an autoclave.
Available lime represents the
total free lime (CaO)
content in a quicklime or hydrate and is the active constituent of a
provides a means of evaluating the concentration of lime.
Building lime may be quick or
hydrated lime (but
usually connotes the latter), whose physical characteristics make it
for structural purposes.
Calcia is the chemical
compound calcium oxide (CaO).
Carbide lime is a waste lime
hydrate by product of
the generation of acetylene from calcium carbide and may occur as a wet
or dry powder of widely varying degrees of purity and particle size. It
and possesses the pungent odour of acetylene.
Chemical lime is a quick or
hydrated lime that is
used for one or more of the many chemical and industrial applications.
it possesses relatively high chemical purity.
Dead burned dolomite is a
specially sintered or
double burned form of dolomitic quicklime, further stabilized by the
of iron that is chemically inactive and is employed primarily as a
for lining open hearth steel furnaces.
Fat lime connotes a pure lime
(quick or hydrated),
distinguishing it from an impure or hydraulic lime it is also used to
lime hydrate that yields a plastic putty for structural purposes.
Finishing lime is a type of
refined hydrated lime,
milled in such a manner that it is suitable for plastering,
finish coat. Putty derived from this hydrate possesses unusually high
Fluxing lime is lump or
pebble quicklime used for
fluxing in steel manufacture–or the term may be applied more broadly to
fluxing of nonferrous metals and glass. It is a type of chemical lime.
Ground burnt lime refers to
ground quicklime used
for agricultural liming.
Hard burned lime is a quicklime
that is calcined at high
temperature and is generally characterized by relatively high density
moderate to low chemical reactivity.
Hydrated lime is a dry powder
obtained by hydrating
quicklime with enough water to satisfy its chemical affinity, forming a
hydroxide due to its chemically combined water. It may be high calcium,
magnesian, dolomitic or hydraulic.
hydrated lime is a
chemically impure form of lime with hydraulic properties of varying
possesses appreciable amounts of silica, alumina, and usually some
chemically combined with much of the lime. It is employed solely for
Lime is a general term that
connotes only a burned
form of lime, usually quicklime, but may also refer to hydrate or
lime. It may be calcitic, magnesian, or dolomitic. It does not apply to
limestone or any carbonate form of lime (although it is often
in this way).
Lime putty is a form of lime
hydrate in a wet,
plastic paste form, containing free water.
slurry is a form of lime
hydrate in aqueous suspension that contains considerable free water.
Lump lime is a physical shape
of quicklime, derived
from vertical kilns.
Magnesia is the chemical
compound magnesium oxide
(MgO) it is an important constituent in dolomitic and magnesian limes.
Masons lime is a hydrated
lime used in mortar for
Milk of lime is a dilute lime
hydrate in aqueous
suspension and is the consistency of milk.
Pebble lime is a physical
shape of quicklime.
Quicklime is a lime oxide
formed by calcining
limestone so that carbon dioxide is liberated. It may be high calcium,
magnesian, or dolomitic and of varying degrees of chemical purity.
Slaked lime is a hydrated
from of lime, as a dry
powder, putty, or aqueous suspension.
Soft burned lime is a
quicklime that is calcined at
relatively low temperature. It is characterized by high porosity and
Type S hydrated lime is an
ASTM designation to
distinguish a structural hydrate from a normal hydrated lime,
N, that possesses specified plasticity and gradation requirements. It
dolomitic or high calcium and is more precisely milled than type N
Unslaked lime is any form of
Whitewash is synonymous with
milk of lime, a dilute
lime hydrate suspension.
PHYSICAL PROPERTIES OF QUICKLIMES
COLOUR, Generally quicklime
is white of varying
degrees of intensity, depending on its chemical purity. The purest
quicklimes are the whitest. Less pure or improperly calcined types may
slight ash gray, buff, or yellowish cast. The quicklime is invariably
than its derivative, limestone.
ODOUR. It possesses a faint
but distinctive odour
that is difficult to define. It is slightly earthy and pungent but not
TEXTURE. All quicklimes are
crystallite conglomerates vary greatly in size and spacing in their
Some appear to be amorphous, but they are microcrystalline.
CRYSTAL STRUCTURE. X ray
diffraction reveals that a
pure calcitic oxide crystallizes in the cubic system as depicted in
Fig. 1. The
edges of the cube are 4.797 Å in length, with calcium atoms located
Magnesium oxide possesses the
same cubic crystal
lattice as CaO, except that the MgO crystal is slightly smaller and
with edge lengths of 4.203 Å. This accounts for the slightly higher
density of dolomitic quicklime.
POROSITY DENSITY. The degree
of porosity of
commercial quicklime varies widely in percent of pore space from 18 to
with an average value of about 35%, depending on the structure of the
limestone, temperature, and severity of calcinations. Dead burned
much lower porosity of 8–12 %.
SPECIFIC GRAVITY. The true
specific gravity of pure
calcium oxide is 3.34, but this presupposes zero porosity, a conditions
impossible to achieve in manufacture. Values have been reported at
lower, but 3.34 appears to be a generally recognized average value.
limes may range as low as 3.0 pure dolomitic oxides may range as high
The apparent specific gravity
varies similarly, from
1.6 to 2.8. Average values for commercial oxides are 2.0 2.2. Values
dolomitic quicklimes average about 3–4% more than the preceding. Dead
has the highest value of all–an average of 3.2.
BULK DENSITY. The same
variance pertaining to
specific gravity is prevalent as well as the added variable of the
physical size and gradation of the quicklime particle. The range in
Ib/ft3 is 48 70 (769–1121 kg/m3), with an estimated average of 55 60
(881 961 Kg/m3) for commercial quicklime of pebble size. Lump size is
lower, and ground or pulverized is 12 15% greater than this average
larger the particle and the more restricted the gradation, the lower
Values for dolomitic average
3 4% greater than those
for high calcium.
HARDNESS. Hard burned and
quicklime lies between 3 and 4 on the Mohs scale. Ordinary quicklime is
variable, but is usually between 3 and 2. The same broad divergence in
and strength in limestones is manifest in their derivative limes.
The only values reported are 145 × 10 7 between 300 and 700°C and 138 ×
between 0 and 1700°C. These data probably only represent the magnitude
measurement certainly a variance would exist with commercial quicklimes.
Resistivity of 71 × 108
ohms/cm at 15°C (59°F), declining to 91 ohms at 1466°C (2671°F), has
calculated. The presence of nitrogen depresses values.
REFRACTIVE INDEX. The pure
calcitic oxide is 1.83
and the value of commercial quicklime ranges between 1.70 and 1.82. A
1.736 for pure MgO means that dolomitic quicklime has a slightly lower
than CaO. Both types possess slight refractive properties.
LUMINESCENCE. All lime oxides
are very luminescent
at high temperatures in the calcining range of 900°C (1652°F) and
origin of the term limelight.
THERMAL CONDUCTIVITY. It has
been estimated at
0.0015 0.002 cal/cm3. sec.°C temperature difference, but this value may
HEAT OF FUSION. It is
doubtful whether this has ever
been accurately measured 28,000 cal/mole has been estimated as the
POINT. Recognized values
for CaO are 2570°C (4658°F) and for MgO are 2800°C (5072°F), with
A eutectic mixture of about 50%
CaCO3 and 50% CaO is
reported to melt at 1240°C under high pressure of 30,000 mm.
A recent investigation of the
system CaO MgO,
involving X ray diffraction and optical methods, that may comprise the
authoritative data, reveals a maximum solid solution of MgO, in a CaO
of 17% weight and a maximum solid solution of CaO in the MgO lattice of
weight, both at temperatures of 2370°C. In both instances the extent of
solution is higher than that reported by other investigators. Melting
the eutectic 67% CaO and 33% MgO is 2370°C for 100% Cao, 2625°C for
2825°C. Figure 2 shows the phase equilibrium diagram calculated by
HEAT OF COMBINATION. Same
value as for heat of
formation, given later.
BOILING POINT. Values for CaO
are 2850°C (5162°F)
and for MgO are 3600°C (6512°F), with dolomitic oxides intermediate.
ANALYTICAL TESTING OF LIMESTONE AND LIME
Methods of test and chemical
and physical analysis
of limestones and limes are increasingly important to the consumer as a
of evaluating the specific (type or grade of) product required for
performance among the myriad uses in which these products are consumed.
analyses are considerably more involved (with more alternative methods)
most other basic chemicals and materials, owing to their wider range in
and chemical and physical characteristics. For example, sulfur is
more uniform in its chemical characteristics than limestone even
basalt, and trap rock tend to be more uniform in their physical
limestone. Certainly sulfuric acid, soda ash, chlorine, and most basic
chemicals are more uniform than quick and hydrated limes per se in both
chemical and physical properties. Therefore the consumer generally
much wider range of qualities from which to select, thus leading to
individual specifications or tolerances for the producer to meet. This
the producers increasing reliance on quality control testing in
processing to ensure conformity with these requirements.
Many of these tests and
analytical methods are
controversial, and often there is disagreement between buyer and seller
tests that are the most accurate, realistic, and equitable to adopt.
Furthermore, there is appreciable inconsistency among similar classes
consumers on the tolerances they demand. For example, one steel company
emphatic that 0.03% sulfur is the maximum amount permissible in
is consumed for fluxing steel yet another steel company making the same
steel may be satisfied with 0.06% sulfur. As a result, a lime or
who desires to sell to a wide variety of consumers must necessarily
systematic program of quality control testing. Delivery refusals of
material by the consumer are most costly to him.
Probably the greatest
influence toward quality
standardization of lime and limestone in the United Sates and Canada
specifications promulgated by the American Society of Testing
consumers may ignore these ASTM materials specifications and methods of
Since adoption of these standards is strictly voluntary. Yet these
specifications do comprise a guide or basis on which a consumer can
own individual specification by modifications. These standards are
prepared by the consumers. Producers, and general interest members,
presumably these standards should be objective and unbiased–equitable
concerned. Two ASTM committees are involved Committee C 7 on Lime has
lime materials specifications for numerous uses. Sampling procedures
of test for chemical and physical analyses for both lime and limestone
Committee D 4 on Road and Paving Materials has written many tests and
specifications applicable to limestone and other mineral aggregates for
phases of construction in which the physical characteristics are the
controlling factor. There are also federal specifications and test
but these are usually almost a duplication of ASTM. Some foreign
similar specifications, but these are generally instigated by their
Some of these ASTM tests are
too laborious and time consuming
for quality control testing by producers and consumers except as a
check or when maximum accuracy is needed in event of a dispute between
and seller. Because of this such detailed tests are regarded as referee
For quality control testing often special rapid short test are
are widely employed, since they provide reasonably or sufficiently
results for routine testing. Some of these short tests along with other
supplementary investigative procedures will be reviewed briefly along
more important ASTM standards.
More than any
other factor, the accuracy of tests on limestone aggregate is
contingent on how
representative the sample is. In testing graded aggregate the principal
is segregation of coarse and fine fractions, obscuring their true
Considerable care is necessary to minimize this inherent tendency of
samples to segregate, and sampling procedures of ASTM D 75 for stone
aggregate is recommended. This includes sampling of stone from ledges
quarries from outcroppings of field stone and boulders at the crushing
after final blending and screening at point of delivery. The minimum
the sample depends on its maximum particle size, as shown in Table 1.
employed to determine hardness, toughness, and resistance to abrasion
impact of all types of highway aggregate are described briefly as
The Los Angeles Abrasion Test
(ASTM C 131) is a
severe accelerated test for measuring the abrasive resistance of
involves testing different specified weights and gradations of stone in
Angeles machine, which comprises an enclosed, hollow steel cylinder
an abrasive charge of a prescribed number of steel spheres (adjusted
different stone gradation classifications) are tumbled together by a
mechanism. After the specified number of revolutions at 30 33 rpm, the
is screened to determine the abrasive loss in weight of the stone and
is calculated the percent of wear of the stone. Specifications for
percent of wear generally range between 30 and 60%, contingent on
stone available and stringency of requirement.
The Deval Test (ASTM D 289)
is another accelerated
abrasion resistance test. It consists of a small cast iron cylinder
inclined at 30° with the horizontal axis, around which it is rotated at
5 kg of stone, consisting of 50 cubical shaped fractions, is introduced
the machine and subjected to 10,000 revolutions. The loss in weight due
attrition is calculated by sieving through a No. 12 mesh (1. 68 mm)
the percentage of wear is then determined. The Deval test may also be
into an impact test by introducing steel shot with the stone. This
abrasion resulting in a higher percentage of wear.
The Page Impact Test I (ASTM
D 3) measures the
toughness of rock by determining the resistance to impact. In a
designed machine a small cylinder of stone, cored from the rock to be
is placed on an anvil and on the stone specimen is laid a 1 kg plunger.
A 2 kg
hammer is then dropped on the plunger from successively increasing
heights of 1
cm (0.4 in.) until the core fractures. The final height in centimeters
which the hammer falls determines the toughness of the rock. There are
modifications of this hammer test.
The Dorry Hardness Test is
still another accelerated
abrasive resistance test. A small core of stone, specially machined for
test, is placed in firm contact against a revolving steel disc on which
mesh (0.6 0.4 mm) quartz sand is fed. After 1000 revolutions the loss
of the stone core is calculated. The coefficient of hardness is equal
to 20 weight
strength tests with
hydraulic presses in which crushing strength of the stone in psi (KPa)
measured are rarely employed, since most stone is regarded as amply
compression for highway uses. Furthermore, it is a costly test, since
blocks or cylinders must be precisely machined so that both sides are
completely level and smooth.
Of the preceding tests the
Los Angeles Abrasion Test
is the most widely utilized. It is the most severe test but is also
the most realistic in simulating the abrasive action of traffic on
are various calculations on specific gravity of stone that reveal the
density, porosity, and absorption and provide an indirect indication of
hardness and weatherability of the stone. Two types of specific gravity
determined (ASTM C 127 128)
Bulk specific gravity of the
stone is defined as the
ratio of weight in air of a given volume of a permeable material,
both its permeable and impermeable voids, in relation to weight of an
volume of distilled water.
Apparent specific gravity is
the ratio of weight in
air of a given volume of the impermeable portion of a permeable
solid rock) in relation to weight in air of the same volume of
In effect this is the same as the bulk specific gravity minus the
These values are obtained from the
so called wire basket
test. A 5 kg stone sample is oven dried to constant weight (A),
water for 24 hr, then removed and surface dried by hand with a towel
weighed (B). The sample is then placed in a wire basket, and its weight
water (C) is measured.
A quick test for specific
gravity can be measured
with the Beckman Air Comparison Pycnometer. This has been employed
with hydrated lime and whiting.
The unit weight of a fine, coarse, or
mixed aggregate is
governed by ASTM C 29, which prescribes three alternative methods of
aggregate in a specified size cylinder that is dependent on the maximum
the aggregate. These three procedures that comprise rodding or jigging
shoveling techniques are also contingent on the maximum size of
is present and serve to consolidate the aggregate to the maximum
net weight of the consolidated aggregate is determined.
and Gradation. The
physical sizes and gradations of stone are determined by screening the
through standard round or square hole wire cloth or plate sieves (ASTM
E 11 70).
A method of sieving by ovendrying the aggregate for plus No. 200 mesh
sizes is stipulated in ASTM C 136. Both the percents passing or
retained on the
different sieve sizes are recorded.
For measuring size of mixed
aggregates finer than
the No. 200 sieve (74 µ) a procedure is outlined in ASTM C 117. This
of washing a sample of the aggregate in a prescribed manner. The
water containing suspended and dissolved materials is passed through a
sieve. This might consist of clay, stone dust, and water soluble
salts. The loss in weight from the wash treatment is calculated as
weight of the original sample. This is the percentage of material finer
the No. 200 sieve.
A dry method of sieving
mineral fillers, most of
which pass a No. 200 sieve, is described in ASTM D 546.
The constancy of gradation is
expressed by the
fineness modulus of an aggregate. It is an empirical number determined
adding the cumulative percentages retained on, say, the Nos. 100, 50,
8, 4, and 0.375 in., 0.75 in., 1.5 in., and 3 in. (O.15 76.2 mm) square
sieves and dividing this sum by 100. This provides a figure of the
of a given gradation. However, different gradations may possess
the same fineness modulus. This factor may be specified to control the
uniformity of graded aggregate for Portland cement concrete, and
may require that the variation in the fineness modulus not exceed 0.2.
Standard aggregate gradations
the degree of absorption of a rock is soundness, since generally the
porous the stone, the more moisture it will absorb, which accentuates
susceptibility to weathering. If the moisture freezes, a disruptive,
pressure is exerted by the ice lenses that induce the aggregate to
defoliate, or disintegrate. Aggregates very greatly in their resistance
deleterious effect of freezing and thawing cycles. Also visible
of an aggregates soundness is speculative, since the size, shape, and
of the stones pore structure, which cannot be observed, influence the
of disruption through frost action. Therefore, accelerated laboratory
have been contrived to evaluate soundness and weatherability. The most
employed soundness tests are the sodium sulfate or magnesium sulfate
(ASTM C 88).
This consists of immersing
the aggregate samples in
a saturated solution of either sodium or magnesium sulfate at 70°F
18 hr. The sample is then removed, oven dried at 215 220°F (101 104°C),
then cooled to 70°F (21°C). This cycle of immersion and hot drying is
usually five times (or a specified number of cycles) and the percent of
determined. Usually the limiting percent is 10 20.
For stone used in trickling
filters of sewage plants
an extremely severe requirement of 20 cycles is often specified with
loss. Only relatively few sources of limestone can meet such a
of Mg(So4)2 is more disruptive than NaSo4. This test is regarded as
unreasonably severe by many engineers in spite of widespread
other special freeze thaw tests have been introduced. However, no test
advanced appears to be generally acceptable and realistically
an excess of alkali (Na2O and K2O) in aggregate may create a
on Portland cement concrete, particularly if the cement or mixing water
high in such alkalis. In order to test the soundness of a combination
aggregates, cement, and mixing water, the so called mortar bar test, an
reactivity test with cement aggregate mixtures, is employed (ASTM C
is an involved, detailed test with all conditions, equipment, and
mortar bars are made
from one part Portland cement to two and one fourth parts graded
weight. After molding, they are stored in a moist closet for 24 hr then
are removed from the mold. The length of the bar is measured and
the mold in the damp closet. Daily or monthly recordings of lineal
(usually expansions) are made for 28 days, one year, or any specified
time. At conclusion total expansion is calculated along with observable
physical changes in the bar, such as warping, cracking, surface
This alleged test resembles more of a
research project very
complicated, costly to conduct, and lacking in reproducibility.
soundness test (ASTM C
289) is a chemical method of determining the potential reactivity of
with alkalis in portland cement. It is indicated by the extent of
during 24 hr at 80°C between NaOH solution and the aggregate that has
crushed and screened to pass a No. 50 sieve (0.3 mm) and retained on a
sieve (0.15 mm). This is also a complicated test, but it is more
simpler than the mortar bar soundness test.
Bitumen–Aggregate Mixtures. Aggregate
varies in its ability to retain a bituminous film in the presence of
bitumen aggregate combinations that possess poor retention cause the
to strip or ravel from the pavement. ASTM D 1664 describes coating and
immersion procedures to determine if stripping occurs or the degree of
stripping prevalent. This test is only applicable to cut back and
asphalts and tars. Much of this test is dependent on visual
observation, so it
is only generally and not quantitatively indicative. There are many
modifications of this test as well as other stripping and bituminous
tests, one of the most important of which is the Immersion Compression
developed by the U.S. Bureau of Public Roads.
Although the reaction of
aggregates with bitumens
cannot be predicted with certainty, as a generalization the acidic
rocks are more prone to strip than basic types, like limestone and
stone and aggregate are classed as hydrophilic, since they possess a
for water than asphalt the basic aggregates are called hydrophobic.
possess better adhesive qualities for bitumens, even under wet
texture, colour, grain size and pattern, or geologic origin of the
of importance, polished thin sections of the stone in question are
microscopic examination. Such Petrographic analysis is more related to
information that testing, since no limits can be set, except as
reflectivity. Otherwise, the information obtained is utilized
arbitrarily or as
engineering judgment. The most sophisticated microanalysis instrument
to be the scanning electron microscope for these studies.
Other miscellaneous tests for use as construction aggregate
of the percent of
flat and elongated fractions in a graded aggregate, since cubical
stone are most desired. This is controlled by specifying a maximum
percentage for odd shapes.
of percent of
lightweight pieces and soft particles in coarse aggregate that would
of fire resistant
qualities of aggregate.
extent of clay lumps in
The tendency of limestone to polish
under simulated action
of traffic is covered by ASTM D 3319. Several states have established
criteria to eliminate aggregate that contribute to slippery pavements
bituminous surfaced roads.
There are 21 ASTM use of
for many construction purposes. There are countless modifications of
specifications written by many diverse consumer groups, state highway
departments, public works department, U.S. Engineers, U.S. Navy, Bureau
Reclamation, consulting engineers, architects, and so on. Generally one
authoritative group, the American Association of State Transportation
(AASTO), endorses the ASTM standards.
Reflectivity. The degree of
whiteness is an
extremely important determination in limestone, chalk, marble, and
whiting and precipitated calcium carbonate, although there is a dearth
in the many individual consumer requirements. Reflectivity measurement
obtained with the G. E. Spectrophotometer at 550 wavelength (similar to
tristimulus filter) or equivalent equipment. It is also applicable to
lime. Details on this measurement are contained in specification C 110.
LIMESTONE CHEMICAL ANALYSES
Analytical chemical test
methods on the composition
of limestone, including its impurities, are adequately contained in
ASTM C 25 72,
which also contains identical methods for quicklime and hydrated limes.
that is equally applicable to both limestone and lime, such as
determinations of impurities, will be reviewed later in the section
Chemical Analysis. Those tests directly applicable to limestone, such
on ignition, CO2 content, free water, and organic content, will be
briefly as follows
Limestone weighing 0.5 or 1.0 g is placed in a weighed platinum
covered with a lid, and then heated gradually in an electric muffle
to about 1000°C. The sample is maintained at this temperature until a
weight is obtained. This means that all volatiles have been expelled.
difference between the original weight of the sample and the final
represents the loss on ignition.
Limestone weighing 1 g is placed in a fast bottomed weighing bottle and
heated uncovered in a ventilated drying oven at 120°C for 2 hr. After
the bottle should be quickly sealed, cooled in a desiccator, and then
just before weighing. The loss in weight represents only mechanical or
hygroscopic moisture, no other volatile.
There are two standard methods of determining CO2 content. The first
boiling 0.5 g of limestone with dilute HCI (11) in a small Erlenmeyer
attached to a condenser from above. The CO2 gas evolved from this
passes through a drying and decontaminating system of CaCl2 and
to absorption tubes filled with soda lime, which entraps the CO2. CaCl2
desiccates final traces of water. Air, free of CO2, is introduced
throughout the system during the test and at a greater rate after the
When CO2 is being absorbed, the absorption tubes heat up readily. When
tubes cool, they are disconnected and allowed to stand in the balance
until two weights, taken thirty minutes apart, agree within 0.5 mg.
used in this test must be porous.
The second (alternative)
method is quite similar to
the first except that a specially designed Midvale bulb, packed
with glass wool, P2O5, and ascarite is used to absorb the CO2 that is
This bulb is detached and weighed with a second Midvale bulb as
Free moisture is desiccated and acid volatiles are recovered separately
a true CO2 content is obtained by difference.
Determination of the organic
content of limestone is extremely difficult to measure with accuracy
simple, completely accurate method has been advanced. (ASTM makes no
for this test.) It is usually calculated by determining the free carbon
content. One method consists of liberating the CO2 by boiling the stone
and passing the volatiles, including the free carbon, into a mixture of
sulfuric and chromic acids that oxidize the organic matter. In other
volatiles are boiled off and filtered through asbestos, which collects
carbon for subsequent organic combustion of the free carbon. At best
values are simply close quantitative estimates.
PHYSICAL TESTS OF LIME
There is only ASTM
specification (C 110 71)
embracing physical tests on burned lime products, but it is an omnibus
specification since it includes tests on residues of quicklime and
lime, standard consistency of putty, plasticity measurements, soundness
hydrate lime, popping and pitting, water retention, slaking rate, and
rate. Other analytical methods not recognized by ASTM will be included
appropriate, but before describing these tests a review of sampling
on lime and limestone (ASTM C 50 57) is propitious.
Sampling. The importance of agreement
between producer and
consumer on where the sampling will take place–at producers plant or at
destination–is emphasized. Since a producer can be victimized by the
careless handling, improper protection, and delayed shipment that
quality, from his standpoint sampling at his plant is preferable.
placed on expeditious sampling so as to minimize exposure of the lime
(With limestone there is no problem in this particular.) Samples should
taken in triplicate and immediately sealed in air tight, moisture proof
containers. Each sample shall weigh at least 5 lb (2.25 kg), provided
One sample should be
immediately delivered to the
consignee the second sample is for the consignor, if requested the
retained with the seal unbroken for a possible independent test.
To obtain a representative
sample of lump or
granular material in bulk, 50 lb (22.5 kg) are sampled for each unit of
of bulk material, even though 5 lb (2.25 kg) may only be required for
When lime is stored in piles or carloads, care should be exercised not
select material from the top or bottom. Ten shovelfuls are recommended
taken from different parts of the pile or carload, at least 1 ft (0.3
the surface. The 5 lb samples are obtained by mixing and quartering all
shovelfuls. When sampling is effected at producers plant from conveyors
bins, a similar volume of material should be taken at regular intervals
of all at once.
With packaged material at
least 1% of the packages
should be sampled with at least 1 lb (0.45 kg)/ bag being removed.
sampling should then be mixed and quartered to provide the (3) 5 lb
With powdered material in
bulk, a sampling tube is
specified that will remove a core at least 1 in. (2.5 cm) in diameter
sufficiently long to penetrate into the interior–not the bottom or top.
minimum of 50 lb shall be taken from each 30 ton unit, mixed and
the 5 lb triplicate samples.
At the laboratory lump or
granular material to be
tested should be ground to pass a No. 100 sieve (0.15 mm).
In case of rejection the
manufacturer must be
notified within one week after completion of tests with the cause of
stated. Each of the contracting parties may make claim for a retest
week of the original test report. Expense of retesting must be borne by
party demanding it. Should the parties still be in disagreement, the
sample of material should be delivered unopened to a mutually
referee laboratory for test, and their findings are binding on both
matter (core and impurities) in quicklime is determined by weighing the
and calculating its percent from the weight of the original sample,
which is at
least 5 lb. Lump material should be first crushed so that it passes a 1
sieve pulverized material is tested as received. The sample is then
carefully into a putty of maximum yield and is allowed to stand for 1
putty is then washed through a No. 20 sieve by a stream of water at
pressure. Washing is continued until the residue remaining visually
be nothing but coarse, sand like particles. The residue is then dried
at 212 215°F.
With hydrated lime a 100 g
sample is placed on a
No.30 sieve (0.59 mm) that is nested above a No. 200 sieve (74 µ). The
is washed through the meshes by a stream of water. No material must be
over the sides of either screen. Washing is continued until both sieves
clear of hydrate, but in no case for longer than 30 min. Residues from
screens are then dried to a constant weight in an atmosphere free of
CO2 at a
temperature between 212 and 248°F (100–120°C). The percentage residue
sieve is calculated, based on the original weight of the sample, and
separately or cumulatively.
Consistency of Putty.
Hydrated lime weighing 300 g is mixed with sufficient water to form a
putty and stirred to assure intimate mixing. Type N hydrate putty is
covered with a wet cloth for 16 24 hr before testing. Type S hydrate
be tested immediately after preparation.
The equipment employed is a
apparatus. Putty is added flush to the top of a nonabsorbent mold, 4 cm
in.) height, 7 cm at base, and 6 cm at top, which rests on a glass
plunger is lowered in contact to the putty surface and an initial
taken. The plunger is released for 30 sec and another reading is taken.
Standard putty consistency is obtained when a penetration of 20 mm ± 5
obtained in 30 sec. If putty is substandard in consistency, the sample
returned to original putty. More water is added, mixed for 2 3 min, and
retest is made as above. If penetration then exceeds standard, the
should be discarded and a new one prepared.
A special apparatus known as the Emley Plasticimeter is used in this
similar type of mold as employed in the standard consistency test is
with water, placed on a porcelain or disposable plaster base plate, and
flush to the top with a lime putty of standard consistency. The mold is
removed carefully and vertically without distorting the mound of putty.
base plate with putty is on a turntable. A motor rotates the turntable
revolution in 6 min, 40 sec and rises a thirteenth of an inch per
Before rotation is commenced, a disc from above is placed in contact
paste. This is intended to simulate the action of a trowel applying
to an absorbent wall base. Timing is critical. The turntable should not
in motion until exactly 120 sec after the putty is first added to the
Thus, the following times must be precisely recorded
motor (and rotation).
Record scale reading each
minute until completion of
test is complete when
scale reaches 100 or
scale value falls (reading
less than previous one) or
scale reading remains
constant for three consecutive readings or the specimen has visibly
broken bond with the base plate.
some degree of reproducibility in this test is a base plate with the
degree of absorption that has been standardized at not less than 40 g
moisture absorption when the paste is immersed in water at room
24 hr. Meticulous care of base plates is necessary–cleaning thoroughly,
and soon–to maintain proper degree of porosity.
The Emley test is the only test recognized by ASTM. However, even
it readily acknowledge its shortcomings, particularly lack of
caused principally by base plates that lack uniformity in suction as
the varying skills of operators. Yet in spite of such criticism it
still is the
most satisfactory method thus far advanced and certainly is informative
rheological properties and workability of limes. However, this method
been adopted by the United States and Canada.
The United Kingdom employs a
nonabsorbent flow table
for measuring workability. The number of times the flow table is bumped
in flattening a truncated cone of putty of standard consistency to
its original diameter. On this test the British specify a minimum of 10
for hydrated lime and quicklime putty, respectively–values that would
regarded as extremely low in the United States, probably substandard.
A so called Carson blotter
test will also indicate
in a crude way the degree of plasticity. A glob of putty of standard
consistency is placed on a filter pad or blotter and is spread over the
with a spatula or putty knife. The number of strokes required before
loses its moisture and balls up under the spatula is an approximate
plasticity, although obviously of completely unpredictable
Retention (and Flow
Values). An indirect measure of plasticity and workability of
sanded mortars is the water retention test, since frequently lime that
possesses a high water retentive capacity has a correspondingly high
plasticity value (and vice versa) with limes of low water retentive
weighing 500 g and standard
Ottawa sand weighing 1500 g are intermixed with a measured amount of
water in a
nonabsorbent bowl. Hydrated lime is first wetted in the water before
is added or if lime putty is employed, it is first converted to a
sand is gradually added, amid stirring and kneading action with a
The apparatus initially used
for this test is a flow
table mounted on a vertical shaft in such a manner that it can be
dropped a fixed height of 0.5 in. (12.7 mm) by means of a rotating cam.
surface is of nonabsorbent, non corrodible metal and should be so
that it slowly revolves on each drop (1 revolution for every 25 drops).
nonabsorbent flow mold, 2 in, in height, 4 in. (5 and 10 cm) in inside
at the base, and 2.75 in. (70.5 mm) inside diameter at the top, is
the center of the flow table and filled, flush to the top, with the
sanded lime mortar. The mortar is pressed into the mold with fingertips
assure complete filling without voids, and the mold is carefully
table is then dropped 25 times in 15 sec. The mortar flow is the
increase in diameter of the flattening mortar mass, expressed as
original diameter. This standardizing value is an essential
prerequisite to the
water retention test itself. If the flow is less than 100%. More water
to the mortar until on retesting the flow measures 100 115%. The
mortar is returned to the original bowl and remixed for 135 seconds. If
flow exceeds 115%, the sample should be discarded and a new batch made.
The water retention apparatus
of a water aspirator controlled by a mercury column relief and
connected by way
of a three way stopcock to a funnel on which rests a perforated dish
nonabsorbent material. A specified grade of filter paper is then fitted
and tightly to the bottom of the dish and moistened.
Immediately after the flow
test described previously,
the remaining mortar on the flow table is returned to the original
and remixed for 30 sec. It is then rapidly distributed uniformly,
compaction, over the sheet of dampened filter paper in the perforated
flush to the top of the dish by use of a straightedge. The dish is
the funnel, and a vacuum is applied. After 60 sec of suction of water
mortar, the stopcock is turned off in order to expose the funnel to
pressure. The mortar is then removed from the dish with a spatula and
to the mold on the flow table, where it is filled completely with
compaction flush to the top. A second flow value is then obtained in
manner as previously described by dropping the flow table this value is
as the flow after suction. The whole test (or what appears to be a
tests) should be conducted as rapidly as possible and should never
min from start to finish.
A high value or a percent of
85 95 indicates that a
lime possesses high water retentive capacity by resisting the
imposed suction, described earlier. A value of 75 85% would indicate
intermediate water retention. In contrast to lime, a portland cement
would only possess 50 60% water retention. This test is most indicative
mortar tests. Since water retention is an essential characteristic for
absorbent masonry units. Otherwise, such porous units would quickly
moisture from a mortar of low water retentivity before it could harden
and a poor bond at the mortar unit interface would result. That is why
it is an
almost invariable requirement in all masonry mortar specifications.
Differences in the water
retentivity capacity of
mortars composed of different limes, cements, and proportions of both
empirically observed by a crude quick blotter test. A glob of unsanded
putty of standard consistency or a flow of 100 115 is placed on filter
(150 lb/ream). The filter is immediately inverted and the number of
from its application to the appearance of moisture soaking through the
recorded. Contingent on the test conditions, such as percent of flow,
of paper, and atmospheric humidity, 4 30 sec might expire before
Soundness. Unsoundness in
limes, characterized by
cracking, pits and pops, bulging or distorted surfaces of a freshly
neat lime putty, gauged putty, or sanded putty, is caused primarily by
of coarse particles, particularly +No. 30 mesh (0.6 mm) materials, and
lesser extent +No. 200 mesh (74 µ) particles may be contributory. The
of unhydrated oxides (generally MgO) in the lime is also a source of
unsoundness because of the possibility of delayed hydration. Actually
milling of the hydrate in an air separator at the point of manufacture
remove all coarse particles is the most effective sinecure against unsoundness, and
in a similar manner
removal of all course particles from quicklime putty by screening is
effective. If the gradation of a hydrated lime reveals a virtual
coarse particles, then from a practical standpoint there is no need for
soundness test, except possibly in the case of the controversial normal
dolomitic hydrated lime. Yet before modern hydrate milling techniques
perfected, unsoundness from coarse particles was a chronic problem. A
cumbersome, highly subjective pitting and popping test was formerly
evaluate the soundness of lime hydrates, particularly for plastering.
achieving much finer milling, this test has been almost completely
the United States.
The ASTM lime
committee has resisted adopting a test to measure unsoundness,
expansion from delayed hydration of unhydrated oxides, largely because
accelerated test yet advanced is regarded as reasonably emulative of
conditions. An autoclave test is cited in Specification C 110 that
molding under pressure hydrated lime or lime cement limestone sand
into tablets. It may be of qualitative significance but not
it lacks reproducibility.
England, South Africa, and other
countries employ the Le
Chatelier mold test (or slight modifications of it) in measuring
damaging expansion in lime. These molds are filled with a workable
composed of varying ratios of lime, cement, and standard sand,
such as 116, 219, or 3112. After being allowed to set for 48 hr, they
steamed for 3 hr and the extent of linear expansion is measured. One
permissible limit of expansion is 10 mm.
This characteristic of mortar materials has some relationship to
workability, although it has never been correlated and it may not be
proportional in a quantitative way. However, as a generalization, the
plastic limes possess the greatest sand carrying capacity, which means
be mixed with larger volumetric proportions of sand and still provide
workability without being oversanded. Limes of poor to moderate
less sand carrying capacity and Portland cement averages 50 75% less
than a far, plastic lime, as determined by the Voss Extrusion Energy
(also called Plastometer).
This apparatus provides the only
realistic test for
measuring this property, although it is not included in the ASTM
rarely in any specification. The test consists of extruding a mortar
confined conditions in a cylinder and measuring the pressure exerted in
extrusion. It the mortar extrudes completely and easily and at low
is judged workable and carrying the optimum amount of sand.
Although pure lime is never
employed in mortar for its mechanical strength, compressive strength
requirements for lime and lime cement mortars are frequently specified.
hydraulic limes compressive and tensile strengths would be of some
much more than with fat (pure) limes.
The criteria for compressive
strength tests on
mortars are largely ASTM C109 75, a specification promulgated by the
It consists of molding 2 × 2
in. (5 × 5 cm) mortar
cubes and then deviating from the above specification in the method of
the cubes. Instead of underwater curing specified for cement mortars,
performed in a moist closet, or with cycles of wetting and drying, or
case of straight or very high lime content mortars, just laboratory
are then broken at 7 and 28 days with strengths reported in psi (kPa).
The setting time of fat lime
cement) is of no interest and is only applicable to hydraulic lime,
or straight cement mortars. The same standard test is employed a
test with the Gilmore needle and Vicat apparatus (ASTM C266 74).
Rate. ASTM has
recognized the following settling rate test for many years
Ten g of lime hydrate is placed in
a 100 ml glass stoppered,
graduated cylinder and is wet down with 50 ml of CO2 free distilled
room temperature. It is mixed thoroughly for 2 min, including inversion
cylinder by hand. The contents are allowed to stand for 30 min and then
diluted to the 100 ml mark with more CO2 free distilled water. After
mixing, contents are allowed to stand for 24 hr. Sedimentation height
of meniscus is then visually taken at 0.25, 0.5, 0.75, 1, 2, 4, and 24
Rate. Probably the
most equitable slaking rate test for quicklime is the current ASTM
standard, contained in C 110, Physical Tests for Lime, since allowances
made for different types and qualities of quicklimes. However, this and
slaking tests are invariably controversial.
The procedure consists of preparing
sample–No. 6 sieve size–as rapidly as possible to prevent air slaking.
is defined High
reactivity is completely slaked within 10 min medium is completely
within 10 20 min low requires more than 20 min for complete reaction.
Readings are continued until
temperature rise is
less than 0.5°C (0.9°F) in three consecutive readings. Total active
time will be computed from the first of these three readings.
This initial starting
temperature is subtracted from
the final temperature to obtain the total temperature rise. Before
of slaking, temperature rise can be similarly computed for any earlier
like 30 sec. Values are plotted on a curve.
There are many slaking rate
tests, but most are
analogous to the preceding. Many lime manufacturers check lime
reactivity in a
very cursory manner by simply mixing approximately a like amount of
and water and visually observe the reaction. There is nothing learned
quantitatively from such a crude, quick test, but it can be meaningful
person experienced with lime. Any appreciable change in slaking rate
The American Water Works
Association in their AWWA
Standard B202 77 for Quicklime and Hydrated Lime has contrived a
slaking rate test from ASTM. They evaluate limes by the rapidity of
achieving a temperature rise of 72°F (40°C). That is, in 3 min or less
highly reactive 3 6 min, medium reactive and over 6 min, low reactive.
not differentiate between types of lime and specify 400 ml water to 100
No. 6 mesh (3.36 mm) high calcium quicklime.
mechanical sieving based on sieve sizes established in ASTM E 11 70 is
virtually the only gradation test required for all lime and limestone,
whiting, which employs other methods of particle size determination.
Sieve sizes extend down to
the No. 400 sieve (37 µ),
but the lime industry has generally standardized on the No. 325 sieve
(44 µ) as
being the lowest practical sieving limit to employ for reasonable
standard dry sieving method is satisfactory for quicklime and limestone
totally unsatisfactory for hydrated lime. With the latter a wet sieving
procedure, is strongly recommended. Otherwise, on dry sieving hydrates
agglomerate, even though they adhere loosely together, and will not
through to the small sieve sizes, thereby distorting the gradation and
it appear to be coarser than it actually is. However, in wet sieving
stream of water applied at low pressure, the agglomerates readily break
countless microparticles, usually of subsieve sizes, and pass through
finest screens. With hydrates most of the gradation specifications are
to control or limit the coarse fractions (residues), such as a maximum
retained on the No. 30 mesh (0.6mm) and a maximum of 15% retained on
200 mesh (74 µ). A few individual consumers specifications are known to
95 or 98% passing a No. 325 mesh (44 µ), but this would represent the
stringent gradation requirement for hydrate.
For quality control testing
of No. 325 mesh
limestone whiting, wet sieving is also practiced, generally adhering to
test procedure 1 61 developed by the Pulverized Limestone Institute,
after wet screening, involves drying, mechanical agitation, and final
of the No. 325 mesh residue.
However, other evaluation
tests are employed largely
for research and general technical information that pertain to particle
and its distribution. These are employed more for determination of
(micron sizes) the shape and form of the microparticles, whether they
cubical, plate like, or needle shaped the range in surface areas for
particles and the average surface area for a representative volume or
petrographic analysis (thin sections) molecular structure and even the
(pore size distribution) of these microparticles in angstrom units. The
increasing recognition that surface area is of greater significance
particle size for many applications of limestone flour, whiting, and
probably lead ultimately to specifications predicated on a minimum
area. (This method is now employed as standard practice for Portland
ASTM specifications C 150 76a, C 204 75, and C 115 74.) At least, one
manufacturer uses the Blaine Air Permeability method that measures
in quality control testing of hydrated lime and quicklime putty. Thus,
future lime consumers may conceivably specify that hydrated lime must
minimum surface area of, say, 15,000 or 20,000 cm2/g.
The need for
individualization that has prevailed in
exploration for deposits and the extraction of the stone is just as
in the design of a plant for conversion of the stone into marketable or
products. The same variables exist–the physical characteristics of the
be crushed and screened, the chemical requirement (impurity tolerances)
demand conformance, and lastly, and at this juncture the most important
requirement, the sizes or gradations of stone that are desired. Thus, a
with adequate capacity, tailor made to the particular terrain and sizes
quality of stone required, is essential.
There are no foolproof,
detailed blueprints for such
a plant. In fact, if an existing modern plant of highest efficiency was
duplicated exactly, it might easily prove to be totally unsuitable at a
location. So in designing a new plant it is prudent to seek advice from
engineering consultants specializing in this field and from
equipment for stone processing. In view of this situation, the
treat this subject generally with emphasis on practical plant design
considerations and suggestions on avoidance and correction of operating
For the specifics of plant
design, past issues of
Pit and Quarry and Rock Products contain numerous valuable case history
articles on many varied plants, providing specifications (and brand
equipment and performance data, and clearly demonstrate how
plant is. For the countless modifications in the basic types of
most complete information source is the annual pit and Quarry Handbook
Purchasing Guide, published by Pit and Quarry in Chicago. Almost every
type and model of equipment now in commercial use in the limestone,
aggregate industries are illustrated and described in detail.
Figures 1 depict flow diagrams of
typical modern stone
Obviously even though
numerous ranges of stone
gradations may be desired as primary products, other plus, minus, and
intermediate sizes are also accumulated. These undesirable sizes should
marketed as by products, the return from which enhances the profits of
primary products. This principle is equally valid whether the stone
are sold or are consumed to produce more highly refined products, like
lime, and portland cement. In the event that these submarginal sizes
gradations are unmarketable or unusable, they have to be stockpiled at
convenient location on the premises, like overburden. Such material is
classified by the industry as spalls (or spall piles). Again, as in the
overburden, spall accumulations should be deposited in an area that
interfere with plant processing and quarrying. It is bad practice to
intermingle overburden and spalls. These piles should be segregated,
subsequently a profitable outlet for this stone may emerge otherwise
potential value is usually dissipated in a heterogeneous waste pile.
of subsequent screening and classifying is often too formidable.
Next to blasting, primary
crushing is the most
effective method of stone size reduction, far more satisfactory than
blasting. However, for high activity it is essential that the crushers
correlated with the city of the bucket of the shovel or loader used in
the blasted. The crusher should be able to accommodate the largest
in the bucket can efficiently handle. Proper selection minimizes the
oversized rock jamming the crusher and obstructing the flow of it. A
may pass through the crusher but then interlock edged with smaller
forcing the crusher to a standstill. There is absolute protection
jams. When jamming delays occur, they are corrected by cumbersome hand
by prying rocks loose with the metal crowbars or using pneumatic hammer
A costly piece of auxiliary
equipment, called a
hydraulic impulse breaker, aid to be able within minutes to fracture
boulder into manageable is that clear the opening. Electrically
under remote control the impulse breaker is handled by the crusher
from his control it thus reducing downtime and averting dangerous hand
The machine with variable speed control imparts the necessary impacts
fragrant the rock. Another crusher plant design detail that minimizes
instructions is to install an apron, pan, or vibrating feeder that
under a bin or hopper and induces a steady, smooth conveyance of stone
crusher. This also tends to prevent choke feeding that generates are
which are undesirable in some plants.
Basically, stone is crushed
in two ways by
compression or impact impression, typified by the jaw and gyratory
crushers. Consists of a slow application of load (as pressure) on rock.
piece of rock must be restrained to remain under load, an equal and
force mates shear stresses within the stone causing it to crack and
contrast, impact on which impact breakers and hammer mill crushers are
indicated subjects the stone to sudden force, that is, to sharp, rapid,
repeated blows. Since for limestone most primary crushing is performed
by a jaw
and gyratory crushers and impact breaker, only brief mention is made of
primary crushers, such as the single and double roll crusher, which are
compression types. These units are mainly used for softer species of
and other minerals. The hammer mill, closely related in crushing action
impact breaker, is employed to some extent but its prime particle is in
Of these types the jaw is the
crusher and until 1960 and the gyratory dominated primary crushing of
limestone. Since then, impact breakers have become of equal importance,
particularly for cement and other uses that desire a high percentage of
and small fractions. Since a number of manufacturers fabricate all
it is possible to obtain unbiased, reliable information on their
for a specific situation. Many widely varying conditions affect a
selection, such as size of loading bucket, top stone size into crusher,
crusher capacity, hardness and moisture content of stone, desired
and sizes (product mix), estimated idle time, and so on. Some large
may use two or three types for different gradations. No single type is
per se, only for individualized conditions.
Crusher. The original
Blake or double toggle, dual jaw type is still widely used.
this are the single toggle or overhead eccentric type and another with
moveable jaws. The Blake type has one stationary jaw against which the
compressed by the movable jaw. The discharge end of the jaw is
providing some latitude in accommodating different top sizes. When the
raw stone into this crusher is controlled with a feeder, a slightly
crusher can be used. Then grizzlies are optionally employed for
clay and stone funes.
have smooth steel surfaces, the shape of the crushed stone tends to be
flat and elongated, similar in shape to what the gyratory yields.
the surface of one jaw is corrugated steel, a larger percentage of
shapes results. The jaw is much lower in profile than the gyratory,
only about half as much headroom for the same capacity unit. Also wider
settings can be made at the discharge end than with the gyratory. But
same size unit the gyratory has over twice as much capacity as the jaw,
largest capacity gyratory has five to six times greater capacity than
largest jaw. In capacity, Jaws range between 20 and 600 tons/hr. Sizes
crushers range from 24 × 36 in. to 66 × 84 in. (0.61 × 0.92 and 1.67 ×
This range of sizes crushes down to 3 5 in. (7.5 12.5 cm) top size,
same as the gyratory. In balance there appears to be a consensus that
is less costly than the gyratory for lower capacities.
crusher consists of a conical head inside an outer concave bowl.
impelled by a slow gyratory or eccentric (not rotary) movement of the
head that compresses the stone against the fixed concave crushing
crushing force remains uniform. Its capacity is greater than those of
types of primary crushers, ranging from 225 to 3000 tons/hr. The
of these units ranges from 26 to 72 in. (0.66 1.9 m), with the smallest
discharge openings ranging between 3.5 and 9 in. (8.8 22.5 cm).
Compared to the
jaw for equal capacities, the gyratory weighs and costs less. It also
slightly less horsepower than the jaw for equivalent capacities because
Its main disadvantages are
greater headroom, more
restricted discharge openings, yielding of only a small percent of
stone (mostly flattish) and, sometimes, greater maintenance costs.
when high, continuous capacity is required, this unit usually provides
economical crushing system.
Breaker. The impact
breaker consists of one or two massive impeller breakers that rotate at
of 250 1000 rpm and shatters rock of comparable size to the other two
But this initial impact is only the start. Fragments of the original
are hurled at high velocity against steel breaker bars inside the
chamber as well as colliding with flying rock, causing further breakage
reduction in size. Pieces of stone that are still oversized go through
cycle of violent impact and collision until they are small enough to
through the adjustable breaker bars or grate. In effect, this is a form
closed circuit crushing.
Thus, this machine offers a
higher ratio of size
reduction than either the jaw or gyratory. But increasing speed and
the openings of vertical and horizontal bar spacings, crushing is
producing sizes down to 1.5 2 in. (3.75 5 cm) top size–smaller than
primary crushers except the hammer mill. Thus, if the primary product
aggregate or lime kiln feed, secondary crushing may be unnecessary,
possibly for by products.
predominate from impact crushers, more than from any other crusher.
breakage from ricochet and collision occurs without additional
energy requirements are less. Capacities range from 300 to 2000
double impeller breaker possesses the greatest capacity.
With all primary crushers
when stone is still too
large to convey from the crusher down chutes to a conveyor belt, it may
directly into another feeding hopper either for the secondary crusher
or onto a
conveyor belt in closer proximity. This conserves belt life from the
of heavy falling stone. This practice is judicious when stone fines and
are present, since fines lubricate the chute, causing the stone to
higher velocity. An alternative is use of a grizzly chute that permits
fall on the belt first, cushioning the descent of the larger stone.