Chapter-1.pptx

Chapter-1: Metallic Minerals
and Their Occurrences

Metallurgy: Metallurgy is the process of extraction of metals in
their pure form from their ores. Metallurgy includes the
preparation of alloys and the mechanical and heat treatments given
to the metals for imparting necessary desired properties to them.
The physical and chemical methods employed for the purpose are
called metallurgical processes.
Mineral: Metals occur mainly in the earth’s crust, sometimes in the
native or free elemental form, but usually as compounds with other
elements. Naturally-occurring elements and compounds are
known as minerals.
Generally, minerals are homogeneous crystalline solids; some have
fairly definite composition, others exist over a range of composition.
They may contain extra elements in solid solution.
Rock: Rocks are aggregates of one or more minerals and have
different characteristics corresponding to their period and
mode of formation.

Ore: The desired mineral or minerals, together with the gangue,
constitute the ore. Thus, ore can be defined briefly as a mineral
aggregate containing one or more metals in profitable form.
From all minerals, metal or metals cannot be extracted economically.
The minerals from which metals can be extracted economically are
called ore. For example, 𝑍𝑛𝑆 is an ore of zinc.
Gangue: Usually in mining the valuable mineral, a certain
amount of waste in the form of other associated or neighboring
minerals must inadvertently be included which is called
gangue. Common gangue minerals are silica (𝑆𝑖𝑂2) as quartz and
various silicates, aluminum oxide as such, but often as silicate,
calcite ( 𝐶𝑎𝐶𝑂3 ), dolomite ( 𝑀𝑔𝐶𝑂3 ∙ 𝐶𝑎𝐶𝑂3 ), barytes ( 𝐵𝑎𝑆𝑂4 ),
fluorspar (𝐶𝑎𝐹2) and various iron compounds.

The differences among mineral, ore and gangue
Mineral Ore Gangue
Naturally occurring
elements and compounds
are known as minerals.
Ore can be defined as a
mineral aggregate
containing one or more
metals in profitable form.
Usually in mining the
valuable mineral, a
certain amount of waste
in the form of other
associated or neighboring
minerals must
inadvertently be included
which is called gangue.
Directly obtained from
nature.
Obtained from minerals. Obtained from minerals
and ores.
Every mineral is not ore. Every ore is mineral. Gangue is waste.
Metals cannot be
extracted from all
minerals.
Metals can be extracted
from all ores.
No metals can be
extracted from gangue.
Usually, minerals are
found as solid stone in
the earth’s crust.
Ores are found as oxides,
sulfides and carbonates
of various metals.
Gangues are found as
silica, silicate, carbonate,
aluminum oxide and iron
compounds with ore.
For example, 𝑍𝑛𝑆, 𝐴𝑢. For example, 𝑍𝑛𝑂. For example, 𝑆𝑖𝑂2.

Important minerals of some common metals
Metal Mineral Chemical formula
Copper (Cu)
Chalcopyrite 𝐶𝑢𝐹𝑒𝑆2
Chalcocite 𝐶𝑢2𝑆
Covellite 𝐶𝑢𝑆
Bornite 𝐶𝑢5𝐹𝑒𝑆4
Enargite 𝐶𝑢3𝐴𝑠𝑆4
Cuprite 𝐶𝑢2𝑂
Malachite 𝐶𝑢𝐶𝑂2 ∙ 𝐶𝑢(𝑂𝐻)2
Native copper 𝐶𝑢
Silver (Ag) Native silver 𝐴𝑔
Argentite 𝐴𝑔2𝑆
Cerargyrite 𝐴𝑔𝐶𝑙
Gold (Au)
Native gold 𝐴𝑢
Calaverite/sylvanite 𝐴𝑢, 𝐴𝑔 𝑇𝑒2
Petzite (𝐴𝑢, 𝐴𝑔)2𝑇𝑒
Magnesium (Mg)
Magnesite 𝑀𝑔𝐶𝑂3
Dolomite 𝑀𝑔𝐶𝑂3 ∙ 𝐶𝑎𝐶𝑂3
Calcium (Ca)
Gypsum 𝐶𝑎𝑆𝑂4 ∙ 2𝐻2𝑂
Calcite 𝐶𝑎𝐶𝑂3

Zinc (𝑍𝑛)
Zinc blend/sphalerite 𝑍𝑛𝑆
Calamine 𝑍𝑛𝐶𝑂3
Aluminum (𝐴𝑙)
Bauxite 𝐴𝑙2𝑂3 ∙ 2𝐻2𝑂
Corundum 𝐴𝑙2𝑂3
Lead (𝑃𝑏)
Galena 𝑃𝑏𝑆
Anglesite 𝑃𝑏𝑆𝑂4
Cerussite 𝑃𝑏𝐶𝑂3
Matlokite 𝑃𝑏𝐶𝑙2 ∙ 𝑃𝑏𝑂
Iron (𝐹𝑒)
Magnetite 𝐹𝑒3𝑂4
Hematite 𝐹𝑒2𝑂3
Limonite 2𝐹𝑒2𝑂3 ∙ 2𝐻2𝑂
Goethite 𝐹𝑒2𝑂3 ∙ 𝐻2𝑂
Siderite 𝐹𝑒𝐶𝑂3
Nickel (𝑁𝑖)
Pentlandite/sudbury ore 𝐹𝑒𝑆2 ∙ 𝐶𝑢𝑆 ∙ 𝑁𝑖𝑆
Garnierite 𝑀𝑔, 𝑁𝑖 𝑆𝑖𝑂3 ∙ 𝑛𝐻2𝑂
Niccolite/kupfernickel 𝑁𝑖𝐴𝑠
Nickel glance 𝑁𝑖𝐴𝑠𝑆
Titanium (𝑇𝑖)
Rutile 𝑇𝑖𝑂2
Ilmenite 𝐹𝑒𝑇𝑖𝑂3
Mercury (𝐻𝑔) Cinnabar 𝐻𝑔𝑆

Tin (𝑆𝑛)
Tinstone/cassiterite 𝑆𝑛𝑂2
Tin pyrites 𝑆𝑛𝑆2 ∙ 𝐶𝑢2𝑆, 𝐹𝑒𝑆
Sodium (𝑁𝑎)
Rock salt 𝑁𝑎𝐶𝑙
Chile salt petre 𝑁𝑎𝑁𝑂3
Sodium sesqui carbonate 𝑁𝑎2𝐶𝑂3 ∙ 𝑁𝑎𝐻𝐶𝑂3 ∙ 2𝐻2𝑂
Sodium aluminum fluoride 𝑁𝑎3𝐴𝑙𝐹6
Feldspar 𝑁𝑎𝐴𝑙𝑆𝑖3𝑂8
Potassium (𝐾)
Bengal salt petre 𝐾𝑁𝑂3
Sylvine 𝐾𝐶𝑙
Urenium (𝑈) Pitch blende 𝑈3𝑂8
Cobalt (𝐶𝑜) Cobalt glance 𝐶𝑜𝐴𝑠𝑆

Beneficiation of minerals: Beneficiation of minerals is a process
which consists of size-reducing processes i.e., breaking of large
particle ores into small particle ores, enrichment of metal by partial
removing of gangue and preparing of ores for metal extracting. Ores
from mine usually are of large size. So, their size is reduced by
means of various size-reducing machines. Then the particles are
grinded into fine powder with grinders. At last various processes
such as physical, heat or chemical treatments are used for
enrichment of metals in ores. Ores are such heated that they are not
melted.
Importance of size reduction: The ores collected from mine are
usually of large size. Metal cannot be extracted from large-sized
ores. Because ore transportation is difficult in various steps of
extraction. Moreover, removal of gangue, roasting, calcination and
various chemical treatments are very difficult for large size. But
these can be solved, and production is increased by size-reducing of
ores. So, size reduction plays an important role in extractive
metallurgy.

The naturally occurring minerals contain gangue such as dust, sand and
other wastes. For metal extraction, gangue must be removed from
minerals. Various processes are followed for this purpose such as:
A.Concentration process
a.Gravity concentration method
i. Jigging
ii.Vanning
iii.Tabling
b.Flotation concentration method
i. Collective
ii.Flotation
c.Magnetic method
B.Sink-and-float method
C.Thermal method
a.Rotary drying or calcining
b.Roasting
i. Multi hearth
ii.Fluo solid roasting
Various methods used for mineral separation

Flux and slag
 Metals and non-metals and some other components constitute what is
known as slag. According to their chemical properties, these oxides may
be classified into three groups:
a. Basic oxides, such as 𝐶𝑎𝑂, 𝑀𝑔𝑂, 𝐹𝑒𝑂, 𝑀𝑛𝑂, 𝑁𝑎2𝑂 and 𝐾2𝑂.
b. Acidic oxides, such as 𝑆𝑖𝑂2, 𝑃2𝑂5, 𝑇𝑖𝑂2, 𝑉2𝑂5 etc.
c. Amphoteric oxides, such as 𝐴𝑙2𝑂3, 𝑉2𝑂3, 𝐶𝑟2𝑂3 etc.
 The gangue mineral in the ore is removed by adding another chemical
substance, called flux. A substance added to convert the gangue or
matrix into fusible mass is called flux. The fusible mass is known as
slag. The flux reacts with gangue to form slag, which is generally
obtained as an upper liquid layer over molten metal in the furnace.
Flux + gangue/matrix → Slag

Flux and slag
Fluxes are generally of two types:
a) Acidic fluxes: When the ore is associated with basic impurities such as
𝐹𝑒𝑂, 𝐶𝑎𝑂, 𝑀𝑔𝑂 etc., a suitable acid flux such as 𝑆𝑖𝑂2, 𝑃2𝑂5 etc. is used.
For example, in the extraction of copper, the ferrous oxide (𝐹𝑒𝑂), a basic
impurity is removed by using silica (𝑆𝑖𝑂2) as the acid flux.
𝐹𝑒𝑂 + 𝑆𝑖𝑂2 → 𝐹𝑒𝑆𝑖𝑂3 (ferrous silicate)
Gangue Flux Slag
Similarly, lime may be removed with silica (acidic flux).
𝐶𝑎𝑂 + 𝑆𝑖𝑂2 → 𝐶𝑎𝑆𝑖𝑂3 (calcium silicate)
Gangue Flux Slag
b) Basic fluxes: If the ore is associated with acidic impurities such as
𝑆𝑖𝑂2, 𝑃2𝑂5 etc., then the flux used must be basic (e.g., 𝐶𝑎𝑂, 𝑀𝑔𝑂 etc.).
𝐶𝑎𝑂 + 𝑆𝑖𝑂2 → 𝐶𝑎𝑆𝑖𝑂3 (calcium silicate)
Gangue Flux Slag
𝑀𝑔𝑂 + 𝑆𝑖𝑂2 → 𝑀𝑔𝑆𝑖𝑂3 (magnesium silicate)
Gangue Flux Slag
The fusible mass, known as slag is removed and used in road making as
well as in the manufacturing of cement and fertilizers. Thomas slag is
calcium phosphate, 𝐶𝑎3 𝑃𝑂4 2.

Comminution or size reduction: By which mechanical process, naturally
occurring large size ores are reduced into small size ores is called
comminution. It includes breaking, crushing and grinding.
Breaking: Breaking converts run-of-mine ore to any size between about
6 𝑖𝑛𝑐ℎ and 2 𝑖𝑛𝑐ℎ. Jaw breaker is a typical breaker.
Jaw breaker consists of a fixed jaw and a moving jaw. The angle between
fixed jaw and moving jaw is 30° and the upper mouth opening is for ore
feeding. The moving jaw is attached with an electric drive and the toggles
are moved by means of the electric motor. The jaws exert very high
pressure upon ores between them. Therefore, the ores are broken into
small size and the output is collected by the lower narrow hole.
Size reduction

Figure: Principles of typical jaw breaker
Size reduction

Crushing: Crushing reduces breaking minerals to between about 1 𝑖𝑛𝑐ℎ
and 1
8 𝑖𝑛𝑐ℎ. Symons cone crusher is used for this purpose. Symons cone
crusher is a circular rotating crusher. Ores are fed from up of the crusher
and the main shaft is rotated by means of electric belt. Therefore, the shaft
strikes the ores and they become reduced.
Size reduction
Figure: Symons cone crusher

Grinding: Grinding reduces ores of about 14 inch or smaller size to the
range 0.02-0.002 inch or less. Ball mill or rod mill are the typical grinders.
Rod mill is typical cylinder-shaped tank which rotates, and the inside is
furnished with some rods. Feeding is done through one end and after
striking with rods because of rotating of the tank the ores become small and
small and they are outputted through another side.
In case of ball mill balls are used instead of rod.
Size reduction
Figure: Rod mil for grinding Figure: Ball mill for grinding

Closed-circuit operation is generally a continuous recirculation operation.
By which process different sized ore particles are classified by recirculation
operation is called closed-circuit operation. The best proportional products
are found in this process rather than other operations.
Description: In this process, ores are fed into a ball mill arranged with a
circuit. The ores enter into a mechanical classifier after grinding. The
classifier divides the ore particles into two parts. One part is obtained as
finished product and another part of comparatively big and coarse particles
is again fed into ball mill and finished product is obtained from them.
Size reduction: Closed-circuit grinding operation

Sorting or grading: The particles in as-mined or comminuted ore usually
have a wide size-range. With rich as-mined ore, sorting can be used to
remove coarse sizes for comminution and fine sizes for agglomeration.
For sizes down to about 0.05 𝑖𝑛𝑐ℎ, ore is sorted by screening or sieving,
that is, sorting by size or sizing. The screens may be made of woven steel
or other metal wire, steel rods, punched steel plate or of steel or cast-iron
bars, depending on the size of ore being handled. The bar screens used for
coarse material are known as grizzlies; they may be stationary or moving or
made of rollers. Usually, the other types of screens for finer mineral are
shaken by mechanical or electrical means; the trammel is a rotating
cylindrical screen. Feed to screens may be wet or dry ore.
Screens are not generally efficient for sizes smaller than about 0.05 𝑖𝑛𝑐ℎ
and fine mineral is sorted by utilizing the different rates of fall of the various
particles in water and sometimes in air; this is known as classification.
Following some classifiers are given:
 Evans launder classifiers
 Allen cone classifiers
 Dorr-rake classifiers
 Dorr-thickener classifiers
Size separation

Figure: Screening by trommels
Size separation

Evans launder classifier
Evans launder classifier for dividing up comminuted ore for feed to various
cleaning machines consists of a through along which the ore is carried as a
pulp in a horizontal water current. In the bottom of the through are a number
of compartments in which uprising currents of water are maintained, the
strength of these currents decreasing from feed to discharge end. The larger
and heavier one particles settle out in the first compartments and the smaller
in later ones. The products are drawn off periodically or continuously through
holes or spigots. A very fine suspension over-flows at the discharge end as
well.
Figure: Evans launder classifier
Size separation

Concentration of ores: The actual cleaning operations in ore-dressing are
known as concentration, the purpose being to reduce the ratio of gangue to
valuable mineral. The process of removing gangue or matrix (non-metallic
and rocky minerals, such as quartz, mica, feldspars and other silicates)
from the metal ore is called concentration of ores. Concentrating is done
based upon various properties of ore such as density, specific gravity etc.
Importance: Following the importance of concentration of ores is given:
i. It is easy to use small particle ores in various steps of metal extraction.
ii. Enrichment of valuable metals by removing gangue easily and in low
expense.
iii. Differentiating various precious metal compounds.
iv. Contact with ores with corresponding reagents becomes easy in main
operation of metal extraction.
v. Extraction of metal with ease and economically.
Methods: Concentration methods are of three types:
1. Gravity concentration method
2. Flotation concentration method
3. Magnetic concentration method
Concentration of ores

Ratio of concentration: Ratio of concentration is equal to the weight of
the concentrate divided by the weight of the original ore. This index and the
ratio of enrichment would be equal if there were no loss in the talling.
Ratio of concentration =
the weight of the concentrate
the weight of the original ore
Ratio of enrichment: The ratio of enrichment indicates the amount of
cleaning and is the ratio of the percentage of valuable mineral in the
concentrate to that in the original ore.
Ratio of enrichment =
percentage of valuable mineral in concentrate
percentage of valuable mineral in original ore
Percentage recovery: The percentage recovery shows the loss entailed in
concentration and is the percentage of the valuable mineral contained in the
ore that is recovered in the concentrate.
Relation: The relation among the terms ‘ratio of concentration’, ‘ratio of
enrichment’ and ‘% recovery’ is
Ratio of enrichment = Ratio of concentration × percentage recovery
Some definition related to concentration of ores

In gravity concentration method, ores are concentrated depending upon
the differences among their density and specific gravity. More the difference
in specific gravity, easier to differentiate them. The difference in specific
gravity between the minerals to be separated should best be 1 or greater;
particle size and shape also affect separation.
This method is of three types:
 Jigging
 Tabling
 Vanning
Jigging: The plunger type fixed-sieve jig is the typical one. Jigs deal
efficiently with ore in the size range 1.5−0.08 𝑖𝑛𝑐ℎ. The ore is fed on to a
screen which is submerged in water and contained in a tank. The ore is
stratified by means of pulsion (upward) and suction (downward) currents of
water passing through the screen. Concentrate is removed from the screen
by a gate mechanism. A valuable hutch product composed of fine particles
that have been drawn through the screen collects at the bottom of the tank.
Talling is discharged at one side of the machine.
Fixed-sieve jigs contain one or more jigging compartments (two, three or
four are common) connected together, each with a sieve and plunger and
separated by cross partitions.
Gravity concentration method

Figure: Jigging machine

Tabling: The Wilfley is the best-known form of concentrating table. Tables
deal with size range 0.08 − 0.008 𝑖𝑛𝑐ℎ. It consists of a partly smooth and
partly riffled or shallow ribbed surface, which is slightly inclined to the
horizontal plane. In operation, the table is shaken rapidly backwards and
forwards in the direction of its length with such acceleration that particles on
it receive an impetus to move from one end to the other. The ore pulp is fed
across the table down the slight slope (on to the riffled portion). Due to the
shaking motion, the ore is stratified with the heavier valuable mineral at the
bottom, where it is well protected behind the riffles from the water flowing
down the table (extra water is fed). As the ore is moved along the riffles by
the shaking motion, the top-lying gangue is washed away by the water to
discharge as talling. The underlying valuable mineral continues to move
along, gradually becoming less protected with more gangue being
removed. Finally, the valuable mineral comes to the plane portion of the
table, where it drops from rib to rib, under-going more cleaning and
discharging as concentrate; a middling is also made.

Figure: Wilfley table

Vanning: The vanner is the most outstanding example of a once
important class of concentrators that has been rendered nearly obsolete by
flotation. The vanners can be used for finer sizes, although not less than
about 0.0004 𝑖𝑛𝑐ℎ. The simplest consisted of a stationary slopi9ng surface
of wood, cloth or rubber. The pulp was fed down the slope with water,
whereupon the slower moving valuable mineral settling to the bottom
tended to be held by the surface, while the lighter gangue was washed
away.
The Frue vanner is the best-known continuous kind; it consists of a
slightly inclined endless belt moving up the slope while being shaken
sideways. Ore and water are fed near the top; the gangue is washed down
and discharged as talling at the bottom. The concentrate being discharged
at the top.
Figure: Diagram
of Frue vanner

If one of the ore or gangue is magnetic and another is non-magnetic, then this
process is followed.
There is a variety of magnetic machines using drums or belts to bring the ore into
the magnetic field and to remove the attracted material. Direct-current electro-
magnets are used, high intensity for attracting weakly magnetic and low intensity for
strongly magnetic minerals. Often a number of magnets are arranged together with
alternating poles, an arrangement which gives better opportunity for mechanically
entrapped non-magnetic particles to escape. The feed may be wet or dry ore; the
machines usually work on either type but not both. The main factor governing size is
that adequate release of valuable mineral should have been made. The lower size
limit is about 0.003 𝑖𝑛𝑐ℎ and generally the closer the sizing the better. This method
is very popular for iron ores.
Magnetic concentration method
Figure: Magnetic pulley

Nowadays flotation is the most used method for concentrating sulfide
ores. This is of following two types:
 Bulk flotation method: In this process, the same ores are floated
together and then again separated.
 Selective flotation method: In this process, valuable minerals of
complex ores are separated. Here 𝑝𝐻 controlling is very important. Here
𝑝𝐻 controlling is very important. The 𝑝𝐻 is kept between 7 − 13 using
𝑁𝑎𝐶𝑂3, 𝐶𝑎𝑂 etc.
Principle of flotation concentration method: The ore is first obtained as
a fine suspension in water by fine grinding in ball or rod mills in closed
circuit with mechanical classifiers. The particle size is generally best less
than about 0.01 𝑖𝑛𝑐ℎ yet greater than 0.0002 𝑖𝑛𝑐ℎ. The dilution of the pulp
ranges from about 5 − 40% solids by weight. Air is bubbled through this
pulp contained in a cell or tank and due to the previous addition of various
chemicals and proper agitation, the valuable mineral particles become
attached to the air bubbles and are carried by them to the surface to form a
fairly stable mineralized forth, which is skimmed off. The gangue particles
are unaffected and remain in the pulp.
Flotation concentration method

Various chemicals such as followings are added:
Frothing agents: Frothing agents are added to produce a dry, regular strong and
fairly stable forth. The frothing agents are complex organic compounds containing
one part with a strong affinity of water (a wettable, water-avid or polar complex) and
the other with reverse properties (a non-wettable or non-polar complex). Typical
examples are cresylic acid, pine, eucalyptus and camphor oils in very small
quantities (0.001 − 0.01%).
Collecting or promoting agents: They must be introduced to give the desired
mineral the right kind of surface for flotation. For example, xanthates such as
potassium/sodium ethyl, butyl or amyl xanthates are the commonest commercial
collecting agent.
Modifying agents: Modifying agent is notably depressants which prevent
collection of certain minerals. For example, 𝑁𝑎𝐶𝑙, 𝑁𝑎2𝑆𝑂4 etc.
Activators: Activators remove the effects of depressants or make certain minerals
respond to collection when otherwise they would not do so. For example,
𝐶𝑢𝑆𝑂4, 𝑁𝑎2𝑆 etc.
Conditioners: Conditions are used to control 𝑝𝐻 of the solution. For example,
𝐶𝑎𝑂, 𝑁𝑎2𝐶𝑂3 etc.
After adding the above reagents, air is flown from the lower part of the tank by a
narrow hole. The air shakes the mixture. So, the ores go above as froth and the
gangue remains in the lower part. Then the froth is removed, and the ore is
separated.

Figure: Flotation machine

Difference between flotation and gravity concentration
method
Flotation process Gravity concentration process
It requires small space. It requires big space.
Low expense. Comparatively high expanse.
Here ores are separated depending
upon their property of wetting with oil
or water.
Here ores are separated depending
upon their sizes and specific gravity.
Various chemicals such as frothing
agent, collecting agent etc. are
added.
No chemicals are needed.
No pretreatment is required for
concentrating.
Pretreatment is required for
concentrating.
𝑝𝐻 controlling is important. 𝑝𝐻 controlling is not necessary.
Very fine particles ( 0.01 −
0.0002 𝑖𝑛𝑐ℎ) are separated.
Less fine particles ( 0.08 −
0.008 𝑖𝑛𝑐ℎ) are separated.
In this process, sulfide ores are
readily separated but oxide ores
cannot be separated.
Any kind of ore can be separated
depending upon specific gravity.

This is a comparatively recent process especially for ores and is now soundly
established. Gravity is essentially the only factor involved in separation. The
comminuted ore, generally with finer sizes removed, is put into a fluid having a
specific gravity intermediate between those of the minerals to be separated. In the
case of ores, the valuable mineral is recovered as sink and the waste as float.
In this process, separation is carried out in tanks. The floating mineral overflows or
is scraped into a trough. The settled minerals are removed mechanically from the
bottom of the tank or drawn off in some way. A middling may be made by varying
the density of the medium from top to bottom of the tanks. Currents in the medium
may cause particle size and shape to play some part in separation. This process is
used for 𝑃𝑏, 𝑍𝑛, 𝐹𝑒 ores, cassiterite, magnesite, coal and other non-metal minerals.
Sink-and-float process (heavy-media separation)
Figure: Tank for sink-
and-float separation

In calcining and roasting, the ore is heated at a moderate temperature
without fusion, meanwhile being stirred in some way. Therefore, the ore is not
melted but oxidized by oxygen.
Benefits of calcining and roasting: Followings are the benefits of
calcining [a – c(i)] and roasting [c(ii) – g]:
a. To remove moisture combined naturally, included during handling and
storage or introduced during concentration. Concentrates are generally first
de-watered with thickeners followed in some cases by filtration.
b. To convert a carbonate to an oxide by driving off carbon oxide.
𝐶𝑎𝐶𝑂3→
∆
𝐶𝑎𝑂 + 𝐶𝑂2
𝐹𝑒𝐶𝑂3→
∆
𝐹𝑒𝑂 + 𝐶𝑂2
c. (i) To drive off organic matter.
(ii) To drive off organic matter (more high temperature).
d. To remove elements such as arsenic and antimony as their volatile oxides,
which may be recovered from the furnace flues or from the flue gases.
𝑆𝑏2𝑆3 + 𝑂2→
∆
𝑆𝑏2𝑂3 + 𝑆𝑂2
𝐴𝑠2𝑆3 + 𝑂2→
∆
𝐴𝑠2𝑂3 + 𝑆𝑂2
Calcining and roasting

e. To oxidize a sulfide to an oxide; for example
2𝑃𝑏𝑆 + 3𝑂2 → 2𝑃𝑏𝑂 + 2𝑆𝑂2
2𝑍𝑛𝑆 + 3𝑂2 → 2𝑍𝑛𝑂 + 2𝑆𝑂2
Or to burn off part of the sulfur prior to matte-smelting (roaster gases
are often used for sulfuric acid manufacture).
f. By careful control of roasting conditions to produce a soluble sulfate from
a sulfide; this is known as ‘sulfating’ or ‘sulfatizing roasting’.
𝐶𝑢𝑆 + 2𝑂2→
∆
𝐶𝑢𝑆𝑂4
𝑍𝑛𝑆 + 2𝑂2→
∆
𝑍𝑛𝑆𝑂4
g. ‘Chloridizing’ roasting, that is to convert the main mineral to a soluble
chloride by heating with common salt or some other source of chlorine.
Calcining and roasting

Difference between calcination and roasting
Calcination Roasting
Calcination is the process in which
rotating ores are heated less than
their melting point in absence of air
and the volatile gangues attached
with ore are removed.
Roasting is process in which grinded
ores are such heated less than their
melting point in presence of excess
air that the ores are not melted but
they are oxidized by oxygen of air.
The ores become inflated and
porous.
The ores form compounds of oxide,
chloride, sulfate etc.
Here the reaction is dissociation
reaction.
𝐶𝑎𝐶𝑂3 → 𝐶𝑎𝑂 + 𝐶𝑂2
Here the reaction is oxidation
reaction.
𝑍𝑛𝑆 + 𝑂2 → 𝑍𝑛𝑂 + 𝑆𝑂2
It is carried in absence of air. It is carried in presence of air.

Sintering consists of the agglomeration of material too fine for efficient
extraction in the blast-furnace, because of high dust losses. The treatment
has considerable application with iron ores. There are two common
machines:
 The Greenawalt
 The Dwight-Lloyd
Purposes of sintering: Following the purposes of sintering are given:
i. Sulfur eliminating from ore
ii. For increasing porosity, intimateness and ability to reduce.
iii. To make sinter from very fine powder.
iv. For increasing the working area of ore.
v. To change the oxidation of iron.
Sintering

Diagram of the FluoSolids roaster

Dwight-Lloyd sintering machine

Chapter-1.pptx

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