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I have been discussing extraction of ferro alloys and ferro alloying elements. Now do
not be confused when I use them intermittently. Ferro alloying elements are those, which go
into making ferroalloys. And I have been repeating that very often we need these alloying elements
in steel, and it is easier to add these alloying elements as ferro alloys, but there are times
when we want the ferro alloying element in elemental form for other uses. They are not
always used for alloying there are other uses.
So, let us go back to a slide I had shown earlier. These are the common ferroalloys;
ferrochromium, ferromanganese, ferrovanadium, ferrotungsten, ferromolybdenum, ferro boron,
ferrozirconium, ferrochromium manganese, and I would repeat this, we want these ferro alloys
because these elements called ferro alloying elements are required for alloying of steel.
It is easier to produce them in ferroalloy form and then add to steel. So, it is not
only easier to produce they will mix very quickly and that is the advantage of why we
are producing them as ferroalloys. But sometimes we need them in elemental form.
I have given you example of how chromium is produced from chromate by sodium carbonate
roasting, getting making a chromate, and then treating that with sulphuric acid to produce
N a 2 C r 2 o 7, and then from there we produce pure chromium oxide, which can go for electrolysis
or aluminothermy reduction. Now, there are many oxides in nature, which
we which will go for ferro alloying elements, but we sometimes need them as pure metals
also. And there are elaborate flow sheets for making of these elements by first always
producing pure oxide.
Like here is an example for vanadium oxide, which comes from a uranium ore that contains
a 0.2 to 0.4 percent of U 2 O 8, 2 percent vanadium, B 2 O 5. The idea here is not we
want make ferrovanadium. First we will try to; we are thinking to first try to produce
pure F e 2 O 3, a pure V 2 O 3 and then worry [why/worry] what to do.
Now, it has to go through a many chemical steps. Some of the steps, you need not answer,
but there is a very logic for all these things, why we do. Eventually why we try to get everything
in a solution then by controlling PH or we get different precipitates. You can precipitate
out uranium oxide. You can precipitate out vanadium as an oxide.
Similarly, there are tungsten ores. Incidentally we do have some tungsten ores in Rajasthan,
place called Degana, but very low grade. Because tungsten is very heavy, using gravity separation,
we can get a concentrate going up to 60 percent of W O 3.
Again that goes for soda roasting, which is a very standard procedure to produce Na 2
W O 4. Grind, leach by water, filter it, you get rid of the residue and get a soluble compound
of tungsten, then by hydrochloric acid treatment, we can precipitate W O 3. If you want pure
tungsten then you have to start with W O 3.
Similarly, tantalum, niobium; incidentally, the word columbite, there are two words for
the element niobium; columbium, as well as niobium.
So, when we are saying columbite, is actually ore of niobium and tantalum. Now, here let
me make small remark. You will find it is a columbite tantalite ore. There are these
two elements are called twins; columbium and tantalum. No matter what you do, it is very
difficult to separate them. There is another twin like this called zirconium
and hafnium. No matter what you do with zirconium there is always some hafnium associated and
whatever happens to the zirconium compound will happen to the hafnium compound. But sometimes
you do not want the twins together. We want them separated. Now this is a subject of a
lot of studies in laboratories. How you separate zirconium and hafnium? How
do you separate niobium and tantalum? I, myself, have worked on zirconium and hafnium, separation
for a long time, but that is not the subject of my discussion now.
Here there is a elaborate flow sheet. Here the aim is not only to treat these oxides
to come to a pure oxide, the concentrate, but also to separate niobium and tantalum.
And you see what a complicated flow sheet one has to adopt, and at stages one has to
use hydrofluoric acid, which is a very dangerous reagent, and that there is no simple way of
separating tantalum and niobium. But there is a process where we separate tantalum and
niobium. These two are separate. So, what I am saying is there are many oxides
in nature from where we first produce a pure oxide and then try to produce the metal. In
many cases, many such oxides will be taken into a halide form by chlorination, and then
from the halide it will be easier to produce the metal, either through electrolysis or
through an aluminothermic reduction, Thus, I will discuss in the next module, when I
discuss actually next to next, when I discuss metals from halides.
Anyway, I will stop talking about production of ferro alloying elements in elemental form.
Now I will go back to ferro alloys because that is the main subject of our discussion.
Why do we need ferro alloys? I said they are very important there are some uses mentioned
here, but I will discuss the uses little more in detail little later.
We need ferroalloys for alloying that is well accepted; that you know steel properties have
to be modified by if you want to have a stainless steel; you have to add nickel and chromium.
You will not add pure nickel metal or pure chromium. You will adjust a composition by
adding ferronickel and ferrochromium, but apart from that we also need ferroalloys for
many other things. We need them for deoxidation of steel and other gases too.
When there is… In after steelmaking is a process of oxidation and look at the way,
ferrous metallurgy works. You have iron ore, oxygen level very high, in the blast furnace
we have a reducing atmosphere, we produce pig iron, and under reducing conditions oxygen
level is low. Now, we remove impurities from pig iron by an oxidation process either in
a say from bottom blown or top blown converter whatever you blow oxygen. So, initially we
remove the oxygen then we again add oxygen, so when we get steel the oxygen level is high,
we need to remove that again and we have to use a deoxidizer.
And very often this ferro alloys are used as deoxidizers because the ferro alloying
elements form very stable oxides. They also form stable nitrides. So, they are used for
removing both oxygen as well as nitrogen. Titanium and this is zirconium not zinc, they
form stable nitrides, whereas ferrosilicon, ferromanganese, ferrotitanium, are usually
used as deoxidizers. So, if you want to add nitrogen we go for ferrotitanium, ferrozirconium
also. Then ferrosilicon, ferronickel, is also added to control graphite morphology in cast
irons. And ferroalloys, I mentioned can be produced by aluminothermic reduction. Then
you get a ferroalloy which has no carbon. They can also be produced by carbon smelting
in arc furnaces, in that case you will have carbides in the ferroalloys and you have to
find a way of removing the carbon from the ferroalloys.
To remove excess carbon one has to introduce an element which reduces solubility of carbon.
During carbon reduction, impurities are removed by oxidizing slag’s, controlled oxidation
of carbon or finally, oxidation of carbon under vacuum. These are the three standard
techniques of removing carbon from high carbon ferroalloys. I will discuss that little later,
but first of all, let me spend some time on uses of ferroalloys, and what kind of resources
we have in our country as regards the sources are concerned.
Now, unfortunately I haven’t made a slide out of this. So, I will have to read out something
about ferroalloys, and their uses. Ferrochrome, both high and medium carbon ferrochrome, carbon
can be 2 to 8 percent or chromium 78 to 68 to 71 percent.
They are use to supply chromium for stainless steel making and to produce alloy steels for
mining and milling operations. So, we need ferrochrome in many applications. I am mentioning
here that it is for adding chromium to steel and also for making various kinds of alloys
that will be required for mining and milling applications.
We need low carbon ferrochrome where carbon should be as low as 0 to 2 percent for finishing
additions in stainless steel making. There are some requirements in stainless steel making
where carbon cannot be tolerated. There it has to be low carbon ferrochrome. Ferrosilicon
is mainly used as a deoxidizer in a steel industry that you have an oxidized bath add
ferrosilicon; silicon will react with oxygen, oxygen remove as silica.
Ferrosilicon promotes formation of graphite as I had mentioned and by decomposition of
Fe 3 C. So, it also used to produce malleable iron containing nodular graphite. Limited
additions of silicon to low carbon steel improves tensile strength, yield strength, and impact
strength, and Fe Si carbon alloys silicon up to 4.5 percent are suitable for magnetic
material with high resistivity and permeability with reduced core losses; so, all kinds of
application. Why do we need ferrotungsten? Ferrotungsten
is for manufacturing of tungsten steels. You know tungsten imparts hardness. So, for high
speed steel, such as steels having ability to retain hardness at high temperatures and
therefore, used as machine tools we need tungsten steels. So, we have to use them as ferrotungsten.
A typical composition will be tungsten 18 percent, chromium 4 percent, vanadium and
cobalt. We can we also have precipitation hardening tungsten alloys and iron vanadium,
ferrovanadium is used for imparting fine grain size to steels that improves mechanical properties.
Ferromanganese, of course, without ferromanganese the steel industry will be dead. Ferromanganese
is of vital importance. It required for deoxidation of steel, desulphurization of steel. For every
ton of steel that we are producing we need 5 to 6 k g of manganese. So, as we expand
the steel industry, ferromanganese production also has to increase. Alloy steels containing
almost 14 percent of manganese are used in manufacturing of jaw crushers, railway equipment
like tracks, points, crossings and switches. Without manganese in steel, it is unthinkable
and the manganese added as ferromanganese. High carbon ferromanganese is generally used
for additions to carbon steels where carbon is tolerated in steel. You can add high carbon
ferromanganese, but low carbon variety will be used only of alloy steels where it is necessary
to have low carbon levels. Ferrozirconium is sometimes used for deoxidizing, sometime
for scavenging, and then zirconium treatment improves shock resistance properties and therefore,
steels are treated or steels thus treated are used for tools like rock drills.
And lastly ferrotitanium, it is also used for deoxidation, it is also used for alloying,
it is a strong carbide stabilizer, and titanium is used in austenitic stainless steels to
prevent intergranular corrosion. Its addition also improves hardening characteristics of
plane chromium steel. So, variety of applications of this ferro alloys and we need them for
steel industry or it cannot survive without the ferro alloy industry.
What about India’s situation as regards the ferro alloys? We are very fortunate in
having good deposits of chromium and as I mentioned there are most of it is in Orissa.
It is estimated there are about 3.5 million tons with one million ton of chromium content
higher than 48 percent; they are available. Manganese, total deposits about 180 million
tons, about 120 million tons, with manganese content higher than 46 percent. So, India
is rich so far as chromium and manganese deposits are concerned. Tungsten has very limited deposits.
It comes in the form of wolframite with tungsten content, it can be very high, but the ores
are of very low grade. For Titanium, India has huge deposits of titanium,
extensive deposits, estimated at about 250 million tons. Ilmenite, which is Fe O. Ti
O 2 or rutile, only Ti O 2, they are found, mixed with beach sands. All along our eastern
coasts, as well as, western coasts and vanadium also we have total deposits about 20 to 25
million tons with vanadium content only 0.2 to 2.5 percent.
So, these are the resources we have. A very common thing that we need is ferronickel that
has to come from nickel sources that is very limited in India. We do not have nickel resources
as such, but we do have nickel as chromite overburden. You see the chromite mines in
the top layer about 0.6 to 0.8 percent, nickel is available, it has been known for a long
time. So, before chromite mining, the top layers
are separated out and they have been kept there for many years now and they have made
mountains in Sukinda valley of Orissa, you see big hills. Those hills have this chromite
overburden containing say 0.5, 0.6 or 0.8 percent nickel. On the whole, a huge amount
of nickel is there, but we still have not got a process for extracting that nickel,
we are working on it. I will come to this in a later thing where
we talk about metals from sulphides. Nickel also comes from sulphides, and nickel also
comes from oxide sources. Maybe I will take it up in this lecture also, but in India good
nickel reserves are not there, but nickel is associated with chromate reserves; low
grade nickel reserves are there. So, this India has all the reason to go for
a vibrant ferro alloying, ferro alloy industry and its happening also. There are many ferro
alloying plants. Now, I will now not discuss aluminothermic reduction. I have given an
example of aluminothermic reduction; say in the case of manganese, you can produce the
metal, if you want to produce ferroalloy then all you need is iron addition.
But generally for large scale production of say ferrochromium, ferronickel, ferrotitanium
etcetera, we need to go for a carbon reduction, which will give carbon in the product, then
finally, you have to find a way of removing the carbon, and as I mentioned there are three
standard techniques for getting rid of the carbon in the ferroalloy.
First will be having produced that ferroalloy, which has carbon, it has to be treated by
an oxidizing slag. The oxidizing slag will oxidize the carbon and remove it. The other
thing could be remove the carbon by oxidation through oxygen injection. Now, this may sound
very interesting that suppose you have a ferroalloy like ferrochrome, at high temperature it has
carbon, and I say you can remove the carbon by injecting at high temperature, oxygen into
the bath. You may think this is going to oxidize chromium
or oxidize the ferroalloy; this does not happen, because if you go back to the Ellingham diagrams
you will find at very high temperatures carbon monoxide is becoming more stable as compared
to the metal oxides. So, if we inject oxygen into the bath, you have an exothermic heat
heating the bath and if the bath temperature increases, oxygen will react with carbon,
in preference to chromium or manganese or iron.
So, in the industry very often carbon is removed by oxygen injection, and that is not oxidizing
ferroalloy, it is removing carbon, because that carbon monoxide is now thermodynamically
more feasible, more stable. The third will be something very obvious. If you apply vacuum
and then C O would get eliminated, because carbon monoxide will form in the gaseous form,
so the reaction of formation under oxidizing conditions, carbon will form carbon monoxide
and by vacuum treatment we can remove. These are the standard techniques.
If I discuss one particular process, like say for ferrochrome, this will become clearer.
Now, let us proceed. In this book that I have referred to many times, my book on non-ferrous
metals production, many pages have been devoted to production of individual ferroalloys.
Whatever has been written is still very sketchy, because there can be a course on ferroalloy
production, which will run for one whole semester, but you do not have to go know all about ferro
alloying making; you need to know the principle. So, just whatever I am saying now and little
bit from the book should do.
Let us talk about production of low carbon ferrochrome alloy. Now, generally how do you
produce ferroalloy by carbothermic reduction? You will have an electric furnace. You will
take the concentrate, say chromite, manganese ore, whatever. You bring in carbon, you reduce,
and you get the metal because there is always iron oxide or you add the iron ore and you
get iron as an element and you also get carbon because the ferro alloying and even it will
form carbon. And then you find a way of refining that as
I said by various processes such as treatment with oxidizing slags or by raising it to high
temperature oxygen induction or by vacuum. Now here is a method called Triplex process
for production of low carbon ferrochrome. How do you go here? We will start with chrome
ore. It will be smelted using by reducing agent coke; of course, you will also add fluxes
like quartz, lime. So that you produce a slag, that slag will
go to wasted, it will only have 3 percent Cr 2 O 3. The alloy we will produce by smelting
would have 68 percent chromium; around it will have some silicon because from quartz
some silicon will come. It will have some carbon. So, here is the carbon that we would
like to remove. We will crush; we will smelt again adding quartz and coke, we will produce
an alloy which will now have more of silicon. We crush chrome ore lime refines; we can produce
a slag that has 20 to 23percent Cr 2 O 3. It will go back to smelting and it will produce
low carbon ferrochrome. There are many flow sheets about different
kind of ferroalloys. Now, one ferroalloy that attracts us is something that I would like
to mention here and that is ferronickel. Now little while ago I told you that India does
not have nickel resources, but India does have nickel in the chromite overburden.
So, let me discuss a possible way of getting nickel from that chromite overburden. Now
again what is chromite overburden? We have chromite in chromite mines. In the top layer
is what we call overburden. This layer contains nickel to the extent of say 0.4 to 0.7 percent
and in the chromite mines of Orissa they have been all removed before mining. They have
stock piled in big hills in a place called Sukinda hills.
There are millions of tons there now. So, if you consider this percentage of nickel
in them, we already have a reserve of thousands of tons of nickel staying there, without serving
any purpose. So, a lot of effort has gone into finding a process of extracting nickel
from this chromite overburden, and the laboratory with which we were I was associated regional
research laboratory at Bhubaneswar. Now it is called institute of minerals and materials
technology. It took up this problem on a priority basis.
We are not the first to do that. National and metallurgical laboratory also studied
this problem some 30 years ago and the essential approach for treating similar overburdens
is very well known. All over the world people extract nickel from sources where nickel can
be 1.1, 1.2, may be maximum 1.8 percent nickel, and for that standard pyrometallurgical techniques
are available. Actually we have gone and seen many plants
in other countries, but nobody has worked with any starting material with less than
1.1 or 1.2 nickel. Then our first thing was to see can we do something to this fairly
loaded overburden and bring it up to something like 1.1 percent nickel. We found it is possible.
We found a way of using a flotation process to upgrade nickel to almost 1.1 or 1 to 1.1
by using a flotation process, and the idea was simply to take out the gangue material
of floatation, and we found that the nickel is mostly associated with iron, after what
is rest. Rest is silica, iron etcetera with a mineral called goethite which is there.
Then the standard technique all over the world is this that you have nickel, say roughly
one percent as starting material. It will be; it will go through an open earth or rhetorical
reduction process. It has to go through a reduction step. Now, in the reduction step,
nickel is very easily reduced to the metallic form and if you have the Fe 2 O 3, and other
things, you can reduce to something like Fe 2 O 4. This we can magnetically separate or
we can take this, try to find the leaching process and selectively take out nickel. So,
many such approaches have been tried out to get a starting material, where nickel percentage
will be high. Then, attempts have been made to produce ferronickel by arc smelting.
Now, say hypothetically we have a starting material with x amount of nickel and y amount of iron plus gangue.
Gangue means silica etcetera. You want to reduce it by carbon. You go to high temperature.
Now, you should know that nickel oxide is very easily reduced. It does not need much
partial pressure of C O; it is very easily reduced. So, if you have a starting material
which has some nickel and it has some iron oxides, it is very easy to produce nickel,
but the now the question comes is balancing between. What will it produce? It will produce
ferronickel because iron will also be reduced, nickel will also get reduced.
Now, if you continue reduction for a long time then you will get more nickel out, but
you will also get more iron out. If you do it for a small time, you will get initially
very pure nickel, very high grade ferronickel, but recovery of nickel will not be enough.
So, we have a contradiction here. If you want higher grade ferronickel means nickel percentage
is lower then total nickel recovery is low. Now, if you settle for lower grade ferronickel
means nickel content is lower, then total nickel recovery can be high. Try to understand
the dilemma. I have a starting material which say has 1 percent, 2 percent nickel oxide
or whatever. You put everything in an electric arc furnace reduce by carbon. It also has
iron oxides. So, carbon will very easily reduce nickel initially, but nickel oxide reduction
would take time. You have to balance between the grades of ferronickel we want and the
total nickel recovery, if you want to take out every amount of nickel that is there in
the ore then we will continue the reduction process for a long time. In that process you
will end up with lot of iron also, in ferronickel. If you do not continue for a long time you
will get something which has higher percentages of nickel, but total recovery of nickel from
the initial charge would be low. So, these balancing acts one has to try out look at
the economics. Lot of work is going on in India on this, but we have in those Sukinda
overburden, huge amounts of nickel there. And remember India needs may be 20000 to 30000
tons of nickel per year or even more for alloying purposes, all that nickel is being imported.
Nickel is a strategy metal without that we cannot do. We have the resources, but they
are low grade resources, they are not high grade resources, and we have to develop our
own technology. Internationally, there is no technology suitable for these low grade
resources. But we are almost there, we can do it, but then there are many problems why
although something looks ok on paper in the laboratory, the technology is there can be
commercial process, but there are many reasons why it does not go and make an industry. So,
I think with that I will conclude a module five about production of metals from oxides.
Before I end, I would introduce the next module, which would be module five.
Now, in the next module, we are going to discuss production of metals from sulphide sources,
and what will be the metals, they are the metals of ancient times; copper, lead, zinc.
These sulphides are often found in nature all mixed together because the sulphides intermix
very well. Another peculiar thing about sulphides is they are very good solvents for precious
metals. Now, we think of silver, gold, platinum, etcetera, we do not find them lying around
in earth’s crust. Of course, there is something like Subarnarekha where gold particle are
flowing down the river. They were chunks of gold available in the
new world when the Spanish conquerors came to South America they were amazed to hear
stories of cities paved with gold. It was not exactly true, but it was almost true because
huge amounts of gold were there with the original inhabitants who were later called Red Indians.
There huge amounts of gold’s in them. That is what drew more and more people from Europe
who massacred them, left right and center, at that time may be native gold was available
in plenty. But now gold will be found as grains embedded in rocks or in sand and everything.
But gold, platinum silver, etcetera are also there in supplied deposits, because millions
of years ago when earth formed and the you know your oxides and sulphides, and all kinds
of things, the sulphides dissolved these. So, we will find the supplied metallurgy will
not only give us the metals of ancient times they would also give us as byproducts, a very
valuable byproducts of precious metal, and very often many processing steps, the cost
of processing step, will be met by the value of the byproducts that will come in sulphide
metallurgy. Now, sulphide metallurgy should be obvious
to you, is a very old thing, and people have been working on sulphides for centuries. So,
many things that are done today, have come from ancient times, and only now people understand
why those things are done they wealthy at that.
Basically, I was concerned with general principles of extraction and refining. You have seen
that you may have two oxides or three oxides which look similar, but the way the metals
are extracted from them may be quite different, and even if a method is similar they are all
intricacies which are very different. The time now has come to move on from oxides to
another kind of starting material and they are sulphides.
I was mentioning that sulphides are very good solvents. They mix amongst themselves, they
also dissolve precious metals, but there are no sulphide deposits which are very rich.
Now that is another problem, like in oxides can be very rich deposits such as deposits
of aluminum, deposits of iron, deposits of magnesium, calcium; they can be very high
in the metal content. For sulphides that is not true, but ancient someone had found out
how to start with this very low grade materials also.
Now, I would not go back to the ancient processes that I had discussed in the very beginning
and it is not right to go into discussion of those things, but let me start with this
problem today that what you do with a sulphide mineral where the metal content copper or
zinc is only about one percent or even less. There is no other source of that metal which
is richer in terms of the metal content. Now, fortunately somebody found out and very exciting
process called Flotation for enriching such ores.
Now, it is because of such discoveries, which can be accidental or which could be results
of trial and error that many metallurgical processes have evolved. In flotation, the
whole idea is very similar to the way we clean our clothes. Now when our clothes are dirty
and why they are dirty because dirt particles are sticking to the textile.
Now, if you shake it, they would not go. If you put it in water and rinse, some will go,
the rest will not go, but if we put our clothes in soap solution and you rinse the soap bubbles
that come out they take out the particles of dirt with them. Why do the particles of
dirt move up with the soap bubbles? It is because of some surface tension phenomena
that the dirt particles are attracted more to the surface of the soap bubble than to
the surface of the of the cotton textile. So, as the soap bubbles rise they take the
dirt with them and they float up, and if you take out the froth, you will find it is very
dirty. All the dirt is in that. There is a similar process in the case of sulphides.
I do not know who discovered it. Exactly same process it is called, ‘Froth Flotation’.
You create a froth using a frothing agent, and the whole idea would be when these bubbles
raise, the particles of sulphide minerals stick together. They will rise whereas, the
gangue the dirt, silica, alumina, soil, etcetera, they will not rise.
Now, this also means that you have to make the particles very fine otherwise soap bubbles
will not be able to carry them up with them. So, froth flotation will necessarily require
also fine grinding. So, if we have an ore, a sulphide ore in which we have the metal
sulphides, it has to be ground very fine so that sulphide minerals are in a very fine
form, then they will be treated to forth flotation. There are various reagents which create this
froth and the bubbles when they rise they will take the sulphide minerals with them
to come to the surface. So, if the surface is cleaned off, we get
a concentrate which can have 25 to 30 percent of the sulphide ore. So, in one jump we go
from one percent or less to 25 to 30 percent metal. Once you have that you got a starting;
you can start. So, in all sulphide metallurgy the first step will be concentration with
the froth flotation.
To introduce module six, which I am about to start now, the learning objectives would
be the complex nature of sulphides and sulphide metallurgy. Then, we will go to discuss pyrometallurgical
extraction process, individual for copper, zinc, lead, nickel, etcetera because nickel
is also found as sulphides in many places. We will talk about hydrometallurgical extraction
processes because many of these metals particularly zinc can be extracted by pyrometallurgy, as
well as by hydrometallurgy. Then, we will talk about something called, ‘Process Fuel
Equivalent’, that how do we analyze or compare processes from the point of view of energy
consumption, for that we will need a criterion called, ‘Process Fuel Equivalent’.
Now, before I proceed further, you should know, what are the general methods of getting
metal from a metal sulphide? There are some very standard approaches. One is thermal decomposition.
There are many sulphides which simply decompose on heating; example is mercury sulphide, Hg
S. All one has to do is to heat it, it will give
mercury and sulphide, but it is an exception. It does not happen in all cases of sulphide.
In other cases we can go for roasting and subsequent reduction, means from the sulphide,
you produce an oxide by roasting then you reduce by carbon that is very obvious.
The third method is very interesting and it is relevant for copper that you start with
a sulphide concentrate, you roast not to produce an oxide of copper, but only an oxide of the
impurity element iron, and then that iron oxide is taken away in the slag, you are left
with a sulphide of copper and iron; that is called matte.
So, in copper, we will not produce copper oxide for reduction. We will produce what
is known as matte. We take the sulphide. We will roast it not completely, but incompletely
so that the iron sulphide and copper sulphide are getting roasted. Iron sulphide is incompletely
roasted; most of it is forms oxide and is taken away, copper sulphide remains intact.
And we get a product of copper sulphide and iron sulphide, which is called matte. That
matte goes for smelting and that smelting is also of different kind. You do not have
to reduce by carbon. We will see simply by controlled oxidation from the sulphide mixture
you can get copper straight away. So, that is the third route.
Flash smelting is an improved step, improved process of combining roasting and matte smelting.
Then if we can produce a pure metal sulphide, you can always go for metallothermic reduction
also, because there are some metals like calcium which can produce very stable sulphide and
so these base metal sulphides can be reduced. Then there are hydrometallurgical processsing
where the sulphide concentrate can be roasted to make oxide, and leached taken into solution
and that from the solution by chemical treatment, solvent extraction, ion exchange, precipitation
will produce finally get a pure solution to neutralize or whatever, so that will be hydrometallurgical
processing, or we can take the sulphide, from there you can get a chloride, and from the
chlorides you produce the metal. And there is electrolytic refining of matte directly
to pure metal; that also have to try. So, there is a variety of options and that is
what makes sulphide metallurgy very complex. In some cases there are two or three ways
it can be done and what we choose depends on economics, depends on the kind of circumstances,
in which you are, and depends on the expertise you have. So, we will discuss these things
in module six in detail, starting from the next lecture. Thank you.