Well friends, I have started talking about
imperial smelting process which is not exactly
a modification of the lead blast furnace although
it is similar. It is much more than a modified
version because it has an attachment vital
attachment for recovery of zinc which come
out from the top as zinc vapors. You understand
this now that whereas, the lead blast furnace
is designed to take only the product of roasting
of lead sulphide concentrates that is done
in a sintering machine which produces lead
oxide, lead sulphate. But this furnace is
designed to take a mixture of oxides of lead
and zinc which come out of roasting, sintering
of zinc sulphide, lead sulphide combination.
So, from the ore which has both the sulphides
we get them as a concentrate where both the
sulphides are floated together, there is no
attempt to separate them. The only attempt
is to recover as much as possible of the sulphides
that are present, then they will be calcined
and roasted to produce the charge necessary
for the imperial smelting furnace in this
they have to be we have to have granular material,
it cannot be very fine.
Now, I have also mentioned that this case
the furnace is square cross section, operates
at about 1000 degrees more or less similar
to the blast furnace operations which operates
at 1200 degrees. I did mention why it is called
imperial smelting furnace, you should guess
the very word imperial should tell us that
it was developed in England. So, it has come
from United Kingdom that is why they have
named it as imperial smelting.
Now, the trickiest part of this entire operation
is condensation of the zinc vapor which is
based on a very simple principle of physical
metallurgy, the phase diagram of lead and
zinc. Now, here is the phase diagram of lead
and zinc, this you should understand.
Lead has a melting point of 327 degrees zinc
has a melting point of 419. If you go to these
temperatures 2 liquids separate out, if you
add at a temperature below 327 degrees then
you have lead and zinc in a solid solution.
If we exceed 327 degrees then lead will melt
out. So, here you will have liquid lead and
zinc. Zinc 
will be solid, lead will separate out as a
liquid. If we go beyond 419 then we begin
to get 2 liquids. One liquid is very rich
in zinc, the other liquid is very rich in
lead. If we go to a temperature like this
we will have a liquid which is richer in zinc,
we will have a liquid richer in lead and this
actually comes down.
But if we are somewhere here just above the
melting point on zinc there is very little
zinc very little lead in that water, separate
it out and the some amount of zinc which is
in the other liquid. So, here we get 2 liquids
this liquid and that liquid. Their relative
proportion will depend on the lever rule,
where we are and where you are standing.
If you are standing here, if this is the in
the phase diagram if this is the composition
then you this you will have this composition
and that composition and the ratios will be
inversely proportional. How much effort will
be there.
This is made use of in the zinc vapor condensation.
The principle is this, the vapors are coming
out of top and these are the condensation
chambers, this is condensation chamber is
shown in magnified version.
The furnace gases which contain about 6 percent
zinc vapors, the rest will be CO CO 2 as they
come here they are splashed by lead liquid
at a temperature of around 450 degrees. So,
liquid lead is splashed on to the zinc vapor
and that bath now has that zinc vapor in solution
because if you go back to the temperature
500 degrees 450 or so. If you refer to this
thing you will find now the lead can dissolve
so much of zinc.
So, what happens is exit gases will have very
little zinc in them only 0.24 percent and
rest will be CO CO 2, but most of the zinc
vapors are condensed and taken into a lead
bath. Now, this lead bath would contain 2
to 4 percent zinc according to the phase diagram
there on the right hand side then it is cooled
and it gets separated out cooled only slightly,
it will cool down from 500, 1000 degrees it
is coming, lead bath is at about 500 degrees,
it is cooled to 450 degrees and immediately
2 separate layers come out liquid lead and
zinc layer as per the phase diagram.
If you go back to the phase diagram, if you
come down to about 450 which is slightly here
you are getting 1 liquid of this composition,
another liquid of this composition. So, 2
layers are coming 1 zinc layer which is almost
pure zinc and a lead layer which has very
little zinc. This lead is again pumped back.
This lead will go back for splashing again,
the lead that is recirculated contains 2.15
zinc and the zinc rich alloy will come out
here. So, this is what is happening.
You are, you are taking out lead with 2.4
percent zinc, bit of zinc separates out, some
zinc is left behind, then it is recirculated
in that process gradually you get a zinc rich
alloy and you and the lead continuously recirculated.
So, the it goes to a zinc holding tank it
is all based on control of the temperature,
liquid lead splashed on to zinc vapors it
will dissolve zinc, then it will be cooled,
it will give up zinc, it will remain liquid,
it will be pumped back. This is the zinc recovery
system of imperial smelting process
It is difficult because one has to pump a
very heavy element like lead. So, it is a
tricky proposition and it is the liquid is
being pumped at a temperatures of 450 degrees,
450 degrees going and the and the entire operation
is switching between 450 and 560 or so.
Now, during my discussions you must have heard
me say the word zinc recovery from lead slag’s
because even in the slag that comes out of
the imperial smelting process, some zinc will
come out.
Lot of zinc will also come out of the lead
blast furnace and lead blast furnace slags
normally contain 15 to 18 percent zinc. Zinc
in solution in lead slags. How do we recover
that because it is there some kind of a silicate.
Now, they do that we employ a process called
slag fuming process at about 1200 degree centigrade
in water jacketed reactors no refractory,
but water jacketed for reasons I do not clearly
understand. But if you have a water jacketed
reactor and there is it is water cooled then
there is always a frozen crust, solid crust
all around which acts like the protective
refractory.
In that furnace, in the bath you have to go
to this temperature because you are treating
slags and melting points of slags are around
that little below, to that is added coal injected
coal and air. So, you are actually gasifying
coal inside a slag phase.
So, coal will form CO and CO 2 on gasification.
This CO reacts with ZnO slag to form zinc
vapors. So, it is a reduction reaction, there
is zinc inside the slag, ZnO inside the slag
phase itself you inject carbon and oxygen
and these 2 react coal carbon as coal, these
2 react gasify coal the CO formed reduces
zinc oxide, zinc vapors come out. This is
an endothermic reaction. Because all oxide
reduction processes by CO are endothermic.
So, it tends to cool the entire bath, the
heat can be compensated like this, above the
bath when zinc vapors come out, it reacts
with the oxygen in atmosphere forms ZnO fumes,
that is exothermic.
Also the CO that is coming out it will form
CO 2 beyond as it comes out or it can be combusted
to form CO 2, that is also exothermic. That
will give heat to the bath. So, some heat
is gained by oxidation of zinc and oxidation
of CO. This is the fuming process by which
you are recovering zinc from the slag essentially
as zinc oxide fumes Now, this fumes zinc fumes
on zinc oxide fumes are collected in bags.
There are bag collection bags of zinc. If
you can do that we can recover nearly 90 percent
of zinc from the slag and then we will also
improve recovery of lead about 19 percent.
The zinc fumes that come it will go to the
zinc plant, to get zinc out of that it will
either go for pyrometallurgical processing
or for hydrometallurgical processing. Now,
here is a small sketch to show how with blowing
time the process will proceed, this is blowing
time, blowing of carbon and oxygen in slag
and this is percentage zinc in slag. Obviously,
the percentage zinc in slag which is shown
here and here will drop with time because
gradually zinc is going out of the slag phase.
Whereas fuming rate the rate at which zinc
is coming out which is shown on this side
initially it would be high, but it blowing
time gradually the fuming rate will drop because
there is not enough zinc oxide left in the
slag. So, typically we need in minutes say
120 to 140 minutes to come somewhere here
and about 180 minutes about 3 hours of blowing
of carbon and oxygen to recover most of the
zinc oxide from the slag phase, that is where
the fuming rate becomes very low.
Now, beyond this if you continue in the blowing
your fuming rate actually it is already has
dropped, it would drop even further and zinc
in the slag has already dropped and may be
its not going to drop any further.
So, somewhere here one has to draw a balance
and you have to let go small amount, very
small amount of zinc in the slag, it is not
worth trying to recover that. So, you are
coming to a situation which we often call
the state of diminishing return. Means if
we go on trying more the elemental advantage
you get is not coming with the efforts you
are putting in. So, somewhere it has to stop.
So, this is called zinc fuming process which
is which has to be applied for slags out of
lead blast furnace for recovery of zinc.
I have talked about the process now. I would
like to say few words on nickel. Now, you
may wonder why I am discussing nickel now
because earlier I have referred to nickel
as a metal which comes from oxides sources.
The reason I am bringing in nickel at the
stage again is because nickel is also obtained
from sulphide ores and there are many countries
in this world which has sulphidic nickel deposits.
So, we can say that both oxides and sulphide
ores are available and both of them need to
be expert.
Why are we interested in nickel because nickel
is a strategically important metal, you know
when you use the word strategy you must know
what it means, the word strategic has 2 implications.
When we say this is of strategic mean it means
in the long term perspective, it is required
means you will need it for very long term
to satisfy objectives even in the long term.
It also means that it has military and defense
applications.
Because military is of vital importance. So,
many alloys would need nickel for defense
and also there are many industries which will
continue to nickel for a long time. So, nickel
is a strategic importance. In India, like
in many other countries it is a strategic
importance, but import all our nickel. We
do not produce nickel excepting for small
quantities which we are obtaining from secondary
sources. Let me talk about them first.
When I was working in Bhubaneswar, an entrepreneur
met me saying that I live in Khanpur and there
is an explosives factory there, there are
fertilizers factories and many of them use
catalysts in their operation and many of these
catalysts have nickel in them. Now, after
they are used they throw away those catalysts
called waste catalysts and there are small
hills of these waste catalysts and he went
and found out they contain metals like nickel,
copper, zinc in very good quantities much
more than ores available anywhere. So, he
bought them.
He said I would like to get nickel out of
this. So, we tried to help him to establish
a process for recovery of nickel from waste
catalysts. In also in many chemical processes
nickel is a very important catalyst. So, we
have this waste catalysts in our country and
people have here and there found some ways
of recovering nickel. There are also some
waste materials available from abroad may
be alloys, may be chemicals etcetera which
have nickel in them. The country buys them
and some companies try to process nickel from
them, these are secondary we can call secondary
nickel.
But from ores available in the country we
do not have a industry not even in a small
scale industry to produce nickel.
Now, nickel 
is vitally needed as a strategic material
because of its alloying properties. We may
not use nickel as such, but nickel alloys
are necessary in chemical processing because
of their high strength properties, corrosion
resistance.
In space research, nuclear reactor engineering
etcetera for many alloys we need nickel. There
are more than 3000 commercial alloys for mechanical
properties and corrosion resistance qualities
of nickel and of course, you know there is
a group of metals called monel metals. These
comprise of nickel and copper mainly with
some other things of various proportions.
There is in the market an alloy which looks
like silver, it is called German silver. It
is prepared by mixing zinc, copper and nickel,
German silver.
Of course I even mentioned use of nickel as
catalysts in many chemicals, but maximum uses
in the form of alloys. So, for alloying if
it is an iron based alloy we can use as ferroalloy,
if it is not an iron based alloy then we have
to put it as nickel metal. For example if
we have to make German silver or you have
to make a nickel copper alloy you cannot use
a ferroalloy, we have to have nickel in elemental
form. Now, in the world there are many places
with the sulphide ores, average the mineral
composition may be Ni 2 FeS 4 or NiFe 9 S
3 there could be other competitions.
But like copper, zinc, lead sulphides these
sulphides are also mixed with some other sulphides
because sulphides as I have been mentioning
are very good solvents. Now, here are some
figures about world production of nickel ores.
I do not know whether you can read them, but
I will just read out 1 or 2 figures. In Europe
in 1960 2.1000 tons of sulphide ores were
mined, in 75 5.01000 tons means 5000 tons
of sulphide ores were mined, oxide ores mined
were 8.6 oxide ores were more.
But in a place in Africa there are more sulphide
ores as there are not and in 1990 75000 tons
of sulphide ores were mined. In Canada huge
deposits of sulphide, nickel sulphides and
some 340000 tons of the sulphide ores were
mined. In USA they have oxide ores, no sulphide
ores There is only in Canada and also in that
also in the form of sea nodules also has sulphides,
but in most countries this sulphide ores are
not there, Canada is an exception, but there
are there nickel is there in oxide form in
many countries.
And if you look at this figures India has
very small quantities of oxide in oxide form
and in the chromite overburden that we mentioned
it has been estimated that we have already
taken out some 185000 tons of nickel ores
which are there. Now, how do we proceed for
extraction of nickel from sulphide. Here is
a flow sheet called nickel extraction inco.
This inco is a very famous company which is
based in Canada and you can see they are processing
in the nickel ores like this. Because they
are sulphides, the ores will be like copper
sulphide very low grade. In this inco ore
there is only 1.3 percent copper and 1.2 percent
nickel as low grade as that, there will be
ground and there will be floatation, tailings
will lose a little bit of copper and nickel.
But the bulk copper nickel concentrate will
have 6 percent nickel and 7 percent copper.
So, we get a bulk concentrate. We float both
of them together, then they separate copper
concentrate and concentrate. Then, we will
get a concentrate 30 percent copper and 1
percent nickel and we will get a main nickel
concentrate which will have 10 percent nickel,
2 percent copper this becomes now the starting
point. It will now undergo a pyrometallurgical
processing very much like copper sulphide
processing, where we will go through a matte
route. Through a route that will involve sulphides.
So, this nickel concentrate sulphides which
would have 10 percent nickel and 2 percent
copper will go for roasting a reverberatory
furnace smelting just like in the case of
copper there will be slag discard and this
will now produce a matte. If somewhere there
is a copper slag available that can go in
here because we need in the matte copper also.
So, nickel sulphide processing also involves
a matte which is a mixture of sulphides containing
20 percent nickel 7 percent copper, it will
be it will go undergo converting like exactly
like in the case of nickel the slag will go
back to the reverberatory furnace.
In converting we will have matte 50 percent
nickel, 25 percent copper there is a slight
difference here. In the case of copper converting
by converting a straight way we are producing
blister copper. In this case we do not do
that, we produce a product which goes for
slow cooling, grinding and magnetic separation
to finally, get a low copper nickel sulphide
and high copper nickel sulphide. So, 2 products
they aim at basically to produce nickel sulphide.
So, the matte processing will be to prepare
like in the case of copper matte smelting
you wanted to have white metal and then that
will be converted to blister copper. No, here
they first produce the nickel.
Then it will go to a different pyrometallurgical
processing as you see here fluid bed roasting,
nickel oxide it can be marketed as such or
it can be reduced to produce metallic liquid
for the market. It can go for fluid bed roasting
to get nickel oxide, it can be deduced, this
can be carbonylation means nickel pellets
and nickel powder reduction smelting, electrolysis,
electro nickel all these. So, in the sulphide,
nickel sulphide processing the aim will be
different. The aim will be to go to a matte
phase and not the metal directly, then the
sulphide will be will undergo a pyrometallurgical
processing through the oxide route.
Now, the oxide ores are much more abundant
than the sulphuric than the sulphide sulfidic
ores. It should be sulfidic and the oxidic
ores are called nickeliferous laterites. They
are associated with iron oxide deposits typically
containing 1 percent nickel and 40 to 50 percent
iron in overburden means in the top layers.
There can be more nickel in layers below and
typically this kind of a composition we can
expect where nickel is in solid solution with
FeO.
In India, this is there in chromite mines
of Sukinda. Sukinda valley is in Orissa, it
is full of chromite and lot of chromite mining
takes place there. Now, during chromite mining
they take the top layer out and they keep
it at 1 stage and hoping that in future some
day we will extract nickel out of that. So,
when I was working in Bhubaneswar they said
that you must go and see the chromite overburden
which has nickel and we were interested in
extracting nickel. So, I was taken there I
was standing on top of a hill and then I asked
some people Where is that chromite overburden?
Where there is nickel? Then I was told that
you are standing on top of that.
So, there is a there is a hill of that chromite
overburden containing say around 0.7, 0.8
percent nickel which is waiting for somebody
to come and extract nickel. The rest of the
place after the top layer has come out they
are doing chromite mining that is going on,
but this nickel overburden containing overburden
is simply waiting.
What do we do with it, that in oxide oxidic
ores nickel is associated with nickel laterites,
laterites are iron oxides. Now, to understand
the behavior of these ores when heated we
can take help of differential thermal analysis
which I have explained once. Let me explain
it once again. In differential thermal analysis
we have 2 small crucibles placed side by side
as shown.
And they are heated in a furnace there are
2 temperatures, the there are 2 thermocouples
attached to them measure the temperature difference
between these. Now, the sample whose behavior
we want to study during heating is kept in
1, the other crucible contains a reference
material like alumina where nothing happens.
Now, when we heat in a furnace these crucibles
placed in such a manner that in the beginning
the temperature difference between them is
zero because they are both getting heated
up.
But if something happens in this crucible
either exothermic or endothermic then the
delta T will be registered either this way
or that way. Because if it is endothermic
temperature will be arrested here this will
go up, if it is exothermic temperature will
go up here and the and it will go beyond this.
Of course, this will not continue when it
is over it will come back to the base line
again.
The simple technique is used to understand
the behavior of any ores and minerals during
heating and I will come back to this in a
later lecture about behavior of sulphides
when they are heated.
But let us discuss how nickel laterites behave
during heating. Here, I show a typical sorry
a typical d t a plot for a particular laterite
ore composition is given here 1.7 nickel,
2.0 2.5 25 percent iron, 24 percent silica
and 18 percent MgO. Now, as we heat this ore
the d t analysis shows the following. The
small endothermic peak at W which is at about
100 degrees is due to evolution of a small
amount of water from an already dried sample
which has been dried, sun dried some moisture
is still left, the ore from the mines contain
lot of water, some has moisture, some in combined
form we have to remove that also.
So, the first endothermic peak shows endothermic
evolution of water, it absorbs water. Now,
there is another big endothermic peak at G.
What is the G? The second endothermic peak
G at about 230 degrees is due to goethite
decomposition and goethite is 2FeO OH, this
phase is called goethite and it decomposes
into Fe 2 O 3 and H 2 O.
So, goethite mineral which is FeO OH it decomposes
at about 230 degrees to give out Fe 2 O 3
and combine water H 2 O. Now, this is a very
important observation because it has been
found mineralogically that the nickel is actually
always associated with the goethite phase.
So, before this temperature nickel is inside
the goethite phase almost dormant, but the
moment that goethite decomposition takes place,
nickel that was liberated to goethite with
was associated with goethite is now liberated.
It becomes active, nickel oxide becomes active
and it can be very easily deduced.
Then we come to the third endothermic peak,
this third endothermic peak refers which has
about 530 degrees, it refers to dehydration
of serpentine. Now, serpentine is a mineral
which is there in the ore its composition
is magnesium 6 Si 4 O 10 OH 8 its very mineral.
This oxide in the serpentine becomes active
above 600 degrees. The next exothermic peak,
this is very critical. The serpentine phase
crystallizes that SC at about here shows crystallization
of serpentine.
Now, the next exothermic peak SC at 800 which
represents the re crystallization of the magnesium
silicate which is liberated from serpentine
into olivine, it is Mg 2 SiO 4. If this happens
then nickel oxide is locked up in that phase.
The substances is when you are heating a lateritic
ore water comes out, goethite decomposes liberates
NiO which was in the goethite.
Then the serpentine phase goes through decomposition
and recrystallization. If that happens then
nickel oxide goes into that serpentine phase
and becomes in active. It is not available
for reduction. So, whatever we do will have
to be done below 800 degrees, this is the
substance of that.
So, we can say that in ores which are lateritic
everything has to be all pyrometallurgical
operations must be below 800 degrees to ensure
that nickel is not locked up in a serpentine
recrystallize phase. However when there are
limonitic iron ore which has which have more
iron content 40 to 50 percent Fe that would
not have the serpentine peaks. But a serpentinic
ore with low iron content 8 to 10 percent
Fe will not have the goethite dehydration
peak of the lack of goethite mineral in the
ore hence does not have the peak of serpentine.
So, there are some laterites which are easier
to reduce than the serpentinic ores because
of the olivine recrystallization and locking
up of the nickel oxide in the olivine will
not take place, what I am saying basically
is not all nickel ores are alike.
And 1 has to first go through when the laboratory
test to know what happens when we are heated,
when is nickel oxide easily available for
reduction and unless those things are done
we simply cannot be a pyrometallurgical step.
To understand now better what we will do for
preferential nickel reduction we have to go
see the simple phase diagram, not phase diagram
that this diagram which shows that which shows
the different phases at different as a function
of percentage CO gas, it is something very
similar to what you may have learnt in iron
oxide reduction.
If we have temperatures in this range and
CO in this range then we should have a final
product nickel and Fe 3 O 4. If we maintain
temperatures and CO CO 2 composition in this
range, we can produce nickel, nickel FeO and
of course, if we go to percentage CO higher
than this in temperature ranges like this
you can produce both nickel as well as iron
metal elemental form. This is the kind of
guidance we get from this diagram, you must
have seen similar thing in the case iron ore
reduction.
Now, 1 restriction we have put is in the ores,
some ores where we have goethite serpentine
and all these at least in Indian ores we never
go beyond 800 degrees, all operations would
be on this side. Now, if we can reduce the
lateritic ore which has nickel oxide initially
locked up in the goethite phase and then liberated,
then we can very easily produce nickel Fe
3 O 4 or nickel and FeO. It is quite easy
to do.
Nickel oxide is very easy to reduce. What
we depend? We depend on the final processing.
Now, by keeping control temperature and p
c o one can produce nickel and FeO if we want
to leach out FeO or you can leave nickel and
FeO and Fe 3 O 4, we cannot handle nickel
and Fe 2 O 3 that will not be desirable because
Fe 2 O 3 is difficult to leach. In smelting,
reduction smelting calcined ores are smelted
in electric furnaces with 1550 to 1650 degrees.
Now, there we do not have to worry about all
these. Whatever we have nickel oxide Fe 2
O 3 everything we can smelt at temperature
of 1550 to 1650 degrees. We reduce both nickel
from the oxide as well as iron for the oxide
and you produce a ferronickel. And since we
are using carbon as a reducing agent if you
give long time more nickel will come out,
more iron will also come out, nickel comes
out earlier because it is very easy to reduce.
So, initially we can produce a high nickel
ferro ferronickel, but total recovery of nickel
would be low because we need more time to
take out all nickel.
So, one has to draw a compromise between recovery
of nickel and the grade of ferronickel, but
we can take out both iron and nickel as ferronickel
from the charge. Now, in pyrometallurgy we
go bit differently. We combine the initial
reduction of the lateritic ores to such an
extent that we produce nickel and FeO Fe 3
O 4 and this nickel can go for ammoniacal
leaching. So, that charge which has been reduced
under controlled atmosphere and there are
furnaces, 1 is that rotating hearth furnace
or it can be the rotary kiln that can now
be sent for ammonia leaching, nickel can be
easily leached by ammonia to produce nickel
amine from which we can precipitate nickel
carbonate and nickel carbonate has a easy
market. Because nickel carbonate if it is
added anywhere it will easily decompose and
produce metallic nickel.
So, from these oxidic ores one can produce
ferronickel, one can produce metallic nickel,
for that we have to go for electrolysis by
this by decomposing ferronickel carbonate
into nickel oxide dissolving in an acid solution
electrolysis it may not be necessary, if it
is for alloying if we add nickel carbonate
it will decompose very easily.
So, what we want is we have to keep in mind
what it is what we want. If we want ferronickel
we have to go for smelting, but we can also
produce elemental nickel by initial this reduction
roasting followed by leaching of nickel. Now,
this sort of work has been done in India and
I will in the next lecture come back to this
subject and give you little more data and
discuss it more thoroughly.
Now, let me end today’s lecture by discussing
a subject which might become important in
the future. See. So, far what we have done
is that we talked about sulphides undergoing
a floatation process. We can either get a
copper fraction which goes for copper extraction
or we take zinc sulphide concentrate goes
for zinc or lead sulphide goes for lead extraction
or copper lead and zinc together which goes
for imperial smelting process.
But there are quite a few sulphide deposits
which can which are known as multi-metal deposits
or mix sulphide deposits which are not very
easily amenable for differential floatation
to get rich concentrate of this or that or
the third metal, they may be very low grade
also. Now, this mix sulphide deposits are
growing attention in India because India is
not very rich in terms of the deposits of
copper, zinc and lead. How do we proceed to
treat complex sulphides of lead, copper and
zinc.
Now, here are some simple some hints, but
this I may discuss later on. First of all
we need to find a concentration technique,
floatation is 1, we can also employ gravity
separation to separate large extent zinc,
lead, copper altogether, differential floatation
is something we employed on sulphide minerals,
total recovery of all the sulphides or fraction
this fraction separately. But for this we
need that the minerals are present at discrete
minerals. Suppose, we want to separate copper,
lead and zinc the minerals must be discrete.
Zinc, sphalerite, galena, copper pyrites if
they exist as distinct minerals, then differential
floatation is possible. But very often they
are not distinct minerals, they are all mixed
together like in copper pyrite you have Cu
2 S and FeS not as a solid solution, it is
a separate mineral CuFeS 2 there can be such
minerals which combine this elements if that
is there then by floatation you cannot get
different fraction.
If you do a retort distillation we can separate
zinc, like in the retort process for zinc
if you take a calcine which has both lead
and zinc like in imperial smelting process,
zinc can be separated out, lead copper will
be left in the gangue.
And the zinc finally, obtained contain some
lead there will be some lead. We can think
of electrolysis to produce zinc from a leach
liquor containing lead and copper in addition
to zinc. Now, this I will discuss I have to
think 1 can apply liquation to produce molten
lead zinc bath containing 1 to 0.2 percent
lead, lead containing 0.5 percent zinc something
that we have been employed in imperial smelting
process.
So, many things have been thought of as to
how you handle a mix sulphide, but ultimately
people think that when you have a sulphide
deposit all kinds of sulphides, the best way
to go will be to employ a hydrometallurgical
technique. And here the aim will be of course,
the technique will have to be depend on the
gangue minerals and the percentage compositions
of various nonferrous present in the ore and
the bulk concentrates, it will always depend
on that. But the first major step in hydrometallurgical
method will be absorption of nonferrous metallic
values in solution and leaving behind a major
part of iron in the leaching. Iron is the
part in the sulphides is not what we want.
So, if there is a bulk sulphide concentrate.
We have to find a way to take all the metals
in the solution, copper, zinc, lead and others,
but not iron in the solution. Iron must be
rejected that if we can do that we have a
very big very good starting point.
Then the next step should be solution, purification,
separation nonferrous metals from each other
by cementation, precipitation, solvent extraction,
oil electrolysis, fluidized bed roasting helps
in selective conversion of nonferrous metals
in the ores and concentrate to sulphates.
If you have fluidized bed roasting where p
s o 2 and p o 2 are controlled then from the
calcine selectively we can get sulphates and
oxides and sulphates can be of a particular
metal, can be can go dissolve in water and
taken out and things like that.
So, this after flow solid roasting we can
have soluble, soluble’s in dilute acid or
water and to that will give a some separation
etcetera many other things are possible. Right
now we are not doing that, mainly the industry
is working on concentrates which are very
rich in copper pyrites CuFeS 2 goes for copper
extraction. And on concentrates which are
zinc and lead, if they are separated by floatation
that goes for zinc extraction, lead extraction
separately. If they are floated together it
goes for imperial smelting process, this is
the state of affairs in our country. But very
soon we will have to deal with some deposits
where we have to do something for when there
are all the 3 metals present there, we have
to find how effectively we can extract them
in separately. I will discuss that some other
time. Thank you
