Mod-01 Lec-23 Lecture-23-Hydrometallurgy of Copper

Mod-01 Lec-23 Lecture-23-Hydrometallurgy of Copper

Now, you have known by now, that 85 percent
of the copper is produced industrially by pyrometallurgical operations and we have discussed
them in detail. In hydrometallurgical operations, no high temperatures are involved, things
happen in eco solutions, which means you have to bring copper from the mineral into eco
solutions. Now, for centuries people have found that
in copper mines where water accumulates, there is copper in a mine waters. In other words,
in natural conditions also, from from the copper in the mines where there are pools
of water, copper comes into solution. And actually such solutions were used centuries
ago, to produce copper by cementation using iron powder or iron finings.
You know, if you have copper sulphate and you put iron in that, copper precipitates,
iron dissolves. So, in the mine waters where the copper was in solution and the solution
could be tell, you know if you put copper sulphate, you know it is blue, people recovered
copper that way. Now, this was known, but it takes months,
if not years to produce a soluble solution suitable for commercial exploitation. You
cannot put copper concentrates in a pond and think that, it will dissolve and give you
a solution of copper, because this sulphide; copper sulphate that does not happen; it will
happen it will take years. But in the early part of 20th century, it
was accidentally discovered the certain types of bacteria considerably accelerated this
process of natural conversion of copper into soluble soluble sulphates. Schematically,
we can show it like this. Say, suppose approximately if took, if it
took 100 days for the natural process to recover 100 percent mineral extracted from the mines
with bacteria, it will be far more rapid. And they were surprised that they were certain
mines where very quickly, that in mine waters soluble copper was appearing.
Then, they found this is true in natural conversion of many kinds of sulphides, such as not only
iron sulphide or some other arsenopyrite. It will be for other copper minerals, of course
for chalcopyrite, there are other minerals of sulphur, of copper, various minerals. They
found they were all sensitive to the bacterial a leaching phenomenon, there are many others,
you can consider more book. So, actually it was not copper that was responsible,
it was the sulphur that was critical in bacterial leaching. And finally, the bacteria bacteria
that were studied and identified were found to be of families of which are known as thiobacillus
thiooxidans or thiobacillus ferooxidans ferooxidans and ferrobacillus, these are the three most
important types. What do these bacteria do, the role of these
bacteria is to grow in purely inorganic media, this bacteria do not need oxygen air to grow.
They they obtain their energy by oxidizing inorganic substances such as sulphur and thiosulphate,
the oxidation of these inorganic constituents give them the energy, and oxidation of ferrous
iron to ferric iron that conversion give the energy to survive and grow.
A biological catalyst called enzyme is also synthesized by the bacteria that helps in
acceleration of the rate of oxidation reactions. Forget about what the bacteria do, I will
not go into the details of that, but the essentially these bacteria speed up the processes of oxidation
of sulphur. .
Then dissolution of copper, conversion of ferrous
iron to ferric iron, other reactions for oxidation of iron, essentially what happens is that,
if we write the metal sulphide oxidation by ferric iron to be this. One of the functions
of the bacteria is to reoxidize ferrous iron to ferric iron so that we are constantly getting
ferric iron that will dissolve the metal sulphide to produce metal ions in solution; this is
what the bacterial oxidation does. And in the case of copper, it is generally
believed that in the case of iron, this reaction is what brings soluble F e S O 4; this is
slow and not influenced by bacteria. But under slightly alkaline or acidic condition, this
ferrous sulphate is reacts to produce this, this is fast and influenced by bacteria. And
then the ferric sulphate, this will hydrolyses and sulphuric acid is liberated by reaction
like this, then we have many other reactions, essentially the dissolution of copper sulphide,
we can write as reaction with ferric sulphate to produce copper sulphate 2 F e S O 4 plus
2 S and constantly the ferrous iron is converted to ferric iron by bacterial action.
So, if there are bacteria, then this goes on and on and the leaching reaction is speeded
up. Similar things happen in the case of uranium ores also, and uranium ores also have been
found to come into solution through the reaction of not these bacteria, there are other kinds
of bacteria. Now, this bacteria are sometimes there already
or they can be introduced, they can be first grown in the laboratory and then introduced
in the environment. For these bacteria, there are also some conditions for survival and
growth. I mean in the temperature should be right, they operate well in medium temperatures,
in very cold climates, they will not to work, you get temperatures very very become very
high, they will not survive, there are some conditions of p h etcetera etcetera etcetera.
Now, it was found where it happened, naturally the conditions were very right, but we can
create those conditions if we know how bacteria leaching will be very effective. Now, very
large scale r and d work on such bacteria leaching of some sulphide ores are being carried
out in our country, but still not a commercial process. For a commercial process, for hydrometallurgy,
we have to use chemicals to take copper into solution.
So, I will not discuss the effects, the bacteria leaching for too much. I did not mention the
conditions, let me mention that, and then you will appreciate why bacteria leaching
can be ideal for our condition. First of all, temperature has a marked effect on conversion
of ferrous to ferric iron through bacterial action and this is the most critical step.
Maximum bacterial activity is between 30 to 35 degree centigrade, these are the ideal
temperatures available in our climate, 30 to 35 degrees the bacteria are most effective.
If the temperature is above this, bacterial activity would come down; beyond 50, it will
almost stop and at a temperature higher than 70 degrees, of course micro organisms become
sterile and they are destroyed. Of course, in nature there are no temperatures like 70
degrees, but you know people have done to find out what happens to the bacteria, they
becomes sterile and then they will die. If the temperature decreases below 30 degrees,
the activity also decreases and at a temperature below 18 degree centigrade, there is hardly
any bacterial activity. So, in cold climate bacterial activity cannot be exploited, our
country has a ideal climate, 30 to 35 degrees. Of course, they are living organisms. So,
they have to be fed with nutrients some food to grow and some obvious nutrients would be
where there is ferrous iron like F e S O 4, F e S 2, ammonium sulphate, ferrous sulphate,
these are the nutrients to the leaching solution. If they are added, then the increase the ferrous
iron concentration increases and therefore, conversion from ferrous to ferric which is
the, which on which the bacteria thrive, that also is there. And bacteria become more active,
and rate and extent of conversion both will increase. There are other factors like, it
is a surface phenomenon, after all bacteria will reside on the surface of the mineral
particle and react there. Therefore, the particle size of the solids
which are undergoing bacterial leaching are important, fine as solids will be more amenable
to bacteria leaching. And once it ground the ore, surface area available is lot more leaching
rate will be high, because surface area for bacteria too come and grow is more. There
are some problems always, you must understand, if you make the deposit very fine, then the
bacterial action may begin to draw because the permeability you drop. Because in all
these, air needs to be supplied you will find in all reactions air is required.
So, if the particles have very fine, the permeability is low and air cannot get access to all the
sides where bacterial action is taking place. It will also help if you have a shallow bed,
means if you have a very deep bed with lot of water level, then the bacterial action
is very effective, it should be a shallow bed, you know wide area with fine concentrates
lying around ideal for bacterial action. What about direct sunlight? In our country
there is a lot of sunlight, it is been found that if there is too much of direct sunlight,
then the bacterial action is not destroyed, but it is very much adversely effected, like
you know all humans also. You know, if if we are put in the sun in a desert, we really
cannot be very active, we need hot humid conditions. But not too much of light, bacteria will not
die, but they will not be so active. It is very sensitive to ultraviolet light;
even a short exposure will completely stabilize bacteria. So, preferably some kind of a shade
would be ideal for bacterial action, then it needs aeration also and they are active
only in acid media. So, the acidity will have to be controlled p h will have to be controlled,
they have to be aeration and ideally a p h value of 2 to 3.5 should be maintained, that
kind of a p h value is ideal both above and below this bacterial action will drop, at
p h value around 6 when it is almost becoming neutral oxidation is inhibited.
And if it becomes alkaline, means if it is goes well beyond 7 bacteria die. So, the bacteria
lived in acid conditions, not in alkaline conditions. Supply of oxygen is vital and
there has to be aeration in a portion of the bacterial solution and subsequently the aerative
solution will have to be supplied to this side.
So, from a central aerated solution it is sprinkled on to the rest of it. So, there
are this conditions, but the scope is very good in India for bacterial leaching operations
where the sulphide ores are often lean and they must be exploited by hydrometallurgical
methods. The climate often hot and humid is ideally suited for bacterial activity, but
then strangely most r and d work in bacterial leaching has been done in the west. In our
country, it is only last 15 or 20 years that we have started this work and there are some
fields where bacterial leaching is being tried out.
There is also a question of finding the right kind of bacteria. I think in the west, they
have experimented with different kinds of bacteria that are highly effective. People
say that, if a bacteria is found to be very effective in one climate, it may not be so
in another climate, but then you know like all living organisms, bacteria can also acclimatize
themselves in climate changes. So, even if initially some bacteria may not
be so effective, when you try it out given time they might start becoming active. So,
these are various studies that are being carried out in our country to find the right kind
of bacteria, the right kind of conditions. And at least in the case of sulphide minerals,
there are now tries being carried out in some fields and this is, this from the Ghatsila
based Copper Corporation that these studies are happening in somewhere in Madhya Pradesh.
But as I said, these are still in not in; you know in the r and d stage, this is not
found an industrial application. For industrial application, we need a process where chemically
we will convert in the copper minerals into a solution. Now, let see how we do that. Now, there are
two ways, two things that are become common that get soluble copper chloride or produce
soluble copper sulphate. Both chloride in solution and sulphate in solution can be electrolyzed
to produce copper through electrolysis of eco solutions.
Now, for copper chloride rod, the copper concentrate has to be ground always. Whenever we are going
for leaching, we have to go for fine ores leaching at about 106 degrees which means
you need again an auto claim, why above 100 degrees? Because, we accelerate the process
of leaching. Leaching will be by a ferric chloride solution,
it is called ferric chloride leaching process. Copper will be taken into solution, you filter,
this solids will go for solvent extraction to get elemental sulphur, the liquid will
go to the cementation route, that you put iron filings, copper will precipitate, the
filtration will give a liquid from which through crystallization we can be recover F e C l
2, by roasting we produce hydrochloric acid gas. And then after electrolysis, we can get
hydrogen and this chlorine which will go for ferric chloride regeneration, because from
here it is coming here and so, we will get copper.
Unfortunately, this process always sound in theory is not very attractive from the energy
point of view. Surprisingly, although it is a room temperature process, on the whole we
needs more energy than compared to a pyrometallurgical process.
You might think it is ironical, but in this case it is not. Because, you have seen that
in copper metallurgy reactions are exothermic, you are not supplying heat from outside to
carry out the reactions here, essentially supplying heat to take care of the heat losses
in some reactors. Otherwise if you do things well, you do not need any supply.
So, the bigger the reactor, the more continuous the process, the heat requirements become
lower, whereas in a process like this, of course grinding is there also in pyrometallurgy.
But in all this leaching, you need an auto clay evaporation, you need electricity to
operate autoclaves at higher temperatures, you need lot of this pumping of fluid from
here to there, you need solvents which are expensive, you need filtration, the operational
steps are there, there is a fire refining here finally to get copper, all this actually
adds up to the energy requirements. So, it has not been found very attractive, commercially,
but the next one is more attractive. It is to get copper sulphate into solution,
now one’s obvious way will be that, you take copper pyrites concentrate and you roast
to produce copper oxide and that dissolve by sulphuric acid to get copper sulphate,
but no, there is a simpler way of doing that. If you go back to my lectures general lectures
on roasting, we have seen that if you take a metal oxide and if you oxidize metal sulphide
and oxidize, you can generate a whole whole range of products, could be a lower oxide,
could be a sulphate, could be a compound which both has some oxides, some sulphate etcetera
etcetera. It all depends on how you control a partial
pressure of sulphur and partial pressure of oxygen. So, the copper sulphide can be converted
straight to copper sulphate by roasting operation. And then that copper sulphate would simply
dissolve in water, you do not have to bring in acid, as a matter of fact in that process,
you generate S O 2 which you go for sulphuric acid generation. Now, look at this diagram, this figure shows
the stability regions in the C u O S system in a fluid bed roaster. A roasting temperature
higher than 650 is required to achieve good roasting kinetics, 700 degree centigrade is
optimum when partial pressure of S O 2 lies between this and this and P o 2 lies between
this and this. Let see what is that we are plotting here,
we are plotting free energies of decomposition of the whatever is written here as a function
of temperatures, free energies of decomposition, mind you. This is the line for C u O, this
is the line for C u O, C u O S O 4, and this is the line of C u S O 4. We have also plotted
here the line for P S O 2 and P o 2 combination of 0.4 and 0.4 and P S O 2 and P o 2 combination
of 0.9 and 0.1, more or less 0.1 0.1. Now, if we had somewhere here, we will always
produce copper sulphate. If you go into this region, will produce C u C u S O 4, if you
go beyond this, will produce C u O. Going beyond this means, going to a very high temperatures
and it is more easily done, if you have the S O 2 or P o 2 things high.
Now, the ideal operational zone is here. In this zone, we produce copper sulphate that
is ideally suited for going into solution. And these are the names of the various processes,
how they operate, see these are a processes from different countries are named here in
different, there are many plants operating, these are the names, who and they use this
combination of S O 2 and O 2 to get directly from copper sulphide copper sulphate.
And this copper sulphate would be taken into solution, and then during subsequent electro
winning of copper sulphate solution obtained from the dilute acid leaching of the roasted
concentrate C u H 2 S O 4 is generated. The reaction is C u S O 4 H 2 O C u half O
2, the sulphuric acid in the spent electrolyte used for the vat leaching of copper oxides
ores. If such copper oxide ores are not available, H 2 S O 4 is utilized with either lime or
limestone and rejected as gypsum. So, some amount of H 2 s o 4 will be used
to dissolve some C u O into solution or into we are also getting soluble sulphate by a
control roasting operation. I would stop this subject here, and now I
would like to move into another a metal and that is lead.
Now, let me mention here that there are experts who work on copper metallurgy, there are experts
who who who work only in one segment of copper metallurgy, one can discuss in detail either
roasting or smelting or converting, one can discuss with theory of all this, we can talk
about the plant design, the process design, the equipment design.
But basically, I think in this course, what we need to do is to get an over view of the
entire subject of production of non ferrous metals. So, I am going to some basic concepts
and at the end, I would like to come back to one or two extraction of processes.
I will look at them little more critically, taking as a specific example, how you analyze
for energy, how you analyze for process steps. But at this moment, let me rush through all
this metals without going in to too much of detail. So, I move on to lead, now the lead
finds many many uses. And maybe I can draw a diagram for you to
make it simpler, you know that batteries constitutes almost a third of that, 32 percent going to
batteries, this is the more important. Then comes antiknock compounds we use in cables,
17 percent sheets and pipes, there are miscellaneous uses in many things. So, lead is a very very
important metal not one time, lead because it is it can be found very easily, use to
be, use to use, were used in piping. Even in our childhood, in our wash basins, it was
connected to the water supply through lead pipes. And you will be surprised to know that
the Romans used lead pipes for their water supply, because there was no other material
easily available at that time, they did not have those quantities of iron pipes. And lead
was also very easy to lay down, it could be it was flexible, it could be given any shape
they wanted, it could be bent, it it could be also may be diameter could be may increased
or decreased in case they wanted to have connections, those lead pipes are still there in Roman
Ruins. And they have stayed like this intact, but
these days we cannot use lead in piping, because people know about the toxic effects of lead,
there can be lead poisoning. If you were drinking that water which is coming through a lead
pipes day in and day out, then there are problems, so lead is no longer used in pipes.
Besides, there are now cheaper materials more effective, we have steel, we have plastics,
and we have polymers and all kinds of things. But at one time, lead was used, but lead is
still used in cable sheathing, may be you want the flexible cable, you can have a sheathing
of lead, very effective. But then, the maximum use is in batteries
and advantage there is where a battery is thrown out, that lead can be taken out and
reused very easily. So, it can be re circulated, in our country most lead is for re circulation
is coming from batteries. Unfortunately, it is done in an unorganized
sector, in Calcutta there are not dozens, but hundreds of units where lead batteries,
lead from batteries are being re processed to produce lead for the market.
Now, when there is a some raids on that, they simply close down, they go to another place
and start operation. The problem there is, they do not worry about pollution problems,
because whenever you are melting lead, lead fumes are generated. It creates high vapour
pressure fumes, those fumes are lither, it causes all kinds of problems but, you know
the labourers either do not know or they do not have from all over the country. Besides
if there are people who are doing it locally, people find it very easy to select of to them
and so, anywhere you you buy this battery, they are very very willing to give you some
price for the whole batteries and they reprocessed that, they goes to those who reprocess lead.
Anyway, so all I wanted to mention is, in the batteries which uses maximum and as as
the automating industry expense in our country, more lead is required that the more secondary
lead, let us leave it there. The common ore of lead is galena which is written as P b
S and because it is a sulphide, it is always associated with zinc sulphide, iron sulphide,
copper sulphide, several precious metals can be there, and some carbonate is also there.
But then, extraction of lead from galena seems to be a very straight forward, you see what
we need is simply blast furnace reduction of lead oxide by carbon, the in theory, the
it can be done at a temperature below 1200 degrees. In blast furnace operation, we need
7, for iron production we need 1700 degrees. In lead blast furnace, one operates just about
1200 degree centigrade, blast furnace is also a shorter in height, but one problem here
is that, lead sulphide is coming from a floatation process. You know from a sulphide ore which
has copper sulphide, lead sulphide, zinc sulphide. Lead sulphide concentrate is obtained by a
differentials floatation process that requires very fine ore to start with. So, what one
obtains is also in very fine form, the concentrate will be very fine. When that lead sulphide
is roasted to produce lead oxide, it will also be fine, that fines cannot be charged
in blast furnace, because you know how blast furnace operates.
It is a vertical reactor in which the oxide charge is reduced by carbon, there are Tuyere’s
from with oxygen is coming, air is coming to oxidize the coke to produce C O, that C
O will have to permit through the bed for reduction, so if if their finds they they
simply cannot go through. In the case of iron blast furnace also, one needs particles of
iron ore, initially they use to have iron ore particles from the mines of a certain
size. Now, sinter sulphate, sinters are made from
finder particles by the process of sintering. Sintering means you take a lot of smaller
particles, let them undergo incipient fusion. Incipient fusion means only fusion on the
particle surfaces so that smaller particles agglomerate. So, from a fine we can produce
agglomerates of the size we want, typically it will be several centimeters, so a kind
of nodules. Once you have produced those agglomerates, that agglomerate will be charged in the blast
furnace so that in the furnace, there will be sufficient permeability for the gases to
go through. You cannot charge the fine oxide you have
obtained from roasting operation, you need sinters, and to repeat sinters are agglomerates
of fines obtained through incipient fusion of particular matter which create bigger particles,
which one packed will have enough permeability in them. Now, there are different kinds of sintering
machines, a simple sintering machine is a bag sintering, where in a sinter port the
fines are charged along with some fuel, no sorry the fuel a small amount of combustible
fuel is given here, this is burnt to make a flame and then a section is given from the
top to the bottom. So, the flame front moves, flame moves through the charge, you might
need little bit of fuel inside also. So, basically we need that a flame will go
through the whole charge not very slowly, the whole idea is not to melt anything, but
as the flame goes to this this particles begin to stick to each other, because only the surfaces
are melted. And from once we get we get particles, irregular shaped, the size can be controlled
by the speed of movement of the flame front which is controlled by the vacuum, also the
initial particles size of this and some other parameters.
So, the whole idea is from fines, we get particular matter but, this is a batch process and you
fill it up, you you do sintering, then pour it out, and then start all of again. But now, there are continuous operations,
continuous sintering operation and the standard machine is called Dwight Lloyd sintering machine.
There the basic scheme is that, fines are poured on to a moving belt somewhere here,
as they come the sintering operation will take place and from here continuously sinters
are discharged. So, on the bed as they move the, there is a vacuum the and there is a
flame here, burning the flame flint is moving through and gradually, it starts sintering
here, finally the whole bed get sintered and everything is poured out of it.
So, sintering begins here, some particles are sintered and as we go on and on bed, the
whole thing particles will gets sintered, they will report that. So, this is a sintering
machine and operates in a continuous manner, this is a must for lead blast furnace. Now,
the requirement of strength of the sinter is not as critical in the case of iron blast
furnace, because the blast furnace has smaller insides, but still, it is those sintered particles
which have to stand the weight of the entire bed. In that, there will be, the coke will
be there, so initially the whole bed is maintained by coke and this particle the porosity.
Now, in the sintering machine, roasting is below 800 degrees, because sintering is a
process of oxidation below the fusion point. We do not want fusion, this is the machine
name and sinters for blast furnace melting using fluxes, you also incorporate into the
sinter some limestone and quartz. So, they will create the slag in the blast
furnace operation, so lead sulphide will become lead oxide in the sintering machine. There
will be a certain amount of P b O, S i O 2 can also form, because we have introduced
a little bit of quartz and you can also, if there is a lead sulphate, we can also form
this. In the lead blast furnace now, this oxide
will be reduced by carbon to produce lead, we will also introduce some scrap iron in
the charge, in the blast furnace charge to ensure that if there is a silicate in the
charge or if it is in this slag, it will produce a liberate lead. So, the charge will have
fluxes, sinters, coke and some scrap iron, that will be the charge for the lead blast
furnace. Now, in the case of all lead blast furnaces,
a very critical thing is a bag filter, everywhere you will find whenever they are talking about
lead blast furnace. At the top of the furnace, there is a filter to trap all lead fumes or
lead oxide fumes. Otherwise the entire plant would would not be environmentally safe and
at the top of the furnace, either bag houses will be there or electrostatic precipitators
can also be there, like we have for iron blast furnaces to recover the lead fumes from outgoing
gases, and we show you one cutaway views of this.
Now, the blast furnace smelting in the case of iron ore smelting, we get two layers. We
produce pig iron at the bottom and above that is a slag layer. In the case of lead, four
distinct layers are produced in the blast furnace, and they have to be tapped separately.
Incidentally, the lead blast furnaces are not circular, there kind of elliptical, there
are some design requirement, they are slightly elliptical, the height is smaller. Otherwise,
there are many similarities with the iron blast furnace, but obviously, the blast furnace
for iron making is always far more sophisticated. Now, what are the layers? Remember the lead
is very heavy, so we have at the bottom lead; the specific gravity is 11, because the lead
has many things also in it. And there is another distinct layer call spiss, there is an e missing
spiss which is essentially an intermetallic compound F e A s 4 with some other impurities
is about 6. And then there is a matte, because there is always some copper in lead, so there
will be a matte with specific gravity is 5.
And above that, there is a slag and there there is a mistake there, I think the just
a minute. This specific gravity, I think it is not 8.6, it will be 2.6, please check the
book, because slags mostly silicates around 2.6 or so.
So, it floats on top of a matte, if there is no copper sulphide at all then there may
not be any matte, but if there is any copper sulphide it will come out as matte which would
have dissolve some other element, then there is a there is a lot of arsenic and iron that
will form this F e A s 4. And then at the bottom, there is a lead and it is called the
base bullion, because it is at the bottom, it is called base bullion. So, this is the
simple technique for making lead in the lead blast furnace, yes I have the figure now,
this is actually 3.6 sorry, this 8 is 3.6 3.6 3 5 6 and 11.
Now, this is not the end of lead extraction process, actually this is the beginning, because
producing the bullion in a blast furnace is straight forward. Then, we have the question
of how you purify this lead and recover all that is there in solution is lead and there
all kinds of things in this lead base bullion. So, we come to the treatment of base bullion
now, how we are going to treat this base bullion. Now, for that again we have to go into a flow
sheet. Now, before that flow sheet, let us go back to what we have done in lead extraction,
what we have done? We start with a lead ore which has lead sulphide, zinc sulphide, copper
sulphide, and iron sulphide necessarily in varying amounts, it will also have some other
elements, and it will also have silica necessarily. After concentration, zinc sulphide can be
separated fairly easily in the sintering machine. We will produce a sinter, but it will also
give you fumes of Z n O, C d O, P b O and it will go for zinc recovery, if there are
such fumes. Now, the blast furnace using the sinters will
produce slag, the slag will have some zinc and therefore, zinc has to be recovered from
lead slag and therefore, that we have what we call a fume in process, that I will discuss.
Then we have a layer, below that which would be matte plus spice, it will have arsenic
and iron. On top, there is now and then there is a in the bottom, we have the base bullion,
of course the gas that is etcetera go out. It is this bullion now, we have to think of
pretty, this would necessarily have some copper, it will also have some arsenic, it will have
other elements, it will also have precious elements like silver, gold etcetera, and balance
would be lead. So, I will discuss the treatment of base bullion in the next lecture. So, now
let me quickly recapitulate what we did today, we started with hydrometallurgy of copper
and I mentioned that in hydrometallurgy, the idea is not to use high temperature reactors,
you go list to have copper in solution, aqueous solutions. From there we want to get copper
out, so electrolysis or whatever method. Now, in nature in copper mines, copper dissolves
naturally in water bodies, but it takes many many months, I mean years, it was accidently
discovered that some bacteria can expedite this process.
These bacteria do not need for their life oxygen, they thrive on inorganic constituents
and they derive energy from reaction such as ferrous oxide, ferrous iron, being oxidized
to ferric iron. Many many things happen, but if there is a sulphur or sulphate, if there
is a ferrous iron, then the bacteria can be effective and they for more rapidly than natural
process can bring in into solution copper. It is applicable a bacterial action in many
many minerals, mostly suphide minerals, but also oxide minerals like uranium, the different
kinds of bacteria people have are trying them out, bacteria leaching has been applicable
for gold also in leaching, but we will not get into that now.
But then in the industry today, we cannot depend on bacteria leaching as of now. Because
for that, you need very shallow beds, fast areas and you you have to wait for months,
if you want to do it in an industrial scale, you have to use chemicals to build copper
into solution. We can do it by ferric chloride leaching, but then, we have seen it is not
very active commercially, what is active commercially is sulphate process.
We can roast copper minerals under control conditions to produce sulphate or we can also
leach by hydrochloric hydrosulphuric acid to bring copper oxide into sulphate solution,
this sulphate solution can go for cementation, electrolyze or whatever. Then we came to lead
metallurgy, which look straight forward to start with excepting that for reduction in
a blast furnace, the fine concentrate which becomes fine roasted oxide, they have to be
agglomerated using a sintering process. So, the sinters are charge in the blast furnace,
along with cock, along with fluxes and some scrap iron also for recovery of a lead.
And then, lead will come out at the base as a bullion and there are some other layers
as I mentioned, that base bullion is in pure lead which contain some valuable impurities
and we have to now treat that base bullion for recovery of those valuable, by products
as well as to produce pure lead, this I will do in the next lecture. Thank you.

1 Comment

  1. Today around 25% of the world’s copper is recovered using SX, i.e. hydrometallurgy. Thus, a figure of 85%Cu from pyro route seems very high! (Murdoch-2008?, THE SOLVENT EXTRACTION OF SOME MAJOR METALS AN OVERVIE, Henkel Australia Pty ltd)

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