And the extraction of metal using a reducing agent and applying the seducing agent on an oxide.

The question comes to mind. That is the only way that we can extract metal from its ore answer is no. Yes, there are other alternative methods, also where you need not to make oxides and use a reducing agent like coke, but electron is a reducing agent and this these methods, where electrons are reducing agent, they are called electrochemical methodology of metallurgy. So, in this case electrons can be produced either in a solution or in a molten state of the salt. So, electrolysis is carried out. You know very well that in electrolysis electrons are easily produced, so electrolysis is carried out in solution or in molten state and reduction is done by electron of the matter, so obviously, for this kind of reduction, you have to use the relationship between ∆G and electrode potential. The ∆G naught is related with the electrode potential by this equation. In this equation, n is the number of electrons required for reduction of a metal, for example, if you have Then for one atom of iron, +3, you require 3 electrons, so the value of n for such a reduction will be 3 for The value will be 2, and what is F, it is faraday. Its value is around 95000 and it is required for 1 electron reduction process the charge in coulombs required for 1 electron process. Now, this E zero is very crucial for electrochemical methodology of metallurgy, because if this E zero is negative, then delta zero will become positive and the reaction will not become impossible or non-feasible, so E zero. Redox couple formed in the system, because whenever there is electrolysis there is a some at one electrode electrons are produced at another electrode electrons are absorbed, so obviously this whole makes the redox couple, and if the E zero is negative, such metals are called more reactive. Metals reduction will be very difficult so for application of this electrochemical method of metallurgy, the essential requirement is that E zero values of the redox couple should be positive. If it is positive, it will give the ∆G negative and the electrochemical process will be feasible. So, this ultimately boils down that very reactive metals will be difficult to reduce at a they will be required. They may require very high potential, or it will be difficult to reduce them, but those which are less reactive can be easily reduced. Let me give you an example: you have copper iron in this reaction. They are retained more reactive, metal iron is more reactive than copper, so it goes into the solution when this reaction happens and, if you take say, for example, here in place of copper sodium. This reaction cannot happen. That is sodium + iron. If you want to carry out this reaction, this reaction cannot happen because the metal is more reactive than the iron, so iron cannot reduce a more reactive metal, but it can easily reduce a less reactive metal, and copper is a less reactive metal. So, in electrolysis, the copper ion is discharged at negative electrode, which we call as cathode in deposited, whereas iron goes into the solution in place of copper. Now, the best example of this electro metallurgy is isolation of aluminum from its ore alumina. Now, alumina as such cannot be dissolved in any solvent because it is refractory material, refractive materials are those which cannot be dissolved in acid easily or they can be dissolved in base, but with difficulty. So, what do we do? We dissolve alumina in calcium fluoride and a complex of aluminum with fluoride. Now, this brings the conductivity into the melt, and this also dissolves alumina. So, alumina is in a molten state by reacting with them. The alumina is in a molten state. Now, this fuse matrix is electrolyzed how electrolysis is carried out. This is carried out in a cell. The diagram of the cell is shown. It has a carbon line, steel container, which has carbon line, a carbon line containing a steel container, and this acts as a cathode. Now we have anode, which is made of graphite. We have an anode which is made of graphite. Graphite is carbon, so carbon undergoes there in a commercial setup. Several such electrodes are used because electrolysis is carried out at a very large scale and when the electricity is carried out, aluminum is formed in a molten state and from here from this outlet aluminium is taken out. This process is called hall-Heroult process, and if you look at the overall reaction which takes place is alumina is reduced by. In fact, carbon into aluminium metal and carbon dioxide is a byproduct, now the oxygen which is liberated at anode. It does not go in the atmosphere just like that. It reacts with the carbon of anode and produces carbon monoxide and carbon dioxide. So, in these electrolytes electrolytic process, you will notice that real reduction is done by carbon. The process is basically electro is based on the electrolysis and if it is calculated that for each kilogram of aluminium, which is produced how much carbon is burnt, it is around 0.5 kilogram of carbon from the anode which is burnt for each kilogram of aluminium. The electrolytic reactions which occur at cathode aluminium is formed at anode. It is formed and these electrons, which are liberated here they are used here to reduce aluminum ion into aluminium metal. Now, there is another way of extracting metal from the ore. It is called hydro metallurgy. It is used for low grade oars. What are low grade oars low grade oats, which have less percentage of desired metal? If there is copper ore, then desired metal is copper, so a low-grade ore of copper will have less percentage of the copper which is present in good ores. In such cases. First you have to concentrate on the ore and ore is basically for concentration is least out with acid, what is leaching out, it is constitute continuously treated with acid, so that in a form of salt is passes into solution. Now, when the solution is enriched with copper, say, for example, in this particular case, then the copper can be reduced with the help of hydrogen directly or copper can be reduced with the help of a metal which is more active than copper. You know you have learned earlier that iron is a more active metal than copper. So, if the iron is scraps are added to this copper solution, the copper is reduced and iron goes into the solution in the form of iron, because this, whether a metal is more reactive or less reactive. This is given in electrochemical series those metals which are above a particular metal. They are considered to be more active. Those which are below they are considered less active. So, in the electrochemical series, iron is present in case of above the copper. A question may be asked that there are other metals also which are present above the iron. Why is iron chosen? I just explain to you zinc is another metal which is above copper and can be used for reduction of copper ions from a solution into copper metal. But if the reduction is carried out with zinc reduction is also faster, but here the economics decides which metal has to be used. Zinc is much costlier than iron, so using iron scraps is economical. That is the reason that commercially iron is used to reduce copper ions from a solution in hydro material. Now, so far, we have been talking about reduction and you showing that giving an important showing or giving the impression that reduction is the only possible way of getting or extracting metal from the ore. It is not true for extracting elements or for isolation of elements. In general, from any source, oxidation is also or may be used. . It is more suitable for non-metals. Now, chlorine is very widely used to disinfect the drinking water in all water supplies from the municipality they are the chlorine is used as an agent to disinfect the water, so water is chlorinated, so chlorine is required in very large amounts. The biggest source of chlorine. Chlorine is brine. What is brine? Brine is basically a sodium chloride solution called brine and seawater is effectively a sodium chloride solution or called brine. It may be called brine now this chlorine, if it is oxidized it gives sodium hydroxide and chlorine gas. If this brine is electrolyzed, then chloride ions are oxidized and result in chlorine gas and sodium hydroxide or the solution becomes alkaline. If you look the feasibility of this reaction, you can you see the ∆G value for this reaction is positive. So, if you want to make the ∆G negative in this equation, you have to use a E zero negative of the order of 2.2 volt, and so, if you use an external emf, which is greater than 2.2 volt, the chlorine from the brine solution can be Oxidized, the oxidation is not limited to non-metals. It is also known that some metal may be obtained from the ore by using oxidation process, silver and gold these two precious metals are present in the earth crust in native form. What is native form? Native form means that they are not in combination with sulphide or oxide, just free gold and silver, some dust or some rocks may be around them, so they are leashed with cyanide what cyanide does when they are treated with cyanide, cyanide oxidizes them. Both gold as well as silver, now, this metal by oxidation of cyanide, comes into a complex form from this complex. They can be obtained back by using zinc as a reducing agent. You can get back copper, so zincs act as a reducing agent. So basically, the oxidation process is involved in the overall extraction of metal for ores, from ores in these two examples: silver and gold. Ultimately, we have obtained the metal by using a reducing agent. This is unlikely in the case of chloride, from where we are getting chlorine directly by oxidation. Here we are using oxidation as a supporting procedure. The isolation of metals has three steps. We do this isolation from ore, so the first step is converting this ore or dress up to a form convertible to metal convertible form is oxide. The next step is to convert oxide or other forms suitable for conversion to metal. At this stage, the metal which we get is not pure, it is impure metal. So, what to do to improve its purity? You have to refine it. So, this step, which is called refining of metal, is very important to get the pure metal, so metal extract it by any method using any reducing agent using electrolysis or any other method is contaminated. It is very important to note that it is contaminated to prepare metals of high purity from this contaminated metal is called refining. The question may be: can there be a universal method for refining answer is no universal method, then how do we decide that about the method for defining to decide about the method of defining? We have to see the properties of the metal and impurity present because from different doors, the metal extracted may have different impurities and different kinds of metals may have different associated impurities. So, two things are important properties of the metal and second the impurity which is present. Now, they vary from the source of the metal extraction as well. Some generally used techniques for refining are distillation liquidation, electrolysis zone, refining, vapor, phase refining, chromatographic methods. So, depending upon the nature of the metal, we can use the method for refining, so the first is distillation. Now this distillation. Obviously, you know that you must have used distilled water, then how we get the distilled water. We boil the water and collect the vapors so for applying distillation to the purification of the metal. The important criterion is that the boiling point of the metal should be low. For example, of zinc or mercury, you know mercury is liquid at room temperature. Its boiling point is low, so just like water, we can convert some higher temperature than that of water mercury into vapors. Those mercury vapors can be condensed into the fuel into the form of pure mercury, so impure metal is evaporated, and pure metal is obtained, as distillate term means the vapors are condensed to liquid form. Vapors are condensed by cooling liquid form. We call that the liquid a distillate, so for application of the distillation, the essential requirement is that low boiling point of the metal. So, it has a restricted application. It cannot be used for any kind of metal, but only for those which have low boiling points. The equation is used for low melting point metals. What is done, in fact the metal is converted into a molten state and then it is allowed to flow on a sloppy floor. Sloppy floor means just like that sloppy floor. It is allowed to flow on this kind of sloppy floor. So, what happens when the molten metal runs down the floor and the impurities, which have not been melted or which are solid? At that point, they stay back on the surface in metal, which is in molten state rolls down the floor. The example is tin for this kind of purification now for liquidation. Also, the essential requirement for a metal is that it should have a low melting point. The third method for refining the metal is electrolytic refining. This is of wider application. It is used for a larger number of metal ions then, or what is possible application of distillation or liquidation in comparison to those possible applications. Electronic electrolytic refining has wider applications. The principle is based on the fact that impure metal is made anode and a strip of the same metal is used as a cathode. They are made a part of a cell. They are made part of a cell anode cathode. This cell is filled with an electrolyte which contains the same metal, which we want to purify. This has electrolyte containing the metal to be purified. Then electric current is passed between these two electrodes, the from anode the metal dissolves into the solution and is deposited in pure form as a cathode. Now, what will happen to those which are not deposited on the cathode? They can be divided into two categories. The more basic metals remain in the solution and the less basic metal basically make an anode mud. They are reduced, less basic ones and they are just deposited on the bottom of this cell and this deposit is called anode mut. The two reactions which are occurring in this electrolysis cell they are at anode metal is converted into metal ion and free electrons. These free electrons are taken by metal near the cathode and metal ions by the near which are near the cathode, and they are converted. Those metal lines are converted into metal, and they are deposited on the cathode. So, in this electrolytic cell, as current passes the cathode becomes thicker, and anode becomes thinner and thinner as the process goes on. I just exemplify this electrolytic refining, with refining of copper anode is made of impure copper. Pure copper strip is used as a cathode electrolyte, which is used in the cell, is copper sulphate electrolysis gives electrons to copper ions present in the solution at cathode and deposits copper, whereas at anode the reverse reaction happens that copper ions from the anode goes into solution giving you and electrons, so transfer of copper in pure from cathode happens. You have studied that impure copper is called blister copper. This has a variety of impurities, antimony, selenium, tellurium, silver, gold, platinum. They are less basic than copper, so they settle. They are reduced and settled at the bottom of the electrolysis cell and called together as anode mud. These metals, which are deposited in the form of anode, mart basically recovered, and they are expensive, so the cost of electrolytic refining is also recovered. Zinc may also be refined in this way. If you want to refine zinc in a similar way, you have to make an anode of impure zinc cathode of pure zinc, and you can use zinc sulphate as an electrolyte for this purpose. The third method which is used for purification of metal is called zone refining in this. Basically, what we do if I demonstrate that, if you have a rod of impure metal, then in nutshell, the procedure of zone refining, is such that the impurities move in this direction, and we make the pure metal move in this direction. So, after some time there is a divider on the left side of which has impurities on the right side of which has pure metal and we cut from here and remove all the impurities, now on what principle this zone defining works. This zone refining works on the principle that impurities are more soluble in melting than in solid state of the metal. So, what do we do? Basically, we take a metal rod and in an inert atmosphere, we heat it. We require an energy atmosphere, because if we use air the metal may be converted into oxide, so inert atmosphere is required to keep metal in metallic form. Now, this is heated by two induction coils, which are around it, as shown in this figure now the principle that impurities are more soluble in the melt. So, suppose these induction coils are here. So, this part is in a molten state of what will happen? The impurities will move into this melt and nearby metal will become pure, so we start from here and move our heating towards this direction so slowly, the impurities will be shifted to the left side and pure metal will be go on shifting to the right side. So, we start the circular mobile heater by fixing at one end of the rod of the impure metal. Then we move it towards the right side and after some time all impurities are collected around this end and pure metal is the rest of the part of the rod. Now, in one go, the metal does not become pure using this kind of zone refining. So, what we have to do, we have to repeat it. We have several times so after repeating this kind of heating several times the metal becomes slowly pure, and the impurities are collected on one end of the rod and another end of the rod, or a major part of the rod becomes pure metal. What we do is then cut out the zone which has impurities and use the remaining purified metal. This method is useful for making semi conducting materials of high, for example, germanium silicon boron, gallium indium. The next method is vapor phase refining. This method was first used for nickel. The principle of the method is based on the fact that metal can be converted into a volatile compound and collected as vapors, so metal impure. It reacts with something so that M, a which is formed is volatile in nature. The presumption is that in an impure metal, only metal interacts or reacts with a resulting volatile metal in other impurities. Do not show this kind of reaction, now so metal specific, which we want to purify is converted into a volatile compound, and this volatile compound is decomposed to give pure metal so for applying vapor phase refining the two basic requirements are. It should give a volatile compound. First and the volatile compound should be easily decomposable. These are the two basic requirements, so it should have a reaction which converts it into a volatile compound, and the volatile compound is decomposed to pure metal. Volatile compound with an available reagent and second, is it should decompose? Otherwise, recovery by this method will not be easy as I told you that, for the first time this vapor phase refining was used for nickel in the process is called Mond process. Nickel, if it is heated in a stream of carbon monoxide, is converted into nickel carbonyl or more specifically, nitric tetracarbonyl. No other metal generally found as impurity with nickel, gives any carbonyl when reacted with carbon monoxide. So, the first condition is followed that it has a very specific reaction with carbon monoxide. Now, this volatile complex nickel tetracarbonyl, if it is heated to 450 to 470 K it decomposes to give nickel metal, now this temperature is not too high, so at a very low temperature. The nickel is converted into a volatile compound and the volatile compound nickel carbonyl is converted also at a much lower temperature to nickel back. No other metal shows this reaction, so this is very specific and is widely used for refining nickel. A very similar method in principle has been reported by Vaughn Eichel. It is called one oracle method for zirconium and titanium. Zirconium and titanium are known to form refractory oxides, so they have oxygen. They are also associated with nitrogen compounds or anions, both of the kind of impurities on which are containing oxygen, or which are containing nitrogen. They can be removed by this method. Now, what is done in this method is crude. Metal is heated in an evacuated vessel with iodine. What is an evacuated vessel a container in which vacuum has been created. This iodine reacts with the metal forming iodides, which are covalent in nature, volatile and volatilized very easily or converted into vapors very easily. This metal iodide can be decomposed on a tungsten filament electrically heated about 1800 K. In this case, the temperature is somewhat higher, but you see in case of mount process with nickel, but it is not easy to remove zirconium contaminated with oxygen containing entities or titanium contaminated with oxygen or nitrogen containing entities, because they are very refractory in nature. So, considering that fact in view this temperature is considerably good to use this method for refining zirconium and titanium. The decomposition reaction is shown below where the zirconium delta iodide is converted back into zirconium into iodine. Just by heating. The chromatographic methods in principle can be used for defining metal but using chromatographic separation. The metal cannot be used directly in a solid-state form, as you have obtained from the ore. Separation is possible of compounds. Separation is possible only of compounds and the principle of chromatographic separation is that if you have a mixture, you absorb it on an adsorbent, then pass an element or solvent which, when runs through this adsorbent, takes away the least absorbed compound with it. After that, the next least absorbed compound or iron goes out, and this process goes on and, in the end, the most strongly adsorbed compound or iron comes out. This process is carried out generally in a column I just demonstrated. This is a glass column; it is filled with the adsorbent. The entities which have to be separated are put on the top, then the solvent, which is also called eluent, or a gas. If these compounds can be volatilized or can be kept in a gaseous state, when this column is heated, then you can use gas also, but generally it is done with the liquid or solvent when it passes through this column, the least absorbed comes out. First, then the next least absorbed comes out from this column, so this process goes on. This process goes on because different components which you have absorbed on the column are interacting with the adsorbent to different extents. Some are strongly absorbed, some are weakly absorbed and as a result, there is a separation. So, if you look at this column before coming out of the first compound and you somehow have a coloring agent to identify these entities, then the column has different kind of bands found or zones formed for different entities. But if you go on running, then these zones will go on moving and getting out of the column, so to apply chromatographic separation to metal ions. You have to convert the solid matter into a compound without that it is not possible to apply this method. Now, this column, apart from adsorbent, can be of ion exchange. Ion exchange are of two types, cation exchange or anion exchange. This cation exchange has sodium ions and a matrix which is negatively charged anion exchange ion exchangers, have say, chloride ion and a resin bed which is positively charged so on this cation exchange. If you pass the metal line, the metal line will replace sodium and when you are converting impure metal into a solution, all metal, ions or impurities, or most of them, will be converted into cations, those cations will be having higher binding ability with the exchange Regin, and so they will replace sodium. They will bind with resin, so at the top. This will be the situation that resin has metal lines, now this situation, if you pass through this an end, which is say, for example, a complexing agent, what will happen these metal ions will form complex? If I give you an example, EDTA, ethylene diamond tetra acetic acid, these metal ions will combine with the EDTA forming complex. This complex, formed by different mental ions will not have the same stability. They will be differing in stability, so those which are forming a very strong complex with EDTA will leave the rays in bed and come out as a complex. So, when you pass EDTA solution, it will run down into the conical flask. After that, the metal ion, which has formed the next least stable complex, that is the stability of its complex is greater than this one but lesser than rest of the metal ions. It will make a complex which will run down through this column. Now, in this chromatography there are basically two phases: one is mobile phase another is stationary phase. In this example, the stationary phase is the ion exchange ratio. If we are using an absorbent, then the stationary phase is absorbent. Mobile phase is EDTA solution which I have demonstrated, or it can be any other solution, or it can be gas also. It can be liquid, also another liquid on the left side, an automatic system is shown in which the solvent is pumped through column and the entities which are coming out. They are detected with the help of a detector, so this is an automatic system which can be used for separation of the metal ions, as well as for detection of the metal lines. Let me take a few examples of this kind of separation based on column chromatography. The first thing is that impure metal has to be brought into the solution. Suppose we have brought impure metal into the solution, then the question may be asked can this procedure separate? The kilogram amount of metal line answer is no. It is applicable only to a smaller level of metal line separation. A small amount can be purified very important. So, what is the advantage? A small amount of the can be purified, but the advantage is that very closely associated entities or species can be removed from the metal. What are very similar species which are present in as impurities? The best example is that of lanthanides. You know that lanthanides differ very little in their properties. If you want to separate one lanthanide, say, for example, cerium from other lanthanides, then it is very difficult to use any other method except the chromatographic method or solvent extraction method which are of in principle of similar type. So, the elements I just told you are complex agents: there are a large number of complex agents in it. It can be chlorite, it can be EDTA, or it can be any other organic acid. So, what is separating metal, ions metal ions are not getting separated by their absorbing ability or by their iron exchange ability with the with the resin. They are getting separated because different metal ions form complex of varying solubility with the element the complexing agent, which is present in the element it forms of complex of various stability, so obviously varying solubility, and that is responsible for separation. Now, let me first demonstrate how ion exchange separation or anion exchange can be used for separation of iron, cobalt and nickel or other metal lines. This is based on the fact that the metal ions form complexes. What kind of complex is anionic, and these complexes are absorbed on anion exchanger in this particular example: iron. This kind of complexity, formed , , , , it will depend on that what is the concentration of chloride ion, which is present, now so the complex which is least stable out of these will be easily decomposed if the concentration of chloride ion is lowered and the one Which is stable will remain in the solution will remain in the anionic form. So, if we take 90% acetone and 10% hydrochloric acid, cobalt and nickel form complexes which remain stable or which are more stable than the complex formed by iron and, but all these complexes are absorbed on an ion exchanger. So, if you lower iron it is not absorbed strongly. So, if you lower the concentration of acid, the nickel and cobalt remain in the anionic form, but iron very quickly loses its complex and becomes cationic form, and you know very well that cation cannot remain with the anion exchanger. So, iron comes out first and after that nickel comes out and finally cobalt comes out because cobalt complex is more stable than the nickel complex. This chromatography, which is based on the ion exchange, is called ion exchange chromatography. The naming of chromatography is generally done either using the adsorbent, which is used or the technique which is used. If you are carrying out a separation in column, then whatever adsorbent or ion exchange you are using, we call it column chromatography. So, this ionization chromatography, where cation exchanger regions are used, is a very well-known method for separation of lanthanoids, and this is executed in column. So, it is also called column chromatography.

Now the solution of citrate lactate or the other salts, whose anions form negatively charged complex with the lanthanoid, are used to wash the ions from the column. Basically, in the column, this is having cation exchanger resin. So, if you pass a complexing agent, then there will be a competition between the complexing agent in the resin for the metal line. If the complexing agent makes a very strong compound or complex with the metal with a particular metal ion, it will take out the metal from the cation exchanges, but if the cation resin strongly binds the metal ion, then complexing agent will be not able to do it. Unless the concentration of complexing agent slowly - slowly builds up in the column, and this is what happens in case of lanthanides, they are very similar in charge, which is generally three plus. They are also because of lengthening contraction. They are very similar in size, but in spite of that, the difference in the size is enough for making the complexes of different stability. Now, once a complex is formed, it cannot be held by resin. It will come out so ions that form a stable complex. They move of the column and the one which moves very weak complex. They will come out slowly or later those which form stable complex. They will come out first, so the separation is based on the stability of the complex. So, in general, what we can say is that cation exchange is not selective. It is not separating the metal ions. What is separating metal? Ions is basically the differential, complex formation, so for, lanthanides the exchanger just acts like an undiscriminating sponge, that is, it absorbs all cations and real separation is by the fact that these lengthen irons make a weaker, complex or a stronger complex with the complexing agent. So, this is the summary of the refining methods which are used in isolation of metals.