Occurrence, Extraction and Isolation of Lithium, Beryllium and Fluorine
The chemistry of extracting metal from their ores and utilising them for useful purposes is called metallurgy. The process of metallurgy mainly depends upon the nature of the ores and the impurities present in them therefore in metailurgical prcess different steps are involved, some of them are discussed below:
Crushing and Grinding of ore:
When the impurities present in the ore are quite distanct, they can be removed by hand picking and the remaining part is broken into small pieces by hammering and then by jaw crushers the small pieces of the ore are therefore grinded in ball mills or stamp mill into finely powdered ore.
Cocentration or dressing of the ore:
Since the ores are obtained from the earth crust, these are generally found mixed with a large number of impurities like clay, sand, limestone silicates etc. These impurities are known as gangue or matrix. The removal of these impurities from the powdered ore is known as dressing since dressing. Since dressing of the ore gradually increases the percentage of this metal. It is also knoe=wn as concentratin of the ore and the ore without any impurities as concentrate. The ore is concentrated by the following methods:
1_Gravity separation or hydraulic classifier method :
This method of concentrating ore is based on the difference in specific gravities(dendities) of te ore particles and impurities in this method, the powdered ore is introduced through a hopper in hydraulic classifier and is eglitated with a running stream of water, so that the heavier ore particles settle down rapidly at the bottom while the ligher impurities ( called as gangue ) are washed away with the water as shown in figure 7.01
Genrally, oxides and carbonates ores are concentrated by this method.
2_Electromegnetic Separation method:
This method is adopted when either the ore or the impurities are magnetic in nature. The two can be separated from each other by means of electromagnetic separator. A magnetic separate impurities from the ore the finely powdered ore is dropped through the hopper on the belt moving over electromagnetic roller and falls just below to the roller while the non-magnetic position falls farther away from the magnetic roller, as shown in figure 7.02,
By this method chromite ore , FeO.Cr2C3 (an ore of Cr) being magnetic can be separated from the non magnetic siliceous impurities.
3_ Froth floatation method:
This process is especially used for concentrating sulphide ores of Pb, Zn, Fe etc. like PbS (galena), ZnS( zinc blende), Ag2S(home silver) FeS2(pyrite) respectively and is based on different wetting characteristics of the ore and gangue particles with water and pine oil. Th gangue particles are preferentially wetted by water while the ore particles are wetted by pine oil. In this method the finely powdered ore is mixed with water and a small amount of pine oil ( a foaming agent) is taken in a big tank.
The whole mass is then agitated violently with air. The ore particles which are preferentially wetted by oil rise to the surface along with froth while the gangue particles abetted by water.
become heavier settle down slowly to the bottom as shown in the diagram. The froth carrying ore particles overflows the floatation tank and collected into the other side tank where the ore particles settle down after some time(see figure 7.030
For better result in certain cases the following chemicals are also used during the process
- Collectors : Sodium or potassium ethyl xanthate are used as collectors. These get attached with the particles of the sulphide ore and make them water-repellant so that the ore particle pass on into the froth.
- Activators and depressants : When a mineral contains other minerals as impurities. the addition of these agents activate or depress the frothing property of other minerals present as impurities and thus helps in their separation. CuSO4 is an example of activator while sodium or potassium cyanides are the examples of depressants.
(C) Calcination and Roasting:
Calcination is a process in which concentrated ore is heated in furnace generally in the absence of air to expel water from a hydrated oxide or CO2 from a carbonate at a temperature below their melting points.For example:
While roasting is a wider term used to denote the process in which the concentrated ore (generally
sulphide) is heated alone or it after mixing with other materials is heated strongly in the excess of air
or Oz below its melting points. For example:
These two processes make the mass porous so that it can easily be reduced to the metallic state in the next operation. These processes are carried out in various type of fumaces such as reverberatory furnace, blast furnace etc,
D] Reduction to Free metals:
In order to extract metals from calcined or roasted ore various reducing agents are used in either of the following ways:
1- Reduction by carbon (Smelting):
The oxides of less electropositive metals like Pb, Fe, Zn, Sn, Cu etc may be reduced by strongly heating them with carbon, coal or coko. Roduction of oxide with carbon at high temperature is known as ‘smelting:
In practice, the calcined or roasted ore is mixed with coke and flux and heated in suitable furnace in presence of a controlled supply of air, so that the flux reacts with the impurities (gangue) to form easily fusible material called ‘lag’
which is lighter than ore. Slag is immiscible in molten metal and can thus be easily separated from the metal. The nature of
the flux used depends upon the nature of the impurities to be removed. It is of two types:
(a) Acidic flux: [eg. Silica (SIO2) borax (B2O3). P2O5 etc) :It is used to remove the basic impurities like Cao. Mgo, FeO etc.
(b) Basic flux: (e.g. Caco. MgCo,. Fe2O3. CaO etc): It is used to remove acidic impunity like SIO2, P2O5 etc.
2- Alumino-thermic reduction :
Certain oxides like Fe2O3, Cr2O3, Mngon etc which can not be reduced by carbon can be reduced to free metal by Al powder. This type of reduction is called Gold-Schmidt’s alumino-thermic process. In such case, Al is used as a reducing agent. A mixture of the metallic oxide and Al-powder is used which is commonly known as thennite. Equations representing this process are:
3- Electrolytic reduction :
The highly active metals like Li, Na, K, Ca, Mg, Al etc are extracted by the electrolysis of their oxides, hydroxides or chlorides in fused state. When the fused mass is electrolyzed in an electrolytic cell, metals is deposited at the cathode. For example:
4-By precipitation or Hydrometallurgy :
This method is based on the fact that more electropositive metals displace less electropositive metals from their salt solution For example in the extraction of Ag following reactions are carried out.
Similarly, Ag can also be obtained from Ag() salts by adding other active metals like Cu and Cu is isolated from Cu (1) solution by adding iron and so on.
5- Reduction by carbon monoxide :
6- Reduction by water gas :
This method is generally used for the separation of nickel from its oxide.
D] Refining of crude metals ( Purification ):
The metals obtained from the ores by any one of the above reduction processes are generally impure and are known as crude metals, hence their refining is essential. The crude metals are generally refined by the following processes.
By electrolytic process :
Cr, Cu, Zn, Ag, Au, Sn, Pb, Ni, Al, etc are refined electrically. The impure metal is made the anode of the electrolytic cell and is connected to the positive terminal of the battery. Whereas a thin plate of pure metal is made cathode of the cell and it is connected to the negative terminal of the battery. A solution of a soluble salt of the metal is used as the electrolyte. On electrolysis pure metal is deposited at the cathode and soluble impurities go into the solution while the insoluble matter settles at the bottom that is called the ‘anode mud’. This process gives metals of high purity
2-By amalgamation process:
This process is used for the extraction of Ag and Au and is based on the fact that when these metais react with Hg, form Ag-Hg and Au Hg couples, which are commonly known as ‘silver-amalgam’ and ‘gold-amalgam’ respectively. When amalgamated silver or gold is allowed to distill in an iron retort. Hg, being more volatile, distills off and Ag or Au metal is left behind in the retort.
By liquation process :
This process is used for the purification of the metal which itself is readily fusible but the impurities present in it are not. This process is used for the purification of Sn and Zn and for removing Pb from Zn-Ag alloy.
By fractional distillation process:
This process is used to purify those metals which themselves are less volatile and the impurities associated with it are non-volatile and Vice-versa. Metals like Zn, Cd and Hg are refined by this process.
By oxidation process:
It is generally employed for refining those metals which are associated with such impurities that can easily oxidized into their oxides
In 1817 this element was discovered by Artvedson who gave the name ‘lithia’ because of its strong alkaline nature (Lishia means strong). He discovered Lithium in the mineral Petal/to and spodumene and found that its carbonates are insoluble in water as compared to other alkali metals and chlorides are hygroscopic in nature. A trace amount of Lithium is also found in milk, blood, plants and animal Kingdom.
Lithium does not occur in free state. It is fairly widely distributed in nature and is about twice as plentiful as lead. In India it is found in Bihar, Mysore, Rajasthan and Kashmir In the form of lepidolite. Some of the important minerals of lithium are as follows:
Lithium salts also occur in certain spring waters and in some plants such as tobacco beet and sugar cane.
Extraction of Lithium from its ores:
From the ores, lithium is extracted as UCI and then subjected to electrolysis to get pure lithium. The whole process is carried out in the following steps:
Step 1: (A) Preparation of LICI:
1- By fusion method in this mothod, the finely powdered lepidolite or spodumene ore is taken and fused with a mixture of BaCO3, BaSO4 and K SO, When fused is obtained gets separated into two layers
- Upper layer consists of sulphates and carbonates of Li, Na, K
- Lower layer consists of silicates of Al and Ba
From the upper layer LI SO, and Llaco, are separated and dissolved in water. Now whole of this aqueous solution is treated with BaCl2 so that LI SOA is converted into soluble LICI and LI2CO3 remains unaffected by BaCI2. The soluble LICI is concentrated and evaporated to dryness and extracted with pyride.
(ii) By acid treatment method:
The finaly powder petatite or spodumene ore is digested with cone, h2so4 and evaporated to dryness. The dried mass is then extracted with water when silica (SIO2 ) is removed as insoluble residus and the filterate containing sulphate of Li, AI, Fe and Mg is obtained in which the FeSO4 and MgSO4 were present as impurities . Now the soulution is treated with Na2CO3 to convert AI, Fe and Mg sulphate into their insoluble carbonates wheres Li2SO remains in solution. This solution is concentrated and again treated with excess of Na2CO3 to convert LI2SO4 into insoluble LI2CO3 which on treatment with HCI gives LICI.
(B) Electrolysis of fused LICI (Down’s Process):
A mixture of LICI and KCI (1:1) is fused and subjected to electrolysis in an electrolytic cell KCI is added to increase the conductivity of tused mixture and decrease the fusion temperature of LJCI from 613 °C to 400 °C. The electrolytic cell is operated at temperature 400° to 420 °C and at the voltage of B-9 volts. The mixture is electrolysed in an electrolytic cell which consists of graphite anode and a ring shaped steel cathode. The cathode is surrounded by cast iron gauze diaphram In lower portion to separate L and Cl2 formed in the cell as shown in figure 7.04. Cl2 gas is obtained at anode and escapes via the hood whereas L metal is obtained at cathode in Inverted tough T which is rised up to the pipe P and then collected into vessel V.
Fig.7.04 : Preparation of lithium metal by the electrolysis of fused mixture of Lici and KCI
Chemical Properties :
- There is no effect of dry air on Li but it is oxidised with moist air. When heated above fusion point (180°C) it burns and forms oxides and nitrides.
- It also reacts with S. Hy halogen and CO2 at fusion point and forms salts.
Action with H20 :
Li directly reacts with water and form LIOH and H2
Action with acids :
L is strong electropositive metal and liberates Hy when treated with dil. and conc. hydrochloric and sulphuric acids. Reaction with H2SO4 is slow and with HCl is violent and catches fire.
- Ll also forms complex hydrides like LIAIH4, LIBH4 which can be used as a reducing agent.
Formation of complex hydrides :
Lithium in molten state reacts with P. As Sb, Si, S and Se at high temperature end forms phosphide, arsenide, stelbinide, silicide, sulphide and selenide respectively.
Uses of Lithium:
- Lithium salts are used to make glasses and pottery to increase their fluidity
- is also used in manufacture of alloys to improve their tensile strength and corrosion resistance Li-Pb siloy is used to make the bearings and sheaths of electric cables.
- is used as deoxidiser in the purification of Cu and Ni.
- In medicine, the thium extrate and salicylate are used for the relief of gout to stabilire the lithium urate which is faitly soluble in. H2
- As lubricants : LIOH is used in the manufacture of high lubricating greases.
- It is also used in thermonuclear energy as an ingredient of high energy fuels for propulsion of intercontinental rockets.
Anomalous Behaviour of Lithium :
- The properties of lithium and its compounds differ far more from those of the other group IA elemerts and their compounds due to diagonal relationship with magnesium. Some common differences are given below:
- The melting and boiling points of lithium metal are much higher than those for the other Group IA elements
- Lithium is much harder than the other group IA elements.
- Lithium reacts the least readily with oxygen, forming the normal oxide. It forms a peroxide only with great difficulty, and the higher oxides are unstable.
- Lithium Hydroxide is less basic than the other alkali metal hydroxides and therefore many of its salts are less stable. Li2CO3. LINO3, and LiOH all form the oxide on gentle heating, though the analogous compounds of the rest of the group I are stable. Lithium forms a bicarbonate in solution, it does not form a solid bloarbonate, whereas the other alkali metals form stable solid bicarbonates.
- Lithium forms a nitride LaN like Mg whereas other alkali metais do not form their nitrides
- Lithium reacts directly with carbon to form an Ionic carbide, like Mg. Whereas other alkali metals do not.
- Lithium has a great tendency to form complexes because of its great polarisation power than have the other heavier elements of group IA. For example Lil forms solid ammoniatod salt: U(NHS) I when treated with armonia.
- The halides and alkyls of lithium are far more covalent than the corresponding sodium compounds and because of this covalency they are soluble in organic solvents.
- The lithium ion itself and also its compounds, are oasily hydrated as compared to that of its rest elements of the group IA.
The similarity between thium and magnesium is called diagonal relationship. The diagonal relationship arises because of the effects of both size and charge. On descending a group, the atoms and ions increase in size and on moving from left to right in the periodic table, the size decreases. Whereas on moving diagonally, the size remains nearly the same. For example: lithium is smaller than sodium but lithium and magnesium are similar in sizo. The size of Lit = 0.76 A and Mg = 0.72 A so in situations where size is important some behaviour should also be similar.