Question
Fri October 26, 2012 By:
 

How is lithium extracted from its ore?

Expert Reply
Mon October 29, 2012
The ores of the lithium are the lepidolite also known as lithia mica, the petalite, spodumene, the triphylite and the amblygonite. Lithium is an alkali metal and very reactive, very strong reducing agents. The usual methods of the mineral extraction cannot be used because

(1) It can not be isolated by the reduction of its oxides it is very strong reducing agent.

(2) It can not be extracted from the ores by the electrolysis of their aqueous solutions, as the formed metals will immediately react with water giving their hydroxides instead.

(3) Lithium (and all other alkali metals) react violently with water. So it can not be prepared from the aqueous solution of its salt by the normal metal displacement method.

So keeping these problems in mind, lithium is generally isolated by  electrolysis of their fused metal halides. This takes two steps. The minerals are first of all converted into lithium chloride by any one of the following methods:

(1) Acid treatment method -- It's finely powdered and boiled with sulfuric acid. The insoluble bits that is formed in the process is removed by simple filtration. The acid solution is treated with sodium carbonate to precipitate iron and aluminum. Then, excess of sodium carbonate is added to the filtrate to precipitate lithium as lithium carbonate. It is filtered and dissolved in hydrochloric acid to obtain lithium chloride, which is purified by extraction with alcohol.

(2) Fusion method -- The ore is finely powdered and fused with a mixture of barium carbonate, barium sulfate and potassium sulfate. The fused mass is separated into two layers, the upper layer consists of lithium, sodium and potassium sulfates and the lower layer consists of barium sulfate, alumina and silica. The upper layer is separated, dissolved in water and the solution treated with barium chloride solution. Barium sulfate gets precipitated while the chlorides of lithium, sodium and potassium remain in solution. The precipitate of barium sulfate is filtered off and the filtrate is evaporated to dryness. The residue that's formed consists of the mixture of alkali metal chlorides, and then lithium chloride is dissolved out in pyridine (other alkali metal chlorides are insoluble). Finally... the pyridine is distilled off leaving the lithium chloride behind.

Now here in step two, the dry lithium chloride is fused with potassium chloride and electrolysed in an electrolytic cell. Potassium chloride is added to lower the temperature and increase the conductivity of lithium chloride. The cell is operated at a temperature of about 720 K and a voltage of 8 to 9 volts is applied. The reaction goes like this...

LiCl --> (Li+) + (Cl-)

(Li+) + (e-) --> Li

2(Cl-) + 2(e-) --> Cl2

Now you're almost done. The chlorine gas is liberated and leaves the cell through an exit and the molten lithium metal rises to the surface of the fused electrolyte and collects in the cast iron enclosure surrounding the cathode. BOOM! You can now remove that lithium and put it on the market to make things like very strong lithium-ion batteries for your laptop.
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