Manufacture of Metals and Compounds

In is a rich indium ore . A specific iron-black mineral, indite Feln S,, is found in Siberia but it is very rare. 

Thallium minerals are rare too. N. A. E. Nordenskiold found one in Sweden in 1866. 

It had the composition (Cu,Tl,Ag)2Se. In order to honor Sir WilHam Crookes, the discoverer of thalHum, he named the mineral crookesite. ThalHumis recovered from the roasting of pyrite in connection with the production of sulfuric add and as a by-product of zinc and lead production from sphalerite and galena. Manganese nodules, found on the ocean floor, contain thalHum. 

Indium is mainly won from residues during the metallurgical treatment of indium-rich zinc and lead ores. The residues are dissolved in acid and indium chloride precipitates at the inlet of chlorine gas. The indium chloride is purified from tin, copper and lead using liquid-liquid extraction. A concentrated indium solution is obtained, from which indium is precipitated on zinc sheets. The spongy metal is scraped off, fused and cast into bars. For normal use, purification by electrolysis is satisfactory. For semiconductor purposes, repeated electrolysis and zone melting create an extreme purity. In 2001 the refined indium production was about 300 tonnes. 

Thallium is prepared from filter dust obtained after roasting of sulfide ores. The dust is dissolved in sulfuric acid. Then thallium co-precipitates with lead sulfate. The lead manufactured by reduction with coke contains thallium metal. Lead is first removed in two electrolytic processes, and in a second step thallium is precipitated on a steel cathode. As an alternative, thallium can be won from a sulfuric acid solution with an ion-exchange technique. The annual production of thallium compounds corresponds to 30 tonnes of thallium, but the production of the metal is not large - in the whole world less than 10 tonnes. 

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