Indium electrolytic refining

Crude indium obtained, for example, as a byproduct of the New Jersey Zinc refining process contains 2-5% impurities, about 0.8% Pb, 0.5% Zn, 0.5% Sn, 0.01-0.1% Cu, and 0.01-0.05% Fe. Since Zn separates together with the In in the subsequent electrolytic refining, crude indium is first freed of Zn as follows it is heated at 800-1000°C in an iron tube closed atone end and sufficiently long to prevent spray losses. Steam is blown through the melt, by means... 

Production. Indium is recovered from fumes, dusts, slags, residues, and alloys from zinc or lead—zinc smelting. The source material itself, a reduction bullion, flue dust, or electrolytic slime intermediate, is leached with sulfuric or hydrochloric acid, the solutions are concentrated, if necessary, and cmde indium is recovered as 99+% metal. This impure indium is then refined to 99.99%, 99.999%, 99.9999%, or higher grades by a variety of classical chemical and electrochemical processes. 

In electrorefining, the metal to be refined is used as the anode whic dissolves in the electrolyte and is deposited as electrolytic-grade mett at the cathode. The impurities present in the anode remain on it, fall oi to the bottom of the cell as slime, or go into solution but are prevente. from moving toward the cathode by precipitation with some chemics reagent such as another metal added to the electrolyte. The buildup c metallic impurities that are dissolved but not deposited at the cathode i reduced by circulation of fresh electrolyte through the cells. Electrorefinin techniques are used in producing gold, silver, copper, nickel, cobalt, lead tin, antimony, bismuth, indium, and mercury. 

---