Flotation smelting

The abundance of indium in the earth s cmst is probably about 0.1 ppm, similat to that of silver. It is found in trace amounts in many minerals, particulady in the sulfide ores of zinc and to a lesser extent in association with sulfides of copper, tin, and lead. Indium follows zinc through flotation concentration, and commercial recovery of the metal is achieved by treating residues, flue dusts, slags, and metallic intermediates in zinc smelting and associated lead (qv) and copper (qv) smelting (see Metallurgy, EXTRACTIVE Zinc and zinc alloys). 

The isolation of zinc, over 90% of which is from sulfide ores, depends on conventional physical concentration of the ore by sedimentation or flotation techniques. This is followed by roasting to produce the oxides the SO2 which is generated is used to produce sulfuric acid. The ZnO is then either treated electrolytically or smelted with coke. In the former case the zinc is leached from the crude ZnO with dil H2SO4, at which point cadmium is precipitated by the addition of zinc dust. The ZnS04 solution is then electrolysed and the metal deposited — in a state of 99.95% purity — on to aluminium cathodes. 

Zinc, Zn, is found mainly as its sulfide, ZnS, in sphalerite, often in association with lead ores (see Fig. 15.11). The ore is concentrated by froth flotation, and the metal is extracted by roasting and then smelting with coke ... 

Liquid-solid distributions are involved in ion-exchange and other adsorption-based separation processes, separation processes based on crystallization or precipitation, flotation processes for ore dressing, and smelting processes. 

The major ores of Zn are zinc blende ZnS (also known as sphalerite) and calamine ZnC03. Much more Zn is now produced from ZnS which is concentrated from its rock matrix by flotation or sedimentation. The concentrate is then roasted to generate ZnO, which is smelted with coke, or which is dissolved in H2SO4 and the solution is electrolyzed. 

All the ores are concentrated in complex mills by selective froth flotation lu produce individual copper, zinc, lead, and, infrequently, silver concentrates. The copper and lead concentrates are smelted to produce lead and copper bullions from which silver is recovered by electrolytic or fine refining. The silver bearing zinc concentrates are commonly processed by leaching and electrolytic methods. Silver is ultimately recovered as a byproduct from zinc plant residues. Canada is a leading silver mining country. Other important sources of silver are Mexico, die United States, Peru, the former U.S.S.R., and Australia. See also Mineralogy. 

Many ores of zinc arc concentrated by flotation before smelting. Sulfide ores and carbonate ores are then converted to oxide by roasting ... 

If the sedimentary sulfur deposits lie near the surface, the sulfur ore is mined. The sulfur is then extracted by smelting (Sicily) or by distillation at temperatures above 440°C. A combination of flotation and subsequent smelting is also operated (Poland). 

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