Acid and Microbial Leach Processes

Oxidation of insoluble mineral sulfides to the usually water-soluble sulfates (PbS04 is an exception) can also be carried out in many cases by microbial leaching, that is, by the use of bacteria such as Thiobacillus fer-rooxidans which can use the sulfide-sulfate redox cycle to drive metabolic processes. The overall reaction still consumes oxygen 

Heap (dump) acid leaching of copper sulfide ores is possible with the aid of microbial oxidation. Not all copper minerals are sulfidic, however— malachite, azurite, and chrysocolla are basic copper carbonates-—and sulfuric acid heap leaching of low-grade copper carbonate ores can give solutions from which the Cu ion can be separated by solvent extraction (Section 17.3) and copper metal obtained by electrowinning. 

Other sulfide-oxidizing processes include the use of nitric acid, a strong oxidant, in place of sulfuric acid  

Better yet, the metal sulfide may be made the anode of an electrolytic cell, in which the electrolyte is H2S04(aq) and hydrogen evolution is the cathodic reaction  

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