Mercury production from sulphide concentrates by cupric chloride leaching and aqueous electrolysis

The Bureau of Mines developed a hydrometallurgical method for treating mercury sulfide concentrates to recover mercury. Sulfide flotation concentrate from the McDermitt Mine (Nevada) was leached in a cupric chloride solution at 80° C. The cupric chloride concentration of the solution was maintained during leaching by chlorine sparging. Mercury extractions exceeded 99 pct in 3 h of leaching. After leaching, the pH of the solution was increased from 1 to 4.5 to precipitate copper as atacamite. The pregnant solution, which typically contained 100 g/L Hg, was sent to electrolysis to produce highpurity mercury metal, and chlorine for recycle. In a 200-A electrolytic cell operated for 24 h, current efficiency was 99 pct, and the energy requirement was 2 kw·h/kg of mercury produced. Mercury removal from the waste stream was also investigated. Iron or zinc cementation, sulfide precipitation with H2S, and activated carbon adsorption all decreased the mercury concentration from 10 g/L to 0.01 mg/L.