Bisulphide extraction process patented in Montana

A bio-oxidation and bisulphide leaching process that may compete with cyanidation has been patented in the U.S.

Yellowstone Environmental Science of Bozeman, Mont., developed the 2-stage process (T.N.M., Aug. 21/95), which first oxidizes sulphide minerals in the ores, then converts the sulphates produced in the first step to bisulphides. The precious metals are then brought into solution.

Advantages of the bisulphide process include the low toxicity of bisulphides, low operating costs, the

destruction of carbonaceous materials that can cause gold to precipitate from cyanide solutions, and possibly higher recovery rates.