Use of Ozone for Gold Extraction from a Highly Refractory Concentrate

Precious metals are generally recovered from their ores by cyanide leaching. When the gold or silver are locked up in the mineral matrix, they remain unrecovered and the ore is classified as refractory to cyanidation. Ozonization in acidic media of an arsenopyritic-pyritic highly refractory gold concentrate (110 g Au/t) as a treatment prior to cyanidation was evaluated. While the conventional cyanidation of this concentrate recovers only 9% of the gold, a pretreatment with ozone before the cyanidation increases the gold recovery to 23%. The rest of the gold is in solid solution with the matrix. Even if this increase in gold extraction is not large enough to economically process this specific concentrate, it demonstrates that the gold locked up in pyrite or arsenopyrite could be recovered by ozonating the ore before cyanidation.