Studies on environmentally friendly leaching processes in China

The newly developed green leaching processes for chromium, lead and gold ex traction from ores or concentrates are described. The chromium is extracted from the iron chromite ore with fused sodium hydroxide at 500-550 degreesC as sodium chromate. The galena in lead sulfide concentrate is converted in to lead carbonate in ammonium or sodium carbonate solution at 50-80 degrees C followed by the separation of lead carbonate formed from the unconverted sulfide ores by flotation. Gold associated with sulfide ore (such as pyrite and chalcopyrite) can be extracted into sodium thiosulfate solution withou t any pretreatment such as roasting, high pressure aqueous oxidation or bac teria pre-leaching.