Pyrite flotation from gold leach residues

Abstract

GENMIN Process Research has been investigating the possibility of a low cost pyrite flotation process suitable for cyanidation leach residue. The flotation of auriferous pyrite in gold leach residues through traditional techniques is only possible after conditioning with sulphuric acid to overcome depression by cyanide and hydroxide. Recent testwork at both GENMIN Process Research and on site at Buffelsfontein Gold Mine suggested that the auriferous pyrite contained in the cyanide residues could be floated by using an amine as a collector. The amine float, although slow, gave 83% S (tot) recovery during rougher flotation. It was then found that washing and repulping the leach residue with fresh water results in pyrite which can be readily floated under alkaline conditions. Investigating further showed that it is in washing the cyanide residue filter cake prior to repulping that the depression of the pyrite is determined. In this way 95.3% S (tot) was recovered with the addition of fresh water, CuSO 4, SIBX and frother. Washing and repulping in plant water containing ±100 ppm cyanide, as is plant practice using barren cycle water from the zinc precipitation circuit (PPT) results in the effective depression of the pyrite. In the laboratory, only 2.9% S (tot) was recovered using this procedure.