Reprocessing old mine tailings to recover copper and precious metals using froth flotation

The old tailings from mine dumps in Namibia contain not only copper but also precious metals and other metal values, such as lead and zinc, which should be recovered to supplement the production of metals from ores. X-ray fluorescence (XRF) analysis of the tailings showed that it contained 0.8% Cu, 40 ppm Au, 60 ppm Ag, 0.9% Pb, 0.7% Zn and 1% Fe. Batch roughing tests were conducted to investigate the effect of pH, collector (PAX) dosage, and sulphidiser (Na2S) dosage on the recovery of copper and precious metals (Ag and Au). Results for flotation test work showed that recovery of metal values depends on the three operating variables. Maximum recoveries of Cu (52%), Ag (53%) and Au (44%) were achieved at pH 10.5, PAX dosage of 47 g/t, Na2S dosage of 109 g/t and 12-minute residence time. Testwork is still in progress to improve the recoveries of copper, gold and silver.