Effect of biological pretreatment on metal extraction from flotation tailings for chloride leaching

This study focuses on investigating the extraction of gold, copper, iron, nickel, cobalt, and zinc present in the flotation tailings. The studied sample contained iron (3.56%), copper (0.09%), and gold (0.2 ppm) as major target elements, whereas cobalt (0.04%), nickel (0.03%) and zinc (0.04%) were trace elements of interest. Primarily, bioleaching with mixed acidophilic culture was applied as a pretreatment process for the recovery of nickel, cobalt, and zinc, as well as for iron removal. The effect of solid concentration (5-12.5%) in bioleaching was investigated at pH 1.8 and the temperature was kept at 32 °C. The highest extractions of nickel, cobalt, zinc, and iron at 5% and 7.5% solid concentrations in the bioleaching experiments were 90%, 60%, 86% and 67%, respectively. Dissolution of gold and copper was not observed. The residues from bioleaching pretreatment were applied for chemical chloride leaching to extract gold and copper into the solution. In chloride leaching, the highest extractions of copper and gold were 98% and 63%, respectively. In addition, residual nickel, cobalt, and zinc were dissolved into the solution with the extraction of 99%, 80%, and 90%, respectively. In all chloride leaching experiments, the highest extractions of iron, copper, gold, nickel, cobalt, and zinc were observed with biologically pretreated feed. Alternatively, residues from bioleaching were also subjected to conventional cyanide leaching. Dissolutions of copper, nickel, cobalt and zinc were shown to be higher in chloride solution, however, 7%-unit more of gold could be extracted by cyanidation. With these findings, it appears that the combination of biological pretreatment and chloride leaching can provide a non-toxic process for improved valuable metals extraction from low-grade tailings.