Effect of water salinity on the bioleaching of copper, nickel and cobalt from the sulphidic tailing of Golgohar Iron Mine, Iran

Abstract This study investigates the influence of salinity on the bioleaching efficiency of a copper‑nickel‑cobalt bearing sulphidic tailing obtained from Golgohar iron ore desulphurization plant (Sirjan, Iran). The effects of several critical parameters including, suspension pH, nutrient medium, microorganism type, and pulp density were investigated on the extraction of copper, cobalt and nickel from the sulphidic tailing at different levels of sodium chloride concentration. Bioleaching efficiency was also evaluated in the presence of saline local and process waters. Results showed that maximum extraction of nickel (87%) and cobalt (69%) was achieved at the initial pH of 1.8, the pulp density of 10%, Norris nutrient medium containing 10 g/L sodium chloride, and using moderately thermophilic microorganisms. However, maximum copper extraction (~90%) was obtained in the presence of local water. It was also found that the local and process waters containing around 15.5 and 8.3 g/L chloride ions, respectively, increased metal extraction about 25% and 10% in comparison to distilled water at the first two days. Nevertheless, the metal extraction decreased at the end of the process in both water types mainly due to the formation of gypsum and jarosite precipitates, which were found by SEM/EDS analyses. Furthermore, at the initial pH of 1.5, the extraction of valuable metals was significantly improved (20–60% increase at first 9 days) in the presence of 5 g/L sodium chloride; whereas a further increase (to 10 g/L sodium chloride) had a negative effect on the extractions. Increasing the pulp density from 5% (w/v) to 10% decreased the nickel and cobalt extraction about 26% and 21%, respectively; however, copper extraction increased around 5% which could be related to the lower level of oxidation-reduction potential of the suspension at the higher pulp density. It can be concluded that the low levels of salinity (up to 5 g/L sodium chloride addition) could have a positive effect on the efficiency of the bioleaching process.