Bioleaching process for Cu–Pb–Zn bulk concentrate at high pulp density

Bioleaching of metals from a Cu–Pb–Zn sulphide bulk concentrate was studied using a developed consortium consisting of Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Leptospirillum ferrooxidans and heterotrophic organisms. In a shake flask, copper and zinc extraction increased up to 20% (w/v) pulp density at an overall extraction rate of 0.61 and 4.2 g/L/day for copper and zinc, respectively, at 32 °C. But at 25% pulp density, the extraction rate decreased to 0.41 and 4.0 g/L/day. A semi-continuous process resulted in 79% and 82% copper and zinc extraction at rates of 0.66 and 4.92 g/L/day. While a 5-L Laboratory Stirred Tank Reactor (LSTR) gave a 1.15- and 1.55-fold increase in copper and zinc extraction compared to a shake flask at 20% pulp density with a further increase when operated semi-continuously. This resulted in 85.3% and 80% copper and zinc extraction in 5 and 6 days, respectively. When the pulp was added in smaller fractions at an interval of 12 h, the extraction time reduced from 6 to 5 days even at 25% and 30% pulp density. The highest extraction rate was 0.88 and 10.19 g/L/day for copper and zinc. Bioleaching also resulted in 83% galena oxidation from the concentrate. Continuous bioleaching with controlled addition of pulp could provide an economically viable technology for metal extraction from polymetallic bulk concentrate.