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 degreesC. 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. (C) 2004 Elsevier B.V. All rights reserved.