Bioleaching of low-grade sphalerite using a column reactor

The effects of several variables on zinc recovery in column bioleaching have been investigated. The ore contained sphalerite and pyrite as the main sulfide minerals and chalcopyrite and galena as minor minerals. Tests were carried out using a bench-scale column leach reactor which was inoculated with mesophilic (Acidithiobacillus ferrooxidans) and thermophilic (Sulfobacillus) iron oxidizing bacteria; initially isolated from the Sarcheshmeh chalcopyrite concentrate (Kerman, Iran) and Kooshk sphalerite concentrate (Yazd, Iran), respectively. In the inoculated column, jarosite and elemental sulfur were formed. The leaching rate of sphalerite tended to increase with dissolved ferric ion concentration. Microscopic counts of bacteria in the solution tended to be higher at lower pH ranges. Furthermore, the effect of a decreasing particle size on the rate of zinc leaching was enhanced at low pH values. Results show that the maximum zinc recovery was achieved using a thermophilic culture. Zinc dissolution reached 72% and 85% for the mesophilic and thermophilic strains, respectively, after 120 days at column temperatures ranging from 28 to 42 °C.