Microbial leaching of a low-grade sphalerite ore using a draft tube fluidized bed bioreactor

The use of a draft tube fluidized bed bioreactor (DTFBB) has been successfully demonstrated for the bioleaching of a chalcopyrite concentrate (Mousavi, et. al., 2005). In the present paper this technique was used for the bioleaching of zinc from a sphalerite bearing low-grade ore. A strain of the thermophilic bacterium, Sulfobacillus, has been isolated from the Kooshk lead and zinc mine near the city of Yazd (Iran) and is tested at temperatures 47 °C–72 °C. This is compared to leaching with a strain of the mesophile Acidithiobacillus ferrooxidans, which has been adapted to the high levels of zinc and the presence of the low-grade ore, and which was tested at temperatures 18 °C–42 °C. The effects of using the two temperature ranges, as well as varying pH in the range 1.2 to 1.8, and solid concentration in the range 1–20% w/v, on Zn recovery, ferrous, ferric and total iron concentrations and cells number were investigated in two batch DTFBBs with external recycling streams. The best conditions for leaching by mesophilic and thermophilic strains occurred at 10% w/v pulp density, giving 87% and 91.4% Zn recovery respectively, after 9 days.