Bioprocessing of refractory oxide ores by bioreduction: extraction of silver, molybdenum, and copper.

Mn- or Fe-reducing bacteria of the Bacillus polymyxa and Bacillus circulans groups were cultured and slurried with oxide silver or molybdenum ores in 2 L bioreactors. The growth medium was analysed periodically for solubilised metals by atomic absorption spectroscopy or ICP. The bacteria release target metal ions by dissolving the crystals of pyrolusite, goethite, and haematite within which they are trapped, while their metabolic end-products such as organic acids dissolve zinc and copper without lowering the growth medium pH below 5. Silver recovery from an Arizona manganiferous ore was only 13.7% for a 0.1% cyanide bottle roll, but for bioreductive leaching was 86%, rising to 94.5% if cyanidation of leached solids followed; solubilisation of Mn was 99.8%, Cu up to 99%, and Zn 91%. Molybdenum recovery from a Nevada iron oxide ore was 1.8% for a 5% H2SO4 bottle roll, but 93% for bioreduction.
Mn- or Fe-reducing bacteria of the Bacillus polymyxa and Bacillus circulans groups were cultured and slurried with oxide silver or molybdenum ores in 2 L bioreactors. The growth medium was analysed periodically for solubilised metals by atomic absorption spectroscopy or ICP. The bacteria release target metal ions by dissolving the crystals of pyrolusite, goethite, and haematite within which they are trapped, while their metabolic end-products such as organic acids dissolve zinc and copper without lowering the growth medium pH below 5. Silver recovery from an Arizona manganiferous ore was only 13.7% for a 0.1% cyanide bottle roll, but for bioreductive leaching was 86%, rising to 94.5% if cyanidation of leached solids followed; solubilisation of Mn was 99.8%, Cu up to 99%, and Zn 91%. Molybdenum recovery from a Nevada iron oxide ore was 1.8% for a 5% H2SO4 bottle roll, but 93% for bioreduction.