Issues in Bioleaching: To Inoculate or not to Inoculate

Abstract

Two active bioleaching microbial strains were isolated from a zinc mineral sample. These bacteria isolates were grown on media containing sulfur or iron and reintroduced, individually or in combination, to the original mineral sample in controlled shake-flask bioleaching experiments. Uninoculated controls were included but no attempt was made to sterilize the solid material. On the contrary, growth of the same indigenous microorganisms was encouraged in the control flasks. Zinc was leached from both inoculated and uninoculated mineral at the same rate. The only difference was that the lag times before onset of leaching were shorter if active bacteria were present from the very beginning. In all cases, zinc was leached preferentially over iron. This difference was even more pronounced on leaching by sulfur-grown bacteria which did not extract iron to the same degree as iron-grown bacteria. When total leaching times required for 100% zinc extraction were compared, no statistically significant difference was observed between the inoculated and uninoculated tests. This conclusion may have some bearing on experimental and process design, when decisions must be made on whether to stimulate leaching by addition of extraneous bacteria or by fostering the proliferation of indigenous microorganisms.

Keywords:

• Bioleaching
• inoculation
• Thiobacillus
• ferrooxidans
• thiooxidans

Notes

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