A novel mineral processing by flotation using Thiobacillus ferrooxidans

Abstract

Oxidative leaching of metals by Thiobacillus ferrooxidans has proven useful in mineral processing. Here, we report on a new use for T. ferrooxidans whereby bacterial adhesion is used to remove pyrite from mixtures of sulfide minerals during flotation. Under control conditions, the floatabilities of 5 sulfide minerals tested (pyrite, chalcocite, molybdenite, millerite and galena) ranged from 88 to 99%. Upon addition of T. ferrooxidans , the floatability of pyrite was significantly suppressed to less than 20%. In contrast, addition of the bacterium had little or no effect on the floatabilities of the other minerals, even when they were present in relatively large quantities: Their floatabilities remained in the range of 70 to 94%. T. ferrooxidans thus appears to selectively suppress pyrite floatability. As a consequence, 84 to 95% of pyrite was removed from mineral mixtures, while 73 to 100% of non-pyrite sulfide minerals were recovered. The suppression of pyrite floatability was caused by bacterial adhesion to pyrite surfaces. The number of cells adhering to pyrite was significantly larger than the number adhering other minerals. These results suggest that flotation with T. ferrooxidans may provide a novel approach to mineral processing in which the biological functions involved in cell adhesion play a key role in the separation of minerals.