A Novel Mineral Flotation Process 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, in which bacterial adhesion is used to remove pyrite from mixtures of sulfide minerals during flotation. Under control conditions, the floatabilities of five sulfide minerals tested (pyrite, chalcocite, molybdenite, millerite, and galena) ranged from 90 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 effect on the floatabilities of the other minerals, even when they were present in relatively large quantities: their floatabilities remained in the range of 81 to 98%. T. ferrooxidans thus appears to selectively suppress pyrite floatability. As a consequence, 77 to 95% of pyrite was removed from mineral mixtures while 72 to 100% of nonpyrite sulfide minerals was recovered. The suppression of pyrite floatability was caused by bacterial adhesion to pyrite surfaces. When normalized to the mineral surface area, the number of cells adhering to pyrite was significantly larger than the number adhering to 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.

Biodepression of Copper-Activated Pyrite with Acidithiobacillus ferrooxidans in Flotation with Fresh and Seawater

“…These recoveries are very low compared to the results without A. ferrooxidans shown in Figure2, indicating that the bacteria are able to depress pyrite. The depressant effect of A. ferrooxidans on pyrite has also been reported by other authors and is attributable to the adhesion of the bacteria to the mineral[10][11][12][13][14][15]19]. At 2.5 × 10 −5 M (triangles) and 5 × 10 −5 M (circles) of CuSO 4 , the recoveries of pyrite were slightly greater than without CuSO 4 at all pH values, showing the effect of the copper activation.…”

“…Figure3shows the effect of A. ferrooxidans in the recovery of pyrite at different concentrations of CuSO 4 in freshwater. Without CuSO 4 (squares), the recoveries were between 10 and 38% at the entire pH range studied(4)(5)(6)(7)(8)(9)(10)(11)(12). These recoveries are very low compared to the results without A. ferrooxidans shown in Figure2, indicating that the bacteria are able to depress pyrite.…”

“…The bacterium Acidithiobacillus ferrooxidans has been studied as a pyrite depressant in flotation with freshwater and seawater showing good results [10][11][12][13][14][15][16][17]. However, the effect of bacteria as a depressant of Cu-activated pyrite has not been investigated.…”

Towards the Biobeneficiation of PGMs: Reviewing the Opportunities

“…The addition of Acidithiobacillus ferrooxidans has been noted to promote the selective flotation of chalcopyrite under acidic and alkaline conditions, leaving behind pyrite [56]. The bacterium preferentially attaches to the pyrite surfaces, rendering the mineral hydrophilic [10,57]. The use of A. ferrooxidans reduced pyrite floatability by ~70%.…”

“…The extent of bacterial adhesion onto a mineral surface depends on the mineral's chemical composition as well as on the dissolution and toxicity of the mineral substrate [9]. Bacterial surfaces generally have hydrophilic characteristics [5,10,11]; therefore, when bacteria adsorb onto mineral surfaces, they induce hydrophilicity and cause the mineral surfaces to be depressed in the flotation environment. However, there are cases where bacteria can cause either hydrophilicity or hydrophobicity, e.g., Bacillus pumilus and Alicyclobacillus ferrooxidans [12].…”