The effects of fluoride and aluminum ions on ferrous-iron oxidation and copper sulfide bioleaching with Sulfobacillus thermosulfidooxidans

Microorganisms that grow at high temperatures can improve Fe(II) bio-oxidation and thereby its technological applications, such as bioleaching and H2S removal. Conversely, elements present in industrial growth media, such as fluoride, can inhibit bacterial growth and iron bio-oxidation. In this work, the influence of fluoride on the kinetics of ferrous-iron bio-oxidation with Sulfobacillus thermosulfidooxidans was investigated. The effects of fluoride concentrations (0–0.5 mmol L−1) on both iron oxidation and bacterial growth rates were assessed. In addition, the effect of the addition of aluminum, which was intended to complex free fluoride and reduce the concentration of HF through the formation of aluminum–fluoride complexes, was also investigated. The results show that 0.5 mmol L−1 NaF completely inhibited bacterial growth within 60 h. Nevertheless, fluoride toxicity to S. thermosulfidooxidans was minimized by control of the aluminum–fluoride ratio in the system because, at a 2:1 aluminum–fluoride molar ratio, bacterial growth was similar to that observed in the absence of fluoride ions. Despite a slower bacterial growth rate, fluoride concentrations less than the inhibitory concentration increased the Fe(II) oxidation rate. Successful copper bioleaching (80–100%) from fluoride-containing sulfide ores (1% total fluoride) was demonstrated in the presence of aluminum.

► Fluoride-containing gangue minerals are soluble in bioleaching liquors. ► Fluoride at 10 mg L−1 completely inhibits S. thermosulfidooxidans growth. ► Al/F molar ratios of 2 and higher provides efficient fluoride detoxification. ► Fe(II) oxidation is increased at sub-lethal fluoride concentrations. ► Bioleaching in the presence of fluoride containing minerals is accomplished with aluminum.