Mechanism of aluminum complexation in oxidative activity of leaching bacteria in a fluoride-containing bioleaching system

Abstract

Accumulation of toxic ions in leachate is one factor limiting bioleaching applications. The effect of fluoride ions on the growth of bioleaching microorganisms has been extensively emphasized. In this study, HF is found to be the toxic form of fluoride that affects the bacterial activity under acidic conditions. The added aluminum could compete with H+ to complex with F−, thus significantly decrease the concentration of HF and finally reduce the toxicity of fluoride to bacteria. When F−/Al3+ concentration ratio is 0.5:1.0, Fe2+ oxidation rate could reach 0.167 g·L−1·h−1, close to that of the biotic control group (0.195 g·L−1·h−1). The competitive complexation mechanism of fluoride by \({\text{AlF}}_{n}^{3 - n}\) results in stability constants of \({\text{AlF}}_{n}^{3 - n}\) complex (7.00) that are larger than those of HF (3.18). The F−/Al3+ concentration ratio in the medium could affect the speciation of \({\text{AlF}}_{n}^{3 - n}\) complex. With the decrease in F−/Al3+ concentration ratio, the coordination numbers of \({\text{AlF}}_{n}^{3 - n}\) decrease. Finally, the feasibility of fluoride detoxification by aluminum ion is verified. This work has meaningful implications for fluoride-containing bacterial bioleaching systems.