Research of Fluoride Detoxified by Cation and Its Competitive Complexation Mechanism in Fluoride-bearing Bioleaching System

In order to solve the problem of fluoride inhibition on leaching microorganisms in bioleaching system, the chemical properties of fluorine were proposed. The competition complexation of metal cations was utilized to alternate the free F^- into complex state, thus made it possible for bacteria growth under high fluoride concentrations. The effects of different metal-fluoride complexes on bacteria growth were compared. The results show that the stability of AlF₃ and FeF₃ has no obvious effect on the bacteria growth, and MgF₂ dissolves in the leaching system to release F^- ions, which has a toxic effect on bacteria. Through thermodynamic analysis, it is found that the competitive complexation mechanism of Al³⁺ and Fe³⁺ to fluoride ions and the non-competitive complexation of Mg²⁺ ion to fluorine are in accordance with the laws of thermodynamics. The detoxification abilities of different cations (Al³⁺, Fe³⁺) to fluoride ions were compared. The experiment results of different metal cations competitive complexation to fluorine show that Al³⁺ and Fe³⁺ are able to detoxify to fluorine, the detoxification ability to fluorine is in the order of Al³⁺>Fe³⁺. The complex species were calculated by PHREEQC. The results show that the complex species can be controlled by adjusting the concentration ratio of fluoride and metal ions in the solution, and with the decrease of the concentration ratio of fluorine and metal ions, the coordination number moves to the low coordination direction.