Inhibition kinetics of iron oxidation by Leptospirillum ferriphilum in the presence of ferric, nickel and zinc ions

The inhibition kinetics of iron oxidation was studied in a Leptospirillum ferriphilum-dominated, fluidized bed bioreactor culture, which was challenged with various concentrations of Fe3+, Zn2+ and Ni2+. Iron(II) was oxidized in the presence of binary combinations of 40 g/L Fe3+ + 10 g/L Ni2+, 30 g/L Fe3+ + 40 g/L Zn2+, 60 g/L Zn2+ + 10 g/L Ni2+ and 60 g/L Ni2+ + 10 g/L Zn2+. The data showed that L. ferriphilum was insensitive to the test metals, suggesting that the bacterium has application in ferric ion regeneration processes in circuits involving tank bioleaching of zinc and nickel sulfide concentrates. A combined method for determining the type and coefficients of inhibition was developed and validated with data from batch Fe2+ oxidation experiments at pH 1.1 ± 0.2. Iron(III) competitively inhibited Fe2+ oxidation, whereas Zn2+ and Ni2+ conformed to non-competitive inhibition model with inhibition coefficients (Kii) of 49.1 and 62.7 g/L, respectively. However, Mg2+ and Na+ had a compounding effect on Zn2+ toxicity. The combined competitive and non-competitive inhibition model was applied for data on iron oxidation in the presence of Fe3+ + Zn2+, Fe3+ + Ni2+ and Zn2+ + Ni2+ and good agreement was generally found between the model predictions and experimental data. The combined model can be used to predict the kinetics of bacterial iron oxidation in ferric ion regeneration for zinc and nickel concentrate tank leaching.