The inhibition kinetics of iron oxidation was studied in a Leptospirillum ferriphilum-dominated, fluidized bed bioreactor culture, which was challenged with various concentrations of Fe(3+), Zn(2+) and Ni(2+). Iron(II) was oxidized in the presence of binary combinations of 40 g/L Fe(3+) + 10 g/L Ni(2+), 30 g/L Fe3(+) + 40 g/L Zn(2+). 60 g/L Zn(2+) + 10 g/L Ni(2+) and 60 g/L Ni(2+) + 10 g/L Zn(2+). 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 Fe(2+) oxidation experiments at pH 1.1 +/- 0.2. Iron(III) competitively inhibited Fe(2+) oxidation, whereas Zn(2+) and Ni(2+) conformed to non-competitive inhibition model with inhibition coefficients (K(ii)) of 49.1 and 62.7 g/L respectively. However, Mg(2+) and Na(+) had a compounding effect on Zn(2+) toxicity. The combined competitive and non-competitive inhibition model was applied for data on iron oxidation in the presence of Fe(3+) + Zn(2+), Fe(3+) + Ni(2+) and Zn(2+) + Ni(2+) 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. (C) 2009 Elsevier B.V. All rights reserved.