Inhibition Kinetics of Iron Oxidation by <i>Leptospirillum ferriphilum</i> to Residual Thiocyanate Present in Bioremediated Cyanidation Tailings Wastewater

Abstract

Inhibition of iron oxidation by Leptospirillum ferriphilum in the presence of thiocyanate (SCN-) was studied in small-scale batch experiments. The L. ferriphilum culture was challenged with SCN- over a range of 0 mg/l to 10 mg/l. The data showed that L. ferriphilum was able to utilise ferrous iron at low-level concentrations of SCN- (0.25 mg/l to 1.75 mg/l), however exhibited a reduction in oxidation rate relative to the control (0 mg/l). Moreover, introduction of SCN- at low-level concentrations resulted in a lag in iron oxidation activity, specifically at concentrations of 1 mg/l, 1.25 mg/l and 1.75 mg/l. No iron oxidation was observed at SCN- concentrations above 1.75 mg/l, indicating complete inhibition. As L. ferriphilum is the dominant iron oxidising bacteria within biooxidation tanks, evidence of sustained iron oxidation activity at low-level SCN- concentrations affirms the potential of recycling bioremediated cyanidation wastewater within biooxidation circuits in bioprocesses for gold recovery from sulfidic minerals as residual SCN- concentrations in remediated effluent are reportedly lower than 0.25 mg/l. The inhibition kinetics of this system need to be explored further in order to develop a deeper understanding of the system such that it may be applied to inform process operation.