Athanasios Kotsiopoulos

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

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.