Comparative efficiency of three advanced

Grinding and flotation of sulfide-containing ores produce metastable, partially oxidized sulfur compounds known as thiosalts, which are notorious contributors to receiving water bodies’ toxicity by producing delayed acidity. Thus, the continuous optimization of thiosalts oxidation into sulfate is required before treated mine water is discharged into natural streams, as thiosalts oxidation slows down at low temperatures and in the absence of UV. With this aim, the present study evaluated the treatment of thiosalts at initial concentrations of 100 mg/L, 290 mg/L and 630 mg/L using three advanced oxidation processes (AOPs): (1) wet peroxoferrates (Fe(VI)), 65 mg/L; (2) ozone microbubbles (O3-microbubbles), 75 g sparging rate; and (3) hydrogen peroxide (H2O2), 21:1 (H2O2:thiosalts) molar ratio, at 8 °C and 22 °C. All treatability tests were performed on synthetic effluents, while H2O2 efficiency was also assessed with a real effluent, a leachate of non-desulfurized tailings collected at a flotation plant. Results showed that O3-microbubbles gave better efficiency (99%) than Fe(VI) (82%) or H2O2 (efficiency removal at 22 °C (90%) was reached after 1 hour. The AOPs tested proved promising for thiosalts removal. The O3-microbubbles showed the best efficiency in terms of thiosalts removal and treatment time. Moreover, H2O2 allowed for better thiosalts removal than Fe(VI), but proved inefficient at oxidizing other intermediate S species and required longer treatment time.