Stability of Coatings on Sulfide Minerals in Acidic and Low-Temperature Environments

Abstract

The effectiveness of silicate- and phosphate-based surface coating agents (Na2SiO3, CaSiO3, and KH2PO4) in inhibiting the oxidation of sulfide minerals in acidic and low temperature conditions was studied. Rock samples were coated using two oxidation methods: H2O2 was mixed with the coating agents in one, whereas in the second, H2O2 was applied to the rock surface prior to the coating agent. The second approach was ineffective, but with Method 1, the pH (5) was above the pH (3.6) of the uncoated control sample. Oxidation, calculated after 14 weeks, had been suppressed by up to 96 and 65%, as indicated by the release of Fe2+ and SO4 (2-), respectively. All three coating agents (at concentrations of 0.1 and 0.3 M) suppressed the release of Fe2+ (< 3 mg L- 1). Na2SiO3 inhibited Fe2+ and SO4 (2-) release by 94 and 65%, respectively. Surface protection (or oxidation inhibition) efficiencies of KH2PO4 (in terms of Fe2+ release) were 67, 94, and 96% with 0.05, 0.1, and 0.3 M, respectively. The Na2SiO3 and CaSiO3 coatings, irrespective of their concentrations, reduced iron oxidation by 94 and 84%, respectively. Fourier transform infrared spectroscopy analysis of the Na2SiO3 treated samples showed the presence of iron silicate coatings. Based on this work, coating of rock samples with silicate or phosphate can reduce the oxidation rate of sulfide minerals in acidic and low temperature conditions.