Long-term field test for inhibiting the oxidation of iron sulfide using coating agent

Abstract

The effectiveness of silicate- and phosphate-based surface coating agents (Na2SiO3 and KH2PO4) in inhibiting the oxidation of iron sulfide minerals were investigated with pyrite and rock sample containing iron sulfide mineral. Film formation by both surface coating agents was confirmed by surface analysis. The pulverized pyrite surface, layered with Na2SiO3 and KH2PO4 of 0.1 M, was suppressed from oxidation in accelerated oxidizing condition with H2O2, as measured in terms of SO42- concentration (77 and 23%, respectively) in the leachate. Coating rock samples with silicate or phosphate reduced oxidation up to 54 and 33%, respectively.

The inhibition effects in acidic and low temperature conditions were studied by column experiments. The oxidation rate with silicate-based film, calculated after 14 weeks, was found to have been suppressed by 94-96% and 95-97% in acidic condition, on the basis of the release of Fe2+ and SO42−, respectively.

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The effectiveness was also observed in low temperature condition by 94-97% and 58-65%, respectively. The phosphate-based film with higher concentration of KH2PO4 (0.1 and 0.3 M) showed the similar level of inhibition efficiency, but phosphate-based film with low concentration (0.05 M) did not inhibit the oxidation at all. Thus, coating of rock samples with silicate can significantly reduce the oxidation rate of iron sulfide minerals in acidic and low temperature conditions.

To investigate methods for effective film formation, rock samples were coated using two oxidation methods: H2O2 was mixed with coating agents in one method, and H2O2 was applied to the sample surface prior to the use of a coating agent in the other method. Application of surface coating agent after applying oxidant had no efficiency on oxidation inhibition. It was confirmed that the surface coating agent and oxidant (H2O2) should be applied in a mixture to form a film.

Silicate coating agents were applied at the Boeun (Chungcheongbuk-do, Republic of Korea) outcrop site and their oxidation inhibition efficiency for iron sulfide minerals was monitored with a long-term experiment (449 days). The experimental results suggested that the treatment was highly effective in suppression of release of Fe2+ and SO42- by 99% and 98%, respectively. The result might be applicable in field conditions for inhibiting iron sulfide oxidation.