Potential Microencapsulation of Pyrite by Artificial Inducement of Ferric Phosphate Coatings
Pyrite in mining waste is initially oxidized by the atmospheric O2, releasing acidity and Fe2+. At a pH below 3.5, Fe2+ is rapidly reoxidixed by Thiobacillus ferrooxidans to Fe3+, which oxidizes pyrite at a much faster rate than O2. Commonly, the approach used in preventing pyrite oxidation in the field involves the use of limestone. This approach, however, has a short span of effectiveness because the surfaces of pyrite particles in mining waste are still exposed to the atmospheric O2 after treatment. The objective of this study was to examine the feasibility in controlling pyrite oxidation by creating an FePO4 coating on pyrite surfaces to block access of the atmospheric O2 to pyritic surfaces. The coating methodology involved leaching pyrite using a chromatographic column with a 1 cm i.d. and a flow rate of 0.5 mL min−1 at 40°C with a PO4 solution containing hydrogen peroxide (H2O2); when this solution reached pyrite surfaces, H2O2 oxidized the surface portion of pyrite and released Fe3+ so that Fe phosphate precipitated and formed a passive coating on pyritic surfaces. This laboratory-scale study demonstrated that Fe phosphate coatings on pyritic surfaces could be established with a solution containing as low as 10−4 tool L−1 phosphate and 0.03 mol L−1 H2O2 and that the FePO4 phosphate coating could effectively protect pyrite from oxidizing further.
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