Potential Microencapsulation of Pyrite by Artificial Inducement of Ferric Phosphate Coatings
1995
Evangelou, V. P.
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. Contribution from the Dep. of Agronomy, Univ. of Kentucky Agric. Exp. Stn. The investigation reported in this paper (no. 94-3-39) is in connection with a project of the Kentucky Agric. Exp. Stn. and is published with the approval of the director.
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