POTENTIAL MICROENCAPSULATION OF PYRITE BY ARTIFICIAL INDUCEMENT OF FERRIC PHOSPHATE COATINGS

Pyrite in mining waste is initially oxidized by the atmospheric O-2, 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 O-2. 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 O-2 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 O-2 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 degrees 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) mol L(-1) phosphate and 0.03 mol L(-1) H2O2 and that the FePO4 phosphate coating could effectively protect pyrite from oxidizing further.