Suppression of Pyrite Oxidation with Iron-phosphate Coating: Technique for Prevention of Acid Mine Drainage

Abstract

This study was aimed to evaluate the feasibility of an iron-phosphate coating on pyrite surfaces for inhibiting an oxidation that is expected to prevent acid mine drainage (AMD). Prior to the experiments, pyrite samples (av. 425-850 μm in size) were mixed with sand (av. 1-2 mm in size) with a ratio of 1:4. Coating process was conducted in batch experiments that were treating with various concentrations of coating solutions, i.e., hydrogen peroxide (H₂O₂), sodium acetate (NaAc) and potassium dihydrogen phosphate (KH₂PO₄) at different contact times. Subsequently, leaching test was performed in columns (10 mm in diameter) using 0.145 M of the oxidizing solution (H₂O₂) at different times. Remaining phosphate, releasing iron and pH were recorded to estimate the degree of pyrite oxidation. Treating with the coating solution, a mixture of 0.3 M KH₂PO₄ + 0.2 M H₂O₂ + 0.2 M NaAc, with 20 min contact time appeared to be the optimum condition to create iron-phosphate formation on pyrite surfaces. Phosphate remains in the solution is the lowest concentration after coating process (0.497-0.745 mg L^-1). The treated pyrite yielded leaching solution with pH ranging from 6.45 to 7.23 and low iron concentration releasing (0.008-0.151 mg L^-1). In addition, phosphate coated on the pyrite surface was quantitatively analyzed using Electron Probe Micro Analyzer (EPMA); consequently, the highest amount was also detected from the samples treated by such solution.

Keywords : acid mine drainage, pyrite oxidation, iron-phosphate coating