Applied Environmental Research

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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.

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