Acid mine drainage prevention by suppression of pyrite oxidation with iron-phosphate coating on pyrite surfaces

Abstract

This study was aimed to examine the feasibility and determining the optimum condition of creating an iron-phosphate coating on pyrite surfaces for inhibiting pyrite oxidation and preventing acid mine drainage (AMD). Pyrite used in this study was collected from the gold mine, Amphoe Thap Khlo, Changwat Phichit (Akara Mining Limited), northern Thailand. Prior to the experiments, pyrite samples (425-850 [micro]m) were mixed with sand in average size of 1-2 mm in ratios 1:4 for preparing samples. The experimental procedures comprise the coating process and leaching study. Coating process was conducted in batches by treating with various coating solution containing hydrogen peroxide (H[subscript 2]O[subscript 2]), sodium acetate (NaAc) and potassium hydrogen phosphate (KH[subscript 2] PO[subscript 4])at different contact times for determining the optimum condition for coating at different conditions. Leaching study was performed in columns, 10 mm of diameter by leaching with 0.145 M of the oxidizing solution at different times for examining the resistance of coated pyrite to oxidizing condition. Phosphate remains, iron released and pH were analyzed for estimating the degree of pyrite oxidation. The results of this study show that treating with the coating solution B (0.3 M KH [subscript 2] PO [subscript 4] + 0.2 M H[subscript 2]O [subscript 2] + 0.2 M NaAc) at the time of t20 is the optimum condition for establishing iron-phosphate formation on pyrite surfaces. Phosphate remains in solution is the lowest concentration after coating process (0.497 - 0.745 mg/l). pH ranges from 6.45 to 7.23 and iron released in leachate tends to be low concentration (0.008-0.151 mg/l). In addition, the quantity of phosphate coated on the pyrite surface analyzed using Electron Probe Micro Analyzer (EPMA) is the highest. Solution B was consequently applied to soil mining waste from coal mine which it yielded satisfactory result. However, detailed study and economic concern would be taken into account.