Comparative testing between conventional and microencapsulation approaches in controlling pyrite oxidation

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Oxidation of pyrite in mining waste or overburden is the main source of acid mine drainage (AMD) production, which causes major environmental pollution. Presently, the most common method of controlling AMD is through the mixing of alkaline substances, such as limestone, with the AMD producing materials. However, the effectiveness of this method is still questionable due to the potential for iron armoring. Pyrite microencapsulation, utilizing either phosphate or silica coatings, is a novel approach for controlling AMD that is under development in our laboratory. Although under laboratory conditions these approaches have been shown to be very effective in controlling pyrite oxidation, testing under natural conditions for possible field application is necessary. We are monitoring an outdoor leaching column experiment to evaluate the performance of both conventional and microencapsulation approaches for controlling AMD. The experiment consists of control, limestone, phosphate, and silica treatments on mine spoil and tailing samples contained in leaching columns and set up in the field. Preliminary results indicate that, after a period of nineteen months in the field, application of microencapsulation and conventional approaches significantly reduced pyrite oxidation. Among the microencapsulation approaches used with the mine spoil, the silica coatings seemed to be superior. The average leachate sample pH was 1.9 from the control, 2.1 from the limestone, 4.6 from the phosphate and 5.9 from the silica coatings. The results of these outdoor leaching experiments have shown that the application of silica coatings could offer an improved solution for the abatement of AMD. However, long-term monitoring and evaluation are still needed.