ABSTRACT
This chapter discusses the optimal conditions for generating stable, oxidation-proof ferric phosphate or iron oxide coatings on the surface of pyrite based on results from leaching columns of coal refuse pyritic shale. Leaching the pyritic shale with the coating solution adjusted to pH did not lead to any significant suppression of pyrite oxidation. The necessity of adjusting the pH somewhere near 5 for effective pyrite microencapsulation to occur was demonstrated. Pyrite particles buried in aggregates cannot be coated with iron phosphate and can produce acid once the aggregates disintegrate. Coating and leaching-oxidation tests were carried out using 0.5 g of the pyritic shale sample mixed with approximately 1 g of sand and using a miscible displacement technique. Preliminary experiments on synthesis of iron phosphate indicate that precipitation of iron phosphate is determined by degree of supersaturation of solution with respect to iron phosphate and the molar ratio of phosphate to Fe.
