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The present method induces an oxidation-proof ferric phosphate coating on iron sulfide such as pyrite and marcasite. The method includes the steps of placing the pyrite to be treated in a reaction vessel and leaching the pyrite with a coating composition including water, an oxidizing agent and a phosphate coating agent. Examples of oxidizing agents include hydrogen peroxide, sodium hypochlorite, potassium hypochlorite and mixtures thereof. The phosphate coating agent may be potassium dihydrogen phosphate. In order to ensure the formation of the stable coating, the leaching is performed at a pH of substantially 5 and at a temperature of substantially 40° C. Additionally, the oxidizing agent is maintained at a concentration of substantially 0.1% by weight of the coating composition while the concentration of the phosphate coating agent is maintained at at least substantially 10-4 M/l.


University of Kentucky Research Foundation, Lexington, Ky.

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