LAUSR

Abstract The sulfidic wastes produced from mining activities when exposed to atmospheric oxidizing conditions during disposal and in the absence of sufficient alkaline minerals can result in the generation of acidity as well as the release of toxic metals and metalloids. An emerging technique to prevent acid generation is the formation of protective coating layers on the surface of sulfide grains (mainly pyrite) in order to inhibit the oxidation process. The composition of phosphate coating and its effectiveness in inhibiting pyrite oxidation under oxidizing conditions is investigated in the present study. A combination of wet-chemical, microscopic (SEM/EDS) and spectroscopic techniques (FTIR, XPS) was used. The experiments involved treatment of pyritic tailings with solutions containing PO43− and H2O2 at pH 5.5. Based on the results, the protective coating layer around pyrite particles is composed mainly of Fe(II)-phosphates followed by Fe(III)-phosphate, iron (hydr)oxides and iron oxyhydroxysulfate phases. The optimum conditions for the development of an efficient protective layer on pyrite particles correspond to treatment with 0.01 M PO43− for 48 h. In this case, the oxidative dissolution of sulfur was reduced by 66%, as compared to the non-treated pyrite sample.