Valorization of waste from coal mining pyrite beneficiation

Abstract

The coal mining industries generate a considerable volume of pyrite-rich tailings (FeS2). However, pyrite waste is potentially reusable. Therefore, this study aimed to evaluate possible ways of waste and effluent valorization that are generated during the processing of coal mining pyrite (R1). Raw R1 were subjected to two consecutive leaching processes in distilled water (20 g/L, 70 °C) under mechanical stirring for 40 min. After each process, the suspension was removed with a siphon. The suspension and the decanted material were vacuum filtered. The pyrite concentrate (beneficiated R1) and the solid beneficiation waste (SBW) were dried in a vacuum oven at 40 °C. To the partially distilled iron- and calcium- rich effluents, 95% ethyl alcohol was added in the 1:1 volumetric ratio. Precipitated solid was extracted by vacuum filtration and dried in a vacuum oven at 40 °C. Procedure with ethyl alcohol was repeated for the remaining effluent. New solid obtained was dried at room temperature and subjected to a heat treatment at 780 °C for 2 h. The final effluent was distilled to recover ethyl alcohol. The products of all processes were characterized. The SBW has a high fixed carbon content (28.99%) and high gross calorific value, 3163 kcal/kg, making it feasible to be used for energy generation. For the effluents treatment, partial distillation with subsequent addition of ethyl alcohol was found to be satisfactory, resulting in two by-products: CaSO4·2H2O and FeSO4·7H2O. The hematite obtained by heat treatment of ferrous sulfate is very similar to Alpha Aesar standard.