Valorization of iron pyrite from coal mining in southern Brazil

Coal mining tailings, primarily the sulfide-rich fraction, when subjected to environmental action, acidify drainage and contaminate soil and water with heavy metals, such as lead. These tailings can be divided into three residual fractions: R1 (rich in pyrite), R2 (rich in clay minerals) and R3 (rich in carbon). The eventual valorization of these fractions qualifies them as by-products, making them potentially reusable instead of being only waste, which can reduce the environmental impacts caused by this industrial activity. Therefore, this work presents a route of beneficiation for the fraction that is rich in pyrite (R1) based on leaching of the material in water and decantation and suspension mechanisms, providing alternatives for all the waste and generated effluents. The beneficiation process increased the pyrite content of the R1 fraction and generated two solid waste products with distinct characteristics: one with a high calorific value of 2339.00 kcal/kg and another one rich in iron oxide sulfate hydroxide (Fe3.6Fe0.9(O, OH, SO4)(9)). After remediation by simple distillation, the effluents from the beneficiation process presented pH and levels of heavy metals compatible with the Brazilian resolution. The phytotoxicity biotest with Allium cepa L. indicated that these effluents do not inhibit root growth.