Biohydrometallurgical Process to Produce the Coagulant Ferric Sulfate from the Pyrite Present in Coal Tailings

This work aims to study, by biohydrometallurgy, the production of the ferric sulfate coagulant from the pyrite (FeS2) present in coal tailings. Leaching experiments were carried out at laboratory scale with a coal tailing from the Santa Catarina mining site (Brazil) considering the following conditions: (a) sterile, (b) non-sterile, (c) inoculated with acidophilic bacteria, and (d) inoculated with acidophilic bacteria and addition of nutrients. Liquor samples were collected weekly for analysis of total iron, sulfate, and the amount of Acidithiobacillus ferrooxidans bacteria. The quantity of bacteria, the pyrite oxidation rate, and the production of iron sulfate were higher in the column inoculated with bacteria and provided the optimal conditions for nutrients. It was possible to produce an aqueous solution, rich in ferric sulfate, which could be used as a coagulant. Water treatment tests, carried out at the laboratory, demonstrate that this coagulant is equally efficient when compared with conventional coagulants (ferric sulfate and aluminum sulfate).