Sulfuric Acid Bioproduction and Its Application in Rare Earth Extraction from Phosphogypsum

Industrial production of sulfuric acid requires a high amount of energy and in remote regions such as mineral extraction pits, in situ production becomes unfeasible. This work proposes an alternative for the production of H2SO4 that uses sulfur-oxidizing microorganisms. The production capacity of this acid in a mesophilic (30 degrees C) and a thermophilic (65 degrees C) condition was studied by three collected consortia from acid mine drainage and compared with Acidithiobacillus thiooxidans. It was found that At. thiooxidans presented higher sulfuric acid production than the consortia collected and, therefore, it was selected for the bioleaching of rare earths elements (REEs) from phosphogypsum (PG). Due to the acid consumption of phosphogypsum, the two-step bioleaching condition resulted in higher REEs extraction (98% Nd, 60% Ce, 58% La, and 62% Y) when compared to one-step bioleaching (28% Nd, 17% Ce, 18% La, and 30% Y). The process was performed on a reactor scale and it was possible to extract 55.0% of the REEs contained in 300 g of waste and concentrate them into 0.922 g of rare earth oxalates, with a final yield of 52.5%, showing that the proposed bioprocess has potential application even in remote areas due to its low energy consumption when compared to traditional processes.