BATCH AND HEAP BIOLEACHING OF URANIUM FROM CONTAMINATED SEDIMENTS OF A NATURAL WETLAND

FLORENCIA PRETZ; MARÍA BELÉN PRADOS; GASTON FOUGA; GUSTAVO CURUTCHET

Marsella

Simposio; Seventh International Symposium on Environmental Biotechnology and Engineering; 2023

Pollution with heavy metals is very problematic due to their persistency and toxicity, evenat low concentrations. In Pilcaniyeu, a village located in the southern region of Argentina,there is a natural wetland anthropogenically contaminated with metals such as uranium,nickel and copper.This work aimed to develop bioleaching experiments in order to release uranium from thesediments of the contaminated wetland. This technique stimulates the metabolism of aci-dophilic microorganisms generating acid and oxidation of reduced sulphur compounds andFe(II), and therefore solubilizes metals from the solid matrix.Samples from the coast and the bottom of the wetland were taken. For learning aboutits characteristics, chemical and physical analyses were run, such as pH, humidity, organicmatter and amount of sulphides, sulphates and metals. Also, structural analyses were made,including particle size, porosity, DRX and granulometric characterization. The sample fromthe bottom presented a higher concentration of uranium than from the coast (236 mg U/kgand 46 mg U/kg respectively). Because of that, it was chosen to develop the bioleachingassays. These were carried out in batch conditions with stock strains of A. ferrooxidans andA. thiooxidans, adding them to stirring flasks containing sediments from the bottom of thewetland. This was not done with native bacteria because they could not be isolated fromthe wetland due to a lack of sulphides and reduced iron. Several combinations of electrondonor sources (Fe(II) and elemental sulphur) were tested and blanks without bacteria werealso run.The bioleaching was achieved and the optimum conditions were found, when acid was generated by the addition of S and Fe(II). Then laboratory-scale heap bioleaching was developed, using the best conditions obtained in batch. The heaps were inoculated with A. ferrooxidans and A. thiooxidans, and the culture medium was recirculated every day. In the batch experiments, 100% of uranium recovery was obtained while a 49% in the heaps. Although both experiences were made at a laboratory scale, it is a big step to successfully achieve heap bioleaching because this technique is the one applied on a large scale. In this sense, the obtained results are found to be promising for advances in the treatment of contaminated sediments.