Characterization and processing of radioactive uranium containing waste sludge by sulfuric acid leaching

Abstract

A large amount of solid radioactive uranium containing wastes are accumulated in sludge dumps because of exploitation of nuclear industry enterprises. These dumps are located in open air and undergoes by leaching of radionuclides and weathering. The purpose of this work was to study the possibility of processing of uranium containing sludge from storage facilities with sulfuric acid solutions. At the initial stage of the investigation, the phase composition of the initial sludge was determined. It was found that the studied samples consisted of CaSO4.2 H2O, CaCO3, CaF2, Ca3Si(OH)6(CO3)(SO4)·12 H2O and SiO2. Then, uranium was leached from the sludge with sulfuric acid solutions (60–200 g L−1) at a temperature of 20–80 °C. The sulfuric acid concentration of 200 g L−1 and a temperature of 80 °C provided the maximum uranium recovery degree 98%. The uranium concentration in the productive solution was 341.4 mg L−1. Studies of the residue after leaching by XRD have shown that the main phase was CaSO4.2 H2O (76–94%); the samples also contained CaCO3 (2.5–3%), CaF2 (16%) and SiO2 (1–5%). Productive solutions were processed using the strongly basic anion-exchangers Purolite A660/4759, Granion AS-7 U, Bestion BD200, AMP, and AM-p. It was determined that the Purolite A660/4759 had the highest dynamic exchange capacity at full saturation by uranium (44.9 g kg−1).