The selective recovery of rare earth from radioactive waste residue using improved oxamic acid for environmental and resource concerns

Abstract

Because radioactive elements may migrate with rainwater and pollute the environment, the treatment of rare earth (RE) radioactive waste residue is of great significance. The process is helpful to recover RE and radioactive element, also reduce the volume of solid pollutants. In this paper, a novel oil-soluble oxamic acid extractant was synthesized to separate RE and Th from the waste residue. The low water soluble extractant 2-(didecylamino)-2-oxoacetic acid (DDOA) could be dissolved in common industrial diluent and used to remove low concentration of radioactive element Th from RE. The loading capacity of DDOA to Th is 2.81 g/L, which can meet the needs of treating ion adsorbed RE waste residue. The whole extraction process was carried out at lower acidities. After 3 times of stripping with 3 mol/L hydrochloric acid, the total stripping capacity of Th reached 98%. Slope analysis method indicates that 2 mol DDOA could extract 1 mol Th4+ in the extraction process. After five cycles, the extraction efficiency of Th could be maintained at 98%. After 4-stage extraction and 3-stage scrubbing, the concentration of Th in the RE aqueous phase outlet was lower than 0.22 mg/L, and the yield of RE was 95%. After oxalic acid precipitation, the recovery of RE could reach 80%. Overall, due to the high selectivity, better oil solubility, simplified fractional extraction, Th in radioactive slag could be efficiently removed and RE could be enriched.