Efficient and clean release of uranium and zirconium in hazardous uranium purification waste by combined alkali decomposition and acid leaching process

Abstract

Large amount of hazardous waste generated by the uranium purification process poses a potential threat to the environment. However, it also contains valuable metals like uranium and zirconium worth recovering. It is extremely difficult to extract uranium and zirconium and process such waste slag harmlessly by conventional methods because of its complex composition and a large amount of silicate coating. Therefore, this work proposed a new method for efficient and clean release of uranium and zirconium by alkali disaggregation coupled with acid leaching in hazardous uranium purification waste streams. NaOH was used to react with silicates to destroy the structure of the waste slag, then the target elements of uranium and zirconium were exposed. At the same time, NaOH reacted with ZrP2O7 in the waste residue to form acid soluble Zr(OH)4. Then, HNO3 was used to react with uranium and zirconium to produce soluble UO2(NO3)2 and ZrO(NO3)2. Under optimized conditions, i.e., NaOH concentration of 140 g/L, liquid-solid ratio of 4:1, reaction time of 1 h, and water washing dosage of 4 mL/g, the leaching rates of uranium and zirconium were enhanced to 99.12 % and 96.77 %, respectively. Meanwhile, the content of uranium and zirconium in the slags decreased from 13.325 g/kg and 133.392 g/kg to as low as 0.287 g/kg and 11.444 g/kg, respectively, which meets the internationally required clean release standard. This study will provide a viable way for secondary resource recycling and clean release of waste containing valued metals.