Experimental Study On Extraction Of Uranium From High Grade Uranium Residue Using Supercritical CO₂ Fluid

Radioactive wastes produced during the processing of uranium fuel elements are characterized by high uranium content and high recovery value.At present,the treatment of uranium in ordinary radioactive solid waste are mainly acid-base process,concentrated acid maturation and high temperature roasting.The conventional leaching method is easy to produce more waste liquid in the treatment of solid waste,which causes pollution again.A new method for recovery of high grade uranium waste residue based on supercritical CO2 fluid extraction technology is presented in this paper.The supercritical CO2 fluid extraction technology can simplify the operation,reduce the amount of solvent used,achieve a better recovery effect,and then reduce the uranium content in the waste residue.In addition,the effects of chelating agent,entrainer,pressure,temperature and time on the extraction rate were studied experimentally,and the extraction process was optimized to reduce the environmental pressure and realize the secondary recovery of uranium resources.It provides further theoretical and technical reference for the treatment and recovery of high grade uranium waste residue.The main contents and results of this paper are as follows:(1)Through comparative analysis,during the extraction of uranium in supercritical CO2 fluid,the extraction rate of uranium in the presence of water was significantly higher than that in anhydrous state.(2)The extraction effects of five chelating agents and their mixtures of tributyl phosphate(TBP),trifluoroacetyl acetone(TAA),acetyl acetone(AA),hexafluoro acetyl acetone(HFA)and thiophenyl trifluoro acetone(TTA)in supercritical CO2 fluid were studied under the same pressure,temperature and time.The results show that the extraction rate of uranium by the mixed chelating agent of TTA and TBP is 60.53%,which is the higest.(3)The extraction rate of uranium can be greatly increased when 5ml ethanol was used as the entrainer under the same pressure,temperature and time.The extraction rate of uranium by the mixed chelating agent of TAA+TBP,AA+TBP,HFA+TBP,TTA+TBP are 71.62%,65.43%,80.33%,86.25%.And the TTA+TBP shows the greatest improvement with the extraction rate increased by 6.12%.(4)The effects of pressure,temperature and time on the extraction rate of uranium were studied by using the optimum medium.As a result,the highest extraction rate of uranium of 92.35% can be achieved at 15 MPa,60oC for 90 min.