Studies On The Extraction Of Sr²⁺ Using DCH18C6/Ionic Liquids Solvents System

Nuclear powers have been operating for more than seventy years,and has accumulated a large number of high level liquid waste.⁹⁰Sr(t_1/2=28.79a),one of the most significant fission nuclides in high level liquid waste（HLLW）,has the characteristics of high radioactivity and strong heat release.It is beneficial for the final treatment of nuclear wastes to remove⁹⁰Sr from HLLW by shortening the geological storage time of radioactive liquid waste and reducing the cost.In this paper,solvent extraction method has been adopted to remove Sr²⁺from the aqueous solution,in which dicyclohexano-18-crown-6（DCH18C6）is used as extractant,and several ionic liquid solvents C_nmimNTf₂（n=2,4,6）and C₄mimPF₆ are selected as diluents,respectively.The effects of the variety of ionic liquid,extractiontime,crown ether concentration and nitrate acid concentration in the aqueous phase on the extraction of Sr²⁺and how to strip strontium from ionic liquids have been investigated by experiment.And the synergistic effects of tri-n-butyl phosphate（TBP）and ionic liquid has studied.The results indicate that,the higher the viscosity of the ionic liquid is,the longer the time to attain reaction equilibrium is.For C₄mimPF₆,whose viscosity 272.0mPa·s is the largest in these four ionic liquids,it takes about 40 minutes for the solvent system to attain reaction equilibrium.In DCH18C6/ionic liquids solvents system,the reaction of the extraction of strontium ion is exothermic reaction.When the concentration of DCH18C6 is 0.03 mol/L,four systemswith different ionic liquidshave better extractionperformance of strontium ions,and theorderofextractionperformanceisC₂mimNTf₂>C₄mimNTf₂>C₄mimPF₆>C₆mimNTf₂.The extraction performance of DCH18C6/ionic liquids solvents system are greatly influenced by nitrate acid in the aqueous phase,andfirst declineRapidly then increase slightly with the increase of concentration of nitric acid.Addition of Na⁺,K⁺and Fe³⁺,respectively,is shown to decrease the extraction of strontium,and the extraction performance increase because of the salting out effectwhen the aqueous phase add Al³⁺in DCH18C6/C₄mimNTf₂system.Different back-extractionshave different ability of extraction of strontium ion,and extraction ability of deionized waterwas the weakest,while KCl is good.It was found that the shorter ionic liquids has the alkyl carbon chain,the more difficult strip strontium from ionic liquids,C₂mimNTf₂>C₄mimNTf₂>C₆mimNTf₂,in the same anion of three kinds of ionic liquids.The reaction of reversingextraction strontium from ionic liquids is endothermic reaction by KCl,and back extraction ratio of strontium first increases then tends to stable with the increase of temperature.The introduction of the TBP can produce synergistic extraction effect with ionic liquids,and synergistic interactions first increases then decreaseswith the increase of the TBP volumeof organic phase.When organic phase contains 50%TBP,the ability of extraction strontium of system is best.Due to salting out effect,extractionsystems with the TBP+50%IL（C₄mimNTf₂,C₆mimNTf₂,C₄mimPF₆）mixed organic phase as the diluents have good extraction effect of the strontium from highlevel waste liquid.