Study On The Extraction Of Strontium With N,N’-dimethyl-N,N’-dioctyldiglcolamide

⁹⁰Sr(t_1/2=28.79a),one of significant fission products that is usually carried into High Level Waste（HLW）,has the characteristics of high radioactivity and strong heat release.It is necessary to separate it from HLW.Recent years,tridentate diglycolamide（containing ether linkage between two amide groups）reveals high affinity for lanthanides and actinides and had been widely studied in the partitioning of HLW.It also has similar properties to those of crown ethers because of the ether oxygen bond.The extraction behaviors of strontiumfromnitricacidmediumwereinvestigatedwith N,N’-dimethyl-N,N’-dioctyldiglcolamide（DMDODGA）in 40/60（v/v）%1-octanol/kerosene and ionic liquids[C₆mim][Tf₂N].The concentration of Sr²⁺in aqueous phase was measured by inductively coupled plasma mass spectrometry（ICP-MS）and the acidity of aqueous phase was determined by acid-base titration.The main results are concluded as follows:The extraction behaviors of nitric acid with DMDODGA in 40/60（v/v）%1-octanol/kerosene were investigated by corresponding solution method.The results show that it forms 1:1 adduct between DMDODGA and HNO₃ when the aqueous HNO₃concentration of extraction equilibrium less than 2.3mol/L;when the aqueous HNO₃concentration of extraction equilibrium between 2.3mol/L to 3.3mol/L,DMDODGA and HNO₃ form 1:1 and 1:2 adducts;DMDODGA and HNO₃ may form 1:3 adduct when the aqueous HNO₃ concentration of extraction equilibrium above 3.3mol/L.Using 40/60（v/v）%1-octanol/kerosene as diluent,the extraction distribution ratio of strontium(D_Sr)increases gradually with the increase of HNO₃ concentration until 1mol/L and then begins to decrease when the initial acidity is 0⁵mol/L,in which process salting-out effect of NO₃^-and the competitive extraction of H⁺dominate the extraction at low acidity and high acidity,respectively;D_Sr decreases with the increase of the initial strontium concentration in the aqueous phase because of the decrease of the free DMDODGAconcentration.Thecomposition of extracted complexis Sr（NO₃）₂·3DMDODGA and the logarithm of the equilibrium constant lgK was 4.01 at 25℃;The enthalpy change?H,entropy change?S,Gibbs free energy change（at 25℃）in the extraction process are-105.5 kJ/mol,-270.5 J/（mol·K）and-24.88 kJ/mol,respectively.Using ionic liquid[C₆mim][Tf₂N]as diluent,D_Sr decreases gradually with the increase of HNO₃ concentration when the initial acidity is 0⁵mol/L,and the competitive effect of H⁺is the main factor affecting the distribution ratio;The composition of extracted complex is[Sr·3DMDODGA]²⁺in the ionic liquid phase and the logarithm of the conditional equilibrium constant lgK_ex was 4.19 at 25℃.[C₆mim][Tf₂N]can be considered as a synergistic agent of DMDODGA in the extraction process in the system of DMDODGA-[C₆mim][Tf₂N]-40%1-octanol/kerosene.