Using In-situ Synthesis Of Hydrotalcite For The Separation And Immobilization Of Simulated Radionuclides Europium And Thorium

In-situ synthesis of hydrotalcite was used for the separation and immobilizationof single simulated radionuclide (Eu or Th) and simultaneous separation andimmobilization of double simulated radionuclides (Eu and Th) with high valencestate in this thesis. The amount of simulated radionuclide Th incorporated into thecrystal lattices of hydrotalcite was improved by using NH3·H2O and (NH4)2CO3mixed solution as the precipitation agents instead of NaOH and Na2CO3.The effects of pH, molar ratio of divalent and trivalent metal cations (R), andinitial concentration of simulated radionuclides (C) on the separation efficiency ofsimulated radionuclides were investigated systematically by the analysis of removalrates of simulated radionuclides and XRD patterns of synthetic samples and theircalcined samples to determine the optimal conditions for the separation of simulatedradionuclides. The optimal conditions for the separation of Eu were determined tobe pH=10, R=3.0, and initial CEu=600mg·L-1, respectively. The optimal conditionsfor the separation of Th were determined to be pH=10, R=3.0, and initial CTh=160mg·L-1, respectively. The optimal pH, R, initial CEu，and initial CThfor the simultaneousseparation of Eu and Th were determined to be10,3.0,500mg·L-1, and140mg·L-1,respectively. Under the optimal separation conditions, all the removal rates of simulatedradionuclides were above99%, the separated simulated radionuclides wereincorporated into the crystal lattices of hydrotalcite, and then were immobilized inthe structure of spinel wasteform by calcining.The effects of calcining temperature and package capacity of simulatedradionuclides on the immobilization efficiency were studied by the analysis of XRDpatterns of spinel wasteforms and the leaching results to ascertain the optimalconditions for immobilization of simulated radionuclides. All the optimal calciningtemperatures for the preparation of simulated radionuclides doped spinel wasteformwere1100oC. The optimal package capacity of Eu for the preparation of Eu dopedspinel wasteform was3.18wt%, the optimal package capacity of Th for thepreparation of Th doped spinel wasteform was0.989wt%, and the optimal packagecapacities of Eu and Th for the preparation of Eu and Th simultaneously dopedspinel wasteform were3.099wt%and0.866wt%, respectively. The leachingresults indicated that the simulated radionuclides doped spinel wasteform prepared under the optimal conditions had good chemical durabilities.