Preparation Of Silica-based Composite Functional Materials And Study On Its Adsorption And Separation Behavior Of Ruthenium,rhodium,and Palladium

With the restart and expansion of nuclear power in recent years,nuclear power plays an increasingly important role in the adjustment of energy structure.At the same time,more and more spent fuel is produced during the operation of nuclear power plants.The treatment and disposal of high level liquid waste(HLLW)generated by PUREX(Plutonium and Uranium Recovery by Extraction)process is a key link in the nuclear fuel cycle,which is of great significance to the sustainable development of nuclear energy.The contents of ruthenium(Ru),rhodium(Rh),and palladium(Pd)account for about 13 wt%of the total heavy metals in HLLW.With the development of nuclear power,its fission productions are comparable to natural reserves and are important secondary resources of PGMS.At present,the main method of HLLW disposal is glass solidification.However,the presence of Ru,Rh and Pd increases the melting point of the glass and tends to form independent phases during the glass solidification process,which leads to the inhomogeneity of the glass matrix and the decrease of the stability.Therefore,it is necessary to remove Ru,Rh,and Pd from HLLW before immobilization,which not only eliminats the possible problems during vitrification also improve the quality of the final waste form.In this work,two silica-based composite functional materials named SiPyRe and iso Bu-BTP/Si O₂-P were prepared by in-situ polymerization and vacuum impregnation methods respectively for efficient removal of Ru,Rh,and Pd.Considering that HLLW is a nitric acid system,the adsorption performance and interaction mechanism between adsorbents and Ru,Rh,and Pd in HNO₃ solution were further studied to provide technical support for the separation of Ru,Rh and Pd from HLLW.The main results are as follows:(1)A silica-based adsorbent named SiPyRe was prepared by in-situ polymerization method for removel of Ru,Rh,and Pd from nitric acid solution.The as-prepared SiPyRe resin was characterized by SEM-EDS,BET,TG-DSC analysis,which revealed its characterization of mesoporous structure and large specific surface area.SiPyRe resin exhibited excellent adsorption selectivity towards Pd and almost no adsorption towards Ru and Rh.Even at high acidity(1M HNO₃),the saturated adsorption capacity of resin towards Pd was 0.36 mmol/g,and the adsorption equilibrium was obtained within 1 hour.The adsorption behavior of SiPyRe towards Pd matched well with pseudo-second-order kinetic model and Langmuir isotherm model,which indicated the adsorption process of Pd were monolayer chemisorption.Besides,the adsorbed Pd can be desorbed by0.1 M HNO₃-0.1 M thiourea with the rate of over 98%.XPS and FT-IR analysis demonstrated the strong coordination mechanism between nitrogen-containing functional groups(C-N=C)and Pd(II)during the whole adsorption process and meantime anion groups(NO₃^-)were involved to maintain charge balance.(2)In view of the strong adsorption of SiPyRe towards Pd but poor adsorption on Ru and Rh,an inorganic-organic composite functional material iso Bu-BTP/Si O₂-P was synthesized by vacuum impregnation method for adsorption of Ru,Rh,and Pd.The effects of HNO₃ concentration,Na NO₃concentration,temperature,contact time,competition metal ions,and initial metal ions concentration on the adsorption behavior of iso Bu-BTP/Si O₂-P were studied.The experimental data were fitted by kinetic models,isotherm models,and thermodynamic model.The adsorption equilibrium of Ru,Rh,and Pd on iso Bu-BTP/Si O₂-P were obtained within 1 d,1d,0.5 h respectively at 328 K in 0.1 M HNO₃-3 M Na NO₃ solution.And the saturation adsorption capacities for Ru,Rh,Pd were 0.37,0.34,0.71 mmol/g,respectively.Iso Bu-BTP/Si O₂-P exhibited excellent adsorption selectivity(SF_{PGMs/other metals}>40)in 1 M HNO₃ solution at 328K.The adsorption equilibrium of Ru,Rh,Pd were obtained within 2 d,3 d,and 1d,and the saturation adsorption capacities were 0.35,0.32,1.05 mmol/g respectively.The adsorption behavior of iso Bu-BTP/Si O₂-P towards PGMs in both 0.1 M HNO₃-3 M Na NO₃ and 1 M HNO₃ solution conforms to pseudo-second-order kinetic model,Langmuir isotherm model and D-R isotherm model,indicating that the adsorption process of PGMs were monolayer chemisorption.The adsorption thermodynamics results showed that the adsorption process was spontaneous endothermic reaction.The desorption performances of iso Bu-BTP/Si O₂-P were studied.In the desorption stage,the adsorbed Ln(III),²⁴¹Am,Pd(II),Rh(III),and Ru(III)can be desorbed by water,0.01 M DTPA,0.1 M HNO₃-0.1 M thiourea,5 M HCl,and Na Cl O(AR)solution respectively and then separated from each other.Finally,a simple process for separating Ru,Rh,and Pd from simulated HLLW using iso Bu-BTP/Si O₂-P was proposed.Both XPS and FT-IR techniques were employed to explore interaction mechanism between iso Bu-BTP/Si O₂-P and Ru,Rh,and Pd.FTIR and XPS analyses demonstrated the strong interaction between C-N=C and metal ions during the whole adsorption process and meantime NO₃^-were involved to maintain charge balance.