| The partitioning process for treatment of HLLW as a crucial part of the repro-cessing of closed nuclear fuel cycle is meaningful to ensure sustainable development of nuclear energy in the future.Reprocessing of spent nuclear fuel by PUREX gener-ates HLLW containing large amounts of PGMs including palladium?Pd?,rutheni-um?Ru?,rhodium?Rh?whose most nuclides are stable or relatively short lived,ac-counting for about 15%of HLLW?5.6 kg/1tHU,45 GWd/t?,they can be tolerated for many industrial applications through certain decay,so,how to separate PGMs effec-tively from HLLW has always been a hot issue and difficult problem in the field of international nuclear science and technology.In addition,palladium is known to ob-struct producing of vitrified waste before geologic disposal.Therefore,the selective separation and recovery of PGMs from HLLW is desired,the selective separation and recovery of palladium from HLLW can not only solve the problem in process of vitri-fication but also reuse the valuable nuclides into useful resource.Separation of palla-dium from HLLW using four kinds of adsorption materials modified by graft-polymerized polyolefin-based fiber functional group:Smopex?-105 FG,Smopex?-102 FG,Smopex?-234 FG,Smopex?-234 FG by the batch method has been investigated,as well as the adsorption characteristics from both kinetics and thermo-dynamics under different variables including HNO3 concentration,contact time,ini-tial metal ions concentration and temperature influence the adsorption behavior,to make further demonstration of the main factors that influence the process and degree of adsorption reaction;meanwhile,different kinds of desorption solvents were used to the desorption of palladium from the adsorbed adsorbents under different variables including concentration of desorption solvents,contact time,temperature influence the desorption behavior,to determine the optimal desorption conditions of Pd???.Following results were obtained:1.It can be seen from the research on the static adsorption,desorption behavior of Pd???onto fibrous Smopex?-105 FG adsorbent that the adsorption material with functional group of Vinylpyridine exhibited outstanding performance in Pd???ab-sorption in a wide range of HNO3 concentration?0.001-5.0 M?,Kd up to 26547 cm3·g-1when HNO3 concentration was 0.001 M.Kinetic study revealed that sorption process of Pd???on the adsorbent could be described successfully by pseudo-second-order kinetic model,isotherm modeling indicated that the adsorption behavior of Pd???on the adsorbent could be described well by Langmuir model,with maximum monolayer adsorption capacity of 2.107 mmol·g-1,2.586 mmol·g-1 in 1 and 3 MHNO3 solution,respectively;the thermodynamical parameters:?G°<0,?H°>0,?S°>0,demon-strating that adsorption process of Pd???by fibrous Smopex?-105 FG adsorbent was spontaneous and endothermic,irreversible and higher temperature was advantageous for the adsorption reaction.According to the study on static desorption,desorption percentage of 22.54%,2.181%were obtained at 323 K with contact time of 24 h for Pd???using 5 MHNO3 solution,0.01 MDTPA solution,respectively.2.It turned out from the research on the behavior of static adsorption,desorption of Pd???onto fibrous Smopex?-102 FG adsorbent that the adsorbent with functional group of Acrylic acid showed good absorption performance under low acidity,and Kd was 142.0 cm3·g-1 in 0.001 MHNO3 solution.The sorption process of Pd???on the adsorbent could be described well by pseudo-second-order kinetic model,Freundlich isothermal model exhibited the good fit for the Pd???adsorption process;thermody-namic study indicated that spontaneous endothermic,irreversible nature of this ad-sorption process.Based on the research of static desorption,Pd???was desorbed effi-ciently by 0.01 MDTPA and EDTA solution at 323 K with contact time of 24 h and desorption percentage of Pd???was estimated to be 63.39%,57.48%,severally.3.It was demonstrated from the research on the behavior of static adsorption,desorption of Pd???onto fibrous Smopex?-111 FG,Smopex?-234 FG adsorbents that the adsorbent with functional group of Styrylthiol showed almost no adsorption for Pd???,the adsorbent with functional group of Mercaptoethylacrylate exhibited unsat-isfactory sorption for Pd???during whole experimental range of HNO3 concentration,values of Kd increased with the increase of HNO3 concentration and Kd was 22.04cm3·g-1 in 5 M HNO3 solution;kinetic process of the adsorption of Pd???on fibrous Smopex?-234 FG adsorbent could be described well by pseudo-second-order kinetic model,the sorption isotherm of Pd???on fibrous Smopex?-234 FG adsorbent was found to follow the Langmuir isotherm model with maximum monolayer adsorption capacity(Qmax)of 0.0940 mmol·g-1;Seen from adsorption thermodynamic parameters,this adsorption process was a spontaneous endothermic and irreversible,high temper-ature was better for adsorption process.It can be learned from the resaerch on static desorption of adsorbed fibrous Smopex?-234 FG adsorbent that desorption percentage of Pd???reached more than 13%by different concentration of EDTA solution and about 13%by different concentration of DTPA solution at 298 K with contact time of24 h.Based on these results,fibrous Smopex?-105 FG adsorbent with functional group of Vinylpyridine exhibited excellent performance in Pd???absorption in a wide range of HNO3 concentration,fibrous Smopex?-102 FG adsorbent with functional group of Acrylic acid had good absorption effect for Pd???only in range of low HNO3 concentration,fibrous Smopex?-111 FG adsorbent with functional group of Styrylthiol showed almost no adsorption for Pd???,fibrous Smopex?-234 FG adsor-bent with functional group of Mercaptoethylacrylate exhibited poor sorption for Pd???.Fibrous Smopex?-105 FG adsorbent was proved to be one of the very prospective adsorbent for selective separation of Pd???from HLLW in four kinds of adsorption materials modified by graft-polymerized polyolefin-based fiber functional group,and it's distinguished adsorption performance may originate from the strong coordination effect of functional group of vinylpyridine on the adsorbent for Pd???,the adsorbent with functional group of Styrylthiol was proved to be unsuitable to be applied to sep-arate Pd???from HLLW.This research provides an alternative new way of thinking and technical guid-ance for the selective separation of palladium from HLLW and also provide certain foundational information for the development and application of adsorption materials that have strong adsorption property for Pd???from HLLW. |
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