Adsorption Mechanism Study On Chromatographic Separation And Richment Of Platinum Group Metals From Simulated High Level Liquid Waste

To ensure a sustainable development of nuclear energy in the future,the establishment of a partitioning process for treatment of high level liquid waste?HLLW?is one of the chanllenging tasks in closed nuclear fuel cycle.High level liquid waste contains significant quantities the platinum group metals?PGMs?including platinum,rhodium and ruthenium.PGMs are very important elements in a field of chemical,pharmaceytical,electronic and petroleum industries.On the other hand,PGMs are known to obstruct producing of vitrified waste before geologic disposal.For these reasons,the selective separation and recovery of PGMs from HLLW can not only solve the problem in process of vitrification but also reuse the valuable nuclides into useful resource.Therefore,the selective separation and recovery of PGMs from HLLW is desired.For this purpose,a novel silica-based macroporous adsorbent?Crea+TODGA?/SiO₂-P was synthesized to selective separate PGMs from HLLW using extraction chromatography.The adsorbent was prepared by impregnatingtheCrea?N',N'-di-n-hexyl-thiodiglycolamide?andTODGA?N',N'-dimethyl-N',N'-di-n-octyl-thiodiglycolamide?two extractants into SiO₂ silica based polymer support.The adsorption properties towards PGMs,breakthrough behavior of Pd and chromatographic separation,were investigated by batch and columnmethodsrespectively.Besides,thestabilityofadsorbent?Crea+TODGA?/SiO₂-P against HNO₃ solution was examined.Following results were obtained.?1?A novel silica-basedadsorbent?Crea+TODGA?/SiO₂-Pwas synthesized.The microstructure and composition of the adsorbent were characterized by SEM,TEM and TG-DTA.?2?The adsorption properties of 11 typical metal elements,Zr????Mo?VI??Pd????Ru????Rh????La????Ce????Nd????Sm????Gd???and Re?V??in HLLW were examined.The result showed that?Crea+TODGA?/SiO₂-P adsorbent exhibited good adsorption selectivity for PGMs over the other fission product element in 2.0-5.0 M HNO₃ solution.This adsorbent showed strong affinity to Pd???but almost no adsorption for rare earth elements.?3?In batch experiment,the effects of contact time,temperature,metal ions concentrations and the choice of elution solution on the adsorption and desorption onto the?Crea+TODGA?/SiO₂-P adsorbent were investigated.The adsorption isotherms,thermodynamic and kinetics parameters of PGMs in adsorption process were calculated from the results of batch experiment.The results showed that?Crea+TODGA?/SiO₂-P adsorbent showed good adsorption affinity for Pd???and the adsorption process of Pd???could be expressed by the pseudo-second order model.Meanwhile,the adsorption process could occur spontaneously and was confirmed to be an exothermic reaction.The adsorption isotherms of Ruand Pd on?Crea+TODGA?/SiO₂-P adsorbent followed the Langmuir adsorption isotherm,and the maximum adsorption capacities were estimated to bePd:61.62 mg/g,Ru:31.32mg/g.?4?Breakthrough curve experimentsof Pd???were carried out feeding 5 mM Pd in 3 M HNO₃ solution into?Crea+TODGA?/SiO₂-P packed column under different flow rates.The maximun breakthrough capacities at 0.3 cm³/min,0.6 cm³/min and 0.9cm³/min flow rate were44.4 mg/g?42.5 mg/g and 41.6 mg/g,respectively.The results showed that the flow rate had slightly effect on the adsorption of Pd???under the wide experimental conditions.?5?In column experiments,the separation behavior of 11 typical metal elementsin HLLW were performed by?Crea+TODGA?/SiO₂-P column.At 298 K,Ru???andRh???showed no and weak adsorption towards?Crea+TODGA?/SiO₂-P and quick broke through the column along the feed.Mo?VI?andRe?V??leaked out the column along with the 3.0 M HNO₃ washing solution.Earth elements La????Ce????Nd???and Sm???leaked out the column along with the water.Then Pd was eluted by0.2 M thiourea-0.1 M HNO₃ solution efficiently and the total elution percentage of Pd at 298 K was estimated to be 55.56%.With 0.01 M DTPA solution into the column,Zr???and Gd???were eluted showing a narrow elution band without tailing.At 323K,the separation behavior of 11 typical metal elementson?Crea+TODGA?/SiO₂-P column were consistent with that at 298 K.And the elution percentage was calculated to 74.15%for Pd at 323 K.?6?The stability of?Crea+TODGA?/SiO₂-P adsorbent against HNO₃ solution were investigated by batch method and the degradation parts of dissolved in liquid phase were estimated by total organic carbon?TOC?analyzer.The adsorption ability of?Crea+TODGA?/SiO₂-P for Pd???and the content of TOC leaked decreased with the increasing of HNO₃ concentration.While the content of TOC leaked from the adsorbent after 28 days were 1095 ppm?298 K?and 2989 ppm?323 K?,respectively.Therefore,the adsorbent showed good stability at 298 K after contact with nitric acid for a long time and?Crea+TODGA?/SiO₂-P can be proposed as an applicable and efficient absorbent for separation of Pd???in 3 M HNO₃ at 298 K.Based on these results,the process of selective separating PGMs from HLLW is feasible using one?Crea+TODGA?/SiO₂-P columnwhich is based on the synergetic effect of Crea andTODGA two extractants.Ru???andRh???showed no and weak adsorption towards?Crea+TODGA?/SiO₂-P and quick leaked out the column along the feed.Then Ru???andRh???are separated from earth elements.And Pd was eluted by thiourea-HNO₃solution efficiently.Finally,a reasonable optimization partitioning process for the separation and enrichment of PGMs from HLLW was proposed for industrial utilization by means of extraction chromatography technology using?Crea+TODGA?/SiO₂-P packed column.