Adsorption Behaviors Of Silica-based Hexacyanoferrate For Palladium(Ⅱ)

Palladium,as a nobel precious metal,applied intensively in industry,yet its surface reserves are very scarce.Over 1.05×10⁴ t HM spent fuel produced every year worldwide.In addition to recyclable uranium and plutonium,the spent fuel contains a large amount of palladium.Based on closed nuclear fuel cycle,the goal of advanced nuclear fuel cycle is to maximize the use of uranium resources and minimize the emission of radioactive wastes.Moreover,in the vitrification of high-level liquid waste（HLLW）,palladium would form nonhomogeneous phases at the bottom of the melter,thus waken the mechanical behavior of solidified body.Therefore,separation of palladium in the HLLW may not only facilitate vitrification,reduce the amount of radioactive waste,but also bring considerable economic benefits.In this study,nickel hexacyanoferrate was loaded into the porous support SiO₂particles by inner pore crystallization method to synthesize silica-based nickel hexacyanoferrate（KNi HC/SiO₂）adsorbent.The adsorbent was characterized by SEM,EDS,XRD and XPS to explore the micro-mechanism of the adsorption process.The results showed that nickel hexacyanoferrate was successfully impregnated into pores of SiO₂ support,the surface of adsorbent was smooth,the porosity and average pore size of KNi HC/SiO₂ is 52.9%and between 29～40 nm.The adsorption of KNi HC/SiO₂ for palladium is the interaction of ion-exchange and redox reaction.In the nitric acid medium solution,the distribution coefficient of KNi HC/SiO₂ for Pd（II）decreases with increasing nitric acid concentration.In 3 M HNO₃ medium,the K_d value of Pd（II）reaches reach up to 3.6×10³cm³/g.The adsorption of KNi HC/SiO₂ for Pd（II）can reach equilibrium in less than 60 minutes,and the adsorption capacity is more than 0.2 mmol/g.The adsorption kinetics and isotherms fitted well with the pseudo-second-order model and Langmuir model.The co-existing noble metals Rh（Ⅲ）and Ru（Ⅲ）have ignorable affection on adsorption for palladium.In the column experiments,the increase of flow rate would decrease the breakthrough volume.In the hydrochloric acid medium solution,the distribution coefficient of KNi HC/SiO₂ for Pd（II）increases with increasing nitric acid concentration.The adsorption kinetics is relatively slow,needs over 18 hours to reach the equilibrium.The adsorption kinetics and isotherms fitted well with the pseudo-second-order model and Langmuir model.The co-existing noble metals have no affection on adsorption for palladium.Thiourea can desorb the palladium in the KNi HC/SiO₂.The concentration of thiourea lower than0.01 M,the desorption would not destroy the crystal structure of KNi HC/SiO₂,while the concentration of thiourea bigger than 0.2 M would destroy the crystal structure.Above all,the KNi HC/SiO₂ adsorbent possess excellent selectivity and adsorption capacity for palladium,which is a promising material to selectively separate and recover of palladium.