Selective separation of Pd(II) through ion exchange and oxidation-reduction with hexacyanoferrates from high-level liquid waste

A macro porous silica-based nickel hexacyanoferrate (KNiHC/SiO2) adsorbent was synthesized for separation of palladium (Pd(II)) from high-level liquid waste (HLLW). Based on XPS analysis, the Pd 3d512 spectrum at 344.4 eV corresponds to metallic palladium Pd(0), indicating that ion-exchange and redox reactions occur in the adsorption of Pd. Mercury intrusion porosimeter (MIP) test results show that the average pore size of KNiHC/SiO2 is 37.6 nm. The adsorption of KNiHC/SiO2 for Pd(II) reaches the equilibrium state within 1 h and follows the pseudo-second-order kinetic model, which indicates chemical adsorption. The maximum adsorption capacity of the adsorbent for Pd(II) in the mixture of 1 M NaNO3 and 3 M HNO3 is 46.09 mg/g. The experimental data fit well with the Langmuir and Redlich-Peterson isotherm models. Furthermore, KNiHC/SiO2 exhibits high selectivity toward Pd(II) over co-existing noble metals, namely, Rh(III) and Ru(III) within a wide range of HNO3 concentrations. The sharp S-shaped breakthrough curves in different feed flow rates suggest the excellent dynamic adsorption performance of the adsorbent in column systems.