Separation and recovery of heat-generating elements and platinum group metals from high-level radioactive liquid waste: development of a silica-type impregnated adsorbent

To develop a simple process to separate the heat-generating elements cesium (Cs(I)) and strontium (Sr(II)) and platinum group metals from high-level radioactive liquid waste (HLLW), an adsorbent was prepared by impregnating a silica-based polymer support (SiO2-P) with 1,3-[(2,4-diethylheptylethoxy)oxy]-2,4-crown-6-calix[4]arene (Calix[4]arene-R14), 4,4',(5')-di-(tert-butyl-cyclohexano)-18-crown-6 (DtBuCH18C6), N,N'-dimethyl-N,N'-dihexyl-thioglycolamide (Crea), and tri-n-octylamine (TOA). The adsorption performance of the prepared (Calix[4]arene-R14 + DtBuCH18C6 + Crea + TOA)/SiO2-P adsorbent for simulated HLLW was investigated by varying the contact time, nitric acid (HNO3) solution concentration, solution temperature, and adsorption capacity. The chemical stability of the adsorbent under various HNO3 solution concentrations was evaluated using total organic carbon content. Results indicate that the prepared adsorbent has a high affinity for palladium(II), ruthenium(III), Cs(I), Sr(II), barium (Ba(II)), and rhenium(VII) compared to other coexisting metal ions, adsorption capacity, and shows excellent chemical stability in HNO3 solution. Furthermore, a separation chromatography experiment using the prepared (Calix[4]arene-R14 + DtBuCH18C6 + Crea + TOA)/SiO2-P adsorbent-packed column was carried out with the aim of simplifying the separation process in a single column.