A macroporous silica-based 4,4′,(5′)-di(t-butylcyclohexano)-18-crown-6 (DtBuCH18C6)-impregnated polymeric composite, (DtBuCH18C6 + Oct)/SiO2-P, was synthesized by molecular modification of DtBuCH18C6 with 1-octanol through hydrogen bonding. This was achieved by impregnating and immobilizing DtBuCH18C6 and 1-octanol molecules in the pores of macroporous SiO2-P particles possessing a mean pore diameter of 50 μm. The adsorption of some fission and non-fission products contained in highly active liquid waste (HLW) such as Ru(III), Mo(VI), Pd(II), Na(I), K(I), Cs(I), Sr(II), Ba(II), La(III) and Y(III) onto (DtBuCH18C6 + Oct)/SiO2-P was investigated at 298 K. The effects of contact time and HNO3 concentration within the range 0.1–5.0 M were examined. Increasing the HNO3 concentration from 0.1 M to 2.0 M led to a significant increase in the adsorption of Sr(II), followed by a decrease when the HNO3 concentration was increased further to 5.0 M. The optimum concentration of HNO3 in the adsorption of Sr(II) onto (DtBuCH18C6 + Oct)/SiO2-P was determined as 2.0 M. For the other ions examined with the exception of Ba(II), very weak or almost non-existent adsorption capacities were observed at all HNO3concentrations. The leaching of total organic carbon (TOC) from (DtBuCH18C6 + Oct)/SiO2-P into the aqueous phase was evaluated. Over the HNO3 concentration range 0.1–3.0 M, the quantity of TOC leached was ca. 40 ppm compared with 355.8–373.3 ppm at HNO3 concentrations above 4.0 M. Significant reduction of TOC leaching from the macroporous silica-based DtBuCH18C6-impregnated polymeric composite was achieved in 2.0 M HNO3. Such behaviour could be of great benefit in using (DtBuCH18C6 + Oct)/SiO2-P for the partitioning of Sr(II) from HLW by extraction chromatography.
Trends of Nitrogen Oxide Release during Thermal Decomposition of Nitrates in Highly Active Liquid Waste