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In the present study, a porous silica-based covalent organic framework incorporated composite was prepared using a solvothermal reaction and the following wet-impregnation method. Multiple characterization methods including Scanning electron microscope, Fourier transform infrared spectroscopy, X-ray powder diffraction confirmed the surface morphology, thermal stability, and pore structure of the as-prepared composite. The adsorption performances of the prepared composite toward palladium [Pd(II)] from simulated high-level liquid waste were systematically investigated using batch experiments under the effect of contact time, solution temperature, and nitric acid solution.

(HDEHP + Hexa)/SiO2-P, a silica-based adsorbent, was prepared and used to separate Y(III) from a mixed solution of Sr(II) and Y(III). The adsorption behavior of the adsorbent was investigated using batch tests. The adsorbent exhibited high adsorption performance for Y(III) in low nitric acid concentrations and weak adsorption performance for Y(III) at higher concentrations. In contrast, Sr(II) was not adsorbed in either acid concentration range. The same tendency was observed under hydrochloric acid conditions. Y(III) separation from a mixed solution of Sr(II) and Y(III) was verified by a column test. Overall, the (HDEHP + Hexa)/SiO2-P adsorbent can separate Y(III) from Sr(II).

Adsorption and separation performances of a microporous silica-based (DAMIA-EH + TOA)/SiO2-P adsorbent towards Pd(II) were systematically investigated under the effect of contact time, temperature, concentration of nitric acid, chromatography etc. in a simulated high-level liquid waste containing 14 kinds of representative co-existing metal ions. Successful recovery of around 97.95% Pd(II) was achieved under the elution with 0.01 M Tu (pH = 2) solution in column experiment.

To separate Y(III) from a Sr(II)–Y(II) mixture, two silica-based adsorbents, CMPO/SiO2-P and (CMPO + Dodec)/SiO2-P were prepared by impregnating octyl(phenyl)-N,N-diisobutylcarbamoyl methylphosphine oxide (CMPO) extractant and a molecule modifier (1-Dodecanol) into macroporous silica/polymer composite support (SiO2-P). The Adsorbents showed high adsorption affinity to Y(III) and weak adsorption affinity to Sr(II) in HNO3 solution. The amount of adsorbed Y(III) increased with the HNO3 in the solution. The amount of adsorbed Y(III) increased with contact time and reached equilibrium within 30 min. The results showed that a pseudo-second-order kinetic model with a high correlation coefficient described the adsorption process better than other kinetic models. Successful Y(III) separation from Sr(II)–Y(III) mixture in HNO3 solution was achieved.

To evaluate the redox behavior of $${\text{VO}}^{2 + } / {\text{VO}}_{2}^{ + }$$ as a simulant of $${\text{NpO}}_{2}^{ + } / {\text{NpO}}_{2}^{2 + }$$ in boiling nitric acid solution, i.e., typical operating conditions for nuclear fuel reprocessing plants, oxidation rate measurements for VO2+ in boiling and non-boiling nitric acid solutions, thermodynamic calculations, and kinetic calculations were performed. The results indicated that the apparent oxidation rate of VO2+ to $${\text{VO}}_{2}^{ + }$$ is accelerated by a decrease in $${\text{NO}}_{2}^{ - }$$ and HNO2 concentrations owing to the boiling phenomena of nitric acid solution.

To separate heat-generating Cs from high-level liquid waste (HLLW), the extraction of Cs(I) using 1,3-[(2,4-diethylheptylethoxy)oxy]-2,4-crown-6-calix[4]arene (calix[4]arene-R14) in combination with 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) ionic liquids ([C n mim][NTf2], where n = 2, 4, and 6) was investigated. Under moderately acidic conditions, the calix[4]arene-R14/[C n mim][NTf2] system showed a higher extraction efficiency (ECs) than that exhibited by the conventional calix[4]arene-R14/dichloromethane system. All extraction processes reached equilibrium within 5 min. Slope analysis revealed that the Cs:calix[4]arene-R14 inclusion complex has a 1:1 stoichiometry. The extraction was found to be exothermic and influenced by the presence of Na(I). These extraction systems exhibited high efficiency and selectivity for Cs(I) in simulated HLLW.

To separate Mo(VI) from high-level liquid waste, a silica-based (anti-DEHDO + Dodec)/SiO2-P adsorbent was synthesized by impregnating an anti-isomer of 5,8-dietyl-7-hydroxy-6-dodecanonoxime (DEHDO) as a hydroxyoxime-type extractant and a molecule modifier of 1-dodecanol into a SiO2-P support, where “P” indicates the polymerized styrene–divinylbenzene inside macroporous SiO2 particles. Adsorption and separation behaviors of Mo(VI) in HNO3 solutions onto the adsorbent were investigated by batch and column methods, respectively. The adsorbent can effectively adsorb Mo(VI) in both methods. In addition, Pd(II) and Zr(IV) contained in the simulated high-level liquid waste were successfully isolated by the adsorbent packed column, respectively.

To discuss the applicability of a novel macroporous silica-based (MOTDGA–TOA)/SiO2-P adsorbent which was developed to separate platinum group metals (PGMs) from high level liquid waste by extraction chromatography to radiation field, batch adsorption behavior, stability of the adsorbent and retention capability of PGMs under irradiation were investigated by using gamma-ray emitted from 60Co. Difference of adsorption behaviors of Ru(III), Rh(III) and Pd(II) were not observed with or without the irradiation up to 100 kGy of absorbed dose at least. The retention ratio of Pd(II) showed very gradual decrease, and was over 99 % at absorbed dose of about 800 kGy.

To separate minor actinides from high level liquid waste (HLLW) of PUREX reprocessing, a silica-based macroporous isobutyl-BTP/SiO2-P adsorbent was synthesized by impregnating isobutyl-BTP (2,6-di(5,6-diisobutyl-1,2,4-triazin-3-yl)pyridine) extractant into the macroporous SiO2-P support with a mean diameter of 60 μm. A partitioning process using extraction chromatography for the treatment of HLLW was designed consisting five separation columns. As a partly work focused on isobutyl-BTP/SiO2-P separation column, adsorption behavior of 241Am and trivalent rare earth (RE) from simulated HLLW onto silica-based isobutyl-BTP/SiO2-P adsorbent was investigated by batch method. Meanwhile, the chemical and radiolytic stabilities of isobutyl-BTP/SiO2-P adsorbent against 0.01 M HNO3 solution and γ-ray irradiation were studied. It was found that isobutyl-BTP/SiO2-P adsorbent exhibited good adsorption selectivity for 241Am over RE(III) in 0.01 M HNO3 solution and showed weak or no adsorption affinity to light and middle RE(III) groups. In addition, in stability experiments, isobutyl-BTP adsorbent showed excellent stability against 0.01 M HNO3 solution and γ-ray irradiation over 4 months contact time.

To understand the separation behavior of Zr(IV) in the partitioning process for high level liquid waste, a silica-based macroporous adsorbent (TODGA/SiO2-P) was prepared by impregnating N,N,N′,N′-tetraoctyl-3-oxapentane-1,5-diamide (TODGA) into a macroporous silica/polymer composite particles support (SiO2-P). Adsorption and desorption behavior of Zr(IV) from nitric acid solution onto silica-based TODGA/SiO2-P adsorbent were investigated by batch experiment. It was found that TODGA/SiO2-P showed strong adsorption affinity to Zr(IV) and this adsorption process reached equilibrium state around 6 h at 298 K. Meanwhile, HNO3 concentration had no significant effect on the adsorption of Zr(IV) above 1 M. From calculated thermodynamic parameters, this adsorption process could occur spontaneously at the given temperature and was confirmed to be an exothermic reaction. This adsorption process could be expressed by Langmuir monomolecular layer adsorption mode and the maximum adsorption capacity were determined to be 0.283 and 0.512 mmol/g for Zr(IV) at 298 and 323 K, respectively. In addition, more than 90 % of Zr(IV) adsorbed onto adsorbent could be desorbed with 0.01 M diethylenetriamine pentaacetic acid solution within 24 h at 298 K.

Curium was separated and recovered as an oxalate from a Cm–Pu mixed oxide which had been a 244Cm oxide sample prepared more than 40 years ago and the ratio of 244Cm to 240Pu was estimated to 0.2:0.8. Radiochemical analyses of the solution prepared by dissolving the Cm–Pu mixed oxide in nitric acid revealed that the oxide contained about 1 at% of 243Am impurity. To obtain high purity curium solution, plutonium and americium were removed from the solution by an anion exchange method and by chromatographic separation using tertiary pyridine resin embedded in silica beads with nitric acid/methanol mixed solution, respectively. Curium oxalate, a precursor compound of curium oxide, was prepared from the purified curium solution. 11.9 mg of Cm oxalate having some amounts of impurities, which are 243Am (5.4 at%) and 240Pu (0.3 at%) was obtained without Am removal procedure. Meanwhile, 12.0 mg of Cm oxalate (99.8 at% over actinides) was obtained with the procedure including Am removals. Both of the obtained Cm oxalate sample were supplied for the syntheses and measurements of the thermochemical properties of curium compounds.

To separate platinum group metals (PGMs) from high level liquid waste (HLLW), a novel silica-based (Crea + TOA)/SiO2–P adsorbent was synthesized by impregnating Crea (N′,N′-di-n-hexyl-thiodiglycolamide) and TOA (trioctylamine) two extractants into the macroporous SiO2–P support with a mean diameter of 60 μm. Adsorption properties and behavior of PGMs from simulated HLLW onto the novel silica-based (Crea + TOA)/SiO2–P adsorbent were investigated by batch method. It was found that (Crea + TOA)/SiO2–P adsorbent exhibited good adsorption selectivity for PGMs over the other tested fission product element in a wide HNO3 concentration. This adsorbent showed strong affinity to Pd(II) but almost no adsorption for rare earth elements. Adsorption process of PGMs could be expressed by Langmuir monomolecular layer adsorption mode and be governed by the chemisorption process. In addition, the adsorption isotherms and thermodynamic parameters of tested elements were calculated by Langmuir equation, Freundlich equation and van’t Hoff equation, respectively.

To separate the long-life and significant fission product elements from high level liquid waste (HLLW), a novel partitioning process for the treatment of HLLW has been studied experimentally based on column separation technique using macroporous silica-based adsorbents. This process consists of (1) Cs and Rb are removed by the first separation column packed with (calix[4] + dodecanol)/SiO2–P adsorbent; (2) Sr and Ba are eluted out by the second separation column packed with (DtBuCH18C6 + dodecanol)/SiO2–P adsorbent; (3) Pd is partitioned by the third separation column packed with MOTDGA–TOA/SiO2–P adsorbent; (4) Ru, Rh and Mo can be separated by the fourth separation column packed with TODGA/SiO2–P adsorbent; (5) Am is separated from RE by the fifth column is packed with isobutyl-BTP/SiO2–P adsorbent. The experimental results indicated that this partitioning process is essentially feasible.

A macroporous silica-based supramolecular recognition absorbent (Calix[4] + Dodecanol)/SiO2–P, was prepared by successive impregnation and fixing the 1,3-[(2,4-diethylheptylethoxy)oxy]-2,4-crown-6-Calix[4]arene (Calix[4]arene-R14) and its molecule modifier 1-Dodecanol onto SiO2 silica-based polymer support. The characterization of (Calix[4] + Dodecanol)/SiO2–P was examined by thermal gravimetry and differential thermal analysis and electron probe microanalysis. Relatively large separation factors of Cs and other metal ions (α Cs/M + ) above 60 were obtained in the presence of 3 M HNO3. The adsorption data of Cs(I) fitted well with Langmuir isotherm and the maximum adsorption capacity was estimated to be 0.19 mmol g−1. The Cs(I) in 3 M HNO3 were also effectively adsorption on (Calix[4] + Dodecanol)/SiO2–P in the column operation, and the loaded Cs(I) was successfully eluted with an eluent of H2O. The column packed with (Calix[4] + Dodecanol)/SiO2–P had excellent reusability after three cycles.

In order to develop a direct separation process for trivalent minor actinides from fission products in high level liquid waste (HLLW) by extraction chromatography, a novel macroporous silica-based 2,6-bis(5,6-diisohexyl)-1,2,4-triazin-3-yl)pyridine resin (isohexyl-BTP/SiO2-P resin) was prepared. The content of isohexyl-BTP extractant in the resin was as high as 33.3 wt%. The resin exhibited much higher adsorption affinity for Am(III) in 2–3 M (mol/L) HNO3 solution over U and FP which are contained in HLLW. The kinetic data were analyzed using pseudo-second-order equation. The results suggested that the Eu(III), Gd(III), and Dy(III) adsorption was well explained by the pseudo-second-order equation. Quantitative desorption for adsorbed elements was achieved by using H2O or thiourea as eluting agents. However, the kinetics of adsorption and desorption were rather slow and this drawback needs to be resolved. Stability of the resin against HNO3 was also examined. It was found that the resin was considerably stable against ≤4 M HNO3 solution for the reasons of an extremely small leakage of the extractant into the solution from the resin and the adsorption performance keeping for rare earths in 3 M HNO3 solution.

Electrochemical behavior of NpO22+ on platinum (Pt) and glassy carbon (GC) electrodes have been studied in an aqueous 3M HNO3 solution using cyclic voltammetry and spectroelectrochemical method. The NpO22+ species was found to be reduced to Np(V) quasi-reversibly with the formal redox potential of +0.907 V (Pt) and +0.909 V (GC). The reduction process of NpO22+ in an aqueous 3M HNO3 solution was also followed spectroelectrochemically by using an optical transparent thin layer electrode cell. It was found that the absorption spectra measured at the applied potentials in the range of +1.05 to +0.65 V have isosbestic points at 1051 and 1124 nm and the evaluated electron stoichiometry is 0.93. These results indicate that the reduction product of NpO22+ is NpO2+. Further details for reaction mechanism of Np(VI) are discussed on the basis of digital simulation of the experimental cyclic voltammograms.