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Abstract: Novel crystalline actinide materials can be used to immobilize uranium and transuranium elements at radioactive waste disposal sites. However, the stability and dissolution of such phases are still poorly understood. In this study, we investigated the dissolution kinetics of two uranyl borates and one plutonyl borate, UO2B2O4 (UBO), Na[(UO2)B6O10(OH)]·2H2O (NaUBO), and PuO2[B8O11(OH)4] (PuBO), with three different ligands, i.e., bicarbonate, phosphate, and natural humic acid (HA). These actinide borates were chosen because they possess different topologies that may influence dissolution. In the presence of bicarbonate, the apparent steady-state concentration of dissolved U(VI) and surface area-normalized dissolution rates were much higher for UBO compared to NaUBO. Uranyl phosphate, most likely in the form of (UO2)3(PO4)2(H2O)4, was precipitated on the surface of residual particles of UBO and NaUBO with phosphate. The dissolution rate of PuBO in NaNO3 solution was much higher than UBO or NaUBO. This study revealed that actinide borate crystal dissolution was substantially influenced by crystalline structures of actinide borates and aqueous ligands. [Copyright &y& Elsevier]

Bis(2-propyloxy)calix[4]arene-crown-6 ( L1 ) is a ligand with high affinity in the extraction of Cs(I). In this work, acrylamido and propionamido groups are decorated at the opposite site of 2-propyloxy on the phenyl ring of L1 , giving rise to the derivatives L2 and L3 , respectively. Complexation of all the three ligands with Cs(I) is characterized by NMR, spectrophotometric titration, crystal structure and DFT calculation. Both the NMR and spectrophotometric analysis suggest more significant variation of electron density on the phenyl rings in L2 and L3 than that in L1 in complexation with Cs(I). The stability constants (log β ) of the complexes are calculated to be 6.0 ± 0.1, 6.2 ± 0.1 and 6.3 ± 0.1 for Cs- L1 , Cs- L2 and Cs- L3 , respectively, by fitting of the absorption spectra. As reflected by the crystal structures and DFT calculations, the complexed cesium cation interacts with the crown ether moiety, the two rotated phenyl rings and the acrylamido/propionamido groups in L2 / L3 , which can be regarded as an intramolecular triple cooperative effect. Extraction of Cs(I) from aqueous solution is performed, and the distribution ratio is in line with the findings in stability constant and interaction energy. This work contributes to further improvement of the extraction of cesium cation by 1,3-alternate calix[4]arene-crown-6. [ABSTRACT FROM AUTHOR]