Xiaomei Xu, Zhiyong Liu, Shitong Yang, Lanhua Chen, Juan Diwu, Yu Yang, Evgeny V. Alekseev, Zhifang Chai , Thomas E. Albrecht-Schmitt, Shuao Wang*. "Potassium Uranium Borate 3D Framework Compound Resulted from Temperature Directed Hydroborate Condensation: Structure, Spectroscopy, and Solution Stability Studies". Dalton Trans., 2016, 45, 15464-15472.
Abstract:
The linear geometry nature of the uranyl unit has limited further coordination in a plane, resulting in only three uranyl borate frameworks reported so far formed by boric acid flux reactions conducted at 190 °C. Here in this work, by elevating the reaction temperatureto 250 °C, a potassium uranyl borate K[(UO2)B6O10(OH)]∙H2O (KUBO-4) framework structure was synthesized that shares the same layer topology with the reported KUBO-1. The KUBO-4 was characterized with single crystal XRD, SHG and fluorescence spectra, and TG/DSC measurements. A deep understanding regarding the dissolution behaviours of uranyl borate and its correlation with structure dimensionality is achieved via solubility studies of the KUBO-1 (2D) and KUBO-4(3D) performed using ICP-MS, powder XRD, and fluorescence spectroscopy techniques, whose results all lead to conclusive findings of the lack of stability of borate in the selected systems. More importantly, our work has captured for the first time, the phase transition steps of actinide borates in the nitrate, HA and phosphate solutions. Owing to the strong complexations between borates and f-elementsobserved in WIPP, especially hexa-valent uranium and trivalent lanthanides that masking the influence induced by carbonate, those data are essential for predicting the fate of actinides in the borate-rich repositories.
