Interfacial Engineering Improved the Selective Extraction of Uranyl from Saline Water by Nano-Mg(OH)₂ and the Underlying Mechanism

Abundant salts and complex constituents pose challenges to the enrichment of trace-level uranyl from field water samples. On the basis of the chemical behavior of the uranyl cation in several physical–chemical conditions (in the presence of MgCl₂ etc.), we developed a facile and green strategy to improve the uranyl extraction from field water samples, different from the traditional way with organic impregnation. In our systems about nano-Mg­(OH)₂ treating salt lake brine, when the adsorbent is pretreated with a trace amount of UO₂²⁺ ion, the ability to extract uranyl from brine can increase by 2–5 times. The molecular dynamics simulation and time-resolved laser-induced fluorescence spectroscopy analysis show that, in the preadsorption stage, UO₂²⁺ ions can steadily bind to the Mg­(OH)₂ (001) surface because of the interaction with surface hydroxyl groups. When pretreated Mg­(OH)₂ was exposed to brine, the coordination interaction between the preloaded UO₂²⁺ ion and the [UO₂(CO₃)_<i>x</i>^(2x–2)–] in solution engenders good selectivity and affinity for uranyl over competitive ions in brine. Besides, the coordination number of UO₂²⁺ by carbonate oxygen is large, which further facilitates subsequent adsorption. Such strategy does not introduce other impurities and can apply to metal-oxides-type adsorbents, e.g., TiO₂. This study should shed light on further improvement of efficient uranyl extraction from field samples and give insights into the mechanism understanding of uranyl adsorption in real systems