Adsorption-Induced Crystallization of U-Rich Nanocrystals on Nano-Mg(OH)2 and the Aqueous Uranyl Enrichment

The mechanism of the interaction between nano-Mg(OH)2 adsorbent and uranyl in water was studied. At trace levels, the uranyl is adsorbed as a monolayer on nano-Mg(OH)2, and occupied a small proportion of the adsorption sites. As the uranyl concentration crosses over a threshold, continuous increase of adsorption capacity takes place. It indicates that, by taking the pre-adsorbed uranyl as the nucleation centers, the additional uranyl crystallizes and forms U-rich nanocrystals well-scattered on the surface of nano-Mg(OH)2. A strategy of inducing fast crystal growth of nano-Mg(OH)2 to micrometer-sized Na2Mg(CO3)2 enables the desorption and enrichment of uranyl. The recycling and reuse of nano-Mg(OH)2 can be achieved simultaneously. The finding in this work provides fundamental understanding of the efficient usage of nano-Mg(OH)2 in practical applications.