Selective adsorption of uranium(VI) by clay minerals from saline conditions: Molecular dynamics simulations

Abstract

Uranium represents one of the most radioactive and toxic metals. A systematic study of UO₂²⁺ adsorption by clay minerals is conducted using molecular dynamics, especially from highly saline conditions where a majority of uranium is detected. UO₂²⁺ adsorption and exchange occur favorably at basal rather than other surfaces. Clay minerals, especially beidellite, are UO₂²⁺-selective, and adsorption selectivity increases at higher salinity. Adsorption and selectivity are regulated by charge location and surface structure, and enhanced by temperature elevation, showing stronger coupling at higher UO₂²⁺ concentrations. Co-existing metal ions affect UO₂²⁺ adsorption more than anions, and thermodynamic preference of cation exchange follows as Ca²⁺ > K⁺ > Na⁺ and CO₃²⁻ > Cl⁻ while kinetic preference has reversed trends. Higher CO₃²⁻ concentrations are necessary for coupling with Na⁺ vs. Ca²⁺. Results promote the understanding of UO₂²⁺ adsorption by clay materials, and are beneficial to uranium contamination management and nuclear fuels utilization.