U(VI) sequestration by Al-rich minerals: Mechanism on phase dependence and the influence of natural organic matter

Uranium and uranium-containing pollutants are excessively released into the environment, leading to serious water and soil contamination. Minerals such as alumina are naturally abundant and frequently affect the fate and migration behavior of uranium ions. A thorough understanding of the migration and immobilization behavior of uranium on Al-rich minerals (e.g., α-alumina [α-Al2O3] and γ-alumina [γ-Al2O3)]) is essential for unraveling numerous environmental issues. We performed a systematic comparative analysis of U(VI) retention by α-/γ-alumina. The effects of coexisting ions and natural organic matter were explored. Solution pH contributed critically to the retention of U(VI) by α-/γ-alumina. The adsorption rate of γ-Al2O3 for U(VI) removal was faster than that of α-Al2O3, reaching equilibrium within 15 min with a high removal efficiency of 94.43%. PO43− ions significantly promoted U(VI) adsorption, especially for the case of α-Al2O3. The addition of phosphate resulted in a 15-fold enhancement in adsorption capacity. Humic acid promoted U(VI) removal by γ-Al2O3 under acidic conditions while strong inhibition on both α-Al2O3 and γ-Al2O3 in basic conditions. The removal mechanism of U(VI) by alumina is mainly ascribable to electrostatic interaction and surface complexation from various oxygenated functional groups. The present findings are pivotal to the understanding of uranium migration and immobilization in the environment.