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., a-alumina [alpha-Al2O3] and gamma-alumina [gamma-Al2O3)]) is essential for unraveling numerous environmental issues. We performed a systematic comparative analysis of U(VI) retention by alpha-/gamma-alumina. The effects of coexisting ions and natural organic matter were explored. Solution pH contributed critically to the retention of U(VI) by alpha-/gamma-alumina. The adsorption rate of gamma-Al2O3 for U(VI) removal was faster than that of alpha-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 alpha-Al2O3. The addition of phosphate resulted in a 15-fold enhancement in adsorption capacity. Humic acid promoted U(VI) removal by gamma-Al2O3 under acidic conditions while strong inhibition on both alpha-Al2O3 and gamma-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.

Automated summary

The study emphasizes the critical role of solution pH in the retention of U(VI) by alpha-/gamma-alumina, with gamma-Al2O3 showing higher removal efficiency. Phosphate ions significantly promote U(VI) adsorption, while humic acid has different effects on U(VI) removal by alumina under different conditions.