Selective adsorption of U(VI) in multi-carbonate solutions by g-C3N4/ZrO2-loaded amidoxime polyacrylonitrile.

Uranium extraction from seawater is essential for the sustainable development of nuclear energy. Nevertheless, the complex coexistence of ions in seawater can significantly impact the practical uranium species distribution and uranium adsorption process. In this paper, a novel g-C 3 N 4 /ZrO 2 -loaded amidoxime polyacrylonitrile (g-C 3 N 4 /ZrO 2 -AO) was synthesized and investigated as an adsorbent for uranium in U(VI)–CO 3 , Ca/Mg–U(VI)–CO 3 , U(VI)–P–CO 3 and U(VI)–X–CO 3 (X = F, Cl, Br, I) solutions. The uranium adsorption capacity (q e) of g-C 3 N 4 /ZrO 2 -A reached ∼104.5 + 1.5 mg·g 1 in U(VI)–CO 3 solution, which correlated with a monolayer chemisorption process. High pH and [NaHCO 3 ] decreased q e values because of the electrostatic repulsion and occupation of adsorption sites by excess CO 3 2-. Adsorption of uranium by g-C 3 N 4 /ZrO 2 -AO was impeded in the Ca/Mg–U(VI)–CO 3 , U(VI)–P–CO 3 and U(VI)–X–CO 3 (X = F, Cl, Br, I) solutions, possibly due to the formation of various U(VI) complexes. The amidoxime groups inside the g-C 3 N 4 /ZrO 2 -AO have been proved with good uranium selectivity. FTIR and XPS verified the NH 2 -C N-OH and Zr-OH acted as the primary U(Ⅵ) adsorption sites. This paper opens up opportunities for practical applications of amidoxime polyacrylonitrile-based composites towards the uranium recovery from seawater. [Display omitted] [ABSTRACT FROM AUTHOR]