Selective adsorption of uranium (VI) from wastewater using a UiO-66/calcium alginate/hydrothermal carbon composite material.

Uranium mining, smelting, and nuclear industries generate a considerable amount of wastewater containing uranium. To treat this wastewater effectively and inexpensively, a novel hydrogel material (cUiO-66/CA) was developed by co-immobilizing UiO-66 with calcium alginate and hydrothermal carbon. Batch tests were conducted to determine the optimal adsorption conditions for uranium using cUiO-66/CA, and the adsorption behavior was spontaneous and endothermic, confirming the quasi-second-order dynamics model and the Langmuir model. At a temperature of 308.15 K and pH = 4, the maximum adsorption capacity of uranium was 337.77 mg g. The surface appearance and interior structure of the material were analyzed using SEM, FTIR, XPS, BET, and XRD techniques. The results indicated two possible uranium adsorption processes of cUiO-66/CA: (1) Ca and UO ion exchange process and (2) coordination of uranyl ions with hydroxyl and carboxyl ions to form complexes. cUiO-66/CA exhibited strong selectivity for U (VI) in a multicomponent mixed solution and uranium-containing wastewater, with uranium removal rates of 99.03 % and 81.45 %, respectively. The hydrogel material demonstrated excellent acid resistance, and the uranium adsorption rate exceeded 98 % in the pH range of 3-8. Therefore, this study suggests that cUiO-66/CA has the potential to treat uranium-containing wastewater in a broad pH range.