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^-1. 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) Ca²⁺ and UO₂²⁺ 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.

High efficiency electrochemical separation of uranium(VI) from uranium-containing wastewater by microbial fuel cells with different cathodes

As an emerging versatile technology for separating uranium from uranium-containing wastewater (UCW), microbial fuel cell (MFC) offers a novel approach to UCW treatment. Its cathode is essential for the treatment of UCW. To thoroughly investigate the efficacy of MFC in treating UCW, investigations were conducted using MFCs with five materials (containing iron sheet (IP), stainless steel mesh (SSM), carbon cloth (CC), carbon brush (CB), and nickel foam (NF)) as cathodes. The results revealed that each MFC system performed differently in terms of carbon source degradation, uranium removal, and electricity production. In terms of carbon source degradation, CB-MFC showed the best performance. The best uranium removal method was NF-MFC, and the best electricity production method was carbon-based cathode MFC. Five MFC systems demonstrated stable performance and consistent difference over five cycles, with CC-MFC outperforming the others. Furthermore, SEM and XPS characterization of the cathode materials before and after the experiment revealed that a significant amount of U(IV) was generated during the uranium removal process, indicating that uranium ions were primarily removed by electrochemical reduction precipitation. This study confirmed that abiotic cathode MFC had a high UCW removal potential and served as a good guideline for obtaining the best cathode for MFC.