Calcium-Aluminum bimetallic compound enhanced bentonite for uranium removal from water

[Background] The efficient and green removal of uranium from water holds significant strategic importance for the sustainable development of the future nuclear industry. [Purpose] This study aims to prepare a calcium-aluminum bimetallic compound modified bentonite composite material (CA-BTN) and investigate its uranium removal performance and adsorption mechanism. [Methods] CA-BTN was simply prepared through hydrothermal methods and its adsorption performance and mechanisms were analyzed using various modern characterization techniques and single-factor experiments. The effects of time, initial pH value, uranium concentration, temperature, ionic strength, and interfering ions on uranium adsorption were studied, and adsorption kinetics, isotherms, and thermodynamics were fitted. Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM/EDS), X-ray Diffraction Spectroscopy (XRD), hydrophilicity, X-ray Photoelectron Spectroscopy (XPS), and Fourier Transform Infrared Spectroscopy (FTIR) were employed to characterize and analyze the adsorption behavior and mechanisms. [Results] The results indicate that the equilibrium adsorption capacity of uranium is approximately 74.82 mg∙g-1 at a pH of 4.0 and a temperature of 25°C. The adsorption capacity of CA-BTN for uranium increases with the initial pH value, initial U(VI) concentration, and temperature, while still maintaining good uranium removal performance even in the presence of interfering ions. Under the conditions of an initial uranium concentration of 10.00 mg/L, a pH of 4.0, and a temperature of 25°C, the uranium removal rate exceeds 98%. The adsorption behavior is a spontaneous monolayer chemisorption process, which can be described by the pseudo-second-order kinetics model and Langmuir fitting. Hydrophilicity measurements indicate that CA-BTN exhibits excellent hydrophilicity. XRD and SEM-EDS results reveal the crystalline structure and micro-morphology of bentonite and calcium-aluminum bimetallic compounds present in CA-BTN. The results from XPS and FTIR tests indicate that CA-BTN removes uranium through a coordination mechanism without undergoing redox reactions. [Conclusions] This study provides technical and theoretical references for the synthesis of bentonite-based adsorbent materials and their application in the removal of uranium from radioactive wastewater.