Abstract:Adsorption methods are widely used in the treatment of uranium-containing wastewater, and biochar is used to make adsorbents due to its advantages of low cost, no secondary pollution, good stability, and large specific surface area. Several scholars have used walnut shells to prepare biochar for removing pollutants from water bodies. However, due to limited binding sites and slow adsorption rates, the adsorption capacity of raw biochar for radionuclides is limited. Therefore, composite material technology is required to enhance the adsorption capacity of biochar. This study utilized zero-valent manganese (nZVMn) with strong reducing properties to modify walnut shell biochar, preparing biochar-loaded nano-zero-valent manganese composite material (nZVMn-WBC). The uranium removal capacity of the composite material was investigated through experimental conditions. The uranium removal mechanism of the composite material was explored using adsorption kinetics, reduction kinetics, isothermal adsorption models, and modern characterization techniques such as SEM, XPS, and XRD, leading to the following main conclusions. Under optimal experimental conditions of pH 5.5, material dosage of 0.01g, adsorption time of 90 min, initial uranium concentration of 300mg·L-1, and room temperature, the maximum adsorption capacity of nZVMn-WBC reached 473.48mg·g-1, indicating its promising application prospects for the efficient removal of U(Ⅵ）. Stability tests show that nZVMn-WBC has excellent anti-interference performance. The first four uranium removal performances are good, but the fifth uranium removal performance decreases, possibly due to material loss during the test and the destruction of surface functional groups by the resolving agent. In practical applications, this effect can be compensated for by increasing the dosage. The changes in the physical and chemical properties of nZVMn-WBC before and after uranium adsorption were analyzed, and it was concluded that the uranium removal process mainly relied on chemical adsorption, which was a surface monolayer adsorption method accompanied by a reduction process, as well as electrostatic adsorption and surface complexation between Mn-OH and U(Ⅵ）.
