Removal of U(VI) from wastewater by sulfhydryl-functionalized biomass carbon supported nano-zero-valent iron through synergistic effect of adsorption and reduction

• Sulfhydryl-functionalized magnetic biochar (NZVI-BC-SH) was prepared from grapefruit peel by several methods, ensuring a win-win effect of restoring the environment while treating agricultural and forestry waste. • The adsorption capacity of NZVI-BC-SH for uranium ion was 273.0 mg/g, which has a high adsorption capacity among the materials reported in the known literature. • The analysis of the adsorption mechanism shows that the removal of uranyl ions by NZVI-BC-SH is mainly a synergistic effect of adsorption and reduction. Biomass carbon adsorption materials have the advantages of a simple preparation process, mild synthesis conditions, and easy surface modification, etc. In this study, biomass carbon was prepared from discarded grapefruit peel, and modified by 3-mercaptopropyltriethoxysilane. Nanometer zero-valent iron, obtained by the reduction between ferrous sulfate and sodium borohydride, was loaded on the modified biomass carbon. Using the foregoing procedure, magnetic sulfhydryl-functionalized biomass carbon (NZVI-BC-SH) was produced to treat uranium-contaminated wastewater. SEM, TEM, BET, FT-IR, XRD, VSM, and XPS were made on NZVI-BC-SH to investigate its physical and chemical properties. NZVI-BC-SH had a specific surface area of 200.00 m 2 /g, average pore size of 7.38 nm, and pore volume of 0.037 cm 3 /g according to the results. The adsorption capacity of NZVI-BC-SH for uranium ion was 273.0 mg/g under the optimized condition ( C 0 = 35.0 mg/L, pH = 7, t = 540 min, m/V = 125 mg/L and T = 35 °C). The isotherm of adsorption of NZVI-BC-SH for uranyl ions follows the Langmuir isotherm, and the kinetics of adsorption adhere to the semi kinetic parameters. The thermodynamic characteristics (ΔG < 0, ΔS > 0, ΔH > 0) demonstrate that NZVI-BC-SH adsorption to uranyl ions is a spontaneous endothermic reaction. Based on XPS measurements, NZVI-BC-SH removed the U(VI) by the synergistic action of adsorption and reduction. The adsorption process is mainly a surface complexation between U(VI) and the sulfhydryl and carboxyl groups on the surface of NZVI-BC-SH. The reduction process is the conversion of U(VI) to U(IV) via the reducibility of zero-valent iron. The findings indicate that the NZVI-BC-SH material would be a superb adsorbent and has a bright future in the treatment of uranium-containing wastewater.