Carbothermal Reduction for Preparing nZVI/BC to Extract Uranium: Insight into the Iron Species Dependent Uranium Adsorption Behavior

Abstract

Currently, a lot of uranium containing wastewater was generated in China, which required efficient treatment before being discharged. Immobilization of uranium on ZVI has attracted many concerns from researchers in the world wide. Surface oxidation and agglomeration limited the efficiency of nano zero-valent iron (nZVI) in remediation of uranium pollution. In this work, a green carbothermal reduction process was conducted to prepare environmental friendly biochar-supported ZVI (nZVI/BC). Immobilization behavior of uranium on nZVI/Cs, oxidized nZVI/Cs and Fe3O4 from wastewater were investigated. The iron salt was converted into iron oxides at 700 °C, further being reduced into nZVI in the presence of ferric chloride and ferric nitrate being carbonization of starch at 800 and 900 °C. The uranium adsorption capacities were different from the carbonization temperature and iron sources, which depended on the transformation of iron species. The maximum adsorption capacities of nano-flake FeCl/C (1:4–900) and nanoparticles FeN/C (1:4–900) for U(VI) were 34.82 and 55.14 mg/g. The removal efficiencies of FeCl/C (1:4–900) and nanoparticles FeN/C (1:4–900) were higher than that of 44% for C–Fe3O4. The SEM-mapping and XPS analysis of nZVI/Cs after U(VI) adsorption indicated that the immobilization of U(VI) was ascribed to simultaneous adsorption and reduction.