Uranyl separation from wastewater on the porous Fe-BC synthesized through coupling carbothermal reduction and ZnCl2 activation

Nano zero-valent iron (nZVI) has been widely reported to attract uranium (U(VI)) from wastewater through surface adsorption and reduction. However, surface oxidation and agglomeration of nZVI significantly limited the application of nZVI in removing U(VI) from wastewater. In this study, a novel porous nZVI/BC composite (Fe₁Zn₃-BC(900)) was synthesized via a one-step process coupling carbothermal reduction and ZnCl₂ activation. In this process, ferric chloride and zinc chloride were employed as the Fe and Zn precursors, while starch was utilized as the biochar precursor. Zn and Fe were formed in the carbothermal reduction process. The Zn was sacrificed through evaporation to increase the porosity, providing sufficient inner space for well-dispersing the nZVI, what could be wrapped and protected by the porous carbon. Besides, the galvanic cell between the nZVI-C interface was formed, accelerating the electron transfer for reduction of U(VI) into U(IV). As expected, the Fe₁Zn₃-BC(900) performed a high efficiency of 94.3% for separating the U(VI) in an initial concentration of 10 mg/L within 30 min, confirming the positive effect of ZnCl₂ sacrifice on enhancing separation of U(VI) onto the Fe₁Zn₃-BC(900). The high uranium removal efficiency can be attributed to the fact that the enhanced porosity resulting from Zn evaporation facilitates U(VI) adsorption. The reduction of U(VI) is further facilitated by the high dispersion of nZVI and the formation of Fe/C galvanic cell. Therefore, this work has developed a promising method to address the agglomeration of nZVI in the separation of U(VI) from wastewater, which provides a new idea for the subsequent efficient uranium removal.