A high surface area mesoporous silica adsorbent for uranium uptake from lean uranium solutions: Template assisted preparation of mesoporous silica and its functionalization with iminodiacetic acid

Abstract

The feasibility of uranium recovery from lean uranium solutions (like seawater) having extremely low concentrations has been explored using an iminodiacetic acid (ImDAc) modified mesoporous silica (MPS) adsorbent (MPS-ImDAc). Foremost, synthesis of the MPS, its chemical modification using ImDAc and characterization were emphasized. The MPS was prepared by a template assisted preparative route, and the incorporation of ImDAc moiety to the MPS was accomplished through chemical functionalization. Subsequently, the adsorption efficacy of the MPS-ImDAc has been investigated as a function of the pH of the aqueous medium, kinetics of adsorption, uranium loading to the adsorbent, and the effect of interfering elements. Zeta potential analyses were also conducted to investigate the role of ImDAc functional groups and charges at different pH values, and the study suggested that the negatively charged acetate moiety is likely responsible for adsorption above pH.The adsorption has been modeled using pseudo-first and second order kinetic and the Langmuir adsorption isotherm models. Superior adsorption of uranium above pH 4, based on cation exchange mechanism that leads to an adsorption capacity of approximately 110 mg/g was observed. Adsorption characteristics have been investigated from a synthetic seawater composition with all possible interfering elements, and the study confirmed that though sodium is significantly present in sea water, it has negligible adsorption to ImDAc and thus pose no competition to uranium adsorption. Small pore size and massive surface area of MPS in combination with uranium selective ImDAc functional group offer excellent uranium adsorption.