Construction of dopamine supported Mg(Ca)Al layered double hydroxides with enhanced adsorption properties for uranium.

A novel dopamine-supported Mg(Ca)Al layered double hydroxide composite was synthesized by co-precipitation method. The existence of Ca and dopamine could promote the capture of uranium on the layered double hydroxides. In batch experiments, the composite exhibited good uranium removal performance, including high adsorption capacity (687.3 mg/g), strong anti-interference and good reusability (the removal percentage was still higher than 90 % after five cycles). At low initial uranium concentration, the uranium removal percentage on the composite exceeded 99.7 % and the residual concentration of uranium in the solution was <0.03 mg/L, reaching the limited standard of the World Health Organization. The studies of adsorption kinetics and isotherm indicated that the uranium adsorption behavior on the composite conformed to the pseudo-second-order kinetic and Langmuir isotherm models, suggesting that the process was a monolayer adsorption dominated by chemical adsorption. Furthermore, the high-efficiency uranium adsorption on the Mg(Ca)Al layered double hydroxide was mainly attributed to the strong complexation between the active sites (-OH and -NH) and uranium, the precipitation of interlayer intercalation ions (CO and OH) to uranium and the ion exchange of Ca to uranium. Due to these advantages, the dopamine-supported Mg(Ca)Al layered double hydroxide composite is expected to be used as fine adsorbent to remove uranium from wastewater.