Ultra-fast adsorption of radioactive-U(VI) and Cs(I) with high adsorption capacity towards CAA@MgAlFe spongy-like aerogel: Mechanism and application feasibility study

Abstract

Secure disposal of radioactive wastewater had aroused global concerns for human health and ecological environment. Uranium (U) and Cesium (Cs) were both typical radioactive elements detected in contaminated water bodies. In response to the environmental problem, a spongy-like aerogel adsorbent was firstly prepared for the removal of radioactive U(VI) and Cs(I) and potential application in sea water. MgAlFe layered double hydroxides (LDHs) were prepared by hydrothermal method, and were then gelated by freeze-drying technique to synthesize the calcium alginate aerogels doped with MgAlFe LDHs (CAA@MgAlFe). The prepared CAA@MgAlFe was a kind of porous sponge-like aerogel, on which the LDHs dispersed uniformly. Batch adsorption experiments presented that the adsorption of U(VI) and Cs(I) could reach the equilibrium rapidly in only 4 min and 3 min, respectively. This suggested the reduction of radioactive exposure during the treatment was at a high extent. The adsorption capacities of U(VI) and Cs(I) were as high as 533 and 58 mg/g, respectively. Furthermore, the adsorption isotherms showed that U(VI) and Cs(I) matched well with the Langmuir and Freundlich models, respectively. CAA@MgAlFe could be easily separated and compressed, and its application on sea water was proved to be feasible. The adsorption mechanism of CAA@MgAlFe towards U(VI) included complexation, ion exchange and reduction, while that of Cs(I) was electrostatic attraction.