Zwitterionic-surfactant modified LAPONITE®s for removal of ions (Cs+, Sr2+ and Co2+) from aqueous solutions as a sustainable recovery method for radionuclides from aqueous wastes

Abstract

The synthesis of zwitterionic-surfactant modified LAPONITE®s (LAP-CBs) was investigated as a function of the surfactant loading in order to obtain a suitable adsorbent for the removal of Co²⁺, Sr²⁺ and Cs⁺ ions from aqueous solutions. The proper adsorption of surfactant was characterized by several techniques that emphasized the modification of the surfactant distribution between the interlayer space and the surface of LAPONITE® (LAP), with increasing loading of surfactant. The organophilic character of the obtained LAP-CBs strongly affected their affinity for the targeted contaminants. The adsorption of Sr²⁺ was lower on LAP-CBs in comparison to that on LAP, while the adsorption of Co²⁺ and Cs⁺ was strongly improved. The competition between Sr²⁺ and Cs⁺ was important for LAP-CBs adsorption, whereas no competition was found when using LAP, indicating that the adsorption mechanism differed depending on the adsorbent. The desorption of contaminants was performed in various solutions and confirmed these mechanisms. Whereas Cs⁺ and Sr²⁺ were adsorbed through cation exchange onto LAP-CBs, as highlighted by a significant desorption in saline solution, the desorption of Co²⁺ from LAP-CBs was very poor whatever the composition of the release solution, indicating adsorption by complexation. Finally, increasing the load of surfactant decreased the adsorption capacity of the adsorbent for all of the investigated contaminants. The arrangement of the surfactant, within the interlayer space or on the surface of LAP, was therefore a critical factor when considering the potential of this material to durably remove radionuclides from low-level radioactive wastewaters.