Uptake of cesium by the hydroxysulfate green rust-modified composite aluminosilicate materials, mathematical modeling, and mechanisms

Abstract

The ecological hazards caused by the radioactive cesium (Cs) contaminants are long-standing and field-wide. In this study, the green rust (GR) was chemically formed and loaded onto the composite aluminosilicate materials (CAM) to enhance the adsorption capacities, environmental adaptability, and recyclability of CAM materials (GR-CAM) for Cs+ removal. The maximum monolayer adsorption capacities (mg/g) of GR-CAM for Cs+ adsorptions at pH of 2, 7, and 12 were 67.11, 104.93, and 129.03, respectively. The suitability of the pseudo-first-order kinetic model and Langmuir model for predicting Cs+ removal efficiencies and describing the isothermal fittings were observable and provable. Cs+ ions rebalanced the structural charge of GR-CAM by replacing some monovalent or divalent cations in mineral structures. The chemical loading of GR diversified the micromorphologies of CAM in different pH environments during the heterogeneous adsorption. The modification of GR strengthened the role of ion exchange in increasing the adsorption of Cs+ into GR-CAM. The excellent immobilization of Cs+ ions in GR-CAM in an alkaline environment was attributed to the formation of composite geopolymers. The different pH environments induced different adsorption mechanisms of GR-CAM towards Cs+ ions due to the sandwich structure of GR-CAM such as ion exchange, inner transferring, chemisorption, and co-precipitation.