β-Cyclodextrin-loaded minerals as novel sorbents for enhanced adsorption of Cd2+ and Pb2+ from aqueous solutions.

The use of minerals to capture heavy metal pollution is limited by their capacity. Here, β-cyclodextrin (β-CD) with a good ability to capture heavy metals is loaded onto the surface of zeolite and vermiculite to adsorb lead and cadmium ions. Using epichlorohydrin (EPI) as a crosslinking agent, β-CD is loaded onto zeolite and vermiculite, as confirmed by a characterization analysis. Isothermal adsorption of Cd2+ and Pb2+ by the loaded minerals is tested at different concentrations, while contact time, pH, and kinetic and thermodynamic characteristics of the adsorption processes are analyzed. The amount of β-CD and crosslinker loaded onto a unit mass of zeolite is higher than that of vermiculite due to the unique porous structure of the zeolite surface. After β-CD loading, the adsorption saturation of zeolite for Cd2+ and Pb2+ are 93.06 and 175.25 mg/g, respectively. The adsorption saturation of Cd2+ and Pd2+ by β-CD-loaded vermiculite is 68.65 and 126.35 mg/g, respectively. The mechanism study revealed that the adsorption process of lead and cadmium ions by β-CD-loaded minerals was combined by diffusional movement with a chemical exchange of ionizable protons or cations, as well as by chemical bonding among heavy metal ions and functional groups (-OH, -COOH and CO).