Analysis of Cadmium Retention Mechanisms by a Smectite Clay in the Presence of Carbonates

Cadmium (Cd) is a toxic heavy metal with very low permissible exposure limits and is, thus, a very dangerous pollutant for the environment and public health and is considered by the World Health Organisation as one of the ten chemicals of major public concern. Adsorption onto solid phases and (co)precipitation processes are the most powerful mechanisms to retain pollutants and limit their migration; thus, the understanding of these processes is fundamental for assessing the risks of their presence in the environment. In this study, the immobilisation of Cd by smectite clay has been investigated by batch sorption tests, and the experimental data were interpreted with a thermodynamic model, including cation exchange and surface complexation processes. The model can describe the adsorption of Cd in smectite under a wide range of experimental conditions (pH, ionic strength, and Cd concentration). Under the conditions analysed in this study, the precipitation of otavite (CdCO3) is shown to have a limited contribution to Cd immobilisation.

Automated summary

Cadmium is a highly toxic heavy metal pollutant with strict exposure limits. This study investigated the immobilization of cadmium by smectite clay through batch sorption tests and utilized a thermodynamic model to interpret the experimental data. The results showed that the precipitation of otavite (CdCO3) has a limited contribution to the immobilization of cadmium under the studied conditions.