Cobalt adsorption on montmorillonite: investigating the influence of dehydration on adsorption properties

Cobalt is often released into the natural environment through industrial waste from alloying industries and acid mine drainage. Additionally, it exists as a radionuclide (⁶⁰Co) contributing to high-level radioactive waste. Smectite is a mineral that can be useful for adsorption and isolation of this element. In this investigation, Cheto-type montmorillonite (Cheto-MM), a source clay mineral of The Clay Mineral Society's (CMS) with well-established characteristics, was used as the primary material. The study aimed to assess how cobalt adsorption is affected by the adsorption site in the presence of interlayer water and after subsequent dehydration through heating. Adsorption kinetics and adsorption isotherm models were employed to explore the cobalt adsorption mechanism on Cheto-MM.

Results demonstrated notable variations in adsorption characteristics post-dehydration and subsequent shrinkage. Approximately 38% of cobalt was found to adsorb at the edge of Cheto-MM, while about 62% was adsorbed at the interlayer site, indicating the significant influence of the interlayer on cobalt adsorption in Cheto-MM. Adsorption kinetic models showed that the cobalt adsorption kinetics on Cheto-MM can be explained by a pseudo-second-order model. Moreover, isotherm experimental result was best represented by the Langmuir isotherm adsorption model. This study provides fundamental insights into cobalt adsorption characteristics on montmorillonite, emphasizing distinct adsorption sites. Such findings are instrumental in predicting smectite's adsorption behavior in high-level radioactive waste disposal sites in the future.