Acid activation of bentonite: structural transformation and sorption performance for uranium, cesium, and strontium

Acid activation of bentonite clay is an effective approach for producing porous sorbents and acid catalysts. In this study, the influence of acid treatment on the structure and sorption properties of montmorillonite (MMT) was examined. Natural MMT was treated with hydrochloric and nitric acids of different concentrations under various thermal conditions. The samples were characterized by XRD, SEM, EPMA, low-temperature N₂ adsorption–desorption, and potentiometric titration. Acid activation resulted in the replacement of interlayer cations with protons and partial leaching of Mg²⁺, Fe³⁺, and Al³⁺ from the lattice, leading to an increase in specific surface area from 89 m²/g to 287 m²/g. The uranium sorption capacity increased from 56 µmol/g to 127 µmol/g due to the formation of new sites for sorption. In contrast, strontium and cesium sorption decreased, except for nitric acid treatment, which enhanced Cs⁺ uptake to 310 µmol/g. The Langmuir model provided the best fit to the sorption data, indicating a predominant monolayer chemisorption mechanism. The type and strength of acid determine the structural stability and selectivity of the sorbent. Mild activation, especially with nitric acid, preserves the clay framework and improves its suitability for uranium removal and further modification in environmental remediation applications.