Mechanism of chlorpheniramine adsorption on Ca-montmorillonite

► Montmorillonite could adsorb as much as 0.72 mmol g−1 of chlorpheniramine (CP). ► Both external and interlayer surfaces were available for CP uptake. ► Cation exchange was responsible for CP uptake as confirmed by cation desorption. ► Fast CP uptake indicated montmorillonite being a good sorbent for CP removal.