Adsorption of Zn2+ and Cu2+ onto sulphate and phosphate-modified bentonite

► Phosphate is adsorbed onto bentonite by chemisorption mechanism. ► There is the formation of diprotonated monodentate mononuclear complex between phosphate and bentonite. ► Metal ions are adsorbed onto phosphate-modified bentonite by ion-exchange mechanism. ► Sulphates are held onto bentonite by physisorption mechanism.