The binding energy between the interlayer cations and montmorillonite layers and its influence on Pb2 + adsorption

• Forces driving the cation exchange reaction were simulated by molecular simulation.
• Trivalent cations have a strong interaction with Mt layers than divalent cations.
• The effect of valence is stronger than radius relatively.
• The adsorption sequencing was Ca + Mt > Mg + Mt > Fe + Mt.

Raw montmorillonite (Mt) was cation-exchanged with Ca2 +, Mg2 +, and Fe3 +, and Pb2 + was tested for its adsorption on the exchanged Mt. The d-value and the cation exchange capacity (CEC) of Ca-exchanged montmorillonite (Ca2 + + Mt) were larger than those of Mg-exchanged montmorillonite (Mg2 + + Mt) and Fe-exchanged montmorillonite (Fe3 + + Mt). The Pb2 + adsorption on the homoionic Mt was fast and the amount of Pb2 + adsorption followed the order of Ca2 + + Mt > Mg2 + + Mt > Fe3 + + Mt. Simulation of Pb2 + adsorption on the Mt revealed a much larger energy drop when Pb2 + is substituting for Ca2 + in comparison to Pb2 + exchanging for Fe3 +.