Interaction of metal ions with montmorillonite and vermiculite

The behaviour of montmorillonite and vermiculite toward adsorption of Cd2+, Pb2+, Zn2+, Mn2+, Cu2+ and Zn2+ was compared. In general, the uptake of metal ions on both clay minerals decreased with decreasing of pH and in the presence of ligands forming stable complexes. Metal ion retention on montmorillonite was less affected by the competition of sodium ions at high ionic strengths with respect to vermiculite. On the other hand, the total capacity of vermiculite with respect to the investigated metal ions was found to be much higher than that of montmorillonite, whereas the order of affinity of the metal ions for the two clay minerals was similar, i.e.: Pb2+ = Cd2+ < Cu2+ < Zn2+ < Mn2+ < Ni2+ for montmorillonite and Pb2+ < Cu2+ < Cd2+ < Zn2+ < Ni2+ < Mn2+ for vermiculite. The similarities and differences between the two clay minerals were also investigated by principal component analysis and hierarchical cluster analysis. The results of this study may be used to predict the uptake efficiency of these adsorbents in view of their application for the removal of metal ions from contaminated effluents. The choice of vermiculite or montmorillonite for the uptake of metal ions or other elements will depend on the composition of the effluent to be treated.