Influence of clay-solute interactions on aqueous heavy metal ion levels

The extent to which heavy metal ions (Cu, Pb, Zn, Cd) are removed from aqueous solution by clay suspensions (kaolinite, illite or montmorillonite) has been shown to vary with the nature of the clay, solution pH, concentration of competing cations, and the nature (and concentration) of any ligands present. The amount sorbed increases gradually with pH until the threshold value for formation of sparingly soluble hydroxy complexes is reached. The affinity order for divalent cations, and the nature of the sorption process also appear to vary with clay type.