Immobilization of heavy metals by polynuclear aluminium and montmorillonite compounds

Modified montmorillonite compounds and polynuclear Al-13 were investigated as potential binding agents to reduce heavy metal solubility in soil solutions. The experiments were carried out in batch reactors with solutions/suspensions containing montmorillonite, polynuclear Al-13, Al-montmorillonite, or Al-13-montmorillonite. Nickel, copper, and zinc were adsorbed specifically on Al-montmorillonite and Al-13-montmorillonite. These three metals were also incorporated in the interlayers of Al-montmorillonite and Al-13-montmorillonite during the aging processes. Al-montmorillonite was most effective in the pH ranges 6-8 for nickel and zinc, 4-6 for copper, and 7-9 for cadmium. The immobilization of the heavy metal cations by Al-13-montmorillonite was restricted to a smaller pH range. The polynuclear Ails decreased the dissolved concentrations of nickel, copper, and zinc by specific binding from pH 6.1 to pH 7.5. In the pH range 5.8-6.1 nickel, copper, zinc, cadmium, and lead formed soluble complexes with Al-13, which remained dissolved during 30 weeks. In summary, the four binding agents were found to immobilize nickel, copper, zinc, and cadmium, whereas the effect on the solubility of lead was rather small. Therefore, the aluminium based binding agents may be used for the gentle remediation of soils polluted by nickel, copper, zinc, or cadmium.