Immobilization of zinc and cadmium by montmorillonite compounds: Effects of aging and subsequent acidification

The addition of aluminum treated montmorillonites as binding agents that im mobilize heavy metals is an innovative approach for the remediation of arab le soils polluted with heavy metals. We investigated the influence of aging and subsequent sudden acidification on the binding of zinc and cadmium by montmorillonite, Al-montmorillonite and Al-13-montmorillonite, The addition of HCl led to a drop in pH and a partial remobilization of the sorbed heav y metals. Al-montmorillonite and Al-13-montmorillonite exhibited a higher p H buffer capacity than montmorillonite. With increasing aging, sorption of zinc on Al-montmorillonite and Al-13-montmorillonite increased, probably du e to a partial incorporation in the aluminum hydroxide lattice. Sorption a nd desorption were hysteretic with respect to pH, i.e., desorption required lower pH Values than adsorption to reach the same state of metal partition ing between solid phase and solution. In addition, these minerals enhance t he pH buffer capacity of the soil. The results suggest that Al-montmorillon ite and Al-13-montmorillonite are suitable minerals to be used as binding a gents for the gentle immobilization of heavy metals in polluted soils.