Phytofiltration of hazardous metal ions by alfalfa: a study of calcium and magnesium interferences

Previous batch laboratory experiments performed to determine the potential ability of seven different varieties of Medicago sativa (Alfalfa, African variety) revealed that the shoots tissue-derived population was able to efficiently bind copper(II) and nickel(II) from aqueous solutions. Batch laboratory interference studies were performed with various calcium and magnesium concentrations (0.1 mM-1 M) in order to ascertain the effects of these ions on the heavy metal binding ability of African alfalfa shoots. Results from these studies have shown that calcium and magnesium did not seriously reduce the binding of copper(II), lead(II), to African alfalfa shoot tissues. However, high concentrations of calcium and magnesium, to some extent, reduced chromium(III), cadmium(II), nickel(II), and zinc(II) binding to African shoot tissues. In addition, all these experiments were repeated maintaining constant ionic strength, and similar results were obtained. Interference studies were also conducted in order to determine the effects of hard cations under flow conditions with silica immobilized African alfalfa shoots. Column experiments under flow conditions produced similar results than batch laboratory experiments. The information obtained from these studies will be useful for an innovative method to remove and recover heavy metal ions from contaminated waters. (C) 1997 Elsevier Science B.V.