PHYTOFILTRATION OF HAZARDOUS CADMIUM, CHROMIUM, LEAD AND ZINC IONS BYBIOMASS OF MEDICAGO-SATIVA (ALFALFA)

Previous laboratory batch experiments of Medicago sativa (Alfalfa) ind icated that the African shoots population had an appreciable ability t o bind copper(II) and nickel(II) ions from aqueous solution. Batch lab oratory pH profile, time dependency and capacity experiments were perf ormed to determine the binding ability of the African shoots for cadmi um(II), chromium(III), chromium(VI), lead(II), and zinc(II). Batch pH profile experiments for the mentioned ions indicated that the optimum pH for metal binding is approximately 5.0. Time dependency experiments for all the metals studied showed that metal binding to the African a lfalfa shoots occurred within 5 min. Binding capacity experiments reve aled the following amounts of metal ions bound per gram of biomass: 7. 1 mg Cd(II), 7.7 mg Cr(III), 43 mg Pb(II), and 4.9 mg Zn(II). However, no binding occurred for chromium(VI). Nearly all of the metals studie d were recoverable by treatment with 0.1 M HCl. Column experiments wer e performed to study the binding of Cd(II), Cr(III), Cr(VI), Pb(II) an d Zn(II) to silica-immobilized African alfalfa shoots under flow condi tions. These experiments showed that the silica immobilized African al falfa shoots were effective for removing metal ions from solution, and over 90% of the bound Pb(II), Cu(II), NI(II), and Zn(II), and over 70 %Cd(II), were recovered after treatment with 10 bed volumes of 0.1 M H Cl. The results from these studies will be useful for a novel phytofil tration technology to remove and recover heavy metal ions from aqueous solution. (C) 1998 Elsevier Science B.V.