Phytofiltration potential of saltbush (Atriplex canescens) to clean up heavy metal contaminated waters.

摘要

Heavy metals such as cadmium, copper, chromium, lead and zinc enter into bodies of water mainly from industrial processes. Once into the water, heavy metals might be absorbed and bioaccumulated by plants and animals, eventually becoming available for human consumption. Traditional remediation methods are costly and might be associated with health risks. Because of this, authorities and researchers are trying to improve current water cleanup techniques. Phytofiltration has been found to be one of the most promising techniques for metal removal from polluted water. This research investigated the phytofiltration potential of stems, leaves, and flowers of saltbush plant to clean up Cd(II), Cr(III), Cr(VI), Cu(II), Pb(II), and Zn(II) from aqueous solutions. pH profile, metal adsorption capacity, time dependence, adsorption isotherm, effect of hard cations, single and multimetal adsorption, and metal stripping studies were performed. Chemical modification of carboxyl and ester groups on the native biomass, in addition to spectroscopic studies, were performed to investigate the binding mechanism and the functional groups that play the major role in the biosorption of the studied metals. Also, the performance of the silica-immobilized saltbush biomass was studied under flow conditions. The results demonstrated that the binding of Cd(II), Cr(III), Cu(II), Pb(II), and Zn(II) increased as pH increased from 2.0 to 6.0, with the highest percentage bound in the pH range of 4.0 to 6.0. The highest percentage bound by the native biomass was in the range of 74-81% for Cd, 91-98%, for Cr(III) 48-89% for Cu, 89-94% for Pb, and 65-73% for Zn. Compared to the native, the esterified biomass bound less metal. The hydrolyzed biomass had a binding capacity that was about 50% more compared to the native biomass for Cd(II), Cr(IIl), Cu(II), and Zn(II), while for Pb(II), it was at least 50% less. On the other hand, the Cr(VI) binding by both native and hydrolyzed biomasses decreased as pH increased, with a binding capacity lower than 0.4 mg/g. The binding of the studied metals with the biomass occurred within 10 minutes or less of reaction time. Adsorption isotherms showed that the Freundlich model fits the biosorption data better than the Langmuir model. The maximal monolayer capacities (KF) were found to be 5.79·10-2, 3.25·10-2, 1.14·10 -2 175.5·10-2, 10.5·10-2, and 6.3·10-2 mol/g for Cr(III), Cd(II), Cr(VI), Pb(II), Zn(II), and Cu(II), respectively. Thermodynamics parameters suggested that the biosorption of Cd(II), Cr(III), and Pb(II) follow an ionic exchange mechanism.;FTIR results confirmed that the chemical modification was successful and that the carboxyl functionality was the main group responsible for metal binding. (Abstract shortened by UMI.).