Adsorption of Zn in Mixed Mineral Systems in the Presence of Ligands as a Function of pH.

Naturally occurring ligands in the soil environment play an important role in the adsorption of metals onto mineral surfaces. Ligands may enhance metal adsorption due to electrostatic interaction or by formation of ternary surface complexes or surface precipitates. Ligands may also hinder metal adsorption if the complexes formed with metals are poorly sorbed to the mineral surface.

 This study investigates the effect of organic and inorganic ligands (citrate, humic acid, siderophore and phosphate) on Zn adsorption in systems consisting of more than one mineral surface. The mixed mineral systems are composed of the following combinations of minerals: goethite and gibbsite, goethite and kaolinite, ferrihydrite and gibbsite, ferrihydrite and kaolinite. Adsorption is carried out in 50ml centrifuge tubes at a 1:1 metal to ligand molar ratio and pH range of 4.5 to 7.5. In addition, Spectroscopic techniques are utilized to characterize the adsorption mechanisms of Zn in the presence and absence of ligands at the various pH levels. This study should provide insight into the role of ligands in increasing or decreasing the adsorption of metals in mixed mineral systems.