Geochemical dispersion of heavy metals via organic complexing: A laboratory study of copper,lead, zinc,and nickel behaviour at a simulated sediment-water boundary

Data are presented in this study from laboratory model experiments describing the behaviour of Cu, Pb, Zn and Ni at a simulated sediment-water boundary. The interactions involved are sorption by kaolin and by bentonite, organic complexing in solution by fulvic acid and by humic acid, carbonate reactions, hydrolysis, and desorption of the cations from a clay-bound phase and from their metal hydroxides by the organic acids. The organic acids increase the solubility of Cu, Zn and Ni in the presence of clay. The Pb solubility is variable and can even decrease, particularly at acidic pH, with organic complexing likely due to colloidal coagulation. Both Zn and Ni are influenced by hydrolysis at basic pH. When carbonate was added to the metal-organic acid-clay mixtures, a further decrease in solubility was observed for Ni and, to a lesser extent, for Zn. The organic acids prove capable of remobilizing Cu, Pb, Zn and Ni from the solid phases examined. However, there is a general kinetic hindrance to the desorption particularly at basic pH. Copper desorption appears to be the most kinetically hindered. Conclusions pertinent to the geochemical dispersion of these metals are drawn.