Wednesday, November 15, 2006

Copper Sorption on Smectite Clays in the Presence of Organic Acids.

Leah Baugher, Univ. of Idaho, Dept. of PSES, Moscow, ID 83844-2339

Processes affecting the fate and transport of trace metals in the environment are controlled by sorption to solid phases. Determining sorption mechanisms in natural samples is difficult because of the heterogeneity of the solid phase, as well as the various species present in the solution. Thus, to better understand speciation in soils it is necessary to study simplified systems in which primary interactions occurring in the environment can be elucidated. In this project we are investigating the reaction mechanisms that occur in ternary systems consisting of smectite minerals, organic acids, and the trace metal Cu using batch studies and X-ray adsorption spectroscopy (XAS). Variables in the batch studies included Cu concentration, pH and ionic strength. X-ray adsorption spectroscopy was used to evaluate the molecular environment of select samples from the batch studies. Results from the isotherm and pH studies show decreased Cu sorption with all of the organic acids. The inhibited adsorption was most pronounced at lower ionic strength. The greatest decrease was observed using citric acid, while acetate appeared to have minimal effect. Preliminary interpretation of XAS results shows a unique Cu complex in the presence of citrate, while spectra from the Cu-acetate system are similar to Cu sorption with no ligand present. Further analysis of the XAS data will provide us with insights into how the various ligands impact adsorption mechanisms. Mechanistic understanding of trace metal behavior in soils will allow for improved models to be developed that explain processes regulating metal availability for uptake and transport.