Monday, November 13, 2006

Influence of Inorganic Ligands on the Adsorption of 2-Ketogluconate.

Michael Essington, 2506 E.J. Chapman Drive, Ag Campus, University of Tennessee, Univervisy of Tennessee, Biosystems Eng & Soil Sci., Knoxville, TN 37996-4531 and Robert Anderson, Biosystems Eng. & Soil Science, Univ. of Tenn., 2506 E.J. Chapman Dr., Knoxville, TN 37996-4531.

The low-molecular mass organic acid anion 2-ketogluconate (kG) is produced via microbial activity in rhizosphere soils and may exist in significant and sustained concentrations. One of the mechanisms by which this organic anion may influence the chemistry of soil systems is through adsorption by constant-potential minerals. This study examines the adsorption of kG onto gibbsite, kaolinite, and goethite in the presence or absence of phosphate (PO4), arsenate (AsO4), and sulfate (SO4) as a function of pH and ionic strength. The adsorption of kG is a function of solution pH and independent of ionic strength. Further, kG  adsorption was decreased at all pH values in the presence of PO4 and AsO4, but was not significantly affected by the presence of SO4. These findings strongly suggest that kG adsorption occurs via chemisorption mechanisms. The addition of kG to gibbsite containing preadsorbed PO4 did not result in PO4 displacement, regardless of the concentration of kG. However, the addition of PO4 to gibbsite containing preadsorbed kG resulted in an adsorption envelope that was similar to that obtained when PO4 and kG were added simultaneously. Ligand adsorption was modeled using the adsorption edge data and the CD-MUSIC model. The kG adsorption data was described by the formation of mononuclear-monodentate and binuclear-bidentate surface complexes. The chemical models developed to describe ligand adsorption in single-ligand (gibbsite) systems were employed to predict ligand retention in the kaolinite and multi-ligand systems. In general, the predicted adsorption of kG, PO4, AsO4, and SO4 as a function of pH was adequately described. The findings of this study indicate that kG is specifically retained by common soil minerals and may impact the phytoavailability of PO4 and other specifically-retained ligands in the rhizosphere.

Handout (.pdf format, 849.0 kb)