Effect\nof Fulvic Acid Surface Coatings on Plutonium Sorption and Desorption\nKinetics on Goethite

Abstract

The\nrates and extent of plutonium (Pu) sorption and desorption onto mineral\nsurfaces are important parameters for predicting Pu mobility in subsurface\nenvironments. The presence of natural organic matter, such as fulvic\nacid (FA), may influence these parameters. We investigated the effects\nof FA on Pu­(IV) sorption/desorption onto goethite in two scenarios:\nwhen FA was (1) initially present in solution or (2) found as organic\ncoatings on the mineral surface. A low pH was used to maximize FA\ncoatings on goethite. Experiments were combined with kinetic modeling\nand speciation calculations to interpret variations in Pu sorption\nrates in the presence of FA. Our results indicate that FA can change\nthe rates and extent of Pu sorption onto goethite at pH 4. Differences\nin the kinetics of Pu sorption were observed as a function of the\nconcentration and initial form of FA. The fraction of desorbed Pu\ndecreased in the presence of FA, indicating that organic matter can\nstabilize sorbed Pu on goethite. These results suggest that ternary\nPu–FA–mineral complexes could enhance colloid-facilitated\nPu transport. However, more representative natural conditions need\nto be investigated to quantify the relevance of these findings.