Effect of hydroxamate siderophores on Fe release and Pb(II) adsorption by goethite

Hydroxamate siderophores are biologically-synthesized, Fe(III)-specific lig ands which are common in soil environments. In this paper, we report an inv estigation of their adsorption by the iron oxyhydroxide, goethite; their in fluence on goethite dissolution kinetics; and their ability to affect Pb(II ) adsorption by the goethite surface. The siderophores used were desferriox amine B (DFO-B), a fungal siderophore, and desferrioxamine D-1, an acetyl d erivative of DFO-B (DFO-D1). Siderophore adsorption isotherms yielded maxim um surface concentrations of 1.5 (DFO-B) or 3.5 (DFO-D1) mu mol/g at pH 6.6 , whereas adsorption envelopes showed either cation-like (DFO-B) or ligand- like (DFO-D1) behavior. Above pH 8, the adsorbed concentrations of both sid erophores were similar. The dissolution rate of goethite in the presence of 240 mu M DFO-B or DFO-D1 was 0.02 or 0.17 mu mol/g hr, respectively. Compa rison of these results with related literature data. on the reactions betwe en goethite and acetohydroxamic acid, a monohydroxamate ligand, suggested t hat the three hydroxamate groups in DFO-D1 coordinate to Fe(III) surface si tes relatively independently. The results also demonstrated a significant d epleting effect of 240 mu M DFO-B or DFO-D1 on Pb(II) adsorption by goethit e at pH > 6.5, but there was no effect of adsorbed Pb(II) on the goethite d issolution rate. Copyright (C) 1999 Elsevier Science Ltd.