Heavy Metal Sorption on Clay Minerals Affected by the Siderophore Desferrioxamine B

Siderophores are released by microorganisms to ensure their iron nutrition through the dissolution of iron(III) oxides. These compounds can also chelate divalent heavy metal ions and may therefore affect heavy metal sorption and mobility in soils. Using model systems, we studied the influence of the hydroxamate siderophore desferrioxamine B (DFOB) on the adsorption of Cu, Zn, and Cd on Na-montmorillonite and kaolinite. In the absence of heavy metals, DFOB was adsorbed onto montmorillonite much stronger than onto kaolinite. In montmorillonite suspensions, heavy metal sorption was enhanced by DFOB due to electrostatic interactions. Only at high pH values, a mobilizing effect of DFOB was observed for Zn and Cd. In kaolinite suspensions, DFOB drastically diminished heavy metal sorption. Surface complexation modeling revealed that the different effects of DFOB on the metal sorption by kaolinite and montmorillonite can be explained by the large difference in their permanent negative surface charge responsible for the attraction of the positively charged metal DFOB complexes. The effect of DFOB on the adsorption of heavy metal ions on montmorillonite and kaolinite decreased in the sequence Cu > Zn > Cd in accordance with complex stability constants.