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 chela te 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) an the adsorption of Cu, Zn, and Cd on Na-montmorillonite and kaolinite. In the absence of heavy met als, DFOB was adsorbed onto montmorillonite much stranger than onto kaolini te. In montmorillonite suspensions, heavy metal sorption was enhanced by DF OB due to electrostatic interactions. Only at high pH values, a mobilizing effect of DFOB was observed for Zn and Cd. In kaolinite suspensions, DFOB d rastically diminished heavy metal sorption. Surface complexation modeling r evealed that;the different effects of DFOB on the metal sorption by kaolini te and montmorillonite can be explained by the large difference in their pe rmanent negative surface charge responsible for the attraction of the posit ively charged metal DFOB complexes. The effect of DFOB on the adsorption of heavy metal ions on montmorillonite and kaolinite decreased in the sequenc e Cu > Zn > Cd in accordance with complex stability constants.