Interaction of Iron Chelating Agents with Clay Minerals

摘要

Organic ligands play an important role in metal transport and availability in soils. However, their interaction with the solid phase of soils has not been sufficiently investigated. Two efficient Fe chelators were investigated in this study, as free ligands as well as Fe complexes: (i) the microbial siderophore ferrioxamine B (desferrioxamine B [DFOB] and ferrioxamine B [FOB], respectively); (ii) the synthetic chelating agent ethylenediamine di-o-hydroxyphenylacetic acid (EDDHA and FeEDDHA, respectively). Batch experiments were conducted to characterize their adsorption to Ca- and Na-montmorillonite as well as to Fe-montmorillonite (for EDDHA and FeEDDHA) and Ca-kaolinite. Kinetics of adsorption, equilibrium adsorption isotherms, and effects of pH on adsorption were measured. Adsorption of DFOB and FOB to montmorillonite was rapid and adsorption isotherms indicated high affinity. The type of saturating cation affected the adsorption of DFOB but not that of FOB. Significant hysteresis between adsorption and desorption was exhibited. The effect of Ca2+ in solution on desorption compared with that of Na+, was found to vary with their solution concentrations. Ethylenediamine di-o-hydroxyphenylacetic acid adsorption to montmorillonite exhibited a linear adsorption isotherm and significantly higher affinity than that of FeEDDHA. The adsorption decreased significantly with the following order of saturating cation: Ca2+ > Fe3+ > Na+. Adsorption of all examined substances to kaolinite was extremely low. Adsorption mechanisms of DFOB and EDDHA and their Fe complexes to clays and the environmental implications are discussed.