A Spectroscopic Study of Lead (Pb(II)) and Siderophore Sorption to Montmorillonite

Solution analysis through the use of inductively coupled plasma optical emission spectroscopy and ultraviolet-visible spectroscopy was coupled with solids analysis by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy to investigate the sorption characteristics of Pb(II) and desferrioxamine B (DFOB) on montmorillonite. Attenuated total reflectance Ì¢‰âÂ' FTIR (ATR-FTIR) and speciation modeling of the system were also conducted. Between pH 4 and 8, Pb(II) and DFOB were found to enhance one another's sorption to montmorillonite. Maximum sorption of Pb(II) in the presence of DFOB was ~118 Ì_å_mol/g; maximum sorption of DFOB in the presence of Pb(II) was ~140Ì_å_mol/g. Sorption density of Pb(II) on montmorillonite in the presence of DFOB increased from ~15% of initial Pb(II) at pH 3 to ~ 90% at pH 7.5. Modeling and FTIR showed that the presence of DFOB also decreased the formation of Pb-bearing precipitates. XRD showed the potential for coabsorption of a Pb+DFOB complex(es) in the interlayer of montmorillonite at pH 5.5 and 7.5 due to changes in the interlayer spacings. The presence of a Pb+DFOB complex(es) was further implicated by the emergence of a new FTIR peak in the presence of both Pb(II) and DFOB on self-supporting clay films at 1577 cm-1; this peak was also present under aqueous conditions in the ATR-FTIR study at 1570 cm-1. In both cases, this peak was attributed to the shift of the hydroxamate C=O stretch located at1607 cm-1 in aqueous DFO-B. Shifts of the AlFe3+OH and AlMgOH bends under FTIR and ATR-FTIR in the presence of DFOB and Pb+DFOB also point to interlayer absorption. Throughout this study, FTIR and ATR-FTIR have proven to be useful techniques for studying metal-siderophore interactions on clays. For the Pb+DFOB complex, coabsorption in the interlayer is likely the most common sorption mechanism at pH 5.5 and 7.5 under air-dried and aqueous conditions, although its precise structure cannot be determined from the methods used.