A spectroscopic study of the effects of a microbial siderophore on Pb adsorption to kaolinite

作者：Mishra Bhoopesh; Haack Elizabeth A; Maurice Patricia A^*; Bunker Bruce A

来源：Chemical Geology, 2010, 275(3-4): 199-207.

DOI：10.1016/j.chemgeo.2010.05.009

• Pb
• Kaolinite
• Siderophore
• Desferrioxamine-B
• EXAFS
• XANES
• Ternary complex
• Type A ternary complex
• Adsorption
• Precipitation

Batch adsorption experiments were combined with X-ray Absorption Spectroscopy (XAS) analysis to determine the mechanism(s) whereby the microbial trihydroxamate siderophore ligand desferrioxamine-B (DFO-B) affects Pb sorption to kaolinite at pH 4, 6, and 7.5 (in 0.1 M NaCLO4, 22 degrees C; Pb:DFO-B ratio 120:240 mu M). In the absence of DFO-B, Pb adsorbs only slightly to kaolinite at pH 4, by a combination of inner- and outer-sphere complexation. Adsorption increases at pH 6, and sorption (adsorption/surface precipitation) further increases at pH 7.5. At pH 4. DFO-B does not bind Pb in solution appreciably, and the Pb adsorption mechanism(s) is unchanged by the presence of DFO-B. At pH 6, DFO-B slightly enhances Pb adsorption, due at least in part to formation of a DFO-B-Pb-kaolinite type A ternary surface complex. At pH 7.5, DFO-B decreases Pb sorption and Pb adsorption is dominated by a DFO-B-Pb-kaolinite type A ternary surface complex. Although XAS and thermodynamic speciation modeling indicate that Pb is bound by multiple DFO-B functional groups in solution at pH 7.5, the DFO-B-Pb-kaolinite surface complex appears to involve only a single hydroxamate group. This study thus demonstrates that the detailed structure of a ternary surface complex cannot necessarily be predicted from the structure of the solution organic-metal complex.

• 出版日期2010-8