X-Ray Absorption Spectroscopic Evidence for the Formation of Pb(Ⅱ) Inner-Sphere Adsorption Complexes and Precipitates at the Alkaline Soil-Water Interface
HU Ning-jing1, 2, LUO Yong-ming2*, HUANG Peng3, HU Tian-dou4, XIE Ya-ning4, WU Zi-yu4, SHI Xue-fa1
1. First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China 2. Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China 3. Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266072, China 4. Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100039, China
Abstract：Adsorption mechanisms of Pb on soil with high CaCO3 content were investigated by combined batch sorption and X-ray absorption fine structure (XAFS). Date from the batch equilibrium studies showed that Pb sorption was nonlinear and was well fitted to Langmiur isotherm. The XAFS data indicated that Pb could be adsorbed via the inner-sphere complex, the precipitation of calcium carbonate containing Pb (PbCaCO3), and outer-sphere Pb sorption complex. The formations of inner-sphere complexes and PbCaCO3 implied strong metal interactions with the surfaces the mechanistic reason for the affinity of Pb for CaCO3 as observed in macroscopic studies. At low metal concentration, 500 mg·L-1 of initial Pb, radial distance of the first-shell Pb—O (R1) was 0.169 2 nm, however, at 1 000 mg·L-1 of initial Pb, the R1 was 0.166 8 nm. These revealed that the percentage of inner-sphere complexes increased when the initial Pb was increased from 500 to 1 000 mg·L-1.
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