Integrated Approaches of X-Ray Absorption Spectroscopic and Electron Microscopic Techniques on Zinc Speciation and Characterization in a Final Sewage Sludge Product
- Bojeong Kim *abc,
- Clément Levardde,
- Mitsuhiro Murayamafg,
- Gordon E. Browndh and
- Michael F. Hochellaab
- a Dep. of Geosciences, Virginia Tech, Blacksburg, VA 24061
b Institute for Critical Technology and Applied Science, Environmental Nanoscience and Technology Laboratory, Virginia Tech, Blacksburg, VA 24061
c Dep. of Earth and Environmental Science, College of Science and Technology, Temple University, Philadelphia, PA 19122
d Surface & Aqueous Geochemistry Group, Dep. of Geological & Environmental Sciences, Stanford Univ., Stanford, CA 94305-2115
e Aix-Marseille Université, CNRS, IRD, CEREGE UM34, 13545 Aix en Provence, France
f Dep. of Materials Science and Engineering, Virginia Tech, Blacksburg, VA 24061
g Institute for Critical Technology and Applied Science, Nanoscale Characterization and Fabrication Laboratory, Virginia Tech, Blacksburg, VA 24061
h Dep. of Photon Science and Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, MS 69, Menlo Park, CA 94025
Integration of complementary techniques can be powerful for the investigation of metal speciation and characterization in complex and heterogeneous environmental samples, such as sewage sludge products. In the present study, we combined analytical transmission electron microscopy (TEM)-based techniques with X-ray absorption spectroscopy (XAS) to identify and characterize nanocrystalline zinc sulfide (ZnS), considered to be the dominant Zn-containing phase in the final stage of sewage sludge material of a full-scale municipal wastewater treatment plant. We also developed sample preparation procedures to preserve the organic and sulfur-rich nature of sewage sludge matrices for microscopic and spectroscopic analyses. Analytical TEM results indicate individual ZnS nanocrystals to be in the size range of 2.5 to 7.5 nm in diameter, forming aggregates of a few hundred nanometers. Observed lattice spacings match sphalerite. The ratio of S to Zn for the ZnS nanocrystals is estimated to be 1.4, suggesting that S is present in excess. The XAS results on the Zn speciation in the bulk sludge material also support the TEM observation that approximately 80% of the total Zn has the local structure of a 3-nm ZnS nanoparticle reference material. Because sewage sludge is frequently used as a soil amendment on agricultural lands, future studies that investigate the oxidative dissolution rate of ZnS nanoparticles as a function of size and aggregation state and the change of Zn speciation during post sludge-processing and soil residency are warranted to help determine the bioavailability of sludge-born Zn in the soil environment.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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