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Roberts, D.R. and D.L. Sparks. Zinc speciation in a smelter-contaminated soil profile using bulk and microspectroscopic techniques. Environ. Sci. Tech.36: 1742-1750.
Environ. Sci. Technol., 36 (8), 1742 -1750, 2002. 10.1021/es015516c S0013-936X(01)05516-X
Web Release Date: March 8, 2002
Copyright © 2002 American Chemical Society
Zinc Speciation in a Smelter-Contaminated Soil Profile Using Bulk and Microspectroscopic Techniques
Darryl R. Roberts,* A. C. Scheinost, and D. L. Sparks
Department of Plant and Soil Sciences, University of Delaware, Newark, Delaware 19717, and Department of Environmental Sciences, ETHZ, Switzerland
Received for review May 7, 2001
Revised manuscript received December 14, 2001
Accepted December 19, 2001
A soil profile contaminated as a result of Zn smelting operations from the historic Palmerton, PA smelting facility was characterized using X-ray absorption fine structure spectroscopy (XAFS) and X-ray diffraction (XRD) as bulk techniques, coupled with electron microprobe (EM), and microfocused XAFS as microscopic techniques to determinethe chemical forms of Zn and elucidate its geochemical fate. The black, organic matter-rich topsoil contained 6200 mg/kg Zn and was strongly acidic (pH 3.2). Bulk XAFS revealed that about 2/3 of Zn was bound in franklinite and 1/3 bound in sphalerite. Both minerals may have been aerially deposited from the smelter operation. Microspectroscopy detected also minor amounts of Zn adsorbed to Fe and Mn (hydr)oxides as inner-sphere sorption complexes, which may have formed after weathering of the Zn minerals. About 10% of thetotal Zn in this sample could be easily leached. In contrast, the yellowish, loamy subsoil contained less Zn (890 mg/kg) and had a higher pH of 3.9. XAFS revealed that Zn was mostly bound to Al-groups and to a lesser extent to Fe and Mn (hydr)oxides. Minor amounts of outer-sphere complexes or organic matter-bound Zn species could also be detected. About 70% of the total Zn content could be easily leached, indicating that outer-sphere sorption complexes have been underestimated and/or inner-sphere sorption complexes are weak due to the low pH. The Zn forms in the subsoil most likely derive from weathering of the Zn minerals in the topsoil. Due to the lack of minerals incorporating Zn and due to the low pH, the availability of Zn in the subsoil is as high as in the topsoil, while the total concentration is almost 1 order of magnitude smaller.