Quantitative determination of cerussite (lead carbonate) by X-ray powder diffraction and inferences for lead speciation and transport in stream sediments from a former lead mining area in Scotland |
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| Institution: | 1. Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen, Scotland AB15 8QH, UK;2. Department of Plant and Soil Science, University of Aberdeen, Scotland AB24 3UU, UK;1. College of Mechanical and Transportation Engineering, China University of Petroleum—Beijing, 18 Fuxue Road, Changping, Beijing 102249, China;2. College of Petroleum Engineering, China University of Petroleum—Beijing, 18 Fuxue Road, Changping, Beijing 102249, China;1. Department of Geology, California State University, 5500 University Parkway, San Bernardino, CA 92407, USA;2. Department of Earth Sciences, University of California Riverside, 900 University Avenue, Riverside, CA 92521, USA;3. Malbunka Copper Mine, 5 Tenth Avenue, West Moonah, Tasmania 7009, Australia;4. Mineral Resources Tasmania, PO Box 56, Rosny Park, Tasmania 7018, Australia;1. Nuclear and Radiological Regulatory Authority, Cairo, Egypt;2. Chemistry Department, Faculty of Science, Ain Shams University, Cairo, Egypt;1. Faculty of Chemistry, University of Wroc?aw, ul. F. Joliot-Curie 14, 50-383 Wroc?aw, Poland;2. Department of Chemistry, Kyiv National Taras Shevchenko University, Volodymyrska Street 64, Kyiv 01601, Ukraine;1. Laboratoire de Modélisation et Simulation en Sciences des Matériaux, Université Djillali Liabès de Sidi Bel-Abbés, Sidi Bel-Abbés, 22000, Algeria;2. Faculté des Sciences de la Nature et de la Vie, Université Hassiba Benbouali, Chlef, 02000, Algeria |
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| Abstract: | Most current investigations of sites contaminated with heavy metals (e.g. Pb, Zn, Cu) emphasise the importance of determining the amounts of physical and chemical forms of metals rather than just the total amounts present. Chemical extraction techniques used for this purpose are inevitably operationally defined. A more direct approach to the identification of crystalline forms can be made by mineralogical techniques such as X-ray powder diffraction (XRPD), but quantitative determination of a particular form is not often attempted. Recent advances in methods of analysis and sample preparation for XRPD mean that it is now a relatively simple matter to obtain quantitative XRPD data. Here, it is applied to the quantitative determination of the forms of Pb in different size-fractions of stream sediment samples from Leadhills/Wanlockhead, SW Scotland, an historic Pb mining area. Comparison of the XRPD analyses with determinations of Pb by atomic absorption spectrophotometry demonstrates that a large proportion of the Pb present in the stream sediments is in the form of cerussite (PbCO3). Furthermore, the cerussite tends to be concentrated in the silt fraction and is even a minor component of the clay-size fraction. However, quantitative analysis of fractions <6 μm indicates that cerussite alone cannot account for all the Pb in this size range. Indirectly, this result suggests that Pb adsorbed to clay minerals, organic matter and/or amorphous Fe and Mn oxides may be proportionally more important for the <6 μm materials. Sediment in this size range, however, typically accounts for no more than 1% by weight of the total stream bed sediment samples collected in the study area. In relation to its size distribution, the mobility of Pb within the wider environment is most likely to occur principally through physical transport of fine particles. |
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