Measuring reactive pools of Cd,Pb and Zn in coal fly ash from the UK using isotopic dilution assays |
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| Institution: | 1. CNRS/UPPA, Laboratoire de Chimie Analytique Bio-inorganique et Environnement (LCABIE), UMR5254, Hélioparc, 2, Av. Pr. Angot, 64053 Pau, France;2. CNRS, UPR 3404, FRC3115 — Centre de Génétique Moléculaire, 91198 Gif-sur-Yvette, France;3. Department of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland;1. Department of Chemistry, Faculty of Science, Masaryk University, Kotlá?ská 2, Brno 61135, Czech Republic;2. CEITEC, Masaryk University, Kamenice 5, Brno 62500, Czech Republic;3. Institute of Geology, The Czech Academy of Sciences, Kamýcká 6, Praha 16500, Czech Republic;4. Institute of Archaeology, The Czech Academy of Sciences, Letenská 4, Praha 11801, Czech Republic |
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| Abstract: | Large volumes of coal fly ash are continually being produced and stockpiled around the world and can be a source of environmentally sensitive trace elements. Whilst leaching tests are used for regulatory purposes, these provide little information about the true geochemical behaviour and ‘reactivity’ of trace elements in coal ash because they are poorly selective. Isotope dilution (ID) assays are frequently used in soil geochemistry as a means of measuring the reactive pools of trace metals that are in equilibrium with soil pore waters. This paper examines the applicability of multi-element ID assays in measuring the labile or reactive pool of Cd, Pb and Zn in a range of fresh and weathered fly ash, where pH is generally much more alkaline than in soils. The method generally worked well using 0.0005 M EDTA as a background electrolyte as it provided robust analytical ICP-MS measurements as well as fulfilling the important principle of ID that non-labile metal should not be solubilised. Reactive pools were equivalent to 0.5–3% of the total Pb pool and 4–13% of the total Cd pool. For Zn, where samples had pH < 11.5, the reactive Zn pool varied between 0.3% and 2%; when fresh ash samples with pH > 11.5 were tested, the method failed as the spiked isotope appeared to be sorbed or precipitated. Ash weathering was found to exert little impact on the lability of Cd, Pb and Zn. Isotope dilution results were compared with 0.43 M HNO3 and 0.05 M EDTA extractions, these commonly being used as analogues of the ID assay, and concluded that these can be used as fast, cost-effective and simple proxies for the ID assays. Results suggest that ID methods can be used to enhance knowledge of trace element behaviour in fresh and weathered fly ash. |
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