Differences in antimony and arsenic releases from lead smelter fly ash in soils

Emissions from lead (Pb) smelting have long been recognized as one of the most important local sources of metal/metalloid pollution, with resultant releases of antimony (Sb) and arsenic (As). In order to understand the dynamics and fate of the metalloids originating from smelter-derived contamination, we studied the reactivity of secondary Pb smelter fly ash in acidic soils with a special emphasis on the release and subsequent mobility of the Sb and As. Polyamide test bags filled with 0.5 g of fly ash were placed in different soils in two experiments: (i) a short-term (21 days) laboratory pot experiment using two different soils (forest and agricultural) and soil pore-water sampling: and (ii) in a long-term (1 year) in situ experiment in soils developed under different vegetation covers (spruce, beech, and meadow). The mass losses indicated that more than 60% of the fly ash was dissolved during both experiments. A significantly higher release of As into soil waters was observed during the pot experiment (similar to 40 mu g/L, stabilized after 48 h). In contrast, low concentrations of Sb close to that of the blank incubations were reported in the soil water (0.5-1.5 mu g/L). No significant changes in the Sb concentrations or in the chemical fractionation were detected in the soils after exposure. A slight concentration gradient was observed for As, indicating its mobilization towards the bottom of the pot. An increase of the Sb concentration in the soil (up to 1.8x) was observed after 1 year in the in situ experiment, particularly in the litter and organic soil horizons under the tree stands. Interestingly, the expected increase in the As concentration in the soil after exposure was only observed in the litter horizons. This phenomenon may be related to significant changes in the soils' hydraulic properties in the mineral soil horizons; this is caused by soil probe excavating and subsequent faster flushing of the As from the mobile soil fractions, or from the mechanical transport of As-bearing soil particulates. The TEM-EDS-SAED observations indicated that formation of secondary mimetite (Pb-5(AsO4)(3)Cl) and Sn-bearing bindheimite (Pb-2(Sb,Sn)(2)O-6(O,OH)) were the most important mineralogical controls of Sb and As release from the Pb smelter fly ash. (C) 2012 Elsevier GmbH. All rights reserved.