Zn isotope study of atmospheric emissions and dry depositions within a 5 km radius of a Pb–Zn refinery

The present paper examines the use of zinc isotopes as tracers of atmospheric sources and focuses on the potential fractionation of Zn isotopes through anthropogenic processes. In order to do so, Zn isotopic ratios are measured in enriched ores and airborne particles associated with pyrometallurgical activities of one of the major Pb–Zn refineries in France. Supporting the isotopic investigation, this paper also compares morphological and chemical characteristics of Zn particles collected on dry deposition plates (“environmental samples”) placed within a 5km radius of the smelter, with those of Zn particles collected inside the plant (“process samples”), i.e. dust collected from the main exhaust system of the plant. To ensure a constant isotopic “supply”, the refinery processed a specific set of ores during the sampling campaigns, as agreed with the executive staff of the plant. Enriched ores and dust produced by the successive Zn extraction steps show strong isotope fractionation (from −0.66 to +0.22‰) mainly related to evaporation processes within the blast furnaces. Dust from the main chimney displays a δ66Zn value of −0.67‰. Application of the Rayleigh equation to evaluate the fractionation factor associated with the Zn vapor produced after a free evaporation gives a range of α ore/vapor from 1.0004 to 1.0008. The dry deposits, collected on plates downwind of the refinery, display δ66Zn variations of up to +0.7‰. However, it is to be noted that between 190 and 1250m from the main chimney of the refinery, the dry deposits show a high level of large (>10μm) Zn, S, Fe and O bearing aggregates characterized by positive δ66Zn values (+0.02 to +0.19‰). These airborne particles probably derive from the re-suspension of slag heaps and local emissions from the working-units. In contrast, from 1720 to 4560m, the dry... [Copyright &y& Elsevier]