Environ. Sci. Technol. 2004, 38, 5281-5289
Speciation of PM10 Sources of Airborne Nonferrous Metals within the 3-km Zone of Lead/Zinc Smelters YANN BATONNEAU,† C L A U D E B R E M A R D , * ,† LEON GENGEMBRE,‡ JACKY LAUREYNS,† AGNES LE MAGUER,§ DIDIER LE MAGUER,§ ESPERANZA PERDRIX,| AND SOPHIE SOBANSKA† Laboratoire de Spectrochimie IR et Raman, UMR-CNRS 8516, CERLA FR-CNRS 2416 and Laboratoire de Catalyse, UMR-CNRS 8010, Universite´ de Lille I, F-59655 Villeneuve d’Ascq, Cedex France, EA-1040, Ecole Nationale Supe´rieure de Chimie de Lille, BP 108, F-59652 Villeneuve d’Ascq, Cedex France, and De´partement Chimie et Environnement, Ecole des Mines de Douai, BP 838, F-59508 Douai, Cedex France
The purpose of this study was to estimate the speciation of PM10 sources of airborne Pb, Zn, and Cd metals (PM10 is an aerosol standard of aerodynamic diameter less than 10 µm.) in the atmosphere of a 3 km zone surrounding lead/ zinc facilities in operation for a century. Many powdered samples were collected in stacks of working units (grilling, furnace, and refinery), outdoor storages (ores, recycled materials), surrounding waste slag (4 Mt), and polluted topsoils (3 km). PM10 samples were generated from the raw powders by using artificial resuspension and collection devices. The bulk PM10 multielemental analyses were determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES). The proportions in mass of Pb (50%), Zn (40%), and Cd (1%) contents and associated metals (traces) reach the proportions of corresponding raw powdered samples of ores, recycled materials, and fumesize emissions of plants without specific enrichment. In contrast, Pb (8%) and Zn (15%) contents of PM10 of slag deposit were found to be markedly higher than those of raw dust, Pb (4%), and Zn (9%), respectively. In the same way, Pb (0.18%), Zn (0.20%), and Cd (0.004%) were enriched by 1.7, 2.1, and 2.3 times, respectively, in PM10 as compared with raw top-soil corresponding values. X-ray wavelength dispersive electron-microprobe (EM-WDS) microanalysis did not indicate well-defined phases or simple stoichiometries of all the PM10 samples at the level of the spatial resolution (1 µm3). X-ray photoelectron spectroscopy (XPS) indicated that minor elements such as Cd, Hg, and C are more concentrated on the particle surface than in the bulk of PM10 generated by the smelting processes. (XPS) provided also the average speciation of the surface of PM10; Pb * Corresponding author fax: (33) 3 20 43 67 55; e-mail:
[email protected]. † Laboratoire de Spectrochimie IR et Raman. ‡ Laboratoire de Catalyse. § Ecole Nationale Supe ´ rieure de Chimie. | Ecole des Mines de Douai. 10.1021/es0497173 CCC: $27.50 Published on Web 09/04/2004
2004 American Chemical Society
is mainly represented as PbSO4, Zn as ZnS, and Cd as CdS or CdSO4, and small amounts of coke were also detected. The speciation of bulk PM10 crystallized compounds was deduced from XRD diffractograms with a raw estimation of the relative quantities. PbS and ZnS were found to be the major phases in PM10 generated by the smelting facilities with PbSO4, PbSO4‚PbO, PbSO4‚4PbO, Pb metal, and ZnO as minor phases. The slag waste PM10 was found to contain some amounts of PbCO3, PbSO4‚PbO, and ZnFe2O4 phases. The large heterogeneity at the level of the individual particle generates severe overlap of chemical information even at the µm scale using electron microprobe (WDS) and Raman microprobe techniques. Fortunately, scanning Raman microspectrometry combined with SIMPle-touse Interactive Self-modeling Mixture Analysis (SIMPLISMA) performed the PM10 speciation at the level of individual particles. The speciation of major Pb, Zn, and Cd compounds of PM10 stack emissions and wind blown dust of ores and recycled materials were found to be PbSO4, PbSO4‚ PbO, PbSO4‚4PbO, PbO, metallic Pb, ZnS, ZnO, and CdS. The PM10 dust of slag waste was found to contain PbCO3, Pb(OH)2‚2PbCO3, PbSO4‚PbO, and ZnS, while PM10-bound Pb, Zn of the top-soils contain Pb5(PO4)3Cl, ZnFe2O4 as well as Pb(II) and Zn(II) compounds adsorbed on Fe(III) oxides and in association with clays.
Introduction Historically, most airborne nonferrous metals were emitted by metallurgic factories and vehicles. Nowadays, lead, zinc, and associated metals are normally not present in high concentration in the atmosphere of Western Europe and North America because of stricter emission standards and the phase-out of leaded gasoline (1). Because they have caused intensive historic contamination of their neighborhood and are large and few in number, the primary lead and zinc smelters are well-identified in the world. To date, there are approximately 200 lead and zinc smelters and refineries spread in 37 countries in the world. Their current and/or past activities contribute especially to the local and regional anomalies of atmospheric pollution by lead, zinc, and associated metals. The release in the troposphere of fumes and dust through the stacks of smelters using pyrometallurgic processes is well-recognized as a source of fine particulate matter containing metallic compounds (2-6). However another source of airborne Pb, Zn, and associated metals has to be considered such as resuspension of aerosol size particles of surrounding ores stocks, polluted top-soils, and smelter waste slag (7, 8). Fine ores, soil, and waste particles may be suspended in the troposphere by the action of wind or by mechanical disturbances. Particulate matter has serious environmental and healthrelated consequences because it contains a wide variety of toxic organic and metallic compounds. The environmental protection agency of several countries set an aerosol standard of aerodynamic diameter less than 10 µm (PM10). Recent research suggests that there is no safe level of PM10 in the atmosphere to which we may be exposed. The increasing interest in PM2.5 results from the hypothesis that fine particles are of greater concern human health (9). However, fugitive airborne dust that contributes to air pollution is often a large fraction of PM10. To our knowledge, there are many published results related to metal contents of dust emitted by smelters or VOL. 38, NO. 20, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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generated by the action of wind (2-9). In contrast, the published works that documented the metal speciation of fume and dust emissions were found to be less numerous (3-5). We present here, the results of several elemental and molecular analyses performed on PM10 samples generated by artificial resuspension of dust collected in stacks of working units, raw materials, waste slag, and polluted top-soils sampled in a 3-km zone surrounding the lead/zinc smelting facilities. The approach taken in the present study was intended to clarify the nonferrous metal speciation of PM10 emissions and resuspensions. The metal speciation is an important determinant in human toxicity and in bioavailability.
Experimental Section Lead and Zinc Smelters Site. Facilities of the site under study included a lead smelting plant, a mixed zinc/lead smelting plant, and a refinery plant. They were located in the same area at Noyelles-Godault, a small town located in the north of France. The three processes within the smelters that operated at high temperatures (900-1350 °C) were the grilling, blast furnace, and refinery. The smelters have been in operation since 1870 until the final shutdown in 2003. The pyrometallurgic processes used several Zn and Pb concentrated ores and Pb-based materials from recycled batteries and generated fume-sized dust and Pb and Zn slag. Powdered enriched ores, recycled battery, and byproducts might be stored simply outside. Near the industrial facilities, there are at least 4 Mt of waste slag containing several heavy metals. After a long stay outside, slag piles represent an important environmental problem through the slag degradation and the generation of wind-blown fine particles particularly at the top of the heap. For more than one century, the smelting activities have polluted a large area of soil around the site by release in the atmosphere of SO2 and dust containing heavy metals. The most polluted sector is centered at least 3 km on the working units. The nonferrous concentrations of unprotected soils were found to be in the following ranges: 4000-200 mg/kg for Pb, 2000-250 mg/kg for Zn, and 40-2 mg/kg for Cd. The mean geological backgrounds of reference soils were found to be 20, 55, and 0.1 mg/kg, for Pb, Zn, and Cd, respectively (10, 11). Wind erosion will be most severe when soil moisture is low, wind velocity is high, the soil surface is smooth, and vegetative cover is minimal. PM10 Dust Sampling. Dust samples (LG, LF) were collected in the exit pipes of the grilling (G) and furnace (F) units of the lead (L) plant as detailed previously (3). Dust samples (ZG, ZR, ZF) were collected in the exit pipes of the grilling, recycling, and furnace units of the lead/zinc plant (Z). The size fraction of particles smaller than 10 µm was estimated previously ranging between 50 and 70% (3). Some powdered samples of representative lead ores (O1), zinc ores (O2), mixed lead-zinc ores (O3), and recycled byproducts (R) were collected. The size distribution of O1, O2, O3, and R particles showed that more than 50% of the particles were found to be smaller than 10 µm. Samples of waste slag particles (WS) were collected at the top of the heap and dried. Only 20% of the particles were found to be inferior to 10 µm. A polluted top-soil sample (S) was collected at 1.3 km from the main stack of the facilities in a high contaminated area (10, 11). The soil was chosen as the typical cultivated soil representative of the polluted-area tilled soils. The considered horizon (0-20 cm) is calcareous with pH around 8.3. It contains carbonate minerals such as calcite (3000 mg/kg) and quite a low amount of organic matter (10, 11). The granulometric distribution of dried soil showed that the fine fraction (
