Environ. Sci. Technol. 1999, 33, 1334-1339
Microchemical Investigations of Dust Emitted by a Lead Smelter S O P H I E S O B A N S K A , †,§ N A T A C H A R I C Q , †,‡ A G N EÅ S L A B O U D I G U E , † R E N EÄ G U I L L E R M O , † C L A U D E B R EÄ M A R D , * , ‡ J A C K Y L A U R E Y N S , ‡ JEAN CLAUDE MERLIN,‡ AND JEAN PIERRE WIGNACOURT§ De´partement Chimie et Environnement, Ecole des Mines de Douai, 941, rue Charles Bourseul BP 838 Douai Cedex France, Laboratoire de Spectrochimie Infrarouge et Raman du CNRS UMR-CNRS 8516, Baˆt C5, Universite´ de Lille I, 59655 Villeneuve d’Ascq Cedex France, and URA-CNRS 452, ENSC de Lille BP 108, Baˆt C7, Universite´ de Lille I, 59652 Villeneuve d’Ascq Cedex France
Dusts emitted by an important pyrometallurgical lead smelter have been sampled within the pipes of the grilling and furnace working units before and after the filtering systems, respectively. Particle size distribution, elementary analyses, and X-ray powder diffraction analysis indicate PbS, PbSO4, PbSO4‚PbO, Pb, ZnS small particles less than 5 µm in size to contribute mainly to the current atmospheric pollution. Although at least 90% of dust are retained on the filters, the amounts of the respirable smaller particles are significantly larger in the current emission. The average chemical speciation was found to be analogous for the dust samples collected before and after the filters. The scanning electron microscopy associated with energydispersive X-ray analysis and Raman microspectrometry established the morphology and chemical composition at the level of individual particles. A lot of minor compounds (RPbO, β-PbO, FeS2, FeO, Fe3O4, R-Fe2O3, FeCO3, CaSO4‚ 2H2O, CaCO3, CdS, ...) were found as small heterogeneous individual particles (less than 5 µm) in the heterogeneous particles of grilling dust. Among the homogeneous particles of furnace dust, amorphous C, β-PbO, PbO‚PbCl2, FeO, CdS, CdSO4 were often detected as homogeneous mixtures with the major compounds within the particles.
Introduction The danger to health from heavy metallic residues in soil and dust is now widely accepted. During seven decades, nonferrous foundries located in the north of France have given off tons of dust which have polluted the surrounding fields with compounds containing lead, zinc, cadmium, ... etc. The pollution may present danger to people or animals living in the neighborhood of contaminated sites, via dust ingestion, agriculture, and gardening. Thirty years ago, the set up of filter systems reduced markedly the emission of dust in the atmosphere from these metallurgic factories. A lot of previous works report about airborne dust from nonferrous foundries (1-4), street dusts (3, 5-7), or wet and * Corresponding author phone: 33 20 434 125; FAX: 33 20 436755; e-mail:
[email protected]. † Ecole des Mines de Douai. ‡ Centre d’Etude et de Recherches Lasers et Applications. § Laboratoire de Cristallochimie et Physicochimie du Solide. 1334
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dry atmospherical deposits (8-12) located in different parts of the world. Attention of their authors is mainly focused on the characterization of metallic compounds of dust in order to identify the source of pollution (13). The present work is a part of a large Environmental Concerted Research Program about a polluted area located around the lead smelter under study to establish the evolution of the pollution over a long period and the impact on the local flora, fauna, and human health. Here, we provide a new insight concerning the particle size distribution, the metallic content, and the speciation of metals in current dust emitted by the chimneystack of the lead smelter (∼16 t per year) using pyrometallurgical processes. The filter systems set up to clean the emissions of both grilling and furnace units of the smelter are analogous. Two types of dust samples were collected before and after the filter systems within the pipes. The first ones are representative of the residual current dust emissions from the chimney. The second ones can be representative of the main source of the lead pollution from 1900 to 1975 because the lead ores and the pyrometallurgical processes are practically unchanged over a century, except the battery recycling. The knowledge of the number, size, and chemical composition of the fine particles is a valuable aid to the industrial hygienist in the evaluation of toxicity. Several questions are in demand at the level of individual particles of dust emitted by nonferrous foundries, particularly the nature of the metallic compounds and the association between the metallic compounds. While the techniques of determination of the dust average properties have been applied widely, those of chemical speciation at the level of the particle are less well established (2, 4). In the present work, conventional techniques available for powder samples (size distribution, elementary analysis, and X-ray powder diffraction) were used to provide evidence of the average properties of the dust. However, emphasis was set about the microphysicochemical investigations at the level of individual particles of dust using both elemental and molecular microanalyses through energy-dispersive X-ray microspectrometry and Raman scattering microspectrometry, respectively (14).
Experimental Section Lead Smelter. The pyrometallurgical processes of the smelter consists of two major working units: the ore grilling (grill) and the “ water jacket ” furnace (furnace), before the refinement into work lead. The enriched ore, on average, contains 60-75% of lead (PbS), 3-10% of zinc (ZnS), 0.51% of copper (CuS), and Bi, Cd, Sb, As and Sn at trace level (less than 0.3%). To obtain a better yield of the grilling process, SiO2, CaCO3, and Fe2O3 were added to the enriched ore. The feed to the sintering machine is ignited by downdraft, oxidation continues by updraft on the main section of the sintering strand, and the temperature was around 1200 °C. The cleaned offgas containing SO2 passes to a sulfuric acid plant. Oxidized sinter product is broken and crushed to provide a size suitable for charging to the furnace. Lump sinter, lead sulfate, and preheated coke are charged at the furnace top. An air blast heated to 800 °C enters near the base of the furnace, and the temperature inside the furnace was estimated to be 1500 °C. It should be noted that the added lead sulfate is obtained from used batteries for the lead recycling process. Identical filter systems have been set up in these pipes to reduce the dust emission into the atmosphere. The two pipes come out of these units into the principal chimneystacks, which evacuate the residual fumes and dusts. 10.1021/es9805270 CCC: $18.00
1999 American Chemical Society Published on Web 03/27/1999
Sample Collection. Samples called “grill before filter” and “furnace before filter” were collected in the pipes before the filters for the grilling unit and the furnace unit, respectively. Dust samples called “grill after filter” and “furnace after filter” were taken behind the filters of the grilling unit and furnace unit, respectively. The filter systems of the grilling and furnace units are identical. To obtain representative samples of average emissions, dust quantities were collected during two months of emission. Granulometry. Size characterization of the dust particles was investigated by laser granulometric analyses using a Counter LS 320 granulometric instrument, which permitted particle size measurement in the 0.4-200 µm range. The dust samples were dispersed in a hexametaphosphate solution and observed in water. No sample fractionation into physical size fractions as well as into magnetic and nonmagnetic fractions or into density fractions was undertaken. The distribution values of the submicrometer particles were corrected taking into account the real and imaginary parts of the refractive index. Multielemental Analysis. Quantitative elemental analyses (Ca, Cd, Cu, Fe, Mn, Pb, S, and Zn) were carried out by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP/AES) of homogeneous solutions prepared as follow. Standard solutions were used as references. Weighted amounts of dry dust were digested at 100 °C in a clean Teflon vessel with a 4:1 ratio of concentrated perchloric acid and fluoride acid in high purity dissolved in bidistilled water. The solid residue was dissolved in 100 cm-3 of nitric acid and hydrochloric acid mixture. X-ray Powder Diffraction (XRPD). X-ray powder diffraction patterns of numerous samples of dust were obtained using Siemens D 5000 diffractometer with the monochromatic copper (KR) X-ray radiation. In addition, several samples were collected directly in the pipes after the cleaning dust systems through air filtering devices. The crystallized compounds were identified by comparison of experimental diffractograms of compounds with a database. We estimated the different crystallized compounds ratio using the relative intensity of strongest X-ray pattern peak of each compound of the mixture. The patterns of pure powdered compounds and known powder mixtures as standard were recorded with identical experimental conditions to correct as far as possible the absorption phenomena. The peak area was estimated using a profile fitting program and a pseudo-voigt profile simulation function. Scanning Electron Microscopy/Energy Dispersive X-ray Spectrometry (SEM/EDS). The SEM observation of morphological examination and energy-dispersive X-ray microanalyses of individual dust particles were performed with an Environmental Scanning Electron Microscope Electroscan ENSEM model 2020 of Oxford instrument equipped with EDS microprobe. The SEM and the EDS elemental analyses were obtained from numerous dust samples dispersed on aluminum stubs without any carbon coating process. Both raster and spot mode analyses were performed through the EDS spectrometry. The raster mode is useful for establishing the interparticle distribution of selected elements. The spot mode is helpful to identify the elemental composition of an individual particle. The electron beam can be focused on a single particle, and the analytical volume is estimated to be around 5 µm3. Optical Microscopy/Raman Microspectrometry. The optical observation of the particles was carried out using a standard microscope. The particles were mounted on a glass strip without any special preparation. In some cases, samples collected through fiberglass filter directly in the pipes after the cleaning dust systems were analyzed as obtained. The molecular microanalyses were performed using a LABRAM Raman spectrometer manufactured by Instruments SA Dilor.
TABLE 1. Granulometric Distribution of Dusts (% Mass) particle size (µm) 100
grill grill furnace furnace before filter after filter before filter after filter 2.8 67.8 28.0 1.4 0
5.4 73.6 21 0 0
2 14.5 60.5 23.0 0
8 39.5 30.5 22.0 0
The Raman scattering of the sample was excited using the 514.5 or 632.8 nm lines of an argon or a helium-neon laser, respectively. The excitation of the Raman scattering through several laser lines allowed for choosing better experimental conditions, reducing the parasite fluorescence background of the spectra, and avoiding destroying the area under study. The laser beam was focused on a single particle through a high-aperture microscope objective (×80, ×100, or ×160), and the scattered light was collected through the same objective. A multichannel sensitive detection system permits the use of a very low laser power at the sample, typically less than 5 mW. The analytical volume is estimated to be 1 µm3 using the confocal technique (15). Each typical particle has been analyzed in the 2000-100 cm-1 wavenumber range in different points. Most of the inorganic compounds exhibit their characteristic Raman features in this wavenumber range. The identification of the chemical compounds in the individual particles was achieved by comparison with previously reported Raman spectra of the expected compounds through the wavenumbers of the Raman features as well as the relative intensities (14-16). In some cases, it was necessary to record Raman spectra of unusual chemical compounds such as the defined compounds of the R-Fe2O3PbO or PbO-PbSO4 mixtures to provide clear evidence of the nature of chemical products corresponding to the Raman features of the particles under study (17). It should be noted that the colored compounds with light absorption in the wavelength region of the exciting laser lines could exhibit intense Raman features due to the resonance Raman effect. In this case the Raman relative intensities depend dramatically on the wavelength of the exciting laser line. The chemical species repartition within a particle can be performed using the micro-Raman confocal scanning spectrometer (18).
Results and Discussion Granulometric Repartition of Dusts. The typical results of the average granulometric distribution of the samples collected during two months is illustrated in Table 1; all the attempts made provide analogous results. The dust samples collected before the filter of the grill unit show a large distribution of the particle size between 0.4 and 100 µm. Seventy percent of particles have a size less than 10 µm with major part of particles around 5 µm in size, whereas 30% lie in the 10-100 µm size range. Dusts emitted from the furnace unit possess two main size ranges. Fifteen percent of particles have a size less than 10 µm, whereas 85% lie in the 10-100 µm size range with the major part of particles around 40 µm in size. After the filter system of the grilling unit, approximately 4% of the dust collected before the filter were collected by our sample apparatus during the same period. Eighty percent of particles have a size less than 10 µm with major part of particles around 4 µm in size, whereas 20% lie in the 10-100 µm size range. The particle size distribution of the dust samples collected after the filter of the grill pipe was found to be analogous to the size distribution found for before filter samples. After the filter system of the furnace unit, approximately 7% of the dust collected before the filter were collected by VOL. 33, NO. 9, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 2. Elemental Composition of Dusts (% of Mass) element % of mass Ca Cd Cu Fe Mn Pb S Zn others (Si, O)
TABLE 3. X-ray Powder Diffraction Analysis of Dustsa
grill before grill after furnace before furnace after filter filter filter filter 1.7 0.2 0.3 5.0 0.1 68.9 13.8 3.7 6.3
2.0 0.3 0.4 6.9 0.09 56.7 15.5 3.7 14.4
9
identified compound
grill before filter 1.2 0.05 0.003 65.4 10.3 6.3 8.3
1.3 0.03
73.0 11.6 6.8 7.3
our sampling apparatus over two months. The particle sizes between 0.4 and 100 µm are found to exhibit a higher amount of small particles than the samples collected before the filter. Fifty percent of particles have size under 10 µm with major part of particles around 2 µm in size, and 50% have size between 10 and 100 µm. In this case, as expected, the filter system retains preferentially the larger particles of the dust. It should be noted that the efficiency of this type of filter appears to depend essentially on the quantity and the size of the particles retained on the filter. The most important emission of dust occurs probably when the filters are changed and cleaned. Just after the setting up of a new filter all the particles with a size less than the pore size (100 µm) pass through the filter. Nevertheless, when amounts of dust plug the filter, the efficiency of the filter increases. The behaviors exhibited in Table 1 are representative of average primary emission over two months of the both sources of pollution from the exit pipes. The airborne particles collected at several sites within other zinc-lead smelting works exhibit average particle sizes less than 20 µm (4), whereas larger particles were found in atmospherically deposited dust (5-11, 19, 20). However, in this later case, correlations between the heavy metal content and the particle size reveal that the metal concentration increased as the particle size decreased (11). Multielemental Analysis of Dust. The elemental analysis (Ca, Cd, Cu, Fe, Mn, Pb, S, and Zn) of dust samples are summarized in Table 2. As expected, all dust samples contain lead (about 60%) and sulfur (10-15%) as major elements. Zinc and cadmium are present at a significant level only in dust provided by the furnace unit, whereas the highest copper, iron, manganese, and calcium contents were found in dust samples collected in the grilling unit. The remaining elements to complete to 100% the state of the elementary analyses are expected to be O, Si, and metals at trace levels. It can be noticed that the elemental analyses were found to be analogous before and after the filtering systems of the grilling and furnace working units, respectively. No efficient selective filtering of the metallic elements of dust through the present systems occurs. Powdered X-ray Diffraction of Dust. X-ray diffraction patterns provide direct evidence of the crystallized compounds in the dusts. Table 3 summarizes the main results of the major phases as well as the estimates of the relative quantities. Some minor but significant differences were noted between the grilling and furnace samples, whereas the X-ray patterns of the samples collected before and after the filters are found to be similar for the grilling and furnace unit, respectively. The major phases containing lead detected in the grilling dusts are lead sulfide, PbS (galena), lead sulfate, PbSO4 (anglesite), and lead oxosulfate (PbSO4‚PbO) (1-6) and to a lesser extent zinc as zinc sulfide ZnS (wurzite). The grilling dusts contain highest amount of crystallized iron compounds, FeS2 (pyrite), R-Fe2O3 (hematite), and R-FeOOH (goethite). The major phases containing lead detected in the furnace dusts are found to be lead sulfide, PbS (galena), lead 1336
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PbS PbSO4, PbSO4‚PbO ZnS R-FeOOH, Fe2O3, FeS2 grill after filter PbS PbSO4, PbSO4‚PbO ZnS R-FeOOH, Fe2O3, FeS2 furnace before filter PbS PbSO4, Pb, PbSO4‚PbO ZnS, ZnO, CdS, CdSO4, Pb2O2Cl2 furnace after filter PbS PbSO4, Pb, PbSO4‚PbO, Pb2O2Cl2 ZnS, ZnO, CdS, CdSO4 a
estimated % of phases 60 20 15 5 60 20 15 5 55 25 20 55 25 20
The major compounds are written in bold.
oxosulfate (PbSO4‚PbO), and lead as metal Pb (1-6) whereas lead sulfate, PbSO4 (anglesite), and lead oxochloride (PbCl2‚ PbO) were found as minor phases. It is probable that the chloride compound arises from the polymer of the recycling process of batteries. The zinc element is represented as ZnS and ZnO, whereas the cadmium element is represented through CdS and CdSO4. Zinc sulfide could not be quantified because of its too small of an amount. However, the addition of CdS, CdSO4, ZnO, and noncrystallized phase amount represents an important proportion (20%), whereas zinc sulfate (ZnSO4) was not detected in all dust samples. The chemical speciation of dust emitted by all the lead smelting operations have been performed previously by powder X-ray diffraction (1, 4). All the major phases found are analogous to that determined in the present work. However, the chemical speciation depend markedly on the type of operations (ore handling, sintering, grilling, furnace, ...). A large part of the crystalline phases emitted by the lead smelting operations except PbS, ZnS, or CdS were found in street dusts (6). Electronic Microscopy and Elementary Microanalysis of Particles. Initial ESEM observations on all dust samples collected within the pipe of the grilling unit point out some isolated crystallized particles with well-defined shapes (cubic, parallepipedic, ...) with average size around 10 µm. Among 500 observed particles, 50 were found to possess well-defined shape with size more than 10 µm (Table 4). The major particles are less than 5 µm in size with no predominant morphology or geometric forms (2). However, the particles appear heterogeneous in shape. These investigations showed that particles from the grilling unit collected before and after the filter have on average similar heterogeneous size and shape characteristics. According to the electronic microscope measurements the average size of the particles appear less than that obtained through granulometric analysis; the particles are probably associated as aggregates when they are suspended in liquid before the measurements by laser granulometric analyses. The X-ray image distribution of elements for the grilling particles (Figure 1a) pointed out that lead is present in most of the small and large particles in association with the S element with marked difference in the concentrations in these particles. This association Pb/S can be related to PbS, PbSO4, or PbO‚PbSO4 compound. However, the elements such as calcium, iron, silicon, and zinc appear to be concentrated in particular grains (Figure 1a). The association Zn/S can be related to ZnS or ZnSO4 compound, whereas the association Pb/Fe, Pb/Si, and Pb/Ca cannot be related to any defined compound but rather to particles of mixtures of compounds or aggregates of particles (3, 21). From several attempts using the spot mode from 200 particles without physical fraction-
TABLE 4: Microelementary Analysis (Energy-Dispersive X-ray Spectrometry) of Dust Particles size elements X-ray image distribution element association
grill after filter
furnace after filter
90% < 10 µm, 10 µm < 10% < 20 µm Ca, Cu, Fe, Pb, S, Si, Zn heterogeneous particles in shape and elemental composition Pb/S, Zn/S, Pb/Fe, Pb/Si, Pb/Ca
80% < 10 µm, 10 µm < 20% < 20 µm Cl, Cu, Cd, Pb, S, Si, Zn homogeneous particles in shape and elemental composition no evident association
FIGURE 1. (a) Distribution of elements (X-ray emission) in particles collected in the pipe of the grilling unit of the smelter, 10 µm. b) Distribution of elements (X-ray emission) in particles collected in the pipe of the furnace unit of the smelter, 10 µm. ation, the average repartition of the elements of grilling dust does not depend significantly on the size of the particles. Furnace unit dust and particularly that collected after the filter exhibits a lot of particles less than 3 µm in size. Among 500 observed particles 100 are more than 10 µm in size, but all the particles exhibit also an homogeneous aspect in shape despite different sizes. According to the electronic microscope measurements the average size of the particles appears less than that obtained through granulometric analysis. As already observed for the grilling samples, the particles are probably associated as aggregates when they are suspended in liquid
before the laser measurements. The EDS spectra yielded to the local elemental analysis and therefore are in accurate agreement with the average elemental analyses concerning the bulk dust. However, the X-ray image distribution of elements for the furnace particles (Figure 1b) pointed out the apparently homogeneous repartition of the elements (Cd, Cl, Fe, Pb, S, Zn) at the level of the spatial resolution of the instrument used within the major studied particles. In this respect, we were not able to conclude at elemental associations defining compounds for furnace samples because of the apparent homogeneous elemental distribution. From VOL. 33, NO. 9, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 5. Micromolecular Analysis (Raman Scattering (cm-1)) of Dust Particles sample
compound
band position (cm-1)
ref
PbS PbSO4 4PbO‚PbSO4 FeO Fe3O4 FeS2 R-Fe2O3 FeCO3 CaCO3 CaSO4, 2H2O C R-PbO β-PbO CdS ZnS PbS PbSO4 PbO.PbSO4 C FeO β-PbO CdS
140/271/433/969 440/608/636/974/1153 271/434/602/656/963/1058 623/661 224/535/656 345/378 159/223/285/290/403 298/730/1090 280/713/1086 178/413/492/613/668/1006/1134 1353/1585 148/345 145/294 301/597 215/346/425/619 135/297/428/970 433/446/604/980 301/342/373/974 1338/1600 611/658 145/295 301/601
(22) (23) (23) (24) (30) (25) (26) (27) (27) (28) (29) (23) (23) (31) (31) (22) (23) (23) (29) (24) (23) (31)
description of particles
Grill After Filter
black-grey black-grey black-grey orange orange red-light red white white white-grey black-diffuse red yellow white
Furnace After Filter
black (5 µm) black-grey black-grey black-diffuse orange yellow (10 µm) black aggregate
several attempts using the spot mode from 200 particles without physical fractionation, the average repartition of the elements of furnace dust does not depend significantly on the size of the particles. ESEM/EDS provides excellent definition of the probable sources of individual metal-containing particles. However, the ability of this technique to establish the amounts of metal is poor. This is because only those particles having high metal concentrations are detected. In addition, the number of particles to be studied through microanalytical techniques is always poor by comparison with techniques available for bulk powdered samples. Optical Microscopy and Molecular Microanalysis of Particles. The particles of the grilling dust hold different colors such as red, orange, black, white, or gray, but no evident association between forms and colors appeared on the optical images. However the optical images provide valuable indications about the heterogeneity among the particles and inside individual particles. Therefore, the Raman microspectrometry investigations provide a straightforward molecular identification of the chemical species between these elements through their vibrational and electronic properties (14-16). Each typical particle has been analyzed at different points in the 2000100 cm-1 wavenumber range which is typical of the vibrational properties of metallic compounds. The Raman microspectrometry technique permitted to point a spot of an individual particle with a spatial resolution of about 1 µm3. So, minor compounds and noncrystallized phases could be detected. It should be noted that the sensibility of the technique depends mainly on the Raman scattering cross section (band intensity) of the compound but weakly on the physical state, amorphous, or crystalline (bandwidth). All the vibrational characteristics obtained from the present Raman microspectrometric experiments of dusts are listed in Table 5. They are found to be in accurate agreement with those reported previously or recorded for chemical compounds (Figure 2). Concerning grilling samples, the Pb/S association was characterized as PbS, PbSO4, PbSO4‚PbO and PbSO4‚4PbO over the major part of the particles, as individual particles or as mixtures in individual particles (22, 23). The Zn/S association was characterized as ZnS as individual particles through the Raman features (Table 5) or as mixtures in particles. ZnSO4 was not detected even as a minor compound; it is probable that ZnSO4 is not stable at the temperature of the grilling process, as previously reported (4). The Raman 1338
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FIGURE 2. Characteristic Raman spectra recorded in the spot mode (1 µm3) of three individual particles of dust collected in the pipe of the grilling unit of the smelter. microspectrometric investigations of particles (Table 5) are in accurate agreement with XRD results (Table 3) concerning the major chemical species in dust but yielded identification of supplementary minor compounds as isolated particles or as aggregates of particles: R-PbO, β-PbO, FeS2, FeO, Fe3O4, R-Fe2O3, FeCO3, CaSO4‚2H2O, CaCO3, and CdS (22-28). In contrast to EDS analysis (Table 4), the Raman scattering permitted to identification of the carbon element as amorphous carbon (29). The association between Pb and Fe elements detected by ESEM/EDS within individual particles was identified by Raman scattering as PbS/FeO, PbS/PbSO4/ Fe2O3, R-PbO/Fe2O3, and R-PbO/FeO compound mixtures. However, some frequency shifts and intensity changes provided evidence of some interactions particularly between R-Fe2O3 and PbSO4. No clear evidence was found concerning the defined compounds between PbO and Fe2O3 (17). In the same way, the Pb/Ca elemental association in some particles is found to be PbO/CaCO3 compound mixture. Surprisingly, as expected lead carbonate PbCO3 or PbCO3‚PbO were not detected in the vicinity of CaCO3 (calcite). The Pb and Si elemental association detected by ESEM/EDS microanalyses was not clearly identified by Raman microspectrometry because of the weak Raman cross section of the silicates. However, weak and broad bands around 500, 800, and 1200 cm-1 can be representative of silica or lead silicate glasses. The PbS, CdS, and FeS2 phases were simultaneously identified in individual particles by Raman microspectrometry; some
program. We are also grateful to the foundry authorities for their voluntary participation in the project. The centre d′Etude et de Recherches Laser et Applications (CERLA) is supported by the “Ministe`re charge´ de la Recherche”, the “Re´gion NordPas de calais”, and the “Fonds Europe´en de De´veloppement Economique des Re´gions”.
Literature Cited
FIGURE 3. Characteristic Raman spectra recorded in the spot mode (1 µm3) of three individual particles of dust collected in the pipe of the furnace unit of the smelter. frequency shifts indicate some physical interactions. Analogous conclusion can be drawn from the Raman investigations of particles with ZnS, FeCO3, and CaSO4‚2H2O compounds. An overview of the dust samples collected in the furnace before and after the filter was provided by the optical microscopy. The particles obtained from furnace appear to be homogeneous in size, shape, and color. The Pb/S elemental association was characterized as PbS, PbSO4, and PbSO4‚PbO compounds through the Raman features, whereas the Zn/S elemental association was characterized as ZnS in mixture with PbS and PbSO4 in particles (Table 5). ZnSO4 was not detected even as a minor compound. Supplementary minor compounds such as amorphous C, β-PbO, FeO, and CdS were detected as aggregates of particles or as homogeneous mixtures in individual particles. The particles obtained from furnace appear to be homogeneous in chemical content. PbS, PbSO4, and PbSO4‚PbO were found to be the major metallic compounds contained in the dust emitted by the furnace working unit as individual particles, aggregates of particles or as mixtures within particles. Supplementary minor compounds such as amorphous C, β-PbO, PbO‚PbCl2, FeO, CdS, and CdSO4 were often detected as aggregates of particles or as homogeneous mixtures in particles. All the chemical speciation results obtained from Raman scattering were found to be analogous for furnace samples collected before and after the filter (Figure 3). Lots of particles less than 10 µm in size were observed in the dusts emitted from the grilling unit as well as the furnace unit (16 t/an) and can correspond to the potential respirable fraction of dust. The presence of lead as PbS, PbSO4, PbO‚ PbSO4, Pb, and zinc as ZnS small particles is the predominant source of pollution. The minor compounds containing Cd, Fe, Ca, Si, and amorphous C appear as individual particles (grilling) or in association with major lead compounds (furnace). Under different environmental conditions, different physicochemical transformations will occur before to fall out on the soils. The physicochemical properties of the atmospherically deposited dust are in close relation to the toxicity, the migration in soils, and bioavailability. It is probable that the current dust emissions from the lead smelter under study can be representative of the main source of the lead pollution of the neighborhood from 1900 to nowadays because the lead ores, the pyrometallurgical processes, and the neighborhood are practically unchanged over a century, except the battery recycling and the filter systems were demonstrated to act as quantitative extractor of dust.
Acknowledgments We are most grateful to the Nord - Pas de Calais Council and French Government for financial support of this research
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Received for review May 21, 1998. Revised manuscript received January 18, 1999. Accepted January 26, 1999. ES9805270 VOL. 33, NO. 9, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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