Lead-Zinc 2010 Edited by: A. Siegmund, L. Centomo, C. Geenen, N. Piret, G. Richards and R. Stephens TMS (The Minerals, Metals & Materials Society), 2010
CHARACTERIZATION OF THE HEAVY METALS CONTAMINATION DUE TO A LEAD SMELTER IN BAHIA, BRAZIL *L.R.P. de Andrade Lima1, L.A. Bernardez2 1
Federal University of Bahia – Laboratory of Mineral Processing and Extractive Metallurgy C.P. 6974, Salvador, Bahia, Brazil, 41000-000 (*Corresponding author:
[email protected]) 2
Ingenium Consultoria em Engenharia Ltd. Av. Estados Unidos, n.523, Sala 1213 Salvador, Bahia, Brazil, 40010-020
ABSTRACT From 1960 to 1993 a primary lead smelter operated in Brazil, close to the Todos os Santos Bay. Several studies since the 1970s have indicated the high blood values of lead and cadmium in the population living less than one kilometre from the plant. A recent survey with children indicated that the lead and cadmium contamination is still found in this region, after the plant closed down. The disposed lead slag has been appointed as the main source of this contamination, despite the fact that the heaps are protected from rainwater by a large impervious clay layer. The state government, geotechnical specialists and some private companies proposed the re-mobilization and treatment of slag heaps by hydrochloric acid leaching followed by solvent extraction as a possible solution for this serious heavy metals pollution problem. The main objective of this paper is demonstrate that the primary disposed lead slag is relatively stable in normal environmental conditions, and the main source of the heavy metals contamination in Bahia is due to the lead smelter dust emissions from the roasting-smelting processes, rich in lead, zinc, cadmium and arsenic oxides. This material remains in the top of the clay rich soil that characterizes this region, and the lead content is about 10800 ppm (exceeds 20000 ppm in some places), the zinc content is about 682 ppm and the arsenic is about 397 ppm. This paper presents a characterization of the slag, soil, and the chimney flue dust, which indicated alternatives to the soil decontamination based on the anglesite leaching.
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INTRODUCTION From 1960 to 1993 a primary lead smelter operated in the state of Bahia, Brazil, close to the Todos os Santos Bay (Figure 1). This plant treated a galena concentrate from the flotation plant of Boquira Mine, also located in Bahia. Since the 1970s several studies have shown that the population around the smelter has been affected by lead and cadmium [1-13]. An epidemiological survey of children born after the lead smelter closedown indicates that a significant portion of the population still have high levels of lead and cadmium in their blood [12]. The lead blast furnace slag, disposed of close to the smelter and dispersed in the city as a construction material, was indicated as the potential heavy metals reservoir that would release these elements continuously into the ground water [12]. This paper presents the characterization of the lead slag, soil and flue dusts collected in the chimney and sheds light on the origin of the current heavy metals contamination in this region.
Figure 1 - Map of South America showing the location of Salvador, Bahia and details of the Todos os Santos Bay and the smelter location at Santo Amaro city. The Santo Amaro lead smelter used the classical sinter-roasting process (with a Dwight-Lloyd sintering machine for agglomeration) followed by smelting (with Water-Jackets furnace) and refining. The smelter could process about 46.2 x 103 tons/year of galena concentrate with about 65% lead. In the roasting-smelting processes the galena concentrate was blended with limestone from mollusc shells, scrap iron, coal and sand. The resulting metal phase was rich in lead, silver, copper, antimony, arsenic, tin, and bismuth, and the slag was rich in iron, calcium, zinc, and silicates. The refining step included “softening” (removal of copper, tin, antimony, arsenic, and bismuth) and desilverization (removal of silver). The removal of copper used the fact that copper solubility in lead reduces by reducing the temperature. The residual copper is then eliminated from the lead by precipitation with the addition of sulphur. The copper free bullion is then treated to remove tin, antimony and arsenic by oxidation with air at about 800oC. Silver was recovered using the Parkes process, which consists of the addition of zinc and precipitation of Ag-Zn intermetalic compounds, which were treated to recover silver. The bismuth was also removed as an intermetalic compound by adding calcium and magnesium, which are treated to recover a lead-bismuth alloy. Zinc was recovered by vacuum distillation at 600o C. Finally the residual oxides were eliminated from the lead by washing (leaching) with sodium hydroxide. The slag left the furnace at a temperature of about 1200oC and was granulated by quenching the molten slag with water. In the sinterroasting process, in addition to gases (mainly SO2 and SO3), large amounts of flue dust were produced and sent to a 90 m stack (Figure 2).
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Figure 2 - Photos showing the lead smelter site, the Subaé River, and the plant chimney
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MATERIALS AND METHODS A sampling campaign was performed in December 2002 at the slag heaps of the smelter. The vegetation and the protective clay layer of the heaps were removed in different points of the heaps and about 30 kg of slag was collected. The sample was washed with water to eliminate plant roots and leaves and the small particles of soil and clay. After drying at room temperature, it was gently homogenized and small samples were collected and further used in the characterization study. Three sampling campaigns were performed between December 2009 and February 2010 at the smelter region to collect soil, flue dust and to perform in situ analysis in several points. The X-ray diffraction analysis was performed using a Shimadzu XRD-6000 diffratometer with CuKα radiation. The scanning electron microscope JEOL 840-A equipped with a X-ray dispersion energy spectrometry system (EDS) was used to evaluate the composition and the texture of the particles of the slag. The samples were mounted with an epoxy resin and carefully polished to avoid sample contamination and particle deformation. Several analytical methods were used to evaluate the slag, soil and flue dust content. These methods included instrumental neutron activation analyses (INAA), induced coupled plasma (ICP-AES), induced coupled plasma and mass spectroscopy (ICP-MS) with acid digestion, fusion with lithium metaborate/tetraborate followed by induced coupled plasma (FUS-ICP), X ray fluorescence (XRF), and combustion and infrared identification (LECO). The neutron activation analyses were performed at the Department of Physical Engineering of the Polytechnic School (University of Montreal, Canada), and the other analyses were performed at the Activation Laboratories Ltd, (Canada). RESULTS AND DISCUSSIONS Lead Slag Table 1 presents the concentration of the major constituents of the lead slag. The analytical method used for the identification of each element is also presented in this table. The main constituents of the tailings are iron, calcium and silicon, which account for about 67% of the weight. The sample also contains zinc, magnesium, lead, aluminium, carbon, and manganese, which accounts for 99.98%. The elements content is in agreement with the lead pyrometallurgical process, which uses limestone, scrap iron and sand to reduce the lead oxide generated from roasting the galena concentrate. The zinc is due to the small amount of spharelite in the galena concentrate.
Fe2O3 CaO SiO2 ZnO MgO PbO Al2O3 MnO Na2O K2O TiO2 C S
Table 1 - Concentration of the major constituents in the slag Concentration % Analytical method 28.10 ICP-MS 23.11 ICP-MS 21.39 INAA 9.47 ICP-OES 5.44 ICP-MS 4.06 ICP-OES 3.56 ICP-MS 1.44 INAA 0.27 ICP-MS 0.26 ICP-MS 0.25 INAA 2.26 LECO 0.37 LECO
Figure 3 presents a backscattering scanning electron microscope image of polished slag particles. This image shows several regions with different grey tonalities in the sample. The white spots are metallic lead. The light grey regions are dendrites and spherical inclusions rich in Fe, Mn, Zn, and O (see EDS spectra at Figure 3b), possibly of franklinite and wüstite [13,14]. The dark grey regions are the slag matrix rich in Si, Ca, Mg, and O (see EDS spectra at Figure 3c), possibly of kirschsteinite [13,14]. Figure 4 shows the mapping of the major elements of the slag. Note that Si, Ca and Mg are the main components of the slag matrix and Fe, O and Zn are the main components of the clear grey zones.
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(3a)
Figure 3a - Backscattering scanning electron microscope images of the lead slag and EDS (b &c) analysis of two spots of the sample, composition of the grey particle in the image center, and composition of the dark zone in the left down side of the image.
Si
Ca
Fe
O
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Pb
Zn
Mg
Al
Figure 4 - Mapping of the major constituents in the slag for the scanning electron microscope image shown in Figure 3.
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Contaminated Soil
Table 2 presents the concentration of the major constituents of the soil close to the lead smelter (UTM x=529408, y=8614041). The analytical method used for the identification of each element is also presented in this table. The main constituents of the soil are silicon, aluminium, iron, potassium, magnesium, calcium and lead, which account for about 74% of the weight. The sample also contains titanium, phosphorous, sodium, manganese, zinc, and barium, and volatiles which accounts for 96.4%. The elements content is in agreement with the region geology, which indicates several close deposits of manganese oxide, phosphate, carbonate, ilmenite, and barite in the region. In addition, the soil in this region is very rich in clay mineral and quartz, which explain the high silicon, aluminium, iron, potassium, and magnesium contents. Table 2 - Concentration of the major constituents in the soil Concentration % Analytical Method SiO2 48.31 FUS-ICP Al2O3 12.46 FUS-ICP Fe2O3 7.38 FUS-ICP K2O 2.04 FUS-ICP MgO 1.92 FUS-ICP CaO 1.01 FUS-ICP PbO 0.905 ICP-OES TiO2 0.895 FUS-ICP P2O5 0.23 FUS-ICP Na2O 0.22 FUS-ICP MnO 0.121 FUS-ICP ZnO 0.081 ICP-OES BaO 0.036 FUS-ICP S 0.07 LECO L.O.I. 20.79 Table 3 presents an in situ evaluation of the some elements content in the top soil in two regions close to the lead smelter. Note that the lead and arsenic contents, which have anthropogenic origin, are very high in both cases. This high metal content in the top soil is surprising, because the plant closedown 17 years ago. In spite the fact that the rain intensity in this region is relatively frequent, it was identified that the elements penetration in the soil is very low. This effect is explained by the larger clay content of the soil and the strong interaction with the metals. Table 3 – Soil metal content in the N-NW direction of the chimney (in situ analysis using XRF) Region 1 Region 2 Pb 6897.85 10737.7 ppm Zn 791.19 681.74 ppm As 451.44 397.19 ppm Cu 112.56 312.97 ppm Mn 697.36 523.37 ppm Cr 80.56 0 ppm Ti 5983.55 0 ppm Figure 5 presents a backscattering scanning electron microscope image of the contaminated soil particles. This image depicts an anglesite (PbSO4) crystal, white region inside a dark grey particle, which is the matrix silicate, clay. One remarks that the larger size of this crystal of anglesite has approximated 40µm, but there are small spots of white regions disperse in other particles. Figure 6 presents the lead content in the top soil in the region of the Santo Amaro Lead Smelter. These values were measured in situ using XRF. The origin of the plot is the chimney location. One remarks that the larger points, which indicate high lead content, are concentrated in a specific zone that is relatively close to the chimney, about 600 m. One clearly notes that these data has a tendency of accumulation in between North and West of the chaminey. Figure 7 shows the polar histogram for the wind direction (three a day for one year, specifically 2000) to the closest national metrological station, located in Cruz das Almas city. One notes a correlation between the lead content in the top soil and the most frequent wind directions.
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Figure 5 - Backscattering scanning electron microscope images of the contaminated soil.
UTM Northing (y)
528000 8615000
528500
529000
529500
530000
530500
531000
531500
532000 8615000
8614500
8614500
8614000
8614000 600 m
8613500
8613500
8613000 528000
528500
529000
529500
530000
530500
531000
531500
8613000 532000
UTM Easting (x) Figure 6 – Distribution of the lead content in the top soil in the region of the smelter. 0
315
45
270
90 0
225
100
200
300
400
500
135
180
Figure 7 - Rose Diagram for the wind direction at Cruz das Almas city in 2000
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Chimney Flue Dust The metals content were analysed in situ inside the chimney stack, but in most of the cases the values were not very high. Flue dust was collected inside the chimney from the upper zone. The fine powder was analysed by XRF. Table 4 shows the results of the flue dust composition. One remarks a larger loss of mass by heating at 450oC (about 72%). One notes also a very high lead, arsenic, cadmium, selenium, mercury and tellurium content in the flue dust. Table 4 - Chimney flue dust composition
Pb Fe As Se Cd Zn Ba Te Hg Sb Cs K Cu Sn Ti Ca Sr Ag Pd Cr L.O.I. 450oC
% % % % % % % % ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm %
12.51 1.68 1.33 0.4722 0.3531 0.3652 0.2054 0.1455 730 775 643 881 424 469 623 553 183 164 92 56 72
The X ray diffraction of the flue dust (Figure 8) clearly shows that the major phases in this material are sulphur and anglesite (PbSO4). These results show that the anglesite found in the soil was dispersed by the plant chimney; therefore, this was the main contamination source. 1800 Sulfur Anglisite
1500
Intensity
1200
900
600
300
0 10
20
30
40
50
60
70
80
90
2 Theta (degree)
Figure 8 – Diffratogram for the flue dust collected in the chimney
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These results shows that anglesite is the lead bearing compound in the soil. Preliminary soil washing with diluted acid-chloride ion in an oxidant solution, which extract about 80% of the lead of the soil, 70% of the zinc and more that 70% of the arsenic. After the solid-liquid separation the heavy metals can be precipted by sodium sulphide and disposed or purified to recover the metals. CONCLUSIONS A characterization of the lead smelter slag, soil and flue dust at the vicinity of a primary lead smelter located in Santo Amaro, Brazil, is presented in this study. The results shows that the main constituents of the slag are iron, calcium, silicon, zinc, magnesium, lead, aluminium and manganese; the cadmium content of the slag is very low and the uranium, strontium, copper and arsenic content are relatively high. The SEM images and EDS element identification confirm that the lead in the slag is metallic lead that is stable in normal environmental conditions. The zinc occurs as zinc iron manganese oxide. It was identified that the main lead bearing compound in the contaminated soil is anglesite (PbSO4). The distribution of the lead in the top soil follows the wind predominate directions. The characterization of the flue dust collected in the chimney show high sulphur, lead, cadmium, zinc and mercury. The major lead phase in this material is anglesite, which has low solubility. This fine-grained material remains in the top soil, which is rich in clay and has low permeability; however, it can be leached by acidified, oxidant water. Thus, the source of the heavy metals contamination reported in Santo Amaro is related to the lead sulphate smelter dust emissions from the roasting-smelting processes. ACKNOWLEDGMENTS The authors express their gratitude to Jose Roberto Pinho de Andrade Lima and Jose Lamartine de Andrade Lima Neto for valuable aid and discussions during the sampling campaigns. The Brazilian Institute of Meteorology (INMET) is acknowledged for provide the wind direction and speed data used in this study. REFERENCES 1.
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Papers originally presented at Lead-Zinc 2010, held in conjunction with COM 2010 and reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum.
Edited by A. Siegmund, L. Centomo, C. Geenen, N. Piret, G. Richards and R. Stephens
A John Wiley & Sons, Inc., Publication
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PREFACE Lead-Zinc 2010 is the fifth decennial symposium by the Minerals, Metals and Materials Society (TMS), which is devoted to the theory and practice of the Lead and Zinc extractive metallurgy. It continues the decennial conference series initiated by the American Institute of Mining, Metallurgical, and Petroleum Engineers (AIME) with the pioneer first meeting in St. Louis in 1970, and subsequent conferences organized by TMS in Las Vegas in 1980, Anaheim in 1990, and Pittsburgh in 2000. Throughout that time, other international societies have also offered major lead-zinc meetings, including MetSoc in 1998 and 2008, and the Mining and Materials Processing Institute of Japan (MMIJ) in 1995 and 2005. This TMS Fall Extraction & Process Metallurgy Meeting is held in conjunction with the 2010 Conference of Metallurgists, the premier annual event of the Metallurgical Society of the Canadian Institute of Mining, Metallurgy and Petroleum (MetSoc), and is co-sponsored by the Gesellschaft fuer Bergbau, Metallurgie, Rohstoff- und Umwelttechnik (GDMB), and the Mining and Materials Processing Institute of Japan (MMIJ). With the global consolidation of the lead and zinc industry, it is important that the different metallurgical societies worldwide are working together in order to avoid conferences scheduled too close together as well as overlapping. Pooling the resources of TMS and MetSoc and the close sponsorship of GDMB and MMIJ was an imperative and effective approach to offering a meeting of the highest value and quality, and making the PbZn 2010 an efficient, productive and attractive event. It is also the first time that Lead-Zinc 2010 received enhanced involvement from the Chinese lead and zinc industry. Antaike, a subsidiary of the China Nonferrous Metals Industry Association (CNIA), not only is presenting a plenary presentation describing the Chinese Lead and Zinc Industry, but is also heading a Chinese delegation which will attend the symposium. Lead-Zinc 2010 will provide an international forum for the lead and zinc processing industries bringing together operators, engineers and researchers to exchange information regarding all aspects of current processing technologies for primary and secondary lead and zinc, as well as emerging technologies for both metals. The symposium scope extends from process fundamentals to operational practices, and also includes the important aspect of environmental issues. At the operations level, comprehensive reviews of the major applications of both metals are outlined. Emphasis will be placed on recent commercial developments with less energy intensive technologies which are in harmony with environmental conservation. At the research level, the emphasis is placed on a better understanding of existing technologies and the development of new processing concepts. Environmental concerns which are associated with the processing of both metals are considered, along with acceptable treatment and handling of by-products, wastes and bleed streams by the industry. A highlight of the conference will be a series of plenary lectures by industry leaders offering overviews of economical, environmental, and marketing topics. The proceedings volume of the Lead-Zinc Symposium is the culmination of almost two years work, which includes the preparation of the papers by the authors, as well as editing and indexing by the editors. The proceedings volume contains 116 papers from 23 countries divided into 3 plenary sessions and 21 technical sessions and is a reflection of all aspects of lead and zinc processing, including the global business trends of the metals, plant operations, fundamental developments, emerging technologies and environmental considerations. It is the editors sincere hope that the proceedings volume will remain a valuable record of the Lead-Zinc 2010 symposium, and that it will become a standard reference for the processing of Lead and Zinc. The production of the proceedings volume was a major undertaking, and many individuals were involved over the course of several months. The editors would like to extend their sincere appreciation to Ronona Saunders and Brigitte Farah from MetSoc, as well as Christina Raabe and Chris Wood from TMS, for their assistance in the production of the proceedings volume of the Lead-Zinc 2010 symposium. Vancouver October 2010
Andreas Siegmund Conference Chair (TMS)
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Characterization of Industrially Electrowon Zinc: An Investigation of Sticky and Non-Sticky Deposit Behaviour ...........................................................................................827 D. Dhak, M. Chen, E. Asselin, S. DiCarlo, and A. Alfantazi
Secondary Zinc Processing II Different Ways of Using Waelz Oxide Overview and Evaluation ............................................841 J. Ruetten Evaluation and Recycling Potential of Different Zinc Containing Residues from Metallurgical Industry ...............................................................................................................851 J. Antrekowitsch, S. Steinlechner, and G. Schneeberger SDHL Waelz Technology: State of the Art for Recycling of Zinc-Containing Residues..........861 M. Gamroth, and K. Mager The Topical Waelz Process for Recycling of Eaf DustState-of-the-Art and Future Challenges .....................................................................................871 J. Ruetten Modernization of Eaf Dust Processing Technology at Bolesáaw Recycling Ltd., Poland .........883 D. Krupka, P. Kapias, J. Czekaj, J. Galicki, and J. Jakubowski Simultaneous Recovery of Various Metals from Zinc Containing Residues on a Reducing Metal Bath .................................................................................................................................889 S. Steinlechner, and J. Antrekowitsch Research and Development of Complex Technology for Zinc and Indium Recovery from Oxidized Raw Material and Waste Utiliziation .........................................................................899 P. Alexandrovich
Environmental Practices Lead Environmental and Health Performance at Met-Mex Peñoles...................................................903 H. Ordaz, R. Morari, and M. Rodríguez Characterization of the Heavy Metals Contamination Due to a Lead Smelter in Bahia, Brazil ..........................................................................................................................917 L. de Andrade Lima, and L. Bernardez Maximum Control of Air Emissions from a Large Secondary Lead Smelter in an Urban Environment ..............................................................................................................................929 T. Ellis, and S. Bevans A Possibility of CRT Recycling in a Lead Smelter from an Environmental Point of View ......935 E. Shibata, T. Nakamura, and T. Shiratori xi
