Scanning Electron Microscope Approaches to Heavy Metal Polluted Soils in the Vicinity of the Copper Smelter


	Bildiri Özetleri
Ana Sayfaya Dönüş

Back To The Main List

Scanning Electron Microscope Approaches to Heavy Metal Polluted Soils in the Vicinity of the Copper Smelter

Jerzy Weber

Agricultural University of Wroclaw, Institute of Soil Science and Agricultural Environment Protection, Wroclaw, Poland.

Abstract

This paper deals with submicroscopic properties of the soil environment polluted by emissions of copper smelters in Poland. Soil thin sections and loose grains selected from the soil material as well as samples of emitted dust were examined with the scanning electron microscope with an energy depressive X-ray analyser (SEM-EDXRA) and electron microprobe analyser (EMA). Submicroscopic methods provided new information on morphological forms and distribution patterns of soil components being the source of the excess quantities of heavy metals in contaminated soils. However, sensitivity of SEM-EDXRA chemical analysis was relatively low, and did not enable to examine dispersed forms of pollutants. Investigations indicated that heavy-metal-bearing components of industrial origin existed in the soil material as nodules, conglomerates of fine particles as well as single grains of different morphology, from irregular grains to spherules. They indicated chemical composition of sulphides and/or aluminosilicates, and represented primary particles emitted by smelters. Secondary components, being transformed in soil, existed as diffuse nodules and dark in colour soil aggregates, containing heavy metals in more dispersed forms that can be easier mobilised.

Introduction

It has been found that heavy metal pollution has a harmful effect on life; therefore in recent years much attention has been given to such problems of the environment. Studies by numerous investigators have shown that atmospheric fallout from ore smelters can contribute significantly to soil properties. Most of the previous works on the soils polluted by smelting has attempted to assess the degree of contamination and to explain the trace elements distribution in the soil in terms of distance from the smelter and depth in the soil profile. Although quite a bit of literature is available on chemical forms of heavy metals, as well as their availability to plants, solubility, mobility and fixation with different components of soil material (Kabata-Pendias & Pendias 1992), there is very little information about micromorphological properties of polluted soils (McSweeney et al. 1994). Conventional microscopic methods were used to characterise changes in properties of soil polluted by emissions of copper smelter (Drozd & Kowalinski 1977), but this technique did not allow for characterising the chemical composition of soil components investigated in thin section. Application of submicroscopic methods by Bisdom et al. (1983, 1990) opened new possibilities, connected with determination of the distribution of heavy metals in the soil material. Scanning electron microscopy was used in the investigation of soil material contaminated with heavy metals in laboratory experiment (Robert et al. 1989), as well as in studies of fly ash particles (Dudas & Warren 1987) and fossil fuel combustion residues (Mattigod et al. 1990). Heavy metal distribution in sewage sludge and sewage sludge amended soils was detected by Essington & Mattigod (1991) and Lee & Kittrick (1984), while electron micro-beam analysis of hydromorphic soils contaminated with heavy metals enabled to indicate Zn and Pb migration to clay coatings (Brummer et al. 1991; Hiller & Brummer 1991). The soil environment polluted with heavy metals emitted by copper smelter was preliminary studied with submicroscopic methods by Kowalinski & Weber (1988), and Weber (1993, 1995). The object of this work was to characterise submicromorphological properties of soil components being the source of excess quantities of heavy metals in the soil environment contaminated by emissions of copper smelters.

Materials and Methods

Soil located in the vicinity up to 1 km from two copper smelters, as well as samples of dust emitted were investigated. Legnica and Glogow copper smelters operate for 30 - 40 years at the Lubin Copper Belt, Lower Silesia, SW Poland. There are no other major industries in both area, thus soil contamination with heavy metals originates only from smelters. Annual rainfall in this area is approximately 600 mm (mostly as summer rainfall), while mean annual temperature is about 8oC. Both regions are characterised by relatively flat topography with slightly developed slopes. Examined soils were previously used as arable soils, but due to pollution with dusts and gases, areas close to smelters have been changed into a waste land, where only occasional wild plants exist. Soils were limed and ploughed several times, to decrease the availability of heavy metals and to prevent the vanishing of vegetation. Presently, the vegetation covers most of the area.

Soil thin sections and loose material were analysed with a binocular, light polarising and scanning electron microscope. Samples were collected from the surface layer of the soil. Dust samples collected from snow cover in the vicinity of copper smelter were analysed as well. For soil thin section preparation, undisturbed soil samples were collected from each horizon. They were air-dried and vacuum-impregnated with polyester resin. Non-covered soil thin sections of size about 50 x 70 mm were examined with the polarising microscope, then selected fragments were cut off and coated with carbon film for submicroscopic investigations. The Stereoscan 180 Cambridge scanning electron microscope (SEM-EDXRA) and Jeol JXA-5A electron microprobe analyser (EMA) were used for submicroscopic investigation. Results and Discussion Surface layers of soils in the vicinity of both copper smelters contained high amounts of heavy metals. Copper and lead concentration in some places reaches 10,000 and 5,000 mg·kg-1, respectively (Weber 1995). Traditional micromorphological investigations of soil thin sections revealed existence of opaque nodules, which cannot be chemically characterised with optical microscope. The application of submicroscopic techniques allows observations under much higher magnification, and determination of chemical composition of studied fragments of thin section (Fig. 1), as well as distribution of particular elements in observed area (Fig. 2).

Usually grains containing high amounts of heavy metals are observed in scanning electron microscope image as much brighter than other constituents of soil material. Nodule shown at Fig. 1 has sharp boundaries, and represents primary particles emitted by copper smelter. Its chemical composition was dominated by silicon, lead and/or sulphur. Sensitivity of X-ray fluorescence analysis of scanning electron microscope did not allow detecting lead and sulphur separately, however presence of both elements was confirmed by investigation under electron microprobe analyser (Fig. 2). X-ray image of the distribution of Cu, Pb and S indicated that copper and sulphur were dispersed uniformly through the nodule, while lead content was lower in the left part of the nodule. The examinations conducted under higher magnification revealed more details and indicated that nodule did not show uniform structure (Fig. 3). In some places it was build up of small rounded and irregular silicate-like grains, as well as grains enriched with heavy metals, mainly sulphides. Another type of structure indicated places, where amorphous-like substance occurred. Glossy bubble-like grain shown at the right photo of the Fig. 3 is a remnant after melting processes. It was composed mainly of lead and sulphur, and indicated the same chemical composition as amorphous-like material, as well as irregular grains.

Examination of loose material selected from humus horizon pointed out that industry-originated particles could exist in the soil material as single grains, as well. They were of silt or fine sand size, and during investigation with binocular were distinguished from other grains by dark colour. They often consisted of iron, sulphur, and silicon, and contained different amounts of heavy metals. Although they were single grains, they were not homogeneous, and indicated different chemical composition form place to place (Fig. 4).

Specific and very characteristic loose grains are spherules, which developed as result of rapid cooling of drops of melted mass (Fig. 5). Since the EDXRA analysis characterised chemical composition of a very thin surface layer of examined object, investigations of loose material were not informative about the composition of a whole grain, as well as the internal structure. Nevertheless, observations provided morphological characteristics of particles, and appeared sufficient to confirm their industrial origin on the basis of high content of heavy metals.

Samples of dust emitted by copper smelters were collected directly from the snow cover in the vicinity of smelter. Dust samples contained particles of very different size and shape, which were characterised by Weber (1995). The large distribution of sizes was characteristic for samples collected close to the copper smelter, as well as some distance away from the smelter. Presence of heavy metal rich particles was clearly marked in the chemical composition of the dust; however, the particles mainly consisted of silicate-like minerals that did not contain heavy metals.

Investigation indicated, that dusts emitted by copper smelter consisted of particles that did not differ significantly from those selected from the soil material. This pointed out that previously characterised particles, selected from the soil material, represented primary nodules and grains, and soil processes had not modified them. The secondary forms of pollutants, being transformed in the soil, were represented by dark in colour soil aggregates, distinguished during soil thin sections investigations with an optical microscope. The sensitivity of X-ray chemical analysis was not sufficient to detect dispersed forms of heavy metals, but they revealed the presence of fine grains consisted from heavy metals (Fig. 6). In another aggregate fine grains containing lanthanum elements - characteristic for chimney emissions (Kabata-Pendis & Pendias 1992) - were found (Fig. 7).

Described examinations have provided some micromorphological details, but further submicroscopic research is needed to recognise distribution of heavy metals and processes operating in the soil environment polluted by industrial pollution. Investigation of the distribution of dispersed forms of heavy metals needs application of advanced techniques, such as synchrotron x-ray, to provide more information enabling better understanding the processes of soil degradation in heavy metal polluted areas. Synchrotron X-ray source seems to be the most promising technique (Schultze & Smith 1990, Schultze & Bertsch 1994).

Conclusions

References

. Bisdom, E.B.A., Boekestein, A., Curmi, P., Lagas, P., Letsch, A.C., Loch, J.G.P., Nauta, R. & Wells C.B., 1983. Submicroscopy and chemistry of heavy-metal-contaminated precipitates from column experiments simulating conditions in a soil beneath a landfill. Geoderma 30, 1-20.
. Bisdom, E.B.A., Tessier, D. & Schoute J.F.Th., 1990. Micromorphological techniques in research and teaching. In: Douglas, L.A. (ed.) Soil Micromorphology. Elsevier Sci. Publ., Amsterdam-London-New York-Tokyo, 581-603.
. Brummer, G.W., Hornburg, V. & Hiller, D.A., 1991. Heavy metal pollution of soils. Mittleilungen der Deutschen Bodenkundlich Gesellschaft 63, 31-42.
. Drozd, J. & Kowalinski S., 1977. Zmiany niektórych wlasciwosci gleb pod wplywem zanieczyszczen emitowanych przez hute miedzi Legnica. Roczniki Gleboznawcze, 28, 2, 49-75.
. Dudas, M.J. & Warren, C.J., 1987. Submicroscopic model of fly ash particles. Geoderma 40, 101-114.
. Essington, M.E. & Mattigod, S.V., 1991. Trace element solid phase associations in sewage sludge and sewage sludge-treated soil. Soil Science Society of America Journal 55, 350-356.
. Hiller, D.A. & Brummer G.W.: Electron microbeam analysis for the determination of heavy metal bound forms in soils of varying heavy metal pollution. Mittleilungen der Deutschen Bodenkundlich Gesellschaft 66, 1991, 1085-1089.
. Kabata-Pendias, A. & Pendias, H., 1992. Trace elements in soils and plants. 2nd edition. CRS Press Inc. Boca Raton, 365 pp.
. Kowalinski, S. & Weber, J., 1988. A micromorphological study of a brown leached soil profile polluted by the copper smelter Legnica (Poland) since 1959. Catena 15, 303-317.
. Lee, F.Y.& Kittrick, J.A., 1984. Electron microprobe analysis of elements associated with zinc and copper in an oxidizing and anaerobic soil environment. Soil Science Society of America Journal 48, 3, 548-554.
. Mattigod, S.V., Dhanpt, R., Lary, L.E. & Ainsworth, C.C. 1990. Geochemical factors controlling the mobilization of inorganic constituents from fossil fuel combustion residues: I. Review of the major elements. Journal Environmental Quality 19, 188-201.
. McSweeney, K., Weber, J., Arocena, L. & Yao, L., 1994. Micromorphological easement of degraded soil-landscapes. In: Transactions of 15th World Congress of Soil Science, Acapulco, Mexico, 6a, 270-280.
. Robert, M., Venau G. & Elsass, F., 1989. Etude sur modeles de la fixation et de la localisation de certains elements pollutants (Cd, Cu). Report. Contrat Ministre Environment 86081. Code INRA 2574A, INRA Versaille, France.
. Schultze, D.G. & Smith, J.V., (Eds).1990. Synchrotron X-ray sources new opportunities in the soil and environmental sciences: Workshop report. Argonne National Laboratory, USA.
. Schultze, D.G. & Bertsch P.M., 1994. Synchrotron X-ray techniques in soil chemistry and mineralogy research. In: Transactions of 15th World Congress of Soil Science, Acapulco, Mexico, 3a, 100-107.
. Weber, J., 1993. Submicroscopic investigation of soil polluted by heavy metals. In: Eijsakers, H.J.P. & Hamers, T. (Eds), Integrated Soil and Sediment Research: A Basis for Proper Protection. Kluwer Academic Publisher, Dordrecht/Boston/London, 284-286.
. Weber, J., 1995. Submicromorphological characteristics of soil environment changed by copper smelters emissions. Zeszyty Naukowe Akademii Rolniczej we Wroclawiu 269, Rozprawy CXXXVI, 61 pp.

Sayfa Başı