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Sphericity as a characteristic of solids from fossil fuel burning in a Lake Michigan sediment
MM-7037 81 050763-07fO2 00 0 Copyright 0 1981. Pcrpamon Press Lid
NOTE Sphericity as a characteristic of solids from fossil fuel burning in a Lske Michigan sediment JOHNJ. GRIFFINand EDWARD D.
GOLDBERG
Scripps Institution of Oceanography, La Jolla, CA 92093, U.S.A.
(Received 14 July 1980; accepted in revisedform 23 December 1980) Abstract-The property of spheticity is used to identify some anthropogenic particles in a Lake Michigan sediment. Three classes of products from high temperature processes, primarily fossil fuel burning, have been isolated: charcoals, iron oxides and aluminosilicates. The morphologies, structures and surface characteristics are indicative of the combustion process.
INTRODUCIION
ing, these nonreactive particles do not soften and do not take on spheroidal shapes. They retain their XN AN X?WI~TIGATIONupon the nature of charcoal original structures. The final morphology of these particles in Lake Michigan sediments, we observed partially combusted carbon particles will range from that their surface morphologies and their surface tex- elongate, prismatic structures showing well preserved tures are indicative of their origin (GRIFFIN and woody features to structureless fragments. The inorganic minerals of coal include clays, carboGOLDBERG, 1979). In general, the charcoal derived from oil burning is spherical ~~~ph~~) with a deiinates, silicates and pyrite. Upon coal ~mbustion the cate, convoluted, layered structure. Coal combustion clay minerals may form muiiite, whereas the pyrite transforms to hematite and magnetite. The inorganic carbon particles are sometimes spheroidal, however, their network structure is more robust. Also present partick% released during the combustion, which are elongate particles, sometimes showing remnant constitute a part of the flyash, will have spherical plant structure. The carbon particles derived from morphologies with surface appearances ranging from biosphere burning commonly have ratios of length to clear and glassy to black and metallic. Fuel oil is introduced to furnaces as a spray of oil width greater than three. These partides often display the fine details of plant cellular structure. droplets, whereas coal burned in modem power The nature of the combusted material and the plants is ground to particles less than a few hundred nature of the combustion process determine the types microns in size. As the droplets pass through the of charcoal produced. The components of coal, for flame, the volatile components vaporize and burn. example, can be divided into three groups on the The rno~holo~ of the in~mpleteiy combusted oil basis of their behaviors during combustion: (1) carbon particles will range from perforated spheres to reactive organic materials containing resin, tar and lacy delicate, sponge-like spheroids to homogenous vofatiles; (2) a non-reactive organic material with a fragments. The rno~ho~ogi~ and particle sizes clearly high C/H ratio, and (3) inorganic materials (CADY, will be dependent upon the operating parameters of 1942). The reactive components, which make up the combustion process (GOLDSTEINand SIEGMUNCE, about 60-90”/, of the coal, consist of vitrinite, wood 1976). Most of the carbon particles will be spheroidal tissues with or without structure; exinite and resinite, or fragments of spheres. fossilized remains of spores and algal fragments; and The charcoal residues from grass, brush and forest semifusinite, a traction stage between vitrinite and fires generally show definite woody cellular structures. fusinite with occasional cellular structure. The reac- The common morphology will be elongate-prismatic tive organic components soften when heated and lose with well preserved wood ceils; however, irregular their volatile products; the charcoal residue may have fra~ents will also be produced. Burning of plants spheroidal shapes with surface voids. Their final containing large quantities of pitch and resin can morphologies will range in shape from solid spheres yield carbon particles that resemble those produced and cenospheres to fragments depending on the time, from coal burning. The biomass type and the burning temperature and other operating parameters of the temperature govern the morphology and structure of combustion process. the particles. The common non-reactive organic corn~n~ts of Ihe microscopic examination of charcoals procoal are: micrinite, a structureless phase and fusinite, duced in the combustion of coal, oil and wood india well-defined woody cellular structure. During burncate characteristic particle shapes and surface textures 763
764
Notes
(GRIFFIN and GOLDBERG. 1979). The shapes can be categorized into three groups: (i) porous, spheroidal; (ii) elongate-prismatic, and (iii) irregular fragments. In addition, the surface. texture can be characterized into three classes: (b) smooth, homogenous; (a) rough, irregular with pits or cells, and (c) etched, convoluted layered structures. The combination of these features can be especially useful in determining the origin of carbon particles found in environmental samples (Fig. 1). The spheroidal shaped particles with smooth homogenous surfaces between the pores are common in charcoals from coal burning. The etched, convoluted layer structures between pores are unique to charcoals from fuel oil combustion. Some spheroidal particles from coal burning may not show smooth surfaces, but a rough irregular pitted surface. Eiongate. prismatic particles are not produced in fuel oil burning; however, charcoal from both coal and wood burning may have these shapes. Several other properties of the particles provide guidance in assigning origins to sedimentary charcoals. Samples with associated unburned coal particles or wood fragments would indicate combustion products from coal and wood burning respectively. Also, we have noted differences in charcoals, produced by wood and coal burning, with similar morphologies, through studies with the scanning electron microscope. The wood particles appear brighter with less detailed surface definition than the coal particles. The wood carbon appears less dense to the electron beam with the electrons penetrating deeper within the particle resulting in less surface resolution but greater illumination. The coal particles, on the other hand, appear to be more dense to the electron beam with less electron penetration and a consequential better surface detail. These characteristics, useful to seek out the sources of carbon particles, have been applied to isolates from Lake Michigan sediments to extend our initial results (GRIFFIN and GOLDBERG, 1979). Further. with the realization that spherical products often result from high temperature combustion processes, we have sought other materials from fossil fuel burning in the deposit using sphericity as a characterizing criterion.
RESULTS AND DISCUSSION Carbon particles extracted from Lake Michigan sediments (GRIFFIN and GOLDBERG, 1979) were analyzed quantitatively and then morphologies were determined (SMITH et al., 1975). Prior to 1900, the carbon concentrations were lower than those in more recently deposited strata and were relatively constant (Fig. 2). The majority of the particles were elongateprismatic in shape with many showing woody cellular structures (Fig. 2). No particles that had the characteristics of oil and coal origins were evident. The charcoal concentrations and morphologies changed beginning around 1900 and a transition
period occurred up to around 1930. Herein, the charcoal concentrations doubled and the particle morphology changed from the dominant elongateprismatic shape with many distinct, wood-like cellular features to a complex mixture of porous spheres and smooth to rough elongate-prismatic and irregulator fragments. The spheroidal particles had smooth to rough textures, indicating a coal source. This period, 1900 to 1930, was one of great industrialization and intensive coal burning (EDGINGTONand ROBBINS, 1976). Another doubling of charcoal production took place between 1930 and 1960. The carbon particles were porous spheres with smaller amounts of elongate-prismatic and irregular fragments. The smooth to rough textures of the spheres suggested that coal combustion was the primary source of carbon. The first evidence of oil burning was in the 1948-1953 sample with some particles having the etched, convoluted layer texture, characteristic of oil. After 1960, the charcoal concentrations decreased probably as a result of improved procedures to retain flyash (EDGING-ION and Roeet~s, 1976), but the particle morphology cont@med to be dominated by spheres. The particles were characteristic of coal, however, oil particles were more abundant than in the 1950-1964 samples. The trend toward sphericity is also observed in another collective of particles from the Lake Michigan sediments-the fraction with high magnetic susceptibility. Isolation techniques are described by GOLDLIERGet al. (1981). Prior to 1900, these particles were primarily irregularly shaped grains of magnetite and hematite. Following this era, as fossil fuel burning displaced wood burning as an energy source, an increasing concentration of black magnetic spheres was found. These spheres, characteristic of Ryash, probably resulted from the fusion of iron rich components in the fossil fuels (Fig. 3). Using sphericity as an indicator of anthropogenic particles, we had sought out non-magnetic spheres other than charcoal in our Lake Michigan samples. We have observed what appears to be mullite particles (Fig. 3) on this basis. The structure and morphology are similar to those observed for mullite isolated from flyash (HULETTand WEINBERGER, 1979). Thus, it appears that anthropogenic contributions to sediments, produced at high temperatures. have the characteristic of sphericity. Clearly, this may be of great use in separating out other particles produced at high temperatures. This guide should be used with caution, inasmuch as there are some naturally occurring spherical particles, such as pyrite and the cosmic spherules. Still, careful examination of spherical particles extracted from sediments and atmospheric dusts may provide tracers for the types and intensities of high temperature anthropogenic activities. These tracers clearly will provide supplemental information in acid rain, biomass burning and pollution control studies. for example.
~iCROS0~
COAL
TEXTURE
Fig. l(a).
SURFACE
COAL
COAL WOOD
COAL WOOD
Oil.
ETCHED, CONVOLUTED, LAYERED
Fig. 1. Classification of charcoal particles according lo their shapes and surbce textures. The shapes (vertical axis) are viewed under 1000 x magnification and the surface textures (horizontal axis) are observed under So00 x m_gnification.
WOOD COAL
Fig. I(b).
ROOGH, IRREGULAR t PITTED OTCELLULAR
SURFACE TEXTURE
WOOD
COAL
SMOOTH
MICROSCOPIC
._.-.
_.
20pm
10pm Fig. 3. Additional scanning electron micrographs of particles from the Lake Michigan Core: (a) Highly magnetic particles from the pre-1900 period. The shapes are angular and are representative of sedimentary particles. (b) Highly magnetic particles from the post 1900 period. Note the mixture of angular and spherical shapes. The spheres in the sediments are similar to the magnetic spheres found in coal fly ash. (c) A close-up of a group of spheres extracted from the 5-10 cm sediment. (d) 15,000 x magnification of a portion of the surface of the sphere that is outlined in (c). Note the growth of acicufar crystals of muilite.
768
Notes Acknowledgements-This work was supported by Grant DOE EY-76-S-03-0034 PA 84, with the Division of Biology and Medicine, Environmental Sciences Branch, Department of Energy.
REFERENCES CADY G. H. (1942) Modem concept of the physical constituents of coal. J. Gtd. SO, 337-356. EDCINC~TON D. W. and ROBBINSJ. A. (1976) Records of lead deposition in Lake Michigan sediments since 1800. Enoiron. Sci. Technd. 10, 266-274. GOLDBERG E. D., HODGE V. F., GRIFFINJ. J. and KOIDE M. (1981) The impact of fossil fuel combustion on the sedi-
769
ments of Lake Michigan. Environ. Sci. Technol. (in press). GOLDSTEIN H. L. and SIEGMUNCE C. W. (1976) Influence of heavy oil composition and boiler combustion conditions on particulate emissions. Environ. Sci. Technol. 10, 1109-1114. GRIFFINJ. J. and GOLDBERGE. D. (1979) Morphologies and origin of elemental carbon in the environment. Science 2@6, 563-565. HULEIT L. D. and WEINBERGER A. J. (1980) Some etching
studies of the microstructure and composition of large aluminosilicate particles in flyash from coal burning power plants. Enoiron. Sci. Technol. 14, 965-970. SMITH D. M., GR~ J. J. and GOLDBERGE. D. (1975) Spectrometric method for the quantitative determination of elemental carbon. And. Chem. 47, 233-238.
NOTE Sphericity as a characteristic of solids from fossil fuel burning in a Lske Michigan sediment JOHNJ. GRIFFINand EDWARD D.
GOLDBERG
Scripps Institution of Oceanography, La Jolla, CA 92093, U.S.A.
(Received 14 July 1980; accepted in revisedform 23 December 1980) Abstract-The property of spheticity is used to identify some anthropogenic particles in a Lake Michigan sediment. Three classes of products from high temperature processes, primarily fossil fuel burning, have been isolated: charcoals, iron oxides and aluminosilicates. The morphologies, structures and surface characteristics are indicative of the combustion process.
INTRODUCIION
ing, these nonreactive particles do not soften and do not take on spheroidal shapes. They retain their XN AN X?WI~TIGATIONupon the nature of charcoal original structures. The final morphology of these particles in Lake Michigan sediments, we observed partially combusted carbon particles will range from that their surface morphologies and their surface tex- elongate, prismatic structures showing well preserved tures are indicative of their origin (GRIFFIN and woody features to structureless fragments. The inorganic minerals of coal include clays, carboGOLDBERG, 1979). In general, the charcoal derived from oil burning is spherical ~~~ph~~) with a deiinates, silicates and pyrite. Upon coal ~mbustion the cate, convoluted, layered structure. Coal combustion clay minerals may form muiiite, whereas the pyrite transforms to hematite and magnetite. The inorganic carbon particles are sometimes spheroidal, however, their network structure is more robust. Also present partick% released during the combustion, which are elongate particles, sometimes showing remnant constitute a part of the flyash, will have spherical plant structure. The carbon particles derived from morphologies with surface appearances ranging from biosphere burning commonly have ratios of length to clear and glassy to black and metallic. Fuel oil is introduced to furnaces as a spray of oil width greater than three. These partides often display the fine details of plant cellular structure. droplets, whereas coal burned in modem power The nature of the combusted material and the plants is ground to particles less than a few hundred nature of the combustion process determine the types microns in size. As the droplets pass through the of charcoal produced. The components of coal, for flame, the volatile components vaporize and burn. example, can be divided into three groups on the The rno~holo~ of the in~mpleteiy combusted oil basis of their behaviors during combustion: (1) carbon particles will range from perforated spheres to reactive organic materials containing resin, tar and lacy delicate, sponge-like spheroids to homogenous vofatiles; (2) a non-reactive organic material with a fragments. The rno~ho~ogi~ and particle sizes clearly high C/H ratio, and (3) inorganic materials (CADY, will be dependent upon the operating parameters of 1942). The reactive components, which make up the combustion process (GOLDSTEINand SIEGMUNCE, about 60-90”/, of the coal, consist of vitrinite, wood 1976). Most of the carbon particles will be spheroidal tissues with or without structure; exinite and resinite, or fragments of spheres. fossilized remains of spores and algal fragments; and The charcoal residues from grass, brush and forest semifusinite, a traction stage between vitrinite and fires generally show definite woody cellular structures. fusinite with occasional cellular structure. The reac- The common morphology will be elongate-prismatic tive organic components soften when heated and lose with well preserved wood ceils; however, irregular their volatile products; the charcoal residue may have fra~ents will also be produced. Burning of plants spheroidal shapes with surface voids. Their final containing large quantities of pitch and resin can morphologies will range in shape from solid spheres yield carbon particles that resemble those produced and cenospheres to fragments depending on the time, from coal burning. The biomass type and the burning temperature and other operating parameters of the temperature govern the morphology and structure of combustion process. the particles. The common non-reactive organic corn~n~ts of Ihe microscopic examination of charcoals procoal are: micrinite, a structureless phase and fusinite, duced in the combustion of coal, oil and wood india well-defined woody cellular structure. During burncate characteristic particle shapes and surface textures 763
764
Notes
(GRIFFIN and GOLDBERG. 1979). The shapes can be categorized into three groups: (i) porous, spheroidal; (ii) elongate-prismatic, and (iii) irregular fragments. In addition, the surface. texture can be characterized into three classes: (b) smooth, homogenous; (a) rough, irregular with pits or cells, and (c) etched, convoluted layered structures. The combination of these features can be especially useful in determining the origin of carbon particles found in environmental samples (Fig. 1). The spheroidal shaped particles with smooth homogenous surfaces between the pores are common in charcoals from coal burning. The etched, convoluted layer structures between pores are unique to charcoals from fuel oil combustion. Some spheroidal particles from coal burning may not show smooth surfaces, but a rough irregular pitted surface. Eiongate. prismatic particles are not produced in fuel oil burning; however, charcoal from both coal and wood burning may have these shapes. Several other properties of the particles provide guidance in assigning origins to sedimentary charcoals. Samples with associated unburned coal particles or wood fragments would indicate combustion products from coal and wood burning respectively. Also, we have noted differences in charcoals, produced by wood and coal burning, with similar morphologies, through studies with the scanning electron microscope. The wood particles appear brighter with less detailed surface definition than the coal particles. The wood carbon appears less dense to the electron beam with the electrons penetrating deeper within the particle resulting in less surface resolution but greater illumination. The coal particles, on the other hand, appear to be more dense to the electron beam with less electron penetration and a consequential better surface detail. These characteristics, useful to seek out the sources of carbon particles, have been applied to isolates from Lake Michigan sediments to extend our initial results (GRIFFIN and GOLDBERG, 1979). Further. with the realization that spherical products often result from high temperature combustion processes, we have sought other materials from fossil fuel burning in the deposit using sphericity as a characterizing criterion.
RESULTS AND DISCUSSION Carbon particles extracted from Lake Michigan sediments (GRIFFIN and GOLDBERG, 1979) were analyzed quantitatively and then morphologies were determined (SMITH et al., 1975). Prior to 1900, the carbon concentrations were lower than those in more recently deposited strata and were relatively constant (Fig. 2). The majority of the particles were elongateprismatic in shape with many showing woody cellular structures (Fig. 2). No particles that had the characteristics of oil and coal origins were evident. The charcoal concentrations and morphologies changed beginning around 1900 and a transition
period occurred up to around 1930. Herein, the charcoal concentrations doubled and the particle morphology changed from the dominant elongateprismatic shape with many distinct, wood-like cellular features to a complex mixture of porous spheres and smooth to rough elongate-prismatic and irregulator fragments. The spheroidal particles had smooth to rough textures, indicating a coal source. This period, 1900 to 1930, was one of great industrialization and intensive coal burning (EDGINGTONand ROBBINS, 1976). Another doubling of charcoal production took place between 1930 and 1960. The carbon particles were porous spheres with smaller amounts of elongate-prismatic and irregular fragments. The smooth to rough textures of the spheres suggested that coal combustion was the primary source of carbon. The first evidence of oil burning was in the 1948-1953 sample with some particles having the etched, convoluted layer texture, characteristic of oil. After 1960, the charcoal concentrations decreased probably as a result of improved procedures to retain flyash (EDGING-ION and Roeet~s, 1976), but the particle morphology cont@med to be dominated by spheres. The particles were characteristic of coal, however, oil particles were more abundant than in the 1950-1964 samples. The trend toward sphericity is also observed in another collective of particles from the Lake Michigan sediments-the fraction with high magnetic susceptibility. Isolation techniques are described by GOLDLIERGet al. (1981). Prior to 1900, these particles were primarily irregularly shaped grains of magnetite and hematite. Following this era, as fossil fuel burning displaced wood burning as an energy source, an increasing concentration of black magnetic spheres was found. These spheres, characteristic of Ryash, probably resulted from the fusion of iron rich components in the fossil fuels (Fig. 3). Using sphericity as an indicator of anthropogenic particles, we had sought out non-magnetic spheres other than charcoal in our Lake Michigan samples. We have observed what appears to be mullite particles (Fig. 3) on this basis. The structure and morphology are similar to those observed for mullite isolated from flyash (HULETTand WEINBERGER, 1979). Thus, it appears that anthropogenic contributions to sediments, produced at high temperatures. have the characteristic of sphericity. Clearly, this may be of great use in separating out other particles produced at high temperatures. This guide should be used with caution, inasmuch as there are some naturally occurring spherical particles, such as pyrite and the cosmic spherules. Still, careful examination of spherical particles extracted from sediments and atmospheric dusts may provide tracers for the types and intensities of high temperature anthropogenic activities. These tracers clearly will provide supplemental information in acid rain, biomass burning and pollution control studies. for example.
~iCROS0~
COAL
TEXTURE
Fig. l(a).
SURFACE
COAL
COAL WOOD
COAL WOOD
Oil.
ETCHED, CONVOLUTED, LAYERED
Fig. 1. Classification of charcoal particles according lo their shapes and surbce textures. The shapes (vertical axis) are viewed under 1000 x magnification and the surface textures (horizontal axis) are observed under So00 x m_gnification.
WOOD COAL
Fig. I(b).
ROOGH, IRREGULAR t PITTED OTCELLULAR
SURFACE TEXTURE
WOOD
COAL
SMOOTH
MICROSCOPIC
._.-.
_.
20pm
10pm Fig. 3. Additional scanning electron micrographs of particles from the Lake Michigan Core: (a) Highly magnetic particles from the pre-1900 period. The shapes are angular and are representative of sedimentary particles. (b) Highly magnetic particles from the post 1900 period. Note the mixture of angular and spherical shapes. The spheres in the sediments are similar to the magnetic spheres found in coal fly ash. (c) A close-up of a group of spheres extracted from the 5-10 cm sediment. (d) 15,000 x magnification of a portion of the surface of the sphere that is outlined in (c). Note the growth of acicufar crystals of muilite.
768
Notes Acknowledgements-This work was supported by Grant DOE EY-76-S-03-0034 PA 84, with the Division of Biology and Medicine, Environmental Sciences Branch, Department of Energy.
REFERENCES CADY G. H. (1942) Modem concept of the physical constituents of coal. J. Gtd. SO, 337-356. EDCINC~TON D. W. and ROBBINSJ. A. (1976) Records of lead deposition in Lake Michigan sediments since 1800. Enoiron. Sci. Technd. 10, 266-274. GOLDBERG E. D., HODGE V. F., GRIFFINJ. J. and KOIDE M. (1981) The impact of fossil fuel combustion on the sedi-
769
ments of Lake Michigan. Environ. Sci. Technol. (in press). GOLDSTEIN H. L. and SIEGMUNCE C. W. (1976) Influence of heavy oil composition and boiler combustion conditions on particulate emissions. Environ. Sci. Technol. 10, 1109-1114. GRIFFINJ. J. and GOLDBERGE. D. (1979) Morphologies and origin of elemental carbon in the environment. Science 2@6, 563-565. HULEIT L. D. and WEINBERGER A. J. (1980) Some etching
studies of the microstructure and composition of large aluminosilicate particles in flyash from coal burning power plants. Enoiron. Sci. Technol. 14, 965-970. SMITH D. M., GR~ J. J. and GOLDBERGE. D. (1975) Spectrometric method for the quantitative determination of elemental carbon. And. Chem. 47, 233-238.