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Bruland, K. W. In Chemical Oceanography; Riley, J. P., Chester, R., Eds.; Academic Press: London, 1983; Vol. 8, Chapter 45. Adelseck, C. G., Jr.; Anderson, T,F. Geology 1978, 6, 388-391.
Williams, P. M. In CaBS Progress Report V ,DOE, 1988. Gorsline, D. S. University of Southern California, Los Angeles, personal communication, 1988. Francois, R. Geochim. Cosmochim; Acta 1987,51,17-27. Froelich, P. N.; Klinkhammer, G. P.; Bender, M. L.; Luedtke, N. A.; Heath, G. R.; Cullen, D.; Dauphin, P.; Hammond, D.; Hartman, B.; Maynard, V. Geochim. Cosmochim. Acta 1977,43, 1075-1090. Jahnke, R. In CaBS Progress Report IV, DOE, 1987.
(41) Lyle, M. Limnol. Oceanogr. 1983,28, 1026-1033. (42) Dymond, J.; Lyle, M.; Finney, B.; Piper, D. Z.; Murphy, K.; Conard, R.; Pisias, N. G. Geochim. Cosmochim. Acta 1984, 48, 931-949. (43) Klinkhammer, G. P. Earth Planet. Sci. Lett. 1980, 49, 81-101. (44) Fischer, K.; Dymond, J.; Lyle, M.; Soutar, A.; Rau, S. Geochim. Cosmochim. Acta 1986,50, 1535-1543. (45) Johnson, K, S.; Stout, P. M.; Berelson, W. M.; SakamotoArnold, C. M. Nature 1988, 332, 527-530.
Received for review January 26, 1988. Revised manuscript received August 11,1988. Accepted October 3,1988. This research was supported by US.Department of Energy Grant No. DEFG05-85ER60340.
Adsorption and Photodegradation of Pyrene on Magnetic, Carbonaceous, and Mineral Subfractions of Coal Stack Ash T. D. J. Dunstan, Robert F. Mauldln, Zhong Jlnxlan, Anthony D. Hipps, E. L. Wehry,” and Gleb Mamantov+
Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996 Two coal stack ashes have been separated into three principal subfractions (carbonaceous, mineral, and magnetic). Photoreactivities and adsorptivities of pyrene on the three subfractions have been determined, the latter by gas-solid chromatography. For each ash, the carbonaceous subfraction is the strongest adsorbent and has the greatest ability to stabilize adsorbed pyrene toward photodegradation, while the mineral subfraction is a much weaker adsorbent and pyrene adsorbed on it shows relatively high photoreactivity. The magnetic subfraction is the weakest adsorbent, but any pyrene adsorbed on its surface is relatively resistant to photodegradation. The presence of even a small quantity of carbon in coal ash leads to stabilization of adsorbed pyrene toward photodegradation, by comparison with silica, alumina, or glass surfaces. The relative quantity of carbon in coal ash appears to be the main factor determining the extent of photochemical reactivity of pyrene adsorbed on the surface. In coal ashes that contain a relatively large quantity of iron, the magnetic particles may play a minor role in stabilizing adsorbed pyrene toward photodegradation.
Introduction Organic compounds released in the vapor phase by combustion sources are cooled as they enter the atmosphere. As cooling occurs, relatively involatile compounds, including many polycyclic aromatic hydrocarbons (PAHs) and their derivatives, condense on the surfaces of ambient particles (1-3). PAHs and their derivatives, extracted from sampled airborne particulate matter, are both carcinogenic and mutagenic (4-8). An important class of atmospheric particulate matter consists of ash produced from minerals and carbon in coal (9). Studies of PAH-laden particles to infer the atmospheric residence times of PAHs, and the identities and possible toxicities of the products formed by photooxidation, have been performed under both real and simulated environmental conditions (10-1 7). We have previously studied the photochemical transformation of several PAHs deposited from the vapor phase on eight coal stack ashes of diverse properties and origins (17).PAHs were deposited from the vapor phase, rather than liquid solution, to simulate the known mechanism for deposition of PAHs on fly ash during combustion of coal (6-8). 0013-936X/89/0923-0303$01.50/0
The results of these studies (17)showed that (a) all coal ashes stabilize PAHs toward photodegradation, by comparison with silica, alumina, or glass surfaces; (b) different coal ashes stabilize adsorbed pyrene or benzo[a]pyrene to photodegradation with different efficiencies, with ashes relatively high in carbon and/or iron content showing the greatest stabilization of adsorbed PAHs; and (c) suppression of photolysis of adsorbed organics can arise in part from the “inner filter effect” of the highly colored and porous ash substrates. Coal stack ash is a complex inhomogeneous mixture of particle sizes, shapes, and colors. It is an aluminosilicate material comprising several distinct phases (18-20). They include the following: (a) a mullite-quartz “crystalline” phase (of composition ranging from 2A1203.Si02 to 3A1203.2Si02);(b) an aluminosilicate glassy phase containing various impurities including iron; (c) a magnetic phase, which may be a “magnetic spinel” (FeA1,OJ (19, 20) or a mixture of Fe203and Fe304(18,21,22);and (d) a carbonaceous phase (23-26). For the eight stack ashes previously studied (13,Si02and Al2O3, together with CaO and MgO, comprise 70-96% of the weight of the ash; oxides of iron account for 2.4-24% of the composition; and carbon accounts for only 0.3-5.5% of the composition. To compare the ability of coal ash particles of different chemical composition to stabilize adsorbed PAHs, we have separated two stack ashes into three principal subfractions (viz., mineral, magnetic, and carbonaceous). In our earlier studies ( I 7),these two ashes exhibited substantially different abilities to suppress photolysis of adsorbed PAHs. The first ash is Kaneb (KA), with relatively high carbon content (5.5%), on which adsorbed PAHs underwent relatively inefficient photodegradation. The second is Texas (TX) lignite ash, with a low carbon content (0.64%), on which adsorbed PAHs underwent relatively efficient photodegradation. We compare the photoreactivities of pyrene adsorbed on subfractions of each ash and use gas-solid chromatography (27-30) to characterize the affinities of the various subfractions for pyrene vapor. Pyrene was chosen as a representative PAH for these studies. Pyrene is a relatively stable PAH encountered largely in the particulate (rather than gaseous) phase in atmospheric samples; it is a major PAH camponent of atmospheric particles transported over long distances (31).
0 1989 American Chemical Society
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Table I. Mass Distribution and Carbon Content of Different Size Fractions of Coal Stack Ashes
Table 11. Compositions of KA and TX Ashes and Their Subfractions
ash
w
% of unfractnated asha
% Ca
KA
