Environ. Sci. Technol. 1988, 22, 1506-1508
NOTES Effect of Hydrofluoric or Hydrochloric Acid Pretreatment on the Ultrasonic Extraction of Organic Materials from Fly Ash for Chromatographic Analysis Colin D. Chriswell," Ikue Ogawa, Melvin J. Tschetter, and Richard Markuszewski
Ames Laboratory, US. Department of Energy, Iowa State University, Ames, Iowa 5001 1 In order to increase the amounts of organic material extracted ultrasonically from fly ash for chromatographic analyses, the effects of acid pretreatment were investigated. Fly ash samples were extracted without pretreatment, after pretreatment with hydrofluoric acid (HF), and after pretreatment with hydrochloric acid (HC1). Gas and liquid chromatographic profiles of the extracted materials revealed that both HF and HC1 pretreatments led to the recovery of greater amounts of organic material than without pretreatment, and pretreatment with HF increased the recovery of organic material significantly more than pretreatment with HCl. The effectiveness of HF pretreatment is believed to be due to dissolution of sorbing matter, such as silica and metal salts, originally present in the fly ash. Chromatograms of the extracts of HC1pretreated fly ash samples did contain some more intense peaks than those found in chromatograms of HF-pretreated fly ash. These findings indicate that pretreatment with HF alone is not effective in releasing all of the organic components from fly ash. H
Introduction Characterization of organic species adsorbed on particles emitted during combustion is an essential step in assessing the potential health and environmental effects of the combustion of coal. Extraction of the organic species from such particles is the first step in their characterization. Soxhlet, ultrasonic, and other extraction techniques are widely used (1-5). However, these procedures are only effective in removing a small fraction of the total organic material originally present on the emitted particles ( 2 , 6 , 7). It is reasonable to assume that extraction of particles is difficult because their matrices contain silica, alumina, metal oxides, and possibly even activated carbon, all of which are excellent adsorbents for organic compounds. It has, in fact, been found that fly ash arising from the combustion of coal can be used to sorb organics as well as trace elements from ash pond effluents (8) and to adsorb low molecular weight aromatic hydrocarbons and polychlorinated biphenyls from boiler sluice water (9) and even from hydrocarbon solvents (IO). In previously reported work, the components typically present on fly ash samples from the Ames municipal power plant have been reported to include alkanes, aromatic hydrocarbons, polycyclic aromatic hydrocarbons, organic acids, and phenols (11,12). Of these components, only two, decane at 1.5 mg/kg and phenol at 1.1mg/kg, have been determined at concentrations on the fly ash exceeding 1 PPm. Previously, it has been shown that recovery of organic materials from glass-fiber filters (13) and from magnesium silicate (Florid) (14) is facilitated by dissolving the sample matrix with hydrofluoric acid (HF). In the present work, 1506
Environ. Scl. Technol., Vol. 22, No. 12, 1988
particulates, i.e., fly ash, formed during the combustion of a mixture of coal and refuse-derived fuel were pretreated with HF in an attempt to dissolve any silica present and to deactivate or partially dissolve other inorganic components. It was anticipated that this approach would lead to enhanced extraction of organic materials from the fly ash.
Experimental Section HF Pretreatment of Fly Ash. Electrostatic precipitator fly ash was collected at the Ames municipal power plant during the combustion of a mixture of coal and refuse-derived fuel. The fly ash samples were collected directly from the cold-side electrostatic precipitator hoppers. Three 50-g samples of this fly ash were weighed into 300-mL platinum dishes and wetted with 25 mL of organic-free water. Each sample was cooled in an ice bath for 10 min, and 25 mL of reagent-grade 48% HF (Fisher Scientific, Pittsburgh, PA) was added with constant stirring during addition. The sample was then allowed to react a t room temperature overnight (-16 h). The reacted sample was then heated to a temperature of -50 "C on a hot plate for 1.5 h. The sample was next cooled and transferred to a centrifuge tube, and the solids remaining in the sample were separated by centrifugation. The aqueous phase was decanted into a separatory funnel, and the remaining solids were washed with organic-free water and then separated again by centrifugation. The second aqueous phase was added to the initial washing in the separatory funnel, and the solids were transferred to a 100-mL beaker. Blank determinations were performed as above on duplicate samples of magnesium silicate. HCl Pretreatment of Fly Ash. Replicate samples of fly ash were treated in manner identical with that described above, except that hydrochloric acid (HC1) was used in place of HF for the acid pretreatment. Solvent Extraction. Aqueous phases arising from the acidic pretreatment of fly ash were extracted with three 50-mL aliquots of dichloromethane, three 50-mL aliquots of benzene and, after adjustment of pH to 11 with 10% sodium hydroxide solution, with three additional aliquots of benzene. The extracts were concentrated by distillation to a volume of approximately 10 mL over a steam bath using a three-ball Snyder condenser and then further evaporated to a final volume of 1 mL under a stream of nitrogen gas. Ultrasonic Extraction. Solid residues remaining after the HF and HC1 pretreatments and untreated samples of fly ash were mixed with 50-mL portions of dichloromethane and extracted for 5 min by use of an Artex-Sonic 300 Dismembrator equipped with a medium tip and operated at 240 W. The solvent was removed by filtration
0013-936X/88/0922-1506$01.50/0
0 1988 American Chemical Society
through a medium-porosity sintered glass filter, and the residue was reextracted in the same manner two additional times with 50-mL portions of dichloromethane and three additional times with 50-mL portions of a 20240 methanol-benzene mixture. The combined extracts were reduced in volume to 1mL as described above. Extracts of residues from the acid pretreatments were combined with the extracts of the aqueous phases. Chromatographic Profiles of Extracts. The constituents of the extracts were separated by gas and liquid chromatography. An SP8000 liquid chromatograph (Spectra Physics, Santa Clara, CA) equipped with a 254nm fixed UV detector, a variable UV-vis detector (Tracor, Austin, TX), and an Aminco-Bowman spectrofluorometer with a 9-pL flow cell (American Instruments, Silver Spring, MD) was used for the liquid chromatographic separations, and a Tracor Model 560 gas chromatograph equipped with flame ionization detectors was used for the gas chromatographic separations. Liquid chromatographic separations were performed as follows: with a Zorbak CI8 5-pm column, 4.6 mm 0.d. X 25 cm long; a temperature of 25 "C; an initial mobile-phase composition of 20% acetonitrile and 80% water, a linear gradient to 50% acetonitrile in 10 min, 15 min at 50% acetonitrile, and then an increase to 100% acetonitrile in 20 min; 25-pL samples; and flow rates of 1.0 mL/min. Gas chromatographicseparations were obtained by using a 2 mm x 2 m column packed with 3% OV-17 on 8O/lOO mesh Supelcoport. Injections (5 pL) were made at an injection port temperature of 250 "C and a detector temperature of 275 "C. The column was held at 60 "C for 2 min, then programmed to 250 "C at 10 "C/min, and held at the final temperature for 10 min.
Results and Discussion In the present work, the limited goal was to determine the feasibility of the concept of dissolution or deactivation of mineral matter in fly ash by acid treatment to enhance the removal of adsorbed organic material. This goal was economically accomplished by comparison of chromatographic profiles of components isolated from fly ash samples by ultrasonic extraction alone and by ultrasonic extractions after HCl and HF pretreatment. Individual components extracted were not identified in this work because identifications have previously been made on extracts of the same fly ash (11,12). Comparison of Gas Chromatographic Profiles. The chromatographic profiles of the organic compounds extracted from fly ash with and without acid pretreatments are depicted in Figure 1. The total area under all peaks arising from the gas chromatographic separation of extracted components was integrated and compared for the three extraction procedures used. Ultrasonic treatment alone of the fly ash samples led to an average recovery of 0.2 mg of organic material/kg of fly ash, ultrasonic treatment after HC1 extraction led to an average recovery of 1 mg/kg, and ultrasonic extraction after HF pretreatment led to an average recovery of 14 mg/kg. Blank determinations performed on magnesium silicate samples resulted in the recovery of no detectable components. Acid pretreatment of fly ash samples was thus shown to result in greater recovery of organic materials than extraction without pretreatment, as is evident in Figure 1. The HC1- and HF-pretreated extraction samples yielded dissimilar gas chromatographic profiles, indicating that the HF pretreatment likely enhances the extraction of different components that does the HCl pretreatment. Thus, HF pretreatment alone increases the total amount of extracted material but does not lead to the effective recovery
n
ULTRAS0 NIC EXTRACT I 0 N NO PRETREATMENT
X
ULTRASONIC EXTRACTION HCL PRETREATMENT
(j
ULTRASONIC EXTRACTION HF PRETREATMENT
s
N
x Figure 1. Gas chromatographic profile of fly ash extracts.
of every organic component from fly ash. A significant difference in the gas chromatographic profiles is the presence of a major constituent in the HF extract. This constituent was identified by gas chromatography/mass spectrometry as phenol. The concentration of phenol in the HF extract was found to be 13 mg/kg by comparison of peak area with an external standard. The total amount of all other components separated was approximately the same whether HF or HC1 pretreatments were used. In previous work with fly ash samples from the same source, which were not acid treated before extraction, phenol was also found to be a major constituent (11,12), but the highest concentrations previously found were only -1.1 mg/kg while concentrations below 0.1 mg/kg were more typical. It is reasonable that acid treatment of fly ash would enhance the recovery of phenol by converting any phenolate ions present to more extractable, neutral forms. However, this effect would be expected to be the same regardless of the acid used. One possible explanation for the high concentrations determined is that phenol may be bound with silicaceous material and is only released upon dissolution of that material with HF. Another possibility is that phenol is formed from some nonchromatographable precursor by reactions involving HF. Because no phenol was detected in blank determinations, the phenol determined was not an artifact related to the HF or the apparatus used. Comparison of Liquid Chromatographic Profiles. As shown in Figure 2, HF pretreatment of fly ash resulted in the recovery of more components with intense absorbances at 270 nm and greater fluorescenceintensities than did either the HC1 pretreatment or extraction of fly ash with no Pretreatment. Profiles similar to those at 270 nm were obtained for absorbance detection at 254 nm. If it is assumed that the components separated by the three techniques had similar molar absorptivities and fluorescence quantum eficiencies, then these profiles indicate that significantlymore material was recovered by using the HF pretreatment prior to ultrasonic extraction of the fly ash. However, it is also of interest to note that when different detection schemes were used, the extracts arising from HC1 Environ. Sci. Technol., Vol. 22, No. 12, 1988
1507
Registry No. HF, 7664-39-3;HC1,7647-01-0; CH2C12,75-09-2. ULTRA SONIC E X T R A CTI 0 N
2 X
NO PRETREATMENT
2 X
-
ULTRASONIC EXTRACTION
lD
X
H C L PRETREATMENT
-f lD
X
ULT R A S 0 NI C E XT R ACT1 0 N
UF PRETREATMENT
X
Figure 2. Liquld chromatographic profiles of fly ash extracts. Lower
traces for UV absorbance detection at 270 nm; upper traces for fluorescence detection at 305-nm excitation and 420-nm emission.
pretreatment always had some components yielding more intense peaks than the extracts arising after HF pretreatment. This confirms the observations from the gas chromatographic profiles that HF pretreatment alone does not provide a means for isolating all of the organic components from fly ash. Conclusions
Pretreatment of fly ash with HF or with HC1 before ultrasonic extraction leads to the recovery of far greater amounts of organic materials than does ultrasonic extraction alone. Pretreatment of fly ash with HF before ultrasonic extraction appears to lead to recovery of far greater amounts of organic materials than does pretreatment of fly ash with HC1. However, pretreatment with HC1 does lead to the recovery of many different components than does pretreatment with HF. Acknowledgments
We appreciate the helpful discussions and advice offered by H. J. Svec, J. S. Fritz, G. A. Junk, and J. J. Richard.
1508
Environ. Sci. Technoi., Voi. 22, No. 12, 1988
Literature Cited (1) Stanley, T. W.; Meker, J. E.; Morgan, M. J. Environ. Sci.
Tech. 1967, 1, 927. (2) Griest, W. H.; Yeatts, L. B., Jr.; Caton, J. E. Anal. Chem. 1980, 52, 199. (3) Sucre, L.; Jennings, W.; Fisher, G. L.; Raabe, 0. G.; Olechae, J. Trace Organic Analysis: A New Frontier i n Analytical Chemistry; Hertz, H. S., Cheder, S. N., Eds.; National Bureau of Standards Special Publication 519; U.S. Government Printing Office: Washington, DC, 1979; p 109. (4) Clemo, G. R. Tetrahedron 1973,29, 3987. ( 5 ) Clemo, G. R. Tetrahedron 1970,26, 5845. ( 6 ) Griest, W. H.; Guerin, M. R. Identification and Quantification of Polynuclear Organic Matter in Particulates from Coal-Fired Power Plants; EPRI-EPA Report; Oak Ridge National Laboratory: Oak Ridge, TN, 1979; p 1095. (7) Caton, J. E.; Griest, W. H.; Yeatts; L. B.; Henderson, G. M.; Tomkins, B. A. Presented a t the Analytical Chemistry Division Information Meeting, Oak Ridge National Laboratory, Oak Ridge, T N June 1979. (8) Liskowitz, J. W.; Trattner, R. B.; Grow, J. M.; Sheih, M. S.; King, J. A,; Kohut, J.; Zwillenberg, M. In Fossil Fuels Utilization: Environmental Concerns; Markuszewski, R., Blaustein, B. D., Eds.; ACS Symposium Series 319; American Chemical Society: Washington, DC, 1986; p 332. (9) Junk, G. A,; Richard, J. J.; Avery, M. J.; Conzemius, R. J.; Benson, J. E.; Chriswell, C. D. Physical Coal Cleaning: Characterization of Constituents in Waste and Process Streams; NTIS, DE87001097, 1987. (10) Junk, G. A.; Richard, J. J.; Ames Laboratory USDOE, Ames, IA, unpublished work. (11) Junk, G. A,; Chriswell, C. D.; Richard, J. J.; Avery, M. J. "Environmental Effects of Using Municipal Solid Waste as a Supplementary Fuel-Organic Compounds"; Ames Laboratory Quarterly Report-July 1-September 30,1984; prepared for the Pollutant Characterization and Safety Division, Office of Health and Environmental Research, Office of Energy Research, Department of Energy; IS-4875, UC-BOE, NTIS, March 1985; pp 94-127. (12) Avery, M. J.; Chriswell, C. D.; Junk, G. A.; Richard, J. J., Environmental Impact of Co-combustion of Coal and Municipal Waste Organic Compounds; IS-4894, UC-20e, NTIS, 1986. (13) Kukreja, V. P.; Bove, J. L. J . Environ. Sci. Health 1976, A l l , 517. (14) Kissinger, L. D. Ph.D. Dissertation, Iowa State University, Ames, IA, 1978; p 104. Received for review January 26, 1988. Accepted M a y 2, 1988. Ames Laboratory is operated for the US.Department of Energy by Iowa State University under Contract No. W-7405-ENG-82. This work was supported in part by the Assistant Secretary for Environment through the Office of Health and Environmental Research and in part by the Assistant Secretary for Fossil Energy.
