Leaching of Boron from Coal Ash James A. Cox*, Gary L. Lundquist', Andrzej Przyjazny2, and C. David 'Schmulbach Department of Chemistry and Biochemistry, Southern Illinois University at Carbondale, Carbondale, 111. 62901
in the expected range for Illinois coal, but the 170 ppm sample is well above the average ( I ) .
Coal fly ash contains significant levels of boron, which is potentially phytotoxic if it is in a soluble state. The quantity of boron leached and the factors that influence the leaching process were studied. Boron levels in fly ash were found as high as 1900 ppm, and about 50% was leachable into water. The leaching rate was greater into acid solution, but the total soluble quantity was independent of pH over the range 6-8. The boron content of bottom ash was 960 ppm, and it was essentially insoluble. Treatment of ash for 30 min at 1200 "C decreased the leachable boron in fly ash to 6% of the total. From ESCA spectra of fly ash, before and after leaching, it was apparent that the boron is initially in two independent chemical states, one of which is insoluble. Coal typically contains 5-200 ppm B, depending upon the area from which it is mined ( I ) . Consideration of published data leads to the conclusion that the boron is concentrated in the ash (2).As disposal of industrial ash waste commonly involves the sluicing of ash in large lagoons, the extent to which boron is leached from the ash is a matter of interest, particularly in light of the probable increased burning of coal in energy production. The problem is especially significant because there is an unusually narrow range over which boron is transformed from a beneficial plant nutrient to a phytotoxic substance (3,4 ) . The toxic level also varies extensively with species ( 3 4 , soil pH ( 6 ) , and soil type (7). In the present study the percentage of leachable boron in ash was measured, and certain factors that influence the rate and extent of the leaching process were investigated. Experimental
The determinations of the total quantity of boron in coal and ash were generally by dc arc emission spectrometry. An Applied Research Laboratory spectrographic analyzer, Model 26000-1, was used. The concentrations were evaluated by comparison of the unknowns, diluted 1 : l O with spectroscopic grade graphite (National Carbon Co.), to working curves prepared by dilution of 0.709/0 Bz03 low boron glass (National Bureau of Standards) with graphite; selected results were verified by standard addition of that glass. The excitation was by a 10-A full-wave rectified arc applied for 1min to samples packed in L4261-5PK (National Carbon Co.) electrodes. Intensities were estimated by the log sector method. The results of the arc emission procedure were verified by spectrophotometry following ignition of the coal or ash in the presence of calcium hydroxide (8). The carminic acid spectrophotometric procedure was used in this case as well as for the other determinations of boron in solution (9). The ESCA experiments were performed by Physical Electronics Industries, Inc. (Eden Prairie, Minn.). The samples investigated were treated as discussed below. Coal and ash samples were provided by Illinois Power Co. (Decatur, Ill.) in ca. 2-kg lots. Representative fractions were dried at 110 OC, mixed and powdered with a stainless steel ball mill, and sieved with a 120-mesh screen. The original sources were Southern Illinois coal (2 lots, 118 and 170 ppm B) and a low-sulfur Western coal (135 ppm B). The former values fall Present address, E t h y l Corp., Baton Rouge, La. Present address, Chemistry Department, Technical University of Gdansk, Gdansk, Poland.
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Environmental Science & Technology
Results and Discussion To determine the extent of leaching of boron (as borate or boric acid), 0.5-g samples of fly ash or bottom ash were stirred in 200 mL of HzO at room temperature for 2 h and filtered; it was independently established that all the soluble boron was leached well within 2 h under these conditions. The total quantity of boron (as borate) in the filtrate was determined and compared to the total boron originally in the fly ash. The results are summarized in Table I. Clearly, a large fraction of the boron in the fly ash is in a soluble state, whereas the boron in the bottom ash is essentially insoluble. The total quantity of boron leached does not depend significantly upon pH. Over the pH range 6-8, the percent leached is 50 f 5; at pH 10,38%is leached. The latter pH is out of the normal range for natural waters. The rate of leaching is, however, pH dependent. The initial rate of dissolution is increased by an increase in acidity (Figure 1).Also apparent from Figure 1 is the fact that the leaching is very rapid. A 15-min contact of the fly ash to water is sufficient to leach all of the soluble boron from the ash. Thus, the boron content of an ash sluice pond effluent cannot be controlled by the design of the pond (contact time of the ash with water) or by adjustment of the pH of the system. The above results suggest two points about the state of boron in ash. At least two independent chemical states of boron must be present in fly ash, and one or more is insoluble. Second, the soluble species is not present in bottom ash. The first point was substantiated by ESCA. Spectra were obtained from dry fly ash and from a sample of fly ash that had been leached and redried. The interpretation of the spectra was complicated by surface charging which caused an apparent 3-eV peak shift and by the fact that the B-level was very near the detection limit of the technique. The unleached Table 1. Percentage of Boron Leached from Coal Ash Coal source (ppm B In coal)
Ash type
Southern Illinois (170) Southern Illinois (170) Western low sulfur (135)
Fly
a
ppm B, ash
1900
Bottom Fly
960 1320
% B leacheda
45 f 9 0.1 f 0.1 34 f 4
Leaching solutions, pH 6-8 phosphate buffers at 0.1 ionic strength.
10
2C
30
40
5C
53
Time,Sec Figure 1. Effect of pH on rate of leaching of boron from fly ash A: pH 4.55 phosphate buffer at 0 OC;B: pH 7 . 4 0 phosphate buffer at 0 OC. 1 g of ash was mixed with 100 mL of buffer; B: ppm determined in 1-mL fractions removed by suction filtration at stated times
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Table II. Thermal Flxatlon of Boron in Fly Ash a Firing time
0
1 min 5 min
30 min 8h 30 min a
Temp,
O
C
... 1200 1200 1200 1200
800
Ash from 118 ppm B Southern Illinois coal.
% 6 leachableb
34 13 7
6 6 33
These data indicate that a thermal treatment may be a successful means of preventing excessive quantities of boron from coal fly ash from entering water systems. However, for the method to be practical, an efficient means of increasing the residence time of the ash in the high-temperature zone of the furnace must be developed. Alternatively, the use of boron-specific ion-exchange resins as a posttreatment can be employed in certain situations that have moderate flow volumes and where high-B effluents represent an environmental hazard ( I 0).
Determined as in Table I.
sample showed two boron 1s binding energies (at 192 and 187 eV); the peak intensities were in the ratio suggested from the data in Table I. The 192-eV peak was also present in the leached and redried fly ash sample. The surface concentration in the bottom ash sample was below the detection limit. Qualitative identification of the B-species was not possible because of the lack of appropriate standards and the abovementioned interpretation problems. I t was noted, however, that the persistent peak may be a polyborate or borosilicate since these species readily form at high temperatures. Also, borax shows a peak a t 191 eV and would be expected to have an electronic environment similar to these species. That the boron in the bottom ash did not leach indicated that it may be possible to thermally fix the boron in fly ash; a major difference in the history of the ashes is the residence time in the hot zones of the furnace. A series of identical fly ash samples, 0.5 g, were heated in a muffle furnace for different times a t two temperatures and were subsequently mixed for 1 h in 200 mL of pH 4.5 phosphate buffer. The results are shown in Table 11.An identical study with Western coal ash also showed the pattern that firing at 1200 “C rapidly converted the boron to an insoluble state.
Acknowledgment
Interpretation of the ESCA data was aided by L. E. Davis, Physical Electronics Industries. Literature Cited (1) Ruch, R. R., Gluskoter, H. J., Shimp, N. F., Environmental Ge-
ology Notes, No. 72, Illinois St. Geological Survey, Aug. 1974. (2) Von Lehmdem, D. J., Jangers, R. H., Lee, R. E., Anal. Chem., 46, 239 (1974). (3) Eaton, F. M., J . Agric. Res., 69,237 (1944). (4) MacKay, D. C., Langille, W. M., Chipman, E. W., Can. J. Soil Sci., 42,302 (1962). (6) Gupta, U. C., Soil Sci. SOC.Am. Proc., 36, 332 (1972). (7) Hatcher, J. T., Blair, G. Y., Bower, C. A,, Soil Sci., 88, 98 (1959). (8) Nemodrak, A., Karalova, Z., “Analytical Chemistry of Boron,” Siwan Press, Jerusalem, Israel, 1964. (9) “Standard Methods for the Examination of Water and Wastewater, 13th ed.,” American Public Health Assoc., Washington, D.C., 1971. (10) Kunin, R., “A Macroreticular Boron-Specific Ion-Exchange Resin,” in “Trace Elements in the Environment,” E. L. Kothny, Ed., Advances in Chemistry Series 123, American Chemical Society, Washington, D.C., 1973.
Received for review September 22,1977. Accepted December 19,1977. Work supported by a grant from Illinois Power Co., Dscatur, Ill., to J.A.C. and C.D.S.
Trace Elements in the Flesh and Liver of Two Fish Species from Polluted and Unpolluted Areas of the Aegean Sea Apostolos P. Grimanis”, Demetrios Zafiropoulos, and Maria Vassilaki-Grimani Department of Chemistry, Nuclear Research Center “Demokritos”, Aghia Paraskevi Attikis, Athens, Greece
Ten trace elements (As, Cd, Co, Cu, Fe, Hg, Rb, Sb, Se, and Zn) were determined by neutron activation analysis in the flesh and liver of the two edible fishes Sargus annularis and Gobius niger caught from polluted and unpolluted areas of the Aegean Sea. Increased levels of arsenic were found in the flesh of Sargus annularis from the polluted areas studied. Arsenic levels were also increased in the flesh and liver of Gobius niger from the Athens sewage outfall area. Elevated concentrations of mercury were found in the flesh of Sargus annularis and in the flesh and liver of Gobius niger from a sea area close to Mytelene Harbor in the island of Lesvos. No significant differences were found for all the other elements determined. Elevated levels of arsenic and mercury found in these two species of edible fish from polluted areas were not high enough to render them dangerous for human consumption.
Trace elements from anthropogenic activities and natural processes enter the marine environment. Increasing inputs from various treated or untreated municipal and industrial effluents, agricultural runoff or increased runoff due to the disturbance of drainage basins, as well as from the atmo-
sphere, threaten to alter quantitatively and qualitatively the natural biogeochemical cycles. Trace elements, some of which are toxic, may accumulate in edible marine organisms, thus endangering human health (1-3). The domestic and industrial wastewater for most of the greater Athens, Greece, area is discharged into the relatively shallow waters of Keratsini and Elefsis Bays at the upper end of Saronikos Gulf of the Aegean Sea. Such discharges are known to contain organic and inorganic micropollutants including toxic trace elements ( 4 , 5 ) . According to a recent study (6),the discharge of industrial and domestic wastes in the Keratsini and Elefsis Bays of the upper Saronikos Gulf has resulted in elevated concentrations of toxic and other trace elements in sediments of at least 100 km2 of seafloor. Principal source areas appeared to be the industrial plants at the entrance of Piraeus Harbor, the Athens sewage outfall, and the industries in the northern and eastern Elefsis Bay. Edible fish tissues of Pagellus erythrinus collected from the Keratsini Bay were also found to contain 2-2.5 times higher As and similar Hg concentrations compared to those found in the same species of fish collected from an unpolluted area of the Aegean Sea (7). In this paper we present the results of a more intensive multielement study-made by neutron activation analy-
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