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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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Suggested Citation:"COAL COMBUSTION." National Research Council. 1980. Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health. Washington, DC: The National Academies Press. doi: 10.17226/19799.
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5 COAL COMBUSTION Estimated total amounts of trace elements mobilized in the environment from coal use in 1975, compared with those mobilized in the form of industrial and consumer products, are presented in Table 15. The data show that the amounts of beryllium, lithium, selenium, and vanadium mobilized throuqh coal use are one to two times qreater than those mobilized throuqh industrial and consumer products. The amounts of boron, barium, and cobalt mobilized are 39, 22, and 17 percent, respectively, of those mobilized by industrial and consumer products. Mobilization of antimony, cadmium, fluorine, mercury, and molybdenum from coal use is 3 to 6 percent of the amounts mobilized in the form of industrial and consumer products. Compared with industrial and consumer product mobilization, amounts of chromium, copper, lead, nickel, and zinc mobilized by coal use are quite small, in each instance equivalent to less than 2 percent (Table 15). COMBUSTION RESIDUES Residues from coal-fired power-qeneration plants in qeneral can be assiqned to the followinq cateqories: •boiler bottom ash (boiler slaq)1 • fly ash, captured in emission-control devices and/or emitted to the atmosphere throuqh stacks1 • flue-qas desulfurization (FGD) sludqe resultinq from the removal of S02 from the combustion qases1 • atmospheric qases1 and • wastewaters. The quantities of wastewater in contact with coal-derived trace elements are small in comparison with those of other waste streams noted previously1 however, some of the ash constituents miqht be dissolved in this water. Fiqure 12 is a residual-flow diaqram showinq staqes where the various types of residues are qenerated. Three cateqories of boiler are conunonly used in power-qeneration plants. These are stoker-fired boilers, cyclone furnaces, and pulverized-coal-fired (PC-fired) furnaces. The use of stoker-fired 64

65 TABLE 15 Estimates of Annual Mobilization of Trace Elements into the Environment from Coal Use and Industrial and Consumer Products Industrial and a b Coal Use Consumer Product Use Ratio of Coal Element (tons/year) (tons/year) to Product Use As 1,669 Sb 389 12,987 0.030 Ba 166,890 757,000 0.220 Be 389 192 2.03 B 38,941 100,000 0.389 Cd 111 3,340 0.033 Cr 3,894 256,000 0.015 Co 1,112 6,400 0.174 Ca 5,563 1,530,000 0.004 F 35,046 606,000 0.058 Pb 2,782 1,300,000 0.002 Li 3,894 3,540 1.10 Hg 68 1,932 0.035 Mo 834 25, 872 0.032 Ni 2,782 146,500 0.019 Se 723 530 1. 36 v 8,345 5,500 1.52 Zn 10,570 1,232,000 0.009 aFor 1975 with coal use of 556,301,000 tons and assuming that concen- trations of trace elements in all coal used are equal to mean values for subbftuminous coal. From Hittman Associates, Inc. (1977). bl975 consumption. From U.S. Bureau of Mines (1977). boilers for major electric power qeneration stations is diminishinq1 however, their use in smaller industrial plants is expected to increase as these plants convert from oil firinq to coal firinq. They represent a potential source of widely dispersed, low-level emissions, which are frequently poorly controlled by the operators. Hiqh temperatures encountered in the fuel beds could result in volatilization of some elements that are not normally vaporized in larqe PC-fired furnaces. Construction of new cyclone furnaces in electric power qeneration stations has essentially stopped because of problems associated with emissions of oxides of nitroqen. In the cyclone unit, 70 to 80 percent of the ash is melted and is continuously tapped from the bottom of the furnace as slaq. The remaininq 20 to 30 percent is collected from the stack qas by techniques similar to those used in the PC-fired units. The PC-fired boiler unit is of two types--wet and dry bottom--with newer units being almost exclusively the latter. In both, the bottom of the fire box contains one or more hopper-shaped openinqs through which 20 to

66 LIMESTONE OR LIME: COAL (SLURRY FORM) FURNACE: DUST ELECTROSTATIC COAL CYCLONE COLLECTOR: PRECIPITATOR: PULVERIZER - - - - WET BOTTOM LARGE FINE DRY BOTTOM PARTICU- FLY ASH LATES CLARIFIER PYRITE ,.._........__.,. RECYCLE 5-15% SOLIDS I BOTTOM HYDROBIN WATER I ASH FLY FLY FGD SLUDGE OR SLAG ASH ASH I ~ I + • \:ffaofhWJ:•:·:AS0~r·5ff+trN<r·PONDllti} ~ I ··:·:·:·:·:·:·.·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·;·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:· TRUCKER ' \ \ COMBINED FLY ASH FLY ASH FGD SLUDGE \ AND BOTTOM ASH 80% SOLID \ I \ ~ \ j FIGURE 12 Flow diaqram of a coal-fired power plant equipped with FGD sludqe system (Bern, 1976). 30 percent of the ash in the form of larqe fused pieces drops into a water-filled hopper, whence they are subsequently sluiced to a settlinq pond. The wet-bottom furnace, whether PC or cyclone, operates at hiqher temperatures in the fire box so that more of the ash is melted and flows throuqh a slaq tap into a water-filled hopper below. This material is referred to as boiler slaq. Small ash particles entrained with the combustion products from the boiler are collected at the stack by means such as electrostatic precipitators and baq filters (fly ash) and wet scrubbers (FGD sludqe), with collection efficiencies as hiqh as 95 to 99.7 percent by weight. The percentaqe of bottom ash, boiler slaq, and fly ash in relation to the furnace confiquration is shown in Table 16. The amount of bottom ash, boiler slaq, and fly ash produced in the United States in 1971 was estimated at approximately 10, 5, and 27 million tons, respectively (Brackett, 1973). In 1974, ash production soared to a record hiqh of 59.5 million tons (National Ash Association, 1975). The main uses for these types of coal ashes are manufacturing cement, fill material, and road and airport-runway construction. The amounts of bottom ash, boiler slaq, and fly ash used in 1971 were 16.0, 75.2, and 11.7 percent of their respective totals produced that year. Increased coal consumption and increased efficiency of ash collection by the power-qeneration industries will result in production of qreater

67 TABLE 16 Percentage of Coal Ash from Various Furnace Configurationsa Bottom Boiler Fly Ash Slag Ash Furnace (percent) (percent) (percent) Stoker fired, traveling 100 Stoker fired, spreader 45-85 15-55 Cyclone fired 80-85 15-20 Pulverized coal, wet bottom 50 50 Pulverized coal, dry bottom 20-25 75-80 asource: Bern (1976) • quantities of ash. The need for new utilization and/or proper methods of disposal is evident. Data on the amount of coal residues emitted to the atmosphere and subsequently deposited on veqetation and soils are rather limited, because of the obvious difficulties involved in such measurements. However, mass balance estimates have been made to measure the approximate amount and/or rate of fine particulate emission. Table 17 gives an example of the percentaqe of fly ash (ash in the flue qas) in three different power stations. Collection efficiencies better than 99 percent are shown for the noncyclone boiler stations. Estimates made over the past several decades by the U.S. Bureau of Mines suqqest that fly ash released to the atmosphere is about 10 percent of the total amount of ash in (the combusted) coal. The estimated amounts of 25 trace elements discharqed into the atmosphere from three coal-fired steam plants with a combined daily coal consumption of 25,000 tons are shown in Table 18. The need to remove substantial quantities of S01 from the flue qases is dictated by the Federal Clean Air Act and by state and local requlations. This leqislation requires the power industry to use TABLE 17 Percentage of Fly Ash in the Flue Gas at Three Power Stationsa Fly Ash (percent Station Description of total ash) 1. Wyoming, subbituminous coal, 0.3 750 MW 2. Wyoming, subbituminous coal, 0.7 350 MW 3. North Dakota, lignite coal, 250 MW asource: U.S. Environmental Protection Agency (1975). bThis is a cyclone boiler station.

68 TABLE 18 Combined Daily Atmospheric Discharge of Elements from Coal-Fired Steam Plantsa Atmospheric Discharge Element (kg/day) Al 510 As 3.4 Ba 5.1 Br 96 (gaseous) Ca 170 Cd 0.2 Co 0.3 Cr 5.1 Cs 0.2 Fe 3400 Hg 1.7 (gaseous) K 153 Mg 850 Mn 3.3 Na 68 Pb 3.3 Rb 1.2 s 150,000 (gaseous so2 ) Sb 3.3 Se 6.9 (90% gaseous) Th 0.2 Ti 68 u 0.3 v 6.8 Zn 34 aModified from Andren et al. (1974). The data are for three coal-fired steam plants with a combined daily coal consumption of approximately 23,000 metric tons. special equipment to remove S02 from the flue qases. The wet-scrubbinq method is currently preferred, in which a slurry of lime or limestone is contacted with the flue qas. Typical annual production of sludqe, and for comparison, ash by a 1000-MW power plant equipped with lime/limestone flue-qas desulfurization system is shown in Table 19. By 1985, the estimated annual production of FGD sludqe will amount to 37 million tons originatinq from 42,535 MW capacity havinq FGD systems in operation (Bern, 1976). A more recent technoloqy to minimize S02 emission from coal combustion uses fluidized-bed combustion boilers where crushed coal is burned on a bed of inert ash and crushed limestone. The lime reacts with S02 released durinq the combustion of the coal to form sulfates. The resultinq fluidized-bed boiler (FBB) waste is a qranular solid material consistinq of CaS04 , unreacted Cao, other metal oxides, and fly ash. As this technoloqy is only in its infancy, no satisfactory estimate of the FBB waste can be projected. Because the present coal use is dominated by electric power qeneration, which will also maintain the qreatest qrowth in use, the

69 TABLE 19 Typical Coal-Residue Production in a 1000-MW Power Station Controlled with Lime/Limestone Flue-Gas Desulfurization (FGD) Systema,b Production (tons) Residue Wet Dry Coal ash (80 percent solids) 422,000 338,000 Limestone sludge (50 percent solids) 762,800 383,400 Lime sludge (50 percent solids) 622,400 311,200 TOTAL 1,807,200 1,032,600 asource: Bern (1976). bThe station consumes 2,556,928 tons of coal annually. The coal contains 3 percent sulfur and 13 percent ash; scrubber- removal efficiency is 85 percent. following discussion will focus on the combustion residual streams outlined in Figure 12. Furthermore, because western coals are expected to be developed more rapidly than eastern coals, emphasis will be on residues from western coals. Physical Properties Fly ash and bottom ash are characterized by low specific gravities and bulk densities (Table 20), which make them good structural fill materials and also allow them to be used to form lightweight aggregates and comparatively lightweight building blocks. The bulk density of FGD sludge will vary with its solids content. Limestone sludge has greater dewatering capacity than lime-derived sludge. At the Mojave Generating Station, limestone was selected as the prime reagent in a series of exhaustive tests with 175-MW scrubber modules by the Southern California Edison Company. The limestone sludge has 65 percent solids by settling, 75 percent solids by centrifugation or free drainage, and 80 percent solids by filtration. This distribution results from large amounts of gypsum (CaS04 • 2H 20) in the sludge. Lime sludge generated at the Tennessee Valley Authority's Shawnee Generating Station had 45 percent solids by settling, 55 percent solids by free drainage, 57 percent solids by centrifugation, and 63 percent solids by filtration. Bottom ash is highly permeable, whereas the permeability of fly ash in relation to bottom ash is low. As a result, bottom ash is used as a drainage blanket on various fill structures. Particle size of bottom ash and boiler slags ranges from coarse gravel to fine sand. They overlap at the fine end with fly ash. The particle size distribution of fly ash and FGD sludge is shown in Table 21. More than.70 percent of the fly-ash mass is made of particles of <53 f.&m (micrometers, average particle diameter) or particles with diameters equivalent to those of silt (2 to SO f.&m) and clay (<2 f.&m). Rees and Sidrak (1956) have also shown that fly ash derived from British coal sources is made up of particles principally in the silt and clay size range. Cope (1962) also showed that fly ash contains from 30 to 60

70 TABLE 20 Some Physical Parameters of Coal Residuesa Bottom Ash and Parameters Fly Ash Boiler Slag FGD Sludge Specific gravity 2.1-2.6 2.5-2.6 2.3-2.5 Bulk density (g/cm 3 ) 1.12-1.28 1.15-1.49 l.42b Permeability (cm/s) 0.05 x 10- 5 to 8 x 10-s 0.025-0.094 10-~-10-B Average moisture con- 15 20 82-185 tent (percent) Compaction indices Maximum dry density 1.19-1.49 1.16-1.87 1.29-1.52 (g/cm 3 ) Optimum moisture 19.5-32 13.8-26.2 20-29 content (percent) asource: Bern (1976). b The bulk density of FGD sludge depends on the moisture content of the material. The value given is for a 50 percent moisture sludge. percent silt-sized particles and from 0 to 4 percent clay-sized particles. The grain size distribution of untreated and combined sludge and fly ash is similar (Table 21). Approximately 95 percent of the particles of this material are of the silt size range, and about 5 percent or less are in the clay size range. The morphology of coal-ash particles has been examined by a number of investigators (Fisher et al., 19761 Natusch et al., 19751 Paulson and Ramsden, 19701 Straughan et al., 1978). Scanning electron microscopic (SEM) observation of fly ash reported by Fisher et al. (1976) demonstrated that fly ash is composed of large, hollow, spherical, aluminosilicate particles called plerospheres (or cenospheres), which have smaller particles attached to their surfaces and enclosed within their cavities. SEM studies conducted by Page et al. (1979) on fly-ash particles in the size range 1 to 53 f.&m obtained from the Mojave Generating Station (Figure 13) confirmed the observations made by others on the plerospherical structure of the material. However, plerospheres were absent when particle diameters were less ~han 8 f.&m• Particles in this range showed a strong tendency toward agglomeration with smaller particles of submicrometer size attached to their surfaces. Size and shape of coal-ash particles are important not only for engineering considerations but also from the standpoint of precipitation efficiency in power plants, chemical reactivity, solubility of elements contained in the ash, transportability in the atmosphere, and rates of deposition. Precipitation efficiency in power plants is increased when particles are spherically shaped and when the particle diameter is above 5 f.&m (Paulson and Ramsden, 1970). Small particles have larger total surface areas available for chemical reactions, travel longer distances, and have longer residence time in the atmosphere. Inclusion of smaller

71 TABLE 21 Particle Size Distribution of Fly Ash and Flue-Gas Desulfurization (FGD) Sludge a b Fly Ash FGD Sludge Particle Diameter Mass Fraction Particle Diameter Mass Fraction (µm) (percent) (µm) (percent) Wet Sedimentation Untreated >50 32.5 74-2000 2 2-50 63.2 2-74 95 <2 4.3 <2 3 Dry Sieving, Centrifugation and Light Microscopyc 1:1 FGD Sludge/Fly Ash >1000 0.1 74-2000 1 500-1000 2.6 2-74 94 250-500 1.8 <2 5 105-250 7.2 53-105 16.2 30-53 16.5 12-30 11.5 2-12 36.1 <2 6.5 asource: Page et al. (1979). b Source: Bern (1976). cParticles of >53 µm were separated by dry sieving, and those of <53 µm were separated by dry centrifugation and their size estimated by light and elec- tron microscopy. particles within cavities of larqer particles may reduce the solubility of the former when fly-ash particles come in contact with water. Chemical Composition The chemical composition of coal combustion ash is influenced by the composition of the source coal and by plant operatinq conditions. Compositions of different particle sizes of each from a qiven plant may differ, and the residues are causally related to the ash, sulfur, and calcium content of the coal consumed. As was shown in Table 13, the process of coal cleaninq removes a number of trace elements from coal, which alters the chemical composition of the residues. Influence of Operatinq Conditions The vaporization temperatures of the hiqhly volatile elements (e.q., mercury, arsenic, cadmium, selenium, antimony, and thallium) vary accordinq to whether the element is in an elemental or an oxidized state (Table 22). Thus, temperature and oxidation potential of the furnace are important factors in determininq trace-element enrichment or depletion in the various types of residues produced. The percentaqe of

-.J N FIGURE 13 Plerosphere with submicrometer spherical inclusions and attached surface spheres: (a) 2000x, (b) 6000x (Pa9e_§_t..,Al., 1979).

73 elements that are introduced with the coal and retained in each of the three major coal residues is shown in Table 23. An enrichment is indicated when the fraction of the element exceeds that of the residue itself. It is worth noting that about 80, 98, and 88 percent, respectively, of the total mass of chlorine, mercury, and sulfur entering the stream from coal are lost to the atmosphere in the flue gas. Kaakinen et al. (197S) have shown that as residues pass through stages of the power-plant configuration from bottom ash to inlet fly ash to outlet fly ash, progressive increases in the concentrations of copper, zinc, arsenic, molybdenum, antimony, lead, selenium, and mercury occur (Table 24). These authors also showed that concentrations of aluminum, iron, rubidium, strontium, yttrium, and niobium were essentially equal in all combustion residues. Observations by Block and Dams (1976) on ashes derived from Belgian coal sources indicated that magnesium, aluminum, calcium, scandium, titanium, chromium, iron, cobalt, rubidium, barium, and mercury were depleted in the ash in relation to the original coal composition. However, chlorine, zinc, copper, arsenic, selenium, bromine, antimony, iodine, and mercury were enriched in the fly ash. Because of selective volatilization and subsequent elemental enrichment in particles emitted from stacks, Bertine and Goldberg (1971) estimated that the amounts of arsenic, mercury, cadmium, tin, antimony, lead, zinc, thallium, silver, and bismuth mobilized to the atmosphere from fossil-fuel burning are more than 20 times greater than would be predicted from the concentration of the particular element in the coal. A relation between particle size and the chemical composition of coal residues has been confirmed by a number of investigators. In all investigations, an inverse relationship is observed between the concentrations of certain elements and particle size. Davison et al. (1974) demonstrated that lead, thallium, antimony, cadmium, selenium, arsenic, zinc, nickel, chromium, and sulfur were markedly increased with decreasing particle size of ashes derived from Indiana coal sources fractionated in the range of 0.6S to >74 Jllll• Similar observations on boron, cadmium, chromium, copper, manganese, nickel, lead, and uranium were made by Lee and von Lehmden (1973) in the size range of l.S to 2S ,.m. The concentrations of gallium, germanium, mercury, and lead showed an approximately threefold increase between the coarse (>SO Jllll) and fine (<2 Jllll) fly ash of Australian coal sources (Swaine, 1977). Fly ash from the Mojave Generating Station was fractionated into particles with diameters in the ranges of >2SO and <SO Jllll (Page et al., 1979). Similar trends were manifested with respect to dependence of the chemical composition of fly ash on particle size. In this study, 29 elements (arsenic, boron, cadmium, cerium, cesium, chromium, cobalt, copper, gallium, hafnium, lanthanum, manganese, molybdenum, nickel, lead, antimony, scandium, rubidium, selenium, thallium, zinc, zirconium, neodymium, samarium, ytterbium, europium, lutetium, terbium, and uranium) were reported in fractions of <S3 and >2SO Jllll• The <S3-Jllll fraction was also fractionated into particles with effective diameters in the ranges of SO to 20, 20 to 13, 13 to 8, 8 to 3, and 3 to 1 Jllll• Compared with the S3- to 20-Jllll fraction, the 3- to l-Jllll fraction showed substantial enrichment of calcium, sulfur, sodium, phosphorus, zinc, molybdenum, copper, nickel, cadmium, and lead (Page et al., 1979).

74 TABLE 22 Boiling Points and Relative Order of Volatility of Inorganic Species Possibly Evolved During Coal Combustiona Species Boiling or Subliming Species Boiling or Subliming Below 1550°c Above 1550°C As, As203, As2S3 Al, Al203 Ba Bao Bi BeO Ca Bi203 Cd, CdO, CdS c Cr(C0)6, CrCl3, CrS (1550°C) cao K Co, CoO, Cos Mg Cr, Cr203 Ni (CO)!+ Cu, CuO PbCl2, PbO, PbS Fe, Fe203, Fe301+, FeO Rb MgO, MgS Se, Se02, Se03 Mn, MnO, Mn02 Sb, Sb2S3Sb203 Ni, NiO SnS Pb (1620-1750°C) Sr Si, Si02 Tl, Tl20, Tl203 Sn, sno,, SrO Zn, ZnS SrO Ti, Ti02 1 TiO u, U02 ZnO Relative Order of Volatility Oxides, sulfates, carbonates, silicates, and phosphates As "' Hg > Cd > Pb "' Bi "' Tl > Ag "' Zn > Cu "' Ga > Sn > Li "' Na "' K"' Rb "' Cs Elemental state ~>b>~>~>~2M>fi>Mn>~==~==~>~==~ Sulfides As "' Hg > Sn "' Ge ~ Cd > Sb "' Pb ~ Bi > Zn "' Tl > Cu > Fe "' Co "' Ni "' Mn "' Ag asources: Modified from Davison et al. (1974) and Bertine and Goldberg (1971). Table 25 illustrates the effect of particle size of fly ash on the concentration of 17 trace elements as reported by Ondov et al. (1976). The ranqe of concentration increase in the <3-p.m fraction as compared with the >15-p.m fraction was from 1.5-fold for manqanese to 11.5-fold for cadmium. In this study (Ondov et al., 1976), the authors found little or no enrichment for aluminum, calcium, iron, potassium, sodium, nickel, titanium, maqnesium, cerium, cesium, dysprosium, europium, hafnium, lanthanum, neodymium, rubidium, scandium, samarium, strontium, tantalum, terbium, thallium, and ytterbium in this size ranqe. The availability of elements in coal fly ash is not only a function of particle size and concentration but also of depth in individual coal fly-ash plerospheres. Linton et al. (1976) have shown that beryllium, carbon, calcium, chromium, potassium, lithium, manqanese, sodium, phosphorus, lead, sulfur, thallium, vanadium, and zinc were

75 TABLE 23 Percentage of Elements Entering with Coal Discharged in Various Coal Residuesa,b Sluice Ashe Precipitator Flue Gase Element (22.2\) Ashd (77.l\) (0.7\) Aluminum (Al) 20.5 78.8 0.7 Antimony (Sb) 2.7 93.4 3.9 Arsenic (As) 0.8 99.l 0.05 Barium (Ba) 16.0 83.9 <0.09 Beryllium (Be) 16.9 81.0 <2.0 Boron (B) 12.l 83.2 4.7 Cadmium (Cd) <15.7 80.5 <3.8 Calcium (Ca) 18.5 80.7 0.8 Chlorine (Cl) 16.0 3.8 80.2 Chromium (Cr) 13.9 73.7 12.4 Cobalt (Co) 15.6 82.9 1.5 Copper (Cu) 12.7 86.5 0.8 Fluorine (F) 1.1 91.3 7.6 Iron (Fe) 27.9 71.3 0.8 Lead (Pb) 10.3 82.2 7.5 Magnesium (Mg) 17.2 82.0 0.8 Manganese (Mn) 17.3 81.5 1.2 Mercury (Hg) 2.1 0 97.9 Molybdenum (Mo) 12.8 77.8 9.4 Nickel (Ni) 13.6 68.2 18.2 Selenium (Se) 1.4 60.9 27.7 Silver (Ag) 3.2 95.5 1.3 Sulfur (S) 3.4 8.8 87.8 Titanium (Ti) 21.l 78.3 0.6 Uranium (U) 18.0 80.5 1.5 Vanadium (V) 15.3 82.3 2.4 Zinc (Zn) 29.4 68.0 2.6 asources: Schwitzgebel et al. (1975) and U.S. Environmental Pro- tection Agency (1975). bAt a 350-MW station equipped with an electrostatic precipitator burning subbituminous coal at the rate of 124 metric tons/h. cBottom ash sluiced to a settling pond wire. dAsh obtained by electrostatic precipitator. eFly ash in the flue gas. preferentially concentrated on the particle surface as compared with their concentrations at a distance inside the particle 500 1 from the aurface1 however, the nature of the surface of particles is not known with certainty. Collin (1974) cited by Swaine (1977) suggested that on each particle there are three more or less distinct outer layers. The innermost of these layers mainly consists of calcium compounds, the outermost layer is acidic, consisting mainly of sulfuric acid. Between these layers there is a neutral region, intermediate in composition between the outermost and the innermost layer. Davison et al. (1974) suggested that under very high temperatures of combustion c-1600•c), volatilization of trace elements occurs followed by preferential condensation or adsorption onto the smallest particles.

76 TABLE 24 Progressive Trace-Element Enrichment in a Coal-Fired Power Plant (ppm) a Sample Cu Zn As Mo Sb Pb Se Hg Coal 9.6 7.3 0.99 1.9 0.070 Bottom ash 82 58 15 3.50 2.8 <5 7.7 0.140 Precipitator ash 230 250 120 41.00 14.0 66 27 0.310 (inlet) Precipitator ash 320 370 150 60.00 18.0 130 62 (outlet) aSource: Kaakinen et al. (1975). Samples were collected at a 180-MW unit, Public Service Company, Boulder, Colorado. Thus, the magnitude of the surface area of particles affects the amounts of the trace element retained by such mechanism. Swaine (1977) estimated that a typical value for the surface area of fly ash is of the order of 1 m2 /g. Surface areas of bottom ash, inlet precipitator ash (ash entering the precipitator in the flue-gas stream), and outlet TABLE 25 Effect of Fly-Ash Particle Size on the Concentration of Some Trace Elements (ppm) a Size Ran9e (µm) Element >15 8-15 3-8 <3 As 13.7 56 87 132 Be 6.3 8.5 9.5 10.3 Cd 0.4 1.6 2.8 4.6 Co 8.9 16.3 19 21 Cr 28 49 59 63 Cu 56 89 107 137 Ga 43 l16 140 178 Mn 207 231 261 317 Mo 9.1 28 40 50 Ni 25 37 44 40 Pb 73 169 226 278 Sb 2.6 8.3 13 20.6 Se 19 59 78 198 u 8.8 16 22 29 v 86 178 244 327 w 3.4 8.6 16 24 Zn 71 194 304 550 a Source: Ondov et al. (1976).

77 precipitator ash {ash exiting the precipitator in the flue-gas stream) measured by Kaakinen et al. (1975) were, respectively, 0.38, 3.06, and 4.76 m2 /g. These authors indicated that enrichment of trace elements in coal combustion is determined by the physicochemical properties of the elements and their chemical compounds in coal and combustion products, the nature of the coal-burning process, and chemical reactions occurring in the emission-control devices. An enrichment ratio {Rij) of each element {i) in each outlet stream {j) relative to the total outlet can be defined by the equation: R;i - 6 6 L M;j IL Aj j=l j=l where Mij is the flow rate of trace element 1 in outlet stream jJ Aj is the flow rate of aluminum in that stream, and n is the total number of outlet streams. The value of the enrichment ratio indicates whether an element is enriched {Rij > 1.0), nonenriched {Rij = 1.0), or depleted {Rij < 1.0) in an outlet stream relative to aluminum and relative to the total condensed outlet. Aluminum is chosen as a reference element because it is nonvolatile at furnace temperatures and its concentrations in inlet and outlet fly ashes are approximately equal. Enrichment ratios were compared to the various measures of element volatility, melting points, boiling points, and vapor pressures of elemental and oxide forms. Enrichment ratios based on the oxide forms showed excellent agreement with volatility of these forms. Solid and Slurry Residues The inorganic constituents in coal and associated mineral matter are redistributed among the bottom ash, fly ash, combustion gases, and the FGD sludge, as a result of coal combustion. The primary product of breakdown of clay is mullite {Al 6 Si 20 13 ) , of pyrite it is ferric oxide, and of calcite it is calcium oxides, while quartz and some silicates remain unchanged. Quartz, mullite, gypsum, and iron oxides have been identified in fly ash {Page et al., 19791 Swaine, 1977). The chemical composition of bottom ash and FGD sludge produced in a western power station in relation to the chemical composition of the source coal is shown in Table 26. Concentrations of antimony, bromine, cadmium, chlorine, erbium, copper, fluorine, iodine, selenium, silver, tin, and tungsten in bottom ash were either similar to, or less than, those found in the source coal. Manganese was somewhat unique, showing a concentration in bottom ash 41 times greater than in coal. Concentrations of zinc, lithium, and hafnium were from 11.5 to 18.4 times more concentrated in bottom ash than coal1 those of strontium, beryllium, boron, cesium, gadolinium, samarium, scandium, terbium, thorium, thulium, and uranium from 5 to 10 times1 and the remaining elements from 1 to 5 times more concentrated in bottom ash than in coal. In general, the concentrations of most elements in the solids of FGD sludges did not differ by more than a factor of 2 {more or less) from

78 TABLE 26 Chemical Composition of Bottom Ash and FGD Sludge (ppm) and Element Enrichment Ratios in a 330-MW Subbituminous Coal-Fired Power Planta Enrichment Ratiol> FGD Sludge Bottom Ash FGD Slud9e FGD Slud9e Element Bottom Ash (Solids) Coal Coal Bottom Ash Mn 3300 2200 41 28 0.7 p 1800 1700 2.8 2.7 0.9 Sr 970 860 7 6 0.9 Sb 0.49 0.82 1.1 1.9 1. 7 As 5.4 17 4.2 13.l 3.2 Ba 320 110 2.5 0.9 0.3 Be 11 7.5 5.9 3.9 0.7 B 800 530 7.3 4.8 0.7 Br 1.5 0.98 0.9 0.6 0.7 Cd 0.67 0.89 1.1 1.4 1. 3 Ce 200 100 3.6 1.8 0.5 Cs 4.3 2.8 6.5 4.2 0.7 Cl 26 17 0.3 0.2 0.7 Cr 110 180 3.8 6.2 1.6 Co 26 17 4.4 2.9 0.7 Cu 120 340 4.8 13.6 2.8 Dy 4.2 2.8 2.6 1.8 0.7 Er 0.48 0.48 0.9 0.9 1.0 Eu l 0.69 1.2 0.8 0.7 F 91 300 0.3 0.9 3.3 Gd 0.69 1.1 5.3 8.5 1.6 Ga 27 48 7.3 12.9 1.8 Ge 2.8 4.0 4.9 7.0 1.4 Hf 5.7 1.8 18.4 5.8 0.3 Ho o. 31 0.20 2.1 1. 3 0.6 I 0.6 0.2 0.5 0.2 0.3 La 31 20 3.4 2.2 0.7 Pb 8 27 2.8 9.3 3.4 Li 860 2 12.8 0.03 0.002 Lu 0.15 0.10 1.9 1. 3 0.7 Mo 35 23 2.4 1.6 0.9 Nd 130 84 1. 7 1.1 0.7 Ni 28 19 2.2 1.5 0.7 Nb 18 24 3.3 4.4 1. 3

79 TABLE 26 (continued) Enrichment Ratiob FGD Sludge Bottom Ash FGD Sludge FGD Sludge Element Bottom Ash (Solids) Coal Coal Bottom Ash Pr 11 7.6 1.6 1.1 0.7 Rb 23 32 2.6 3.6 1.4 Sm 1.9 1.3 5.8 3.9 0.7 Sc 80 53 6.2 4.1 0.7 Se 0.87 5.8 0.5 3.6 6.7 Ag 0.14 0.19 0.6 0.8 1.4 Te 0.16 0.09 1.6 0.9 0.6 Tb 0.46 0.15 5.1 1. 7 0.3 Th 13 18 5.0 6.9 1.4 Tm 0.26 0.12 6.5 3.0 0.5 Sn 2.0 3.1 1.1 1. 7 1.6 w 3.7 5.0 1.1 1.5 1.4 u 23 7.2 9.2 2.9 0.3 v 180 280 2.5 3.8 1.6 Yb 1 1.4 3.7 5.2 1.4 y 75 50 4.4 2.9 0.7 Zn 10 66 11. 5 76 6.6 Zr 62 76 2 2.5 1.2 asource: U.S. Environmental Protection Agency (1975). bRatios are calculated on the basis of the chemical composition of coal used at this station. those of the bottom ash. Exceptions were arsenic, bismuth, copper, fluorine, lead, selenium, and zinc, which were concentrated by more than a factor of 2 in FGD sludqe compared with bottom ash, and barium, hafnium, iodine, lithium, terbium, and uranium, which were concentrated by more than a factor of 2 in bottom ash than in FGD sludqe. Table 27 qives the averaqe and ranqe of the elemental composition of fly ash and soils. The major components of fly ash--silicon, aluminum, calcium, maqnesium, iron, sodium, potassium, and titanium--make up from 35 to 70 percent of the total elemental composition of fly ash. Fisher et al. (1976) indicated that the composition of fly ash from western U.S. coals could be approximated by the formula,

80 TABLE 27 Chemical Composition of Fly Ash and Soila Range Average Element Fly Ash Soil Fly Ash Soil Element (percent) Al 0.1-17.3 4-30 11. 7 7.1 Si 19.1-28.6 25-33 26.6 33 Ca 0.11-12.6 0.7-50 4.4 1.4 Mg 0.04-6.02 0.06-0.6 0.9 0.5 Na 0.01-0.66 0.04-3.0 0.6 1.4 I<. 0.19-3.0 0.04-3.0 0.8 1.4 Fe 1-26 0.7-55 4.1 3.8 Mn 0.01-0.3 0.01-0.4 0.02 0.09 s 0.1-1. 5 0.01-0.2 0.2 0.08 p 0.04-0.8 0.13 0.07 Sr 0.03-0.3 0.05-0.4 0.09 0.03 Ba 0.011-0. 5 0.01-0.3 0.3 0.05 Ti 0.16-0.7 0.5 0.5 Element (ppm) Sb 1.6-202 0.6-10 1.6 6 As 2.8-6300 0.1-40 9 6 Be 3-7 0.1-100 5.5 6 B 48-618 2-100 390 10 Br 0.7-5.3 1.8 25 Cd 0. 7-130 0.01-7 1.0 0.06 Ce 22-133 150 50 Cs 5 Cl 10-1000 47 Cr 10-690 5-300 54 100 Co 7-49 1-40 12.6 8 Cu 14-1000 2-100 63 26 F 100-610 30-300 201 200 Gd 1.4 1.0 Ga 15-93 15-70 33 30 Ge 3.3 1.0 La 12-72 70 30 Pb 7-279 2-100 48 10 Li 50-1064 1-2000 70 30 Mo 7-117 0.2-5.0 10 2 Ni 10-4300 10-1000 34 40 Nb 20 21 Rb 30-600 43 100 Sc 3.7-141 10-25 15.6 7 Se 0.2-134 0.1-2.0 7.6 0.2 Ag 0.04-5 0.1-8.0 0.3 0.1 Te 0.02-0.2 0.2 10.1 Tl 0.8-1. 7 1. 2 5.0 Sn 3.3-63 0.1-300 3.3 10.0 v 50-1000 20-250 119 100 Zn 36-1333 10-300" 72 50 Zr 50-1286 60-2000 200 300 aThe range of fly-ash composition represents literature values taken mainly from Block and Dams (1975), Bern (1976), Swaine (1977), Martens (1971), Mulford and Martens (1971), Martens et al. (1970), Doran and Martens (1972), and Page et al. (1979). The average composition of fly ash was taken from data of Swanson (1972), Schwitzgebel et al. (1975), and Page et al. (1979) for ashes derived from western U.S. coal sources. Soil composition was derived mainly from Bowen (1966) and Lisk (1972).

81 Based on the average chemical composition of soils shown in Table 27, application of fly ash to agricultural soils will probably result in soil enrichments of calcium, barium, strontium, sulfur, boron, molybdenum, selenium, and lead. Limited enrichments of other elements are also possible, depending on the rate of application, climate, and type of soil and fly ash. Of the trace elements shown, boron, molybdenum, and selenium are of concern. Boron is toxic to plants in relatively small concentrations in soil, and molybdenum and selenium are toxic to animals when present above some critical concentrations in the plant tissue. Water Extracts from Residues As the basic concern is the availability of trace elements to the biological systems, measurement of water solubility of the elements is used to reflect this bioavailability. The major- and trace-element contents in saturation extracts (extracts obtained from soils saturated with water) from fly ash obtained at the Mojave Generating Station compared with those for 68 soils from California as reported by Bradford et al. (1971) are shown in Table 28. The high pH of saturation extracts from fly ash was responsible in part for the relatively low solubility of most elements. Concentrations of calcium, sodium, barium, strontium, and molybdenum were higher in the fly-ash extracts than in the soil extracts. Barium and strontium contents of the pH 12.5 fly-ash extract were more than SO-fold greater than the mean values of these two elements in 68 soil extracts, suggesting that saturation extract concentrations of barium and strontium, in certain source- and site- specific instances, may serve as a good indicator of the extent of fly- ash contamination of soils (Bradford et al., 1978). Acidifying the ash to pH 6.5 greatly increased the solubility of most elements (Table 28). Concentrations of calcium, magnesium, strontium, boron, manganese, and molybdenum in the acidified fly-ash extract were considerably greater than their corresponding concentrations in saturation extracts of fly ash without acidification. The pH of soils, in general, ranges between 4.0 and 8.2. Because soils usually have a high capacity to resist changes in pH, if fly ash were mixed with soil in amounts equivalent to a few percent by weight, the resultant equilibrium pH should fall in the range common to soils. Table 29 shows the composition of leachates from coal ash and FGD sludge of a western power station. For comparative purposes, water- quality criteria for public supplies and irrigation water are also indicated in Table 29. Leachates from a mixture of fly ash and bottom ash (4:1) contain excessive concentrations of barium, molybdenum, and selenium, compared to standards for public water supplies and/or irrigation water. Concentrations of boron, fluorine, molybdenum, and selenium in the FGD-sludge leachates exceed those established for public water supplies and/or irrigation waters. The data presented in Table 29 indicate that those elements present in residues from coal combustion that are most apt to contaminate water supplies are barium, boron, fluorine, molybdenum, and selenium.

82 TABLE 28 A Comparison of Major and Trace-Element Contents in Saturation Extracts of Mojave Fly Ash and 68 California Soilsa Fly Ash (µg/ml) Concentration in Water Soluble Water Soluble Soil Saturation Before pH Adjust- After pH Adjust- Extracts (µg/ml) Element ment (pH 12. 5) ment (pH 6.5) Mean Median Ca 476 38,234 128 60.0 Mg <l 849 38 12.4 Na 287 900 524 45.0 K <100 <100 20 10.0 Si <0.6 <0.6 3.1 5.0 B <0.6 65 3.1 <O.l Ba 50 15 0.26 0.10 Sr 61 333 0.93 0.18 Al <2 <2 0.40 <0.01 Cr <l <l 0.01 <0.01 Fe 0.01 0.11 0.05 0.03 Mn <0.01 1.3 0.17 <0.01 Cu 0.01 0.02 0.04 0.03 Zn 0.02 0.08 0.07 0.04 Mo 0.12 1.11 0.73 <0.01 Ni 0.01 0.13 0.02 <0.01 Co <0.01 0.09 0.06 <0.01 v <0.01 0.02 0.07 0.01 Pb <0.02 <0.02 0.05 <0.01 Cd <0.01 0.03 Ag <0.001 <0.001 asource: Bradford et al. (1971, 1978). Atmospheric Deposition The quantity of trace elements emitted to the atmosphere from stationary sources depends on such factors as concentration in coal, boiler confiquration and load, properties of the element and its compounds, and the effectiveness of particle control devices. Paulson and Ramsden (1970) have also indicated that the microlithotype of the source coal plays an important role in determining the precipitation efficiency of the electrostatic precipitators. They pointed out that some coals are rich in fusite (a coal microlithotype), which results in production of fine fly ashes that are predominantly of submicrometer size, hence difficult to precipitate. With the use of a cascade impacter, Lee et al. (1975) were able to show that between the inlet and the outlet of an electrostatic precipitator, the fraction of particles of >S 1'111 decreased

83 TABLE 29 Comparison of Trace-Element Concentrations of Leachates from Coal Ash (a Mixture of 80 Percent Fly Ash and 20 Percent Bottom Ash) and FGD Sludge to the Reconunended Maximum Concentrations for Public Water Supplies and Irrigation Waters (mg/liter) Concentration in Leachate Reconunended Maximum Concentration forb froma Public Water Irrigation Element Coal Ash FGD Sludge Supplies Wat ere Arsenic <0.002 <0.002 0.10 0.10 Barium 40 2.0 1.0 Beryllium 0.003 0.002 0.10 Boron 0.03 2.6 0.75 Cadmium <0.001 0.0005 0.01 0.01 Chromium <0.001 0.001 0.05 0.10 Fluorined 2.3 31.5 1.4-2.4 1.0 Mercury 0.0006 0.0005 0.002 Lead 0.0068 0.0056 0.05 5 Manganese <0.002 <0.002 0.05 0.20 Molybdenum 0.047 0.063 0.01 Nickel <0.05 <0.05 0.20 Selenium 0.009 0.045 0.01 Vanadium <0.10 <O.l 0.10 Zinc 0.038 0.005 5.0 2.0 a Source: Rad' . ian Corporation (1975). Data are for a Southwest power station burning low-sulfur coal. b Source: U.S. Environmental Protection Agency (1973). cRecommended maximum concentrations of trace elements in irrigation waters used for sensitive crops on soils with low capacities to retain the elements in unavailable forms. dReconunended maximum concentration depends on mean annual temperature of the region1 as temperature increases maximum concentrations decrease. from 96 to 48 percent, while that of the <5-,.m particles increased from 4 to 52 percent. They also showed that chromium, lead, antimony, zinc, and selenium were predominantly in the 0- to 1-,.m size ranqe1 cadmium, iron, and vanadium in the 1- to 5-,.m ranqe1 nickel in the 5- to 10-,.m ra~qe, and manqanese was completely removed by the control device. Zoller et al. (1975) estimated that the amount of fly ash emitted from the stack of two 710-MW coal-burninq units consuminq 116 tons/h of coal with 10 percent ash and 1 percent sulfur was on the order of 1.2 tons/h. This amounts to about 1 percent of the amount of coal used or about 10 percent of the amount of ash produced. Klein and Russell (1973) found that soils around a coal-burninq facility_{650 MW, 90 percent precipitator efficiency) were enriched in •ilver, cadmium, cobalt, chromium, copper, iron, mercury, nickel,

84 titanium, and zinc. They also found that plant materials (native grass, maple leaves, and pine needles) were enriched in cadmium, iron, nickel, and zinc. Soil enrichment, except for mercury, was correlated with wind patterns and metal content of coal. Bradford et al. (1971), however, concluded that four years of operation at the Mojave Generating Station resulted in no measurable contamination of either soil or vegetation in the region surrounding the facility. Anderson and Smith (1977) examined concentrations of mercury in the surface 2 cm of soil within 20 km of a 1200-MW coal-burning facility (Table 30). Soils sampled in the northerly directions (prevailing downwind) contained higher concentrations than those sampled in the southerly directions. Despite some increased concentrations of mercury, however, the projected soil enrichments of the element over a 3S-year period are not critical. A mass deposition model was formulated by Jurinak et al. (1977) for particulates emitted from a hypothetical 3000-MW coal-burning facility situated in a semiarid environment. Some of the basic assumptions of this model are emission rate, l.OS tons/h; deposition velocity, 0.03 to 0.1 m/sec; particle size distribution for particles >10 1'111 that was 3 percent of 2S-l'lll radius, S percent of 12.S-l'lll radius, and 10 percent of 7.S-1'111 radius. Deposition rates established by this model are shown in Figure 14 for the winter, spring, summer, and fall seasons. The changes in pattern of deposition with season were modeled to reflect changes in the wind speed and direction and atmospheric stabilities. Deposition was found to be highest in summer and lowest in fall. Total particulate mass deposition ranged from 10 to SO kg km-z month-1. The model also predicted that fallout over a SO-year period would be insignificant with TABLE 30 Mercury Concentrations of Surface 2 cm of Soil in a Region Within 20 km of a Coal-Fired Power Plant in Illinoisa Mean Mercury Concentration Number of After 7 Years of Operation Observations (µg/g) Direction from power plant NW 15 0.019 SW 20 0.015 NE 21 0.022 SE 17 0.016 Maximum concentration observed 0.037 Projected lifetime enrichment Uncultivated soil 0.110 Cultivated soil 0.015 asource: Anderson and Smith (1977), 1200-MW facility. Coal used had a mean Hg concentration of 0.2 µg of Hg/g.

85 regard to the total amount of zinc, chromium, lead, and cadmium originating from the stack and deposited in the final environmental sink for the region. Fallout, however, would contribute 65 percent of the mercury loading of this sink. Based on the maximum deposition rate ( 50 kg km-2 month- 1 ) found by Jurinak et al. (1977) and concentration of trace elements in the <3-pm fraction (Table 25), the concentration of fly-ash-derived trace elements in plants and soils was estimated by Page et al. (1979). These are shown in Tables 31 and 32 and are compared with their typical values in plants and soils. These estimates show measurable, but small, enrichments in plants or soils in trace elements originating from stack emissions. Lyon (1977) and Vaughan et al. (1975) arrived at similar conclusions using different approaches to estimated fallout. W I NTER SPRI N G 0 10 0 10 20 0 30km SUMMER FAL L kg km2 mo- 1 10 20 30 40 50 G:::J R•:·;·l liil!l 11111 - FIGURE 14 Mass deposition near a hypothetical 3000-MW coal-fired power plant located in the southwestern United States (Jurinak et al., 1977).

86 TABLE 31 Estimated Maximum Deposition of Trace Elements onto Soil Adjacent to a Coal-Fired Power Planta (microgram of element per gram of soil) Conunon Soil Amount De~sited Concentrations Element Annual Lifetimel> Typical Range As 0.00039 0.014 6 0.1-40 Cd 0.000014 0.0005 0.06 0.01-7 Pb 0.00082 0.029 15 2-200 Mo 0.00015 0.0052 2 0.2-5 Se 0.00059 0.021 0.2 0.01-2 u 0.000087 0.003 1 0.1-10 Zn 0.00163 0.057 50 10-300 Sb 0.000061 0.0021 6 2-10 Be 0.00003 0.0011 6 0.1-40 Cr 0.00019 0.0066 100 5-3000 Co 0.000062 0.0022 8 1-40 Cu 0.00041 0.0144 20 2-100 Ga 0.00053 0.0182 30 0.4-300 Ni 0.00012 0.0042 40 10-1000 Th 0.0009 0.0032 5 0.1-12 v 0.00097 0.034 100 20-500 ~rom Page et al. (1977) and Ondov et al. (1976). 3000-MW power plant, western U.S. coal, electrostatic precipitator efficiency of 99 percent. bAssuming a 35-year lifetime. Disposal and Recycling of Collected Residues on Land The collected residues from coal-fired electric power plants have been in the past, and in all probability will continue to be, disposed or recycled on land. Land-disposal techniques utilized include landfill, lagooning, and land spreading. In situations where the residues are spread onto land that supports either agricultural crops or native vegetation, trace elements in fly ash could adversely affect the productivity of the land or the quality of the vegetation grown. Therefore, a comprehensive understanding of the chemical, physical, and biological changes that occur when residues from coal-fired power plants are mixed with soils is essential to evaluate the effect that these changes will have on the productivity of the land and trace-element composition of the vegetation.

87 TABLE 32 Estimated Trace-Element Contamination of Vegetation Arising from Emission from a Coal-Fired Power Planta (microgram of element per gram of dry matter) Concentration Deposited Typical Concentration Element on Vegetationb for Vegetation As 0.07 0.4 Cd 0.002 0.2 Cr 0.034 1.5 Cu 0.074 10 Pb 0.15 3 Mo 0.027 1 Se 0.107 0.2 Zn o. 30 25 Sb 0.011 0.06 Be 0.006 0.03 Co 0.011 <1.0 Ga 0.096 1.2 Ni 0.021 5 Th 0.016 0.05 u 0.016 0.04 v 0.18 1 a Sources: From Page et al. (1979), Jurinak et al. (1977), and Ondov et al. (1976). 3000-MW power plant, western U.S. coal, electrostatic precipitator efficiency of 99 percent. bAsswnptions: 100 percent canopy, yield 3770 kg of dry matter per hectare, 4-month exposure, particulates deposited are <3 µm, and all particulates deposited remain with harvested crop. Chemical Properties of Fly-Ash-Amended Soila Table 33 presents the pH, electrical conductivity, and soluble calcium plus maqneaium, boron, and S04 -S (sulfur present as S04 but expressed as elemental sulfur) in soils amended with Mojave fly ash, at rates ranging up to 8 percent by weight (-180 metric tons/ha) and cropped to brittlebuah (Encelia farinoaa) under greenhouse conditions for 8 months. The results of a field study conducted by Plank et al. (1975) with two acid soils amended with fly ash at cumulative rates of 144 metric tons/ha, and cropped to corn for 2 years, are given in Table 34. Application of fly ash, regardless of its source, increased the pH of soils, irrespective of their type. The calcareous soil (Xerollic C&lciorthid, fine, loamy, mixed tnermic), Arizo (Typic Torriorthient, aandy,--akeletal, mixed, thermic), however, buffered this effect over an 8-month period of cropping (Table 33). Acid soils [Redding (Abruptic Durexeralof, coarse, loamy, kaolinitic, thermic), Groseclose (Typic, Bapludult, clayey, mixed, meaic), and Woodstown (Aquic Hapludult, fine,

88 TABLE 33 Select Chemical Properties of Soils Amended with Fly Ash and Cropped Under Greenhouse Conditions to Brittlebush (Encelia Earinosa) for 8 months Fly Ash H c Solubled Extractablee Addeda ECeb p SE_ Ca + Mq B S04 - S (percent) (nunhos/cm) Initial Final (meq/liter) (µg/ml) (µg/g) Ariza Calcareous Soil 0 l. 3 8.0 7.9 10.8 2.3 1.3 l 1.2 8.9 7.9 10.0 5.5 55 2 1.5 9.9 8.0 11.l 6.3 129 4 2.2 10.5 7.9 19.3 7.0 223 8 3.2 10.6 7.9 32.0 11. l 388 Redding Acid Soil 0 1.5 5.5 4.8 7.6 0.4 14 l 2.6 6.9 6.1 19.7 2.8 20 2 2.2 7.7 7.2 21.4 3.7 49 4 3.2 8.7 7.6 30.4 5.2 128 8 3.7 9.9 7.8 46.7 8.0 276 a Fly ash obtained from the Mojave Generating Station. bECe is the electrical conductivity of the soil saturation extract. cPHsp is the pH of the soil saturation paste. The initial pH is obta1ned approximately 2 weeks after preparing the soil/fly-ash mixtures, and the final pH is obtained after soils were cropped for 8 months. d Amounts dissolved in saturation extract from soil. eAmounts extracted with l N anunonium acetate (NH 40Ac). loamy, siliceous, meaic)] continued to maintain pH levels greater than those of controls over the 8-month growth period (Tables 32 and 33). Analyses of acid soils showed evidence of calcium carbonate formation at rates of fly ash of 2 percent or greater (Page et al., 1979). Thia finding is probably the result of the high concentrations of hydroxyl ions in fly ash reacting with carbon dioxide released by the roots. The efficiency of fly ash as liming material was most recently compared with that of calcium carbonates by Phung et al. (1978). Results showed that the fly ash used (see Table 28 for chemical composition) had a neutralizing capacity 35 to 50 percent that of commercial limestone. The authors showed that fly ash and limestone are effective in increasing the levels of soluble and exchangeable calcium and in reducing the concentrations of exchangeable aluminum and manganese to levels not toxic to plants. The soil used in the study was a Reyes silt clay (Sulfic Haplaquept, fine, mixed, acid, thermic) that required the application of an amount of fly ash equivalent to 115 metric tons/ha to raise its pH from 4.1 to 6.3. Soila with coarser texture and/or higher base saturation will probably require leaser amounts of fly ash to attain the same final pH. The increase in electrical conductivity of the soil saturation extract (ECe) with application of fly ash varied among soils and crops (Table 33). The data, however, indicate substantial gains in the

89 TABLE 34 Effect of Fly Ash on Soil pH and on Calcium Plus Magnesium and Boron from Displaced Soil Solutions of Groseclose and Woodstown Soils Cropped to Corn for 2 Yearsa b ad Fly Ash Added ca+ Mgd (metric tons/ha) (meq/liter) (µg/ml) Groseclose Soil 0 5.8 3.18 0.33 144 6.6 4.99 0.49 Woodstown Soil 0 5.4 1.88 0.30 144 5.8 3.10 0.59 asource: Plank et al. (1975). b Weathered Glen Lyn fly ash; pH of a 1:1 water sus- pension of this fly ash was 7.8, and the material contained Ca+ Mg and B at concentrations of 3.4 per- cent and 100 µg/g, respectively. cThe pH of the surface 15 cm of soil. dData shown are average concentrations of 4 consecu- tive depths, 0-15, 15-30, 30-46, and 46-61 cm. content of total soluble salts (as measured by the electrical conductivity) of soils amended with fly ash. Similar observations were made by Mulford and Martens (1971), who noted that the ECe of Tatum silt loam (Typic Hapludult, clayey, mixed, thermic) was increased from 1 mmho/cm to 4.4 mmhos/cm with application of 5 percent fly ash. Salt- sensitive crops are injured when the ECe exceeds 4 mmhos/cm (Richards, 1954). Soils receiving high applications of fly ash might thus be unfavorably affected, and leaching of excess salts from the soil would become necessary for the maintenance of good crop growth. Studies conducted by Page et al. (1977) on the efficiency of Colorado River water in leaching of soluble salts induced in Baywood sandy soil (Entic Haploxeroll, sandy, mixed, thermic) by the application of 5 percent fly ash to the top 3 cm of a soil column showed that approximately 60 surface cm of applied water were required to bring the salt level in the soil to levels comparable with the background levels. Achievement of such a quantity of water is feasible under normal practices in irrigation agriculture. Application of 8 percent fly ash produced boron concentration in saturation extracts from the Arizo and Redding soils of approximately 8 and 11 ~g/ml, respectively (Table 33). These concentrations are from fivefold to twentyfold that of the initial boron concentration. The hot-water-soluble boron (a diagnostic technique used to evaluate boron deficiency) of Groseclose and Woodstown soils (Table 34) and of Tatum soil (Mulford and Martens, 1971) was also increased on incorporation of fly ash into these soils. In the latter soil, application of 1.7 percent of fly ash (618 ppm total boron) increased the hot-water boron

90 content of the soil from <l to about 15 ~g/g. These observations and others (Plank and Martens, 1974) show that soils could be greatly enriched in soluble boron by fly-ash application. As boron-sensitive crops are injured at relatively low concentrations in the saturation extract Cl ~g of B/ml) (Bingham, 1973), leaching of excess boron in fly- ash-treated soils may be necessary for optimum growth of plants. Approximately the same amount of water that was required to leach excess salts in the top 3 cm of Baywood soil columns was also required to bring the boron concentration in leachates of this soil to levels comparable with the check soil (Page et al., 1977). This finding indicates that excess salinity and boron could simultaneously be reduced in soils amended with fly ash, if appropriate leaching regimes were maintained. Application of 8 percent fly ash markedly increased the sulfur content of soils (Table 33). The lB ammonium acetate (lB NH40Ac) soluble-sulfur concentration in the soil at this rate was approximately 300 ~g/g S04-S. This concentration agrees well with predicted concentrations, based on the average S04-S of this fly ash (0.4 percent). Furthermore, addition of gypsum (CaS04 • 2H 2 0) to Arizo soil cropped with alfalfa produced concentrations of S04-S in the soil similar to those produced by fly ash when the latter was added at equal rates of sulfur (Elseewi et al., 1978b). The authors concluded that the availability of fly-ash sulfur appears equal to gypsum sulfur, an indication that sulfur in the former exists in a chemical form very similar to that of gypsum. Response of plants to sulfur in fly ash, as discussed in a subsequent section, was quite remarkable. Three soils of varying chemical properties were incubated at moisture contents of one-third bar and saturation for a period of 29 weeks with rates of fly ash ranging from 0 to 1 percent (Page et al., 1977). Soil pH and salinity were increased regardless of the moisture content of incubation. No appreciable changes in the concentrations of iron, manganese, copper, zinc, molybdenum, nickel, and lead in the soil saturation extract were detected. However, concentrations of calcium, magnesium, barium, strontium, and boron in the soil saturation extract increased, in some cases rather dramatically, in relation to the amount of fly ash added. The increases varied in magnitude between soils, with acid soils, in general, showing the greatest increases. Diethylene- triaminepentaacetic-acid-(DTPA)-extractable metals also varied depending on rate of fly-ash addition and soil type. The incubation study showed that mixing the soil with up to 1 percent fly ash will not cause harmful enrichment of soil in trace metals, except possibly for boron. Physical Properties of Fly-Ash-Amended Soils Application of fly ash to agricultural soils in amounts greater than a few percent generally has a significant impact on the physical properties of soil, the quantities and effects being influenced by the properties of the specific fly ash and soil involved. Chang et al. (1977) conducted a greenhouse experiment with five soils amended with Mojave fly ash at rates ranging up to 50 percent by volume and cropped to barley. Physical parameters such as water content at 20 cbar, water release, bulk density, hydraulic conductivity, and modulus of rupture were measured. Results showed that the addition of up to 10 percent fly

91 ash to the soil did not siqnif icantly affect the amount of water retained by soils. At rates qreater than 10 percent by volume, water retention by soils increased with increasinq rates of fly-ash application. The volume of water released to the plant root system was likewise unaffected by up to 10 percent fly ash in the soil but was siqnificantly reduced at rates hiqher than 10 percent by volume. Addition of fly ash proqressively decreased the bulk density of soils. Hydraulic conductivity measurements, however, indicated that althouqh the bulk density was decreased, passaqe of water throuqh soils reached a maximum at a fly-ash rate characteristic of each soil, beyond which it declined. Sharp reductions in the modulus of rupture (an index of soil strenqth) were obtained at low rates of fly-ash application to soils. This reduction would indicate less cohesiveness of soil particles after the addition of fly ash, thus increasinq the potential of erosion of fly-ash-amended soils. Mineral Composition of Plants Grown on Fly-Ash-Amended Soils Effects of fly-ash incorporation in soils on the mineral composition of alfalfa qrown on calcareous and acid soils amended with up to 8 percent fly ash are shown in Table 35. Plants were adequately fertilized with nitroqen, phosphorus, and potassium from a mixed fertilizer. Elements most affected by fly-ash applications are phosphorus, sulfur, calcium, sodium, zinc, boron, and manqanese. The phosphorus and zinc contents were qenerally reduced with fly-ash application; those of calcium, sodium, and boron were qenerally increased. In alfalfa, as well as in several other plant species tested, manqanese showed two distinctly different trends in plants qrown on acid and on calcareous soils. Under acid-soil conditions, the first application of fly ash sharply reduces the manqanese content of plants. Under calcareous conditions, plants show a moderate increase in manqanese content up to a certain level of fly-ash addition (2 to 4 percent). Reductions in phosphorus and zinc concentrations in the plant tissue were not sufficient to induce deficiencies of these elements in the plants. Reduced availability of zinc with application of alkaline fly ash was also observed by Schnappinqer et al. (1975) on corn qrown on a sliqhtly acid soil Frederick silt loam (Typic Paluedult, clayey, kaolinitic, mesic) amended with fly ash at rates ranqinq from o.e to 13 percent by weiqht. Addition of acidic fly ash to the same soil increased zinc uptake and corrected the deficiency in plants. Thus, althouqh fly ash contains phosphorus and zinc, the hiqh alkalinity of the material and of the soil and fly-ash mixtures appears to curtail the availability of these elements to plants. The increase in sulfur availability to plants (Table 35) was associated with siqnificant yield improvement in a number of plant species. Furthermore, the availability of fly-ash sulfur compares well with that of sulfuric acid, qypsum, and sewaqe sludqe, as revealed by a series of qreenhouse studies conducted by Elseewi et al. (1978b,c) with alfalfa, Bermuda qrass, white clover, and turnips. Results of the turnip_experiment are shown in Table 36, as an example of the essentially equal availability of sulfur in fly ash, sewaqe sludqe, and qypsum. -Application of these materials at the rate of 25, 50, and 100

92 TABLE 35 Concentrations of Various Elements in Alfalfa Tops from Plants Grown on Fly- Ash-Amended Soilsa Fly Ash in Soil Percent 119/g (d!l'. wei2ht) (percent) N p K s Ca Mg Na Fe B Zn Cu Mn Ariza Calcareous Soil 0 2.2 0.47 2.9 0.08 1.4 0.22 317 85 106 39 5.9 73 1 2.7 0.27 1.9 0.19 2.0 0.20 318 80 148 23 5.3 144 2 2.7 0.27 1.9 0.11 2.4 0.24 550 85 183 25 6.1. 148 4 3.0 0.30 2.1 0.19 3.2 0.30 593 105 222 35 5.8 141 8 3.0 0.27 1.8 0.23 2.5 0.32 853 105 337 28 6.0 92 Redding Acid Soil 0 3.4 0.65 3.6 0.10 1.4 0.34 632 231 87 56 5.8 441 1 4.0 0.60 3.6 0.24 1. 7 0.32 697 252 90 50 6.2 150 2 4.1 0.55 3.5 0.33 2.0 0.32 753 222 93 45 5.8 150 4 3.8 0.47 3.7 0.34 2.3 0.37 821 218 101 46 6.5 133 8 4.3 0.40 3.6 0.31 2.4 0.43 672 207 137 39 6.5 145 asource: Page et al. (1977). TABLE 36 Dry Matter Yield, Sulfur Content of Tissue, and Sulfur Uptake of Turnips Grown on Josephine Soil Amended with Three Rates of Fly Ash-Sulfur, Gyps\Dll-Sulfur, and Sewage Sludge-Sulfura Rate of Sulfur Dry Matter Sulfur Content (percent, Addition Yield dry wei2ht) Sulfur Uptake (mg/kg) Cg/container) Root Petiole Leaf (mg/container) Check 25.8 0.02 0.01 0.02 3.9 25 gypsum 41.8 0.14 0.18 0.14 67.8 25 fly ash 42.3 0.16 0.14 0.11 58.3 25 sludge 39.8 0.13 0.13 0.06 40.6 50 gypsum 42.8 0.26 0.34 0.42 164.9 50 fly ash 45.8 0.24 0.27 0.21 101.3 50 sludge 53.8 0.15 0.22 0.17 88.6 100 gypsum 41.0 0.27 0.46 0.56 180.4 100 fly ash 48.8 0.28 0.36 0.31 143.5 100 sludge 64.5 0.22 0. 39 0.42 199.8 LSD, b 5 percent 6.5 0.04 0.05 0.07 30.9 asource: Elseewi et al. (1978b, c) • bLeast s1gn1 icant difference. . 'f'

93 mg of S/kg of soil increased the yield and sulfur content of turnips grown on the sulfur-deficient Josephine soil (Typic Haploxealts, fine, loamy, mixed, mesic). Increased levels of sodium and boron in plants grown on fly-ash- amended soils (Table 35) had no adverse effects on the growth of alfalfa but were partially responsible for yield reductions in lettuce (Elseewi et al., 1978a). The availability of boron in fly ash to alfalfa was shown by Mulford and Martens (1971) and Plank and Martens (1974) to be essentially equal to that of sodium borate-boron; however, the availability decreased with time, as indicated by results of a 3-year field experiment with alfalfa (Plank and Martens, 1974). Table 37 shows selected analyses of molybdenum in various plant species grown on calcareous and acid soils amended with fly ash. The molybdenum concentrations shown in Table 37 reached levels as high as 22.0 and 44.4 ~g of Mo/g in alfalfa and white clover, respectively. The data, however, indicate that the availability of fly-ash molybdenum is inversely related to time. Doran and Martens (1972) observed that the availability of fly-ash molybdenum to alfalfa was approximately equal to that of sodium molybdate. Analyses for strontium, barium, selenium, cobalt, scandium, rubidium, chromium, tungsten, antimony, silicon, calcium, cerium, thorium, beryllium, arsenic, samarium, europium, and mercury in plants grown on fly-ash-amended soils showed that only strontium, barium, selenium, cobalt, and cesium exhibit definite concentration trends in the plant tissue with increasing rates of fly-ash application to soil (Table 38). The increase in strontium may serve as an index of fly-ash deposition on soils and vegetation in areas adjacent to coal-fired power plants. The increase in selenium, when combined with the increase in molybdenum, indicates potential animal nutritional problems associated with fly-ash application. Selenium in the range 0.04 to 0.2 ppm and molybdenum at levels less than 1.0 ppm (dry weight basis) are required in animal diets (Allaway, 1968). At the same time, concentrations in plants in the ranges of 5 to 20 ppm of molybdenum and 4 to 5 ppm of selenium are potentially dangerous to animals (Allaway, 1968). Higher levels of molybdenum can produce a disorder called "molybdenosis," or molybdenum-induced copper deficiency in animals. Results from field and greenhouse studies with fly ash indicate that selenium concentrations in some crop species approached the foregoing critical levels (Furr et al., 1977; Straughan et al., 1979) and in one particular circumstance exceeded these levels (Gutenmann et al., 1976). Tests with small animals showed elevated selenium and molybdenum concentrations in their tissues and organs when they were fed plant rations grown on fly-ash- amended soils (Furr et al., 1978; Gutenmann et al., 1976; Stoewsand et al., 1978). Plant Growth on Fly-Ash-Amended Soils Rees and Sidrak (1956) noted that growth of Atriplex plants was improved with coal-ash application to soil in the presence of an adequate supply of nitrogen. Hodgson and Holliday (1966) grouped some crop species according to their tolerance to pulverized fuel ash (Table 39). Based on their classification, legumes, beets, and most grasses appear to be

94 TABLE 37 Molybdenum Concentrations of Various Plant Species Grown on Arizo Calcareous and Redding Acid Soils Amended with Fly Asha,b (µg/g, dry weight) Percentage of Fly Ash in Soil Plant Species 0 2 4 8 Arizo Soil Alfalfa First clipping 4.5 7.5 17.0 22.0 Sixth clipping 1.4 2.7 4.3 9.5 Eleventh clipping 1.8 1.8 1.9 4.2 Bermuda grass First clipping 1.2 2.7 5.9 4.4 White clover Second clipping 2.5 1. 7 10.0 17.5 Brittlebush Leaf sample 1.1 3.4 4.5 8.1 Redding Soil Alfalfa First clipping 0.9 5.2 7.8 17.2 Sixth clipping 2.0 3.4 7.5 9.5 Eleventh clipping 3.2 3.6 5.1 5.7 Bermuda grass First clipping 0.5 4.7 5.2 5.5 Fourth clipping 0.9 2.8 4.3 4.5 White clover Second clipping 2.8 11.6 44.4 41.6 Brittlebush Leaf sample 0.9 4.6 6.1 7.6 asource: Page et al. (1979). bExcept for brittlebush, analysis was performed on composites of whole tops of plants. tolerant of fly ash. Beans and peas, however, are sensitive exceptions. The authors indicated that response of plants to fly ash is determined mainly by their ability to withstand excessive concentrations of solub1e salts, boron, and possibly hiqh pH in the soil. Application of fly ash, weathered for approximately 3 years in a power-plant disposal laqoon, at the rate of 144 metric tons/ha (6.4 percent) increased the yield of corn on Woodstown soil {Table 40) by approximately 27 percent {Plank et al., 1975). The increase in yield was attributed to increased water availability to plants. Application of 2.6 to 5.2 percent fly ash to Fredrick silt loam nearly doubled the yield of corn as a result of increased availability of zinc {Schnappinqer et al., 1975). Increased rates of application of fly ash to Groseclose silty loam increased the availability of molybdenum to alfalfa and markedly increased its yield {Doran and Martens, 1972).

95 TABLE 38 Neutron Activation Analysis of Trace Elements in Plants Grown on Fly-Ash-Amended Arizo Soil Elements Showing Definite Concentration Trendsa (µg/g, dry weight) Fly Ash (percent) Sr Ba Se Co Cs Alfalfa 0 30 4.5 0.2 0.14 0.026 0.5 77 9.3 1.1 0.12 0.060 1.0 125 18.0 1. 7 0.12 0.071 2.0 196 25.0 2.8 0.16 0.0.70 4.0 226 28.0 4.5 o. 36 0.053 8.0 364 45.0 4.6 0.45 0.105 Lettuce 0 30 6.4 0.14 0.040 0.5 41 7.4 0.6 0.13 0.050 1.0 62 56.0 1.0 0.21 0.120 2.0 79 10.0 2.1 0.16 0.080 4.0 11.0 2.8 0.19 0.120 8.0 152 36.0 3.9 0.51 0.180 asource: Page et al. (1977). TABLE 39 Tolerance of Some Crop Species to Pulverized Fuel Asha Moderately Moderately Tolerant Tolerant Sensitive Sensitive Red beets Cabbage Brussels sprouts Barley Spinach Turnip Cauliflower Oats Sweet clover Rape Rye Broad bean Perennial White mustard Wheat Dwarf bean ryegrass Radish Peas Red fescue Carrot Potatoes Red clover Buckwheat White clover Lettuce Alfalfa Strawberry clover Meadow fescue Meadow grass. aSource: Hodgson and Holliday (1966).

96 TABLE 40 Yield Response of Corn and Alfalfa to Application of Fly Ash Fly Ash Yield Rate Increase Source (percent) (percent) Cause Corn-Fredrick Silty LoazrP Muskingum River 2.6 98.7 Muskingum River 5.2 98.7 Increased availability of Zn Phillip Sporn 3.4 17.3 Phillip Sporn 6.8 48.0 Corn-Westmoreland Silty Clay LoanF Muskingum River 7.9 43.8 Increased availability of Zn Alfalfa~Groseclose Silty LoarrP Kanawha River 2.2 25 Kanawha River 4.4 61 Kanawha River 8.8 132 Increased availability of Mo Crawford Edison 0.3 61 Crawford Edison 0.6 150 Crawford Edison 1.2 132 Corn-Woodstown Loamy Fine Sande Glen Lyn Glen Lyn 4~8 6.4 20 27 } Increased availability of water aschnappinger et al. (1975). b Doran and Martens (1972). cPlank et al. (1975). Results of qreenhouse experiments conducted by Paqe et al. (1977) with plants qrown on calcareous and acid soils amended with Mojave fly ash are summarized in Table 41. Growth of alfalfa, Bermuda qrass, white clover, Swiss chard, and brittlebush was improved by application of this fly ash to soils. The increase in yield was attributed, in all cases, to increased availability of sulfur to plants from fly ash. Yields of lettuce, corn, and radish were depressed as the rate of application of fly ash was increased. Yield depression in lettuce was siqnificantly related to increased salinity and boron in the soil as a result of the fly ash. Disposal in Surf ace Waters The potential use of fly ash to purify polluted lake and river waters as well as ocean disposal has been studied by Tenney and Echelberqer (1970), Hiqqins et al. (1976), and Thomson (1963). Fly ash has a strong

97 TABLE 41 Summary of Dry Matter Yield Data of Various Plant Species Grown under Greenhouse Conditions on Soils Amended with Variable Rates of Mojave Fly Asha Fly Ash Relative Yield (Eercent) in Soil Bermuda White Swiss Brittle- (percent) Alfalfa Grass Clover Lettuce Chard bushb Arizo Soil 0 100 100 100 100 100 100 1 240 182 185 69 117 125 2 315 172 276 39 114 133 4 343 183 210 20 122 142 8 306 156 150 35 87 102 Redding Soil 0 100 100 100 100 100 100 1 184 144 133 74 116 118 2 259 155 89 162 130 4 261 141 27 68 127 120 8 274 153 47 14 89 107 Corn Radish Domino Soil 0 100 100 2 109 53 4 103 32 8 52 21 20 26 17 40 4 17 Redding Soil 0 100 100 2 47 50 4 36 11 8 27 13 20 7 8 40 7 13 asource: Page et al. (1977). bA native desert plant species co11Unon to the Mojave Desert. capacity to reduce excessive concentrations of phosphorus and also to remove undesirable color and organic contaminants from these waters. The reduction in phosphate concentrations is attributed to the formation of insoluble calcium-phosphate compounds under conditions of high pH and high content of free ca~ ions, which are prevalent in water extracts from many fly ashes. As much as 95 percent of the initial phosphorus concentration was removed by the addition of fly ash to Stone Lake (Michigan) water at the rate of 10 g/l (Tenney and Echelberger, 1970). Higgins et al. (1976) studied the effectiveness of fly ash in removing excessive phosphorus concentrations from Lake Charles waters. They concluded that, although ponded fly ash is capable of removing some

98 phosphorus, not enouqh is removed to justify its use for that purpose alone. They also showed that a 5-cm layer of fly ash on lake sediments was sufficient to prevent phosphorus release for extended periods. Because of its relatively larqe surface area and residual carbon content, fly ash has a hiqh adsorption capacity and is capable of removinq many constituents from lake water. Examples of orqanic materials that were effectively removed by fly ash are alkylbenzenesulfonate (ABS), phenols, trinitrotoluene (TNT), refractory orqanic materials, colors, taste, odor, bacteria, and alqae. Approximately 65 to 70 percent of the total orqanic materials in Stone Lake water were removed also by the addition of 10 q of fly ash/l to the lake water (Tenney and Echelberqer, 1970). Fly-ash additions to lake waters do not appear to impair other water-quality parameters. For example, water hardness and sulfate concentrations in lake waters did not increase beyond the critical levels prescribed by the U.S. Public Health Service (1962). Thomson (1963) has also shown that fly-ash addition at levels up to and includinq 10 q/l is not harmful to the aquatic life of a water body. He examined the mortality threshold of fish in fly-ash suspensions created by disposinq of fly ash in the ocean and observed no injurious effects from the fly-ash concentrations indicated above. Neutralization of Acid Mine Drainaqe Various treatment and control procedures have been suqqested for the reclamation of acid mine drainaqe (AMO) waters. Direct chemical neutralization of the acidic components of these waters appears to be the most widely accepted and used. AMO waters are characterized by low pH and hiqh content of iron. Because of the presence of siqnificant concentrations of calcium and OH ions in water extracts from most fly ashes, they have the potential of beinq used as aqents in the neutralization of AMO waters. The effectiveness of fly ash in neutralizinq AMO waters was demonstrated by Tenney and Echelberqer (1970). The amount of fly ash needed to increase the pH of these AMO waters to acceptable levels (::7) depends to a larqe extent on the acidity of the waters and the alkalinity of the fly ash used. Such AMO waters with hiqh iron concentrations, hence hiqher acidities, tend to have hiqher bufferinq capacity than water containinq lesser concentrations of iron and acidity, thus requirinq qreater quantities of fly ash to neutralize their acidity. Expressinq total acidity in terms of milliqrams of calcium carbonate per liter (mq of CaC0 3 /l), Tenney and Echelberqer (1970) have shown that waters containinq approximately 3 q/l require fly-ash additions at the rate of 150 q/l to achieve neutrality (pH 7.3). Acid mine waters containinq only about 100 mq/l total acidity required the addition of about 5 q of fly ash/l to achieve such neutrality. These results suqqest that other acid industrial wastewaters could be treated with fly ash. Pickle liquor and platinq solutions are examples. Additions of fly ash miqht also restore acid boq lakes.

99 Use of Fly Ash as a Physical Conditioner of Waste Sludges A number of inert materials have been used to condition the sludge for dewatering. Examples of these materials are coke, bone ash, peat, paper pulp, ground blast-furnace slag, diatomaceous earth, sawdust, crushed coal, activated carbon, and fly ash. Tenney and Echelberger (1970) indicated that fly ash is an excellent conditioner of various waste sludges such as those from paper mills, rubber plants, and municipal wastewater. They also conducted a study on the effectiveness of fly ash as a dewatering agent for activated sludge. Their results indicated that a specific fly-ash concentration of one part fly ash to ten parts sludge, by weight, gave optimum rate of dewatering. This rate corresponded to additions of 50 to 75 g of fly ash/l of sludge. Aside from improving the filterability of the sludge- fly-ash cake, fly ash lowered the residual moisture content of the cake and thereby increased its potential fuel value. Their study showed a reduction of 20 percent in the moisture content of the cake. Tenney and Echelberger (1970) concluded that sludge particles are bonded to the surface of fly-ash particles by means of chemical and/or electrostatic interactions that give appreciable rigidity to the sludge- fly-ash lattice; therefore, the sludge particles are held securely during vacuum filtration. Such a mechanism increased porosity and allowed for the relatively unrestricted egress of water. HEALTH EFFECTS Occupational Health Health effects from occupational exposure to trace metals from steam- electric plant processes have not been documented. Public Health The potential impact on the environment will come from stack emissions of fine particulates, which are subsequently deposited on the biological systems and from the disposal of collected residues. Studies conducted by Natusch and Wallace (1974) and Linton et al. (1976) indicate that a number of potentially toxic trace elements, including lead, cadmium, antimony, selenium, nickel, vanadium, zinc, cobalt, bromine, manganese, and S04 , predominate in small particles emitted from high-temperature combustion sources. Deposition in the respiratory tract depends on particle size, as is illustrated in Figure 15. Particles of 1-pm diameter or less are deposited almost exclusively in the lung (Figure 15). As was shown earlier, such particles are enriched in trace elements to a great extent, particularly at the surface that comes in contact with tissues. Little is known about the fate of metals emitted from tall stacks. Both modelinq efforts and systematic grid sampling around power plants have indicated that less than 10 percent of the metals emissions can be accounted for within 50 km of the plant. The predicted air concentrations of known mutagens, teratogens, and carcinogens near a

100 1.0 0.9 c 0.8 IJ.J ..... (/) 0.7 0 a.. IJ.J 0.6 FIGURE 15 Respiratory deposi- c tion efficiencies for inhaled z 0.5 particles (U.S. Department of 0 ..... Health, Education, and Welfare, u 0.4 1969). <( a:: LL 0.3 0.2 0.1 0 10·2 10· 1 10° 10 1 10 2 PARTICLE DIAMETER Cµ.m) 1400-MWe plant are (except for beryllium) orders of maqnitude less than acceptable concentrations (Table 42) (Crockett and Kinnison, 19771 Swaine, 19771 Vauqhan et al., 1975). The specific trace-metal components of the particulate portion of the SOx-particulate complex stronqly influence the response of experimental animals to the aerosol mixture. Copper, manqanese, vanadium, and iron particles plus S02 produce increases in airway resistance in animals several times qreater than that produced by S02 alone. These metals are known promotinq aqents of the conversion of sulfur dioxide to sulfuric acid, considered to be the most irritatinq sulfate species (Amdur, 1976). In experimental heteroqeneous droplet systems, manqanese and iron are cocatalysts of the conversion of sulfur dioxide to sulfate (Beilke and Gravenhorst, 1977). Trace-metal synerqism with other air pollutants may well be the mechanism of qreatest concern to public health, especially considerinq the lonq-range transport underqone by qases and small particulates emitted from tall stacks. Vaughan et al. (1975) modeled the behavior and accumulation of trace metals in soil, water, biota, and humans that could be emitted from a hypothetical 1400-MWe coal-fired plant sited in a semiarid western watershed and burninq representative western coal. They concluded that the hazard incurred from direct inhalation would be neqliqible, because respirable (submicrometer) particulates constituted 1/100 or less of the total particle burden, which was an order of maqnitude less than present urban air-pollution concentrations. This findinq was supported by Baser and Morris (1977), who computed excess deaths attributable to trace

101 TABLE 42 Predicted Air Concentrations of Airborne Trace Elements in the Vicinity of a 1400-MWe Coal-Fired Power Plant Compared with Acceptable Air Concentrationsa Predicted Air Acceptable Air Concentrations Concentrations Element (µg m-3) (µg m-3) As (V) or total 1.2 x 10-4 0.1 As (III) 1 x 10-S Be 2.9 x 10- 4 5 x 10-3 Cd 1.2 x 10- 4 0.05 Cr 7.2 x 10-6 0.05 Cr (VI insol) 1 x 10-6 F 0.01 Hg 0.1 Hg organic 0.01 Mo 2.4 x 10-4 0.1 Ni 4.8 x 10-4 0.01 Ni carbonyl 1 x 10- 6 Pb 2.4 x 10-4 1.0 Sb 2.4 x 10-s 0.1 Se 2.4 x 10-s 0.1 Ti 3.0 x 10- 6 0.01 u 3.0 x 10- 3 0.01 v 2.4 x 10-4 0.05 asource: Van Hook and Shults (1976). metal exposure from a hypothetical 1000-MWe coal-burninq plant (Table 43). The predicted impacts on drinkinq-water concentrations were several orders of maqnitude lower than those proposed as maximum acceptable concentration standards for potability. Cadmium, molybdenum, and tunqsten showed 30 to 100 percent increases in qreen plants, assuminq partial solubility of exoqenously supplied metals. The incremental burden for the remaininq metals was about 11 percent of reported content. The size of these chanqes, which occur over 40 years of plant operation, are small in comparison with those routinely encountered throuqh fertilization of crops. Attention was called to molybdenum, which has a stimulatinq effect on both anaerobic denitrification and nitroqen fixation reactions. The first reaction could be destructive to aqriculture by depletinq soils of available nitroqen1 the second is a limitinq one and critical to aqricultural productivity. The study concludes that the inqestion of plants for food appears to be the only consequential pathway of anthropoqenic elements to man. In qeneral, excessive bioaccumulation is not expected unless the bioavailability of exoqenous fractions is orders of maqnitude qreater than that of endoqenous fractions.

102 TABLE 43 Projected Annual Excess Mortality from Selected Trace Metals and Iron Related to Air Emissions from a 1000-MWe Coal-Fired Planta Range of Magnitude of Trace Range of Cone Excess Mortality Annual Excess Mortality Metal in Coal (ppm) Coefficientb (exponents) Cd 0.01-28 15.1 E-4 to E-1 Cr 4.4-60 9.9 E-3 to E-2 v 10-50 11.2 E-2 to E-2 Fe 1500-7520 15.8 EO to EO Mn 6-100 3.1 E-4 to E-2 Ni 4-61 5.3 E-3 to E-2 Zn 5.3-1610 3.7 E-3 to E-1 c E-4 to E-1 Hg 0.04-33 c E-3 to E-1 Pb 2-106 c E-5 to E-1 Be 0.1-1000 c E-3 to E-1 As 2-25 c E-3 to E-2 Se 1.2-7.7 asource: Baser and Morris (1977). bUnit of coefficient is excess deaths per 10 5 persons per microgram of metal per cubic meter of air. cCoefficient not giveni 15.1 used. Radioactive elements are present in stack qas and ash piles. 112Rn and 110Rn are released in qases from the stacks and account for most of the 7 x l0-3 mrem/yr per 1400-MWe coal-fired plant. In comparison, the whole-body dose equivalent rate from all natural sources is 80 ± 40 mrem/yr. Assuminq that the radon-release percentaqe from coal-ash piles is similar to the radon-release percentaqe from uranium-tailinqs piles (about 5 percent), ash collected and sorted over the 30-year lifetime of a 1000-MWe plant miqht have a 3.4- to 15-times qreater radon-release rate, dependinq on the type of coal, than natural backqround (Van Book and Shults, 1976). Pondinq and qround burial of sludqe, slaq, and fly ash represent probable sources of water contamination. These residues contain the less-volatile trace elements, but acidification of fly ash increases the solubility of most elements, an indicator of bioloqical availability for leachinq. Arsenic, lead, and selenium are present in the scrubber liquor in concentrations qreater than the allowable drinkinq-water standards (Bern, 19761 U.S. Public Health Service, 1962). One test project showed no effects on qroundwater from disposal of either treated or untreated sludqe (Flinq, 1976), but it is difficult to extrapolate these findinqs to other locations and soils because of the wide variability in soils for filtration. Measures to prevent contamination of qroundwater and surface waters may be required (Bern, 1976).

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