WATER QUALITY EFFECTS OF AQUEOUS FLY ASH DISPOSAL
Gregory D. Reed, Assistant Professor
Civil Engineering Department
University of Missouri
Kansas City, Missouri 64110
Dee T. Mitchell, Assistant Professor
David G. Parker, Associate Professor
Civil Engineering Department
University of Arkansas
Fayetteville, Arkansas 72701
INTRODUCTION
The demand for electrical energy has been increasing rapidly in the United States.   By
the beginning of this decade, coal-fired power generating plants accounted for 44% of the
total generating capacity [ 1 ].  The present trend is to build more coal-fired power facilities because of the restricted availability and rapidly increasing cost of natural gas and petroleum products, and the safety, fuel availability and construction time problems of nuclear
plants.   It appears reasonable to expect an increase in the percentage as well as the number
of coal-fired power plants.   The increased use of coal will produce additional quantities
of fly ash, one of the waste products of burning pulverized coal.   Presently, between
30 and 40 million tons of fly ash are being collected from the flue gases of the existing
coal facilities.   This quantity will increase in proportion to the amounts of coal burned.
The fly ash generated by these plants is, and will continue to be, a disposal problem.
Presently less than 10% of the fly ash collected is utilized in some process other than
direct burial.   Virtually all of the disposal and utilization techniques expose ash to water
at one time or another.   The exposure ranges from complete immersion of the fly ash,
such as in pond, sluicing, or water and wastewater activities, to intermittent percolation
of fill areas.
Several authors [2-7] have identified possible water quality problems associated with
particular fly ash disposal sites.   These papers reported different chemical constituents,
but high concentrations of boron, sulfate, iron, dissolved solids, and manganese were
Listed in one or more of the articles.   This type of information along with a recognition
of its chemical composition, points out the potential water quality degradation properties of fly ash.
Fly ash is composed of the original coal constituents not vaporized by combustion.
Fly ash from a highly efficient furnace is essentially noncombustible material that is,
in effect, a concentration of the impurities that were present in the coal.   The particle
diameter ranges from 0.5 to 100 ju with a mean diameter of 1 to 5 p and a specific
surface area of 3300 to 6400 square centimeters per gram [6J.   Microscopic observations
and the work of Pearson and Galloway [8], DiGioia and Nuzzo [9J, and Yerushalmi
et al., [10] show fly ash particles to be spherical in shape.
The physical and chemical properties of fly ash depend upon the type of coal and the
method of combustion.   Table I is a listing of typical chemical constituents.   Generally,
fly ash is mostly silica, calcium oxide, alumina, iron oxide, magnesium oxide, and sulfur
oxide.   Many elements are present in trace amounts, depending on the type of coal.   In
addition, Davidson, et al., [13] found a marked increase in the concentrations of Pb, Ti,
Sb, Cd, Se, As, Zn, Ni, Cr and S with a decrease in particle size.   They proposed that
preferential condensation and adsorption accounted for the increase.   Many potentially
harmful elements are present in fly ash and apparently may be located on the surface.
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