SORPTIVE CHARACTERISTICS OF HEAVY METALS
IN FLY ASH - SOIL ENVIRONMENTS
Thomas L. Theis, Assistant Professor
John L. Wirth, Graduate Student
Richard O. Richter. Graduate Student
Jerry J. Marley, Associate Professor
Department of Civil Engineering
University of Notre Dame
Notre Dame, Indiana 46556
INTRODUCTION
Recent studies have addressed the subject of the biogeochemical cycling of trace elements
associated with coal within and in the vicinity of combustion or utilization processes [1-6].
The principal industry of interest has  understandably been the electric utilities and most of
the above studies have centered on fossil fuel generating stations.
Within these systems there are two major sources of trace contaminants to the local
environment, stack gases and fine metallic aerosols not removed by control equipment and
the ash residues of the combustion process.   These residues are made up of particles collected by control equipment (fly ash) and left behind on furnace gratings (bottom ash).
Most studies have shown those elements which display a volatile behavior (such as mercury
and selenium) are lost primarily in stack gases while others are concentrated on the fly ash
particles.
In 1975, approximately 36 million tons of fly ash were produced in the United States [7].
The disposal of this material is normally achieved by temporary ponding (usually on site)
followed by mining and subsequent deposition as fill material.   Occasionally the ash is used
as fill directly.   Although large pressures exist for disposing of the material in more useful
and creative ways, no consistent utilization trend is evident and, in fact, it appears that
stockpiles of fly ash will continue to grow as reliance upon coal as a fuel source increases [8!
Thus, large amounts of this material are brought into contact with soil and water environments.
It has been shown, and confirmed by electron micrographs in this study, that fly ash
consists of many small (0.5-100 p diameter) glass-like particles of a remarkably spherical
character [9].   During the combustion process many different metal oxides condense on
the cooling ash spheres forming a surface coating.   The composition of this coating is highly
variable from ash to ash and is primarily responsible for the alteration of aquatic solution
conditions.
In examining the problems of trace metal chemistry in fly ash, it is important to be aware
of the existence of various metal "pools" to which the trace metals may be sorbed.   While
the thermodynamic properties of most individual trace metals have been aptly described,
their anticipated behavior may nevertheless be at considerable variance with that actually
displayed in the presence of these sorptive reservoirs.   It has been shown that amorphous
iron and aluminum oxides, manganese dioxide, and various types of organics possess high
affinities for many trace metals [10-12].   Although most fly ashes contain little volatile
matter, as will be seen they do have high levels of iron, aluminum   and manganese associated
with them.
The aims of the current phase of this study were twofold:   (a) to   define those chemical
parameters   of fly ash which are important in characterizing the release of trace metal contaminants into solution, and (b) to examine attenuation effects once trace metals are released
into the soil/groundwater environment.
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