FIXATION MECHANISMS IN SOLIDIFICATION/STABILIZATION
OF INORGANIC HAZARDOUS WASTES
Paul L. Bishop, Professor
Stephen B. Ransom, Graduate Student
David L. Gress, Associate Professor
Department of Civil Engineering
University of New Hampshire
Durham, New Hampshire 03824
INTRODUCTION
Approximately 40 to 60 million wet metric tons of hazardous inorganic wastes are currently generated per year in the United States, mostly in liquid sludge form. In 1980, an estimated 90% of this
material was disposed of by environmentally unacceptable methods [1]. There are over 50,000 dumps
and 180,000 open pits, ponds and lagoons across the nation that contain some significant amount of
hazardous waste; as many as 2,000 of these sites present potentially imminent public health hazards
[2], In spite of this, only four new hazardous waste facilities have been licensed anywhere in the nation
in the last five years.
The regulations promulgated under the Resource Conservation and Recovery Act (RCRA) have
forced industry to look at alternative approaches for the disposal of hazardous wastes. Essentially,
RCRA has stipulated standards for siting, design and operation of disposal facilities. One alternative
for the disposal of hazardous wastes is to utilize a technique known as solidification/stabilization.
Solidification refers to disposal techniques that can fixate or encapsulate wastes into a solid, cemen-
titious matrix. Stabilization techniques chemically and physically bind the waste with a solidification
agent [3]. Together, solidification/stabilization treatment systems: (1) improve handling and physical
characteristics of the waste; (2) decrease the surface area across which transfer or loss of contained
pollutants can occur; and (3) limit the solubility of or detoxify any constituents contained in the
waste [4]. Solidification is a technique that has been used in Japan and Europe for many years. In the
United States, solidification techniques have been practiced primarily with radioactive wastes, while
less environmentally acceptable methods have usually been used for hazardous wastes.
Interest has recently increased in solidification/stabilization techniques because of RCRA, since a
hazardous waste can possibly be treated by this process in such a manner that it becomes non-
hazardous. A waste is considered nonhazardous if its toxicity, as determined by an extraction test in
accordance with specific EPA regulations, meets certain standards. These standards are such that the
concentrations of specified contaminants in the leachate cannot exceed 100 times the EPA's drinking
water regulations [5].
This research evaluated a solidification/stabilization process designed to trap inorganic hazardous
wastes (heavy metals) within a portland cement matrix, thereby creating an essentially inert, non-hazardous product. Characteristics of the solidified/stabilized product, including compressive strength
and metal concentration in the leachate, were evaluated. In addition, the influence of particle size on
metal leaching rate was investigated.
METHODS
The wastes used for this research were synthetic wastes prepared in the laboratory. The three
heavy metals used (cadmium, chromium and lead) were in the form of cadmium chloride (CdCl2),
potassium  dichromate  (K2Cr207),  and  lead  chloride  (PbCl2),  respectively.  The  potassium
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