Section 13. HAZARDOUS AND TOXIC WASTES
HAZARDOUS WASTE FIXATION
USING DRY FLUE GAS WASTE
Dennis W. Weeter, Professor
Department of Civil Engineering
The University of Tennessee
Knoxville, Tennessee 37966
Due to the cost of transportation and disposal of hazardous wastes approaching $110-
330 per metric ton, generators are looking for lower-cost options. Solidification, or fixation,
may be available for many classes of hazardous wastes. However, commercially available
fixating agents (cements, silicates, others) may cost $50-83 per metric ton, making fixation
costly as well. Therefore, it is important to investigate high-volume, low-cost materials as
potential fixating agents.
This study presents the results from using dry flue gas dusts as fixating agent for several
hazardous wastes and sludges. One dust originates from flue gas desulfurization where a
CaO slurry is sprayed into the stack gas and S02 is reacted with the CaO to form CaS04/
S03. These reacted producted, along with the fly ash, are then removed at the baghouse.
Since many dry, calcium-based FGD systems are being specified and constructed today,
the waste product may become high-volume and readily available. A second dust originates
in the baghouse of a lime kiln plant which is coal fired. The dust contains CaO, CaC03, and
fly ash. Pozzolonic reactions occur when wetted. Also.this is a high-volume waste.
In previous work [1,2] the pozzolonic reaction capability of dry, calcium-based FGD
wastes is discussed. Optimum moisture content, maximum dry compacted density, uncon-
fined compressive strength, and leaching characteristics of the waste were determined. In
summary, when compacted with moisture the waste undergoes a pozzolanic reaction similar
to that obtained with lime and fly ash. Strengths up to 13,794 kPa were obtained. The
waste, raw and fixed, did not violate leaching standards [3].
The wastes evaluated in this study included a cadmium plating sludge, a chromium
plating sludge, waste oil sludge, and a waste slurry from an aluminum can reclamation
center. Two different methods were pursued. The chromium plating sludge was dewatered
and blended with the lime kiln dust on a dry mass basis whereas the other three wastes
were added as a slurry to the FGD waste (approximately 60% FGD to 40% waste slurry).
EXPERIMENTAL METHODS
The cadmium sludge, waste oil sludge, and aluminum can waste were mixed with dry
FGD waste and compacted via the Proctor procedure [4] into Harvard miniature molds
to form 3.3-cm by 7.31-cm cylindrical blocks. Samples were ejected, wrapped in plastic,
dipped in wax, and rapidly cured for seven days at 47.8 C. Samples were then evaluated
for unconfined compressive strength (UCS) [4].
Samples, raw and cured, were then leached to determine the hazard potential. Two
samples, raw and fixed, were leached using acetic acid. The same procedure was followed
using deionized water on raw and fixed samples.
The chromium waste was treated such that a liquid sludge sample (2-4% by weight)
had a mass of lime kiln dust added to it whereupon the mixture was passed through a
plate and frame press filter and dewatered to 30% moisture. Cylinders were cut from the
pressed mixture and cured as discussed earlier. Following curing, the waste was analyzed
for UCS and leachate (acid and deionized water) characteristics. Leachate analytical procedures were by EPA-specified procedures [5).
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