Section 8.    HAZARDOUS AND TOXIC WASTES
LEACHABILITY COMPARISON OF FOUR
HAZARDOUS WASTE SOLIDIFICATION PROCESSES
Pierre L. Cote, Process Development Engineer
Environment Canada
Wastewater Technology Centre
Burlington, Ontario L7R 4A6
Donald P. Hamilton, Technologist
Zenon Environmental Enterprises Ltd.
Burlington, Ontario L7R 4A6
INTRODUCTION
Solidification involves mixing a waste with one or more additives. It is used to improve the handling and physical characteristics of aqueous wastes. The treatment also decreases waste teachability
and has the potential to detoxify the hazardous constituents contained in the waste. Several surveys
and reviews of the existing processes have recently been published [1-3].
A majority of the commercially available waste solidification processes are proprietary and most
of the performance and cost data available in the literature have been published by vendors of the
technologies. A number of comparative evaluation studies of the physical properties and environmental stability of solidified wastes have been conducted by regulatory agencies [4-10]. In each of
these studies, the wastes were solidified by the vendors. Although this approach allowed testing of the
supposedly optimal formulation of each process, it did not generate information on process variability. Furthermore, the lack of information about the processes limited interpretation of the test
results. Since no economic data was available, performance analyses of the various processes could
not be conducted on a cost/benefit basis. Finally, meaningful comparisons could not always be made
among the leaching test results since dilution of the contaminants in the solidified wastes resulting
from various additive amounts was not taken into account.
A research program was developed at the Wastewater Technology Centre (WTC), Burlington,
Ontario, to evaluate the main hazardous waste solidification technologies [11]. The program is limited
to the solidification of inorganic aqueous wastes (that may contain small fractions of organics) using
inorganic additives. It features use of synthetic wastes to carefully control the experimental conditions, in-house solidification and testing, generation of cost data and use of leaching tests that allow
the results to be interpreted based on mass transport theories. This paper presents the results of a
teachability comparison of four generic processes applied to three synthetic wastes.
BACKGROUND
This section contains background information on the WTC research program that provides the
basis and rationale for the experimental design presented in the next section.
Solidification
Four generic solidification processes based on the addition of fly ash-lime, fly ash-cement,
bentonite-cement and soluble silicates-cement were investigated. The four processes are proprietary
(US patent RE29 783, UK patent 1 485 625, US patent 4 149 968, and US patent 3 837 872, respectively). The main additives specified in the patents were used. However, no attempt was made to
pretreat the wastes or use tertiary additives in order to reduce the leachability of specific contaminants.
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