2001 International Ash Utilization Symposium, Center for Applied Energy Research, University of Kentucky, Paper #86. Copyright is held by the Authors.

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Combined Statistical Model for the Leaching of Heavy Metals from Fly Ash Solidified/Stabilized Wastes

Lucy Mar Camacho¹, Stuart Munson McGee²

¹Universidad Autónoma de Ciudad Juárez, Engineering and Technology Institute, Ave. del Charro 610, Ciudad Juárez, Chih., México;

²New Mexico State University, Chemical Engineering Department, Box 30001/Dept. 3805/ Las Cruces, New Mexico 88003

An adequate method for the disposal of hazardous wastes without causing pollution of groundwater is the solidification/stabilization process. This method consists of combining fly ash material with waste to obtain a solidified form. The United States Environmental Protection Agency (EPA) has developed the toxicity characteristic leaching procedure (TCLP) to establish the environmental acceptability of the solidified/stabilized waste for land disposal. In this test, the waste is contacted with an acidic media under non-equilibrium conditions. The concentration of material leached from the waste after 18 hours of continuous agitation is measured.

The purpose of this article is to present the results obtained from the application of a combined statistical model developed to quantify the amount of heavy metals released from the solidified/stabilized waste to the leaching solution. The TCLP test is run in a semi-batch mode during 100 hours to simulate real environmental conditions. Three metals of relevant importance in the environmental pol ution are analyzed namely, chromium, cadmium and aluminum. The model would allow selecting the most appropriate process conditions in the formation of the solidified waste and to minimize the release of the metals. The model is based on a simplex-centroid and a 26-3 fractional factorial experimental design. Fitted equations representing the maximum and final metal release to the leaching solutions are developed. A linear polynomial equation was found to quantify the amount of chromium and cadmium release, while a third degree polynomial was required for the same purpose for aluminum.

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