Sol-Gel Stabilization of Heavy Metal Waste

Abstract : The Army is continually faced with the disposal or treatment of media contaminated with heavy metals such as lead, chromium, and cadmium. The types of media are varied and include soils, ashes, and sludges. Waste having a leachable metal concentration above the Toxicity Characteristic Leaching Procedure limit established by the U.S. Environmental Protection Agency can be treated to render it non-hazardous. Several stabilization/solidification (S/S) processes are used for the treatment of hazardous wastes. Vitrification, for example, incorporates hazardous waste into glass, but the high temperatures needed to make the glass are undesirable. Sol-gel chemistry is a means to make glass at low temperatures. Also, the heavy metals can be chemically incorporated in the glass matrix rather than merely encapsulated. This work examines the ability of sol-gel chemistry to replace vitrification as an S/S technique. A recipe was formulated for immobilizing lead in glass by the sol-gel process. The merits of the process are discussed. Results showed that sol-gel processing stabilized some lead from solutions and encapsulated some metals in a glass matrix. However, sol-gel was found to be too sensitive to chemistry, too limited in application, and too expensive to compete with current S/S processes.