COMPOSITION AND PROPERTIES OF GLASS-CERAMICS PRODUCED FROM INCINERATOR RESIDUALS

Vitrification of waste materials is a method that is well established as a means to immobilize inorganic constituents in the waste. Vitrific ation has been extensively applied in remediation of nuclear wastes by engineering the glass composition to serve as a host to the radionucl ides, and to achieve maximum resistance to solution by leaching media. Vitrification of non-nuclear, hazardous wastes has been extensively r esearched and applied in a few remediation projects/processes. These e fforts with hazardous wastes have involved forming a glass followed by casting billets or by slag granulation processes. Prior to this resea rch, formation of glass ceramics, i.e. substantially crystalline produ cts, in waste remediation efforts had not been reported. This research utilized hazardous waste incinerator residuals in the form of slag, b aghouse dust, and water treatment sludge in a two-step process of vitr ification and recrystallization to produce a repository for ''regulate d'' metals within the resulting glass ceramic. The residuals contained magnesia. alumina, iron oxide, and silica as major constituents, and their chemical composition was adjusted to yield the desired crystalli ne phases after melting between 1400-1465 degrees C. The glass was cas t into graphite crucibles and annealed. The samples were then recrysta llized by reheating to 975-l000 degrees C forming phases of enstatite, forsterite, hercynite, magnesioferrite, pseudobrookite and spinel. Mi crographs of the recrystallized samples indicate that phase separation occurs at 850 degrees C with crystals growing from a droplet-type pha se. At the optimum recrystallization temperature of 975-1000 degrees C , a finely crystalline microstructure develops with low porosity. This type of microstructure provides both high compressive strength and lo w leachability in the remediated product.