MECHANISM AND CONDITIONS OF CLAY FORMATION DURING NATURAL WEATHERING OF MSWI BOTTOM ASH

Municipal solid waste incinerator (MSWI) bottom ash is the slag-like m aterial produced by the incineration of municipal waste and is predomi nantly composed of glassy constituents, which include inherited manufa ctured glasses and glasses formed during incineration, Previous result s indicate evidence of neoformation of well-ordered clay (illite) from glasses in MSWI bottom ash after 12 y of natural weathering. We inves tigated the mechanism and conditions of clay formation from glasses du ring natural weathering using transmission electron microscopy (TEM), experimental leaching experiments and ammonium oxalate extractions. It was concluded that the high surface area and initially high ''active' ' Al and associated Si content predispose the ash to form clay mineral s on a relatively short time scale. This work provides evidence that t he composition of secondary amorphous aluminosilicate and thus, the ty pe of clay mineral which may form, is determined by the pH of the pore solution rather than by the glass composition. Presumably alternate w etting and drying of the ash during disposal greatly accelerates the f ormation of well-ordered clays.