Melting of fly ashes and product properties

Abstract

Combustion of municipal waste yields fly ashes. The ashes contain hazardous metals in a soluble form. Recycling or disposal of such residues requires separation of the hazardous metals or vitrification of ashes. The glass product must be chemically durable enough to prevent significant leaching of the hazardous metals. The vitrification process requires knowledge of the viscosity and the crystallization properties of the melt and of the electrical resistivity if the melt is directly heated. These properties were investigated in dependence of the temperature and the chemical melt composition and the results are presented graphically so that melt properties can be predicted for certain melt composition ranges. The chemical durabihty was measured using various test methods (Soxhlet, ISO 719, „Swiss Test"). The chemical durability was also tested as a function of temperature, pH value, glass surface area to solution volume ratio and the content of organics (citric acid, humic acid) in the solution. First results are presented.