Effect of the Main Composition of Solid Waste Incineration Ash on Melting Characteristics and Qualities of Melted Slag
Atsushi Yoshino*, Kiyoshi Momonoi** and Toshiya Komatsu**Abstract
Melting of solid waste incineration ash, which vitrifies the ash through thermal treatment, is expected to be an effective recycling technology. In this study, the effects of the composition of the main ingredients of ash (SiO2, CaO, and Al2O3) in artificial ash (SiO2-CaO-Al2O3-Fe2O3-Na2O-P2O5-PbO) on the following properties were investigated, 1) the melting characteristics of ash from an economic perspective, 2) the physical strength of melted slag as a measure of its quality, 3) the leaching characteristics of a heavy metal (Pb) from melted slag in view of environmental safety.
Melting characteristics were evaluated by a method of microheating (JIS K 2151). The lowest hemisphere temperature was found at basicity (CaO/SiO2) of 0.54-1.07 with an Al2O3 ratio of about 10mol%. The physical strength of slag was evaluated by an abrasion test. The strength had a close relationship with the crystallinity of the slag, and the weight loss of crystallized slag was much lower that of uncrystallized slag. Pb leaching concentration was more than 1mg/L at basicity of 0.53-3.2 with Al2O3 ratio of 6-15mol%.
In conclusion, the properties were greatly influenced not only by basicity but also by a change in the Al2O3 ratio, and trade-off relations in the properties were observed. Therefore, the optimum composition range of ash should be determined according to the purpose of reuse.
Key words: ash melting, basicity, Al2O3, melting characteristics, slag quality