Development of Waste Melting System and the Utilization of the Melted Slag

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Solid waste melting, which vitrifies wastes by thermal treatment, is accepted as an effective recycling technology. In this study, effects of the main composition (SiO2, CaO, and Al2O3) of ash on various properties in melting were studied. Items examined were such as : (1) melting characteristics of ash from an economic view, (2) physical strength of melted slag in view of its quality, (3) leaching characteristics of heavy metal (Pb) from melted slag in view of environmental safety.Melting characteristics was evaluated by method of microheating (JIS K 2151). The lowest melting point was found in the basicity (Cao/SiO2) of 0.54-1.07 with Al2O3 ratio of about 10mol%. Physical strength of slag was evaluated by an abrasion test. The strength had a close relationship with the crystallinity of slag, and the weight loss of crystallized slag in the test was much lower that of uncrystallized slag. Leaching of Pb from melteh slag was examined by leaching test with acid condition of pH=4. Pb leaching concentration was more than 1mg/L in the basicity of 0.53-3.2 with Al2O3 ratio of 6-15 mol%.As the results, it was shown that the properties were greatly influenced not only by basicity but also by a change of Al2O3 ratio, and trade-off relations existed in the properties. Therefore, adjustment of main ash composition should be done according to the purpose of recycling.In addition, the utilization of the melted slag such as a material for a self-compacting concrete, was investigated.