Crystallization and Strength of the Molten Slag on Sewage Sludge Melting Process

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In the melting process, sewage sludge is melted in the high temperature range of 1300 to 1500 ﾟC which is beyond the pouring point of sludge inorganics and a large volume reduction and stabilization of heavy metals in the slag are expected to greater than incineration process.On the other hand, methods of converting glasses slag made from processed sewage sludge to crystalline slag has been investigated to reuse them as construction materials. Crystalyzation of slag is greatly affected by in-organic component parts in the sludge. The results are as follows.1. Though a mixture of SiO_2, Al_2O_3, CaO and Fe_2O_3 contained in sewage sludge in-organics require a very high temperature to be melted, the melting temperature dropped about 200 ﾟC with the adjustment of inorganic component ratio of Na_2O/CaO (between 0.2-0.4) by Na-added and Ca-added.2. The maximum nucleation temperature of polymer-added sewage sludge is about 700ﾟC, and the maximum crystal growth temperature is about 1100ﾟC. The crystalline slag is made by holding the solid solution at 1100ﾟC during 1 hr and cooling the molten slag. Also, the crystalline slag is easily made by re-heating a glasses slag.3. Strength of a slag is affected by SiO_2 contents in a slag. Strength of a slag increases with increasing of SiO_2 contents, but viscosity of liquids affected by SiO_2 contents causes a high melting temperature. It is suggested that the adjustment of basicity (CaO/SiO_2 ratio : about 1.0) makes the melting temperature lower.