Preparation of glasses and glass-ceramics prerared from sewage sludge and incinerator ash.

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A huge amount of waste suhstances are generated each year, although we have only limited landfill sites available to disposal of these waste. It is an important and urgent problem how to deal with these waste and how to reuse as valuable materials. The main components of the sewage sludge are inorganic SiO_2-CaO-Al_2O_3-Fe_2O_3 after removal of water and organic substamces. The incinerator ash also has similar compositions.In the present study, the sewage sludge and incinerator ash were melted at 1350-1450ﾟC and after cooling, glasses were obtained. It was shown that these glasses have similar compositions and properties to these of aluminosilicate glasses.However, these glasses have strong black color and completely opaque. The glasses of the same compositions prepared from chemical reagents were not so opaque, compared with those from wastes. Color origins were deduced to be carbon, silicon or some sulfide compounds. By simulation, it was shown that, even small amounts less than analytic detection, the glasses can be completely opaque if very fine opaque particles are distributed in the glasses.It was shown that the glasses from waste have almost same chemical durability as the window glasses in the solution of pH7-10. But in the acidic solution, the durability was slightly less than that of window glasses.The glass-ceramics have possibility to being stronger than the mother glasses. In order to prepare excellent glass-ceramics, proper crystal nucleation agents are necessary. It was found that FeS promotes crystallization of the glasses from waste.