Vitrification by melting process is the only technical process for safe immobilization and destruction of environmentally dangerous components in waste materials. Toxic filter dusts, which are produced in incineration plants, serve as an example of such wastes. The principal problems of all vitrification methods developed are the wide composition variations of the input materials, the risk of new filter dust formation by necessary flue gas cleaning plants, especially of sulphur compounds, the lack of knowledge of melting behaviour, and achieving chemical long-term stability of the resulting waste glasses. Melting experiments with model systems show that the typical composition range of incineration filter dust allows synthesis of resulting glasses without addition of other materials. With a carbon content of more than 5wt% the glasses are black.
