Abstract: At least two parameters (.delta., Inst) of which it is known that their variation influences the state of the spark erosion process (F, W) are fed to a logic device (5) in which a set of rules is stored. The logic device processes the parameters fed with the aid of the stored rules according to the laws of fuzzy logic, and generates at least one output signal (.epsilon.) which is fed to a controller (6) of at least one parameter, in order to match or at least approximate the currently prevailing state of the spark erosion process to a currently desired state of the spark erosion process.

Abstract: In the processing of mainly inorganic refuse incineration products polluted by heavy metals and/or heavy metal compounds, and/or analogues of such products, to give environmentally acceptable products by melt-thermal treatment, an iron-containing melt is used whose iron content can be adjusted by addition of iron or an iron compound. The melt is first melted above 1300.degree. C. in a reactor. The melt is then oxidized with vigorous agitation by blowing in oxygen-containing gas until all the metals and metal compounds present in the reactor have been converted to the oxide form, the melt being kept above 1450.degree. C. and preferably at about 1500.degree. C., at least at the end of the oxidation. Subsequently, the melt is reduced, preferably by means of a part fraction of the refuse incineration product and/or iron, preferably in the form of scrap, and/or hydrogen. The reduction can then be continued by means of added aluminum and/or calcium and/or ferrosilicon.