THERMOCHEMICAL TREATMENT OF WASTE MATERIALS

摘要

Residues generated by the metallurgical industry are often mixtures of materials, which leads to an inferior utilisation or are difficult to utilize. Thermochemical treatment of solid slags in an arc furnace is one of the best ways to recycle various hazardous wastes effectively, because it enables the separation of different fractions. In the production of stainless steel a slag containing a residual metallic fraction is generated. Furthermore, the slag contains heavy metal oxides, most notably chromium(Ⅲ)-oxide (Cr_2O_3), which formation during the decarburisation process cannot be prevented completely. Due to the amount of chromium and chromium compounds, the slag from stainless steel production can potentially have an impact on the environment. In arc furnace treatment the heavy metal compounds can be reduced to their elemental form by carbon from the graphite electrodes or other supplementary reducing agents. The resulting metallic and mineral fractions are separated based on their densities. The goal is to recover completely the pure metallic fraction and to convert the mineral part to a cement clinker substitute or a high-value construction material. In order to reach this goal the process conditions will be adapted for most effective reduction conditions and an optimum transfer of heavy metals (e.g. Cr) from the slag to the metallic fraction. The molten mineral fraction is removed from the furnace batch-wise. Different reducing agents or additives can affect the slag composition and will used to optimise both, the effectiveness of reduction and the slag properties. Usually silicon or silicon alloys have been used so far for the reduction. The application of alternative reducing agents, for example, aluminium dross will be tested. The final product is free of harmful compounds and can be used as a raw material for different applications.