Schwermetall- und chloridhaltige Filterstäube. I. Phasenanalysen und Modellversuche zum Recycling

Flue Dusts Containing Heavy Metal Ions and Chloride.I. Phase Analysis, Model Experiments for Recycling Four flue dusts from a cement factory, an electric-furnace steelmaking plant and a municipal waste plant were analyzed by powder diffraction methods. Chloride combines above all with alkali ions or heavy metal ions, especially yielding PbCl₂ and KPb₂Cl₅. The controlled sublimation of these chloride compounds in open crucibles was developed and optimized in our laboratory. Between 850°C and 1150°C and at reaction times from 30 min up to 12 h, the chloride content decreases to below 0.1 wt-%. The sublimed phase mainly consists of alkali and lead chloride. Zinc is found in the flue dust as oxide and is enriched during this process. Recent investigations with a small waelz kiln give analogous results. With our procedure, the manufacturer by himself is able to exploit flue dusts containing a large amount of heavy metal elements and chloride which cannot be deposited. The remaining product contains mainly zinc oxide which can be recycled in the zinc industry or returned to the production process. The sublimed chloride compounds may be recycled in the potash industry.