Pickling sludges from Avesta Sheffield AB, Sweden and Sandvik Steel AB, Sweden, have been studied in this work. The chemical characterisation of the sludges have been made by chemical analysis, X-ray diffraction analysis, particle size distribution, scanning electron microscopy and thermal analysis. These two sludges have many common characteristics. The dry matter in the filter cakes heated up at 120 deg C is about 35-40 percent. After drying at 120 deg C the sludges still contain between 10-15 percent water, which evaporates in the temperature range 120-600 deg C. The mean particle size is about 3.7 mu m for both sludges. The filter cakes are amorphous. Several crystalline phases were identified after heating. Scanning electron microscopy studies show that the elements Fe, Ni, Cr, F, Ca are evenly distributed in the particles. The reduction properties of the sludges with petroleum coke have been studied in laboratory scale. The metallization degree of iron and nickel reached 90-99 percent and 75-97percent, respectively. Influence of retention time and amount of reductant as well as need of protecting agent were also investigated.
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