A ferrochrome converter (CRC) is used for removal of silicon and carbon from ferrochrome in stainless steel production. The raw materials are molten ferrochrome and stainless steel scrap, and the process produces a raw material for argon-oxygen-decarburization (AOD). The zinc content prevents the utilization of CRC dust (CRCD). The objective of this work is characterization and sulfuric acid leaching of CRCD and evaluation of formation mechanisms and the effects of mineralogy and microstructure on the hydrometallurgical treatment. CRCD contains critical (Cr, fluorite) and economically important (Fe, Zn) materials. The mineralogy and microstructure of CRCD are complex. The dust has been formed by many mechanisms. Lime and ferrosilicon prove that take-off of solid particles during charging is important. Also, ejection of liquid droplets is considerable because ferrochrome and slag spheres are common. The highest Zn dissolution is 93-94% and at the same time 5-15% of Cr is leached. The existence of zincite explains the high dissolution of zinc. The encapsulation, e.g., magnesiochromite enclosed into glass, explains the low chromium dissolution. The best selectivity for Zn extraction over iron, chromium, and nickel is achieved with 0.5 M, at 30 and 60 8C
In production of stainless steel 10-70 kg of dusts per tonne of steel is produced. The final rolling and pickling stages produce significant amounts of metal-rich wastes and acid sludge. The dusts are usually treated by pyrometallurgical methods such as plasma processing or Waelz kiln. Hydrometallurgical methods have been developed especially for the recovery of zinc from electric arc furnace (EAF) dusts, focusing on unalloyed steel EAF dust. A new concept has been developed to selectively leach out zinc from stainless steel production dusts enabling recycling the remaining iron, nickel and chromium compounds back to melting. Zinc can be dissolved using either a strong alkaline solution or strong acid solution. Factors affecting the leaching efficiency have been determined. Mineralogical factors limiting the zinc dissolution have been determined and pre-treatment methods have been developed. Using the optimal conditions the zinc level in the treated dust has been low enough allowing recycling of the dust to melting.
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