Antti Kekki

New hydrometallurgical approaches for stainless steel dust treatment

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.