Development of a pyrometallurgical technique to recycle stainless steel wastes

Abstract

It is estimated that wastes containing over 20 million lb of chromium and 8 million lb of nickel are generated annually in the production of stainless steel in the United States. These wastes, consisting of flue dusts, swarfs and mill scale are virtually all sent to dumps and landfills because of the lack of an acceptable recycling technology. The Bureau of Mines of the United States Department of the Interior, whose activities include conservation of mineral resources by the recovery of metal values from industrial wastes, has developed a method for recovering over 80 % of the chromium and 90 % of the iron and nickel contained in pelletized mixtures of these stainless steel wastes. The Bureau's two-stage recovery technique relies on an initial reduction with carbon contained in the pellets, during meltdown in the arc furnace. This is followed by an addition of ferrosilicon to recover further chromium from the slag. The result is a master alloy suitable for recycling by charging to commercial stainless steel heats. A variation in procedure involves adding pellets directly to the production furnace to replace part of the stainless scrap charge. The technique has been validated in heats of 1 500 and 2 000 lb and more recently in industrially produced heats of 12.5 – 17 tons. Details of the pelletizing and furnacing and data on recoveries are presented.