Recovery Of Metals

RECOVERY OF METAL VALUES FROM ELECTRIC ARC FURNACE DUST

BY

C. A. Pickles
Department of Mining Engineering

Queen’s University

Kingston, Ontario
Canada, K7L 3N6




SUMMARY

Electric arc furnace (EAF) dust is produced when iron and steel scrap is remelted in an electric arc furnace. This dust is considered as a hazardous waste in most industrialized countries since itfails the toxicity test for lead, cadmium and chromium. As an alternative to landfilling, other options have been developed to treat the dust and these include: hydrometallurgical, pyrometallurgical, and hybrid pyrometallurgical - hydrometallurgical processes. Since the EAF dust is generated from scrap, then it contains not only iron and numerous non - ferrous metals but also sodium, potassiumchlorine and fluorine. This combination of elements complicates any process which is developed to recover the metal values.

In the treatment processes, the ultimate aim is to recover the valuable metals in a pure concentrated form. However, this goal is difficult to achieve, economically, because of the complicated chemical and physical nature of the dust. Usually, the most important step inthe process is the separation of the iron from the non - ferrous metals such as zinc, lead, and cadmium. Considerable research effort has been put into developing new processes but most of them did not reach pilot scale testing. Some were comnercialized for a period of time and then were abandoned. Perhaps the major reason for the numerous failures to develop a suitable process for dusttreatment is that it is more economical to extract zinc, lead, cadmium or iron from the naturally occurring raw materials. Thus, in effect, the steel company has to pay an economic penalty for the treatment of the dust and the recovery of the metals.

Some general aspects of the pyrometallurgical, the hydrometallurgical and the hybrid processes will be described in this paper. In each case, somefundamental information is given which is then followed by a description of some typical processes. Also, some of the more recent research activity in this area will be discussed.

INTRODUCTION

Electric arc furnace flue dust is considered as a hazardous waste in most industrialized countries since it fails the toxicity test for lead, cadmium, and chromium. It is generated duringelectric arc furnace steelmaking from iron - containing scrap. A large percentage of the scrap is recycled automobile bodies. It is widely reported that about 10 to 20 kg of electric arc furnace dust are generated per tonne of steel produced (l - 4). In the the last three decades, the electric arc furnace’s share of total steel output has been increasing at the expense of integrated iron and steelproduction and this trend will likely continue, particularly in North America, Europe and Japan. For example, in the United States 43.3 percent of the steel was produced in mini - mills in 1997 (5). To some extent, the growth of mini - mills has been brought about by an ever – increasing concern for enviromental issues. The recycling of steel scrap has obvious economic and resource conservationbenefits. As a result of these developments, there has been an increasing volume of electric arc furnace dust to be treated. It is reported that over 1.4 million tons of electric arc furnace dust are produced by the iron and steel industry(6). In Canada, the dust can be stockpiled but this is not possible in the United States. However, it can be stabilized and landfilled and about 40 percent of thedust is landfilled in the United States (7). Although great efforts have been made over the last few decades and various treatment technologies and processes have been developed, none of them have been entirely satisfactory. Thus, new technologies and processes are still emerging.

The dusts from carbon steelmaking are all rich in zinc and lead, while the dusts from stainless steelmaking...