EAF dust

It is important to note that EAF dust is a hazardous waste because of its high concentrations of lead and cadmium. With 550,000 tons of EAF dust generated annually in the U.S., there is great potential to reduce the volume of this hazardous waste. The motivation for reducing this waste not only lies with the cost of air pollution controls, but with the cost for disposal. U.S. 

The primary hazardous components of EAF dust are zinc, lead, and cadmium nickel and chromium are present when stainless steels are manufactured. 

The composition of EAF dust can vary greatly, depending on scrap composition and furnace additives. EAF dust usually has a zinc content of more than 15%, with a range of 5 to 35%. Other metals present in EAF dust include lead (2-7%), cadmium (generally 0.1-0.2% but can be up to 2.5% where stainless steel cases of nickel-cadmium batteries are melted), chromium (up to 15%), and nickel (up to 4%). 

Recover zinc from EAF dust containing more than 15% total zinc recycle EAF dust to the extent feasible. 

The primary leachable hazardous constituents of EAF emission control dust/sludge are lead, cadmium, and hexavalent chromium. Generally, 20 to 40 lb of EAF dust per ton of steel are generated, depending on the mill s specific operating practices, with an average of about 35 lb/t of steel melted.1 Table 2.11 shows the typical ranges of concentration of each of these elements in EAF dust. 

Cooled and solidified slag is crushed and screened to recover metafiles for recycle or reuse and the lower metallic aggregate is used in construction applications. The slag produced in EAFs is either reused or landfilled. EAF dust is conveyed into a gas cleaning system.1... 

In this process EAF dust, other zinc-bearing wastes, recycled materials, coke or coal, lime, and silica are mixed and fed to a rotary furnace. The zinc and other volatile nonferrous metals in the feed are entrained in the furnace off-gas and are carried from the furnace to an external dust collection system. The resulting oxide (zinc calcine) is a crude zinc-bearing product that is further refined at zinc smelters. A byproduct of the process is a nonhazardous, iron-rich slag that can be used in road construction. Solidification technologies change the physical form of the waste to produce a solid structure in which the contaminant is mechanically trapped. 

For the most part, the zinc materials recovered from secondary materials such as slab zinc, alloys, dusts, and compounds are comparable in quality to primary products. Zinc in brass is the principal form of secondary recovery, although secondary slab zinc has risen substantially over the last few years because it has been the principal zinc product of electric arc furnace (EAF) dust recycling. Impure zinc oxide products and zinc-bearing slags are sometimes used as trace element additives in fertilizers and animal feeds. About 10% of the domestic requirement for zinc is satisfied by old scrap. 

McElroy, R. O. Murray, W. Developments in the Terra Gaia process for the treatment of EAF dust. Iron Control and Disposal, Proceedings of the International Symposium on Iron Control in Hydrometallurgy, 2nd, Ottawa, Oct. 20-23, 1996, 505-517. 

Lowest available toxicity characteristic leaching procedure (TCLP) leachate levels for any process treating EAF dust. 

The zinc content of EAF dust can be removed by sulphating, using iron sulfate derived from a waste product in some steelmaking processes, pickle liquor residue, as the main... 

EAF dust recycling R Morris 1985, Chaubal 1982, Kellogg 1966, Krishnan 1982 and 1983, Miyashita 1976, Bounds 1983... 

The ionic liquid ChCl with urea was applied to the processing of electric arc furnace (EAF) dust by Abbott and coworkers [18]. It was found that the solubility of ZnO, Cu O, and PbO was good, zinc and lead can be selectively removed and subsequently electrowon from the liquid, whereas the insoluble iron and aluminosilicates can be recycled through the electric arc furnace. The process developed for treating EAF dust involves extraction of lead and zinc from matrix, isolation of lead, and recovery of zinc. The pilot plant built for 5-kg dust extraction batches is given in Fig. 5.1 [19]. 

Fig. 5.1 Schematic diagram of the cell for extracting lead and zinc from electric arc furnace (EAF) dust together with a photograph of the pilot plant built for 5-kg dust extraction batches (Reproduced from Ref [19], with kind permission of The Royal Society of Chemistry)...

Table 3.9 Chemical composition of EAF dust from steel foundries [32, CAEF, 1997]...

The main benefit of the technique is a decrease in the net amount of dust sent out by the foimdry, for disposal or recovery. The produced dust contains a higher load of metals. This allows the recovery of Zn from the EAF dusts. The technique results in an enrichment of the Zn in die cupola dust, while for Pb a larger share ends up in the iron. If the Zn is effectively recuperated from the dust, the technique decreases the heavy metal load of the final dust for disposal, as well as its amount. On the other hand, the amount of slag produced, increases. 

Operational data from EAF steelmaking show a plant which recycles 75 % EAF dust from an original yield of 20 - 22 kgA, and so only has to take care of about 50 % of the dust, with an average zinc content of 35 %. 

Type of Secondaries i Mainly Zinc dominated Battery Paste, EAF-Dust, Waelz Oxide, ... 

At the same time, changes were introduced in the feed residues from the electrolytic zinc plant are processed with some addition of zinc-bearing materials from the waste water treatment plant, and other secondaries like EAF dusts coming from steel mills (electric arc... 

Electric arc furnace (EAF) dusts have become a significant source of feed for the ISP. These contain up to 35% Zn and environmental legislation in developed coxmtries is discouraging the previous practice of dumping EAF dusts. In a number of countries the Waelz process to produce zinc oxides treats these dusts. In some cases these oxides are hot briquetted as a direct feed for the ISF. An alternative method of treating steel plant and other dusts is to inject them directly into the furnace through the tuyeres. 

M. Mastuno, Y. Ojima and A. Kaikake, Recent Development of EAF Dust Treatment Operation at Sumitomo , Zinc Lead 95. T. Azakami, N. Masuko, J.E. Dutrizac and E. Ozberk, Eds., The Mining and Materials Processing Institute of Japan, Tokyo, Japan, 1995,432-441. 

---