5.2 to 5.6 X 106 Btu per net ton of raw steel
Largest sources: melting and refining Particulate: iron oxide (melting); calcium oxide (refining)
Largest source: wet/semiwet air cleaning systems
EAF slag: 50-75% reused
K061: EAF dust/sludge
Major components: Fe, Zn, Cr, and their oxides
Total generation: ~900,000 t/yr
Although the significant water requirement in EAFs is for noncontact cooling purpose, few furnaces also discharge significant process wastewater. Most electric arc furnaces are operated with dry air cleaning systems with no process wastewater discharges. Other noncontact water applications include water-cooled ductwork, roof, sidewalls, doors, lances, panels, cables, and arms. These systems usually incorporate evaporative cooling towers or closed cooling loops.1 A small number of wet and semiwet air cleaning systems are also in use.
The pollutants of concern are the same as in wet basic oxygen furnaces, but the concentration of metals (primarily lead and zinc, but also arsenic, cadmium, copper, chromium, and selenium) in wastewater is higher because of the higher percentage of scrap charged. Wastewater treatment operations are similar to those for the wet basic oxygen furnaces, including sedimentation in clarifiers or thickeners and recycle of the water.14
The two major byproducts generated during EAF steel making are slag and dust. As a result of the oxidation of phosphorus, silicon, manganese, carbon, and other materials during melting, a slag containing some of these oxidation products is formed on top of the molten metal. Electric arc furnaces produce between 110 and 420 lb of slag for every ton of molten steel made, with an average value of about 230 lb/t.1 EAF dust is made up of the particulate matter and gases produced during the EAF process. The particulate matter removed from emissions in a dry system is referred to as EAF dust and the particulate matter removed by a wet system is the EAF sludge.
The dust (or sludge) removed from EAF emissions is a listed hazardous waste, K061. The primary component is iron or iron oxides; a typical EAF dust contains 24% iron by weight. In cases where lower grades of scrap are used (generally for carbon steel production), EAF dust can contain large amounts of zinc and lead (as high as 44% ZnO and 4% PbO). Similarly, stainless steel production yields dust with high percentages of chromium and nickel oxides (as high as 12% Cr2O3 and 3% NiO). EAF dust also contains cadmium in concentrations on the order of about 0.1% by weight. Other possible EAF dust components include other metals and flux.1
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.
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