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Waste Materials

EAFs produce metal dusts, slag, and gaseous emissions. 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 composi- tion and furnace additives. EAF dust usually has a zinc content of more than 15%, with a range of 5–35%. 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%). Generally, an EAF produces 10 kilograms of dust per metric ton (kg/t) of steel, with a range of 5–30 kg/t, depending on factors such as furnace character- istics and scrap quality. Major pollutants present in the air emissions include particulates (1,000 milligrams per normal cubic meter, mg/Nm3), nitrogen oxides from cutting, scarfing, and pick- ling operations, and acid fumes (3,000 mg/Nm3) from pickling operations. Both nitrogen oxides and acid fumes vary with steel quality.
Mini mills generate up to 80 cubic meters of wastewater per metric ton (m3/t) of steel prod- uct. Untreated wastewaters contain high levels of total suspended solids (up to 3,000 milligrams per liter, mg/l), copper (up to 170 mg/l), lead (10 mg/l), total chromium (3,500 mg/l), hexavalent chromium (200 mg/l), nickel (4,600 mg/l), and oil and grease (130 mg/l). Chrome and nickel concentrations result mainly from pickling operations. The characteristics of the wastewater depend on the type of steel, the form- ing and finishing operations, and the quality of scrap used as feed to the process.
Solid wastes, excluding EAF dust and waste- water treatment sludges, are generated at a rate of 20 kg/t of steel product. Sludges and scale from acid pickling, especially in stainless steel manufacturing, contain heavy metals such as chromium (up to 700 mg/kg), lead (up to 700 mg/kg), and nickel (400 mg/kg). These levels may be even higher for some stainless steels.

Pollution Prevention and Control
The following pollution prevention measures should be considered :
• Locate EAFs in enclosed buildings.
• Improve feed quality by using selected scrap to reduce the release of pollutants to the environment.
• Use dry dust collection methods such as fabric filters.

Replace ingot teeming with continuous casting. Use continuous casting for semifinished and finished products wherever feasible. In some cases, continuous charging may be feasible and effective for controlling dust emissions.
• Use bottom tapping of EAFs to prevent dust emissions.
• Control water consumption by proper design of spray nozzles and cooling water systems.
• Segregate wastewaters containing lubricating oils from other wastewater streams and remove oil.
• Recycle mill scale to the sinter plant in an integrated steel plant.
• Use acid-free methods (mechanical methods such as blasting) for descaling, where feasible.
• In the pickling process, use countercurrent flow of rinse water; use indirect methods for
heating and pickling baths.
• Use closed-loop systems for pickling; regenerate and recover acids from spent pickling liquor using resin bed, retorting, or other regeneration methods such as vacuum crystallization of sulfuric acid baths.
• Use electrochemical methods in combination with pickling to lower acid consumption.
• Reduce nitrogen oxide (NOx) emissions by use of natural gas as fuel, use low-NOx burners, and use hydrogen peroxide and urea in stain- less steel pickling baths.
• Recycle slags and other residuals from manufacturing operations for use in construction and other industries.
• Recover zinc from EAF dust containing more than 15% total zinc; recycle EAF dust to the extent feasible.

Target Pollution Loads
High water use is associated with cooling. Recycle wastewaters to reduce the discharge rate to less than 5 m3/t of steel produced, including indirect cooling waters.
The recommended pollution prevention measures can achieve the target levels.


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Products Management
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