Competition is picking up in the electric-arc furnace (EF) zinc dust recovery business. The frontrunner in the industry, Monaca, Pa.-based Horsehead Corp., scored a coup late last year, when it signed a long-term agreement to handle all of the baghouse dust from Nucor Corp.'s three steel mills in the Carolinas its Darlington, S.C., bar mill; its Berkeley County sheet mill; and the Nucor Steel-Hertford plate mill in Cofield, N.C. (AMM, Dec. 27).
Horsehead, which gathers spent zinc dust from mini-mill melt shops and skimmings and drosses from hot-dip galvanizers to refine into reusable zinc oxides and Prime Western Grade zinc metal, plans to build new regional EF dust recycling facilities near Nucor's Carolina steel mills and have them on-stream by 2009.
Horsehead now has four facilities that handle baghouse dust its Palmerton, Pa., plant north of Allentown in eastern Pennsylvania, a plant in Chicago, another in Rockwood, Tenn., and a fourth in Beaumont, Texas. It started up a second Waelz kiln at its Rockwood plant late last year, doubling the EF dust-processing capacity there.
Three of its plants use the Waelz kiln process to winnow away other metals and materials and enrich its zinc content. Baghouse dust from mini-mills typically contains about 20-percent zinc until processed in Horsehead's kilns, which raise the zinc content to about mid-50-percent.
Ali Alavi, Horsehead's vice president of corporate administration, said that while the company uses Waelz kilns at three of its facilities, at Beaumont it uses its own flame-reactor technology developed at its Monaca plant.
"It takes the EF dust and produces the same product at the end of the day. It is just a slightly different process," he said.
Horsehead ships some reclaimed zinc to its zinc calcinators to further refine the zinc to the upper-60-percent level and yield a by-product called polymetallic concentrate. This is shipped to its Bartlesville, Okla., facility, where a hydrometallurgical process makes zinc calcine to serve as feedstock to produce zinc metal and zinc oxide.
Horsehead's Waelz kilns produce two distinct products, Alavi said. One is a crude zinc oxide product that is shipped to Monaca for further refining. The other is an iron-rich material called IRM, which Horsehead sells primarily for use as an aggregate in the asphalt industry and as an iron source in the cement-making process.
"The crude zinc oxide affords the company more opportunities," Alavi said. "We can do a couple of things with it. Some we take to our Monaca facilities, where it is refined into Prime Western Grade zinc. Some of its metal output is sold to hot-dip galvanizers." Horsehead then takes back the skimmings and drosses and once again reclaims the material.
The zinc metal and zinc oxides that come from Horsehead's Monaca plant are derived from recycled metals. "The company does not use zinc concentrate or zinc ore. Clearly that has been our model, so I certainly think our business model is one that promotes the principles of sustainable development," Alavi said.
Horsehead's newest competitor is Steel Dust Recycling LLC (SDR), led by veteran zinc industry executive Russ Robinson. His company has built a Waelz kiln facility in northwestern Alabama to recycle 110,000 tons of EF dust annually, much of it from SeverCorr LLC's new steel mill in Columbus, Miss. Robinson, former president of Houston-based U.S. Zinc Corp., and Tom Knepper, a Waelz expert, formed SDR a little more than a year ago.
The Waelz kiln is the preferred technology for treating EF dust, Robinson said. A lot of money has been spent over the years on other technologies to process and treat EF dust, but most of them haven't worked as well as the Waelz kiln, he said.
About 25 percent of SDR's feedstock will come from SeverCorr's 1.5-million-ton-a-year sheet steel mill. If SeverCorr expands as planned to 3 million tons, it would supply up to 50 percent of the material fed into the kiln, Robinson said.
In addition to the SeverCorr mill, SDR is looking to pick up material from other EF mills in the southern United States. At its opening ceremonies in mid-July, Robinson noted that steel mills in the region are busier these days and that his company was already thinking about expansion.
SDR will recover zinc from the dust and supply it to zinc smelters and refiners in North America and around the world. The remaining steel-based slag will be available to cement producers or for road aggregate.
"You are taking electric furnace dust that has approximately 20-percent zinc and you are upgrading to 60-percent zinc," he said. "At 60-percent zinc, it can be sold to zinc smelters around the world as a substitute for zinc concentrate. The smelters will further refine the zinc and sell it back to the galvanizing industry. It's sort of a full-circle recycling loop."
When dust arrives at the SDR plant, it is pelletized with water and coke, then charged into the kiln. In the kiln's reaction zone, the metal oxides are reduced at about 1,100 degrees Celsius so that zinc and lead emerge from the charge as metal vapors. The hot, dust-laden gas is then cooled and the zinc oxide is collected in a precipitator.
Most of the zinc trapped in the EF melt shop's baghouse comes from automotive shredded scrap because all auto bodies are galvanized before they are painted. Basic oxygen furnace steel mills don't generate this zinc-rich dust; it is solely a by-product of the mini-mills' melt shops.