Whether driven by feelings of environmental
stewardship or ever-tightening environmental standards, the end
result is the same steel industry views and practices for
handling electric-arc furnace (EF) dust are changing.
Zinc isn't the problem in the dust generated
by the steel industry's EF shops; other elements in the melt
shop's by-product have prompted the U.S. Environmental
Protection Agency (EPA) to label it a hazardous waste named
In the past, mini-mills and some other EF
shops looked at it as simply a waste product to be hauled away.
Some sent it to processors who, if they didn't extract much
metal from the dust, turned it into a solid that could be
disposed of. That practice has changed for many EF steelmakers.
The material is now turned over to one of a handful of
companies that recover the zinc and iron. When the zinc is
removed, what is left is an iron-rich material. Unfortunately,
it also contains elements like chromium, lead and mercury that
are deemed too toxic for landfills. Should that material or
those compounds containing the elements deteriorate, they could
leach into the local water table and contaminate it. That's why
the EPA has restricted its use. Much of the iron-rich material
is used as aggregate in asphalt and concrete, some of which is
rendered inert and some recaptured as iron.
Chromium, mercury and a whole list of other
materials have been designated as hazardous by the EPA,
according to Elaine Laps, a spokeswoman for Timken Co. But the
Canton, Ohio-based company has made sure that it is handled
properly. Timken has a sophisticated system that collects all
of the melt shop's baghouse dust and ensures that none escapes
into the atmosphere. "We went back to recycling because it was
the right thing to do. It is more expensive to do it this way,
but it is what the company wanted to do," she said.
Timken's decision to install an elaborate
collection system with piping and vacuum lines wasn't
financial-based; it was environmental, Laps said. "They take
absolutely every step necessary to make sure that dust does not
get into the air."
Timken's system includes sealed pipes and a
vacuum system, so the dust is always contained. The vacuum
system pulls the dust through pipes into a silo, where it is
stored until it's collected by the contractor. Even while the
dust is poured into the truck, another vacuum system is running
to capture any fugitive dust.
Steelmakers are uncertain of the percentages
of various elements fumed off from the furnaces. Melters focus
on the residuals left in the heat and ensuring they don't
exceed specifications. Few seem to know whether the proportion
of zinc collected in the baghouses has risen in recent years as
more and more vehicles made with electrogalvanized sheet steel
reach the end of their useful lives and are shredded.
One scrap buyer at an EF mill said he assumes
the volume has grown, but added that the melters haven't
complained. "Zinc isn't the bad actor as far as they are
concerned," he said, because it is blown off into the baghouse.
"The real problem is the copper. If it's too high, we've blown
Most mini-mills and EF melt shops have a
fourth hole on the furnace that collects much of the dust and
delivers it to the baghouse and silos, said Barry Smith,
environmental engineer at Steel Dynamics Inc. (SDI), Butler,
Ind. The other three holes in the roof of the furnace are for
the electrodes. Some, like SDI, also have hoods over their
furnaces to capture so-called fugitive emissions from the
furnaces. These also help to keep dust off crane rails and
provide a better working environment inside the mill.
Some zinc and other metals might still be
trapped in the melt, but the melters keep track of the
chemistry and make sure they don't exceed what customers will
accept, Smith said. However, "most is fumed off and condenses
into the dust."
There are alternatives to shipping the dust
to companies that recapture the zinc at refineries. A few
companies treat the dust on-site at some mills to render it
inert and suitable for disposal in a Class D non-hazardous
landfill. Others want the iron-rich material as well as the
zinc. Baghouse dust can contain as much as 60-percent iron and
perhaps 25-percent zinc.
Not all of the dust processors are interested
in iron, but there are a few, Smith said. One is British-based
ZincOx Resources Plc, which operates the Big River Zinc smelter
in St. Louis and is building an EF zinc dust recovery plant in
York, Ohio. ZincOx will recapture the zinc then take the
iron-rich material and further refine that to produce
high-grade iron like pig iron.
Still, it doesn't matter if the material
collected in the silo is as safe as mom's apple pie, Smith
said, noting that the EPA has ruled that it is a hazardous
waste and it must be handled as such. "We have to abide by all
the rules, training, documentation, disposal and transportation
associated with a hazardous waste, and it is quite a burden,"
he added. "Everybody is under very tight standards not to let
this dust waft out of the building and openings. The whole
steel industry has a lot of mechanisms available to them that
they have employed to keep a clean shop."