Galvanized Scrap Enters the Mainstream

Car and truck buyers have hailed the use of galvanized steel as a rust inhibitor. For scrap processors and consumers, however, the presence of galvanized metals has created some challenges.

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August 4, 2001

Adding galvanized coatings to vehicle bodies has been praised by consumer advocates and auto industry analysts as a great step forward in erasing the “planned obsolescence” image with which auto companies were once condemned.

In the span of less than two decades, galvanized coatings have moved from an experiment to an industry standard procedure. The addition of the coatings—consisting of zinc as their primary material—has extended automobile body integrity and even average vehicle life spans.

But what proved to be a winning procedure for most auto industry participants created new challenges for scrap processors and scrap consumers.

The problem has its roots in the chemistry of steel making. Steel mills require specific raw material “recipes” to produce steel products with the properties needed by the builders and manufacturers who will ultimately use the steel. These recipes contain narrow margins of error. Scrap shipments to mills that have too much zinc—the material present in galvanized auto bodies—can create problems during the melt stage.

A SIMMERING PROBLEM

In terms of steel chemistry, the presence of too much zinc in a scrap melt can lead to two separate problems, one that is health-related and the other affecting product quality.

“As you melt down the galvanized scrap, most of that zinc melts long before the steel and vaporizes, leaving the furnace in the form of zinc oxide—a white dust,” says Dr. Richard Burlingame, a Cleveland metallurgist.

The dust is unwelcome in the melt shop not merely because it is a nuisance, according to Burlingame. “In large enough quantities, zinc oxide poses a health threat,” he notes. “Wherever you have zinc, you have some lead and some cadmium in small percentages.”

Consequently, as mills have encountered increasing amounts of galvanized scrap, they have become much more diligent in making sure that furnace emissions are carefully controlled and—in the case of zinc oxide and other powders emitted—routed to a baghouse recovery area.

The zinc that is “boiled” out during the melt, which is about 98% or more of it, presents the first problem. The second problem, however, concerns the trace amount of zinc which remains in the bath and which--if present to the extent of .01% or more--can create porosity in the continuous cast product, according to Burlingame. As the steel solidifies, the dissolved zinc in the bath is suddenly released as zinc vapor, which tends to form gas cavities in the solid steel. As the zinc content of the bath increases, the porosity problem worsens until gaping interconnected holes may be observed in cross-sections. “The result can be 100% scrap,” says Burlingame.

The very same zinc porosity has been observed in ferrous castings when a foundry has melted too much galvanized scrap.

The zinc-induced condition is not yet common, says Burlingame, in part because melt shop operators are aware of the need to prevent it. He also notes that even with the increased presence of galvanized auto body parts in scrap, there are probably few ferrous scrap shipments that contain enough zinc to cause the problem.

Shredded scrap may indeed contain a fair amount of zinc-coated steel. But he estimates that currently only 40% to 50% of the ferrous weight of the average shred shipment is made up of galvanized auto body parts. The balance consists of non-coated auto parts (such as engine blocks) and non-auto shreddables such as appliances.

“Since we have probably not yet reached the peak level of galvanized metal in scrapped cars, the amount of zinc will probably keep rising for a few more years,” notes Burlingame.

Prompt scrap shipments from auto body stamping plants may offer the highest zinc content. Other scrap items that usually have galvanized coatings include roadside guardrails, light posts and other exterior fixtures, and agricultural equipment.

Some processors have actually been able to reduce the extent to which they formerly separated galvanized steel scrap from non-coated scrap. Stuart Simms of The Parkwood Iron & Metal Co., Cleveland, says that just a decade ago “galvanized sheet metal and bushlings were always kept separate from other scrap and they would only go to one or two select mills.”

Now, it is easier for Simms to count the number of mills that won’t accept galvanized scrap rather than those that will take it.

Simms believes that as automotive factory bundles began including more galvanized scrap in the 1980s, most steel mills made the necessary adjustments to accept it. “Once those bundles had the increased presence of galvanized, it became hard for the mills to say they would accept it from auto factories but not from dealers,” says Simms. “Once the baghouses and other pieces of equipment were in place, it became acceptable to find galvanized scrap in dealer bundles.”

Processors who operate auto shredders, however, found themselves dealing with many of the same environmental issues as steel mills. Through an assortment of cyclones, scrubbers and baghouses, dust created during the shredding process must be handled properly.

TAKING A POWDER

A recurring theme in stories from the scrap and recycling industries is that of a problem being turned into an opportunity. That theme is certainly present in the story of how zinc oxide furnace dust became a marketable commodity.

As zinc-coated scrap increased its presence in melt shops, the need for mills to install systems to handle the resulting zinc oxide became apparent. What also became apparent was that while the zinc oxide was a problem if not handled correctly, it could also be an opportunity in some instances.

Zinc oxide as a material is used by manufacturers in several sectors. The powder is used in paint, varnish, enamel, and as coloring in ceramics, glass, ink, cosmetics and matches.

Companies such as Horsehead Industries, New York, through its Horsehead Resource Development Co. Inc. subsidiary, Palmerton, Pa., have contracted with mills to recover and recycle their furnace dust—including dust with zinc.

By the mid-1990s, Horsehead Resource Development Co. was recycling 400,000 tons of hazardous and non-hazardous filter cake and dust. In addition to zinc, marketable metals recovered through the process have included lead, cadmium, iron and calcium metals.

The existing dust collection systems at mills—as well as the potential to profitably recycle some of the dust—have proven to provide a workable solution for many scrap consumers.

A PROMPT SOLUTION?

Implementing a new way of recovering zinc from galvanized scrap has been the mission of an Indiana company that may finally be nearing its goal.

Since 1991, Metal Recovery Technologies Inc. (MRTI), East Chicago, Ind., has designed and now operates a pilot plant using its patented de-zincing process. The process, in which galvanized scrap is bathed in a caustic solution to dissolve and separate the zinc, was created through the joint efforts of researchers from MRTI and Argonne National Laboratories, with funding help from the U.S. Department of Energy and the American Iron and Steel Institute.

In the MRTI process, galvanized scrap is shredded and sent by conveyor to a de-zincing tank. In the tank, the shredded scrap passes through a rotary reactor submerged in a caustic solution that dissolves the galvanized coating, forming a liquid sodium zincate solution. The de-zinced steel scrap is further washed, becoming reusable “black scrap.” A proprietary electrowinning system extracts the zinc from the solution in the tank. The extracted zinc is dried and resold as powder to galvanizers and other end users.

The publicly-traded MRTI has yet to establish itself as a bulk processor of galvanized scrap, much to the chagrin of its shareholders, who as of press time owned stock trading at 19 cents per share. MRTI asked GM to consider a proposal to build a plant that would have processed some 250,000 tons of prompt galvanized scrap annually from GM stamping plants, but the project has not advanced. MRTI did receive approval on 16 recent patent applications.

MRTI is pinning its hopes on the notion that auto makers and other producers of prompt galvanized scrap—as well as consuming steel mini-mills—will prefer their de-zincing process to the current procedure of melting galvanized scrap as is and collecting the resulting dust at the mill.

“As the cost of waste treatment and disposal continues to rise, a cost-effective method for changing galvanized to black scrap will become increasingly more important to the iron and steel industries,” reads part of the text in an MRTI corporate description that is titled “The Largest Zinc Mine in the World.”

Corporate officers have recently acknowledged, though, that the company still needs to clear some hurdles before becoming a significant presence in the scrap processing market.

“The only bump in the road has been a completed financing package,” MRTI vice president Leon J. Lohman stated earlier this year. That would seem to be a significant bump that may have been only partially smoothed out in late February when the company announced that a $3 million funding package from European sources was nearly in place.

Lohman also referred to past missteps by MRTI. Referring to his initial review of operations when he started with MRTI in the spring of 1997, Lohman says, “It quickly became evident that the [East Chicago] site was under-engineered. While major pieces of equipment were of the proper type, they were undersized in terms of capacity or just plain not strong enough to withstand the rigors of long-term continuous production.”

MRTI chairman Michael Lucas remains optimistic that the East Chicago plant will soon be operating profitably. “It has been independently confirmed that our zinc powder product meets smelter cementation specifications, which has a premium value of approximately 60% over LME/SHG ingot prices,” he says. “Plugging in this added value to our East Chicago plant results in a projected profit of approximately $3 million per year.”

HERE TO STAY

While the methods for processing zinc-coated scrap might change, there seems little doubt that galvanized scrap will continue to arrive in the yards of ferrous processors.

After the first Japanese vehicle imports with galvanized coatings entered the U.S. in 1979, the benefits of the process became rapidly apparent. According to the American Zinc Association, Washington, the average vehicle now contains 37 pounds of zinc—17 pounds in the form of corrosion-protection coatings and another 20 pounds in the form of zinc die cast parts such as door handles and locks.

Material Sciences Corp., Chicago, reports industry-wide shipments of 3.4 million tons of galvanized steel for autos and light trucks in 1996. The company’s Walbridge Coatings subsidiary (a joint venture between MSC, Bethlehem Steel Corp. and Inland Steel) reported a 7% increase in revenues in 1997 and a 5% increase in shipments.

“The American consumer demanded a rust-free car, and the automotive industry did a spectacular job in responding,” says Burlingame. “Now the scrap processing and steel industries have to make sure they can digest this galvanized scrap.”

The author is managing editor of Recycling Today.

 

Sidebar

 

It’s hard to imagine a metallic element benefiting from positive public relations, but one can argue zinc has done just that.

The almost instant acceptance of galvanized coatings is just one of several success stories for zinc in the last quarter of the 20th century. Zinc has prospered in other new or growing markets, including:

*           as a natural insect repellent and dermatological sun screen

*            brass—an alloy created from copper and zinc—has enjoyed growth in several rod and tubing applications

*           zinc air batteries—which can store a charge six times more powerful than other batteries, according to the American Zinc Association—are attempting to establish market share in the portable computer and electric-powered vehicle markets

*            segments of the medical community are touting zinc as a substance that can boost the immune system and even help wounds heal more quickly.

The makers of one cold-fighting product that contains zinc claim their lozenges have been clinically proven to shorten the duration of the common cold by as much as four days while also reducing the severity of the symptoms.

As with most things, however, the cliché of too much of a good thing being dangerous certainly applies to some forms of zinc. Zinc miners and others exposed to significant amounts of zinc dust and zinc oxide can suffer from a syndrome known as the “zinc shakes.” The temporary nervous condition, also known as metal fume fever, induces chills, fever, muscular pain, nausea and vomiting.

Zinc shakes aside, the notion that zinc is responsible for longer-lasting automobiles and that it can successfully fight the common cold has helped put the metal on the positive side of the ledger sheet in the minds of many Americans.