The Separation Game

Scrap recycling is a business in which profits turn not on thousands of dollars but on pennies a pound.
   For auto shredders, profitability hinges on the ability to eke out every ounce of metal from their shredded stream. As margins narrow and environmental restrictions tighten, shredders are taking a closer look at what gets left behind in their auto shredder residue, or ASR—the material that’s left over after the ferrous portion is removed.
   Thirty to 35 years ago, ASR came off the shredder, into trucks, and went to the landfill. It’s not that simple anymore.
   Today, it’s estimated that for every 100 tons of shredded scrap produced, about 3 percent, or 3 tons, of mixed nonferrous metals is generated. The aluminum content of this nonferrous mixture can be as high as 60 to 70 percent, with smaller percentages of copper, brass, stainless steel, and zinc. Using our example of 3 tons of mixed nonferrous metals, that’s the equivalent of 3,600 to 4,200 pounds of aluminum alone in the mixture.
   Given the value of aluminum and the other nonferrous, these metals are like buried treasure in ASR. As Andy Wahl, media plant manager for Newell Recycling of Atlanta Inc. (East Point, Ga.), asserts, “The value of the nonferrous metals recovered from residue can be a tremendous boost to the profits of shredder operators and helps compensate for downturns in the ferrous scrap market.”
   The question is: How to recover that metallic treasure?

Sink-Float: A Tried-and-True Approach
A shredder basically has two choices when it comes to ASR: Process the residue further on-site to upgrade its value or recover the metals, or sell it as is to a specialized media-separation plant.
   Before the development of the eddy-current nonferrous separator more than 10 years ago, virtually all shredders sold their ASR without any further processing to a media plant. That plant would separate the nonmetallics from the metals using a rising-current separator, run the residue through a water bath to float off wood and plastic, then separate the aluminum, wire, and rock from the copper, brass, stainless steel, and zinc. An eddy current would then sort the aluminum from the wire and rock.
   “The eddy-current separator has now taken the place at the shredder of the first two steps in the separation process that used to happen at the media plant,” says Lenny Siesco, owner of Jigsaw Recycling L.L.C. (Belgium, Wis.) and an associate with Osborn Engineering Inc. (Tulsa, Okla.). “By passing the residue over an eddy current, the shredder can remove most of the trash. This creates a pile of nonferrous metallics that’s of higher value because it has a higher metallic content.” Such a pile, he says, can be as much as 95 percent metallics after the eddy current.
   But as Dick Wolanski, a senior vice president with Huron Valley Steel Corp. (Belleville, Mich.), points out, “The eddy-current upgrading of the ASR prior to the shipment of the concentrate to a media plant has to be done with care so as to recover all the metal content of the residue. It’s quite easy and enticing to produce a high grade of the metal concentrate while unwittingly losing half the metal in the residue.”
   While some of the 200 to 220 shredders in the United States still sell their residue without processing it further, the trend is to run it through an eddy current first to concentrate the metals and add value.
   A number of technologies have been tried over the years in the quest for the separation technique with the highest aluminum recovery rate and the lowest cost. Still, most residue processors find that the sink-float approach using heavy media is the most cost-effective way to pull the aluminum out of the nonferrous metal mix.
   Such heavy-media separation is based on the principle of specific gravity, or density of materials. Water, with a specific gravity of 1, is the benchmark. Materials with a specific gravity less than 1 will float in water. Wood, for example, has a specific gravity of 0.35 to 0.80.
In heavy-media operations, a dense powder, either ferrosilicon or magnetite, is mixed with water to create two different slurry baths, one with a specific gravity of 1.8, the other with a specific gravity of 3.3.
   As residue passes through the first slurry, light items such as rubber, plastics, magnesium, and thin-gauge aluminum are separated from the heavier aluminum, copper, brass, stainless steel, and zinc.
   In the second slurry stage, aluminum (whose specific gravity is 2.7) floats to the top with wire and rock. As the drum rotates, the heavier zinc, brass, copper and stainless steel—commonly called the mixed or sink metals—fall to the bottom of the drum and are carried by rotation to a top discharge chute and out the mouth of the drum, while the aluminum flows over with the excess slurry.
   An eddy current is then used to separate the aluminum from the wire and rock. Finally, the aluminum is spray-washed, dried, and ready for sale or further processing in on-site melting facilities.
   The two main reasons experts keep coming back to sink-float are its high volume (10 to 40 tons an hour) and its low cost. Plus, in state-of-the-art media plants, environmental concerns are virtually nonexistent. “The process water works in a closed-loop cleaning system with no water discharge to the environment,” notes Wolanski. “The solid residue is treated to render it nonleachable in EPA-approved tests.”

Different Strokes for Different Folks
The scenario of a shredder producing residue, running it through an eddy current, and selling it to a media plant, while typical, is an oversimplification. In reality, there are as many different ways of handling residue as there are shredders.
   Audubon Metals L.L.C. (Henderson, Ky.) is one example. The company runs a heavy-media separation plant and is a secondary aluminum smelter, making it both a producer and consumer of secondary aluminum. “Our operational goal is to recover as many aluminum units as possible from residue and improve its quality as much as possible for the smelting operation,” says Jim Butkus, general manager.
   Though the Audubon operation is a partnership with David Joseph Co., Audubon is also in the market as an independent media plant and smelter. Audubon buys residue from Joseph Co. and sells aluminum to a Joseph Co. smelter, though it isn’t obligated to do so. In fact, Joseph Co. generates less than a third of the company’s feedstock, and its smelter buys less than 50 percent of Audubon’s product, says Butkus.
   A shredder doesn’t have to be as big as Joseph Co. to make operating an on-site media plant cost-effective. It’s strictly a numbers game that each shredder must evaluate for itself. “For some shredders it makes sense, depending on their volume, their wage scale, if they have a home for the mixed metal, and if they’re doing their own smelting,” says Siesco.
   As Wahl adds, “If market conditions are such that there’s a big difference between the selling price of the residue and the value of the recovered metals, that’s the time when shredders think about having their own media operation, which hasn’t been the case over the last couple of years.”
   Another approach to making an on-site media plant economically feasible is to increase the throughput. That’s what Star Recycling (Midlothian, Texas)—a division of TXI Chaparral Steel—has done in its ASR processing operation.
Chaparral, a minimill steelmaker, backed into the separation business, first by buying a shredder, then installing a residue processing facility to complete the cycle.
   Star Recycling, which opened in March 1998, uses proprietary sink-float technology to increase throughput and recovery rates. In its first nine months of operation, the plant processed 130,000 tons of low-grade residue and recovered 18,000 tons of nonferrous metal—about a 14-percent recovery rate.

Are Dry Processes the Answer?
Innovation—either through new applications of existing technology like Star Recycling or the development of totally new separation technology—is what the industry needs. The search is on worldwide for the process that will improve yields and reduce the costs of separation. Some innovators believe the future lies in dry separation methods replacing the wet ones.
   The Sandflo system, produced by Rutherford Light Alloy (Grantham, England), attempts to combine the advantages of sink-float with a dry medium. It’s essentially a dry sink-float system that uses a circulating bed of sand instead of a water-based slurry. The makers claim the system produces better results for the same or lower cost than conventional ferrosilicon-based systems.
   The Sandflo process operates on the same principle as other sink-float systems. Feedstock that’s clean and uniform in size drops into a circulating bed of sand. The lighter metals stay near the top and leave the tank via an inclined chute. Heavier particles sink in the sand and exit by a lower chute.
   Ferrous Processing and Trading Co. (Detroit) has been using the Sandflo technology for two years, notes Richard Kenny, executive vice president of nonferrous metals. In fact, he assisted Rutherford Light Alloy in developing the system, applying his 30 years of aluminum expertise to the project.
   Prior to installing the Sandflo, Ferrous Processing used airflow separation, but Kenny saw Sandflo “as an opportunity to upgrade the quality of our product.” Using this system, Ferrous Processing now produces aluminum of sufficient quality to sell into the secondary market.
   Kenny is the first to admit that Sandflo isn’t the system for everybody. Ferrous Processing’s system, he notes, has been customized for its own needs, plus the firm has installed specialized downstream equipment that maximizes the system’s performance.
   Though Sandflo has been criticized as being too slow and too expensive to be realistic, Kenny says his downstream setup solves both problems. The company recovers 3,000 pounds an hour from each of its four parallel Sandflo systems for a total of 12,000 pounds an hour.

A Heavy Problem
Whether separation takes place in sand or ferrosilicon media, the problem at the end of the day is the same: What to do with the sink metals—the copper, brass, stainless steel, and zinc?
   Huron Valley separates the sink metals in-house through its own high-tech process. First, it runs the metals through an elaborate system of eddy-current separators, which extract stainless steel from the mixture. Then, the remaining copper, brass, and zinc are run through a system that uses proprietary computerized imaging technology and jets of air to sort the metals into different streams.
   Rather than do such separation themselves, some shredders and media plants simply ship their mixed metals to the Far East for hand sorting.
   “At one time, we used to selectively smelt the mixed metals to remove some of the other metal, but currently it’s more cost-efficient to ship it overseas for hand sorting,” says Wahl.
Wahl’s goal is to find a technology to separate the mixed metals on-site. The “problem of the heavies” also plagues
   Siesco, who has spent five years trying to solve it. He maintains that the solution to the mixed metals lies in some variation of sink-float technology. He’s convinced that zinc can be removed by flotation, though it means boosting the slurry to a specific gravity of 7, which is tantamount to “pumping peanut butter,” he says.
   Though some media separation experts denounce this idea as impossible, Wahl says, “It’s a dream now, but you should never say no. There could be a new medium or new technology in the future to make it possible.”
   The economics of separating the sink metals is what drives Siesco and others to continue their quest. As is, unsorted mixed metals have a certain value. The more you can segregate them, the more value you add. In essence, “you’re going after separating the red metals from the gray metals,” Wahl says. “That’s what it’s all about.”

Systems for Single Shredders
As shredder operators strive to mine more of the metallic value in their residue, they must decide how much of the recovery to do themselves and how much to leave to specialized media separators. With a price tag of $4 million to $5 million and capacities in the hundreds of tons, conventional media plants are too pricey and too large for most shredders to install.
   In response, several manufacturers have tried to carve out a niche for themselves by creating media plants for single shredding operations. These systems focus on the separation of light from heavier metals rather than the more sophisticated separation of zinc from the heavier fraction including copper, brass, and stainless steel, Wolanski says.
   Oberlander Recycling Technik GmbH (Dusseldorf, Germany) was one of the first manufacturers to design a media system for a single shredder. The unit, introduced in the United States in 1997, uses conventional ferrosilicon heavy-media technology to process 4 to 6 tons of residue an hour. A unit that size could easily keep up with production from a single shredder.
   Last year, Osborn Engineering also unveiled what it calls a “mini-media plant” for shredders. The company temporarily mothballed the concept when the scrap markets dipped, but it has revived the line this year. Like the Oberlander system, the Osborn unit is compact, though it has a slightly higher capacity of 6 to 8 tons of residue an hour, Siesco says.
   These systems, however, face the same environmental challenges as large media operations, such as the closed-loop circulation of process water and treatment of solid residue, notes Wolanski.
   “The cost of these environmentally required operations doesn’t scale down in proportion to the throughput,” he states. “Hence, while several people are trying to develop small-scale media plants, these either haven’t yet dealt with the environmental issues or aren’t cost-competitive with the larger media operations.”
   Another point, he asserts, is that “the economics of shred sorting are very throughput-sensitive, and smaller operations can’t compete with low Far East labor costs and low container freight rates to the Far East.” •