March/April 1995
With improvements in eddy current technology, more and more automobile shredder operators are squeezing metals from shredder residue. And some are even taking it a step further, mining old fluff for nonferrous scrap.
By Jeff Borsecnik
Jeff Borsecnik is an associate editor for Scrap Processing and Recycling
David Woody, president of Texas Shredder Inc. and Interra Aluminum Inc. (San Antonio), recalls an era just a few decades ago when automobile shredder operators concentrated on recovering only the ferrous portion of their feedstock. In fact, he says, most didn’t even bother with the non-ferrous fraction, which, because of its limited market potential, was often simply disposed of along with shredder fluff—more property known as automobile shredder residue, or ASR
That's practically heresy today. Thanks to dramatic improvements in separation equipment and increased marketability of the nonferrous portion of a shredder's output, shredder operators now not only recover and market the nonferrous stream from their shredders, but many also separate out the nonferrous material contained in their ASR.
What's more, some are going a step further: mining metal buried in old ASR.
Woody, for one, has been trying to squeeze metals from ASR for more than a decade. During the early 1980s, he headed a project that "strip mined" nonferrous rich ASR and ran it through a cascade system at the Owens Industrial Products Division of Owens Steel (Lexington, S.C.), a scrap-based steelmaker that had for a time simply retained the nonferrous frag in its residue. And today, he is overseeing another project at Owens—the mining of a large volume of stored old ASR.
Owens is not alone in working to recover metals from old shredder residue, and as long as nonferrous markets remain relatively strong, there could soon be more shredder operators digging through old for marketable metal. As Woody puts it, "If aluminum prices hold, people are going to be going everywhere to extract the stuff."
That gets to the main reason for mining fluff, old or new: to grab back metal accidentally stolen by a shredder's cleaning system to become part of the ASR.
Just how much metal might be contained in a pile of ASR varies widely, depending especially on the material shredded and the shredding system employed, but there are studies that offer some clues. A 1984 U.S. Bureau of Mines study on the shredding of the then-new generation of smaller, lighter-weight cars, for example, found that about 12 percent of the nonferrous metal in those vehicles was lost as part of the shredder's fluff stream. And last year, Osborn Engineering Inc. (Tulsa, Okla.) evaluated dozens of current-generation ASR samples and found the average nonferrous content to be 2 ½ to 3 percent, the vast majority of it aluminum. (Separation systems incidentally collect more light metals than heavy ones.) ASR also contains ferrous fines, typically in about the same amounts as the aluminum, according to Marlin Bills, president of Osborn Engineering.
While a nonferrous content of just a few percent may not seem like much, it can add up. Look at it this way: Processing 100 tons of material per hour through a shredder is likely to generate about 20 tons hourly of ASR. Assuming 3 percent metal in the fluff, that's 1,200 pounds of metal thrown into the fluff per hour. If you figure it's all aluminum and has a selling price of, say, 50 cents per pound, that's $600 worth of metal trapped in the residue every hour. And if that shredder ran 2,000 hours a year, the total comes out to $1.2 million in potentially recoverable aluminum in one shredder's ASR.
These estimates are based on newly generated ASR, of course, and old fluff is likely to differ in nonferrous content, though not necessarily for the worse. Very old material might be rich in nonferrous, for example, in situations where there were no markets for the nonferrous stream as it was generated, relegating it to disposal as part of the ASR. Also, Woody notes, increasingly stringent quality requirements of consumers in recent times have actually boosted the level of metals in new ASR as cleaning systems have been souped up to ensure that almost no extraneous material remains in the shredder's streams of salable metal.
Old ASR also differs from new material in other respects, which could affect mining it. "New [ASR] is a pleasure to work with," says Woody. "It doesn't bind up, doesn't cake up. It's cotton as opposed to compacted cotton. The old stuff gets compacted, mud entrapped, so it's harder to liberate the aluminum." Such factors make issues like feeding and material depth more important and trickier than in systems processing only new ASR. The metals in the old ASR also show some wear— "some is aluminum only a mother could love," says Woody—with ferrous material suffering from rust and other metals becoming discolored with oxidation.
The Environmental Angle
Beyond those potential buried dollars are environmental factors that have encouraged some to take a shovel to that old fluff pile. Shredding operations with their own ASR landfills might be concerned about the potential for liability down the road, for instance, or they might target old ASR storage sites for mining as a side effect of a landfill closure. That latter scenario is exactly what prompted a fluff mining project about to get under way at Yorke Doliner & Co.'s Rockledge, Fla. facility. It's an attempt to squeeze value out of landfilled material that needs to be unearthed anyway as part of the closure of an 8-acre landfill that has been absorbing ASR since the 1960s. About 40 percent of the deposited material must be shifted so that the landfill can be configured to meet state closure rules concerning slopes and borders.
The mining operation is intended to minimize the costs of the final capping of the landfill. "We're expecting the proceeds we get out of the fluff will more than offset the cost of excavation—which has to be done anyway," says Dan Smith, manager of the project.
But in this case, metal recovery is only part of the picture. The company needs a vast amount of soil for the cap, and the going rate in Florida is $3.50 to $5 a cubic yard. Thus, part of Yorke Doliner's mining mission will be to recover soil originally laid in the landfill to prevent fires from generating spontaneously in ASR lying in the hot Florida sun.
Potential metal recovery, then, is simply an added reward for the company, which it's happy to take advantage of while it can. But as Smith notes: "The metal markets could drop and then it wouldn't be feasible at all. Say we get halfway through and the markets drop, we may just forget about mining the metal. "In any case, however, the soil would still be recovered.
There are other cases where shredder operators that were prompted by environmental pressures to unearth old ASR have found mining the material to be worthwhile even if metal recovery alone is not profitable, according to W.Z. Baumgartner Jr., president of W.Z. Baumgartner and Associates (Brentwood, Tenn.), an environmental consulting fm that has worked with a number of U.S. shredding operations. "Suppose you can save enough in metal recovery to cover the cost of disposal and buying equipment," he poses. "That's a win-win situation."
But, barring a near-no-choice situation, is choosing to mine an ASR landfill a decision to open Pandora's box? "I don't think there would be any real environmental problems," says Baumgartner. "But I differentiate between environmental and regulatory problems." He explains: "All states have rules for opening and closing landfills, and if you decide to open one up, the questions is,What are you going to have to do once you pick the scab off the thing?"
Eddy and Beyond
If ASR mining still appeals, here are some basic thoughts on what it might take to develop a system to do so.
The heart of the system—equipment wise—is an eddy current separator (ECS) capable of handling huge volumes of material in a rugged environment. Such separators use rapidly alternating magnetic fields to repulse nonferrous metals, ejecting them from a mixed stream of materials such as ASR. (For a primer on ECSs, see the July/August 1992 issue of Scrap Processing and Recycling.)
Eddy current systems have become a hot topic in the shredding business in the last few years, with many facilities putting ECSs to use to upgrade their nonferrous output as well as to recapture lightweight metal from ASR, new or old. Still, shredder operators using ECSs are a minority, albeit perhaps a rapidly growing one. Several educated guessers put the number of operators using ECS at anywhere from a few dozen to 60 or 70 out of the 210 or so North American shredder installations.
The speed of acceptance has been slowed, apparently, by the cost of ECSs, which rely on extremely powerful, sophisticated, and expensive "rare earth" magnets. In addition, some shredder operators have been turned off of ECSs because of the reported frustrations of early users who found some of the initial systems—disparaged as "toys" by some—too low in capacity and too mechanically sensitive for demanding scrap processing applications.
But improved technology and strong metal markets seem to be boosting ECSs' popularity. "I would venture to say as many as a third of the shredders either have or are seriously considering putting one in," says Baumgartner.
Beyond an eddy current separator, the key to developing a fluff mining system, says Woody, lies in material handling equipment and procedures. Backing him up on this point is David Peck, president of Peck Recycling Co. (Richmond, Va.), which was troubled by material handling problems on a pioneering ASR-mining project that processed 250,000 tons of material in an around-the-clock operation that ran for nearly a year and recovered between 5 million and 6 million pounds of aluminum. "I wouldn't underestimate what it takes to pick up mountains of dirt and move them to a conveying system," he says.
A steady rate of flow is important for the system to be effective, so some sort of adjustable feed hopper up front is necessary. Yorke Doliner designed and built its own metered feed hopper, which Smith compares to equipment used in aggregate and coal handling operations. It's basically a large, rugged bin with a conveyor underneath fed at a controlled rate. A mechanism in the hopper also breaks up agglomerated material.
A Look at the Action
The first processing step in fluff mining is getting out ferrous fines, which are strongly attracted to the ECS magnets and can heat up and work their way into sensitive components, destroying the system.
Trommels or large power screens are typically used initially. Yorke Doliner plans to use a shaker table screen first to run off the large material, followed by a trommel to loosen everything up and screen out fines and
Determining the trommel screen size is important to making the most of this step and involves balancing metal losses against screen clogging hassles. In addition, the condition of the ASR, especially moisture content, is a key factor in this determination. Thus, what's right for one operation, may not be best for another. Yorke Doliner, for instance, plans to try 1/2-inch screens, while the Owens Steel project has been using a 3/4-inch screen. The best option, several sources suggest, is to use adjustable equipment that allows screen size changes.
Head pulley or overhead magnets following the trommel/shaker can pull out most of the remaining ferrous fines.
Next, the ASR may be further size-classified or fed directly to an ECS. For the eddy current magnets to function at optimal levels, the material must be spread out, perhaps using a vibrating table.
Opinions differ on the necessity of size classifying. Some projects have used several ECSs running parallel to handle specific-sized fractions, which required sizing equipment to break the old ASR down into like-sized fractions. But a new, very high-capacity ECS from Huron Valley Steel Corp. (Belleville, Mich.) can handle any particle size of greater than 1/4-inch and in a volume "far greater" than any other ECS, according to Woody, who has put the Huron Mark V to the test at Owens Industrial and reports that the machine can do the job alone and without initial sizing.
(Woody, who sells the Huron ECS as well as other brands, is quick to note that several other ECSs can also do the trick, especially in systems aimed at current-generation, but no other unit has the capacity of the Mark V, which may be necessary for a large-scale landfill mining project. Bills, whose firm also produces ECSs, counters that operations running at such a high volume may well have to run the material twice, essentially cutting the production capacity of the ECS in half.)
Yorke Doliner will also use the Huron ECS, processing material 1/2 to 6 inches in size. Smith reports that the company also plans to experiment with hand-picking larger material to determine whether it will be worth the cost of labor to retrieve oversized metal items such as stripping that turn up in the waste pile.
Several sources note that the appearance—and, hence, marketability—of the metal recovered from old ASR can be improved by running it through the system more than once, or even sending it through the shredder again.
The Jury's Still Out
The number of shredder operators who have tried mining old residue is hard to pin down. It may be that only a large handful have actually put the idea to work, though
Woody guesses that perhaps 15 or 20 have tried or are trying. Based on other shredders' reactions to the Owens project, however, he predicts that "there will be many more soon as long as the nonferrous market holds."
The jury is still out on whether such newcomers to the world of mining old shredder residue will see a positive fmancia1 return on their efforts. If they experience the kinds of results Owens has seen thus far and Yorke Doliner expects to record, chances are they'll be glad they made the move. Woody estimates that the Owens system is capturing all but perhaps 5 percent of the residual metal in the ASR. The bottom line is still fuzzy, however, since the project has only been running since August. Smith, meanwhile, says Yorke Doliner expects a recovery rate in the "high 90s," but it will be some time before that project's results can be evaluated.
On the other hand, those considering a fluff mining project should also know that a few early projects, kept largely under wraps, reportedly have not met expectations and their sponsors, perhaps damned to make the mistakes of pioneers, are not anxious to discuss them.
One thing's clear though, say today's ASR miners: Lots of questions remain to be answered, and there's plenty of room for further experimentation.
With improvements in eddy current technology, more and more automobile shredder operators are squeezing metals from shredder residue. And some are even taking it a step further, mining old fluff for nonferrous scrap.