Managing and remaking metals
Aluminum recycling technologies
 The automotive and aluminum industries are researching the use of laser-induced-breakdown spectroscopy for sorting aluminum alloys out of automotive scrap. (Image courtesy of The Aluminum Association.) Click to enlarge |
The technology is a potential boon to automakers and suppliers by enabling the recovery of greater quantities of high-strength, high-performance aluminum. Ultimately, this will allow greater use of either recycled or primary automotive aluminum—which weigh less than steel. Nearly 90% of automotive aluminum today is recovered and recycled. While aluminum represents less than 10% of the average vehicle by weight, it accounts for roughly half of its value as scrap.
"The techniques we're exploring will allow us to recapture more of the value and performance capability of the many high-quality aluminum alloys that are used in our vehicles," said Jim Quinn, a GM engineer who serves as Chairman of the U.S. Automotive Partnership, Automotive Metals, U.S. Council for Automotive Research (USCAR). "Current separating techniques only allow us to separate aluminum from other materials in scrapped vehicles. The recovered aluminum is then recycled into castings. But the new techniques will enable us to separate cast aluminum from wrought and even differentiate between wrought alloys." USCAR is the umbrella organization of DaimlerChrysler, Ford, and GM formed in 1992 to strengthen the technology base of the domestic auto industry through cooperative, pre-competitive research carried out in conjunction with the DOE.
Called laser-induced-breakdown spectroscopy (LIBS), the new process uses a laser to first clean the surface of the particle by laser ablation, and then it employs a laser pulse to hit the same spot on the particle as it moves down a conveyer belt. This second laser pulse vaporizes a small amount of material from the metal's surface, creating a small, highly luminescent plume of plasma, or ionized gas. To quantitatively determine the metal's chemical makeup, the plume is then analyzed by a technique called optical emission spectroscopy. Once the verification is made, the scrap is sorted by alloy on a piece-by-piece basis.
This method of separating scrap materials is being evaluated by a Belleville, MI, metals processing firm, Huron Valley Steel Corp. The Auto Aluminum Alliance is working with Huron Valley as part of a one-year agreement launched last August.
 The steel shred is magnetically loaded into a rail car or truck, or stockpiled for future shipment to end markets or steel mills, where it is recycled to produce new steel. |
LIBS is significant because it provides a practical way of sorting the scrap at commercially viable rates. Such alloys used to be sorted manually, a slow and costly process. It is estimated that the first commercial sorting center using this technology will be able to analyze and sort 45 million kg (100 million lb) of aluminum per year.
"Each year, automakers are using greater amounts of aluminum," said Klimisch. "This advanced scrap sorting process will help ensure that automakers have a more affordable supply of recycled aluminum for the future. It also shows the great strides that can occur when the automotive, aluminum, and scrap industries work together to solve technical challenges."
Increasing the efficiency of recycling aluminum does more than add value to recycling aluminum for automakers, it also reduces energy consumption. The production of recycled aluminum requires just 5% of the energy needed to produce primary materials, according to the Auto Aluminum Alliance.
Kobe Steel, Ltd. has done its own research into recycling along with Nippon Paint Co., Ltd. and Fountec Co. Ltd., announcing in May that aluminum sludge from automobile manufacturing can be reused in aluminum production. Recycling this waste has the potential to enable automakers to reduce the cost of sludge disposal, as well as protect the environment.
Aluminum sludge arises from a chemical treatment given to car bodies. To improve paint adhesiveness and corrosion resistance, car bodies often undergo zinc-phosphate treatment before they are painted. Aluminum leaches into the treatment solution and is precipitated as cryolite, a mineral consisting of sodium, aluminum, and fluoride.
To date, the cryolite recovered from the sludge has been disposed of in landfills. According to the companies, in this new application the recycled cryolite is used in the production of aluminum as a flux for degassing.
