Pictured above, from left: Hyunju Lee and Brajendra Mishra in a Worcester Polytechnic Institute lab in the U.S. working on the “Recovery of Valuable Metals from Flue Dust and Other Fines from Mechanical Treatment of E-Scrap” project.
Operators of auto shredding plants and downstream systems have spent decades collaborating with technology providers to purify and maximize the metals yielded by the shredding process.
The use of stronger and strategically placed magnets has helped shredder operators upgrade their ferrous shred grades. The nonferrous portion is sometimes referred to as auto shredder residue (ASR) despite the presence of considerable amounts of aluminum, copper, stainless steel and other marketable scrap metals.
The technological leaps and bounds that have been made in downstream sorting have allowed for the creation of increasingly clean grades of nonferrous metals that meet defined specifications.
Additional attention and research is now going into recovering the tiniest pieces, sometimes known as fines, from the ASR stream.
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While identifying and extracting medium-sized pieces of metal from the ASR stream will continue to be the focus of recyclers’ attention, satisfaction with that technology may have reached a point that they are inquiring about harvesting the smaller pieces.
“The biggest interest we’ve seen lately is with grinding ASR fines,” says Dick Reeves, the director of resource recovery with United States-based General Kinematics. “We must have run two dozen tests [for customers] since ISRI2017,” adds Reeves.
The additional processing step involves grinding the numerous materials found in ASR, but the purpose is all about the metal.
“Specifically, we’ve been testing the 0-to-20-millimeter ASR fines that have already been processed, but still contain nonferrous metal, rock, glass, smaller pieces of rubber and wood,” says Reeves. “By grinding this up, the hard minerals get pulverized while the metal remains intact, although slightly deformed. Screening is easily achieved afterward to concentrate the metals fraction.”
The emerging process joins several other forms of separation and screening that are used to harvest metallic fines from ASR and other mixed materials streams.
United States-based Eriez introduced its Ultra High-Frequency (UHF) Eddy Current Separator in 2016. The device has been designed to recover aluminum, copper and other nonferrous fines as small as 2 to 3 millimeters from ASR.
According to Eriez, early UHF customers have reported “a quick return on investment with profits increasing by up to $20,000 per month after installing this equipment.”
The UHF eddy current features a rotor and design that creates ultra-high-frequency changes that can result in a recovery rate “that is impossible to match with traditional eddy current technology,” states Eriez.
To develop its technology, Eriez indicates it has “established strategic partnerships with two outside firms” to collaborate on further advances.
Research is the key to new technology, and collaborative research into new methods of handling ASR and other mixed materials is taking place in the U.S., Europe and beyond.
The research that occurs at universities often is funded by companies and trade groups who would like to see a payoff, but most such funders know that payoff is not guaranteed or may not occur for several years down the road.
Two recent academic research projects have focused on harvesting metals in the electronic scrap stream, but the research findings may ultimately have an impact on how ASR is handled—especially as new car models feature growing amounts of circuit boards and electronics.
A March 2018 Recycling Today online article by Victoria Birk Hill summarizes a research project being undertaken by the Center for Resource Recovery & Recycling (CR3), a global, multi-university National Science Foundation collaborative.
Birk Hill is marketing director at the Metal Processing Institute of Worcester Polytechnic Institute in Massachusetts in the U.S., one of the collaborating universities along with the University of Tokyo; KU Leuven in Belgium; and the Colorado School of Mines, also in the U.S.
With organizations like Solving the E-waste Problem (StEP) estimating the world produced nearly 54 million tons of used electrical and electronic products in 2012, funding is becoming available to upgrade recycling methods, writes Birk Hill.
StEP forecasts that e-scrap generation number to have been 33 percent higher, at 72 million tons, in 2017, according to an article on the LiveScience website.
CR3 has been developing technologies that recover, recycle and reuse materials throughout the manufacturing process, with a focus on iron and steel, nonferrous metals (including gold, silver, copper and zinc), light metals, rare earths and photovoltaic metals and high-value refractory metals.
One recent CR3 project, according to Birk Hill, has been exploring ways to safely recover and reuse the metals found in the fine particles that are generated during mechanical processing and in flue dust collected in electronic scrap smelting operations.
A research study titled “Recovery of Valuable Metals from Flue Dust and Other Fines from Mechanical Treatment of E-Scrap” is being conducted at CR3, under the direction of Brajendra Mishra, Kenneth G. Merriam Professor of Mechanical Engineering at Worcester Polytechnic Institute (WPI) in Massachusetts and the director of CR3. Hyunju Lee, a post-doctoral student at WPI, is the lead researcher.
“Up until this point, the recovery process of flue dust from the e-waste smelting process has not been fully understood, because there is insufficient information about the constituents of the dust,” says Mishra. “This project will evaluate the potential for cost-effective and technologically viable methods for recovering valuable metals from the flue dust generated in e-waste by using physicochemical methods, which will help industry address the e-waste challenge.”
CR3 began working on its research project in the fall of 2015 and is on track to complete the project later in 2018.
Flue dust samples were provided by a CR3 supporter, a worldwide leader in copper production. Size separation of the nine sample types was performed to analyze the composition for metal value segregation. According to Birk Hill, composition and crystal phase identification were done using ICP (inductively coupled plasma) mass spectrometry and XRD (X-ray diffraction), respectively.
Researchers conducted magnetic separation to separate magnetic and non-magnetic materials in the size fractions found to contain high metal value.
The research team also has conducted selective leaching for gold, silver and copper using acid solutions. Gold and silver leaching efficiency is approximately 90 percent, and 100 percent through one-step leaching. Through a two-step process, gold and silver leaching efficiency is obtained at about 98 percent and 100 percent, respectively.
Birk Hill writes the researchers at CR3 are conducting extraction experiments for gold and silver. An economic analysis will be completed to evaluate which process is most cost effective and technologically viable for recovering metals.
CP3 contends the high content of valuable and precious metals in e-scrap fines and the “easy application” of leaching and precipitation steps that allow almost complete selective recoveries provide confidence in the economic viability. Thus, the scheme is easily adaptable by e-scrap recyclers, and potentially by processors of ASR fines.
A project at Linnaeus University in Sweden is further removed from auto shredding, but it could yield a process that would help identify and segregate some of the toxic elements that prevent portions of the ASR stream from being recycled.
The research focuses on mobile phones found in landfills and is being designed to extract 99 percent “of the dangerous metals found in glass from mobile devices, TV screens and crystal glass - all hazardous waste materials commonly found at landfills,” according to the researchers.
Yahya Jani, part of the environmental science and chemical engineering faculty at Linnaeus University, has developed a method he thinks “can be further developed at an industrial facility for the recycling of both glass and metals of high purity.” (The dissertation on it can be found here.)
The Linnaeus researchers have been mining landfills for mobile phones and other devices to use as the subject for their research. Jani states, “More than 50 percent of the deposited waste dumped at landfills and open dump sites can be recycled as energy or reused as raw materials. These materials can be used as secondary resources in different industries instead of being forgotten or viewed as garbage.”
He continues, “I developed a method that enables the extraction of 99 percent of the metals from the glass waste that was dumped at glass works and published the results. The methods I’ve developed to extract metals from glass waste can be used to extract metals from all types of glass, like, for instance, the glass in old TV sets, smartphones and computers. Thus, this method can be further developed at an industrial facility for the recycling of both glass and metals of high purity.”
Ongoing research into emerging separation and recovery methods may yet help handlers of ASR have more options to divert a higher percentage of this material from landfills.