Electrically exciting sorting

Features - Scrap Metals Supplement

A team of researchers has developed a new eddy current separator designed to improve nonferrous sorting.

January 2, 2020

© vector_v / stock.adobe.com

Changes to China’s scrap import policies have reduced outlets for zorba, leading auto shredder operators in the U.S. to look for alternative options for the zorba they generate. For some, that has meant investing in equipment to further sort this material. Although traditional eddy current separators are effective at sorting nonferrous metals from nonmetallic materials, these machines fall short when trying to sort nonferrous metals from one another. This means recyclers have had to invest in sensor-based sorting technology or sink-float technology to further refine this material.

However, a team of researchers at the University of Utah, Salt Lake City, and EDX Magnetics LLC, a company associated with the research team at the University of Utah, have been working to remedy metals sorting challenges using high-frequency electromagnets and a new form of eddy current sorter employing electrodynamic sorting (EDX). The research was led by Raj Rajamani, who is a professor of metallurgical engineering at the University of Utah. Research associates for this project included James Nagel, Dave Cohrs and Jacob Salgado.

One issue the researchers aimed to solve was recovering aluminum from zorba. The widespread use of eddy current separators among auto shredders operators means they have a tendency to produce relatively similar mixtures, Nagel says. One of the more common products produced by auto shredders is zorba, which is loosely defined as any combination of nonferrous scrap metals that is predominantly aluminum. However, zorba can be a tough grade to sort further, Nagel says.

A grant from the Reducing EMbodied-Energy And Decreasing Emissions (REMADE) Institute, West Henrietta, New York, helped the team of researchers construct a high-throughput electrodynamic sorter that can process zorba at a rate of about 1 ton per hour.

With the electrodynamic sorter, as lightweight aluminum particles pass through a magnetic field, electrical eddy currents are induced and the particles are propelled over a mechanical divider. The aluminum is recovered from the rest of the zorba, producing a clean, high- purity aluminum that can be sold directly to a smelter, says Nagel, who also is a co-founder of EDX Magnetics.

“This machine works well at upgrading zorba,” he says. “We have a very good machine that works on fine zorba—zorba in the ¼-inch-to-1-inch size range. It’s very good at getting aluminum out of that material with high purity. You can also upgrade your zorba to twitch. It also upgrades the drops of your copper concentrates, so you can get more value out of that.”

Exciting technology

Rajamani first began researching magnets and eddy currents about a decade ago with hopes of developing an electrodynamic sorter. About five to six years ago, he submitted a proposal to develop an electrodynamic sorter to the Advanced Research Projects Agency-Energy (ARPA-E), which funded the basic research.

Nagel says Rajamani and his team partnered with the REMADE Institute to scale the technology and make it more practical for use in scrap metal recycling.

Photo: EDX Magnetics LLC

Nagel adds that while the concept of EDX has been around for decades, EDX Magnetics’ machine is the first embodiment that “really works” to sort nonferrous metals.

EDX Magnetics’ electrodynamic sorter operates similarly to a traditional eddy current separator, Nagel says. The main difference is that eddy current separators are mechanical and feature a rotating cylinder, whereas the electrodynamic sorting machine features a nonmoving electrically excited field.

“The traditional eddy current is physically moving a permanent magnet,” he says. “You have to mechanically move the magnet near the metallic object in order to excite the eddy current. We have an electromagnet, so it’s magnetic material that you excite with an electrical current, and that creates a magnetic field. There’s nothing moving. It’s a solid block with an electrical current exciting it.”

Nagel says the key principle with EDX technology is the high frequency of excitation that allows users to sort nonferrous metals from other nonferrous metals.

EDX Magnetics’ electrodynamic sorting system begins with a vibratory feeder that distributes scrap material onto a conveyor belt. Embedded within the conveyor assembly is an electromagnet core that is excited by an alternating electrical current. The tips of the electromagnet are placed in direct contact with the underside of the conveyor belt so that scrap particles can pass directly through the magnetic field overhead.

Depending on factors such as electrical conductivity, mass density and physical geometry, some of the particles will repel up and away from the magnet. These particles are referred to as “throws.” Any particles that pass through the field without significant deflection are referred to as “drops.” A mechanical splitter separates the throws from the drops, which collect in corresponding bins.

Because of the excessive heat that builds up in the electromagnets, an axial flow fan is used to circulate air through the cores to maintain a stable temperature. Nagel says the EDX technology also serves as an alternative to density separation technologies.

“[Density separation technology] exists and people are using it, but it’s expensive,” he says. “There is a huge processing cost with it—you may need to clean and dry materials. There are regulatory hurdles [to that model] as well. All these factors come together to determine whether that technology is viable or not.”

Prepping to go to market

Lab testing on the technology was completed between February 2018 and November 2019, and Nagel says EDX Magnetics is almost in a position to sell the electrodynamic sorter commercially. But first, he says, the researchers need to test the machine in a scrap yard setting for a few months. Once the researchers know the machine can operate for three-to-four months in a scrap yard with no major failures, Nagel says EDX Magnetics will be ready to start taking orders.

He adds that the machine’s cost will be on par with that of a traditional eddy current separator. However, Nagel explains, this technology isn’t meant to replace eddy current separators; it supplements them by providing a better sort. “Most eddy currents, they’re very good at getting metal out of nonmetal, but they aren’t very good at sorting metal after the fact,” he says. “This machine would come after a traditional eddy current.”

Based on the lab testing, Nagel adds that the electrodynamic sorter can comfortably sort zorba at a rate of about 1 ton per hour. It can be pushed to about 1.5 tons per hour, but he says “that is the upward limit of pushing material through.”

This technology offers other advantages in nonferrous sorting, Nagel adds. One benefit is that the machine can sort particles that are as small as 1 millimeter. The sorter requires only 4-to-5 kilowatts of power to operate. Also, the machine operates efficiently in warm and cold climates alike, but it achieves even better results in cold temperatures, he says.

Nagel adds that the electrodynamic sorter can be targeted to process other grades of nonferrous metals beyond zorba, as well. “This technology can be applied to other materials; just focus it on the greatest need.”

The author is managing editor of Recycling Today and can be reached at msmalley@gie.net.