Scientists at a US Department of Energy laboratory have developed unique tools that can be used to remove shredded plastics from electronics and are planning to demonstrate them to processors.
Argonne National Laboratory officials developed techniques that can be used to separate e-plastic polymers and remove contaminants such as metals. The wet-based separation process enables salt-free sorting according to density in swim-sink tanks.
“We have an effective opportunity to demonstrate this technology with in-house funding to potential industry partners interested in licensing technologies,” said Jeff Spangenberger, group leader, materials recycling at Argonne National Laboratory near Chicago. “Ultimately, I’m looking for people, companies, who would like us to demonstrate our equipment to see if we can add value to their waste streams or a product stream.”
In an interview with Plastics Recycling Update, Spangenberger explained that the process was developed years ago to recover materials from car shredder residues. But the researchers also wanted to see if the separation techniques work with electronic waste and other streams.
A modified float sink method
In some ways, the technologies include modifications to current float sink techniques that can be used to sort mixes of plastics, metals, and other materials that come at the end of an electronics shredder and separation line. In swim-sink tanks, heavier materials sink to the bottom and lighter ones swim.
A number of North American e-waste processors and plastics recyclers have installed float-sink systems to improve the quality of the plastics coming out of their shredders and to reclaim metals that would otherwise be shipped with mixed plastics. These include BoMET Polymer Solutions, eCycle Solutions, Owl Electronic Recycling, Plastic Recycling, Inc., and Universal Recycling Technologies. Many cited stricter export market specifications in their decision to invest in equipment.
Salts are often used in sink-swim systems to increase the density of the water, which enables separations that would otherwise not be possible in pure water. For example, ABS and HIPS, which are common e-plastics, sink together with metals, glass and other heavier materials in unchanged water. However, if enough salts are used, these styrenic polymers will float.
However, the use of salts in these systems raises concerns about equipment corrosion and wastewater treatment, Spangenberger noted.
Argonne National Lab scientists developed two wet separation processes to eliminate the need for salts. One is called foam floatation, which has been used in mineral processing for years. This process makes some materials hydrophobic and others hydrophilic. When air is introduced, the hydrophobic materials stick to the air bubbles and float to the surface, explains Spangenberger.
The other process is similar to elutriation, in which lighter materials are skimmed off by flowing air, but a speed of water is used to separate the materials.
Making cleaner plastics and metals
Researchers have taken samples of shredded e-waste through the sorting processes that work well with low-quality scrap like shredded printers, Spangenberger said. The techniques can be used to make a clean fraction of styrene (HIPS, ABS, and PS) for sale, he noted. It can be used to remove metals that have not been caught by magnets or eddy current collectors and end up in the shredded plastic.
Spangenberger said he wanted to process samples of e-waste from recycling companies. He envisions starting smaller samples – maybe 100 pounds – and then maybe moving on to large-scale trials with 10,000 pounds, he said. He said he had funds to hold large-scale demonstrations for two electronics recycling companies.
The ultimate goal is to license the technology so that it can be widely used to improve recycling, thereby recovering the energy that went into making the materials, he said. Interested companies can send an email to Spangenberger [email protected].
A version of this story appeared in E-Scrap News on September 16.