Argonne’s Approach to Recycling Shredder Residue Leads to Greener World, Profitable Polymers

recycling

More than 12 million vehicles reach the end of their useful life each year in the U.S. Most of each vehicle is recycled (primarily the metals), but about 25% of the materials end up being sent to landfills as shredder residue, which also includes other industrial waste sources such as scraps from electronics and home appliances.

Shredder residue contains polymers and residual metals that, if recovered, can be recycled profitably.

Novel technologies developed by the U.S. Department of Energy’s Argonne National Laboratory can enable industry to economically recover these materials from end-of-life vehicles (ELVs) and other sources to make valuable products, including auto parts (e.g., spare tire covers, steering column covers, and battery trays).

Vehicle recycling in North America is a $10-billion, market-driven industry that provides more than 100,000 jobs, benefiting the economy, reducing energy use for vehicle manufacture, and protecting the environment from contamination by metals.

As vehicles become smaller and lighter to improve fuel economy, auto manufacturers will incorporate relatively higher percentages of lightweight, nonmetallic materials such as plastics, foam, and carbon fiber composites. With the share of metal in cars and trucks dwindling, the recycling industry needs technologies for nonmetallic scrap recovery to help maintain its profits.

The U.S. government and industry have partnered to devise economical methods for recovering valuable contents from shredder residue.

One new technology, developed at Argonne National Laboratory, can separate many types of polymers and residual metals from the residue at a yield never before attained in the recycling industry.

The Argonne-developed process consists of two basic steps. In the first step, mechanical separation concentrates the plastics and residual metals into a manageable fraction, and conventional sinkor-float techniques separate some of the plastics in the concentrate based on differences in density.

Individual plastics are then separated using other techniques such as froth flotation, a process for separating water-shedding (hydrophobic) materials from water-attracting (hydrophilic) materials.

The typical waste stream generated by shredders contains about 25% to 40% recoverable polymers, including polypropylene, polyethylene, rubber foam acrylonitrile butadiene styrene (ABS), and high-impact polystyrene (HIPS).

Plastics such as ABS and HIPS are readily separable from other plastics, but not from each other because they share the same density. Fortunately, Argonne’s froth flotation technology can separate HIPS from ABS.

Altered water chemistry enables an air bubble to attach to hydrophobic HIPS, lowering its apparent density relative to ABS. As a result, HIPS floats away from ABS, which sinks in the solution.

Argonne developed a 2-ton-perhour pilot plant to determine optimal operating conditions and process economics.

The laboratory then evaluated potential business opportunities for specific recovery applications. As a result, Argonne worked with a commercial shredder to build a 20-ton-per-hour pilot plant that performs both mechanical and sink-float separations. Argonne also worked with the United States Council for Automotive Research’s (USCAR) Vehicle Recycling Partnership and the American Chemistry Council’s Plastics Division under a Cooperative Research and Development Agreement structured by the Department of Energy to advance ELV recycling.

Argonne’s energy-saving approach to recycling shredder residue will reduce waste, offer an environmentally friendly alternative to more expensive virgin plastics, and make the process of recycling cars more sustainable and profitable.