Recovering Materials from Shredder Residue

Obsolete automobiles, home appliances and other metal-containing scrap are shredded for the recovery of metals. More than 50% of the material shredded is automobiles. In the United States, shredders generate about 5 million tons of shredder residue every year. Similar amounts are produced in Europe and in the Pacific Rim. Because recycling shredder waste has not been profitable, most of it ends up in landfills; smaller amounts are incinerated.

Argonne researchers have developed and tested a process to recover polymers and metals from shredder residue. A 2-ton/hr pilot plant, consisting of a mechanical separation facility and a six-stage wet density/froth flotation plant, was built at Argonne. In the mechanical part of the plant, the shredder waste was separated into five primary components: a polymer fraction (about 45% by weight), a residual metals concentrate (about 10% by weight), a polyurethane foam portion (about 5% by weight), an organic-rich fraction (about 25% by weight) and a metal oxides fraction (about 15% by weight). The polymer fraction was then separated further in the wet density/froth flotation system to recover individual plastic types or compatible families of polymers.

About 110 tons of shredder residue were mechanically separated. The process included sizing equipment, size separating equipment, including a two-stage trommel (a spinning drum enabling separation of particles by size or shape), and metal recovery equipment. Recyclable materials were then recovered from the five fractions. About 50 tons of the recovered polymers were separated in the wet density/froth flotation system.

This bulk separation system, which processes two tons of shredder residue per hour, separates the waste into five components: polymers, residual metals, polyurethane foam, an organic-rich fraction and an oxides fraction.	The full-scale foam washing system designed by Argonne, built by Almco and installed in the Salyp N.V. of Belgium demonstration plant.

Polymers. Dozens of different types of polymers are used in automotive applications today; shredder residue contains all of them, as well as other classes of polymers that are used in metal-bearing scrap (e.g., obsolete appliances) that the shredder might process. Through pilot-scale research, Argonne has been able to recover those plastics that are present in the largest volumes and/or have the highest potential value. The plastics are separated by flotation techniques, including a froth-flotation technology that Argonne originally developed for the separation of plastics from home appliances and electronics. Polymers recovered from shredder residue include polyethylene, polypropylene, acrylonitrile butadiene styrene, high-impact polystyrene and various rubber compounds.

Residual Metals. The residual ferrous and nonferrous metals were liberated from the shredder residue in the mechanical separation facility and then recovered with conventional metals-sorting technology. In the Argonne process, more than 95% of the residual metals contained in shredder residue were recovered.

Polyurethane Foam. Unsurprisingly, the polyurethane foam recovered from shredder residue is dirty. Argonne developed and patented a process for producing a clean polyurethane foam from the residue. The process was developed and tested at a shredder site, after which more than 2 tons of cleaned foam were supplied to customers for evaluation. The customers “rebonded” the foam and used it to produce carpet padding for testing in automotive applications. The foam met all of the performance requirements of the rebonders and their automotive customers. This technology garnered an R&D 100 award in 2000 and was licensed to Salyp N.V. of Belgium, where a full-scale commercial demonstration plant has been built. The technical feasibility of converting the foams to chemicals has also been confirmed by Troy Polymers, Inc.

Organic-Rich Fraction. A sized organic-rich fraction consisting of a mixture of plastics, rubber, fabrics and fibers is also recovered from shredder residue. The technical feasibility of using this material as a feedstock to produce substitute fuel has been confirmed by Changing World Technologies, Inc.

Oxide Fraction. The oxide fraction, which includes particles measuring less than about 1/16 inch, contains metal oxides, glass, dirt and some organic material. Magnetic separation of the oxide fraction yielded a concentrated iron oxide that showed promise as a source of iron for the cement industry. During a pilot demonstration at a shredder facility, Argonne produced about 50 tons of this material to be used for testing by the cement industry.

This research was sponsored by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program and conducted under a Cooperative Research and Development Agreement (CRADA) with the Vehicle Recycling Partnership (composed of Chrysler, Ford and General Motors) and the American Chemistry Council–Plastics Division.

April 2008