A Closer Look

When it comes to the plastics recovered from electronic scrap, the question ultimately becomes one of differentiating the many plastics used in manufacturing of electronics, whether the material has been shredded or manually disassembled.

The human eye, for example, has a tough time differentiating between ABS (acrylonitrile butadiene styrene) and polypropylene (PP). However, optical sorting equipment is capable of performing this task. That’s why an increasing number of recyclers are interested in optical sorting technology for their operations. While the technology does not perform miracles, it works well within certain boundaries.

"But," he adds, "as long as we stay within the manufacturer’s parameters, it is working just fine."

IMS Electronics Recycling has just stepped up to optical sorting. This fall, the company installed a unit in its San Diego location and plans to add one into its Washington state facility in December. IMS is certified by the state of California to collect and recycle electronics, including computers, telephone systems and CRTs (cathode ray tubes), covered under the state’s Electronic Waste Recycling Act of 2003, or SB 20.

Ed Siegel, general manager at IMS, says the company is using sorters from MSS Inc. of Nashville, Tenn., a sister company to IMS.

"Our shredder system was designed to produce 2-inch pieces so we could use [optical] sorting," Siegel explains.

IMS has a metal sort, which is similar to an eddy current, only it ejects material with air.

A second system separates the plastics. "We can identify up to 10 resin types," Siegel says.

"The e-scrap field is in development, and the use of optical scanning seems to be a new trend," Michael Drolet, optical equipment specialist with Machinex Inc., Plessisville, Québec, Canada, says. The main reason is the improved ability of such machines to identify and separate the different types of plastics present in the electronic devices, he adds. "This cleaner separation helps improve marketability of the products," Drolet says.

He notes optical sorting appears more efficient than conventional methods of manually dismantling and identifying the plastic components or density separation of the shredded plastics fraction.

Optical sorting equipment usually requires less floor space than other sorting methods, Drolet adds.

"I think two factors have combined to increase interest," John Thomsen, engineering manager at National Recovery Technologies (NRT), an equipment engineering and manufacturing company based in Nashville, says of optical sorting. "First, there is more general interest in recycling of electronics and more volume being collected for recycling. Therefore, more companies are looking for processing ideas, and the existing companies are looking for ways to increase processing capacity.

"Second," he says, "I think there is demand for an alternative to merely sending electronics to a low-labor-cost country, where all kinds of environmental and humanitarian problems often arise."

Optical sorting, like any type of sorting technology, only make sense for certain applications, notes Felix Hottenstein, sales director for MSS. "The setup and configuration of the system may be different for every facility. Market conditions have to be taken into account very strongly to decide what piece of equipment should be used for what type of segregation," he says.

One reason for the popularity of such technology is the increase in revenue by being able to sell pre-sorted materials to plastics and metal reclaimers. "With metal prices having been so high, everybody is trying to recover more metals out of the mix (besides what can be recovered using "standard" magnet and eddy-current technology)," Hottenstein says.

"Being able to sell specific plastic resins may be advantageous as well, although markets for pre-sorted individual plastic resins still have to be developed," Hottenstein says.

He notes that many customers don’t just want to ship shredded electronic scrap overseas anymore (whether driven by conscience or legislation). Optical sorting can help them to sell products domestically at the highest price possible, he says. Hottenstein adds that this is not only true for optical sorting, per se, but for any other advanced sorting technology, including electro-static separation, froth floatation, air classification and the like, that is able to segregate one type of material from the mix.

There are several approaches to optical sorting:

• Infrared (IR) detection of different polymers to sort among the various plastics that are part of the recycled electronics stream;

• Visible light and image processing to distinguish among different components; and

• Metal detection and separation based on X-rays, magnetism and eddy-current devices.

The IR systems on the market analyze the light reflected off the sample to determine its properties. The system examines the reflection pattern emitted, compares it to its database and sorts accordingly.

Hottenstein agrees that any optical sorting machine needs to be post-shredder, just like the magnet and eddy-current separator.

"If it is certain that the material coming from the shredder is always the same, then an optical sorting module could be installed in-line," he says. "If many different materials are being processed, we would probably recommend installing it off-line to make material handling easier and to make sure the shredder can be used to its maximum potential," he says. This also would help avoid bottlenecks.

Thomsen says he thinks the basic methods of size separation and metal detection should be applied first to shredded electronics, and optical methods should be used subsequently to improve the value/recovery from the materials streams.

Determining the optimal particle size when using optical sorting technology in a recycling operation is really a matter of cost.

Drolet says an optical sorter would work well for any fraction surfaces that are between 1 and 150 square inches. "Larger than that, it gets hard to handle," he says, "and smaller reduces the efficiency of the machine."

He says Machinex usually tries to offer the highest definition camera package available when dealing with e-scrap because the difference between some of the plastics is quite small.

Drolet says, "When integrated into an automated processing line, a typical setup would be a shredder to size the fraction, a fine disc screen mainly to remove glass, magnets to remove metal and then the optical sorter."

Since most processors already use magnet, eddy-current and screening technology at their plants, they have a head start on this setup. They may also have other components—such as de-stoners—in place to segregate material. "Most of those components are installed ‘in-line’ in the process," Hottenstein points out.

In some applications, optical sorters are integrated into the main lines to perform a certain task. "However," Hottenstein says, "the strength of the newer generation optical sorters (color, near-infrared, X-ray) is such that they are very flexible as to what materials they can sort. Different sort configurations can be programmed for different incoming materials."

He notes that all three e-Sort modules that MSS sells in the United States (employing near-infrared, color and metal detection) are set up as "stand-alone" systems, so the different materials can be processed in batches.

Smaller particle sizes also can decrease throughput.

Thomsen says, in general, it starts to become economically burdensome to apply optical sorting to pieces smaller than about 2 centimeters or 3 centimeters across.

"This economic threshold is affected by many things, such as the value of the objects," he says. Here, he presumes the material is of a similar character based on a previous mechanical separation. Also in question is the material’s suitability for further mechanical separation. For example, small plastic pieces could be subjected to an additional density or perhaps chemical separation process. There also are limitations and boundaries to the practicality of sorting the myriad polymers and different colors of plastics.

"There is a large volume of that material, and due to the trend toward black and darker colors, the automatic identification of it is more difficult," Thomsen says.

Most manufacturers will admit that dark colors are difficult for optical equipment to handle. That is because optical systems rely on light reflecting off the material, and black items instead absorb light.

"Evaluate your process," advises CTR’s Campbell. CTR begins the process with two in-line shredders. The first shredder reduces infeed material to a 3-inch square size. The second shredder further reduces the material to a 1.5-inch-by-1.5-inch-by-variable particle size. Magnets follow each shredder and recover ferrous material from the stream. Further downstream is an eddy current separator that recovers nonferrous material while discharging plastics and residual metals into different directions.

Campbell finds the equipment installed at CTR processes at the manufacturer’s advertised rates.

Siegel says the IMS setup puts dark plastics on a pass-through. The company’s line is designed for future expansion. "Our module has a position for dark that we have available for an X-ray system," he says. "That’s our next step, sometime in the middle of next year.

"The X-ray will give us a huge spectrum for dark material as well as fire retardants," Siegel says.

"Our machine is quite amenable to changing sorts," Campbell says of the optical sorting equipment in use at CTR Electronic Recycling.

Switching from one material to another is simple because most of the "brains" in optical sorting equipment is in the software. By changing the software parameters, users can change the machine’s view and the criteria on which to base sorting.

Maintenance is pretty straight-forward, too, Campbell says of optical sorting equipment. "As long as you follow the manufacturer’s recommendations, you’ll have no issues at all," he concludes.

The author is a contributing editor to Recycling Today and can be contacted at curt@curtharler.com.