The Eyes Have It

Optical sorting equipment is a growing component of many material recovery facilities (MRFs), where the technology is commonly used to sort plastics from fiber or by type, such as HDPE (high-density polyethylene) from PET (polyethylene terephthalate). The equipment also has found a home at electronics recycling operations, where it is used to sort a variety of materials, including plastics that have been treated with brominated flame retardants as well as circuit boards.

GETTING TECHNICAL

Optical sorters use a variety of sensor technologies to perform various sorting tasks at electronics recycling facilities. The most common technologies in use are near-infrared, or NIR, and X-ray.

“We are using multi-spectral NIR technology to classify the different plastics types,” says Peter Mayer, sorting technology sales manager for Germany-based S+S Separation and Sorting Technology GmbH. “In order to achieve a high sorting efficiency, we evaluate the reflection of the infrared light at up to 256 independent wavelengths at the same time per scan and, therefore, are able to do a very precise material identification, even if the objects which are being inspected are dirty.”

Felix Hottenstein, sales director for MSS Co., Nashville, Tenn., says NIR technology has been used for 20 years to sort mixed plastics by type as well as to sort plastics from fiber. “For special applications, such as PVC (polyvinyl chloride) sorting from PET as well as sorting flame-retardant (FR) materials from non-FR materials, transmission X-ray technology has been used for many years as well,” he says. “For color sorting of the plastics, color camera/vision systems are used.”

TiTech, with headquarters in Norway and Germany, also offers optical sorting units that employ NIR technology to sort plastics by type. “Although we can reach high recovery and purity rates with the TiTech Autosort, sorting plastics optically is not that popular due to two reasons: The limitation of NIR technology is that it cannot sort very dark or black items and the percentage of black plastics can be very high in electronic scrap,” says Alex Wolf, a sales engineer with TiTech, which is distributed in the North America by Van Dyk Baler Corp., Stamford, Conn.

“Plastics, even when sorted to pure grades, are far less valuable than metals,” he continues. “For an e-scrap processor, it makes economical sense to invest in metals sorting technology [rather] than in plastics. For them it makes more economical sense to send the mixed plastics to processors who specialize in plastics processing and sort higher volumes.”

However, optical sorting equipment also can play a role in recovering metals in electronics recycling applications.

MINDING THE METAL

“Optical sorting is used for sorting of circuit boards (mostly by identifying the specific green/beige/red/blue color) as well as copper wires (by color and shape),” Hottenstein says. “A good example of this would be to further sort the nonferrous materials that have been sorted out by an eddy current separator in the upstream process by type of material: aluminum, copper, brass, etc.”

When an induction-type metal detector is added, he continues, additional metals can be sorted, such as magnetic and non-magnetic stainless steel.

“The most popular application for the TiTech CombiSense is sorting circuit boards due to their high value and their high content in the processed stream,” Wolf says.

To perform such a sort, optical units typically combine the information from different sensors, like color, material type and metals content, to identify the printed circuit boards, Mayer says.

While optical sorting can benefit electronics recyclers, whether it’s incorporated into a facility can hinge on a number of factors.

GOING OPTICAL

Hottenstein says the decision to add optical sorting equipment in an electronics recycling facility typically hinges on three factors: tons processed per year, local markets and geography and current legislation, which he points out is “more stringent” in Europe, requiring a higher recovery rate that leads to the incorporation of high-end technology.

Hottenstein says, “We have small sized companies as existing customers who swear by the technology and large potential customers who are still hesitant to buy.”

He adds that mechanical separation technology has improved in recent years and is sufficient to meet the needs of many recyclers.

Wolf says the decision often hinges on the facility’s processing volume. “While some of them seem to process high volumes, it turns out that only a small fraction goes through their shredding line,” he says. “Mostly high-grade e-scrap such as CPUs and printers are run through the shredder; monitors are heavy and subject to manual disassembly for the most part.

He continues, “As a rule of thumb, it makes sense for a processor to add a Finder if he processes around 500,000 to 1 million pounds per month, depending on how much high-grade he runs.”

Wolf adds that in today’s market, a company can realize a return on investment (ROI) within a year. However, he notes, “ROI greatly depends on the volume that is being processed, what is being sorted and what value it has in today’s market. For processors able to process several shifts a day, the ROI can be less than half a year.” Hottenstein says it should take no longer than 24 months for an electronics recycler to achieve ROI, while Mayer says the payback can take as many as three years, depending on the installation in question.

Generally, optical sorting equipment is installed downstream of the shredder after mechanical separation devices such as magnets, eddy current and air classifiers. For optimal separation, sources generally recommend particle sizes ranging from ? to 2 inches. Hottenstein adds that particles can be as small as 2 millimeters for color sorting applications.

“The larger the particles, the easier and more reliable they can be identified,” he says. “But if they are too large, the different materials will not be liberated from each other and no type of sorting (mechanical, optical, etc.) will be effective.”

Wolf says, “Shredding smaller often leads to better liberation of the shredded material; you will have fewer commingled pieces, like a piece of plastics with a bolt in it. However, the cost for running the shredder is higher the smaller you shred.” He adds, “Typically you see operations shredding to less than 2 inches, which seems to be a good compromise between running cost and liberation.”

Optical sorting equipment holds potential in a number of recycling industry segments, from material recovery facilities to plastics reclaimers to metals recyclers, but Nathanaël Lortie of Eagle Vizion, Sherbrooke, Ontario, says he sees great potential for optical sorting in electronics recycling applications. “It’s growing and it will be big, but for the time being, electronics recyclers are just getting used to it.”

Hottenstein also says electronics recycling holds the most potential in terms of incorporating optical sorting. “Because e-scrap is the fastest growing recycling area, it also has the fastest growing potential,” he says. “But there are still so many untapped markets and customers that all sectors with keep holding very good potential.”

The author is managing editor of Recycling Today magazine and can be contacted at dtoto@gie.net.