Jolted: Cable scrap

As the science of cable recycling has advanced, and tonnages of scrap cable recycled have increased, recycling is one arena in which new processing technology to yield increased recovery can pay dividends. Therefore, it is not surprising that recyclers increasingly are attempting to recover virtually 100% of the valuable copper, including what is left behind with the plastic insulation waste.

It is possible to almost completely recover these residual copper fractions from insulation in a dry process with electrostatic separators such as the Hamos KWS electrostatic separator.
 

Copper recycling process

Prior to the use of electrostatic separation, cables must be ground until the copper falls away from the insulation. Thin wires require very fine granulation in particular to loosen the mechanical bond between the copper wire and plastic insulation.

After granulation, copper and plastic are separated by gravity separation, or “setting” tables. The setting tables are adjusted so that the copper may be as much as 100% pure. This is especially important, since even the smallest impurities in the copper fraction leads to significant revenue reduction. Copper smelters only pay the highest prices for so-called “No. 1 copper,” so the aim is to always produce the copper fraction with maximum purity.

For technical reasons, however, it is difficult to produce copper with 100% purity and at the same time also produce a “copper-free” plastic fraction using a gravity separation table. Particularly when processing mixed cables (namely cables containing course and fine wires and strands) or thin telephone cables, the cable recycler can expect to lose a small amount of fine copper wires and dust together with the insulation. Typical copper losses here can—depending on cable type—amount to between 2% and 12%, a proportion that implies significant financial losses as processing volumes increase.

Dry electrostatic separators can be ideal for very economic separation of even the smallest and finest residual copper particles from cable scrap. Wet separation methods, such as so-called “water tables,” have the disadvantage that further processing of wet plastics into plastic products may not be economic in light of the additional drying time required. In addition, major problems can arise if ambient temperatures are low.

Dry working electrostatic metal separators, such as the Hamos KWS system, make use of differences in conductivity between metal and plastic for separation. After electrostatically charging the fractions with high voltage, the metal and plastic fractions subsequently discharge on a fixed roll surface. While metal particles discharge immediately and fall off the roll surface, the plastic particles discharge very slowly and adhere to the roll surface.

Purity of the individual separated products is adjusted to an optimal level using splitters. The separated plastic fractions are extracted from the equipment with integrated conveying screws, causing the metal fraction to fall to the bottom of a metal container located underneath the equipment.

Electrostatic separators are available in different sizes and throughput levels. Typical production machines for cable processing separate at a rate of about 1,760 to 2,200 pounds per hour. Throughput rates of several tons per hour can be achieved by using high performance equipment and putting several separators in parallel.
 

Building a showcase

MTB based in Trept, France, is both a manufacturer of granulation equipment as well as a recycler of wire and cable scrap. With an annual recycling capacity of 40,000 tonnes, MTB is one of the largest European cable recycling companies.

Jean-Philippe Fusier, CEO of MTB, also recently installed several Hamos KWS electrostatic separators.

“After installation of the Hamos electrostatic separators at the end of our copper cable line we separate all the fine and extremely fine metal particles, even metal dust, from cable insulation,” Fusier says. “In the past we have lost all this copper together with the residual insulation material. Our Hamos KWS electrostatic separators recover the valuable metal fractions in the simplest way and simultaneously produce a metal-free plastic product.” Fusier says he was surprised about how quickly the company was able to earn a return on its investment, having installed the equipment several months ago.

Fusier says the Trept facility’s cable recycling line is considered to be something of a company showcase, with customers from all over the world touring the plant to see MTB’s cable recycling equipment, including electrostatic separators, in operation (see sidebar below).

In recent months MTB also has been working on re-using the final polyvinyl chloride (PVC) insulation as valuable commodity. Because of the fact that postconsumer cable plastics are a complex mixture of PVC, rubber, polyethylene (PE), cross-linked PE and many other plastics, the direct re-use of such material is only possible for low-grade applications. In addition, old cables that are brought in for treatment may have a chemical composition that is not compatible with today’s modern PVC materials. The plastic fraction is therefore either disposed of or further processed into various simple products. In Germany or England, for example, several companies are producing traffic sign pedestals from cable waste.

Meanwhile, MTB has sought to produce more pure PVC products, and to do this has also invested in Hamos EKS electrostatic plastic separators, designed to enrich or upgrade the PVC content from mixed cable regrind materials.

“We have high amounts of cable scrap coming directly from cable production,” says Fusier. “We process such cleaner input materials separate from postconsumer cables. After metal separation the residual insulation is now separated in a clean PVC fraction, using our new electrostatic plastic separators.”

Fusier says the EKS process uses the effect of the PVC fraction becoming predominantly negatively charged in a specially developed charging unit. Meanwhile, rubber, PE and other foreign plastics in the mixed material take on positive charges. Subsequent separation in a high-voltage field results in highly enriched PVC fractions and PVC-depleted residual plastics. The concentrated PVC is now extruded to pellets while residual non-melting impurities are separated by melt filtration. (This activity is driven with an industrial partner, Fusier points out.)

Fusier adds that because of good surface quality and superior technical properties, the extruded material from the PVC pellets reaches a quality level that is close to virgin material.

“I am sure that there are numerous new application possibilities beyond the present use of traffic sign pedestals and similar applications,” he says. “We are in close contact with several potential end users, producing more complex and filigree-structure products made of these PVC concentrates. I hope to build up a new customer base for this clean cable PVC,” says Fusier.

In the United States, Hamos KWS electrostatic separators are sold by Copper Recovery, Inc. based in Huntington Beach, California.

Chris Carlson, CEO and managing director of Copper Recovery, is also operating his own cable line and has been using KWS electrostatic systems for metal recovery for several years.

“We use our electrostatic separator all the time in production. We have calculated the separation cost per hour to be well below $25,” he comments. Carlson says this price includes all costs, including financing and depreciation. “Due to these low operating costs combined with high metal recovery rates, our electrostatic separator has amortised after just a few weeks of operation,” he remarks.

Carlson says the company has a small scale KWS system available for use by customers interested in running small samples of material.

The copper yield from cable recycling plants therefore can be increased by the aid of electrostatic separation technology. Because of its dry operation, recovery of nearly all residual metals, high operational efficiency and in particular the rapid amortisation of such electrostatic separators for metal separation, the technology can serve as a complement to modern used cable processing plants.

Should the cable insulation not be disposed of, but made into a product, electrostatic separation technology can be applied in this area as well.

The author is managing director of Hamos GmbH, based in Penzberg, Germany, and can be reached at dr.k@hamos.com.