separation. The average metal content of PCBs is 28% (by weight), mainly, copper, lead, and tin, points out Zhenming cuses on technologies capable of With the February 2009 deadline Xu, the corresponding author of capturing or creating usable mafor the U.S. switch to digital telethe ES&T papers discussed in terials from the printed circuit vision signals fast approaching, this article. boards (PCBs) used in electronconsumers are expected to inun“One metric ton of PCBs conics. PCBs are by weight the most date the country’s landfills and tains more than 10 times electronics recycling centhe concentration of preters with millions of obsocious metals contained in lete TVs. Although the content-rich minerals. federal government has Therefore, from the reyet to invest substantially covery of valuable matein technologies for recyrials and wastecling old electronics, a management viewpoints, small but vocal group of recycling of PCBs is sigacademic researchers, innificant,” Xu says. St. Dedustry scientists, and envinis adds, “Recycling can ronmental organizations is play a positive role in adtrying to change the status dressing climate change quo. The group hopes to by conserving resources persuade policy makers to initiate funding to cope A significant proportion of e-waste, like discarded TVs, ends such as precious metals contained in electronics with what the Electronics up in developing countries, where it is burned, releasing toxic dioxins into the air. and displacing the energy TakeBack Coalition, an valuable component of waste impacts associated with environmental group, calls electronics, says Renee St. Demining or otherwise producing “the fastest growing waste stream nis, director of Hewlett-Packnecessary raw materials.” in the U.S.” ard’s (HP’s) Product Take Back Xu and his colleagues are foIn the meantime, other counoperations, which recycles more cusing on how a technology tries are conducting important electronics than any other comknown as corona electrostatic research into new technologies pany operating in the U.S., acseparation, which is widely used for recycling electronic waste or cording to the U.S. EPA. in the mining industry, can be “e-waste”. Three papers recently Because the components of used for separating waste PCBs published in ES&T and Energy & PCBs vary widely, a major chal(Environ. Sci. Technol. 2007, 41, Fuels discuss solutions being relenge for recyclers is separating 1995-2000; 2008, 42, 624-628). searched in China and Eastern the semiconductor chips, metals, The technology separates materiEurope. wires, and plastics into usable als on the basis of the particles’ Developing such technologies materials. The standard proceability to conduct electricity. Paris challenging because of the dure is to use magnetic and ticles that conduct electricity are toxicity of many electronics eddy current processing to sepacharged by electrostatic induction components. According to the rate the magnetic fraction (iron and attracted to an electrode. Silicon Valley Toxics Coalition, and steel) and aluminum, says What Xu calls “ion bombardan environmental group, just the University of Cambridge’s ment” of the second electrode one computer can contain hun(U.K.) Derek Fray, a professor of then pins the nonconductive pardreds of chemicals, including materials chemistry who is also ticles to the surface of a rotating lead, mercury, cadmium, bromideveloping technologies for reroll electrode. nated flame retardants (BFRs), cycling PCBs. “The extreme difference in the and polyvinyl chloride. Many of For the past 5 years, researchelectric conductivity or specific these chemicals are known to ers at China’s Shanghai Jiao electric resistance between metcause cancer, respiratory illness, Tong University’s School of Enals and nonmetals supplies an and reproductive problems. And vironmental Science and Engiexcellent condition for the sucburning e-waste can produce neering have been investigating cessful implementation of a coharmful dioxins. how to improve the efficiencies rona electrostatic separation in Much of the research into imof technologies capable of such recycling of [e-]waste,” Xu says. proving e-waste recycling foISTOCKPHOTO
Producing usable materials from e-waste
6782 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / September 15, 2008
10.1021/es801954d
2008 American Chemical Society
Published on Web 07/30/2008
The latest incarnation of the technology, which is used with a two-step separation process, is discussed in one of Xu’s new papers. Tests by Xu’s team show that it can improve production speeds by 50%, compared with conventional electrostatic separation, while significantly reducing the percentage of PCBs that cannot be recycled. “The important thing is to get a clean separation between the metallic and nonmetallic components for subsequent processing,” Fray says. “The work by [Xu’s team] seems to achieve that goal and is probably a significant advance,” he says. Once the metals are separated from the nonmetals, the conventional approach is to send the waste metals to a copper-smelting operation equipped with environmental controls to capture emissions such as SO2, according to St. Denis. There are currently four such smelters in the world, she says. “[Smelting] enables the copper and the precious metals to be recovered, but many other metals are lost to the slag phase, which is discarded,” Fray adds. The second paper by Xu’s team shows how the nonmetal portions of waste PCBs can be used to produce what they call a “kind of nonmetallic plate.” They contend that this plate’s chemical composition and mechanical performance are preferable to those of wood and that the material could be used for products such as sewer grates, park benches, and fences. “We strongly believe that [the] nonmetallic plate[s] have [a] potential market in [the] building industry,” Xu says. He says that he signed a contract on the recycling of waste PCBs with Shanghai Xin Jinqiao Industrial Waste Management Co., Ltd., in May and
that “we will produce large-scale prototypes using a high-quality compression machine . . . in the near future.” The presence of BFRs, such as tetrabromobisphenol A (TBBPA, the main flame retardant used in PCBs), in this nonmetal plate is a cause for concern, according to Pat Costner, science adviser to the International POPs Elimination Network, a nonprofit environmental group. TBBPA’s use is not banned or restricted in any countrysalthough Norway has been considering such a bansbut the chemical could end up in the nonmetal plate, together with any dioxin-like compounds that previous research has shown can form during e-waste processing, she notes. Xu concurs that further studies are needed to investigate the presence of BFRs in his group’s nonmetallic plate. He also points out that they “may be considered as a flame retardant for the nonmetallic plate.” Because BFRs cannot be removed from the plastics portions of electronics products, this “presents a significant recycling and reuse challenge,” St. Denis says. In her testimony at a hearing on e-waste held in late April by the U.S. House of Representatives’ Committee on Science and Technology, she urged Congress to support research on reuse opportunities for plastics containing banned or restricted chemicals, such as PBDE flame retardants. Although she says that HP has pledged to stop using BFRs in its products by 2009, she points out that bromine is contained in the vast majority of e-waste that is currently being recycled. The third recent paper to discuss a technique for processing waste PCBs was written by a team
of researchers from Romania and Turkey led by Cornelia Vasile of Romania’s national Petru Poni Institute of Macromolecular Chemistry. They used pyrolysis to produce a fuel oil from the waste and succeeded in removing “almost all of the hazardous toxic components” in their attempts to render it suitable for use by the petrochemical industry. “The process might be cost-effective if it could be integrated in a petrochemical plant using the existent installations and equipment,” Vasile contends. But the team has yet to approach companies to gauge their interest in the process, she adds. “The yields do not seem very high, and it is probably cheaper to prepare these oils, etc., by more conventional routes,” Fray says. Eric Williams of Arizona State University’s department of civil and environmental engineering agrees. However, the technique does address the problems posed by BFRs in waste PCBs, says Williams. In the long run, “green” design and engineering focused on designing electronics products for recyclability and reducing their use of toxic materials should solve many of the problems currently associated with e-waste, argues Ted Smith, chair of the nonprofit Electronics TakeBack Coalition. In fact, he is convinced that forwardlooking companies like HP are already beginning to make important headway in tackling these issues. However, Smith stresses that such innovative design cannot help companies—or governments—cope with the e-waste problems they are facing right now. —KELLYN BETTS
September 15, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 6783
