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A solution that uses toxic waste to clean up toxins

Hazardous, I tell you - and I’m not talking about the manufacturers’ customer service. STEVE YEATER/AP

The manufacture of electrical and electronic equipment is one of the fastest growing industries in the world, fuelled by increased consumption and by the equipment’s relatively short lifespan. As a result the quantity of discarded and obsolete electronics (e-waste) is growing at an alarming rate, driven by the technological innovation that produces new models to buy, and the rising incomes of those who buy them.

The sharp increase in the amount of e-waste has meant devoting more attention to looking for novel ways of tackling the problem, as our research group has done. E-waste causes serious environmental problems worldwide. Huge volumes of scrapped computers, monitors, televisions and kitchen white goods are sent to landfill, as there are almost no industry incentives to recycle or re-use.

E-waste contains a lot of harmful elements: toxic metals such as arsenic, barium, beryllium, cadmium, hexavalent chromium, lead, mercury, and selenium. Add to that dioxins, brominated flame retardants, chloro-flouro carbons (CFCs), polychlorinated biphenyls (PCBs) and polyvinyl chloride which, despite being a very common plastic, is largely chlorine that is poisonous if burned and inhaled.

This is not municipal rubbish; it is hazardous, toxic waste. Left unchecked, dumping and inappropriate disposal will damage the environment and economic development for a long time, as in places like Ghana, Nigeria, India and China which receive millions of tonnes of e-waste from Europe and the US each year. However, many nations recognise this, and legislation such as the European Union’s Waste Electrical and Electronic Equipment (WEEE) Directive requires domestic collection and recovery rates of 45% within four years, 65% within seven years and bans the export of e-waste outside the EU.

Extracting value, not adding it

In recent years, a wider understanding of the problem and changing economics has led to better recycling and material recovery, including the valuable metals found in scrap electronics. The e-waste is divided into circuit boards, plastic cases, metal frames, glass screens and so on, before being shredded and pulverised. Various methods are then used so that the distinct metallic and non-metallic materials can be individually separated.

These methods – which include heating, grinding to a powder and dissolution, and centrifuges – take advantage of the materials’ different melting point, density, conductivity and electromagnetism. The drawback is that they are energy-intensive and costly, and hence only economically profitable if the products are of reasonably high value.

Although the metal concentrate – copper or gold reclaimed from the circuit boards, processors or memory chips for example – is marketable and suitable for re-use, the non-metallic, powdered remnant is worth little. It tends to be either dumped in landfill, creating further environmental problems, or used as industrial filler in the cement and asphalt industries. But since this residue, chiefly comprised of plastic and aluminosilicates, makes up a considerable amount of the e-waste stream, it’s essential to find a way of adding value to it. This would make the recycling process more profitable, attract more investors and decrease the amount of e-waste that ends up in landfills and incinerators, or pollutes the developing world.

Toxic e-waste that eats itself

Our research group at the Hong Kong University of Science and Technology has developed an innovative chemical process that alters the surface of this low-value waste material and converts it to a nanoporous material.

The team tested this modified material and found it excellent at cleaning up toxic heavy metal pollutants found in wastewater. When this material is applied to solutions containing toxic heavy metal ions they are attracted to its surface, as it functions as an adsorbent. In fact this material removes such pollutants much more efficiently than the current range of expensive, industrial adsorbents/ion exchangers commonly in use.

Economically speaking, this waste material that was once a circuit board has a very low cost, a high yield and the reaction requires only low temperatures – three major advantages this novel material has over its commercial counterparts. So it should be of great commercial interest – adding the necessary value to the recycling process that should help spur investment in keeping e-waste out of landfill. It is vital that society and the industry in particular adopt a more sustainable approach the problems of end-of-life electronics.

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