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Urban Mining and e-waste

Recovering gold from e-waste with new technology

Precious metals are some of the most valuable materials in e-waste; recycling them is important in the context of resource efficiency and avoiding pollution, says EU Commission’s Waste Electrical and Electronic Equipment recycling (WEEE). A big problem is that current methods of recovering gold and other metals from e-waste tend to use large amounts of energy, but researchers have proposed a new chemical-processing system that can be carried out at ambient temperature and pressure.

“Recovering resources from end-of-life products has been called ‘urban mining’, and will be important to achieve the aims of the EU’s circular economy. For example, gold may be recovered from circuit boards in computers and mobile phones, and from cables and jack connectors.”

WEEE says over 53 million tonnes (Mt) of e-waste was generated in 2019, predicted to grow to 74 Mt in 2030 Meanwhile, new electronics include about 8% of all gold produced each year – about 250 tonnes.

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“The researchers developed a method using a hydrometallurgical process, using chemical reactions in liquids. This is preferable to pyrometallurgical methods (using high temperatures), say the researchers, which produce harmful gases and dust, cost more, and require a large amount of energy. For example, some standard processes require materials to be heated to 1 200°C for 12 hours to separate components.”

“The process involves leaching elements from the waste material, followed by their selective recovery from a solution via chemical reduction.”

WEEE says results showed that 99% of gold from e-waste could be leached into the first solution, and, in separate tests on mobile phone PCBs and ceramic Intel CPUs, the researchers retrieved 95% and 80% of the leached gold.

“The final products were relatively pure, but they noted that some residual plastic remained in gold recovered from RAM. Similarly, high levels of platinum (89%) and palladium (100%) were recovered from spent catalytic converters, and 99% of palladium from turbine residues2.”

“This efficient process provides a way of recycling precious metals and preventing pollution from e-waste and other waste streams – such as from automotive and aircraft industries – say the researchers, though further optimisation could improve the degree of purity of recovered metals. If the technology could be scaled up, it may offer a more energy-efficient method of metal recovery than currently practised by commercial firms”, WEEE says.

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