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There鈥檚 gold in them thar SIM cards, but most of it gets thrown away. In 2016 alone, discarding electronics wasted gold worth a reported . Currently only 20 per cent of e-waste is recycled, but that could get a boost thanks to a cheap way of chipping the gold off SIM card surfaces with ultrasound.

of Sandia National Laboratories in Albuquerque, New Mexico, and his team developed a process that induces cavitation 鈥� microscopic bubbles that crop up when sound is passed through water 鈥� on the surface of SIM cards. These bubbles explode violently, producing high pressures and temperatures as high as 4700掳C.

鈥淲e believe, but haven鈥檛 proven, that the ejected metal is actually molten,鈥� Huber says. They鈥檝e shown that their technique can harvest gold and nickel, soft and hard metals respectively, and an alloy of gold and silver.

Soap and water

To extract gold from surfaces such as SIM cards, Huber鈥檚 team first covered them with a cheap surfactant whose molecules form a single layer on the surface. Then they poured on a thin layer of another surfactant, and finally covered the whole arrangement with water.

When they exposed the SIM cards to ultrasonic waves, microscopic bubbles formed and naturally collapsed violently, creating tiny but powerful explosions that cratered the surface. From the craters, microjets of gold particles were ejected as debris and got captured in the liquids above, from which they could later be easily extracted.

鈥淚t could be applied to reclaim some of the $3.5 billion-worth of palladium waste, and while requiring further investigation, it should be applicable to rare-earth metals, the next target we鈥檒l investigate in detail,鈥� says Huber.

He says the process is cheap and has practically no environmental impact, unlike existing processes for extracting precious metals from electronic waste that rely on incineration or harmful solvents.

鈥淐onventional methods may release dioxins into the environment, for example,鈥� says , technical director of the British Metals Recycling Association in Huntingdon, UK. 鈥淗owever, we鈥檙e not yet clear on whether the technique is economically viable, or scalable to deal with the huge quantities of e-waste currently collected, treated and recycled,鈥� he says.

Read more: Gadget boom sees e-waste in Asia spike 63 per cent in 5 years