In 2022, the world produced about 62 million tonnes of electronic waste, which is enough to fill more than 1.5 million garbage trucks. This is 82% more than in 2010, and the number is expected to reach 82 million tonnes by 2030. Old laptops, phones and other devices in this waste often contain valuable metals like gold, but less than a quarter of it is collected and recycled properly.
A team at Flinders University has come up with a new way to get gold out of both e-waste and mined rock without using toxic chemicals like cyanide or mercury. Their method, published in Nature Sustainability, could make gold recovery safer for people and the environment.
Gold is important in many areas, from jewellery and currency to electronics, chemical manufacturing and aerospace. But most of the gold supply still comes from mining processes that use cyanide salts or mercury metal. Large-scale mining often uses cyanide to dissolve gold from ore, which can harm wildlife and contaminate the environment. Small-scale and artisanal miners often use mercury, which forms an amalgam with gold before being heated to release the metal. This is the largest source of mercury pollution on Earth and is dangerous for both miners and surrounding ecosystems.
The new process starts with trichloroisocyanuric acid, a chemical already used in water treatment and pool cleaning. When activated with a halide catalyst in salt water, it dissolves gold from ore or e-waste. The gold is then captured using a polysulfide polymer sorbent made from elemental sulphur, a cheap and abundant byproduct of the petroleum industry. This polymer can pick out gold even when other metals are present.
Once the gold is bound to the polymer, it can be recovered in high purity by either heating the polymer (pyrolysis) or breaking it back down into its original monomer building block (depolymerization). The polymer can then be remade and reused. The team also developed ways to recycle the leaching chemical and the water used in the process.
Tests showed the method works on ore, old computer circuit boards and other gold-containing waste. “Our goal is to support these miners economically while offering safer alternatives to mercury,” the researchers said, adding that millions of artisanal miners depend on mercury-based methods.
While the results are promising, the researchers say there is still work to do. They need to scale up production of the polymer, fine-tune the recycling steps and make sure the process is cost-competitive with traditional methods. They also see potential for “urban mining” — recovering gold from e-waste — which could reduce the need for environmentally damaging primary mining.
As the study notes, “Overall, this work provides a viable approach to achieve greener gold production from both primary and secondary resources, improving the sustainability of the gold supply.”
Source: The Conversation, Nature
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