A group of researchers and scientists in Singapore has discovered that orange peel can be used to extract precious metals from spent lithium-ion batteries.
Almost 1.5 billion tonnes of food waste and 50 million tonnes of used electronics are generated around the world every year. The novel solution tackles both waste streams at the same time and could lead to a ‘low-cost, sustainable approach to recycling the growing heaps of batteries that end up in landfill every year’, according to the R&D team at Nanyang Technological University.
Existing commercial processes for recycling spent batteries involve first chopping them up and then crushing them to make a powdery material. During the smelting process, the powder is heated beyond 500°C to separate the metals. In the leaching process, this material is treated with strong chemicals such as acids and hydrogen peroxide.
The Singapore scientists say this final process can be eliminated. Instead, they rely on oven-dried orange peels which are ground into a powder and then mixed with citric acid.
‘Using this mixture instead, we were able to extract around 90% of the lithium, cobalt, nickel and manganese from used lithium-ion batteries,’ reports materials science and engineering professor Dalton Tay. The result is similar to that possible with conventional chemical methods with the added benefit that the solid residue left behind is non-toxic.
‘The key to the extraction lies in the cellulose present in orange peels,’ explains Tay. Heat converts the cellulose into sugars that enhance the recovery of metals from battery waste while antioxidants in the peels, such as flavonoids and phenolic acids, could be helping as well.
The team used the recovered metals to make lithium-ion batteries, which stored almost as much charge as new batteries. The researchers are now working on improving the lifecycle of their recycled batteries.
‘With this solution, we not only have an answer to the problem of resource depletion by keeping these precious metals in use as much as possible but also the problem of e-waste and food waste – both a growing global crisis,’ Tay concludes.
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