Recently, a team of researchers from Nanyang Technological University (NTU) in Singapore successfully developed a method using extracts from discarded fruit peels to recycle precious metals from used lithium-ion batteries, thereby creating new, low-cost, and environmentally friendly batteries.
In a practical experiment, scientists used extracts from orange peels to efficiently recover precious metals from battery waste. They then manufactured new batteries from these recovered metals. This approach, which transforms waste into a resource, would simultaneously address two problems: food waste and electronic waste, while supporting the development of a less wasteful circular economy where resources are used for as long as possible. It is estimated that approximately 1.3 billion tons of food waste and 50 million tons of electronic waste are generated globally each year, placing a huge burden on the environment and requiring extensive cleanup and disposal efforts.
Used batteries are often processed at high temperatures (above 500°C) to melt down valuable metals. This process releases dangerous toxic gases and secondary pollutants that pose risks to human health and the environment. This is why scientists are driven to find biodegradable materials that are both safe and sustainable.
"In Singapore, a resource-scarce country, the process of extracting precious metals from all kinds of discarded electronic devices is extremely important. With this method, we not only address the issue of resource depletion by keeping as many precious metals reusable as possible, but also the problem of accumulating electronic waste and food waste," said Professor Dalton Tay, a member of the research team.
Sustainable, low-cost approach
The 'hydraulic metallurgy' method—using water as a solvent for extraction—is increasingly being studied as a viable alternative to current, costly, and highly toxic battery waste recycling processes. This method involves shredding and grinding used batteries to form a pulped material known as 'black mass.' Researchers then extract valuable metals from the black mass by dissolving it in a mixture of strong or weak acids plus other chemicals such as hydrogen peroxide under heat, before allowing the metals to precipitate. However, while relatively more environmentally friendly than conventional methods, the industrial-scale use of such strong chemicals can still generate significant amounts of secondary pollutants, posing safety and health risks.
The NTU research team discovered that a combination of dried, powdered orange peel and citric acid, a weak organic acid found in citrus fruits, can achieve a similar goal, but in a much safer way.
In practical experiments, the research team found that their method successfully extracted approximately 90% of cobalt, lithium, nickel, and manganese from used lithium-ion batteries, achieving an efficiency comparable to the method using hydrogen peroxide.
"The key lies in the cellulose found in orange peels, which is converted into sugars by the heat generated during the extraction process. These sugars help enhance the recovery of metals from battery waste. In addition, some of the natural antioxidants in orange peels, such as flavonoids and phenolic acids, may also contribute to this process ," Professor Dalton Tay said.
More importantly, the solid residues generated from this process are considered non-toxic, indicating that this is truly an ideal method in every respect.
Using the recovered metal, scientists are continuing to create new lithium-ion batteries with similar charging capabilities to commercial batteries. Further research is underway to optimize the charge-discharge cycle performance of this new type of battery.
In addition, the research team is currently seeking to further improve the performance of batteries created from processed waste, as well as optimize conditions for scaling up production and explore the possibility of eliminating the use of acid in the process.
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