Scientists have developed an innovative method of creating new batteries by using orange peel waste to extract and reuse precious metals from old lithium-ion batteries. The process is eco-friendly, efficient, and produces minimal waste.
The team, led by Singapore’s Nanyang Technological University (NTU), kills two birds with one stone with their waste-to-resource approach by tackling both food waste and electronics waste. This approach also supports the expansion of a circular economy with zero waste, in which resources are used for as long as possible.
Assistant Prof. Dalton Tay, of the NTU School of Materials Science & Engineering, said:
In Singapore, a resource-scarce country, this process of urban mining to extract valuable metals from all kinds of discarded electronics becomes very important. With this method, we not only tackle 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 accumulation – both a growing global crisis.
This is a significant find since approximately 1.3B tons of food waste and 50M tones of e-waste are produced globally every year.
Since the recycling process of e-waste releases harmful toxic gases, researchers have explored alternative approaches that use weak acid solutions with hydrogen peroxide to extract the metals or stronger acid solutions. However, these alternatives either rely on hydrogen peroxide, which is unstable and hazardous, or produce secondary pollutants that threaten health and safety risks.
Professor Madhavi Srinivasan, from NTU’s School of Materials Science & Engineering and the NTU Singapore-CEA Alliance for Research in Circular Economy (NTU SCARCE) lab, explained:
Current industrial recycling processes of e-waste are energy-intensive and emit harmful pollutants and liquid waste, pointing to an urgent need for eco-friendly methods as the amount of e-waste grows. Our team has demonstrated that it is possible to do so with biodegradable substances. These findings build on our existing body of work at SCARCE under NTU’s Energy Research Institute (ERI@N). The SCARCE lab was set up to develop greener ways of recycling e-waste. It is also part of the NTU Smart Campus initiative, which aims to develop technologically advanced solutions for a sustainable future.
Another alternative approach to recycling e-waste, called hydrometallurgy, uses water as a solvent for extraction. This technique involves grinding up used batteries to form a crushed material known as ‘black mass.’ Valuable metals are then extracted from the black mass by dissolving it in a mixture of either strong acids or weak acids that contain chemicals such as hydrogen peroxide under heat, before the metals precipitate.
The NTU scientists found that the combination of citric acid, a weak organic acid from citrus fruits, and oven-dried orange peels that are ground into powder can achieve comparable results. In the laboratory, the team successfully extracted approximately 90% of lithium, cobalt, manganese, and nickel from spent lithium-ion batteries using this approach.
Tay said:
The key lies in the cellulose found in orange peel, which is converted into sugars under heat during the extraction process. These sugars enhance the recovery of metals from battery waste. Naturally-occurring antioxidants found in orange peel, such as flavonoids and phenolic acids, could have contributed to this enhancement as well.
The team then used the recovered materials to assemble new lithium-ion batteries, which exhibited similar charge capacity to commercial ones. As a bonus, solid remains produced from this process were found to be non-toxic, suggesting that this method is environmentally comprehensive.
Prof. Srinivasan added:
This waste-to-resource approach could also potentially be extended to other types of cellulose-rich fruit and vegetable waste, as well as lithium-ion battery types such as lithium, iron, phosphate, and lithium, nickel, manganese, and cobalt oxide. This would help to make great strides towards the new circular economy of e-waste, and power our lives in a greener and more sustainable manner.
The NTU team published the study on July 9, 2020, in the scientific journal Environmental Science & Technology. NTU is one of Singapore’s top universities, and it’s a very beautiful one too! See the stunning campus for yourself in the photos below.
