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Chemical Engineering

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Fruit peels help recover metals from e-waste

| By Gerald Ondrey

Scientists from Nanyang Technological University (NTU; Singapore;, led by professor Madhavi Srinivasan, have developed a method of using orange peel waste to extract precious metals from spent lithium-ion batteries and to make batteries from those recovered metals, creating minimal waste in the process.

“Currently, industrial e-waste recycling processes are energy-intensive and emit harmful pollutants and liquid waste, pointing to a need for eco-friendly methods as the amount of e-waste grows,” says Srinivasan. “Our team has demonstrated that this is possible with biodegradable substances.”

A method that has been increasingly explored involves hydrometallurgy, using water as a solvent for extraction. In this process spent batteries are shredded and crushed to form a material called “black mass.” Metals are then extracted from the black mass by dissolving it in a mix of acids and other chemicals, such as hydrogen peroxide under heat. However, using such strong chemicals on an industrial scale would generate a large amount of pollutants.

The NTU team found that the combination of orange peel that has been oven-dried and ground into powder, and citric acid, can achieve the same goal. The team found that its approach extracted about 90% of cobalt, lithium, nickel and manganese from spent lithium-ion batteries — an efficiency comparable to the method using hydrogen peroxide.

The key lies in the cellulose in orange peel. The cellulose is converted into sugars under heat during the extraction process. These sugars enhance the recovery of metals from battery waste. Antioxidants found in orange peel, such as flavonoids and phenolic acids may also have contributed to this enhancement. Solid residues generated from this process were found to be non-toxic.