Study finds safer method for rechargeable battery recycling

Researchers at Chalmers University of Technology in Sweden have come up with a new way of recycling the metals found in rechargeable batteries, with less harmful effects for people and the environment, while maintaining the same level of efficiency.

The study investigates how fossil-based chemicals used in metal recovery can be replaced with alternatives produced from renewable biomass.

To make metal recovery both efficient and economically viable, metals must be separated and purified before they can be reused. The production of batteries and other high-value products often requires metals of a high degree of purity.

In some cases, using higher-purity raw materials can lead to the exclusion of less favourable materials (for both the environment and human safety), such as mercury. For example, in the past, the shelf life of non-rechargeable batteries was extended by adding mercury to the zinc electrode. However, with higher-purity zinc, it is possible to produce an equally stable battery that is free from mercury.

“If we do not separate and purify materials during recycling, their quality will gradually deteriorate. Ultimately, we risk ending up with materials that can no longer be used in advanced applications, and the whole purpose of recycling is lost,” said Mark Foreman, Associate Professor at the Department of Chemistry and Chemical Engineering at Chalmers.

Solvent extraction is a widely used method for separating and purifying metals in battery recycling, as well as in mining, the nuclear industry and in other industrial sectors. Today, the diluents used in these processes are typically produced from fossil-based feedstocks.

“In our study, we wanted to demonstrate that renewable biomass, for example, by-products from the forestry industry, can be used to produce alternative diluents. In this case, we investigated two aromatic compounds that could also be used directly in existing industrial production lines,” said Daniel Keywan Hoffmann, PhD student at Chalmers and first author of the study.

The study shows that the aromatic compounds perform just as well as conventional commercial alternatives in the extraction of several important metals. Furthermore, they could be implemented directly in existing industrial production lines.

How the new biobased dilutents are created: The feedstock molecules are shown in blue on the left. These pass through sulfuric acid and create the new biobased dilutents, seen on the right in grey and white, which can be used for safer battery recycling. Image credit: Chalmers University of Technology | Mark Foreman

“It is expensive for industry to rebuild factories or invest in entirely new infrastructure to improve sustainability. If the existing processes and equipment can be used while simply switching to a significantly safer chemical, the barrier to change becomes much lower and far less expensive,” Hoffmann said.

The researchers found that the two aromatic compounds used in the study have higher flash points and lower volatility than several commercially used alternatives. This means a lower risk of fire and reduced exposure to hazardous substances for workers in recycling facilities.

“If we can achieve the same performance as current processes while reducing risks to people and the environment, that represents a significant benefit for everyone,” Foreman said.

The researchers emphasise that manufacturing processes would need to be optimised, and the availability of renewable feedstocks increased, to make the approach cost-effective.

“We hope our work can inspire industry to think differently. Sustainable alternatives do not necessarily require starting from scratch. In many cases, replacing certain chemicals may be enough,” Hoffmann said.

The study has been published in RSC Sustainability.

Top image credit: iStock.com/adventtr