Fungus promises to crack Li-ion battery recycling problem

American researchers have successfully used three types of fungus to extract lithium and cobalt from spent lithium-ion batteries.

The discovery, described as the world’s first, paves way for an innovative recycling process that could potentially solve the battery waste problem.

“The demand for lithium is rising rapidly, and it is not sustainable to keep mining new lithium resources," said Jeffrey A Cunningham, leader of the research team at the University of South Florida. "The idea first came from a student who had experience extracting some metals from waste slag left over from smelting operations. We were watching the huge growth in smartphones and all the other products with rechargeable batteries, so we shifted our focus.”

Though rechargeable, Li-ion batteries lose their capacity over time. Eventually, they deteriorate so much that they can no longer serve their original purpose. As no commercially available recycling method currently exists, most of the batteries end up in landfills or incinerators. At this stage the batteries still contain expensive materials that are also potentially harmful to the environment.

The fungi method developed by the South Florida team has several advantages over other recycling techniques.

Cunningham said the method is safer and potentially cheaper as it requires neither high temperatures nor harsh chemicals.

"Fungi are a very cheap source of labour," the researcher said. "Fungi naturally generate organic acids, and the acids work to leach out the metals."

Based on previous experiments with metal extraction from other types of waste products, Cunningham and his colleague Valerie Harwood selected three strains of fungi – aspergillus niger, penicilium simplicissimum and penicillium chrysogenum.

"We reasoned that the extraction mechanisms should be similar, and, if they are, these fungi could probably work to extract lithium and cobalt from spent batteries," Cunningham explained.

For the process to work, the batteries first need to be dismantled and their cathodes, which contain the metals, pulverised.

"Through the interaction of the fungus, acid and pulverized cathode, we can extract the valuable cobalt and lithium,” said Cunningham. “We are aiming to recover nearly all of the original material."

In the experiments, the researchers found that oxalic and citric acid generated by the fungi can retrieve up to 85 per cent of the lithium and 48 per cent of the cobalt.

Following the extraction, the metals remain trapped in a liquid acidic medium.

"We have ideas about how to remove cobalt and lithium from the acid, but at this point, they remain ideas," Cunningham admitted. "However, figuring out the initial extraction with fungi was a big step forward."

Other researchers are also using fungi to extract metals from electronic scrap, but Cunningham believes his team is the only one studying fungal bioleaching for spent rechargeable batteries.

 

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