No battery lasts forever. Even the rechargeable lithium-ion batteries used evermore in tablets, laptops and smartphones don’t have an indefinite lifespan. Although there are international regulations controlling the disposal of these batteries, many still end up in landfills or incinerators. Not only can this harm the environment, but the valuable resources are also not recovered, resulting in an increase in demand and price for lithium. In the long run, this is not sustainable. Batteries being burnt also generate potentially toxic air emissions. Although it’s unclear how many electronic products are recycled, the U.S. leads the way globally as the largest generator of electronic waste.
Researchers at the University of South Florida have shifted their attention from extracting metals from waste slag left over from smelting operations, to using the same techniques to extract cobalt and lithium from waste batteries. Jeffrey A. Cunningham, Ph.D., the project’s team leader, attributes the idea to a student who had been using naturally occurring fungi in the extraction process. One of the benefits of this method is that it is environmentally friendly.
Cunningham describes fungi as a very cheap source of labor. Other methods used to extract cobalt, lithium and other metals from used batteries use harsh chemicals and require high temperatures – both of which are not environmentally friendly. By using fungi and placing them in an environment where they can do their work, Cunningham’s team has found an environmentally safe way to achieve the same result.
Cunningham and Valerie Harwood, Ph.D., originally selected three specific strains of fungi (Penicillium chrysogenum, Penicillium simplicissimum and Aspergillus niger) because it is known they are effective at extracting metals from waste products. Logic dictates that if the extraction mechanisms is similar, this trio could also work to extract lithium and cobalt from used batteries.
The process starts by dismantling the batteries and pulverizing the cathodes. The remaining pulp is then exposed to the fungus. Organic acids naturally produced by the fungi leaches the metals out of the batteries. The researchers’ aim is to extract nearly all of the original valuable cobalt and lithium using this method.
One of the three acids generated, gluconic acid, was found not to be effective for extracting either lithium or cobalt. The other two organic acids, citric acid and oxalic acid, extract as much as 48 percent of the cobalt and an impressive 85 percent of the lithium from the pulverized cathodes. After extraction by the fungi, the metals currently remain in a liquid acidic medium.
The team’s next challenge is to remove the two elements from that ‘soup’. Although they have some ideas on how to go about this, these have not yet been tested as they first focused on getting the initial extraction done. Further research is also done in fungal bioleaching for spent rechargeable batteries by exploring the acids different fungal strains produce.