Although rechargeable batteries in smartphones, cars and tablets can be charged again and again, they don’t last forever. Old batteries often wind up in landfills or incinerators, potentially harming the environment. And valuable materials remain locked inside. Now, a team of researchers is turning to naturally occurring fungi to drive an environmentally friendly recycling process to extract cobalt and lithium from tons of waste batteries.
The researchers will present their work today at the 252nd National Meeting & Exposition of the American Chemical Society (ACS). ACS, the world’s largest scientific society, is holding the meeting here through Thursday. It features more than 9,000 presentations on a wide range of science topics.
“The idea first came from a student who had experience extracting some metals from waste slag left over from smelting operations,” says Jeffrey A. Cunningham, Ph.D., the project’s team leader. “We were watching the huge growth in smartphones and all the other products with rechargeable batteries, so we shifted our focus. The demand for lithium is rising rapidly, and it is not sustainable to keep mining new lithium resources,” he adds.
Although a global problem, the U.S. leads the way as the largest generator of electronic waste. It is unclear how many electronic products are recycled. Most likely, many head to a landfill to slowly break down in the environment or go to an incinerator to be burned, generating potentially toxic air emissions.
While other methods exist to separate lithium, cobalt and other metals, they require high temperatures and harsh chemicals. Cunningham’s team is developing an environmentally safe way to do this with organisms found in nature — fungi in this case — and putting them in an environment where they can do their work. “Fungi are a very cheap source of labor,” he points out.
To drive the process, Cunningham and Valerie Harwood, Ph.D., both at the University of South Florida, are using three strains of fungi — Aspergillus niger, Penicillium simplicissimum andPenicillium chrysogenum. “We selected these strains of fungi because they have been observed to be effective at extracting metals from other types of waste products,” Cunningham says. “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.”
The team first dismantles the batteries and pulverizes the cathodes. Then, they expose the remaining pulp to the fungus. “Fungi naturally generate organic acids, and the acids work to leach out the metals,” Cunningham explains. “Through the interaction of the fungus, acid and pulverized cathode, we can extract the valuable cobalt and lithium. We are aiming to recover nearly all of the original material.”
Results so far show that using oxalic acid and citric acid, two of the organic acids generated by the fungi, up to 85 percent of the lithium and up to 48 percent of the cobalt from the cathodes of spent batteries were extracted. Gluconic acid, however, was not effective for extracting either metal.
The cobalt and lithium remain in a liquid acidic medium after fungal exposure, Cunningham notes. Now his focus is on how to get the two elements out of that liquid.
“We have ideas about how to remove cobalt and lithium from the acid, but at this point, they remain ideas,” he says. “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.
Cunningham, Harwood and graduate student Aldo Lobos are now exploring different fungal strains, the acids they produce and the acids’ efficiencies at extracting metals in different environments.
Learn more: Fungi recycle rechargeable lithium-ion batteries
Microbiologists unravel relationship among plants, mycorrhizal fungi
An ancient, mutually beneficial relationship between plants and fungi could make agriculture more sustainable by reducing the need for chemical fertilizers, according to professor Heike Bücking of the South Dakota State University Department of Biology and Microbiology.
For more than 500 million years, the majority of land plants have shared their carbohydrates with arbuscular mycorrhizal fungi that colonize their root systems, Bücking explained. In exchange, these fungi provide plants with nitrogen and phosphorous, and improve the stress resistance of their host.
These fungi are seen as living fossils and explore the soil with its hyphae in the search for nutrients, and deliver these nutrients to its host. As reward the host plant transfers anywhere from 4 to 20 percent of its photosynthetically fixed carbon to these mycorrhizal symbionts.
“We think these fungi have the potential to increase the biomass production of bioenergy crops and the yield of food crops and do so in a more sustainable and environmentally friendly way,” said Bücking. She studies these interactions in food and bioenergy crops including wheat, corn, soybeans, alfalfa, clover and perennial grasses, such as prairie cordgrass.
Her research has been supported by the National Science Foundation, South Dakota Wheat Commission, Sun Grant Initiative, Soybean Research and Promotion Council and the U.S. Department of Energy – Joint Genome Initiative.
Defining plant-fungi relationships
Supply and demand determine the amount of nutrients that plant and fungi exchange in this mutualistic relationship, according to Bücking. To unravel these complex interactions, she collaborates with researchers at the Vrije Universiteit in Amsterdam and the University of British Columbia as well as other South Dakota Agricultural Experiment Station researchers.
“Though a host plant is colonized by multiple fungi species simultaneously, the plant knows exactly where certain benefits are coming from. The host plant can distinguish between good and bad fungal behavior and allocates resources accordingly,” she said, noting that the host plant transfers anywhere from 4 to 20 percent of its photosynthetically fixed carbon to mycorrhizal fungi.
These fungi also form common mycorrhizal networks that give them access to multiple hosts. Her research showed that when host plants were shaded and thus decreased their carbohydrate allocation, fungi responded by reducing their nutrient share.
Optimizing fungi for specific crops
She and her collaborators have also found that some fungi are more beneficial than others. For example, Bücking and her collaborators evaluated the relationship between alfalfa and 31 different isolates of 10 arbuscular mycorrhizal fungal species.
They then classified the fungal isolates as high-, medium- or low-performance isolates. The researchers found that high-performance isolates increased the biomass and nutrient uptake of alfalfa by more than 170 percent, while the low-performance ones did not have any effect on growth.
However, those that benefit one crop may not provide the same nutrients or benefits to another crop species, she cautioned. “Even different isolates of one fungal species can behave differently, and it will be necessary to identify fungi that are optimally adapted to their specific environment and host plant to get the highest plant benefit.
Adapting to stressors
In addition to providing nutrients, these fungi can protect food and bioenergy crops from environmental stresses, such as drought, salinity and heavy metals, and diseases, Bücking explained. “All the stresses that a plant can potentially be exposed to are generally improved by mycorrhizal interactions.”
Increasing tolerance through conventional breeding generally targets only one specific stress factor, but crops are often subjected to multiple stresses simultaneously, she pointed out. “These fungi, if used efficiently, can provide the plant with an improved resistance against stresses that are often difficult for us to predict.”
However, she added, more research is necessary to better understand how this ancient symbiosis between land plants and fungi can be used to its full potential.