New chemical separations enable battery recycling, biodiesel
When recycling cans and bottles, at some point it becomes necessary to separate out plastic from metal. When recycling car batteries, getting out the most valuable metals also requires a separation, but this time it entails a specific kind of chemical separation process.
The cobalt, manganese and nickel found in battery cathodes are expensive to mine and scientists have for years sought a way to create new batteries from spent ones.
When a car battery reaches the end of its life, it goes to an automotive shredder that chops it up. Getting out the useful chemicals from these chopped up batteries is no easy task. Researchers at the U.S. Department of Energy's (DOE) Argonne National Laboratory have turned to a process called capacitive deionization that uses the electric charges of nickel, manganese and cobalt to select them out from the waste stream.
"There are different separation technologies used for different purposes, based on physical principles, chemical principles and electrochemical principles," said Argonne engineer Lauren Valentino. "There's only so much you can do with mechanical processes in the first step, so we turn to things like membrane, adsorbent and capacitive deionization technologies, which can all be used to recapture chemicals of interest."
According to Valentino, battery recycling is complicated because not all car batteries are the same. “It’s hard to control what you get when it comes time to recycle a car battery,” she said. “When the battery is shredded, you have all sorts of things mixed together — cathode, anode, electrolyte and separator.”
Recycling a battery requires breaking down and separating large chemical components into basic elements. "Building a battery is like building a tower out of Legos," Valentino said. "You use small blocks with different shapes to build a tower, but if you want to re-build, you have to take apart and sort all of the bricks to get what you need."
One major advantage of capacitive deionization is that it is flexible. According to Valentino, it can be used to accommodate different materials and various operating strategies by controlling flow rates and operating time. "By controlling both the material and how it is implemented, we're able to really tailor the elements and chemicals that we're separating out," she said.
The capacitive deionization process that Valentino and her colleagues use for battery recycling also has uses in other areas, including bioenergy production. Valentino leads the Bioprocessing Separations Consortium, a group of researchers from six national laboratories that together research and develop separations processes and technology needed for the conversion of biomass to biofuel. (The group was established in 2016 by DOE's Bioenergy Technologies Office within the Office of Energy Efficiency and Renewable Energy.)
"At some point there is a conversion step followed by a separations process," Valentino said. "What comes out of these reactors is a complex mixture with many different components, and we have to be able to isolate and concentrate the products of interest in the system to catalytically upgrade them to produce the biofuels we're after."
Unlike the battery recycling technology, which targets positively charged ions, bioenergy production requires Valentino and her colleagues to search for negatively charged molecules. "Essentially, our capacitive deionization acts like a 'claw' that picks out the molecules we're interested in."
Once separated, these compounds are versatile and can be converted into hydrocarbon biofuels, such as renewable diesel or sustainable aviation fuel. "We are just beginning to explore the different ways in which more efficient separations can make transportation more sustainable," she said. "There's still much we have left to discover."
This research is funded, in part, by the National Science Foundation.
Source: https://www.anl.gov/