39 JULY 2023 WorldWide Drilling Resource® Recovering Rare Earth Elements in a Flash Adapted from Information by Rice University Rare earth elements (REEs) aren’t actually rare at all; they are simply hard to get and hard to recycle, but a flash of intuition led Rice University scientists toward a possible solution. Rice University chemist James Tour explained how his lab successfully extracted enough REEs from waste to resolve issues for manufacturers using its flash Joule heating process. The flash Joule heating process, first introduced in 2020, is capable of producing graphene from any solid carbon source. It has now been applied to three sources of rare earth elements - coal fly ash (CFA), bauxite residue, and electronic waste - to recover rare earth metals, which have magnetic and electronic properties. “The U.S. used to mine rare earth elements, but you get a lot of radioactive elements as well,” Tour explained. “You’re not allowed to reinject the water, and it has to be disposed of, which is expensive and problematic. On the day the U.S. did away with all rare earth mining, the foreign sources raised their price tenfold.” There’s plenty of incentive to recycle what’s already been mined. Much of it is piled up or buried in fly ash, the by-product of coal-fired power plants. “We have mountains of it,” Tour said. “The residue of burning coal is silicon, aluminum, iron, and calcium oxides that form glass around the trace elements, making them very hard to extract.” While industrial extraction from these wastes commonly involves leaching with strong acid, a time-consuming, nongreen process, the Rice lab heats fly ash and other materials (combined with carbon black to enhance conductivity) to about 5430ºF (3000ºC) in a second. The process turns the waste into highly soluble “activated REE species.” According to Tour, treating fly ash by flash Joule heating, “breaks the glass that encases these elements and converts REE phosphates to metal oxides that dissolve much more easily.” In experiments led by postdoctoral researcher and lead author Bing Deng, researchers found flash Joule heating CFA more than doubled the yield of most of the REEs using very mild acid compared to leaching untreated CFA in strong acids. “The strategy is general for various wastes,” Bing said. “We proved that the REE recovery yields were improved from coal fly ash, bauxite residue, and electronic wastes by the same activation process.” Bauxite residue, sometimes called red mud, is the by-product of aluminum production, while electronic waste comes from outdated devices like computers and smart phones. The generality of the process makes it especially promising as millions of tons of bauxite residue and electronic waste are also produced every year. Rice University chemist James Tour and postdoctoral researcher Bing Deng setting up a flash Joule heating experiment. Photo by Jeff Fitlow. MIN 2023 JUBILEE Booth 1611
RkJQdWJsaXNoZXIy NDk4Mzk=