Finding and extracting enough rare earth minerals to power the growing number of mobile phones is a tough challenge that can wreak havoc on the environment — but new techniques could help.
Researchers say they have removed valuable rare earth elements (REE) from waste at high enough yields to resolve issues for manufacturers while boosting their profits. The scientists said in a recent paper that their process is kinder to the environment because it uses less energy than other methods and turns the stream of acid often used to recover the elements into a trickle.
“A smartphone can have as many as eight different REEs in it,” Rice University chemist James Tour, the author of the study, told Digital Trends in an interview. “The red, blue, and green screen colors are enhanced by REEs, as are the vibrating mechanism and the speakers.”
Tour’s lab used a special heating process that produces graphene from any solid carbon source to recover rare earth metals. The minerals have magnetic and electronic properties critical to modern electronics and green technologies.
While industrial extraction from coal fly ash, bauxite residue, and electronic waste usually involves strong acid — a time-consuming, non-green process — the Rice lab heats fly ash and other materials to about 5,432 degrees Fahrenheit in a second. The process turns the waste into highly soluble “activated REE species.”
Tour said 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.” Industrial processes use a 15-molar concentration of nitric acid to extract the materials; the Rice process uses a much milder 0.1-molar concentration of hydrochloric acid that still yields more product.
The researchers found flash heating coal fly ash (CFA) more than doubled the yield of most rare earth elements using very mild acid than leaching untreated CFA in strong acids.
“The strategy is general for various wastes,” Bing Deng, one of the researchers, said. “We proved that the REE recovery yields were improved from coal fly ash, bauxite residue, and electronic wastes by the same activation process.”
Deloitte Global predicts that smartphones — the world’s most popular consumer electronics devices that are expected to have an installed base of 4.5 billion in 2022 — will generate 146 million tons of CO2 or equivalent emissions this year alone.
“The fast turnover of new phones each year is a problem as we consume technology at a fast pace, which also has environmental impacts,” Alexander Gysi, a professor in the Department of Earth & Environmental Science at the New Mexico Institute of Mining & Technology, told Digital Trends in an interview.
While recycling would help cut emissions, mining is still cheaper and necessary to keep up with the growing demand for tech devices, said Gysi. Every year, their components become smaller and lighter, have a higher battery life, and are remixed to increase the quality of displays, he added.
“Our cell phones are supercharged with the REE and other metals like copper and gold; hence being able to reuse some of the parts to extract REE would be beneficial, but we are not there yet.”
Gysi said that extracting REE from natural mineral deposits can be difficult, because these different REEs occur together in various mineral types. To extract the minerals requires mechanical or physical separation as well as chemical separation.
“This process can also involve chemicals that need to be treated carefully via mine waste recovery,” Gysi said. “With the mining and extraction regulations in North America, it could be beneficial to do it locally and in a responsible way, but it is likely to be more expensive and needs incentives to do so.”
Gysi’s lab is working on new REE extraction techniques. The researchers investigated how REEs are separated chemically in natural systems in supercritical hydrothermal fluids in the Earth’s crust.
“These are essentially high temperature and pressure water solutions,” Gysi said. “We study how different acid/bases and ligands like chloride, fluoride, and hydroxyl can bind to the REE, enhance their solubility, and even help fractionate them. This will permit predicting these metals’ solubility and fractionation behavior and could also potentially be used to develop new technologies.”
Computers might also boost efforts to find rare minerals. Researchers have proposed an artificial intelligence (AI) system that could study a database of rare earth minerals, recognize patterns, and then enable it to spot new potential matches.
Before the advent of AI or machine learning (ML), the discovery of new materials was based on trial and error, materials scientist Prashant Singh, from the Ames Laboratory at Iowa State University and the author of the new study, told Digital Trends in an interview.
“The process to take a newly discovered material from lab to market may take 20-30 years, but AI/ML can significantly speed up this process by simulating material properties on computers before setting foot in a lab,” Singh said. “This makes the AI/ML useful for discovering technologically useful compounds.”