Young-Shin Jun, a professor at the University of Washington has found a way to extract rare earths from coal fly ash, a fine powdery waste product of coal combustion.
In virtually all modern electronic devices, such as mobile phones, computers, televisions and even vehicles of all kinds, rare earth elements (REEs) are used, which comprise a group of 17 metallic elements.
Despite the fact that the demand for these elements has been increasing every year and, in fact, it is vital for the electric car industryits offer is limited by geopolitical factors and its extraction is carried out through environmentally unsustainable practices.
To address this problem, the professor of energy, environmental and chemical engineering at the McKelvey School of Engineering at the Washington University in St. LouisYoung-Shin Jun, together with his team, have developed a proof-of-concept solution that involves extracting REEs from coal fly ash, a fine powdery residue produced by coal combustion.
“We wanted to use a greener process to extract REE than traditionally more harmful processes”states Jun. “Since the charcoal has already been used, this process is ultimately a pathway to waste product reduction and remediation.”
How to extract rare earths from coal dust
The teacher Young Shin Jun and his former PhD student, Yaguang Zhu, now a postdoctoral fellow at Princeton University, have developed an innovative extraction process using supercritical fluid.
This is a substance that is in a state between liquid and gas when exposed to a temperature and pressure above its critical point. This method, commonly used to decaffeinate coffee, allows critically necessary REEs to be recovered from coal fly ash that would otherwise have been disposed of in a landfill.
According to Jun’s team, more than 79 million metric tons of ash coal flywheels each year in the United States, and the potential value of REEs that could be extracted from them is estimated at more than $4 billion annually.
In their study published in the March 2023 issue of RSC Sustainability, the team demonstrated that common and accessible supercritical fluids, such as carbon dioxide (CO2), nitrogen and air, can extract REEs and separate impurities very efficiently.
Furthermore, by experimenting with coal fly ash, they found that supercritical carbon dioxide reduces concentrations of impurities in the final REE product. The final products obtained contained up to 6.47% REEcompared to 0.0234% in the initial source of coal fly ash.
“The uniqueness of our work is not only using the CO2 supercritical, but also to show that supercritical air and nitrogenwith a temperature and pressure much lower than those required for CO2they can effectively extract REEs,” explains Jun, who also heads the Environmental Laboratory for Nanochemistry.
“We can use lower temperatures and pressures with nitrogen or air to extract the rare earth elements from coal fly ash, which means lower energy cost. Of course, the CO2 Supercritical works better, but supercritical air or nitrogen could do a much better job compared to traditional high-temperature boiling with acids and organic solvents for REE extraction.”
A two-step process
June’s team has developed a two-step extraction process that allows metal ions present in coal fly ash, including REEs and impurities, to be extracted using nitric acid to form metal nitrates.
In a second stage, metal nitrates react with tributyl phosphate to separate REEs from impurities. This multi-stage extraction process collects the REEs and reduces the concentration of impurities in the final product.
One advantage of Jun’s method is that does not require high roasting temperatures or strong acids and toxic organic solvents used in traditional extraction processes, which also reduces the amount of waste generated.
Additionally, the nitric acid and tributyl phosphate used in the process can be recycled multiple times without affecting its efficiency, minimizing disposal issues.
These advances in REE extraction from coal fly ash could be an important step towards eliminating unsustainable extraction practices and meeting the growing demand for these essential elements of modern technology.
Jun’s team now works with the university’s Office of Technology Management, which has applied for a patent on the process.
Why rare earths are important in the automotive industry
In the automotive industry, rare earths are especially important in the manufacture of electric motors and LED lighting systems for vehicles.
The electric motors They use permanent magnets that contain neodymium, a rare earth element. These neodymium magnets are especially valuable due to their high resistance to demagnetization, making them ideal for maintaining magnetic force in harsh conditions and at high temperatures.
As a result, the neodymium it is critical in the design of efficient and compact electric motors for electric vehicles.
In addition to neodymium, other rare earth elements such as dysprosium and praseodymium They are used in the manufacture of electric motors to improve the thermal stability and corrosion resistance of neodymium magnets.
As for the LED lighting systemsrare earths are also an important component.
LEDs use yttrium phosphor, another rare earth element, to convert the blue light generated by light-emitting diodes into white light for interior and exterior vehicle lighting.
