Peggy Greb / USGOV-USDA-ARS.
Some rare earth oxides — clockwise from center: praseodymium, cerium, lanthanum, neodymium, samarium, and gadolinium.
New research has discovered a more efficient extraction method by reusing coal mining waste.
Researchers in the United States have developed a new method to extract rare earth elements (REEs) from coal mining waste, potentially offering a most efficient way to obtain essential materials for modern technologies such as electric vehicles, wind turbines and smartphones.
A team led by scientists at Northeastern University demonstrated a extraction process up to three times more efficient than existing approaches. The method uses a slurry of finely ground rock, water and coal waste left over after mining operations and is stored in large containment areas to prevent environmental contamination. The findings were in the journal Environmental Science & Technology.
Although rare earth elements are relatively abundant in the Earth’s crust, they are notoriously difficult to extract and purify. In coal waste, REEs are tightly bound to clay minerals, a structural challenge that has limited the effectiveness of previous recovery methods. As a result, much of this waste has been reused as filler in construction or discarded in landfills.
According to estimates cited by researchers, more than 600 kilotons of elements of rare earths in every 1.5 billion tons of coal waste, explains the .
The newly developed process involves two main steps. Firstly, the coal waste undergoes an alkaline pre-treatment, during which it is heated using microwave energy. Next, an acid digestion phase occurs with nitric acid, which separates the rare earth elements from the surrounding rock.
Alkaline and microwave treatment changes the structure of the minerals surrounding the rare earth elements, making the more porous material and easier to process. As a result, the subsequent acid treatment manages to release a significantly greater proportion of the valuable elements.
“It turns out that what we are doing is actually change the solid structure of this material,” said Damilola Daramola, a chemical biologist at Northeastern University and member of the research team.
One of the main elements recovered through the process is the neodymiumused in high-performance magnets found in electric motors, data storage devices and renewable energy technologies. Demand for neodymium and other rare earth elements is expected to grow rapidly as countries accelerate the transition to low-carbon energy systems.
Despite promising results, challenges remain. The process is currently expensive and may be difficult to scale up for industrial use. Furthermore, the composition of coal waste varies depending on location, meaning the method would have to be adapted to different locations. The researchers also note that other valuable elements present in coal waste, such as magnesium, could be extracted along with rare earth elements.
