Medical X-ray machines use electromagnetic radiation — radiant energy with wavelengths shorter those produced by visible light — to gain information about what is happening inside the human body. Likewise, airport security checkpoints employ X-rays to examine the internal contents of travelers’ baggage.
Similarly, NETL researchers are using powerful light sources at U.S. Department of Energy (DOE) facilities to enhance their fundamental understanding of rare earth elements (REEs) and their mysterious chemical bonds. In doing so, they hope to find a better way to optimize potential extraction of valuable REEs and other trace metals from rock, coal and coal combustion byproducts.
A synchrotron is a source of extremely bright light — including visible light, infrared light, ultraviolet light and X-rays — about 100 million times brighter than the X-rays used for medical imaging. Synchrotron technologies offer distinct advantages for geomaterials analysis, providing insight into a material’s chemistry, crystal structure, electronic structure and magnetic properties based on how its electrons, photons and more react to the radiation.
DOE synchrotron facilities have provided valuable data for NETL researchers investigating trace metal behavior within carbon dioxide storage reservoirs and caprocks, the impact of iron and sulfur chemistry on wellbore cements, uranium speciation within Marcellus shale and more. NETL’s Christina Lopano, Ph.D., and Mengling Stuckman, Ph.D., lead a team of scientists seeking to better understand the chemical structure of REEs found in coal and coal combustion byproducts using advanced characterization techniques available at the Stanford Synchrotron Radiation Light Source (SSRL) at the Stanford Linear Accelerator Consortium’s National Accelerator Laboratory in Menlo Park, California. (The facility is run for DOE by Stanford University.)
Seventeen elements within the periodic table are referred to as REEs, including the lanthanide series and elements scandium and yttrium. REEs are essential for modern technologies — such as cell phones, LED screens and solar panels — but they are often found in low concentrations and challenging to extract. China provides the bulk of the world’s supply.
Coal combustion byproducts, such as coal fly ash and acid mine drainage, are being explored as potential sources for a domestic supply of REEs; however, the REE binding environments within these waste products can be highly variable and remain largely a mystery to scientists.
“Advanced characterization is essential to develop an economically viable way to recover REEs,” Lopano said. “We need to better understand what is holding onto these REEs, so we can develop an effective method to optimize REE extraction and the recovery of a pure REE product.”
Innovative synchrotron-based characterization enabled researchers to detect and characterize trace amounts of REEs with greater precision and identify the most appropriate chemicals to target the REE-bearing phases and concentrate the REEs. Thanks to insights gained from NETL’s characterization research, scientists have used recyclable or biodegradable acids and organic solvents under mildly acidic and room-temperature bench-scale conditions to extract and concentrate REEs from coal fly ash, yielding an impressive 12 percent by weight total REEs. That outcome far exceeds NETL’s program goal of 2 percent by weight total REEs.
The team also modified an extraction method (based on the characterization results) to harvest REEs and other precious metals from passively remediated mine drainage solids, yielding products with 3 percent REEs and 16 percent cobalt, which has comparable market value and is used in manufacturing high-strength alloys.
As NETL seeks to develop technological solutions to the nation’s energy challenges, micro- and nano-scale insights are critical to expedite cost-effective technology development. Synchrotron facilities and other innovative tools within DOE’s national laboratory system are informing groundbreaking technologies aimed at finding alternative uses for coal byproducts to stimulate the economy and contribute to America’s energy independence.