Sandia uses citric acid to extract Rare Earth elements from common coal ash

Globally just three countries, with one being China, control over 85% of all of the world’s rare earth metals which is why many governments are racing to try and find new compounds and materials that can replace them, and there’s been some success, albeit fleeting.

Rare earth metals are used in some of the most cutting edge products today, from semiconductors and quantum computers to weapons systems, and are so important they’re considered a national security matter, so this week many experts paused for breath when Sandia National Laboratories announced that its researchers have successfully extracted Rare Earth Elements (REEs) from common coal ash using little more than food grade citric acid which s found in citrus fruits. And, if this extraction method proves economically and industrially scalable, this could be tremendous news for several reasons.

REEs are a collection of 17 metals - the 15 lanthanides on the Periodic Table of the Elements, as well as Scandium and Yttrium - that are essential to the production of high-tech consumer devices such as cell phones and computer hard drives, defense industry components such as electronic displays and guidance systems, and clean energy products such as EV batteries and generators in wind turbines. As such, the demand for REEs is enormous, and is expected to grow astronomically in coming years.

The usual method for producing REEs is through heavy mining, and then the chemical extraction and precipitation of the REEs from the mined ore. China has long dominated REE mining and extraction, and while their total global mining share is dropping as other nations ramp up their efforts, they still account for about 50% of REE mining. One big reason for that is that environmental regulations make it difficult in developed countries to both mine the necessary ore, and to chemically extract the REEs. Mines take years and sometimes decades for approvals in the US, and regulations for handling the chemicals traditionally used make it difficult to process ore there economically.

Sandia’s use of citric acid would be a tremendous breakthrough on the processing end. It’s naturally present in citrus fruits, as well as pineapple and tomatoes. It’s a commonly used ingredient in canned foods, soft drinks and wine. So it would present a much more environmentally friendly extraction method than the highly toxic chemicals that are currently used.

The new extraction method is also focused on coal ash, which is waste from burning coal that’s relatively rich in REEs with concentrations ranging from 192 to 1668 ppm, and so the two pieces of news have huge potential benefits for the US and other governments around the world.

For starters they eliminate the need for mining, which as mentioned above can be a difficult proposition in developed nations. Coal ash exists in staggering quantities in the US, in over 1,400 landfills in 45 states, to the tune of billions of tons nationwide, and the country continues to generate over 130 million tons of coal ash annually with a number of projects already underway looking at extracting the REE content from this waste and from other coal resources.

For example, the University of Wyoming School of Energy Resources (UW-SER) was awarded two grants from the Department of Energy (DOE) for projects that both kicked off on September 1, one in the Powder River Basin and the other in the Greater Green River and Wind River Basins.

“The UW-SER, in cooperation with the DOE, has been researching rare earth elements resources that lie in coal and coal ash,” said Scott Quillinan, Senior Director of Research at UW-SER. “The research program seeks to develop a full domestic supply chain for rare-earth elements including exploration, mining, extraction, processing and manufacturing. We are realizing that the rare earth element resources in Wyoming’s coal basins could be a substantial global resource. Rare earth element extraction technologies like the one being developed at Sandia, and at other national laboratories, are an important piece of the puzzle.”

What’s more, the Sandia announcement spells out how the extraction of the REEs from coal ash detoxifies it as well, making it more attractive for reuse in other products, such as wallboard, concrete, roofing materials and bricks. That could help begin whittling down the vast quantities of coal ash around the country, which present an ongoing environmental challenge due to the threat of leakage of toxic residues.

“Today roughly 40% of coal ash is recycled and reused in various building products, for example cements, plasters, wallboard, soil amendments, etc.,” Quillinan said. “Rare earth element recovery from the coal ash is another added benefit.”

There are some challenges hidden in the positive news from Sandia, however.

“This appears to be an innovative concept for leaching REEs from fly ash and coal refuse,” said Donna Castro, CEO and Partner at PMO Virginia a company that researches and promotes innovative uses of coal and coal refuse, including REE extraction.

“While this eco- friendly technology may offer multiple advantages such as being biodegradable, it does face a few challenging questions. For example, the recovery rate is lower, approximately 42%, as compared to 80% recovery rates in current methods we have experienced. The length of time it takes to leach the material appears to be 24 hours as compared to a few hours with traditional methods. The question of whether it’s economically viable and the methodology effective in terms of the separation and isolation of each REE, as well as the recovery of other elements such as aluminum and iron need to be addressed as well as the consumption rate of the citric acid.”

Clearly further R&D is required to fully determine the viability of the Sandia breakthrough, but any means for domestic production of much needed REEs is a huge boost for the US because not only is China currently half of the global source for the metals themselves, but it also produces 95% of the world’s finished REE components. Providing domestic sources for these critical metals, combined with various ongoing efforts to build up domestic finished components production, will help reduce the US’ reliance on potentially hostile international suppliers.