PNNL studies carbon negative REE mining

Chosen as one of 16 projects across 12 states, Pacific Northwest National Laboratory's "Re-Mining Red Mud Waste for CO2 Capture and Storage and Critical Element Recovery" (RMCCS-CER) project will receive $1 million in funding to advance a technology that may kill two birds with one stone in the race for critical materials.

Announced in November, as part of the U.S. Department of Energy's Advanced Research Projects Agency-Energy (ARPA-E) Mining Innovations for Negative Emissions Resource Recovery (MINER) program, $39 million in funding will be split between 16 projects to develop market-ready technologies intended to increase domestic supplies of critical elements required for the clean energy transition.

The selected projects, led by universities, national laboratories, and the private sector, aim to develop commercially scalable technologies that will enable greater domestic supplies of copper, nickel, lithium, cobalt, rare earths, and other critical elements.

And one of those projects is PNNL's research on bauxite residue, otherwise known as red mud.

Led by PNNL chemical engineer Xin Zhang and joined by Arizona State University Professor Alexandra Navrotsky, the objective of the project is to use supercritical carbon dioxide to recover critical elements, especially rare earth elements, from aluminum production wastes while also capturing some of the CO2 in stable carbonates.

Perhaps one of the most potentially viable solutions to retrieving critical elements, REE separation technologies are being pushed to the forefront to offset the need for these valuable materials in renewable energy tech like solar panels, wind turbines, and every battery and engine in electric vehicles.

However, this is so far proving not enough, so research avenues into other methods have become imperative, such as the readily abundant red mud that lies strewn in waste pits throughout the world.

Two birds with one stone

As it turns out, the tailings left behind from mining aluminum, as well as copper, gold, silver, zinc, and other more common metals, offer potential unconventional sources of critical minerals while also chalking up a win for the environment.

It is estimated that the tailings disposed of by mining companies each year contain US$112 trillion worth of raw materials, with just 1% of that value being enough to make a fortune 500 company.

Among the most common examples of this potentially valuable waste comes from the process of aluminum refinement; the residue becomes something known as bauxite tailings or "red mud."

For every ton of alumina produced, nearly two tons of this red mud is left behind – a Tesla car is made of about one ton of aluminum, yet this produces roughly three to four tons of more red mud.

You can read into greater detail about red mud waste and other unconventional critical mineral recovery at Outside-the-box critical minerals sources in the Critical Minerals Alliances 2022 magazine, published by Data Mine North in September.

Already researching methods to capture CO2 in natural basalt formations, PNNL thinks it can combine the benefits of reducing bauxite waste and recovering critical minerals with carbon capture to ultimately produce a multiplicative effect in reducing environmental hazards.

You can read about PNNL's research into carbon capture at Rock solid technique for capturing CO2 in the October 26, 2022 edition of Metal Tech News.

Combining in-situ and ex-situ techniques to determine the solubility and thermodynamic features of rare earth minerals, PNNL's project will begin like most research endeavors, with data.

As these minerals include carbonates produced by reacting CO2 with rare earths, this information on the most effective chemistries, among other things, will be fed into a new database of REE mineral characteristics.

Once developed, the team will use machine learning to identify conditions suited for optimized rare earths recovery.

"We're very excited about this project," said Zhang. "The REE characteristics database will be an extremely useful resource for researchers and industry working with REEs. Recovery, separation and purification are incredibly important for generating usable REEs."

Much like trace minerals lead miners to silver and gold, with a new age approach to creating identifying markers for REEs, in conjunction with different markers on their ability to sequester carbon dioxide, a powerful tool is in the making.

In addition to Arizona State, the project team also includes Washington State University researchers. Collaborating together, the team hopes to generate new experimental data and examine the literature to build rare earth elements solubility and thermodynamic databases.

Ultimately, this will lay the fundamental groundwork for the final goal of developing carbon-negative re-mining technologies that use captured carbon dioxide to create stable carbonate minerals and provide a symbiotic technology that will hopefully begin to improve current climate conditions.