Using carbon dioxide to recover more critical minerals

NevadaToday

ARPA-E representatives, including Program Director Douglas Wicks, met with students at the University of Nevada, Reno.

Nevada Gold Mines Professor Pengbo Chu in the Department of Mining and Metallurgical Engineering recently received a grant from the Advanced Research Projects Agency – Energy (ARPA-E) within the Department of Energy. The grant was part of the Mining Innovations for Negative Emissions (MINER) program led by the program director Douglas Wicks. The goals of the MINER program include using carbon dixoide to decrease mineral processing (comminution) energy, increase critical mineral yield, and reduce minerals tailing losses.

"The U.S. is very fortunate that we have a very high-grade rare earth ore," Chu said.

The project will incorporate mineral carbonation to develop new workflows and methodology for recovering more rare earth minerals. Critical minerals are minerals that will be used in different decarbonization technologies.

The process Chu is proposing starts with high-pressure grinding rolls, which mechanically break down the material from larger, basketball-sized rocks to cherry-sized rocks. The high-pressure grinding rolls already save comminution energy when compared to the crushing technologies that are more commonly used, up to 50 percent.After the rocks are made smaller, the minerals will go through X-ray transmission sorting, which determines the density of different rocks. Because rare earth minerals tend to be denser, the rock rich in those minerals is sorted one way in an existing process, while less-dense material is sorted another way. The less-dense material is chemically processed through a carbonation process, which uses pressurized carbon dioxide to convert silicate minerals to carbonate minerals, softening them.

After it undergoes a carbonation process, the softened material goes through another mechanical process, a ball mill. The softening of the material means the ball mill doesn't require as much energy to process the material. Additionally, it is easier to control the size of the product, which is important for the next step in processing, froth flotation.Once the material goes through the ball mill, rare earth elements are exposed and can be retrieved through established froth floatation processes.

"There is a sweet spot for flotation to work," Chu said, referring to the size of the product. If the rock particles are too big or too small, froth flotation doesn't work as well to extract the material of interest.

The application of mineral carbonation to soften the rock presents a new approach to control the rock size during comminution. The new approach is expected to not only reduce the current energy consumption during mineral processing but also makes the process carbon negative.While Chu expects this process to maximize output, he will try different workflows that reorder some of the processes to determine which method retrieves the most material while using the least energy. The process can also be used to recover material from waste tailings, which can have high concentrations of rare earth elements.

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Using carbon dioxide to recover more critical minerals