Researchers have recently discovered a new method to extract rare earth elements, or REE, from the drainage of acid mines through CO2 mineralization. Penn State University researchers published their discovery in a paper in the online Chemical Engineering Journal.


Rare Earth Elements

REEs or Rare earth elements are a mineral group composed of seventeen minerals, which are useful for making advanced technological devices like electric vehicle batteries. Rare earth elements are also used for computer memory, in rechargeable batteries, DVDs, phones, fluorescent lights, and magnets. The US considers them critical to its national and economic security.

Most REEs are imported from other countries such as China, which provides 85 percent of the supply all over the world.

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Drainage from Acid Mines

Waste from acid mines, or AMDs, that are produced from coal mines in Appalachia may contain a lot of REEs because of the high mineral concentration in that area. Furthermore, they are already undergoing treatment and collection because of their negative environmental impacts.

As pyrite or iron sulfide is extracted during mining and comes into contact with water and air, it creates a residue, which oxidizes the material and produces sulfuric acid, breaking down rocks. This causes contamination of the water by toxic metals.


The New Extraction Method

The researchers have devised a formula composed of two stages to process the AMD to let them extract a significant REE amount in the material.

With this new method, a lesser amount of chemicals have been used as compared to other previous methods. Treatment methods that have been previously used involved collecting the AMD into a pond and putting chemicals in it to neutralize its pH. This causes the metals to precipitate, settling out from the water.

From the resulting sludge, roughly 70 percent REEs may be recovered. The rest of the REEs will be discarded together with the water.

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The researchers from Penn State found that they can increase the yield higher than seventy percent through the addition of carbon dioxide into the AMD. They then make the pH neutral so that it can be accepted for remediation. Chemical reactions are formed by the CO2, which form solid mineral carbonates. 

The carbonate products form bonds with the REEs. It is then solidified and separated from water at a low pH. The new method can recover 90 percent aluminum at a pH level 5, while 85 percent of REEs are recovered at pH level 7.

Researchers found that recovering a similar REE amount from the AMD with the use of older methods, more chemicals need to be used to be able to increase its pH level above 7.


Importance of the Discovery

Study author Mohammad Rezaee said that by merely modifying the older methods a bit, a lot fewer chemicals need to be utilized while getting a higher yield of REEs at the same time.

It is an inexpensive, environmentally friendly, and efficient method, according to Penn State Center for Critical Minerals director and energy and mineral engineering professor Sarma Pisupati.

According to the researchers, a lower recovery cost will make the new method competitive in the REE market.

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