NETL creates technology to detect aluminium impurities in REEs

March 15, 2023

The sensing material is a metal-organic framework thin film which emits blue light in the presence of water and becomes significantly more intense in the presence of aluminum ions (Courtesy NETL)
The sensing material is a metal-organic framework thin film which emits blue light in the presence of water and becomes significantly more intense in the presence of aluminum ions (Courtesy NETL)

Researchers from the National Energy Technology Laboratory (NETL), a US-based national laboratory under the country’s Department of Energy (DOE) Office of Fossil Energy, have developed what is described as an effective, renewable technology which can detect aluminium in Rare Earth Element (REE) sources. This is expected to clear the way for more effective recovery of Rare Earths.

The importance of the drive to secure more domestic REEs is reflected in the US government’s investments in recovery technologies. Since January 2021, the DOE has invested $25 million in twenty-one projects in Appalachia, the Gulf Coast, and other west and midwest locations to support the production of REEs and critical minerals in traditional fossil fuel-producing communities across the country. The DOE also recently announced up to $156 million in funding from the Bipartisan Infrastructure Law for a first-of-a-kind facility to extract and separate REEs and critical minerals from unconventional sources like mining waste.

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The concentration of aluminium is often significantly higher than that of REEs in coal waste byproduct feeds, and the presence of Al can interfere with REE extraction and purification processes. Therefore, the detection of such impurities is said to be very important during REE processing. Impurities can be divided into two groups according to their value: low-value elements and high-value elements. Aluminium and iron represent typical low-value elements often associated with REEs in primary and secondary raw materials.

The new NETL-developed sensing material is a metal-organic framework thin film made of copper linked by 2-aminoterephthalic acid. The high-quality film can be grown within thirty minutes using a metal oxide template at room temperature, which eliminates the need for external heating or specialised equipment. The film emits blue light in the presence of water and becomes significantly more intense in the presence of aluminium ions.

As a proof-of-concept, the manufactured sensing films were tested on three fly ash leachates, and the fluorescence intensity correlated well with the aluminium concentration in the samples, highlighting the sensor’s potential for real-world use. The same sensing film may also be recycled for multiple sensing cycles. Taken together, the NETL work presents a simple, scalable method for fabricating high-performance sensors to detect aluminum in solutions.

NETL researchers Scott Crawford, John Baltrus, Ki-Joong Kim, and Nathan Diemler developed the highly sensitive material that can be used to detect part-per-billion concentrations of aluminum.

In addition to detecting an impurity in REE feedstocks, removing and refining aluminium from liquid sources can also provide an additional domestic source of the raw material for the aluminium industry.

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