Physicochemical Methods to Recover Rare-Earth Elements from Appalachian Coals Lead to 70% to 84% Recovery Rate

Highlights

• Researchers at West Virginia University studied rare-earth element recovery from Appalachian Basin coals using calcination and sodium carbonate roasting techniques.
• The study achieved a maximum recovery rate of 70-84% of total rare-earth elements using a combination of pre-treatments and citric acid leaching.
• Physicochemical recycling techniques for rare-earth element recovery from coal and coal by-products can generally achieve rates between 60-90% under optimized conditions.

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Shikha Sharma, PhD (opens in a new tab), a  Marshall S. Miller Energy Professor of Geology and Rachel Yesenchak, PhD**,** both with the Department of Geology & Geography, West Virginia University, and colleague report on the output of a study involving growing interest in the development of unconventional rare-earth element (REE) resources, such as coal and coal byproducts, to help secure domestic supplies of these elements.  Their findings were published in the peer-reviewed journal Minerals (opens in a new tab).

This study brings us to the region known for Appalachian Basin coals, a geology involving enriched rare-earth elements. However, access is not easy nor straightforward.   Methods to recover the elements are often impeded by a resistant aluminosilicate matrix.

The Study

Enter this study exploring the use of calcination and sodium carbonate roasting pre-treatments combined with dilute acid leaching to recover rare-earth elements from Appalachian Basin coals and underclay.

So, what did the authors find? The team report (opens in a new tab)  the outcomes of the study suggest that rare-earth element recovery after calcination is dependent on the original mineralogy of samples and that light rare-earth minerals may be more easily decomposed than heavy rare-earth minerals, a helpful differentiation.

The authors point out:

“Sodium carbonate roasting can enhance the recovery of both light and heavy rare-earth elements.” In fact, the authors report achieving a maximum recovery ranging from 70% to 84% of total rare-earth elements based on the combination of calcination and sodium carbonate roasting, followed by 0.25 M citric acid leaching.

An important outcome given the intensifying demand for rare-earth elements should only grow due to their general criticality, the need to diversify away from China dependence, and the move to clean energy and the general trend of decarbonization.

Review of Literature

The recovery rate of REEs from coal using physicochemical recycling techniques can vary significantly depending on several factors, such as the specific type of coal, the concentration of REEs in the coal or coal ash, and the exact methods used in the extraction process.

In general, physicochemical methods, which include techniques like acid leaching, solvent extraction, and ion exchange, can achieve REE recovery rates from coal and coal by-products ranging from 60% to 90% under optimized conditions.

Method	Summary
Coal Ash	In coal fly ash, which is often richer in rare earth elements than raw coal, recovery rates through physicochemical methods can reach around 80% or even higher when using strong acidic leaching combined with solvent extraction.
Acid Leaching	This common technique in physicochemical recycling uses acids like hydrochloric or sulfuric acid to dissolve rare earth elements from coal and coal by-products. Leaching efficiency is highly dependent on temperature, acid concentration, and reaction time and can yield recovery rates between 60% and 85%.
Ion Exchange and Solvent Extraction	These methods, often used in combination with leaching, help purify and separate REEs from other elements in the leachate, refining recovery rates to around 90% in some cases.

Some Challenges

The complex mineralogy of coal, low REE concentrations, and the presence of other elements (like iron, aluminum, and silicon) can make achieving high recovery rates challenging. Additionally, physicochemical processes can be costly and environmentally taxing due to the chemicals involved.

So, while physicochemical recycling techniques can yield reasonably high recovery rates, achieving consistent rates above 90% remains difficult due to the varied composition of coal and coal by-product.