RECOVERY OF RARE EARTH ELEMENTS FROM COAL AND COAL BY-PRODUCTS

Rare earth elements (REEs) play an important role in the global economy. Many of the renewable energy and energy-efficient technologies rely heavily on components made from REEs. To diverse the supply chain of these critical materials, the U.S. Department of Energy National Energy Technology Laboratory recently initiated research to support the development of technologies and processes for the recovery of REEs from abundant U.S. domestic coal and by-products. Coal is an important resource, both in the United States and around the world and is a potential source of REEs. In this work, particle size separation, float-sink separation and magnetic separation of various coal and coal by-product samples were carried out to investigate the feasibility of using these physical separation methods for REE enrichment. The samples include fly ash, bottom ash, clean coal, coal refuse and clay. Samples were analyzed using ICP-MS, ICP-OES, TGA and CHNS methods. Results indicate that the REE contents in fly ash generally increase as the ash particle size decrease. The results also suggest that density separation is the most effective method for REE enrichment compared with other methods tested in this work. The combination of these physical separation methods would be beneficial. In addition, the results also showed that the REE concentration in coal on the whole coal basis increased with increasing ash yields while the REE concentration on the ash basis reduced as the ash yields increased. Based on the correlation of REE concentration with the ash yield as well as the REE distribution pattern, a simple method was developed to quantitatively determine the organic association of REEs in coal. The model predictions showed a very good agreement with experimental data. The result suggested that approximately 25% of REEs in the low-ash Appalachian coal used in this work is associated with organic matter.