(633e) Examination of the Distribution and Form of the Rare Earth Elements in a Metalliferous Lignite Coal

According to the U.S. Department of Energy National Energy Technology Laboratory, rare earth elements (REE) provide significant value to our national security, energy independence, environmental future, and economic growth. REEs are utilized in a suite of high importance end-uses, such as cell phones, hybrid/electric vehicles, magnets, computer components, catalysts and many others. The unique magnetic properties of REEs, in particular, make them crucial materials for the growing renewable energy and electric automotive markets. REEs are used in the strongest permanent magnets currently known, and are used in generators for wind turbines and in electric motors. These same types of magnets, as well as other critical REE-based products are used in a host of military defense applications, as well.

China, in part due to its deposits of a unique REE resource (ion-adsorbed clays) that combines high quantities of the more valuable heavy and critical REE, as well as simple and low cost extraction, dominates the global supply market. In 2010, China established new quotas on exports of REEs, which resulted in huge increases in REE prices peaking in 2011 due to an expected supply shortage for critical applications. As a result, production at the California-based Mountain Pass Mine was re-started after several years of dormancy. However, after peaking in price in 2011, prices have dropped substantially to slightly above 2010 levels, challenging the profitability of non-China based production which consists mainly of hard rock deposits, that are deficient in critical REE and heavy REE. Some researchers have noted that mining of the Mountain Pass and similar resources will neither mitigate the crisis in REE resources nor eliminate the shortage of the most critical REE, but will only result in overproduction of excessive cerium.

China accounted for about 83% of the total global REE supply in 2016, down from about 95% prior to 2010. Meanwhile, the US production was zero, with the Mountain Pass mine having declared bankruptcy and closing operations in the last quarter of 2015. The U.S. is currently 100% import reliant for REEs. Although still dominating global supply of the heavy REE, some researchers have estimated that the Chinese ion-adsorbed clays resource will only last another 15-20 years. The Chinese clays represent essentially the entire global supply of heavy REE and most of the critical REE. Further, the bulk of Chinese reserves and production is from a hard rock deposit (Bayan Obo Mine) that contains only trace amounts of heavy REE, and supplies roughly 80% of the global light REE demand. Due to its limited supply, and because the Chinese clay resource is rich in heavy and critical REE, while most other traditional resources are deficient in these less common and more valuable elements, it is imperative that new domestic sources of REEs, especially the heavy and critical REE, be identified and processes be developed to produce them. Coal and coal byproducts have recently been identified as one of these potential new resources for REEs.

As part of the US Department of Energy effort to identify alternative domestic sources of Rare Earth Elements (REE), the University of North Dakota was awarded a project (DE-FE0027006) to determine the feasibility of recovery of REE from North Dakota lignite coal and related feedstocks. The project team includes the University of North Dakota, Microbeam Technologies (MTI), Barr Engineering, Pacific Northwest National Laboratory (PNNL), and MLJ Consulting with the support of the cost share partners North American Coal Company, Great River Energy, Great Northern Properties, Minnkota Power Cooperative, the North Dakota University System, and the North Dakota Industrial Commission/Lignite Research Program. Technical support is also being provided by the North Dakota Geological Survey.

The project is currently in its final year of a 3-year effort and is focusing on demonstrating a novel technology for REE recovery from pre-combustion lignite coal and evaluating the overall process economics. Technical results to date have been highly promising, and the REE recovery process takes advantage of the unique properties of lignite in which the REE are weakly associated with the organic components in the coal. This is unlike higher-rank coals, such as Eastern U.S. bituminous coals that predominantly contain the REE associated in hard mineral forms. Locations in North Dakota have also been discovered that contain coals with REE concentration as high as 650 ppm (dry coal basis) or 2300 ppm (ash basis), which are exceptionally high levels.

Prior testing at UND has identified that the REE are enriched in the light specific gravity (SG) fractions of the lignite. Recently, an REE-rich lignite, containing about 260 ppm REE on a dry whole coal basis was subjected to multi-specific gravity float-sink separations. The goals of this effort were the following: i) SG fractions with highest REE concentration, ii) SG fractions with highest extractable REE content, iii) ash yield as a function of SG, iv) mineralogy as a function of ash yield, and v) mineral/REE liberation as a function of particle size and SG. The ultimate objective of this testing was to select the optimum SG range of the coal to use for the process development testing.

This presentation and paper will first provide an overview of UND’s efforts related to REE from lignite and the key results of technology development to date, and subsequently describe in detail the results of the above SG separations and analysis. The experimental testing and results described are not only important to the process development, but also provide new insights into the modes of occurrence of the REE and other important minerals/elements in the lignite. The results show that selection of the appropriate SG range results in a significant increase in REE concentration as well as an improvement in REE recovery and extraction selectivity. This type of approach can also be applied at the commercial-scale with conventional coal cleaning techniques.