(763f) Recovery of Rare Earth Elements from North Dakota Lignite and Lignite-Related Feedstocks

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 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 motors for hybrid/electric vehicles. 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 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 carbonatite 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 carbonatite-type deposit (Bayan Obo) that contains only trace amounts of heavy REE (98.7% light 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 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, Barr Engineering, and Pacific Northwest National Laboratory (PNNL) with the support of the cost share partners North American Coal Company, Great River Energy, and the North Dakota Industrial Commission/Lignite Energy Council as well as technical support from the North Dakota Geological Survey. The overall goal of this Phase I project was to develop an economically viable and environmentally benign process to concentrate REE to a goal of 2 weight percent to form a synthetic mixed REE ore. As part of the project, an extensive sampling and analysis campaign was completed to identify promising feedstocks, which was followed by laboratory-scale concentration testing and a technical and economic feasibility study. Finally, the design of a bench-scale test system was developed, which is to be constructed and tested in a subsequent Phase II project, if awarded by DOE. This paper will provide the results of the Phase I project and the plans for a subsequent Phase II project.

The originally proposed concept involved recovery of REE from the reject stream of the Great River Energy lignite drying system located at the Coal Creek Station power plant in North Dakota. However, upon further investigation in the project, it was discovered that on an ash-basis, the REE are more concentrated in certain locations within the coal seams than in the associated roof/floor sediments. Therefore, the focus for the remainder of the project was shifted towards development of methods to concentrate the REEs from these selected coal seams.

Laboratory testing of a novel concentrating method has shown very high recovery of about 80-90% of the REEs from two potential feedstocks, ranging from 580 to 2300 ppm REE content on an ash basis, with excellent selectivity/recovery of the critical and heavy REE. Details of a processing scheme to economically concentrate the REE to the goal of 2 weight percent using a simple and environmentally benign method have been established. The project team has also developed the concepts for integration of the REE recovery process within an existing coal conversion facility that will provide cost-saving synergies, multiple saleable product streams, and infrastructure to reduce costs. Based on the results of the Phase I work, the project team believes North Dakota lignite-related feedstocks to be a highly promising alternative domestic source of REE that will limit dependence on foreign supply.