Rare earth element resource evaluation of coal byproducts: A case study from the Powder River Basin, Wyoming

Abstract

Domestic Rare Earth Element sources and production are limited in the United States and currently rely on final processing overseas. Increasing demand and resource security domestically has led to significant investigation into rare earth element domestic resources. Much of this work focuses on unconventional potential ore stocks, including coal and coal byproducts. This investigation focuses on coal byproducts generated as ash from coal burning power stations. Wyoming's Powder River Basin hosts the largest U.S. coal stocks for energy production, providing approximately 40% of all thermal coal mined in the U.S. In this effort, in section I, we have studied coal byproducts for rare earth element concentrations and compare these data to current alternative resource knowledge. We find that coal byproducts in this investigation are consistently high enough in rare earth element concentration (above the current Department of Energy 300 ppm cutoff grade) to warrant consideration as a promising potential resource. Rare earth element behavior within the host coal seams is also considered in an effort to better understand resource prospecting and ore body description. In Section II, we evaluate the economic feasibility of rare earth extraction from Powder River Basin coal byproducts using net present value analysis and the rare earth concentrations data from Section I. We calculate the break-even ash-to-oxide output and input unit costs for four coal stations in the Powder River Basin. All four stations have break-even unit costs that are higher than the mine-to-oxide operating cost reported for a traditional rare earth element mine. This is a promising result, especially given that it is more costly to refine rare earths from mined material than from ash. The results are highly sensitive to rare earth prices: given low long-term prices, none of the four stations can feasibly break even. Section III summarizes federal policy considerations in rare earth element resource development. The history of policy development, most recent focus on rare earth element specific funding legislation, paired with section I and II herein, suggest a robust opportunity for development of Wyoming based coal byproducts as a partial solution to current domestic rare earth element short falls and strategic needs. © 2022 Elsevier Ltd