Rare earth elements (REE) are essential for modern technologies — cell phones, LED screens, wind turbines, magnets, and solar panels all rely on REEs. Although relatively abundant in nature, REEs are often found distributed in low concentrations and are challenging to extract. China provides the bulk of the world’s supply, often mining and processing the materials with significant environmental consequences. In recent years, the US Dept. of Energy (DOE) has made it a mission to develop cost-effective and environmentally sustainable recovery of REE and other critical metals (CM) from domestic resources. The reclamation of rare earth elements (REEs) from coal related waste materials is proposed due to their abundances and fast availability as waste products with oftentimes enriched REE content. Just as the coal provenance can vary, so can the subsequent nature of the ash; resulting in differing sources of REE and CM in the ash.<br/><br/>Advanced characterization is utilized to study how REE and CM are bound in these coal ashes. Traditional characterization technologies (e.g., SEM, XRD) are not sensitive enough to provide meaningful results from samples with low REE concentrations or amorphous REEs retaining phases. Therefore, synchrotron μXRF and μXANES, were performed at Stanford Synchrotron Radiation Lightsource (SSRL) on over 30 ash specimens to understand the micro-scale REE binding environments. These analyses have shown that (1) the distribution and speciation of light REEs and heavy REEs are different in compositionally-diverse ash materials. (2) REE-bearing phases can be oxidized during coal combustion, that will further influence REE recovery efficiencies from different feedstocks collected in different areas of the country. The resulting work will provide fundamental geochemical knowledge of REE entrapment during coal combustion to inform innovated and targeted REE recovery with minimized waste and environmental impacts. The innovations driven by characterization have the potential to offset the cost of ash disposal while reducing the environmental footprint of critical mineral extraction.

Resources from the ashes: Utilizing synchrotron characterization to determine REE binding and subsequent extraction from coal waste materials

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.