Critical Mineral Relationships in Global Coal Ash.pdf

Denise Levitan, United States Geological Survey

Description

Critical Mineral Relationships in Global Coal Ash Authors Dr. Denise Levitan - United States - United States Geological Survey Abstract Coal ash can be enriched in critical minerals (as defined by the U.S. Geological Survey’s 2022 list), including rare earth elements (REEs), relative to many other geologic materials. This study compiled literature-reported chemical data from approximately 600 coal-fired power plant ash samples for a meta-analysis. All samples had reported concentration measurements for each of the lanthanides and yttrium (collectively termed REY), but the availability of additional chemical parameters, information about feed coals, and plant specifications varied. Initial analysis of ash chemical data included univariate statistical summaries and bivariate correlations. The total (summed) REY concentration data were approximately log-normally distributed with a geometric mean around 400 ppm. Around 70% of the samples evaluated had total REY concentrations exceeding the U.S. Department of Energy’s suggested 300 ppm interest level. Total REY concentrations showed strong direct correlations with individual REEs (including scandium, measured in ~70% of samples), thorium, and titanium. Individual REE concentrations were used to calculate outlook coefficient (Coutl), a measure of critical REEs relative to excessive REEs defined by Seredin and Dai (2012, DOI:10.1016/j.coal.2011.11.001). Coutl generally ranged between 0.5 and 2.5, with an approximate log-normal distribution and a geometric mean around 1.0. Over 95% of samples evaluated had Coutl above the “promising” threshold of 0.7, but these values were not correlated with total REY concentrations. Thus, a high concentration of REY does not necessarily indicate a favorable proportion of critical REEs; both factors may need to be considered when evaluating coal ash as a source material. The initial results of this study substantiate the potential use of coal ash as a source of critical minerals, particularly REEs. Most of the samples evaluated in this worldwide dataset had promising concentrations of total REY and/or proportions of economically favorable REEs, but the variability suggests some ash types are likely more promising REE sources.

 
May 16th, 8:00 AM May 16th, 8:30 AM

Critical Mineral Relationships in Global Coal Ash.pdf

Grand Rapids, Michigan

Critical Mineral Relationships in Global Coal Ash Authors Dr. Denise Levitan - United States - United States Geological Survey Abstract Coal ash can be enriched in critical minerals (as defined by the U.S. Geological Survey’s 2022 list), including rare earth elements (REEs), relative to many other geologic materials. This study compiled literature-reported chemical data from approximately 600 coal-fired power plant ash samples for a meta-analysis. All samples had reported concentration measurements for each of the lanthanides and yttrium (collectively termed REY), but the availability of additional chemical parameters, information about feed coals, and plant specifications varied. Initial analysis of ash chemical data included univariate statistical summaries and bivariate correlations. The total (summed) REY concentration data were approximately log-normally distributed with a geometric mean around 400 ppm. Around 70% of the samples evaluated had total REY concentrations exceeding the U.S. Department of Energy’s suggested 300 ppm interest level. Total REY concentrations showed strong direct correlations with individual REEs (including scandium, measured in ~70% of samples), thorium, and titanium. Individual REE concentrations were used to calculate outlook coefficient (Coutl), a measure of critical REEs relative to excessive REEs defined by Seredin and Dai (2012, DOI:10.1016/j.coal.2011.11.001). Coutl generally ranged between 0.5 and 2.5, with an approximate log-normal distribution and a geometric mean around 1.0. Over 95% of samples evaluated had Coutl above the “promising” threshold of 0.7, but these values were not correlated with total REY concentrations. Thus, a high concentration of REY does not necessarily indicate a favorable proportion of critical REEs; both factors may need to be considered when evaluating coal ash as a source material. The initial results of this study substantiate the potential use of coal ash as a source of critical minerals, particularly REEs. Most of the samples evaluated in this worldwide dataset had promising concentrations of total REY and/or proportions of economically favorable REEs, but the variability suggests some ash types are likely more promising REE sources.