Rare earth elements (REEs) are critical for many high-tech electronic devices and for renewable energy generation, but their supply is geopolitically limited, and they are often extracted through environmentally unsustainable mining practices. Coal-based resources (CBRs) including coal, bottom ash, and coal fly ash, have recently emerged as a promising REE source. However, their extremely complicated chemical compositions motivate the development of more energy efficient, environmentally-friendly, and highly specific processes for recovering and enriching REEs. Our work presents a novel REE extraction process that uses supercritical CO2 (scCO2) to directly and selectively extract REEs by from solid CBR matrices. Instead of using organic solvent, the application of green solvent (scCO2) would alleviate potential environmental concerns. Moreover, scCO2 is a great solvent for the extractant tributyl phosphate–nitric acid (TBP-HNO3) and enables selectively extract REEs over major impurities, such as Si, Ca, Al, and Mg. Capitalizing on metal ions’ different water affinities, we further separate the REEs and impurities via a multistage stripping process. Even more favorably, the extractant can be reused in our process, minimizing the organic chemical demand and waste generation. By generating high concentrations of highly pure REEs from a widely available resource, our novel extraction process can help meet the growing demand for REEs.

Environmentally-friendly and high yielding extraction of rare earth elements from coal-based resources using supercritical CO2

ACS Fall 2020 Virtual Meeting

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