Rare earth elements (REEs) have many critical uses in components used in advanced technology (e.g., electric vehicles, industrial magnets) and the lack of a reliable domestic supply has been identified by the US DOE as a vulnerability to US economic security. Our research focuses on developing an economical process for extracting REEs from coal fly ash (the waste product left over after coal is burned for electricity generation) by coupling a hydrothermal extraction process with the engineering of a ligand-associated media for concentrating REEs from the extraction liquid (Fig 1). Traditional REE extraction requires large amounts of acids (including hydrofluoric acid) and organic solvents. Our process may provide an organic solvent-free and environmentally friendly method of extracting and recovering REEs. In addition, the residual material left after REE extraction will have most of the problematic toxic materials removed, which will allow the “beneficiation” of large amounts of fly ash to be used as building materials with less risk of metal leaching. We will discuss the process of collecting and characterizing fly ash and wastewater sludge feedstock from coal-fired power plants near Detroit, MI by scanning electron microscopy (SEM) and x-ray diffraction (XRD). Ash samples were then subjected to high pH hydrothermal conditions from 100-350 °C to produce a REE enriched leachate. A commercially available ligand (DIPEX) has been successfully loaded to a commercially available organosilica media. DIPEX-associated organosilica surface loading can exceed 4x (mass/mass basis) and in simplified sorption experiments with Nd solutions (pH 2-3), the DIPEX-organosilica media can sorb &gt;90 mg Nd per g of media. Recovery of the sorbed Nd is achieved with HCl resulting in concentrated solutions. After precipitation, we aim to achieve &gt;2% (wt/wt) enrichment, which is significant for a relatively green process. Column experiments are being conducted to evaluate the optimal ligand/media ratio for repeat use cycling and this process is a promising application of green chemistry for extracting valuable materials from a waste product.

Using green chemistry for REE recovery from coal fly ash: Hydrothermal extraction and ligand-associated media sorption

2019 Fall National Meeting

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