Rare earth elements (REEs) have many critical uses in advanced technology 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 and power plant wastewater sludge by coupling a hydrothermal extraction process with the engineering of a ligand-associated media for concentrating REEs from the extraction liquid (Figure 1). We will first discuss the economics of REE recovery and the process of collecting and characterizing fly ash and wastewater sludge feedstocks from coal-fired power plants near Detroit, MI by scanning electron microscopy (SEM), x-ray diffraction (XRD), and x-ray florescence (XRF). Ash samples are then subjected to hydrothermal conditions from 100-350 °C for 1-24 h at Los Alamos National Laboratory and leachate concentrations are measured by inductively coupled plasma-mass spectroscopy (ICP-MS) and compared to hydrofluoric acid digestion results. Experiments designed to aid in ligand selection and loading optimization show that DIPEX (and dipentyl pentylphosphonate) can be successfully loaded to a commercially available swellable organically modified silica (SOMS) media. Preliminary results show that DIPEX-associated SOMS surface loading can exceed 4x (mass/mass basis) and in simplified sorption experiments with Nd solutions (pH 2-3), the DIPEX-SOMS media can sorb &gt;90 mg Nd per g of media. Recovery of the sorbed Nd with low pH solutions has exhibited variable efficiency. The high DIPEX loading media (4 g DIPEX/ g dry media) has shown little desorption with strong acids; however, near complete recovery was achieved with lower surface loadings (0.05 g DIPEX/ g dry media). Column experiments are being conducted to evaluate the optimal ligand/media ratio for repeated use. Completive sorption with Fe and other major cations is also being evaluated.

Coupled hydrothermal extraction and ligand-associated media sorption for REE recovery from coal fly ash

2019 Spring National Meeting

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