Microalgae for the Extraction and Separation of Rare Earths: An STXM Study of Ce, Gd, and P

Rare earth elements (lanthanides) are critical materials for many applications, particularly those involved in new energy. Extracting these elements economically from low-concentration sources may be challenging. This study investigates the interaction of Ce and Gd with microalgae that have been triggered to form phosphate-rich granules. Lanthanides usually occur in nature as phosphates, and therefore, we hypothesized that phosphate accumulation in microalgae may facilitate lanthanide sequestration. Synchrotron-based scanning transmission X-ray microspectroscopy (STXM) was used to map the distribution of Gd, Ce, and P in and around cells of Chlamydomonas reinhardtii. STXM provided X-ray absorption (XAS) spectra at the Gd M4,5-edge, the Ce M4,5-edge, and the P K-edge, supported by bulk X-ray absorption spectroscopy at another beamline, and elemental maps from scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS). Gd was associated with P in polyphosphate granules within C. reinhardtii and with P outside the cells. Ce was associated with P outside the microalgal cells but not with the P granules inside the cells. Gd and Ce were found to react with phosphate to form a distinct compound apparent in X-ray absorption near edge spectroscopy (XANES) of bulk samples. However, this compound is not found in the P granules that are coincident with Gd inside the alga. These differences in uptake by the microalga between Ce and Gd may suggest a selective extraction technique and could be generalized to other rare earth elements that are otherwise hard to separate.

Keyword(s)

Lanthanide, cerium, gadolinium, phosphorus, XAS, XAFS, Gd M5-edge, Ce M5-edge, P K-edge

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Plouviez Maxence, Guieysse Benoit, Wolmarans Karla, Matinong Andrea Marie E., Buwalda Olivia, Thånell Karina, Beinik Igor, Tuyishime J. R. Marius, Mitchell Valerie, Kappen Peter, Flynn David, Jauffrais Thierry, Haverkamp Richard G. (2024). Microalgae for the Extraction and Separation of Rare Earths: An STXM Study of Ce, Gd, and P. ACS Sustainable Resource Management. INPRESS. https://doi.org/10.1021/acssusresmgt.4c00237, https://archimer.ifremer.fr/doc/00915/102712/

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