A1 Journal article (refereed)
Alkyl-Substituted Aminobis(phosphonates) : Efficient Precipitating Agents for Rare Earth Elements, Thorium, and Uranium in Aqueous Solutions (2021)

Virtanen, E. J., Perämäki, S., Helttunen, K., Väisänen, A., & Moilanen, J. O. (2021). Alkyl-Substituted Aminobis(phosphonates) : Efficient Precipitating Agents for Rare Earth Elements, Thorium, and Uranium in Aqueous Solutions. ACS Omega, 6(37), 23977-23987. https://doi.org/10.1021/acsomega.1c02982

JYU authors or editors

Virtanen, Emilia
Perämäki, Siiri
Helttunen, Kaisa
Väisänen, Ari
Moilanen, Jani

Publication details

All authors or editors: Virtanen, Emilia J.; Perämäki, Siiri; Helttunen, Kaisa; Väisänen, Ari; Moilanen, Jani O.

Journal or series: ACS Omega

ISSN: 2470-1343

eISSN: 2470-1343

Publication year: 2021

Publication date: 13/09/2021

Volume: 6

Issue number: 37

Pages range: 23977-23987

Publisher: American Chemical Society (ACS)

Publication country: United States

Publication language: English

DOI: https://doi.org/10.1021/acsomega.1c02982

Publication open access: Openly available

Publication channel open access: Open Access channel

Publication is parallel published (JYX): https://jyx.jyu.fi/handle/123456789/77823

Abstract

The efficient and environmentally sustainable separation process for rare earth elements (REE), especially for adjacent lanthanoids, remains a challenge due to the chemical similarity of REEs. Tetravalent actinoids, thorium, and traces of uranium are also present in concentrates of REEs, making their separation relevant. This study reports six simple water-soluble aminobis(phosphonate) ligands, RN[CH2P(O)(OH)2]2 (1 R = CH2CH3, 2 R = (CH2)2CH3, 3 R = (CH2)3CH3, 4 R = (CH2)4CH3, 5 R = (CH2)5CH3, 6 R = CH2CH(C2H5)(CH2)3CH3) as precipitating agents for REEs, Th, and U, as well as gives insight into the coordination modes of the utilized ligands with REEs at the molecular level. Aminobis(phosphonates) 4–6 with longer carbon chains were found to separate selectively thorium, uranium, and scandium from REEs with short precipitation time (15 min) and excellent separation factors that generally range from 100 to 2000 in acidic aqueous solution. Ligands 1–6 also improved separation factors for adjacent lanthanoids in comparison to traditional oxalate precipitation agents. Importantly, precipitated metals can be recovered from the ligands with 3 molar HNO3 with no observed ligand decomposition enabling the possibility of recycling the ligands in the separation process. NMR-monitored pH titrations for 1 showed deprotonation steps at pKa 1.3, 5.55, and >10.5, which indicate that the ligands remain in a deprotonated [L]−1 form in the pH range of 0–4 used in the precipitation studies. 31P NMR titration studies between 1 and M(NO3)3 (M = Y, La, Lu) gave satisfactory fits for 1:3, 1:2, and 1:1 metal–ligand stoichiometries for Y, La, and Lu, respectively, according to an F-test. Therefore, aminobis(phosphonate) precipitation agents 1–6 are likely to form metal complexes with fewer ligands than traditional separation agents like DEHPA, which coordinates to REEs in 1:6 metal–ligand ratio.

Keywords: metals; ligands; precipitation (active); titration

Free keywords: metals; ligands; lanthanides; precipitation; titration

Fields of science: