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Alkyl-Substituted Aminobis(phosphonates)—Efficient Precipitating Agents for Rare Earth Elements, Thorium, and Uranium in Aqueous Solutions
[Image: see text] 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...
Autores principales: | , , , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
Publicado: |
American Chemical Society
2021
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Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8459412/ https://www.ncbi.nlm.nih.gov/pubmed/34568676 http://dx.doi.org/10.1021/acsomega.1c02982 |
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author | Virtanen, Emilia J. Perämäki, Siiri Helttunen, Kaisa Väisänen, Ari Moilanen, Jani O. |
author_facet | Virtanen, Emilia J. Perämäki, Siiri Helttunen, Kaisa Väisänen, Ari Moilanen, Jani O. |
author_sort | Virtanen, Emilia J. |
collection | PubMed |
description | [Image: see text] 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[CH(2)P(O)(OH)(2)](2) (1 R = CH(2)CH(3), 2 R = (CH(2))(2)CH(3), 3 R = (CH(2))(3)CH(3), 4 R = (CH(2))(4)CH(3), 5 R = (CH(2))(5)CH(3), 6 R = CH(2)CH(C(2)H(5))(CH(2))(3)CH(3)) 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 HNO(3) 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 pK(a) 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. (31)P NMR titration studies between 1 and M(NO(3))(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. |
format | Online Article Text |
id | pubmed-8459412 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2021 |
publisher | American Chemical Society |
record_format | MEDLINE/PubMed |
spelling | pubmed-84594122021-09-24 Alkyl-Substituted Aminobis(phosphonates)—Efficient Precipitating Agents for Rare Earth Elements, Thorium, and Uranium in Aqueous Solutions Virtanen, Emilia J. Perämäki, Siiri Helttunen, Kaisa Väisänen, Ari Moilanen, Jani O. ACS Omega [Image: see text] 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[CH(2)P(O)(OH)(2)](2) (1 R = CH(2)CH(3), 2 R = (CH(2))(2)CH(3), 3 R = (CH(2))(3)CH(3), 4 R = (CH(2))(4)CH(3), 5 R = (CH(2))(5)CH(3), 6 R = CH(2)CH(C(2)H(5))(CH(2))(3)CH(3)) 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 HNO(3) 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 pK(a) 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. (31)P NMR titration studies between 1 and M(NO(3))(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. American Chemical Society 2021-09-13 /pmc/articles/PMC8459412/ /pubmed/34568676 http://dx.doi.org/10.1021/acsomega.1c02982 Text en © 2021 The Authors. Published by American Chemical Society https://creativecommons.org/licenses/by/4.0/Permits the broadest form of re-use including for commercial purposes, provided that author attribution and integrity are maintained (https://creativecommons.org/licenses/by/4.0/). |
spellingShingle | Virtanen, Emilia J. Perämäki, Siiri Helttunen, Kaisa Väisänen, Ari Moilanen, Jani O. Alkyl-Substituted Aminobis(phosphonates)—Efficient Precipitating Agents for Rare Earth Elements, Thorium, and Uranium in Aqueous Solutions |
title | Alkyl-Substituted Aminobis(phosphonates)—Efficient
Precipitating Agents for Rare Earth Elements, Thorium, and Uranium
in Aqueous Solutions |
title_full | Alkyl-Substituted Aminobis(phosphonates)—Efficient
Precipitating Agents for Rare Earth Elements, Thorium, and Uranium
in Aqueous Solutions |
title_fullStr | Alkyl-Substituted Aminobis(phosphonates)—Efficient
Precipitating Agents for Rare Earth Elements, Thorium, and Uranium
in Aqueous Solutions |
title_full_unstemmed | Alkyl-Substituted Aminobis(phosphonates)—Efficient
Precipitating Agents for Rare Earth Elements, Thorium, and Uranium
in Aqueous Solutions |
title_short | Alkyl-Substituted Aminobis(phosphonates)—Efficient
Precipitating Agents for Rare Earth Elements, Thorium, and Uranium
in Aqueous Solutions |
title_sort | alkyl-substituted aminobis(phosphonates)—efficient
precipitating agents for rare earth elements, thorium, and uranium
in aqueous solutions |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8459412/ https://www.ncbi.nlm.nih.gov/pubmed/34568676 http://dx.doi.org/10.1021/acsomega.1c02982 |
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