Praseodymium element Critical Material
The element Pr, distinct from dissolved Pr(III), its salts and oxides, Pr-containing magnet alloys and ore or waste resources. The US2025 designation applies to the named praseodymium mineral commodity. Evidence below concerns cell-free protein chromatography of a synthetic binary solution, not microbial growth on an ore or industrial recovery.
Identifiers & Classification
| System | Identifier | Label |
|---|---|---|
| CHEBI |
CHEBI:49828
|
praseodymium atom |
Criticality Designations
| Jurisdiction | List Name | Edition / Document | Classification | Source |
|---|---|---|---|---|
| United States of America | USGS Final List of Critical Minerals | 2025; Federal Register 90:50494-50497, 7 November 2025 | critical |
usgs2025
|
Microbial & Biochemical Mechanisms (1)
Praseodymium separation from lanthanum using immobilized Melba-LanM
separation
Microbial
Associated Organisms:
Methylobacterium sp. 13MFTsu3.1M2 (NCBITaxon:1502776)
Melba-LanM, ortholog o-36 attributed by the study to Methylobacterium sp. 13MFTsu3.1M2, retained Pr(III) more strongly than La(III) during acid elution of a binary feed. The purified bacterial protein carried a terminal GSGC tag and was immobilized on agarose. Microbial involvement denotes protein origin and recombinant production; no living cells were present in the metal-separation step. Escherichia coli BL21(DE3) was the expression host, not the organism of origin.
Experimental Context & Analytical Limits:
Methods, Column experiments III, specify a 0.8 mL agarose bed in a 0.5 cm by 5 cm column, pre-equilibrated with 10 mM glycine at pH 3 for 20 minutes. The synthetic binary feed contained 0.4 mM of each ion, 0.8 mM total, applied for two minutes at approximately 0.32 mL/min and a reported 10% capacity. After a 20-minute water wash, the elution used pH 2.4 for 140 minutes then pH 1.5 for 25 minutes. Fractions were analyzed by ICP-MS; one fraction represented one 0.8 mL bed volume. Mex-LanM, ortholog o-621, was the protein comparator. Figure 6d represents one run. Separately fabricated 0.4 mL columns with a new protein batch were tested in three independent runs in Extended Data Figure 8; their scale and elution schedule differ. Column operating temperature was not explicitly stated. Neither complex waste leachates nor industrial deployment were demonstrated.
Methods, Column experiments III, specify a 0.8 mL agarose bed in a 0.5 cm by 5 cm column, pre-equilibrated with 10 mM glycine at pH 3 for 20 minutes. The synthetic binary feed contained 0.4 mM of each ion, 0.8 mM total, applied for two minutes at approximately 0.32 mL/min and a reported 10% capacity. After a 20-minute water wash, the elution used pH 2.4 for 140 minutes then pH 1.5 for 25 minutes. Fractions were analyzed by ICP-MS; one fraction represented one 0.8 mL bed volume. Mex-LanM, ortholog o-621, was the protein comparator. Figure 6d represents one run. Separately fabricated 0.4 mL columns with a new protein batch were tested in three independent runs in Extended Data Figure 8; their scale and elution schedule differ. Column operating temperature was not explicitly stated. Neither complex waste leachates nor industrial deployment were demonstrated.
Curated Evidence Points:
Support
Source:
diep2026
Figure 6d and Results, C5 LanMs reject lanthanum for enhanced RE separations, report above 99.9 mol% Pr purity and 83.2% yield for the selected aqueous Pr fraction. The figure labels these 99.97% and 83.16%; its shaded collection region spans bed volumes 48-80. In Source Data Figure 6, sheet o36 Agarose La-Pr, summing Pr values in that region divided by Pr across all 96 tabulated fractions reproduces the rounded 83.16% value. This supports a fraction-recovery interpretation, not an independently verified feed-to-product mass balance or isolated elemental-Pr yield. Mex-LanM largely co-eluted Pr and La under the same binary protocol.
Partial
Source:
diep2026
Results and Extended Data Figure 8d report 96.5 +/- 0.2 mol% Pr purity and 72.0 +/- 5.8% yield for the three repeat runs, lower than the single Figure 6d result. Selected repeat fractions were 53-93; the first elution step is shown at pH 2.5, not the pH 2.4 of Figure 6d. Thus the best purity is conditional on the tested protein preparation, scale and collection window. The comparison supports this protein-based separation, not a unique cellular process, separation from every competing REE, or a requirement for biological metabolism. No exact causal amino-acid substitution is established by the separation experiment.
Sources & References
-
chebi_praseodymium: ChEBI CHEBI:49828 - praseodymium atom; formula Pr, net charge 0
https://www.ebi.ac.uk/chebi/CHEBI:49828 (accessed 2026-10-11) -
usgs2025: USGS (2025). Final 2025 List of Critical Minerals. Federal Register 90:50494-50497, document 2025-19813; named praseodymium entry.
https://www.govinfo.gov/content/pkg/FR-2025-11-07/html/2025-19813.htm (accessed 2026-10-11) -
diep2026: Diep, Madsen, Choi et al. (2026). A family portrait of lanmodulin selectivity for enhanced rare-earth separations. Nature Chemical Biology 22:829-839; DOI 10.1038/s41589-026-02176-3, PMID 41851437, PMC13128445. Figure 6d, Extended Data Figure 8c-d, Methods, Supplementary Figures 37-40 and associated source data.
https://doi.org/10.1038/s41589-026-02176-3 (accessed 2026-10-11) -
ncbi_melba_origin: NCBI Taxonomy 1502776 - Methylobacterium sp. 13MFTsu3.1M2; species-rank node for the study-named protein-origin organism.
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=1502776 (accessed 2026-10-11)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-11T06:27:14Z |
Codex (GPT-6; Codex) | CREATE | Added verified elemental identity, dated US2025 criticality and qualified cell-free protein separation evidence after primary-source inspection; retained experimental and source limitations. Independent scientific review is recorded separately. |
Record source: data/records/praseodymium.yaml