Compreignacite mineral
Compreignacite is the potassium uranyl oxide hydroxide hydrate mineral K2(UO2)6O4(OH)6(H2O)7, approved as IMA 1964-026 and listed with status A in September 2026. It is distinct from elemental uranium, uranium commodities and the synthetic sodium analogue called Na-compreignacite. Burns refined natural type-locality material from Margnac, Haute-Vienne, France in orthorhombic Pnnm; partially occupied interlayer potassium and water sites support the revised seven-water formula. The dissolution study below used synthetic K-bearing material represented with eight waters and a nonideal measured U:K ratio. Its preparation is not silently equated with ideal natural material. No criticality, microbial mechanism or industrial deployment is inferred.
Microbial & Biochemical Mechanisms (1)
Abiotic dissolution of synthetic K-compreignacite in flowing porewater
other
Synthetic K-bearing compreignacite mixed with quartz released uranium under flowing simulated porewater. Much more uranium left the columns in the higher-carbonate, higher-pH solution. Carbonate, pH, other solution constituents, initial mineral loading and run duration differed between treatments; this comparison does not isolate a carbonate-only causal effect. Initial potassium leaching and altered surface structure were observed or inferred, while uranyl-group detachment and ternary carbonate complexation remain proposed molecular explanations.
Experimental Context & Analytical Limits:
Synthetic material was prepared from uranyl nitrate and K2CO3 at approximately pH 5 and 100-105 degrees C for 24 hours, washed and air-dried. XRD, vibrational spectroscopy and EXAFS supported the phase assignment; TGA gave 6.60 percent mass loss interpreted as approximately eight waters. Table 3 gives U:K = 2.13 ± 0.05 rather than the ideal 3. Duplicate K columns were dry-packed with cleaned quartz and run upward at room temperature and ambient atmospheric CO2. Low-carbonate arms A/B used 0.21 mM total carbon, influent pH 6.65, 0.2363/0.2351 g mineral and 0.037 mL/min for 173 hours. High-carbonate arms C/D used 2.78 mM total carbon, pH 8.40, 0.0510/0.0524 g mineral and 0.035/0.037 mL/min for 190 hours. These are pH values after tubing, not reservoir or constant effluent pH. Nylon 0.2 micrometre filters bracketed the columns; ICP-MS measured effluent uranium. Quartz controls with and without dissolved uranium were included.
Synthetic material was prepared from uranyl nitrate and K2CO3 at approximately pH 5 and 100-105 degrees C for 24 hours, washed and air-dried. XRD, vibrational spectroscopy and EXAFS supported the phase assignment; TGA gave 6.60 percent mass loss interpreted as approximately eight waters. Table 3 gives U:K = 2.13 ± 0.05 rather than the ideal 3. Duplicate K columns were dry-packed with cleaned quartz and run upward at room temperature and ambient atmospheric CO2. Low-carbonate arms A/B used 0.21 mM total carbon, influent pH 6.65, 0.2363/0.2351 g mineral and 0.037 mL/min for 173 hours. High-carbonate arms C/D used 2.78 mM total carbon, pH 8.40, 0.0510/0.0524 g mineral and 0.035/0.037 mL/min for 190 hours. These are pH values after tubing, not reservoir or constant effluent pH. Nylon 0.2 micrometre filters bracketed the columns; ICP-MS measured effluent uranium. Quartz controls with and without dissolved uranium were included.
Curated Evidence Points:
Support
Source:
reinoso_maset2017
Table 2 reports 99.5 and 99.6 percent of initial uranium remaining in low-carbonate K columns A/B, compared with 37.7 and 41.7 percent in high-carbonate K columns C/D. Remaining amounts were calculated from initial loading minus integrated effluent release; they are not independent final-solid assays or purified-product recovery. Figures 2-3 show an initial pulse and approximate later steady state in low-carbonate arms, whereas high-carbonate arms did not attain steady uranium release. The published 58-87 percent removal range pools K and Na arms and is not assigned wholesale to this K mineral.
Partial
Source:
reinoso_maset2017
Table 6 reports duplicate-average RT-TST-VF optimized overall rates of 1.28e-13 and 1.57e-10 mol/m2/s for low and high carbonate K arms. These model-derived surface-area-normalized rates include fitted mineral volume and transport assumptions; they are not direct elementary rate constants. Corresponding steady-state-method estimates were 8.46e-13 and 6.02e-11. Sections 4.1-4.3 acknowledge possible early loss of sub-0.2 micrometre particles or colloids. The rate models assume stoichiometric dissolution and omit interlayer cation exchange. Microscopy and EXAFS support alteration but do not directly image a unique rate-determining atomic detachment step.
Partial
Source:
reinoso_maset2017_si
Table S3 uses seven-water compreignacite equilibria, whereas the main manuscript's synthesis and dissolution equation use eight waters. Figure S9 calculates speciation for uranium-added control solutions, whose compositions differ from the mineral influents in Table 1; its curves are not direct measurements of the dissolving-column effluent. SI chemistry and fitted sorption assumptions do not establish a measured percentage of a particular aqueous uranyl complex.
Context_only
Source:
reinoso_maset2017
Section 3.2.2 associates approximately 76 micromol/g solid U with high-carbonate K treatment, while Table 3 assigns 75.9 to low-carbonate and 16.2 to high-carbonate treatment. Section 4.2 calls the starting K material potassium-deficient despite Table 3's U:K ratio below three. Those conflicting solid composition interpretations are not reconciled by assumption or used to calculate an additional recovery. The source's sodium analogue remains a comparator, not a second natural identity or interchangeable K-mineral result.
Sources & References
-
ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. Compreignacite row, PDF page 49; status and accession definitions page 1. Fresh official PDF and row inspected.
https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-16) -
burns1998: Burns PC (1998). The structure of compreignacite, K2[(UO2)3O2(OH)3]2(H2O)7. Canadian Mineralogist 36:1061-1067. Complete seven-page published article inspected through RRUFF. Natural sample and methods page 1062; site occupancies Table 2; revised hydration and interlayer model pages 1065-1066. Hydrogen positions and deposited structure factors were not independently determined here; no verified DOI is assigned to this article.
https://www.rruff.net/doclib/cm/vol36/CM36_1061.pdf (accessed 2026-10-16) -
reinoso_maset2017: Reinoso-Maset E, Steefel CI, Um W, Chorover J, O'Day PA (2017). Rates and mechanisms of uranyl oxyhydroxide mineral dissolution. Geochimica et Cosmochimica Acta 207:298-321. DOI 10.1016/j.gca.2017.03.009. Complete 56-page accepted manuscript from official OSTI deposit 1349074 inspected, including main text, Figures 1-8 and Tables 1-6. Locators refer to manuscript printed pages, not final journal pagination: methods 6-15, results 16-23, discussion 23-31, Tables 1-3 pages 47-50 and Table 6 page 55. Final typeset main article was not acquired.
https://doi.org/10.1016/j.gca.2017.03.009 (accessed 2026-10-16) -
reinoso_maset2017_si: Reinoso-Maset et al. (2017), Supporting Information, 17 pages, DOI 10.1016/j.gca.2017.03.009. Publisher PDF acquired and inspected. Quartz preparation S1 page 2; control columns Figure S2 page 3; model chemistry Table S3 pages 8-9; sorption assumptions S5 and Table S4 pages 10-11; modeled rate comparison Figure S8 page 15; calculated control-solution speciation Figure S9 page 16.
https://ars.els-cdn.com/content/image/1-s2.0-S0016703717301473-mmc1.pdf (accessed 2026-10-16)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-16T05:59:16.058723Z |
codex (GPT-6; codex) | CREATE | Added verified natural identity and synthetic K-bearing column dissolution with distinct fitted rates, hydration and source conflicts. |
Record source: data/records/compreignacite.yaml