An integrated study of uranyl mineral dissolution processes: etch pit formation, effects of cations in solution, and secondary precipitation
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Bibliographic record
Abstract
Abstract Understanding the mechanism(s) of uranium-mineral dissolution is crucial for predictive modeling of U mobility in the subsurface. In order to understand how pH and type of cation in solution may affect dissolution, experiments were performed on mainly single crystals of curite, Pb 2+ 3 (H 2 O) 2 [(UO 2 ) 4 O 4 (OH) 3 ] 2 , becquerelite, Ca(H 2 O) 8 [(UO 2 ) 6 O 4 (OH) 6 ], billietite, Ba(H 2 O) 7 [(UO 2 ) 6 O 4 (OH) 6 ], fourmarierite Pb 2+ 1−x (H 2 O) 4 [(UO 2 ) 4 O 3−2x (OH) 4+2x ] ( x = 0.00–0.50), uranophane, Ca(H 2 O) 5 [(UO 2 )(SiO 3 OH)] 2 , zippeite, K 3 (H 2 O) 3 [(UO 2 ) 4 (SO 4 ) 2 O 3 (OH)], and Na-substituted metaschoepite, Na 1−x [(UO 2 ) 4 O 2−x (OH) 5+x ] (H 2 O) n . Solutions included: deionized water; aqueous HCl solutions at pH 3.5 and 2; 0.5 mol L −1 Pb(II)-, Ba-, Sr-, Ca-, Mg-, HCl solutions at pH 2; 1.0 mol L −1 Na- and K-HCl solutions at pH 2; and a 0.1 mol L −1 Na 2 CO 3 solution at pH 10.5. Uranyl mineral basal surface microtopography, micromorphology, and composition were examined prior to, and after dissolution experiments on micrometer scale specimens using atomic force microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. Evolution of etch pit depth at different pH values and experimental durations can be explained using a stepwave dissolution model. Effects of the cation in solution on etch pit symmetry and morphology can be explained using an adsorption model involving specific surface sites. Surface precipitation of the following phases was observed: (a) a highly-hydrated uranyl-hydroxy-hydrate in ultrapure water (on all minerals), (b) a Na-uranyl-hydroxy-hydrate in Na 2 CO 3 solution of pH 10.5 (on uranyl-hydroxy-hydrate minerals), (c) a Na-uranyl-carbonate on zippeite, (d) Ba- and Pb-uranyl-hydroxy-hydrates in Ba-HCl and Pb-HCl solutions of pH 2 (on uranophane), (e) a (SiO x (OH) 4−2x ) phase in solutions of pH 2 (uranophane), and (f) sulfate-bearing phases in solutions of pH 2 and 3.5 (on zippeite).
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it