Étude de la mobilité du radium-226 en milieu naturel anthropisé par approches expérimentales et modélisation géochimique
Notice bibliographique
Résumé
226Ra, a radioactive decay product of 238U and the most prevalent naturally occurring isotope of radium leads to many environmental issues in various industries due to its half-life of 1600 years: hydrothermal energy, seawater desalination and zircon production among others. The most impacted industries are the extractive ones: shale oil and gas production, coal, phosphate and uranium extraction. 226Ra remains in tailings from U mines and its mobility is controlled by retention mechanisms: sorption on mineral surfaces (iron oxy-hydroxydes, phyllosilicates, zeolites) and organic matter, or by the formation of solid solutions (sulfate minerals such as barite and carbonate minerals). The average concentration in lithospheric rocks being 32Bq / kg, or 1ppt, the identification of the retention mechanisms of this radionuclide at the scale of the material sampled in the field is made difficult because it is an ultra-trace element. Sequential extractions are commonly used to assess the retention of trace elements, but this technique is subject to experimental and analytical artefacts which are exacerbated in the case of an ultra-trace element. In this work, geochemical modeling of sequential extractions experiments has indeed shown that this technique leads to biased interpretations, particularly in the case of 226Ra which is remobilized during the different extraction steps. In order to have a better understanding of the retention of 226Ra and its distribution in heterogeneous and fine-grained materials, including mine tailings, a new approach has been developed. This approach combines alpha autoradiography, chemical elemental cartographies and mineralogical characterizations obtained on petrographic thin sections. A direct global analysis of the activity of the sample at the petrographic thin section scale is thus possible. This method was first qualified on model samples containing a single synthetic or natural mineral playing an important role in the retention of 226Ra in the natural environment. It was then tested on an assemblage of three of the main minerals responsible for the retention, namely: barite, clay minerals and iron oxy-hydroxydes. Finally, it was applied to U-mine tailings. A first set of samples comes from the French post-mining storage sites of Bellezane, where the tailings are stored under a solid cover, and from Bois Noirs Limouzat, which uses a liquid cover. A second set of tailings sample comes from the on-going ore processing facility of McClean Lake, Canada, which uses a tailings neutralization process by barite precipitation. The results show that barite is the main trap of 226Ra via the formation of a solid solution (Ba, Ra)SO4 in all these tailings from different sites. Over a few years, with or without neutralization by barite precipitation, it appears that this solid solution tends towards a recrystallization equilibrium which controls the concentration of 226Ra in solution. These results will subsequently be integrated into reactive transport type modeling to predict the long-term behavior of these tailings.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,019 | 0,003 |
| Méta-épidémiologie (sens strict) | 0,001 | 0,001 |
| Méta-épidémiologie (sens large) | 0,001 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,002 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,001 | 0,002 |
| Intégrité de la recherche | 0,001 | 0,004 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».