Investigations into the synthesis, characterisation and uranium extraction of the pyrochlore mineral betafite
Notice bibliographique
Résumé
The usage of nuclear power, to generate base-load electricity, has steadily increased in acceptance as a more environmentally friendly alternative to fossil fuels since its first commercial introduction in the 1950s. Increasing consumption of uranium and the rising demand for nuclear fuel has led to a deficiency of high grade uraninite and pitchblende deposits. This has led to increased attention on the refractory uranium pyrochlore betafite due to its abundance in currently exploited uranium deposits.<br><br>In this document primary work was conducted on natural betafite from Ambatofotsy Madagascar, Miarinarivo Madagascar and Silver Crater Mine, Canada. X-ray diffraction analysis showed that anatase was the only crystalline compound present in each of the unheated samples. After being heated to 1200 °C all samples exhibited diffraction lines characteristic of betafite and rutile, indicating that the betafite present in the preheated samples was amorphous (metamict). Electron probe microanalysis of the samples showed a high degree of compositional heterogeneity throughout each sample, most likely caused by aqueous fluid interactions forming secondary alteration products. All unheated samples were subject to a sulfuric acid leach over 6 h with the extent of uranium dissolution correlated with the degree of alteration. The most highly altered sample had 42% U dissolution while the least-altered exhibited only 7%.<br><br>Due to the differences in the degree of alteration observed in the natural samples it was decided to synthesise a pure betafite sample via a solid state synthesis route. The optimum conditions for the synthesis of betafite were found to be heating the reactants required at 1150 °C for 48 h under an inert gas atmosphere. XPS analysis of the sample showed that the uranium in the synthesised betafite was predominately present in the U5+ oxidation state. A minor amount of U6+ was also detected which was possibly due to surface oxidation.<br><br>Dissolution studies were then conducted on the synthetic betafite to investigate the influence of various parameters on leaching. The results showed the uranium dissolution curves obtained over a range of experimental conditions demonstrated three discrete segments representing significantly different rates of uranium dissolution. The first segment occurred in the initial minute and involved extremely rapid dissolution. This segment made up for the majority of the overall uranium dissolution obtained over the test period (~2.0% U). The second segment between 1 – 120 minutes was characterised by slow uranium dissolution rates which could be partially influenced by altering the experimental conditions. The uranium dissolution rate in the third segment was negligible due to passivation of the sample surface leaving no exposed uranium available for leaching.<br><br>Long term dissolution studies were also conducted on the synthetic betafite sample in order to determine the leach rate over a 90 day leach period. The results of these experiments showed very minor influences were observed when each of the standard parameters (temperature, [H2SO4], [FeTOT] and redox potential) were studied. The influence of fluoride addition showed a slightly greater leach rate than that achieved with high acid concentration, though the main difference between this experiment and other experiments conducted with no fluoride was the solubilisation of the metals Ti, Nb and Ta which were not observed to leach in experiments where fluoride was not added.<br><br>Post leach characterisation of synthetic betafite identified only minor changes occurred in the sample. These changes included the formation of pyrochlore and a greater concentration of rutile was observed to be present. Analysis via XPS of the post leach residues showed the samples contained similar U oxidation states to those observed in the preleached samples. Moreover, significantly greater Ta was observed via XPS in the post leach sample indicating that the Ta concentration had increased on the surface of the mineral. This indicated a possible passivation layer which caused the low rate of dissolution that was observed to occur.
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 | 0,001 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,001 | 0,000 |
| Communication savante | 0,000 | 0,001 |
| Science ouverte | 0,001 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 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 ».