A fundamental study of the acidic pressure oxidation of orpiment and pyrite and high temperature
Notice bibliographique
Résumé
The acidic pressure oxidation of pyrite (FeS2) and orpiment (As2S3), as a pretreatment of refractory gold ores, has been studied by investigating the reaction chemistry and kinetics. The effects of retention time, temperature, particle size, oxygen partial pressure, pulp density, sulfuric acid concentration, and cupric ions were evaluated for both minerals. The effect of ferric ions on the oxidation rate of As(III) to As(V) was also examined. Also, the effects of mole ratio of Fe/As on the oxidation of pyrite and orpiment mixtures were evaluated. During the acidic pressure oxidation of orpiment, most of the arsenic was found to be in the trivalent state after 2 hours oxidation at temperatures ranging from 170 to 230°C, and subsequent oxidation to As(V) with oxygen was very slow. Cupric ions do not affect the oxidation of As(III). However, the rate of oxidation of As(III) to As(V) is rapid in the presence of ferric ions. Sulfate becomes the predominant product species only at temperatures above 190°C. The oxidation kinetics are controlled by product layer diffusion with an Arrhenius activation energy of 22.2 kJ/mol (5.31 kcal/mol) over the temperature range of 170 to 210°C. However, as temperature increases above 210°C, the rate-controlling step switches to a surface chemical reaction with an Arrhenius activation energy of 50.0 kJ/mol (12.0 kcal/mol). The initial reaction rate is approximately -1/5 order with respect to pulp density, and 1/4 order with respect to oxygen partial pressure in the system studied. During the acidic pressure oxidation of pyrite, ferric, instead of ferrous, is the initial product at high temperatures. No elemental sulfur was found at temperatures above 190°C. An activation energy of 33.2 kJ/mol (7.94 kcal/mol) was observed over the temperature range 170 to 230°C. The reaction order with respect to oxygen partial pressure was found to be 1/2 at 210°C, which indicates an electrochemical mechanism of oxidation. The oxidation kinetics follow shrinking particle behavior. The surface chemical reaction is the rate-controlling step. The passivating shrinking sphere model was developed to represent the pressure oxidation of pyrite in the system studied at high temperature, based on the batch experimental data, which can be used to further develop a mathematical model to simulate continuous autoclave oxidation. During the acidic pressure oxidation of mixtures of pyrite and orpiment, As(III) generated from orpiment was oxidized rapidly to very low levels in the presence of pyrite or the Fe(III)/Fe(II) couple. However, the oxidation rate of ferrous decreased in the presence of orpiment. Iron arsenate was generated in all tests conducted for the mixture, which is of critical importance in view of the current controversy surrounding the environmental stability of these compounds. Elemental sulfur was produced only at low ratios of Fe/As. The pressure oxidation of orpiment is much slower than that of pyrite due to the formation of elemental sulfur. However, when the two minerals are mixed together, preferential leaching for orpiment is feasible due to galvanic effects. Thus orpiment oxidation is accelerated, while oxidation of the nobler pyrite is slowed.
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 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 | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,001 |
| 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 source (Gemma direct ou Codex distillé), 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 ».