Étude de l'absorption des gaz acides dans des solvants mixtes : développement d'une approche expérimentale originale et modélisation des données par une équation d'état d'électrolytes

The aim of this study is the characterisation of VLE and chemical equilibria for the systems CO2/Diethanolamine-(DEA)/H2O/MeOH and CO2/Diethanolamine-(DEA)/H2O/PEG400. The effect of physical solvent composition on CO2 absorption has been studied using four compositions (from 0% to 30wt% of alcohol with a fixed composition-30%- of DEA), the measurement being made at T=298.15K and at various CO2 loading (0 to 0.9). The experimental measures concerned a both solubility data and liquid phase analysis was obtained. The effect of MeOH composition has been studied using the original experimental device developed previously (Sidi-Boumedine, 2003). For the system with PEG 400, a new experimental device excluding the pressure limitation of the precedent experimental device was developed. The original data base obtained, including the new solubility data and the liquid phase composition, allows the modelling of the system CO2/DEA/H2O/MeOH using an electrolyte equation of state (Fürst, 1993) representing the equilibrium properties of the system and the liquid phase speciation.Le but du présent travail est la caractérisation des équilibres chimiques et des ELV pour les systèmes CO2/Diethanolamine(DEA)/H2O/MeOH et CO2 /Diethanolamine (DEA)/H2O/ PEG400. L'effet de composition du solvant physique sur l'absorption du CO2 a été étudié en utilisant quatre compositions (de 0% à 30% en masse d'alcool avec une composition fixe - 30% - de DEA), les mesures étant réalisées à une température de 298,15K et à divers taux de charge en CO2 (de 0 à 0,9). Les mesures expérimentales réalisées concernaient à la fois des données de solubilité et des donnée de spéciation. Ainsi, L'effet de composition de MeOH a été étudié en utilisant le dispositif expérimental original déjà utilisé pour l'analyse des systèmes Eau-DEA-CO2 (Sidi-Boumedine, 2003). Pour le système avec PEG 400, un nouvel dispositif expérimental permettant d'écarter la limitation de pression du précédent dispositif a été développé. La base de données originale obtenue comprenant des nouvelles données de solubilité et de composition de la phase liquide a permis la modélisation du système CO2/DEA/H2O/CH3OH en utilisant une équation d'état d'électrolyte développée au laboratoire (Fürst, 1993) représentant ainsi les propriétés d'équilibre du système que la spéciation en phase liquide

Influence of dissolved oxygen on the bioleaching efficiency under oxygen enriched atmosphere

International audienceThe use of oxygen enriched air is a common practice in high-temperature bioleaching tests (> 70°C) to overcome oxygen solubility limitation and reduced the energy costs of the process. Air is usually preferred in medium and low-temperature operations mainly for technical and economic constraints. Nevertheless, under high-sulfide loading conditions - high-grade metal sulfide concentrates and high solids concentration - the microbial and chemical demand for oxygen is significantly increased during the bioleaching process. If not satisfied, this high oxygen demand might limit the oxidation efficiency. Therefore it requires the injection of large amounts of air. Sparging with oxygen enriched gas instead of air may offer an interesting alternative process option to improve gas transfer in the bioleaching reactor and to provide an adequate oxygen supply in order to satisfy the oxygen demand. It might be useful to develop innovative alternative to the classical stirred tank reactor (STR) technology. However, the use of such conditions can lead to much higher dissolved oxygen (DO) concentrations than those encountered with air. Very few papers have been devoted to the study of the optimal range of DO concentrations for bioleaching processes. Most of them reported an inhibitory effect of DO concentrations above 5 ppm. The purpose of this study was to investigate the influence of DO on the bioleaching efficiency under oxygen-enriched atmosphere in 21 L stirred tank reactor at 42°C. Bioleaching experiments were performed in continuous mode with sulfide-rich tailings wastes composed mainly of pyrite (51%) and quartz using the “BRGM-KCC” bacterial consortia. The solid load was close to 20% (w/w). Using various oxygen supply conditions (partial pressure, gas rate), the DO concentration in the reactor varied between 4 and 17 ppm. For a DO ranging from 4 to 13 ppm, a good bacterial oxidizing activity was observed and the sulfide dissolution efficiency increased with the DO concentration. It is assumed that this improvement of the bioleaching efficiency was linked to an increase of the oxygen transfer rate from the gas phase to the liquid phase rather than a direct effect of the DO level. When the DO concentration reached 17 ppm a significant decrease of the microbial activity and consequently of the oxygen consumption was noticed. These results show that there is a critical value above which the DO concentration is detrimental to the activity of the bioleach microorganisms present in the “BRGM-KCC” consortia but this value is much higher than the one usually mentioned in the literature