Kinetcis of silicothermic reduction of clacined dolomite in flowing argon atmosphere
The magnesium vapour extracted is removed using vacuum condition to condense as a dense metal. Thermodynamic analysis of this process has been carried out in the past to predict the distribution of the metal impurities in condensed magnesium. The results suggested that a number of impurities in different phases formed in the region between reaction zone and condenser. The thermodynamic results only are not sufficient to describe the process, and the knowledge of the kinetics of the Pidgeon process is required. Kinetics plays important role to give more insight to the process such as for process design and control.
Silicothermic Reduction of Dolomite Ore Under Inert Atmosphere
Abstract Magnesium metal was produced from dolomite ore under inert atmosphere using ferrosilicon as a reducing agent. The kinetics of the silicothermic reduction process was studied at a temperature range from 1150-1300 °C. The charges studied are in the form of briquettes. The parameters studied are silicon stoichiometry, temperature and time of preheating, calcium fluoride additive, molar ratios of calcium oxide/magnesium oxide, flow rate of inert gas, briquetting pressure, temperature and time of reduction process. The maximum reduction extent of about 92% was achieved when using charges in the form of briquettes containing 2.5 wt.% CaF2, CaO/MgO molar ratio of 1.6 and using silicon as reductant with its weight ratio/MgO equals 1.45 at 1300 °C for 5 hours. The discussion takes into considerations the type of intermediate compounds formed during the reduction and the mechanism of the silicothermic reduction process. It was found that the silicothermic reduction process of dolomite ore is a solid-state reaction controlled by diffusion of reacted species and the apparent activation energy obtained equals 306 KJ.mol-1. On a produit du magnésium-métal à partir de minerai de dolomite en atmosphère inerte en utilisant du ferrosilicium comme agent de réduction. On a étudié la cinétique du procédé de réduction silico-thermique dans une gamme de température de 1150-1300 °C. Les charges étudiées avaient la forme de briquettes. Les paramètres étudiés incluent la stoechiométrie du silicium, la température et la durée de préchauffage, l’addition de fluorure de calcium, les rapports molaires oxyde de calcium/oxyde de magnésium, le taux d’écoulement du gaz inerte, la pression de mise en briquette, la température et la durée du procédé de réduction. La réduction maximum d’environ 92% a été obtenue lorsqu’on utilisait des charges en forme de briquettes contenant 2.5% en poids de CaF2, avec un rapport molaire CaO/MgO de 1.6 et avec du silicium comme agent de réduction, avec un rapport de son poids/MgO égal à 1.45, à 1300 °C pendant 5 heures. La discussion prends en considération le type de composés intermédiaires formés lors de la réduction et le mécanisme du procédé de réduction silico-thermique. On a trouvé que le procédé de réduction silico-thermique du minerai de dolomite était une réaction à l’état solide contrôlée par la diffusion des espèces ayant réagi; on a obtenu une énergie d’activation apparente égale à 306 kJ.mol-1.
Coated-wire electrodes containing polymer immobilized ionophores blended with poly(vinyl chloride).
Polymers containing covalently attached 18-crown-6 or 2.2.2 cryptand units were incorporated into plasticized PVC membranes and the composite membranes were examined as potassium ion sensor elements. Ionophores were linked to carboxy-PVC and to poly(acrylic acid) via amide linkages to an alkyl spacer unit. Coated-wire electrodes (CWEs) from the immobilized ionophores gave acceptable responses, but conventional ion-selective membrane electrodes (ISEs) prepared by solvent casting were inactive. Dip-cast membranes did give active ISEs. Potassium electrode performance was independent of the loading of the ionophore within the acrylate support polymer, but depended upon the spacer length. Ion selectivity varied with the ionophore loading within the support polymer. Selectivity is a composite of the ionophore selectivity and ion-exchange interactions with the acrylate backbone, giving selectivities akin to carboxylate substituted crown ethers, notably enhanced monovalent/divalent ion discrimination relative to the ionophore in solution. Polymer immobilization extended the lifetime of active electrodes.