Procédé de préparation de ferrates (VI)

Procédé de préparation de granulés de ferrate (VI) comprenant l'enrobage de particules solides d'un hydroxyde de métal alcalin et/ou alcalino-terreux par des particules solides d'un ou de plusieurs sels ou oxydes de Fe(II) et/ou Fe(III), suivie par la conversion dans un réacteur à lit fluide du ou des sels ou oxydes de Fe(II) et/ou Fe(III) en ferrate (VI) dans un gaz de fluidisation contenant du chlore

Extraction des métaux de valeur des concentrés de chalcopyrite et de chromite par chloruration

UnavailableLa métallurgie extractive de métaux non ferreux tels que le cuivre, etc. génère des effluents gazeux et liquides ainsi que des déchets solides. Malgré les efforts faits par ce secteur d'activité, ces rejets, même partiels, posent des problèmes pour l'environnement. Ce travail est focalisée sur la possibilité de la chloruration sélective des concentrés de chalcopyrite et de chromite dans le but de récupérer ou de concentrer les métaux de valeur. Deux concentrés de chalcopyrite et un concentré de chromite ont été utilisés. La chloruration de ces solides est réalisée en montage horizontal et en ATG. La caractérisation physico-chimique des échantillons de départ et des produits de réaction est réalisée par MEB, DRX, MSE et Analyse Chimique. La chloruration des concentrés de chalcopyrite par le mélange Cl2+N2 est possible à 300°C et aboutit à la chloruration quasi totale de sulfures et à la volatilisation complète des chlorures de fer et de soufre. Plus de 95% du cuivre de la chalcopyrite se trouvent dans le résidu. Un schéma de procède est proposé pour le traitement du concentré de chalcopyrite permettant la récupération de chlorure de cuivre et de soufre élémentaire ainsi que le recyclage du chlore. L’extraction totale du chrome est possible par la carbochloruration du concentré de chromite aux environs de 900°C. La quasi-totalité du fer et une partie du chrome peuvent être extraits soit par l'oxychloruration à 950°C soit par carbochloruration à 550°C. Des schémas des procédés sont proposés. Ces schémas peuvent être appliqués pour le traitement et le recyclage de déchets contenant de chrome comme les catalyseurs, réfracteurs usés, les sables de fonderies, etc

Kinetics of carbochlorination of chromium (III) oxide

International audienceKinetics of the carbochlorination of Cr2O3 has been studied with Cl2+CO gas mixtures between 500 °C to 900 °C using thermogravimetric analysis. The apparent activation energy is about 100 kJ/mol. Mathematical fitting of the experimental data suggests that the shrinking sphere model is the most adequate to describe the carbochlorination mechanism of chromium oxide and that is controlled by the chemical reaction. In the temperature range of 550 °C to 800 °C, the reaction order is about 1.34 and is independent of temperature. Changing the Cl2+CO content from 15 pct to 100 pct increases the reaction rate and does not affect the reaction mechanism. Similarly, changing the ratio of Cl2/(Cl2+CO) from 0.125 to 0.857 do not modify the carbochlorination mechanism of Cr2O3. In these conditions, the reaction rate passes through a maximum when using a chlorinating gas mixture having a Cl2/(Cl2+CO) ratio of about 0.5

Recycling policy in the European Union

International audienceRecycling in the European Union (EU) has benefited from R&D efforts and strict environmental regulations of the EU's members. Thanks to the adoption of sustainable development policies by the EU's European Institutions, economic incentives are expected to further strengthen the recycling industry. Moreover, the historical accumulation of non-ferrous metals in Europe will likely enhance secondary metal production. Also contributing to EU recycling is mining in East European countries and the resulting industrial waste. The rate of growth of the recycling industry is expected to approach double digits for at least this decade

Chlorination: a potential approach for the beneficiation of chromite

International audienceOne of the criteria to define the market value of chromite concentrate is its chromium to iron ratio. Changing this ratio for a definite chromite mineral is impossible by physical processing. This study investigated the possibility of increasing this ratio through the carbochlorination and the oxychlorination of chromite concentrates. Experiments are carried out up to 1000°C. The characteristics of samples and reaction products are determined by SEM, XRD and chemical analysis. The carbochlorination of a chromite concentrate at about 600°C leads to the selective partial elimination of iron allowing a higher Cr/Fe ratio of the treated concentrate. Selective extraction of iron could also be achieved at about 950°C by oxychlorination. In this case, a part of chromium contained in the concentrate is recovered as chromium oxychloride. The obtained residue had high content of Cr, Mg and Al oxides. Such material has probably better chemical and thermal properties that may be useful for foundry and refractory applications. Two flow-sheets for the beneficiation of the chromite concentrates using carbo- and oxychlorination are suggested

Kinetics of oxychlorination of chromium (III) oxide

International audienceThe kinetics of oxychlorination of pure Cr2O3 with Cl2+O2 gas mixtures is studied by ThermoGravimetric Analysis (TGA) in non and isothermal conditions up to 1000°C. The reaction of Cr2O3 with Cl2+O2 chlorination gas mixtures starts at about 550°C and the reaction product is CrO2Cl2. The oxychlorination rate of Cr2O3 is almost proportional to the chlorine partial pressure and to the fourth root of the oxygen partial pressure in the chlorinating gas mixtures. At 800°C, the maximum chlorination rate is obtained using a gas mixture having a Cl2/O2 ratio equal to 4. The apparent activation energy of the oxychlorination reaction of Cr2O3 is 87 and 46 kJ/mol at temperatures lower and higher than 650°C, respectively. By varying the chlorine and the oxygen partial pressures of the oxychlorinating gas mixtures at temperatures higher than 550°C, it is possible to extract selectively the chromium chlorinated compounds from the chromium bearing materials

Kinetics of chlorination of chromite

International audienceChlorination can be an efficient alternative for the physical beneficiation of refractory metals' bearing materials. The chlorination of a chromite mineral was studied up to 1050 °C using thermogravimetric analysis. The effects of the gas flow rate, temperature and partial pressure of the reactive gases on the reaction rate were studied in isothermal conditions. Only FeCr 2O 4 could be chlorinated up to 1000 °C by Cl 2+O 2 and Cl 2+N 2 gas mixtures generating chromium oxychloride (CrO 2Cl 2) that can be recovered by cooling the gas phase. The oxychlorination can ameliorate the characteristics of chromite bearing materials and/or the recovery of the chromium compounds from its wastes