Chlorination Of Alumina Research Articles

Chlorination of Alumina Obtained from Nepheline Concentrate Processing and Comparative Assessment of the Complete Aluminum Production Cycle

Abstract—Extended tests of alumina fluid chlorination are performed. The implementation of the chlorine technology is possible when using alumina, which has a high reactivity with chlorine. The improved nepheline technology for obtaining such an oxide is proposed: non-desilicated aluminate liquors undergo carbonization followed by separation of aluminum hydroxide with sodium hydroaluminosilicate and its calcination at 600–800°C. The proposed upgrade, compared to the existing method, is less energy intensive. Two-stage desilication is eliminated, and more favorable conditions are created for the low-temperature digestion of sintered material, reducing the secondary losses of alumina and alkali. The technological parameters of charge chlorination, both powdered and pelleted, are worked out on a scaled-up installation in fluidized bed conditions. The operational and capital cost of a complete aluminum production cycle based on the chlorine technology are evaluated in comparison with the conventional alumina production according to the Bayer process and subsequent electrolysis of cryolite-alumina melts. The comparative cost analysis has shown the advantages of the chlorine technology at the stage of aluminum chloride electrolysis (up to 30%) and the presence of additional costs at the stage of obtaining the intermediate product for chlorination. The chlorine method of aluminum production in modern conditions has the prospects of development not as a mass technology, but as an effective process for obtaining high-purity aluminum (HPA) in small workshops.

Хлорирование оксида алюминия, полученного при переработке нефелинового концентрата и сравнительная оценка полного цикла производства алюминия

Хлорирование оксида алюминия, полученного при переработке нефелинового концентрата и сравнительная оценка полного цикла производства алюминия

Synthesis of magnesium aluminate spinel by periclase and alumina chlorination

A pyrometallurgical route for the synthesis of magnesium aluminate spinel by thermal treatment of a mechanical mixture containing 29wt% MgO (periclase) and 71wt% Al2O3 (alumina) in chlorine atmosphere was developed and the results were compared with those obtained by calcining the same mixture of oxides in air atmosphere. Isothermal and non-isothermal assays were performed in an experimental piece of equipment adapted to work in corrosive atmospheres. Both reagents and products were analyzed by differential thermal analysis (DTA), X-ray diffraction (XRD) and X-ray fluorescence (XRF). Thermal treatment in Cl2 atmosphere of the MgO–Al2O3 mixture produces magnesium aluminate spinel at 700°C, while in air, magnesium spinel is generated at 930°C. The synthesis reaction of magnesium aluminate spinel was complete at 800°C.

Carbothermic Reduction and Chlorination of Alumina with Coal in Vacuum

Metal aluminum was produced in a vacuum furnace using coal as reductant and aluminum chloride as chlorination agent and examined by means of XRD and SEM. The produced metal aluminum was impure. Reaction mechanism analysis showed that the carbothermic reduction of alumina with coal occurred following the chlorination, then metal aluminum was accquired and condensed on the collecting plate. A probable mechanism concerning carbothermic reduction and chlorination was discussed.

An FT-IR and Reactor Study of the Dehydrochlorination Activity of CuCl2/γ-Al2O3-Based Oxychlorination Catalysts

The conversion of ethylchloride into ethylene+HCl on pure and doped alumina supports and on CuCl2–Al2O3-based oxychlorination catalysts has been investigated by pulse reactor and FT-IR spectroscopy. FT-IR spectra of ethylchloride adsorbed on γ-Al2O3 show weakly molecularly adsorbed species and ethoxy groups formed by nucleophilic substitution. Additionally, adsorbed diethylether is also observed. The analysis of the gas-phase species shows that ethoxy groups decompose, giving rise to ethylene at 523 K. Under the same conditions, gaseous HCl is also released from the surface and diethylether is also observed in the gas phase. Chlorination of alumina with HCl only partially hinders the dehydrochlorination mechanism occurring through ethoxy groups. Experiments performed on alumina doped with MgCl2 and KCl indicate that the site reactivity scale for EtCl conversion to ethylene is the following: bare Al2O3>CuCl2 on Al2O3>MgCl2 on Al2O3>KCl on Al2O3. Doping with MgCl2 and in particular with KCl limits the activity of the bare support in the dehydrochlorination. These data strongly support the previous proposal that the exposed alumina surface catalyzes the dehydrochlorination of EDC to VCM, with a consequent loss in selectivity in the oxychlorination reactor. The beneficial effect of doping with KCl and MgCl2 is due to the reduced dehydrochlorination activity.

Photolytic effects in alumina chlorination

The temperature dependence of the rate of chlorination of α-alumina with CO/Cl2 gas mixtures exhibits an anomaly, a departure from the normal Arrhenius behavior, in the range 650 to 850°C; it is manifested as a local maximum in the Arrhenius plot at 670°C followed by a local minimum in the range 770 to 850°C. By carefully studying the effect of irradiation of the CO/Cl2 gas mixtures on the rate of chlorination of α-alumina, it is shown that such an anomaly, which has been observed in the chlorination of various metallic oxides, is most likely due to the photochemical formation of phosgene (COCl2) by ambient light incident on the reactant gas mixture during its transport to the main reactor. Phosgene is a better chlorinating agent than a CO/Cl2 mixture. The mechanism of chlorination of α-Al2O3 by CO/Cl2 mixtures subjected to the light emitted by a high-pressure Hg-vapor lamp is elucidated.

Chlorination of alumina in kaolinitic clay

The chlorination of alumina in kaolinitic clay with Cl2 and CO gas mixtures was studied gravimetrically. The effects of the calcination method and of NaCl addition on the reactivity of the clay were examined. Fast reaction rates were achieved only with samples previously exposed to a sulfating treatment. Optimum conditions, with maximum yield and selectivity to A1C13 and minimum SiO2 conversion, were found between 770 and 970 K. At higher temperatures the SiCl4 formed poisons the reactive alumina surface by selective chemisorption with a marked decrease of the reaction rate.

塩浴を反応媒体とするボーキサイトの塩化

Bauxite was chlorinated in molten salts using chlorine gas and carbon to produce Alcoa Electrolyte such as AlCl3-NaCl-KCl melt. Chlorine gas was mildly introduced at 820°C into the suspension of bauxite and carbon powder in NaCl-KCl eutectics. AlCl3-FeCl3-NaCl-KCl melts are obtained without significant loss of AlCl3, carbon and chlorine gas. Hematite in bauxite dissolves in molten NaCl-KCl salt. Chlorination of alumina is enhanced by ferric chloride. Selective chlorination of bauxite is performed with hydrogen chloride gas and carbon in NaCl-KCl salt bath to give FeCl2 not FeCl3. The selective chlorination to remove hematite as FeCl3 is also achieved when a large amount of bauxite is introduced in a small amount of molten salt.