Synthesis of Highly Dispersed Aluminum Magnesium Oxides from the Product of Centrifugal Thermal Activation of Gibbsite

Abstract

The possibility of preparing magnesium aluminate by the reaction of the product of centrifugal thermal activation of gibbsite with a saturated aqueous solution of magnesium nitrate at room temperature and 150°С was studied by X-ray diffraction, thermal, microscopic, adsorption, and chemical analysis methods. The reaction at 150°C between the components taken in the stoichiometric ratio with respect to the cations yields the phase of a layered double hydroxide [Mg_0.33Al_0.66(OH)₂](NO₃)_0.6·0.013H₂O. Its heat treatment at 550°C ensures the formation of stoichiometric spinel MgAl₂O₄ with the specific surface area of ~150 m² g^–1. Traditional impregnation of the product of centrifugal thermal activation of gibbsite with a concentrated magnesium nitrate solution, taken in an amount corresponding to the moisture capacity of the solid phase, at room temperature, followed by heat treatment at 550°С, yields a solid solution based on the low-temperature form γ-Al₂O₃ with the specific surface area of ~180 m² g^–1, containing ~4.55 wt % Mg. The samples obtained differ in the particle morphology and in the magnesium content on the surface. As compared to the traditional coprecipitation method, the suggested procedure allows considerable reduction of the reactant amounts and number of process steps and minimization or complete elimination of the wastewater formation.