Synthesis of complex alumina-cobalt systems using thermally activated gibbsite product

Using the methods of X-ray phase, thermal, microscopic, adsorption, and chemical analyses, the possibility of obtaining high-percentage mixed alumina-cobalt spinels by hydrochemical treatment under room or hydrothermal conditions of powder suspensions of the product of centrifugal thermal activation of gibbsite in aqueous solutions of cobaltous nitrate is studied and shown. Thermal treatment of hydrochemical interaction products, viz. xerogels in the range of 350–850°C, is established to lead to the formation of Co3O4 and CoAl2O4 spinel phases with their different ratio depending on the synthesis conditions. Thus, hydrochemical treatment of suspensions at room temperature provides, after calcination, the predominant formation of the Co3O4 phase while hydrothermal treatment at 150°C leads to a deeper interaction of suspension components at the treatment stage, forming CoAl2O4 after thermal treatment. It is noted that the maximum content of spinel of CoAl2O4 type (90% according to H2-TPR data) is observed for the hydrothermal product calcined at 850°C. The considered method is concluded to allow obtaining complex alumina-cobalt compounds with different phase ratio, reducing the number of initial reagents, preparation stages, completely excluding effluents, as well as reducing the total amount of nitrates by 75 wt.%, as compared to the nitrate classical co-precipitation scheme.