REACTION-MECHANISM PRODUCING BARIUM HEXAFERRITES FROM GEOTHITE AND BARIUM HYDROXIDE BY HYDROTHERMAL METHOD

In this study, the reaction of goethite (alpha-FeOOH(s)) and barium hydroxide (Ba(OH)2) in an alkaline solution was carried out by a hydrothermal method at a high temperature and pressure in a batch closed reactor. The reaction was noted to proceed in a homogeneous phase, from which alpha-FeOOH(s) was first dissolved in the alkaline solution. Then, the dissolved alpha-FeOOH(s) (or Fe(OH)4- (aq)) reacted with Ba(OH)2 to yield the desired products, such as: BaO.6Fe2O3 or 5BaO.4Fe2O3, in the main reactions. Portions of the dissolved alpha-FeOOH(s) (or Fe(OH)4- (aq)) were converted to alpha-Fe2O3 at the early stage of the reaction and at the end of the reaction when the reaction was unfavorable in producing the main products in the main reactions. The reaction, which concerned the sequential steps in a homogeneous phase, were confirmed by experimental observation. The possible products obtained included BaO.6Fe2O3 and 5BaO.4Fe2O3 in the main reactions and alpha-Fe2O3(S) in the side reaction, depending on the mole ratio of Ba(OH)2 reactant to the 1/2(alpha-FeOOH(s)) reactant. The product, 5BaO.4Fe2O3, was identified as a new product. A reaction mechanism in the homogeneous reaction was proposed for further kinetic study.