SIZE CONTROL IN THE FORMATION OF EXTREMELY FINE GOETHITE PARTICLES BY OXIDATION OF ALKALINE SUSPENSIONS OF FERROUS HYDROXIDE

The kinetics for oxidation of an aqueous alkaline suspension of ferrous hydroxide leading to formation of fine goethite particles was reconfirmed. The mean size of the needle-like goethite particles can be correlated well to the oxidation rate. Phenomenologically, host nuclei are generated in the early stage of the reaction, and afterwards particle growth mainly occurs through hydrolysis of ferric hydroxo-complex (intermediate species) with the number of host nuclei held almost constant. The particle size can be expected to be approximately governed by the number of host nuclei generated in the early stage of the reaction and the initial concentration of total Fe(II). By shifting the oxygen concentration in the feed stream to a lower level at a low conversion, the size distribution of the prepared particles becomes narrow.