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Abstract
Needle-like goethite particles were synthesized by air oxidation of an alkaline suspension of ferrous hydroxide using a standard-type bubble column of 10cm in internal diameter and 64 cm in height at a constant temperature of 40°C. Specifically, the effect of aging step by N2 stream prior to the oxidation step was investigated on both the oxidation rate and the final particle size based on the major axis of needle-like goethite particle. The time dependence of the fractional oxidation of total ferrous species with incorporated aging step exceeded that in the absence of aging step. The velocity of N2 in the aging step had negligible influence on the time dependence of the fractional oxidation. For the aging period exceeding 30min, the mean particle size was almost independent of the aging period. The mean size could be correlated considerably well with the oxidation rate, that is, decreased with increasing oxidation rate with and without incorporated aging step.