Abstract
Iron oxides and iron oxyhydroxides find wide applications as magnetic materials, adsorbents for wastewater treatment and pigments. This study addresses the formation of anisotropic α-FeOOH (goethite) nanorods during air oxidation of ferrous hydroxide slurries. The effects of concentration and aeration rate on reaction kinetics and particle size and shape have been studied. It could be shown that the gas-to-liquid oxygen mass transfer is the rate determining step for the reaction. We derive a rate equation for goethite formation which is coupled to a two-dimensional growth model. Aggregation is considered with an oriented attachment model based on Brownian motion of the nanorods. Simulated and experimental results agree very well for both the length and width distributions of the particles. In particular, the new model provides a predictive tool to study the effect of process conditions on the evolution of particle size and shape.
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