REACTION KINETICES AND CONTROLS OF SIZE AND SHAPE OF GOETHITE FINE PARTICLES IN THE PRODUCTION PROCESS BY AIR OXIDATION OF ALKALINE SUSPENSION OF FERROUS HYDROXIDE

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Abstract
The formation of goethite particles by air oxidation of alkaline suspension of ferrous hydroxide is composed of (i) the formation step of ferric hydroxo-complex by oxidation of HFeO2ion, (ii) the formation step of goethite by hydrolysis of the ferric hydroxo-complex, and (iii) the deposition step of goethite particles. The oxidation reaction has been found to complete in the liquid film around the gas bubble, whereas the formation of goethite has been found to mainly occur in the bulk liquid phase. The oxidation reaction was apparently zero-order with respect to Fe(II) and first-order with respect to dissolved oxygen. The prepared goethite particles are needle-like shapes whose mean size ranges from 0.18 to 0.28 μm. As the oxidation reaction rate increases, the mean size of the needle-like particles becomes small and the size distribution becomes sharp

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