Study on forced hydrolysis reaction of acidic Fe2(SO4)3 solution—structure and properties of precipitates

The phase composition, morphology, and inner structure of the particles precipitated from a forced hydrolysis reaction of acidic Fe2(SO4)3 solution were examined. The shape and size of precipitated particles strongly depended on the concentration of the reactants in the starting solution, particularly on that of Fe2(SO4)3. The relatively lower concentration of Fe2(SO4)3 produced acicular or rod-like multi-domainic goethite particles, while the higher one provided irregularly shaped hydronium jarosite particles. This difference strongly depended on the pH of the aging solution; acicular goethite particles were produced at pH≥1.6 though jarosite was produced at pH≤1.5. The large goethite and jarosite particles exhibited a high microporosity. The time resolved transmission electron microscope (TEM) observation technique revealed that the rate of hydrolysis reaction for producing goethite was fast and the particle growth was almost terminated after aging for 1 day. On the contrary, the system favoring precipitation of jarosite exhibited a phase transformation from cubic and hexagonal basic iron(III) sulfate, produced in the early stage of the reaction until 10 h, to large irregular jarosite particles.