Precipitation of Cerium Sulfate Converted from Cerium Oxide in Sulfuric Acid Solutions and the Conversion Kinetics

抄録

The conversion of cerium (IV) oxide into cerium (IV) sulfate in sulfuric acid solutions was studied in a batch-type glass reactor under atmospheric pressure. The effects of agitation speed, acid concentration, reaction temperature, initial amount of cerium (IV) oxide per sulfuric acid solutions (C/S), and particle size on the conversion process were investigated. All experiments were carried out in the range of 8–14 mol/dm³ for sulfuric acid concentration, 105–135°C for reaction temperature, 0.04–0.28 mol/dm³ for C/S, and 2.5–112.5 µm for average particle size. The conversion process involves the dissolution of cerium (IV) oxide and the precipitation of cerium (IV) sulfate. Cerium (IV) oxide reacted with sulfuric acid very slowly and then dissolved cerium (IV) in a saturated condition directly formed cerium (IV) sulfate indicating that the conversion rate was controlled by the dissolution rate of cerium (IV) oxide. Increases in sulfuric acid concentration and reaction temperature increased the dissolution rate, whereas increase in particle size decreased it. However, the C/S had no effect on the dissolution rate. In terms of the yield of precipitated cerium (IV) sulfate after reaction equilibrium, increases in sulfuric acid concentration and C/S increased the yield. However, the particle size and the reaction temperature had no effect on the yield of precipitated cerium (IV) sulfate. The kinetics of cerium (IV) oxide dissolution, under various conditions of sulfuric acid concentration, reaction temperature, C/S, and particle size, was interpreted by a shrinking core model with chemical reaction. The variation of rate constant upon dissolution with temperature obeyed the Arrhenius equation with an activation energy of 123 kJ/mol.