Abstract:Conversion of SrSO₄ to acidic strontium oxalate hydrate (H[Sr(C₂O₄)_1.5(H₂O)]) in aqueous H₂C₂O₄ solutions proceeds as a consecutive reaction. In the first step of the consecutive reaction, SrSO₄ reacts with H₂C₂O₄ and pseudomorphic conversion to SrC₂O₄·H₂O occurs. In the second step, SrC₂O₄·H₂O reacts with H₂C₂O₄ to form H[Sr(C₂O₄)_1.5(H₂O)]. Sr(HC₂O₄)(C₂O₄)_0.5·H₂O crystallizes during cooling of the reaction mixture to room temperature if the solution reaches the saturation concentration of H[Sr(C₂O₄)_1.5(H₂O)]. The aims of this study are the derivation of reaction rate equations and the determination of the kinetic parameters such as pre-exponential factor, apparent activation energy and order of H₂C₂O₄ concentration for each reaction step. Fractional conversions of SrSO₄ were calculated using the quantitative amounts of dissolved S and Sr. It was determined that the reaction rate increased at the initial time of reaction by increasing the temperature using solutions with approximately same H₂C₂O₄ concentrations. The reaction extends very slowly after a certain time in solutions with low H₂C₂O₄ concentration and ends by the formation of a protective layer of SrC₂O₄·H₂O around the surfaces of solid particles. Fractional conversion of SrSO₄ is increased by increasing concentration of H₂C₂O₄ at constant temperature. Kinetic model equations were derived using shrinking core model for each step.

Key words: celestite concentrate; pseudomorphic conversion; rate equations; kinetic parameters; conversion reaction