Kinetics of celestite conversion to acidic strontium oxalate hydrate in aqueous solution of oxalic acid

Abstract

Abstract Conversion of SrSO 4 to acidic strontium oxalate hydrate (H[Sr(C 2 O 4 ) 1.5 (H 2 O)]) in aqueous H 2 C 2 O 4 solutions proceeds as a consecutive reaction. In the first step of the consecutive reaction, SrSO 4 reacts with H 2 C 2 O 4 and pseudomorphic conversion to SrC 2 O 4 ·H 2 O occurs. In the second step, SrC 2 O 4 ·H 2 O reacts with H 2 C 2 O 4 to form H[Sr(C 2 O 4 ) 1.5 (H 2 O)]. Sr(HC 2 O 4 )(C 2 O 4 ) 0.5 ·H 2 O crystallizes during cooling of the reaction mixture to room temperature if the solution reaches the saturation concentration of H[Sr(C 2 O 4 ) 1.5 (H 2 O)]. 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 H 2 C 2 O 4 concentration for each reaction step. Fractional conversions of SrSO 4 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 H 2 C 2 O 4 concentrations. The reaction extends very slowly after a certain time in solutions with low H 2 C 2 O 4 concentration and ends by the formation of a protective layer of SrC 2 O 4 ·H 2 O around the surfaces of solid particles. Fractional conversion of SrSO 4 is increased by increasing concentration of H 2 C 2 O 4 at constant temperature. Kinetic model equations were derived using shrinking core model for each step.