草酸水溶液中天青石转化为酸性草酸锶水合物的动力学

摘要

H2C2O4水溶液中SrSO4转化为酸性草酸锶水合物(H[Sr(C2O4)1.5(H2O)])的反应为连串反应.在连串反应的第一步,SrSO4与H2C2O4反应,转化为赝晶SrC2O4·H2O.第二步,SrC2O4·H2O与H2C2O4反应,生成H[Sr(C2O4)1.5(H2O)].如果溶液达到H[Sr(C2O4)1.5(H2O)]的饱和浓度,当反应混合物冷却至室温时,Sr(HC2O4)(C2O4)0.5·H2O发生结晶.根据溶解的S和Sr的量计算SrSO4的转化率发现,对于H2C2O4浓度大致相同的溶液,反应初始阶段的反应速率随着温度的升高而增大;在低H2C2O4浓度溶液中,一定时间之后反应进行缓慢,并且由于固体颗粒表面形成SrC2O4·H2O保护层而停止;在一定温度下,SrSO4的转化率随着H2C2O4浓度的增加而增大.利用收缩核模型得到每一步骤的动力学方程.%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.