Abstract:

The precipitation crystallization kinetics model for fluorite was deduced based on the two-step crystallization theory of mass diffusion and surface reaction. Using calcium chloride as precipitating agent, the crystallization kinetic data for fluorite were measured in steam ammonia wastewater using batch crystallization and on-line particle monitoring technologies. The crystallization kinetics model parameters were optimized with nonlinear optimization techniques and verified by experimental data. The results showed that the model and model parameters were nice with the average relative error of about 3.37% between the model values and the experimental data. The fluorite precipitation crystallization process was controlled by surface reaction and coalescence phenomenon between fluorite particles happened. Simulation results with the kinetics model indicated that when the initial calcium ion concentration was constant, the higher the initial concentration of fluoride ions, the faster the fluoride ion concentration decline in the initial stage. The initial fluoride ion concentration was too high or too low, eventually they were unfavorable for lower fluoride ion concentration. Appropriate increase in operating temperature may promote fluorine ion purification, however, too high temperature was negative.

Key words: wastewater, precipitation, crystallization, kinetic modeling

摘要：

以质量扩散-表面反应两步结晶理论为基础,推导出氟化钙沉淀结晶动力学模型,以蒸氨废水为研究对象,氯化钙为沉淀剂,采用间歇结晶和在线粒度监测技术测定了氟化钙结晶动力学数据,采用非线性优化技术获得了氟化钙结晶动力学模型参数,并对该模型进行了实验验证,结果表明模型及模型参数效果良好,模型值与实验值平均相对误差为3.37%。氟化钙沉淀结晶过程属于表面反应控制过程,氟化钙存在明显的聚结现象。模型模拟结果表明:钙离子浓度一定时,氟离子初始浓度越高则初始阶段氟离子浓度下降越快,初始氟离子浓度过高或过低,最终均不利获得较低的氟离子浓度;适当提高操作温度可以促进氟离子的净化,但温度过高则不利。

关键词: 废水, 沉淀, 结晶, 动力学模型