盐卤硼酸盐化学 ⅩⅢ.2MgO·2B_2O_3·MgCl_2·14H_2O结晶动力学研究

Chemistry of Borate in Salt Lake Brine ⅩⅢ Study on Crystallization Kinetics of 2 MgO·2 B_2O_3·MgCl_2·14H_2O

对MgO-B_2O_3-MgCl_2-H_2O浓盐溶液结晶析出氯柱硼镁石(2MgO·2B_2O_3·MgCl_2·14H_2O)的动力学过程进行了研究。利用单纯形优化法配合Runge-Kutta微分方程组数值解法对实验数据进行处理,给出了结晶动力学方程。并对硼在溶液中的存在形式进行了讨论,提出了结晶反应机理,同时考察了温度和氯化镁浓度对结晶速率的影响。

In order to investigate the optimal condition for the synthesis of the new solid phase, 2 MgO·2 B_2O_3·MgCl_2·14H_2O. We studied its crystallization kinetics from solution containing 0.65%MgO, 1.14%B_2O_3 and 24%, 28%, 32%MgCl_2 respectively.The experiments were carried out without stiring. At different time interval, solution sample was taken for analysis and its lensity and pH were determined, until solution density remained basically constant. Then, solid phase was separated and identified by chemioal analysis. IR-spectra, X-ray powder diffraction and thermal analysis.The results show that crystallization kinetic curves (c_(MgB_2O(OH)_6^(2-)-t) are all in reverse S-shape. Below 40℃, the rate of crystal growth inoreases with the rising of temperature, but above 40℃, it decreases. At 30℃ isothermally, the rate of crystallization decreases with the increasing of MgCl_2-concentration. Within the range of this experimental temperature and concentration, there is only one kind of solid phase, 2MgO·2 B_2O_2·MgCl_2·14H_2O crystallizing out from the solution.An appropriate mathematical modification of Nielsen's mononuclear layer and polynuclear layer controllod growth mechanism has been made. With the aid of simple optimum method and Runge-Kutta digital solution of differential equation system, the experimental data was fitted. The kinetic equation of the crystallization reactions was given and a mechanism of crystallization reactions was proposed.