成矿作用过程中, 温压条件改变导致矿物溶解重结晶, 溶液中溶质浓度发生变化。 从溶液中析出晶体的粒度同时存在着时间和空间的分布, 是复杂的动力学过程。 当前对矿物在流体中溶解重结晶动力学研究主要使用高压釜或活塞圆筒等封闭设备测定溶液溶质浓度的变化或固相矿物的形态变化, 降温淬火反应会影响样品的真实组成。 使用可进行原位观测的金刚石压腔结合拉曼光谱分析技术, 研究无水芒硝-饱和Na2SO4溶液随体系温度压力变化所出现的晶体溶解重结晶过程。 通过原位观测无水芒硝溶解、 结晶变化来探究硫酸钠晶体在不同温压条件下的溶解结晶动力学反应机制。 结果表明常温条件下无水芒硝拉曼位移分别位于449.9, 620.5, 632.9, 647.4, 993.3, 1 101.8, 1 132.2和1 153.1 cm-1。 随着体系温度的缓慢升高, 固相Na2SO4的晶形不断发生变化, 温度至193 ℃时无水芒硝(Na2SO4)完全溶解, 降温重结晶出现了新的1 196.5 cm-1拉曼特征峰, 重结晶晶体为芒硝(Na2SO4·10H2O); 金刚石原位观测结果显示迅速升温过程中无水芒硝发生部分溶解重结晶, 重结晶区域拉曼特征峰显示依然为无水芒硝。 拉曼光谱定量分析结果显示, 溶液中SO2-4, H2O的拉曼谱峰面积比值参数更能反映SO2-4浓度的变化, 体系达到溶解重结晶平衡状态时, SO2-4/H2O峰面积比值AR为(0.016 6±0.000 4), 误差为2.4%。 应用Johnson-Mehl-Avrami-Kolmogorov(JMAK)模型结合溶液中SO2-4/H2O峰面积比值变化对体系中固相无水Na2SO4的溶解重结晶过程进行动力学拟合, 计算得出无水硫酸钠在109 ℃条件下的溶解结晶反应的反应级数为1.266 7, 反应平衡常数为0.001 26。 综上所述, 水热金刚石压腔装置实验步骤少, 过程简便, 可避免由于淬火过程中退化交换作用等造成的误差, 应用水热金刚石压腔原位观测的装置优势结合拉曼光谱定量分析技术可实现高温高压条件下矿物在水溶液中溶解结晶动力学过程的原位观察和测定, 是一种高效的动力学研究手段。

During the mineralization process, the dissolution of primary mineral and the formation of secondary mineral could happen on the conditions of changing temperature and pressure. The dissolution and recrystallization of the minerals would cause the changing concentration of the solute, and the crystal which is from recrystallization depends on the reaction process. The process of dissolution and recrystallization is a complex dynamic process. At present, high-pressure autoclave and piston-cylinder are mainly used for the study of the kinetics on the dissolution and recrystallization of the minerals, whereas the cooling quenching reaction will affect the true composition of the sample. In this experiment, the process of the crystal recrystallization of thenardite saturated Na2SO4 solution with the change of temperature and pressure was traced by using the in-situ observation of diamond anvil cell with Raman spectroscopy. The dissolution and recrystallization kinetics of sodium sulfate crystals during different temperature and pressure conditions were investigated by in situ observation and spectrometry. The results showed that the Raman spectroscopy of thenardite at room temperature were 449.9, 620.5, 632.9, 647.4, 993.3, 1 101.8, 1 132.2 and 1 153.1 cm-1 respectively. The crystal shape of solid thenardite changed continuously with the slow increase of temperature, and thenardite was dissolved completely when system temperature reached to 193 ℃. The recrystallized crystal appeared with decreasing temperature rapidly, and the new 1 196.5 cm-1 Raman characteristic peak of recrystallized crystal showed the appeared crystal was mirabilite (Na2SO4·10H2O). In-situ observation of diamond showed that thenardite partially dissolveed and recrystallized during the rapid heating process, and the Raman characteristic peak of the recrystallized region was still thenardite. The process of dissolution and crystallization was controlled by diffusion. The Raman spectroscopy improved can be used for quantitative analysis. Compared with the parameter of peak intensity, area and SO2-4/H2O intensity ratio in the system solution, the area ratio of SO2-4/H2O in the solution reflected the change of SO2-4 concentration precisely in the solution during the reaction. The SO2-4/H2O peak area ratio (AR) is (0.016 6±0.000 4), and the error is 2.4% when solution reaches the dissolved recrystallization equilibrium state. Based on Johnson-Mehl-Avrami-Kolmogorov (JMAK) model and the SO2-4/H2O peak area ratio in the solution, the kinetics fitting of dissolution and recrystallization can be simulated. The results showed that the reaction order of dissolution and crystallization of anhydrous sodium sulfate is 1.266 7 and the equilibrium constant of the reaction is 0.001 26 at the temperature of 109 ℃. In summary, the device of hydrothermal diamond anvil cell is simple to operate, and can also avoid errors caused by degeneration and exchange in the quenching process. The advantage of in-situ observation of hydrothermal diamond anvil cell combined with Raman spectroscopy quantitative analysis can be applied to the kinetics of dissolution and crystallization of minerals in aqueous solution under high temperature and high pressure conditions. It is an efficient kinetic research method and is of great significance for studying rapid phase transition.