水热金刚石压腔结合拉曼光谱技术进行Na<sub>2</sub>SO<sub>4</sub>-水体系溶解结晶动力学研究

doi:10.3964/j.issn.1000-0593(2019)12-3698-07

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Abstract 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 SO^2-₄/H₂O intensity ratio in the system solution, the area ratio of SO^2-₄/H₂O in the solution reflected the change of SO^2-₄ concentration precisely in the solution during the reaction. The SO^2-₄/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 SO^2-₄/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.

Key words：HDAC; High pressure and high temperature; Raman spectroscopy; Dissolution and recrystallization; Kinetics researches

Received: 2019-06-20 Accepted: 2019-10-09

ZTFLH:

O657.3

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https://www.gpxygpfx.com/EN/10.3964/j.issn.1000-0593(2019)12-3698-07 OR https://www.gpxygpfx.com/EN/Y2019/V39/I12/3698