托素湖湖水蒸发过程中析盐及其pH值的变化规律研究

Regularity of Salt Separation and the Variation of pH Values in the Process of Evaporation in Tuosu Lake Water

盐湖卤水蒸发是提取盐湖有益成分的主要途径之一,当前盐湖卤水的蒸发实验主要集中在矿化程度较高的盐湖和咸水湖中,蒸出矿物以硫酸盐和氯化物为主。为了获得湖水蒸发过程中从低矿化度到高矿化度全阶段的析盐和pH值变化规律,用托素湖微咸水在恒温室内开展28±2℃蒸发实验。托素湖为硫酸镁亚型微咸水湖(矿化度27.8 g/L),整个蒸发过程中pH值由8.92持续降低到6.108;矿物析出顺序为三水菱镁矿—文石—石盐—六水泻盐—白钠镁矾—五水泻盐—四水泻盐,共有七组盐类析出。卤水pH值的变化主要受矿物相变化控制,在碳酸盐析出过程中pH由8.529迅速降低到7.205,而后以析出矿物石盐为主的石盐—硫酸盐析出阶段pH降低到6.887,之后在白钠镁为主的硫酸盐—石盐阶段pH缓慢降低到6.29。同时分析了石膏、芒硝、泻利盐等矿物未析出的原因。通过托素湖湖水蒸发实验,可以更全面地认识硫酸镁亚型盐湖演化全过程中的矿物沉积规律及物理化学性质变化。

Evaporation of salt lake brine is one of the main approaches to extract salt lake resources.At present, evaporation experiments of salt lake brine are mainly focused on salt lake and saline lake with high salinities.In order to obtain the salt evolution and pH value change rule from low to high salinity in the whole process of lake evaporation, this paper carried out evaporation experiment of 28 ± 2℃ in a thermostatic chamber with the brackish water of Tuosu lake.Tuosu lake was a brackish lake of magnesium sulfate subtype(salinity 27.8 g/L).During the whole evaporation process, the pH values were reduced from 8.92 to 6.108 continuously.The sequence of mineral precipitation is nesquehonite-aragonite-halite-hexahydrite-bloedite-pentahydrite-starkeyite, and there are seven sets of salt precipitation sequence.The variation of the pH values of brine is mainly controlled by the change of the mineral phase.In the course of carbonate precipitation, the pH values decrease from 8.529 to 7.205 steeply, and then the pH value decreases to 6.887 at the precipitation stage of halite-sulfate salts, which is dominated by halite.Later, the pH value smoothly decreases to 6.29 at the stage of sulfate-halite salts dominated by bloedite.Meanwhile the reason why the minerals such as gypsum, mirabilite and epsomite were not precipitated was analyzed.According to the evaporation experiment of Tuosu lake, we can comprehend the mineral precipitation regularity and the variation of physical and chemical properties of salt lake more comprehensively.