Experimental Investigations on the Dissolution Process of Dolomite by Sulfate-Rich Geothermal Water: A Case Study of the Shuijing Hot Springs in Guizhou Province

The dissolution of dolomite can not only provide the chemical components in hot springs but also provide a high-quality reservoir for geothermal resources. However, there is still debate about the main controlling factors and mechanisms of the dissolution process of dolomite. The Shuijing hot springs in Guizhou Province are rich in SO42− and the geothermal reservoir is dolomite, which provides an excellent opportunity to understand the role of SO42− in the dissolution process of dolomite. In this paper, water–rock interaction experiments were conducted at different temperatures to study the effects of SO42−, pH, and CO2 on the dissolution of dolomite from the Shuijing hot springs geothermal reservoir. The results indicate that temperature is a significant factor affecting the chemical composition of hot springs water, with higher temperatures having a more pronounced effect on the dissolution of dolomite. At lower temperatures of 25 °C and 90 °C, the molar ratio of the released Ca2+ and Mg2+ during the dissolution of dolomite in the initial reaction stage generally approaches the Ca/Mg molar ratio of dolomite, exhibiting congruent dissolution. However, at elevated temperatures of 150 °C, the released Ca/Mg molar ratio surpasses the Ca/Mg molar ratio of dolomite, demonstrating an incongruent dissolution characteristic with Ca2+ being preferentially released over Mg2+. Additionally, the relative importance of CO2, SO42− and pH on the dissolution degree of dolomite is CO2 > SO42− > pH = 4 > pH = 7 > pH = 10. The promotion effect of SO42− on dolomite dissolution indicates that the greater the SO42− concentration, the stronger the dissolution of dolomite, and its dissolution ability is enhanced with the increase in temperature. Furthermore, the effect of CO2 on the dissolution of dolomite is stronger than that of SO42−, leading to the oscillating fluctuation trend of the released Ca2+ and Mg2+.