4.4.2. Analysis of the Effect of pH on Minerals

After statistical analysis, the pH variation range of the site groundwater was 7.55–9.26, so the trend of minerals in the aquifer was further determined by analyzing the effect of pH variation on the saturation index of minerals. Taking S01 as an example, the pH was taken as 7.55, 8, 8.26, 9 and 9.26, respectively, which can truly reflect the trend of dissolution and precipitation of minerals in the aquifer.

As can be seen from Figure 9, the saturation index of dolomite, calcite, aragonite and MgCr2O4 is increasing with the increase of pH, indicating that MgCr2O4 was more prone to precipitation in the alkaline environment, mainly because the ionic activity product increases with the increase of pH under the condition of constant temperature, which led to the easy precipitation. With the increase of pH, the saturation index of Na2Cr2O7, K2Cr2O7 and CrCl3 were decreasing, indicating that the dissolution of Na2Cr2O7, K2Cr2O7 and CrCl3 was more likely to occur in the alkaline environment, mainly because the ionic activity product decreased with the increase of pH under the condition of constant temperature, which led to the dissolution to occur easily, and the saturation index of the remaining minerals was less affected by the change of pH.

**Figure 9.** The influence of pH on the SI of minerals.
