## 3 Analysis and Discussion
### Discussion
#### 3.5.2 Relationship Between pH and Chemical Dissolution Rate  
Fitting analysis of dissolution per unit area for three rock specimens under static dissolution conditions across varying acidity levels of phosphogypsum leachate revealed an exponential relationship between leachate pH and areal dissolution rates. As illustrated by the fitted equations in Figure 10b, the dissolution per unit area decreased progressively with increasing leachate pH, exhibiting a diminishing rate of decrease that asymptotically approached stability at higher pH values.  
To investigate whether an exponential relationship exists between pH and chemical dissolution rates, we conducted statistical analysis of pH variations and corresponding dissolution rates under leachate conditions with initial pH = 2. The results demonstrated a rapid initial decline in dissolution rates with increasing pH, followed by progressive stabilization. Comparative fitting of experimental data using both power function (Asym2 Sig model) and exponential functions revealed superior correlation coefficients for the power function model (Figure 10c), indicating that the pH-dissolution rate relationship adheres more closely to the Asym2 Sig power-law formulation. Further validation through analogous fitting analyses across multiple leachate pH groups (Figure 10d-f) consistently yielded high correlation coefficients, confirming the generalized applicability of the power function in describing these geochemical interactions.  
Figure 10: Fitting analysis: (**a**) electrolyte conductivity vs. the chemical dissolution rate; (**b**) pH vs. dissolution amount per unit area; (**c–f**) pH vs. the chemical dissolution rate.  
3.5.3. Influence of the Presence or Absence of Hydrodynamic Conditions on Dissolution Effects  
Significant disparities in dissolution efficacy were observed between static and dynamic experimental conditions. Comparative analysis of chemical dissolution rates at 24 h post-experiment initiation revealed that dynamic systems consistently exhibited 7.37-12.26 times higher rates than static systems across varying initial leachate pH levels (2-4), with the discrepancy amplifying under lower pH conditions, as demonstrated in Figure 11.  
The pronounced disparity in chemical dissolution rates between static and dynamic experimental conditions arises from three interconnected mechanisms. Primarily, the transition to hydrodynamic conditions facilitates enhanced leachate penetration into rock pores and fractures, substantially expanding reactive interfacial areas between H\({}^{+}\) ions and carbonate mineral surfaces, thereby accelerating dissolution kinetics. Additionally, the intensified dissociation of weak acids (e.g., hydrofluoric acid, phosphoric acid) under dynamic flow elevates leachate H\({}^{+}\) concentrations, further amplifying proton-driven dissolution processes. Crucially, hydrodynamic forcing induces advective mass transport dominance, which dramatically enhances H\({}^{+}\) delivery efficiency to reactive sites through accelerated convective transfer, synergistically elevating overall dissolution rates. This mechanistic cascade explains the order-of-magnitude enhancement in chemical dissolution rates observed under dynamic conditions compared to static systems.