## 2 Materials and Methods
### Thermodynamic Modeling
#### 2.5.2 Initial Conditions  
The compositions of three material types were selected for the calculations--marls, limestones, tailings, and solutions from the settling pond (Tables 2 and 3). \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Sample** & **2/55** & **3/60** & **4/11** & **4/25** & **5/65** & **6/38** \\ \hline
**Rock Type** & **Limestone** & **Marl** & **Tails** & **Tails** & **Marl** & **Limestone** \\ \hline Well & t2 & t3 & t4 & t4 & t5 & t6 \\ \hline Depth, m & 55 & 60 & 11 & 25 & 65 & 38 \\ \hline \multicolumn{6}{c}{Component concentration, wt.\%} \\ \hline SiO\({}_{2}\) & 43.21 & 15.80 & 24.77 & 21.90 & 33.48 & 5.81 \\ \hline TiO\({}_{2}\) & 0.39 & 0.11 & 0.61 & 0.72 & 0.54 & 0.06 \\ \hline Al\({}_{2}\)O\({}_{3}\) & 9.11 & 2.18 & 2.60 & 2.54 & 9.78 & 1.34 \\ \hline Fe\({}_{2}\)O\({}_{3}\) & 3.42 & 1.20 & 6.17 & 4.72 & 5.18 & 0.60 \\ \hline MnO & 0.03 & 0.02 & 0.09 & 0.09 & 0.10 & 0.01 \\ \hline MgO & 5.45 & 3.18 & 21.87 & 20.28 & 6.00 & 5.08 \\ \hline CaO & 14.36 & 40.30 & 19.20 & 21.15 & 17.67 & 45.72 \\ \hline Na\({}_{2}\)O & 0.15 & 0.12 & 0.08 & 0.09 & 0.35 & 0.11 \\ \hline K\({}_{2}\)O & 3.89 & 0.82 & 0.43 & 0.44 & 3.45 & 0.29 \\ \hline P\({}_{2}\)O\({}_{5}\) & 0.05 & 0.04 & 0.25 & 0.28 & 0.13 & 0.03 \\ \hline BaO & 0.02 & \textless{}0.01 & 0.05 & 0.07 & 0.02 & \textless{}0.01 \\ \hline SO\({}_{3}\) & 1.97 & 1.59 & 1.48 & 1.34 & 3.44 & 0.20 \\ \hline V\({}_{2}\)O\({}_{5}\) & 0.01 & \textless{}0.01 & 0.01 & 0.01 & 0.01 & \textless{}0.01 \\ \hline Cr\({}_{2}\)O\({}_{3}\) & \textless{}0.01 & \textless{}0.01 & 0.09 & 0.08 & \textless{}0.01 & \textless{}0.01 \\ \hline \end{tabular}
\end{table} 
Table 2: Composition of dam rocks taken for thermodynamic modeling of the “water–rock” interaction. Figure 6: Scheme of thermodynamic modeling of the interaction of dam rocks with industrial water. The calculation was carried out for the 21 chemical elements. Equilibrium was calculated for 480 possible ions in solution and 860 minerals based on the thermodynamic data. In the model, the pressure and oxygen content were assumed to be atmospheric and the tested temperature values ranged from 2 to 8 \({}^{\circ}\)C. In this temperature range, the equilibrium composition of solutions and the mineral composition were found to be unchanged; therefore, T = 2 \({}^{\circ}\)C was selected, as this most closely corresponds to field observations in the study area. In the first stage, equilibria in solutions were calculated using the example of sample A01 (Table 3). It was assumed that the oxygen content in the system corresponds to atmospheric oxidizing conditions. Under these conditions, the calculated pH value of the system is fully consistent with the measured one. This allows us to verify the simulation results with field observations. The degree of dissolution and transformation of the rock is determined by the ratio of water-rock interaction. To estimate the amount of rock that reacts and dissolves, field observations are necessary. We applied a method of evaluating the ratio of changes in bicarbonate ions in the solutions of the settling pond and the storage pond, which indirectly indicates the dissolution of carbonate minerals in the filtering dam of the tailing dump. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sample** & **2/55** & **3/60** & **4/11** & **4/25** & **5/65** & **6/38** \\ \hline
**Rock Type** & **Limestone** & **Marl** & **Tails** & **Tails** & **Marl** & **Limestone** \\ \hline NiO & \textless{}0.01 & \textless{}0.01 & 0.08 & 0.06 & \textless{}0.01 & \textless{}0.01 \\ \hline LOI & 18.15 & 34.52 & 22.26 & 26.29 & 19.68 & 40.99 \\ \hline SUM & 100.21 & 99.86 & 100.05 & 100.06 & 99.84 & 100.23 \\ \hline The main phases of the mineral composition & Quartz calcite & Calcite anfortite quartz & Magnetic quartz pyrite & Magnetic & Pyrite, calcite, & Pyrite impurities calcite quartz & Calcite dolomite \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._