## 2 Materials
### Tailings Characterization
These can react with sodium hydroxide or some component of the tailings, causing impurities or undesired components that alter the results. The chemical composition of the oxides for the copper flotation tailings of Minera San Pedro, according to official sources from the Chilean National Geology and Mining Service (Sernageomin), is shown in Table 3:  
Figure 4 shows the particle size distribution of the copper flotation tailing used, obtained using Ro-Tap tests, which consists of passing the particulate matter through a \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Element** & **Concentration (\%)** & **Element** & **Concentration (\%)** \\ \hline Si & 26.95 & K & 1.19 \\ Al & 9.50 & Ti & 0.60 \\ Fe & 8.05 & Mn & 0.25 \\ Ca & 3.28 & S & 0.12 \\ Na & 2.67 & Cr & \textless{}0.01 \\ Mg & 2.10 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Tailings chemical characterization test results using ICP. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Element** & **Concentration (mg/L)** & **Element** & **Concentration (mg/L)** \\ \hline S & 215 & Ta & \textless{}1.00 \\ K & 210 & Th & \textless{}1.00 \\ Na & 158 & Tl & \textless{}1.00 \\ K & 28 & W & \textless{}1.00 \\ Mg & 23 & As & \textless{}0.50 \\ Al & \textless{}5 & La & \textless{}0.50 \\ Fe & \textless{}5 & Li & \textless{}0.50 \\ Ti & \textless{}5 & P & \textless{}0.50 \\ Sr & 1.7 & Sb & \textless{}0.50 \\ Ga & \textless{}1.00 & Sc & \textless{}0.50 \\ Nb & \textless{}1.00 & Te & \textless{}0.50 \\ Sn & \textless{}1.00 & Ag & \textless{}0.25 \\ - & - & Bi & \textless{}0.25 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Chemical characterization test results of industrial water using ICP. \begin{table}
\begin{tabular}{c c} \hline \hline
**Oxide Chemical Composition** & **\%** \\ \hline SiO\({}_{2}\) & 52.81 \\ Al\({}_{2}\)O\({}_{3}\) & 14.26 \\ TiO\({}_{2}\) & 1.01 \\ Fe\({}_{2}\)O\({}_{3}\) & 10.47 \\ CaO & 5.18 \\ MgO & 5.35 \\ MnO & 0.18 \\ Na\({}_{2}\)O & 3.67 \\ K\({}_{2}\)O & 2.06 \\ P\({}_{2}\)O\({}_{5}\) & 0.32 \\ PPC & 3.62 \\ SO\({}_{3}\) & \textless{}0.01 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Oxide chemical composition for the tailings. series of sieves; a laser was used to analyze the smallest particle sizes, which consisted of analyzing the light diffraction of suspended particles. Both tests were performed in the laboratory of the JRI research center (CIMS-JRI). The Atterberg limits of the tailings, i.e., those water contents at which the behavior of the soil is modified, are presented in Table 4.  
Based on the tailings' particle size and their Atterberg limits, and according to the Unified Soil Classification System (USCS), the tailings were classified as a low plasticity silt loam, as seen in Figure 5, i.e., inorganic silt with low compressibility. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Liquid limit & 23.3\% \\ Plastic limit & 19.7\% \\ Shrinkage limit & 20.5\% \\ Plasticity index & 3.5\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Atterberg limits of the tailing used. Figure 4: Tailings particle size curve used. Figure 5: Casagrande abacus. To finish the complete characterization of the tailings, rheology tests were performed at CIMS-JRI using a Haake RheoStress 6000 rheometer with an FL100 paddle probe at a shear rate of 0.1 1/s for 60 s, obtaining the tailings yield stress and viscosity, as well as the pH at different concentrations of solids (Cp). The results are presented in Table 5. The aforementioned measurements were all performed at ambient temperature. The results shown in Table 5 show the rheological test for the tailing samples by considering different Cp values (solids contents) for which the yield stress was obtained. It was observed that as the solids content Cp increased from 50% to 70%, the yield stress also increased from 1.85 Pa to 68 Pa, respectively, mainly due to the fact that the water present in the tailings decreased.