## 2 Materials  
### Tailings Characterization  
The copper tailings used in this research came from the San Pedro Mining Company, located in Til Til, Chile, where polymetallic copper and silver concentrates are obtained. The type of deposit from which these concentrates are extracted corresponds to a copper porphyry, where the main element of interest that is extracted is copper. The tailings produced from this mine were filtered, obtaining an average solid content (%Cp) of 85% (Figure 1). The average solids density of the tailings was 2.79 \(\pm\) 0.12 g/cm\({}^{3}\). In addition, process water samples were taken to be used in the formation of the geopolymers. X-ray diffraction (XRD) analysis of the copper flotation tailing used is shown in Figure 2. This copper tailing is a crystalline material composed mainly of albite (NaAlSi\({}_{3}\)O\({}_{8}\)), and to a lesser extent, clinochlore (Mg\({}_{5}\)Al(AlSi\({}_{3}\)O\({}_{10}\))(OH)\({}_{8}\)), quartz (SiO\({}_{2}\)), epidote (Ca\({}_{2}\)(Al\({}_{2}\),Fe)(SiO\({}_{4}\))(Si\({}_{2}\)O\({}_{7}\))O(OH)), and orthoclase (KAlSi\({}_{3}\)O\({}_{8}\)). Figure 1: Tailings from the San Pedro mine, Til Til, Chile. Figure 2: XRD pattern of unreacted copper flotation tailing. Unlike previous research in which dry tailings were used [21; 22; 23], for this study, we used tailings with a solids concentration of 83%, which is the method developed in previous research by [PERSON] et al. [1]. Process water was used for the homogenization of the tailings to reduce the production costs of the geopolymers, which were produced by adding process water until a tailings pulp with a solids concentration Cp of 70% was obtained. After this homogenization, the tailings pulp was filtered to obtain a tailings pulp with a solids concentration Cp of 83% (Figure 3). The chemical composition of the copper tailings used in this investigation was obtained using an inductively coupled plasma test (ICP), where an Andes Analytical Assay was performed. The results presented in Table 1 corresponded to average values obtained from the analysis of several samples of the tailings used. The ICP analysis was performed under the Accredited Method ISO 17025.Of.2005 INN, LE1386, using an analytical balance with a minimum precision of 1 mg to weigh the sample and prepare it for leaching at a temperature of 23 \(\pm\) 2 \({}^{\circ}\)C for 18 \(\pm\) 2 h at 30 \(\pm\) 2 rpm. Then, a precipitation test was performed for which a 20 mL extract was taken and 2 mL of HNO\({}_{3}\) was added; if precipitation was observed, the rest of the extract was not acidified and the measurement was obtained. If the extract showed no precipitation, it was acidified with HNO\({}_{3}\) acid to pH = 2 and stored at 4 \({}^{\circ}\)C for subsequent measurement. Subsequently, 2.5 mL of the 20 mL extract was diluted and poured into a 50 mL volumetric flask containing 12.5 mL of quenched aqua regia to perform the ICP-MS measurement with an Aurora Bruker ICP-MS, USA, at the Andes Analytical Assay Laboratory: 3 AAA in Chile. From the characterization of the tailings presented in Table 1, it was observed that the main element in its composition was silicon and, to a lesser extent, aluminum and iron, with the first two being fundamental for the synthesis of the geopolymer. From Table 1, it is seen that the tailings used had a Si/Al ratio of 2.83, which, according to previous studies, [3], is close to the optimal range for the formation of geopolymers (Si/Al ratios close to 2.0). Figure 3: Tailings pulp with a Cp of 83% [1]. Characterization of the industrial water used for the homogenization of the tailings was also carried out using the inductively coupled plasma (ICP) test, where the same procedure previously described was used to obtain the results. In addition, as in the case of the tailings, the results obtained correspond to the average values obtained from the analysis of several samples. These results are presented in Table 2.  
Table 2 shows that the highest concentration corresponded to sulfur ions.