*2.2. FeS2*

For this study, a cubic pyrite crystal obtained from the Navajún Mine (La Rioja, Spain) was used. This sample was reduced in size with the use of a cone crusher at laboratory level and later a sprayer. It was then classified through meshes sieves until reaching a size range of −75 + 53 μm. It was then analyzed chemically by atomic emission spectrometry via induction-coupled plasma (ICP-AES), developed in the Applied Geochemistry Laboratory of the Department of Geological Sciences of the Catholic University of the North. Table 2 shows the chemical composition of the samples.

**Table 2.** Chemical composition.


X-ray diffraction analyses (XRD) of the pyrite were performed on a Bruker D8 ADVANCE diffractometer (Billerica, MA, US) with Cu λ = 1.5406 Å radiation generated at 40 kV and 30 mA. The analysis and identification of the crystalline phases were obtained using the DIFFRAC.EVA V4.2.1 program, with the Powder Diffraction File of ICDD database (PDF-2 (2004)) (Billerica, MA, US). According to the initial qualitative analysis of XRD, the primary mineral phase in the samples was pyrite, whose main peaks are at 33.153◦, 37.121◦ and 40.797◦. These peaks correspond to those given in the reference pattern PDF 01-1295 (ICDD, 2004). As seen in Figure 1, the analysis showed the sample has a purity of 99.40%.

**Figure 1.** X-ray diffractogram for the pyrite mineral.
