Figure 3 – Chemical composition of PT1, PT2, PT3, and PT4 determined by XRF. The sulphide tailings (PT1) are dominated by Fe (40.8 %) and S (32.1 %), with additional components including Si (13.7 %), Al (4.7 %), Ca (1.7 %), and Mg (1.3 %). Trace metals such as Zn (6.6 mg/g), Cu (4.1 mg/g), Pb (4.8 mg/g), and As (3.4 mg/g) were also detected, along with Ti, Mn, Sb, Sn, and Cd. The granite sludge (PT2) is mainly composed of SiO2 (69.47 %), followed by Al2O3 (14.56 %), K2O (4.30 %), Na2O (3.07 %) and CaO (3.08 %), with Fe2O3 present at 2.52 %, and minor amounts of Ba, Rb, Sr, Cr and Ce. The marble sludge (PT3) showed a predominance of CaO, followed by SiO2, MgO, Al2O3 and Fe2O3, with minor oxides including K2O, TiO2, SO3 and Na2O, as well as trace elements such as Sr, Cl, Sc, Ce, Ba, Co and Rb. The limestone sludge (PT4) is characterized by a high CaO content (~54 %) as the main component, followed by smaller amounts of MgO, SiO2, Al2O3 and Fe2O3, along with minor oxides such as K2O, Na2O, SO3 and TiO2. 3.3 Mineralogical Composition X-ray diffraction (XRD) with Rietveld refinement was performed on the four mine residue samples at SECIL (Figure 4). PT1 is dominated by pyrite (59.5 %), together with quartz (14.6 %), kaolinite (4.3 %), chlorite (7.7 %), calcite (10.1 %), and smaller proportions of dolomite, hematite, mica, feldspar, illite and periclase. PT2 is mainly composed of anorthite (29.4 %), quartz (27.5 %), albite (16.5 %), orthoclase (11.2 %) and calcite (1.9 %), with minor components including muscovite (1.0 %), dolomite (0.5 %), vermiculite (1.4 %), montmorillonite (1.1 %), biotite (3.0 %), lepidolite (1.4 %), microcline (1.8 %), rutile (1.0 %), gibbsite (0.3 %) and traces of mica/feldspar. PT3 is characterized by calcite (89.8 %) as the dominant phase, followed by quartz (2.3 %), magnesite (2.1 %), kaolinite (1.8 %), dolomite (1.7 %) and chlorite (1.4 %), with minor amounts of arcanite (0.5 %) and muscovite (0.5 %). PT4 shows calcite (95.2 %) as the predominant phase, with
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