680 Figure 4 – Mineralogical composition of PT1, PT2, PT3, and PT4 determined by XRD-Rietveld. 3.4 Samples pH and moisture content The pH determinations were carried out at FEUP, and the results of pH measurements in solutions with distilled water and CaCl2 are presented in Table 1. The difference in the results between the two methods can be neglected. The PT1 samples exhibited a pH of approximately 6, indicating slight acidity. PT2 displayed pH values ranging from 9.04 to 9.57; PT3, 7.56 to 8.51; and PT4, 7.41 to 7.86, all suggesting mildly alkaline conditions. Table 1 – Mine residues pH determined in solution with distilled water and CaCl2 solution PT1 PT2 PT3 PT4 Sub-sample H2O CaCl2 H2O CaCl2 H2O CaCl2 H2O CaCl2 A 5.80 5.75 9.04 8.82 7.80 7.56 7.91 7.49 B 5.86 5.74 9.26 8.91 7.62 7.75 7.90 7.48 C 5.94 5.79 9.44 8.97 8.51 8.05 7.67 7.46 D 5.92 5.94 9.57 8.93 8.43 8.05 7.86 7.41 Moisture content was determined at both SECIL and FEUP in accordance with EN 1097-5. PT1 showed moisture levels of approximately 44%, while PT2 presented 33%. For PT3 and PT4 samples, moisture content was not assessed because both were delivered and analyzed as dry materials. 3.5 Microstructural Characteristics Scanning electron microscopy (SEM) was performed to examine the particle morphology and surface characteristics of the mining waste samples. The analyses were conducted at CUT, INOE and FEUP (Figure 5). The SEM images show that all samples exhibit similar granular morphology without distinct or characteristic structural features. The particles appear irregular in shape, with no specific morphological patterns observed among the different materials. Although SEM images may vary with the equipment used, consistent grain sizes were observed across the analyzed samples.
RkJQdWJsaXNoZXIy MTM0Mzk2