678 chemical composition by XRF. The results were compared with the chemical composition of the unleached samples, expressed as mass percentages. The potential for acid generation was evaluated using the NAG (Net Acid Generation) prediction test (particularly relevant for the PT1). This test determines the balance between the acid-producing and acidconsuming components of tailings/waste rock samples. NAG results provide acid rock drainage characteristics based on the complete oxidation of sulfide content in the samples. Acid that is produced by oxidation is consumed by carbonates and/or other acid-consuming components present in the material. The pH of the solution is measured (NAG pH), and the remaining acid after the reaction is titrated with standardized NaOH is used to determine the amount of net acid produced (Miller et al., 1997; AMIRA, 2002). 3. RESULTS AND DISCUSSION 3.1 Particle Size Analysis The particle size distributions of four types of mine residues are presented in Figure 2. The particle size of PT1 ranges from 0.47 to 724 µm, with broadly consistent cumulative curves across the analyzed subsamples, although a slight deviation was observed in sub-sample C. The PT2 sample comprises particles ranging in size from 0.24 to 1258 µm, with minor deviations in the coarser fractions but overall consistent cumulative behaviour. The PT3 shows a distribution between 0.1 and 1000 µm, and PT4 shows a narrower size range from 0.316 to 181.97 µm, with cumulative curves very similar across the analyzed sub-samples. Figure 2 – Particle size distribution of PT1, PT2, PT3, and PT4 determined by laser diffraction. 3.2 Chemical Composition Chemical composition analysis was performed to identify the major and trace elements present in the mine residues and to support the assessment of their potential valorization pathways. The analysis was done by X-ray fluorescence (XRF) at SECIL and FEUP (Figure 3).
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