Figure 6 – EDS analysis spectra of PT1, PT2, PT3, and PT4. 3.6 Chemical Stability and Potential for Acid Generation Considering the results of the natural leaching tests and the elemental chemical analysis of the solid fraction before and after leaching, it is concluded that most chemical elements were not leached and therefore these materials are chemically stable. However, the NAG test conducted on sample PT1 classified this material as potentially acid-forming. In this context, the primary strategy for valorization should focus on reprocessing, aiming to recover both valuable elements and remove harmful substances that could impede the material's reuse in other applications. An experimental plan is underway to study the recovery of critical raw materials via hydrometallurgical processes. The strategy for this experimental plan is to extract Zn, Cu, Pb, and Ag via sequential leaching. Several kinetic tests were already systematically carried out to provide zinc concentrates for further hydrometallurgical tests. 4. CONCLUSIONS This study evaluated the valorization potential of four mining waste materials, sulphide tailings, granite sludge, marble sludge, and limestone sludge, through an integrated physicochemical and mineralogical characterization approach. Overall, the results provided a clear comparative understanding of the mineralogical, chemical, and physical properties of the four mining waste materials. The results showed that the sulphide tailings have high contents of Fe, S, Zn, Pb, As, and Cu and have the potential to generate acid rock drainage. From the distribution of metals by different particle sizes, it was possible to conclude that the largest amount of target metals (Cu, Zn, and Pb) are found below 11 microns. The sulphide tailings sample has the greatest potential for the recovery of critical raw materials. Granite sludge is mainly composed of silica-rich phases, with quartz and feldspar as dominant constituents. The water/moisture content of the studied granite sludge is suitable for direct incorporation into ceramic pastes without a prior drying stage. Particle size distribution is < 0.24 µm, a desirable size for ceramic pastes, avoiding the fragmentation, grinding, and particle size separation associated with the use of feldspars for this purpose. The main disadvantage of incorporating granite sludge into ceramic pastes is the reddish colour it acquires at temperatures above 1000 ºC, which can limit its use in traditionally white ceramic products. Further beneficiation tests are underway at HU to PT3 PT4
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