677 circuit of a copper mine processing plant (ST). Granite sludge was obtained from a granite quarry (GS), marble sludge was collected from a marble quarrying and processing site (MS), while limestone sludge was obtained from a limestone production site (LS). The geographical locations of the sampling sites are presented in Figure 1. Figure 1 – Location of the collected samples of mining wastes. 2.2 Characterization Tecniques To evaluate the physical, chemical, mineralogical, and environmental properties of the four mining waste samples, a comprehensive characterization study was carried out in collaboration with several academic and industrial laboratories: Faculty of Engineering of University of Porto (FEUP, Portugal); Secil building materials company (SECIL, Portugal); National Institute of Research and Development for Optoelectronics (INOE, Romania); Chalmers University of Technology (CU, Sweden); University of Granada (UGR, Spain) and Hacettepe University (HU, Türkiye). The experimental methods included particle size distribution, chemical elemental composition, mineralogical composition, pH, moisture content, microstructural characteristics, chemical stability, and potential for acid generation. The samples were oven-dried at 60 °C until constant weight (the weight remained constant for 2 consecutive readings after 48 h), homogenized, and divided into 4 subsamples to ensure consistent results across the characterization and tests. The grain-size distribution of the four types of mining wastes was determined using the Laser Diffraction technique on a Malvern Mastersizer 2000 Hydro G particle size analyzer. The elemental chemical composition was determined by X-ray Fluorescence (XRF) using an Oxford XRF Analyser (X-MET). Mineralogical composition was determined by X-ray diffraction with Rietveld refinement, and the microstructural analysis was determined by Scanning Electron Microscopy with Energy-Dispersive Spectroscopy (SEM/EDS). The pH was determined in aqueous solution by two methods: with distilled water at a 1:1 solid-liquid ratio and with 0.01 M CaCl2 at a 1:2 solid-liquid ratio (Black 1965). Chemical stability was assessed through dynamic natural leaching tests in accordance with Standard EN 12457-4 (Characterization of waste - Leaching - Compliance test for leaching of granular waste materials and sludges - Part 4) (CEN, 2003). After the test, the leached solid samples were dried and then analyzed for
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