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The presence of calcium sulfate in the process water during the coal flotation greatly influences the recovery and selectivity of the separation. The concentrations of calcium and sulfate ions modify mineral hydrophobicity by altering surface properties resulting in depression or activation of the mineral species. An investigation to evaluate the statistical significance of the effect of the pH and concentration of calcium and sulfate ions on coal flotation was carried out; for this purpose, a 23 factorial design was implemented. A p-value < 0.05 was determined for the effect of calcium and sulfate ion concentrations, indicating that it is statistically significant. The interactions between factors (pH × calcium, pH × sulfate, calcium × sulfate and pH × calcium × sulfate) are also statistically significant, but the interaction between the concentration of calcium and sulfate ions has a notable influence according to the F statistic value. Employing 800 and 1920 mg/L of calcium and sulfate ions as experimental conditions yields a recovery of 90.4% with a concentrate containing 13% ash. [ABSTRACT FROM AUTHOR]

Electronic waste (e‐waste) contains metallic values that can be recovered by hydrometallurgical methods. This investigation addresses the leaching kinetics of e‐waste for the recovery of copper in H2SO4‐H2O2 media with the objective of determining the rate‐controlling step in monosize particle systems. The results are then used to develop a kinetic model for copper dissolution in multisize particle systems. It is shown that in a monosize particle system, Cu dissolves completely in 150 min at 2 M H2SO4 and 0.2 M H2O2. The rate‐controlling step for this process is chemical reaction with an activation energy of 47.8 kJ/mol. The kinetic model for Cu dissolution in multisize particle systems is developed by applying an optimization method that considers the size distribution and the copper content of each of the size fractions. The results show that the model predicts satisfactorily the Cu dissolution kinetics and reveals that Cu particles with mean sizes of 79, 141, 237, 398.5, and 605 μm react completely in times varying from 15 to 120 min. Coarser Cu particles do not react completely in a time interval of up to 120 min. E‐waste losses 57.6% of its initial weight when subjected to the leaching process and solid residue has gold and silver grades of 2 402.35 and 9 035.29 g/ton, respectively. [ABSTRACT FROM AUTHOR]