The leaching kinetics of chalcopyrite is sluggish due to the refractory nature of chalcopyrite and the formation of passive layers. In this study, the effect of mechanical activation on the leaching behavior and mechanism was studied by leaching tests, electrochemical measurements, particle size distribution analysis, scanning electron microscope (SEM), X-ray diffraction (XRD), differential scanning calorimetry-thermogravimetric analysis (DSC-TGA), X-ray photoelectron spectroscopy (XPS) and electron microprobe. The results show that mechanical activation can greatly promote the chalcopyrite leaching kinetics, and the copper extraction was increased from 14.1% to 55.7% and 91.8% after primary and secondary mechanical activation, respectively. The electrochemical study results indicated that mechanical activation did not change the cathodic reactions kinetics, however, the anodic dissolution kinetics was significantly promoted. XRD and DSC-TGA results show that mechanical activation treatment can effectively activate chalcopyrite due to the grain size reduction, formation of crystal defects and lattice deformation. The main solid product of chalcopyrite leaching is elemental sulfur. Besides particle size reduction, the reduction of grain size, formation of crystal defects and lattice deformation can increase the strain energy and instability of chalcopyrite, which plays an important role in improving chalcopyrite leaching kinetics.

Selective catalytic reduction of nitrogen oxides with NH₃ (NH₃-SCR) is still the most commonly used control technology for nitrogen oxides emission. Specifically, the application of rare earth materials has become more and more extensive. CeO₂ was widely developed in NH₃-SCR reaction due to its good redox performance, proper surface acidity and abundant resource reserves. Therefore, a large number of papers in the literature have described the research of cerium-based catalysts. This review critically summarized the development of the different components of cerium-based catalysts, and characterized the preparation methods, the catalytic performance and reaction mechanisms of the cerium-based catalysts for NH₃-SCR. The purpose of this review is to highlight: (1) the modification effect of the various metal elements for cerium-based catalysts; (2) various synthesis methods of the cerium-based catalysts; and (3) the physicochemical properties of the various catalysts and clarify their relations to catalytic performances, particularly in the presence of SO₂ and H₂O. Finally, we hope that this work can give timely technical guidance and valuable insights for the applications of NH₃-SCR in the field of NO_x control.

The use of citrate as an alternative reagent to ammonia in thiosulfate solutions offers an environmentally friendly, nontoxic, and cost-effective leaching method for gold extraction from ore/concentrate. In this work, the behavior of gold disc with copper-citrate-thiosulfate solutions has been investigated to identify the leaching mechanism of gold in the complex system of citrate-thiosulfate. The experimental parameters include rotating speed of gold disc, temperature, solution pH, and composition of lixiviant. The addition of copper and citrate in thiosulfate solutions can accelerate gold dissolution rate by about an order of magnitude. For the copper-citrate-thiosulfate system, thiosulfate ion works as the complexing agent for aurous ion, and it is extremely critical to the gold leaching process. The results of kinetic analysis of the leaching data indicate a chemical reaction-controlled process under the experimental conditions, giving an activation energy of 49.74 kJ/mol. The reaction orders of gold leaching with respect to copper, citrate, and thiosulfate concentration in copper-citrate-thiosulfate solutions are 0.95, −1.49, and 1.18, respectively. An acceptable gold leaching rate of 0.18 to 0.27 μmol·m⁻²·s⁻¹ could be obtained under the conditions of above 0.1 mol/L copper and thiosulfate concentrations.