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.

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.

The leaching behaviors of gold and silver from a complex sulfide concentrate in copper-tartrate-thiosulfate solutions were investigated in this paper. Experimental parameters, including temperature, initial pulp pH, and concentration of copper, tartrate, and thiosulfate, were systematically studied. The copper-tartrate-thiosulfate leaching system exhibits promising performance in dealing with the complex sulfide concentrate. Thiosulfate consumption could be greatly reduced due to the in-situ generation of thiosulfate derived from sulfur or disulfide ions. Increasing the temperature and concentrations of copper, tartrate, and thiosulfate can promote gold leaching. A low tartrate content and a moderate increase in temperature and copper and thiosulfate concentrations can accelerate silver leaching, but a higher temperature or copper content may depress silver extraction. A suitable pulp pH is critical for gold and silver leaching in copper-tartrate-thiosulfate solutions. An extraction of 74.50% Au and 36.33% Ag was obtained with the direct leaching of the concentrate, while the percentages can be significantly increased up to 82.60% and 70.38%, respectively, when leaching the calcine following the oxidative roasting pretreatment. The recycling of leaching solutions demonstrates that a suitable free tartrate content is of great significance in maintaining the stability of the novel system. As an alternative to the traditional cyanide or copper-ammonia-thiosulfate leaching processes, the copper-tartrate-thiosulfate leaching system provides an environmentally friendly, nontoxic, and relatively low-cost method for gold and silver leaching from ores or concentrates.

The feasibility of using emulsion liquid membranes (ELMs) with the guanidine extractant LIX 7950 as the mobile carrier for detoxifying copper-containing waste cyanide solutions has been determined. Relatively stable ELMs can be maintained under suitable stirring speed during mixing ELMs and the external solution. Effective extraction of copper cyanides by ELMs only occurs at pH below 11. High copper concentration in the external phase and high volume ratio of the external phase to ELMs result in high transport rates of copper and cyanide. High molar ratio of cyanide to copper tends to suppress copper extraction. The presence of thiocyanate ion significantly depresses the transport of copper and cyanide through the membrane while the thiosulfate ion produces less impact on copper removal by ELMs. Zinc and nickel cyanides can also be effectively extracted by ELMs. More than 90% copper and cyanide can be effectively removed from alkaline cyanide solutions by ELMs under suitable experimental conditions, indicating the effectiveness of using the designed ELM for recovering copper and cyanide from waste cyanide solutions

Pyrite-rich cyanide tailings (CTs) are industrial hazardous solid wastes arising from the gold mining industry. Every year, hundreds of millions of tons of cyanide tailings are produced and discharged to tailings dams. It is of great significance to dispose of cyanide tailings harmlessly and resourcefully. The feasibility of calcination of calcium sulphoaluminate (CSA) cement clinker using pyrite-rich cyanide tailings as Fe₂O₃ and SO₃ sources was investigated for this paper. The behavior of pyrite during the calcination of cyanide tailings under various calcination conditions and the properties of calcium sulphoaluminate cement clinker were examined. The results show that it is feasible to produce calcium sulphoaluminate cement clinker using pyrite-rich cyanide tailings. The optimal conditions for the calcination of calcium sulphoaluminate cement using pyrite-rich cyanide tailings are confirmed. During the calcination process, the cyanides decompose into carbonate, CO₂, and N₂. The pyrite decomposes into Fe₂O₃ and SO₂, and they react with CaO and Al₂O₃ to form the intermediates of CaSO₄, 2CaO·Fe₂O₃, and CaO·2Al₂O₃, which further react to form 3CaO·3Al₂O₃·CaSO₄, 4CaO·Al₂O₃·Fe₂O₃, and 12CaO·7Al₂O₃. The calcium sulphoaluminate cement prepared by pyrite-rich cyanide tailings exhibits excellent mechanical properties and meets the compressive strength criteria of 42.5 grade calcium sulphoaluminate cement.

Mercury continues to receive attention across a variety of disciplines due to its high mobility and high toxicity to human health and the environment. Sources of mercury-containing solid waste may come from nonferrous metallurgy, mercury mining, electro remediation process, and the chemical manufacturing industry. Significant efforts and resources have been leveraged to develop effective remediation technologies to reduce the hazardous effect of mercury-contaminated waste. Research and development on mercury recovery from mercury-contaminated wastes is reviewed in this article. Though the thermal treatment technologies are used in practice, leaching processes including acid leaching, alkaline leaching and bioleaching, using different lixiviants, have also been developed. It is difficult to conclude which technology offers the best outcomes. However, leaching processes can normally be performed at the site of contamination and can usually remove mercury permanently from wastes in a relatively safe and controlled manner – this is not always true for thermal treatments. Leaching processes can be used independently or in conjunction with other treatment technologies. The selection of leaching lixiviants is highly dependent on the characteristics of the different waste streams. Speciation and coordination of mercury in waste can be critical for application of a recovery technology, especially for leaching processes.