Dielectric Properties of Zinc Sulfide Concentrate during the Roasting at Microwave Frequencies

Evaluation of a green-sustainable industrialized cleaner utilization for refractory cyanide tailings containing sulfur

In order to achieve the clean treatment of refractory cyanide tailings containing sulfur, a novel microwave-assisted chlorination thermal treatment recovery technology was proposed in this paper. On the basis of studying the mineralogy of cyanide tailings, the treatment capacity of common chlorinated agents for refractory cyanide tailings containing sulfur was compared. CaCl₂ as the best chlorination agent, gold recovery and chlorine removal rates were 85.2% and 95%, under the optimal conditions. The specific action mechanism of CaCl₂ in the process of microwave roasting was studied. Under the action of microwave, CaCl₂ accelerated decomposition into chlorine-containing gas and rapidly diffused in cracks caused by thermal stress to ensure gold volatilization and chlorination. Finally, the approach and mechanism of removing residual harmful substances in roasting slag were proposed based on the environmental assessment of roasting slag. Environmental pollution and corrosion of building materials can be effectively avoided in the later transportation and secondary utilization of roasting slag.

Microwave Roasting Characteristics of Cuprous Chloride Residue from Zinc Hydrometallurgy

High-efficiency dechlorination processes are crucial for the clean utilization of CuCl waste residue from zinc hydrometallurgical processes. A new method of oxygen-enriched microwave roasting has been proposed to improve the dechlorination process. The cavity perturbation method was used in this paper to measure the permittivity of a CuCl residue at various temperatures and apparent densities. The results show that temperature had a more significant effect on the loss tangent when it exceeded 400 °C more than that of apparent densities. The degree of dechlorination of CuCl residue exceeded 93% after 90 min of microwave roasting at 450 °C and 150 mL/min oxygen flow, which was 12% higher than that of conventional calcination. The elemental distribution in samples was studied using single-point, linear, and lateral scans at the microscale, and the microstructure and phase changes of the CuCl residue under a microwave field were characterized by XRD and SEM-EDS. This study shows that microwaves can promote the dechlorination reaction by decreasing the activation energy from 52.69 kJ/mol to 42.36 kJ/mol.

High Temperature Dielectric Properties of Iron- and Zinc-Bearing Products during Carbothermic Reduction by Microwave Heating

In this work, the carbothermic reduction of iron- and zinc-bearing products is studied through in situ microwave heating, dielectric properties monitoring, and mass spectrometry up to high temperatures (1000 °C). The results are correlated to the information provided by conventional analysis techniques such as differential scanning calorimetry (DSC) and thermogravimetry (TG). This combination allows a detailed study of seven different process stages with an accurate determination of the reaction temperatures, providing new evidence about the particular conditions of this microwave-driven reduction process. The presented results suggest that molecular vibrations imposed by the microwave field are presumably the reason for reactions taking place at lower temperatures than those observed in the conventional process. This work also explores the influence of other parameters, such as the apparent density or the amount of carbonaceous material, on the resulting dielectric properties, providing useful information for the development of a potential microwave industrial application in the metallurgy field.

Microwave field: High temperature dielectric properties and heating characteristics of waste hydrodesulfurization catalysts

The exploration of the dielectric properties of waste hydrodesulfurization catalysts has important guiding significance for the development of microwave heat treatment of waste hydrodesulfurization catalysts for the recovery of valuable metals. The resonant cavity perturbation technique was used to measure the dielectric properties of waste catalyst and the mixture of waste catalyst and Na₂CO₃ during roasting from room temperature to 700 °C at 2450 MHz. The heating properties of the waste catalyst and mixture of waste catalyst and Na₂CO₃ were determined in the microwave field. The results show that the waste catalyst and the mixture of waste catalyst and Na₂CO₃ exhibit strong microwave response capability, and the dielectric constant, dielectric loss factor, and dielectric loss tangent increase with increasing temperature; from 20 to 300 °C, the waste catalyst and the mixture of waste catalyst and Na₂CO₃ heated at a slower rate, while the material heated rapidly from 300 to 700 °C. In addition, the mechanism of microwave action has been proposed based on the study of dielectric properties and heating properties in the microwave field.