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The microwave irradiation is used to roast zinc slag oxidation dust in the presence of concentrated sulfuric acid with the aim of accelerating roasting process. The roasted material is leached with tap water for the recovery of zinc and indium. The influence of roasting temperature, particle size, and the ratio of acid to ZSOD mass on the rate of roasting reactions were investigated. The results show that the extraction rate of zinc and indium increases with increasing the roasting temperature and the ratio of acid to ZSOD mass, while decreases with increase in the particle size. The samples were characterized using XRD and SEM. Under the conditions employed in the present work a maximum recovery of 94% and 90% of zinc and indium could be achieved. Shrinking core model was used to describe the kinetic parameters and to identify the rate controlling step. Both zinc and indium extraction were controlled by the internal diffusion in the solid product layer, with the apparent activation energy of the roasting reaction were 15.94 kJ/mol and 12.68 kJ/mol respectively. The reaction order with respect to concentrated sulphuric acid was 1.75 and 1.59 for zinc and indium, respectively. [ABSTRACT FROM AUTHOR]

The clean utilization of the CuCl residue containing chloride produced from zinc hydrometallurgy residue is very important for the recycling of valuable metals. In order to strengthen the process of dechlorination, a new method of microwave roasting under the atmosphere of steam and oxygen was put forward. It was demonstrated that the dechlorination rate of CuCl residue by microwave roasting was higher than that of conventional roasting by tubular resistance furnace under the same conditions (temperature, holding time and atmosphere). After roasting at a temperature of 450 °C for 80 min under a gas flow rate of 150 mL/min in microwave filed, the dechlorination rate of CuCl residue was as high as 97%, increasing 18% compared to that of conventional roasting using tubular resistance furnace. The chatacterization of phases variation of CuCl residue in microwave field by means of XRD, SEM-EDS and Raman spectroscopy indicated that the process of dechlorination by microwave roasting under the atmosphere of steam and oxygen was much more efficient than conventional roasting. [ABSTRACT FROM AUTHOR]

• A novel microwave-assisted method for preparing (NH 4) 6 Mo 7 O 24 ∙4H 2 O is proposed. • Microwave roasting is more effective and green compared to conventional roasting. • The leaching process of ammonium molybdate is optimized. • The purity of (NH 4) 6 Mo 7 O 24 ∙4H 2 O prepared by microwave roasting is higher. A novel and efficient microwave oxidation roasting method for preparing ammonium molybdate from molybdenum concentrate has been proposed and compared with the conventional roasting. TG-DTG, XRD, SEM-EDS, EDX and FTIR methods were used for characterization and analysis of oxidation roasting of ammonium molybdate. Based on the results of thermodynamic and dielectric properties of molybdenum concentrate, the effects of roasting temperature, roasting time, material mass and microwave power density on the oxidation degree of molybdenum concentrate were investigated. The influence of leaching agent, the concentrations of nitric acid and ammonia water on the leaching of ammonium molybdate was investigated. Under the same roasting conditions, the degree of oxidation of molybdenum concentrate by microwave roasting was higher than that of conventional roasting. Microwave roasting reduce the heating time of 30 min to reaction temperature and save 2.0 kW/h power in each roasting experiment. The optimal roasting and leaching conditions are as follows: roasting temperature of 600°C, roasting time of 2 h, power density of 100 W/g, nitric acid concentration of 0.80 mol/L, ammonia concentration of 25%. The purity and crystallinity of (NH 4) 6 Mo 7 O 24 ∙4H 2 O prepared by microwave roasting molybdenum concentrate are higher and better stability. [Display omitted] [ABSTRACT FROM AUTHOR]