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The effects of process conditions on preparation of U 3 O 8 by calcination from ammonium uranyl carbonate in microwave fields were assessed and optimized for maximizing the total uranium as well as calcination temperature, adopting as Central Composite Design (CCD) methodology. The process variables assessed were calcination temperature, calcination duration and mass of sample. A quadratic model relating the process variables and the total amount of uranium and U 3 O 8 was proposed eliminating the insignificant parameters. The optimal calcination conditions were estimated to be a calcination temperature of 942.75 K, calcination duration of 8.78 min, with the corresponding total uranium and U 3 O 8 to be 82.07% and 31.33%, 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]

Crofton weed was converted into a high-quality activated carbon (CWAC) via microwave-induced CO2 physical activation. The operational variables including activation temperature, activation duration and CO2 flow rate on the adsorption capability and activated carbon yield were identified. Additionally the surface characteristics of CWAC were characterized by nitrogen adsorption isotherms, FTIR and SEM. The operating variables were optimized utilizing the response surface methodology and were identified to be an activation temperature of 980 °C, an activation duration of 90 min and a CO2 flow rate of 300 ml/min with a iodine adsorption capacity of 972 mg/g and yield of 18.03%. The key parameters that characterize quality of the porous carbon such as the BET surface area, total pore volume and average pore diameter were estimated to be 1036m²/g, 0.71 ml/g and 2.75 nm, respectively. The findings strongly support the feasibility of microwave heating for preparation of high surface area porous carbon from Crofton weed via CO2 activation. [ABSTRACT FROM AUTHOR]

Abstract: This preliminary study examined the role of microwave radiation on precipitation and aging of iron oxyhydroxides at 60°C. It was observed that due to rapid heating under microwave, transformation of two line ferrihydrite to α-Fe2O3 takes place within 4–10h. This is in contrast to the usual aging temperature of >100°C adopted in most conventional studies, and several days of aging. Besides rapid transformation, microwave helps forming nanoparticles, with crystallite size of ~60nm as determined from X-ray diffractograms, and <100nm particles as observed under TEM. Rapid transformation also promotes formation of α-Fe2O3 without the formation of intermediate γ-Fe2O3. This study brought out the advantages of low temperature microwave assisted precipitation/aging as a low energy process to transform iron oxyhydroxides, with likely applications in slurry rheology, synthesis of nanoparticles, and adsorption. [Copyright &y& Elsevier]

Abstract: The temperature rising characteristics of ammonium diurante, triuranium octaoxide (U3O8), and their mixture were investigated under microwave irradiation, aiming at exploring newly theoretical foundation for advanced metallurgical methods. The temperature rising curves showed that ammonium diurante had weak capability to absorb microwave energy, while triuranium octaoxide had the very strong absorption capability. The temperature of mixture containing 20% of U3O8 could rise from room temperature to 1171K within 280s. The ability to absorb microwave energy for the mixture with different ratios increased with the increase in the amount of U3O8. These are in good agreement with the results of Maxwell-Garnett effective medium theory. It is feasible to calcine ammonium diurante by adding of small amounts of U3O8 in microwave fields. [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]