Abstract
Microwave technology has a potential application in the extraction of zinc from sulphide ores, knowledge of the dielectric properties of these ores plays a major role in the microwave design and simulation for any process. The dielectric properties of zinc sulfide concentrate for two different apparent densities-1.54 and 1.63 g/cm3-have been measured by using the resonance cavity perturbation technique at 915 and 2450 MHz during the roasting process for the temperature ranging from room temperature to 850 °C. The variations of dielectric constant, the dielectric loss factor, the dielectric loss tangent and the penetration depth with the temperature, frequency and apparent density have been investigated numerically. The results indicate that the dielectric constant increases as the temperature increases and temperature has a pivotal effect on the dielectric constant, while the dielectric loss factor has a complicated change and all of the temperature, frequency and apparent density have a significant impact to dielectric loss factor. Zinc sulfide concentrate is high loss material from 450 to 800 °C on the basis of theoretical analyses of dielectric loss tangent and penetration depth, its ability of absorbing microwave energy would be enhanced by increasing the apparent density as well. The experimental results also have proved that zinc sulfide concentrate is easy to be heated by microwave energy from 450 to 800 °C. In addition, the experimental date of dielectric constant and loss factor can be fitted perfectly by Boltzmann model and Gauss model, respectively
Highlights
Zinc is the third most commonly used nonferrous metal and has a wide range of applications in the civilian and military fields
The zinc it can be concluded that the loss tangent increases and reaction process accelerates as the apparent sulfide concentrate of bigger apparent density for a given temperature mostly has a higher value of dielectric loss factor, it can be concluded that the loss tangent increases and reaction process accelerates as the apparent density increases suitably, similar results for room temperature can be found in literature [24,25], so we can enhance the ability of absorbing microwave by increasing the apparent density
Filled in an alumina crucible, 30 g zinc sulfide concentrate with the apparent density of 1.63 g/cm3 auxiliary heating by using silicon carbide was employed from room temperature to 450 °C, was heated by 2450 MHz microwave oven at power of 1000 W
Summary
Zinc is the third most commonly used nonferrous metal and has a wide range of applications in the civilian and military fields. The ability of a special material converting microwave energy into heat at a given frequency and temperature is determined by the loss tangent (tan δ). In general a material with high tan δ value at some microwave frequency is required for good absorption and efficient heating. A novel combination of phase transformation by using microwave roasting and leaching, can improve zinc extraction with high energy efficiency and hardly any SO2 emissions [10,11]. It is important to know how the dielectric properties of zinc sulfide concentrate change with the temperature, microwave frequency, and apparent density. The object of this work is to study the dielectric properties of zinc sulfide concentrate as affected by temperature (from room temperature to 850 ◦ C), microwave frequency (915 and 2450 MHz) and apparent density in view of continuous thermal processing. It is hope that the data of dielectric properties in this paper can provide useful guidelines in designing and simulating microwave heating system of zinc sulfide concentrate
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