Microwave-assisted metallurgy

Abstract

Microwave heating has been extensively explored in various fields of materials processing. This technology exhibits unique characteristics including volumetric and selective heating, which eventually lead to many exceptional advantages over conventional processing methods including both energy and cost savings, improved product quality, faster processing and greater ecofriendliness, making microwave heating appropriate for applications in metallurgy. This paper presents a critical review on the use of microwave energy in metallurgy, with emphasis on both fundamentals of microwave heating and recent experimental efforts on extractive metallurgy via pyrometallurgical and/or hydrometallurgical routes. Applications to metallurgical processes for extraction of various metals, including heavy metals (Fe, Ni, Co, Cu, Pb and Zn), light metals (Al and Mg), rare metals (Ti, Mo, W and Re) and precious metals (Au, Ag and Pt), are reviewed and discussed.

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

“…Later increases sharply from 400 to about 800 • C, it can be concluded that the oxidation reaction of zinc sulfide proceed gradually according to the temperature condition of zinc sulfide oxidation reaction [19,20], and there is a main phase transformation in this temperature range as well, Figure 2 also can prove that there are some reactions from 400 to about 800 • C. Lastly drop sharply to an almost stable value, which means main reaction have finished by compared with the dielectric properties of zinc oxide we have measured. The dielectric loss factor is the function of frequency because of dipolar rotation and ionic conduction, and ionic conduction is the dominant mechanism at lower frequencies while dipolar rotation is the main source of dielectric loss at higher microwave frequencies [21,22], as shown in the following equation: The dielectric loss factor at 915 MHz from Figure 3b is smaller than that at 2450 MHz from Figure 3d when the temperature under 400 °C, but reverse results when the temperature above 400 °C. It can be concluded that dipolar rotation is the main contribution to the loss factor when temperature under 400 °C, while ionic conduction contributes mainly to the loss factor when temperature above 400 °C because thermal agitation disturbs the alignment of the molecule dipole with the electric field and conduction increases as the temperature increases, similar results have also been reported by some literature [22,23].…”

Promote Alumina Leaching through Re-Pelleting: Effects of Directional Coating of Calcite on Silicate Grains

“…Leaching was also popular for disposing of ferric bauxite [7,8]. Papassiopi et al [9] developed a method involving microbial dissolution, by which the dissolution ratio of Fe from amorphous Fe 2 O 3 reached up to 95%; however, only 9% Fe could be leached out in crystal form.…”

Digestion of Alumina from Non-Magnetic Material Obtained from Magnetic Separation of Reduced Iron-Rich Diasporic Bauxite with Sodium Salts

“…Many studies have been conducted to separate iron constituents from the iron-rich bauxite by using physical methods [3,11], pyro-and hydro-metallurgical processes [5,[12][13][14], and bio-leaching methods [4,15]. Generally, it is difficult to achieve the sufficient separation of iron due to the complex occurrences and associations of disseminated iron-, aluminum-, and silicon-bearing minerals.…”