Dielectric properties and carbothermic reduction of zinc oxide and zinc ferrite by microwave heating

Abstract

This paper aims to study the dielectric properties and carbothermic reduction of zinc oxide (zincite, ZnO) and zinc ferrite (franklinite, ZnFe2O4) by microwave heating. To achieve this aim, the dielectric properties were measured with an open-ended coaxial method to understand the behaviour of the samples under microwave irradiation. The effects of microwave power, duration time and sample mass on the heating rate, and the effects of the stoichiometric amount of graphite on the reduction of ZnO and decomposition of ZnFe2O4 were investigated. The results show that ZnFe2O4 has significantly higher dielectric properties compared to ZnO. Generally, for both samples, the dielectric values at room temperature were quite low, indicating that both ZnO and ZnFe2O4 are poor microwave absorbers. It was found that the temperatures have a more significant effect on the imaginary permittivities than on the real permittivities. The heating rate showed that the sample temperature increased with increase in microwave power and sample mass. Using 700 W of microwave power and two times the stoichiometric amount of graphite, almost complete reduction of ZnO was achieved in 12 min, while ZnFe2O4 completely decomposed to zincite and wustite in 3 min.

Converting a Microwave Oven into a Plasma Reactor: A Review

“…Although a combination of microwave heating and chemical reactions were reported in the early 1980s, no large-scale oven production was done until rapid synthesis of organic compounds in microwave ovens was performed in 1986 [7,8]. More recently (2017), carbothermic reduction of zinc oxide and zinc ferrites has also been reported [9]. Once the first conversion of a microwave oven into a plasma reactor was reported in 1978 [10], plasma-induced synthesis of inorganic compounds became available [11][12][13], followed by plasma modification of polymer surfaces [14].…”

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

“…This reduction process is well-known in the pyrometallurgical industry which has made use of different technologies including several attempts with microwave heating [1][2][3][5][6][7][8][9][10][11][12][13]. Recent studies have shown microwave technology as a very promising option for the carbothermic reduction and the decrease of the CO 2 emissions in the steel production chain, since iron and steelmaking process residues have good microwave absorbing properties owing to their carbon and iron oxides content.…”

“…Recent studies have shown microwave technology as a very promising option for the carbothermic reduction and the decrease of the CO 2 emissions in the steel production chain, since iron and steelmaking process residues have good microwave absorbing properties owing to their carbon and iron oxides content. Some of the reported advantages are the volumetric and fast heating of the mixture [2,3,5,7], enhanced reaction diffusion kinetics [1,3,6], and a lower demand of carbon needed [1,10] for the reduction process. The possibility to employ wastes with high carbon content such as biochar has been also pointed out by other authors [11,12].…”

“…Several techniques have been reported to measure the dielectric properties of iron ores [14], zinc oxide [6,15], zinc ferrite [6,15,16] or related materials such as electric arc furnace dusts [10][11][12]15,17]. The most widely used technique is the open-ended coaxial probe, because it allows convenient non-invasive dielectric measurements by contacting just one face of the material.…”

Microwave assisted alkaline roasting-water leaching for the valorisation of goethite sludge from zinc refining process

“…Franklinite is a very stable spinel structure that requires other routes than those above mentioned to liberate Zn for dissolution. Those may include several methods to decompose the franklinite structure or to reduce the iron and the zinc present in the spinel, as illustrated in Table 1 (Güler et al, 2011;Havlik et al, 2004;Kazemi and Sichen, 2016;Kukurugya et al, 2015;Omran et al, 2017;Santos et al, 2015;Turan et al, 2004;Stanforth, 2000a, 2000b;Zang et al, 2016). Amongst these techniques, an effective and selective combination of thermal and hydrometallurgical treatments, composed of preliminary hydrolysis-NaOH roasting-NaOH leaching, was explored by Youcai et al to quantitatively extract zinc from franklinite-bearing EAF dusts (Zhao Stanforth, 2000b, 2000a).…”