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In this work, a clean microwave carbothermal reduction of Sb2O3 mineral to prepare metallic antimony ingot is proposed. Response surface methodology was used to optimize condition for microwave carbothermal reduction of Sb2O3. The roasting temperature, roasting duration, carbon powder ratio and NaCl addition ratio was collected to carry out a four-factor and three-level experiment. In the optimized conditions, a >77.0% yield of antimony ingot can be obtained under roasting temperature of 730 °C, roasting time of 60min, carbon powder ratio of 0.3, NaCl addition amount of 4%. More than 99% Sb content of metallic Sb ingot is obtained in the microwave field. The mechanism of microwave carbothermal reduction of Sb2O3 was investigated by XRD, SEM-EDS and Mapping analysis, the results show that the microwave reduction process is divided into three stages based on the melting point of antimony, namely, 25 °C–400 °C, 400 °C–630 °C, and above 630 °C, which differ in terms of phase transformation. In the microwave field, the reduction of Sb2O3 to Sb particles can be completed within 15 min. Microwave metallurgical technology is conducive to the sustainable development of antimony metallurgy, and also provides a clean technology for the metallurgy industry.

Kinetics of antimony production via carbothermal reduction of Sb2O3–carbon powder–NaCl mixture using microwave and conventional heating was investigated to identify the dominant controlling mechanism. Results of conventional heating revealed the temperature range of conventional carbothermal reduction reaction is 500°C to 800°C, with the average activation energy of each stage being 81.97 kJ/mol (α = 0.1–0.5), 65.17 kJ/mol (α = 0.5–0.75), and 69.86 kJ/mol (α = 0.75–1.0), respectively. In the microwave field, the carbothermal reduction reaction of raw materials can be completed at 600°C to obtain antimony, and the weight loss data of the carbothermal reduction process were recorded for the first time. The above results show that the microwave field enhanced the interfacial chemical effect, accelerated the interfacial diffusion from the metal phase to the oxide phase, and reduced the activation energy of the carbon thermal reduction process to 6.85 kJ/mol. The growth index of antimony grain growth process is estimated to be 4.33, controlled by the surface diffusion. These data provide a reliable theoretical basis for studying the reduction reactions of minerals in microwave fields. [ABSTRACT FROM AUTHOR]

Dewatering is considered as extremely significant and primary step to enhance the quality of lignite. A great number of research focus on conventional fluidized-bed drying technology or dynamics. In this paper, the microwave deep drying kinetics of Zhaotong lignite under different power levels and with different sample thicknesses were investigated. The drying kinetics of microwave deep drying was fitted by 13 different drying models given in the literature. Experimental results indicated that the microwave deep drying process exists three segments: increasing-rate, falling-rate and brief constant-rate segment. The drying time decreased and drying rate increased with microwave output power level increase, while the microwave penetration depth in lignite was affected by sample thickness, hence there is an irregular relationship between lignite sample thickness and microwave drying time or drying rate. Based on non-linear regression analysis, the Page model was considered adequate to describe the microwave deep drying behavior of Zhaotong lignite under various conditions, and the model could be used for residual moisture water content prediction at any time during the microwave deep drying process. Effective diffusion coefficient increased along with microwave output power level increase. The activation energy of the moisture emission from the lignite under different power levels was estimated at 10.2202 W/g using modified Arrhenius equation. The pore structure damage was observed in the lignite samples after microwave deep drying by SEM analysis. The surface of upgraded lignite had visible cracks, defects and small fragments compared with the samples by conventional drying. [ABSTRACT FROM AUTHOR]