Influence of Electro-Emulsification on Desulfurization of Rejected Electrolytic Manganese Metal in Electroslag Remelting
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HIGH-PURITY manganese metal (MM), which finds extensive applications in aeronautics, steelmaking, batteries, fertilizer and other fields, is mainly produced by means of electrolysis. To change the crystal structure of the deposited MM, during electrolytic process, sulfur dioxide is added to the catholyte. However, this addition significantly increases the sulfur concentration, resulting in a higher rejection rate of the electrolytic manganese metal (EMM).[1,2] In order to reduce the waste of manganese resource, it is necessary to drop the excess sulfur concentration in the rejected EMM scrap (Figure 1) by electroslag refining (ESR) technology, which has outstanding desulfurization ability.[3] Figure 2 represents the schematic of the ESR unit used for the recycling of the rejected EMM scrap. An alternating current (AC), which is first imposed on the water-cooled electrode, travels through the molten slag QIANG WANG, YU LIU, RU LU, ZHU HE, and GUANGQIANG LI are with the The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, China and also with the Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, Wuhan University of Science and Technology, Wuhan 430081, China. Contact e-mail: [email protected] FANG WANG is with the School of Metallurgy, Northeastern University, Shenyang 110004, China. Manuscript submitted June 5, 2020; accepted October 8, 2020.
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and molten MM, and finally arrives at the water-cooled baseplate. This currents generates the Joule heat in the molten slag layer, significantly increasing its temperature. Therefore, the rejected EMM scrap would be instantaneously melted once it touches the hot molten slag layer. With the continuous feeding of the scrap, molten MM droplets could be observed in the molten slag layer, sinking downward, and forming a liquid metal pool at the mold base. Meanwhile, sulfur dissolved in the molten MM droplet would be shifted to the molten slag during the descending process. The interaction between the AC and self-induced magnetic field gives rise to an inward Lorentz force inside the melt, which magnitude regularly changes at the half frequency of the AC in the ESR process.[4] Due to the varied Lorentz force action, molten MM droplets undergo periodical deformation during their falling, which would change their surface area. The deformation of dispersed molten MM droplets in the continuous molten slag subjected to an external electric field is referred to as electro-emulsification. It is widely used in many applications such as electrospray, ink-jet printing, and transport in microfluidic system.[5–8] In order to assess the interfacial mass transfer, the flow visualization technique was adopted to present the velocity profile in the oscillating-circulating droplet-continuum system.[9] The velocity profile was then incorporated into the continuity equation for predicting the effect of droplet oscillation on the interfacial mass transfer rate. T
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