Manganese Recovery by Silicothermic Reduction of MnO in BaO-MnO-MgO-CaF 2 (-SiO 2 ) Slags
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The refining of high-carbon ferromanganese (HCFeMn), including dephosphorization (de-P) and decarburization (de-C), is one of the most important stages during the FeMn smelting process.[1] The most common reagent for de-P is CaO-based flux due to its low price and high phosphide (P3) capacity under reducing conditions. However, because reducing de-P is not highly practical in industrial applications, BaCO3 or BaO has been proposed as fluxing agents to produce ultra-low phosphorus FeMn (ULPFeMn) under oxidizing conditions, because BaO-based fluxes exhibit relatively high phosphate (PO43) capacity.[2–5] During the de-P stage of the manganese oxygen refining (MOR) process, oxygen is blown into the HCFeMn to make low- and medium-carbon grades.[1] Because manganese has a high affinity for oxygen, the slag composition can thus change to a BaO- and MnO-containing system. Because the slag contains high amounts of MnO (30 to 40 mass pct), it can be transferred to the production of silicomanganese (SiMn) alloys through the chemical reaction between MnO-rich slag and Si-rich melt; this allows duplex processing of
JUNG HO HEO and JOO HYUN PARK are with the Department of Materials Engineering, Hanyang University, Ansan 426-791, Korea. Contact e-mail: [email protected] Manuscript submitted September 16, 2017. METALLURGICAL AND MATERIALS TRANSACTIONS B
FeMn and SiMn. To achieve high yield of manganese from the slag, the mechanism of the silicothermic reduction reaction is a key issue.[6,7] Several authors have investigated the reduction behavior of MnO in multicomponent slag systems under specific conditions.[6,8–18] Although various experimental parameters for the slag–metal reaction have been investigated, such as reductant choice, slag composition, and temperature, the previous work has mainly focused on the use of CaO-based slags. There is a lack of research on the reduction of MnO in molten slag by means of silicothermic reaction, and specifically, only a few studies have been carried out regarding the effect of CaF2 upon the MnO reduction process.[12,16] Recently, we investigated the effect of CaF2 on the silicothermic reduction kinetics of MnO in the CaO-MnO-SiO2-CaF2 slag.[6] We reported that there is a critical CaF2 content to obtain effective MnO reduction, which can be determined by considering the relationship between the reaction kinetics and the thermophysical properties of molten slags. Unfortunately, however, the effect of CaF2 upon the silicothermic reduction of MnO in BaO-containing slag has never been considered with the primary focus on maximizing Mn recovery. Therefore, in the present study, the effect of CaF2 addition upon the silicothermic reduction process under the chemical reaction between BaO-MnO-MgO(-SiO2) slags and SiMn (or FeSi) alloy melts was investigated. Moreover, the viscosities of slags having various CaF2 contents in the BaO-SiO2-10MnO5MgO-CaF2 slag system (BaO/SiO2 = 1.0 mass pct) were directly measured using a rotating cylinder method. Silicothermic reduction experiments were carried out using a hi
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