Element Distribution in the Silicomanganese Production Process
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I.
INTRODUCTION
FERROMANGANESE (FeMn) and silicomanganese (SiMn) alloys are key additions in modern steel production. Both high carbon ferromanganese (HC FeMn) and standard SiMn alloys are produced by carbothermic reduction of oxidic raw materials in Submerged Arc Furnaces (SAF). Standard SiMn with 18 to 20 wt pct Si and 70 wt pct Mn is typically produced from raw materials such as MnO-rich slag from the HC FeMn production process, manganese ores, quartz or quartzite, (Fe)Si-remelts or off-grade qualities of (Fe)Si, and coke.[1] A process temperature of 1600 C to 1650 C is necessary to obtain metal with sufficiently high content of Si and a discard slag with low MnO content.[1] The production process, as well as inand out-going (product) material flows are illustrated in Figure 1, adapted from Reference 2.
YAN MA, ELMIRA MOOSAVI-KHOONSARI, and GABRIELLA M. TRANELL are with the Norwegian University of Science and Technology (NTNU), Alfred Getz vei 2, 7491 Trondheim, Norway. Contact e-mail: [email protected] IDA T. KERO is with the SINTEF Materials and Chemistry, Alfred Getz vei 2, 7465 Trondheim, Norway. Manuscript submitted December 2, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
When a closed SAF is used in manganese alloy production, the furnace off-gas contains a significant amount of dust from fuming reactions in the furnace, and must be scrubbed. A series of wet scrubbers are typically used, yielding a sludge containing the dust and water. The off-gas may be further cleaned before it escapes the plant (in for example, mercury removal units). The reduction reactions of main elements in the SiMn production process are as follows[1]: MnOðl,sÞ þ CðsÞ ¼ MnðlÞ þ COðgÞ
½1:1
SiO2 ðlÞ þ 2CðsÞ ¼ SiðlÞ þ 2COðgÞ
½1:2
In addition to these reactions, reduction, melting, and fuming reactions for a large range of minor and trace elements will take place concurrently in the formation of metal, slag, and gas/dust product phases. The FeSi/Si production process has some similarities with the SiMn process, and the elemental distribution in the Si furnace has been studied by Myrhaug and Tveit.[3] Myrhaug and Tveit established that the behavior of different elements in the FeSi/Si production process depends on several factors: furnace temperature; stability of oxides and carbides of the elements; volatility of the elements/their compounds; solubility of elements in liquid metal; and by which type of raw materials they enter the process. They developed a so-called
Fig. 1—Overview of the material flows in a typical silicomanganese ferroalloy plant, after Olsen et al.[2]
‘‘boiling-point-model’’ to predict the element distribution between the out-going phases in a FeSi/Si furnace. According to this model, elements with boiling temperatures higher than the process temperature predominantly stay in the condensed phase, while elements with boiling temperatures lower than the process temperature mainly go off as fume or gas. If an element is stable as an oxide or sulfide, the boiling point of its compound is applicable. The fundamental
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