The reduction of fluxed and non-fluxed manganese ores by ferromanganese-silicide

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2014-12-12

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Channon, Walter Patrick

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Medium- and low- carbon ferromanganese are produced by the silicotherm ic redixction of slags containing MnO, Because of its importance in the production of refined ferromanganese, the reaction between a premelted Mamatwan manganese ore and various ferromanganese «silicide reducing alloys has been studied with and without additions of fluxing agents. This relatively low grade manganese ore is partially self-fluxing and it is necessary to optimize the amounts and timing of fluxing additions during the production of refined ferromanganese to ensure both efficient electric furnace operation and manganese extraction from the premelt. Therefore, throughout the laboratory investigation, emphasis has been placed on the implications for industrial practice, Alloys containing different silicon concentrations were added to a premelted sample of Mamatwan ore before the sample was introduced into a molybdenum-wound resistance furnace,. The reaction was carried out under an argon atmosphere and the parameters varied were reaction time reaction temperature, alIoy~to*ore ratio, fluxing additions and the silicon contents of the reducing alloy. The effect of stirring of the reacting melt was also examined. The highly exothermic nature of the reactions involved in this investigation constituted a m ajor obstacle to any attempt to maintain close control of temperature in the system. This also adversely affected the possibilities of carrying out controlled equilibrium and kinetic studies in this slag-m etal system* Because of the highly exothermic reaction, temperature appeared to have little effect on the rates of manganese transfer to the metal and silicon transfer to the slag and an apparent equilibrium was rapidly approached, Limits were determined for the favourable effects of fluxing additions and manganese recoveries declined as the CaQ"to~MgO ratio decreased for any percentage of basic flux additions, As the silicon content of the alloy was progressively increased, the recovery of manganese i passed through a maximum and subsequently decreased, Similar results ■were obtained with variations in the a lloy-to-ore ratio/ When aluminium was used as a reducing agent together with silicon, substantial increases in manganese recovery were achieved because the aluminoi >- „ , ,o « resection displaced the apparent equilibrium. The s.ilicor • ’»■* . . of the resulting alloy was above the specifications for refine ' : cioo .anganese. Stirring of the reacting melts decreased the manganese . .-tcovery and this result conflicts with the results of a previous investigation but may be explained by theexotherrnic nature of the silicon reduction reaction. The results obtained when used in conjunction with other physicochem ical data related to this slag^metal system suggest optimum slag compositions fo r m ore efficient manufacture of m edium- and low -carbon ferromanganese ■fom vlamatwan ore, -

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A Dissertation Submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg for the Degree of Master of Science in Engineering. Johannesburg, 1975

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