Process for production of ultra low phosphorous and carbon ferromanganese by using of ferromanganese slag
Disclosed is a method of producing ultra low phosphorus and carbon ferromanganese having 0.1 wt % or less carbon and 0.03 wt % or less phosphorus. The method includes preparing low carbon silicomanganese having low phosphorus content, preparing molten manganese slag, subjecting the molten manganese slag and the low carbon silicomanganese having low phosphorus content to primary mixing and stirring at a ratio of 70˜72:28˜30 in a ladle, thus producing a metal melt and slag, and subjecting the metal melt separated from the above slag and the molten manganese slag identical to that used in the primary mixing and stirring to secondary mixing and stirring, thus producing slag and a metal melt including 91˜93 wt % manganese, 0.60˜0.85 wt % silicon, 0.05˜0.10 wt % carbon and 0.015˜0.02 wt % phosphorus.
1. A method of producing ultralow phosphorus and carbon ferromanganese, comprising:
preparing low carbon silicomanganese having low phosphorus content;
preparing a first molten manganese slag composed mainly of high carbon ferromanganese slag;
subjecting the molten manganese slag and the low carbon silicomanganese having low phosphorus content to primary mixing and stirring at a ratio of 70˜72:28˜30 in a ladle, thus producing separated metal melt and slag;
providing a second molten manganese slag composed mainly of high carbon ferromanganese slag; and
subjecting the metal melt separated from the slag produced in the primary mixing and stirring and the second molten manganese slag to secondary mixing and stirring, thus producing a second slag and a metal melt comprising 91˜93 wt % manganese, 0.60˜0.85 wt % silicon, 0.05˜0.10 wt % carbon and 0.015˜0.02 wt % phosphorus.
2. The method according to claim 1 , wherein the secondary mixing and stirring is performed a further one or two times depending on the temperature of the melt or stirring conditions.
3. The method according to claim 1 , wherein the preparing the low carbon silicomanganese having low phosphorus content is performed by charging low carbon silicomanganese comprising 55˜60 wt % manganese, 25˜30 wt % silicon, 0.04 wt % or less carbon and 0.08˜0.1 wt % phosphorus with iron being a balance into a ladle furnace, supplying a stirring gas including argon or nitrogen while heating the low carbon silicomanganese to 1400˜1650° C., thus making the low carbon silicomanganese homogeneous, adding the homogeneous low carbon silicomanganese with quicklime and fluorite and stirring them for 10˜30 min, so that dephosphorization occurs to thus obtain 0.03 wt % or less phosphorus.
4. The method according to claim 1 , wherein the preparing the molten manganese slag is performed by mixing 8˜10% of manganese dust having 66 wt % manganese, 8˜13% of quicklime, 31˜54% of high carbon ferromanganese slag having 28 wt % manganese, and 30˜53% of recycled high carbon ferromanganese slag having 12˜18% manganese in an electric furnace.
5. The method according to claim 4 , wherein the molten manganese slag has a basicity (CaO/SiO2) of 1.0˜1.1.
6. The method according to claim 1 , wherein the stirring of the primary mixing and stirring is performed for 10˜30 min using an impeller made of alumina.
7. The method according to claim 1 , wherein, among slag produced in the primary mixing and stirring and the secondary mixing and stirring, slag having manganese less than 10% is wasted, and slag having 10% or more manganese is charged again into an electric furnace for producing the molten manganese slag or is recycled, thus recovering manganese.