TITLE:
Smelting method for medium carbon ferromanganese in SAF.
FIELD OF THE INVENTION
The following invention is related to a process route for production of ferromanganese alloy of grade: 70% Mn-1.5% Si-1.5%. The invention focuses on utilization of existing sub-merged arc furnace route in continuous flowablity mode operation for the specific alloy grade. The invention relates to the field of smelting alloy, and more particularly, relates reduction and smelting of manganese bearing materials. The invention also focuses on selective reduction of manganese and iron oxides with selective use of combination of reductants.
BACKGROUND OF THE INVENTION
Ferromanganese contains manganese as a major alloying element. These alloys when added to steel refine the grain structure of the final product. Dissolved in ferrite, it combines with carbon to form stable carbides and hence, improves the strength of steel and, thus its ductility. Low and medium carbon alloys are used in steels where carbon content must be controlled. Alloys of manganese are categorized with the percentage of carbon and are classified as: High (C: 7.5%), Medium (C: 0.5-1.5%) and Low (<0.5%) carbon ferromanganese as given in Table 1.


Traditional technologies for production of ferromanganese include blast furnace or Submerged Arc Furnace route with coke as reductant. The product obtained is carbon saturated iron-manganese alloy with 6-8 wt% C. In ferromanganese alloy, carbon forms solid manganese carbide and complex iron-manganese carbides. This content of carbon needs to be controlled in ferromanganese alloys as it has detrimental effect in quality steel making. In order to produce desired grade for low and medium carbon ferromanganese, three established technologies which are widely followed are:

I. Silicothermic Process: This process utilizes silicon as reductant for production of medium and low carbon ferromanganese. Reductant is usually silicomanganese alloy, sometimes with addition of some ferrosilicon, e.g. 75% FeSi. The liquid Si rich metal is mixed with liquid MnO-CaO slag in the process. The smelting process is carried out in three-phase rotating and rocking furnaces of 2,500 kVA at 111-178 V. The primary reaction is between Si in the metal and MnO dissolved in the oxide mixture.
2MnO (1) + Si (1) = 2Mn (1) + SiO2 (1) Carbon content of the final product corresponds to the carbon content of the silicomanganese alloy. It was been validated that silicomanganese with 22% Si at 1500°C is required to get final product with a maximum of 0.8% C. Primary limitation of this process is with respect to quality of raw materials, since carbon control becomes stringent above 1500°C in the liquid state and is energy intensive as it involves melting of slag and metallic SiMn alloy. Recovery of manganese in the alloy is 85-87% as estimated by experiments and thermodynamic calculations (US 3074793A, US 3652263A, US 3551141 A, US 8268036 B2, US 3138455A). In all the inventions mentioned to use low carbon silicomanganese as raw material as reductant or carried out a process for refining of high carbon silicomanganee to lower the carbon content to less than 0.5% C. II. Decarburization Process: In this process, high carbon ferromanganese alloy, with approximately 7 wt. % C and less than 1% Si, is decarburized by blowing the metal in its liquid state with oxygen gas or combined oxygen/argon mixtures. This process is

popularly known as Manganese Oxygen Refining (MOR), which is similar to basic oxygen
steel process (BOF). In the process due to high affinity of carbon and oxygen, the necessary
temperature of the manganese refining has to be above 1750°C. Such higher temperature
leads to several problems, like severe refractory attack, difficulty in casting of superheated
metal, and difficult slag/metal separation. At operating temperature due to very high vapor
pressure of manganese leads to excessive evaporation and oxidation by excess oxygen which
results in lower yield of alloy.
III. Aluminothermic Process: In this process route, aluminum powder with size distribution
between 1 -3 mm is used as reductant for reduction of manganese ore. In this process,
primary product obtained is ferromanganese alloy with less than 0.1% C (wt. basis). This
process is popularly used after silicothermic process for production of alloy of
ferromanganese with less than 0.5% C. Due to high cost and less control over the quality
of the alloy obtained in terms of silicon, this method holds few drawbacks.
In another publication CN 103667833A, finely grounded high carbon ferromanganese is roasted in air between 500-800°C for 1 to 5h and then the product is cooled to form a compact mass. Product obtained is treated under vacuum in the temperature range of 1000-1200°C, heated l-3h. The process leads to formation of low carbon ferromanganese with percentage of carbon varies between 0.6-0.11. The patent (CN 102586665A) describes a method for producing micro-carbon ferromanganese. In this process, smelting of iron and electrolytic manganese metal powder were

used to produce alloy of desired composition. CN 103643056A applied for a patent for production of low carbon ferromanganese. In this method, steelmaking dust, manganese ore, carbon powder, fluorite and quartz powder is added in the submerged arc furnace results in formation of slag and metal. The alloy obtained contains Mn:50%, C:0.4%, P:0.08%, S:0.04% and balance being Fe.
Patent No. CN103088244A discloses a manganese alloy and preparation method. The method comprises: selection of raw material by weight percentage to calculate the carbon is less than 1.0% of the waste steel; after all of the raw material melting; slagging agent is added to form slag at furnace temperature maintained: 1350 ± 30 ° C; and then followed by adding rest manganese bearing material and finally casting of alloy in ingots.
Publication No. CN 1025 86669A discloses a method for the production of low-carbon ferromanganese. In this process, electrolytic manganese metal flakes or powder is used as primary raw material along with iron of desired quantity. Melt both of these materials in induction arc furnace for specific conditions to obtain alloy ingots of low carbon ferromanganese alloy.
Most of the inventions related to production of manganese ferro alloys utilize smelting of low carbon silicomanganese as raw material. However, all the inventions lead to carry out smelting

process with low carbon silicomanganese as raw material; which itself has low carbon content. High purity silicomanganese used as prime raw material leads to higher process cost and energy consumption during the production of medium or low carbon ferromanganese. Secondly, other process routes concentrate on melting of alloy and slag. Since melting is energy intensive process, which again makes process economically unviable. Most of process for MC ferromanganese production is basically two stage process and thus there is scope to explore other processes which have lower footprint for same product.
Hence, there is scope to produce low and medium carbon ferromanganese with utilization of combination of reductants like high carbon silicomanganese, aluminum and coal or coke as reductants in one step single submerged arc furnace through selective reduction scheme. This innovative process involves continuous mode of operation and charging is carried out in flowablity mode of the specified raw material in SAF.
OBJECTS OF THE INVENTION
An object of the invention is to produce medium and low carbon ferromanganese alloy in submerged arc furnace in a single step in continuous mode operation.

Still another object of the invention is to develop a process charge that can enable use of high carbon silicomanganese in combination with carbon based reductant (coal or coke) and aluminium as reductants.
Another object of invention is to increase the recovery of manganese from slag by allowing in-situ formation of A12O3 resulting in replacing MgO and SiO2.
SUMMARY OF THE INVENTION
This invention relates to A process for producing Fe Mn alloy with < 1.5%C comprising: blending manganese bearing ore of size 6 to 30 mm with reductant of size range 3 to 20mm aluminum sheets of < 10mm alongwith coal/coke as another reductant with flux material to form a burden, changing the said burden in layers in the furnace, arcing is carried out to carry out the reaction, subjecting the said change to the step of smelting and the temperature of the molten bath is controlled between 1550-1650°C, tapping the liquid ferromanganese and slag, separating the ferromanganese alloy and slag material.
In the process of producing MC ferromanganese, manganese bearing raw materials (HC FeMn Slag and ore) in form of lumps with a size range of 6-50 mm feed to the furnace.In the process, dolomite and lime are used as fluxing material. Reductant employed for the reduction purpose is

a mixture of high carbon silicomanganese, aluminium and coke. All these reductants are mixed as per desired stiochiometic composition. Conventionally, either 75% FeSi or low carbon silicomanganese or aluminum is generally used as reductant for achieving medium carbon ferromanganese alloy. Because, due to high cost involved with this reductant; there is a scope to utilize high carbon silicomanganese and carbon source as an alternative reductant.
Thermodynamic calculations and phase analysis shows that final phases in medium carbon silicomangnese are consequently Mn5Si3, Mn7C3 and Mn3Si, in addition to segregated SiC. Thus, by utilization of mixture of reductants (coal/coke and medium carbon silicomanganese) leads to lower the aluminum consumption and even control the dissolution of aluminum in final alloy.
During the reduction, conceptually arc furnace can be sub-divided into three primary reduction zones where selective reduction of manganese and ferrous oxide occurs. Three primary zones are: (a) carbothermic reduction zone (25-700°C); (b) Alumino-silicothermic reduction zone (700-1150°C); and (c) slag reduction zone (1150 - 1600°C). Detailed reaction in each zone is mentioned below.

In zone 1 (T: 25-700°C), mostly carbothermic reduction of manganese and iron oxides takes places. During the reduction process, in the upper part of the furnace carbon monoxide gas coming from the bottom will react with moisture contained in the ore body to produce some hydrogen by water-gas shift reaction which is mild exothermic. This reaction takes place with upcoming off-gas which is coming at temperature range of 300-500°C:

Secondly, dolomite (CaCO3.MgCO3) which is added as flux dissociates to its respective components to form mostly MgO and CO2 as per the reaction scheme provided at a temperature of 500°C:

Another reaction which is thermodynamically possible, but its feasibility canot be determined is the soot formation reaction from the stream gases:

Higher oxides of manganese which are unstable at higher temperatures is unstable in presence of CO gas can be evaluated from the pre-dominance diagram for the temperature range as shown in Figure 1. Pre-dominace reactions define us which reactions will be undertaking as per the gas composition and temperature. Equilibrium calculations show that gas composition is having pO2= -6.4 atm and that temperature range of 400-500°C, major oxides phases in burden are Mn3O4 and Fe2O3 and combined oxides of lime, silica and alumina.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig. 1: shows the Pre-dominace diagram of manganese and iron oxide.
Fig. 2: shows Effect of basic oxides on dissolution of MnO in SiO2-Al2O3 based system 2(a): shows the Binary phase diagram between MnSiO3-Al2O3 with variation of CaO 2(b): shows the Binary phase diagram between MnSiO3-Al2O3 with variation of MgO 2(c): shows the effect of MnO dissolution on liquidus region for constant CaO-MgO-MnO-
Al2O3-SiO2
Fig. 3: shows the detailed process flowsheet for production of MC FeMn in SAF. Fig. 4: shows the Experimental set up for smelting studies

DETAILED DESCRIPTION OF THE INVENTION
Following reactions which are predominating are:

With rise of temperature, some of metallic feed aluminum will start melting depending on the
impurity whose melting temperature varies between 650-700°C.
in Zone 2 (700-1200°C), mostly the reduction of lower oxides of iron are reduced to metallic
solid iron either with aluminum or carbon depends on the free energy of the reaction as provided
below:

Equilibrium calculations show that reduction potential of lower metallic oxides by molten aluminum is much higher than carbon. Usually due to lower reduction potential of iron oxides, iron forms the molten pool which dissolves manganese, carbon and silicon as per the saturation limit for the temperature range. Carbon loss reaction also takes place in the following region at the temperature range of 900°C as per the following reaction and is endothermic in nature which consumes maximum external energy:


Calcium carbonate from the lime dissociates to give CaO and CO2, which reacts with carbon at upper part of the reactor to support carbon loss reaction. These reactions are highly endothermic and thus demands heat which can be supplied by metalothermic reaction and external energy. In Zone 3 (1200-1500°C), most of metallothermic reaction and slag formation is predominant. As per the reaction scheme, the MnO which form involve in forming solid solution with CaO, MgO, A12O3 and SiO2. These complex oxides of manganese are reduced by silicon from silicomanganese, considering all the input carbon from silicomanganese will be part of final alloy. MnO from the slag is slowly reduced by silicon or silicon carbide from the added silicomnganese as per the reaction:

Activity of the silica formed from the reduction is 1 (as pure form). This silica combines with lime in the slag, which leads to form silicates in slag. In this process, activity of MnO increases in the slag. MnO is now available for reduction by silicon. Formation of SiO2 leads to react with calcium dioxide and alumina resulting in forming slag liquid at the temperature range 1200-1250°C.
Figure 2 shows the effect of fluxing agent (lime and magnesia) on liquidius region for MnO dissolution in slag for varying alumina content. Silica formed from the reaction reacts with CaO and MgO from the flux to form CaMg2SiO4 as major component in the slag along with formation

of Ca2Al2SiO7, CaAl2Si2O8 and other MgO, SiO2, Al2O3 based a component which depends on free energy of formation. Some amount of MnO remains in the slag, which reacts with silica to form MnSi03 as primary phase. With addition of CaO and MgO leads to replace MnO from SiO2 and A12O3 and thus activity of MnO increases which is available for reduction by SiC for Si from SiMn. With increase of CaO from 0% to 20%, there dissolution of MnO in slag by decreasing the activity of SiO2. Beyond increase of 20 wt. % of CaO in the system leads to precipitation of MnO as separate solid phase and thus liquidius of the system increase and thus leads to operate the furnace at higher temperatures. It was found that 20% CaO is having equivalent basicity of 1.2 in the slag. Similar phenomenon can be observed for another basic oxide MgO. Thus, an optimum of 10% MgO in the system is ideal for MnO dissolution in the slag. The slag liquidus was calculated for varying MgO replacement to CaO at 16000C for (CaO+MgO)-Al2O3-SiO2-MnO pseudo-ternary slag system. Replacement of 10-20% MgO in place of CaO is most desirable for maintaining liquidus temperature of the slag system. The preferred range of slag basicity (B=1.2 to 1.4) and slag R (R=1.0 to 1.1) are shown in this diagram.
Presence of high silica leads to lower the activity of MnO for a given A12O3 percentage in the slag. Though, MnO activity tend show negative deviation from ideal behavior due to formation of MnAl2O4, but at higher SiO2 based slags Al2O3 have amphoteric nature and thus leads to act

as basic oxide which tends to increase the activity of MnO. Thus, external addition of clay for in-situ formation of A12O3 helps in higher MnO available for reduction. Due to amphoteric nature of alumina and due to presence of non-bridging oxygen formed i.e. Al3+ does a network modifier exists in octahedral coordination with oxygen. Thus, it can be presented in formal equation as:

Thus, from the reaction it can be observed that due to presence of alumina, it acts as network breaker with release of bridging oxygen from the network. Hence, releasing the Mn(II) ions associated with silica network.
Thus, production of medium carbon ferromanganese is usually carried out in fluxing condition
with a usual basicity range of 1.2-1.5 and under this condition following reactions are probable:
MnSi + 2Mn3O4 + 2CaO = Mn + 2CaO.Si02 + 6MnO
MnSi + 2MnO + 2CaO = 3Mn + 2CaO.Si02 ΔG°=-115673-3.98T (at 1683 to 1800 K) J
MnSi + 3MnO + CaO = 3Mn + '/2(2MnO.SiO2) + 1/2 (2CaO.SiO2) ΔG°=-43923-15.09T (at 1683
to 1800 K) J
MnSi + 21/2MnO + CaO = 3Mn + 1/2(MnO.SiO2) + 1/2(2MnO.SiO2) ΔG°=-130980+45.02T (at 1500 to 1683 K) J
MnSi + 2MnO.SiO2 + 4CaO = 3Mn + 2(2Cao.SiO2) ΔG°=-235660+4.97T (at 1683 to 1800 K) J MnSi + 2(MnO.SiO2) + 6 CaO = 3Mn + 3(2CaO.SiO2) ΔG°=-361920-10.37T (at 1400 to 1700 K)J

Therefore, it can be observed that it is feasible to produce manganese alloy in presence of silicon and aluminum as reductant and secondly, in-situ alumina formation is helping in finding optimum manganese recovery during the production medium carbon ferromanganese. Ferromanganese with greater than and equal to 0.5 % and 1.5 % carbon manganese alloy has been elaborated with detailed description and examples. Ferromanganese with mentioned carbon and 1.5 % silicon content has been categorized as medium carbon ferromanganese as per the specifications provided in Table 1. Detailed flowsheet for the process is shown in Figure 3.
The object of the invention is therefore a unique process for the production of ferro-manganese by metallothermic reduction of manganese ore and slag. Experiments were carried out under variety of conditions which includes:
• Varation of Mn/Fe ratio with addition of slag or without addition of slag;
• Effect of slag basicity by varying fluxing agents,
• Effect of CaO/MgO ratio and by variation of "R" ratio of the feed.
Reduction smelting was carried out in a double phase electric arc furnace of capacity of 12 kg as shown in Figure 4.
Each charge mixture consisted of blend of lumps, slag, reductant and flux in different weight ratios, which was further mixed with calculated amounts of ore, slag, flux and reductant. The Mn Ore /slag was prepared in three portion of 100%, 90%, 80% and 70% giving rise to different

Mn/Fe ratios (6.84 -7.85). The Mn/Si ratios are between 7.0-8.2 was maintained by varying the manganese slag with amount of silicomanganese constant. Charge basicity was maintained by addition of lime and dolomite. Slag basicity of (CaO+MgO)/SiO2 between 0.8 - 1.8 have been studied. Analysis has also been performed with R ratio i.e. (CaO+ MgO)/Al2O3 to varying the input aluminum content. Refractory material and cooling of the hearth plays an important role in controlling the alloy composition. A lining of magnesite with 95% MgO ramming material is used as front lining in the hearth followed by backup material of 80% MgO brick. Ore and slag are the primary manganese bearing material during the smelting are sized within a size range of 6-30 mm which mixed with reductants SiMn, Al shots and coke within a size range of 3-20 mm. Flux material and other raw material are charged in layering manner in the furnace.
During the smelting, electrodes are arced in the slag layer leads to reduction. At the end of the test, while tapping of metal and slag; temperature of melt is monitored and temperature was found to vary between 1650-1700°C. Metal and slag was tapped in a graphite crucible and melt was allowed to cool in the crucible. Thereafter, it was taken out and metal and slag were separated manually. After crushing and grinding of metal and slag, their representative samples were prepared by coning and quatering method for the chemical analysis. The following examples show the specific embodiments of the present invention.

EXAMPLES
Manganese ore with 46-48% Mn and having Mn:Fe ratio of 5.1-5.2 of size range 6-30 mm is taken is blended with SiMn of composition: 60 % Mn and 14% Si where taken as primary reductant. Aluminum shots were also blended with charge blend in the proportion of 5-10% in such a manner that slag should have at least 20% alumina. Lime and dolomite lumps were blended with charge mixture as flux material and feed into the furnace. All the raw material is mixed properly and charged in layers. Hearth's front lining was rammed with magnesite. Backup lining is maintained with 80% MgO bricks. Basicity of the charge mixture is varied between 1.0-1.8 by variation of fluxing materials. During the following experiment, "R" ratio (CaO+ MgO/Al2O3) was kept constant at 0.8. Raw material is charged along with additional coke material as reductant. During the initial period of arcing, arc length is increased and arcing done on the first submerged layer. Slowly arc length is decreased and electrodes are inserted in the slag bath to carry-out the final reduction from the metallic reductants. Charge was smelted for limited time interval and smelted material was tapped in the pre-heated graphite crucible and kept for getting cool. After cooling, slag and alloy material are separated and separately chemically analyzed. Table 3 provides the alloy and slag chemistry obtained.

WE CLAIM:
1. A process for producing Fe Mn alloy with < 1.5%C comprising:
blending manganese bearing ore of size 6 to 30 mm with reductant of size range 3 to 20mm aluminum sheets of <10mm alongwith coal/coke as another reductant with flux material to form a burden
changing the said burden in layers in the furnace, arcing is carried out to carry out the reaction,
subjecting the said change to the step of smelting and the temperature of the molten bath is controlled between 1550~1650°C,
tapping the liquid ferromanganese and slag,
separating the ferromanganese alloy and slag material.
2. The process as claimed in claim 1, wherein said ferromanganese alloy contains Mn 70-77%, C0.8 to 1.5%, Si 0.9 to 1.5%, P<0.4%, S<0.02% and the balance being iron.
3. The process as claimed in claim 1, wherein the said reductant is SiMn.

4. The process as claimed in claim 1, wherein the said flux material is lime and dolomite of size range 3 to 10mm.
5. The process as claimed in claim 1, wherein the said smelting method comprises by weight 30 to 40 parts of the manganese bearing ore,
25 to 35 parts of silicomanganese,
20 to 25 parts lime and
5 to 10 parts of aluminum material added submerged arc furnace of addition melt points.
6. The process as claimed in claim 1, wherein the refractory hot facing lining of the furnace is magnesite.
7. The process as claimed in claim 1, wherein the step of smelting is preferred for 1 to 1.5 hours.

8. The process as claimed in claim 1, wherein the said smelting method comprises by weight 30 to 40 parts of the manganese bearing ore, 20 to 30 parts of silicomanganese,
20 to 30 parts lime,
5 to 15 parts of coke and
18 to 20 parts of manganese bearing slag material added submerged arc furnace of addition melt points.
9. The process as claimed in claim 1, wherein by a weight percentage, the following divide ratio, the manganese slag containing MnO~28%, Fe(T)~0.28%, A12O3~16.34%, SiO2~28.06%, CaO~ 16.63%, and MgO~7.27%.
10. The process as claimed in claim 1, wherein by a weight percentage, the following divide ratio, the manganese ore containing Mn(T)~46-48%, Fe(T)~9-15%, A12O3~4-6%, SiO2~l-4%, P~O.2-0.6%, and Mn/Fe~4.5-5.5%.