FIELD OF THE INVENTION
The invention is related to an alternative route for production of ferromanganese with less than 0.5% C via Al-Silicothermic reduction process route. The invention describes utilization of high carbon silicomanganese fines as reductant along with aluminum, all in solid state for treatment of manganese ore. 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. Table 1. Typical manganese alloy and its specifications (Wt %)


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.

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 3551141A, 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 1750oC. 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. Economy of the process is highly dependent on the recovery of manganese of the refined alloy which is typically 90-92%. This process is capable of achieving up to 1% carbon in the alloy, and hence is not suitable for production of ferromanganese alloys with less than 1% carbon.
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 the product obtained with 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 cooling the obtained product
after roasting is pressed to form compact mass. The obtained compact mass is treated
under vacuum and this process is popularly known as vacuum decarburization at a
temperature range of 1000-1200°C, heated l-3h after cooling within the furnace. This
treatment results in leading to formation of low carbon ferromanganese with

percentage of carbon varies between 0.6-0.11. In another application, CN 102586665A; a method for micro-carbon ferromanganese has been invented from smelting of iron and electrolytic manganese metal powder as raw material. This raw materials are melted using electric arc and casted an ingots result in producing the desired product. CN 103643056A applied for a patent, where the invention related to utilization of steelmaking dust along with manganese slag or ore; 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 metal obtained contains Mn:50%, C:0.4%, P:0.08%, S:0.04% and balance being Fe.
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 silicomnagnese is used leads to higher cost and energy consumption during the production of low carbon ferromanganese. In all other process carried out at higher temperature, there is energy consumption in melting the manganese slag or other raw materials, which leads to higher cost. Hence, there is scope to produce low and medium carbon ferromanganese with utilization of high carbon silicomanganese and aluminum as reductant, using conventional thermit process route. Objects of the Invention
An object of the invention is to produce medium and low carbon ferromanganese alloy by starting with a raw material which is having high carbon (2.5 % C) silicomanganese without any refining.
Still another object of the invention is to develop a process charge that can enable use of high carbon silicomanganese with aluminum to produce medium and low carbon ferromanganese using thermit process route.

SUMMARY OF THE INVENTION
In the process of producing medium and low carbon ferromanganese, roasted manganese ore is reduced in a thermit based reduction route in presence of lime as flux, calcium fluoride as viscosity modifier for the slag. Reductant employed for the reduction is a mixture of high carbon silicomanganese and aluminum, mixed in a particular proportion and within specific size range. Conventionally either 75% FeSi or low carbon silicomanganese or aluminum is generally used as reductant for achieving low carbon ferromanganese alloy. But, due to high cost involved with this reductant; there is scope to understand the utilization of high carbon silicomanganese 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 medium carbon silicomanganese leads to lowering the aluminum consumption and even control the dissolution of aluminum in final alloy.
During the reduction, at temperatures above 2000°C is reached inside the bath by oxidation of aluminum and silicon carbide from silicomanganese. During the reduction, temperature of the bath is higher than 2000°C which results in stabilization of carbon as reductant. Thermodynamically it can have been established that the reduction potential of carbon is much greater than Si and Al in reducing the manganese oxide from the manganese ore as presented in Figure 1. With increase of temperature inside the bath, stability of the carbon increase which results in higher reduction potential and results in formation of CO. Thus carbon present as SiC in high carbon ferromanganese helps in reduction of oxides of manganese and iron present in slag. Figure 1 shows the thermodynamics stability of both the reductants in reducing manganese oxide with oxidation state more than 3. During the reduction and smelting in the bath, silicon carbide phase dissociates while reacting with oxides from the manganese-iron bearing ore to form lower oxides of manganese or iron and result in formation of oxides of silicon and release of carbon monoxide gas. This theory is substantiated by combining

theory and experimental evidence. Thermocouple measurements have shown that bath temperature during the reduction can go as high as 1900 and above, after this thermocouple fails. Gibbs free energy minimization for the reaction shows it becomes progressively negative with rise in temperature.

In an embodiment of the invention, an experiment was carried out at 25 kg scale of manganese iron bearing ore and carbon balance is shown in Figure 2.
DETAILED DESCRIPTION OF THE INVENTION
Ferromanganese with less than equal to 0.5% carbon is based on the amount of carbon, silicon and manganese present. Ferromanganese with 0.5% carbon is generally categorized under low carbon ferromanganese with specifications provided in table 1. In industrial operation, low carbon ferromanganese during the production of specialized steels like ultra- low carbon alloy, Interstitial Free and Bake Hardened. Even low carbon ferromanganese acts as constituent in the coating of welding electrodes. Addition of manganese imparts important physical and structural properties to steel like improvement in tensile strength, workability, toughness and resistance to abrasion. Manganese is usually added either as high carbon ferromanganese alloy or unsaturated alloys of carbon like medium and low carbon ferromanganese. By addition of manganese as MC/LC FeMn instead of HCFeMn, approximately 80 % to 93% less carbon is added to the steel. The control of carbon during the steel making process involves time and cost. Hence, there is need for a robust and economical process for production of low carbon ferromanganese, which can save the refining cost during secondary steelmaking and hence overall cost of the production. The present invention provides a method to produce ≤ 0.5% FeMn metalothermic reduction of manganese

bearing raw materials with oxidation state greater than 3; by combination of aluminum and medium carbon silicomanganese as reductants.
The object of the invention is therefore a unique process for the production of ferro-manganese refined by metallothermic reduction, from oxidized ore or slag. The degree of oxidation of the manganese bearing material should at most between 3 to 3.5. Normal manganese ore with major phase as pyrolusite has been reduction roasted in presence of carbon material or carbon based gases. Experiments were conducted to optimize the reduction kinetics with coke, and oxidation state of manganese after reduction should be at most between 3 to 3.3. Optimized condition for reduction is found to be 100 minutes at 700°C with coke as reductant. In order to carry out metalothermic reduction, ore is pulverized to size of 80 micron and it is mixed with medium carbon silicomanganese, aluminum, lime and calcium fluoride. Size distribution of MC SiMn is less than 50 mesh, so that reactivity becomes better with manganese ore which is also maintained within 50-80 mesh size range. Aluminum shots are having bigger size compared to all the other reductants employed. Size range for aluminum varies between 1-3 mm. Medium carbon silicomanganese in the charge mixture is about 12-22% of total aluminum employed for reduction. Lime and calcium fluoride are used as fluxing agents to control the silicon to meet specifications of desired alloy chemistry. The sequence of operations is as follows:
• Manganese ore lumps are roasted with carbon source like charcoal or coal or coke in a shaft type furnace for 120-140 minutes at temperature between 600-700°C. Roasting temperatures are subjective; depending on desired oxidation state required for manganese ore. Manganese ore lumps vary between 700-100 mm in size. Roasting is done in layering fashion by placing manganese ore followed by carbon source and this sequence is repeated. Size of coke varies between 5-15mm with flow of nitrogen is fixed between 1-3 lit/min.

• Roasted manganese ore is crushed in a primary crusher to a size of 10-20
mm. These ore are again pulverized to a size of 80 mesh. All other raw materials are crushed to a size distribution between 50-100 mesh. Aluminum shots are having distribution like: 50-70% less than 1mm and 30% between l-3mm. Aluminum and medium carbon silicomanganese can be used in mixed form or either by using an alloy of aluminum or alloy of silicon or combination of both. Medium carbon silicomanganese to manganese-iron bearing ore in the charge mixture varies in the ratio of 0.08 to 0.1 and MC SiMn to aluminum ratio varies 0.14 to 0.29. Lime which is added as flux and even to control silicon of the alloy varies between 8-12 % depending on the amount of input silicon. Primary role of calcium fluoride is to impart fluidity to the melt and varies 0-4% of the total charge mixture.
• All the material is mixed in a turbo mixture for 30-60 minutes depending on the volume. All the mixture mixed can be compacted by application of pressure to bind the powders with addition of binders like sodium oxalate or molasses.
• Reactor is lined with slag recovered from the previous hits which contains about 70% AI203,18-20% MnO and rest 10 % contains MgO, CaO and other alkali oxides. First the reactor is lined with magnesite bricks and grouted with the slag. This slag is first grounded to a size distribution: 3-5 mm - 20%, lmm-65-70% and 10% material is of finer size. Entraped metal particles are extracted using screening. This slag is mixed with 3% sodium silicate and water. Layers of this material is applied and fired to sinter the mixture. Reactor is designed like cylindrical pit or like half cone shaped with diameter of 2-8 inches in diameter and 8-10 inches in height. This reactor dimensions vary according to the volume of the reaction mixture.

• Mixture is ignited slowly in this reactor and charged is build up by addition of this prepared mixture. Manganese from the ore is reduced with aluminum and silicon from medium carbon silicomanganese. Calcium oxide in the lime reacts with silicate melt to form monocalcium silicate. The theoretical reactions for the process is provided below:

Process flow diagram for the whole process is shown in Figure 3A.
The following examples show the specific embodiments of the present invention. EXAMPLEI
Manganese ore of Mn content 48% with Mn:Fe ratio 5.6 of size 80 mm is layered in a shaft reactor along with charcoal of size varies between 5-10 mm. Layering is done, so that maximum contact area can be obtained for reduction of oxide ore from + 4 oxidation state to +3 oxidation state. Best layering arrangement is placing alternate layers of ore and charcoal. During the reduction roasting process, flow of nitrogen between 1-3 Ipm was maintained inside the furnace. Roasting is performed at 700°C for 120 minutes. Roasted manganese ore lumps are separated from the fines and ash generated by burning of charcoal. Roasted lumps are crushed in a jaw crusher and the crushed samples are pulverized to 70-80 mesh. Pulverized manganese ore is mixed with other raw materials like medium carbon silicomanganese, lime, calcium fluoride and aluminum. Chemical analyses of the raw materials used are provided in Table 2.

Aluminum in the charge is varied according to ore: aluminum ratio, between 2.8-3.66, MC SiMn : 14-18% of aluminum, 10-15% CaO and 0-2% CaF2 are added in the reaction mixture. In the process of making of charge, the charge is prepared in such a manner that exothermic behavior of the reaction can be controlled. In order carry out the practice, the percentage of aluminum is sub-divided into parts and mixed with equal percentage of the ore. Similarly, the flux and oxidizing agent is also added in the mixture as explained above. Reaction performed in pit designed like half cut inverted cone of dimensions: 2" diameter, 8-10" height with inclination of approximately 30-35 degree. Reaction is initiated with a mixture of mill scale, aluminum powder and potassium nitrate. Table 1. Chemical analysis of raw materials used for reduction experiment

Once the reaction starts, due to exothermic behavior of the reaction; reaction propagates like a Shockwave. The flame moves from ignition point to towards periphery and subsequently moves like this until whole charges gets reacted. Afterwards slag and alloy is extracted from the reaction vessel by breaking the slag layer, which releases the metallic alloy. Some of the metal which solidifies within the slag layer is afterwards extracted by crushing and screening. Table 3 provides the alloy and slag chemistry obtained. Figure 3 describes the reactor shape.

WE CLAIM:
1. A process for producing a FeMn alloy with < 0.5% C from a manganese-iron
bearing ore and medium carbon (≤2.5) silicomanganese raw material, the
process comprising:
roasting the manganese-iron bearing ore of size 70 to 100 mm with a carbon source of size 5 to 15 mm under nitrogen atmosphere in a shaft reactor, roasting being performed at a temperature range of 600 to 700°C for 100 to 140 minutes;
crushing the roasted manganese-iron bearing ore to a size of 20 mm; pulverizing the crushed manganese-iron bearing ore to a size of 80 mesh; Pulverizing medium carbon silicomanganese to a size of 80 to 100 mesh; mixing the pulverized roasted manganese-iron bearing ore with pulverized medium carbon silicomanganese, a non-carbonaceous reducing agent of size 1 to 3 mm, lime and calcium fluoride in a turbo mixture; and charging in the reaction mixture in a reaction vessel.
2. The process as claimed in claim 1, wherein the carbon source is selected from a group consisting of coal, coke, charcoal and a mixture thereof.
3. The process as claimed in claim 2, wherein the fixed carbon in the carbon source is greater than 80% by weight.
4. The process as claimed in claim 1, wherein the FeMn alloy comprises, in weight %, Mn: 78 to 85 C, 0.25 to 0.5, Si: 1.5 to 2.5, P<0.2, S<0.05 and balance being iron.
5. The process as claimed in claim 1, wherein the medium carbon silicomanganese raw material comprises carbon between 2.0 to 2.6 weight%, manganese content: 50 to 65 weigh % and silicon: 18 to 20 weight %.

6. The process as claimed in claim 1, wherein the manganese-iron bearing ore has a Mn:Fe ratio greater than 5.0.
7. The process as claimed in claim 1, wherein the non-carbonaceous reducing agent is selected from a group consisting of aluminum shots, silicon, an alloy of aluminum, an alloy of silicon and a combination thereof.
8. The process as claimed in claim 1 further comprising the steps of compacting shape of charge mixture with a binder such as sodium oxalate or molasses.
9. The process as claimed in claim 1, wherein the ratio of manganese-iron bearing ore to medium carbon (≤2.5) silicomanganese raw material is in the range of 0.08 to 0.1.
10. The process as claimed in claim 1, wherein calcium fluoride is used in the charge mixture in the range of 0 to 4 weight % of the charge mixture.
ll.The process as claimed in claim 1, wherein calcium oxide is used in the charge mixture in the range of 8 to 12 weight percent of the charge mixture.