The present invention relates to development of a process for production of manganese nuggets by metallothermic reduction route at lower temperatures. The invention is related to a new process for production of ferromanganese metallic nuggets with carbon between 0.5-1.5% C via Al-Silicothermic reduction process route.
RArKftROlJND 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 and ductility of steel. Carbon content must be controlled in steel to meet the targeted properties. Alloys of manganese are categorized as per percentage of carbon such as: High (C: 7.5%), Medium (C: 0.5-1.5%) and Low (<0.5%) carbon ferromanganese. Table 1 provides details of manganese alloy and its specifications.

Traditional technologies for production of ferromanganese are direct reduction processes and smelting reduction processes. Generally, direct reduction processes convert metallic oxides of the ore into solid state metallic form inside shaft furnaces (e.g., coal or natural gas based furnaces), whereas smelting reduction converts it directly into molten hot metal which uses blast furnace or Submerged Arc Furnace route with coke as reductant.
Solid state metallic reduction to form ferromanganese alloys follow direct reduction route. The product thus 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 makung secondly in molten production route high energy
consumption ocures due to involvment
ferromanganese, three established technologies are: 1 Silicothermic Process: This process utilizes silicon as reductant for production of medium and low carbon ferromanganese. Silicomanganese alloy is used as reductant along with addition of 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. three-phase rotating and rocking furnaces of 2,500 kVA at 111-17. V. The primary reaction is between Si in the metal and MnO dissolved in the oxide mixture.
2MnO (1) + Si (1) - 2Mn (1) + Si02 (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 1500oC is required to get final product with a maximum of 0.8% C. Primary limitation of ft. process is with respect to quality of raw materials, since carbon control becomes stringent above 1500oc in me liquid state and is energy intensive as it involves melting of slagand metallic SiMn alloy. Recovery of manganese in the alloy is 85-87/. as estimeted by experiments and thermodynamic calculations (US 3074793A, US 3652263A, US 3551141A US 8268036 B2 US 3138455A). The cited references mention to use low carbon silicomanganese as raw material as reductant.
II Decarburization Process: In this process, high carbon ferromanganese alloy with approximately 7wt % C and less than 1% Si, is decarburized by blowing the metal in its liquid state with oxygen gas or combined oxygen/argon mixtures. Thisprocess is popularly known as Manganese Oxygen Refining (MOR), which. ,s similar to basic oxygen Steel process (BOF). In me 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 separate, a such a high temperature .high vapor pressure of manganese leads to excessive evaporation and oxidation 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 ,s no. 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 is 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 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 0.6-1.1.
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. These raw materials are melted using electric arc and casted in an ingot result in producing the desired product. CN 103643056A invention is 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 are added in the submerged arc furnace and this 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.
Bhonde and Angal studied the solid state decarburization of high carbon ferromanganese to increase the manganese content and simultaneously reduced the carbon content. Authors tried to decarburize the alloy using calcium carbonate and carbon dixoxide to drive the carbon into carbon monoxide at normal pressure and higher temperatures. The method seems to be promising but could not achieve carbon in the alloy below 3%. Most of the processes developed till date for decarburization of alloys are carried out with molten alloy either by blowing oxygen or with application of vacuum based techniques. All these processes employ comparatively high cost and are not environmental friendly.
Hence, there is need to develop a process that requires less energy, lower reactant consumption, and fines generation, better slag and metal separation.

OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a process for production of
low/medium carbon manganese nuggets with a raw material which is having high carbon (2.5 %
C) silicomanganese without any refining.
Another object of the present invention is to produce metallic manganese nuggets in continuous
process with low energy consumption by 28.6 kWh/kg of alloy produced.
A still further object of the present invention is to propose a process for production of manganese
nuggets where firing at lower temperature results in reducing Al/SiMn consumption.
Yet another object of the present invention is to propose a binding process during making of agglomerates for producing metallic nuggets in such a manner that reaction of aluminum with water can be prevented with sufficient strength. Still another object of the invention is to develop a process charge that can enable use of high
carbon silicomanganese along with aluminum to produce medium and low carbon
ferromanganese.
A further object of this invention is to produce medium/low carbon ferromanganese nuggets
which can be directly charged into steelmaking without generation of fines during sizing of the
alloy.
SUMMARY OF THE INVENTION
In the process of producing medium and low carbon ferromanganese metallic nuggets, lumps of manganese ore are roasted in air oxidation environment or with the aid of reducing gas to convert the manganese from its higher oxidation state usually +4 to lower state to form particularly phases like Mn203 or Mn304 depending on oxygen potential or reduction temperature.
Roasted manganese ore is grinded to size below 100 micron and Dso passing is around 130 micron Grinded ore is dry mixed with aluminum, silicomanganese fines and flux. Aluminium and silicomanganese fines having size less than 150 micron are added in stoichiometric amount to reduce manganese and iron oxides from ore to alloy.
All the charge material is bonded using organic or inorganic binder or mixture of both to coat the particle mixture. This results in making small nuclei which are hydrophobe Water is added slowly into the hydrophobic mixture and small pellets of size 10-15 mm in size are formed lime is added in parts to react with water to form lime slurry which gives binding effect during pelletization.

The pellets are dried at 80-100°C in an oven for 2-4 hours to drive the excess unbound moisture. The basicity ratio of (CaO+MgO)/Si02 (the B2 slag basicity ratio) is kept between 1.2 to 1.8 to reduce the activity of the silica in the slag and simultaneously increasing activity of MnO in slag. Increase of basicity leads to lower viscosity of slag and helps in better slag-metal separation. Green pellets are kept for drying at 90°C for 6 hours to drive off the excess moisture. Compressive strength of the pellet was determined to be about 30-50 kgf. After drying, pellets are heated up to 1200-1300°C for various time intervals varying between 10-30 minutes in nitrogen environment. After reduction, product obtained was molten slag enveloping the metallic surface and the product obtained was crushed to separate slag and metal obtained.
Reductant employed for the reduction is a mixture of high carbon silicomanganese and aluminum, mixed in a particular proportion and within specific size range. In an embodiment of the invention, 75% FeSi or low carbon silicomanganese or aluminum is used as reductant for achieving low carbon ferromanganese alloy. Thermodynamic calculations and phase analysis shows that final phases in medium carbon silicomanganese are MnsSi3, Mn7C3 and Mn3Si, in addition to segregated SiC. Thus, utilization of medium carbon silicomanganese leads to lowering the aluminum consumption and even controls the dissolution of aluminum in final alloy.
During the reduction, adiabatic calculations show that a temperature rise of above 2000°C can be achieved inside the reduction mixture by oxidation of aluminum and silicon carbide from silicomanganese. Such a high temperature results in stabilization of carbon as reductant. With increase of temperature, stability of the carbon increase which results in higher reduction potential and results in formation of CO. Thus, carbon present as SiC in medium carbon silicomanganese helps in reduction of oxides of manganese and iron present in slag. 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. Gibbs free energy minimization for the reaction shows it becomes progressively negative with rise in temperature.


Microstructure analysis shows that metal and slag forms two distinct phases and thus it can be observed that metallic particles can be easily separated by slight crushing of the obtained product.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 shows the XRD analysis of roasted ore which shows peaks of bixbyite as major manganese oxide peaks.
Figure 2 Process flow diagram for production of metallic Fe-Mn nuggets
Figure 3 shows that at higher temperatures the reduction potential of carbon is much higher than Si and Al in reducing manganese as well as iron present in manganese oxides.
Figure 4 shows metallic nuggets and slag produced as per the current process
Figure 5 shows that microstructure analysis with average carbon of about 0.5-1.5%
Figure 6 demonstrates a crucible design as per the current process.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a method to produce 0.5-1.5 % FeMn metallic nuggets by metallothermic reduction of manganese bearing raw materials with oxidation state greater than 3. The reduction is conducted using a combination of aluminum and medium carbon silicomanganese as reductant.
As per the process of the current invention, the degree of oxidation of the manganese bearing material varies between 3 to 3.5. Normal manganese ore with major phase as pyrolusite is reduction roasted in the presence of carbon material or carbon based gases. Experiments were conducted to optimize the reduction kinetics with coke. Oxidation state of manganese after reduction varies 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 metallothermic reduction, cumulative size distribution analysis shows that D80 of the ore sample is 130 micron. Aluminum and silicomanganese fines have size less than 150 micron and added in stoichiometric amount to reduce manganese and iron oxides from ore to alloy.
Medium carbon silicomanganese in the charge mixture is about 12-22% of total aluminum employed for reduction. Dolomite, lime and calcium fluoride are used as fluxing agents to control the silicon and increasing the activity of manganese oxide in slag to meet specifications of desired alloy chemistry.

The process involves the steps of roasting Manganese ore lumps with carbon source like charcoal or coal or coke in a shaft type furnace for 120-140 minutes at a temperature between 600-700°C. At this roasting temperature, partial pressure of oxygen in the reactor is maintained at 10-6 to 10-8 atm. Roasting temperature can be varies depending upon the targeted oxidation state required for manganese ore. Manganese ore lumps vary between 70-100 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 5-15 mm and flow of nitrogen is fixed between 1-3 lit/min.
Roasted manganese ore is thereafter crushed in a primary crusher to a size of 10-20 mm. Roasted manganese ore is grinded to size below 100 micron and D80 passing is around 130 micron. Grinded ore is dry mixed with aluminum, silicomanganese fines and flux. Aluminum and silicomanganese fines have size less than 150 micron and added in stoichiometric amount to reduce manganese and iron oxides from ore to alloy. Medium carbon silicomanganese to manganese-iron bearing ore in the charge mixture varies in the ratio of 0.08 to 0.1 and medium carbon SiMn to aluminum ratio varies 0.14 to 0.29. Lime content varies between 8-12 % depending on the amount of input silicon. Primary role of calcium fluoride is to impart fluidity to the melt and it varies in the range of 0 to 4% of the total charge mixture. Thereafter, the whole composition is mixed in a turbo mixture for 5 to 10 minutes and slowly binder is added in the mixture. Addition of binder results in increasing the viscosity of the mixture and result in formation of small nucleis. These nucleis are transferred to pelletization disk and grown in size with addition of water. The mixture is then compacted by application of pressure to bind the powders with addition of binders like sodium oxalate or molasses.
Pellets of 10-15mm are thus obtained which are subjected to drying for 4-6 hours at 80-120°C. Pellets are transferred to reactor chamber at 120°C and heated to 1000-1200°C in an electric or gas fired furnaces with a heating rate varying between 3-5°C/min. In an embodiment of the invention, the furnace used for the process is rotary hearth furnace with hearth and side wall lined with 98% MgO and 2% A1203 magnesite bricks.
Pellets are transferred to a crucible which is lined with slag from pervious heats which contains about 70% A1203, 18-20% MnO and rest 10 % contains MgO, CaO and other alkali oxides. This slag is first grounded to a size distribution: 3-5 mm - 20%, lmm-65-70% and 10% material is of finer size. Entrapped 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.
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 are provided below:


EXAMPLE I:
Manganese ore of size 20 mm with Mn content 44% and Mn:Fe ratio 6.34 is layered in a shaft furnace along with charcoal of size in the range 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. In an embodiment of the invention, alternate layers of ore and charcoal are placed. During the reduction roasting process, flow of nitrogen between 1-3 1pm was maintained inside the furnace. Roasting is performed at 700°C for 80-120 minutes. Roasted manganese ore lumps are separated from the fines and ash is generated by burning of charcoal. Roasted lumps are crushed and the crushed samples are pulverized to less than 100 micron. Pulverized manganese ore is mixed with other raw materials like medium carbon silicomanganese, lime, calcium fluoride and aluminum. Chemical analysis of the raw materials used is provided in Table 2. Aluminum in the charge is varied according to ore: aluminum ratio, between 2.8-3.66, medium carbon 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. This is ensured by sub-dividing the aluminum percentage into parts and mixing with equal percentage of the ore.
Similarly, the flux and oxidizing agent are also added in the mixture. Dry mixing is performed and about 7-12% molasses is added to form agglomerates along with slurry of other inorganic binder bentonite. Pelletization is performed to form pellets of size 10-15 mm and micro pellets formed are removed by screening. Finally, green pellets are subject to drying for 4-6 hours at 80-120°C.Pellet thus obtained are fired in a tube furnace in a crucible shown in Figure 7 and it is lined with slag material. Pellets are fired and cooled subsequently in nitrogen environment followed by quenching in water. Product thus obtained is crushed to separate metallic nuggets and slag.

WE CLAIM:
1. An Alumino-Silicothermic process for production of ferromagnese alloy nuggets with < 2.5 Carbon, the process comprising:
Roasting of Manganese ore with a carbon sources at a temperature in the range of 500 degree C to 800 deg C;
Crushing and grinding of the roasted Mn ore lumps to a size of at least 80 micron;
Mixing the pulverized Mn ore powder with aluminum or silicomanganese reductant and predetermined quantity of an organic binder;
Adding slurry of an inorganic binder in water; and finally adding fluxing agent followed by agglomeration in a pelletizing or briquetting press;
drying green briquettes at a temperature in the range of 100 degree to 120 degree;
charging the dried briquettes in a reaction vessel coated with high alumina slag;
and firing pellets in gas fired or electrical furnace at at least a temperature of around 11500 degree.
2. The process as claimed in claim 1, wherein FeMn metal nuggets composition comprises in weight percent:

3. The process as claimed in claim 1, wherein the FeMn metal nuggets diameter ranges from 0.5 to 3.0 cm
4. The process as claimed in claim 1, wherein carbon preferably varies in the range of 0.5-1.5%.

5. 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.
6. The process as claimed in claim 5, wherein the fixed carbon in the carbon source is greater than 80% by weight.
7. 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 weight % and silicon: 18 to 20 weight %.
8. The process as claimed in claim 1, organic binder used is sodium oxalate or molasses in the range of 7-12 wt%.
9. The process as claimed in claim 1, inorganic binder used is bentonite or clay in the range 2-5 wt%.

10. The process as claimed in claim 1, wherein die manganese-iron bearing ore has a Mn:Fe ratio of at least 5.0.
11. The process as claimed in claim 1, wherein the aluminum or silicomanganese reductant is selected from a group consisting of aluminum shots, silicon, an alloy of aluminum, an alloy of silicon and a combination thereof.
12. The process as claimed in claim 1, wherein Alumina slag basicity (CaO+MgO/Si02) is between 1.2 to 1.8.
13. The process as claimed in claim 1, wherein the fluxing agent comprises CaF2 and lime.
14. The process as claimed in claim 1, wherein (CaO/A1203) is in the range of 2.2 to 3.5.
15. 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.

16. 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.
17. 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.
18. The process as claimed in claim 1, wherein crucible is lined with alumina slag having composition 70% A1203, 18-20% MnO and rest 10 % contains MgO, CaO and other alkali oxides.
Dated this 28TH day of MARCH, 2016
OF LS.DAVAR & CO. APPLICANTS'AGENT