| Title of Invention | A PROCESS FOR THE PRODUCTION OF SPONGE CHROME FROM METALLURGICAL GRADE FINE CHROMITE CONCENTRATES BY CARBOTHERMIC REACTION |
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| Abstract | The main object of the present invention therefore, is to provide a process for production of sponge chrome with 50% metallic chrome which can be used directly in stainless steel making process. Another object of the present invention is to use the carbon monoxide gas generated during existing submerged arc furnace process as reductant or heat source thereby increasing the utilization of CO gas and in turn reducing the carbon requirement. Yet another object of the present invention is to utilize low grade chromite ores with high silica and iron which are not suitable for direct ferrochrome production and thereby reduce generation of tailings at chromite ore benefication plants. Thus the present invention provides a process for the production of sponge chrome from metallurgical grade fine chromite concentrates, comprising the steps of oxidizing chromite concentrate fines from COB plant; mixing said pre- oxidized chromite concentrates / fines with fluxes, binders and carbon; pelletizing the mixture into pellets; heating the pellets in an inert or reducing atmosphere; separating slag formed by the fluxes present in the charge from the reduced metal by magnetic separation; and further processing in submerged arc furnace or stainless steel making. |
| Full Text | -2- FIELD OF INVENTION The present invention relates to a process for the production of sponge chrome from metallurgical grade fine chromite concentrates by carbothermic reaction. The invention can also be applied for improving the existing submerged arc furnace process (SAF) for production of FeCr. BACKGROUND OF THE INVENTION Sponge chrome can be used as an alloying addition directly in LD process for production of stainless steel or alloy steels. Ferrochrome is produced conventionally by smelting-reduction process in submerged arc furnace (SAF). Most of the Indian chromite ores are inherently suitable for metallurgical applications, in particular to produce FeCr with more than 63% chromium. For submerged arc furnace process, the hard lumpy chromite ores are used. The chromite concentrates and fines are charged in the form of agglomerates (sintered pellets or briquettes). The Submerged arc furnace process is high energy intensive and consumes about 3400 kWh per tonne of FeCr. About 10% Cr2O3 is also lost in this process to the slag. The solid state reduction of MgO- rich Indian chromite is also very difficult due to refractory nature of MgCr2O4 phase. -3- A need therefore exists for extraction of chromium from chromite concentrates / fines and far improving the existing submerged arc furnace (SAF) process for production of FeCr by reducing the energy consumption. SUMMARY OF THE INVENTION The main object of the present invention therefore, is to provide a process for production of sponge chrome with 50% metallic chrome which can be used directly in stainless steel making process. Another object of the present invention is to use the carbon monoxide gas generated during existing submerged arc furnace process as reductant or heat source thereby increasing the utilization of CO gas and in turn reducing the carbon requirement. Yet another object of the present invention is to utilize low grade chromite ores with high silica and iron which are not suitable for direct ferrochrome production and thereby reduce generation of tailings at chromite ore benefication plants. Thus the present invention provides a process for the production of sponge chrome from metallurgical grade fine chromite concentrates, comprising the steps of oxidizing chromite concentrate fines from COB plant; mixing said pre- oxidized chromite concentrates / fines with fluxes, binders and carbon; pelletizing the mixture into pellets; heating the pellets in an inert or reducing atmosphere; separating slag formed by the fluxes present in the charge from the reduced metal by magnetic separation; and further processing in submerged arc furnace or stainless steel making. -4- BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The invention can now be described in detail with the help of the figures of the drawings, where Figure 1 shows the process flow chart of the present invention. Figure 2(a) and 2(b) show respectively optical microscopic image and SEM - BSE image of the microstructure of oxidized chromite. Figure 3 shows the microstructure and X-ray dot map of partially reduced chromite. DETAILED DESCRIPTION The flow chart of the process of the present invention is shown in Figure 1. First the chromite fine concentrated from chromite ore benefication plant is oxidized at 850° - 950° C temperature for 30-90 minutes. This can be done in either a rotary kiln or a fluidized bed furnace. During oxidation reaction, the FeO present in the chromite spinel phase precipitates as Fe2O3 via following reaction: -5- The oxidation reaction generates the vacancies in the spinel lattice as seen from the above reaction. In the microstructure of oxidized chromite of Figure 2, the bright lathe shape phases on grey chromite matrix are of exsolved Fe2O3. The formation Fe2O3 phase on the surface has several advantages: If improves the sinterability of chromite concentrate due to reaction of Fe2O3 with fluxes. The introduction of vacancies facilitates the faster diffusion of Cr3+ in rigid lattice of oxygen anions in spinel structure. It increases the reactivity of the chromite spinel phase due to phase transformation. The metallic Fe or FeO formed on the surface of chromite during early stages of reduction reaction helps reduction of Cr3+ and thereby improves the process yields. The pre-oxidized. chromite concentrates / fines are then mixed with fluxes like SiO2, CaO; binders like bentonite, molasses; and carbon which may be in the form of coal, coke breeze, etc. and palletized in a disc pelletizer. -6- Pre-treated fines concentrate (intermediate product of new process) will produce better quality agglomerates. Pot sintering technique can be employed for agglomeration of pre-treated fires concentrate (intermediate product of new process). The new process will use the CO gas from submerged arc furnace as reductants and heating source, thereby reducing me wastage of CO gas. The pellets are then heated in inert or reducing atmosphere either in rotary kiln or rotating hearth furnace at 1300° - 1450°C temperature for 60 - 180 minutes. The reduction time and temperature depends on concentrations of Mg and Fe oxides in the chromite ore, SiO2: CaO ratio and type of additives used. Special additives are also used to reduce the liquids temperature of slag. In the early stages of reduction reaction most of the iron oxides reduce to metallic iron. The fluxes in the charge form slag above 1300° C. Above 1200° C, in addition to carbon, metallic iron and iron carbides also reduces Cr3+ ions to suboxides and then to metallic chromium and carbides. Above 1300 C temperatures, the MgO and Al2O3 constituents of the spinel reacts with slag and thereby increases the reactivity of Cr3+ The formation Fe rich phase and slag in the early stages of reduction reactions at 1350° C is shown in the X-ray dot maps in Figure 3. Complete metallization of iron oxides and about 50% of Cr2O3 was reduced by this new process. The addition of special catalysts improved the metallization of Cr-oxide. The physical separation of slag from reduced metal (FeCr) is carried out by magnetic separation techniques which will reduce the gangue / slag volume in the product and thereby improve further processing in either submerged arc furnace or stainless steel making. The main object of the present invention therefore, is to provide a process for production of sponge chrome with 50% metallic chrome which can be used directly in stainless steel making process. Another object of the present invention is to use the carbon monoxide gas generated during existing submerged arc furnace process as reductant or heat source thereby increasing the utilization of CO gas and in turn reducing the carbon requirement. Yet another object of the present invention is to utilize low grade chromite ores with high silica and iron which are not suitable for direct ferrochrome production and thereby reduce generation of tailings at chromite ore benefication plants. Thus the present invention provides a process for the production of sponge chrome from metallurgical grade fine chromite concentrates, comprising the steps of oxidizing chromite concentrate fines from COB plant; mixing said pre- oxidized chromite concentrates / fines with fluxes, binders and carbon; pelletizing the mixture into pellets; heating the pellets in an inert or reducing atmosphere; separating slag formed by the fluxes present in the charge from the reduced metal by magnetic separation; and further processing in submerged arc furnace or stainless steel making. |
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00368-kol-2005-description provisional.pdf
368-KOL-2005-CANCELLED PAGES.pdf
368-KOL-2005-CORRESPONDENCE 1..pdf
368-KOL-2005-CORRESPONDENCE 1.1.pdf
368-kol-2005-correspondence 1.2.pdf
368-kol-2005-correspondence.pdf
368-KOL-2005-DESCRIPTION (COMPLETE)-1.1.pdf
368-kol-2005-description (complete).pdf
368-KOL-2005-EXAMINATION REPORT.pdf
368-KOL-2005-GRANTED-CLAIMS.pdf
368-KOL-2005-GRANTED-DESCRIPTION (COMPLETE).pdf
368-KOL-2005-GRANTED-DRAWINGS.pdf
368-KOL-2005-GRANTED-FORM 1.pdf
368-KOL-2005-GRANTED-FORM 2.pdf
368-KOL-2005-GRANTED-FORM 3.pdf
368-KOL-2005-GRANTED-FORM 5.pdf
368-KOL-2005-GRANTED-SPECIFICATION-COMPLETE.pdf
368-KOL-2005-PETITION UNDER RULE 137.pdf
368-KOL-2005-REPLY TO EXAMINATION REPORT 1.1.pdf
368-KOL-2005-REPLY TO EXAMINATION REPORT.pdf
368-kol-2005-specification.pdf
| Patent Number | 261181 | |||||||||||||||
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| Indian Patent Application Number | 368/KOL/2005 | |||||||||||||||
| PG Journal Number | 24/2014 | |||||||||||||||
| Publication Date | 13-Jun-2014 | |||||||||||||||
| Grant Date | 10-Jun-2014 | |||||||||||||||
| Date of Filing | 29-Apr-2005 | |||||||||||||||
| Name of Patentee | TATA STEEL LIMITED | |||||||||||||||
| Applicant Address | RESEARCH AND DEVELOPMENT AND SCIENIFIC SERVICES DIVISION,JAMSHEDPUR-831 001, | |||||||||||||||
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| PCT International Classification Number | C21B 13/00 | |||||||||||||||
| PCT International Application Number | N/A | |||||||||||||||
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