Title of Invention

A PROCESS FOR PRODUCING HIGH STRENGTH PELLETS FROM HIGH GRADE CHROMITE CONCENTRATES.

Abstract

The invention provides a process for producing high strength pellets from high grade chromite concentrates. The method comprises the steps of taking a known quantity of the chromite concentrates and mixing the chromite concentrates with optimized quantity of binders and reductants. The mixture is pellitized under required conditions and the green pellets are cured naturally for a predetermined period of time. The cured pellets are then hardened at a higher temperature in a furnace. The furnace is then cooled to room temperature.

Full Text

FIELD OF APPLICATION The present invention relates to a process for producing high strength pellets from high grade chromite concentrates. BACKGROUND OF THE INVENTION The chromite ore is an indispensable raw material for iron-chromium alloy making. This in turn is used for producing alloy steels. Naturally occurring Indian chromite ores are mostly powdery in nature. On beneficiation of available low grade ores, also results finer size (-1 mm) concentrates. As such these fines cannot be used in conventional AC furnaces. A need therefore, existed for agglomeration (pelletization bricketing and sintering) of these fines for use in iron-chromium alloy making in a conventional submerged arc furnace (SAF). A technology was developed by Outokumpu and commercially practised with all South Africa ores for producing pellets after grinding to fine sizes and making pellets with necessary binders and sintering (heat hardening). However, with Indian chromite fines having more than 2.8 Cr/Fe, this technology could not be applied 'as it is'. This is mainly because of high refractory nature of Indian chromite ores. SUMMARY OF THE INVENTION The main object of the present invention therefore is to agglomerate high grade Indian chromite concentrates for the production of high strength pellets similar to South African sintered pellets under Outokumpu Technology (250 kg / pellet). Another object of the present invention is to produce water-resistant and thermally stable pellets for use in submerged electric arc furnace conditions. These objects are achieved by using higher sintering temperature, additional reductants and different binders. According to the present invention the materials used for producing high strength pellets from high grade chromite concentrates are high grade chromite concentrate and fines with Cr/Fe : 3.1 Cr2O3 : +52 % Particle size : Below 0.5 mm with an average particle size of 100 microns is ground to below 0.15 mm (with 80 % below 0.075 mm fraction) Moisture : 10 % Binder : Naturally occurring inorganic compounds Coke breeze : ~ 3 % Thus the present invention provides a process for producing high strength pellets from high grade chromite concentrates, comprising the steps of: taking a known quantity of the chromite concentrates; mixing the chromite concentrates with two different naturally occurring inorganic minerals as binders, wherein the quantity of binder 1 in the form of alkali dipped clay is 1.5 % by weight and quantity of binder 2 in the form of a calcium salt is 4.0 to 5.0 % by weight; pelletizing the mixture under required conditions; curing the green pellets naturally for a predetermined period of time; heat hardening the cured pellets at a higher temperature in a furnace; and cooling the furnace to room temperature. The process of the present invention will now be described. A known quantity and quality of high grade chromite concentrates is taken and mixed with optimized quantity of binders. From this mixture pellets are prepared using pelletizing disc under required conditions to produce 15-30 mm size pellets. These pellets are naturally cured for about 24 hours. After this, these pellets are heat hardened by introducing these naturally cured pellets in a furnace. The hardening can be carried out at a temperature of 1250 degree C and for about an hour in a reducing atmosphere. The furnace is then cooled to room temperature. The process conditions are as follows: Binder 1 (Inorganic mineral) quantity, % : 1.5 Binder 2 (Inorganic mineral) quantity, % : 4.0-5.0 Coke quantity, % : 3.0-3.5 Green pellets curing time, hrs : 24 Heat hardening temperature, °C : 1250 °C Atmosphere : Reducing Under the above process conditions it is possible to produce pellets with high compressive strength (> 250 kg/pellet), water resistant, and thermally stable properties. These pellets can be used as 80 -100 % feed in a submerged electric arc furnace. WE CLAIM 1. A process for producing high strength pellets from high grade chromite concentrates, comprising the steps of: taking a known quantity of the chromite concentrates; mixing the chromite concentrates with two different naturally occurring inorganic minerals as binders, wherein the quantity of binder 1 in the form of alkali dipped clay is 1.5 % by weight and quantity of binder 2 in the form of a calcium salt is 4.0 to 5.0 % by weight; pelletizing the mixture under required conditions; curing the green pellets naturally for a predetermined period of time; heat hardening the cured pellets at a higher temperature in a furnace; and cooling the furnace to room temperature. 2. The process as claimed in claim 1, wherein the palletizing step is carried out in a palletizing disc. 3. The process as claimed in claim 1, wherein the green pellets are naturally cured for a period of 24 hours. 4. The process as claimed in claim 1, wherein the heat hardening of the cured pellets is carried out in a furnace at a temperature of 1250° C. 5. The process as claimed in claim 6, wherein the heat hardening is carried out for an hour. 6. The process as claimed in claim 6, wherein the heat hardening is carried out in a reducing atmosphere. 7. The process as claimed in claim 1, wherein the size of the pellets is 15 - 30 mm. 8. A process for producing high strength pellets from high grade chromite concentrates, substantially as herein described. The invention provides a process for producing high strength pellets from high grade chromite concentrates. The method comprises the steps of taking a known quantity of the chromite concentrates and mixing the chromite concentrates with optimized quantity of binders and reductants. The mixture is pellitized under required conditions and the green pellets are cured naturally for a predetermined period of time. The cured pellets are then hardened at a higher temperature in a furnace. The furnace is then cooled to room temperature.

Documents:

583-kol-2004-granted-abstract.pdf

583-kol-2004-granted-claims.pdf

583-kol-2004-granted-correspondence.pdf

583-kol-2004-granted-description (complete).pdf

583-kol-2004-granted-examination report.pdf

583-kol-2004-granted-form 1.pdf

583-kol-2004-granted-form 18.pdf

583-kol-2004-granted-form 2.pdf

583-kol-2004-granted-form 3.pdf

583-kol-2004-granted-form 5.pdf

583-kol-2004-granted-gpa.pdf

583-kol-2004-granted-reply to examination report.pdf

583-kol-2004-granted-specification.pdf