Metallic ore pellets

Abstract

The present invention concerns the use of a magnesium-including compound as binder for producing metallic ore fluxed pellets, in particular iron ore fluxed pellets, said magnesium-including compound comprising semi-hydrated dolime fitting the general formula aCa(OH).sub.2.Math.bMg(OH).sub.2.Math.cMgO, a, b, and c being weight fractions wherein the weight fraction b of Mg(OH).sub.2 is between 0.5 and 19.5 % by weight with respect to the total weight of said semi-hydrated dolime.

Claims

1. A process for manufacturing metallic ore fluxed pellets, comprising the steps of: feeding a fine metallic ore concentrate into a container, wherein said fine metallic ore concentrate presents a Blaine fineness comprised between 1500 cm.sup.2/g and 2500 cm.sup.2/g; feeding a binder in said container; adjusting moisture in said container to form a wet mixture; balling and sieving said wet mixture into crude metallic ore fluxed pellets; wherein said binder is a compound which includes magnesium, the compound comprising a semi-hydrated dolime fitting the general formula aCa(OH).sub.2.Math.bMg(OH).sub.2.Math.cMgO, a, b and c being weight fractions wherein the weight fraction b of Mg(OH).sub.2 is between 0.5 and 19.5% by weight with respect to the total weight of said semi-hydrated dolime.

2. The process of claim 1, further comprising a firing step for hardening the crude metallic ore fluxed pellets in an induration furnace.

3. The process of claim 2, wherein said firing step comprises the steps of: drying the crude metallic ore fluxed pellets at 300° C. during a predetermined period of time comprised between 5 min and 15 min for forming dried crude pellets; pre-heating the dried crude metallic ore fluxed pellets at a temperature equal to or higher than 800° C. during a predetermined period of time comprised between 5 min and 20 min for forming pre-heated crude pellets; firing the pre-heated crude metallic ore fluxed pellets at a temperature equal to or higher than 1200° C. during a predetermined duration comprised between 5 min and 20 min to form fired metallic ore fluxed pellets.

4. The process of claim 1, wherein the step of adjusting moisture is a step of adding an aqueous phase to form said mixture.

5. The process of claim 1, wherein the step of adjusting moisture is performed until said mixture presents a moisture content comprised between 5% et 15% by weight with respect to the total weight of said mixture.

6. The process of claim 1, further comprising a step of feeding a flux before the step of adjusting moisture, the flux being preferably selected from the group consisting of calcium carbonate, olivine, pyroxenite, other magnesium silicates and mixture thereof.

7. The process of claim 1, wherein the weight fraction c of MgO is greater than or equal to 5% by weight of MgO with respect to the total weight of said semi-hydrated dolime and is less than or equal to 41% by weight of MgO with respect to the total weight of said semi-hydrated dolime, and wherein the weight fraction a of Ca(OH).sub.2 is greater than or equal to 15% by weight of Ca(OH).sub.2 with respect to the total weight of said semi-hydrated dolime and is less than or equal to 85% by weight of Ca(OH).sub.2 with respect to the total weight of said semi hydrated dolime.

8. The process of claim 1, wherein the weight fraction of said binder is between 0.5% and 5% by weight with respect to the total weight of the pellets.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) By the term “particles” in the sense of the present invention, it is meant the smallest solid discontinuity of the mineral filler which may be observed with a scanning electron microscope (SEM).

(2) By the expression “BET specific surface area”, it is meant in the meaning of the present specification the specific surface area measured by manometry with adsorption of nitrogen at 77 K after degassing under vacuum at a temperature comprised between 150 and 250° C., notably at 190° C. for at least 2 hours and calculated according to the multipoint BET method as described in the ISO 9277:2010E standard.

(3) Advantageously, the semi-hydrated dolime comprises particles presenting a total BJH pore volume consisting of pores with a diameter lower than 1000 Å, obtained from nitrogen desorption comprised between 0.05 and 0.15 cm.sup.3/g.

(4) By the terms “BJH pore volume” according to the present invention, it is meant the pore volume as measured by manometry with adsorption of nitrogen at 77 K after degassing under vacuum at a temperature comprised between 150 and 250° C., notably at 190° C. for at least 2 hours and calculated according to the BJH method, using the desorption curve, with the hypothesis of a cylindrical pore geometry.

(5) By the terms “total pore volume” in the present specification, it is meant the BJH pore volume consisting of pores with a diameter smaller than or equal to 1000 Å.

(6) Preferably, the semi-hydrated dolime comprises particles presenting a d.sub.10 greater or equal to 0.5 μm, in particular about 1 μm.

(7) Moreover, the semi-hydrated dolime comprises advantageously particles presenting a d.sub.50 comprised between 4 μm and 8 μm.

(8) In particular, the semi-hydrated dolime comprises particles presenting a d.sub.97 comprised between 40 μm and 95 μm.

(9) The notation dx represents a diameter expressed in μm, measured by laser granulometry in methanol after sonication, relatively to which X % by volume of the measured particles are smaller or equal.

(10) In another embodiment of the present invention, the metallic ore fluxed pellets, in particular iron ore fluxed pellets, contain metallic ore concentrate, in particular iron ore concentrate, presenting particles having a Blaine fineness comprised between 1500 cm.sup.2/g and 2500 cm.sup.2/g, preferably between 1800 cm.sup.2/g and 2200 cm.sup.2/g.

(11) By the expression “Blaine fineness”, it is meant in the meaning of the present specification fineness measured according to the ASTM standard C-204-07 using an air-permeability apparatus and the Test Method A. The Blaine fineness of particles is the specific surface area expressed as the surface area in square centimetres per gram of particles.

(12) In a particularly preferred embodiment according to the invention, the metallic ore fluxed pellets, in particular iron ore fluxed pellets, present a size distribution characterized by 90% to 98% of the pellets presenting a diameter comprised between 8 to 16 mm.

(13) In a particularly preferred embodiment according to the invention, metallic ore fluxed pellets are iron ore fluxed pellets comprising fine iron ore concentrate selected from the group consisting of magnetite, hematite and mixture thereof.

(14) In another embodiment of the present invention, the metallic ore fluxed pellets, in particular the iron ore fluxed pellets further comprise a flux selected from the group consisting of calcium carbonate, dolomite, olivine, pyroxenite, other magnesium silicates, like dunite, and mixture thereof.

(15) Preferably, said flux is between 0.5% and 15% by weight with respect to the total weight of the pellets.

(16) Advantageously, according to the present invention, the metallic ore fluxed pellets, in particular the iron ore fluxed pellets are crude metallic ore fluxed pellets, in particular crude iron ore fluxed pellets.

(17) The moisture content of the pellets is controlled, even in the absence of bentonite, and the mechanical and metallurgical properties of the pellets are enhanced.

(18) The crude metallic ore fluxed pellets are characterized by a crushing strength before drying (“wet pellet”) which is comprised between 10 and 30 N per pellet and after drying (“dried pellet”) which is comprised between 30 and 90 N per pellet.

(19) The crude metallic ore fluxed pellets according to the present invention present a shock temperature equal to or more than 250° C.

(20) By the terms “shock temperature” it is meant according to the present invention the minimum temperature at which cracks are produced in the wet crude pellets when put inside a hot muffle, directly from room temperature. To this purpose, various samples of crude pellets are submitted individual to gradually increased temperature. Typically, a first sample will be subject to 200° C., a second to 250° C., until cracked pellets are observed in one sample. Those cracks appear very quickly (a few minutes) in the pellets after submission to the setting temperature.

(21) Alternatively, the metallic ore fluxed pellets, in particular the iron ore fluxed pellets according to the present invention are fired metallic ore fluxed pellets, in particular fired iron ore fluxed pellets.

(22) Thanks to the semi-hydrated dolime used as binder in the present invention, the fired pellets presents also enhanced mechanical properties after the hardening process. The crushing strength of the fired pellets according to the present invention measured according to standard ISO 4700 is comprised between 2000 and 5000 N/pellet, preferably comprised between 2500 and 5000 N/pellet.

(23) Moreover, the quality of the fired pellets according to the present invention has been enhanced since the replacement of the minerals contained in the bentonite allows for example the reduction of the volume of slag in the blast-furnace or electric arc furnace after the direct reduction reactor.

(24) Preferably, the fired pellets according to the invention contain less than 10%, in particular less than 5% by weight of SiO.sub.2 with respect to the total weight of the pellets.

(25) The total metal, in particular iron, content in the fired pellets is preferably equal to or higher than 55%, in particular equal to or higher than 60%, advantageously equal to or higher than 65% by weight with respect to the total weight of the pellets.

(26) The metallurgical properties of the fired pellets obtained according to the present invention are a reducibility above 0.70%/minute, following the standard ISO 4695, “Determination of the reducibility by the rate of reduction index”, below 20% swelling (by buoyancy), following the standard ISO 4698, “Determination of the free-swelling index” and a crushing strength after reduction above 150 N/pellet, following the standard ISO 4696 “Determination of low-temperature reduction-disintegration indices by static method». The use of semi-hydrated dolime containing magnesium hydroxide in a proportion comprised between 0.5 and 19.5% by weight as binder in metallic ore fluxed pellets allows therefore the production of metallic ore fluxed pellets with adequate mechanical properties together with an adequate chemical composition for use in electrical or blast furnace.

(27) Other embodiments of the use according to the invention are mentioned in the annexed claims.

(28) The invention relates also to a process for manufacturing metallic ore fluxed pellets, in particular iron ore fluxed pellets comprising the steps of: feeding a fine metallic ore concentrate, in particular a iron ore concentrate in a container; feeding a binder in said container; adjusting moisture in said container to form a wet mixture; balling and sieving said wet mixture into crude metallic ore fluxed pellets, in particular crude iron ore fluxed pellets;
characterized in that said binder is a magnesium-including compound comprising semi-hydrated dolime fitting the general formula aCa(OH).sub.2.Math.bMg(OH).sub.2.Math.cMgO, a, b and c being weight fractions wherein the weight fraction b of Mg(OH).sub.2 is between 0.5 and 19.5% by weight with respect to the total weight of said semi-hydrated dolime.

(29) The balling and the sieving step is preferably performed in a granulating vessel like a drum or disk (pan) which can be the container or not.

(30) The residence time of the wet mixture to form the pellets inside the granulating drum is comprised between 50 and 200 s for pellets presenting a diameter comprised between 8 and 16 mm.

(31) Preferably, the process according to the present invention further comprises the step of hardening the crude metallic ore fluxed pellets, in particular crude iron ore fluxed pellets in an induration furnace.

(32) Said hardening step comprises advantageously the steps of: drying the crude pellets at about 300° C. during a predetermined duration comprised between 5 min and 15 min for forming dried crude pellets; pre-heating the dried crude pellets at a temperature equal to or higher than 800° C. during a predetermined duration comprised between 5 min and 20 min for forming pre-heated crude pellets; firing the pre-heated crude pellets at a temperature equal to or higher than 1200° C. during a predetermined duration comprised between 5 min and 20 min to form fired metallic ore fluxed pellets, in particular fired iron ore fluxed pellets;

(33) Advantageously, according to the present invention, the step of adjusting moisture is a step of adding an aqueous phase to form said wet mixture.

(34) The step of adding an aqueous phase is preferably a gradual addition of the aqueous phase into the powdered mixture.

(35) Preferably the aqueous phase is water.

(36) Advantageously, according to the invention, the step of adjusting moisture is performed until said mixture presents a moisture content comprised between 5% et 15% by weight with respect to the total weight of said mixture.

(37) In another embodiment of the process according to the invention, crude metallic ore fluxed pellets, in particular crude iron ore fluxed pellets present a size distribution characterized by 90% to 98% of the pellets presenting a diameter comprised between 8 to 16 mm.

(38) Preferably, the process according to the invention further comprises a step of feeding a flux before the step of adjusting moisture, the flux being preferably selected from the group consisting of calcium carbonate, olivine, pyroxenite, other magnesium silicates and mixture thereof.

(39) Preferably, the weight fraction c of MgO is greater than or equal to 5%, preferably greater than or equal to 10%, advantageously greater than or equal to 15%, preferentially greater than or equal to 20% by weight of MgO with respect to the total weight of said semi-hydrated dolime and is less than or equal to 41%, preferably less than or equal to 30% by weight of MgO with respect to the total weight of said semi-hydrated dolime, the weight fraction a of Ca(OH).sub.2 is greater than or equal to 15%, preferably greater than or equal to 30%, advantageously greater than or equal to 40%, preferentially greater than or equal to 45% by weight of Ca(OH).sub.2 with respect to the total weight of said semi-hydrated dolime and is less than or equal to 85%, preferably less than or equal to 65%, advantageously less than or equal to 60%, more preferably less than or equal to 55% by weight of Ca(OH).sub.2 with respect to the total weight of said semi-hydrated dolime.

(40) Advantageously, in the process according to the invention, the binder is added in a quantity comprised between 0.5% and 5%, preferably between 0.5% and 1.5% by weight with respect to the total weight of the pellets.

(41) Alternatively, according to the present invention, the weight fraction of semi-hydrated dolime is between 80% and 100%, preferably between 90% and 100%, more preferably between 95% and 100%, advantageously between 97% and 100%, preferably between 98% and 100% by weight with respect to the total weight of the binder. In a particular embodiment of the invention, the semi-hydrated dolime is 100% by weight with respect to the total weight of the binder.

(42) In the process according to the invention, said fine metallic ore concentrate, in particular iron ore concentrate presents advantageously a Blaine fineness comprised between 1500 cm.sup.2/g and 2500 cm.sup.2/g, preferably between 1800 cm.sup.2/g and 2200 cm.sup.2/g.

(43) Other embodiments of the process according to the invention are mentioned in the annexed claims.

(44) The present invention relates also to a metallic ore fluxed pellets. In particular iron ore fluxed pellets composition comprising: a fine metallic ore concentrate, in particular an iron ore concentrate in a quantity comprised between 80 weight % and 99 weight % with respect to the total weight of the metallic ore fluxed pellets composition; a magnesium-including compound as binder in a quantity comprised between 0.1 weight % and 5 weight %, in particular between 0.5 weight % and 1.5 weight % with respect to the total weight of the metallic ore fluxed pellets composition; a moisture content comprised between 5 weight % and 15 weight % with respect to the total weight of the metallic ore fluxed pellets composition;
characterized in that the magnesium-including compound comprises a semi-hydrated dolime fitting the general formula aCa(OH).sub.2.Math.bMg(OH).sub.2.Math.cMgO, a, b, and c being weight fractions wherein the weight fraction b of Mg(OH).sub.2 is between 0.5 and 19.5% by weight with respect to the total weight of said semi-hydrated dolime.

(45) Alternatively, according to the present invention, the weight fraction of semi-hydrated dolime is between 80% and 100%, preferably between 90% and 100%, more preferably between 95% and 100%, advantageously between 97% and 100%, preferably between 98% and 100% by weight with respect to the total weight of the binder. In a particular embodiment of the invention, the semi-hydrated dolime is 100% by weight with respect to the total weight of the binder.

(46) Advantageously, the composition according to the invention further comprises from 0.5 weight % to 15 weight % of additives as fluxes with respect to the total weight of the metallic ore fluxed pellets composition.

(47) Preferably, in the composition according to the invention, the weight fraction c of MgO is greater than or equal to 5%, preferably greater than or equal to 10%, advantageously greater than or equal to 15%, preferentially greater than or equal to 20% by weight of MgO with respect to the total weight of said semi-hydrated dolime and is less than or equal to 41%, preferably less than or equal to 30% by weight of MgO with respect to the total weight of said semi-hydrated dolime, the weight fraction a of Ca(OH).sub.2 is greater than or equal to 15%, preferably greater than or equal to 30%, advantageously greater than or equal to 40%, preferentially greater than or equal to 45% by weight of Ca(OH).sub.2 with respect to the total weight of said semi-hydrated dolime and is less than or equal to 85%, preferably less than or equal to 65%, advantageously less than or equal to 60%, more preferably less than or equal to 55% by weight of Ca(OH).sub.2 with respect to the total weight of said semi-hydrated dolime.

(48) In another embodiment of the composition according to the invention, the semi-hydrated dolime comprises particles presenting BET specific surface area obtained from nitrogen adsorption comprised between 5 and 25 m.sup.2/g, preferably between 10 m.sup.2/g and 20 m.sup.2/g.

(49) Preferably, the semi-hydrated dolime of the composition according to the invention comprises particles presenting a total BJH pore volume consisting of pores with a diameter lower than 1000 Å, obtained from nitrogen desorption comprised between 0.05 and 0.15 cm.sup.3/g.

(50) More preferably, the semi-hydrated dolime comprises particles presenting a size characterized either by a d.sub.10 equal to or greater than 0.5 μm, and/or a d.sub.50 comprised between 4 μm and 8 μm, and/or a d.sub.97 comprised between 40 μm and 95 μm.

(51) Alternatively, the metallic ore concentrate, in particular iron ore concentrate presents particles having a Blaine fineness comprised between 1500 cm.sup.2/g and 2500 cm.sup.2/g, preferably between 1800 cm.sup.2/g and 2200 cm.sup.2/g.

(52) Preferably, the fine iron ore concentrate is selected from the group consisting of magnetite, hematite and mixture thereof.

(53) In a preferred embodiment, the composition according to the invention, further comprises a flux selected from the group consisting of calcium carbonate, dolomite, olivine, pyroxenite, other magnesium silicates, like dunite, and mixture thereof.

(54) Other embodiments of the metallic ore fluxed pellets, in particular iron ore fluxed pellets composition according to the invention are mentioned in the annexed claims.

(55) The present invention relates also to crude metallic ore fluxed pellets, in particular crude iron ore fluxed pellets comprising: a fine metallic ore concentrate, in particular an iron ore concentrate in a quantity comprised between 80 weight % and 99 weight % with respect to the total weight of the crude metallic ore fluxed pellets; a magnesium-including compound as binder in a quantity comprised between 0.1 weight % and 5 weight %, in particular between 0.5 weight % and 1.5 weight % with respect to the total weight of the crude metallic ore fluxed pellets; a moisture content comprised between 5 weight % and 15 weight % with respect to the total weight of the crude metallic ore fluxed pellets;
characterized in that the magnesium-including compound comprises a semi-hydrated dolime fitting the general formula aCa(OH).sub.2.Math.bMg(OH).sub.2.Math.cMgO, a, b, and c being weight fractions wherein the weight fraction b of Mg(OH).sub.2 is between 0.5 and 19.5% by weight with respect to the total weight of said semi-hydrated dolime, said crude metallic ore fluxed pellets.

(56) Alternatively, according to the present invention, the weight fraction of semi-hydrated dolime is between 80% and 100%, preferably between 90% and 100%, more preferably between 95% and 100%, advantageously between 97% and 100%, preferably between 98% and 100% by weight with respect to the total weight of the binder. In a particular embodiment of the invention, the semi-hydrated dolime is 100% by weight with respect to the total weight of the binder.

(57) In particular said crude iron ore fluxed pellets further presenting a crushing strength comprised between 10 and 30 N/pellet.

(58) Advantageously, the crude metallic ore fluxed pellets, in particular crude iron ore fluxed pellets further composes from 0.5 weight % to 15 weight % of additives as fluxes with respect to the total weight of the crude metallic ore fluxed pellets.

(59) Alternatively, according to the present invention, the crude metallic ore fluxed pellets, in particular the crude iron ore fluxed pellets present a shock temperature equal to or higher than 250° C.

(60) Preferably, said crude metallic ore fluxed pellets, in particular said crude iron ore fluxed pellets further present a crushing strength between 30 and 90 N/pellet after drying.

(61) This means that the crude pellets present a crushing strength comprised between 10 and 30 N/pellet before drying, when they are crude wet pellets, and present a crushing strength between 30 and 90 N/pellet after drying, when they are crude dried pellets.

(62) The drying step is performed at about 105° C. during a predetermined duration typically comprised between 12 h and 24 h.

(63) Advantageously, the crude metallic ore fluxed pellets, in particular crude iron ore fluxed pellets according to the invention present a size distribution wherein 90% to 98% of the pellets presents a diameter comprised between 8 to 16 mm.

(64) The crude metallic ore fluxed pellets, in particular crude iron ore fluxed pellets according to the invention comprise advantageously fine iron ore concentrate selected from the group consisting of magnetite, hematite and mixture thereof.

(65) Preferably, the crude metallic ore fluxed pellets, in particular crude iron ore fluxed pellets according to the invention further comprise a flux selected from the group consisting of calcium carbonate, dolomite, olivine, pyroxenite, other magnesium silicates, like dunite, and mixtures thereof.

(66) Advantageously, the crude pellets according to the invention contain metallic ore concentrate, in particular iron ore concentrate presenting particles having a Blaine fineness comprised between 1500 cm.sup.2/g and 2500 cm.sup.2/g, preferably between 1800 cm.sup.2/g and 2200 cm.sup.2/g.

(67) Other embodiments of crude metallic ore fluxed pellets, in particular crude iron ore fluxed pellets according to the invention are mentioned in the annexed claims.

(68) The present invention relates also to fired metallic ore fluxed pellets, in particular fired iron ore fluxed pellets comprising: a metal content equal to or higher than 55%, in particular equal to or higher than 60%, advantageously equal to or higher than 65% by weight with respect to the total weight of the pellets, characterized in that the pellets present a Ca/Mg ratio between 0.8 and 2, in particular between 0.8 and 1.7, most particularly between 0.8 and 1.2 and present a crushing strength measured according to standard ISO 4700 comprised between 2000 and 5000 N/pellet, preferably comprised between 2500 and 5000 N/pellet.

(69) In another embodiment of the fired pellets according to the invention, said fired metallic ore fluxed pellets, in particular fired iron ore fluxed pellets contain less than 10%, in particular less than 5% by weight of SiO.sub.2 with respect to the total weight of the pellets.

(70) The fired metallic ore fluxed pellets, in particular fired iron ore fluxed pellets according to the invention comprise advantageously fine iron ore concentrate selected from the group consisting of magnetite, hematite and mixture thereof.

(71) Preferably, the fired metallic ore fluxed pellets, in particular fired iron ore fluxed pellets according to the invention further comprise a flux selected from the group consisting of calcium carbonate, dolomite, olivine, pyroxenite, other magnesium silicates, like dunite, and mixture thereof.

(72) In a particularly preferred embodiment according to the invention, the fired metallic iron ore fluxed pellets, in particular fired iron ore fluxed pellets present a size distribution wherein 90% to 98% of the pellets presents a diameter comprised between 8 to 16 mm.

(73) Other embodiments of fired metallic ore fluxed pellets, in particular fired iron ore fluxed pellets according to the invention are mentioned in the annexed claims.

Example

(74) A composition containing the binder according to the invention has been implemented and present the characteristics presented in table 1. In table 1, the weight % are expressed with respect to the total weight of the pellets.

(75) TABLE-US-00001 TABLE 1 Basicity expressed as (CaO/SiO.sub.2) 0.75 Mg expressed as MgO (weight %) 1.3 Magnetite (weight %) 57.4 Hematite (weight %) 36.6 Limestone (weight %) 1.2 Dolomite (weight %) 2.8 Semi-hydrated dolime (weight %) 1.5 Bentonite (weight %) 0 Anthracite (weight %) 0.5

(76) The amount of elemental Mg expressed as MgO represents the amount of elemental Mg in the mixture of the different components forming the composition of the pellets.

(77) Limestone and dolomite appear as fluxes. Water is added to composition according to table 1 in order to ball and sieve the resulting wet mixture into crude pellets.

(78) The crude pellets are dried at about 300° C. for forming dried crude pellets. The dried crude pellets are pre-heated at 800° C. for forming pre-heated crude pellets. The pre-heated crude pellets are fired at 1280° C. to form fired pellets. The total cycle time from the drying step to the end of the fifing step is 22.4 minutes and the bed height green balls/hearth layer is 300/100 mm.

(79) The fired pellets present 64.2 weight % of Fe and 4.2 weight % of SiO.sub.2 based on the total weight of the fired pellets.

(80) The crushing strength of the fired pellets measured according to the standard ISO 4700 is 3320 N/pellet.

(81) The fired pellets are subjected to a swelling test according to standard ISO 4698 and afterwards the crushing strength of the pellets is measured according to the standard ISO 4700.

(82) Then, the fired pellets are subjected to a reducibility test according to standard ISO 4695 and afterwards the crushing strength of the pellets is measured according to the standard ISO 4700.

(83) Finally, the fired pellets are subjected to a desintegration test according to standard ISO 4696 and afterwards the crushing strength of the pellets is measured according to the standard ISO 4700.

(84) The results of these measurements are shown in table 2.

(85) TABLE-US-00002 TABLE 2 Crushing strength according to ISO 4700 on 180 pellets after swelling test according ISO 4698 (N/pellet) Crushing strength according to ISO 4700 on 420 pellets after reducibility test according ISO 4695 (N/pellet) Crushing strength according to ISO 4700 on 260 pellets after desintegration test according ISO 4696 (N/pellet)

(86) A composition containing a binder according to the invention has been implemented and presents the characteristics presented in table 3. In table 3, the weight % are expressed with respect to the total weight of the pellets.

(87) TABLE-US-00003 TABLE 3 Basicity expressed as (CaO/SiO.sub.2) 0.2 Mg expressed as MgO (weight %) 1.22 Magnetite (weight %) 49.5 Hematite (weight %) 49.5 Binder comprising semi hydrated 1 dolime (weight %)

(88) The amount of elemental Mg expressed as MgO represents the amount of elemental Mg in the mixture of the different components forming the composition of the pellets.

(89) The composition above comprises 0.6 weight % of coke and 1.52 weight % of olivine both expressed with respect to the sum of the weight of hematite and magnetite.

(90) The binder composition comprising semi hydrated dolime is presented in table 4, wherein the weight % are expressed with respect to the total weight of the binder.

(91) TABLE-US-00004 TABLE 4 Mg(OH)2 (weight %) 1.24 Ca(OH)2 (weight %) 57.41 CaCO3 (weight %) 2.84 CaO (weight %) 4.2 MgO (weight %) 33.1 Fe2O3 (weight %) 0.42 Other impurities (weight %) 0.79

(92) Water is added to the composition in order to ball and sieve the resulting wet mixture into crude pellets.

(93) The crude pellets are dried at about 300° C. for forming dried crude pellets. The dried crude pellets are pre-heated at 800° C. for forming pre-heated crude pellets. The pre-heated crude pellets are fired at 1270° C. to form fired pellets. The total cycle time from the drying step to the end of the firing step is 27.4 min and the bed height green balls/hearth layer is 300/100 mm.

(94) The fired pellets presents 66 weight % of Fe and 2.95 weight % of SiO.sub.2 based on the total weight of the fired pellets.

(95) The crushing strength of the fired pellets measured according to the standard ISO 4700 is 2920 N/pellet.

(96) The fired pellets are subjected to a swelling test according to standard ISO 4698 and afterwards the crushing strength of the pellets is measured according to the standard ISO 4700.

(97) The fired pellets are subjected to a reducibility test according to standard ISO 4695 and afterwards the crushing strength of the pellets is measured according to the standard ISO 4700.

(98) Finally the fired pellets are subjected to a disintegration test according to standard ISO 4696 and afterwards the crushing strength of the pellets is measured according to the standard ISO 4700.

(99) The results of these measurements are shown in table 5.

(100) TABLE-US-00005 TABLE 5 Crushing strength according to ISO 300 4700 on pellets after swelling test according ISO 4698 (N/pellet) Crushing strength according to ISO 310 4700 on pellets after reducibility test according ISO 4695 (N/pellet) Crushing strength according to ISO 210 4700 on pellets after disintegration test according ISO 4696 (N/pellet)

Comparative Example

(101) A composition containing bentonite as binder has been implemented and present the characteristics presented in table 6. In table 6, the weight % are expressed with respect to the total weight of the pellets.

(102) TABLE-US-00006 TABLE 6 Basicity expressed as (CaO/SiO.sub.2) 0.75 Mg, expressed as MgO (weight %) 1.3 Magnetite (weight %) 56.1 Hematite (weight %) 36.3 Limestone (weight %) 1.8 Dolomite (weight %) 4.7 Semi-hydrated dolime (weight %) 0 Bentonite (weight %) 0.6 Anthracite (weight %) 0.5

(103) The amount of elemental Mg expressed as MgO represents the amount of elemental Mg in the mixture of the different components forming the composition of the pellets.

(104) Limestone and dolomite appear as fluxes. Water is added to composition according to table 6 in order to ball and sieve the resulting wet mixture into crude pellets.

(105) The crude pellets are dried at about 300° C. for forming dried crude pellets. The dried crude pellets are pre-heated at 800° C. for forming pre-heated crude pellets. The pre-heated crude pellets are fired at 1280° C. to form fired pellets. The total cycle time from the drying step to the end of the firing step is 22.4 minutes and the bed height green balls/hearth layer is 300/100 mm.

(106) The fired pellets present 63.7 weight % of Fe and 3.5 weight % of SiO.sub.2 based on the total weight of the fired pellets.

(107) The crushing strength of the fired pellets measured according to the standard ISO 4700 is 2410 N/pellet.

(108) The fired pellets are subjected to a swelling test according to standard ISO 4698 and afterwards the crushing strength of the pellets is measured according to the standard ISO 4700.

(109) Then, the fired pellets are subjected to a reducibility test according to standard ISO 4695 and afterwards the crushing strength of the pellets is measured according to the standard ISO 4700.

(110) Finally, the fired pellets are subjected to a desintegration test according to standard ISO 4696 and afterwards the crushing strength of the pellets is measured according to the standard ISO 4700.

(111) The results of these measurements are shown in table 7.

(112) TABLE-US-00007 TABLE 7 Crushing strength according to ISO 4700 on 110 pellets after swelling test according ISO 4698 (N/pellet) Crushing strength according to ISO 4700 on 260 pellets after reducibility test according ISO 4695 (N/pellet) Crushing strength according to ISO 4700 on 150 pellets after desintegration test according ISO 4696 (N/pellet)

(113) As it can be seen from tables 2, 5 and 7, the crushing strengths of the fired pellets made from the composition according to the present invention are well above the one of the pellets containing bentonite as binder.