AGGLOMERATES,A PROCESS FOR PRODUCING THEREOF AND USE THEREOF

Abstract: A process for improving the reactivity, permeability and/or similar characteristics of an ore charge being subjected to down-draught sintering, characterized by including into said charge an active quantity of a micropelletized product produced by balling a fine-grained ore material with the addition of a minor quantity of hydraulic binder and water to a maximum agglomerate size of up to 10 mm (preferably up to 6 mm) which prior to charging onto said sintering device is cured to in average at least50% of the maximum achievable cured strength or of the cured strength obtainable by curing for 28-30 days at room temperature.

Description: AGGLOMERATES, A PROCESS FOR PRODUCING THEREOF AND USE THEREOF This invention is related to agglomerates of a fine-grained mainly inorganic material which are hardened or bonded with a hydraulic binder, a process for producing said agglomerates and the use of said hardened agglomerates in metallurgical processes. The invention is especially related to the type of agglomerates which is usually called "micro pellets" and is preferably produced by balling (rolling, pelletising) a wet fine-grained material in a device which typically consists of a balling drum, balling disc or balling cone, to produce agg¬ lomeration of the fine-grained material when balled (rolled) to preferably essentially spherical balls or "pellets" with a maximum size of preferably up to about 10 mm, usually up to about 6 or 8 mm. The invention is especially related to agglomerating iron ore, especially hematitic or magnetitic iron ore, preferably an iron ore in which 'the iron essentially, preferably to at least 60%, at least 75% or at least 85% is present as magnetite. The invention is also related to such micro pellets comprising hydraulic binder which * after forming are subjected to hardening (bonding) through storing, prefer¬ ably by being spread in a layer of comparatively low height or thickness, e.g. at most 15 meters, preferably at most 10 meters or at most 5 meters or even at most 3 meters in order to prevent that the agglomerates in the lower part of said layer are crushed, for a period of time required for hardening or bonding to a strenght which permits subsequent transport by loading into a railway wagon or a similar treatment and charging into a device for performing a metallurgical process, e.g. a draft sintering device of the travelling grate type or a similar device, without forming an unacceptably large amount of fine-grained material, as is defined in the follow¬ ing with reference to testing methods, such as drop test in free fall or dropping through a tube against a hard bottom surface or against a layer of the tested material with a drop height of at least 15 meters, and by treatment in a rotatin drum of defined dimensions for a certain period of time. Curing in said store, also called low store, is performed preferably for 1 to 14 days, especially from 2 to 7 days. Thereafter further storing can be performed under conditions which permit con¬ tinued curing preferably for a total storing and curing time after the production of at least 15 days, preferably at least 30 days and optionally at least 60 or at least 100 days. Depending upon the conditions the storing can in some cases by restricted to at most 45 days, particularly at most 30 days or at most 15 days or even at most 7 days prior to transporta¬ tion from the production location to the location of use or prior to charging into the metallurgical device for the inten¬ ded use if the product is used at the production location. Usually the transport from the production location to the location of use is performed in lorries, railroad wagons , tran¬ sport belts, as a suspension or dispersion in a carrying, gas or liquid in tubes, in ships or in a similar way under condi¬ tions which would cause the micro pellets produced without the hydraulic binder or without the curing in the low store or the final curing after low store treatment to be weared and denuded at said transport to such an extent that the product does not fulfil the required test standards, especially those stated above. Micro pelletising and micro pellets are well known concepts which are explained e.g. in "Jernkontorets Forskningsuppgift nr 299/77, Senaste rδn inom sintringstekniken" (Jernkontorets Research report nr. 299/77, "Latest progress in sintering technology") especially pages 18-20 as well as the litterature references referred to on said pages, the disclosure of which is included by reference. That which is disclosed in said publication is intended to form a part of. this specification. Micro pellets according to the invention fulfil preferably the definitions stated in said publication and/or said references but the invention is not restricted to said defini- tions . The micro pellet product according to the invention comprises agglomerated particles of varying size, preferably with a largest particle size of 10 mm, especially 8 mm, optionally 6 mm or 5 mm, under certain conditions a largest particle size of 4 mm or 3 mm. This means that at least 75%, especially at least 85% or 90%, optionally at least 95% or 98% or even 100% of the quantity by weight of agglomerated particles or agglo¬ merated particles and unagglomerated feed material, which has been subjected to the agglomeration treatment without being agglomerated, has a particle size within the stated upper limits The lower limit of the agglomerate size is especially the grain size of the feed material but it is also possible to settle a lower limit of the agglomerate size, e.g. by sieving or by controlled agglomeration, such as not below 0.1 mm, not below 0.5 mm, not below 1 mm, not below 2 mm, not below 3 mm or not below 5 mm. Said limit means that at least 75%, pre¬ ferably at least 85% or at least 90%, optionally at least 95% or 98% or even 100% of the quantity by weight of agglomera¬ ted particles or agglomerated particles and unagglomerated feed material has a size which exceeds the stated lower limit. The agglomeration is preferably performed on an agglomerating disc with sloping axis but also any other suitable agglomera¬ ting device, e.g. of agglomerating roll type or similar devices can be used. The agglomerates preferably are of essentially spherical shape which can be achieved e.g_ by rolling. Preferably the particles exhibit a ratio largest diameter:smallest diameter (through the geometrical centre or middle point of the balls) of at most 2, preferably at most 1.5 and especially at most 1.3 or 1.2, said value being fulfilled by at least 50% and pre¬ ferably at least 75% of the particles, based on the weight, especially within the intermediate 50% range of the agglome¬ rate size interval. The agglomeration can be performed in one or more steps, e.g. for building up micro pellets of different composition within different parts, e.g. with a larger or smaller quantity of binder and/or combustible material, especially carbonaceous material, mixed into the outer part of the agglomerates, in relation to the inner part. Said division into layers can pre¬ ferably be performed with agglomerates within the upper 50% range of the agglomerate size range. The outer part of the agglomerates may especially comprise up to 50% of the weight of the agglomerate and optionally comprise at least 10% or at least 25% of said weight, and e.g. at least 50% of the particles showing said layers of different composition may fulfil said request. The material used as feed material for agglomeration consists preferably of a finely divided ore material, especially metal ore material. The agglomerated material consists preferably of a metal ore, e.g. essentially oxidic or sulphidic metal ore, preferably comprising one or more of the metals iron, chromium, copper, lead, -zinc, tin , cobalt, tungsten, manganese, titanium Preferably the material consists of oxidic or hydroxidic iron ore, especially hematite and/or magnetite. Especially preferred is iron ore which to at least 50%, especially at least 75% or at least 85% or even at least 90-95% or 100% consists of magnetite as an iron carrier. Especially suitable is a benefica tion concentrate of the iron ores stated above as well as other ores which have been disintegrated by grinding. Prefer¬ ably the grain size of the material prior to agglomeration may be at most 0.5 mm, especially at most 0.2 mm or at most 0.1 mm •and optionally at most 0.05 mm. This is intended to mean that at least 75%, preferably at least 90% and especially at least 95% or 100% of the metal ore material or similar material has a grain size below said upper limit. The lower limit of the particle size is normally the particle size obtained by grinding, but it is also possible to separate a fine-grained part falling below a certain limit value prior to agglomera¬ tion by sieving or by similar methods. Thus, the lower limit may be selected to 0.05 mm or to 0.01 or 0.04 mm so that e.g. at least 75%, optionally at least 80% and possibly at least 90 or 95% and under certain conditions at least 100% of the quantity by weight has a grain size exceeding a stated lower limit value. For the ores mentioned above, especially for iron ores such as hematiteand/or magnetite, a grain size of 85-100% below 0.1 mm and a specific surface area of at least 500, preferably at least 1000, at least 1200 or at least 1400, under certain 2 conditions at least 1500 or even at least 2000 cm /g is suit¬ able. The upper limit of the specific surface area can usually be selected arbitrarily and may e.g. amount to 6000, up to 5000 or up to 4000 or even up to 3000 and in some cases lower, 2 such as up to 2800 or up to 2500 cm /g. Usual ranges of the 2 ores stated above is e.g. 1500-2800 or 550-2200 cm /g, said values of the specific surface area being calculated according to the "Svensson-method" disclosed in "Jernkontorets Annaler" , vol. 133, issue 2, 1949, pages 33-86. ϊhe bonding of the micro pellet material is performed essen¬ tially or partly with ' hydraulic binder in_ finely divided shape, said binder being mixed into the agglomerates, pre¬ ferably by mixing the binder material with the inorganic feed material, especially iron ore, prior to supplying the ore to the pelletising or agglomerising equipment, e.g. in a mixing drum or mill being.'.arranged prior to the agglomeration equip¬ ment. The binder may also be grinded together with the in¬ organic starting material with simultaneous mixing with said material. As hydraulic binder preferably cement materials of various types are used, such as portland cement which is pro¬ duced by intimitly mixing lime- and clay-containing products or other feed materials comprising SiO , Al„0., and CaO in suitable quantities, said materials being fired and sintered. One may use a so called cement clincer or a further treated grinded clincer which optionally is mixed with further binders, such as up to 2-4% of gipsum. An embodiment of portland cement is quicksetting cement or special cement which quickly reaches high physical strenght values, usually by comprising a higher content of tricalciumsilicate or a lower content of dicalcium silicate than a corresponding normal portland cement and op¬ tionally being more finely disintegrated or grinded. Other embodiments are pozzolanic cement, slag cement and aluminate cement. Slag cement is preferably based on blast-furnace slag, preferably in combination with lime or lime-supplying material such as lime slag cement produced from blast-furnace slag and lime, eisenportland cement (iron portland cement) made fro about 70% of portland cement and about 30% of blast-furnace slag, and blast-furnace cement (Hochofenzement) made from abou 30-70% of blast-furnace slag and 70-30% of portland cement. One may also use aluminate cement prepared by firing to melti of a mixture of lime and bauxite and finely grinding of the molten product. One may also use non-portland cement, e.g. lime and hydraulic limes obtained by burning limestone, pre¬ ferably at about 1000°C. or limestones comprising substantial or effective quantities of Al_0_, SiO« and Fe„0, as impurities which after burning can be cured with water without inter¬ action of carbon dioxide from the air. Said products are also called hydraulic limes. Other suitable binders which can be used together with or instead of portland ' cement and similar are metallurgical slags, such as blast-furnace slag, e.g. acid or basic blast-furnace slag, slag from the LD-process, the aldo-process, Martin-furnace slag, Thomas slag, slag obtained when performing refining in electric steel furnaces for steel production, as well as slag derived or obtained from melting other metals, such as processes for producing lead, copper, zinc, tin , etc. starting e.g. from oxidic or sulphidic ores. The slag used, especially blast-furnace slag, may especially be vitreous, water-granulated blast-furnace slag or blast¬ furnace slag which in other ways has achieved corresponding characteristics, especially reactivity and hydraulic cureing and bonding power. The slag should preferably be basic, espe¬ cially with a basicity CaO/Si0 2 = 1.0-2.0 or above, e.g. 1.0- 1.5. Examples of compositions or analysis values is 28-40%, e.g. 35-40% Si0 2 , 5-17%, e.g. 8-12% Al 2 0g, 29-48%, e.g. 35-45% CaO and 2-13%, e.g. 4-8% MgO. The slag as well as other hydrau¬ lic binder constituents should preferably have a low content of Na 2 0 + K„0, especially when producing agglomerates intended for charging in blast-furnaces and steel-furnaces, such as a content of said compounds below 2%, preferably below 1% or 0.5%, especially below 0.1 or 0.05%. Examples of suitable binders are calcium aluminate cement, CA-cement and calcium ferrit cement (C 4 AF) , having the arbitrary co po- siton 4 CaO.Al-0-..Fe-O o . The quantity of hydraulic binder should be restricted to the lowest quantity which gives the desired strenght. A suitable upper limit, especially in agglomerates of the iron ores mentioned above is at most 6% , preferably at most 5% and especially at most 4% or at most 3%, in some cases at most 2% or even at most 1% based on the weight of the agglomerated solid materials. Combinations of two or more hydraulic binders can preferably be used, such as cement (portland cement, slag cement, aluminate cement, etc.) plus slag, especially blast-furnace slag, cement plus lime, lime plus blast-furnace slag, cement plus blast¬ furnace slag plus lime. A suitable combination is about 10-50% of cement and about 90-50% of slag, such as blast-furnace slag, preferably about 1/3 cement plus about 2/3 slag,- especially blast-furnace slag. Said slag and/or cement may entirely or partly also be substituted with lime (slaked lime) e.g. up to 50% of the cement may be substituted with slaked lime and/or up to 50% of the slag, especially blast-furnace slag, may be substituted with slaked lime. A particular type of blast¬ furnace slag is blast-furnace slag which has been purified from sulphur by the method disclosed in the Swedish published application No. 324 166. A suitable mixture is 10-20% cement, 10-20% lime (burned or slaked) , 60-90% slag, such as blast-furnace slag. It is pre¬ ferable that the hydraulic binder is grinded to a fine particle size , preferably to a specific surface area , according to the definition above , of at least 2000 , preferably at least 3000 and especially at least 5000 cm 2/g. Usually reactivity is im¬ proved with increasing specific surface area and therefore also an even larger specific surface area, such as at least 6000 2 and even at least 7000 cm /g or even at least 8000 or 10000 2 cm /g may be preferable. As regards suitable hydraulic binders which can be used according to the invention and the charac¬ teristics of said binders reference is also made to the Swedish published application No. 324 166 the disclosure of which is included by reference, and the Swedish Patent No. 226 608, the disclosure of which is included by reference. The hydraulic binders used can be grinded separately or to¬ gether to the desired degree of fine particle size. Fuel can also be included into the agglomerated, preferably coke powder, antracit powder or similar carboneous materials, preferably with a relatively low content of volatile consti¬ tuents. When producing micro pellets of iron ore for sintring, especially draft sintring, e.g. on a travelling sinter grate or a similar device the entire quantity of fuel required in the process can be included into the agglomerate, preferably in finely disintegrated state of essentially the same grain size range as the inorganic agglomerated material and/or the binder. Also a minor part of the total required quantity of fuel, e.g. 25-75% of said quantity can be included ' in the agglomerates, especially pellets or balls, and the reminder may conventionally be included as particles, especially as somewhat coarser particles, e.g. particles with a size of essentially above 1 mm, e.g. 1-5 mm or 1-3 mm, which are mixed with the agglomerates and optional other charged constituents . The agglomeration of the fine-grained inorganic material with the binder and optionally other constituents is performed in a wet state, usually with a water content of 5-15%, e.g. 7-10%, whereof a minor quantity is usually sprayed onto the surface of the agglomerated charge when rolling pellets or balls on an agglomerating disc or similar device. In a balling or pelletizing treatment it is also possible to introduce cores (nuclei) , preferably particles, e.g. recircula¬ ted agglomerates, having a particle size above about 1-2 mm which grow in size through repeated passage through the pelle¬ tizing device. Optionally balling (rolling, pelletizing) may be performed in several steps, e.g. two or more steps, with increased binder addition in the last step, e.g. to the contents stated above. Optionally at least 2/3 or the entire quantity of the binder may be added in the last step. The formed agglomerates, optionally -after sieving to remove undersized particles and/or oversized particles or for separate- ing cores or nuclei intended to be recirculated, are trans¬ ferred to a store for curing, preferably a store in which the pelletized material is laid down in a low layer thickness in order to prevent crushing of the agglomerates in the lower part of said layer, e.g. a layer thickness of at most 15 m, at most 10 m, at most 5 m or even at most 3 m, preferably at least 2 m. The uncured (unhardened) agglomerated " (pelletized) material can be spread in said layer from a conveyor belt. e.g. as an elongated or annular heap, e.g. by scraping off from an elonga¬ ted conveyer belt and spreading out in a direction transvers to said conveyor belt so that an elongated heap is gradually formed. The elevation from which the material is dropped is preferably restricted to at most 15 m, preferably at most 10 or at most 5 m. The uncured or green agglomerates may prior to storing be mixed with starting material which is free from binder or with cured or partly cured agglomerates, optionally after separation of a finer or coarser fraction of said mate¬ rials, in order to prevent a tendency of the uncured or green material to form lumps in the curing treatment. Preferably up to 40% or up to 30% of such materials are added, e.g. at least 5% or at least 10%, e.g. 10-20%, based on the weight of the uncured or green material. The storing time in the low store should be at least sufficient for giving a curing strength which permits further transportation and handling of the agg¬ lomerates, e.g. at least 1-2 days up to 5 or 10 days, prefer¬ ably so that the agglomerated material when dropped in free fall from an elevation of 15 m through a tube against a layer of said material or against a concrete floor shows an increase of the quantity of material with a particle size below 0.42 mm and/or below 0.15 mm of at most 20%, preferably at most 15% or at most 10%, said values being obtained after dropping four times with a night of fall of 15 m. After the agglomera¬ tes have achieved said strenght they can be transported from the store and/or stored for a further period of time prior to the final use in an intended process, especially draft sinte¬ ring. The curing temperature is suitably ambient temperature or room temperature, or about 10-40 C. The strenght of the agglomerates can also be stated or measured as the compression strenght of separate agglomerates or balls (pellets) when crushing the agglomerates between flat surfaces. Suitable values for fraction of a diameter size of 4-6 mm is e.g.: minimum strenght after staring in a 'low store: at least 0.2, preferably at least 0.5, at least 1, at least 2 or at least 5 kilograms. Compressive strenght after final storing prior to use: at least 0.3, preferably at least 0.5, at least 1, often at least 2 or at least 5 kilograms, preferably at least 0.2 or at least 0.5 or 1 kilograms higher strenght when after the storing in the low store. After curing the agglomerates to the stated strenght values and/or for the stated minimum period of time the agglomerates are used in the metallurgical process in question, especially draft sintring of iron ore on a travelling sinter grate or similar device. The cured micropellet material may according to the invention comprise up -to 100% of the quantity of charged iron carrier, especially together with recirculated material from draft sintring in e.g. commonly used quantities or may comprise up to 80% and often up to 60% or up to 40% or 20% of the iron carrier in the charge. The lower limit for achieving the desired effect may e.g. amount to 5% or 10% or even 20% or more. Cured micropellet material can according to the invention be arranged homogeneously distributed in the charge bed of a draft sintring device or arranged in one or more layer in said bed, e.g. with at least 60% or at least 75% or even at least 90% of the quantity of the cured micropellet material distri¬ buted in the lower half or one third of said bed or alterna¬ tively in the upper half or one third of the bed or in the central half or one third of the bed hight in order to control or improve the carrying capacity, resistance against disinte¬ gration in the heating step and the reactivity so that optimum values are obtained within different parts of the bed thick¬ ness. Improved permeability and reactivity makes possible an increase of the bed thickness, e.g. to above 30 cm, prefer¬ ably above 35 cm and optionally to above 40 or 50 cm and/or a reduction of the sintring time to a corresponding degree, said comparison especially being made with the same starting material when being micropelletized without addition of the hydraulic binder. The following is an example of the invention: In a process comprising sintering on a sintering band the charge in run A comprised 63.8% fine-grained magnetite concen¬ trate, 27.2% iron ore having a grain size which was suitable for sintering, 1.1% iron sponge ash, 1.5% LD-slag, 2.7% gabbro, 3.7% burnt lime, together 100%, and furthermore 5.0% coke breze, 4.0% lime stone and 30.0% recycled material from the sintering process. In a run B the magnetite concentrate was substituted with a mixture of 20 % by weight of said concentrate and 80% by weight of cured micropellets of said concentrate bonded with 1% of portland cement clincer and 2% of blast-furnace slag which 2 were grinded to a specific surface area of about 6000 cm /g. In a run C said magnetite concentrate was substituted entirely with the cured micropellet material. The production amounted in run A to 31.8, in run B to.35.5 and in run C to 35.9 tons/square meter.24 hours. The product quality was in all said runs satisfactory. Corresponding experiments were performed with the addition of 1% cement and 1% blast-furnace slag with similar results. Further experiments were performed with the same binder add- tives but with micropellets of hematite ore concentrates and mixtures of magnetite and hematite ore concentrates with simi¬ lar improvements of production results. Corresponding experiments with hematitic ores, especially such ores with more than 80% hematite or tropical hematitic ores give similar good results. Examples of such tropical or subtropical hematite ores are South American-ores, e.g. hemtatites from Brasilia, e.g. from Minas Gerais, hematites from Venezuela, e.g. hematites of the orinoco-type. Other examples are West African-hematites, e.g. from Liberia and the Mauretania, e.g. from the Nimba-mine, and Australian hematites, e.g. from the North-West Territory. Such hematites may in addition to hematite also comprise e.g. martite. Thus, the invention can with good result be used also for hematitic ores, e.g. such ores comprising at least 70%, at least 80%, at least 90% or even at least 95% of the Fe as Fe^O.,. For measuring the physical strenght of the micropelletized material according to the invention one may preferably use a device of the type denoted "ISO-Tumbler", i.e. a drum with the diameter 1000 mm and lenght 500 mm comprising two internal lifters with a hight (bredth) of 50 mm. Said drum is charged with 15 kg of dry material and is rotated 200 revolutions at a speed of 25 revolutions/minute. The micropelletized material should preferably be cured to a physical strenght at which after the treatment in the ISO-Tumbler stated above the frac- c: tion of the material with a grain size below 0.15 mm shows an increase with less than 30%, preferably less than 20% and optionally also less than 15% or 10%, based on the weight of the material being tested in the drum. Said increase values are also suitable limit values at the test disclosed above which comprises dropping two or four times with a fall hight of 15 m mentioned above. It is often preferable to expedite the bonding (curing) of the hydraulic binder, especially during the first part of the bonding (curing) reaction, and/or to achieve a supplementary bonding (curing) especially during the first part of bonding after forming the micropellet material. This can be achieved in several ways, e.g. by a) adding a binding accelerator (curing accelerator) to the hydraulic binder, e.g. chlorides, such as calcium chloride or sodium chloride, sodium. carbonate and water glas. The quantity of said additives may e.g. amount to up to 5% of the weight of the binder, e.g. 0.5-4% and especially 1-3%, said ranges being valid especially for chlorides, such as calcium chloride, CaCl 2 .2H_0, and a preferred amount of said and other chlorides is about 2%; b) by decreasing the quantity of calcium sulphate in the cement, e.g. to at most 50% or at most 20% of the quantity of calcium sulphate normally present in portland cement; c) by adding light burnt MgO, preferably in the quantities stated for the accelerator according to a) above, e.g. about 9_.9o- ., d) by adding so called "silica dust" from e-.g. electro steel furnaces or ferro silicon furnaces, i.e. mainly from the gas phase separated silicon oxide, especially silica. The quantity of said additive can likewise be selected within the limits stated for the accelerator according to a) above; e) by subjecting the binder to fine-grinding to a large speci- 2 fie surface area, e.g. at least 6000 cm /g or at least 8000 or 2 10.000 cm /g or above, e.g. at least 12.000, preferably at 2 least 15.000 or even at least 20.000 cm /g; f) by adding residual liquor from cellulose digesting processes e.g. residual liquor from the sulphite process or inorganic constituents obtained from treating said liquor; g) by increasing the temperature in the binding step, e.g. by preheating one or more of the constitutents used in the agglo¬ merating step. Grinding of the binder to a fine particle size may contribute and give a preheating -of the binder, e.g. to about 200 C. Furthermore, the ore concentrate or the agglo¬ merates (pellets, granules) , may be heated prior to, during or after the agglomerating treatment, e.g. with hot combustion flue gases. A suitable temperature increase is at least 10° and preferably at least 20 or at least 30^ above the ambient tempe-rature or the temperature of the starting materials; h) by carbonate hardening through a reaction with CO- , especial ly a reaction with CO- in combustion flue 'gases used for heat¬ ing the material. \ The measures for expediting curing or hardening may of course also be combined so that two or more such measures are used simultaneously. It is also possible to add to the agglomerates other constituents which increase the thermal stablility, such as coal in various forms, e.g. coke, dolomite ,Al-0-.in various forms , bauxite , limestone etc. The agglomerates may also be neutral, acid or basic, calculated e.g. from the ratio CaO+MgO/ SiO- which especially for iron ore agglomerate may be within the ranges below 1 , 0,5 to 1,5, 1 to 2 or 1,5 to 2,5 or above 2. Calcium hydroxide or calcium oxide in various forms, e.g. burnt lime, slaked lime, is normally not used alone as a binder but may form a constituent of the hydraulic binder together with e.g. slag which preferably is reactive with the lime.

Claims: r 6 CLAIMS : 1. A process for improving the reactivity, permeability and/ or similar characteristics of an ore charge being subjected to down-draught sintering, characterized by including into said charge an active quantity of a micropelletized product produced by balling a fine-grained ore material with the addition of a minor quantity of hydraulic binder and water to a maximum agglomerate size of up to 10 mm (preferably up to 6 mm) which prior to charging onto said sintering device is cured to in average at least 50% of the maximum achievable cu <έd ~ strenght or of the cured strenght obtainable by curing for 28-30 days at room temperature. 2. A process according to Claim 1, characterized in that the quantity of hy-draulic binder in the cured micropelletized material is at.most 6% and preferably at most 4% by weight of cement, binding slag, burnt lime or similar hydraulic bin¬ ders, based on the weight of the charge, the quantity of hydraulic binder preferably being at least 0.2%, especially 0.5% or at least 1%, based on the weight of the agglomerated material. 3. A process according to Claim 1 or 2, characterized in that the ore consists of iron ore, especially hematitic or agne- titic iron ore, particularly an iron ore obtained by grinding and wet process benefication. 4. A process according to any of the preceding claims, characterized in that at most 5% and preferably at most 2% of the micropelletized material has an agglomerate size above 5 mm and preferably most 20 or at most 10% of the material has an agglomerate size below 0.5 mm. 5. A process according to any of the preceding claims, characterized by subjecting the micropelletized material immediately after pelletizing to storing in a layer with a layer hight of at most 10 m and preferably at most 5 m for at least 1 day and preferably until the increase of the quanti¬ ty of material with an agglomerate size below 0.42 mm when subjected to free fall four times from a fall height of 15 m is below 20%, said storing being performed prior to transporta¬ tion of the micropelletized material to and charging on an down-draught sintering device. 6. A process according to any of the preceding claims, characterized by charging the microp.elletized material in said down-draught sintering process with a bed hight of at least 35 cm and preferably at least 40 cm, especially at least 50 cm.

Inventors: LINDER R
Applicants: LINDER R, SSAB DIVISION GRUVOR
Application year: 1981
Main classification: C22B1
IPC codes: C22B1