WO1980002566A1

WO1980002566A1 - A process for bonding agglomerates

Info

Publication number: WO1980002566A1
Application number: PCT/SE1980/000144
Authority: WO
Inventors: L Roos
Original assignee: L Roos
Priority date: 1979-05-16
Filing date: 1980-05-16
Publication date: 1980-11-27
Also published as: EP0028649A1; JPS56500693A; NO810147L

Abstract

Process for producing agglomerates, especially rolling balls, of a particulate inorganic material especially an ore material, and is characterized by the addition to the agglomerated material of an inorganic fibrous material.

Description

A PROCESS FOR BONDING AGGLOMERATES.

This invention is related to a process bonding agglomerates of particles of preferably inorganic materials. The invention is characterized by the inclusion into agglomerates of fibres, namely of inorganic materials, such as mineral fibres which may consist of glass fibres, rockwool fibres, slag wool fibres, etc. Preferably fibres of rockwool,stonewcol, or slagwool type are used, prepared e.g. by melting basalt, greenstone, diabase or similar minerals or species of stone, or slag, e.g. with the addition of lime, dolomite or similar materials.

The use of fibres as a binder for agglomerates can be practiced for a plurality of particle types, especially of inorganic materials, especially ores and ore concentrates, such as iron ores, e.g. hematite, magnetite or other iron oxide materials comprising one or more of the oxides FeO,

Fe₃O₄ and Fe₂O₃ as well as other iron oxide materials, such as hydrated oxides, etc.

Other suitable materials are ores of nickel, cobalt, copper, zinc, lead, tungsten, etc. as well as other materials in agglomerated form, e.g. catalyst materials or carriers for catalyst materials, such as alumina.

The grain size of the agglomerated material may vary within broad limits, e.g. up to 1 mm or up to 0.5 mm, preferably up to 0.1 mm, up to 0.05 mm or up to 0.01 mm. The lower limit may also vary within broad limits, e.g. down to 0.1 mm, down to 0.05 mm, down to 0.01 mm or down to 0.001 mm. The upper and lower limits resp. may relate to 100 % of the material but also to a range of e.g. 90 %, 75 % or 50 % of the weight of the material. Also finer or coarser materials may, however, be included in the agglomerates, provided that said materials can be agglomerated. Agglomeration methods of various types may be used, preferably rolling of particled materials to balls or pellets in devices comprising drums, cones or discs.

Agglomeration by rolling to bolls is usually performed with the addition of a liquid, preferably water or an aqueous solution of organic or inorganic materials. It is also possible to include other binders which are commonly used for agglomeration, such as organic glues of various types, especially polymeric materials, such as cellulose and cellulose derivatives, starch materials, curable resins, etc., and inorganic additives, such as bentonite or other clays, lime, cement, such as Portland cement, slag cement, alumina cement. The quantity of said binders may be maintained within the normally used ranges or may be decreased, e.g. to not above 50 or 20 % of the quantities normally used. Fibres which are chemically resistent against cement can be us

The expression "fibres" when used in relation to this invention is intended to include elongated bodies having an extension in the longitudinal direction of at least 5, preferably at least 10 times the extension in any other direction perpendicular thereto. The cross section shape perpendicularly to the longitudinal direction may vary depending upon the method of production but is preferably about circular or with a ratio largest diameter:smallest diameter in the cross section, passing through its point of gravity of not above 5:1, preferably not above 3:1 and especially not above 2:1.

The average diameter of the fibres perpendicularly to the longitudinal direction may vary within broad ranges depending upon the method of production. Preferably at least 90 % of the fibres have a thickness below 1 mm, especially below 0.5 mm and particularly below 0.1 mm or below 0.05 mm. A common upper limit of the thickness is 0.025 mm or even 0.015 mm, sometimes 0.005 mm. The percentage figures may be based on the longitudinal extension of those parts of the fibres having a diameter within said ranges.

Common values of average fibre diameter for mineral fibres are 1 - 10 microns and especially about 2 - 8 microns, particularly about 5 microns.

The lenght of the fibres may vary depending upon the material to be agglomerated. Common upper limits for 100 % and especially 90 % of the fibre quantity is up to 20 mm or up to 10 mm but also shorter fibres such as up to 5 mm, up to 3 mm, up to 1 mm or up to 0.5 mm may be used, in which case preferably at least 50 % and especially at least 90 % of the fibres are shorter than said upper limit values. The fibre length is adapted together with the fibre diameter for the forming method used. The lower limit of the fibre diameter is often 0.1 mm, 1 mm and preferably 5 mm, said lower limits preferably being the lower limit of at least 50 % and preferably at least 90 % of the amount of fibres.

The fibres can be prepared e.g. by forming a melt to fibres by drawing through spinning nozzles, by. forming a stream of a melt to fibres with a rotating drum, rotating disc, rotating wheel,, by blowing a stream of melt to fibres or by combining said methods, such as desintegration of a stream of melt on a wheel or a disk combined with blowing through nozzles.

The composition of mineral fibres may be varied within broad limits and examples of suitable ratios are stated in the following table:

Further examples are stated in the following table. The contents of SiO₂, Al₂O₃, MgO and CaO may vary with 5 % above or below the stated values and the other constituent are optional.

Especially preferred are fibres of rockwool type prepared from basic rocks, e.g. greenstone, basalt, diabase, optionally with addition of lime or dolomite, preferably in a quantity of up to 30 %, e.g. 10 to 20 % by weight. Said fibres may have the following chemical composition in % by weight: SiO₂ 45, Al₂O₃ 14, CaO 20, MgO 7, FeO 6. The contents of said constituents may vary with - 5 %, preferably - 10 % of the content values stated above. Other constituents may consist of other oxides, such as MnO , Na₂O , K₂O , TiO₂ , BaO , B₂O₃ , etc .

The quantity of fibres in the agglomerates preferably is not above or up to 20 % by volume, especially not above 10 % by volume and particularly not above 5 % by volume, but also lower contents, such as not above 2 % by volume or not above 1 % by volume can be used. The lower content limit is preferably at least 0,01 % by volume, especially at least 0,05 and particularly 0,1 % by volume, but also higher contents, such as 0,5 or 1 % by volume can be used as lower content limits. Suitable content ranges are e.g. 0,1 - 5 and especially 0,25 - 2,5 % by volume. Said values are based on the solid materials . volume of the agglomerate particles and the fibres .

The agglomerated particles preferably are of a comparatively spherical shape, e.g. with a difference between the largest and smallest dimension (especially diameters passing through the middle point or point of gravity) of in average not above 5:1.

The fibres can be included homogeneously within the entire volume of the agglomerates or can be distributed with differing fibre density within various parts of the agglomerates, e.g. within average more than 50 % or 75 % of the fibre volume within an outer layer comprising less than 50 % or less than 25 % of the volume of the particle.

The direction of the fibres within the agglomerates may be random or directed or arranged in layers. More than 50 and especially more than 75 % by volume of the fibres may be directed radially or within 30° from a radial direction in the agglomerates or may be directed tangentially or within 30 or 60 from a tangential direction in the agglomerates if the shape of said agglomerates is approximated with the shape of a sphere. The agglomerates may also comprise at least 25, e.g. at least 50 and also at least 75 % by volume of the fibres distributed within more than one and preferably two or three concentric layers. Preferably the fibres within said layers are arranged randomly or predominantly tangentially, e.g. with more than 50 or more than 75 % of the fibres (fibre mass) directed within 60 and preferably within 30 from the tangential direction. Said layers comprise preferably at least 10 %, e.g. at least 25 % or at least 50 % of the total agglomerate volume, and each of said layers preferably comprises at least 5 %, e.g. at least 10 % or at least 25 % of the volume of the agglomerate. The extension in the thickness direction of said layers in relation to the radial extension of the agglomerates may also be at least 5 %, e.g. at least 10 % or optionally at least 25 % or at least 50 % of the radial extension of the agglomerates from an imagined central point or point of gravity. Said values can be related to layers comprising fibres which are arranged alternating with layers free from fibres, or be related to layers with increased content of fibres in relation to adjacent layers.

The size of the agglomerates, especially agglomerates prepared by rolling balls (balling) may amount to e.g. not above 50 mm, preferably not above 40 mm and especially not above 30 mm and optionally particularly not above 15 mm in diameter. The lower limit of the diameter of the agglomerates may also be e.g. above 2 mm, preferably above 5 mm and especially above 8 or 10 mm. Suitable ranges are especially for iron ore balls, e.g. 5 - 20 mm or 10 - 30 mm.

The fibres may be added entirely or partly to the starting material which is subjected to agglomeration, e.g. rolling (balling), e.g. added to an aqueous suspension or pulp of particles prior to dewatering, e.g. fine iron ore particles prior to dewatering, after grinding or benefication or optionally in the benefication step. Fibres added to an aqueous suspension of particles may facilitate the removing of liquid, e.g. dewatering of an aqueous suspension of an ore concentrate. The fibres may also be added entirely or partly prior to or during the agglomeration step, especially rolling to balls (balling). It is also possible to prepare by rolling or balling balls with one or more layers with a high content of fibres alternating with one or more layers with low fibre content or without fibres, especially if the agglomeration or balling (rolling of balls) is performed in several steps with sieving and removal of balls with a size exceeding a certain minimum value in one or more steps followed by a continued balling, in which process the fibres may be added in one or more of the ball rolling (balling) steps or between the ball rolling steps. Fibres may suitably also be added in a later part of a ball rolling step, e.g. close to the outlet from the step so that the fibres are included in the outer part of the agglomerate layer applied in said step, e.g. in a drum (cylinder), cone or disc for rolling of balls (balling) . The agglomeration device may also be operated so that the larger agglomerates in the charge are concentrated in a part of the charge, preferably at the surface of the charge, in which case the fibres may be added preferably to the larger or nearly ready agglomerates (balls).

It is also possible to add a lower quantity by volume of fibres in a first ball rolling (balling) step and a higher content by volume of fibres in a subsequent ball rolling step.

It is especially suitable to perform a finishing ball rolling step or a fibre application step in which fibres are included in a surface layer of the ball for bonding said ball.

It is also possible to add fibres of different composition and/or dimensions, such as thickness and lenght, uniformly and homogeneously within the agglomerates (the expression "agglomerate" comprises in this connection as well as in other connections covered by this invention also balls or pellets,.incl. micropellets < 6-8mm, made by rolling) or uniformly distributed within the same layer of the agglomerates, or optionally fibres of different composition and/or dimensions may be used within different parts of the agglomerates. The fibres may comprise fibres with a low melting point or softening point, preferably below 1000ºC and especially below 800°C, e.g. within the range 500 - 700°C, and fibres of high melting point or softening point, preferably above 1000°C and especially above 1200ºC, in which case the fibres may be distributed within the same parts of the agglomerates or distributed within different parts of the agglomerates. According to one embodiment fibres with low softening point which makespossible good bonding to the particles at a low temperature, are distributed within an outer part of the agglomerates, optionally together with fibres of high softening point, in order to make certain that good bonding at low temperatures is obtained, especially low temperature reduction of the outer part of the iron ore pellets after sintering at low temperature.

The fibres may be added to the agglomerates with production of the fibres in immediate vicinity to the point of addition, e.g. the agglomerating device, and transport of the fibres produced directly to said point, e.g. by air or gas transportation.

It is also possible to modify the surface of the fibres by adding e.g. powderous materials to the fibre surfaces immediately after the fibre forming when the fibres are still in a formable condition, so that the added powderous material is hot bonded to the fibres. The added or applied powderous material may be used for increasing the friction between the fibres and the agglomerated particulate material or may consist of a material which when heated or under the influence of humidity acts as a binder between the fibres and the agglomerated material. Examples of powderous materials which can be added to the fibres are silica, water glass and lime.

For the agglomeration of ores, especially iron ores, it is preferable to use a fibre composition which makes it possible to leave out slag forming constituents entirely or partly from the agglomerates or from the charge in which said agglomerates are included. In this way onm may produce e.g. so-called self-fluxing balls or pellets having a desired ratio (Ca,MgO):SiO₂ (basicity). The basicity may be low (acid balls or pellets), e.g. 0 - 0.5 or up to 0.8 or 1.0, average basicity, e.g. 0.5 - 1.5 or 0.8 - 1.2, and high basicity, e.g. 1.0 - 2.0 or above, e.g. 1.2 - 1.6 or 1.2 - 1.4. Also higher values, e.g. 1.5 - 4 or 1.8 - 3.5, e.g. 2 - 3 may be used. The ratio CaO:CaO+MgO may vary e.g. from 1 to 0.2 or from 0.9 to 0.4, e.g. from 0.8 to 0.5.

Example

When agglomerating (pelletizing) a magnetite concentrate to balls (pellets) by rolling (balling) in a drum, rockwool fibres prepared from a basaltic rock with a softening point of about 1000 - 1100°C. are added. Said fibres are prepared by desintegrating a stream of melt on a rapidly rotating disc and exhibits an average fibre diameter which is essentially within the range 1 - 5 microns. The fibres are added to the magnetite concentrate A) prior to the addition to the pelletizing drum (ball rolling drum)

B) in the ball rolling step performed in said drum, and

C) through a combination of said two measures. The total quantity by weight of added fibres is in different experiments, is 0 ,25 , 0,5 , 1 / 2 ,3-and 5 % by weight. In experiment C) 25,50 and 75 % of the fibre weight was added in the first step in different experiments and the rest in the second step. Fibres with composition A to I and a to g in the tables were tested under the same conditions. The ba 11s are rolled or pelletized to a smallest final size of 10, 15 and 20 mm. In each case an improved quality of the balls (pellets) is obtained, especially in the crude condition but also after firing.

The same experiment is performed with hematite ore concentrate and with a starting material consisting of a hematite ore concentrate and coal breeze in a quantity which is required for firing.

Furthermore, the addition of bentonite in a quantity of about 0.5 and especially 1 % under the conditions stated above is tested and the good results are maintained, and improved.

Experiments with the same kind of basalt fibres were performed by pan sintering of hematitic and magnetitic iron ores.. Additions of 0.1, 0.3, 0.5, 0.75, 1 and 2 % by volume of the fibres were tested. Also in this case the product quality was improved.

Furthermore, balls (pellets) were prepared by the method stated above from hematite ore concentrate and magnetite ore concentrate with a reducing agent mixed into the balls and with the addition of fibre material of the types stated above. The quantity of reducing agent was in this case varied between 20 and 200 % of the quantity required for complete reduction and comprised in various different cases 20, 40, 75, 100, 150 resp. 200 % of said quantity. As a reducing agent coke breeze and coal breeze were used.

Furthermore, balls prepared according to the invention from iron ore concentrates were tested for use in various metallurgical processes, such as the blast furnace process, the electro steel furnace processes, oxygen blast processes, such as the LF-process, the caldo process, the Thomas process, the Martin process. Balls according to the invention with a high content of reducing agent may also be used for direct reduction processes in which the reducing agent in the balls contributes to reduction, e.g. reduction processes performed in a rotating furnace or a shaft furnace.

The produced balls, which may or may not comprise reducing agents and may or may not comprise cold bonding agents (cold binders) and with or without a preliminary sintering are also suitable for various types of direct reduction processes performed with a reducing gas, such as the Wiberg-process, the HL-process and similar processes, in which case the reduction may be performed in a moving or stationary bed, e.g. in a shaft furnace or in charge-wise charged furnaces in which the ball or pellet bed is maintained stationary in the- reduction step.

An especially suitable use is for the reduction in a blast furnace, in which case the fibre* material may optionally partly and preferably to at least 50 % exhibit a high softening point exceeding 1000ºC and especially exceeding 1100 or 1200°C in order to counteract a tendency of the balls to sag, shrink and agglomerate in theproduction step, especially at 1000 - 1100°C. Preferably the composition oi fibre material is.adapted so that the material at higher temperatures, e.g. above 1200 and above 1300ºC gives rapid melting within a restricted temperature range.

In all the processes referred to balls (pellets) and other agglomerated or sintered products according to the invention comprising the fibre materials referred to as strenght increasing agent or fortifying agent and porosity improving agent may be. used as substitute for balls (pellets) and agglomerated products of iron ore concentrates and similar, such as roasted pyrites, in the quantities and in the manner in which such previously used products have previously been used.

As examples of furnaces in which products according to the invention can be used reference can be made to blast furnaces in which heat is involved by burning a fuel, electric blastfurnaces, electric pigiron furnaces, optionally with prereduction, such as prereduction in a rotating furnace or shaft furnace, low shaft furnaces, melt reduction furnaces, LD-converters and other furnaces operating with injection of oxygen or other oxidizing gases, optionally in combination with or together with protective gases, such as argon, water vapour, hydrocarbons and similar, injected . against the surface of the charge and/or through nozzles arranged under the level of the melt especially in the furnace bottom. Examples thereof are the caldo furnace and the dored furnace.

As examples of other minerals which can be treated in the process according to the invention reference may, in addition to the materials mentioned above also be made to ores and minerals comprising chromium, aluminum, manganese, vanadium, uranium, tin, antimony, bismuth, silver and gold.

The process according to the invention is especially suited also for the production of chromium by a process which comprises the preparation of agglomerates from various kinds of chromium ores, e.g. by ball rolling (balling, pelletizing) or briquetting, comprising fibres according to the invention in the quantities mentioned above, e.g. the Cobond-process comprising autoclave leaching at about 200°C.

The addition of fibres according to the invention can also be used for all the materials and minerals stated above in a dewatering step, e.g. by filtering or suction filters and similar devices, when forming the agglomerates, e.g. by ball rolling (balling, pelletizing) or briquetting, e.g. in briquetting presses or by extrusion, the fibre material being included homogeneously or in layers in various manners as disclosed above. The inclusion of a fibre material may also be used for facilitating processes comprising contact with a liquid, such as leaching minerals from the metals stated above or removing unwanted constituents or for recovering dissolvable desired constituents, e.g. by leaching with acid or basic compounds, optionally after a preceeding heat treatment, such as oxidation or reduction by heating in oxidizing or reducing environment.

When using fibres in agglomerates of iron ore and also in other agglomerated products it is for commercial reasons suitable to reduce the content of fibres, preferably to less than 2 or 1 % by volume, especially to not above 0.5 or optionally not above 0.25 % by volume and especially to less than 0.1 % by volume, said contents being related to the real dry volume of solid materials.

When producing an agglomerate , e . g . rolled balls or pellets , especially from iron ore it may be preferable at least 25 % , preferably at least 50 or 75 % of or optionally the entire fibre quantity to the particles prior to forming the agglomerate , e . g . immediately prior to the formation of the agglomerates or into a wet pulp prior to or after dewatering .

Metallurgical slags can be used for making the fibres , e.g. a slag with a higher purity level then the slag normally formed in the process for which the bonded agglomerates are intended to be used as starting material or additive , e.g. slag from an electro-steel furnace e.g. when producing agglomerates of e.g. iron ore for e.g. a blast furnace charge or a steel furnace charge.

Other examples of slag types which can be used for forming fibres suitable for this invention are blast furnace slags, Thomas process siags, slags , Siemens-Martin slags, copper shaft furnace slags, lead shaft furnace slags , etc. Examples of composition ranges are stated in the table below in which the figures relate to composition in % by weight. The rest of the composition up to 100 % may consist of other oxides.

It is usually preferable , especially when making agglomerates comprising iron compounds intended for the production or iron or steel , to reduce the content of alkali metals to a low level, e.g. below 5%, preferable below 3 % and especially below 2% or 1% of the weight of the fibres.

As stated previously the fibres may be combined with other measures or means for bonding agglomerates, such as bonding by heating to hich temperatures,e.g. by heating to above 500, 700, 800 , 900 or 1000°C in which case it is often possible to reduce the bonding temperature with at least 50, preferably at least 100 or at least 200°C cαrpared with the temperature normally used for bonding the same agglomerates without fibres. For many types of agglomerates , especially based on iron compounds heating to not above 1300, not above 1200, not above 1100, not above 1000, not above 900 or not above 800°C may be sufficient. Other bonding methods in which addition of fibres may be used are hydrothermal bonding comprising a hydrothermal reaction especially at temperatures up to 200, 300, 400 or 600ºC with constituents in the agglomerated material and/or the fibres.Furthermore hydraulic binders,e.g. cement, such as portland cement may be combined with the addition of fibres according to the invention, e.g. the "type and amounts of binders used in the so called "Grangcold" method. Suitable contents , e.g. for preparing iron compound agglomerates are e.g. 0,05- 0,1 to 5 and especially 0,5 to .3% byweightof fibres and 1 to 20,e.g from 2, 4 , 6 or 8 up to 20,15 , 10, 8 , 6 or 4 % by weight of cement.

Claims

CLAIMS :

1. A process for producing aggglomerates ,e.g. by rolling balls, pressing briquettes etc. of one or more particulate inorganic materials, e.g. ore materials, characterized by including into the agglomerates one or more fibrous inorganic materials

2. A process according to claim 1, characterized in that the fibres consist of rockwool, diabase wool, slagwool and/ or glass wool.

3. A process according to claim 1 or 2, characterized in that the agglomerated ore material consists of oxidic, sulphidic or hydroxidic ore material, especially an ore material comprising one or more of the valuable constituents iron, nickel, cobalt, copper, zink, lead, tungsten, chromium, aluminum, manganese, vanadium, uranium, tin, antimone, bismuth, silver, gold.

4. A process according to any of the preceding claims, characterized in that the quantity of fibres is up to 10 %, especially up to 5 % and preferably up to 2 % by volume, preferably at least 0.1 %, optional at least 0.2 % and especially at least 0.5 % by volume, calculated on the solid material.

5. A process according to any of the preceding claims, characterized by including the fibres into the agglomerated material when said material is present as an aqueous dispersion and/or before, during and/or after forming the material to agglomerates.

6.A process according to any of the preceding claims,characterized in that the fibres are included homogenously in the agglomerates or with increassd content within one or more concentric layers in the agglomerates , especially within a surfrace layer of at most 50% by volume.

7. A process according to any of the preceding claims characterized in that at least 50% and preferably at least 90% of the fibres have a thickness of between 0,1 and 20 microns, especially between 1 and 10 microns, and a length of up to 50 mm, preferably up to 20 mm and especially up to 10 mm. up to 5, up to 3 , up to 1 or up to 0,5,mm.

8. A process according to any of the preceding claims, characterized by agglomerating iron ore or iron oxide , especially hematitic or magnetitic iron ore, the quantity and composition of the fibres being selected so that the agglomerates exhibit a composition which is suited for a reduction or smelting process , especially so called self fluxing agglomerates. or agglomerates having a basicity (CaO+MgO/SiO₂) above 1, above 1,5 above 1,8 or above 2.