Binder formulations

Abstract

A binder formulation for iron ore pellets, the formulation comprising one or more silicates and a processing aid; a pellet, wherein the pellet comprises the binder preparation; and a method for producing iron ore pellets, the method comprising mixing the binder formulation with particulate iron ore and forming pellets.

Description

[0001] This application is a divisional application of an application with an application date of August 15, 2019, application number 201980068528.3, and invention name “Binder Preparation” (PCT / GB2019 / 052292, national phase entry date April 16, 2021). Technical Field

[0002] The present invention relates to a binder formulation for iron ore pellets, in particular to a binder formulation comprising silicate, iron ore pellets comprising the binder formulation and a method for preparing the same. Background Art

[0003] The production of briquettes from particulate iron ore and other metal ores is well known in the art. Breakup of the agglomerated briquettes is common and a binder (such as cement or clay) is often used to bind the particles together in the hope of improving strength.

[0004] Such briquettes are used in blast furnaces or direct iron reduction (DRI). Briquettes are designed to be strong enough to allow the briquettes to be successfully transported and used in a blast furnace. The briquettes must be able to maintain their integrity through the blast furnace into the melting furnace, otherwise the performance of the blast furnace or DRI equipment may be adversely affected. A problem associated with the use of cement or clay is that this increases the amount of silica in the iron and slag produced at the end of the process.

[0005] The high strength required for such agglomerates limits the use of more expensive binders, such as starch or polyvinyl alcohol (PVA), and it is therefore desirable to provide a cost-effective alternative to existing binder formulations that can provide excellent agglomeration, rapid solidification, and excellent green strength. Summary of the invention

[0006] The present invention is directed to overcoming or ameliorating at least some of these problems.

[0007] Therefore, in a first aspect of the invention, a binder formulation for iron ore pellets is provided, the formulation comprising one or more silicates and a processing aid. It has been shown that the presence of silicates contributes to agglomeration and solidification, which is believed to be due to the promotion of ion exchange between silicate counterions (e.g., sodium) and iron in the iron ore. This results in rapid hardening and excellent green strength, reduces the required solidification time before conveying the agglomerates, and reduces losses during transportation and use in blast furnaces. The inclusion of silicates eliminates the need for an undesirable step of heating the pellets to harden them or a step of comprising a chemical curing agent. The heating step is undesirable because it increases the complexity of the pellet formation process and the energy required increases the cost; chemical curing agents are also typically expensive or require further processing steps (such as the case of using carbon dioxide solidification), so it is advantageous to avoid their use.

[0008] Typically, silicates include Group I silicates or Group II silicates, typically sodium silicate or calcium silicate. It has been found that sodium silicate may be particularly beneficial due to ionic instability. Sodium silicate is also readily available and cheap. In the case of use, the Na:Si ratio of sodium silicate can be greater than 2.5 or 2.8, because at these ratios, the best balance between the viscosity of the dispersion and rapid solidification is obtained. Typically, silicates are present in the range of 60% to 98% by weight, typically 75% to 95% by weight of the formulation. At these levels, rapid solidification is observed, resulting in excellent green strength after the shortest time from pellet formation.

[0009] It should be noted that the term "pellets" includes objects commonly referred to as pellets, bars, pencils slugs. Pellets typically have a maximum average diameter of 20 mm, more typically 16 mm or 15 mm, a minimum average diameter of 2 mm, especially 5 mm, or an average diameter of 10 mm to 12 mm. The common feature of these objects is that they are in a compacted form of material, and they differ mainly in their size and shape.

[0010] The processing aid may comprise an additive selected from the group consisting of a polysaccharide, a cellulosic thickener, and a combination thereof. Typically, the polysaccharide and / or cellulosic thickener is selected from the group consisting of guar gum, gum arabic, xanthan gum, starch, hydroxyethyl cellulose, methyl cellulose, methyl hydroxyethyl cellulose, and a combination thereof. It has been found that these processing aids both thicken and stabilize the pellets, reduce chemical degradation, and improve shelf life. In addition, the selection of non-cement-based processing aids eliminates the common problem of increased slag produced during iron processing, and a feature of the present invention is that no cement-based or clay-based processing aids need to be added. Guar gum and methyl hydroxyethyl cellulose are typically used because it has been found that these processing aids not only help process iron ore into pellets, but can also further improve green strength relative to pellets containing only silicates. Guar gum can be used in situations where the environmental certification of iron ore pellets is important because it is a natural product. The processing aid may be present in the formulation in the range of 5 to 25 wt % or 10 to 20 wt % of the formulation and it has been found that in the case of extrusion processing, these levels of processing aid prevent extruder failure due to plugging or other particulate matter entering the structure of the extrusion machine.

[0011] There can also be a setting agent, which can promote the polymerization of silicates, thereby causing gelation and enhanced agglomeration. The setting agent can be selected from triacetin, glycidyl trimethoxysilane, pyrogenic silica, potassium methylsiliconate and combinations thereof. Typically, the setting agent comprises glycidyl trimethoxysilane because it provides excellent adhesion. The setting agent can exist in the range of 0.5 % by weight to 1.0 % by weight of the binder formulation.

[0012] For example, trace amounts of surfactants such as SLS (Sodium Lauryl Sulphate) may be added to improve the wetting of the iron driven by the additive.

[0013] Waterproofing agents may be used to enhance the weatherability of the pellet material. The waterproofing agent may be combined with the granular material (e.g., by spraying) or as a layer on the outer surface of the pellet. Waterproofing agents include, for example, styrene-acrylate copolymers and asphalt emulsions.

[0014] The binder formulation may be premixed so that the entire formulation is then added to the granulated iron ore during pellet production, thereby providing a "premixed" binder product. Alternatively, the binder formulation may be prepared in situ so that the individual components are added directly to the granulated iron ore where they are mixed with each other and with the iron ore. For example, a processing aid may be added to the iron ore before the silicate, or the silicate may be added before the processing aid. Where the silicate is added before the processing aid, a strong bond is formed between the silicate and the iron, thereby increasing the rate of solidification.

[0015] In a second aspect of the invention, iron ore pellets are provided, comprising a binder formulation according to the first aspect of the invention. The pellets may comprise a range of 1 wt % to 10 wt %, typically 2 wt % to 6 wt % silicate, and independently 0.1 wt % to 2 wt % or 0.5 wt % to 1.5 wt % processing aid. At these levels, the pellets have been found to agglomerate well, be easily processed (particularly by extrusion), and exhibit rapid solidification and green strength.

[0016] The pellets will also contain granular iron ore, which is typically 4 mm or less in diameter, more typically less than 1 mm, or less than 500 μm, or less than 100 μm. This can be determined by being able to pass through a sieve. Typically, at least 10% by weight of the granular material is able to pass through a 100 μm sieve before being formed into pellets. More typically, a sieve size of 30 μm or 20 μm is used to sieve the material. At least 50%, 80%, or 100% of the material can pass through the sieve.

[0017] Typically, iron ore is tailings or dust from, for example, an electric arc furnace. The ore can be magnetite (Fe 3 O 4 ) and / or hematite (Fe 2 O 3 ). Iron ore may contain naturally occurring contaminants.

[0018] The pelletized iron ore may have a moisture content of less than 50%, more typically less than 30% or less than 25%. Typically the moisture content is at least 2% by weight or at least 5% by weight or 10% by weight.

[0019] In a third aspect of the invention, there is provided a method for producing iron ore pellets, the method comprising: mixing a binder formulation according to the first aspect of the invention with granulated iron ore; and forming pellets. Typically, the pellets are formed using a method selected from the group consisting of extrusion, pot pelletizing and briquetting, all of which are known in the art.

[0020] Typically, a twin-shaft batching mixture is used to agglomerate the mixture. In general, a press or extruder is typically used to form pellets. The most common situation is that extrusion technology, particularly low moisture content extrusion (also referred to as stiff extrusion) technology, is used. It has been found that in extrusion, particularly in stiff extrusion technology, the use of the binder formulation significantly reduces the blocking or clogging of the extruder, minimizing processing downtime. In addition, the heat generated by the extrusion process of the mixture dries the mixture, and the ion exchange between the silicate and the iron in the iron ore promotes agglomeration and therefore consolidation. This combination allows the production of strong pellets, which can be ready for transportation soon after production because they require the shortest curing time.

[0021] The pellets are usually cold formed, for example without sintering, or heating to above 60°C, or above 40°C, or 30°C, before being placed in a furnace.

[0022] Depending on the amount of compaction required, the amount of compaction of the pellets can be varied, for example, by subjecting the mixture of granulated iron ore and binder formulation to a greater or lesser vacuum. A greater vacuum will increase the compaction of the pellets. Alternatively, this can be controlled by the amount of pressure used to form the pellets.

[0023] A binder formulation for iron ore pellets, the formulation comprising: sodium silicate in a range of 75 wt % to 95 wt %; a processing aid selected from the group consisting of guar gum and methyl hydroxyethyl cellulose and combinations thereof in a range of 5 wt % to 25 wt %; and a consolidating agent comprising glycidoxypropyltrimethoxysilane in a range of 0.1 wt % or 0.5 wt % to 1.0 wt %.

[0024] Iron ore pellets comprising the binder formulation, the pellets comprising sodium silicate in the range of 1 wt% to 10 wt% and guar gum and / or methyl hydroxyethyl cellulose in the range of 0.1 wt% to 2 wt%.

[0025] A method for producing iron ore pellets, the method comprising: mixing the binder formulation with granulated iron ore; and forming pellets by extrusion.

[0026] Unless otherwise stated, each integer described may be used in combination with any other integer, as will be understood by those skilled in the art. Furthermore, while all aspects of the present invention preferably "include / comprise" the features described in relation to that aspect, it is specifically contemplated that they may "consist of" or "consist essentially of" those features outlined in the claims. Furthermore, unless expressly defined herein, all terms are intended to be given their meanings as commonly understood in the art.

[0027] Furthermore, in the discussion of the present invention, unless otherwise indicated, the disclosure of optional values ​​for the upper or lower limits of the permissible range for a parameter should be interpreted as an implicit statement that each intermediate value (between the smaller and larger alternative values) of the parameter is itself also disclosed as a possible value for the parameter.

[0028] Furthermore, unless otherwise indicated, all numerical values ​​appearing in this application are to be understood as being modified by the term "about".

[0029] In order to more easily understand the present invention, reference will be made to Figure 1 The present invention is further described in detail with reference to the following specific examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Graph showing green strength of pellets containing silicate (dashed line) relative to pellets not containing silicate (dotted line). DETAILED DESCRIPTION

[0031] Iron ore composition

[0032] Analysis of Fe 2 O 3 and Fe 3 O 4 The results are as follows.

[0033] Fe CaO <![CDATA[SiO 2 ]]> MnO <![CDATA[Al 2 THE 3 ]]> <![CDATA[P 2 THE 5 ]]> <![CDATA[K 2 The]]> <![CDATA[TiO 2 ]]> <![CDATA[Na 2 The]]> <![CDATA[Cr 2 THE 3 ]]> A 68.3 0.1 4 0.15 1.69 0.06 0.1 0.4 0.1 B 68.9 0.1 1.35 0.1 3.35 0.07 0.1 0.1 0.1 C 66.6 0 3.98 0.15 1.73 0.06 0 0.1 0 0 D 67.5 0 1.3 0.1 3.43 0.08 0 0.1 0 0 E 68.35 5.2 0.1 0.65 0.1 0 0.1 0 0.2

[0034] The analysis of Samples A and B was performed by the Materials Processing Institute, and the analysis of Samples C to E was performed by the Advanced Metallurgical Group.

[0035] Tested pellet composition

[0036]

[0037] Pellet formation

[0038] Guar gum was added as a powder to the granulated iron ore in a twin-shaft mixer and mixed at high speed. Sodium silicate was then added under stirring. Once a uniform mixture was formed, the mixed batch was extruded using an Edwards and Jones extruder under vacuum (-600 mbar to -1000 mbar) to provide 16 mm densely agglomerated pellets. Prior to testing, the pellets were placed at 30°C to cure for 24 hours.

[0039] Test Method

[0040] The pellets were compared for compressive strength, impact resistance and sinter degradation during reduction. The tests were completed according to the British Standards Institution test guidelines.

[0041] test British Standards ISO Number Compression strength Cold crushing strength 4700 Impact resistance Drum index 3271 Sinter Deterioration Reduction powder 4696-1 and 4696-2

[0042] The results were verified by two independent laboratories, the Materials Processing Institute and the Advanced Metallurgical Group.

[0043] A "drop test" was also completed, which involved repeatedly dropping the pellets from a height of two meters until the pellets broke upon impact. The results are shown in Figure 1 middle.

[0044] Test Data

[0045]

[0046] *Samples of the same preparation, three replicates are shown in the table

[0047] A single formulation sample was tested three times to ensure repeatability. In all cases, the results were above the industry standard for iron ore pellets.

[0048] Specifically, it is desired that the iron ore pellets have a cold crushing strength of greater than 200 kgf, a tumble index value of greater than 90%, an abrasion index value of less than 10, and a reduction pulverization index value of less than 10.

[0049] It can be seen that these values ​​were exceeded for all tests, with the pellets showing particularly good compression green strength, excellent wear characteristics and resistance to sinter degradation.

[0050] Processing Enhancement

[0051] It was observed that in the absence of guar gum, processing was significantly more difficult and the extruder frequently broke down or was overloaded.

[0052] Strength of pellets containing silicates

[0053] Figure 1A comparison between pellets containing silicates and pellets without silicates when repeatedly dropped until broken is shown. Over time, pellets containing silicates show a significantly increased number of drops required to break the pellets, indicating superior green strength relative to pellets without silicates. Specifically, after 400 minutes, pellets without silicates will only survive an average of 3 drops, relative to an average of 2 drops that pellets without silicates survived immediately after production (t=0). In contrast, after only 350 minutes, pellets containing silicates survived an average of 6 drops, relative to an average of 3 drops that pellets containing silicates survived immediately after production.

[0054] It will be appreciated that the methods and formulations of the present invention can be implemented in a variety of different ways, only a few of which have been illustrated and described above.

[0055] This application also involves the following aspects:

[0056] 1. A binder formulation for iron ore pellets, the formulation comprising one or more silicates and a processing aid.

[0057] 2. The formulation of aspect 1, wherein the silicate comprises a Group I silicate or a Group II silicate.

[0058] 3. The formulation according to aspect 1 or aspect 2, wherein the silicate comprises sodium silicate.

[0059] 4. The formulation according to any preceding aspect, wherein the silicate is present in the range of 75% to 95% by weight of the formulation.

[0060] 5. The formulation according to any preceding aspect, wherein the processing aid comprises an additive selected from the group consisting of polysaccharides, cellulosic thickeners, and combinations thereof.

[0061] 6. The formulation according to aspect 5, wherein the polysaccharide and / or cellulose thickener is selected from guar gum, gum arabic, xanthan gum, starch, hydroxyethyl cellulose, methyl cellulose, methyl hydroxyethyl cellulose and combinations thereof.

[0062] 7. The formulation according to any preceding aspect, wherein the processing aid is present in the formulation in the range of 5% to 25% by weight of the formulation.

[0063] 8. The formulation according to any preceding aspect, further comprising a consolidating agent.

[0064] 9. The formulation according to aspect 8, wherein the consolidating agent is selected from the group consisting of triacetin, glycidoxypropyltrimethoxysilane, fumed silica, potassium methylsiliconate, and combinations thereof.

[0065] 10. Iron ore pellets comprising a binder formulation according to any preceding aspect.

[0066] 11. The pellets according to aspect 10, comprising silicate in the range of 1 wt% to 10 wt%.

[0067] 12. The pellets according to aspect 10 or aspect 11, comprising a processing aid in the range of 0.1 wt% to 2 wt%.

[0068] 13. A method for producing iron ore pellets, comprising:

[0069] a. mixing the binder formulation according to any one of aspects 1 to 9 with granular iron ore; and

[0070] b. Forming pellets.

[0071] 14. The method of aspect 13, wherein the pellets are formed using a method selected from the group consisting of extrusion, pan pelletization, and briquetting.

Claims

1. A binder formulation for iron ore pellets, the formulation comprising one or more silicates and a processing aid.

2. The formulation of claim 1, wherein the silicate comprises a Group I silicate or a Group II silicate.

3. A formulation according to claim 1 or claim 2, wherein the silicate comprises sodium silicate.

4. A formulation according to any preceding claim, wherein the silicate is present in the range of 75% to 95% by weight of the formulation.

5. The formulation of any preceding claim, wherein the processing aid comprises an additive selected from the group consisting of a polysaccharide, a cellulosic thickener, and combinations thereof.

6. Iron ore pellets comprising a binder formulation according to any preceding claim.

7. Pellets according to claim 6, comprising silicate in the range of 1 wt% to 10 wt%.

8. Pellets according to claim 6 or claim 7, comprising a processing aid in the range of 0.1 wt% to 2 wt%.

9. A method for producing iron ore pellets, include: a. mixing the binder formulation according to any one of claims 1 to 5 with granular iron ore; as well as b. Forming pellets.

10. The method of claim 9, wherein the pellets are formed using a method selected from the group consisting of extrusion, pan pelletization and briquetting.

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