WO2019034859A1

WO2019034859A1 - Briquette

Info

Publication number: WO2019034859A1
Application number: PCT/GB2018/052300
Authority: WO
Inventors: Colin Metcalfe; Richard Joyce
Original assignee: Phillips, Peter; Hyde, David; Wheeldon, Peter; ESKILDSEN, Jan; Hunt, John
Priority date: 2017-08-14
Filing date: 2018-08-14
Publication date: 2019-02-21
Also published as: GB201712982D0

Abstract

A briquette comprising:(i) a particulate material; and (ii) graphene and/or a derivative thereof.A method for producing the briquette comprising: (i) mixing the particulate material, with the graphene and/or derivative thereof; (ii) compressing the mixture to form a briquette; and (iii) curing the briquette.

Description

Briquette

The invention relates to the use of graphene or derivatives thereof, often in briquettes, and to the production of briquettes, for instance from coal, metal or metal ores. Typically briquettes are formed from particulate material and utilise binders. In the invention, the briquettes may additionally comprise a binder which includes bentonite or a salt thereof.

There exists, worldwide, a huge quantity of powdered minerals. These often arise as waste from industries such as mining, manufacturing and power generation; and if reprocessed, represent a huge potential resource for energy or metal manufacturing. However, such powders are difficult to process into a stable form that can be transported not only to the site of use, but within the large processing plants at their destination.

Binders of various types have been used to stabilise the powders into briquettes, thus reducing explosion hazards and loss of product during transport. However, these briquettes can be prone to damage when handled or dropped, such as from conveyor belts or other transport systems. A briquette must retain its integrity as it passes through the furnace into the melting furnace, otherwise its performance in, for instance, furnaces or DRI plants can be adversely affected. A further concern is degradation of the binder, and so loss of briquette integrity before it reaches the melting furnace. There is also a tendency to disintegrate on contact with water, necessitating the use of waterproofing agents, which in turn increases costs.

There is therefore a need to provide briquettes which are stronger and have improved temperature resistance relative to existing briquettes, if possible without the need to use waterproofing agents, or the use of these at lower levels than is typical in the art. Such briquettes would be more resilient to the conditions encountered during transport and processing, for instance in a blast furnace.

In addition, the machinery forming the briquettes (such as extrusion machinery) must be regularly maintained as a result of component degradation through wear and tear. It would be desirable to provide a briquette, which is formulated to reduce wear and tear on the processing machinery. The invention is intended to overcome or ameliorate at least some aspects of these problems.

Accordingly, in a first aspect of the invention there is provided a briquette comprising : a particulate material; and graphene and/or a derivative thereof. Often, the briquette will comprise graphene, or a salt thereof. Often the salt will be selected from graphene oxide, graphene sulphate, or a combination thereof. As used herein, the term "graphene" is intended to include derivatives thereof, such as those discussed above.

The presence of graphene in the briquette will generally be as a binder, generally the graphene provides a briquette which is has an improved green strength, such that the briquette produced is stronger and has improved temperature resistance, thereby allowing it to survive impact during transportation and to survive the heat of a furnace, allowing it to progress to the melting zone of a, for instance, blast furnace intact. In addition, it has been found that the presence of graphene in the briquette lubricates the extrusion machinery such that not only is wear and tear reduced, but throughput can be increased . Further, the briquette forming machinery is easier to strip down and service. These latter advantages result in a significant reduction in processing down time and thus improved efficiency at the briquette processing plant. As such, the graphene may also be said to function as a lubricant. It has further been observed that graphene provides waterproofing to the briquettes, reducing or eliminating the need to waterproof the briquettes.

The graphene may be present in the range 0.005 to 0.05 wt%, often in the range 0.01 to 0.02 wt%. An advantage of including graphene is that it can be present at very low levels, whilst providing the advantages described. The addition of higher levels of graphene can further improve the strength and temperature resistance, but is not generally needed to provide a briquette which is resilient to transport and processing. However, if desired, the graphene could be present at levels in the range 0.005 to 5 wt%, 0.1 to 3 wt%, or 0.5 to 1.0 wt%.

The graphene may be down-processed graphene. Often the graphene will be added as a powder or dispersion. Often the dispersion will be a water/surfactant dispersion, and often the graphene will be present in the range 5 - 50 wt% of the dispersion, often 10 - 30 wt% or around 20 wt% of the dispersion.

The particle size of the graphene will typically be in the range 0.1 μιη to 5 μιη, often 0.5 m - 2 μιη. Without being bound by theory, it is believed that the graphene reacts with the material being bound, expanding and thereby causing agglomeration.

Whilst the graphene alone is sufficient to provide a briquette which is strong and temperature resistant, the briquette may further comprise a binder. Where a binder is present this will often comprise bentonite or a salt thereof. For instance, the salt may be sodium bentonite or calcium bentonite. As used herein, references to bentonite are intended to include bentonite salts.

Alternatively, the binder may comprise cement. As used herein the term cement is intended to refer to inorganic cements. The briquette may further comprise a binder selected from at least partially saponified polyvinyl alcohol, a combination of polyvinyl alcohol and sodium hydroxide, an alkali metal alkyl siliconate or polyalkyl silicic acid, phenol formaldehyde resin, guar gum (often 5000 cps grade), a combination of guar gum and calcium oxide, anionic polyacrylamide, styrene acrylate emulsion, a polysaccharide binder, and combinations thereof. A binder from this list may be present independently or in addition to bentonite and/or cement. These binders will be selected in line with the function of the briquette, based on the conditions that the briquette will be subjected to and the nature of the particulate matter.

Where the binder is polyvinyl alcohol, this is typically polyvinyl alcohol formed from polyvinyl acetate by replacing the acetic acid radical of acetate with a hydroxyl radical by reacting the polyvinyl acetate with sodium hydroxide in a process called saponification. "Partially saponified" means that some of the acetate groups have been replaced by hydroxyl groups thereby forming at least a partially saponified polyvinyl alcohol containing vinyl alcohol residues. Typically, the polyvinyl alcohol has a degree of saponification of at least 80%, typically at least 85%, at least 90%, at least 95%, 98%, 99% or 100% saponification. Polyvinyl alcohol may be obtained commercially from, for example, Kuraray Europe GmbH of Frankfurt Am Main, Germany. Typically the polyvinyl alcohol is utilised as a solution in water. The polyvinyl alcohol may be modified to include a sodium hydroxide content. Typically the polyvinyl alcohol binder has an active polymer content of 12-13% and a pH in the range 4-6 when in solution.

Where the binder is an alkali metal alkyl siliconate, this may be an alkali metal Ci to C₄ alkyl siliconate, such as an alkali metal methyl siliconate. Alternatively, the methyl group moiety may be replaced by an ethyl, propyl or butyl moiety. Typically the alkali metal is a sodium or potassium, most typically potassium. Most typically potassium methyl siliconate is used, for example, sold under the trade name Silres by Wacker Chemie GmbH. This has been found to create briquettes with better drop resistance. Moreover, it produces surprisingly heat stable briquettes with briquettes capable of substantially maintaining their shape in a reducing atmosphere of up to 1200°C. Alkali metal alkyl siliconates typically react with carbon dioxide during a curing process to produce the equivalent polyalkylsilicic acid, such as a poly Ci to C₄ alkyl silicic acid, for instance poly methyl silicic acid. They are conventionally used as masonry waterproofing agents, however, it has been found that the strength of the briquette can be improved through the addition of siliconate or polyalkyl silicic acid.

Phenol formaldehyde resins are generally known in the art. Typically the resin is a resole or novolac resin made with formaldehyde to phenol ratios of greater than 1, typically around 1.5. The resin may be mixed into the particulate matter as powder or as an aqueous solution.

Guar gum may be added with acrylamide at 4 - 12, most typically 5 - 10 or 8 parts polyacrylamide to 1 part guar gum by weight. Typically 3 parts calcium oxide may be added.

Some very finely powdered material wastes or mineral fines, such as arc furnace mineral wastes, have been found to have problems being mixed with binding agents such as polyvinyl alcohol. The inventors have found that the production of briquettes from such wastes can be advantageously improved using a polysaccharide binder such as starch, especially a pregelatinised potato starch, to replace or be used in combination with polyvinyl alcohol. It may therefore be the case that the briquette comprise a particulate mineral waste or fine, a polysaccharide binder and graphene.

Often, the briquette will comprise 0.01 to 1.5 wt% binder, often 0.1 to 1.0 wt%, or 0.2 to 0.8 wt%. However, where the binder comprises cement, there will often be in the range 5 to 10 wt% binder.

Where the binder comprises polyvinyl alcohol, the briquette may contain 0.01 to 0.8 wt% of binder. More typically, it contains 0.5 wt% or 0.4 wt% or 0.3 wt% polyvinyl alcohol binder. Where the binder comprises alkali metal alkyl siliconate or polyalkylsilicic acid, this is often used in the range 0.01 to 0.5 wt%, more typically 0.5 wt% or 0.2 wt% of the material. Where the binder comprises phenol formaldehyde resin, briquette will often comprise 0.5 to 1.5 wt% of this resin. The use of phenol formaldehyde resin in general, and of these amounts of phenol formaldehyde resin in particular, has been found to provide particular strength benefits where the particulate material is iron ore. Often, where the binder is anionic polyacrylamide, this will be present in the range 0.5 to 1.0 wt%. Where the binder comprises styrene acrylate emulsion this will typically be present in 0.5 to 1.5 wt%, more often typically round 1 wt%. Often the styrene acrylate emulsion will be present in combination with cement. Where this is the case, typically the cements will be present in the range 5 to 10 wt %, typically 8% inorganic cement. The polysaccharide binder may be starch, it may be pregelatinised potato starch. It may be provided as up to 0.8 wt% of the briquette, especially 0.6 wt%, for example, by mixing 10 wt% solution of the binder with the particulate material. Up to 0.5 wt% of polyvinyl alcohol, as defined above, may be added, in particulate where the particulate material is arc furnace waste.

The particulate material may be selected from a metal ore, metal ore containing waste, iron residue, iron filings, mineral waste, a carbonaceous material, arc furnace waste or combinations thereof. Graphene has been found to be particularly advantageous in the binding and lubrication of briquettes where the particulate material is carbonaceous or a metal ore, in particularly iron ore. As noted above, this is believed to be through agglomeration of the graphene with the ore.

Often the metal ore comprises iron ore. The iron ore may be any naturally or non- naturally occurring ore, such as haematite, magnetite, or wustite and may contain naturally occurring contaminants. Where the particulate material is a carbonaceous material, this may be coke, graphite, carbon black, peat or coal. Often the particulate material will comprise coke and/or coal. As used herein, the term "coal" is intended to include lignites, sub-bituminous coal, bituminous coal, steam coal and anthracite. Cokes have been found to be particularly problematic at forming briquettes. However, the combination of a styrene-acrylate emulsion and cement has been found to produce coke briquettes with good properties. The coke particles may be pre-treated with a guar gum solution, typically 35% of a 1% gum solution, where the concentration is 1 wt% guar gum in water. The addition is 35% of the weight of the coke material. This has been found to reduce to porosity of the coke prior to mixing with the styrene acrylate emulsion and cement. Mineral wastes include mill scale, mill sludges, and fines from ores or metal containing wastes.

The metal may be, or the metal ore mineral waste may contain; iron, zinc, nickel, copper, chromium, manganese, gold, platinum, silver, titanium, tin, lead, vanadium, cadmium, beryllium, molybdenum, uranium or mixtures thereof or elemental metal or in the form of, for example, oxides or silicates.

The particulate iron residues are typically from tailing ponds or wash systems and typically are superfine. That is they have at least 90% below 200 microns and typically at least 50% below 20 microns as measured by Fe₂03 content. The iron residues are typically iron oxides. It has been found that the addition of up to 15 wt%, typically 8 wt% or 5 wt% of a metal ore or mineral waste, improves the strength of the briquette. Typically the metal ore is, for example, an iron-containing ore, such as ferrous or ferric oxide. Therefore, the particulate material will often contain in the range 0.01 to 15 wt%, often 0.1 to 8 wt% of a metal ore and/or mineral waste.

It should be noted that the term "briquette" includes objects commonly referred to as pellets, rods, pencils, briquettes and slugs. These objects share the common features of being a compacted form of material and are differentiated principally by their size and shape. The particulate material may be a powder, or filings. Often the particulate material has a particle diameter of 4mm or less (broadest axis). Often the particle diameter will be in the range 0.1mm to 4mm. Often, at least 10 wt% of the particulate material is capable of passing through a 100 μιη sieve prior to forming into a briquette. The formation of briquettes is most useful with materials of these particle diameters, as such fine particles are difficult and hazardous to transport. Further, the presence of the smaller particles of the particulate material improves the packing of the material.

Where the particulate material comprises metal ore or metal ore containing waste, the binder will often comprise phenol formaldehyde resin with optional polyvinyl alcohol and optional guar gum. The polyvinyl alcohol will often be present in the range 0.1 to 0.2 wt%, often around 0.125 wt%, the guar gum may be present in the range 0.5 to 1.05 wt%, often at around 0.5 wt%.

The strength and resilience of the briquette can be further improved by addition of a suitable cross-linking agent. Suitable cross-linking agents include, for example, glutaraldehydes, for example at 0.01 to 5 wt%. Sodium hydroxide, for example 0.1 wt%, may also be used as a cross-linking agent. Other cross-linkers include glyoxal, glyoxal resin, PAAE resin (polyamidoamine epichlorohydrine), melamine formaldehydes, organic titanates (eg Tizor™, Du Pont), boric acid, ammonium, zirconium carbonate and glutaric dialdehyde-bis-sodium bisulphate. Typically up to 5% and more typically 3% or 2 wt% of the cross-linking agent is used. This allows, for example, the amount of binder (such as polyvinyl alcohol) to be reduced from, for example, 0.8 wt% or 0.5 wt% to, for example, 0.3 wt% or 0.4 wt% binder. This is a cost effective way of improving the strength of the material. Therefore, often, the cross-linking agent will be present with a polyvinyl alcohol binder, often this will include a partially saponified component, such that the combination may be: 0.01 to 0.5 wt% fully saponified polyvinyl alcohol, 0.01 to 0.5 wt% partially saponified PVA and 0.01 to 5 wt% of crosslinking agent. Typically a 1 : 1 ratio by weight of fully saponified : partially saponified polyvinyl alcohol is used. Typically 0.01 to 0.04 wt%, especially 0.02 wt% of glutaraldehyde is used as the crosslinking agent when used with polyvinyl alcohols. This combination of polyvinyl alcohol binder and cross-linking agent has been found to be particularly useful in stabilising particulate mineral waste.

As such, it has been determined that the choice of cross-linking agent can improve the properties of briquettes. Another example of this is where the binder comprises 0.01 to 5% polyvinyl alcohol and 0.01 to 0.5 wt%, especially 0.02 wt% sodium hydroxide. Sodium hydroxide has been found to produce improved properties compared to, for example, glutaraldehyde, especially with metal ores and wastes, such as haematite. They may be used or made as defined above.

Coke and coal dusts have been advantageously combined using phenol formaldehyde and a hardener. The briquette may therefore further comprise a hardener. The phenol formaldehyde may be used in amounts up to 4 wt%, or up to 2 wt%. Phenol formaldehyde may be typically used by fixing as an aqueous solution or with the hardener. The hardener may be, for example, glycol triacetate and a gum such as guar gum, acacia gum, and gum arabic. Typically 0.1 to 0.5 wt% glycol triacetate and 0.1 to 0.5 wt% gum are used. This may be cold cured. The briquette may be waterproofed, although the need for this has been found to be reduced in the graphene containing briquettes of the invention. Graphene is not the only binder that provides waterproofing. For instance, alkali metal alkyl siliconates are generally known in the art as waterproofing agents, rather than as materials that impart some structural or binding capability. However, using such siliconates imparts some waterproofing property to the briquette and imports some resilience to the presence of moisture.

However, the briquette may additionally comprise a waterproofing agent to further improve the water resistance, whether the binder is an alkali metal alkyl siliconate, graphene is used alone, or another binder is selected. Where present, the waterproofing agent may be combined with the particulate material or as a layer on the external surface of the briquette.

The waterproofing agent is typically sprayed onto the outer surface of the briquette after the briquette has been formed. Typically waterproofing agents include styrene-acrylate copolymers such as Vinnapas™ SAF 34 (Wacker Chemie AG, Munich, Germany) which is typically a fine particle dispersion of a styrene acrylate copolymer, typically free from alkyl phenol ethoxylate, optionally this may contain 0.05 to 1% guar gum. Alternatively the briquettes may be coated by spraying with a layer of bituminous emulsion. An alternative to spraying of the briquettes with the materials includes, for example, dipping the briquettes in a solution or dispersion of the waterproofing material, or combining the waterproofing material with the particulate material and the binder.

Typically the briquette comprises < 15%, < 10% or <5wt% of water. Water content may be reduced by drying, for example, by adding burnt lime (calcium oxide) at up to typically 3%.

A wetting agent or surfactant, such as a soap solution, may be used to assist the wetting of the particulate material. This may be included at up to 1 wt% or 0.5 wt% or 0.1 wt%. Where present, the binders crosslinking agent and waterproofing agents may be provided as aqueous solutions prior to use with the particulate material.

Typically, the briquettes comprise graphene, a bentonite or cement binder, and optionally the cross-linking agent and/or the waterproofing agent, the remaining material being the particulate material and any moisture present in the material. Typically at least 70%, at least 80%, at least 90% or at least 95% of the briquette is particulate material as defined above.

In a second aspect of the invention there is provided a method for producing a briquette according to the first aspect of the invention comprising : mixing the particulate material, with the graphene; compressing the mixture to form a briquette; and curing the briquette. The method may comprise the additional steps of mixing a binder and/or a cross-linking material with the particulate material. Further, the method may comprise the step of coating the briquette with a waterproofing agent. Often, where this step is present, the waterproofing agent will be sprayed on to the briquette. Typically, mixing is effected using twin-shaft batching mixers, this is as continuous mixers do not typically control the material quantities accurately enough.

Compression may be through the use of a mould, roller pressing or extrusion. Often, a roller press will be used to compress the mixture to form the briquette. A vacuum may be used to improve uptake of the binder where this is present, however this is not generally needed.

The briquette may then be allowed to cure, for example, for 12, 24 or 48 hours. Typically the process is carried out at ambient temperatures, for example, 0 to 40°C, 15 to 30°C, 20 to 25°C or 20°C. Unless otherwise stated, each of the integers described may be used in combination with any other integer as would be understood by the person skilled in the art. Further, although all aspects of the invention preferably "comprise" the features described in relation to that aspect, it is specifically envisaged that they may "consist" or "consist essentially" of those features outlined in the claims. In addition, all terms, unless specifically defined herein, are intended to be given their commonly understood meaning in the art.

Further, in the discussion of the invention, unless stated to the contrary, the disclosure of alternative values for the upper or lower limit of the permitted range of a parameter, is to be construed as an implied statement that each intermediate value of said parameter, lying between the smaller and greater of the alternatives, is itself also disclosed as a possible value for the parameter.

In addition, unless otherwise stated, all numerical values appearing in this application are to be understood as being modified by the term "about". The term "wt%" and analogous terms is intended to mean the percentage by weight of the total briquette composition.

In order that the invention may be more readily understood, it will be described further with reference to the specific examples hereinafter.

Extrusion Flow Rates for Iron Ore Briquettes Table 1 below illustrates the enhancements in throughput that can be observed for two briquette formulations, Formulation A (without graphene) and formulation B (with graphene).

Formulation A (without graphene)

99.5 wt% Iron Ore

0.5 wt% Carrier (Polyvinyl alcohol 47 - 88 grade containing 0.002 wt% crosslinking agent)

Formulation B (with graphene)

99.5 wt% Iron Ore

0.02 wt% Graphene

0.48 wt% Carrier (Polyvinyl alcohol 47 - 88 grade containing 0.002 wt% crosslinking agent) In this particular test, the graphene was injected into the mix process (Lodige ploughshare mixer operating at capacity and 45 rpm).

Table 1

It is therefore clear that the presence of graphene provides for enhanced extrusion rates, and hence greater plant productivity. Further, it was noted that with the formulation that included graphene, the mixer and extrusion apparatus was left in a clean state following discharge. This further increased yield and reduces maintenance for cleaning.

Strength of Briquettes

Table 2 below illustrates the strength improvements that can be observed for a range of particulate materials in the presence of graphene.

Table 2

cellulose

Ferro silicon Methyl 1.03 Not measured dust hydro xyl ethyl

cellulose

* Resistance to compressive load as measured under ISO 4700 (note these values are from an axial measurement)

# Reduction Disintegration Index at 550°C as measured under ISO 4696

The materials selected are as follows:

· VISL Haematite: from Visveswaraya Iron & Steel Limited

• Magnetite El 139 : 60-65 wt% concentrate, 500 micron from Siberia

• Graphene: aqueous dispersion from a variety of sources

• 0.5A 1% 15377 : PVA grade 47 - 88 in 10% aqueous solution of 1% Novolac Resin

· 25-88KL: PVA grade 25 - 88, KURARAY POVAL® 25-88 KL, in 10% aqueous solution

• AIO: PVA grade 47 - 88 in 10% aqueous solution

• Methyl hydroxyl ethyl cellulose: 40 - 50 MPa, 2% solution, 7% addition

As can be seen, in all cases, the cold crushing strength and/or RDI are enhanced where graphene is present. In many cases, both the cold crushing strength and the RDI are enhanced.

Table 3

The materials selected are as follows:

• Iron Ore Magnetite: North America

• 15377 : PVA grade 47 - 88 in powder form

• 47-88: 10% aqueous solution of 1% Novolac Resin

• 25-88KL: PVA grade 25 - 88, KURARAY POVAL® 25-88 KL, in 10% aqueous solution As can be seen Formulation D, comprising a 0.1% dispersion of graphene has a significantly higher compressive strength than where graphene is not present. In addition denser briquettes are formed.

It would be appreciated that the methods of the invention are capable of being implemented in a variety of ways, only a few of which have been illustrated and described above.

Claims

1. A briquette comprising :

(i) a particulate material; and

(ii) graphene and/or a derivative thereof.

2. A briquette according to claim 1, comprising graphene, or a salt thereof.

3. A briquette according to claim 2, comprising graphene, graphene oxide, graphene sulphate, or a combination thereof.

4. A briquette according to any preceding claim, further comprising a binder, the binder comprising bentonite or a salt thereof.

5. A briquette according to any preceding claim, further comprising a binder, the binder comprising cement.

6. A briquette according to claim 5, comprising 5 to 10 wt% binder.

7. A briquette according to any preceding claim, further comprising a binder selected from at least partially saponified polyvinyl alcohol, a combination of polyvinyl alcohol and sodium hydroxide, an alkali metal alkyl siliconate or polyalkyl silicic acid, phenol formaldehyde resin, guar gum, a combination of guar gum and calcium oxide, anionic polyacrylamide, styrene acrylate emulsion, a polysaccharide binder, and combinations thereof.

8. A briquette according to any of claims 1 to 4 and 7, comprising 0.01 to 1.5 wt% binder.

9. A briquette according to any preceding claim, wherein the particulate material is selected from a metal ore, metal ore containing waste, iron residue, iron filings, mineral waste, a carbonaceous material, arc furnace waste or combinations thereof.

10. A briquette according to claim 9, wherein the metal ore comprises iron ore.

11. A briquette according to claim 9, wherein the carbonaceous material comprises coke and/or coal.

12. A briquette according to any preceding claim, wherein the particulate material has a particle diameter of 4mm or less.

13. A briquette according to any preceding claim, wherein at least 10 wt% of the particulate material is capable of passing through a 100 μιη sieve prior to forming into a briquette.

14. A briquette according to any preceding claim, additionally comprising in the range 0.01 to 5 wt% of a cross-linking agent.

15. A briquette according to claim 14, wherein the cross-linking agent comprises glutaraldehyde.

16. A briquette according to any preceding claim, additionally comprising a waterproofing agent, combined with the particulate material or as a layer on the external surface of the briquette.

17. A briquette according to claim 16, wherein the waterproofing agent comprises a styrene-acrylate copolymer or a bitumen emulsion.

18. A briquette according to any preceding claim having a moisture content of < 15 wt%.

19. A briquette according to any preceding claim, further comprising a hardener.

20. A method for producing a briquette according to any preceding claim comprising :

(i) mixing the particulate material, with the graphene and/or derivative thereof;

(ii) compressing the mixture to form a briquette; and

(iii) curing the briquette.

21. A method according to claim 20, further comprising the step of mixing a binder with the particulate material.

22. A method according to claim 20 or claim 21, further comprising the step of mixing a cross-linking material with the particulate material.

23. A method according to any of claims 20 to 22, further comprising the step of coating the briquette with a waterproofing agent.

24. A method according to claim 23, wherein the waterproofing agent is sprayed on to the briquette.