AU2019379427A1

AU2019379427A1 - Geopolymers produced from mineral processing by-products

Info

Publication number: AU2019379427A1
Application number: AU2019379427A
Authority: AU
Inventors: David Preston Gregory
Original assignee: Canasia Australia Pty Ltd
Current assignee: Canasia Australia Pty Ltd
Priority date: 2018-11-16
Filing date: 2019-11-15
Publication date: 2021-06-24
Also published as: BR112021009551A2; WO2020097693A1; EP3880625A4; EP3880625A1

Abstract

A geopolymer composition comprising the reaction product of red mud; a source of calcium; water; and an alkali activator.

Description

"Geopolymers produced from mineral processing by-products" Technical Field

[0001] The present disclosure relates to geopolymers and, more particularly, to geopolymers produced from mineral processing by-products, and method of production thereof.

Background

[0002] The processing of mineral ores to obtain metals typically leads to the generation of large volumes of waste by-products. These by-products often provide a disposal problem as they cannot be readily recycled or repurposed, and it becomes necessary to store the by-products, for example in holding ponds, taking up valuable land space and impacting the surrounding environment.

[0003] Red mud, also known as bauxite tailings, red sludge, bauxite residue, or alumina refinery residues, is a waste by-product from the production of alumina from bauxite using the Bayer process. Red mud comprises a mixture of solid and metallic oxides, including large amounts of iron oxide which provide the red colour.

[0004] In the Bayer process, the bauxite is treated with sodium hydroxide to convert the aluminium oxide present in the bauxite to soluble sodium aluminate and leaving behind undissolved material, the red mud, having a pH of from 10 to 13. The caustic nature presents further difficulties in the storage and handling of red mud due to safety and environmental considerations, or can introduce additional operational costs in the washing of the red mud to reduce the pH.

[0005] For every tonne of alumina produced using the Bayer process, approximately 1 to 2 tonnes of red mud are produced. As the high demand for aluminium metal continues, so too does the demand for storage space for the waste by-products generated by the alumina production process. [0006] Historically, red mud produced at bauxite processing plants would comprise low concentrations of solid and would need to be stored in holding ponds or the like. However, storing low solid content, low viscosity red mud in such ponds places a large demand on land space. As such, other storage methods have been developed in order to reduce the space requirements for storing the large quantities of red mud produced. For example, the use of“stacking” or“dry stacking” has been increasingly employed to meet the storage demands. Dry stacking comprises de-watering the red mud produced during the Bayer process to increase the solids to a concentration whereby stacks of red mud can be formed.

[0007] Another by-product of mineral processing produced in large quantities is ferronickel slag which is a by-product of the manufacturing of ferronickel in electric furnaces.

[0008] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each of the appended claims.

Summary

[0009] Disclosed herein are geopolymer compositions formed from mineral processing by-products, for example red mud and ferronickel slag. It is an advantage of the methods disclosed herein that means are provided to consume mineral processing by-products and reduce the environmental impact of storing the by-products as waste.

It is a further advantage that the geopolymer compositions formed from the mineral processing by-products are suitable for use in construction. In addition,

[0010] According to the present disclosure, there is provided a geopolymer composition comprising the reaction product of: red mud; a source of calcium; water; and an alkali activator.

[0011] The red mud may be pre-treated red mud, for example the red mud may be neutralised, dried and/or ground.

[0012] The source of calcium is not particularly limited and may be a naturally occurring source of calcium or a manufactured source of calcium including by-products of mineral processing. For example, the source of calcium may be selected from the group consisting of: Portland cement, ground blast furnace slag, gypsum, lime, calcite, wollastonite, and combinations thereof.

[0013] The alkali activator may be any suitable alkali activator for initiating the geopolymerisation reaction. For example, the alkali activator may be selected from the group consisting of: metal hydroxides, metal silicates, metal acid salts, metal aluminates, metal aluminosilicates, and combinations thereof. Preferably, the alkali activator is a metal silicate such as lithium silicate, sodium silicate, potassium silicates, rubidium silicate, caesium silicate and combinations thereof. The metal silicate may have a Si02% to M2O ratio in the range of from 1 to 3. More preferably the alkali activator is sodium silicate or potassium silicate.

[0014] The geopolymer composition may further comprise aggregate. The aggregate may comprise a particles of any suitable size, for example from about 10 pm to about 150 mm. The aggregate may comprise coarse aggregate having a particle size, for example, of about 5 mm to about 40 mm and/or fine aggregate having particle size, for example, of about 40 pm to about 400 pm. In some embodiments, the fine aggregate comprises sand.

[0015] In another aspect, the present disclosure provides a method of producing a geopolymer composition, the method comprising: forming a dry mix comprising: red mud; and a source of calcium, mixing the dry mix with water to form a slurry; and adding an alkali activator to the slurry to initiate a geopolymerisation reaction.

[0016] To maximise the surface area of red mud available to react with the alkali activator, the red mud may be further processed throughout the various steps of the method, for example the red mud, along with other ingredients, may be processed in a high-shear mixer, in order to break up agglomerated red mud and allow for an improved reaction with the alkali activator.

[0017] The components making up the dry mix may include moisture and need not be anhydrous. [0018] In some embodiments, the dry mix further comprises aggregate. In some embodiments, the dry mix further comprises fly ash. Forming the dry mix may include mixing the dry mix to form a substantially homogenous mixture.

[0019] Preferably, the geopolymerisation reaction occurs at room temperature.

[0020] In yet another aspect, there is provided a red mud geopolymer composition produced by a method described above, with or without the optional features.

Preferably, the red mud geopolymer composition has a 7 day compressive strength greater than 5 MPa, more preferably greater than 10 MPa, or greater than 15 MPa. Preferably, the geopolymer has a 28 day compressive strength of greater than 10 MPa, preferably greater than 15 MPa, or greater than 20 MPa.

[0021] In still another aspect, there is provided a reaction mixture for forming a geopolymer composition comprising:

35-70% w/w red mud;

5-30% w/w source of calcium;

0-25% w/w aggregate;

0-30% w/w added water; and

5-20% w/w alkali activator.

[0022] The reaction mixture may further comprise further aluminosilicate sources, for example the reaction mixture may comprise up to 10% w/w fly ash.

[0023] According to the present disclosure, there is provided a geopolymer composition comprising the reaction product of: ferronickel slag; a source of calcium; water; and an alkali activator.

[0024] According to another aspect, there is provided a method of producing a geopolymer composition, the method comprising forming a dry mix comprising: forming a dry mix comprising: ferronickel slag; and a source of calcium, mixing the dry mix with water to form a slurry; and adding an alkali activator to the slurry to initiate a geopolymerisation reaction.

[0025] In yet another aspect, there is provided a ferronickel slag geopolymer composition produced by a method described above. Preferably, the ferronickel slag geopolymer composition has a 7 day compressive strength greater than 20 MPa, more preferably greater than 25 MPa, or greater than 30 MPa. Preferably, the geopolymer has a 28 day compressive strength of greater than 30 MPa, preferably greater than 35 MPa, or greater than 40 MPa.

[0026] According to the present disclosure, there is further provided a reaction mixture for forming a geopolymer composition comprising:

35-85% w/w ferronickel slag;

1-20% w/w source of calcium; 0-25% w/w aggregate;

0-20% w/w water; and

5-20% w/w alkali activator.

[0027] In the embodiments of the present disclosure relating to ferronickel slag, the ferronickel slag may be provided as fine particles and/or as coarse particles.

[0028] Optional features of the geopolymer compositions and methods disclosed herein relating to red mud are also optional methods for geopolymer compositions and methods relating to ferronickel slag where appropriate.

Definitions

[0029] With regards to the definitions provided herein, unless stated otherwise, or implicit from the context, the defined terms and phrases include the provided meanings. Unless explicitly stated otherwise, or apparent from context, the terms and phrases below do not exclude the meaning that the term or phrase has acquired by a person skilled in the relevant art. The definitions are provided to aid in describing particular embodiments, and are not intended to limit the claimed invention, because the scope of the invention is limited only by the claims. Furthermore, unless otherwise required by context, singular terms shall include pluralities and plural terms hall include the singular.

[0030] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

[0031] It is to be appreciated that certain features that are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any sub combination.

[0032] Throughout the present specification, various aspects and components of the invention can be presented in a range format. The range format is included for convenience and should not be interpreted as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range, unless specifically indicated. For example, description of a range such as from 1 to 5 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 5, from 3 to 5 etc., as well as individual and partial numbers within the recited range, for example, 1, 2, 3, 4, 5, 5.5 and 6, unless where integers are required or implicit from context. This applies regardless of the breadth of the disclosed range. Where specific values are required, these will be indicated in the specification.

Description of Embodiments

Geopolymers produced from red mud

[0033] With reference to the accompanying examples, there is provided a reaction mixture for forming a geopolymer composition comprising red mud, a source of calcium, water and an alkali activator. There is further provided geopolymer compositions comprising the reaction product of such reaction mixtures.

[0034] The red mud for use in geopolymers according to the present disclosure may be pre-treated. For example, the red mud of the present disclosure may be washed to reduce levels of sodium hydroxide and therefore reduce the pH and provide a neutralised red mud. Additionally or alternatively, the red mud may be dried by any suitable method, for example by being filter pressed, to reduce the water content. [0035] As can be seen in the examples described below, the resulting geopolymers from the washed or neutralised red mud (Red Mud 1) provided greater day 7 strength results.

[0036] The amount of red mud present in the reaction mixture will vary based on properties of the sourced red mud, such as pH, moisture content and mineral composition. The amount of red mud may also be selected to achieve certain desired characteristics of the resulting geopolymer. In an example, the amount of red mud in the reaction mixture is in the range of 35-70% w/w.

[0037] The source of calcium is not particularly limited and may comprise naturally occurring minerals or manufactured products containing calcium compounds. For example, the source of calcium may be selected from the group consisting of: Portland cement, ground blast furnace slag, lime, calcite, wollastonite, and combinations thereof. As with the red mud, the source of calcium may be pre-treated. For example, the source of calcium may be ground to reduce particle size and increase the available surface area of the source of calcium.

[0038] The amount of the source of calcium present in the reaction mixture will vary based on the properties of the source of calcium, for example the type and

concentration of calcium compounds present. In an example, the amount of the source of calcium in the reaction mixture is in the range of 10-30% w/w.

[0039] In a method according to the present disclosure, the red mud and source of calcium are combined to form a dry mix. The dry mix may include further additives, including aggregate, fibres, microspheres, foaming agents, surfactants, dispersants, set retarders and rheology modifiers. In addition, the dry mix may include other sources of aluminosilicates, for example the dry mix may include fly ash.

[0040] Preferably, the dry mix includes aggregate. The amount and size of aggregate added to the dry mix will vary depending on the properties of the aggregate such as density and particle size, as well as the desired properties of the final geopolymer product. For example, coarse aggregate having a particle size of greater than 5 mm may be added to increase compressive strength, and/or fine aggregate having a particle size of less than 5 mm may be added to reduce shrinkage. In an example, the amount of aggregate in the reaction mixture is in the range of 0-30%.

[0041] The reaction mixture may include further additives, including fibres, microspheres, foaming agents, surfactants, dispersants, retarders and rheology modifiers. In some embodiments, the reaction mixture includes fibres, for example cellulose fibres (e.g. rice husk), mineral fibres (e.g. basalt fibres, quartz fibres), glass fibres, carbon fibres, carbon nanotubes, and/or synthetic fibres (e.g. polypropylene fibres, poly amide fibres, poly (amide-hydrazide) fibres, polyacrylonitrile fibres, poly paraphenylene ter ephthal amide fibres). The type, quantities and physical properties of the fibres can be selected based on a number of desired parameters, including cost, and strength and flexibility of the final product.

[0042] The reaction mixture further comprises water which can be added to the dry mix to form a slurry. Preferably, the amount of water added is just enough to form a workable slurry with good dispersion of the components of the dry mix. It has been found that minimising the amount of water present in the reaction mixture helps to reduce shrinkage of the final geopolymer product. The amount of water required to form the slurry will be dependent on the water content of the components of the dry mix. In an example, the amount of added water in the reaction mixture is in the range of 0-30%.

[0043] The slurry formed by the dry mix and added water has been found to have a good stability. The slurry can be stored, handled and transported readily and will remain flowable until such time that the geopolymerisation reaction is initiated.

[0044] An alkali activator is added to the slurry to initiate a geopolymerisation reaction. The alkali activator may be any suitable alkali activator for initiation the geopolymerisation reaction. The alkali activator can be selected from the group consisting of metal hydroxides, metal silicates, metal acid salts (e.g. metal sulphates or carbonates), metal aluminates, metal aluminosilicates, and combinations thereof. Typically, the metal in the alkali activator is potassium or sodium. In an embodiment, the alkali activator is a metal silicate having a Si02% to M20% ratio in the range of 1 to 3. The amount of alkali activator in the reaction mixture will vary depending on the type and concentration, as well as the desired properties of the geopolymer

composition. In an example, the amount of alkali activator in the reaction mixture is in the range of 5-20% w/w.

[0045] After adding the alkali metal silicate to the slurry, the slurry may be formed into a predetermined shape prior to the slurry setting. In some embodiments, the slurry is formed into a brick shape, for example by moulding, extrusion, or any other appropriate production method.

EXAMPLES

[0046] The present disclosure is now described further in the following non-limiting examples.

RED MUD EXAMPLES

RED MUD 1

[0047] Geopolymer compositions were prepared in accordance with the present disclosure from a first sample of red mud, Red Mud 1. The composition of this red mud is shown in Table 1 below, where it can be seen that Red Mud 1 comprises large quantities of magnesium compounds.

Table 1: Composition of Red Mud 1

[0048] Red Mud 1 undergoes a sea water processing step after leaving the bauxite plant in order to reduce concentrations of caustic soda and, therefore, reduce the pH from initial levels of approximately 14. Red mud processed in this matter may also be referred to as neutralised red mud.

[0049] Geopolymer compositions were prepared by dry mixing Red Mud 1 with Portland cement and 5 mm aggregate. Water was then added to the dry mixture and thoroughly mixed to form a slurry. During preparation of the dry mix, it was observed that red mud has a tendency to agglomerate. The addition of water assisted in generating an evenly distributed slurry. Increased concentrations of aggregate and the use of mechanical agitation such as high shear mixing also aided the red mud distribution.

[0050] To the slurry mix was added either sodium or potassium silicate in liquid form, and the mixture stirred briefly to aid distribution and then the mixture was left to set. Strength measurements were conducted at 7 days. A summary of typical formulations prepared using Red Mud 1, the specific gravity, and day 7 strength testing are summarised in Tables 2 and 3 below. Table 2: Red Mud 1 geopolymer compositions

* Agsil 32

* Grade D

Table 3: Red Mud 1 geopolymer compositions - with mechanical agitation

* Grade D

RED MUD 2

[0051] Geopolymer compositions were prepared in accordance with the present disclosure from a second source of red mud, Red Mud 2. The composition of this red mud is shown in Table 4 below.

Table 4: Composition of Red Mud 2

[0052] There are two types of Red Mud 2, Red Mud 2 (wet) which is generated directly from the processing plants, and Red Mud 2 (dry) generated by passing Red Mud 2 (wet) through a filter press.

[0053] Unlike Red Mud 1, Red Mud 2 has not been washed in any way to reduce caustic concentrations. Red Mud 2 displayed a greater stickiness than Red Mud 1 leading to a greater tendency to agglomerate.

[0054] Geopolymer compositions were prepared from Red Mud 2 in the manner described above for Red Mud 1. A summary of typical formulations prepared using Red Mud and day 7 strength testing are summarised in Tables 5 and 6 below.

Table 5: Red Mud 2 geopolymer compositions

^L C-112

Table 6: Red Mud 2 geopolymer compositions - with mechanical agitation

^L C-112

FERRONICKEL SLAG EXAMPLES

[0055] Geopolymer compositions were prepared in accordance with the present disclosure from a sample of ferronickel slag (FNS). The composition of this ferronickel slag is shown in Table 7 below.

Table 7: Composition of Ferronickel Slag

[0056] Formulations comprising as high FNS content as possible were investigated, to allow effective re-use of waste FNS product. FNS is a hard aggregate which cannot be easily ground. Geopolymer compositions were formed from combinations of coarse FNS and fine FNS formed by passing the FNS aggregate through a wet rod mill for an hour, followed by filtering the ground product to provide fine FNS with a water content of approximately 20%, and an average particle size of lOOpm.

[0057] Geopolymer compositions were prepared from FNS by mixing ground (fine) and coarse forms of FNS with a source of calcium, e.g. Portland cement or hydrated lime. The water content in the ground FNS from the milling process was sufficient to generate a slurry such that no additional water was required. To this slurry was added sodium silicate to initiate the geopolymerisation reaction and the mixture was left to set. Strength measurements were conducted at 7 days

[0058] A summary of typical formulations prepared using FNS and day 7 strength testing are summarised in Table 8 below. Table 8: Ferronickel Slag geopolymer compositions

* Grade D

[0059] It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

CLAIMS:

1. A geopolymer composition comprising the reaction product of: red mud; a source of calcium; water; and an alkali activator.

2. A geopolymer composition according to claim 1, wherein the red mud is a neutralised red mud.

3. A geopolymer composition according to claim 1 or claim 2, wherein the source of calcium is selected from the group consisting of: Portland cement, ground blast furnace slag, gypsum, lime, calcite, wollastonite, and combinations thereof

4. A geopolymer composition according to any one of the preceding claims, wherein the alkali activator is selected from the group consisting of: metal hydroxides, metal silicates, metal acid salts, metal aluminates, metal aluminosilicates, and combinations thereof.

5. A geopolymer composition according to claim 4, wherein the alkali activator is a metal silicate.

6. A geopolymer composition according to claim 5, wherein the metal silicate has a SiCk% to WhO% ratio in the range of from 1 to 3.

7. A geopolymer composition according to claim 5 or claim 6, wherein the metal silicate is selected from the group consisting of: lithium silicate, sodium silicate, potassium silicate, rubidium silicate, caesium silicate, and combinations thereof.

8. A geopolymer composition according to claim 7, wherein the metal silicate is sodium silicate or potassium silicate.

9. A geopolymer composition according to any one of the preceding claims, further comprising aggregate.

10. A geopolymer composition according to claim 9, wherein the aggregate comprises coarse aggregate having a particle size of from 5 mm to 40 mm.

11. A geopolymer according to claim 9 or claim 10, wherein the aggregate comprises fine aggregate having a particle size of from 40 pm to 400 pm.

12. A geopolymer according to claim 11, wherein the fine aggregate comprises sand.

13. A method of producing a geopolymer composition, the method comprising: forming a dry mix comprising: red mud; and a source of calcium, mixing the dry mix with water to form a slurry; and adding an alkali activator to the slurry to initiate a geopolymerisation reaction.

14. A method according to claim 13, wherein the dry mix further comprises aggregate.

15. A method according to claim 13 or 14, wherein the dry mix further comprises fly ash.

16. A method according to any one of claims 14 to 16, wherein forming the dry mix comprises mixing the dry mix to form a substantially homogenous mixture.

17. A method according to any one of claim 14 to 17, wherein the

geopolymerisation reaction occurs at room temperature.

18. A geopolymer composition produced by a method according to any one of claims 14 to 18, wherein the geopolymer composition has a 7 day compressive strength greater than 15 MPa.

19. A geopolymer composition produced by a method according to any one of claims 14 to 19, wherein the geopolymer composition has a 28 day compressive strength of greater than 20 MPa.

20. A reaction mixture for forming a geopolymer composition comprising:

35-70% w/w red mud;

10-30% w/w source of calcium;

0-25% w/w aggregate;

0-30% w/w added water; and

5-20% w/w alkali activator.

21. A reaction mixture according to claim 21, further comprising up to 10% w/w fly ash.