WO2024231652A1

WO2024231652A1 - Method for producing alkali metal aluminosilicate

Info

Publication number: WO2024231652A1
Application number: PCT/GB2024/050992
Authority: WO
Inventors: Sean SARGENT
Original assignee: Green Lithium Refining Ltd
Current assignee: Green Lithium Refining Ltd
Priority date: 2023-05-05
Filing date: 2024-04-16
Publication date: 2024-11-14
Anticipated expiration: 2025-11-05
Also published as: GB202306702D0; GB2625399A

Abstract

A method for producing an alkali metal aluminosilicate is described. The method comprises: reacting a lithium-bearing mineral with an alkali metal carbonate in an aqueous medium to form alkali metal aluminosilicate and lithium carbonate, wherein said lithium-bearing mineral is selected from at least one of spodumene, lepidolite, petalite, eucryptite and hectorite, and wherein said alkali metal carbonate is selected from a carbonate of sodium, potassium and/or cesium; separating a solid product comprising at least a portion of the alkali metal aluminosilicate from the aqueous medium; and using the separated solid product to form a binder.

Description

METHOD FOR PRODUCING ALKALI METAL ALUMINOSILICATE

FIELD OF THE INVENTION

[0001] The invention relates to a method for producing an alkali metal aluminosilicate. Particularly, the invention further relates to using a solid product comprising the alkali metal aluminosilicate to form a binder.

BACKGROUND

[0002] Batteries can support the electrification of the global economy and reduce carbon emissions that contribute to global climate change. The demand for batteries for electric vehicles and grid scale energy storage is fast increasing. Refined lithium is a key component for the production of such batteries. Effective and environmentally-friendly refining of lithium is important for the sustainable production of such batteries.

[0003] Battery-grade lithium may be recovered as e.g. lithium hydroxide from lithium-bearing minerals, such as spodumene. For example, the lithium-bearing mineral may be reacted with an alkali metal carbonate to produce lithium carbonate, which may then be reacted with an alkali earth metal hydroxide to produce lithium hydroxide.

[0004] Lithium hydroxide is useful for the manufacture of batteries that enable electricity generated from renewable sources, such as solar and wind, to be stored and released when power is required. As we replace fossil fuels as our primary source of energy and transition to a cleaner, electrified economy, the demand for lithium hydroxide will grow. To meet this demand, more sustainable methods for lithium recovery are required.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figures 1 and 2 illustrate systems for carrying out processes for producing an alkali metal aluminosilicate in accordance with embodiments of the invention.

DESCRIPTION

[0006] According to an aspect of the invention, there is provided a method for producing an alkali metal aluminosilicate. The method comprises: [0007] reacting a lithium-bearing mineral with an alkali metal carbonate in an aqueous medium to form alkali metal aluminosilicate and lithium carbonate, wherein said lithium- bearing mineral is selected from at least one of spodumene, lepidolite, petalite, eucryptite and hectorite, and wherein said alkali metal carbonate is selected from a carbonate of sodium, potassium and/or cesium;

[0008] separating a solid product comprising at least a portion of the alkali metal aluminosilicate from the aqueous medium; and

[0009] using the separated solid product to form a binder, such as a cementitious or geopolymer binder.

[0010] The present disclosure relates to a method for producing a solid product comprising alkali metal aluminosilicate as part of a lithium-recovery process.

[0011] Lithium may be recovered from lithium-bearing minerals including spodumene, lepidolite, petalite, eucryptite and hectorite. To recover lithium hydroxide from such minerals, the minerals may be reacted with an alkali metal carbonate, such as sodium carbonate, to produce lithium carbonate. The lithium carbonate produced may be recovered and/or reacted with an alkali earth metal hydroxide to form lithium hydroxide, which is subsequently recovered. In addition to lithium carbonate, alkali metal aluminosilicate is formed. An example of a lithium-recovery process is described in WO 2019/220004.

[0012] The present inventors have surprisingly found that the alkali metal aluminosilicate formed from the reaction of a lithium-bearing mineral with an alkali metal carbonate, rather than being discarded, may be a separated as a useful solid by-product. This improves the circularity of the overall lithium-recovery process, imparting value to a waste product and reducing the need for complex waste management and/or waste disposal steps.

[0013] In particular, the present inventors have found that the separated product comprising at least a portion of the alkali metal aluminosilicate may be used to form a binder, for example, a cementitious or geopolymer binder. [0014] The lithium-bearing mineral may be reacted with an alkali metal carbonate at a temperature of 160 to 220 °C, preferably 200 to 220 °C, and/or a pressure of 10 to 30 bar, preferably 15 to 25 bar.

[0015] The alkali metal carbonate that is reacted with the lithium-bearing material may be sodium carbonate. In this embodiment, the lithium-bearing mineral reacts with the sodium carbonate in an aqueous medium to form sodium aluminosilicate and lithium carbonate.

[0016] Preferably, the method further comprises reacting the lithium carbonate formed from the reaction between the lithium-bearing mineral with an alkali metal carbonate with an alkali earth metal hydroxide to form lithium hydroxide and alkali earth metal carbonate. In some examples, the alkali earth metal hydroxide may be a hydroxide of calcium and/or magnesium. Preferably, the alkali earth metal hydroxide that is reacted with the lithium carbonate may be calcium hydroxide. Where calcium hydroxide is used, the lithium carbonate reacts with the calcium hydroxide to form lithium hydroxide and calcium carbonate.

[0017] Preferably, the alkali earth metal hydroxide is added to the aqueous medium before separation of the solid product. By separating the solid product after the addition of alkali earth metal hydroxide, the separated solid product may comprise alkali metal aluminosilicate as well as alkali metal carbonate e.g. formed from the reaction between lithium carbonate and the alkali earth metal hydroxide. Without wishing to be bound by any theory, such a mixture may provide the separated product with desirable properties, for example, for use as a binder, such as a cementitious or geopolymer binder.

[0018] As mentioned above, the lithium carbonate formed from the reaction between the lithium-bearing mineral and an alkali metal carbonate can react with alkali earth metal hydroxide to form lithium hydroxide. In some embodiments, the lithium hydroxide produced in the present process may be separated from solids present in the process by solid-liquid separation. The lithium hydroxide may be separated, for example, from alkali metal aluminosilicate and any alkali earth metal carbonate (e.g. calcium carbonate) formed.

[0019] The separated lithium hydroxide may subsequently be crystallised from solution. Accordingly, as well as producing alkali metal aluminosilicate, embodiments of the present invention may also provide a method for recovering lithium hydroxide from a lithium-bearing mineral. In this regard, recovery of lithium hydroxide with a high yield and high purity, typically of battery grade, may be desirable. Battery grade lithium hydroxide as used herein means lithium hydroxide monohydrate crystals having a purity of 56.5% or higher of lithium hydroxide. Lithium hydroxide recovered from the method may also be used for other applications, for example in the pharmaceutical industry.

[0020] As mentioned above, the separated solid product may be used as a binder, for example a construction binder, such as a cementitious or geopolymer binder. The binder may be used to bind and/or form a matrix around aggregate, such as sand, gravel and/or stones. The binder may be mixed with aggregate and water, which sets over time to form concrete.

[0021] Where the solid product is used as a cementitious binder, the solid product may be mixed with a cement such as Portland cement. When used in combination with Portland cement and water, the alkali metal aluminosilicate and any alkali earth metal carbonate present in the solid product may contribute to the formation of calcium silicate hydrates that can contribute to the strength of cementitious materials. Accordingly, by using a mixture of solid product and Portland cement as a binder, the overall amount of Portland cement required may be reduced. In some examples, the solid product may be mixed with Portland cement in a dry weight ratio of 10:1 to 1 :10 to form a binder.

[0022] The manufacture of Portland cement is a highly energy intensive process that involves heating high volumes of raw material to a high temperature e.g. well in excess of 1000 °C. In addition to the CO2 generated from burning fossil fuels to reach these temperatures, the basic raw material used in making Portland cement is calcium carbonate (limestone, CaCCh), and this decomposes during processing to CaO, releasing additional geologically sequestered CO2. Thus, by reducing the proportion of Portland cement required for binder manufacture, embodiments of the method disclosed herein may provide a reduction in CO2 emissions.

[0023] In another embodiment, the separated solid product may be used to form a geopolymer binder. When used as a geopolymer binder, the alkali metal aluminosilicate is preferably not mixed with cement. For example, the binder may comprise less than 15 dry weight % cement, preferably less than 10 dry weight % cement, more preferably less than 5 dry weight % cement, for instance, 0 to 5 dry weight % cement. Without being bound by theory, the alkali metal alumininosilicate and, optionally, any alkali metal carbonate present in the solid product may facilitate the formation of alumino-silicate long-range, covalently bonded, non-crystalline (amorphous) networks that provide strength to the geopolymer structure.

[0024] The binder may be mixed with aggregate and water to form concrete. The concrete may be used in the form of, for example, concrete blocks, paving slabs or other forms useful for construction.

[0025] The source of lithium in the method disclosed herein is a lithium-bearing mineral, wherein the lithium-bearing mineral is preferably selected from at least one of spodumene, lepidolite and petalite.

[0026] In an embodiment, one or more additional sources of lithium may be present in the reaction with alkali metal carbonate. An example of an additional source of lithium is brine. The brine may be subject to one or more additional treatment steps to provide e.g. lithium salts for reaction with the alkali metal carbonate. Examples of lithium salts include lithium sulphate, lithium phosphate, lithium carbonate, and mixtures thereof.

[0027] According to an embodiment of the present invention the lithium-bearing mineral is selected from a mineral containing lithium which has undergone heat treatment, whereby a particularly preferred material is beta-spodumene.

[0028] The method described herein may be carried out in an apparatus for producing an alkali metal aluminosilicate, and optionally lithium hydroxide, from a lithium-bearing mineral. Said apparatus may comprise:

- a pulping unit for pulping the lithium-bearing mineral in the presence of water and an alkali metal carbonate to form a first slurry,

- a first leaching unit for leaching the first slurry at an elevated temperature and pressure to form a second slurry containing lithium carbonate and an alkali metal aluminosilicate,

- a second leaching unit for leaching the second slurry using an alkali earth metal hydroxide to produce a third slurry, - a separation unit for separating a solid product comprising alkali metal aluminosilicate and alkali earth metal carbonate.

Lithium-bearing mineral

[0029] As discussed above, the lithium source is a lithium-bearing mineral selected from at least one of spodumene, lepidolite, petalite, eucryptite and hectorite. Preferably, the lithium- bearing mineral is spodumene, for example beta-spodumene. In one embodiment, the method also comprises pre-treating the lithium-bearing material, such as using a heat treatment. For example, spodumene occurs in nature as alpha-spodumene. However, the alpha-spodumene is preferably converted into beta-spodumene before reaction with alkali metal carbonate. For example, this may be performed by heating the alpha-spodumene to a temperature of approximately 1050 °C for a suitable period of time.

[0030] Additionally, further lithium sources may be included. These additional lithium sources may be added at any suitable point during the process, for example, prior, during or after the lithium-bearing mineral is reacted with alkali metal carbonate. In some examples, such additional lithium sources are added to the reaction mixture prior to reaction with alkali earth hydroxide. These further lithium sources may be derived from brine. The brine may initially be treated to obtain lithium salts such as lithium sulphate, lithium phosphate and lithium carbonate.

[0031] Additional lithium carbonate may also be added during the method disclosed herein. Addition of lithium carbonate salts may be performed prior to or during the reaction of the lithium-bearing mineral with the alkali metal carbonate, or after the reaction between the lithium-bearing mineral and the alkali metal carbonate but prior to reacting lithium carbonate with an alkali earth metal hydroxide.

Reaction with Alkali Metal Carbonate

[0032] The reaction of the lithium-bearing mineral with an alkali metal carbonate is performed in an aqueous medium. The alkali metal carbonate e.g. sodium carbonate may be used in excess. The reaction produces an alkali metal aluminosilicate and lithium carbonate. The reaction may be performed at elevated temperature and/or pressure. For example, the temperature may be 160 to 220 °C, preferably 200 to 220 °C. The pressure may be 10 to 30 bar, for example, 15 to 25 bar.

[0033] To carry out the reaction, the lithium-bearing mineral may be pulped in the presence of water and an alkali metal carbonate. This may produce a first slurry containing crushed solids in an aqueous medium. The pulping may be performed in any suitable vessel or reactor by contacting a feed containing the lithium-bearing mineral with alkali metal carbonate and water.

[0034] The first slurry may then be leached to form a second slurry. Leaching may be performed by subjecting the first slurry to an elevated temperature and pressure. The elevated temperature and pressure may be achieved by using high-pressure steam. Leaching may be performed in an autoclave. Leaching may be performed at elevated temperatures of 160 to 220 °C, preferably 200 to 220 °C. The pressure may be 10 to 30 bar, for example, 15 to 25 bar.

[0035] The lithium-bearing minerals employed in the present disclosure are selected from least one of spodumene, lepidolite, petalite, eucryptite and hectorite. Such minerals are lithium-bearing aluminium silicates. Such lithium-bearing aluminium silicates react with sodium, potassium and/or cesium carbonate to form sodium, potassium and/or cesium aluminium silicate and lithium carbonate.

[0036] In the case of spodumene, for example, the reaction with sodium carbonate can be written as follows:

2 LiAI(SiO₃)₂ + Na₂CO₃ — 2NaAI(SiO₃)₂ + Li₂CO₃

[0037] The sodium aluminium silicate or analcime produced may be separated, for example, with the lithium carbonate for reaction e.g. with an alkali earth hydroxide. The lithium carbonate may have limited solubility, facilitating its separation with the analcime produced. [0038] In one embodiment, the sodium, potassium and/or cesium aluminium silicate and lithium carbonate may be separated in a solid-liquid separation step. The solids may be separated for reaction e.g. with an alkali earth hydroxide. The liquid may be recycled, for example, back to the reaction of the lithium-bearing mineral with an alkali metal carbonate. For example, where the lithium-bearing mineral is pulped in the presence of water and an alkali metal carbonate, the liquid separated in the solid-liquid separation step may be recycled to the pulping step. Additionally or alternatively, the liquid separated may be recycled to the first leaching step.

Optional reaction with Alkali Earth Metal Hydroxide

[0039] In a further step, the lithium carbonate may be reacted with an alkali earth metal hydroxide. Suitable alkali earth metal hydroxides include barium, calcium and/or magnesium hydroxide, preferably calcium hydroxide. The alkali earth metal hydroxide (e.g. calcium hydroxide) reacts with lithium carbonate to produce lithium hydroxide and alkali earth metal carbonate (e.g. calcium carbonate). The calcium carbonate or other alkali earth metal carbonate produced may be separated together with any alkali metal aluminosilicate present and used e.g. as a binder.

[0040] In one embodiment, an alkali earth metal hydroxide may be added to the second slurry after the first leaching step. This addition may be carried out in a further vessel or reactor, optionally after a liquid phase containing excess leaching solution from the first leaching step has been separated and e.g. recycled to the pulping and/or first leaching step. The alkali earth metal hydroxide reacts with lithium carbonate in a second leaching step to form lithium hydroxide and alkali earth metal carbonate. For example, in the case where the alkali earth metal hydroxide is calcium hydroxide, the reaction may be summarised by the following equation:

[0041] This reaction may be carried out at a temperature of 10 to 100 °C, preferably 20 to 60 °C, and suitably 20 to 40 °C. A typical pressure may be 1 to 10 bar, preferably atmospheric pressure. [0042] Preferably, the addition of alkali earth metal hydroxide occurs prior to the separation of alkali metal aluminosilicate from the reaction medium. Accordingly, after the reaction, alkali metal aluminosilicate is also present as a solid component in the reaction medium, together with the alkali earth metal carbonate.

[0043] Where the alkali earth metal hydroxide is calcium hydroxide and sodium carbonate is reacted with the lithium-bearing mineral, analcime (NaAI(SiO₃)₂) is present as the solid component of the product mixture:

[0044] The alkali earth metal hydroxide may be added in an amount that is at least stoichiometric with respect to the amount of lithium carbonate in the aqueous medium.

[0045] In one embodiment, the product mixture may be considered as a third slurry. The slurry may be separated using any suitable solid-liquid separation method to separate the solid product comprising the alkali metal aluminosilicate (e.g. analcime). Preferably, the separated solid product also comprises alkali earth metal carbonate (e.g. calcium carbonate). At least some of the alkali earth metal carbonate present in the solid product may be generated as a result of the reaction between the alkali earth metal hydroxide and lithium carbonate in the aqueous medium.

[0046] In a preferred embodiment, the separated solid product comprises alkali metal aluminosilicate and alkali earth metal carbonate. The separated solid product may comprise solids other than alkali metal aluminosilicate and alkali earth metal carbonate. For example, other mineral components may be present. Examples of other mineral components that may be present include at least one of quartz, feldspars, micas, amphiboles and apatite. Residual lithium carbonate and/or alkali earth metal hydroxide may also be present.

[0047] The separated solid product may comprise 40 to 99 weight % alkali metal aluminosilicate and 1 to 60 weight % alkali earth metal carbonate. Preferably, the separated solid product may comprise 50 to 90 weight % alkali metal aluminosilicate and 5 to 40 weight % alkali earth metal carbonate. More preferably, the separated solid product may comprise 55 to 80 weight % alkali metal aluminosilicate and 5 to 25 weight % alkali earth metal carbonate. Even more preferably, the separated solid product may comprise 60 to 75 weight % alkali metal aluminosilicate and 10 to 20 weight % alkali earth metal carbonate. In some examples, the separated solid product may further comprise alkali earth metal hydroxide (e.g. calcium hydroxide). Alkali earth metal hydroxide (e.g. calcium hydroxide) may be present in an amount of 0 to 5 weight %, preferably 0.1 to 3 weight %.

[0048] The separated solid product may comprise analcime and calcium carbonate. The separated solid product may comprise 40 to 99 weight % analcime and 1 to 60 weight % calcium carbonate. The separated solid product may comprise solids other than analcime and calcium carbonate. For example, other mineral components may be present. Examples of other mineral components that may be present include at least one of quartz, feldspars, micas, amphiboles and apatite. Residual lithium carbonate and/or calcium hydroxide may also be present.

[0049] Preferably, the separated solid product may comprise 50 to 90 weight % analcime and 5 to 40 weight % calcium carbonate. More preferably, the separated solid product may comprise 55 to 80 weight % analcime and 5 to 25 weight % calcium carbonate. Even more preferably, the separated solid product may comprise 60 to 75 weight % analcime and 10 to 20 weight % calcium carbonate. In some examples, the separated solid product may further comprise calcium hydroxide. Calcium hydroxide may be present in an amount of 0 to 5 weight %, preferably 0.1 to 3 weight %.

[0050] As discussed below, the proportions of alkali metal aluminosilicate (e.g. analcime) to alkali earth metal carbonate (e.g. calcium carbonate) may be selected to improve the binding properties of the solid product.

[0051] Separation of the solid product comprising the alkali metal aluminosilicate and optionally alkali earth metal carbonate may be performed by any suitable solid-liquid separation method, typically by thickening and/or filtering. [0052] Following separation of the solid product from the aqueous medium, the solid product may optionally be dried to form a powder. The moisture level of the powder may be controlled to avoid the powder being too readily dispersed by e.g. wind. In some examples, the solid product may be dried to a final moisture content of 10 to 40 weight %, preferably 25 to 35 weight %. In some examples, the solid product may be dried to a final moisture content of less than 10 weight %, less than 5 weight %, less than 2 weight %, less than 1 weight %, less than 0.5 weight %, less than 0.2 weight %, or less than 0.1 weight %. In some examples, the solid product may be dried to a final moisture content of 0.01 to 10 weight %, 0.01 to 5 weight %, 0.01 to 2 weight %, 0.01 to 1 weight %, 0.01 to 0.5 weight %, 0.01 to 0.2 weight %, or 0.01 to 0.1 weight %.

[0053] The grain size of the separated solid product may be less than 500 microns. Mean particle sizes may be 10 to 100 microns.

As discussed herein, the solid product may be used as a binder.

[0054] The lithium hydroxide produced may be separated from the solution to provide solid lithium hydroxide. Any suitable solid-liquid separation method may be used, for example thickening and/or filtering. In an embodiment, lithium hydroxide monohydrate crystals may be recovered from the solution by crystallisation, for example by heating and cooling or alternatively by merely concentrating the solution by heating. Aqueous solution obtained during crystallizing the lithium hydroxide monohydrate may be recovered and recycled to any previous process step, for example, the reaction of the lithium-bearing mineral with alkali metal carbonate, or the reaction of lithium carbonate with alkali earth metal hydroxide. Optionally, this aqueous solution may be pre-treated prior to recycling, for example by adjusting the pH of the solution by carbonation with CO2.

[0055] In an embodiment, purification of the lithium hydroxide-containing solution may be performed, for example by ion exchange, e.g. by using a cation exchange resin.

Optional recovery of lithium carbonate [0056] As an alternative or in addition to reacting the lithium carbonate produced by the reaction between the lithium-bearing mineral and an alkali metal carbonate with an alkali earth metal hydroxide, it may be possible to recover the lithium carbonate from solution. Like lithium hydroxide, lithium carbonate may also be used in the manufacture of batteries.

[0057] As noted above, the reaction between the lithium-bearing mineral and an alkali metal carbonate produces alkali metal aluminosilicate and lithium carbonate. These solids may be separated by a suitable solid-liquid separation method.

[0058] In one embodiment, the solids obtained from this separation step may be recovered and carried to a separate process of recovering pure lithium carbonate in a process that may comprise one or more of the following: (i) mixing the solids containing lithium into an aqueous solution to prepare a further slurry containing lithium carbonate; (ii) carbonating said further slurry containing lithium carbonate by using carbon dioxide for producing a solution containing lithium bicarbonate; (iii) separating solids from the solution containing lithium bicarbonate by solid-liquid separation, and (iv) recovering lithium carbonate by crystallising it from the solution containing lithium bicarbonate.

[0059] The separated solids from step (iii) above comprise alkali metal aluminosilicate. This separated solid product may be used as a binder as described herein.

Binder

[0060] The separated solid product may be used to form a binder that may be useful in construction (construction binder). The binder may be used to bind or form a matrix for aggregate, such as sand, gravel or stone.

[0061] Where the solid product is used as a cementitious binder, the solid product may be mixed with a cement such as Portland cement. When used in combination with Portland cement and water, the alkali metal aluminosilicate and any alkali earth metal carbonate present in the solid product may contribute to the formation of calcium silicate hydrates that are responsible for the strength of cementitious materials. Accordingly using a mixture of solid product and Portland cement as a binder, the overall amount of Portland cement required may be reduced.

[0062] In some examples, the solid product may be mixed with Portland cement in a dry weight ratio of 10:1 to 1 :10 to form a binder. Preferably, the dry weight ratio may be 5:1 to 1 :5, for example 3: 1 to 1 :3 by weight.

[0063] As mentioned above, the manufacture of Portland cement is a highly energy intensive process that involves heating high volumes of raw material to a high temperature e.g. well in excess of 1000 °C. In addition to the CO2 generated from burning fossil fuels to reach these temperatures, the basic raw material used in making Portland cement is calcium carbonate (limestone, CaCOs), and this decomposes during processing to CaO, releasing additional geologically sequestered CO2. Thus, by reducing the proportion of Portland cement required for binder manufacture, embodiments of the method disclosed herein may provide a reduction in CO2 emissions.

[0064] In another embodiment, the separated solid product may be used to form a geopolymer binder. When used as a geopolymer binder, the alkali metal aluminosilicate is preferably not mixed with cement. For example, the binder may comprise less than 15 dry weight % cement, preferably less than 10 dry weight % cement, more preferably less than 5 dry weight % cement, for instance, 0 to 5 dry weight % cement.

[0065] The binder may be mixed with aggregate and water to form concrete. The concrete may be used in the form of, for example, concrete blocks, paving slabs or other forms useful for construction.

[0066] The binder may be used to form concrete that may withstand pressures determined by the design limit. For example, the binder may be used to form concrete that may withstand pressures of at least about 5 MPa, preferably from about 5 to 60 MPa, for example from about 10 to 40 MPa. [0067] The binder may be mixed with an aggregate and water to form concrete. The aggregate may comprise sand, gravel, stones and/or mixtures thereof. The binder may also be used to form e.g. reinforced concrete.

[0068] The solid product may comprise solids other than alkali metal aluminosilicate and alkali earth metal carbonate. For example, other mineral components may be present. Examples of other mineral components that may be present include at least one of quartz, feldspars, micas, amphiboles and apatite. Residual lithium carbonate and/or alkali earth metal hydroxide may also be present.

[0069] The solid product may comprise 40 to 99 weight % alkali metal aluminosilicate and 1 to 60 weight % alkali earth metal carbonate. Preferably, the solid product may comprise 50 to 90 weight % alkali metal aluminosilicate and 5 to 40 weight % alkali earth metal carbonate. More preferably, the solid product may comprise 55 to 80 weight % alkali metal aluminosilicate and 5 to 25 weight % alkali earth metal carbonate. Even more preferably, the solid product may comprise 60 to 75 weight % alkali metal aluminosilicate and 10 to 20 weight % alkali earth metal carbonate. In some examples, the separated solid product may further comprise alkali earth metal hydroxide (e.g. calcium hydroxide). Alkali earth metal hydroxide (e.g. calcium hydroxide) may be present in an amount of 0 to 5 weight %, preferably 0.1 to 3 weight %. x

[0070] In one embodiment, the solid product may comprise analcime and calcium carbonate. The solid product may comprise solids other than analcime and calcium carbonate. For example, other mineral components may be present. Examples of other mineral components that may be present include at least one of quartz, feldspars, micas, amphiboles and apatite. Residual lithium carbonate and/or calcium hydroxide may also be present.

[0071] In one embodiment, the solid product may comprise 40 to 99 weight % analcime and 1 to 60 weight % calcium carbonate. Preferably, the solid product may comprise 50 to 90 weight % analcime and 5 to 40 weight % calcium carbonate. More preferably, the solid product may comprise 55 to 80 weight % analcime and 5 to 25 weight % calcium carbonate. Even more preferably, the solid product may comprise 60 to 75 weight % analcime and 10 to 20 weight % calcium carbonate. In some examples, the separated solid product may further comprise calcium hydroxide. Calcium hydroxide may be present in an amount of 0 to 5 weight %, preferably 0.1 to 3 weight %. [0072] The proportions of alkali metal aluminosilicate (e.g. analcime) to alkali earth metal carbonate (e.g. calcium carbonate) may be selected to improve the binding properties of the solid product. For example, in the case of a cementitious material, the proportions may facilitate the formation of calcium silicate hydrates that are responsible for the strength of cementitious materials. In the case of geopolymers, the proportions may also assist in the formation of alumino-silicate long-range, covalently bonded, non-crystalline (amorphous) networks that hold the geopolymer matrix together. The relative amounts of alkali metal aluminosilicate (e.g. analcime) to alkali earth metal carbonate (e.g. calcium carbonate) may be varied by varying the amount of alkali earth metal hydroxide that is used to react with the lithium carbonate in the aqueous medium. In some examples, the relative amount of alkali earth metal hydroxide (e.g. calcium hydroxide) in the solid product may also be varied by varying the amount of alkali earth metal hydroxide (e.g. calcium hydroxide) that is used to react with the lithium carbonate in the aqueous medium.

[0073] In one embodiment, the solid product has the following composition by weight %:

SiC>2 - 40 to 60 %, preferably 45 to 50%

AI2O3 - 10 to 30 %, preferably 15 to 20 %

Carbonate - 0 to 6 %, preferably 3.5 to 5 %

CaO - 3 to 20%, preferably 8 to 12 %

U2O - 0 to 2%, preferably 0.2 to 0.5 %

Na2<D - 5 to 20%, preferably 9 to 13%

K2O - 0 to 5%, preferably 0.2 to 5 %

Figures 1 and 2

[0074] Embodiments of the method disclosed herein are presented schematically in Figures 1 and 2. Figures 1 and 2 illustrate systems for the production and recovery of lithium hydroxide and a solid product comprising an alkali metal aluminosilicate. The systems include a pulping unit 10, a first leaching unit 20, a second leaching unit 30, separation unit 31 and a crystallisation unit 40. [0075] According to the method of the embodiment depicted in Figure 1 , the method comprises pulping a raw material comprising a lithium-bearing mineral 1 (e.g. spodumene) in the presence of water and an alkali metal carbonate 2 to form a first slurry in a pulping unit 10. A preferred alkali metal carbonate is sodium carbonate. Typically, the alkali metal carbonate is present in excess. After pulping the first slurry is leached 20 to produce a second slurry containing lithium carbonate.

[0076] The leaching is performed in leaching unit 20. Leaching is carried out at a temperature of 160 to 250 °C, preferably 200 to 220 °C. Suitable pressures may be 10 to 30 bar, preferably 15 to 25 bar. Suitable conditions are achieved using high pressure steam.

[0077] The reaction between the lithium-bearing mineral and alkali metal carbonate produces alkali metal aluminosilicate and lithium carbonate. The reaction in the case of spodumene is illustrated by the reaction below:

2 LiAI(SiO₃)₂ + Na₂CO₃ ^2NaAI(SiO₃)₂ + Li₂CO₃

[0078] The slurry containing lithium carbonate is then routed to a second leaching step 30, performed in any suitable vessel or reactor. The second leaching 30 is preferably performed by using an alkali earth metal hydroxide as a leaching agent 3. Suitable alkali earth metal hydroxides are calcium hydroxide and barium hydroxide, calcium hydroxide (Ca(OH)₂) being most preferred. The calcium hydroxide may be prepared by reaction of calcium oxide (CaO) in the aqueous solution. The temperature in the second leaching 30 may be 10-100°C, preferably 20-60°C, and most suitable 20-40°C. A typical pressure for the second leaching step 30 may be 1 -10 bar, preferably atmospheric pressure.

[0079] In the second leaching step in the second leaching unit 30, the alkali earth metal hydroxide reacts with lithium carbonate to form lithium hydroxide and alkali earth metal carbonate. For example, in the case where the alkali earth metal hydroxide is calcium hydroxide, the reaction may be summarised by the following equation: Li₂CO₃ + Ca(OH)₂ 2LiOH + CaCO₃

[0080] Where the alkali earth metal hydroxide is calcium hydroxide and sodium carbonate is reacted with the lithium-bearing mineral, analcime is present as the solid component of the product mixture:

NaAI(SiO₃)₂ + Li₂CO₃ + Ca(OH)₂ 2LiOH + CaCO₃ + NaAI(SiO₃)₂

[0081] After the two leaching steps 20, 30 have been performed, the obtained third lithium hydroxide-containing slurry is separated 31 into a solid phase 5 and a solution. The separation 31 can be carried out using any suitable solid-liquid separation method.

[0082] The separated solid product comprises alkali metal aluminium silicate and optionally alkali earth metal carbonate. In some examples, the solid product may also comprise lithium carbonate and/or calcium hydroxide.

[0083] Preferably, the solid product comprises analcime and calcium carbonate. The separated solid product may be used as a binder.

[0084] After the solid-liquid-separation 31 the solution containing lithium can optionally be purified by using a suitable purifying method. According to an embodiment of the invention, the lithium-containing solution is purified with ion exchange in order to remove further impurities. Typically the purifying by ion exchange is performed by using cation exchange resin. Typically the purifying by ion exchange is performed by using a cation exchange resin, wherein the cation exchange group is for example iminodiacetic acid (IDA) or aminophosphonic acid (APA).

[0085] After the separation 31 and optional purifying, lithium hydroxide monohydrate 4 is recovered by crystallising it in crystallisation unit 40, for example by heating the purified solution in the crystallization unit to evaporate the liquid, or by recrystallizing the monohydrate from a suitable solvent. [0086] Any bleed solution obtained while crystallizing 40 the lithium hydroxide monohydrate can be recovered and recycled to one or more of the previous process steps, for example the pulping step 10, first leaching step 20, second leaching step 30, separation step 31 , and/or an upstream level of the crystallization step 40.

[0087] Referring to Figure 2, this figure illustrates a system that is similar to Figure 1 and like numerals have been used to refer to like parts of the system. However, instead of treating the entirety of the slurry from the second leaching unit 20 with alkali metal hydroxide in the second leaching step 30, the slurry from the second leaching unit 20 is first treated in a solid-liquid separation unit 21. This unit separates solids comprising lithium carbonate and alkali metal silicate from a liquid phase of the slurry. The solids are subjected to the second leaching step 30 with alkali earth metal hydroxide.

[0088] The separation unit 21 can be equipped with a line 211 for carrying a liquid fraction from said separation unit 21 to the pulping unit 10, and/or a line 212 for carrying a liquid fraction from said separation unit 21 to the first leaching unit 20.

[0089] In the method of the present invention, an alkali metal aluminosilicate is produced by reacting a lithium-bearing mineral with an alkali metal carbonate in an aqueous medium to form alkali metal aluminosilicate and lithium carbonate. At least a portion of the alkali metal aluminosilicate is separated from the aqueous medium. The separated alkali metal aluminosilicate is treated to reduce its pH, and/or the separated alkali metal aluminosilicate is used to form a binder.

[0090] The claimed method may be essentially sulphate-free and acid-free, and does not result in the formation of undesired crystallized by-products. Indeed, in the present method the alkali metal aluminosilicate from the reaction of a lithium-bearing mineral and alkali metal carbonate may be usefully employed. When a solid product comprising the alkali metal aluminosilicate is mixed with Portland cement for use as a binder, lower amounts of Portland cement may be required for the production of materials such as concrete, thus producing a less CO2 intensive construction binder. Alternatively, the alkali metal aluminosilicate may itself be used to form a geopolymer binder. This geopolymer binder may be devoid of Portland cement, thus providing a relatively low CO2 intensive binder. In addition, concrete produced using the alkali metal aluminosilicate may demonstrate improved carbon capture, thus also acting to reduce CO2.

[0091] A number of embodiments of the disclosure have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the present disclosure. Accordingly, other embodiments are within the scope of the following claims.

[0092] All headings and sub-headings are used herein for convenience only and should not be construed as limiting the invention in any way.

[0093] The use of any and all examples, or exemplary language (e.g. “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise paragraphed. No language in the specification should be construed as indicating any non-paragraphed element as essential to the practice of the invention.

Claims

1. A method for producing an alkali metal aluminosilicate, said method comprising reacting a lithium-bearing mineral with an alkali metal carbonate in an aqueous medium to form alkali metal aluminosilicate and lithium carbonate, wherein said lithium-bearing mineral is selected from at least one of spodumene, lepidolite, petalite, eucryptite and hectorite, and wherein said alkali metal carbonate is selected from a carbonate of sodium, potassium and/or cesium; separating a solid product comprising at least a portion of the alkali metal aluminosilicate from the aqueous medium; and using the separated solid product to form a binder.

2. A method as claimed in claim 1 , wherein the separated solid product is used to form a binder, for example a cementitious binder or a geopolymer binder.

3. A method as claimed in any one of the preceding claims, wherein the solid product is mixed with Portland cement to form a binder.

4. A method as claimed in claim 3, wherein the solid product is mixed with Portland cement in an amount of 10:1 to 1 :10 to form a binder.

5. A method as claimed in any preceding claim, wherein the binder is mixed with aggregate and water to form concrete.

6. A method as claimed in any one of the preceding claims, wherein the alkali metal carbonate is sodium carbonate.

7. A method as claimed in any one of the preceding claims, wherein the lithium-bearing mineral is reacted with an alkali metal carbonate at a temperature of 160 to 220 °C, preferably 200 to 220 °C, and/or a pressure of 10 to 30 bar, preferably 15 to 25 bar.

8. A method as claimed in any one of the preceding claims, wherein the lithium carbonate formed from the reaction between the lithium-bearing mineral with an alkali metal carbonate is reacted with an alkali earth metal hydroxide to form lithium hydroxide and alkali earth metal carbonate.

9. A method as claimed in claim 8, wherein the alkali earth metal hydroxide is added to the aqueous medium before separation of the solid product.

10. A method as claimed in claim 9, wherein the solid product comprises alkali metal aluminosilicate and alkali earth metal carbonate.

11. A method as claimed in claim 10, wherein the solid product comprises analcime and calcium carbonate.

12. A method as claimed in claim 11, wherein the solid product comprises 50 to 80% analcime and 5 to 20% calcium carbonate.

13. A method as claimed in any one of claims 9 to 12, wherein the lithium hydroxide is separated by solid-liquid separation.

14. A method as claimed in claim 13, wherein the separated lithium hydroxide is crystallised from solution.