WO2025174250A1

WO2025174250A1 - Method and apparatus for purification and separation of solid-state carbon-containing material

Info

Publication number: WO2025174250A1
Application number: PCT/NO2025/050020
Authority: WO
Inventors: Vladimir KOSTKA; Fredrik ROSBERG HANSEN
Original assignee: Bergen Carbon Solutions As
Current assignee: Bergen Carbon Solutions As
Priority date: 2024-02-13
Filing date: 2025-02-12
Publication date: 2025-08-21
Anticipated expiration: 2026-08-13
Also published as: NO20240129A1

Abstract

The present invention relates to a method for purification and separation of solid-state carbon-containing material generated from electrolysis of a molten lithium carbonate elec- trolyte and recovery of lithium carbonate The method comprises obtaining a solid reaction product formed from electrolysis of a molten lithium carbonate salt electrolyte. The solid reaction product is mixed with an aqueous source and carbon dioxide is introduced at a predetermined first pressure to produce carbon dioxide treated aqueous reaction product mixture. The temperature and pressure of the carbon dioxide treated aqueous reaction product mixture is controlled to produce solid-state carbon material and an aqueous solu- tion rich in lithium salts. The solid-state carbon is separated from the aqueous solution rich in lithium salts. Carbon dioxide stream, precipitated lithium carbonate and an aqueous solution poor in lithium salts are generated by controlling the pressure and temperature of the aqueous solution rich in lithium salts. The precipitated lithium carbonate is separated from the aqueous solution poor in lithium salts. The method further comprises one or more of: recycling the recovered precipitated lithium carbonate as a feed source for the molten lithium carbonate salt electrolyte; and/or recycling the recovered aqueous solution poor in lithium salts as at least a portion of the aqueous source.

Description

METHOD AND APPARATUS FOR PURIFICATION AND SEPARATION OF SOLID-

STATE CARBON-CONTAINING MATERIAL

The present invention relates to a method and apparatus for purification and separation of solid-state carbon-containing material generated from electrolysis of a molten lithium carbonate electrolyte, and for the recovery of lithium carbonate.

BACKGROUND OF INVENTION

Electrolysis of a lithium-containing matrix, such as for example molten lithium carbonate (U2CO3), produces carbon in solid-state as a result of carbonate ions being reduced at the cathode, oxygen at the anode and lithium oxide (U2O) dissolved in the electrolyte. The reaction products, which may comprise parts of the electrolyte, such as lithium carbonate, are removed from the electrolysis reactor in solid state. The resulting solid reaction product typically contains significant amounts of solid carbon which will need to be purified before it can be used in downstream processes. Furthermore, lithium carbonate and lithium oxide are valuable resources. Conventional methods for separation of the carbon material have been found to be detrimental to other components of the mixture. For example, conventional methods for separation use strong acid which converts residual lithium carbonate to another lithium salt (such as lithium chloride). Potential recovery of lithium carbonate from a solution of another lithium salt is technically complex process.

There is therefore a need for an efficient method of separating solid-state carbon material generated during electrolysis from a lithium-containing matrix which does not adversely affect the lithium compounds, for example by conversion of lithium carbonate to less valuable lithium salts such as lithium chloride.

SUMMARY OF INVENTION

According to a first aspect of the present invention, there is provided a method for purification and separation of solid-state carbon-containing material generated from electrolysis of a molten lithium carbonate electrolyte and for recovery of lithium carbonate, the method comprising: a) obtaining a solid reaction product formed from electrolysis of a molten lithium carbonate salt electrolyte; b) mixing the solid reaction product with an aqueous source and introducing carbon dioxide at a predetermined first pressure to produce carbon dioxide treated aqueous reaction product mixture; c) controlling the temperature of the carbon dioxide-treated aqueous reaction product mixture and controlling the pressure of the carbon dioxide treated aqueous reaction product mixture to produce solid-state carbon material and an aqueous solution rich in lithium salts; d) separating the solid-state carbon material from the aqueous solution rich in lithium salts; e) controlling the temperature of the aqueous solution rich in lithium salts and the pressure of the aqueous solution rich in lithium salts to generate a carbon dioxide stream, precipitated lithium carbonate and an aqueous solution poor in lithium salts. f) separating precipitated lithium carbonate from the aqueous solution poor in lithium salts; and g) in which the method further comprises one or more of the following steps: recycling at least a portion of the recovered precipitated lithium carbonate as a feed source for the molten lithium carbonate salt electrolyte; and/or recycling at least a portion of the recovered aqueous solution poor in lithium salts as at least a portion of the aqueous source in step b.

The aqueous solution rich in lithium salts may comprise lithium carbonate, lithium oxide, lithium bicarbonate and CO2. A value of total dissolved solids (TDS) of the aqueous solution rich in lithium salts may be higher than 30 g/L. The value of TDS of the aqueous solution rich in lithium salts may be higher than 60 g/L. The value of TDS of the aqueous solution rich in lithium salts may preferably be higher than the value of TDS of the aqueous solution poor in lithium salts.

The aqueous solution poor in lithium salts may comprise dissolved lithium carbonate, lithium oxide, lithium bicarbonate and CO2. A value of TDS of the aqueous solution poor in lithium salts may be lower than 120 g/L. The value of TDS of the aqueous solution poor in lithium salts may be lower than 60 g/L. The value of TDS of the aqueous solution poor in lithium salts may preferably be lower than the value of TDS of the aqueous solution rich in lithium salts.

By lithium salts, it is here meant lithium carbonate, lithium bicarbonate and lithium oxide.

The method may further comprise electrolysing a molten lithium carbonate salt electrolyte in the presence of carbon dioxide to produce a solid reaction product (step a).

The molten lithium carbonate salt electrolyte may further comprise transition metal-based compounds.

The solid reaction product formed from the electrolysis of the molten lithium carbonate salt electrolyte may therefore comprise transition metal-containing material in addition to the solid-state carbon material.

The transition metal-containing material may be integrated within the carbon-containing material.

The transition metal-containing material may be on the outside of the carbon structures of the carbon-containing material. In this case, the transition metal-containing material and the carbon-containing material may be separated as will be explained later.

The transition metal-containing material may be dissolved in the solution of the solid reaction product. In this case, the transition metal-containing material may be removed from the solution as will be explained later.

The aqueous solution rich in lithium salts may further comprise transition metal ions.

The aqueous solution poor in lithium salts may further comprise transition metal ions.

Step d may comprise separating the solid-state carbon and transition metal-containing material from the aqueous solution rich in lithium salts.

At the cathode of an electrolysis reactor, one or more of the reactants are reduced to form solid-state carbon material:

Li2COs(i) ◄ — ► 2Li⁺ + CO3²'

2Li⁺ + O²- ◄- U₂O Lithium oxide and oxygen are generated at the anode.

The solid reaction product may comprise one or more of: carbon; carbon-containing material (for example carbon-heteroatom substances); metal particles (such as for example metal(s) and/or metal oxide(s)); lithium carbonate; lithium oxide; inorganic contaminants (including for example metal particles, carbon particles, metal oxide(s), metal carbide(s), or compounds thereof. The particles or compounds may be partially or wholly confined within a matrix of solidified pure or mixed inorganic salts (for example alkali and/or alkali earth metal carbonates, oxides and/or chlorides, and may include minor components of sulphates, non-chloride halides, hydroxides and/or nitrates)), or any combination thereof.

The solid reaction product may comprise one or more of: carbon; carbon-containing material; metal particles; lithium carbonate; lithium oxide; or any combination thereof.

The solid reaction product may comprise between 1 and 50 wt. % solid carbon, between 0 and 50 wt. % lithium oxide and between 5 and 99 wt. % lithium carbonate. In a preferred embodiment, the solid reaction product may comprise between 1-25 wt. % solid carbon, between 0 and 50 wt. % lithium oxide, and between 75 and 99 wt. % lithium carbonate.

Electrolysis of CO2 with molten lithium carbonate as electrolyte produces lithium oxide in solid state. For a stable electrolysis process, lithium carbonate may be refilled to the elec- trolyser.

Mixing the solid reaction product with an aqueous source and introducing carbon dioxide at a predetermined first pressure (step b) converts lithium oxide to lithium carbonate. Lithium oxide, within the solid reaction product, reacts with water within the aqueous source to product lithium hydroxide. Lithium hydroxide reacts with carbon dioxide to form lithium carbonate. The lithium carbonate recovered in step f may therefore comprise unreacted lithium carbonate from the electrolysis and lithium carbonate converted from lithium oxide. Recycling the recovered precipitated lithium carbonate as a feed source for the molten lithium carbonate salt electrolyte in step g may therefore ensure a stable electrolysis process. In an electrolysis process wherein the recovered precipitated lithium carbonate is used as the electrolyte, CO2 may therefore not need to be added to the electrolysis process.

The particle size of the solid reaction product generated from the electrolysis of the molten lithium carbonate salt electrolyte (step a) may be reduced prior to mixing with an aqueous source and/or being exposed to carbon dioxide (step b). The particle size of the solid re- action product may be reduced using any suitable technique, including but not limited to grinding and/or milling and/or crushing. The particle size of the solid reaction product may be reduced to a particle size of 5 mm. The particle size of the solid reaction product may preferably be reduced to a particle size of 1 mm or smaller.

The solid reaction product may be cooled prior to being supplied to a grinding unit or milling unit.

In one embodiment, the electrolyte (comprising for example molten lithium carbonate and lithium oxide) may be removed from the electrolyser, cooled, and solidified. The electrolyte may then be introduced into step b of the method and treated according to the remaining steps of the method of the present invention.

The solid reaction product may be mixed with the aqueous source prior to introducing carbon dioxide. In one embodiment, the carbon dioxide is introduced to the aqueous source prior to mixing with the solid reaction product.

The aqueous source (step b) preferably comprises water. The aqueous source preferably comprises demineralized water solution. The aqueous source preferably comprises deionized water solution. In one embodiment, the recovered aqueous solution poor in lithium salts (step e) may be introduced into the reaction vessel as at least a portion of the aqueous source together with water (for example as a closed loop).

The solubility of lithium salts in an aqueous solution mixed with CO2 depend on the temperature and the pressure of the aqueous solution mixed with CO2. Controlling the temperature and the pressure of the carbon dioxide-treated aqueous reaction product mixture in step b may therefore enable controlling of the solubility of lithium salts in the carbon dioxide-treated aqueous reaction product mixture. Likewise, controlling the temperature and the pressure of the aqueous solution rich in lithium salts in step e may therefore enable controlling of the solubility of lithium salts in the aqueous solution rich in lithium salts.

The pressure and the temperature in steps c and e may be controlled such that the solubility of lithium salts in the carbon dioxide-treated aqueous reaction product mixture is higher than the solubility of lithium salts in the aqueous solution rich in lithium salts. The lower solubility in step e may result in precipitation of lithium carbonate and an aqueous solution poor in lithium salts.

Step c may comprise maintaining the pressure of the carbon dioxide treated aqueous product mixture at the predetermined first pressure. The carbon dioxide treated aqueous product mixture (step b) is preferably maintained at a predetermined first pressure of no more than 73 barg (7.4 Mpa, pressure at critical point of CO2), preferably no more than 10 barg (1.1 MPa). The carbon dioxide treated aqueous product mixture (step b) is preferably maintained at a predetermined first pressure of at least 0 barg (0.1 MPa), preferably at least 5 barg (0.6 MPa), or preferably at least 2.5 barg (0.35 MPa). The carbon dioxide treated aqueous product mixture (step b) is preferably maintained at a predetermined first pressure of between 0 barg and 73 barg (7.4 MPa), preferably between 2.5 barg and 10 barg (0.35 and 1.1 MPa).

The solubility of lithium salts in the aqueous solution increases as the pressure of the carbon dioxide treated aqueous product mixture increases. Maintaining the pressure of the carbon dioxide-treated aqueous reaction product mixture as high as possible may therefore increase the efficiency of the process.

Step c may comprise maintaining the pressure of the carbon dioxide treated aqueous product mixture at a predetermined first temperature.

The predetermined first temperature of the carbon dioxide-treated aqueous reaction product mixture in step c may be no more than 60°C, preferably no more than 40°C, preferably no more than 20°C. The predetermined first temperature may for example be 35°C, or 10°C, or 5°C. The predetermined first temperature may preferably be above the freezing point of the carbon dioxide-treated aqueous reaction product mixture. The predetermined first temperature may preferably be above the freezing point of the aqueous source. Preferably, the predetermined first temperature may be as close as possible to the freezing point of the carbon dioxide-treated aqueous reaction product mixture, without reaching the freezing point of the carbon dioxide-treated aqueous reaction product mixture. The carbon dioxide treated aqueous reaction product mixture may preferably be at a temperature which is higher than the freezing point of the aqueous source, i.e. preferably of no less than 0°C, preferably no less than 10°C, for example about 20°C. The carbon dioxide treated aqueous reaction product mixture is preferably at a temperature of between no less than the freezing point of the carbon dioxide treated aqueous reaction product mixture and 60°C, preferably between 0°C and 40°C, preferably between 10°C and 40°C for example between 15°C and 20°C, or about 20°C.

The solubility of lithium salts in the aqueous solution increases as the temperature of the solution decreases. Maintaining the temperature of the carbon dioxide-treated aqueous reaction product mixture as low as possible may therefore increase the efficiency of the process.

By maintaining the carbon dioxide treated aqueous reaction product mixture at elevated pressures and low temperatures, the solubility of lithium carbonate may significantly increase and as such steps b and c may help to retain the lithium carbonate in solution.

The temperature of the carbon dioxide-treated aqueous reaction product mixture may be maintained by different means, such as a chilled or cold brine, cold or chilled water, or cold or chilled air.

The term “solid-state carbon” is used herein to include graphite, carbon black, amorphous carbon, carbon nanotubes, graphene, activated carbon, fullerenes, and other solid elemental materials formed within the electrolysis reactor. Solid-state carbon includes only carbon atoms except to the extent that trace impurities are present.

The solid-state carbon material may be separated in step d by for example filtration by sedimentation, by liquid filter, or by floatation.

The solid-state carbon and transition metal-containing material may be separated by for example filtration, by sedimentation, by liquid filter, or by floatation.

In one embodiment, the solid-state carbon material or the solid-state carbon and transition metal-containing material may comprise graphitic material. The graphitic material may be recovered by floatation.

The separation of the solid-state carbon material or the solid-state carbon and transition metal-containing material is preferably carried out under the same or similar pressure conditions and/or the same or similar temperature conditions as steps b and c. This may ensure that the lithium carbonate remains in solution.

The solid-state carbon material or the solid-state carbon and transition metal-containing material may be treated further, for example purified further. For example, the solid-state carbon material or the solid-state carbon and transition metal-containing material may be washed with water. The solid-state carbon material or the solid-state carbon and transition metal-containing material may for example be heated and washed with water. The solid state carbon material or the solid-state carbon and transition metal-containing material may be heated. The solid-state carbon material or the solid-state carbon and transition metal-containing material may comprise particles or bulk material in a particle size ranging from nanoscale to macroscopic size.

The solid-state carbon material or the solid-state carbon and transition metal-containing material may further be dried. In one embodiment, the recovered solid-state carbon and transition metal-containing material may be fed into a further separation device to separate the transition metal-containing material from the carbon-containing material. The transition metal-containing material may be separated from the carbon-containing material by different means such as introduction of a strong acid to the mixture of the transition metal-containing material and the carbon-containing material such that the so transition metal-containing material will may react with the strong acid and will thus be separated from the mixture. The separation of the transition metal-containing material from the carbon containing material may be done or by pyrolysis, wherein an increase in temperature with limited oxygen present may lead to the transition metal-containing material evaporating from the mixture.

The method may further comprise, before step e, a step of separating transition metal ions from the aqueous solution rich in lithium salts. The separation may be done by different means such as an ion exchange process.

The recovered carbon-containing material may further be dried.

The recovered transition metal-containing material may further be dried.

The method may be used to separate other solid material (such as for example metal nanorods) produced by the same method. The solubility of lithium salts in the aqueous solution rich in lithium salts depends on the pressure and the temperature of the aqueous solution rich in lithium salts. Lithium carbonate may precipitate in step e if the solubility of the lithium carbonate is lower in step e than the solubility of the lithium carbonate in step c.

Step e may comprise controlling the temperature and the pressure of the aqueous solution rich in lithium salts such that a solubility of lithium salts in the aqueous solution rich in lithium salts is lower than a solubility of lithium salts in the carbon dioxide-treated aqueous reaction product mixture, to generate a carbon dioxide stream, precipitated lithium carbonate and an aqueous solution poor in lithium salts.

Step e may comprise reducing the pressure of the aqueous solution rich in lithium salts to a predetermined second pressure that is lower than the predetermined first pressure. This may be advantageous because reducing the pressure may decrease the solubility of lithium carbonate in the aqueous solution rich in lithium salts. The decrease in solubility may lead to precipitation of lithium carbonate in step e.

Step e may further comprise maintaining the pressure of the aqueous solution rich in lithium salts at the predetermined second pressure that is lower than the predetermined first pressure.

In step e, reducing the pressure of the aqueous solution rich in lithium salts to a predetermined second pressure may comprise one or more of the following steps: maintaining the temperature of the aqueous solution rich in lithium salts at the predetermined first temperature; reducing the temperature of the aqueous solution rich in lithium salts to the predetermined second temperature that is lower than the predetermined first temperature; maintaining the temperature of the aqueous solution rich in lithium salts at the predetermined second temperature that is lower than the predetermined first temperature; increasing the temperature of the aqueous solution rich in lithium salts to the predetermined second temperature that is higher than the predetermined first temperature; and/or maintaining the temperature of the aqueous solution rich in lithium salts at the predetermined second temperature that is higher than the predetermined first temperature;

In step e, maintaining the pressure of the aqueous solution rich in lithium salts at the predetermined second pressure that is lower than the predetermined first pressure may comprise the steps described above.

Step e may comprise increasing the temperature of the aqueous solution rich in lithium salts to a predetermined second temperature that is higher than the predetermined first temperature. This may be advantageous because increasing the temperature may decrease the solubility of lithium carbonate in the aqueous solution rich in lithium salts. The decrease in solubility may lead to precipitation of lithium carbonate in step e.

Step e may further comprise maintaining the temperature of the aqueous solution rich in lithium salts at the predetermined second temperature that is higher than the predetermined first temperature. In step e, increasing the temperature of the aqueous solution rich in lithium salts to a predetermined second temperature may comprise one or more of the following steps: maintaining the pressure of the aqueous solution rich in lithium salts at the predetermined first pressure; increasing the pressure of the aqueous solution rich in lithium salts to the predetermined second pressure that is higher than the predetermined first pressure; maintaining the pressure of the aqueous solution rich in lithium salts at the predetermined second pressure that is higher than the predetermined first pressure; reducing the pressure of the aqueous solution rich in lithium salts to the predetermined second pressure that is lower than the predetermined first pressure; and/or maintaining the pressure of the aqueous solution rich in lithium salts at the predetermined second pressure that is lower than the predetermined first pressure;

In step e, maintaining the temperature of the aqueous solution rich in lithium salts at the predetermined second temperature that is higher than the predetermined first temperature may comprise the steps described above.

Reducing the pressure in step e to a pressure that is lower than the predetermined first pressure, and/or maintaining the pressure in step e at a pressure that is lower than the predetermined first pressure may advantageously comprise the step of increasing the temperature in step e to a temperature that is higher than the predetermined first temperature, and/or maintaining the temperature in step e at a temperature that is higher than the predetermined first temperature. This may be advantageous because it may further decrease the solubility of lithium carbonate, which may lead to more of the lithium carbonate precipitating, and thus a higher efficiency of the process.

The predetermined second pressure during the precipitation step may preferably be no more than 73 barg (7.4 MPa, the pressure at the critical point of CO2). The predetermined second pressure may preferably be higher than -1.01 barg (0.61 KPa, the pressure of the triple point of water). The predetermined second pressure may preferably be higher than the vapour pressure of water at the predetermined second temperature. For example, if the predetermined second temperature is 90°C, the predetermined second pressure may preferably be higher than -0.31 barg (70KPa). The predetermined second pressure may preferably be less than 10 barg (1.1 MPa), preferably less than 5 barg (0.6 MPa), prefera- bly less than 1 barg (0.2 MPa), preferably 0 barg (0.1 MPa, atmospheric pressure). The predetermined second pressure may preferably be around 0 barg (0.1 MPa).

The temperature of the aqueous solution rich in lithium salts may preferably be lower than the boiling point of the aqueous solution rich in lithium salts and lower than the boiling point of the aqueous solution poor in lithium salts. The predetermined second temperature of the aqueous solution rich in lithium salts may for example be at least 60°C. Preferably, the predetermined second temperature of the aqueous solution rich in lithium salts may be at least 75°C, preferably at least 80°C. The predetermined second temperature of the aqueous solution rich in lithium salts may preferably be no more than 100°C. The predetermined second temperature of the aqueous solution rich in lithium salts may preferably be in a range of between 60°C and 100°C, preferably in a range of between 75°C and 95°C, for example about 90°C.

The separated precipitated lithium carbonate (step f) may be dried prior to be recycled as a feed source for the molten lithium carbonate salt electrolyte (step g).

The separated precipitated lithium carbonate (step f) may be further purified. The separated, precipitated lithium carbonate may be redissolved in water (for example deionised water). The water preferably has a temperature of no more than the predetermined first temperature so that the lithium carbonate may dissolve to provide a lithium carbonate- containing solution. The solution may then be heated to raise the temperature, to for example the predetermined second temperature, such that lithium carbonate may precipitate from solution. For example the temperature of the lithium carbonate-containing solution may be raised to at least 50°C, preferably at least 60°C, for example about 70°C, such that lithium carbonate may precipitate from the solution. The precipitated lithium carbonate may then be separated from solution, by for example filtration, to provide purified lithium carbonate. Further transition metal-containing materials may be recovered in the filtrate obtained from the filtration.

In one embodiment, the purified lithium carbonate may be recycled as a feed source for the molten lithium carbonate salt electrolyte (step g). The purified lithium carbonate may be battery or technical grade lithium carbonate. The purified lithium carbonate may be dried prior to be recycled as a feed source for the molten lithium carbonate salt electrolyte.

The aqueous solution poor in lithium salts (step f) may be concentrated prior to recycling into the reaction vessel as at least a portion of the aqueous source (step g). The aqueous solution poor in lithium salts may be concentrated by maintaining a high temperature of the aqueous solution poor in lithium salts while recycling into the reaction vessel. The aqueous solution poor in lithium salts may be cooled prior to recycling as at least a portion of the aqueous source. The recycling of the aqueous solution poor in lithium salts may increase the yield of regenerated lithium carbonate. A smaller part, for example up to 10 vol.% of the aqueous solution poor in lithium salts may be drained as a blow down of the process.

In another embodiment, the aqueous solution poor in lithium salts (step f) may be cooled prior to recycling into the reaction vessel as at least a portion of the aqueous source (step g).

The carbon dioxide stream may be repressurised (for example compressed) and/or cooled to a predetermined temperature prior to recycling for introduction to the aqueous source as at least a portion of the carbon dioxide introduced in step b. For example, the carbon dioxide stream may be repressurised to the predetermined first pressure, for example to a predetermined first pressure of no more than 73 barg (7.4 MPa). Repressurising the carbon dioxide stream and/or cooling the carbon dioxide stream may result in formation of a condensate. The condensate may be separated from the repressurised and/or cooled carbon dioxide stream before introduction to the aqueous source. At least part of the condensate may be return back to the process for example to the recovered aqueous solution poor in lithium salts in step g. The recycling of the carbon dioxide may reduce the carbon dioxide consumption of the process.

The dioxide stream may comprise a portion of water vapour.

The method of the present invention may be free from addition of strong acid to the solid reaction product. As a result, the method of the present invention may not convert lithium carbonate to another lithium salt, such as lithium chloride. The method of the present invention may therefore be used to efficiently separate the solid-state carbon material, without adversely affecting the lithium compounds. The method may therefore also be used for an easy recovery of lithium carbonate.

The present invention utilises carbon dioxide to increase the solubility of lithium carbonate in an aqueous source. In particular, the presence of carbon dioxide results in lithium carbonate forming metastable bicarbonate:

Li2CO3 (s) + CO2 (g) + H2O (I) ◄ - ► 2UHCO₃(aq) The introduction of carbon dioxide to the solid reaction product in the presence of an aqueous source preferably increases the solubility of lithium carbonate in the aqueous source by approximately five to ten times when compared to the solubility of the solid reaction product in an aqueous source alone.

The present invention may provide for the efficient recovery of lithium carbonate as a result of controlling the temperature and/or pressure in steps c and e. Lithium carbonate is a valuable resource and the ability to recover and purify lithium carbonate from an electrolysis process provides for high profitability.

According to a second aspect of the present invention, there is provided an apparatus for purification and separation of solid-state carbon-containing material generated from electrolysis of a molten lithium carbonate electrolyte and recovery of lithium carbonate, the apparatus comprising: a) a reaction vessel configured in use to receive: a solid reaction product formed from electrolysis of a molten lithium carbonate electrolyte; and an aqueous source; in which the reaction vessel comprises: a first inlet configured in use to receive a pressurised source of carbon dioxide therethrough; a first pressure regulation apparatus configured in use to control the pressure within the reaction vessel; a first temperature regulation apparatus configured in use to control the temperature within the reaction vessel; and an outlet configured in use to provide a carbon dioxide treated aqueous reaction product mixture therethrough; b) a first separation device comprising: an inlet configured in use to be in communication with the outlet of the reaction vessel to receive a carbon dioxide treated aqueous reaction product mixture therethrough; and a first outlet configured in use to provide a solid-state carbon material therethrough; and a second outlet configured in use to provide an aqueous solution rich in lithium salts therethrough; c) an optional second separation device comprising: an inlet configured in use to be in communication with the second outlet of the first separation device to receive the aqueous solution rich in lithium salts therethrough; a first outlet configured in use to provide recovered transition metal ioncontaining materials therethrough; and a second outlet configured in use to provide an aqueous solution rich in lithium salts therethrough; d) a precipitation vessel comprising: an inlet configured in use to be in communication with the second outlet of the first or second separation devices to receive the aqueous solution rich in lithium salts therethrough; a second temperature regulation apparatus configured in use to control the temperature within the precipitation vessel; a second pressure regulation apparatus configured in use to control the pressure within the precipitation vessel; a first outlet configured in use to provide a carbon dioxide stream therethrough; and a second outlet configured in use to provide an aqueous solution poor in lithium salts together with precipitated lithium carbonate therethrough; e) a third separation device comprising: an inlet configured in use to be in communication with the second outlet of the precipitation vessel to receive the aqueous solution poor in lithium salts together with precipitated lithium carbonate therethrough; a first outlet configured in use to provide recovered, precipitated lithium carbonate material therethrough; and a second outlet configured in use to provide a recovered aqueous solution poor in lithium salts therethrough; and in which wherein one or more of: the first outlet of the third separation device is configured in use to be in communication with an electrolyser to supply the recovered precipitated lithium carbonate therethrough as a feed source for a molten lithium carbonate salt electrolyte; and/or the second outlet of the third separation device is configured in use to be in communication with the reaction vessel to provide the recovered aqueous solution poor in lithium salts therethrough as at least a portion of the aqueous source.

In an embodiment of the invention, the first pressure regulation apparatus may further be configured in use to maintain the pressure within the reaction vessel at a predetermined first pressure.

In an embodiment of the invention, the first temperature regulation apparatus may further be configured in use to maintain the temperature within the reaction vessel at a predetermined first temperature.

The first pressure regulation apparatus may be configured in use to maintain the reaction vessel at a predetermined first pressure of no more than 73 barg (7.4 MPa), preferably no more than 10 barg (1.1 MPa). The first pressure regulation apparatus may preferably be configured in use to maintain the reaction vessel at a predetermined first pressure of at least 0 barg (0.1 MPa), preferably at least 5 barg (0.6 MPa), or preferably at least 2.5 barg (0.35 MPa). The first pressure regulation apparatus may preferably be configured in use to maintain the reaction vessel at a predetermined first pressure of between 0 barg and 73 barg (7.4 MPa), preferably between 2.5 barg and 10 barg (0.35 and 1.1 MPa).

The first temperature regulation apparatus may be configured in use to maintain the reaction vessel at a predetermined first temperature of no more than 60°C, preferably no more than 40°C. The first temperature regulation apparatus may be configured in use to maintain the reaction vessel at a predetermined first temperature of for example be 35°C, or 10°C, or 5°C . The predetermined first temperature may preferably be above the freezing point of a solution contained within the reaction vessel. Preferably, the predetermined first temperature may be as close as possible to the freezing point of a solution contained within the reaction vessel, without reaching the freezing point of said solution. Preferably, the first temperature regulation apparatus may be configured in use to maintain the reaction vessel at a predetermined first temperature of no less than 0°C, preferably no less than 10°C, for example about 20°C. The first temperature regulation apparatus may preferably be configured in use to maintain the reaction vessel at a predetermined first temperature of between 0°C and 60°C, preferably between 0°C and 40°C, preferably between 10°C and 40°C, for example about 20°C.

In an embodiment of the invention, the second pressure regulation apparatus may further be configured in use to maintain the pressure within the precipitation vessel at a predetermined second pressure.

In an embodiment of the invention, the second temperature regulation apparatus may further be configured in use to maintain the temperature within the precipitation vessel at a predetermined second temperature.

The second pressure regulation apparatus may be configured in use to maintain the reaction vessel at a predetermined second pressure of preferably no more than 73 barg (7.4 MPa, pressure at critical point of CO2). The second pressure regulation apparatus may be configured in use to maintain the reaction vessel at a predetermined second pressure of preferably higher than -1.01 barg (0.61 KPa, pressure of the triple point of water), preferably higher than vapour pressure of water at the predetermined second temperature. For example, if the predetermined second temperature is 90°C, the predetermined second pressure may preferably be higher than -0.31 barg (70KPa). The second pressure regulation apparatus may be configured in use to maintain the reaction vessel at a predetermined second pressure of preferably less than 10 barg (1.1 MPa), preferably less than the predetermined first pressure, preferably less than 5 barg (0.6MPa), preferably less than 1 barg (0.2 MPa), preferably 0 barg (0.1MPa, atmospheric pressure). The predetermined second pressure may be 0 barg (0.1 MPa).

The second temperature regulation apparatus may be configured in use to maintain the precipitation vessel at a predetermined second temperature of at least 60°C. The second temperature regulation apparatus may preferably be configured in use to maintain the reaction vessel at a predetermined second temperature of at least 75°C, preferably at least 80°C. The predetermined second temperature is preferably no more than 100°C. The second temperature regulation apparatus may preferably be configured in use to maintain the reaction vessel at a predetermined second temperature in a range of between 60°C and 100°C, preferably in a range of between 75°C and 95°C, for example about 90°C. The second temperature regulation apparatus may preferably be configured in use to maintain the precipitation vessel at a predetermined second temperature which is below a boiling point of the aqueous solution rich in lithium salts.

In an embodiment of the invention, the first outlet of the precipitation vessel may be configured in use to be in communication with the first inlet of the reaction vessel to supply the carbon dioxide stream therethrough as at least a portion of the source of carbon dioxide.

The reaction vessel may further comprise a second inlet configured in use to receive the aqueous source therethrough.

The reaction vessel may be configured in use to receive the solid reaction product directly from an electrolyser.

The apparatus may further comprise a grinding unit or milling unit configured in use to receive the solid reaction product prior to be transferred to the reaction vessel. The grinding unit or milling unit is preferably configured to reduce the particle size of the solid reaction product to having a maximum predetermined particle size prior to introduction into the reaction vessel.

The grinding unit or milling unit may comprise an inlet configured in use to provide the solid reaction product therethrough. The grinding unit or milling unit may further comprise an outlet in communication with the reaction vessel, in which the outlet is configured in use to provide a ground or milled solid reaction product having a predetermined maximum particle size therethrough.

The reaction vessel may comprise a third inlet configured in use to be in communication with the outlet of the grinding unit or milling unit.

The reaction vessel is preferably configured to be substantially sealed from an external environment. The reaction vessel is preferably configured in use to be pressurised to a predetermined first pressure.

The first separation device may comprise a filtration device. The filtration device may be a gravitational filter device (for example sedimentation) or liquid filter. In one embodiment, the first separation device may be a floatation device configured in use to separate for example graphitic material.

The first separation device may be in communication with a pressure regulation apparatus and/or temperature regulation apparatus configured in use to maintain the same or similar pressure conditions and/or the same or similar temperature conditions as used for the reaction vessel. For example, the first separation device may be maintained at a predetermined first pressure and a predetermined first temperature.

In an alternative embodiment, the first separation device may be in communication with the first pressure regulation apparatus and/or the first pressure regulation apparatus of the reaction vessel.

The first outlet of the first separation device may be configured in use to provide a solid- state carbon and a transition metal-containing material therethrough.

The first outlet of the first separation device may be in communication with (for example an inlet of) a further separation device for further purification of the solid-state carbon- containing and the transition metal-containing material. The further separation device may for example comprise a first inlet configured in use to be in communication with the first outlet of the first separation device; and an aqueous source (for example demineralised water). The further separation device may comprise a first outlet configured in use to provide purified solid-state carbon-containing material therethrough; and a second outlet configured in use to provide transition metal based compounds therethrough. The transition metal-containing material may be separated from the carbon-containing material by different means such as introduction of a strong acid to the mixture of the transition metalcontaining material and the carbon-containing material such that the transition metalcontaining material may react with the strong acid and thus be separated from the mixture. The separation of the transition metal-containing material from the carbon containing material may be done by pyrolysis, wherein an increase in temperature with limited oxygen present may lead to the transition metal-containing material evaporating from the mixture.

The second outlet of the first separation device may be in communication with an inlet of a second separation device. In this embodiment, the first separation device is preferably configured to supply an aqueous solution rich in lithium salts through the second outlet to the second separation device. The second separation device may be in communication with a pressure regulation apparatus and/or temperature regulation apparatus to maintain the same or similar temperature and/or pressure conditions as the reaction vessel. For example, the second separation device may be maintained at a predetermined first pressure and a predetermined first temperature.

In an alternative embodiment, the second separation device may be in communication with the first pressure regulation apparatus and/or the first pressure regulation apparatus of the reaction vessel.

The second separation device may preferably be configured to separate further impurities, such as transition metal ions, from the aqueous solution rich in lithium salts. Transition metal ions may be separated from the aqueous solution by different means such as by an ion exchange process.

The second separation device may comprise an ion exchange resin.

In one embodiment, the second outlet of the first separation device is in communication with an inlet of the precipitation vessel to supply the aqueous solution rich in lithium salts therethrough.

The precipitation vessel preferably comprises a heating apparatus configured to raise the temperature of the aqueous solution rich in lithium salts received therein to the predetermined second temperature.

The aqueous solution rich in lithium salts may be heated to the predetermined second temperature prior to being introduced into the precipitation vessel. In one embodiment, the aqueous solution rich in lithium salts may be heated to the predetermined second temperature within the precipitation vessel.

The first outlet of the third separation device may be in communication with a further purification unit configured in use to purify the precipitated lithium carbonate further. The further purification unit may be configured in use to remove transition metal-containing material from the precipitated lithium carbonate.

The second outlet of the third separation device may be in communication with a cooling device configured in use to cool the recovered aqueous solution poor in lithium salts, for example prior to being introduced as at least a portion of the aqueous source into the re- action vessel. In one embodiment, the reaction vessel comprises a cooling device to cool the aqueous solution.

In one embodiment, a heat exchange system is configured to exchange energy between the reaction vessel and the precipitation vessel (and optionally the cooling device) to improve efficiency of the apparatus. For example, during cooling of the reaction vessel (and optionally by the cooling device), the excess heat may be supplied to the precipitation vessel by the heat exchange system. In one embodiment, the heat exchange system may be configured to exchange energy between the reaction vessel and the precipitation vessel (and optionally the cooling device) and the optional cooling of the solid reaction product prior to being supplied to a grinding unit or milling unit.

Embodiments of the present invention will now be described in more detail in relation to the accompanying Figures:

BRIEF DESCRIPTION OF FIGURES

Figure 1 is a schematic illustration of the flow chart of the apparatus according to one embodiment of the present invention.

DETAILED DESCRIPTION

With reference to Figure 1, the apparatus 200 comprises an electrolysis reactor 201 for electrolysis of a molten lithium carbonate electrolyte. The electrolysis reactor 201 generates a solid reaction product.

The solid reaction product contains in this example a mixture of solid-state carbon, transition metal-containing material, lithium oxide and lithium carbonate.

The solid reaction product is introduced into a grinding unit 202 to reduce the maximum particle size of the solid reaction product. It is to be understood that any apparatus suitable for reducing the particle size of the solid reaction product could be used, such as for example a milling or crushing unit. The grinding unit 202 is configured to reduce the particle size of the solid reaction product to a predetermined maximum particle size. The ground, or powdered, solid reaction product is then introduced into the reaction vessel 203 of the apparatus. Although in the illustrated embodiment, the solid reaction product is ground prior to being introduced into the reaction vessel, it is to be understood that the solid reaction product may be introduced into the reaction vessel without any particle size reduction step.

The reaction vessel 203 comprises an aqueous source, for example a deionised or demineralised water solution. The reaction vessel 203 also comprises a first inlet configured in use to receive a pressurised source of carbon dioxide therethrough. A first pressure regulation apparatus is in communication with the reaction vessel 203 to maintain the pressure of the reaction vessel 203 at a predetermined first pressure of no more than 73 barg (7.4 MPa), preferably between 2.5 barg and 10 barg (0.35 and 1.1 MPa).

The reaction vessel may typically be a batch reactor, a continuous stirred-tank reactor, a fluidized bed reactor or inline mixer.

A first temperature regulation apparatus is in communication with the reaction vessel 203 to maintain the temperature of the reaction vessel 203 at a predetermined first temperature of between 0°C and 40°C. The reaction vessel 203 further comprises an outlet configured in use to provide a carbon dioxide treated aqueous reaction product mixture therethrough. In this example, the carbon dioxide treated aqueous reaction product mixture comprises an aqueous solution rich in lithium salts, solid-state carbon material and transition metal-containing material (marked as “Rich Li⁺ aqueous solution with carbon and transition metal-based particles” in Figure 1).

In an example (not shown) the reaction vessel 203 comprises a liquid mixer.

The apparatus 200 further comprises a first separation device 204. The first separation device 204 comprises an inlet in communication with the outlet of the reaction vessel 203 to receive the carbon dioxide treated aqueous reaction product mixture therethrough.

The temperature and pressure conditions of the first separation device 204 are approximately equal to the predetermined first temperature and the predetermined first pressure of the reaction vessel 203. The low temperature (between 0°C and 40°C) and high pressure conditions (of up to 73 barg, 7.4 MPa) within the reaction vessel 203 and first separation device 204 may ensure that the lithium carbonate is present in solution thereby enabling the solid-state carbon and transition metal material to be separated efficiently therefrom. The first separation device 204 is a filtration and/or floatation device configured to separate the solid-state carbon and transition metal material from an aqueous solution rich in lithium salts.

The first separation device 204 further comprises a first outlet to provide a solid-state carbon and transition metal-containing material therethrough (marked as “Carbon and transition metal-based particles” in Figure 1); and a second outlet configured to provide the aqueous solution rich in lithium salts therethrough (marked as “Rich Li⁺ aqueous solution” in Figure 1).

As shown in Figure 1 , the apparatus further comprises an optional second separation device 205 comprising an inlet in communication with the second outlet of the first separation device 204 to receive the aqueous solution rich in lithium salts therethrough. The second separation device 205 comprises in this example a means for separating transition metal ions from the aqueous solution rich in lithium salts. The transition metal ions may be separated by for example an ion exchange process using ion exchange resins. The second separation device 205 further comprises a first outlet configured in use to provide recovered transition metal ion-containing materials therethrough (marked as “Transition metal ions” in Figure 1); and a second outlet configured in use to provide an aqueous solution rich in lithium salts.

In another example (not shown) the first separation device 204 and/or the second separation device 205 form part of the reaction vessel 203.

The apparatus further comprises a precipitation vessel 206 comprising an inlet in communication with the second outlet of the first 204 or second 205 separation devices to receive the aqueous solution rich in lithium salts therethrough. The precipitation vessel 206 further comprises a second temperature regulation apparatus configured in use to maintain the precipitation vessel 206 at a predetermined second temperature which, in this example, is greater than the predetermined first temperature of the reaction vessel 203. The precipitation vessel 206 further comprises a second pressure regulation apparatus configured in use to maintain the precipitation vessel at a predetermined second pressure which, in this example, is lower than the predetermined first pressure of the reaction vessel 203. By lowering the pressure and raising the temperature of the precipitation vessel 206 relative to the conditions within the reaction vessel 203, lithium carbonate may be less soluble and may precipitate from solution. The precipitation vessel 206 has a first outlet configured in use to provide a recovered carbon dioxide stream therethrough; and a second outlet con- figured in use to provide an aqueous solution poor in lithium salts together with precipitated lithium carbonate therethrough (marked as “Poor Li⁺ aqueous solution with precipitated U2C03 particles” in Figure 1).

In another example, the second pressure regulation apparatus is configured in use to maintain the precipitation vessel 206 at a predetermined second pressure which is equal to or similar to the predetermined first pressure of the reaction vessel 203, and the second temperature regulation apparatus is configured in use to maintain the precipitation vessel 206 at a predetermined second temperature which is higher to the predetermined first temperature of the reaction vessel 203. This may result in lithium carbonate precipitation from the solution.

In another example, the second pressure regulation apparatus is configured in use to maintain the precipitation vessel 206 at a predetermined second pressure which is lower than the predetermined first pressure of the reaction vessel 203, and the second temperature regulation apparatus is configured in use to maintain the precipitation vessel 206 at a predetermined second temperature which is equal or similar to the predetermined first temperature of the reaction vessel 203. This may result in lithium carbonate precipitation from the solution.

In another example, the second pressure regulation apparatus is configured in use to maintain the precipitation vessel 206 at a predetermined second pressure which is lower than the predetermined first pressure of the reaction vessel 203, and the second temperature regulation apparatus is configured in use to maintain the precipitation vessel 206 at a predetermined second temperature which higher than the predetermined first temperature of the reaction vessel 203. This may result in lithium carbonate precipitation from the solution.

In an example (not shown) the apparatus further comprises a pressure reduction device between the first separation device 204 and the precipitation vessel 206 for reducing the pressure of the aqueous solution rich in lithium salts prior to introducing it to the precipitation vessel 206.

In an example (not shown) the apparatus further comprises a flash tank in fluid communication with the precipitation vessel 206 for partially separating carbon dioxide from the aqueous solution rich in lithium salts. The apparatus further comprises a third separation device 207 comprising an inlet in communication with the second outlet of the precipitation vessel 206 to receive the aqueous solution poor in lithium salts together with precipitated lithium carbonate therethrough. The third separation device 207 comprises a filtration unit to separate and recover precipitated lithium carbonate from the aqueous solution poor in lithium salts.

The third separation device 207 further comprises a first outlet configured in use to provide recovered, precipitated lithium carbonate material therethrough (marked as “Recycled U2CO3” in Figure 1); and a second outlet configured in use to provide a recovered aqueous solution poor in lithium salts therethrough (marked as “Recycled Poor Li⁺ aqueous solution” in Figure 1).

The apparatus further comprises an optional purification unit 210 which is in communication with the first outlet of the third separation device 207. The purification unit 210 is configured to further purify the recovered lithium carbonate material to provide purified lithium carbonate material which is preferably battery grade or technical grade lithium carbonate.

As shown in Figure 1, the first outlet of the precipitation vessel 206 is in communication with the first inlet of the reaction vessel 203 so as to supply the recovered carbon dioxide stream therethrough as at least a portion of the source of carbon dioxide. The recovered carbon dioxide stream may be compressed prior to being supplied to the first inlet of the reaction vessel 203. Furthermore, the recovered carbon dioxide stream may be cooled prior to being supplied to the reaction vessel 203. By recovering the carbon dioxide during precipitation, the method and apparatus of the present invention may reduce the amount of energy and resources required to separate the carbon and transition metal material from the lithium carbonate and the lithium oxide. The method and apparatus of the present invention may provide a closed loop method and may therefore require far lower quantities of carbon dioxide to be used to separate solid-state carbon material from lithium carbonate.

The first outlet of the third separation device 207 is in communication with the electrolyser 201 to supply the recovered precipitated lithium carbonate therethrough as a feed source for a molten lithium carbonate salt electrolyte. Again, this closed loop of the method and apparatus of the present invention may require less resources to be consumed during the separation and purification process, which may result in improved economy and reduced costs. The second outlet of the third separation device 207 is in communication with the reaction vessel 203 to provide the recovered aqueous solution poor in lithium salts therethrough as at least a portion of the aqueous source. As shown in Figure 1 , the apparatus further comprises a cooling unit 208 for cooling the recovered aqueous solution prior to introduction into the reaction vessel 203. Again, this closed loop of the method and apparatus of the present invention may require less resources to be consumed in the form of aqueous source during the separation and purification process. Furthermore, by recycling the aqueous solution poor in lithium salts, the lithium salts may be recovered during a further pass through the precipitation vessel 206 leading to an improved efficiency of the separation process. The apparatus may further comprise a pump for pumping the recovered aqueous solution poor in lithium salts from the second outlet of the third separation device 207 to the reaction vessel 203.

The apparatus further comprises a heat exchange system which is able to transfer heat efficiently between the reaction vessel 203, the precipitation vessel 206 and the cooling unit 208. The heat exchange system may therefore be able to withdraw excess heat from vessels or units which are generating heat and supply this directly to units which require heat, which may provide for a cost effective and energy efficient apparatus.

The first outlet of the first separation device may optionally be in communication with (for example an inlet of) a further separation device 209 for further purification of the solid- state carbon-containing and transition metal-containing material. The further separation device 209 comprises a first inlet in communication with the first outlet of the first separation device 204; and may comprise an aqueous source (for example demineralised water). The further separation device 209 comprises a first outlet configured in use to provide purified solid-state carbon-containing material therethrough; and a second outlet configured in use to provide transition metal based compounds therethrough.

In a first example of the invention, 10-20 wt.% solid reaction product is added to the reaction vessel 203, wherein the solid reaction product comprises 8.9 wt.% carbon containing material, 1.4 wt.% transition metal-containing material, 80.7 wt.% lithium carbonate and 9.0 wt.% lithium oxide. The predetermined first pressure of carbon dioxide introduced into the reaction vessel 203 is 6 barg (0.7 MPa), and the predetermined first temperature of the carbon dioxide treated aqueous reaction product mixture is 20°C. In this second example, the predetermined second pressure of carbon dioxide in the precipitation vessel 206 is 6 barg (0.7 MPa), and the predetermined second temperature of the aqueous solu- tion rich in lithium salts is 90°C. These conditions may result in 1500 g of recovered, precipitated lithium carbonate in a 35 L reaction vessel, in one cycle of the process.

In a second example of the invention, 10-20 wt.% solid reaction product is added to the reaction vessel 203, wherein the solid reaction product comprises 8.9 wt.% carbon containing material, 1.4 wt.% transition metal-containing material, 80.7 wt.% lithium carbonate and 9.0 wt.% lithium oxide. The predetermined first pressure of carbon dioxide introduced into the reaction vessel 203 is 6 barg (0.7 MPa), and the predetermined first temperature of the carbon dioxide treated aqueous reaction product mixture is 20°C. In this third example, the predetermined second pressure of carbon dioxide in the precipitation vessel 206 is 0 barg (0.1 MPa, atmospheric pressure), and the predetermined second temperature of the aqueous solution rich in lithium salts is 90°C. These conditions may result in 1880 g of recovered, precipitated lithium carbonate in a 35 L reaction vessel, in one cycle of the process.

In a third example of the invention, 10-20 wt.% solid reaction product is added to the reaction vessel 203, wherein the solid reaction product comprises 8.9 wt.% carbon containing material, 1.4 wt.% transition metal-containing material, 80.7 wt.% lithium carbonate and 9.0 wt.% lithium oxide. The predetermined first pressure of carbon dioxide introduced into the reaction vessel 203 is 6 barg (0.7 MPa, and the predetermined first temperature of the carbon dioxide treated aqueous reaction product mixture is 20°C. In this fourth example, the predetermined second pressure of carbon dioxide in the precipitation vessel 206 is 16 barg (1.7 MPa), and the predetermined second temperature of the aqueous solution rich in lithium salts is 90°C. These conditions may result in 1320 g of recovered, precipitated lithium carbonate in a 35 L reaction vessel, in one cycle of the process.

In a fourth example of the invention, 10-20 wt.% solid reaction product is added to the reaction vessel 203, wherein the solid reaction product comprises 8.9 wt.% carbon containing material, 1.4 wt.% transition metal-containing material, 80.7 wt.% lithium carbonate and 9.0 wt.% lithium oxide. The predetermined first pressure of carbon dioxide introduced into the reaction vessel 203 is 10 barg (1.1 MPa), and the predetermined first temperature of the carbon dioxide treated aqueous reaction product mixture is 20°C. The temperature and pressure conditions are in this example maintained in the first and second separation devices 204, 205. The predetermined second pressure of carbon dioxide in the precipitation vessel 206 is in this example 0 barg (0.1 MPa, atmospheric pressure), and the predetermined second temperature of the aqueous solution rich in lithium salts is 90°C. The temperature and pressure conditions are in this example maintained in the third separa- tion device 207. These conditions may result in 2080 g of recovered, precipitated lithium carbonate in a 35 L reaction vessel, in one cycle of the process.

The present invention provides a method and apparatus that may efficiently and effectively recover solid-state carbon and lithium carbonate from the solid reaction product gener- ated from electrolysis of molten lithium carbonate. The present invention may enable the solid-state carbon and lithium carbonate to be recovered with reduced energy considerations as a result of the use of an efficient heat transfer system operating in communication with the reaction vessel and precipitation vessel (and optional cooling unit).

Claims

1. A method for purification and separation of solid-state carbon-containing material generated from electrolysis of a molten lithium carbonate electrolyte and recovery of lithium carbonate, the method comprising: a) obtaining a solid reaction product formed from electrolysis of a molten lithium carbonate salt electrolyte; b) mixing the solid reaction product with an aqueous source and introducing carbon dioxide at a predetermined first pressure to produce carbon dioxide treated aqueous reaction product mixture; c) controlling the temperature of the carbon dioxide treated aqueous reaction product mixture and controlling the pressure of the carbon dioxide treated aqueous reaction product mixture to produce solid-state carbon material and an aqueous solution rich in lithium salts; d) separating the solid-state carbon material from the aqueous solution rich in lithium salts; e) controlling the temperature of the aqueous solution rich in lithium salts and the pressure of the aqueous solution rich in lithium salts to generate a carbon dioxide stream, precipitated lithium carbonate and an aqueous solution poor in lithium salts. f) separating precipitated lithium carbonate from the aqueous solution poor in lithium salts; and g) in which the method further comprises one or more of further comprising one or more of the following steps:

- recycling at least a portion of the recovered precipitated lithium carbonate as a feed source for the molten lithium carbonate salt electrolyte; and/or

- recycling at least a portion of the recovered aqueous solution poor in lithium salts as at least a portion of the aqueous source in step b.

2. The method according to claim 1 , in which step c comprises maintaining the temperature of the carbon dioxide treated aqueous reaction product mixture at a predetermined first temperature.

3. The method according to claim 1 or 2, in which step c comprises maintaining the pressure of the carbon dioxide treated aqueous reaction product mixture at the predetermined first pressure.

4. The method according to claim 2 or 3, in which step e comprises increasing the temperature of the aqueous solution rich in lithium salts to a predetermined second temperature which is higher than the predetermined first temperature.

5. The method according to any one of claims 1 to 4, in which step e comprises reducing the pressure of the aqueous solution rich in lithium salts to a predetermined second pressure which is lower than the predetermined first pressure.

6. The method according to any one of claims 1 to 5, in which step g further comprises recycling the carbon dioxide stream by introducing the carbon dioxide stream to the aqueous source as at least a portion of the carbon dioxide introduced in step b.

7. The method according to any one of claims 2 to 6, in which step c comprising maintaining the temperature of the carbon dioxide treated aqueous reaction product mixture at a predetermined first temperature of no more than 60 °C to produce solid-state carbon material and an aqueous solution rich in lithium salts

8. The method according to any one of claims 1 to 7, in which solid-state carbon and transition metal-containing material and an aqueous solution rich in lithium salts are produced in step c, and in which step d comprises separating the solid-state carbon and transition metal-containing material from the aqueous solution rich in lithium salts.

9. The method according to any one of claims 1 to 8, in which the solid reaction product is milled or ground prior to mixing with the aqueous source.

10. The method according to any one of claims 1 to 9, in which the aqueous source comprises demineralized or deionized water solution.

11. The method according to any one of claims 1 to 10, in which the aqueous source comprises at least a portion of the recovered aqueous solution poor in lithium salts.

12. The method according to any preceding claim, in which the predetermined first pressure is no more than 73 barg (7.4 MPa).

13. The method according to any one of claims 2 to 12, in which the predetermined first temperature is higher than the freezing point of the aqueous source.

14. The method according to any one of claims 2 to 13, in which the predetermined first temperature is between 0°C and 40°C.

15. The method according to any preceding claim, in which the solid-state carbon material is separated from the aqueous solution rich in lithium salts by filtration, by sedimentation, by liquid filter or floatation.

16. The method according to claim 8, in which the solid-state carbon material and transition metal-containing material are separated from the aqueous solution rich in lithium salts by filtration, by sedimentation, by liquid filter or by floatation.

17. The method according to any preceding claim, in which the separated solid-state carbon material is dried.

18. The method according to claim 8, in which the separated solid-state carbon material and the transition metal-containing material is dried.

19. The method according to any one of claims 4 to 18, in which the predetermined second temperature of the aqueous solution rich in lithium salts is lower than the boiling point of the aqueous solution rich in lithium salts.

20. The method according to any one of claims 4 to 19, in which the predetermined second temperature of the aqueous solution rich in lithium salts is at least 60°C.

21. The method according to claim any one of claims 4 to 20, in which the predetermined second temperature of the aqueous solution rich in lithium salts is no more than 100°C.

22. The method according to any preceding claim, further comprising purification of the separated precipitated lithium carbonate of step f.

23. The method according to any one of claims 5 to 22, in which the predetermined second pressure is less than or equal to the predetermined first pressure.

24. The method according to any one of claims 5 to 23, in which the predetermined second pressure is 0 barg (0.1 MPa).

25. The method according to any preceding claim, further comprising concentrating the aqueous solution poor in lithium salts prior to recycling as at least a portion of the aqueous source.

26. The method according to any preceding claim, further comprising cooling the aqueous solution poor in lithium salts prior to recycling as at least a portion of the aqueous source.

27. The method according to any one of claims 6 to 26, further comprising repressurising and/or cooling the carbon dioxide stream prior to recycling for introduction to the aqueous source as at least a portion of the carbon dioxide introduced in step b.

28. An apparatus for purification and separation of solid-state carbon-containing material generated from electrolysis of a molten lithium carbonate electrolyte and recovery of lithium carbonate, the apparatus comprising: a) a reaction vessel configured in use to receive: a solid reaction product formed from electrolysis of a molten lithium carbonate electrolyte; and an aqueous source; in which the reaction vessel comprises: a first inlet configured in use to receive a pressurised source of carbon dioxide therethrough; a first pressure regulation apparatus configured in use to control the pressure within the reaction vessel; a first temperature regulation apparatus configured in use to control the temperature within the reaction vessel; and an outlet configured in use to provide a carbon dioxide treated aqueous reaction product mixture therethrough; b) a first separation device comprising: an inlet configured in use to be in communication with the outlet of the reaction vessel to receive a carbon dioxide treated aqueous reaction product mixture therethrough; and a first outlet configured in use to provide a solid-state carbon material therethrough; and a second outlet configured in use to provide an aqueous solution rich in lithium salts therethrough; c) an optional second separation device comprising: an inlet configured in use to be in communication with the second outlet of the first separation device to receive the aqueous solution rich in lithium salts therethrough; a first outlet configured in use to provide recovered transition metal ion-containing materials therethrough; and a second outlet configured in use to provide an aqueous solution rich in lithium salts therethrough; d) a precipitation vessel comprising: an inlet configured in use to be in communication with the second outlet of the first or second separation devices to receive the aqueous solution rich in lithium salts therethrough; a second temperature regulation apparatus configured in use to control the temperature within the precipitation vessel; a second pressure regulation apparatus configured in use to control the pressure within the precipitation vessel; a first outlet configured in use to provide a carbon dioxide stream therethrough; and a second outlet configured in use to provide an aqueous solution poor in lithium salts together with precipitated lithium carbonate therethrough; e) a third separation device comprising: an inlet configured in use to be in communication with the second outlet of the precipitation vessel to receive the aqueous solution poor in lithium salts together with precipitated lithium carbonate therethrough; a first outlet configured in use to provide recovered, precipitated lithium carbonate material therethrough; and a second outlet configured in use to provide a recovered aqueous solution poor in lithium salts therethrough; and in which wherein one or more of:

- the first outlet of the third separation device is configured in use to be in communication with an electrolyser to supply the recovered precipitated lithium carbonate therethrough as a feed source for a molten lithium carbonate salt electrolyte; and/or

- the second outlet of the third separation device is configured in use to be in communication with the reaction vessel to provide the recovered aqueous solution poor in lithium salts therethrough as at least a portion of the aqueous source.

29. The apparatus according to claim 28, in which the first pressure regulation apparatus is further configured in use to maintain the pressure within the reaction vessel at a predetermined first pressure.

30. The apparatus according to claim 28 or 29, in which the first temperature regulation apparatus is further configured in use to maintain the temperature within the reaction vessel at a predetermined first temperature.

31. The apparatus according to any one of claims 28 to 30, in which the second pressure regulation apparatus is further configured in use to maintain the pressure within the precipitation vessel at a predetermined second pressure.

32. The apparatus according to any one of claims 28 to 31 , in which the second temperature regulation apparatus is further configured in use to maintain the temperature within the precipitation vessel at a predetermined second temperature.

33. The apparatus according to any one of claims 28 to 32, in which the first outlet of the precipitation vessel is configured in use to be in communication with the first inlet of the reaction vessel to supply the carbon dioxide stream therethrough as at least a portion of the source of carbon dioxide.

34. The apparatus according to any one of claims 28 to 33, in which the reaction vessel further comprises a second inlet configured in use to receive the aqueous source therethrough.

35. The apparatus according to any one of claims 28 to 34, in which the reaction vessel is configured in use to receive the solid reaction product directly from an elec- trolyser.

36. The apparatus according to any one of claims 28 to 35, further comprising a grinding unit or milling unit configured in use to receive the solid reaction product prior to be transferred to the reaction vessel.

37. The apparatus according to any one of claims 28 to 36, in which the first separation device comprises a filtration device, a sedimentation device, or a floatation device.

38. The apparatus according to any one of claims 28 to 37, in which the first separation device is in communication with a pressure regulation apparatus and/or a temperature regulation apparatus configured in use to maintain the first separation device at the predetermined first pressure and/or predetermined first temperature.

39. The apparatus according to any one of claims 28 to 38, in which the first outlet of the first separation device is configured in use to provide the solid-state carbon and a transition metal-containing material therethrough.

40. The apparatus according to claim 39, in which the first outlet of the first separation device is in communication with a further separation device for further purification of the solid-state carbon and the transition metal-containing material.

41. The apparatus according to any one of claims 28 to 40, in which the second separation device is in communication with a pressure regulation apparatus and/or temperature regulation apparatus to maintain the second separation device at the predetermined first pressure and/or predetermined first temperature.

42. The apparatus according to any one of claims 32 to 41 , in which the precipitation vessel comprises a heating apparatus configured to raise the temperature of the aqueous solution rich in lithium salts received therein to the predetermined second temperature.

43. The apparatus according to any one of claims 31 to 42, in which the second pressure regulation apparatus is configured to maintain the pressure within the precipitation vessel at the predetermined second pressure which is lower than the predetermined first pressure.

44. The apparatus according to any one of claims 28 to 43, in which the first outlet of the third separation device is in communication with a further purification unit configured in use to purify the precipitated lithium carbonate further.

45. The apparatus according to any one of claims 28 to 44, in which the second outlet of the third separation device is in communication with a cooling device configured in use to cool the recovered aqueous solution poor in lithium salts.

46. The apparatus according to any one of claims 28 to 45, further comprising a heat exchange system configured to exchange energy between the reaction vessel and the precipitation vessel, and optionally the cooling device.