Technical Field

[0001] The present disclosure relates to an electrodialysis cell, in particular an electrodialysis cell for producing lithium hydroxide from a lithium-bearing solution.

Background

[0002] The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application.

[0003] Lithium hydroxide (LiOH) is generally produced via an aqueous causticisation reaction between lithium carbonate (U2CO3) and slaked lime (Ca(OH) ₂ ). It is subsequently recovered as a monohydrate salt via evaporative crystallization as a final product. However, to obtain high-purity LiOH products suitable for battery production, additional laborious and expensive purification steps are required to remove impurities introduced with slaked lime. Moreover, the process is reported to return low LiOH yield due to entrainment in calcium carbonate precipitates.

[0004] Subsequently, electrolytic processes for production of high-purity LiOH from U2CO3 solutions or other lithium-bearing solutions (e.g. lithium sulphate or lithium chloride) has become regarded as a simple and low cost alternative.

[0005] A multi-compartment electrodialysis (ED) cell having alternating cation and anion exchange membranes has become a standard configuration for such processes. The ED cell consists of stacks of flat, rectangular membranes and flow channels sandwiched between two or more electrodes. The membrane stack may be oriented in either a horizontal or vertical position.

[0006] The flow channels may be created by spacers (i.e. electrically inert plastic separators) interposed between the membranes. The spacers support the stack and determine the geometry of the flow channel defined between the membranes.

Spacers are an important cell component that affects cell performance. A well performing spacer provides a small inter-electrode distance, adequate means for maintaining the dimensions of the cell, uniform fluid distribution and promotion of efficient mass transport.

[0007] There are two common types of spacers: (1 ) a “sheet flow” spacer comprising an open frame with a plastic screen separating the membranes, and (2) a “tortuous path” spacer in which the spacer is folded back upon itself and the liquid flow channel is much longer than the linear dimensions of the unit. Tortuous spacers provide long flow channels which enable a single-pass flow to be achieved. This avoids the need to apply series of stacks which would result in higher pressure drop across the stacks, constructional difficulty due to multistage arrangement, lower reliability of the system caused by inlet pressure differences of feed and product at the stages, and possible internal leakages.

[0008] Additionally, the spacer should promote turbulent solution flow. Solution flowing through the channel filled by the sheet spacer may follow a so called zig-zag flow pattern. This flow pattern increases the mass transfer coefficients from the solution bulk to the membrane surface and reduces a concentration polarization phenomena occurring in the diffusion layer at the membrane surface. Nevertheless, a highly knitted and low porosity spacer may have a significant effect on the stack resistance, also known as a spacer shadow effect. This is likewise the case for a spacer with a large thickness.

[0009] The assembly of electrodes, membranes and spacers is generally held in compression by a pair of end plates, thereby preventing leakage inside the stack. Additional stacks may be added in series to achieve the desired electrodialysis performance. The assembly may be readily disassembled for cleaning and maintenance.

[0010] Various embodiments of the electrodialysis cell disclosed herein seek to overcome or mitigate at least some of the above mentioned disadvantages. Summary

[0011] The present disclosure provides an electrodialysis cell, in particular an electrodialysis cell for producing lithium hydroxide from a lithium-bearing solution.

[0012] In a first aspect there is provided an electrodialysis cell for producing lithium hydroxide from a lithium-bearing solution, the electrodialysis cell comprising: an anodic compartment and a cathodic compartment separated by a cation exchange membrane configured, in use, to allow migration of lithium cations therethrough from the anodic compartment to the cathodic compartment; the anodic compartment comprising an anode and a first fluid distribution member having an inlet to receive a feedstream of a lithium-bearing solution into the anodic compartment and an outlet to remove a lithium-depleted solution therefrom; the cathodic compartment comprising a cathode and a second fluid distribution member having an inlet to receive a lithium hydroxide solution into the cathodic compartment and an outlet to remove a lithium-enriched hydroxide solution therefrom; the first and second fluid distribution members being interposed between the cation exchange membrane and said respective anode and cathode, wherein said fluid distribution members comprise a frame configured to support one or more permeable spacer sheets in close proximity to the cation exchange membrane; and a pair of opposing end plates to sandwich the anodic and cathodic compartments therebetween.

[0013] In one embodiment, the respective inlets and outlets of the first and second fluid distribution members comprise passages through the frames thereof.

[0014] In one embodiment, the one or more permeable spacer sheets are disposed at or proximal to a side of the frame adjacent to the cation exchange membrane.

[0015] In one embodiment, a respective gasket is interposed between:

(a) the cation exchange membrane and the frames of the first and second fluid distribution members;

(b) the anode and the frame of the first fluid distribution member; and

(c) the cathode and the frame of the second fluid distribution member. [0016] In a further embodiment, a respective gasket may be interposed between the anode and one of the end plates, and the cathode and the other of the end plates.

[0017] In one embodiment, the opposing end plates are provided with correspondingly aligned apertures to receive fasteners therethrough.

[0018] In one embodiment, the cathode and the anode are provided with respective tabs configured, in use, to be electrically coupled to an electric current supply.

[0019] In a second aspect there is provided an assembly of electrodialysis cells for producing lithium hydroxide from a lithium-bearing solution, the assembly comprising: a plurality of alternately arranged anodic and cathodic compartments separated by respective cation exchange membranes configured, in use, to allow migration of lithium cations therethrough from the anodic compartments to the cathodic compartments; each anodic compartment comprising an anode and a first fluid distribution member having an inlet to receive a feedstream of a lithium-bearing solution into the anodic compartment and an outlet to remove a lithium-depleted solution therefrom; each cathodic compartment comprising a cathode and a second fluid distribution member having an inlet to receive a lithium hydroxide solution into the cathodic compartment and an outlet to remove a lithium-enriched hydroxide solution therefrom; the first and second fluid distribution members being interposed between the cation exchange membrane and said respective anode and cathode, wherein said fluid distribution members comprise a frame configured to support one or more permeable spacer sheets in close proximity to the cation exchange membrane; and a pair of opposing end plates to sandwich the plurality of alternately arranged anodic and cathodic compartments therebetween.

[0020] In one embodiment of said assembly, the first and second fluid distribution members are provided with correspondingly aligned male and female fasteners to facilitate alignment and assembly of the alternately arranged anodic and cathodic compartments.

[0021 ] In another embodiment, the respective feed streams for the anodic and cathodic compartments may be manifolded together and delivered to respective inlets of first and second fluid distribution members via respective anodic and cathodic inlet manifolds and the respective product streams of the anodic and cathodic compartments may be manifolded and collected from respective outlets of the first and second fluid distribution members via anodic and cathodic outlet manifolds.

[0022] In one embodiment, the electrodialysis cell assembly may further comprise a support frame configured to support said assembly and allow the number of electrolytic cells in the electrodialysis cell assembly to be varied.

[0023] In another embodiment, the electrodialysis cell assembly may further comprise a support frame configured to support said assembly, the anodic and cathodic inlet manifolds, and the anodic and cathodic outlet manifolds.

[0024] In a third aspect there is provided a system for producing a lithium hydroxide solution from a lithium-bearing solution, the system comprising: an electrodialysis cell assembly as defined above; a source of the lithium-bearing solution in fluid communication with the inlet(s) of the anodic compartment(s); and, an electric current supply associated with the anodes and the cathodes whereby supply of electric current causes lithium cations to migrate from the anodic compartment(s) to the cathodic compartment(s) to produce a lithium-enriched hydroxide solution therein.

Brief Description of Drawings

[0025] Preferred embodiments will now be further described and illustrated, by way of example only, with reference to the accompanying drawings in which:

[0026] Figure 1 is an expanded view of one embodiment of an electrodialysis cell as described herein;

[0027] Figure 2 is a representative view of the electrodialysis cell as shown in Figure 1 ; [0028] Figure 3 is an expanded view of one embodiment of an assembly of electrodialysis cells as described herein;

[0029] Figure 4 is a perspective view of a manifold for delivery or collection of respective solutions from anodic and cathodic compartments of the assembly as shown in Figure 3;

[0030] Figure 5 is a perspective view of a frame to support the assembly of electrodialysis cells as shown in Figure 3;

[0031 ] Figure 6 is a perspective view of one embodiment of the assembly of electrodialysis cells supported by the frame as shown in Figure 5;

[0032] Figure 7 is a graphical representation of free acid and free base concentrations in respective anodic and cathodic compartments as a function of time in an example of operation of the electrodialysis cell as described herein; and

[0033] Figure 8 is a graphical representation of lithium concentration of the anolyte and catholyte sampled from respective anodic and cathodic compartments as a function of time in an example of operation of the electrodialysis cell as described herein.

Description of Embodiments

[0034] The present disclosure relates to an electrodialysis cell, in particular to an electrodialysis cell for producing lithium hydroxide from a lithium-bearing solution.

GENERAL TERMS

[0035] Throughout this specification, unless specifically stated otherwise or the context requires otherwise, reference to a single step, composition of matter, group of steps or group of compositions of matter shall be taken to encompass one and a plurality (i.e. one or more) of those steps, compositions of matter, groups of steps or groups of compositions of matter. Thus, as used herein, the singular forms "a", "an" and "the" include plural aspects unless the context clearly dictates otherwise. For example, reference to "a" includes a single as well as two or more; reference to "an" includes a single as well as two or more; reference to "the" includes a single as well as two or more and so forth.

[0036] Each example of the present disclosure described herein is to be applied mutatis mutandis to each and every other example unless specifically stated otherwise. The present disclosure is not to be limited in scope by the specific examples described herein, which are intended for the purpose of exemplification only. Functionally-equivalent products, compositions and methods are clearly within the scope of the disclosure as described herein.

[0037] The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

[0038] When an element or layer is referred to as being “on”, “engaged to”, “connected to” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to”, “directly connected to” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.).

[0039] Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. [0040] Reference to positional descriptions, such as lower and upper, are to be taken in context of the embodiments depicted in the figures, and are not to be taken as limiting the invention to the literal interpretation of the term but rather as would be understood by the skilled addressee.

[0041] Spatially relative terms, such as “inner,” “outer,” “beneath”, “below”, “lower”, “above”, “upper” and the like, may be used herein for ease of description to describe one element or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0042] The term "and/or", e.g., "X and/or Y" shall be understood to mean either "X and Y" or "X or Y" and shall be taken to provide explicit support for both meanings or for either meaning.

[0043] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. [0045] The term “about” as used herein means within 5%, and more preferably within 1%, of a given value or range. For example, “about 3.7%” means from 3.5 to 3.9%, preferably from 3.66 to 3.74%. When the term “about” is associated with a range of values, e.g., “about X% to Y%”, the term “about” is intended to modify both the lower (X) and upper (Y) values of the recited range. For example, “about 20% to 40%” is equivalent to “about 20% to about 40%”.

ELECTRODIALYSIS CELL

[0046] Referring to Figures 1 to 6, where like numerals refer to like features throughout, there is shown an electrodialysis cell 10 suitable for producing lithium hydroxide from a lithium-bearing solution. The lithium-bearing solution may be an aqueous solution of a lithium compound, such as lithium sulfate, lithium chloride, lithium fluoride, lithium bicarbonate, lithium carbonate, lithium nitrate, lithium acetate, lithium stearate or lithium citrate. The lithium-bearing solution may be a lithium- containing brine or a leachate produced by a process for extracting lithium from a lithium-containing ore. Alternatively, the lithium-bearing solution may be derived from a process which extracts lithium from secondary sources, such as recycled lithium batteries.

[0047] The electrodialysis cell 10 includes an anodic compartment 12 and a cathodic compartment 14 separated by a cation exchange membrane 16. The cation exchange membrane 16 may be any suitable semi-permeable ion exchange membrane capable of selectively allowing migration of lithium cations therethrough from the anodic compartment 12 to the cathodic compartment 14. Examples of suitable semi- permeable ion exchange membranes include, but are not limited to, Nation.

[0048] The anodic compartment 12 includes an anode 18 and a first fluid distribution member 20 interposed between the anode 18 and the cation exchange membrane 16. The first fluid distribution member 20 has an inlet 22 to receive a feedstream lithium bearing solution into the anodic compartment 12 and an outlet 24 to remove a lithium- depleted solution therefrom. It will be appreciated that the lithium-depleted solution has a lower lithium concentration than the feedstream lithium-bearing solution. [0049] The cathodic compartment 14 includes a cathode 26 and a second fluid distribution member 28 interposed between the cathode 26 and the cation exchange membrane 16. The second fluid distribution member 28 has an inlet 30 to receive a dilute lithium hydroxide solution and an outlet 32 to remove a lithium-enriched hydroxide solution therefrom. It will be appreciated that the lithium-enriched hydroxide solution has a higher lithium concentration than the dilute lithium hydroxide solution.

[0050] The first and second fluid distribution members 20, 28 include a rectangular frame 34 and a permeable spacer sheet 36 mounted therein. The frame 34 may be fabricated from a rigid plastic material such as PTFE, PP, PVDF. The thickness of the frame 34 is preferably as low as practically possible to minimise the spacing or gap between the anode 18 and the cathode 26.

[0051 ] The permeable spacer sheet 36 is a woven polymeric material of polypropylene or silicone with a 45° diamond pattern. The permeable spacer sheet 36 has a thickness of about 250 pm to about 600 pm, in particular about 450 pm.

[0052] It will be appreciated that the permeable spacer sheet 36 may be provided as a regular arrangement of panels thereof mounted within the rectangular frame 34.

This particular arrangement of panels is convenient for electrodialysis cells 10 having larger dimensions where the permeable spacer sheet 36 could otherwise become slack and potentially distort over time. The panelled frame would thus allow the permeable spacer sheet 36 to remain taut.

[0053] The permeable spacer sheet 36 is disposed at or proximal to a facing side 38 of the frame 34 adjacent to the cation exchange membrane 16. In this way, although the same type of permeable spacer sheet 36 may be mounted in the first and second fluid distribution members 20, 28, the permeable spacer sheet 36 mounted in the first fluid distribution member 20 in the anodic compartment 12 will be oriented 180° relative to the permeable spacer sheet 36 mounted in the second fluid distribution member 28 in the cathodic compartment 14. Consequently, the permeable spacer sheet 36 mounted in the first fluid distribution member 20 in the anodic compartment 12 will allow the lithium-bearing solution to flow across a surface of said membrane 16, whereas the permeable spacer sheet 36 mounted in the second fluid distribution member 28 in the cathodic compartment 14 will allow lithium-enriched hydroxide solution to flow across the surface of said membrane 15.

[0054] Respective inlets 22, 30 of first and second fluid distribution members 20, 28 are disposed in a lower portion 38 of a side wall 40 of the frame 34, whereas respective outlets 24, 32 of the first and second fluid distribution members 20, 28 are disposed in an upper portion 42 of an opposing side wall 44 of the frame 34. The inlets 22, 32 and outlets 24, 32 include a passage 46 through the side wall 40 or the opposing side wall 44, respectively, and a laterally extending spigot 48. The laterally extending spigot 48 may be operatively connected by one or more conduits, manifolds, valves and the like for transfer of said solutions into and out of the anodic and cathodic compartments 12, 14 of the electrodialysis cell 10. A conduit is any pipe, tube, passageway or the like through which said solutions may be conveyed. An intermediate device, such as a pump or heat exchanger, may be connected inline which the one or more conduits.

[0055] As shown in Figure 1 , a plurality of gaskets 50 are interposed between adjacent components of the electrolysis cell 10 to provide a fluid-tight seal in the anodic and cathodic compartments 12, 14 and prevent fluid leakage therefrom. Each gasket 50 generally corresponds in shape and dimensions to the frame 34 of the first and second fluid distribution members 20, 28. For example, the gasket 50 shown in Figures 1 and 2 is rectangular. The gasket 50 has a thickness of about 1 mm to reduce a gap between the anode and cathode as much as practically possible. The gasket 50 may be fabricated from Gore-Tex GR™, EPDM, PTFE or FPM (Viton™).

[0056] The electrodialysis cell 10 also includes a pair of opposing end plates 52 to clamp the anodic and cathodic compartments 12, 14 therebetween. It will be appreciated that a respective gasket 50 may be interposed between the anode 18 and one of the adjacently disposed end plates 52, and the cathode 26 and the other of the adjacently disposed end plates 52 to provide a fluid-tight seal and prevent leaks.

[0057] The opposing end plates 52 may be provided with correspondingly aligned apertures 54 to receive fasteners therethrough, thereby guiding assembly of the anodic and cathodic compartments 12, 14 and allowing addition (or removal) of further anodic and cathodic compartments 12, 14 as desired. Suitable fasteners include stainless steel bolt nuts and washers. The opposing end plates 52 are generally of larger dimensions than the anodic and cathodic compartments 12, 14 and the apertures 54 may be disposed proximal to the edges of the opposing end plates 52 so that the fasteners do not interfere with or compromise the fluid-tight seals of the anodic and cathodic compartments 12, 14.

[0058] The end plates 52 may be fabricated from stainless steel rather than a rigid plastic material to provide sufficient mechanical strength when clamping the anodic and cathodic compartments 12, 14 and their respective elements together. The end plates may be about 20 mm thick and a layer of insulation may be provided adjacent to the end plate 52 to prevent any current runaway.

[0059] It will be appreciated from the foregoing description that a plurality of anodic and cathodic compartments 12, 14 and their respective components may be alternately arranged and assembled in series between the opposing end plates 52 in an electrodialysis cell assembly 10’, as shown in Figure 3. Adjacent frame members 34 of the first and second fluid distribution members 20, 28 may have corresponding male and female tabs to facilitate alignment and assembly of the plurality of anodic and cathodic compartments 12, 14 in said assembly 10’.

[0060] In the aforesaid electrodialysis cell assembly 10’, the arrangement is such that the respective feed streams for the anodic and cathodic compartments 12, 14 may be manifolded together and delivered to respective inlets 22, 30 of first and second fluid distribution members 20, 28 via respective anodic and cathodic inlet manifolds 54, 56 and the respective product streams of the anodic and cathodic compartments 12,

14 may be likewise manifolded and collected from respective outlets 24, 32 of the first and second fluid distribution members 20, 28 via anodic and cathodic outlet manifolds 58, 60. In this way, the respective feed and product streams of the anodic and cathodic compartments 12, 14 may be prevented from mixing.

[0061] Referring to Figure 4, said manifolds 54, 56, 58, 60 may comprise a generally cylindrical body 62 having a plurality of ports 64 regularly spaced along the length of the body 62 to allow ingress or egress of fluid thereto. Each port 64 is configured to facilitate attachment of one end of a conduit 66, such as a flexible hose. The other end of the conduit 66 is attached to one of the inlets 22, 30 or outlets 24, 32 of the first and second fluid distribution members 20, 28 to provide fluid communication between the manifolds 54, 56, 58, 60 and the anodic and cathodic compartments 12, 14.

[0062] The body 62 is further provided with a port 68 to allow ingress of fluid from an external source via a conduit (not shown) or egress of fluid via a conduit to an external collection site. In the embodiment shown in Figure 4, the port 68 is disposed equidistantly spaced from opposing ends of the body 62 on a lateral side thereof. It will be appreciated, however, that the port 68 may be disposed at or proximal to either of the opposing ends of the body 62 or an underside of the body 62.

[0063] A flange 70 may be disposed on an opposing lateral side of the body 62. The flange 70 may have two or more through holes 72 by which the flange 70 and therefore the body 62 of the manifold 54-60 may be supported, as will be described later.

[0064] Referring to Figure 5, a frame 74 for supporting the electrodialysis cell assembly 10’ is shown. The frame 74 includes a pair of opposing Fl-frames 76 having an upper web member 78 laterally extending between the uppermost ends 80 of opposing upright members 82 of the FI-frame 76 and a lower web member 84 laterally extending between the opposing upright members 82 spaced below a cross member 86 of the FI-frame 76.

[0065] A pair of laterally extending cross members 88 interconnect the corresponding upright members 80 of the opposing Fl-frames 76. The cross members 88 are disposed at a similar effective height as the cross member 86 of the FI-frame 76 so as to provide a generally rectangular frame configured to support a base plate 90.

[0066] The base plate 90 is configured to support the electrodialysis cell assembly 10’ as shown in Figure 6. The base plate 90 may have a plurality of slots 92 which are configured, in use, to accommodate the fasteners of the end plates 52. The slots 92 may be elongate to allow for the number of electrolytic cells 10 in the electrodialysis cell assembly 10’ to be varied according to requirements.

[0067] The upper and lower web members 76, 82 are provided with two or more through holes which are spaced to correspond with the through holes 70 of the flange 68 of the manifold body 62. As shown in Figure 6, the flange 68 of manifold 54, 58 may be attached to an underside of the upper web member 76 with fasteners, such as nuts and bolts, and the flange 68 of manifold 56, 60 may be attached to an upper surface of the lower web member 82 with similar fasteners.

[0068] The anode 18 and the cathode 26 are generally rectangular sheets arranged in facing parallel alignment with each other and the cation exchange membrane 16. Generally the rectangular sheets are about 1 mm thickness.

[0069] The anode 18 and the cathode 26 may be fabricated from an electrically conductive material that is inert or insoluble under the electrodialysis conditions. In particular, the anode 18 may be fabricated from an electrically conductive material having an acceptable oxygen overvoltage and minimum side reactions. Suitable examples of electrically conductive materials from which the anode may be fabricated include, but are not limited to, or a mixed metal oxide, such as an iridium or ruthenium coated mixed metal oxide, or a dimensionally stable anode (DSA). Dimensionally stable anodes comprise a substrate, such as a titanium plate or mesh, with a plurality of metal oxides coated thereon.

[0070] The cathode 26 may be fabricated from an electrically conductive material having a high hydrogen overvoltage and minimum side reactions. Suitable examples of electrically conductive materials from which the cathode 26 may be fabricated include, but are not limited to, metals such as titanium including platinum coated titanium, nickel, niobium, tantalum, zinc tin, lead, platinum, graphite or metal alloys such as stainless steel, in particular 316 stainless steel and Hastelloy. The term ‘Hastelloy’ refers to a group of corrosion-resistant nickel alloys, namely the Ni-Mo and the Ni-Cr-Mo alloys. Hastelloy electrodes are characterized by high resistance to hydrochloric, sulfuric, phosphoric, acetic and formic acids, media containing chloride and fluoride ions.

[0071 ] Each of the anode 18 and the cathode 26 are provided with laterally extending tabs 18a, 26a. A power supply may be configured in electrical communication with the tabs 18a, 26a of the anode 18 and the cathode 26 to supply a cell potential of from about 4.0 V to about 7.0 V to the electrodialysis cell 10 to maintain a current density of less than 4 kA/m ² . The power supply may be a direct current rectifier unit supplied with an amp meter and a volt meter to monitor the voltage a current applied to the electrolysis cell 10.

[0072] In the electrodialysis cell 10, the primary electrochemical reaction at the anode 18 is oxygen evolution, although this may differ depending on the composition of the lithium-bearing solution. For example, the presence of chloride in the lithium bearing solution may mean that chlorine gas would be generated at the anode 18.

The primary electrochemical reaction at the cathode 26 is hydrogen evolution. It will be appreciated that the reaction gases are drawn from the anodic and cathodic compartments 12, 14 through the respective outlets 24, 32 in the frames 34 of the first and second fluid distribution members 20, 28.

[0073] Under the influence of an electric potential, hydroxide ions are produced on the cathode 26 and lithium ions from the anodic compartment 12 migrate through the cation exchange membrane 16 into the cathodic compartment 14, thereby increasing the concentration of lithium hydroxide of the catholyte (i.e. electrolyte in the cathodic compartment 14) and depleting lithium ion content in the anolyte (i.e. electrolyte in the anodic compartment 12).

Examples

[0074] The following example is to be understood as illustrative only of the operation of the electrolysis cell 10 as described with reference to the Figures. It should therefore not be construed as limiting the embodiments of the disclosure in any way.

[0075] An anodic feed solution of 1.5 M U ₂ SO ₄ was supplied to the anodic compartment 12 via inlet 22 and a cathodic feed solution of 0.5 M LiOH was supplied to the cathodic compartment 14 via inlet 30, from respective feed reservoirs. Spent anolyte and lithium-enriched catholyte were withdrawn from the anodic and cathodic compartments 12, 14, via respective outlets 24, 32 and recirculation tubing to feed reservoirs. A moderately high circulation flow rate was applied via a peristaltic pump to ensure good mixing within said compartments 12, 14 and respective feed reservoirs. The temperature of the feed solutions was maintained between about 25 °C and about 27 °C. [0076] A current density of 1000 A/m ² was directly applied to the electrodialysis cell 10 and the cell potential between anode 18 and cathode 26 was measured at regular intervals over a 4 h period. Cell potential gradually decreased from 6.9 V to 4.7 V, whereas the cathode and anode potential were relatively constant over a range of 0.7- 0.8 V throughout the 4 h test period.

[0077] The feed solutions were regularly sampled for chemical composition analysis.

[0078] Figure 7 shows the change in concentration of acid and base concentrations in the anode and cathode compartments 12, 14, respectively. The free acid concentration in the anodic compartment 12 increases with time because hydrogen ions are generated at the anode 18. Likewise, the free base concentration in the cathodic compartment 14 increases with time indicating that hydroxide anions are being generated at the cathode 26.

[0079] Figure 8 shows the change in respective lithium concentrations in the anolyte and the catholyte. The concentration of lithium in the lithium sulphate solution (anolyte) decreased over time, indicating migration of lithium cations from the anodic compartment 12 through the cation exchange membrane 16 to the cathodic compartment 14. Likewise, the lithium hydroxide concentration of the catholyte increased in strength from 41.4 g/L (4.0 w/w%) from an initial LiOH concentration of 11 .7 g/L or 1.2 w/w%. The overall LiOH production rate was calculated to be 9.4 g/h.

[0080] The final LiOH product liquor was analysed for sulphur (S) to examine the level of sulphate anions migration across the membrane and to determine the purity of the enriched LiOH catholyte. The results reported 450 ppm S (i.e., 1 ,348 mg/L SO ₄ ) in the final liquor product after 4 hours of operation of the electrodialysis cell 10. This shows that the LiOH produced is reasonably pure containing only 0.1 w/w % SO ₄ without further downstream processing. The maximum concentration of sulphate impurity in a technical grade LiOH product is typically between 0.03-0.05 w/w %. There is evidence that sulphate anions were gradually reporting to the cathodic compartment 14 albeit at a very small diffusion rate of approximately 0.36 g SO ₄ per hour. There is an apparent increase in the sulphate concentration in the anode compartment because the anolyte volume was decreasing with time. [0081] The current efficiency to produce LiOH was 70%, calculated using Faraday’s Law. Its energy consumption was 8.7 kWh/kg LiOH. Good mass accountabilities were obtained for this test and key results are listed in the following Table.

[0082] It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

^L Calculated based on deviation between total mass in and total mass out.

* Calculated based on deviation between total mass Li in and total mass Li out. ’ Calculated based on deviation between total mass S in and total mass S out.

Table