Method and apparatus for preparing brine for further processing using forward osmosis

Abstract

The invention provides a method and system for preparing a brine for further processing, using forward osmosis to first dilute and then re-concentrate the brine. The dilution is done so the brine can be effectively treated, for example by ion exchange, to reduce the level of contaminants, such as divalent cations. The re-concentration is done to produce a high concentration brine suitable for further processing, such as by electrolysis. The invention reduces both the need to add water to the brine in order to dilute it for treatment, and the energy required to re-concentrate it for electrolysis or other further processing.

Description

[0001] Method and Apparatus for Preparing Brine for Further Processing Using Forward Osmosis

[0002] Field of the Invention

[0003] The invention pertains to the preparation of salt brines, such as lithium brines, for further processing, such as electrolysis, and in particular to the use of forward osmosis in the preparation process.

[0004] Background of the Invention

[0005] Electrochemical processing of ionic solutions such as lithium and sodium salt brines often requires extremely low levels of certain ionic and even organic contaminants. In the case of salt splitting, such as chloralkali electrolysis, contaminants which may cause problems are, for example, calcium and magnesium ions, which may precipitate in the membrane of the electrochemical cell. The precipitation may result over time in an increase in operating voltage, or a decrease in current efficiency, which represent an increase in operating and capital cost for a production facility. It is desirable, for example, for processing of a sodium chloride brine in a membrane chloralkali cell, to achieve concentrations less than 20 ppb for the combination of calcium and magnesium (Li, K., Chuai, H., Lui, H., Zhang, S., & Ma, X. (2021). Revisiting Chlor-Alkali Electrolyzers: from Materials to Devices. Transactions of Tianjin University, 202-216).

[0006] Depending upon the source of the brine, achieving these impurity levels may require several stages of purification. Purification methods may include, for example, one or a combination of evaporative crystallization, nanofiltration, precipitation, adsorption and selective ion exchange. The adsorption and ion exchange steps may be targeted at divalent cations such as magnesium, calcium and strontium, or they may target other elements such as silicon, phosphorus, boron, and sulphur.

[0007] The brine treatment for a membrane chloralkali plant may commonly include both primary brine treatment, typically precipitation, and secondary treatment, typically ion exchange. A combination of precipitation and ion exchange is used for removal of the alkali earth metals, calcium, magnesium and strontium. Membrane treatment processes such as nanofiltration, for divalent ion removal, and reverse osmosis, for partial concentration, may also form part of the purification process.

[0008] For conventional chloralkali brines it is common to conduct the brine treatment operations in a brine which is close to saturation, approximately 300 g / L of sodium chloride. The processes of precipitation and ion exchange are well known for this brine treatment (Thomas F. O'Brien, T. V. (2005). Handbook of Chloralkali Technology. New York: Springer). It is generally possible to reduce calcium to approximately 10 ppm (mg / L) using simple precipitation chemistry. This allows ion exchange using chelating resins to further reduce the hardness (the combination of calcium and magnesium) to below 20 to 30 ppb, which is the recommended maximum for membrane chloralkali cells.

[0009] 300 g / L of sodium chloride corresponds to a molar concentration of 5.1 moles / liter of sodium chloride, close to saturation. In sodium chloride electrolysis circuits, it is typical to feed the cell with a brine of this concentration. The brine is then returned from the electrolysis cells, where the sodium chloride is depleted by between 30% and 50%, to a re-saturator which returns the solution to saturation. The salt after resaturation may contain undesirable materials, such as calcium and magnesium, so the saturator is followed by a brine treatment system.

[0010] Lithium salt brines present different challenges compared to the sodium brine systems. An important feature of the sodium brine treatment system is that the feed is often a crystal salt, and as a result the overall plant water balance is not typically an issue. Water must be introduced continuously into the anolyte side of the circuit because it is continuously being removed by evaporation with the product chlorine and by water transfer across the membrane into the catholyte side of the cell.

[0011] Lithium chloride has a very different solubility curve than that of sodium chloride. At a temperature of 30° C, the solubility of lithium chloride is approximately 572 g / L LiCI, corresponding to a molarity of 13.5 moles LiCI per liter. This is approaching three times the molar solubility of sodium chloride. When lithium chloride is used as a feed stock for conversion to lithium hydroxide, it may be in the form of a solid or a strong solution. A possible solution strength is 40 wt.%, corresponding to 11.9 moles LiCI per liter. These solutions contain contaminants including calcium, magnesium, sodium, potassium, barium and others.

[0012] The high solubility of lithium chloride brines is in some ways convenient for electrolysis processing to produce high-purity battery-grade lithium hydroxide. If the electrolysis cell is fed a brine of approximately 40 wt.% brine, then the circulating anolyte will reach a stable concentration due to water and lithium transfer across the membrane. The amount of water present with the feed to the cell is almost equal to the amounts lost across the electrolysis membrane and by evaporation with the anode product chlorine. Only small changes in concentration by evaporation or dilution of the feed brine is needed to control the cell. However, the concentrated lithium brines present a different problem. Unlike sodium brines, from which calcium and magnesium can be removed by precipitation and ion exchange at close to saturation, some traditional purification methods, when applied to concentrated lithium brines, are ineffective.

[0013] It is only after dilution that the lithium brine can be treated via precipitation to reach comparable calcium levels to the sodium brine treated identically. It is not possible to reduce the level of calcium to less than 10 ppm, the maximum desirable to proceed to downstream ion-exchange, except by first diluting the near saturated lithium brine by a factor of about four or even more.

[0014] Likewise, dilution of the lithium brine is necessary to reach the even lower impurity levels desired for the final lithium salt electrolysis. Table 1 below shows the results for calcium removal from lithium chloride brine by chelating ion exchange from lithium chloride brines at various dilutions. Calcium is used by way of example, but the same is true for other elements.

[0015] Table 1

[0016] Analysis of LiCI solutions showing ppm of impurities after treatment at 8.9 M and 3M . The solutions were treated with activated carbon and ion exchange prior to analysis. The second row shows the ratio of Ca to Li, showing that dilution is effective to remove more total Ca from the LiCI brine.

[0017]

[0018] The treatment of lithium brines for electrolysis accordingly presents different challenges than the treatment of sodium brines. The objective is the same, namely, to produce a brine sufficiently low in contaminants that the electrolysis cell will perform for long periods of time without membrane or electrode deterioration. However, these lithium brines are not easily treated at high concentrations, though this is the form in which they are most readily prepared or are most readily available. Feeding high concentration brines to the electrolysis system most easily satisfies the water requirements without the need for additional expensive evaporation.

[0019] One approach to processing concentrated lithium brines which have an unacceptable level of contamination, would be to dilute the brine ahead of the treatment and then re-concentrate it to a concentration suitable for feed to the electrolysis circuit. In a scenario in which a 40 wt.% lithium chloride brine is diluted to 10 wt.% for purification, it is necessary to add 3 tonnes of dilution water for each tonne of 40% brine which must be processed. This same amount of water must then be evaporated in order to return the brine to its original concentration. In a commercial chemical plant, this amount of water removal requires significant capital investment for the concentration and consumes a large amount of thermal and mechanical energy. Further, in this illustrative case, the evaporation equipment may be large because it is operated under vacuum and may require expensive metallurgy because of the high chloride content. The 40% lithium chloride brine is illustrative only. The need to reduce the cost of processing brines which are more easily treated in a dilute form is more general. There remains a need for an effective and energy efficient method and system for preparing salt brines through dilution for further processing followed by concentration, such as preparing lithium salt brines for processing in an electrolysis system. Summary of the Invention

[0020] The invention provides a method and system for preparing a brine for processing in an electrolyzer or other production process, using forward osmosis to first dilute and then re-concentrate the brine. The dilution is made so the brine can be effectively treated, for example by ion exchange and / or precipitation, to reduce the level of contaminants such as divalent cations. The re-concentration is done to produce a high concentration brine suitable for further processing, such as electrolysis.

[0021] Existing patents, which are discussed below, do not implement both dilution and concentration of the same stream separated by a pretreatment unit which benefits from operating at dilute concentration, which is a significant boon of the invention, capable of reducing the water requirements and energy requirements of the pretreatment steps significantly.

[0022] WO 2023 / 200653 (Alam et al.) discloses a method for processing strong brines containing lithium. The draw solution is fed to a forward osmosis unit in order to dilute it for processing by a nanofiltration module. Due to the higher divalent concentration of the retentate, the retentate has a high osmotic pressure and can be recycled upstream of the forward osmosis unit until ion saturation is reached. The permeate may be subjected to further purification steps or may be added to, or used as, the feed brine for the forward osmosis system which will be concentrated. The method focuses on the complimentary relationship between nanofiltration and forward osmosis. In this relationship, the retentate is able to be recycled for a higher lithium recovery rate.

[0023] US 2023 / 0391641 (Chladek et al.) discloses a system for treating waste water from an industrial plant where the brine is first concentrated by forward osmosis before treatment and diluted by forward osmosis after treatment. The treatment is an electrochemically-based purification system where the product is recirculated back to the industrial plant. Brines are circulated through forward osmosis with an electrochemical cell existing between two feeds.

[0024] US 2015 / 0014248 (Herron et al.) discloses a method of combining reverse osmosis, forward osmosis and nanofiltration to concentrate brines. Brine is concentrated through a forward osmosis system. The draw is passed through a reverse osmosis system where the retentate is passed through multiple nanofiltration systems, concentrating the retentate further with each pass. The permeates are recycled to be used as the feed for the initial forward osmosis system.

[0025] US 2018 / 0147532 (Switzer et al.) discloses a method of using nanofiltration to separate lithium cations from divalent cations. Contaminated lithium brines pass through a nanofiltration cell where the permeate is collected and the retentate is recycled and concentrated through reverse osmosis, forward osmosis or other means. Once ion saturation is reached, the solution is discarded and refreshed. One key differentiating factor between the invention herein and the prior art is the fact that the invention herein uses a single stream changing composition (gains water) through a forward osmosis unit, to enter a pretreatment unit that benefits from operation at lower concentration, before re-entering the forward osmosis unit to supply water to cross the forward osmosis membrane.

[0026] One aspect of the invention provides a method of preparing a brine for further processing, for example in an electrolyzer or other production process, comprising: (a) providing a first stream of brine having a first concentration; (b) reducing the concentration of the first stream by the osmotic flow of water into the first stream, to produce a second stream of brine having a second concentration lower than the first concentration; (c) feeding the second stream of brine to a brine treatment system and treating it to remove contaminants therefrom; (d) providing a third stream of brine which is the dilute treated brine from the brine treatment system; and (e) increasing the concentration of the third stream of brine by the osmotic flow of water from the third stream into the first stream to produce a fourth stream of brine having a third concentration.

[0027] Another aspect of the invention provides a method of preparing a brine for further processing, for example in an electrolyzer, comprising: (a) introducing a brine having a first concentration into a draw chamber of a forward osmosis unit comprising a draw chamber, a feed chamber and a semi-permeable membrane between the draw chamber and the feed chamber; (b) reducing the concentration of the brine in the draw chamber by the osmotic flow of water into the draw chamber from the feed chamber through the semi-permeable membrane to produce a brine having a second concentration lower than the first concentration; (c) feeding the brine produced by the draw chamber to a brine treatment system and treating it to remove contaminants therefrom; (d) feeding the treated brine from the brine treatment system to the feed chamber; and (e) increasing the concentration of the brine in the feed chamber by the osmotic flow of water from the feed chamber into the draw chamber through the semi-permeable membrane to produce a brine having a third concentration.

[0028] Another aspect of the invention provides a system for preparing a brine for further processing, for example in an electrolyzer, comprising: (a) a forward osmosis unit comprising a draw chamber, a feed chamber, and a semi-permeable membrane between the draw chamber and the feed chamber; (b) the draw chamber having an inlet for receiving a brine having a first concentration and an outlet for the outflow of brine having a second concentration lower than the first concentration; (c) a brine treatment system for receiving the brine from the draw chamber outlet, and for treating it to remove contaminants therefrom; (d) the feed chamber having an inlet for receiving the brine from the brine treatment system and an outlet for the outflow of brine having a third concentration higher than the second concentration. In some embodiments of the system, the brine is a lithium salt brine. In some embodiments, the contaminants are divalent cations.

[0029] Further aspects of the invention and features of specific embodiments of the invention are described below.

[0030] Brief Description of the Drawings

[0031] The accompanying drawings illustrate non-limiting example embodiments of the invention.

[0032] Figure 1 is a schematic diagram of a method for processing lithium chloride brines using forward osmosis and brine treatment, according to an embodiment of the invention. Figure 2 is. a schematic diagram of an embodiment of the method of the invention showing example concentrations of lithium chloride brine.

[0033] Figures 3A to 3C are schematic diagrams of examples of forward osmosis units comprising multiple forward osmosis modules connected together.

[0034] Figure 4 is a schematic diagram of an Aquaporin HF002 forward osmosis module of the type used in Examples 1 to 6.

[0035] Figure 5 is a schematic diagram of the Aquaporin HF002 forward osmosis module of Figure 4 showing the lumen and water flux.

[0036] Detailed Description

[0037] Unless the context clearly requires otherwise, throughout the description and the claims:

[0038] • “comprise”, “comprising”, and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”;

[0039] • “connected”, “coupled”, or any variant thereof, means any connection or coupling, either direct or indirect, between two or more elements; the coupling or connection between the elements can be physical, logical, or a combination thereof;

[0040] • “about” in relation to a value means within plus or minus 10% of the numerical value.

[0041] • “or”, in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list;

[0042] • the singular forms “a”, “an”, and “the” also include the meaning of any appropriate plural forms.

[0043] The method and system described herein for preparing a brine for further processing, such as for electrolysis, are applicable to various inorganic salts. These include lithium chloride, lithium nitrate, lithium sulfate, lithium carbonate, sodium chloride, potassium chloride, caesium chloride, copper sulfate, sodium nitrate and sodium sulfate. They also include other inorganic salts having other cations and anions, which salts can benefit from purification in a dilute solution and further processing in a concentrated solution.

[0044] For convenience of description, the specific example of lithium chloride being prepared for electrolysis is set forth in detail herein.

[0045] The system 10 for preparing a lithium salt brine, e.g., a lithium chloride brine, for processing by an electrolyzer is schematically depicted in Figures 1 and 2. The system comprises as its principal components a forward osmosis unit 15 and a brine treatment system 14. The forward osmosis unit 15 has a draw chamber 16, a feed chamber 18, and a semi-permeable membrane 20 separating the two chambers 16, 18.

[0046] For simplicity of illustration, in Figures 1 and 2 the forward osmosis unit 15 is shown as comprising a single forward osmosis module 12, which has the draw chamber, the feed chamber and the semi-permeable membrane. In practice, the forward osmosis unit 15 may comprise a plurality of forward osmosis modules 12 operationally connected together, for example in series (Fig 3A), a combination of series and parallel (Fig. 3B) and / or in crossflow (Fig. 3C) arrangements. These arrangements can be used to modify the fluid velocity in a unit, modify the driving force, and / or increase the surface area where water flux occurs. Figures 3A to 3C depict examples of forward osmosis units 15 each comprising two or more forward osmosis modules 12. In these figures, F(IN) denotes the flow into a feed chamber of the unit, F(OUT) denotes the flow out of a feed chamber of the unit, F denotes the flow between feed chambers of connected modules, D(IN) denotes the flow into a draw chamber of the unit, D(OUT) denotes the flow out of a draw chamber of the unit, and D denotes the flow between draw chambers of connected modules. As a note, the feed and draw solutions can be fed to the opposite chambers if desired. Examples of suitable forward osmosis modules are those commercially available from Aquaporin (Denmark) and Porifera (California). The forward osmosis modules may comprise flat sheets of osmotic membranes, hollow fibers, combinations of the two and other structures. Referring again to Figure 1 , the draw chamber 16 has an inlet 22 for receiving a stream 24 of lithium chloride brine requiring treatment. The brine has a first concentration, for example about 40 wt.%. It will be understood that the brine concentrations depicted in Figure 2 are simply examples of suitable concentrations that can be within various ranges, as further discussed below. The draw chamber has an outlet 26 for the outflow of a stream 28 of lithium chloride brine having a second, lower concentration, for example about 14 wt.%. The concentration in the draw chamber 16 is reduced by the osmotic flow of water from the feed chamber 18 to the draw chamber by virtue of the osmotic pressure difference between the two chambers.

[0047] The stream 28 flows to the brine treatment system 14. In some embodiments, a stream of water 46 may optionally be provided for addition to the stream 28, to slightly lower its concentration prior to feeding it to the brine treatment system 14, for example to a concentration of about 13 wt.%. The dilution stream 46 may not be used, for example where the brine treatment itself provides dilution, which depends on the brine treatment processes used. Water addition may be required only as is needed so that there is a lower osmotic pressure in stream 32 than in stream 28. The brine treatment system 14 is configured to remove ions or compounds from the brine which are deleterious to the performance of the electrolyzer or other process and which are preferentially removed at lower concentrations. For example, it may be configured to remove divalent cations such as calcium, magnesium and strontium, and optionally to also remove one or more of silicon, phosphorus, boron, and sulphur. In some embodiments, the brine treatment system 14 comprises selective ion exchange, optionally in combination with one or more of nanofiltration, ultrafiltration, microfiltration, precipitation and adsorption and other purification techniques.

[0048] The feed chamber 18 of the forward osmosis unit has an inlet 30 for receiving a stream 32 of the lithium chloride brine from the brine treatment system 14, and an outlet 34 for the outflow of a stream 36 of lithium chloride brine having a third concentration higher than the second concentration. In some embodiments, a stream of water 48 may optionally be provided for addition to the stream 32, to lower its concentration prior to feeding it to the feed chamber 18. The draw chamber 16 and the feed chamber 18 of the forward osmosis unit are preferably arranged for countercurrent contact of their respective streams across the semi-permeable membrane 20.

[0049] The stream 36 from the feed chamber flows to an electrolyzer 38. In the lithium chloride example, the electrolyzer produces a stream 40 of lithium hydroxide and a stream 42 of chlorine gas, according to an electrolysis process well known in the art. In other embodiments of the electrolysis process the electrolyzer may produce lithium hydroxide and hydrochloric acid.

[0050] In some embodiments, an evaporator 44 is provided to reduce the water content of the lithium chloride brine in the stream 36, thereby increasing its concentration prior to feeding it to the electrolyzer in stream 45. The exchange of water in the forward osmosis unit leaves only a small amount of water to be evaporated to return the stream to its original concentration. In the example shown in Figure 2, 0.22 tonne of evaporation is required to return the concentration to 40 wt.%, compared with 3 tonnes of water that would be required to be evaporated, where only dilution and evaporation were used instead of forward osmosis. The energy required to remove 1 kg of water from a feed solution using forward osmosis is significantly less than the energy that would be required in an evaporative concentration. It may be less than 0.006% of a simple evaporation and less than 0.1 % of a vapour recompression evaporation method.

[0051] In some embodiments, the evaporator 44 is not used, for example if it is suitable for the overall water balance of the plant to feed the electrolyzer at a slightly lower brine strength (e.g. 32.3 wt.%) than the original incoming concentration fed to the forward osmosis module (e.g. 40 wt.%).

[0052] By way of example, the preparation of a lithium chloride brine for processing in an electrolyzer may be carried out in accordance with the following method. A lithium chloride brine 24, having a concentration of, for example, about 40 wt.%, or in the range of 20% up to 100% of the solubility limit of the salt, alternatively in the range of 30% up to 100% of the solubility limit of the salt, alternatively in the range of 40% up to 100% of the solubility limit of the salt, alternatively in the range of 50% up to

[0053]

[0054] osmosis unit in which it is diluted by the osmotic flow of water into the draw chamber from the feed chamber of the unit through the semi-permeable membrane. The concentration of the brine in the feed chamber is lower than the concentration in the draw chamber: the lithium chloride brine 32 flowing into the feed chamber may be, for example, about 13 wt.%, or in the range of 2% up to 99.9% of the solubility limit of the salt, alternatively in the range of 4% up to 99.9% of the solubility limit of the salt, alternatively in the range of 8% up to 99.9% of the solubility limit of the salt , alternatively in the range of 16% up to 99.9% of the solubility limit of the salt, alternatively in the range of 22% up to 99.9% of the solubility limit of the salt.

[0055] The dilution of the lithium chloride brine in the draw chamber 16 results in a stream of lithium chloride brine 28 having a concentration, for example of about 14 wt.%, or in the range of 2% up to 99.9% of the solubility limit of the salt, alternatively in the range of 8% up to 99.9% of the solubility limit of the salt , alternatively in the range of 16% up to 99.9% of the solubility limit of the salt, alternatively in the range of 22% up to 99.9% of the solubility limit of the salt, flowing out of the draw chamber outlet and to a brine treatment system.

[0056] In some embodiments, the stream of brine flowing out of the draw chamber 16 is further diluted by a small addition of water 46 to it, prior to being fed to the brine treatment system 14. For example, this optional dilution may reduce the concentration of the brine from about 14 wt.% to about 13 wt.% before it is fed to the brine treatment system.

[0057] The lithium chloride brine is treated in the brine treatment system 14 to remove ions or compounds from the brine which are deleterious to downstream process performance, such as in an electrolyzer, a crystallizer, a batch reactor, a liquid phase packed bed reactor, a stirred tank reactor, or a multi-phase reactor such as a trickle bed reactor. In these downstream processes, the contaminants are preferentially removed at lower concentrations.

[0058] In some embodiments, the brine is treated to remove divalent cations such as calcium, magnesium and strontium, and optionally to also remove one or more of silicon, phosphorus and boron. For example, ion exchange may be applied to reduce the concentration of each of the cations to a level of less than 10 ppb. The brine may be treated by one or more of selective ion exchange, ultrafiltration, nanofiltration, precipitation and adsorption.

[0059] In some embodiments, the contaminants to be removed may be various organic materials, for example those arising from lubricants, paints, organic solvents, oils, or greases commonly found at chemical plants; organics present in lignocellulose derivatives; organic acids such as carboxylic and humic and fulvic acids; and benzene, toluene, xylene, and molecules of phenolic nature.

[0060] In some embodiments, the stream of purified lithium chloride brine flowing out of the brine treatment system may be diluted by an addition of water 48 prior to being fed to the feed chamber 18 of the forward osmosis unit 15. For example, this optional dilution may reduce the concentration of lithium chloride brine to a concentration of about 13 wt.%, or in the range of 2% up to 99.9% of the solubility limit of the salt, alternatively in the range of 8% up to 99.9% of the solubility limit of the salt, alternatively in the range of 16% up to 99.9% of the solubility limit of the salt, alternatively in the range of 22% up to 99.9% of the solubility limit of the salt.

[0061] The purified lithium chloride brine from the brine treatment system 14 is fed to the feed chamber 18 of the forward osmosis unit 15. Preferably it flows through the feed chamber countercurrent to the flow through the draw chamber 16. In the feed chamber, the concentration of the lithium chloride brine is increased by the osmotic flow of water into the draw chamber through the semi-permeable membrane 20. The concentration of lithium chloride brine 36 exiting from the outlet 34 of the feed chamber may be, for example, about 32.3 wt.%, or in the range of 15% up to 99.9% of the solubility limit of the salt, alternatively in the range of 25% up to 99.9% of the solubility limit of the salt, alternatively in the range of 35% up to 99.9% of the solubility limit of the salt.

[0062] In some embodiments, the stream of lithium chloride brine from the feed chamber is fed directly to an electrolyzer, in which it is subjected to electrolysis to produce lithium hydroxide and chlorine gas, or to produce lithium hydroxide and hydrochloric acid. It will be understood that where the method is carried out in a system having a forward osmosis unit 15 comprising multiple forward osmosis modules 12 connected together, as described above, the flows are to and from the feed chambers 18 of the multiple modules, and to and from the draw chambers 16 of the multiple modules.

[0063] Examples

[0064] Examples 1 to 6 described below were completed using Aquaporin HF002 modules. A schematic diagram of a single such module is shown in Figure 4. A schematic of the internal operation of the module showing the lumen and water flux is depicted in Figure 5, the flux, in these examples, being from the feed solution in the lumen to the draw outside of the lumen, inside of the shell of the module, unless stated otherwise.

[0065] Example 1

[0066] A single Aquaporin HF002 module, nominal membrane area of 2.3 m2, of flexible lumen type tubes in a shell, was operated with a feed solution which was 14 wt.% LiCI and a draw solution which was 40 wt.% LiCI. In this experiment the draw solution flowed through the lumen tubes and the feed solution was to the shell side. The fluids flowed in counterflow to one another. The results are shown in Table 2 below.

[0067] Table 2

[0068]

[0069] This example showed that water was transported across the membrane at a rate of 533 ml / min.

[0070] Example 2

[0071] A single Aquaporin HF002 module, nominal membrane area of 2.3 m2, of flexible lumen type tubes in a shell, was operated with a feed solution which was 14 wt.%

[0072] LiCI and a draw solution which was 40 wt.% LiCI. In this experiment the draw

[0073] solution flowed through the shell side and the feed solution flowed through the

[0074] lumen side. The fluids flowed in counterflow to one another. The results are shown in Table 3 below. Within the precision of the experiment, the results are identical to Example 1.

[0075] Table 3

[0076]

[0077] Example 3

[0078] Two Aquaporin HF002 modules, adding to give a total nominal membrane area of

[0079] 4.6 m2of flexible lumen type tubes in a shell, were operated with a feed solution

[0080] which was 14 wt.% LiCI and a draw solution which was 40 wt.% LiCI. In this experiment the draw solution flowed through the shell side and the feed solution

[0081] was to the lumen side. The fluids flowed in counterflow to one another with the two feed sides connected in series together and the two draw sides also connected together in series. The results are shown in Table 4 below.

[0082] Table 4

[0083]

[0084] In this example the total flow of lithium in the feed and the draw solutions were very close to one another which would be the case if the same solution were diluted for treatment and then re-concentrated. This was not the case in Example 1 or

[0085] Example 2.

[0086] Example 4

[0087] Example 4 was set up geometrically and with approximately the same flows as

[0088] were used in Example 3. The nominal membrane area of 4.6 m2of flexible lumen type tubes in a shell, were operated with a feed solution which was 14 wt.% LiCI and a draw solution which was 40 wt.% LiCI. In this experiment the draw solution flowed through the shell side and the feed solution was to the lumen side. The fluids flowed in counterflow to one another with the two feed sides connected in series together and the two draw sides also connected together in series. The results are shown in Table 5 below.

[0089] Table 5

[0090]

[0091] In this example, to demonstrate that there was only a very low transfer of ions

[0092] across the forward osmosis membrane with the water, the draw solution, which

[0093] would often be the solution containing contaminants, was spiked with sodium, potassium and magnesium.

[0094] Measurements of concentrations of each of these species, coupled with flowrates for the feed and draw streams were used to determine whether there was

[0095] measurable transfer of contaminants. Within the accuracy of the experiment there was no significant ion transfer along with the water transferred across the forward osmosis membrane. The mass flows for each element are shown in Table 6 below.

[0096] Table 6

[0097]

[0098] Example 5

[0099] Three Aquaporin HF002 modules, adding to give a total nominal membrane area of 6.9 m2of flexible lumen type tubes in a shell, were operated with a feed solution

[0100] which was 14 wt.% LiCI and a draw solution which was 40 wt.% LiCI. In this experiment the draw solution flowed through the shell side and the feed solution

[0101] was to the lumen side. The fluids flowed in counterflow to one another with the

[0102] three feed sides connected in series together and the three draw sides also

[0103] connected together in series. The results are shown in Table 7 below.

[0104] Table 7

[0105]

[0106] As expected, compared to two modules connected in series, three modules

[0107] transferred more water, but for similar feed and draw inlet conditions, an asymptotic limit is approached to the amount of water which can be transferred by increasing the number of modules because the driving force for transfer progressively reduces.

[0108] By using three modules and increasing the feed concentration from 14 wt.% to 30 wt.%, if the objective is to dilute prior to contaminant removal, then reconcentrate, the amount of water required to be evaporated to return the solution to 40 wt.% has been dramatically reduced.

[0109] Example 6 To better understand the pressure drop across the forward osmosis units, and determine the power requirements needed to operate forward osmosis, the pressure drop on the tube and shell sides were measured for water flow on both sides. There was no osmotic water transfer and very little water transfer due to the mechanical pressure gradient across the membrane.

[0110] With 915 mL / min flow on the tube side, the pressure drop on the shell side was measured at different shell flowrates. Likewise, the pressure drop on the tube side was measured at different flowrates with a constant draw side flowrate of 915 mL / min. The results are shown in Table 8 below.

[0111] Table 8

[0112]

[0113] Based upon the pressure drop requirements, the power input for the three forward osmosis modules in series is very low. For a pressure drop of 5.0 psi, a total of 0.1456 kJ of input energy to a pump with a very low 20% shaft efficiency was required per kg of water transferred using the forward osmosis unit with 3 modules in series. This value can be compared with approximately 2590 kJ / kg water evaporated for a simple single stage evaporation process, or 144 kJ / kg for a vapour recompression evaporation (VRE) system. These calculations show that the forward osmosis unit with 3 modules in series required approximately 0.006% of the energy of a simple evaporation or 0.10% of a VRE system.

[0114] In the foregoing description, where a component (e.g. an assembly, device, etc.) is referred to, including reference to a means, it should be interpreted as including as equivalents of that component any component which performs the same function as the described component, including components which are not structurally equivalent to the disclosed structures which perform the function in the illustrated exemplary embodiments of the invention.

[0115] Throughout the foregoing description and the drawings, in which corresponding and like parts are identified by the same reference characters, specific details have been set forth in order to provide a more thorough understanding to persons skilled in the art. However, well known elements may not have been shown or described in detail to avoid unnecessarily obscuring the disclosure. Accordingly, the description and drawings are to be regarded in an illustrative, rather than a restrictive, sense.

[0116] As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the following claims.

Claims

Claims1. A method of preparing a salt brine for further processing, comprising:(a) providing a first stream of brine (24) having a first concentration;(b) reducing the concentration of the first stream (24) by the osmotic flow of water into the first stream, to produce a second stream of brine (28) having a second concentration lower than the first concentration;(c) feeding the second stream of brine (28) to a brine treatment system (14) and treating it to remove contaminants therefrom;(d) providing a third stream (32), comprising the dilute treated brine from the brine treatment system; and(e) increasing the concentration of the third stream of brine (32) by the osmotic flow of water from the third stream (32) into the first stream (24) to produce a fourth stream of brine (36) having a third concentration.

2. The method of claim 1 , further comprising feeding the fourth stream (36) to an electrolyzer (38).

3. The method of claim 1 , further comprising evaporating water from the fourth stream (36) to produce a fifth stream (45) and feeding the fifth stream to an electrolyzer (38).

4. The method of claim 1 , 2 or 3, further comprising, after step (c), adding water (48) to the treated brine from the brine treatment system to reduce its concentration, prior to step (d).

5. A method of preparing a salt brine for further processing, comprising:(a) introducing a brine (24) having a first concentration into a draw chamber (16) of a forward osmosis unit (15) comprising a draw chamber (16), a feed chamber (18) and a semi-permeable membrane (20) between the draw chamber and the feed chamber;(b) reducing the concentration of the brine in the draw chamber by the osmotic flow of water into the draw chamber from the feed chamber through the semi-permeable membrane to produce a brine (28) having a second concentration lower than the first concentration;(c) feeding the brine (28) produced by the draw chamber (16) to a brine treatment system (14) and treating it to remove contaminants therefrom;(d) feeding the treated brine (32) from the brine treatment system to the feed chamber (18); and(e) increasing the concentration of the brine in the feed chamber (18) by the osmotic flow of water from the feed chamber into the draw chamber through the semi-permeable membrane (20) to produce a brine (36) having a third concentration.

6. The method of any one of the preceding claims, wherein the brine is a lithium salt brine.

7. The method of claim 6, wherein the lithium salt is lithium chloride.

8. The method of claim 6, wherein the lithium salt is selected from the group consisting of lithium nitrate, lithium sulfate and lithium carbonate.

9. The method of any one of claims 1 to 5, wherein the brine comprises a salt selected from the group consisting of potassium chloride, caesium chloride, copper sulfate, sodium chloride, sodium nitrate and sodium sulfate.

10. The method of any one of the preceding claims, in which the further processing comprises electrolysis.11 . The method of claim 5, further comprising feeding the brine produced by the feed chamber to an electrolyzer for electrolysis of the brine.

12. The method of claim 5, further comprising evaporating water from the brine (36) produced by the feed chamber (18) to produce a stream (45) having an increased concentration, and feeding the stream (45) having the increased concentration to an electrolyzer.

13. The method of any one of the preceding claims, wherein the first concentration is about 40 wt.%.

14. The method of any one of claims 1 to 10, wherein the first concentration is in the range of 20% of the solubility limit up to 100% of the solubility limit of the salt.

15. The method of any one of claims 1 to 10, wherein the first concentration is in the range of 30% of the solubility limit up to 100% of the solubility limit of the salt.

16. The method of any one of claims 1 to 10, wherein the first concentration is in the range of 40% of the solubility limit up to 100% of the solubility limit of the salt.

17. The method of any one of claims 1 to 10, wherein the first concentration is in the range of 50% of the solubility limit up to 100% of the solubility limit of the salt.

18. The method of any one of the preceding claims, wherein the second concentration is about 14 wt.%.

19. The method of any one of claims 1 to 17, wherein the second concentration is in the range of 2% of the solubility limit up to 99.9 % of the solubility limit of the salt.

20. The method of any one of claims 1 to 17, wherein the second concentration is in the range of 8% of the solubility limit up to 99.9 % of the solubility limit of the salt.

21. The method of any one of claims 1 to 17, wherein the second concentration is in the range of 16% of the solubility limit up to 99.9 % of the solubility limit of the salt.

22. The method of any one of claims 1 to 17, wherein the second concentration is in the range of 22% of the solubility limit up to 99.9 % of the solubility limit of the salt.

23. The method of any one of the preceding claims, wherein the third concentration is about 32.3 wt.%.

24. The method of any one of claims 1 to 22, wherein the third concentration is in the range of 15% of the solubility limit up to 99.9 % of the solubility limit of the salt.

25. The method of any one of claims 1 to 22, wherein the third concentration is in the range of 25% of the solubility limit up to 99.9 % of the solubility limit of the salt.

26. The method of any one of claims 1 to 22, wherein the third concentration is in the range of 35% of the solubility limit up to 99.9 % of the solubility limit of the salt.

27. The method of claim 5, further comprising, after step (b), adding water (46) to the brine (28) produced by the draw chamber to reduce its concentration, prior to step (c).

28. The method of claim 27, wherein the concentration of the brine (28) is reduced to about 13 wt.%.

29. The method of claim 3 or 12, wherein the concentration of the brine (36) is increased by the evaporation to about 40 wt.%.

30. The method of claim 3 or 12, wherein the concentration of the brine (36) is increased by the evaporation up to the solubility limit of the salt.31 . The method of any one of claims 1 to 4, wherein the concentration of the third stream (32) is about 13 wt.%.

32. The method of any one of claims 1 to 4, wherein the concentration of the third stream (32) is in the range of 2% of the solubility limit up to 99.9 % of the solubility limit of the salt.

33. The method of any one of claims 1 to 4, wherein the concentration of the third stream (32) is in the range of 4% of the solubility limit up to 99.9 % of the solubility limit of the salt.

34. The method of any one of claims 1 to 4, wherein the concentration of the third stream (32) is in the range of 8% of the solubility limit up to 99.9 % of the solubility limit of the salt.

35. The method of any one of claims 1 to 4, wherein the concentration of the third stream (32) is in the range of 16% of the solubility limit up to 99.9 % of the solubility limit of the salt.

36. The method of claim 5, wherein the forward osmosis unit (15) comprises a plurality of forward osmosis modules (12) operationally connected together in series, parallel and / or crossflow configurations, and the flow of brine is through therespective draw chambers and flow chambers of the connected forward osmosis modules.

37. The method of any one of the preceding claims, wherein the brine treatment system (14) comprises one or more of selective ion exchange, ultrafiltration, nanofiltration, precipitation and adsorption.

38. The method of claim 5, wherein the brine flowing through the one or more draw chambers in step (b) and the brine flowing through the one or more feed chambers in step (e) are in countercurrent contact across the one or more semi-permeable membranes.

39. The method of any one of the preceding claims, wherein the further processing comprises processing in one or more of an electrolyzer, a crystallizer, a batch reactor, a liquid phase packed bed reactor, a stirred tank reactor, a multi-phase reactor and a trickle bed reactor.

40. The method of any one of the preceding claims, wherein the contaminants comprise divalent cations.41 . The method of claim 40, wherein the divalent cations comprise one or more of calcium, magnesium and strontium.

42. The method of any one of claims 1 to 39, wherein the contaminants comprise one or more of silicon, phosphorus and boron.

43. The method of any one of claims 1 to 39, wherein the contaminants comprise an organic material.

44. The method of claim 43, wherein the organic material comprises one or more of a lubricant, paint, organic solvent, oil and grease.

45. The method of claim 43, wherein the organic material is one present in lignocellulose derivatives.

46. The method of claim 43, wherein the organic material comprises one or more of carboxylic and humic acid, fulvic acid, benzene, toluene, xylene, and phenolic-type molecules.

47. The method of any one of claims 10 to 46, wherein the brine comprises lithium chloride.

48. A system for preparing a brine for further processing, comprising:(a) a forward osmosis unit (15) comprising a draw chamber (16), a feed chamber (18), and a semi-permeable membrane (20) between the draw chamber and the feed chamber;(b) the draw chamber having an inlet (22) for receiving a brine having a first concentration and an outlet (26) for the outflow of brine having a second concentration lower than the first concentration;(c) a brine treatment system (14) for receiving the brine from the draw chamber outlet, and for treating it to remove contaminants;(d) the feed chamber having an inlet (30) for receiving the brine from the brine treatment system and an outlet (34) for the outflow of brine having a third concentration higher than the second concentration.

49. The system of claim 48, wherein the brine comprises lithium chloride.

50. The system of claim 48, wherein the brine treatment system (14) comprises ion exchange and / or precipitation.51 . The system of claim 48, further comprising an evaporator (44) to receive the brine from the feed chamber outlet, and evaporate water from it to increase its concentration.

52. The system of claim 48, further comprising means (46) to add water to the brine between the draw chamber outlet and the brine treatment system.

53. The system of claim 48, further comprising means (48) to add water to the brine between the brine treatment system (14) and the feed chamber inlet (30).

54. The system of any one of claims 48 to 53, wherein the further processing comprises processing in an electrolyzer.

55. The system of any one of claims 48 to 53, wherein the further processing comprises processing in one or more of a crystallizer, a batch reactor, a liquid phase packed bed reactor, a stirred tank reactor, a multi-phase reactor and a trickle bed reactor.

56. The system of any one of claims 48 to 55, wherein the forward osmosis unit (15) comprises a plurality of forward osmosis modules (12) connected together in one or more of series, parallel, and crossflow configurations.

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