IL303677B2

IL303677B2 - Method and system for the production of alkali metal hydroxide salt and other materials from waste

Info

Publication number: IL303677B2
Application number: IL303677A
Authority: IL
Original assignee: Electriq Global Energy Solutions Ltd
Priority date: 2023-06-13
Filing date: 2023-06-13
Publication date: 2024-09-01
Also published as: WO2024257086A1; IL303677A; IL303677B1

Description

- 1 - 303677/ 02930770122- A METHOD AND SYSTEM FOR RECOVERY OF ALKALI METAL HYDROXIDE AND OTHER CHEMICALS FROM WASTE TECHNOLOGICAL FIELD The present disclosure relates to electrodialysis and the use of electrodialysis for recovery of chemical substances from waste.

BACKGROUND ART References considered to be relevant as background to the presently disclosed subject matter are listed below: H. I. Schlesinger, Herbert C. Brown, and A. E. Finholt "The Preparation of Sodium Borohydride by the High Temperature Reaction of Sodium Hydride with Borate Esters" Journal of the American Chemical Society 1953 75 (1), 205-209 DOI: 10.1021/ja01097a0 Handbook of Inorganic. Chemicals. Pradyot Patnaik, Ph.D. McGraw-Hill (pp. 117-118) Gao, W., Fang, Q., Yan, H., Wei, X., & Wu, K. (2021). Recovery of Acid and Base from Sodium Sulfate Containing Lithium Carbonate Using Bipolar Membrane Electrodialysis. Membranes, 11(2), 152.

Acknowledgement of the above references herein is not to be inferred as meaning that these are in any way relevant to the patentability of the presently disclosed subject matter.

BACKGROUND Hydrogen is emerging as a new energy vector outside of its traditional role and gaining more recognition internationally as a viable fuel route. In this connection, borohydrides are being considered as a low-cost hydrogen storage material with high hydrogen generation capacity. The preparation of sodium borohydride from boric acid was originally described by Schlesinger et al. in 1953 in a process called Brown– - 2 - 303677/ 02930770122- Schlesinger process. The Brown–Schlesinger process comprises the preparation of trimethylborate B(OCH3)3 from a boric acid with a consecutive reaction of sodium hydride NaH, with B(OCH3)3, to make the product NaBH4 and the by-product sodium methoxide NaOCH3. Other borohydrides such as LiBH4 and KBH4 can be prepared by the same route by addition of LiOH and KOH to react with the NaBH4 at the last step of the Brown–Schlesinger process.

The borohydrides have the potential to be used as hydrogen carriers thanks to the easy and efficient process of catalytic hydrogen release upon contacting these carriers with water in a dedicated reactor. The by-product of the hydrogen release process is metaborate salt of alkali metal dissolved in water. The metaborate salt of the alkali metal can be regenerated back to its borohydride salt via the Brown–Schlesinger process. The first step of this route is transforming the metaborate salt to the boric acid by its acidification as described by Pradyot Patnaik. Then, the Brown–Schlesinger process can be applied.

GENERAL DESCRIPTION The presently disclosed subject matter provides, in accordance with a first of its aspects, a method for recovering alkali metal hydroxide (XOH) from waste comprising aqueous XBO2 solution, X representing an alkali metal cation.

The method comprises, according to its broadest scope: - subjecting a waste comprising aqueous XBO2 solution, to a first electrodialysis process within a first electrodialysis unit that comprises at least one bipolar membrane, under conditions that provide a first XOH stream and a stream of dealkalized waste and discharging the first XOH stream; and optionally - mixing the de-alkalized waste with an acid HnY, n being an integer to form a slurry mixture of boric acid and XnY; - removing solids from said slurry mixture of boric acid and XnY to form a solid-free aqueous mixture of boric acid and XnY; and - subjecting the solid-free aqueous mixture of boric acid and XnY to a second electrodialysis process within a second electrodialysis unit comprising at least one bipolar membrane, the second electrodialysis unit being different from - 3 - 303677/ 02930770122- the first electrodialysis unit, under conditions that provides residual (desalinated) stream containing boric acid, a second XOH stream and a stream of HnY; - collecting the first XOH steam and the second XOH stream.

The present disclosure also provides, in accordance with a second of its aspects, a system comprising: a first electrodialysis unit configured for receiving waste comprising aqueous XBO2 solution, and for separately discharging XOH and dealkalized waste; and optionally; a second electrodialysis unit, downstream to said first electrodialysis unit, configured for receiving saline boric acid comprising dissolved boric acid and XnY, X representing an alkali metal cation, n representing an integer and Y representing an anion to said alkali metal cation, and for separately discharging at least a second XOH stream and a stream of aqueous solution of HnY.

In some preferred examples, the presently disclosed method and system allow also for the recovery of HnY from the same receiving waste comprising aqueous XBOsolution, as further detailed hereinbelow.

Further, in some preferred examples, the presently disclosed method and system allow also for the recovery of residual BA from the second electrodialysis unit to be further used in the recovery of BA.

BRIEF DESCRIPTION OF THE DRAWINGS In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: Figures 1A-1B provides schematic illustrations of components of a first electrodialysis unit (Figure 1A) and its compartments during operation (Figure 1B), in accordance with a non-limiting example of the presently disclosed subject matter. - 4 - 303677/ 02930770122- Figures 2A-2B provides schematic illustrations of components of a first electrodialysis unit (Figure 2A) and its compartments during operation (Figure 2B), in accordance with another non-limiting example of the presently disclosed subject matter.

Figures 3A-3B provides schematic illustrations of components of a second electrodialysis unit (Figure 3A) and its compartments during operation (Figure 3B), in accordance with a non-limiting example of the presently disclosed subject matter.

Figure 4 provides schematic flow chart illustrating the operation of a system according to a non-limiting example of the presently disclosed subject matter.

Figures 5A-5B are images of a lab scale system according to a non-limiting Example of the presently disclosed subject matter, including whole unit (Figure 5A) and the membrane assembly unit (stack) (Figure 5B).

DETAILED DESCRIPTION The present disclosure is based on the development of a technology that allows the recovery of an alkali metal containing base, e.g. KOH, and preferably also acids, e.g. H2SO4, via electrodialysis processes that utilizes, inter alia, bipolar membranes.

Particularly, although not exclusively, the present technology is directed to the recovery of KOH or NaOH and H2SO4 from spent fuel.

Spent fuel is an aqueous solution produced after completion of hydrogen release process from KBH4, LiBH4 or NaBH4 (referred further as XBH4) according to the following simplified reaction: (Eq. 1) XBH4 + 2 H2O → XBO2 + 4 H2 (g) This spent fuel needs to be recycled back to XBH4 to complete the hydrogen release cycle. The first step of the recycling process is the acidification of the spent fuel (e.g. by H2SO4) to produce boric acid which is the starting point of the XBH4 synthesis: (Eq. 2) nXBO2 + HnY + nH2O → nB(OH)3 + XnY The spent fuel is characterized by high pH due to the presence of XBO2 in aqueous solutions, at high concentrations, near the solubility limit. Without being bound by theory, such high concentration creates a complex of tetraborate structure balanced by the X+ cations, having the following general structure: - 5 - 303677/ 02930770122- The formation of the tetraborate structure results in a high alkaline pH of the waste that results in the formation of also XOH.

(Eq. 3) 4 XBO2 + (n+1)H2O → X2B4O7·nH2O + 2 XOH In the case of X=Na the and n=10 a well-known compound Borax is created (Na2B4O7·10H2O).

Such a high pH generated by XOH liberated from XBO2 in aqueous solution leads to excessive consumption of acid and results in excessive generation of saline waste (XnY).

Generally, the presently disclosed subject matter thus provides methods and systems for recovery of XOH (which can then be used for production of XBH4) and further of HnY (which can then be used for production of boric acid and further XBH4), from waste containing XBO2, by the electrodialysis process aided by a series of membranes, including bi-polar membranes.

It has been found by the inventors that XOH and HnY extracted from spent fuel according to the presently disclosed subject matter, drastically reduce the acid consumption in acidification process and the XOH consumption in XBH4 production process.

It has also been found by the inventors that the presently disclosed methods and systems become especially attractive in the production of KBH4 using H2SO4 as the acid HnY. The following Table 1 compares specific consumption of H2SO4 and KOH in KBHproduction process with and without electrodialysis according to the methods presently disclosed herein.

X + X + - 6 - 303677/ 02930770122- Table 1 – Base and Acid consumption during KBH4 production KBH4 production process KOH consumption H2SO4 consumption kgKOH/kgKBH4 kgH2SO4 /kgKBH4 Conventional Brown Schlesinger process 1.13 1.

With bi-polar membrane electrodialysis 0.13 0.

Table 1 shows that the presently disclosed methods and systems reduce the chemical consumption almost by an order of magnitude, thereby, significantly reducing the cost of the method and the carbon footprint of produced KBH4.

Thus, based on the inventors' current findings, and in accordance with a first of its aspects, the presently disclosed subject matter broadly provides a method comprising: - subjecting the waste comprising aqueous XBO2 solution, to a first electrodialysis process within a first electrodialysis unit that comprises at least one bipolar membrane, under conditions that provide a first XOH stream and a stream of dealkalized waste and discharging the first XOH stream; and optionally, - mixing the dealkalized aqueous waste with an acid HnY, n being an integer to form a slurry mixture of boric acid and XnY; - removing solids from said slurry mixture of boric acid and XnY to form a solid-free mixture of boric acid and XnY; and - subjecting the solid-free aqueous mixture of boric acid and XnY to a second electrodialysis process within a second electrodialysis unit comprising at least one bipolar membrane, the second electrodialysis unit being different from the first electrodialysis unit, under conditions that provides a second XOH stream and a stream of HnY and preferably also stream of residual BA (desalinated BA); - collecting the first XOH steam and the second XOH stream.

In some preferred examples, the method also provides regeneration/recovery of HnY as further described hereinbelow. - 7 - 303677/ 02930770122- Further, based on the inventors' current findings, and in accordance with a second of its aspects, the presently disclosed subject matter broadly provides a system comprising a first electrodialysis unit configured for receiving waste comprising aqueous XBO2 solution, and for separately discharging a first XOH stream and de-alkalized waste; and optionally a second electrodialysis unit, downstream to said first electrodialysis unit, configured for receiving saline boric acid comprising dissolved boric acid and XnY, X representing an alkali metal cation, n representing an integer and Y representing an anion to said alkali metal cation, and for separately discharging, a second XOH stream and aqueous solution of HnY and optionally or preferably also a stream of residual (desalinated) BA.

In the following, all examples and definitions apply to the methods according to the presently disclosed first aspect and to the systems according to the presently disclosed second aspect, mutatis mutandis.

In the context of the presently disclosed subject matter, when referring to "aqueous XBO2 waste " or to "waste comprising aqueous XBO2 solution" it is to be understood to refer to any aqueous based liquid that contains dissolved XBO2, X representing any alkali metal cation.

In the context of the presently disclosed subject matter, when referring to "de-alkalized waste " it is to be understood to refer to any aqueous based liquid that contains dissolved XBO2, X representing any alkali metal cation, yet, with a pH that is lower than the pH of the aqueous XBO2 waste introduced into the first electrodialysis unit.

In some examples of the presently disclosed subject matter, the waste comprising aqueous XBO2 solution is spent fuel having the meaning as described above, i.e. the aqueous solution produced during hydrogen release processes from KBH4, NaBH4 or LiBH4 (referred further as XBH4).

In some examples of the presently disclosed subject matter, X represents potassium, and the spent fuel is thus one comprising KBO2.

In some examples of the presently disclosed subject matter, X represents sodium, and the spent fuel is thus one comprising NaBO2. - 8 - 303677/ 02930770122- In some examples of the presently disclosed subject matter, X represents lithium, and the spent fuel is thus one comprising LiBO2.

In some examples of the presently disclosed subject matter, the waste comprises dissolved XBO2 at a concentration close to XBO2 solubility limit.

In the context of the present disclosure, the term "solubility limit" should be understood to refer to the maximum concentration at which XBO2 can dissolve in water at the method temperature and pressure and represents the point at which no more XBOcan be dissolved in water under the given temperature/pressure conditions.

Thus, in the context of the present disclosure, the term "close to XBO2 solubility limit" should be understood to refer a concentration that is about 1-2wt% below the maximum concentration (solubility limit) of XBO2 in water.

According to the presently disclosed method, the waste comprising aqueous XBO2 solution is subjected to at least one, preferably two electrodialysis processes, each electrodialysis process involves the use of one or more bipolar membrane (BPM) in the respective electrodialysis cell.

Bi-polar membranes are well known in the art and in accordance with the presently disclosed subject matter, the first electrodialysis unit combines BPMs with cationic membranes (CMs) while the second electrodialysis unit combines BPMs with CMs and anionic membranes (AMs), each unit having a specifically selected arrangement of BPMs, CMs and, in case of the second unit, also AMs.

The presently disclosed subject matter can be executed using commercially available BPM, CM and AM.

For example, the BPM, CM and/or AM can be any commercially available heterogeneous CM, AM and BPM membranes such as RALEX membranes by Mega Group Ltd.

Further, for example, the BPM, CM and/or AM can be any commercially available homogeneous CM, AM and BPM membranes such as any one selected from NEOSEPTA, SELEMION, FUJIFILM® and Nafion membranes or other membranes having the same or similar functionality.

Any combination of heterogenous and homogenous membranes can also be used. - 9 - 303677/ 02930770122- The electrodialysis units also include a cathode and an anode.

In some examples, the cathode can be selected from SS316 and Ni based materials. The cathode can be in a form of for example, a plate, foam, mesh structure.

With respect to the anode, since no corrosive gases, such as chlorine, are produced thereon, the anode can be of any type known in the art. In some examples, the anode is Graphite, or DSA© or Platinized Nickel, all being well known and commercially available anodes.

In some examples of the presently disclosed subject matter, the first electrodialysis unit comprises an electrodialysis cell including a membrane arrangement that receives the waste including at least aqueous dissolved XBO2 and results in recovery of a first XOH stream that is collected, and a stream of a stream of dealkalized waste.

In some examples of the presently disclosed subject matter, the first electrodialysis unit comprises a first electrodialysis cell including a first membrane arrangement including a cathode-paired CM and from the anode end of the cell, a repeating set of CM-BPM or a repeating set of CM-BPM-CM.

In the context of the presently disclosed subject matter, when referring to "a repeating set" it is to be understood to refer to a set of membranes which are sequentially repeated in the membrane arrangement.

Thus, in the context of the presently disclosed subject matters when referring to a repeating set of CM-BPM it is to be understood that the membrane arrangement comprises more than one set of CM-BPM. Accordingly, when the repeating unit is CM-BPM the entire membrane arrangement can be defined as Anode-(CM-BPM)i-CM-Cathode, where i represents and integer. Further accordingly, an electrodialysis cell comprising 3 repeating sets of CM-BPM, namely, i is equal to 3, the cell has the arrangement Anode-CM-BPM- CM-BPM- CM-BPM-CM-Cathode.

Further, in the context of the presently disclosed subject matters when referring to a repeating set of CM-BPM-CM it is to be understood that the membrane arrangement comprises more than one set of CM-BPM-CM. Accordingly, when the repeating unit is CM-BPM-CM the entire membrane arrangement can be defined as Anode-(CM-BPM-CM)i-CM-Cathode, where i represents and integer. Further accordingly, an electrodialysis cell comprising 3 repeating sets of CM-BPM-CM, namely, i is equal to 3, - 10 - 303677/ 02930770122- the cell has the arrangement Anode-CM-BPM-CM-CM-BPM-CM-CM-BPM-CM-CM-Cathode.

In some examples of the presently disclosed subject matter, a second electrodialysis unit is included and the second electrodialysis unit comprises a second electrodialysis cell including a second membrane arrangement that receives an aqueous mixture of boric acid (BA) and XnY and provides a second XOH stream and a stream of HnY, and optionally or preferably a stream of residual/ desalinated boric acid.

In some examples of the presently disclosed subject matter, the second electrodialysis unit comprises a second electrodialysis cell including a membrane arrangement including a cathode-paired CM and from the anode end of the cell, a repeating set of CM-BPM-AM.

Thus, in the context of the presently disclosed subject matters when referring to a repeating set of CM-BPM-AM it is to be understood that the membrane arrangement comprises more than one set of CM-BPM-AM. Accordingly, when the repeating unit is CM-BPM-AM the entire membrane arrangement can be defined as Anode-(CM-BPM-AM)i-CM-Cathode, where i represents and integer. Further accordingly, an electrodialysis cell comprising 3 repeating sets of CM-BPM-AM has the arrangement Anode-CM-BPM-AM-CM-BPM-AM-CM-BPM-AM-CM-Cathode.

When a second electrodialysis unit is included, the first XOH stream and the second XOH stream are preferably combined.

In some preferred examples, when the second electrodialysis unit is included, also HnY is recovered, which can be then utilized to produce boric acid, as further described hereinbelow.

More specifically, the presently disclosed method provides at least the recovery of XOH and the method comprises: (a) providing a first electrodialysis unit comprising a first unit inlet end and a first unit outlet end, and extending therebetween a first electrodialysis cell comprising: an anode a cathode paired with a cathode-end CM, - 11 - 303677/ 02930770122- a membrane arrangement stacked between the anode and the cathode-end CM, the membrane arrangement comprising, from the anode end, a repeating set of CM-BPM or a repeating set of CM-BPM-CM; a power source configured for applying a voltage across said cell, the anode, the cathode-end CM and the membrane arrangement providing an array of electrolyte flow compartments, each electrolyte flow compartment having a fluid inlet at the first unit inlet end and fluid outlet at the first unit outlet end, the array of electrolyte flow compartments including: - an electrode wash compartment between the anode and an anode end-CM and between the cathode and the cathode-end CM, - waste treatment compartment between two facing CM in the membrane arrangement comprising CM-BPM-CM repeating set or between BPM and cathode-side CM in the arrangement comprising CM-BPM repeating set; - XOH compartment between a CM and a BPM within a repeating set; and - when the arrangement comprises the CM-BPM-CM repeating set, a block loop compartment between BPM and its cathode-side CM; (b) apply voltage between the anode and said cathode while introducing through the first unit inlet end the following liquids - an electrode wash solution into an anode side electrode wash compartment and into a cathode-side electrode wash compartment; - liquid waste comprising aqueous XBO2 solution, into said waste treatment compartment; and - lean XOH solution into said XOH compartment; and - diluted acid solution HnY, where n represents a number and Y represents an anion of said strong acid, into block loop compartment, if such compartment exists; - 12 - 303677/ 02930770122- the voltage causing transfer of X+ across each CMs and generation of OH- by the BPM, to thereby form a XOH liquid in the XOH compartment and generation of H+ by the BPM in the waste treatment compartment to balance the transfer of X+ to the XOH compartment; and (c) discharging the XOH liquid from the first unit outlet end, the XOH liquid having a concentration greater than XOH concentration in the lean XOH solution.

This high alkaline solution is fed into the first electrodialysis unit for dealkalization.

The operation of the first electrodialysis unit, in accordance with the presently disclosed method, involves the flow of different liquids into the different compartments of the first electrodialysis unit. The flow is from the first unit inlet end towards the first unit outlet end.

Through the electrode wash compartment flows an electrode wash solution. In the context of the presently disclosed subject matter, the electrode wash solution is a solution that contains dissolved XkZ, X having the same meaning as above, namely, an alkali metal cation, k being an integer and Z being a counter anion.

In some examples of the presently disclosed subject matter, wherein the electrode wash solution comprises dissolved XkZ salt, at least the cathode-end CM is has very low permeability (i.e. essentially impermeable) to the Zk-.. In the context of the present disclosure, the low permeability can be understood to mean that at least 99% of the Zk- anions will be kept in the wash solution after a considerable period of operation of the system.

Without being bound thereto and in accordance with some examples, the wash solution has a concentration that provides sufficient conductivity to avoid energy losses and yet a minimal conductivity that will not add to the overall resistance of the system. Higher conductivities are less preferable to avoid excessive chemical loss upon replacement of the solution.

In some examples, the wash solution has a conductivity of > 10 mS/cm.

In some examples of the presently disclosed subject matter, the alkali metal cation of the wash solution is identical to the alkali metal cation in the waste, i.e. in the dissolved XBO2 of the aqueous waste. - 13 - 303677/ 02930770122- In some examples of the presently disclosed subject matter, the wash solution comprises XOH.

In some other examples of the presently disclosed subject matter, the wash solution comprises X2SO4.

Through the waste treatment compartment flows the liquid waste comprising aqueous XBO2 solution.

Through the XOH compartment flows lean XOH solution.

In the context of the presently disclosed subject matter, the term "lean XOH solution" is to be understood to mean a solution of dissolved XOH having a concentration which is lower than final XOH concentration achieved at the end of the treatment process (concentrated XOH solution leaving the XOH compartment outlet). The concentration difference between the lean XOH solution and concentrated XOH solution depends on the overall system configuration. In the BPM systems operating in recycle mode with recycling tank, the concentration difference can be as low as 0.1%wt while in once through systems without recycling the concentration difference can reach 5-10%wt.

Through block loop compartment, if present in the first electrodialysis unit, diluted acid solution HnY, where n represents a number and Y represents an anion of said strong acid.

In the context of the presently disclosed subject matter, the term "diluted HnY solution" is to be understood to mean a solution of dissolved HnY having a concentration that provides minimal conductivity such that it will note add to the overall resistance of the membranes and on the other hand provide sufficient conductivity to avoid energy losses.

In some examples, the diluted HnY solution has a concentration that provides a conductivity of > 10 mS/cm.

As may be appreciated by those versed in the art, higher conductivities are less preferable in order to avoid excessive chemical loss upon replacement of the HnY solution.

In some examples of the presently disclosed subject matter, the term "HnY" refers to a strong acid. - 14 - 303677/ 02930770122- In some examples of the presently disclosed subject matter, HnY is H2SO4.

In some examples of the presently disclosed subject matter, HnY is HCl.

According to the presently disclosed method, the different solutions are introduced into the first electrodialysis cell while voltage is applied between the anode and the cathode.

The applied voltage is selected to cause transfer of X+ across the CMs and generate OH- by the BPM, to thereby form a XOH liquid in the XOH compartment and to generate H+ by the BPM in the waste treatment compartment to balance the transfer of X+ to the XOH compartment.

As a result of operation of the first electrodialysis cell, a first stream of XOH is generated (being a concentrated XOH solution) and is discharged from the cell. The concentration of the XOH in the discharged XOH stream is greater than the concentration of XOH in the lean XOH solution.

In the context of the presently disclosed subject matter, the first unit stream discharged XOH (the concentrated XOH stream) comprises a concentration that is at least 5wt%; at times, at least 7wt%; at times, at least 9wt%; at times, at least 10wt%; at times, at least 12wt%; at times, at least 14wt%. It is to be appreciated that the concentration of XOH in this first stream of XOH discharged from the first electrodialysis unit can be higher, depending on the performance of the ion selective membranes used.

In some examples of the presently disclosed subject matter, the XOH concentration in the first stream of concentrated XOH discharged from the first electrodialysis unit is between about 10wt% and 30wt%; at times, between 10wt% and 25wt%; at times, between 15wt% and 25wt%; at times, between 10wt% and 20wt%; at times, between 10wt% and 15wt%.

Reference is now made to Figure 1A and to Figure 1B providing schematic illustrations of the different compartments and the different streams of solutions being introduced into each compartment in accordance with some examples of the presently disclosed subject matter.

Specifically, Figure 1A provides a schematic illustration of a first electrodialysis unit 100 , comprising a first unit inlet end 102 and a first unit outlet end 104 , and extending therebetween an electrolytic cell 106 including an anode 108 , a cathode 110 paired with - 15 - 303677/ 02930770122- a cathode-end CM 112 , and a membrane arrangement stacked between the anode 108 and the cathode-end CM 112 . The membrane arrangement comprises in this non-limiting example, from the anode end, a plurality of i repeating sets (CM-BPM-CM)i, 114 (1), 114 (2)… 114 (i).

Figure 1A also illustrates a power source 120 connected to anode 108 and cathode 110,configured for applying a voltage across the electrolytic cell 102 , so as to cause the transfer of charged species as explained hereinabove and below and generation of H+ and OH- in BPM.

Figure 1A also illustrates the various array of electrolyte flow compartments as follows: - an electrode wash compartment 122 between anode 108 and anode side (end) CM 124 and between cathode 110 and the cathode-end/paired CM 112 ; - waste treatment compartments 128 between two facing CM (between two repeating sets) in said membrane arrangement; - XOH compartment 130between a CM and a BPM within a repeating set; and - a block loop compartment 132 between BPM and its cathode-side facing CM.

Reference is now made to Figure 1B , which schematically illustrates the electrodialysis unit of Figure 1A , in operation.

For simplicity, the same reference numerals used in Figure 1A, are used to identify components having a same function in Figure 1B. For example, anode 108in Figure 1B is the same anode 108 in Figure 1A.

Figure 1B adds to Figure 1A in illustrating different liquid streams introduced into different compartments, upon activation of a voltage across the cell.

Specifically, Figure 1B illustrates the first electrodialysis unit 100including the first unit inlet end 102 , the first unit outlet end 104 , and extending therebetween the electrolytic cell 106 including the anode 108 , the cathode 110 paired with the cathode- - 16 - 303677/ 02930770122- end CM 112 , and the membrane arrangement stacked between the anode 108 and the cathode-end CM 112 .

In operation, power source (not illustrated in Figure 1B) applies voltage between the anode 108 and the cathode 110 and the following streams of liquids are introduced into the cell: - a stream of an electrode wash solution 140 flow from the first unit inlet end 102 , into the anode side electrode wash compartment 122 and into a cathode-side electrode wash compartment 125 and is discharged from the first unit outlet end 104 via streamline 142and can be circulated back into the electrode wash compartment; - streams of the liquid waste 144 comprising aqueous XBO2 solution flow from the first unit inlet end 102 , into the waste treatment compartments 128 , and are discharges as a stream of de-alkalized waste 146 ; - streams of lean XOH solution 148 flow from the first unit inlet end 102 into the XOH compartments 130 , and is discharged from the cell, via first unit outlet end, as the first stream of XOH 150 ; - streams of diluted acid solution HnY 152 flow from the first unit inlet end 102 into the block loop compartments 132 and is discharged from the first unit outlet end 104 via streamline 154and can be circulated back into the block loop compartment.

In some examples of the presently disclosed subject matter, the stream of waste comprising the aqueous XBO2 solution has a pH of between 12 and 14 and as a result of treatment within the first electrodialysis unit, the pH of the de-alkalized steam of waste is reduced, at times, to a pH of between 9 and 12.

In some examples of the presently disclosed subject matter, the stream of waste comprising the aqueous dissolved XBO2 has a pH of about 14 and as a result of treatment within the first electrodialysis unit, the pH of the de-alkalized steam of waste is reduced, at times, to a pH below 11.

In some examples, the recirculating of the wash solution comprises mixing the electrode wash solution discharged from the unit outlet ends, prior to being re-introduced into each electrode wash compartment. - 17 - 303677/ 02930770122- Further illustrated in Figure 1B , by arrows, is the ions transfer that takes place in the electrodialysis cell upon application of the voltage, including: - the transfer of X+ across each CMs into the XOH compartment and the generation of OH- by the BPM in the XOH compartment, which together provide a XOH solute in the XOH compartment; and - the generation of H+ by the BPM in each waste treatment compartment to balance said transfer of X+ to the XOH compartment; and - the prevention of boron compounds leakage from the liquid waste to the XOH compartment due to the presence of the block loop compartment.

With respect to the block loop compartment it is noted that such compartment may be relevant when using BPM that may be insufficient to prevent penetration of the tetraborate anions (B4O72-) to the XOH stream. This may cause loss of boron containing compounds and decrease yield of production of boric acid, which is processed as further described hereinbelow. When using a block loop as illustrated in Figures 1A-1B , the B4O72- anions face a CM which is typically more selective than BPM and thus prevents any significant leak of the boron compounds to the XOH compartment (XOH stream).

Further, in accordance with some examples, such as those illustrated in Figures 1A-1B , when using a block loop compartment, the waste is fed to compartments that are bound by CM from both the anode side and the cathode side.

As illustrated in Figure 1B , when the electric potential is applied, the X+ cations move towards cathode through the cathode side CM while the B4O72- anions migration towards the anode is blocked by the anode-side CM, separating the liquid waste and block loop compartments.

As further illustrated in Figure 1B , the depletion of positively charged X+ from the waste comprising the aqueous XBO2 solution is balanced by H+ ions transfer from the adjacent block loop. The X+ ions are transferred to the XOH compartments which are bound by CM from the anode side and by BPM from the cathode side. The X+ cations transferred from the liquid waste compartments are captured in XOH compartments since their further migration towards cathode is blocked by the anion part of the BPM. The captured X+ cations are balanced by OH- anions generated by BPM. In this way the - 18 - 303677/ 02930770122- concentration of XOH is increased. The block loop is bound by BPM from the anode side and by the CM from the cathode side.

In some examples of the presently disclosed subject matter, the streams of diluted acid solution HnY 152 comprise a diprotic or triprotic acid. In some examples of the presently disclosed subject matter, the acid in the diluted solution HnY 152 comprise an anion Yn- that is sufficiently large to prevent its penetration to the XOH compartments via the CM.

In some examples of the presently disclosed subject matter, the streams of diluted acid solution HnY 152 comprise H2SO4 acid.

In some examples of the presently disclosed subject matter, the streams of diluted acid solution HnY 152 comprise an organic acid. In this respect, it is note that organic acids can be used given that the anion part has very low permeability through the cation part of the BPM.

The H+ cations from the steam of diluted acid solution HnY move towards the liquid waste compartments through the cathode-side CM. The depletion of H+ ions in the block loop compartment is compensated by the H+ cations generation by the BPM.

Reference is now made to Figures 2A and 2B providing a schematic illustration of a first electrodialysis unit in accordance with another non-limiting example of the presently disclosed subject matter.

For simplicity, like reference numerals to those used in Figures 1A-1B , shifted by 100 are used to identify components having a similar function in Figures 2A-2B . For example, anode 208in Figures 2A-2B is an anode having the same function as anode 108 in Figures 1A-1B .

Similar to Figure 1A , Figure 2A illustrates a first electrodialysis unit 200 , comprising a first unit inlet end 202 and a first unit outlet end 204 , and extending therebetween an electrolytic cell 206 including an anode 208 , a cathode 210 paired with a cathode-end CM 212 , and a membrane arrangement stacked between the anode 208 and the cathode-end CM 212 . Membrane arrangement comprises in this non-limiting example, from the anode end, a plurality of repeating set of CM-BPM, 214 (1), 214 (2)… 214 (i). - 19 - 303677/ 02930770122- Figure 2A also illustrates a power source 220 connected to the anode 208 and the cathode 210,configured for applying a voltage across the electrolytic cell 202 , so as to cause the transfer of charged species as described herein and generation of H+ and OH- in BPM.

Figure 2A also illustrates similar arrays of electrolyte flow compartments including an electrode (anode) wash compartment 222 between anode 208 and an anode-side CM 224 and a further electrode (cathode) wash compartment 225 between cathode 210 and cathode-end/paired CM 212 ; waste treatment compartments 228 between the cation part of the BPM and a cathode-side CM (the CM of a next repeating set or of the cathode paired CM); and the XOH compartments 230between a CM and anion part of BPM (i.e. of the BPM of the same repeating set).

As clearly observed, in the first electrodialysis unit of Figures 2A-2B, there is no block loop compartment.

Reference is now made to Figure 2B , which schematically illustrates the electrodialysis unit of Figure 2A , in operation.

For simplicity, the same reference numerals used in Figure 2A, are used to identify components having the same function in Figure 2B. For example, anode 208in Figure 2B is the same anode 208 in Figure 2A.

Figure 2B adds to Figure 2A in illustrating the different liquid streams introduced into the different compartments, upon activation of a voltage across the cell by the power supply (not illustrated in Figure 2B).

Specifically, Figure 2B illustrates the first electrodialysis unit 200including the first unit inlet end 202 , the first unit outlet end 204 , the and extending therebetween the electrolytic cell 206 including the anode 208 , the cathode 210 paired with the cathode-end CM 212 , and the membrane arrangement stacked between the anode 208 and the cathode-end CM 212 .

In operation, power source (not illustrated in Figure 2B) applies voltage between the anode 208 and the cathode 210 and the following streams of liquid are introduced into the cell: - a stream of an electrode wash solution 240 flow from the first unit inlet end 202 , into the anode side electrode wash compartment 222 and into a cathode-side - 20 - 303677/ 02930770122- electrode wash compartment 225 and is discharged from the first unit outlet end 204 via streamline 242 and can be circulated back into the electrode wash compartment as described above; - streams of the liquid waste 244 comprising aqueous XBO2 solution flow from the first unit inlet end 202 , into the waste treatment compartments 228 , and are discharges as a stream of de-alkalized waste 246 ; and - streams of lean XOH solution 248 flow from the first unit inlet end 202 into the XOH compartments 230 , and is discharged from the cell, via first unit outlet end, as the first stream of XOH 250.

As noted above, the first electrodialysis unit of Figure 2B is lacking the block loop compartments.

Without being bound by theory, when the electric potential is applied, the X+ cations move towards cathode through the CM while the B4O72- anions migration towards anode is blocked by the cation part of the BPM. The depletion of positively charged X+ from the solution is balanced by H+ ions generated by BPM. The X+ ions are transferred to the XOH compartments which are bound by CM from the anode side and by anion part of BPM from the cathode side. The X+ cations transferred from the liquid waste compartments are captured in XOH compartments since their further migration towards cathode is blocked by the anion part of the BPM. The captured X+ cations are balanced by OH- anions generated by BPM. In this way the concentration of XOH is increased. As noted above, the anode and cathode are bound by CM and are washed (preferably by diluted XOH solution) to close the electrical circuit. The XOH washing solution is split and feed both anode and cathode compartments. The outlet XOH washing solution is mixed after exiting the compartments and is recycled back to the process.

Following electrodialysis within the first electrodialysis unit a first stream of XOH is recovered. In some examples of the presently disclosed subject matter, the first stream of XOH is subjected to a least one evaporating process to provide a first unit concentrated XOH that can be stored in a dedicated tank or communicated for further use, e.g. in XBHproduction processes.

Further, the first electrodialysis unit discharges de-alkalized liquid waste. - 21 - 303677/ 02930770122- In the context of the recently disclosed subject matter when referring to "de-alkalized waste" it is to be understood to refer to the aqueous waste solution comprising dissolved XBO2 with a pH that is lower than the pH of the aqueous waste comprising the dissolved XBO2 introduced into the first electrodialysis unit.

As noted above, the waste introduced into the first electrodialysis unit has high alkalinity.

In some examples of the presently disclosed subject matter, the stream of aqueous waste comprising the dissolved XBO2 has a pH of between 12 and 14 and as a result of treatment within the first electrodialysis unit, the pH of the de-alkalized steam of waste is reduced, at times, to a pH of between 9 and 12.

In some examples of the presently disclosed subject matter, the stream of aqueous waste comprising the dissolved XBO2 has a pH of about 14 and as a result of treatment within the first electrodialysis unit, the pH of the de-alkalized steam of waste is reduced, at times, to a pH of less than 11.

In some examples of the presently disclosed subject matter, the dealkalized liquid/aqueous waste is subjected to a process resulting in the regeneration of boric acid. In some examples, the generation comprises a reaction between the dealkalized liquid waste and a strong acid HnY, n being an integer and Y representing an anion to form boric acid and XnY slurry.

In some examples of the presently disclosed subject matter, the generation of boric acid can be represented by the following equation: n XBO2 + HnY + n H2O → n B(OH)3 + XnY.

In some examples of the presently disclosed subject matter, the boric acid and XnY salt are in a form of a slurry. This is due to the limited solubility of boric acid and XnY, resulting in their partial precipitation. Yet, some of the boric acid and the XnY salt remain dissolved and can be separated from the precipitated matter.

In some examples of the presently disclosed subject matter, the dissolved boric acid and XnY (aqueous mixture thereof) are separated from the precipitated matter.

In some examples of the presently disclosed subject matter, the separation is by means of a solid-liquid separator. - 22 - 303677/ 02930770122- Thus, in accordance with some examples of the presently disclosed subject matter, the slurry is introduced into a solid-liquid separator so as to separate between solids comprising solid boric acid and XnY and dissolved aqueous boric acid and dissolved XnY.

In some examples of the presently disclosed subject matter the dissolved aqueous boric acid/ XnY comprises water saturated with dissolved boric acid and dissolved XnY.

In some examples of the presently disclosed subject matter, the solids comprising the boric acid and XnY are dried, i.e. the method further comprises drying the solids.

The solids can be dried by any means known in the art, including drying in an oven, exposing the solids to dry air, etc.

Separation between the boric acid and the XnY can be achieved by the selective dissolution of boric acid.

In some examples, the selective dissolution may involve first dissolving the XnY in a solvent that does not dissolve the boric acid.

In some examples of the presently disclosed subject matter, the dried boric acid is selectively dissolved in an organic solvent.

In some examples of the presently disclosed subject matter, the boric acid organic solvent is selected from the group consisting of short chain alcohols, such as methanol, ethanol, 1-propanol.

In some examples of the presently disclosed subject matter, boric acid organic solvent is methanol.

The dissolving of the dried boric acid in methanol, results in the selective dissolution of boric acid while leaving most of the XnY salt in solid form. This allows for the collection of dissolved boric acid and further utilization of the residual solid XnY salt for the purpose of e.g. generating the acid HnY.

In some examples of the solid XnY salt is dissolved in water.

In some examples, the water dissolved boric acid / XnY obtained from the solid-liquid separator is combined with the water dissolved XnY, in a boric acid tank. The boric acid tank thus comprises a mixture of dissolved boric acid and dissolved XnY, at times, referred to herein by the term "saline boric acid" or "saline BA". This mixture (saline BA) can be further processed to recover further XOH and acid HnY. - 23 - 303677/ 02930770122- In some examples of the presently disclosed subject matter, the saline BA is subjected to a second electrodialysis process utilizing a second electrodialysis unit that is different in the membrane arrangement from that used in the first electrodialysis unit.

In some examples of the presently disclosed subject matter, the method thus further comprises subjecting the saline BA to an electrodialysis reaction within a second electrodialysis unit.

The second electrodialysis unit forming part of the presently disclosed method and system comprises a second unit inlet end and a second unit outlet end, and extending therebetween a second electrodialysis cell comprising: an anode, a cathode paired with a cathode-end CM, a second unit membrane arrangement stacked between the anode and the cathode-end CM, the second unit membrane arrangement comprising, from the anode, a repeating set of CM-BPM-AM; a power source configured for applying a voltage across the second cell, the cathode end CM and the second unit membrane arrangement providing an array of electrolyte flow compartments, each electrolyte flow compartment having a fluid inlet at the second unit inlet end and fluid outlet at the second unit outlet end, the array of electrolyte flow compartments providing: an electrode wash compartment between the anode and an anode side/end CM and between the cathode and the cathode-end CM; XOH compartment between CM and BPM of a repeating set (CM-BPM-AM); XnY compartment between BPM and AM of a repeating set (CM-BPM-AM); and a saline boric acid compartment between an AM and a CM.

In accordance with the presently disclosed method, the subjecting of the saline BA to an electrodialysis reaction within a second electrodialysis unit comprises (a) introducing through the second unit inlet end: - a wash solution into each of said electrode wash compartment; - 24 - 303677/ 02930770122- - lean XOH solution into the XOH compartment; - lean HnY solution into the HnY compartment; and - saline BA into the saline boric acid compartment; and (b) apply voltage between the anode and the cathode, the voltage causing transfer of X+ across each CM, and Yn- across each AM, and causing generation of OH- in the XOH compartment and H+ in the HnY compartment by the BPM; to thereby increase XOH concentration in the XOH compartment and HnY concentration in HnY compartment; and (c) discharging at least the XOH liquid from the second unit outlet end, the XOH liquid having a concentration greater than XOH concentration in the lean XOH solution.

The wash solution of the passing through the electrode compartment of the second electrodialysis unit can be the same or different from the wash solution employed in the first electrodialysis unit, as long as the alkali metal cation is the same as that present in the waste to be treated (i.e. of the XBO2).

In the context of the presently disclosed subject matter, the term "lean HnY solution" that is being introduced into the HnY compartment of the second electrodialysis unit is to be understood to mean the solution having low HnY concentration. The concentration difference between the lean HnY and the discharged final HnY solution depends on the actual process configuration of the industrial scale electrodialysis unit. In once through operation regime the concentration of lean HnY can be lower than 1%wt. In systems having HnY stream recirculated through circulation tank, the concentration difference between lean HnY stream and final HnY stream can be lower than 1%wt.

In the context of the presently disclosed subject matter, the term "saline BA" that is being introduced into the Saline BA compartment of the second electrodialysis unit is to be understood to mean a solution comprising dissolved boric acid and dissolved acid XnY, the XnY having the meaning as described herein.

In some preferred examples of the presently disclosed subject matter, the second electrodialysis unit also provides, in addition to the second stream of XOH, discharging of HnY from the HnY compartment, to be re-used in the presently disclosed method and system. - 25 - 303677/ 02930770122- Reference is now made to Figures 3A-3B providing a schematic illustration of a second electrodialysis unit in accordance with a non-limiting example of the presently disclosed subject matter.

For simplicity, like reference numerals to those used in Figures 1A-1B , shifted by 200 are used to identify components having a similar function in Figures 3A-3B . For example, anode 308in Figures 3A-3B is an anode having the same function as anode 108 in Figures 1A-1B .

Figure 3A illustrates a second electrodialysis unit 320 , comprising a first unit inlet end 302 and a first unit outlet end 304 , and extending therebetween an electrolytic cell 306 including an anode 308 , a cathode 310 paired with a cathode-end CM 312 , and a membrane arrangement stacked between the anode 308 and the cathode-end CM 312 . Membrane arrangement comprises in this non-limiting example, from the anode end, a plurality of repeating set of CM-BPM-AM, 314 (1), 314 (2)… 314 (i).

Figure 3A also illustrates a power source 320 connected to the anode 308 and the cathode 310,configured for applying a voltage across the electrolytic cell 302 , so as to cause the transfer of charged species as described herein and generation of H+ and OH- in BPM.

Figure 3A also illustrates an array of electrolyte flow compartments including an electrode (anode) wash compartment 322 between anode 308 and an anode-end CM 325 and a further electrode (cathode) wash compartment 325 between cathode 310 and cathode-paired CM 312; XOH compartments 330 between CM and BPM; acid compartments 360 between the BPM and AM; and saline boric acid compartments 362 between AM and CM.

Reference is now made to Figure 3B , which schematically illustrates the electrodialysis unit of Figure 3A , in operation.

For simplicity, the same reference numerals used in Figure 3A, are used to identify components having a same function in Figure 3B. For example, anode 308in Figure 3B is the same anode 308 in Figure 3A.

Figure 3B illustrates the different liquid streams introduced into the different compartments illustrated in Figure 3A , upon activation of a voltage across the cell by the source of power supply (not illustrated in Figure 3B). - 26 - 303677/ 02930770122- Specifically, Figure 3B illustrates, inter alia, the second electrodialysis unit 300including the second unit inlet end 302 , the second unit outlet end 304 , and extending therebetween the electrolytic cell 306 including the anode 308 , the cathode 310 paired with the cathode-end CM 312 , and the membrane arrangement stacked between the anode 308 and the cathode-end CM 312 .

In operation, voltage is applied between the anode 308 and the cathode 310 and the following streams of liquids are introduced into the cell's compartments: - a stream of an electrode wash solution 340 flowing from the second unit inlet end 302 , into the anode side electrode wash compartment 322 and into a cathode-side electrode wash compartment 325 , the stream of electrode wash solution being discharged from the second unit outlet end 304 via streamline 342and can be circulated back into the electrode wash compartment as described above; - streams of lean XOH solution 348 flowing from the second unit inlet end 302 into the XOH compartments 330 , which is then discharged from the cell, via second unit outlet end 304 , as a second stream of XOH 350; - streams of lean acid, HnY 364 , flowing from the second unit inlet end 302 into the HnY compartments 360 , which are then discharged from the cell, via second unit outlet end 304 , as a stream of concentrated HnY 366 ; and - streams of saline BA 368 , flowing from the second unit inlet end 302 into the saline BA compartments 362 , which are then discharged from the cell, via second unit outlet end 304 , as a stream of residual BA 370.

Without being bound by theory, HnY compartments receive H+ generated from the BPM and Yn- anion transferred through the AM from the saline BA compartment 362 thus resulting in an increase in the acid HnY concentration in the HnY compartment 360 .

Further, without being bound by theory, the saline BA compartments receive the mixture of dissolve boric acid and dissolved XnY and as a result of the applied potential, the cation X+ is transferred, via CM, to the XOH compartments 330 and the anion Yn- is transferred, via the AM, to the HnY compartments 360 , such that in the stream passing through the saline BA compartments loose most of XnY while maintaining BA . The latter can be explained by the fact that the weekly charged boric acid, B(OH)3, is almost not - 27 - 303677/ 02930770122- attracted to the electrodes and most of it remains in the compartment’s outlet stream which is then directed for further boric acid recovery.

With respect to the wash solution, as also explained above, passing through the electrode compartment it is to be noted that it can be the same or different from the wash solution employed in the first electrodialysis unit, as long as the alkali metal cation is the same.

Thus, for example, while the wash solution in the first electrodialysis unit can be XOH, e.g. KOH, the wash solution in the second electrodialysis unit can be X2SO4, e.g. K2SO4.

As a result of operation of the second electrodialysis cell, the concentration of the second unit XOH being discharged is greater than the concentration of XOH in the lean XOH solution.

In the context of the presently disclosed subject matter, the XOH discharged from the second electrodialysis unit comprises a concentration that is at least 5wt%; at times, at least 7 wt%; at times, at least 9wt%; at times, at least 10wt%; at times, at least 12wt%; at times, at least 14wt%. It is to be appreciated that the concentration of XOH in this second unit discharged XOH can be higher than 12wt%, depending on the performance of the ion selective membranes used.

In some examples of the presently disclosed subject matter, the XOH concentration discharged from the second electrodialysis unit is between about 5wt% and 20wt%; at times, between 5wt% and 15wt%; at times, between 10wt% and 20wt%; at times, between 5wt% and 10wt%; at times, between 8wt% and 15wt%.

In accordance with some examples of the presently disclosed subject matter, the XOH discharged from the second electrodialysis unit is concentrated. Accordingly, the disclosed method also comprises subjecting the second unit XOH from the second unit outlet end to at least one evaporating process to provide second unit concentrated XOH.

In some examples of the presently disclosed subject matter, the second unit XOH from the second unit outlet end is combined with the first unit XOH (from the first electrodialysis unit) prior to being introduced into an evaporator, i.e. the combined XOH is subjected to at least one evaporating process to provide a combined concentrated XOH. - 28 - 303677/ 02930770122- In some examples of the presently disclosed subject matter, the concentrated XOH is collected in a XOH tank.

In some examples of the presently disclosed subject matter, the method also comprises collecting the concentrated HnY generated in the second electrodialysis unit. This allows for the recovery of HnY which can then be reused in for the boric acid production. Thus, in the context of the presently disclosed subject matter, the method also provides recovery of HnY from the HnY compartment of the second electrodialysis unit.

In some examples of the presently disclosed subject matter, HnY represents H2SOand thus, the method provides recovery of H2SO4.

The chemical reactions occurring on the electrodes of the electrodialysis unit (the first and second) are as follows: Neutral pH conditions (Zn- and Wj- are anions of salts): Anode: 2? 2? → ? 2(? )+ 4? ++ 4? −(? 0 = − 1.23 V) Cathode: 4? 2? (? )+ 4? −→ 4??−+ 2? 2(? ) (? 0= −0.83 ? ) Overall reaction in electrode wash stream: 2? 2? (? )→ ? 2(? )+ 2? 2(? ) (? 0= −2.06 ? ) Basic pH conditions (Zn- and Wj- are OH-): Anode: 4??−→ 2? 2? (? )+ ? 2(? )+ 4? − (? 0= −0.4 ? ) Cathode: 4? 2? (? )+ 4? −→ 4??−+ 2? 2(? ) (? 0= −0.83 ? ) Overall reaction in electrode wash stream: 2? 2? (? )→ ? 2(? )+ 2? 2(? ) (? 0= −1.23 ? ) - 29 - 303677/ 02930770122- As can be seen, in both cases the closing of the electrical circuit is achieved by the decomposition of water molecules to O2 and H2 gases. The water loss in electrode wash stream in both the first electrodialysis unit and second electrodialysis unit can be compensated by periodic water makeup, when required. The makeup can be achieved by automatic control of the conductivity of the recycling stream by periodic water addition.

The presently disclosed subject matter, according to a second aspect thereof, also provides a system for regeneration of at least XOH.

In its broadest scope, the system comprises: a first electrodialysis unit configured for receiving waste comprising aqueous XBO2 solution, and for separately discharging a first XOH stream and dealkalized waste; and optionally, a second electrodialysis unit, downstream to said first electrodialysis unit, configured for receiving saline boric acid comprising dissolved boric acid and XnY, X representing an alkali metal cation, n representing an integer and Y representing an anion to said alkali metal cation, and for separately discharging a second XOH stream and aqueous solution of HnY.

Without being bound by theory, in operation, the presently disclosed method and system, provide the following: In the first electrodialysis unit as defined hereinabove, the applied voltage between the anode and the cathode provide for: - transfer of X+ across each CMs; - generation of OH- by the BPM, to thereby form a XOH liquid in the XOH compartment - generation of H+ by the BPM in the waste treatment compartment to balance the transfer of X+ to the XOH compartment; and - separate discharge of a first steam of XOH and a stream of de-alkalized waste.

In some examples of the presently disclosed subject matter, the system comprises a step of subjecting the dealkalized liquid/aqueous waste to a process resulting in the regeneration of boric acid. - 30 - 303677/ 02930770122- In some examples of the presently disclosed subject matter, the system comprises a first mixing chamber configured for mixing the stream of de-alkalized waste with HnY acid (e.g. H2SO4), prior to introducing the aqueous boric acid into the solid-liquid separator.

In some examples, the generation of boric acid comprises a reaction between the dealkalized liquid waste and a strong acid HnY, n being an integer and Y representing an anion to form boric acid and XnY slurry.

In some examples of the presently disclosed subject matter, the system comprises a solid-liquid separator (as described hereinabove) configured to receive the boric acid and XnY slurry and to separate between solution saline boric acid and XnY salt (liquid part) and solid boric acid and XnY containing matter (solid part).

In some examples, the solid boric acid and XnY containing matter is subjected to drying. Thus, in some examples of the presently disclosed subject matter, the system comprises a drying unit configured to dry the solid boric acid-containing matter received from the (boric acid and XnY slurry) solid-liquid separator and second electrodialysis unit.

In some examples of the presently disclosed subject matter, the system comprises boric acid separation unit downstream to the drying unit, the separation unit being configured to selectively dissolve the dried solid boric acid containing matter in an organic solvent and discharge/recover dissolved boric acid, and discharge solid XnY.

In some examples of the presently disclosed subject matter, the system comprises a XnY dissolution unit configured to dissolve solid XnY received from the boric acid separation unit.

In some examples of the presently disclosed subject matter, the system comprises a second mixing chamber configured to mix saline boric acid discharged from the solid-liquid separator with the dissolved XnY received from the XnY dissolution unit, the second mixing chamber being upstream to said second electrodialysis unit and is configured to communicate the mixed dissolved boric acid and XnY into the second electrodialysis unit. In some examples of the presently disclosed subject matter, the liquid saline boric acid containing dissolved XnY salt is collected for further treatment by the second electrodialysis unit, as further described hereinabove and below. - 31 - 303677/ 02930770122- In the second electrodialysis unit as defined hereinabove, the applied voltage between the anode and the cathode provides for: - transfer of X+ across each CM, - transfer of Yn- across each AM, - generation of OH- by said BPM in the XOH compartment - generation of H+ by said BPM in the HnY compartment; and - separate discharge of a second stream of concentrated XOH and a stream of HnY.

In some cases, the second electrodialysis unit as defined hereinabove, the applied voltage between the anode and the cathode also allows to keep a weakly charged boric acid in residual boric acid waste stream for further utilization.

Further in accordance with the presently disclosed subject matter, in some examples, the system also comprises a first evaporator (as described hereinabove), which is configured to evaporate water from the aqueous solution of XOH discharged from the first electrodialysis unit and to discharge first unit concentrated XOH.

In some examples of the presently disclosed subject matter, the system comprises a second evaporator configured to evaporate water from the aqueous solution of HnY received from the second electrodialysis unit and to discharge concentrated HnY.

In some examples of the presently disclosed subject matter, the system comprises a third evaporator between said second electrodialysis unit and said drying unit, said third evaporator being configured to evaporate water from said residual boric acid.

Reference is now made to Figure 4 providing a schematic illustration of a system comprising all the above-described optional system elements and is configured for recovery of XOH and preferably also HnY from aqueous XBO2 waste solution, such as spent fuel, according to some examples of the presently disclosed subject matter.

Specifically, Figure 4 shows a schematic illustration of a system according to some examples of the presently disclosed subject matter, constructed to allow the recovery of XOH from waste containing the aqueous dissolved XBO2 and preferably also recovery of HnY utilized in the process of XOH recovery. - 32 - 303677/ 02930770122- According to the non-limiting illustration of Figure 4 , waste comprising the aqueous dissolved XBO2 (" XBO2 Waste ") is fed to the first electrodialysis unit for dealkalization (" 1 st ED Unit "). As noted hereinbefore, the XBO2 containing waste is an aqueous solution of XBO2 at high concentration near the solubility limit. Such a solution creates a complex tetraborate structure balanced by X+ cations. This process results in a highly alkaline pH of the XBO2 waste due to consecutive liberation of XOH according to the following route: 4 XBO2 + (1+n)·H2O → X2B4O7·nH2O + 2 XOH This solution is fed to the 1st ED Unit composed of the power source, cathode and anode and ion selective membranes arranged in a stack between the cathode and anode.

The membrane arrangement in the 1st ED Unit can have a repeating sequence of CM-BPM-CM as schematically illustrated in Figure 1A (in case of working with a block loop) or a sequence of CM-BPM as schematically illustrated in Figure 2A (in case of working without a block loop).

The 1st ED Unit generates two main process streams. The first stream is a first XOH stream. The first XOH stream is sent to a 1 st Evaporator to increase the XOH concentration to a desired level (e.g. 40wt%-45wt%) and stored in dedicated tank (" XOH Tank "), e.g. for later use in XBH4 production process.

The second stream discharged from the 1st ED Unit is de-alkalized waste which is sent to a boric acid production stage in a BA reactor (" BA Reactor "). In the BA reactor, concentrated acid HnY is added to the dealkalized waste to produce boric acid slurry. As explained above, boric acid has limited solubility and it is precipitated together with the generated salt XnY. Part of the boric acid and XnY salt remain in dissolved form.

The resulting slurry is separated in solid/liquid separator (" Solid-Liquid Separator ") to solid BA + XnY which is sent for drying (" Boric Acid Drying ") and liquid boric acid production waste which is sent to " Waste Collection Tank ".

Dry boric acid and XnY are contacted by methanol in boric acid dissolution (" Boric Acid Dissolution "). As noted above, methanol selectively dissolves the boric acid leaving most of the XnY salt in solid form. The methanol dissolved BA is sent to further use, e.g. in XBH4 production processes, while the solid XnY is sent to water dissolution step (" XnY Dissolution "). The dissolved XnY salt is transferred to the same Waste - 33 - 303677/ 02930770122- Collection Tank into which the liquid BA waste is sent (" Waste Collection Tank ") and is thus mixed with waste from boric acid production step. The total waste stream from the Waste Collection Tank is sent to a 2nd electrodialysis unit (" 2 nd ED Unit ") to recover a second XOH stream, the boric acid and also HnY.

The 2nd ED unit operational principle is detailed hereinabove. The 2nd ED Unit is generally composed of the power source, cathode and anode and ion selective membranes arranged in a stack between the cathode and anode. The membrane arrangement in the nd ED Unit has a repeating sequence of CM-BPM-AM as schematically illustrated in Figure 3A.

The 2nd ED unit generates three main process streams.

A first stream discharged from the 2nd ED Unit is a second XOH stream which is sent to a 1 st Evaporator to increase the XOH concentration to the desired level and stored together with the first XOH stream, in the XOH Tank.

A second stream discharged from the 2nd ED Unit is HnY stream, which is sent to a 2 nd Evaporator to increase the HnY acid concentration to the desired level, which can then be stored in a HnY Tank and from the HnY Tank, communicated to the BA Reactor for reused in the BA production stage.

A third stream comprising desalinated solution containing residual boric acid. This stream is sent to a 3 rd Evaporator to produce solid boric acid which can be then dried in the Boric Acid Drying unit together with the boric acid discharged from the Solid- Liquid Separator .

As used herein, the forms " a ", " an " and " the " include singular as well as plural references unless the context clearly dictates otherwise. For example, the term " a membrane" includes one or more membranes.

Further, as used herein, the term " comprising " is intended to mean that the composition include the recited components, e.g. 1st elecrodialysis unit, but not excluding other elements or components than may form part of the presently disclosed subject matter. The term " consisting essentially of " is used to define methods and systems which include the recited components or elements but exclude other components or elements that may have an essential significance on the performance of the disclsoed methods and systems. - 34 - 303677/ 02930770122- " Consisting of " shall thus mean excluding components or elements that are not specifically recited. Embodiments defined by each of these transition terms are within the scope of this invention.

Further, all numerical values, e.g. when referring the amounts or ranges of the elements constituting the recited compositions, e.g. the streams of XOH are approximations which are varied (+) or (-) by up to 20%, at times by up to 10% of from the stated values. It is to be understood, even if not always explicitly stated that all numerical designations are preceded by the term " about ".

The invention will now be exemplified in the following description of experiments that were carried out in accordance with the invention. It is to be understood that these examples are intended to be in the nature of illustration rather than of limitation. Obviously, many modifications and variations of these examples are possible in light of the above teaching. It is therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise, in a myriad of possible ways, than as specifically described hereinbelow.

DESCRIPTION OF NON-LIMITING EXAMPLES Ion selective membranes: Heterogeneous CM, AM and BPM membranes: RALEX membranes by Mega Group Ltd.

Cathode: SS316 cathode Anode: Graphite anode Experimental system The proof-of-concept experiments were conducted in laboratory scale electrodialysis system provided by Mega Group Ltd. and shown in Figure 5A .

The system consisted of 5 independent circulating loops (the "compartments") marked as D1, D2, E, C1 (not in use in the current example) and C2. Each circulating loop includes a respective dedicated circulating vessel, piping, flowmeter and circulating pump (pump and flowmeter are not shown in Figure 5A). The circulating vessels were submerged in a thermal bath to enable constant temperature conditions during the experiment. - 35 - 303677/ 02930770122- The system also included a dedicated power source (Power supply) with its Power supply Voltmeter and Power supply Amperemeter. The pumps and the power source were operated from a control panel, also shown in Figure 5A.

The system was designed to operate with a single replaceable membrane unit (stack) including a stack of membranes' arrangement that allows the switching between an operation with a block loop circulating stream (D2) and without a block loop circulating stream (where D2 is "not in use"). The system of Figure 5A can also simulate the operation of the 2nd electrodialysis unit, as evident from Table 2 below.

Figure 5B shows that the shown stack of membranes' arrangements also includes an anode plate and a cathode plate with electrical connections to the power source (the power source not shown).

Circulation piping lines were connected to the relevant membrane arrangement port located in electrode plates. The membranes were arranged between the anode and cathode and held by tightening rods.

For lab scale production, sensing electrodes were used and were located between the electrodes and the membrane adjacent thereto. The purpose of the sensing electrodes is to measure the potential drop on the membranes without the interference of the potential drop related to the reaction occurring on the electrodes and electrical system resistance. The potential difference measured by sensing electrodes serves for determination of process energy consumption used for system scale up.

The system shown in Figures 5A-5B was used to test the performance in different configurations of the electrodialysis units. The membrane type and arrangement inside the stack (e.g. with or without the block loop) and accordingly circulating streams were selected to adapt the system for different operating conditions.

Table 2 summarizes the circulating streams’ designation for different system configurations (e.g. with or without the circulation of a block loop stream). - 36 - 303677/ 02930770122- Table 2: Streams designation for different BPM systems configuration D1 D2 E C1 C2 1st electrodialysis unit block loopXOH Block Loop Electrode wash Not in use Aqueous XBOsolution 1 st electrodialysis unit without block loopXOH Not in use Electrode wash Not in use Aqueous XBOsolution 2 nd electrodialysis unitXOH HnY Electrode wash Not in use Saline BA waste Experimental conditions The experimental conditions for the different system configurations include the following: Voltage 20 – 30 V (measured parameter) Amperage 1.9 – 2 A (controlled parameter) Current density 30 mA/cm AM, CM and BPM membranes RALEX membranes by Mega Group Ltd.

No. of repeating membrane sets Effective membrane area 640 cm Temperature 30oC Solution mass 1 kg for all streams Circulation flowrates 500 ml/min for all streams Experiment duration 2-4 hours - 37 - 303677/ 02930770122- Results Operation of 1 st electrodialysis unit with block loop Experiments conducted with spent fuel solutions containing 40%wt KBOshowed that more than 30% of K+ ions can be recovered out of the solution as KOH. The KOH recovery led to pH decrease from pH ~ 14 to pH below 13.

Experiments conducted with spent fuel solutions containing 30%wt KBOshowed that more than 40% of K+ ions can be recovered out of the solution as KOH. The KOH recovery led to pH decrease from pH > 13.8 to pH below 12.

Experiments conducted with spent fuel solutions containing 30%wt KBOshowed that more than 50% of K+ ions can be recovered out of the solution as KOH. The KOH recovery led to pH decrease from pH ~ 13 to pH below 10.

The KOH solution recovered reached concentration of up to 7.5%wt at the end of the experiment. Less than 1% of B4O72- anions were lost from the treated waste stream. The process energy consumption was estimated as ~ 1.5 kWh per 1 kg of recovered KOH.

Operation of 1 st electrodialysis unit without block loop The results obtained without block loop circulation were similar to the results obtained with block loop circulation, except the loss of the B4O72- anions in the former configuration. The B4O72- anions loss from the treated waste stream to the KOH stream increased without the block loop circulation, from ~1% to ~ 5%.

Operation of 2 nd electrodialysis unit The treated saline Boric Acid waste obtained from operating the 1st electrodialysis unit (with or without the operation of a block loop) contained ~ 60 gr of Boric Acid and ~ 120 gr of K2SO4 in one liter of the solution.

The expected level of K+ ions recovery as KOH and SO42- ions recovery as H2SOis more than 90%. The expected loss of weakly charged Boric Acid to the KOH and H2SO4 streams is < 5% in total.

Claims

- 38 - 0293077041- CLAIMS:

1. A method for recovery of alkali metal hydroxide (XOH) from waste comprising aqueous XBO 2 solution, the method comprising: subjecting the waste to a first electrodialysis process within a first electrodialysis unit that comprises at least one bipolar membrane, under conditions that provide a first XOH stream and a stream of de-alkalized waste and discharging the first XOH stream; and optionally mixing the de-alkalized waste with an acid H nY, n being an integer and Y a counter anion to the alkali metal cation to form a slurry of boric acid and X nY; removing solids from said slurry of boric acid and X nY to form a solid-free aqueous mixture of boric acid and XnY; and subjecting the solid-free aqueous mixture of boric acid and XnY to a second electrodialysis process within a second electrodialysis unit comprising at least one bipolar membrane, the second electrodialysis unit being different from the first electrodialysis unit, under conditions that provides a second XOH stream and a stream of HnY; collecting the first XOH steam and the second XOH stream.

2. The method of claim 1, wherein said first electrodialysis unit comprises a first unit inlet end and a first unit outlet end, and extending therebetween a first electrodialysis cell comprising: an anode a cathode paired with a cathode-end CM, a membrane arrangement stacked between said anode and said cathode-end CM, the membrane arrangement comprising, from the anode end, a repeating set of CM-BPM or a repeating set of CM-BPM-CM; a power source configured for applying a voltage across said cell, said anode, said cathode-end CM and said membrane arrangement providing an array of electrolyte flow compartments, each electrolyte flow - 39 - 0293077041- compartment having a fluid inlet at said first unit inlet end and fluid outlet at said first unit outlet end, the array of electrolyte flow compartments including an electrode wash compartment between said anode and said anode paired-CM and between said cathode and said cathode-paired CM, waste treatment compartment between two facing CM in the membrane arrangement comprising CM-BPM-CM repeating set or between BPM and cathode-side CM in the arrangement comprising CM-BPM repeating set; XOH compartment between a CM and a BPM within a repeating set; and when said arrangement comprises said CM-BPM-CM repeating set, a block loop compartment between BPM and its cathode-side CM;

3. The method of claim 2, comprising (a) apply voltage between said anode and said cathode while introducing through said first unit inlet end an electrode wash solution into an anode side electrode wash compartment and into a cathode-side electrode wash compartment; liquid waste comprising aqueous XBO 2 solution, into said waste treatment compartment; and lean XOH solution into said XOH compartment; and diluted acid solution HnY, where n represents a number and Y represents an anion of said strong acid, into block loop compartment, if such compartment exists; said voltage causing transfer of X+ across each CMs and generation of OH- by said BPM, to thereby form a XOH liquid in said XOH compartment and generation of H+ by said BPM in said waste treatment compartment to balance said transfer of X+ to said XOH compartment; and - 40 - 0293077041- (b) discharging at least said first XOH stream from said first unit outlet end, said first XOH stream having a concentration greater than XOH concentration in said lean XOH solution.

4. The method of any one of claims 1 to 3, wherein said alkali metal in said waste is selected from the group consisting of sodium, potassium and lithium.

5. The method of any one of claims 1 to 4, wherein said XBO2 is at a concentration close to its solubility limit.

6. The method of any one of claims 1 to 5, wherein said liquid waste is spent fuel obtained during hydrogen release from XBH 4 based on the following equation (1): (g) 2 + 4 H 2 XBO O 2 + 2 H 4 XBH

7. The method of any one of claims 2 to 6, whenever dependent on claim 2, wherein said electrode wash solution comprises dissolved XkZ salt, X being said alkali metal cation, k being an integer, Zk- being an anion and at least said cathode-end CM is essentially impermeable to said Zk-.

8. The method of claim 7, wherein said XkZ salt is selected from the group consisting of XOH and X2SO4.

9. The method claim 8, wherein concentration of said XOH in said electrode wash solution dissolved XOH lower than the XOH concentration in said waste.

10. The method of any one of claims 2 to 7, whenever dependent on claim 2, comprising recirculating electrode wash solution discharged from first unit outlet ends of each said electrode wash compartment.

11. The method of claim 10, wherein said recirculating comprises mixing the electrode wash solution discharged from said first unit outlet ends, prior to being re-introduced into each electrode wash compartment.

12. The method of any one of claims 1 to 11, comprising subjecting said first XOH stream to at least one evaporating process to provide first unit concentrated XOH.

13. The method of claim 12, comprising collecting said first unit concentrated XOH in a XOH tank. - 41 - 0293077041-

14. The method of any one of claims 1 to 11, wherein said dealkalized waste has a pH of less than 11.

15. The method of any one of claims 1 to 14, wherein said mixing said dealkalized waste with acid HnY results in regenerating boric acid from said dealkalized waste, said regenerating reaction being represented by the following equation (2): n XBO2 + HnY + n H2O n B(OH)3 + XnY.

16. The method of claim 15, comprising introducing said slurry into a solid-liquid separator and separating between solids comprising solid boric acid and solid X nY and saline boric acid comprising aqueous solution saturated with dissolved boric acid and XnY.

17. The method of claim 16, comprising drying said solids comprising the solid boric acid and solid XnY.

18. The method of claim 17, comprising separating solid boric acid from solid X nY, said separating comprises dissolving said solids in methanol, and collecting solid X nY separated from methanol dissolved boric acid.

19. The method of claim 18, comprising dissolving the collected solid XnY in water.

20. The method of claim 16, comprising collecting said saline boric acid into a boric acid tank.

21. The method of claim 19 and 20, further comprising (a) subjecting the saline boric acid to an electrodialysis reaction within a second electrodialysis unit, said second electrodialysis unit comprises a second unit inlet end and a second unit outlet end, and extending therebetween a second electrodialysis cell comprising: an anode, a cathode paired with a cathode-end CM, a second unit membrane arrangement stacked between said anode and said cathode-end CM, the second unit membrane arrangement comprising, from the anode, a repeating set of CM-BPM-AM; a power source configured for applying a voltage across said second cell, - 42 - 0293077041- said cathode-end CM and said second unit membrane arrangement providing an array of electrolyte flow compartments, each electrolyte flow compartment having a fluid inlet at said second unit inlet end and fluid outlet at said second unit outlet end, the array of electrolyte flow compartments including: an electrode wash compartment between said anode and an anode-end CM and between said cathode and its cathode-end CM; XOH compartment between CM and BPM in a repeating set; X nY compartment between BPM and AM in a repeating set; and a saline boric acid compartment between an AM and a cathode side CM in a repeating set; said subjecting comprises introducing through said second unit inlet end a wash solution into each of said electrode wash compartment; lean XOH solution into said XOH compartment; lean H nY solution into said H nY compartment; aqueous boric acid comprising dissolved boric acid and HnY into said saline BA compartment;

22. The method of claim 21, wherein said electrodialysis reaction within the second electrodialysis unit comprises: (a) apply voltage between said anode and said cathode, said voltage causing transfer of X+ across each CM, and Yn- across each AM, to thereby form a second XOH stream in said XOH compartment; and to cause generation of OH- in said XOH compartment and H+ in said HnY compartment by said BPM; and (b) discharging at least said second XOH stream from said second unit outlet end, said second XOH stream having a concentration greater than XOH concentration in said lean XOH solution.

23. The method of claim 22, comprising subjecting said second XOH stream from said second unit outlet end to at least one evaporating process to provide second unit concentrated XOH. - 43 - 0293077041-

24. The method of claim 23, comprising collecting said second unit concentrated XOH in said XOH tank.

25. The method of any one of claims 1 to 24, comprising recovery of H nY.

26. The method of claim 25, whenever dependent on any one of claims 21 to 25, wherein said recovery of HnY is from said HnY compartment.

27. A system comprising a first electrodialysis unit configured for receiving waste comprising aqueous XBO 2 solution, and for separately discharging a first XOH stream and dealkalized waste; and optionally a second electrodialysis unit, downstream to said first electrodialysis unit, configured for receiving saline boric acid comprising dissolved boric acid and XnY, X representing an alkali metal cation, n representing an integer and Y representing an anion to said alkali metal cation, and for separately discharging a second XOH stream and aqueous solution of H nY.

28. The system of claim 27, wherein said first electrodialysis unit comprises a first electrodialysis cell comprising a first unit inlet end and a first unit outlet end, and extending therebetween: an anode a cathode paired with a cathode-end CM, a membrane arrangement stacked between said anode and said cathode-end CM, the membrane arrangement comprising, from the anode end, a repeating set of CM-BPM or a repeating set of CM-BPM-CM; a power source configured for applying a voltage across said cell, said anode, said cathode-end CM and said membrane arrangement providing an array of electrolyte flow compartments, each electrolyte flow compartment having a fluid inlet at said first unit inlet end and fluid outlet at said first unit outlet end, the array of electrolyte flow compartments including an electrode wash compartment between said anode and anode-side CM and between said cathode and cathode paired CM, - 44 - 0293077041- waste treatment compartment between two facing CM in the membrane arrangement comprising CM-BPM-CM repeating set or between BPM and cathode-side CM in the arrangement comprising CM-BPM repeating set, configured to receive waste comprising an aqueous mixture of boric acid and XnY; XOH compartment between a CM and a BPM within a repeating set; and when said arrangement comprises said CM-BPM-CM repeating set, a block loop compartment between BPM and its cathode-side CM.

29. The system of claim 27 or 28, wherein said first electrodialysis unit is configured for applying on said cell voltage causing transfer of X+ across each CMs and generate OH- by said BPM, to thereby form a XOH liquid in said XOH compartment and generate H+ by said BPM in said waste treatment compartment to balance said transfer of X+ to said XOH compartment; and for separately discharging XOH and a stream of said de-alkalized waste .

30. The system of any one of claims 27 to 29, wherein said second electrodialysis unit comprises a second electrodialysis cell comprising a second unit inlet end and a second unit outlet end, and extending therebetween a second electrodialysis cell comprising: an anode, a cathode paired with a cathode-end CM, a second unit membrane arrangement stacked between said anode and said cathode-end CM, the second unit membrane arrangement comprising, from the anode, a repeating set of CM-BPM-AM; a power source configured for applying a voltage across said second cell, said cathode-end CM and said second unit membrane arrangement providing an array of electrolyte flow compartments, each electrolyte flow compartment having a fluid inlet at said second unit inlet end and fluid outlet at said second unit outlet end, the array of electrolyte flow compartments including: an electrode wash compartment between said anode and an anode-end CM and between said cathode and a cathode-end CM, configured to allow flow - 45 - 0293077041- therethrough of a wash solution, from said second unit inlet end to said second unit outlet end; XOH compartment between CM and BPM in a repeating set configured to allow flow therethrough of lean XOH solution, from said second unit inlet end to said second unit outlet end; XnY compartment between BPM and AM in a repeating set configured to allow flow therethrough of lean H nY solution, from said second unit inlet end to said second unit outlet end; and a saline boric acid compartment between an AM and a CM; configured to allow flow therethrough of said aqueous boric acid, from said second unit inlet end to said second unit outlet end.

31. The system of any one of claims 27 to 30, wherein said second electrodialysis unit is configured for applying voltage between said anode and said cathode, said voltage being configured to cause transfer of X+ across each CM, and Yn- across each AM, to thereby form a XOH liquid in said XOH compartment; and to cause generation of OH- in said XOH compartment and H+ in said HnY compartment by said BPM; and separately discharging said second XOH stream and H nY.

32. The system of any one of claims 27 to 31, comprising a first evaporator configured to evaporate water from said aqueous solution of said first XOH stream received from said first electrodialysis unit and to discharge concentrated XOH.

33. The system of any one of claim 27 to 32, comprising a solid-liquid separator configured to receive boric acid slurry and to separate between saline boric acid and solid boric acid containing matter.

34. The system of claim 33, comprising a drying unit, configured to dry solid boric acid containing matter received from any one of said solid-liquid separator and second electrodialysis unit.

35. The system of claim 34, comprising boric acid separation unit downstream to said drying unit, said separation unit configured to selectively dissolve the dried solid boric - 46 - 0293077041- acid containing matter in an organic solvent and separately discharge dissolve boric acid and solid X nY.

36. The system of claim 35, wherein said boric acid organic solvent is a short chain alcohol.

37. The system of claim 36, wherein said organic solvent is methanol.

38. The system of any one of claims 27 to 37, comprising a second evaporator configured to evaporate water from said aqueous solution of H nY and recover concentrated H nY.

39. The system of claim 33 and 38, comprising a first mixing chamber configured for mixing said de-alkalized waste with HnY recovered from said second evaporator, prior to introducing said aqueous boric acid into said solid-liquid separator.

40. The system of any one of claims 27 to 39, comprising a third evaporator configured to concentrate residual boric acid discharged from said second electrodialysis unit.

41. The system of any one of claims 27 to 40, whenever dependent on claim 35, comprising a XnY dissolution unit configured to dissolve said solid XnY.

42. The system of claim 33 and 41, comprising a second mixing chamber configured to mixed saline boric acid discharged from the solid-liquid separator with the dissolved X nY.