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Title:
LOW SODIUM SALT
Document Type and Number:
WIPO Patent Application WO/2013/181708
Kind Code:
A1
Abstract:
The invention relates to a process for producing a reduced sodium salt from a solution in which sodium cations in the reduced sodium salt represent a lower proportion of total cations than in the solution. The process comprises exposing the solution to a sorbent capable of sorbing sodium ions, so as to produce a reduced sodium solution. The sorbent, having sodium ions sorbed therein and/or thereon, is then separated from the reduced sodium solution. Finally, the reduced sodium solution is at least partially evaporated so as to produce the reduced sodium salt in solid form.

Inventors:
PRASAD, Shiva (3 Fraser Street, Constitution Hill, NSW 2145, AU)
RAVAJENDRAM, Vijaya (38 Deakin Place, West Pennant Hills, NSW 2125, AU)
Application Number:
AU2013/000603
Publication Date:
December 12, 2013
Filing Date:
June 06, 2013
Export Citation:
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Assignee:
NEPTUNE BIO-INNOVATIONS (IP) PTY LTD (Level 6, 410 Church StreetNorth Parramatta, NSW 2151, AU)
International Classes:
B01D15/04; B01D15/08; C01D3/06
Other References:
BONELWA MABOVU: "Brine treatment using natural adsorbents", May 2011 (2011-05-01), Retrieved from the Internet
Attorney, Agent or Firm:
SPRUSON & FERGUSON (GPO BOX 3898, Sydney, New South Wales 2001, AU)
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Claims:
Claims:

1. A process for producing a reduced sodium salt from a solution wherein sodium cations in said reduced sodium salt represent a lower proportion of total cations than in said solution, said process comprising:

• exposing the solution to a sorbent capable of sorbing sodium ions, so as to produce a reduced sodium solution;

• separating the sorbent having sodium ions sorbed therein and/or thereon from the reduced sodium solution; and

• at least partially evaporating the reduced sodium solution so as to produce the reduced sodium salt in solid form.

2. The process of claim 1 wherein the solution is sea water, whereby the reduced sodium salt is reduced sodium sea salt.

3. The process of claim 1 or claim 2 wherein the sorbent is a zeolite.

4. The process of claim 3 wherein the zeolite is a naturally occurring zeolite.

5. The process of claim 3 or claim 4 wherein the zeolite has been pretreated with acid.

6. The process of claim 5 wherein the acid is hydrochloric acid.

7. ; The process of claim 5 or claim 6 wherein the acid has a concentration of 0.001 to

0.1M.

8. The process of any one of claims 1 to 7 wherein the sorbent comprises clinoptilolite.

9. The process of any one of claims 1 to 8 wherein the sorbent has a mean particle size between about 0.05 and about 10mm.

10. The process of any one of claims 1 to 9 wherein the sorbent comprises calcium ions whereby the step of exposing comprises exchanging at least some of the sodium ions in the solution by calcium ions.

1 1. The process of any one of claims 1 to 10 wherein the sorbent comprises hydrogen ions whereby the step of exposing comprises exchanging at least some of the sodium ions in the solution by hydrogen ions.

12. The process of claim 11 additionally comprising the step of at least partially neutralising the reduced sodium solution.

13. The process of claim 12 wherein the step of at least partially neutralising comprises adding a hydroxide salt or a carbonate salt to the reduced sodium solution.

14. The process of claim 13 wherein the carbonate salt is calcium carbonate.

15. The process of claim 13 or claim 14 wherein the step of partially neutralising comprises bringing the reduced sodium solution to a pH of between about 6 and about 8.

16. The process of any one of claims 1 to 15 wherein the step of exposing comprises passing the solution through the sorbent, said sorbent being in particulate form.

17. The process of any one of claims 1 to 16 wherein the step of exposing is sufficient to reduce the concentration of sodium in said solution by about 20 to about 60%.

18. The process of any one of claims 1 to 17 comprising recirculating the solution through the sorbent for sufficient time to reduce the concentration of sodium in said solution by about 20 to about 60%.

19. The process of any one of claims 1 to 18 wherein the sorbent is in particulate form and the step of separating comprises passing the reduced sodium solution out of a bed of the sorbent.

20. The process of any one of claims 1 to 19 wherein the step of at least partially evaporating comprises evaporating substantially all of the water from said reduced sodium solution.

21. The process of any one of claims 1 to 19 wherein the step of at least partially evaporating comprises evaporating only a portion of the water from said reduced sodium solution, whereby the reduced sodium salt forms a precipitate in a supernatant liquid, said process additionally comprising the step of separating said precipitate from the supernatant liquid.

22. The process of any one of claims 1 to 21 wherein the step of at least partially evaporating comprises allowing water to evaporate from the reduced sodium solution in an open container.

23. The process of any one of claims 1 to 22 wherein energy inputs to an apparatus for conducting the process are from renewable sources.

24. The process of claim 23 wherein the renewable source is solar energy.

25. The process of any one of claims 1 to 24 comprising regenerating the sorbent after the step of separating, by exposing said sorbent to a regeneration solution capable of removing at least some of the sodium cations therefrom, so as to produce a sodium containing eluent.

26. The process of claim 25 wherein said exposing comprises passing said regeneration solution through a bed of the sorbent.

27. The process of claim 25 or claim 26 wherein the regeneration solution comprises calcium ions and/or hydrogen ions.

28. The process of claim of any one of claims 25 to 27 additionally comprising at least partially evaporating the sodium containing eluent so as to produce a high sodium salt in solid form.

29. The process of claim 28 wherein at least about 95% of anions in the eluent are chloride so that the high sodium salt is at least about 95% pure sodium chloride.

30. An apparatus for producing a reduced sodium salt, said apparatus comprising:

• a source of a feed water containing sodium ions;

• at least one vessel containing a sorbent capable of sorbing sodium ions;

• separator for separating a reduced sodium solution from the sorbent; and

• at least one evaporation device for evaporating water from the reduced sodium solution.

31. The apparatus of claim 30 wherein the source of the feed water comprises a pump and piping in fluid communication with a natural source of saline water and disposed so as to convey the saline water to the vessel containing the sorbent.

32. The apparatus of claim 30 or claim 31 wherein the sorbent is a zeolite.

33. The apparatus of any one of claims 30 to 32 wherein the vessel containing the sorbent comprises one or more of a sorbent column, a containment structure, a fluidised bed.

34. The apparatus of any one of claims 30 to 33 wherein the separator comprises a filter, a mesh, a substantially vertical pipe, a centrifugal separator or more than one of these.

35. The apparatus of any one of claims 30 to 34 wherein the evaporation device comprises a heater, an open evaporation tank pond, a containment structure, a reduced pressure evaporator or more than one of these.

36. The apparatus of any one of claims 30 to 35 comprising a switching valve capable of either recirculating the reduced sodium solution through the sorbent or diverting it to the evaporation device.

37. The apparatus of any one of claims 30 to 36 additionally comprising a sodium sensor for determining a concentration of sodium in the reduced sodium solution.

38. A process for preparing a sorbent for producing a low sodium salt, said process comprising exposing a zeolite to an acidic solution.

39. The process of claim 38 wherein the exposing comprises passing said acidic solution through the zeolite.

40. The process of claim 39, said passing being continued until substantially no more sodium is eluted.

41. The process of any one of claims 38 to 40 wherein the acidic solution comprises a mineral acid.

42. The process of any one of claims 38 to 41 wherein the acidic solution has a concentration of between about 0.001 and about 0.1M.

Description:
Low sodium salt

Technical Field

The present invention relates to a method for producing low sodium salt.

Background of the Invention

Sea salts include trace minerals which are known to promote good health and there is a substantial demand for sea salts to flavour foods. Sea salts have been produced for centuries using the traditional method of allowing natural seawater to evaporate from shallow ponds located in arid climates. As the natural seawater concentrates, crystals of salt begin to form as the concentrate approaches or exceeds saturation. Although very complicated, this process occurs naturally and yields a coveted salt with unique chemistry and properties. The sodium chloride content of these sea salts is typically from 90 to 98%. This is due to the solubility and overwhelming concentration of sodium and chloride found in natural seawater as compared to other components such as magnesium, potassium, and sulfate.

Zeolites are porous three dimensional frameworks that are formed when volcanic ash comes in contact with alkaline water. Currently, there are approximately 45 different types of naturally occurring zeolites and over 200 different types of synthetic zeolite available. Zeolites are framework silicates consisting of interlocking tetrahedrons of Si0 4 and A10 4 . In order to be a zeolite the ratio (Si +Al)/0 must approximately equal 1/2. The alumino-silicate structure is negatively charged and attracts the positive cations that reside within the structure. Unlike most other tectosilicates, zeolites have large vacant spaces or cages in their structures that allow for large cations such as sodium, potassium, barium and calcium and even relatively small molecules and cationic groups such as water, ammonia, carbonate ions and nitrate ions. In the more useful zeolites, the spaces are interconnected and form long wide channels of varying sizes depending on the mineral. These channels allow the easy movement of the resident ions and molecules into and out of the structure. Zeolites are characterized by their ability to lose and absorb water without damage to their crystal structures. The large channels explain the consistent low specific gravity of these minerals.

Zeolites have many useful purposes. They can perform ion exchange, filtering, odour removal, chemical sieve and gas absorption tasks. One major use for zeolites is in detergents as water softeners. Calcium in water can cause it to be "hard" and capable of forming scum and other problems. Zeolites charged with the much less damaging sodium ions can allow the hard water to pass through its structure and exchange the calcium for the sodium ions. This process is reversible. In a similar way zeolites can absorb ions and molecules and thus act as a filter for odour control, toxin removal and as a chemical sieve. Zeolites can have the water in their structures driven off by heat with the basic structure left intact. Then other solutions can be pushed through the structure. The zeolites can then act as a delivery system for the new fluid. This process has applications in medicine, livestock feeds and other types of research.

Zeolites have basically three different structural variations.

• chain-like structures whose minerals form acicular or needle-like prismatic crystals, i.e. natrolite.

• sheet-like structures where the crystals are flattened plate-like or tabular with usually good basal cleavages, i.e. heulandite.

• framework structures where the crystals are more equal in dimensions, i.e. chabazite.

Zeolites include:

• The Analcime Family:

o Analcime (Hydrated Sodium Aluminum Silicate)

o Pollucite (Hydrated Cesium Sodium Aluminum Silicate)

o Wairakite (Hydrated Calcium Sodium Aluminum Silicate)

• Bellbergite (Hydrated Potassium Barium Strontium Sodium Aluminum

Silicate)

Bikitaite (Hydrated Lithium Aluminum Silicate)

Boggsite (Hydrated calcium Sodium Aluminum Silicate)

Brewsterite (Hydrated Strontium Barium Sodium Calcium Aluminum

Silicate)

The Chabazite Family:

o Chabazite (Hydrated Calcium Aluminum Silicate) o Willhendersonite (Hydrated Potassium Calcium Aluminum Silicate) Cowlesite (Hydrated Calcium Aluminum Silicate)

Dachiardite (Hydrated calcium Sodium Potassium Aluminum Silicate) Edingtonite (Hydrated Barium Calcium Aluminum Silicate) Epistilbite (Hydrated Calcium Aluminum Silicate)

Erionite (Hydrated Sodium Potassium Calcium Aluminum Silicate)

Faujasite (Hydrated Sodium Calcium Magnesium Aluminum Silicate) Ferrierite (Hydrated Sodium Potassium Magnesium Calcium Aluminum

Silicate)

The Gismondine Family: o Amicite (Hydrated Potassium Sodium Aluminum Silicate)

o Garronite (Hydrated Calcium Aluminum Silicate)

o Gismondine (Hydrated Barium Calcium Aluminum Silicate)

o Gobbinsite (Hydrated Sodium Potassium Calcium Aluminum Silicate)

• Gmelinite (Hydrated Sodium Calcium Aluminum Silicate)

• Gonnardite (Hydrated Sodium .Calcium Aluminum Silicate)

• Goosecreekite (Hydrated Calcium Aluminum Silicate)

• The Harmotome Family:

o Harmotome (Hydrated Barium Potassium Aluminum Silicate) o Phillipsite (Hydrated Potassium Sodium Calcium Aluminum Silicate) o Wellsite (Hydrated Barium Calcium Potassium Aluminum Silicate)

• The Heulandite Family:

o Clinoptilolite (Hydrated Sodium Potassium Calcium Aluminum Silicate)

o Heulandite (Hydrated Sodium Calcium Aluminum Silicate)

• Laumontite (Hydrated Calcium Aluminum Silicate)

• Levyne (Hydrated Calcium Sodium Potassium Aluminum Silicate)

• Mazzite (Hydrated Potassium Sodium Magnesium Calcium Aluminum Silicate)

• Merlinoite (Hydrated Potassium Sodium Calcium Barium Aluminum Silicate)

• Montesommaite (Hydrated Potassium Sodium Aluminum Silicate)

• Mordenite (Hydrated Sodium Potassium Calcium Aluminum Silicate)

• The Natrolite Family:

o Mesolite (Hydrated Sodium Calcium Aluminum Silicate) o Natrolite (Hydrated Sodium Aluminum Silicate)

o Scolecite (Hydrated Calcium Aluminum Silicate)

• Offretite (Hydrated Calcium Potassium Magnesium Aluminum Silicate)

• Paranatrolite (Hydrated Sodium Aluminum Silicate)

• Paulingite (Hydrated Potassium Calcium Sodium Barium Aluminum Silicate)

• Perlialite (Hydrated Potassium Sodium Calcium Strontium Aluminum Silicate)

• The Stilbite Family: o Barrerite (Hydrated Sodium Potassium Calcium Aluminum Silicate) o Stilbite (Hydrated Sodium Calcium Aluminum Silicate)

o Stellerite (Hydrated Calcium Aluminum Silicate)

• Thomsonite (Hydrated Sodium Calcium Aluminum Silicate)

• Tschernichite (Hydrated Calcium Aluminum Silicate)

• Yugawaralite (Hydrated Calcium Aluminum Silicate)

Health concerns have prompted the introduction of low sodium salts for food use. However, it is believed that the existing products are generally produced synthetically by r

blending purified potassium chloride with ordinary table salts to achieve the reduced sodium content. There is a public perception that addition of "non-natural" components such as potassium chloride is undesirable. It is desirable to produce a natural sea salt with significantly reduced sodium chloride content, e.g., 30 to 70 weight percent, while maintaining the naturally occurring trace elements found in quality sea salts.

A currently known method for reducing sodium in seawater is described in US patent 7,621,968 (Kirchner et ai, 24 November 2009). In this patent, sodium chloride is selectively crystallised from seawater in order to leave a brine containing a reduced level of sodium. A solid salt is then recovered from that brine to provide a low sodium salt which may be used, for example, for human consumption. This method is highly labour intensive and it is difficult to control accurately the level of sodium ion reduction achieved. Accordingly, the product is relatively expensive and of inconsistent quality.

There is therefore a need for an improved process for making low sodium salt.

Object of the Invention

It is the object of the present invention to substantially overcome or at least ameliorate one or more of the above disadvantages. It is a further object to at least partially satisfy the above need.

Summary of the Invention

In a first aspect of the invention there is provided a process for producing a reduced sodium salt from a solution wherein sodium cations in said reduced sodium salt represent a lower proportion of total cations than in said solution. The process comprises:

• exposing the solution to a sorbent capable of sorbing sodium ions, so as to produce a reduced sodium solution;

• separating the sorbent having sodium ions sorbed therein and or thereon from the reduced sodium solution; and • at least partially evaporating the reduced sodium solution so as to produce the reduced sodium salt in solid form.

The following options may be used in conjunction with the first aspect, either individually or in any suitable combination.

Commonly the solution is an aqueous solution. It may have no organic solvents therein. The solution may be sea water. In this case the reduced sodium salt may be reduced sodium sea salt.

The sorbent may be a zeolite. The zeolite may be a naturally occurring zeolite. It may be a hydrated H + aluminium silicate (NepZel-H + ). It may have a particle size between about 0.05 and about 10mm, or about 0.05 and about 2mm. It may be present in a bed or column having a gradation of particle sizes. There may be a continuous gradient of sizes (e.g. a linear gradient) or may be discrete layers of different sized particles. For example, the bed or column may have a range of particle sizes of about 0.05-2mm at the lower portion of the bed or column, about 2.5-4mm towards the middle of the bed or column and about 4-10 mm at the upper portion of the bed or column. The sorbent may comprise of calcium ions, commonly sorbed (either adsorbed or absorbed or both) calcium ions. In this case the step of exposing may comprise exchanging at least some of the sodium ions in the solution by calcium ions.

The zeolite may be pretreated with acid. The acid may be a strong acid, e.g. a mineral acid such as hydrochloric acid. The acid may have a concentration of 0.001 to 0.1M. The zeolite may be an acid treated, or acid loaded, zeolite. The process may comprise the step of treating a zeolite prior to the step of exposing the solution to a zeolite. The zeolite used in the process may be generated by pretreatment of a non-protonated zeolite (e.g. an aluminium silicate, NepZel) with acid.

The sorbent may comprise clinoptilolite or it may comprise heulandite. When used in the present process, these may each be in protonated form.

The sorbent may comprise hydrogen ions. In this case the step of exposing may comprise exchanging at least some of the sodium ions in the solution by hydrogen ions. The process may then additionally comprise the step of at least partially neutralising the reduced sodium solution. The step of at least partially neutralising may comprise adding a hydroxide salt, e.g. sodium hydroxide or potassium hydroxide, or a carbonate salt, e.g. calcium carbonate, to the reduced sodium solution. The step of partially neutralising may comprise bringing the reduced sodium solution to a pH of between about 6 and about 8. The step of neutralising may be conducted prior to the step of at least partially evaporating, or may be conducted concurrently with the step of at least partially evaporating.

The step of exposing may comprise passing the solution through the sorbent. The sorbent may be in particulate form. It may comprise particles of different sizes, as described above.

The step of exposing may be sufficient to reduce the concentration of sodium in the solution by about 20 to about 60%. The process may comprise recirculating the solution through the sorbent. It may comprise recirculating the solution through the sorbent for sufficient time to reduce the concentration of sodium in said solution by about 20 to about 60%. It may comprise monitoring the sodium level of the solution whilst recirculating said solution through the sorbent until said monitoring indicates that the concentration of sodium has been reduced by about 20 to about 60%.

The sorbent may be in particulate form. In this case the step of separating may comprise passing the reduced sodium solution out of a bed of the sorbent.

The step of at least partially evaporating may comprise evaporating at least some, optionally substantially all, of the water from said reduced sodium solution. It may comprise evaporating only a portion of the water from said reduced sodium solution. In the latter case the reduced sodium salt may form a precipitate in a supernatant liquid and the process may additionally comprise the step of separating said precipitate from the supernatant liquid. It will be understood that evaporating, or partially evaporating, a solution is taken in .the context of the present invention to refer to evaporating, or partially evaporating, volatile matter, e.g. a solvent (such as water), from the solution and does not include evaporating non-volatile matter.

The step of at least partially evaporating may comprise allowing water to evaporate form the reduced sodium solution in an open container.

Energy inputs to an apparatus for conducting the process may be from renewable sources. The renewable source may be for example solar energy, wind energy, tidal energy or a combination of these.

The process may additionally comprise regenerating the sorbent after the step of separating by exposing the sorbent to a regeneration solution capable of removing at least some of the sodium cations therefrom, so as to produce a sodium containing eluent. The exposing may comprise passing said regeneration solution through a bed of the sorbent. The regeneration solution may comprise calcium ions and/or hydrogen ions (i.e. it may be acidic). The process may additionally comprise at least partially evaporating the sodium containing eluent so as to produce a high sodium salt in solid form. In an embodiment, at least about 95% of anions in the eluent are chloride so that the high sodium salt is at least about 95% pure sodium chloride.

In an embodiment there is provided a process for producing reduced sodium sea salt from natural sea water. The process comprises:

• exposing the natural sea water to a zeolite, so as to produce a reduced sodium solution;

• separating the zeolite having sodium ions sorbed therein and/or thereon from the reduced sodium solution; and

• at least partially evaporating the reduced sodium solution so as to produce the reduced sodium salt in solid form.

In another embodiment there is provided a process for producing reduced sodium sea salt from natural sea water. The process comprises:

• exposing the natural sea water to a zeolite, so as to produce a reduced sodium solution;

• separating the zeolite having sodium ions sorbed therein and/or thereon from the reduced sodium solution;

• at least partially evaporating the reduced sodium solution so as to produce the reduced sodium salt in solid form;

• exposing the zeolite to a hydrochloric acid solution so as to regenerate the zeolite and produce a sodium containing eluent; and

• at least partially evaporating the sodium containing eluent so as to produce solid sodium chloride.

In either of the above embodiments the zeolite may be an acid treated zeolite. In particular, it may be a clinoptilolite or a heulandite (or a mixture of these) which has been treated with acid, e.g. approximately 0.01M hydrochloric acid, prior to use. The clinoptilolite and heulandite may have different particle sizes or may have the same particle size.

The process may therefore comprise the step of treating the adsorbent (e.g. the zeolite) with an acid, e.g. approximately 0.01 M hydrochloric acid, before the step of exposing the solution to the zeolite. Thus in a further embodiment there is provided a process for producing reduced sodium sea salt from natural sea water, said process comprising:

• pretreating a zeolite with approximately 0.01M hydrochloric acid;

• exposing the natural sea water to the acid treated zeolite, so as to produce a reduced sodium solution; S

• separating the zeolite having sodium ions sorbed therein and/or thereon from the reduced sodium solution; and

• at least partially evaporating the reduced sodium solution so as to produce the reduced sodium salt in solid form.

The invention also provides a reduced sodium salt made by the process of the first aspect. It further provides a sodium chloride of at least 95% by weight purity when made by the process of the first aspect.

In a second aspect of the invention there is provided an apparatus for producing a reduced sodium salt, said apparatus comprising:

• a source of a feed water containing sodium ions;

• at least one vessel containing a sorbent capable of sorbing sodium ions;

• separator for separating a reduced sodium solution from the sorbent; and

• at least one evaporation device for evaporating water from the reduced sodium solution.

The following options may be used in conjunction with the second aspect, either individually or in any suitable combination.

The source of the feed water may be in fluid communication with a natural source of saline water, e.g. the ocean, and may comprise a pump and piping disposed so as to convey the saline water to the vessel containing the sorbent.

The sorbent may be a zeolite, and options therefor, are set out above under the first aspect.

The vessel containing the sorbent may comprise a filtration column, a containment structure, a fluidised bed or any other suitable vessel. The apparatus may comprise more than one of these.

The separator may comprise a filter, a mesh, a vertical pipe (in which case, in operation, the reduced sodium solution may pass upwards whereby the sorbent is separated by gravity), a centrifugal separator or may comprise some other suitable separator, or may comprise more than one of these.

The evaporation device may comprise a heater. It may comprise a solar heater. It may comprise an open evaporation tank/pond or containment structure. It may comprise a reduced pressure evaporator. It may comprise more than one of these.

The apparatus may comprise a switching valve capable of either recirculating the reduced sodium solution through the sorbent or diverting it to the evaporation device. It may comprise a sodium sensor for detecting a sodium concentration in liquid recirculating through the device. The sodium sensor may be electrically coupled to the switching valve. This may enable the switching valve to switch between recirculating and diverting in response to a sensed sodium concentration.

In an embodiment there is provided an apparatus for producing a reduced sodium salt, said apparatus comprising:

• a pump and piping for providing natural sea water to the apparatus;

• at least one vessel containing a zeolite capable of sorbing sodium ions, said vessel being in fluid communication with the piping;

• a separator for separating a reduced sodium solution from the zeolite;

• at least one evaporation pond for evaporating water from the reduced sodium solution; and

In another embodiment there is provided an apparatus for producing a reduced sodium salt, said apparatus comprising:

• a pump and piping for providing natural sea water to the apparatus;

• at least one vessel containing a zeolite capable of sorbing sodium ions, said vessel being in fluid communication with the piping;

• a separator for separating 'a reduced sodium solution from the zeolite;

• at least one evaporation pond for evaporating water from the reduced sodium solution;

• a switching valve capable of either recirculating the reduced sodium solution through the zeolite or diverting it to the evaporation pond

• a regeneration liquid container;

• a regeneration valve capable of allowing the regeneration liquid to pass through the zeolite so as to produce a sodium containing eluent;

• a second evaporation pond for evaporating the sodium containing eluent; and

• a diversion valve for directing the sodium containing eluent to the second evaporation device.

The invention also provides the use of the apparatus of the second aspect for conducting the process of the first aspect. It also provides a reduced sodium salt made using the apparatus of the second aspect. It further provides a sodium chloride of at least 95% by weight purity when made using the apparatus of the second aspect.

In a third aspect of the invention there is provided a process for preparing a sorbent for producing a low sodium salt (e.g. according to the process of the first aspect), said process comprising exposing a zeolite to an acidic solution. The process may comprise passing said acidic solution through the zeolite. It may comprise passing said solution through the zeolite until substantially no more sodium is eluted. It may comprise monitoring the sodium content of a solution exiting the zeolite and passing the acidic solution through the zeolite until said monitoring indicates that the sodium content in said solution exiting the zeolite is below a predetermined level, or is substantially zero. The acidic solution may comprise a mineral acid, e.g. hydrochloric acid. It may have a concentration of between about 0.001 and about 0.1M.

In an embodiment there is provided a process for preparing a sorbent for producing a low sodium salt (e.g. according to the process of the first aspect), said process comprising passing an approximately 0.01M hydrochloric acid solution through a zeolite (e.g. clinoptilolite and/or heulandite), optionally through a bed thereof, until substantially no more sodium is eluted.

Brief Description of the Drawings

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings wherein:

Figures 1 to 3 are flow charts in block diagram form showing different embodiments of the invention;

Figures 4-6 illustrate pictorial view forms showing embodiments of the invention;

Figure 7 is a graph showing the release of naturally bound sodium from zeolite (0.4-1.4 mm) using 0.01 M HC1. This represents an acid treatment of zeolite prior to use in the method described herein. 120 g of zeolite were packed tightly in a filter (33 mm diameter x 155 mm height) and 2L of 0.01 M HC1 was pumped at 17.5 mLs/min. Samples were taken every 100 mLs, filtered (0.45 μηι filter) and analysed using cation exchange chromatography (Hamilton PRP-X200, Isocratic buffer; 4 mM HN0 3 in 30% CH 3 OH:70% H20, 0.8 mL/min, run time 10 mins);

Figure 8 is a graph showing pH change during sodium loading. 112 g of modified zeolite was packed in a filter column (33 mm diameter x 155 mm height) and 3000 ppm (2L) of sodium was pumped at 17 mLs/min. pH measurements were taken every 100 mL; and

Figure 9 is a graph showing regeneration of zeolite with 0.01 M HC1 treatment. 0.22% sodium loaded zeolite was packed in a cylindrical filtration unit (33 mm diameter x 155 mm height) and treated with 0.01 M HC1 solution. Samples were collected at 100 mL intervals at a rate of 17.5 mL/min, filtered (0.45 μπι filter) and measured for sodium content. Detailed Description of Preferred Embodiments

There is a desire for reduced sodium salt for health purposes. There is also a desire for natural products, with as little as possible, preferably no, addition of synthetic chemicals. This invention is directed to at least partially satisfying these desires.

The process of the invention, in a broad form, comprises sorbing sodium ions from a sodium containing solution and evaporating the resulting reduced sodium solution in order to produce a solid of reduced sodium content. The term "sorb" and related terms includes both the concepts of absorbing and adsorbing and may, in particular contexts, refer to either or both of these.

The sodium containing solution is commonly sea water, but may be brackish water or some other naturally occurring sodium containing solution. Alternatively the solution may be from non-natural processes, for example it may be synthesised or may be the product of an industrial process.

The sorbent used for sorbing (adsorbing and/or absorbing) the sodium ions may be an ion exchanger, e.g. a zeolite. Suitable zeolites are described in the Background section of this specification. A particularly suitable zeolite is a hydrated H + aluminium silicate with the following chemistry: (Na, K, Ca) 2 _ 3 A1 3 (A1, Si> 2 Sii 3 03 6 -12H 2 0, hydrated sodium potassium calcium aluminium silicate. This is a tectosilicate of the family heulandite.

The sorbent (ion exchanger) may be used in its protonated or acid form. It may additionally or alternatively comprise other ions such as calcium, potassium, magnesium etc. (or a mixture of ions) which are exchangeable with sodium ions. The sorbent may be in particulate form. It may have a particle size of about 0.05 to about 10mm, or about 0.05 to 5, 0.05 to 2, 0.05 to 1, 0.05 to 0.5, 0.1 to 2, 0.1 to 1, 0.1 to 0.5, 0.2 to 5, 0.5 to 2, 0.5 to 5, 1 to 5, 2 to 5, 0.4 to 1.4, 0.5 to 2, 0.5 to 1, 1 to 10, 2 to 10, 5 to 10 or 1 to 2mm, . e.g. about 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9 or 10mm. This may be a mean particle size or it may be a maximum particle size. The sorbent may have a spread or distribution of particle sizes. It may have a wide distribution of particle sizes or a narrow distribution of particle sizes. If one defines d90 as the particle size below which 90% of the particles lie, and d50 as the particle size below which 50% of the particles lie, the ratio of d90/d50 may be between 1 and 10, or between 1 and 5, 1 and 2, 2 and 10, 5 and 10, 1 and 1.5 or 1.5 and 2, e.g. about 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9 or 10 or may be more than 10. The particles of different sizes may be arranged in a gradient. The gradient may have larger sized particle at the top and smaller sized particle at the bottom or may have smaller sized particle at the top and larger sized particles at the bottom. Other gradients, including non-monotonic gradients, are also envisaged. The ratio of sizes of particles at or near the top to particles at or near the bottom of the sorbent may be between about 10 and about 0.1 (where 10 represents a ratio of 10:1 and 0.1 represents a ratio of 1 to 10), or about 5 to 0.1, 2 to 0.1, 1 to 0.1, 10 to 1, 10 to 2, 10 to 5, 0.5 to 2 or 0.5 to 5, e.g. about 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5, 0.4, 0.3, 0.2 or 0.1. In some embodiments, there is a filter or similar particle removal device upstream of the inlet to the bed of sorbent particles. This serves to remove particulate matter entrained in the brine entering the bed, so as to avoid particulate fouling of the bed. Alternatively or additionally, the bed may be designed so as to have larger particles of sorbent near the inlet end and finer particles nearer the outlet end. In this way the larger particles can act as a particulate filter to restrict penetration of incoming particulates to the finer sorbent particles and thereby inhibit fouling. In this instance, during regeneration of the sorbent in order to remove sorbed sodium ions, the flow of regeneration fluid may be in the opposite direction to the flow of brine during loading of the sorbent, i.e. it may be regenerated in backflush mode. This serves to remove any particulate fouling from the bed as well as regenerating the sorption capacity of the sorbent.

The sorbent may be pretreated by exposing it to an acidic solution. This may comprise passing said acidic solution through the zeolite, for example through a bed thereof, or may comprise agitating (e.g. shaking, stirring, swirling, sonicating etc.) the sorbent in the acidic solution. It may comprise exposing the sorbent, e.g. passing said solution through the sorbent (e.g. through a bed of the sorbent), until substantially no more sodium is eluted. The acidic solution may comprise a mineral acid, e.g. hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, phosphoric acid or some other suitable acid. It may have a concentration of between about 0.001 and about 0.1M, or about 0.001 to 0.01 , 0.01 to 0.1 or 0.005 to 0.05M, e.g. about 0.001, 0.002, 0.005, 0.01, 0.02, 0.05 or 0.1M although in some cases other concentrations may be appropriate.

The step of exposing the solution to the sorbent may comprise passing the solution through the sorbent. The sorbent may be in the form of a bed, commonly a particulate bed, or it may be in a filtration housing, a column, a fluidised bed or some other suitable form. There may be several different or similar containers for the sorbent. For example there may be more than one (e.g. 2, 3, 4, 5, 6, 7, 8, 9 or 10 or more than 10) columns, either in parallel or in series or some in series and some in parallel, or there may be a containment structure containing the sorbent as well as a column containing the sorbent. Usually, although not always, when different types of container (e.g. a containment structure and a column) are used for the sorbent, these will be in sequence. The solution may be passed through the sorbent at a suitable rate for adsorption of sodium ions, i.e. for exchange of ions in the sorbent (e.g. protons or calcium ions) with the sodium ions in the solution. The rate of passing will depend on the scale of the apparatus used, and may be anywhere from about 1 to 10,000L/h, e.g. about 1 to 1000, 1 to 100, 1 to 10, 10 to 10,000, 100 to 10,000, 1000 to 10,000, 10 to 1000, 10 to 100, 100 to 1000 or 500 to lOOL/h, e.g. about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 6000, 7000, 8000, 9000 or 10,000L h.The rate of passing through a single vessel containing the sorbent (e.g. a single column) may be from about 1 to about 100 vessel volumes (or bed volumes) per hour, or about 1 to 50, 1 to 20, 1 to 10, 10 to 100, 20 to 100, 50 to 100, 10 to 50, 10 to 20 or 20 to 50 vessel volumes per hour, e.g. about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90 or 100 vessel volumes per hour.

The solution may be passed through the sorbent at ambient pressure (i.e. about 1 atmosphere) or at elevated pressure. The pressure may be about 1 to lOatm, or about 1 to 5, 1 to 2, 2 to 10, 5 to 10 or 2 to 5atm, e.g. about 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9 or 10 atm, or may be greater than that. Elevated pressures are commonly used when the sorbent is present in a filtration column or adsorption column.

The solution may be passed through the sorbent at ambient temperature or at elevated temperatures or at sub-ambient temperature. In some instances, the temperature of the solution is important in obtaining the desired result. Occasionally saline solutions are used from industrial sources that are above room temperatures. The temperature of the solution may be about 10 to about 70°C, or about 10 to 20, 10 to 30, 10 to 50, 20 to 70, 30 to 70, 50 to 70, 20 to 50, 20 to 30, 30 to 50 or 15 to 25°C, e.g. about 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65 or 70 °C, or in some instances may be greater than 70°. It is thought that operating at above ambient temperatures may increase the sorption capacity of the sorbent towards sodium ions.

Commonly the solution will be recycled through the sorbent for sufficient time to achieve the desired reduction in sodium concentration. This may take from about 0.1 to about 10 hours, depending on the nature of the sorbent (in particular its exchange or sorption capacity), the concentration of sodium in the solution, the rate of passing the solution through the sorbent etc. It may take from about 0.1 to 5, 0.5 to 2, 0.5 to 1, 1 to 10, 2 to 10, 5 to 10, 0.5 to 5, 1 to 5 or 0.5 to 1 hour, e.g. about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9 or 10 hours. The process may comprise detecting a sodium level in the reduced sodium solution which is recycling through the sorbent. It may comprise continuously monitoring the sodium level. It may comprise diverting the reduced sodium solution to an evaporator when the sodium level drops to a preset level. The diverting may comprise switching a switching valve so as to divert the reduced sodium solution to the evaporator once the sodium level drops to a preset level. The process may therefore comprise the step of sending a signal from a sodium level detector to a switching valve (optionally mediated by a data processor such as a computer) so as to cause the switching valve to direct the reduced sodium solution to the evaporator. Correspondingly, the apparatus may comprise a sodium sensor for determining and/or monitoring a sodium level. This may be coupled either directly or via a data processor (e.g. a computer or PLC) to a controllable switching valve. The switching may be performed manually. Thus in one option the sodium sensor generates a signal indicating that the valve should be switched, or that the desired concentration of sodium has been attained. This signal then prompts an operator to manually switch the valve.

The desired sodium level (optionally the preset sodium level for the sodium sensor) may be less than about 80% by weight of total cations, or less than about 70, 60, 50, 40 or 30%, or may be about 10 to about 80%, or about 10 to 70, 10 to 60, 10 to 50, 10 to 40, 10 to 30, 20 to 80, 30 to 80, 40 to 80, 50 to 80, 60 to 80, 10 to 70, 30 to 70, 50 to 70, 40 to 50 or 40 to 60%, e.g. about 10, 20, 30, 40, 50, 60, 70 or 80%. It may be a level such that a solid salt obtained by removing the water from the reduced salt solution complies with Australia New Zealand Food Standards Code 2.10.2: Salt and salt products.

As the reduced sodium solution leaves the sorbent, it will tend to take the sorbent with it if the sorbent is in particulate form. There is therefore a step of separating the sorbent from the liquid. This may comprise filtering, centrifuging or other suitable process. In its simplest form, it may simply comprise passing the liquid upwards through a tube, whereby the sorbent is prevented by gravity from being entrained by the liquid. This requires that the flow rate of the liquid through the tube be sufficiently slow, and the particle size of the sorbent sufficiently large, as to prevent the sorbent being entrained by the liquid. Several of the above separation processes may be combined, for example the tube through which the liquid passes upwards may comprise a filter so as to prevent minor amounts of entrained sorbent from passing.

Once the sodium level in the reduced sodium solution has been reduced sufficiently, it is then at least partially evaporated. Prior to, or concurrent with this, it may be approximately neutralised. The neutralisation may be to about pH 6 to 8, or 6 to 7, 7 to 8 or 6.5 to 7.5, e.g. about 6, 6.5, 7, 7.5 or 8. It may be to a slightly alkaline pH. It may be to a pH similar to that of natural seawater (about 7.5 to 8.4). It may achieved by addition of a suitable basic salt which does not contain sodium, e.g. potassium hydroxide, calcium hydroxide, magnesium hydroxide, potassium carbonate, magnesium carbonate or calcium carbonate (or a mixture of any two or more of these). The reduced sodium solution may be evaporated substantially to dryness. It may be partially evaporated, e.g. evaporated to a volume of less than about, or of about, 50, 40, 30, 20, 10 or 5% or its original volume. It may be evaporated to a degree whereby it exceeds its saturation level so that salt precipitates therefrom. In this case, the supernatant solution may be separated from the precipitated salt, for example by filtration, decanting, centrifuging or more than one of these, or by some other process. The reduced sodium salt, and independently the supernatant solution, may contain other salts than sodium chloride, e.g. one or more of potassium chloride, magnesium chloride, potassium sulphate magnesium sulphate etc. The evaporation may be achieved by allowing the solution to evaporate open to the air, e.g. in an evaporation pond or containment structure. The evaporation may be promoted by passing air or some other gas, optionally heated, over the surface or through the reduced sodium solution and/or by heating the solution itself. The heating, either of the gas or of the solution or both, may be powered by means of renewable energy sources, e.g. solar, wind, etc. or may be powered by conventional sources. Alternatively the evaporation may be by application of reduced pressure to the solution, e.g. in a rotary evaporator, or it may be by means of pervaporation or by a combination of any two or more of the aforementioned processes.

The process may comprise the step of regenerating the sorbent. This is commonly conducted when the ability to sorb sodium ions reduces to an unacceptable level, e.g. when it reduces by at least 50%, or at least 60, 70, 80 or 90%. The regeneration may comprise passing a regeneration solution through the sorbent. The regeneration solution is commonly a solution comprising an ion capable of replacing the sodium in and/or on the sorbent, i.e. the ions may be adsorbed on the sorbent, or may absorbed into the sorbent, or both. Suitable such ions include protons (whereby the regeneration solution is an acid) or calcium ions. The counterion may be any suitable counterions such that the replacing ion remains in solution, e.g. chloride, bromide, sulphate (unless the replacing ion is calcium) etc. A common regeneration solution is hydrochloric acid. It may have a concentration of about 0.1 to 2N, or about 0.1 to 1, 0.1 to 0.5, 0.5 to 2, 1 to 2 or 0.5 to IN. The regeneration of the sorbent generates an eluent that is high in sodium ions relative to the regeneration solution prior to use. In the particular case where the counterion is chloride, this eluent may be used to generate relatively pure sodium chloride. Thus the eluent may be neutralised if necessary, optionally with sodium hydroxide or sodium carbonate, so as to form a sodium chloride solution. The neutralisation may be to about pH 6 to 8, or 6 to 7, 7 to 8 or 6.5 to 7.5, e.g. about 6, 6.5, 7, 7.5 or 8. It may be to a slightly alkaline pH. It may be to a pH similar to that of natural seawater (about 7.5 to 8.4). Evaporation, or partial evaporation, of this solution (by any of the methods described earlier) may produce relatively pure sodium chloride, e.g. at least about 95% pure by weight, or at least about 96, 97, 98 or 99%.

The sorbent may comprise hydrogen ions, in particular exchangeable hydrogen ions. The sorbent may be for example an ion exchanger, or zeolite, in its protonated form, i.e. with hydrogen ions bound into the network. In this case the step of exposing may comprise exchanging at least some of the sodium ions in the solution by hydrogen ions, so as to remove the sodium ions from the liquid and replace them with protons. As a consequence, this step may render the liquid acidic. The process may then additionally comprise the step of at least partially neutralising the reduced sodium solution. This may be achieved by adding a hydroxide salt, e.g. sodium hydroxide or potassium hydroxide, or a carbonate salt, e.g. calcium carbonate, to the reduced sodium solution. Other substances that may be added in order to partially neutralise the liquid may include for example buffers, such as phosphate, tartrate, phthalate diglycolate etc. buffers. The step of partially neutralising may comprise bringing the reduced sodium solution to a pH of between about 6 and about 8, or about 6 to 7, 7 to 8 or 6.5 to 7.5, e.g. about 6, 6.5, 7, 7.5 or 8.

The step of exposing may comprise passing the solution over and or past and/or through the sorbent. In many instances the sorbent is in particulate form. It may be porous, e.g. microporous or nanoporous or mesoporous. In this case the solution, or a portion thereof, may pass into and out of the pores.

The step of exposing may be sufficient to reduce the concentration of sodium in the solution by about 20 to about 60%. In this context, the reduction is not of the original percentage but of the total. Thus, for example if a solution has 90% sodium and is reduced by 50%, the resulting solution would have concentration of 40% (not 45%). From this definition it will be clear that a solution of x% sodium can not be subjected to a reduction of more than x% in its sodium level. The exposing may reduce the concentration of sodium by about 20 to 40, 40 to 60 or 30 to 50%, e.g. by about 20, 30, 40, 50 or 60%. It may reduce the sodium concentration to between about 20 and about 70% of the total cation concentration, or about 20 to 50, 30 to 70 or 40 to 60%, e.g. about 20, 30, 40, 50, 60 or 70%. In some instances, a single pass of the solution through/past the sorbent may be insufficient to reduce the sodium concentration to the desired level. In this case the solution may be recirculated through/past the sorbent. This may enable the use of smaller beds or columns of sorbent whilst still allowing a suitable reduction in sodium.

The step of at least partially evaporating may comprise evaporating substantially all of the water from said reduced sodium solution, i.e. it may comprise evaporating the solution to dryness. It may comprise evaporating only a portion of the water from said reduced sodium solution. In this case the reduced sodium salt may form a precipitate in a supernatant liquid and the process may additionally comprise the step of separating said precipitate from the supernatant liquid. In order to achieve this, it may be necessary to evaporate sufficient of the water to achieve a supersaturated solution, i.e. to evaporate more water than would be required to achieve a saturated solution. A saturated solution of sodium chloride in water at about room temperature is approximately 1 molar. Accordingly, sufficient water should be evaporated that there would be more than about 1 mole of sodium chloride per litre of solution if no precipitation occurred. In some instances it may be necessary to seed crystallisation. This may be done by any of the well known methods, for example adding a small amount of crystalline sodium chloride to the solution. Sufficient water may be evaporated in order to precipitate at least about 50% of the dissolved salts, or at least 60, 70, 80 or 90% thereof, or about 50 to 90, 50 to 70 or 70 to 90% thereof, e.g. about 50, 60, 70, 80, 90 or 95% thereof.

The evaporating may simply comprise allowing water to evaporate form the reduced sodium solution in an open container such as an evaporation pond, an open containment vessel etc. The evaporating may be facilitated by passing a gas, e.g. air, over the surface of the liquid, or passing (e.g. bubbling) the gas through the liquid. Further facilitation may be achieved by heating and/or drying the gas before doing so.

The method described above may be conducted in a purpose built apparatus. A suitable apparatus would therefore comprise a source of a feed water containing sodium ions, at least one vessel containing a sorbent capable of sorbing sodium ions, a separator for separating a reduced sodium solution from the sorbent and at least one evaporation device for evaporating water from the reduced sodium solution.

Feed water source: This typically comprises suitable piping and if necessary pumps in order to bring the feed water into the apparatus. The pumps may be powered by renewable energy such as solar energy, wind energy and the like. The feed water may come from a natural source of saline water, e.g. the ocean, a saline lake, etc. Alternatively the feed water may be a saline solution generated by dissolving salt from a naturally occurring salt deposit in water. Sorbent vessel: The vessel containing the sorbent may comprise a filtration column, a containment structure, a fluidised bed or any other suitable vessel. The apparatus may comprise more than one of these. They may be disposed in parallel or in series, as described elsewhere herein. In a simple example the sorbent may be disposed in a vessel in which an inlet for feed water is located at or near the bottom of the vessel and an outlet is at or near the top. The outlet may simply represent an overflow from the vessel, so that incoming feedwater permeates through the sorbent and reduced sodium permeate flows out of an overflow. In another example, the inlet may be in the form of a tube or pipe leading through the sorbent to a point near the bottom of the vessel. This tube or pipe may have impermeable walls, or may be foraminous or porous. In the latter case, feed water may enter the bed of sorbent in multiple places and permeate through the sorbent to the outlet. In other examples the sorbent vessel may be a filtration column or sorbent column. The feedwater may pass through this vertically or horizontally, and, if vertically, may pass upwards or downwards through the column. The sorbent vessel may be disposed so that, as required, the sorbent may be regenerated by passing a regeneration solution therethrough. This may be passed in the same way as the feedwater or may be passed in the opposite direction (i.e. backwashed). The sorbent vessel may have suitable valves and piping to achieve this. The sorbent vessel in some instances may be pressurisable so that, in use, the step of passing the feedwater through the sorbent may be conducted under pressure. The vessel may be constructed from suitable materials and with suitable wall thickness to withstand the pressure in use.

Separator: The separator may comprise any suitable means for restraining the sorbent. In some instances no separator may be needed. This may for example be the case when the sorbent is in the form of a porous monolithic mass. However more commonly the sorbent is in the form of a particulate material and a separator is required to prevent loss or relocation of the sorbent. Suitable separators include a filter having a pore size suitable for restraining the sorbent, a mesh, a vertical pipe (in which case, in operation, the reduced sodium solution may pass upwards whereby the sorbent is separated by gravity), a centrifugal separator etc. Suitable combinations of these may be used.

Evaporator: The evaporation device may comprise a heater, e.g. a solar powered heater. It may comprise an open evaporation tank/pond or containment structure. It may comprise a reduced pressure evaporator. It may comprise a fan or blower or some other device for passing a gas over the surface of the liquid. Combinations of suitable evaporators, e.g. a heater and a blower, may also be used in order to achieve more efficient or more rapid evaporation. It will be understood that when the evaporation device comprises an open structure, evaporation may be assisted by wind and/or sun.

The apparatus may comprise a switching valve capable of either recirculating the reduced sodium solution through the sorbent or diverting it to the evaporation device. In this case, in operation, the valve would be set for recirculation for sufficient time to reduce the sodium level in the recirculating liquid to a desired level, at which stage the valve would be switched so as to diver the solution to the evaporation device so as to produce solid reduced sodium salt.

In certain embodiments therefore the present invention provides a low sodium sea salt and a method for producing the same. An amount of natural seawater containing sodium, chloride, potassium, magnesium and sulfate ions and optionally other trace minerals is filtered through a containment structure filled with beds of naturally occurring zeolite. Alternatively or additionally the sea water may be pumped through these zeolite filtration units and subsequently pumped into the containment structure. Preferably, the containment structure is located outdoors, optionally in an arid climate, with direct exposure to sunlight. Solar energy or other alternative energy optionally together with conventional energy may be used for evaporation and driving pumps and motors is incorporated as part of the process. The rate of sodium exchanged is depended on the cation exchange capacity of the sorbent used in the process, e.g. a natural zeolite, and on the retention time of the sea water within the bed or the filtration unit, which is in turn dependent on the flow-rate. An amount of the filtered water is evaporated, forming brine. An amount of reduced sodium chloride is crystallized along with the remaining brine. Sodium chloride, potassium sulfate and magnesium sulfate may be crystallized, forming a low sodium sea salt. Commonly the sodium chloride is no more than 70 weight percent of the low sodium sea salt.

The naturally occurring zeolites, once saturated with sodium, may be regenerated using mild hydrochloric or sulphuric acid or other suitable regenerating solution. The residue from the regeneration process may be stored in a second containment structure, which is periodically or continuously exposed to the sun, or evaporated using solar energy or other alternative energy source. An amount of this regenerating solution, after it has been used for regeneration of the sorbent, may be evaporated forming an acidic brine. The pH of the acidic brine may then be adjusted to neutral. An amount of sodium chloride may be crystallized from this, forming high grade sodium chloride. Commonly the sodium chloride concentration in this material is greater than 95 weight percent. The chemistry for cation exchange is determined from initially identifying the chemical composition of sea water. The strong electrolytes sodium and potassium exist in fully ionised form in seawater. In an example of the process of the invention, NepZel-H+ zeolite is loaded in the containment structure, filtration unit or column. The hydrated H+ aluminium silicate crystals have fixed porosity and density. To enable the cation exchange between sodium and or potassium ions and the zeolite, the chemical equilibrium is determined by working out the equilibrium constant. Equilibrium constant obtained from an algebraic equation that relates the molar concentration of reactants and products to one another, and is dependent on pH and temperature of the eluent. The selectivity coefficients observed for NepZel-H+ are Na > K > Mg > Ca, which makes it an ideal sorbent for the present invention where sodium and/or potassium ion concentrations are reduced to form the final product.

We also disclose herein a low sodium sea salt containing a plurality of grains. A substantial proportion of the grains contains from 30 to 70 weight percent sodium chloride and substantial amounts of potassium and magnesium sulfates.

Furthermore there is disclosed a method for producing a high sodium chloride sea salt. In this method, once sodium has been loaded onto the sorbent in order to generate the low sodium salt, the sodium is extracted from the sorbent using a suitable concentration of acid. The extracted sodium solution or brine is then introduced to a containment pond. In some instances, natural sea water may be added to dilute the brine, although this step is not always conducted. The containment pond is then exposed to the sun or powered by solar energy, or any other alternative energy or conventional energy, in order to evaporate part of the water from the brine. This results in crystallisation of sodium salts from the brine, forming a preferably homogenous high sodium chloride sea salt. The sodium chloride content of this material is commonly more than 95 weight percent.

Figure 1 illustrates a simple process according to the present invention. Thus in the uppermost box, seawater is pumped into a containment structure containing a suitable zeolite, preferably acid pretreated. This may involve pumping the seawater in from the bottom of the structure and allowing it to permeate through the zeolite and be removed from the region above the zeolite. In passing through the zeolite, sodium ions are removed from the seawater to generate a permeate with reduced sodium concentration relative to the initial seawater. In the second box, the removed permeate is partially evaporated, commonly in an evaporation pond exposed to sun and air. It is commonly necessary (although not shown in Fig. 1 ) to neutralise the permeate before or during the evaporation step in order to promote efficient crystallisation. This commonly is effected by addition of a base such as calcium carbonate. The evaporation then results in formation of a supernatant brine (third box) and crystallised low sodium salt (fourth box).

, Figure 2 describes a similar process to that of Figure 1, with the exception that the zeolite is contained in a filtration unit (adsorption column). Thus in Figure 2, seawater is pumped through the filtration unit and the resulting reduced sodium brine is transferred to a containment structure. As in Fig. 1, neutralisation is preferably conducted at this stage, although this is not shown in Fig. 2. Evaporation of part of the water results in formation of a supernatant brine and a low sodium salt precipitate which can then be separated from the brine.

Figure 3 describes the regeneration of the zeolite once it has been loaded with sodium (as described in Figs. 1 and 2). Thus the filtration unit is backwashed with an acidic solution such as 0.0 IN hydrochloric acid. This replaces sodium ions on the zeolite with hydrogen ions, and results in an effluent stream (backwash acidified water) containing sodium ions. This is then pumped into a containment structure. Again, not shown in Fig. 3 is a preferable neutralisation step, commonly with sodium hydroxide or sodium carbonate. This results in a neutralised brine. Evaporation of a portion of the water from this results in a concentrated brine and a precipitated salt which is commonly over 95% sodium chloride.

Figures 4 to 6 show different configurations of apparatus for performing the methods described herein for making low sodium salt. In Fig. 4, a source of natural sea water is fed by means of a pump into one or more of three zeolite beds (labelled beds 1 , 2 and 3). Each bed is in the form of a container, optionally an open container, in which the sea water enters near the lowest point. It then percolates upwards through the zeolite in the bed, during which step sodium is adsorbed by the zeolite. In one mode of operation, 1, 2 or 3 beds may be used in parallel, depending on the required flow rate of seawater. Alternatively, a first bed may be used until its zeolite approaches sodium saturation and then a second bed is brought into operation whilst the zeolite in the first bed is regenerated, and similarly with the third bed. To this end there may be a sodium sensor located in the stream exiting each bed for use in determining when the zeolite in that bed is reaching sodium saturation. Brine exiting each bed is passed to a switching valve. Each switching valve is capable of directing the brine either to an evaporation pond (containment structure 1) or to a storage pond (containment structure 2). In operation, the brine will be returned to containment structure 2 until the sodium level has reduced to a desired level (for example 50% sodium). At that point, the switching valve(s) from the active beds will be set to transfer the reduced sodium brine to the evaporation pond. The valves may be manually operable or may be automatically operable, operated by a controller (not shown) which receives a signal related to sodium concentration from the sodium sensor(s) (also not shown). The Evaporation pond is preferably open to air and sun, in order to allow partial evaporation of the water in the brine so as to precipitate low sodium salt.

Figure 5 shows a similar system to that used in Figure 4, however filters 1, 2 and 3, each containing zeolite, are used in place of zeolite beds, and these filters are in series. Thus in operation of the apparatus of Fig. 5, natural seawater is pumped by means of the pump sequentially through zeolite filters 1 to 3. A sensor (not shown) determines whether the sodium level is sufficiently low. If not, the brine is returned to Containment Structure 2, and pumped back through zeolite filters 1 to 3. Once the sodium level is sufficiently low, the switching valve is switched so as to direc the brine to Containment Structure 1. This Evaporation pond is preferably open to air and sun, in order to allow partial evaporation of the water in the brine so as to precipitate low sodium salt.

Figure 6 shows a system similar to that of Figure 5, however filters 1, 2 and 3 are in parallel rather than in series. Thus a pump passes the natural seawater to a switching valve which can direct it either to Containment structure 2 or through filters 1 to 3, in which zeolite adsorbs sodium ions. A second switching valve is disposed so as to direct the resulting low sodium brine either to an evaporation pond (containment structure 1) or to a storage pond (containment structure 2). In operation, water is directed to the zeolites until their flow capacity is reached, at which stage additional seawater is directed to the containment structure 2. Once the low sodium brine exiting the filters has reached a suitably low level, the switching valve is set to direct the brine to the evaporation pond for partial evaporation and generation of low sodium salt. In this configuration, additional valves may be present near the inlets to the filter columns so as to be able to remove one or more for service when they become saturated with sodium, so as to regenerate the saturated zeolite.

EXPERIMENTAL

Sodium Removal and Generation of Zeolite

The methods of the invention, in a common embodiment, are divided into six discrete stages, as set out in the table below. The sorbent used in these experiments was Werris Creek zeolite, which is a clinoptilolite. Zeolite Name Sodium Sodium Amount of % absorbed Stage absorbed released zeolite (g) or released

Stage ! Rinse 1 0 1 12 0

Stage 2 Generation 387 112 0.35

Stage 3 Rinse 2 217 112 0.19

Stage 4 Loading 956 400 0.24

StageS Rinse 3 ■■' ¾( ' .,; '■ 400 - 0.01

Stage 6 Regeneration 1034 400 0.25

The table above also shows the percentage sodium absorbed or released at each stage of the zeolite treatment. As expected, during the initially washing phase (Stage 1), there was no release of sodium from the matrix. However, when the zeolite was treated with acid, 0.35% of sodium was released from the matrix. Moreover, an additional 0.19% was further desorbed from the matrix (Stage 3 - rinse) resulting in a total of 0.54% sodium release. Upon loading however, only 0.24% sodium was absorbed by the zeolite (not the complete 0.54%, as expected). This discrepancy may be a result of the amount of sodium the zeolite is exposed to during its formation. It was hypothesised that the more sodium the zeolite is exposed to, the higher the absorption efficiency. Experiments were then setup where the zeolite was loaded with a 1 M sodium chloride solution (22,000 ppm of Na + ). These results indicated that a 0.5% sodium absorption can be achieved, hence showing that the sodium absorption efficiency of the Werris Creek zeolite is dependent on the loading concentration of sodium.

The above table also shows the sodium absorption and desorption capacity of zeolite. As previously mentioned, the absorption to desorption ratio (0.24/0.25) is approximately 1, indicating that the amount of sodium loaded into the zeolite is similar to the amount being ejected upon regeneration. Importantly, these results reveal that there is no breakdown of the zeolite matrix with the conditions being used.

An initial rinse of the zeolite samples was conducted to remove any bound dust, small particles and debris that could have carried over from the production and manufacturing plants prior to testing. Previous work indicated that the presence of fine particles in zeolite cavities can have an undesirable effect on the sodium absorption ability of zeolites. The small particulates were removed simply by passing DI (deionised) water through the zeolite filtration media. It was observed that the initial DI water rinse contained small particulates, making the solution turbid. However, following approximately 3L of rinse per 112 g zeolite, the eluent was clear, indicating that majority of the debris had been eluted. Chromatographic analysis of the zeolite rinse indicated insignificant levels of sodium and no evidence of potassium in the eluent.

Previous studies on zeolites show that these porous frameworks absorb any cations that are abundant during their natural formation and that zeolite absorption capacity increases drastically following the desorption of these cations. For this reason it is important to remove the absorbed cations to increase the sodium absorption efficiency of zeolites. Three different eluents were used to remove possible bound cations from the zeolites: sulphuric acid, hydrochloric acid and potassium chloride. Table 1 shows the release of sodium from zeolite upon treatment with these eluents.

Table 1 : Release of naturally bound sodium from zeolite (0.4- 1.4mm) using 3 different eluents. Each zeolite sample was shaken in the eluent for 1 hour at room temperature, filtered and measured for pH and metal content using AAS (atomic absorption spectroscopy).

Table 1 indicates that treating Werris Creek zeolites with acid is far more effective at removing naturally bound sodium than potassium chloride treatment. Both sulphuric and hydrochloric acid removed approximately 200 ppm of sodium from zeolites whereas sodium exchange in the presence of potassium was only 15 ppm. However, comparison between the two acids indicates that the hydrochloric acid is a better treatment agent for two reasons;

1. A 0.01 M HC1 solution removes approximately the same amount of sodium than does a 1M sulphuric acid solution. This shows that HC1 treatment is 100 fold more effective at removing sodium. In addition, the cost of sulphuric acid ($329 USD/tonne) is far greater than HC1 when compared ($132 USD/tonne). Not only is the usage of HC1 to treat zeolite 100 fold less, but it also costs 300 times less to pre- treat the Werris Creek zeolite and enhance its sodium absorption capacity.

2. Table 1 indicates that treating Werris Creek zeolite with 1 M sulphuric acid results in pH below 2 whereas treatment with 0.01 M HC1 provideds pH >2. The stronger acid treatment could lead to damage to the zeolite matrix, as zeolites tend to decompose at these pH's and thereby decreasing their absorption efficiency. From these experiments, it was concluded that the best treatment of Werris Creek zeolite is 0.01 HC1 based on the efficiency, cost and stability of the material. Figure 7 shows the release of naturally bound sodium from zeolite when treated with 0.01 M HC1 solution. Upon acid treatment of the zeolite, initially a large amount of sodium is released from the zeolite matrix followed by a more steady release. These results suggest that there are two sites of binding for sodium: surface bound (adsorbed) and intra-matrix bound (absorbed). The initial burst of sodium release (0.1-0.5 L) may therefore be due to sodium that is adsorbed to the surface of the matrix.The later slow release of sodium (0.6-2 L) may be attributed to the sodium that is absorbed within the zeolite matrix and therefore takes a lot longer to be expelled.

Sodium Loading

Following the removal of naturally bound sodium, the zeolite matrix was rinsed with DI water (Stage 3) and introduced to 3000 ppm sodium solution. Table 2 shows the amount and percentage sodium absorbed by zeolite.

Table 2: The sodium absorption capacity of generated zeolite (0.4-1.4 mm). 112 g of zeolite was packed tightly in a filter (33 x 155 mm) and 2L of 0.01 M HC1 was passed through. This was then followed by Stage 3 (Rinse 2) where 1.5 L of DI water was passed until the pH of the eluent was pH 6-7. The zeolite material was then removed and oven dried overnight at 80 °C. The dried zeolite was then repacked in the filter and 3000 ppm sodium solution (1 L) was passed through at 16.2 mL/min. The eluent was collected and analysed for sodium using AAS (atomic absorption spectroscopy).

Results from Table 2 show that the sodium absorption capacity of Werris Creek zeolite after acid treatment is 0.22%. These results are far better than earlier reports which suggested that when treating the Werris Creek zeolite with sulphuric acid (0.01 M), absorption of sodium was approximately 0.1%. In comparison, treating Werris Creek zeolite with the same concentration of HC1 demonstrated that approximately 220 mg of sodium is absorbed by 100 g of zeolite (0.22%). This shows that generating Werris Creek zeolites with HC1 is twice as efficient than using the same amount of sulphuric acid. Figure 8 demonstrates that upon sodium introduction, initially there is a significant decrease in the pH followed by a slow recovery to pH 3.5. These results suggest that the zeolite matrix after treatment with HC1 (Generation), is charged with protons. Due to the preference of the zeolite towards sodium, these protons are easily exchangeable for sodium. Therefore as the sodium is introduced, it readily exchanges for the protons thereby releasing H + cations and decreasing the overall pH of the solution. From Figure 8, it can be seen that the pH of the eluent never recovers to neutrality (pH 6-7). This shows that during the course of the experiment, the zeolite continues to exchange protons for sodium, showing the preference it has for sodium over protons. After passing 2 L of 3000 ppm sodium, the pH was still approximately 3.5, indicating that there are still protons being ejected from the matrix in exchange for sodium. This suggests that, had the contact time of sodium been longer, a larger percentage of sodium would have been absorbed, and the overall sodium absorption capacity of the Werris Creek zeolite would thereby have been increased.

Experiments were also conducted to investigate the regeneration ability of Werris Creek zeolite. Following the rinse, the loaded zeolite was washed with 0.01 M HC1 solution. This treatment was similar to that used for removing the naturally bound sodium from zeolite during Stage 2. Figure 9 shows the release of sodium and the consequent regeneration of the zeolite upon acid treatment.

As the zeolite is treated with acid, a large amount of sodium is ejected from the matrix followed by an exponential decrease. These results suggest that the behaviour of the zeolite matrix does not change. Moreover, the amount of sodium that was loaded in the matrix is almost similar to the amount that was ejected during the regeneration phase, i.e., the ratio of absorption to desorption is approximately 1.