Claims:1. A method for obtaining high purity sodium chloride, the method comprising:
subjecting a saltwater comprising sodium chloride, and impurities including sulphate, magnesium, calcium and bromide to nanofiltration and chelation to obtain a softened water;
mixing the softened water with sodium hypochlorite such that the ratio of sodium hypochlorite to bromide in the mixture is in the range of 1:1 to 1:2, at a pH in the range of 3.5-5.5; and
heating the mixture to remove bromine gas and evaporate water to obtain the high purity sodium chloride.
2. The method as claimed in claim 1, wherein the softened water is obtained by first subjecting the saltwater to the nanofiltration to obtain a permeate and then subjecting the permeate to the chelation.
3. The method as claimed in claim 1, wherein the softened water is obtained by first subjecting the saltwater to the chelation to obtain an eluate and then subjecting the eluate to the nanofiltration.
4. The method as claimed in claim 1, wherein the softened water comprises calcium and magnesium in the range of 1-12.5 ppm and sulfate in the range of 6-75 ppm.
5. The method as claimed in claim 1, wherein the saltwater is prepared by mixing 5-25% wt/wt salt with water.
6. The method as claimed in claim 5, wherein the salt is obtained from seawater.
7. The method as claimed in claim 5, wherein the salt comprises 98-99% sodium chloride, 500-2000 ppm magnesium and calcium ions, 1500- 3000 ppm sulphate ions, and 200-500 ppm bromide.
8. The method as claimed in claim 1, wherein the saltwater is seawater.
9. The method as claimed in claim 2 or 3 wherein the chelation includes passing the permeate or the saltwater through a chelating resin.
10. The method as claimed in claim 9, wherein the chelating resin is a divalent cation selective resin.
11. The method as claimed in claim 2 or 3 wherein the nanofiltration includes passing the saltwater or the eluate through nanofiltration spiral membrane of 150-300 Da.
12. The method as claimed in claim 1, wherein the saltwater is subjected to a pretreatment prior to the nanofiltration and/or the chelation.
13. The method as claimed in claim 12, wherein the pretreatment is selected from the group consisting of sediment filtration, microfiltration, and gravitational filtration.
14. The method as claimed in claim 1, wherein the pH is adjusted in the range of 3.5-5.5 by adding hydrochloric acid.
15. The method as claimed in claim 1, wherein the high purity sodium chloride comprises calcium and magnesium ions in the range of 0.001-0.005 % w/w; sulphate in the range of 0.005-0.03 % w/w and bromide in the range of 0.001-0.01 % w/w.
16. A system (100) for obtaining high purity sodium chloride, the system (100) comprising:
a nanofiltration unit (102) comprising an inlet (202), one or more nanofiltration membrane(s) (204), and an outlet (206);
a chelation unit (104) comprising an inlet (208), a chelating resin (210), and an outlet (212); and
an evaporation unit (106) comprising one or more inlet(s), means for heating (218), and one or more outlet(s) (216).
17. The system (100) as claimed in claim 16, wherein
the nanofiltration unit (102) is configured to receive saltwater from its inlet (202), pass the saltwater through the one or more nanofiltration membrane(s) (204) to obtain a permeate and release the permeate from its outlet (206); and
the chelation unit (104) is configured to receive the permeate from its inlet (208), pass the permeate through the chelating resin (210) to obtain a softened water, and release the softened water from its outlet (212).
18. The system (100) as claimed in claim 16, wherein
the chelation unit (104) is configured to receive saltwater from its inlet (208), pass the saltwater through the chelating resin (210) to obtain an eluate and release the eluate from its outlet (212); and
the nanofiltration unit (102) is configured to receive the eluate from its inlet (202), pass the eluate through the one or more nanofiltration membrane(s) (204) to obtain a softened water and release the softened water from its outlet (206).
19. The system (100) as claimed in claim 17 or 18, wherein the evaporation unit (106) is configured
to receive the softened water, sodium hypochlorite and hydrochloric acid from its one or more inlet(s) (214);
heat the mixture of the softened water, sodium hypochlorite and hydrochloric acid to evaporate water by the means for heating (218); and
release water and bromine gas from its one or more outlet(s) (216).
20. The system (100) as claimed in any of claims 17-19, wherein the softened water comprises calcium and magnesium in a range of 1-12.5 ppm and sulfate in a range of 6-75 ppm.
21. The system (100) as claimed in claim 16, wherein the system (100) comprises a pretreatment unit configured to receive the saltwater and remove sediments and foreign particles before the saltwater is sent to the nanofiltration unit (102) and/or the chelation unit (104).
22. The system (100) as claimed in claim 21, wherein the pretreatment unit comprises a sedimentation filtration unit, a microfiltration unit, and/or a gravitation filtration unit.
23. The system (100) as claimed in claim 16, wherein the saltwater is prepared by mixing 5-25% wt/wt salt with water.
24. The system (100) as claimed in claim 23, wherein the salt is obtained from seawater.
25. The system (100) as claimed in claim 23, wherein the salt comprises 98-99% sodium chloride, 500-2000 ppm magnesium and calcium ions, 1500- 3000 ppm sulphate ions, and 200-500 ppm bromide.
26. The system (100) as claimed in claim 16, wherein the saltwater is seawater.
27. The system (100) as claimed in claim 16, wherein the chelating resin is a divalent cation selective resin.
28. The system (100) as claimed in claim 16, wherein the one or more nanofiltration membrane (204) is a nanofiltration spiral membrane of 150-300 Da.
29. The system (100) as claimed in claim 16, wherein the high purity sodium chloride comprises calcium and magnesium ions in the range of 0.001-0.005% w/w; sulphate in the range of 0.005-0.03 % w/w and bromide in the range of 0.001-0.01 % w/w.
, Description:FIELD OF INVENTION
The present disclosure relates to a method and a system for obtaining sodium chloride. Specifically, it relates to a method and a system for obtaining high purity sodium chloride from saltwater.

BACKGROUND
Sodium chloride is most commonly obtained by evaporative concentration of seawater or of other naturally occurring brines, typically by using open-air evaporation lagoons or thermal concentration equipment and processes. The seawater contains many solutes and impurities, for example, calcium, magnesium, sulfates, carbonates/bicarbonates, bromide, and insoluble substances, which are carried forward to the final product. Thus, the salt obtained from the seawater also includes undesirable, solutes and impurities. A number of applications, such as cosmetic and pharmaceuticals require sodium chloride of high purity, which is substantially free of the undesirable chemical or taste components. Many processes for obtaining high purity sodium chloride are known in the art.

US5221528A discloses a process for the preparation of sodium chloride, which involves purification of crude brine by precipitating and separating calcium and magnesium in the form of insoluble compounds, followed by evaporating water from the obtained purified brine and separating the sodium chloride crystallized in the process, followed by crystallizing and separating sodium sulfate from the mother liquor and returning the sodium sulfate to the crude brine to be purified.

US9737827B2 discloses a system for removing high purity salt from a brine. The system includes a first evaporator configured to receive a brine stream, to produce a first output comprising a sodium chloride slurry, and to produce a first intermediate output. The system also includes a second evaporator fluidly coupled to the first evaporator and configured to receive the first intermediate output, to produce a first recovery output, and to produce a second intermediate output. The system further includes a third evaporator fluidly coupled to the second evaporator and configured to receive the second intermediate output and to produce a second recovery output. The first recovery output and the second recovery output are used to produce the brine stream received by the first evaporator.

WO2002006158A1 discloses a process for the production of sodium chloride from seawater or brine. The process involves crystallizing sodium chloride from seawater or brine, wherein the seawater or brine is previously contacted with red mud or a red mud derivative to reduce the levels of impurities.

EP2300371A1 discloses a process for producing sodium chloride comprising the steps of (i) preparing a brine comprising at least 150 g/l of sodium chloride by dissolving a sodium chloride source in water, (ii) subjecting the resulting brine to a eutectic freeze crystallization step by indirect cooling of said brine, resulting in the formation of ice, sodium chloride dihydrate, and a mother liquor, (iii) separating the sodium chloride dihydrate formed in step (ii) from the ice and optionally mother liquor at the eutectic temperature, such that a sodium chloride dihydrate-rich stream is formed, and (iv) feeding said sodium chloride dihydrate-rich stream to a re-crystallizer to form sodium chloride and a mother liquor.

SUMMARY
The present disclosure relates to a method for obtaining high purity sodium chloride. The method comprises subjecting a saltwater comprising sodium chloride, and impurities including sulphate, magnesium, calcium and bromide to nanofiltration and chelation to obtain a softened water; mixing the softened water with sodium hypochlorite such that the ratio of sodium hypochlorite to bromide in the mixture is in the range of 1:1 to 2:1, at a pH in the range of 3.5-5.5; and heating the mixture to remove bromine gas and evaporate water to obtain the high purity sodium chloride.
The present disclosure also relates to a system (100) for obtaining high purity sodium chloride. The system (100) comprises a nanofiltration unit (102) comprising an inlet (202), one or more nanofiltration membrane(s) (204), and an outlet (206); a chelation unit (104) comprising an inlet (208), a chelating resin (210), and an outlet (212); and an evaporation unit (106) comprising one or more inlet(s) (214), means for heating (218), and one or more outlet(s) (216).

BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 depicts a system 100 for obtaining high purity sodium chloride, in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION
For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended, such alterations and further modifications in the disclosed composition and method, and such further applications of the principles of the disclosure therein being contemplated as would normally occur to one skilled in the art to which the disclosure relates.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the disclosure and are not intended to be restrictive thereof.
Reference throughout this specification to “one embodiment”, “an embodiment” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrase “in one embodiment”, “in an embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
The terms “a,” “an,”, and “the” are used to refer to “one or more” (i.e. to at least one) of the grammatical object of the article.
The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion and are not intended to be construed as “consists of only”, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure, the preferred methods, and materials are now described.
The present disclosure relates to a method for obtaining high purity sodium chloride. The method comprises subjecting a saltwater comprising sodium chloride, and impurities including sulphate, magnesium, calcium and bromide to nanofiltration and chelation to obtain a softened water; mixing the softened water with sodium hypochlorite to obtain a mixture such that the ratio of sodium hypochlorite to bromide in the mixture is in the range of 1:1 to 2:1, at a pH in the range of 3.5-5.5; and heating the mixture to remove bromine gas and evaporate water to obtain the high purity sodium chloride.
In accordance with an embodiment, the saltwater is prepared by mixing 5-25% wt/wt salt with water. In accordance with an embodiment, the salt is derived from seawater by using conventional methods, for example, solar evaporation or vacuum evaporation. In accordance with an embodiment, the salt comprises 98-99% sodium chloride, 500-2000 ppm magnesium and calcium ions, 1500- 3000 ppm sulphate ions, and 200-500 ppm bromide. In accordance with an embodiment the saltwater is seawater.

The pH of the saltwater is in the range of 7.5-9.5. In accordance with an embodiment, the saltwater comprises 5-25 wt% sodium chloride, 25-500 ppm magnesium and calcium ions, 75-750 ppm sulphate ions, and 10-125 ppm bromide.
The saltwater can be subjected to the nanofiltration and the chelation in any order to obtain the softened water. The nanofiltration results in the depletion or reduction in the concentration of sulfates. The chelation results in the depletion or reduction in the concentration of calcium and magnesium. The softened water so obtained has reduced concentration of sulfate, calcium and magnesium compared to the saltwater. In accordance with an embodiment, the softened water comprises calcium and magnesium in the range of 1-12.5 ppm and sulfate in the range of 6-75 ppm.
Any suitable nanofiltration membrane may be used for the nanofiltration. In accordance with an embodiment, the nanofiltration membrane is a nano filtration spiral membrane of 150-300
Daltons (Da). In accordance with an embodiment, more than one nanofiltration membrane are used.
The nanofiltration is performed at a feed flow rate in the range of 4-40 liters per hour, a feed pressure in the range of 5.5-16 bar, a reverse pressure in the range of 5-15.5 bar. The nanofiltration is performed at an ambient temperature. In accordance with an embodiment, it is performed at a temperature of ±25 °C.
In an embodiment, the softened water is obtained by first subjecting the saltwater to the nanofiltration to obtain a permeate and a retentate. The permeate contains reduced concentration of sulfates compared to the saltwater. In accordance with an embodiment, the permeate contains sulfates in the range of 6-75 ppm. In accordance with an embodiment, the permeate is collected at a rate of 4-14 liters per hour. The permeate so obtained is then subjected to the chelation. In an embodiment, the retentate is rejected. In another embodiment, the retentate is further processed to recover minerals such as calcium sulfate, magnesium sulfate, and sodium sulfate.
In another embodiment, the softened water is obtained by first subjecting the saltwater to the chelation to obtain an eluate. The eluate so obtained contains reduced concentration of calcium and magnesium. In accordance with an embodiment, the eluate contains calcium and magnesium in the range of 1-12.5 ppm. The eluate so obtained is then subjected to the nanofiltration.
The chelation includes passing the saltwater or the permeate, as the case may be, through a chelating resin or one or more towers of the chelating resin. The chelating resin towers can be arranged in a series or parallelly. In accordance with an embodiment, the chelating resin is a divalent cation selective resin. In an example, the chelating resin comprises a crosslinked polystyrene matrix containing amino phosphonic acid functional groups and is capable of forming a chelate (complex) exclusively with divalent cation, for example Ca2+, Mg2+, Ba2+ etc.
The chelation is performed at a feed flow rate in the range of 170-550 ml/min, feed pressure of 1 atm. The chelation is performed at an ambient temperature. In accordance with an embodiment, it is performed at a temperature of ±25 °C.
In accordance with an embodiment, after the chelation, calcium and magnesium are recovered from the chelating resin for further use. The recovery may be done by subjecting the chelating resin after the chelation to acid treatment and caustic wash.
Prior to the nanofiltration and/or the chelation, the saltwater may be subjected to pretreatment to remove any foreign impurities, sediments etc. The pretreatment can be done by any suitable method. Examples of the suitable methods include but are not limited to sediment filtration, microfiltration, and gravitational filtration. In accordance with an embodiment, the prefiltration is performed using a ceramic filter. In an embodiment, the prefiltration is performed using a ceramic filter and is carried out at a feed flow rate in the range of 40-50 liters per hour, feed pressure of 1.5-2.0 bar, reverse pressure of 1.4-1.9 bar. The prefiltration is performed at an ambient temperature. In accordance with an embodiment, it is performed at a temperature of ±25 °C.
In accordance with an embodiment, the pH of the mixture of the softened water and sodium hypochlorite is adjusted in the range of 3.5-5.5 by adding hydrochloric acid.
In accordance with an embodiment, water and bromine gas so produced are recovered and stored for further use.
In accordance with an embodiment, the high purity sodium chloride comprises calcium and magnesium ions in the range of 10-50 ppm; sulphate in the range of 50-300 ppm and bromide in the range of 10-100 ppm.
The present disclosure also relates to a system for obtaining the high purity sodium chloride. The system comprises a nanofiltration unit, a chelation unit, and an evaporation unit. The nanofiltration unit and the chelation unit can be present in the system in any order.
FIG. 1 depicts system 100 for obtaining the high purity sodium chloride in accordance with an embodiment of the present disclosure. System 100 comprises nanofiltration unit 102, chelation unit 104 and evaporation unit 106. In an embodiment, nanofiltration unit 102 is installed before chelation unit 104. In other embodiment, chelation unit 104 is installed before nanofiltration unit 102.
In accordance with an embodiment, nanofiltration unit 102 comprises inlet 202, one or more nanofiltration membrane(s) 204, and outlet 206. In accordance with an embodiment, nanofiltration unit 102 further comprises a second outlet for releasing retentate. The one or more nanofiltration membrane(s) 204 may be housed in a housing unit (not shown).
In accordance with an embodiment, the retentate is released from the second outlet (not shown) and transferred to another unit for storage and further processing to recover calcium sulfate, magnesium sulfate and sodium sulfate.
One or more nanofiltration membrane(s) 204 may be any suitable nanofiltration membrane(s). In accordance with an embodiment, one or more nanofiltration membrane(s) 204 is/are nano filtration spiral membrane of 150-300 Da.
Chelation unit 104 comprises inlet 208, chelating resin 210, and outlet 212. In accordance with an embodiment chelating resin 210 is a divalent cation selective resin. In accordance with an embodiment, chelating resin 210 is in a form of one or more tower(s). The said towers can be arranged in a series or parallelly. In an example, the chelating resin comprises a crosslinked polystyrene matrix containing amino phosphonic acid functional groups and is capable of forming a chelate (complex) exclusively with di valent cation, for example Ca2+, Mg2+, Ba2+ etc.
Evaporation unit 106 comprises one or more inlet(s) 214, one or more outlet(s) 216 and means for heating 218.
In accordance with an embodiment, nanofiltration unit 102 is configured to receive saltwater from inlet 202, pass the saltwater through the one or more nanofiltration membrane(s) 204 to obtain a permeate and release the permeate from outlet 206. Chelation unit 106 is configured to receive the permeate from outlet 206 through its inlet 208, pass the permeate through the chelating resin 210 to obtain softened water, and release the softened water from outlet 212.
In accordance with an embodiment, chelation unit 104 is configured to receive saltwater from inlet 208, pass the saltwater through chelating resin 210 to obtain an eluate and release the eluate from outlet 212. Nanofiltration unit 102 is configured to receive the eluate from outlet 212 through inlet 202, pass the eluate through one or more nanofiltration membrane(s) 204 to obtain softened water and release the softened water from outlet 206.
In accordance with an embodiment, after the chelation, calcium, magnesium, and other divalent impurities such as zinc, Barium are recovered from the chelating resin 210.
Evaporation unit 106 is configured to receive the softened water, sodium hypochlorite and hydrochloric acid from its one or more inlet(s) 214 and heat the mixture by means of heating 218. Sodium hypochlorite is added in an amount such that the ratio of sodium hypochlorite to bromide in the mixture is in the range of 1:1 to 2:1 at a pH in the range of 3.5-5.5. The hydrochloric acid is used to adjust the pH of the mixture in the range of 3.5-5.5.
The mixing and the heating results in conversion of bromide present in the mixture into bromine gas. The heating also results in the evaporation of water. Water and bromine gas so formed are released from one or more outlets 216. In accordance with an embodiment, water and bromine gas are collected and stored for further use or processing.
In accordance with an embodiment, at least of one or more inlet(s) 214 are configured to receive softened water from outlet 206. In another embodiment, at least of one or more inlet(s) 214 is configured to receive softened water from outlet 212.
In accordance with an embodiment means for heating 218 is a steam generator.
The softened water contains reduced concentration of sulfates, calcium, and magnesium. In accordance with an embodiment, the softened water comprises calcium and magnesium in the range of 1-12.5 ppm and sulfate in the range of 6-75 ppm.
In an embodiment, system 100 comprises a pretreatment unit (not shown) installed at the beginning i.e., before nanofiltration 102 and/or chelation unit 104. The pretreatment unit is configured to receive the saltwater and remove sediments and foreign particles before the saltwater is sent to nanofiltration unit 104 or chelation unit 106.
In accordance with an embodiment, the pretreatment unit may be a sedimentation filtration unit, a microfiltration unit, and/or a gravitation filtration unit.
In accordance with an embodiment, the saltwater comprises 5-25% wt/wt salt. In accordance with an embodiment, the salt is obtained from seawater. In a specific embodiment, the salt comprises 98-99% sodium chloride, 500-2000 ppm magnesium and calcium ions, 1500- 3000 ppm sulphate ions, and 200-500 ppm bromide. In an embodiment, the saltwater is seawater.
In accordance with an embodiment, the high purity sodium chloride comprises calcium and magnesium ions in the range of 10-50 ppm; sulphate in the range of 50-300 ppm and bromide in the range of 10-100 ppm.
The process according to the present disclosure is further illustrated by the following examples.
EXAMPLES
Example 1 - Removal of Sulfate by Nanofiltration: Salt water was prepared by mixing 25% w/w vacuum dried salt with water. The salt contained 98.5% w/w sodium chloride, 0.16%w/w calcium and magnesium, 0.23% w/w sulfate, and 0.028% w/w bromide. The salt was devoid of any additives and anticaking agent. 5 litres of the saltwater was subjected to nanofiltration using a DL1812 membrane (Type: spiral wound, MWCO 150-300 Daltons) with area of 0.37m2. The parameters of the nanofiltration were as follows:
- Feed flow rate: 4.2 liters per hour
- Feed pressure: 10.5 bar
- Reverse pressure: 10 bar (?P = 0.5 Bar)
- Temperature: 25 °C
The nanofiltration yielded 4.5 litres of permeate and 0.5 litres of retentate. The permeate was collected at a rate of 4.2 liters per hour. The composition of the feed, the permeate and the retentate are provided in Table 1.

Table 1: The Composition of the Feed, the Permeate and the Retentate
Parameter/Content Feed (25%w/w solution) Permeate (25%w/w solution) Retentate (25%w/w solution)
Volume 5.0 litre 4.5 litre 0.5 litre
Sodium 98500 ppm 98500 ppm 98500 ppm
Calcium 400 ppm 275 ppm 600 ppm
Sulphate 575 ppm 50 ppm 1100 ppm
TDS 144000 ppm 137300 ppm 139000 ppm

The permeate was subjected to drying to obtain sulfate depleted sodium chloride. Table 2 provides the composition of the sulfate depleted sodium chloride obtained after nanofiltration and drying.
Table 2: The composition of the purified sodium chloride obtained after nanofiltration
Content Concentration
Sodium Chloride 99.5 %w/w
Calcium and Magnesium 0.11 %w/w
Sulfate 0.02 %w/w
Bromide 0.028 %w/w

Example 2 - Removal of Calcium and Magnesium by Chelation: Saltwater was prepared by mixing 25% w/w vacuum dried salt with water. The salt contained 98.5% w/w sodium chloride, 0.16%w/w calcium and magnesium, 0.23% w/w sulfate, and 0.028% w/w bromide. The salt was devoid of any additives and anticaking agent. 10 litres of the saltwater was passed through INDION® BSR, chelating ion exchange resin column. The parameters for the chelation were as follows:
- Feed flow rate: 4BV per hour i.e., 550 ml/hr
- Feed pressure: 1 atm
- Temperature: 25 °C
Eluate obtained after chelation was collected and dried to obtain calcium and magnesium depleted sodium chloride. Table 3 provides the composition of the calcium and magnesium depleted sodium chloride obtained after the chelation and drying.

Table 3: The composition of the purified sodium chloride obtained after chelation
Content Concentration
Sodium Chloride 99.5 % w/w
Calcium and Magnesium 0.002 % w/w
Sulfate 0.23 % w/w
Bromide 0.028 % w/w

Example 3 - Removal of Bromide: Saltwater was prepared by mixing 10% w/w vacuum dried salt with water. The salt contained 98.5%w/w sodium chloride, 0.16%w/w calcium and magnesium, 0.23% w/w sulfate, and 0.028% w/w bromide. The salt was devoid of any additives and anticaking agent. 1 litre of the saltwater was mixed with 0.1M hydrochloric acid and sodium hypochlorite. Sodium hypochlorite (4% active chlorine) was used in an amount such that the molar ratio of bromide to sodium hypochlorite in the mixture was 1:1.5 at pH 3.5-4.5. The mixture was heated to evaporate water and release bromine gas. Table 4 provides the composition of the bromide depleted sodium chloride so obtained.

Table 4: The composition of the bromide depleted sodium chloride
Content Concentration
Sodium Chloride 99.5 % w/w
Calcium and Magnesium 0.16 % w/w
Sulfate 0.23 % w/w
Bromide 0.006 % w/w

Example 4 - Preparation of High Purity Sodium Chloride: 25 kg of vacuum dried salt was dissolved in 235 kg of water to obtain saltwater. The salt contained 98.5% w/w sodium chloride, 0.16%w/w calcium and magnesium, 0.23% w/w sulfate, and 0.028% w/w bromide. The salt was devoid of any additives and anticaking agent.
Prefiltration: The saltwater was subjected to prefiltration using a ceramic filter (150 Da) having 0.25 m2 area to remove any foreign particles, sediments etc. The parameters for the prefiltration were as follows:
- Feed flow rate: 40 liters per hour
- Feed pressure: 1.8 bar
- Reverse pressure: 1.7 bar
- Temperature: 25 °C
Nanofiltration: 100 liters of the filtrate obtained after the prefiltration, was subjected to nanofiltration using a DL1812 membrane (Type: spiral wound, MWCO 150-300 Daltons) with area of 0.37m2. The parameters of the nanofiltration were as follows:
- Feed flow rate: 35 liters per hour
- Feed pressure: 10 bar pressure
- Reverse pressure: 9 bar (?P = 1 Bar)
- Temperature: 25 °C
87.5 liters of a permeate and 12.5 liters of a retentate was collected after the nanofiltration. The permeate was collected at 30 liters per hour rate.
Chelation: The permeate was subjected to chelation by passing it through INDION® BSR. The parameters for the chelation were as follows:
- Feed flow rate: 1.5BV per hour i.e., 24 liters per hr
- Feed pressure: 1 atm
- Temperature: 25 °C
The eluate (softened water with reduced concentration of sulfates, calcium and magnesium) was collected after the chelation.
Chemical Treatment/Bromide Removal: 5 kg of the eluate or the softened water was mixed with hydrochloric acid and sodium hypochlorite such that the molar ratio of bromide to sodium hypochlorite was 1:1.5 at pH 3.5-4.5. The mixture so obtained was heated and evaporated to dryness to get high purity sodium salt and release bromine gas. The composition of the high purity sodium chloride in provided in Table 5.

Table 5: The Composition of the High Purity Sodium Chloride
Content Concentration
Sodium Chloride 99.5 % w/w
Calcium and Magnesium 0.002% w/w
Sulfate 0.02% w/w
Bromide 0.006% w/w

Example 5 - Preparation of High Purity Sodium Chloride: Saltwater was prepared by mixing 10% w/w with water. High purity sodium chloride was obtained from the saltwater using the different feed volumes of the saltwater at different pH by subjecting the saltwater to prefiltration, nanofiltration and chelation in various sequence in three different batches.
Prefiltration: The saltwater was subjected to prefiltration using a ceramic filter (150 Da) having 0.25 m2 area to remove any foreign particles, sediments etc. The parameters for the prefiltration were as follows:
- Feed flow rate: 40 liters per hour
- Feed pressure: 1.8 bar
- Reverse pressure: 1.7 bar
- Temperature: 25 °C
Nanofiltration: The nanofiltration was performed using a DL1812 membrane (Type: spiral wound, MWCO 150-300 Daltons) with area of 0.37m2. The parameters of the nanofiltration were as follows:
- Feed flow rate: 4.2 liters per hour
- Feed pressure: 10.5 bar pressure
- Reverse pressure: 10 bar (?P = 0.5 Bar)
- Temperature: 25 °C
Chelation: The chelation was performed by passing it through INDION® BSR. The parameters for the chelation were as follows:
- Feed flow rate: 1.5 BV per hour i.e., 24 liters per hour
- Feed pressure: 1 atm
- Temperature: 25 °C
Table 6: Details of the Batches
Parameter Batch 1 Batch 2 Batch 3
Feed (to the microfiltration unit) 100 liters 100 liters 50 liters
pH of the saltwater 9.0 4.5 9.0
Sequence of Filtration Prefiltration followed by nanofiltration followed by chelation Prefiltration followed by nanofiltration followed by chelation Prefiltration followed by chelation followed by nanofiltration

The eluates (softened water with reduced concentration of sulfates, calcium, and magnesium) obtained in the case of batch 1 and 2 and the permeate (softened water with reduced concentration of sulfates, calcium and magnesium) obtained in the case of batch 3 were subjected to chemical treatment for bromide removal. The eluate was collected at a rate of 24 liters per hour. The permeate was collected at a rate of 30 liters per hour. For the chemical treatment, the permeate or the eluate, as the case may be, was mixed with sodium hypochlorite and hydrochloric acid such that the molar ratio of bromide to sodium hypochlorite was 1:1.5 at pH 3.5- 4.5. Bromide removal was carried out in 10 a liter glass beaker. The mixture so obtained was heated and evaporated to dryness to get high purity sodium chloride and release bromine gas.

Product Characterization: The high purity sodium chloride was as per the IP 2018 testing protocols. Table 7 shows the Indian Pharmacopoeia (IP) grade test parameters analysis of the high purity sodium chloride obtained from batches 1-3.
Table 7: IP grade Test Parameters Analysis
S. No. Specification Normal Sodium Chloride* High Purity Sodium Chloride (Batch 1) High Purity Sodium Chloride (Batch 2) High Purity Sodium Chloride (Batch 3) IP Grade Limit
1 Acidity or alkalinity
1.6 ml of 0.01 N of HCl
0.1 ml of 0.01 N HCl
0.1 ml of 0.01 N HCl
0.1 ml of 0.01 N HCl
0.5 ml of 0.01 N HCl or 0.01 NaOH

2 Sulphate
2300 ppm
200 ppm
200 ppm
200 ppm
Up to 300 ppm

3 Bromide
280 ppm
56 ppm
40 ppm
49 ppm
Up to 100 ppm

4 Calcium and Magnesium
1600 ppm
20 ppm
20 ppm
20 ppm
Up to 50 ppm

5 Loss on Drying 1.5%
0.36
0.30
0.45
Up to 1%

*Normal sodium chloride: Vacuum dried sodium chloride obtained from seawater at the Mithapur Plant, Tata Chemicals Limited.

SPECIFIC EMBODIMENTS ARE DESCRIBED BELOW
A method for obtaining high purity sodium chloride, the method comprising subjecting a saltwater comprising sodium chloride, and impurities including sulphate, magnesium, calcium and bromide to nanofiltration and chelation to obtain a softened water; mixing the softened water with sodium hypochlorite such that the ratio of sodium hypochlorite to bromide in the mixture is in the range of 1:1 to 1:2, at a pH in the range of 3.5-5.5; and heating the mixture to remove bromine gas and evaporate water to obtain the high purity sodium chloride.
Such method(s), wherein the softened water is obtained by first subjecting the saltwater to the nanofiltration to obtain a permeate and then subjecting the permeate to the chelation.
Such method(s), wherein the softened water is obtained by first subjecting the saltwater to the chelation to obtain an eluate and then subjecting the eluate to the nanofiltration.
Such method(s), wherein the softened water comprises calcium and magnesium in the range of 1-12.5 ppm and sulfate in the range of 6-75 ppm.
Such method(s), wherein the saltwater is prepared by mixing 5-25% wt/wt salt with water.
Such method(s), wherein the salt is obtained from seawater.
Such method(s), wherein the salt comprises 98-99% sodium chloride, 500-2000 ppm magnesium and calcium ions, 1500- 3000 ppm sulphate ions, and 200-500 ppm bromide.
Such method(s), wherein the saltwater is seawater.
Such method(s), wherein the chelation includes passing the permeate or the saltwater through a chelating resin.
Such method(s), wherein the chelating resin is a divalent cation selective resin.
Such method(s), wherein the nanofiltration includes passing the saltwater or the eluate through nanofiltration spiral membrane of 150-300 Da.
Such method(s), wherein the saltwater is subjected to a pretreatment prior to the nanofiltration and/or the chelation.
Such method(s), wherein the pretreatment is selected from the group consisting of sediment filtration, microfiltration, and gravitational filtration.
Such method(s), wherein the pH is adjusted in the range of 3.5-5.5 by adding hydrochloric acid.
Such method(s), wherein the high purity sodium chloride comprises calcium and magnesium ions in the range of 0.001-0.005 % w/w; sulphate in the range of 0.005-0.03 % w/w and bromide in the range of 0.001-0.01 % w/w.

FURTHER SPECIFIC EMBODIMENTS ARE DESCRIBED BELOW
A system for obtaining high purity sodium chloride, the system comprising: a nanofiltration unit comprising an inlet, one or more nanofiltration membrane(s) and an outlet; a chelation unit comprising an inlet, a chelating resin and an outlet; and an evaporation unit comprising one or more inlet(s), means for heating, and one or more outlet(s).
Such systems, wherein the nanofiltration unit is configured to receive saltwater from its inlet, pass the saltwater through the one or more nanofiltration membrane(s) to obtain a permeate and release the permeate from its outlet; and the chelation unit is configured to receive the permeate from its inlet, pass the permeate through the chelating resin to obtain a softened water, and release the softened water from its outlet.
Such systems, wherein the chelation unit is configured to receive saltwater from its inlet, pass the saltwater through the chelating resin to obtain an eluate and release the eluate from its outlet; and the nanofiltration unit is configured to receive the eluate from its inlet, pass the eluate through the one or more nanofiltration membrane(s) to obtain a softened water and release the softened water from its outlet.
Such systems, wherein the evaporation unit is configured to receive the softened water, sodium hypochlorite and hydrochloric acid from its one or more inlet(s); heat the mixture of the softened water, sodium hypochlorite and hydrochloric acid to evaporate water by the means for heating; and release water and bromine gas from its one or more outlet(s).
Such systems, wherein the softened water comprises calcium and magnesium in the range of 1-12.5 ppm and sulfate in the range of 6-75 ppm.
Such systems, wherein the system comprises a pretreatment unit configured to receive the saltwater and remove sediments and foreign particles before the saltwater is sent to the nanofiltration unit and/or the chelation unit.
Such systems, wherein the pretreatment unit comprises a sedimentation filtration unit, a microfiltration unit and/or a gravitation filtration unit.
Such systems, wherein the saltwater is prepared by mixing 5-25% wt/wt salt with water.
Such systems, wherein the salt is obtained from seawater.
Such systems, wherein the salt comprises 98-99% sodium chloride, 500-2000 ppm magnesium and calcium ions, 1500- 3000 ppm sulphate ions, and 200-500 ppm bromide.
Such systems, wherein the saltwater is seawater.
Such systems, wherein the chelating resin is a divalent cation selective resin.
Such systems, wherein the one or more nanofiltration membrane is a nanofiltration spiral membrane of 150-300 Da.

Such systems, wherein the high purity sodium chloride comprises calcium and magnesium ions in the range of 0.001-0.005% w/w; sulphate in the range of 0.005-0.03 % w/w and bromide in the range of 0.001-0.01 % w/w.
INDUSTRIAL APPLICABILITY
The present disclosure provides a simple, economical and efficient method for obtaining high purity sodium chloride. The high purity sodium chloride is IP grade and food grade. The high purity sodium chloride is suitable for cosmetics or personal care, pharmaceutical and food applications. The disclosed method also yields useful by-products, for example, sulfates, calcium, magnesium, and bromine gas, which can be recovered and used.