JP4273203B2 - Method for producing high purity sodium chloride - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing high-purity sodium chloride by selectively recovering sodium chloride using diffusion dialysis.
[0002]
[Prior art]
As a raw material for industrially producing sodium chloride, seawater, brine, raw salt, rock salt and the like are mainly used.
And in the natural seawater, for example, in addition to 10.5561 g of sodium ions per 1 kg, 1.2720 g of magnesium ions, 0.4001 g of calcium ions, 0.3800 g of potassium ions, 0.0133 g of strontium ions, As anions, hydrochloric acid ions (18.9799 g), sulfate ions (2.6486 g), and bicarbonate ions (0.1397 g) are contained.
[0003]
In general, when sodium chloride is produced from natural seawater, sodium chloride is first concentrated by electrodialysis using an ion exchange membrane, and the resulting sodium chloride concentrate is used as membrane brine or simply brine. However, in this brine, for example, 72.357 g of sodium ion, 1.734 g of calcium ion, 2.522 g of magnesium ion, 3.787 g of potassium ion, 125.113 g of hydrochloric acid ion, and 0.445 g of sulfate ion per liter. It is included.
[0004]
On the other hand, the ionic composition of the raw salt is based on mass, for example, 38.4% sodium ion, 0.05% calcium ion, 0.03% magnesium ion, 0.02% potassium ion, 59.3% hydrochloric acid ion, The ion composition of the rock salt is, based on mass, for example, 38.9% sodium ion, 0.02% calcium ion, 0.01% magnesium ion, 0.02% potassium ion, hydrochloric acid. Ion 60.0% and sulfate ion 0.12%.
[0005]
And, in the production of sodium chloride, if the removal of calcium ions present as impurities is insufficient, it combines with carbonate ions and sulfate ions to produce insoluble calcium carbonate and calcium sulfate, which reduces the quality of sodium chloride. Cause. If magnesium ions remain in the sodium chloride crystal before the drying step, magnesium chloride decomposes in the subsequent drying step to produce basic magnesium chloride and absorb carbon dioxide in the air into the sodium chloride crystal. Cause insoluble calcium carbonate.
[0006]
By the way, until now, in order to obtain sodium chloride crystals from seawater or dilute sodium chloride solutions such as brackish water, a method in which particles such as limestone, marble, calcite, etc. are contacted with this solution (see Patent Document 1) As a purification method of crude sodium chloride, a method is used in which particles of solar salt are sifted while flowing in saturated saline solution to remove a portion having a small particle size and a large amount of impurities (see Patent Document 2), contaminated with potassium chloride and sulfate ions. A method of adding a calcium compound to sodium chloride brine, precipitating and removing sulfate ions as calcium sulfate, and precipitating sodium chloride crystals from the remaining liquid has been proposed (see Patent Document 3).
[0007]
Furthermore, as a method of removing calcium ions and magnesium ions in sodium chloride derived from brackish water, raw salt, or rock salt, calcium ions are precipitated and removed as calcium carbonate with soda ash or caustic soda, and magnesium ions are removed from water. A method of precipitating and removing as magnesium oxide (see Non-Patent Document 1), adding a non-solvent to an aqueous solution to crystallize sodium chloride crystals, filtering off, dissolving in water again, repeating the same operation, and calcium A method for removing ions and magnesium ions is known.
[0008]
However, the method of treating with such chemicals has the disadvantage that a large-scale apparatus is required and a long time is required for treating a large amount of sodium chloride, and crystallization is not possible. The method of repeating involves energy consumption for each crystallization and is unavoidable to be expensive.
[0009]
On the other hand, sulfate ions present as impurity anions cause calcium sulfate to precipitate faster than sodium chloride in the crystallization process, adhere to the heated part of the evaporation tube, significantly reduce thermal conductivity, and inhibit productivity. At the same time, the calcium sulfate once adhered is peeled off and mixed into the sodium chloride crystal, causing a decrease in purity.
[0010]
In addition, as a method of removing sulfate ions in sodium chloride derived from brine, raw salt or rock salt, barium chloride is added and precipitated as barium sulfate and removed, but barium is a deleterious substance. In addition, use in large quantities is not preferable for health care and is therefore unsuitable for industrial implementation.
[0011]
Calcium sulfate caused by sulfate ions usually forms fine crystals and does not grow any more, so it exists as a suspension in an aqueous solution. And so far, the product sodium chloride crystal has been manufactured by removing gypsum fine crystals from sodium chloride crystal in the separation and dehydration step after crystallization. However, in this method, gypsum enters the crystallizer. However, it does not solve the decrease in productivity and the decrease in purity due to contamination with foreign matter.
[0012]
[Patent Document 1]
JP-A-53-91151 (Claims and others)
[Patent Document 2]
JP-A-8-119627 (Claims and others)
[Patent Document 3]
JP-T-2002-523330 (Claims and others)
[Non-Patent Document 1]
"Journal of the Seawater Society of Japan", Volume 47, 1993, p375-378.
[0013]
[Problems to be solved by the invention]
Under such circumstances, the present invention is present in the seawater, brackish water, raw salt or rock salt together with sodium chloride as a main component, and as impurities, magnesium ions and calcium ions which become obstacles in the production of sodium chloride, Alternatively, it is an object of the present invention to provide a method for producing high-purity sodium chloride by efficiently removing sulfate ions that generate insoluble matters such as gypsum.
[0014]
[Means for Solving the Problems]
The present inventors conducted extensive research to develop a method for efficiently removing magnesium ions, calcium ions, and sulfate ions forming gypsum present as impurity ions in seawater, brine, raw salt, or rock salt. As a result, when the aqueous solution of sodium chloride containing these impurity ions is subjected to diffusion dialysis, the monovalent ions pass through the dialysis membrane faster than the multivalent ions. Ions and hydrochloric acid ions can be separated from multivalent ions , and at this time, a mosaic charged membrane is used as a dialysis membrane, and the aqueous flow rate of sodium chloride containing impurity ions and deionized water are reduced to the former flow rate 5. When countercurrently to be flow as more than double, it found that sodium chloride coming selectively efflux the initial portion, based on this finding It has led to the completion of the present invention Te.
[0015]
That is, the present invention allows a high-concentration sodium chloride aqueous solution containing multivalent ions as contaminant ions to flow on one side of the diffusion dialysis membrane and deionized water to the other side, and Using the difference in diffusion rate, sodium ions and chloride ions are preferentially transferred to deionized water and separated from multivalent ions. five times more than the flow rate of the flow velocity of deionized water, causes a counter-current manner flow over time fractionated deionized water from the start dialysis, collecting the initial fraction, sodium chloride fraction thereof A method for producing high-purity sodium chloride, characterized in that is crystallized and recovered.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The method of the present invention removes polyvalent ions of impurities from sodium chloride using the behavior between ions specific to the diffusion dialysis membrane when a mosaic charged membrane is used as the diffusion dialysis membrane.
This diffusion dialysis membrane separates solutes that are uniformly dissolved in a solvent without applying a large pressure difference to both sides of the membrane, by simply contacting solutions with different solute concentrations on both sides of the membrane. can be separated more solutes species in the diffusion dialysis membrane, row a concentration gradient of the solute caused both interfaces of the membrane as the driving force, the separation by utilizing the difference in diffusion rate of solute moving in film I can .
[0017]
In the method of the present invention, a mosaic charged membrane having excellent separability against ions is used as the diffusion dialysis membrane .
As the high-concentration sodium chloride aqueous solution, it is preferable to use a sodium chloride aqueous solution having a concentration of usually 10% or more and a saturation concentration.
[0018]
Next, the method of the present invention will be described in more detail with reference to the accompanying drawings.
FIG. 1 is a system diagram of an apparatus suitable for carrying out the method of the present invention. A dialysis tank 1 is separated into a raw material liquid storage part 3 and a deionized water storage part 4 by a diffusion dialysis membrane 2. A sodium chloride aqueous solution, for example, a sodium chloride aqueous solution containing impurities is supplied from a brine tank 5 via a flow path switching valve 7 to the raw material liquid storage unit 3 through a flow switching valve 7. It is discharged to the reservoir 8.
On the other hand, deionized water is supplied to the deionized water storage unit 4 from the deionized water tank 9 by the water pump 10, contacts the diffusion dialysis membrane 2, and is collected by the fraction collector 11.
[0019]
In this case , a countercurrent dialysis method is used in the method of the present invention. That is, under normal pressure equilibrium dialysis, the equilibrium dialysis method, such as pressure equilibrium dialysis method, the resulting concentration of sodium chloride is below 50% of the raw material solution, the use of countercurrent dialysis, diffusion into the deionized water side Therefore, the concentration of sodium chloride obtained can be made higher than 50% of the raw material liquid . At this time, the higher the flow rate on the raw material solution, that is, the sodium chloride aqueous solution side, than the deionized water side, the higher the sodium chloride concentration after dialysis can be made. Therefore, the flow rate on the sodium chloride aqueous solution side is set to a range of 5 times or more, preferably 8 times or more, the flow rate on the deionized water side.
[0020]
In the process of the present invention, when the supply of the raw material liquid to the raw material liquid containing portion 3 continuously, concentrated sodium chloride fraction obtained by removing the magnesium ions and calcium ions and sulfate ions, a limited transmembrane initial ion Only part . However, the intermittent operation is advantageous because the initial amount can be obtained for each addition. In order to perform intermittently, the flow path switching valve 7 is switched to temporarily supply deionized water from the deionized water tank 12 to the raw material liquid storage unit 3.
[0021]
In the method of the present invention, as the diffusion dialysis membrane 2, a mosaic charged membrane in which a large number of pairs, preferably 20 to 100 pairs, are laminated via a spacer is used . When the concentrated sodium chloride aqueous solution is supplied to the raw material liquid storage unit 3 side of the diffusion dialysis membrane 2 and the deionized water is supplied countercurrently to the deionized water storage unit 4 side, the concentrated solution partitioned by the diffusion dialysis membrane 2 is used. Due to the difference in concentration of ions between the sodium chloride aqueous solution 3 side and the deionized water 4 side, ions diffusely move from the concentrated sodium chloride aqueous solution 3 side to the deionized water 4 side. At this time, a monovalent ion moves faster than an ion having a bivalent or higher valence. Therefore, sodium ions and hydrochloric acid ions, which are monovalent ions in sodium chloride, pass through the diffusion dialysis membrane 2 faster than polyvalent ions such as calcium ions, magnesium ions and sulfate ions, and move to the deionized water 4 side. To do. By utilizing the difference in the membrane permeation rate of ions, sodium chloride in a concentrated aqueous sodium chloride solution containing polyvalent ions such as calcium ions, magnesium ions, and sulfate ions as contaminant ions can be concentrated.
[0022]
As described above, the method of the present invention is a diffusion dialysis method and uses a difference in the concentration of ions, so there is no need for DC power to move ions as in electrodialysis, the running cost is low, and electrodialysis is performed. There is no drawback such as high cost due to the exchange of the ion exchange membrane. Furthermore, it has advantages such as simple equipment and easy maintenance.
[0023]
In the method of the present invention, high-purity sodium chloride crystals are recovered by crystallization from a sodium chloride aqueous solution from which contaminant ions have been removed by diffusion dialysis. For this crystallization, either an evaporation crystallization method or a reaction crystallization method may be used. As the non-solvent used in the reaction crystallization method, alcohols such as methyl alcohol, ethyl alcohol, and propyl alcohol are preferable.
[0024]
The high-purity sodium chloride obtained by the method of the present invention can take either liquid or solid form.
[0025]
【Example】
EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
[0026]
Example 1
TSD-10 type diffusion dialysis tank (manufactured by Tokuyama Corporation) as a diffusion dialysis membrane tank, mosaic charged membrane (manufactured by Dainichi Seika Co., Ltd., effective membrane area 10 dm ² / sheet, 50 sheets) as a diffusion dialysis membrane Pump, distilled water pump, brine tank, two distilled water tanks, salt solution (refers to the fraction where salt has diffused and moved into distilled water after passing through the diffusion dialysis membrane), fraction Using a device that includes a collector and a sample addition channel switching device to the sodium chloride solution (for example, brine) side, the calcium ion, magnesium ion, and sulfate ion in the approximately 20.6% sodium chloride aqueous solution (membrane brine) can be removed. went. The ion component composition of membrane brine used as the added sample is about 72.357 g / liter of sodium ions (corresponding to 35.1% of the total salt amount), about 1.734 g / liter of calcium ions (corresponding to 0.842%). About 2.522 g / liter of magnesium ion (corresponding to 1.22%), about 3.787 g / liter of potassium ion (corresponding to 1.84%), about 125.113 g / liter of hydrochloric acid ion (corresponding to 60.7%) ), Sulfate ion 0.445 g / liter (corresponding to 0.216%).
[0027]
By counter-current dialysis, the flow rate on the sodium chloride solution (membrane brine) side is set to 2.55 liters / minute, the flow rate on the distilled water side is set to 0.3 liters / minute, and the flow rate on the sodium chloride solution (membrane brine) side is set. The experiment was conducted at 8.5 times the flow rate on the distilled water side. First, connect the flow path switching device on the sodium chloride solution (membrane brine) side to the flow path where distilled water flows from the distilled water tank to the diffusion dialyzer, and supply distilled water with the sodium chloride solution (membrane brine) side feed pump. Liquid was sent. During the experiment, distilled water was continuously supplied from the distilled water tank to the distilled water side of the diffusion dialysis apparatus using a distilled water feed pump. Next, the channel switching device on the sodium chloride solution (membrane brine) side is switched to block the channel from which distilled water flows from the distilled water tank to the sodium chloride solution (membrane brine) side of the diffusion dialyzer, The sodium chloride solution (membrane brine) from the tank is connected to the sodium chloride solution (membrane brine) side of the diffusion dialyzer, and the sodium chloride solution (membrane brine) side feed pump is used to connect the sodium chloride solution (membrane brine). Membrane brine) was fed.
[0028]
A liquid (called salt solution) flowing out from the distilled water side of the diffusion dialysis apparatus was collected with a fraction collector with a fractionation time of one fraction being 10 minutes. Sorting of the salt solution fraction was started from the time when the flow path switching device was switched and the sodium chloride solution (membrane brine) began to be fed to the sodium chloride solution (membrane brine) side of the diffusion dialyzer. The sodium ion concentration, calcium ion concentration and magnesium ion concentration in the collected salt solution fraction were quantified by atomic absorption spectrometry. The sulfate ion concentration in the collected salt solution fraction was quantified by ion chromatography. At this time, the relationship between the salt solution fraction from the diffusion dialysis membrane and the concentration of each component (mg / liter) was determined. The concentration distribution curve thus obtained is shown in FIG. From this figure, it can be seen that calcium ions, magnesium ions, and sulfate ions in the aqueous sodium chloride solution (membrane brine) are removed in the early stage of diffusion dialysis.
[0029]
The salt solution fraction No. in the initial stage of diffusion dialysis was used. In No. 6, the sodium ion concentration was 47041 mg / liter, the calcium ion concentration was 352 mg / liter, the magnesium ion concentration was 486 mg / liter, and the sulfate ion concentration was 51.1 mg / liter. The salt solution fraction no. After 6 was concentrated with an evaporator, ethyl alcohol was added to precipitate sodium chloride crystals. The crystals were separated by filtration and dried to obtain high purity sodium chloride.
The sodium chloride crystals thus obtained were dissolved in water and analyzed by atomic absorption spectrometry as a 10% by mass aqueous solution. As a result, the calcium ion concentration was 23 mg / liter and the magnesium ion concentration was 9 mg / liter. From the above, according to the present invention, the sulfate ion concentration causing gypsum causing problems of production efficiency reduction and foreign matter contamination is reduced to 17.5% or less of the sulfate ion concentration (455 mg / liter) in brine. I know what I can do. Moreover, it turns out that the high purity sodium chloride which reduced calcium ion and magnesium ion by this invention is obtained.
[0030]
Comparative Example The membrane brine used in Example 1 was not subjected to diffusion dialysis, and ethyl alcohol was added in the same manner as in Example 1 to obtain sodium chloride crystals. The sodium chloride crystals thus obtained were dissolved in water and analyzed by atomic absorption spectrometry as a 10% by mass aqueous solution. As a result, the calcium ion concentration was 248 mg / liter and the magnesium ion concentration was 41 mg / liter. This value was found to be higher than that of the example.
[0031]
【The invention's effect】
According to the method of the present invention, when sodium chloride is produced, magnesium ion, calcium ion and sulfate ion, which are multivalent ions, are removed from sodium chloride by diffusion dialysis, and then crystallized from an aqueous solution to produce magnesium ion. And high-purity sodium chloride from which calcium ions have been removed can be obtained. Moreover, since the sodium chloride aqueous solution in which the sulfate ion is reduced to about 20% or less can be obtained after the diffusion dialysis process, generation of gypsum that causes a decrease in production efficiency and contamination with foreign substances can be suppressed.
[Brief description of the drawings]
FIG. 1 is a system diagram of an apparatus suitable for carrying out the method of the present invention.
FIG. 2 is a graph showing a concentration distribution curve of a salt solution fraction in Examples.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Dialysis tank 2 Diffusion dialysis membrane 3 Raw material liquid storage part 4 Deionized water storage part 5 Brine tank 6 Liquid feed pump 7 Flow path switching valve 8 Brine reservoir 9 Deionized water tank 10 Water supply pump 11 Fraction collector 12 Deionized water tank

Claims (3)

A high-concentration sodium chloride solution containing multivalent ions as contaminant ions is flowed to one side of the diffusion dialysis membrane and deionized water to the other side, and the difference in diffusion rate between monovalent ions and multivalent ions is used. In order to preferentially transfer sodium ions and chloride ions to deionized water and separate them from multivalent ions, a mosaic charged membrane is used as a diffusion dialysis membrane, and a high-concentration sodium chloride aqueous solution is used for the flow rate of deionized water. Flow countercurrently at a flow rate of 5 times or more, fractionate deionized water over time from the start of dialysis, collect the initial fraction, crystallize and collect sodium chloride from the fraction A method for producing high-purity sodium chloride characterized by the above. 2. The high purity according to claim 1 , wherein the initial fraction is a fraction having a lower content ratio of polyvalent ions to sodium in the fraction than a content ratio of polyvalent ions to sodium ions contained in the stock solution. A method for producing sodium chloride. Process for producing a high-purity sodium chloride according to claim 1, wherein the initial fractions the fraction collected in the range of 50 to 90 minutes from the start dialysis.

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