JPH10251014A - Method for removing sulfate ion in aqueous alkali metallic chloride solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove sulfate ions in an aq. alkali metallic chloride soln. at a low cost of equipment without causing deterioration to a slurried state or requiring a special filter for solid-liq. separation and its maintenance by using coarse zirconium hydroxide as a sulfate ion adsorbent in a fixed bed system. SOLUTION: When sulfate ions in an aq. alkali metallic chloride soln. are adsorbed and removed with zirconium hydroxide, fine powdery zirconium hydroxide is granulated to 0.1-3mm diameter with a proper binder and the granulated zirconium hydroxide is used as an adsorbent in a fixed bed system. In a process for adsorbing and removing sulfate ions, the alkali metallic chloride soln. is adjusted to pH1-3 and fed at 3-30hr<-1> space velocity. In a process for desorbing the adsorbed sulfate ions, an aq. alkali soln. for desorption is adjusted to pH10-13 and fed at 3-30hr<-1> space velocity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing sulfate ions from an alkali metal chloride aqueous solution, and more particularly, to economically and efficiently removing sulfate ions from an alkali metal chloride aqueous solution using zirconium hydroxide. On how to do it. INDUSTRIAL APPLICABILITY The present invention can be very suitably applied particularly to removal of sulfate ions, which are impurities in salt water in ion exchange membrane method salt electrolysis.

[0002]

2. Description of the Related Art As a method for removing sulfate ions from an aqueous alkali metal chloride solution, there is a barium salt method and the like. However, such a method is problematic in that raw materials are toxic and expensive, solid industrial waste treatment and cost increase. For this reason, various alternative methods have been studied. For example, a method of using zirconium hydroxide to adsorb acidic and desorb alkaline has been proposed and put into practical use (Japanese Patent Publication No. 6-2).
1032). This method has a particle diameter of 1 to 20 μm and a water content of 3
This is a method in which ４０40% by weight of zirconium hydroxide is sequentially brought into contact with salt water containing acidic sulfate ions and alkaline water in a slurry state, and sulfate ions can be removed very economically and effectively with a small amount of adsorbent. Further, a method has been proposed in which a macroporous cation exchange resin carrying a polymerized zirconium hydrate is used to adsorb acidicly and desorb it alkalinely (JP-A-60-4403).
6).

[0003]

[Problems to be solved by the invention]
The method proposed in US Pat.
In order to use fine zirconium hydroxide of 0 μm,
Since a special filtration device using a fine filter cloth is used for solid-liquid separation after the salt water treatment, maintenance work such as replacement of the filter cloth is required, and the equipment becomes expensive. Further, the method proposed in Japanese Patent Application Laid-Open No. 60-44056 discloses a method in which a macroporous cation exchange resin supporting a polymerized zirconium hydrate has a low sulfate ion adsorption capacity of less than 20 g / liter-cation exchange resin. In addition, there is a problem that the equipment becomes large.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that the particle diameter is 0.1 to 0.1.
The present inventors have found a method of using 3 mm of zirconium hydroxide as an adsorbent in a fixed state without substantially flowing and stirring, and reached the present invention. In other words, the present invention uses zirconium hydroxide having a particle diameter of 0.1 to 3 mm as an adsorbent when zirconium hydroxide is used to adsorb and remove sulfate ions in an alkali metal chloride aqueous solution. The method includes a method for removing sulfate ions, which is characterized by using a fixed bed method. In a preferred embodiment of the present invention, the pH of the aqueous alkali metal chloride solution in the adsorption step of adsorbing and removing sulfate ions from the aqueous alkali metal chloride solution is adjusted to 1 to 3 and a reaction space velocity SV.
In the range of 3 to 30 Hr ^-1 , the pH of the alkaline water in the desorption step of desorbing the sulfate ions adsorbed by the adsorbent from the adsorbent is 10 to 13, and the reaction space velocity SV is 3 to 30 hr.
It is controlled within the range of 30 hr- ¹ .

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the drawings. FIG. 1 shows an example of an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an acid- and alkali-resistant reaction tower, for example, a rubber-lined vessel. In the reaction tower 1, granular zirconium hydroxide as a sulfate ion adsorbent is charged. Salt water 4 containing sulfate ions is added to the pH adjusting tank 2 and adjusted to a predetermined acidic pH with hydrochloric acid 5 and then introduced into the reaction tower 1 at a predetermined flow rate to carry out the adsorption reaction in a one-pass system, a circulation system or a partial recycling system. And adsorb the sulfate ions to the adsorbent. The salt water removed by adsorbing all or a part of the adsorbed ions to the adsorbent is taken out from the outlet 1
Extract from 0. Subsequently, water 6 is introduced into the reaction tower 1 to wash the adsorbent, salts and the like adhering to the adsorbent are removed, and the washed water is extracted from the outlet 9.

Next, the sulfate ions adsorbed by the adsorbent are desorbed. That is, water 8 is added to the pH adjusting tank 3 and adjusted to a predetermined alkaline pH with sodium hydroxide 7, then introduced into the reaction tower 1 at a predetermined flow rate, and the desorption reaction is carried out in a one-pass system and a circulation system. Desorb sulfate ions from Water containing sulfate ions is extracted from the extraction port 11. Thereafter, water 6 is introduced into the reaction tower 1 to wash the adsorbent, alkalis, sulfate ions and the like adhering to the adsorbent are removed, and the washed water is extracted from the outlet 9. Less than,
The above adsorption / desorption operation is repeated.

[0007] The concentration of the alkali metal chloride is not particularly limited, and sulfate ions in a concentrated aqueous solution, for example, a saline solution of about 5 mol / liter can be efficiently removed. There is no particular limitation on the sulfate ion concentration,
For example, a solution having a concentration of about 0.1 to 20 g / liter can be treated, and the temperature is not particularly limited.

As the adsorbent, zirconium hydroxide (also called hydrated zirconium oxide) is used. ZrO in chemical formula
Compounds represented by (OH) ₂ .nH ₂ O (n = 0.5 to 3.0) are particularly preferred. 1000 ° C dry weight loss is 50-6
It is about 0%. The present compound is usually in the form of a fine powder of about 10 μm, and this powder is mixed with a suitable binder to a particle size of 0.1 to 0.1 μm.
It is granulated to 3.0 mm, preferably 0.5 to 2 mm and used in the present invention. When the particle size is less than 0.1 mm, the material is easily fluidized, deteriorates to a slurry state, cannot be easily separated into solid and liquid after salt water treatment, requires a special filtration device, and is difficult to maintain and reuse. On the other hand, if it exceeds 3.0 mm, the ability to adsorb sulfate ions decreases.

The adsorption reaction is carried out under acidic conditions, and the lower the pH, the larger the adsorption capacity. Under extremely low pH conditions, the dissolution of the adsorbent starts, and at a high pH, the adsorptive capacity decreases, which is not preferable. Therefore, the range of pH 1 to 3 is preferable. The required amount of acid follows the following reaction formula. ZrO (OH) ₂ + 2H
⁺ + SO ₄ ^2- → ZrOSO ₄ + 2H ₂ O The adsorption capacity depends on the particle size of the adsorbent, but within the particle size range of the present invention, for example, 1 kg at pH 2
Can adsorb 20 to 50 g of sulfate ions. The reaction space velocity SV is preferably 3 to 30 Hr ^-1 ,
More preferably, it is in the range of 5 to 30 Hr- ¹ . If it is less than 3 Hr ^-1 , the treatment speed is slow and inefficient, while if it exceeds 30 Hr ^-1 , the adsorptive capacity is undesirably reduced. The reaction can be suitably performed at a temperature ranging from room temperature to about 90 ° C. as described above. If the temperature exceeds 90 ° C., the adsorbent is easily crushed, which is not preferable.

[0010] A desorption reaction for desorbing sulfate ions from the adsorbent having adsorbed sulfate ions is carried out by bringing the adsorbent into contact with an alkaline aqueous solution, whereby the adsorbent releases sulfate ions, and the sulfate ions are released again. Regenerated to a form that can be adsorbed. ZrOSO ₄ + 2NaOH → ZrO (OH) ₂ + 2Na ⁺
+ SO ₄ ^2-A suitable pH is in the range of 10-13 and a suitable reaction space velocity SV is in the range of 3-30 Hr- ¹ . When the pH is lower than 10, the reaction is slow, and when the pH is higher than 13, alkali tends to be wasted. If the reaction space velocity is less than 3 Hr ^-1 , the treatment speed is slow and inefficient, while if it exceeds 30 Hr ^-1 , the desorption ability is undesirably reduced. Suitable temperatures range from room temperature to 90 ° C. When the temperature exceeds 90 ° C., as described above, the adsorbent is easily crushed, which is not preferable.

As described above, the adsorbent used in the present invention has a risk of dissolution at a pH of less than 1. On the other hand, the adsorption capacity increases as the pH decreases. As a method of solving this conflicting condition setting, a method of partially recirculating the salt water from which the sulfate ions have been removed by adsorption to the inlet of the reaction tower is preferable. According to this method, even at the same pH, the ratio of the hydrogen ion concentration to the sulfate ion concentration can be increased, and as a result, the sulfate ion removal rate can be increased. 0 to 80% of the salt water flowing out of the reaction tower can be recycled. Recirculation beyond this would make the SV too large and impractical.

[0012]

EXAMPLES Hereinafter, the present invention will be described more specifically based on examples, but the present invention is not limited to these examples. In the following Examples and Comparative Examples, the apparatus shown in FIG. 1 was used. Example 1 About 5 liters of brine 4 containing sulfate ions was supplied to the pH adjusting tank 2 from the outlet of the electrolytic cell in the salt electrolysis step of the ion exchange membrane method. The NaCl concentration of the salt water was 201 g / liter, and the SO ₄ ²⁻ concentration was 5.5 g / liter. 0.11 mol / of hydrochloric acid 5
Add 1 liter and control the pH in the pH adjustment tank 2 to 1.
2.5 l / hr was introduced into the reaction tower 1 which was previously filled with 500 g (500 ml) of an adsorbent having a particle size of 1.25 mm, which had been washed with alkaline water and changed to an alkaline type.
The solution was subjected to a one-pass treatment at 、 60 ° C., and the salt water from which the sulfate ions had been adsorbed and removed was discharged from the outlet 10. After the end of the adsorption reaction,
The salt water remaining in the reaction tower 1 is withdrawn from the outlet 9, water 6 is introduced into the reaction tower 1 to wash the adsorbent, and the outlet 9.
I extracted more.

Next, 5 liters of water 8 was added to the pH adjusting tank 3 and 0.22 mol / liter of sodium hydroxide 7 was added to control the pH in the pH adjusting tank 3 to 13 so that the reaction column 1
At a rate of 1.8 liter / Hr, and the room temperature (15
-20 ° C.), and the water containing the desorbed sulfate ions was drained from the outlet 11. After the completion of the desorption reaction, the remaining water in the reaction tower 1 was withdrawn from the outlet 9, water 6 was introduced into the reaction tower 1 to wash the adsorbent, and withdrawn from the outlet 9. Table 1 shows the analytical values of each sulfate ion.
As shown in Table 2.

[0014]

[Table 1] As is clear from Table 1, the removal rate was 73%, and the dissolution of the adsorbent was extremely small.

[0015]

[Table 2] As is apparent from Table 2, the desorption rate was 92% and the dissolution of the adsorbent was small.

Example 2 In Example 2, an adsorption reaction was carried out by a circulation system in which the treated salt water from which sulfate ions had been removed by 1 kg (1 liter) of the adsorbent was returned to the pH adjusting tank 2 again. The amount of test salt water was 7.8 liters, and the flow rate was 21.6 liters / Hr.
The pH in the pH adjusting tank 2 was controlled to 1.5 with hydrochloric acid 5, and the adsorption reaction temperature was 50 to 60 ° C.

The desorption reaction was carried out by a circulation system in the same manner as the adsorption reaction. The amount of alkaline water is 5.0 liters, and the flow rate is 21.6 liters / Hr as in the adsorption reaction conditions.
And In addition, the pH adjustment tank 3 is controlled by sodium hydroxide 7.
PH is controlled to 13 and the desorption reaction temperature is 50-60 ° C
And

[0018]

[Table 3] As is clear from Table 3, when the removal rate was 82% and the pH, which is the adsorption reaction condition, was controlled at 1.5, there was no dissolution of the adsorbent.

[0019]

[Table 4] As is clear from Table 4, the desorption rate was 86%, and the adsorbent did not dissolve at all.

Example 3 In Example 3, an adsorption reaction was performed as a partial recycling method in which only a fixed amount of the treated salt water from which sulfate ions had been removed by 1 kg (1 liter) of the adsorbent was returned to the pH adjustment tank 2 again. The flow rate of the test salt water was 3.3 liters / Hr, and the flow rate of partly recycled was 6.7 liters / Hr. The pH at the inlet of the reaction tower was controlled to 1.5 with hydrochloric acid 5, and the adsorption reaction temperature was 50 to 60 ° C.

A desorption reaction was carried out in the same manner as in Example 2 using a circulation system. However, the flow rate of the test alkaline water was 5 liter / Hr. The pH in the pH adjusting tank 3 was controlled to 13 with sodium hydroxide 7, and the desorption reaction temperature was set to room temperature (10 to 20 ° C).

[0022]

[Table 5] As is clear from Table 5, the removal rate was 61%, and the dissolution of the adsorbent was small.

[0023]

[Table 6] As is clear from Table 6, the desorption rate was 86% and the adsorbent was not dissolved at all.

Example 4 An adsorption reaction was carried out in the same manner as in Example 1.
However, the test salt water flow rate was 20.0 liter / Hr.
Also, 0.15 mol / l of hydrochloric acid 5 was added to control the pH in the pH adjusting tank 2 to 0.8.

An adsorption reaction was performed in the same manner as in Example 1. However, the test alkaline water flow rate was 20.0 liter / Hr. In addition, sodium hydroxide 7
The pH in the H adjustment tank 3 was controlled at 9.

[0026]

[Table 7] As is clear from Table 7, the adsorbent had a reduced ability to adsorb sulfate ions, and dissolution of the adsorbent was observed.

[0027]

[Table 8] As is clear from Table 8, the desorption rate also decreased.

Comparative Example 1 Using an adsorbent having a particle diameter of 0.01 mm, an adsorption reaction was carried out in the same manner as in Example 1. However, the flow rate of the test salt water was 3.9 liter / Hr. Also, hydrochloric acid 5 was added to 0.1
The pH in the pH adjustment tank 2 was controlled to 1 by adding 3 mol / l.

[0029]

[Table 9] As is clear from Table 9, the dissolution of the adsorbent was remarkable, and the adsorbent deteriorated to a slurry state and could not be reused.

Comparative Example 2 Using an adsorbent having a particle diameter of 5.0 mm, an adsorption reaction was carried out in the same manner as in Example 1. However, the flow rate of the test salt water was 3.9 liter / Hr. Also, hydrochloric acid 5 was added to 0.1
The pH in the pH adjustment tank 2 was controlled to 1 by adding 3 mol / l.

[0031]

[Table 10] As is apparent from Table 10, almost no sulfate ion adsorption ability of the adsorbent was recognized.

[0032]

As described above, the present invention provides a large particle size water having a particle size of 0.1 to 3 mm instead of the conventionally used sulfate ion adsorbent (zirconium hydroxide having a particle size of 1 to 20 μm). By using zirconium oxide and using a fixed bed method, there is no deterioration to the slurry state, special filtration equipment using filter cloth for solid-liquid separation in the conventional method, maintenance work associated with the filtration equipment and No stirring equipment is required, and reuse is easy. In addition, the facility cost is greatly reduced, and its usefulness is extremely large.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of an apparatus used to carry out the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Reaction tank 2 pH adjustment tank 3 pH adjustment tank 4 Sulfate ion-containing salt water 5 Hydrochloric acid 6 Water 7 Sodium hydroxide 8 Water 9 Extraction port of washing water containing residual saline or sulfate ion 10 Extraction port of salt water after removal of sulfate ion adsorption 11 Water outlet containing desorbed sulfate ions

Continued on the front page (72) Inventor Motoyoshi Yoshino 608-259 Kamiyoshi, Higashikamiyoshicho, Kakogawa, Hyogo (72) Inventor Koji Saiki 4-6-1-815 Hojo-cho, Toyonaka-shi, Osaka

Claims (3)

[Claims] 1. A method for adsorbing and removing sulfate ions in an aqueous alkali metal chloride solution using zirconium hydroxide,
A method for removing sulfate ions, wherein zirconium hydroxide having a particle diameter of 0.1 to 3 mm is used as an adsorbent and zirconium hydroxide is used in a fixed bed system. 2. The pH of the aqueous alkali metal chloride solution and the reaction space velocity SV of 3 to 3 in the adsorption step of adsorbing and removing sulfate ions from the aqueous alkali metal chloride solution.
Controlled in the range of 30Hr ^-1, 3~30Hr the pH to 10-13 and the reaction space velocity SV of alkaline water in the desorption step of desorbing sulfate ions adsorbed on the adsorbent from the adsorbent
^{2. The} method for removing sulfate ions according to claim 1, wherein the control is performed within a range of ^-1 . 3. The method for removing sulfate ions according to claim 1, wherein in the adsorption step, a part of the alkali metal chloride aqueous solution from which the sulfate ions have been adsorbed and removed is recycled to the inlet of the adsorption step.