JPH0985060A - Desalting of salt-water containing scale forming component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a salt-water desalting method using an electrodialytic method capable of achieving a highly desalted water obtaining rate using salt- water containing a scale forming component, especially, calcium ions and sulfate ions. SOLUTION: When salt-water 12 containing a scale forming component is desalted by using an electrodialytic device 9 constituted by using a cation exchange membrane, an anion exchange membrane, an anode and a cathode as principal parts, seawater 13 is used as a conc. soln. to desalt salt-water 12.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a desalination method for removing ionic components from brine containing ionic components by electrodialysis (hereinafter referred to as ED).

[0002]

2. Description of the Related Art FIG. 2 is an explanatory view showing the principle of ED method brine desalination. A cation exchange membrane 1 (C) that selectively permeates cations (eg Na ⁺ ) and anions (eg Cl).
2) and an anion exchange membrane 2 (A) which selectively permeate ( ^- ) are arranged alternately as shown in FIG. 2, and a pair of anode 3 and cathode 4 are arranged at both ends thereof.

The anode 3 side is the anion exchange membrane 2 and the cathode 4 side is the cation exchange membrane 1, and the dilution chamber 5 is divided, and the anode 3 side is the cation exchange membrane 1 and the cathode 4 side is the anion exchange membrane 2. When the brine 7 and 8 are passed through the concentrated chambers 6 respectively and a DC voltage is applied between the anode 3 and the cathode 4 at both ends, the ionic components in the brine are electrophoresed as shown in FIG. Desalination of the salt occurs, and concentration of the salt occurs in the concentrating chamber 6. From this point of view, the liquid passing through the diluting chamber 5 is generally called the diluting liquid 7, and the liquid passing through the concentrating chamber 6 is called the condensing liquid 8.

Prevention of scale formation is extremely important for stable operation over a long period of time when desalting brine by using the ED method. When calcium salt, sulfate ion, phosphate ion, carbonate ion and other scale-forming components are contained in the brine, it prevents the generation of scale on the inside of the concentrating chamber 6, the surface of the ion-exchange membrane facing the concentrating chamber 6 and the inside of the ion-exchange membrane. It is a very important point technically. The prevention of scale deposition in the concentrating chamber 6 can be generally achieved by keeping the concentration of the scale-forming component in the concentrate 8 below the solubility of the scale. A general technique to prevent scale precipitation has not been established, and it is necessary to confirm it using actual equipment and brine.

However, in any case, the concentration of the scale-forming component in the concentrate 8 must be kept below the solubility of the scale. When demineralizing the brine by the ED method, in the prior art, since the diluting liquid 7 and the concentrating liquid 8 exclusively use the brine from the same brine source, the total amount of the brine used (A) is limited due to the solubility limitation. There was a limitation in increasing the ratio (B) / (A) ≡α of the deionized water acquisition amount (B) to

For example, chemistry and industry, 16 , NO. 6,9
0, (1963), total dissolved solids 1,450ppm,
Calcium ion concentration 208ppm, sulfate ion concentration 68
An example of desalting 3 ppm of underground brine by the ED method is introduced, but α = 57.1%. Also, industrial water, 136 ,
60, (1970) also introduces an example of desalination of underground brine by the ED method, where α = 88%. An example of seawater desalination by the ED method is introduced in Industrial Water, 239 , 80, (1978), but in this case, the brine is seawater, and the dilution water 7 and the concentrated water 8 are the same. Seawater, which is the source of the saltwater, is used, and α = 50 to 60%. In addition to this, there are many examples of desalination of brine by the ED method. However, when desalting brine other than those in foreign countries, there is no example of using seawater as the concentrate 8, and both of the dilution water 7 and the concentrate 8 are used. , Because we use the brine from the same source,
There was a constraint on the upper limit of.

On the other hand, in recent years, the concentration of nitrate nitrogen in groundwater has increased due to the effects of fertilization on agricultural plants and underground infiltration of livestock excrement for many years, and the number of cases where the drinking water standard value exceeds 10 ppm is increasing. As a particularly serious case, the problem of drinking water on a remote island located in the southern part of Japan is being highlighted. Many of these remote islands are rich in limestone geology, and their groundwater is not only contaminated with nitrate nitrogen, but also has the problem of high total dissolved solids concentration and high calcium hardness. . Moreover, the amount of brine itself is not abundant, and increasing the desalination water acquisition rate α is a very important need.

[0008]

The present invention has been made in view of the prior art as described above, and achieves a high demineralized water acquisition rate by using a brine containing scale-forming components, particularly calcium ions and sulfate ions. E if possible
It is an object of the present invention to provide a method for desalinizing brine by method D.

[0009]

[Means for Solving the Problems] As described above, it is generally easy to obtain seawater on many remote islands that have groundwater problems such as high nitrate nitrogen and total dissolved solids and high calcium hardness. . It was also known that the solubility of sparingly soluble salts in seawater, especially calcium sulfate, is generally higher than that in pure water, but it contains a scale-forming component, especially calcium ion and sulfate ion, as a diluent. It was unknown whether or not highly desalinated water could be obtained in the system that used salt water and seawater as the concentrate without the above-mentioned scale formation troubles.

The present inventor, as will be described in detail in the examples below,
As a result of earnest studies, it was found that by using seawater as a concentrate, valuable brine can be converted to desalted water without waste, and the present invention has been completed.

That is, the present invention uses an electrodialyzer composed mainly of a cation exchange membrane, an anion exchange membrane, an anode and a cathode as a concentrated liquid when desalting brine containing scale-forming components. The present invention relates to a desalination method of brine, which is characterized by using seawater.

Since the present invention uses seawater as a concentrated liquid, it is possible to limit the existence of infinite seawater without wasting valuable brine as compared with the prior art in which brine from the same brine source is used as a concentrated liquid. In addition to having the advantage that the purpose can be achieved by using, in the case of brine having a bicarbonate ion concentration higher than that of seawater, as compared with the prior art,
It also has the economic advantage of reducing the amount of acid used for adjusting the pH of the concentrate as a secondary effect.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic diagram and flow sheet of an apparatus for explaining an embodiment of the present invention. An embodiment will be described below with reference to FIG.

(Embodiment 1) The ED electrodialyzer 9 has an effective energization area of 236 mm (length) x 220 mm (width) x 0.2 mm.
It consists of 50 pairs of (thick) anion / cation exchange membrane, one pair of anode (platinum-plated titanium plate) and cathode (stainless steel plate), and the ion exchange membrane is ACIPLE manufactured by Asahi Kasei Corporation.
X (trade name) A-201 and K-101 are used. In FIG. 1, 50 dilution chambers are collectively shown as D,
The 51 concentrating chambers are collectively labeled as C. 10 and 11 are a diluting liquid circulating tank and a concentrate circulating tank, respectively, and their capacities are 50 L and 20 L, respectively. Boiled water 12 and concentrated liquid circulation tank 11 are placed in the diluted liquid circulation tank 10.
The seawater 13 is made up by a diaphragm type metering pump (not shown in FIG. 1). Further, a mineral acid 14 for pH adjustment is added to the concentrated liquid circulation tank 11.

Brine water having the composition and concentration shown in Table 1 is used as the diluent, and seawater having the composition and concentration shown in Table 2 is used as the concentrate.
The operation was performed under the conditions shown in Table 3.

[0016]

[Table 1]

[0017]

[Table 2]

[0018]

[Table 3]

Seawater was passed through the anode chamber 17 containing the anode at a rate of 2 liters / minute, and the liquid passing through the anode chamber was discharged to the outside of the apparatus. Also, the cathode chamber 18 in which the cathode is stored
For this, brine is circulated at a rate of 2 liters / minute with the pH adjusted to 2.0 with hydrochloric acid, and the pH is adjusted to 2.0 while adding diluted acid during operation.
Adjusted to ± 0.2. The operation is performed by the overflow liquid 15 from the diluent circulating tank 10 and the concentrate circulating tank 1
After the composition and concentration of overflow liquid 16 from No. 1 became constant, it was continued for another 72 hours. Table 4 shows the compositions and concentrations of the overflow liquids 15 and 16 after 72 hours have passed.

[0020]

[Table 4]

The current efficiency of desalting was 80.1%.
After the operation was completed, the ED device was disassembled and inspected, and no abnormality such as scale deposition was found. The deionized water acquisition rate α in this example was about 100% within the error range of the measurement.

(Example 2) Brine water having the composition and concentration shown in Table 5 was used as the diluting solution, and seawater having the composition shown in Table 2 was used as the concentrating solution, and the operation was carried out under the conditions shown in Table 6. Other conditions were the same as in Example 1. Table 7 shows the composition and concentration of the obtained overflow liquid.

[0023]

[Table 5]

[0024]

[Table 6]

[0025]

[Table 7]

The current efficiency of desalting was 81.1%.
After the operation was completed, the ED device was disassembled and inspected, and no abnormality such as scale deposition was found. The deionized water acquisition rate α in this example was about 100% within the error range of the measurement.

Comparative Example 1 Boiled water having the composition and concentration shown in Table 1 was used for both the diluted solution and the concentrated solution, and the operation was performed under the conditions shown in Table 8. Other conditions were the same as in Example 1. Table 9 shows the composition and concentration of the obtained overflow liquid.

[0028]

[Table 8]

[0029]

[Table 9]

The current efficiency of desalting was 85.8%.
After the operation was completed, the ED device was disassembled and inspected, and no abnormality such as scale deposition was found. The desalinated water acquisition rate α in this comparative example was 80.2%.

(Comparative Example 2) The operation was performed under the same conditions as in Comparative Example 1 except that the amount of the concentrated solution makeup 13 was 0.32 liters / minute and the current value was 0.81 amperes.
Table 10 shows the composition and concentration of the obtained overflow liquid.

[0032]

[Table 10]

The current efficiency of desalting was 83.6%.
Further, after the operation was completed, the ED device was disassembled and inspected, and scale deposits of calcium sulfate were found in a total of 18 places inside the concentration chamber, on the surface of the ion exchange membrane, and inside the ion exchange membrane. The desalinated water acquisition rate α in this comparative example was 82.4%.

(Comparative Example 3) Using brine having the composition and concentration shown in Table 5, operation was carried out under the conditions shown in Table 11. Other conditions were the same as in Example 1. Table 12 shows the composition and concentration of the obtained overflow liquid.

[0035]

[Table 11]

[0036]

[Table 12]

The current efficiency of desalting was 84.0%.
Further, when the ED device was disassembled and inspected after the operation was completed, calcium sulfate scale deposition was found in a total of 13 places inside the concentration chamber, inside the ion exchange membrane, and inside the ion exchange membrane. The deionized water acquisition rate α in this comparative example was 75.6%.

In Comparative Example 1, although no abnormalities such as scale formation were found, only a demineralized water acquisition rate of 80.2% was obtained. In Comparative Example 2, it was observed that the scale was generated although the operation was performed at a desalination water acquisition rate as high as 82.4%.

That is, in the case of desalting brine having the composition and concentration shown in Table 1, in order to be able to operate without scale formation in the prior art, the desalinated water acquisition rate must be kept to 80.2 to 82.4% or less. I won't. On the other hand, in Example 1, although a smaller amount of concentrated liquid make-up was used than in Comparative Examples 1 and 2, there was no scale formation, and operation was possible with a demineralized water acquisition rate of about 100%. there were. The same can be said when comparing Comparative Example 3 and Example 2.

[0040]

As described in detail above, according to the present invention, when desalting brine containing scale-forming components, particularly calcium ions and sulfate ions by the ED method, almost all of the brine used is converted to desalinated water. It becomes possible.

[Brief description of drawings]

FIG. 1 is a schematic diagram and a flow sheet of an apparatus for explaining an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the principle of ED method brine desalination.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Cation exchange membrane 2 ... Anion exchange membrane 3 ... Anode 4 ... Cathode 5 ... Diluting chamber 6 ... Concentration chamber 7 ... Brine water (diluting liquid) 8 ... Brine water (concentrating liquid) 9 ... Electrodialysis device 10 ... Diluting liquid circulation Tank 11 ... Concentrated liquid circulation tank 12 ... Brine water 13 ... Seawater 14 ... Mineral acid 15 ... Overflow liquid 16 ... Overflow liquid 17 ... Anode chamber 18 ... Cathode chamber

Claims (2)

[Claims] 1. A concentrated solution for desalting brine other than seawater containing scale-forming components by using an electrodialyzer composed mainly of a cation exchange membrane, an anion exchange membrane, an anode and a cathode. A method for desalinating brine, which comprises using seawater as the water. 2. The desalting method according to claim 1, wherein the scale-forming component is calcium ion and sulfate ion.