JPS593405B2 - Salt water purification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying salt water in which impurities in raw salt are removed using a packed bed of adsorbent.

As a method for purifying salt water, for example, in alkaline chloride electrolysis, a method of sedimentation and removal of impurities using a purifying agent is conventionally used.

In other words, the large amounts of magnesium and calcium contained in the raw salt are removed by precipitation as magnesium hydroxide and calcium carbonate using an alkaline agent, and the heavy metals contained in trace amounts are removed, for example, by co-precipitation in iron chloride. It is being said.

However, with this method, the production sedimentation rate is slow,
In addition, since the nature of most of the precipitates is permeable, supernatant liquid separation is usually performed, which inevitably leads to the risk of contamination with precipitates, and the filtration of these precipitates is difficult, so they are used only partially. It's nothing more than that.

The continuous purification method that is commonly used today involves adding an alkaline agent while flowing unpurified brine, and continuously removing the supernatant liquid.

However, with this method, impurities are often mixed into the supernatant liquid due to convection phenomena caused by changes in outside temperature or slight differences in the specific gravity of salt water, so the supernatant liquid is further passed through a sand filter layer, etc. needs to be removed.

Even in this method, the flow rate of the salt water is limited to about 1 m/hr or less because the sedimentation rate of the formed precipitate is slow.

Therefore, the amount of accumulated salt water in the total circulation becomes enormous.

Therefore, large-capacity sedimentation tanks, filtration tanks, alkali purification tanks, and other equipment are required.

The present invention is intended to solve the above problems,
That is, raw salt-dissolved brine is added to a packed bed made of a chelate-forming water-insoluble resin that can form an intramolecular complex with magnesium and calcium selected from the group A below and has an N-CH2C0OH group at a space velocity of 20 hr or less and pH ,3~
This salt water purification method is characterized by removing magnesium and calcium from the salt water by adjusting the voltage of 10 Vc and passing the solution through the salt water.

However, A represents a styrene-butadiene copolymer, an epichlorohydrin polymer, an N-phenylglycine-glycidyl methacrylate copolymer, or a styrene-divinylbenzene copolymer.

It is known that a chelate resin obtained by adding iminodiacetic acid to a styrene-divinylbenzene copolymer has a higher affinity for alkaline earth metal ions than for alkali metal ions.

(Hidetake Kakihana: Kozo Narita ed. [Latest Ion Exchange JP, 23-
24°1960).

Also, a method has been reported for separating and quantifying magnesium and calcium from a concentrated salt solution using a polyamine acetic acid type chelate resin.

(“Analytical Chemistry” Journal of the Japanese Society of Analytical Chemistry, Vol. 7゜No.
9, F, 565-568).

There is no disclosure of the technology and industrial advantages of purifying a large amount of raw salt-dissolved brine using a packed bed method.

The particle size of the chelate-forming water-soluble resin (hereinafter referred to as chelate resin) is about 10 to 60 mesh.

The salt water after dissolving the raw salt is brought into contact with the packed bed of these chelate resins, and the space velocity is H20hr.
The following are suitable, and the pH of the salt water is preferably in the range of 3 to 10.

As shown in the experimental examples below, these chelate resins are far superior in their ability to adsorb calcium and magnesium compared to ordinary 54C ion exchange resins.

Moreover, its activity does not decrease even after long-term use.

That is, cation exchange resins useful for softening hard water have an effect of removing calcium and magnesium in concentrated salt water that is only about 1>10 or less than that of chelate resins.

Furthermore, the above-mentioned chelate resin is relatively easy to regenerate, and methods such as passing a mineral acid solution through a packed bed after use to elute impurities and washing it with a weakly alkaline solution are used.

Since the method of the present invention uses an impurity adsorption operation using a packed bed instead of impurity sedimentation removal using an alkaline agent, various steps and equipment such as a sedimentation tank, an alkaline purification agent tank, and an operation for recovering salt from the sediment can be omitted. Vine.

That is, the first feature of the method of the present invention is that by adsorbing and removing impurities in salt water through a chemical reaction, it has the significant effect of greatly reducing the size of salt water equipment.

Furthermore, in the conventional method, due to the slow settling speed i of the impurity precipitate as described above, a huge amount of circulating salt water remained, but according to the method of the present invention, only the flowing contact of the packed bed is performed. Therefore, it is possible to reduce the retention amount to approximately 1/10 of that of the conventional method.

Furthermore, such a reduction in residence time prevents a decrease in the temperature of the circulating salt water and suppresses an increase in electrolysis voltage.

The second major advantage of the method of the present invention is that by employing such a chemical adsorption method, the magnesium content, which has a particularly acute effect on electrolytic results, can be further reduced than in conventional methods or ion exchange resin adsorption methods. .

Another advantage of the process of the invention is that, as with conventional processes, an alkaline agent is used as a refining agent to increase the actual product yield of ceric or caustic.

In the alkaline salt electrolysis process, only about 10 to 15 parts of the alkali content in the salt water is decomposed in the electrolytic cell, so the remaining 85 to 15 parts
Because 90% of the alkali chloride is recycled, the flow rate is enormous, and unlike conventional methods, magnesium hydroxide,
In order to sufficiently precipitate calcium carbonate, it is necessary to add a large excess of caustic alkali and alkali carbonate than the equivalent amount of VC hamagnesium and calcium, and the excess amount is completely wasted, and the amount is considerable. 1 to 1 of the production volume of caustic alkali, which is the target product.
Since the second stage is consumed for the above-mentioned magsasilum precipitation, the product that can actually be obtained is 98 to 99% of the production amount.

It goes without saying that an equivalent amount of hydrochloric acid is required to neutralize such excess caustic alkali.

In the case of the method of the present invention, there is no need to add such a purifying agent, so that the yield can be substantially increased.

In addition, in the conventional method, alkali carbonate is used as one of the alkaline refining agents to remove calcium as calcium carbonate, but during refining, the excess carbonate gets into the brine after purification, and it is stored in the electrolytic bath. It becomes carbon dioxide gas and is included in the generated chlorine gas, reducing the purity of the chlorine gas.

According to the method of the present invention, since there is no need to add alkali carbonate, there is no fear that the purity of chlorine gas will decrease due to carbon dioxide gas caused by the purifying agent.

It is of course possible to use the salt water purification process in the method of the present invention in series or in parallel with a salt water purification process using a conventional sedimentation method.

Experimental example A column packed with each of the following resins (diameter 30 mm, height 6
00mm) with saline solution (NaC1280?/1..

Ca 8.6"?/-1sMf? 1.9"@/4
pH 10.2) was passed through the solution at a space velocity of 15 hr', and the impurity concentration after passing was measured.

Resin A: Chelate resin having an epichlorohydrin polymer as a base material and iminodiacetic acid groups (particle size: 20-50 mesh) Resin B: Strongly acidic cation exchange resin (Amberlite IR-120) Resin C: Weakly acidic Cation exchange resin (Amberlite IRC-84) Example 1. Raw salt saturated brine (NaC 7310 fl/Z 2M?
50"fl/Z z Ca 250"li'/
Z) was adjusted to pH 5.5 and allowed to flow down at a rate of 3 m3/hr (space velocity 15 hr-1), and the MV Hao in the purified brine after passing through was 7772! // t t C
a was 1.2772p/A.

Comparative Example 1 The raw salt saturated brine used in Example iK was adjusted to pH 10.4 by adding caustic soda and soda carbonate, and allowed to stand to settle the formed precipitate. When the supernatant liquid was filtered, the result was MPu 3.4-/1.
) Can5.8~/, l.

Example 2 A chelate resin having 10 to 50 meshes of styrene-butadiene copolymer as a base material and having iminodiacetic acid groups was placed in the same column as in Example 1 for 200 meshes. - Filled with raw salt (potassium chloride) saturated brine CKCt 340? /l.

MV 36wt, Ca 270mfl/i) p
Adjust to H6, 2rn”/hr (space velocity 10hr-t
), the M2 in the sugar brine after passing through was
It became 0.3 '%'/lt Ca uo, 5 Ki/IK.

Comparative Example 2 Example 2 Caustic potash and potassium carbonate were added to the raw salt saturated brine used in VC to adjust the pH to 10.2, and the resulting precipitate was allowed to settle, and the supernatant liquid was filtered. /
t, Catri was 8.8~/L.

Example 3 Fresh salt water (Na
CZ 275? /Z, pH 2,4, temperature 80℃
) was dechlorinated by suctioning air to adjust the pH to 7.4, saturate the raw salt, filter it, and then pass it through the same chelate resin-packed column as in Example 1 under the same conditions, resulting in MV.

1,2 yv/t, Ca 1.87 ng/l, and temperature 74°C.

Comparative Example 3 When the raw salt saturated brine of Example 3 was purified by precipitation using a conventional method using caustic soda and soda carbonate, MV was 2.
3772! iI/t, Ca 7.4”fl/t
, the temperature was 68°C.

Example 4 A packed tower with a diameter of 450 mm (packed height: 63 mm) filled with 100 tons of chelate resin made of a copolymer of N-phenylglycine and glycysyl methacrylate of 20 to 60 meshes.
om) K raw salt saturated brine (Na C1310t/l, Mf
? 4σ111fl/L, Ca25011117
/l) was adjusted to pH 6 and allowed to flow down at a rate of 0.7 m3/hr (space velocity 7 hr'). /d, 0.9 m3/t)Ca
[1,2ml! /lVc 71 fc.

Claims (1)

[Scope of Claims] Raw salt-dissolved salt water is placed in a packed bed made of a chelate-forming water-insoluble resin capable of forming an intramolecular complex with magnesium and calcium selected from the group A below, which has an I N-0H2COOH group. Speed 20hr' or less, pH 3-10Vc adjustment 1-ff
A method for purifying salt water, which comprises removing magnesium and calcium from the salt water. However, Aid represents styrene-butadiene copolymer, epichlorohydrin polymer, N-phenyl-glycine-glycidyl methacrylate copolymer, and styrene-divinylbenzene copolymer.