JPS60141619A - Method for purifying aqueous alkali chloride solution for electrolysis - Google Patents

Abstract

PURPOSE:To remove calcium and magnesium contents effectively by treating an aq. alkali chloride soln. for electrolysis with sulfurous acid (sulfite) and thereafter bringing said soln. into contact with a chelate resin. CONSTITUTION:(Acidic) alkali sulfite is added to an aq. alkali chloride soln. for electrolysis in the proportion of about 10-100mol times the content of mercury contained in said aq. soln. to convert the mercury into stable complex ions Hg(SO3)2<-->. Next, said aq. soln. is brought into contact with a chelate resin (e.g. ''Diaion CR-10'' manufactured by Mitsubishikasei Co.) (about 5-12pH of aq. soln. and about <=30hr<-1> superficial velocity in a column), and calcium ions and magnesium ions contained in said soln. are adsorbed by the chelate resin and removed. On this occasion, the mercury complex ions are not adsorbed by the resin, therefore the deterioration in resin capacity due to the adsorption of mercury is not caused.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying an aqueous alkali chloride solution for electrolysis.

When producing chlorine and caustic alkali by electrolyzing an aqueous alkali chloride solution, it is particularly necessary to sufficiently remove calcium and magnesium components when purifying the aqueous alkali chloride solution used as a raw material. Particularly in the case of the recently developed ion exchange electrolysis method, aqueous alkaline chloride and aqueous caustic alkaline solutions come into contact through a cation exchange membrane, so the calcium and magnesium ions come into contact with hydroxide ions inside the ion exchange membrane. and form a dissolvable salt.
C This tends to cause an increase in electrolytic voltage and damage to the ion exchange membrane. Therefore, in the case of ion-exchange membrane electrolysis, strict purification of the raw n-alkaline chloride aqueous solution is required compared to electrolysis using the conventional mercury method or asbestos diaphragm method.

In particular, it is necessary to remove calcium ions to at least 0.2 mg/(? or less, preferably 0.05 ml'U or less, and magnesium ions to about the same extent. The N production method uses an alkaline agent to sediment and remove magnesium and calcium components as magnesium hydroxide and calcium carbonate, but there is a limit to the separation efficiency by sedimentation, and the solids in the supernatant liquid are removed. Infiltration is completely unavoidable, and generally the supernatant liquid of the precipitated mta is further filtered and used as an electrolytic solution. However, the purified salt water obtained by this method still contains several mg/(1 or more lucium). However, magnesium content usually remains in excess of lll1g/p.Recently, therefore, the removal of calcium and magnesium from an aqueous alkali chloride solution using a chelate resin has attracted attention, and it is known that almost complete purification can be achieved.

However, for example, when the salt water used in mercury method electrolysis is used for ion exchange membrane electrolysis, or when mercury method electrolysis and ion exchange membrane electrolysis are co-located, the alkaline chloride aqueous solution contains a considerable amount of mercury. . Then C mercury is clean.
(Since the adsorption capacity to the resin is greater than that of alkaline earth metal salts such as calcium and magnesium, they are adsorbed first, which causes the adsorption capacity of calcium and magnesium ions to decrease.Also, in industrial implementation, It is essential to regenerate the chelate resin, but since mercury is extremely strongly adsorbed to the chelate resin, it is extremely difficult to remove it by a simple pickling section, resulting in even more inactivation. .

The present inventors have completed the present invention as a result of intensive research to solve these problems.

That is, the present invention is a method for purifying an aqueous alkali chloride solution for electrolysis using a chelate resin, in which sulfite or its salt is added in advance to stabilize the mercury in the aqueous solution as a sulfite complex ion, and then brought into contact with a chelate resin to remove calcium content. , a method for purifying an aqueous alkali chloride solution for electrolysis, characterized by removing magnesium content.

The sulfite used in the present invention may be either a neutral salt or an acidic salt, and usually an alkali sulfite or an acidic alkali sulfite is preferred. If the aqueous alkali chloride solution does not contain oxidizing substances such as free chlorine, the amount added is sufficient as long as it is above the area where mercury contained in the aqueous alkali chloride solution forms a complex ion of l1g(SO3)z. A molar ratio of 10 to 100 with respect to mercury is sufficient. Mercury sulfite complex ions can also be generated by blowing sulfur dioxide gas into salt water. These various chemicals may be added at any point in the salt water line before entering the chelate resin, but it is usually effective to add them after the dechlorination process of the fresh salt water discharged from the electrolytic cell.

In this way, the contained mercury is converted into a stable complex ion t1g (SO
3) When the salt water prepared in 2 is brought into contact with the chelate resin, mercury is not adsorbed to the chelate resin at all, and calcium ions and magnesium ions can be removed to almost a trace state.

The chelate resin used in the present invention is based on a styrene-divinylbenzene copolymer, a styrene-butadiene copolymer, an epichlorohydrin polymer, a phenol, or an aldehyde condensate, and has an iminodiacetic acid group as a functional group.
Examples include chelate resins having aminophosphoric acid groups.

The superficial velocity at which such a chelate resin is brought into contact with an aqueous alkali chloride solution for electrolysis is approximately 30 groups! The following are suitable, and the pH of the solution is suitably in the range of 5 to 12, preferably DH6 to 11.

If the pH is outside the above range, the bond between the chelate resin and ions will be weak, and sufficient adsorption capacity will not be exhibited.

An example of a substance that forms a complex ion with C mercury in salt water and stabilizes it in the solution is chloride ion.

Mercury forms complex ions when there are sufficient chlorine ions in salt water, but the ability of chlorine ions to form complex ions is much weaker than that of sulfite ions, and in the subsequent Kiri-1 to resin adsorption process, mercury forms complex ions. As a result, mercury is adsorbed and adsorption of calcium and magnesium components is inhibited. In the method of the present invention, sulfite ions form extremely stable complex ions with mercury, and there is no risk of them dissociating again and mercury being adsorbed to the resin. Also, if sulfites or the like are added in excess, It is oxidized to @ acid ions in the electrolytic cell, but the alkali chloride aqueous solution used for ion exchange desorption electrolysis usually contains 10 a/
1 of sulfate ions, such sulfate ions do not have an adverse effect on the cation exchange membrane, nor do they affect the purity of chlorine gas generated during electrolysis. The increase in sulfate ions due to the addition of salt is usually about 10% and its influence can be ignored.

After use, the chelate resin can be washed with a mineral acid such as hydrochloric acid to easily elute the adsorbed calcium and magnesium ions, and then washed with a caustic alkaline solution to neutralize it and regenerate it. This makes it possible to avoid a decrease in adsorption capacity due to repeated use of the chelate resin.

Example 1. Comparative Example 1 Saturated crudely purified brine used in mercury method electrolysis (crudely purified brine in which -2Ca has been precipitated and separated by the precipitation method, Na
(u310 (1/17, CE 2.0-2.8 a
, /1, l'Ig 0.8-1.8B/A', H
a 10-13u/17, D+ 9.2. temperature 15
A chelate resin (manufactured by Mitsubishi Kasei Corporation) containing styrene-divinylbenzene as a base material and having an iminodiacetic acid group is prepared by adding salt water to which 0.8 (1#) of tutria sulfite (0.8 °C) is added.

Product name Daiseion CR-10) Flow rate 31 to a polyvinyl chloride column (inner diameter 28n) packed with 300
2/hI・(SVlohr-') Knee' Ca was lowered. When the impurity content of the treated salt water was measured at 81 degrees, the results shown in Table 1 were obtained.

For comparison, the results of treatment with chelate resin under exactly the same conditions except that thutrium sulfite was not added are shown in the first table.
Shown in the table.

Table 1 Regeneration of chelate resin with impurities adsorbed in this way
-To1c411, more? Table 2 shows the results of elution and regeneration using N-Na0)fo, 51 and purification of the same brine.

Table 2 Instead of the resin used in Example 1, a chelate resin having an aminophosphoric acid group based on direzivinylbenzene (manufactured by Diamond Jamrock Co., Ltd., trade name: Decoolite ES-467) was used, and acidic sulfite was added to the same salt water. It was carried out under exactly the same conditions as in Example 1, except that sodium 0.5Q/II was added and l) H was adjusted to 10.5. For comparison, salt water to which no acidic sulfite was added was allowed to flow down onto the resin, and the impurity concentrations were measured. Table 3 shows the results.

Table 3 Elution and regeneration were carried out in the same manner as in Comparative Example 1, and the same brine was purified again. Table 4 shows the results.

Table 4 Example 3 Saturated crudely purified brine used in mercury method electrolysis (crudely purified brine in which 11Ca has been precipitated and separated by a normal precipitation method, Na(7) 310 g/R, Ca 2.0 to 2.5 mg /
l), ? 0.5-1.6trg/l, Hg1
1-15 mg/l, pf-I 10.2. temperature 15
After blowing in 150p of sulfur dioxide gas per ml, brine whose ptl was adjusted to 10.2 was poured into the chelate resin-filled column used in Example 1 at iJ 31 / h+.
(SV 101n・-1). When the impurity concentration of the treated salt water was measured, the results shown in Table 5 were obtained.

Table 5 The chelate resin that had adsorbed impurities was subjected to elution regeneration in the same manner as in Example 1, and the same salt water was allowed to flow down again, and the results are shown in Table 6.

Table 6

Claims (1)

[Claims] In a method of purifying an aqueous alkali chloride solution for electrolysis using a chelate resin, sulfite sulfite or its salt is added to remove mercury from the water solution. 1. A method for purifying an aqueous alkali chloride solution for electrolysis, which comprises stabilizing the acid and then contacting it with a chelate resin to remove calcium and magnesium.