JPS603009B2 - Separation and reuse method of Cr(V1) ions in chlorate production electrolyte - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for converting chromate ions and dichromate ions [Cr
(W) Collectively called ions.

This invention relates to a method for separating Cr(W) ions and reusing the separated Cr(W) ions for the production of chlorate. In the electrolytic oxidation process of sodium chloride for producing chlorate, the electrolytic solution mainly consists of sodium chlorate and sodium chloride, but Cr() ions are usually added as a reduction inhibitor.

The toxicity of Cr(W) ions to living organisms is well known. Therefore, if even a small amount of Cr(W) ions is discharged as waste liquid, it will cause major environmental problems and pollution, so it is necessary to take measures to prevent Cr(W) ions from being discharged outside the reaction system. Cr(
M) Turtle liquid containing ions exhibits a characteristic yellow color, and when sodium chlorate crystals are crystallized from this electrolyte, Cr(W) ions attach to the crystallized crystals, resulting in a yellow color. This reduces the product value of sodium chlorate crystals. Currently, these attached Cr(W) ions are removed by water washing or recrystallization, and in order to create a purified chlorate solution, a method is used in which the recrystallized crystals are dissolved in water again, which requires a complicated process. and equipment are required. Also,
Sodium chlorate and hydrochloric acid are continuously fed into a single reaction tank and reacted. Chlorine dioxide and chlorine are extracted from the system along with water vapor, and solid sodium chloride, which crystallizes as water evaporates, is produced as a by-product. Continuous type diacid I○ recovered as
A method of adding palladium as a catalyst in order to efficiently produce irido-dioxide in a mirror element generation tank is disclosed, for example, in Samurai Seki Shokoichi No. 47893 and Tokusekki Shokoichi No. 74296.
It has been proposed in the Publication No.

However, in this continuous type chlorine dioxide generation tank, when the fin solution consisting of sodium chlorate and sodium chloride containing Cr(W) ions is reacted with hydrochloric acid, water evaporates as the reaction progresses. , the (M) ions are concentrated and accumulated in C, and this concentrated and accumulated Cr
When the concentration of () ions becomes high, the boiling point rises, leading to an abnormal temperature rise in the reaction chamber, or causing the momme point of the added catalyst, such as acting as a catalytic shield. In this continuous type phosphoric acid Q enrichment generation tank, it is practically difficult to remove Cr(W) ions by water washing or recrystallization. Furthermore, if Cr (machi) ions are discharged out of the reaction system, they may cause environmental problems due to their purity, or they may be wasteful as new 〇 (W) ions must be added in the next electrolysis process. will arise. A method for removing and recovering Cr(W) ions from waste liquid containing Cr(W) ions using an anion exchange resin is described in, for example, Jiko Sho 41-190.
It has been proposed in Publications No. 53, Hakama Kokai Kyukyu-Yo No. (Town) There was no known method of reusing ions in the past, and Cr(W) was extracted from the electrolyzed solution for chlorate production.
There has been a strong desire to effectively establish a closed recycling system that separates ions and reuses the separated C(W) ions as an electrolyte.

The purpose of the present invention is to separate Cr(machi) ions from a chlorate electrolyte containing concentrated alkali metal chlorates, alkali metal chlorides and Cr(W) ions, and to
The aim is to establish an effective closed recycling system in which ions are returned to the electrolytic process and reused. The present inventors have conducted various studies to achieve the above object, and as a result, have completed an effective method for separating Cr(W) ions in a chlorate production electrolyte and reusing them.

That is, the pH of the chlorate electrolyte is adjusted to a range of 1 to 5,
Cr(W) by passing through an anion exchange resin column
A chlorate solution with separated ions can be obtained.
On the other hand, in regenerating the anion exchange resin, 1.0
~5.0 mol/alkali metal chloride and 0.1-5
．． 0 mol/0.05 to 1 containing alkali metal chlorate
．． It has been found that it is effective to recover Cr (Cr) ions from the molten rock using a 0 molar aqueous solution of alkali metal hydroxide as a regenerating agent. Furthermore, the alkali metal hydroxide aqueous solution in which (W) ions are recovered by melting with C can be used in the electrolytic process for producing chlorate after neutralization. In addition, the chlorate electrolyte solution, which has been adjusted to have a mottling of 1 to 5 and passed through an anion exchange resin column to separate Cr ions, can be used as a continuous solution with water evaporation. The second scale of the formula can be supplied to the chlorine generation tank and subjected to the chlorine dioxide generation reaction. In order to remove Cr(W) ions in the electrolyte using an anion exchange resin, as shown in Figure 1, it is better to lower the electrolyte as much as possible for more efficient separation. separation is difficult.

Note that other liquid passing conditions in FIG. 1 are shown in Example 1. However, since the electrolyte contains concentrated alkali metal chlorates and alkali metal chlorides, it becomes extremely unstable at low concentrations, and decomposes to generate chlorine dioxide and chlorine in the range of less than 1. . When the number of spots is larger than 5, the ability to adsorb Cr(W) ions decreases. Therefore,
In order to maintain the stability of the electrolyte and to sufficiently separate Cr(W) ions, it is necessary to adjust the feed of the electrolyte to a pH of 1 to 5. It is in the range of 5-3. In addition, a method has been proposed in the Publication No. 3-3 of 1977 in which water containing chromate ions is adjusted to acidity, and then brought into contact with a weakly basic anion exchange resin to remove chromate ions from an aqueous solution. However, the preferred range of acidity adjustment in this method is 3 to 5.5.

However, in the method of the present invention, as is clear from FIG. 1, solutions 1.5-3 are preferable to 3-5.5. It is desirable to use hydrochloric acid or nitric acid to adjust the pH. When the electrolyte was adjusted to 1.5 to 3 in this way,
As shown in Figure 1, 95% of Cr(W) ions contained in the electrolytic solution are
% or more can be separated. Examples of anion exchange resins include Amberlite IRA400, IRA410,
IRA900 (both trade names manufactured by Organo Co., Ltd.) can be used.

The electrolytic solution from which Cr (machi) ions have been separated is sent to a sodium chlorate storage tank or a sodium chlorate crystallization process.

FIG. 2 shows a flow sheet of a method for sending the electrolytic solution from which Cr (machi) ions have been separated to the crystallization step. When sodium chlorate crystals are crystallized in the crystallization step, sodium chlorate crystals to which Cr(W) ions are not attached can be obtained. Next, regarding the liquid composition of the regenerant, the Cr ions adsorbed on the anion exchange resin can also be dissolved by using a concentrated alkali metal hydroxide solution alone. However, in order to return this solution consisting of Cr ions and concentrated alkali metal hydroxide to the electrolytic process, it must be neutralized with Taitoyo's acid, and a large amount of salt solution must be treated. , it is also economically disadvantageous.
However, when an aqueous alkali metal hydroxide solution containing 1.0 to 50 moles of the alkali metal chloride and 0.1 to 5.0 moles of the alkali metal chloride as a regenerant, the alkali metal Hydroxide concentration is 0.05~
Only 1.0 mol/so is available, and it can be returned to the electrolytic process by neutralization with a small amount of acid. Alkali metal hydroxide concentration is 0.
If it is less than 0.05 mol/Z, it is not possible to obtain sufficient harbor rock,
If it is 1.0 mol/Z or more, the amount of acid required for neutralization will increase, and the amount of treatment will increase. That is, by using an alkali metal hydroxide aqueous solution of an alkali metal chloride and an alkali metal chlorate as a regenerating agent, it is possible to obtain a sufficient amount of Cr ions more efficiently than an anion exchange resin. At the same time, an effective closed cycle system was established in which the separated Cr(W) ions are returned to the electrolytic process and reused. The alkali metal chloride concentration needs to be 1.0 mol/or more in consideration of recirculation to the electrolytic process, and is limited by its upper limit of 5.0 mol/solute solubility. Further, if the alkali metal chlorate concentration is less than 0.1 mol/l, the effect is not small, and the solubility is limited by the upper limit of 50 mol/l. The aqueous alkali metal hydroxide solution containing the alkali metal chloride and alkali metal chlorate obtained by dissolving Cr(W) ions can be neutralized with hydrochloric acid or nitric acid and returned to the electrolytic process for producing chlorate. . In the present invention, the alkali metal chlorate is sodium chlorate or potassium chlorate, and the alkali metal chloride is sodium chloride or potassium chloride. Since the chlorate production electrolyte contains concentrated alkali metal chlorates and alkali metal salts, the specific gravity of the liquid is greater than the specific gravity of the anion exchange resin, and the anion exchanger in the chlorate production electrolyte. The sword resin will float.

In order to prevent this floating, it is desirable to pass the chlorate production electrolyte in an upward flow, and at this time, if the regenerant is passed in a downward flow, the efficiency of dissolution is good. In addition, two anion exchange resin towers are used in parallel, and Cr(machi) is extracted from the chlorate electrolyte.
Continuous processing is possible by alternately performing liquid formation for separating ions and regeneration for recovering (W) ions by lysis using C. FIG. 3 shows a flow sheet for supplying the chlorate production electrolyte from which Cr ions have been removed to a continuous type diacid, ion, and enrichment generating tank accompanied by water evaporation.

A continuous diacid chloride generating tank with water evaporation is one in which an alkali metal chlorate and hydrochloric acid are continuously supplied and reacted under reduced pressure in a single generating tank. When hydrochloric acid is used, chlorine dioxide and chlorine are generated through the main reaction represented by equation '1' and the side reaction represented by equation '2). N
aCI0312HCI→CI0211/piece 120NaC
I + day 20 (1) NaCI030qHCI → 3CI20 NaCI + insect day 20 (2) The generated chlorine dioxide and chlorine are taken out of the system along with water vapor, solid sodium chloride crystallizes as the water evaporates, and byproducts will be collected as.

At this time, in order to increase the reaction yield of equation '1), which is the main reaction for producing chlorine dioxide, a catalyst such as palladium rust is added. By the way, this reaction is carried out continuously, so when a chlorate electrolyte containing Cr ions is supplied and reacted with hydrochloric acid, the concentration and crystallization of sodium chloride and the concentration of Cr ions occur at the same time. Accumulation occurs, eventually leading to crystallization of sodium dichromate. Such a high concentration of Cr(W) ions causes an abnormal increase in the boiling point and acts as a catalyst groove, but as shown in Figure 3, a chlorate electrolyte from which Cr(W) ions have been removed is supplied. This can be prevented by reacting. Moreover, solid sodium chloride recovered as a by-product can be used as an aqueous alkali metal hydroxide solution and a regenerating agent together with an alkali metal chlorate.
The other steps are the same as those described in FIG. According to the method of the present invention, by separating Cr(M) ions in the electrolyte solution, Cr(M) ions are separated in the crystallization process of chlorate crystals.
It is advantageously possible to obtain crystals to which no W) ions are attached, and it is also advantageously possible to obtain purified aqueous chlorate solutions free of Cr(W) ions.

Furthermore, in a continuous chlorine dioxide generating tank, it is possible to prevent an increase in the boiling point due to accumulation of Cr ions and to prevent defects as a catalyst base. Note that Cr adsorbed on the anion exchange resin
(Machi) Ions can be efficiently eluted and recovered, and after neutralization with a small amount of acid, they can be returned to the electrolytic process. Next, the present invention will be explained by examples.

Example 1 374 mol of NaCIQ taken out from an electrolytic cell for chlorate production, 12.00 mol of NaC/2, 0.03 mol of Cr ion/1, pH 6.9
Using hydrochloric acid, the electrolysis finished solution with a solution composition of
Adjusted to.

Inner light filled with anion exchange resin IRA4001〆3.
Two columns were used in parallel, and the treated water and regenerant were alternately passed through the column. That is, the treated solution was passed through one column in an upward flow to separate 96.5% of Cr(M) ions, and similarly passed through the other column to separate Cr(M) ions.
Town) A crab lysate from which ions were separated was obtained. The electrolytic solution from which the Cr(W) ions were separated was sent to a step of crystallizing sodium chlorate crystals, and the crystals were crystallized by a conventional method. As a result, the number of Cr(W) ions attached to the crystal is 0. It was a teaching style. next,
Ion exchange that adsorbed Cr() ions The answer is NaCl
4.6 mol/end, NaCI031-09 mol/end, tocho aOHO. 85 sleeves of regenerating agent consisting of 1 mole/metre were regenerated. As a result, NaC is 14.6 mol, NaCIQI. 0
9 mol/so, Cr(M) ion 0.03 terion/so, laOHO. A molten acid solution containing 1 mol/ml was obtained. This eluate was adjusted to a speck of 060 with hydrochloric acid and returned to the electrolytic cell for producing sodium chlorate. In the electrolytic cell, M-l
As a result of electrolytic oxidation at a current density of 25 A'd using the r electrode as an anode, NaCI033.70 mol/so,
NaCII-95 mol., Cr(W) ion 0l. 0
An electrolyzed solution with a pH of 6.90 was obtained.
The pH of the chlorate production electrolyte in this Example 1 was set to 1-
FIG. 1 shows the separation rate of Cr ions when the ion exchange resin was passed through the ion exchange resin at various values within the range of 6.

Example 2 3.70 mol/day of aCIQ, NaCII. 95 mol/night, Cr(W) ion 0.03 terion/zo, pH
The electrolysis finished solution with a liquid composition of 6.90 was heated to axis 2 using hydrochloric acid.
．． Adjusted to 39.

Inner diameter 3.5 filled with anion exchange resin Melon A4001
Two pine columns were used in parallel, and the process was carried out continuously by alternately passing the treated water and the regenerant. That is, the treated solution was passed through one column with an upward flow of 96.
5% of Cr(W) ions were separated and the solution was similarly passed through the other column to obtain an electrolytic solution in which Cr(W) ions were separated. The electrolytic solution from which the Cr(W) ions were separated was sent to a storage tank to be supplied to a continuous chlorine dioxide generation tank.

The continuous diacid/chlorine generating tank consists of a glass vessel with a reaction volume of 3. The reaction solution composition is NaCI031 mol/〆, N
aC14.8 mol/so, HCIO. 17 mol/sleeve, and 3.9×1 catalyst produced from palladium and glycine
0-4 mol/filler was added. Reaction temperature 7 to 0, reaction pressure 1
An electrolytic solution from which Cr(W) ions were separated at 85 Hg was supplied at a flow rate of 7.2/min. At this time, the reaction yield of the chlorine dioxide production reaction was 962%, which was 2.4% per hour.
4 moles of common salt precipitated. Next, the ion exchange tower that adsorbed Cr() ions contained 14.6 mol/day of NaC and 14.6 mol/day of NaCl.
031.09 mol/〆, NaOHO. 85 sleeves of regenerant consisting of 1 mole/regenerator were regenerated. The salt used for producing this regenerant was salt crystallized from a continuous chlorine dioxide generating tank. As a result, NaC14.6 mol/night, NaCI03
1.09 mol/Z, Cr(W) ion 0.03 terion/〆, NaOHO. A syneresis liquid consisting of 1 mol/ml was obtained. This eluate was adjusted to pH 6.60 with hydrochloric acid and returned to the electrolytic cell for producing sodium chlorate.

In the electrolytic cell, a Pt-lr electrode was used as an anode, and as a result of electrolytic oxidation at a current density of 25 A/d, N
aCI033.74 Molnoyu, NaCII. 93 mol/
Z, Cr(W) ion 0.03 Tion/Y, mother 6.
It was possible to obtain 90% of the electrolyzed solution. Comparative Example 1 In a continuous chlorine dioxide generation tank, if an electrolytic solution that does not separate Cr(W) ions is supplied and the reaction continues, Cr(W)
Ions accumulate.

1.6 In a glass reaction vessel with a reaction volume, the initial concentration of NaCIQI. 25 mol/so, NaCi4.62
Mol/Yu, HCIO. 15 mol/〆, catalyst produced from palladium and glycine 1.22 x 10-3 mol/〆, NaCl 033.96 mol/〆, NaC 12.02
When a decomposition solution consisting of Cr(W) ions and 3.1×10-2 terions/mole was supplied at a flow rate of 37 m/min and the reaction was continued, the reaction solution composition changed over a period of 3 months through continuous reaction. is NaCIQI. 25 mol/Z, NaCII. 0 mol/
So, Cr(W) ion 9.0 Cu ion/Z, HCII
．． It is expected to be 36 mol/Z.

Therefore, in order to observe changes in the reaction yield and reaction conditions of the chlorine dioxide production reaction in a state where Cr(W) ions are accumulated, a reaction solution with the same composition as the expected composition was prepared, and an electrolyte solution was added. When the reaction is continued with the reaction pressure 175 Hg, the reaction temperature is 89. The temperature rose to 0, and an abnormal rise in boiling point was observed.

Further, the reaction yield of the chlorine dioxide production reaction decreased to 861%. Example 3 Anion exchange resin IRA4001 was packed into a column with an internal diameter of 3.5 to form an ion exchange tower, and 0.27 terions of Cr(W) ions were adsorbed.

NaCIQI. 5 mol/Z, NaC 12.0 mol/〆,
NaOHO. When eluted with a regenerant containing 1 mol/mole, an elution curve (■) in FIG. 4 was obtained. Comparative Example 2 Anion exchange resin IRA4001 was packed into a column with an inner diameter of 3.5 mm to serve as an ion exchange tower, and 0.27 terion of Cr(W) ions were adsorbed.

NaC133 mol/so, NaOHO. When eluted with a regenerating agent consisting of 1 mol of acetate, an elution curve indicated by ■ in FIG. 4 was obtained. Comparative Example 3 Anion exchange resin IRA4001 was packed into a column with an inner diameter of 35 mm to serve as an ion exchange tower, and 0.27 terions of Cr ions were adsorbed.

NaOHO. Even when eluted with a regenerant containing 1 mol/m
It was not possible to dissolve r() ions. Example 4 and Comparative Example 4 Anion exchange resin IRA40013 was packed in a column with an inner diameter of 13.5 to form an ion exchange column.

In this ion exchange column, 0.003 terion of C [(W)
Adsorbed ions. This was eluted and recovered with a regenerating solution (solute solution) having the liquid composition shown in Table 1. The concentration of each component in the extract is expressed in moles/sleeve. Table 1 shows the ratio of the amount of solvent to the amount of adsorption of Cr(W) ions when using Soto liquid 40.

Table 1 As is clear from Table 1, the NaOH in the solution was 0.05
When the concentration is lower than mol/Z, the scale rate is low and Cr(W
) Ions cannot be recovered sufficiently.

Also, if NaOH is 1.50 mol, the solubility ratio will not be improved compared to 0.89 mol, and moreover, more acid will be required for neutralization, which is inappropriate. Furthermore, NaOH
NaCIQ and Na
When CI is not included, the elution rate decreases. Example 5 and Comparative Example 5 Anion exchange resin IRA4001 was packed into a column with an inner diameter of 3.5 mm and subjected to ion exchange.

This exchange column adsorbed 0.3 ion of C (W) ions. This is the regenerating liquid (adjacent liquid) with the liquid composition shown in Table 2.
The ship was evacuated from the port and recovered. The concentration of each component in the eluent is expressed in moles/sleeve. Table 2 shows the amount of solvent relative to the adsorbed amount of Cr(W) ions when three eluents were used, that is, the separation rate (%). Table 2 As is clear from Table 2, even if the solution contains NaOH at 0'' mol/〆, NaCI is less than 1.0 mol/〆.
1 mole/in the comparative example, the solvent ratio is significantly reduced.

Moreover, even if NaCI is 1.0 mol/〆 or more, NaCl
When I03 is less than 0.1 mol/mol, the eluting ratio is lower than 70%, whereas it is 70% or more in the example.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between M of the electrolyte and separation rate when Cr(W) ions in the electrolyte are separated using an anion exchange resin column, and Figures 2 and 3 are diagrams showing the method of the present invention. Fig. 4 is a melting point curve diagram of Cr ("machi") ions adsorbed in an anion exchange resin column depending on the components of the regenerant. Traditional 4 illustrations

Claims (1)

[Claims] 1. Alkali metal chlorate, alkali metal chloride and C
A chlorate production electrolyte containing r(VI) ions has a pH of 1 to 5.
Cr(
VI) Obtaining a chlorate solution with separated ions and
(VI) Into the anion exchange resin tower that adsorbed ions, 1.
0-5.0 mol/l alkali metal chloride and 0.1-5.0 mol/l
0.05 containing 5.0 mol/l alkali metal chlorate
~1.0 mol/l of alkali metal hydroxide aqueous solution is passed through the resin to elute Cr(VI) ions, and the resulting alkali metal hydroxide aqueous solution containing Cr(VI) ions is poured into the resin. 1. A method for separating and reusing Cr(VI) ions in a chlorate production electrolyte, the method comprising using the Cr(VI) ion in an electrolytic solution for chlorate production after hydrogenation. 2. The method according to claim 1, wherein the pH of the chlorate production electrolyte is adjusted to 1.5 to 3. 3. The chlorate electrolyte is passed through the anion exchange resin tower in an upward flow, and the C of the alkali metal hydroxide aqueous solution is
The method according to claim 1 or 2, wherein the anion exchange resin adsorbed with r(VI) ions is passed through the column in a downward flow. 4 The anion exchange resin towers are used in parallel, and Cr(VI)
3. The method according to claim 1, 2 or 3, wherein passing a liquid for separating ions and passing a liquid for eluating Cr(VI) ions are carried out alternately. 5 Alkali metal chlorate, alkali metal chloride and C
A chlorate electrolyte containing r(VI) ions is adjusted to a pH range of 1 to 5 and passed through an anion exchange resin column to produce Cr(VI).
A chlorate solution with separated ions is obtained and the solution is fed to a continuous chlorine dioxide generation tank with water evaporation, while Cr
(VI) Into the anion exchange resin tower that adsorbed ions, 1.
0-5.0 mol/l alkali metal chloride and 0.1-5.0 mol/l
0.05 containing 5.0 mol/l alkali metal chlorate
~1.0 mol/l of alkali metal hydroxide aqueous solution is passed through the resin to elute Cr(VI) ions, and the resulting alkali metal hydroxide aqueous solution containing Cr(VI) ions is poured into the resin. 1. A method for separating and reusing Cr(VI) ions in a chlorate electrolyte, which is characterized in that the Cr(VI) ions are used in an electrolytic process for producing chlorate. 6. The method according to claim 5, wherein the pH of the chlorate production electrolyte is adjusted to 1.5 to 3. 7. Claim 5, wherein the alkali metal chloride in the alkali metal hydroxide aqueous solution is an alkali metal chloride crystallized as a by-product from the continuous chlorine dioxide generating tank accompanied by evaporation of water. or the method described in paragraph 6. 8 The chlorate electrolyte is passed through the anion exchange resin column in an upward flow, and the C of the alkali metal hydroxide aqueous solution is
8. The method according to claim 5, 6 or 7, wherein the anion exchange resin adsorbed with r(VI) ions is passed through the column in a downward flow. 9 The anion exchange resin towers are used in parallel, and Cr(VI)
Claims 5 and 6, in which passing liquid for separating ions and passing liquid for eluating Cr(VI) ions are carried out alternately.
The method described in paragraph 7 or 8.