JP6712706B2 - Method for suppressing volatilization of cyanogen chloride - Google Patents

Description

The present invention relates to a method for suppressing volatilization of cyanogen chloride. More specifically, the present invention relates to a method for suppressing volatilization of cyanogen chloride generated by treatment of wastewater containing cyanide by the alkali chlorine method or the like.

Since cyanide has a strong adverse effect on the ecosystem, cyanide-containing wastewater (also called “cyan wastewater”) cannot be released to nature as it is. Cyan drainage standards are established based on the Water Pollution Control Law, and cyanide removal treatment is performed to satisfy this standard (1 mg/L or less), and only waste water that has been rendered harmless can be discharged to sewage. In addition, in some regions, the ordinance defines additional drainage standards that are lower than the above drainage standards. It should be noted that the cyanide-containing wastewater usually contains a high-concentration thiocyanate of cyan or higher.

Conventionally, various methods have been proposed and put to practical use as a method for removing cyanide from cyanide-containing wastewater, but each method has advantages and disadvantages, and is properly used depending on the situation of the wastewater.
Examples of such a method include oxidative decomposition methods such as alkali chlorine method, ozone oxidation method and electrolytic oxidation method (electrolysis method); insoluble complex methods such as dark blue method, zinc white method and reduced copper salt method; biological treatment method. A hydrothermal reaction such as a thermal hydrolysis method or a wet oxidation method.

Further, in Japanese Patent Laid-Open No. 2007-216225 (Patent Document 1), after coal gasification wastewater generated when the gas obtained by partial oxidation of coal is washed is subjected to coagulation sedimentation treatment to remove suspended substances, After adjusting the pH of the coal gasification wastewater from which suspended substances have been removed to 3 to 6 and irradiating it with ultraviolet rays in the presence of an oxidant, adjusting it to pH 7 or above and aerating with steam or air to remove ammonia. At the same time, a method for treating coal gasification wastewater is disclosed in which thiosulfate ions, thiocyanate ions and ferrocyanate ions contained as COD-derived substances are decomposed together with cyan.
Further, in Japanese Patent Laid-Open No. 11-033571 (Patent Document 2), a first step in which ozone is allowed to act on wastewater containing ammoniacal nitrogen and thiocyanate ions, and a chlorine-based oxidizing agent is added to the treated water in the first step. There is disclosed a method of treating wastewater, which comprises a second step of allowing the second step to act, and optionally a third step of causing copper ions to act on the treated water of the second step.

JP, 2007-216225, A Japanese Patent Laid-Open No. 11-033571

Among the conventional methods for treating cyanide-containing wastewater, the alkali-chlorine method of adjusting the cyanide-containing wastewater to be alkaline and then injecting a chlorine-based oxidizing agent to oxidize and decompose cyanide is relatively widely used in various industrial fields. .. However, in the treatment of wastewater containing cyanogen and the like by the alkali chlorine method, a cyanide compound or a thiocyanate compound reacts with sodium hypochlorite in the reaction of the first step, which is toxic and vaporizes at a boiling point of 13°C. A non-electrolytic cyanogen chloride (CNCl) that is easy to generate is produced.
However, a method for suppressing the volatilization of cyanogen chloride has not been proposed in the above-mentioned conventional techniques.
Therefore, it is an object of the present invention to provide a method capable of simply, safely and reliably suppressing the volatilization of cyanogen chloride generated in the treatment of wastewater containing cyanogen by the alkali chlorine method or the like.

The inventors of the present invention have conducted intensive studies to solve the above problems, and as a result, adjust the pH to 12 or more, add hydrogen peroxide, or adjust the pH to 12 or more and add hydrogen peroxide, To a wastewater containing cyanide and/or thiocyanic acid, instead of adding a chlorine-based oxidant from the surface of the wastewater, it is injected into the wastewater to treat the contents such as cyanide and They have found that volatilization can be suppressed, and have completed the present invention.

Thus, according to the present invention, previously measured total content of the cyan and / or thiocyanate in the waste water containing cyanide and / or thiocyanate, and / or the total content after adjusting the waste water over pH12 Add 0.05 mol equivalent or more of hydrogen peroxide to the total amount of the waste water, and expose the atmosphere of chlorine-based oxidizer to the waste water in an effective chlorine concentration of 0.01 mol equivalent or more with respect to the total content. and poured or fed to none, volatilization suppression method of cyanogen chloride, characterized in that to suppress the volatilization of cyanogen chloride from the waste water is provided.

According to the present invention, it is possible to provide a method capable of simply, safely and reliably suppressing the volatilization of cyanogen chloride generated in the treatment of wastewater containing cyanogen or the like.

Further, the method for suppressing volatilization of cyanogen chloride of the present invention exerts the above effect more when at least one of the following conditions is satisfied.
(1) The chlorine-based oxidizing agent is sodium hypochlorite, potassium hypochlorite or N-chlorosulfamate.
(2) The total content of cyanogen and thiocyanic acid in the waste water was measured in advance, hydrogen peroxide was added in an amount of 0.05 molar equivalent or more to the measured total content, and the chlorine-based oxidizing agent was used as the effective chlorine concentration. As 0.01 mol equivalent or more.

The method for suppressing volatilization of cyanogen chloride according to the present invention is a method in which a chlorine-based oxidizing agent is injected into the wastewater after adjusting the pH of the wastewater containing cyanide and/or thiocyanate to 12 or more and/or in the presence of hydrogen peroxide. It is characterized by suppressing the volatilization of cyanogen chloride from the waste water after injection.

Although the mechanism of action of the method for suppressing volatilization of cyanogen chloride of the present invention is not clear, the present inventors have found that cyanogen chloride produced in wastewater containing cyanogen, etc., efficiently and rapidly produces cyanate in wastewater. It is thought that the volatilization of cyanogen chloride itself is suppressed by being hydrolyzed to (CNO ⁻ ).

(Waste water)
The wastewater to be treated in the present invention is not particularly limited as long as it contains cyan and/or thiocyanic acid and salts thereof, and examples thereof include an iron factory, a chemical factory, a plating factory, a coke manufacturing factory, and a metal surface treatment. Treatment of cyanide-containing wastewater containing metal cyanide compounds, cyanide ions, cyanide complexes, cyanocomplex ions, thiocyanate ions, etc. emitted from factories, cyanide-containing wastewater emitted in the process of treating radioactively contaminated water, and soil Cyan-containing wastewater discharged from the device, as well as cyanide-treated wastewater treated by conventional methods.

(Method for suppressing volatilization of cyanogen chloride)
In the method for suppressing the volatilization of cyanogen chloride of the present invention, a chlorine-based oxidizing agent is injected into the wastewater after adjusting the pH of the wastewater to 12 or more and/or in the presence of hydrogen peroxide.
In particular, a mode in which the pH of the wastewater is adjusted to 12 or more and then the chlorine-based oxidizing agent is injected into the wastewater in the presence of hydrogen peroxide is a preferable mode in which the excellent effects of the present invention are more effectively exhibited.
The feature of the present invention lies in that it is injected into wastewater, and "injection" means not to add a chlorine-based oxidant from the liquid surface of the wastewater but to contact the chlorine-based oxidant with the atmosphere. It means to inject (deliver) into the waste water without using.

(PH adjustment)
To adjust the pH of the wastewater, an alkali that does not interfere with the reaction in the treatment of the present invention, for example, sodium hydroxide water, may be added to the treatment wastewater.
If the adjusted pH is 12 or more, the effect of the present invention is easily exhibited, but even if the pH is less than 12, the effect of the present invention is exhibited by making wastewater in the presence of hydrogen peroxide.

(Addition of hydrogen peroxide)
To bring the wastewater into the presence of hydrogen peroxide, for example, hydrogen peroxide solution may be added to the wastewater.
Examples of the hydrogen peroxide used in the present invention include hydrogen peroxide aqueous solutions having a concentration of 3 to 60%, which are commercially available mainly for industrial use.
Alternatively, hydrogen peroxide generated from a hydrogen peroxide supply compound (also referred to as “hydrogen peroxide generator”) or hydrogen peroxide generated by electrolysis of water or an alkaline solution can be used.
Hydrogen peroxide-supplying compounds include percarbonate, perboric acid, inorganic peracids such as peroxysulfuric acid, organic peracids such as peracetic acid, and salts thereof that can release hydrogen peroxide in water. Examples of these salts include sodium percarbonate and sodium perborate.
The above-mentioned hydrogen peroxide and hydrogen peroxide-supplying compound may be used by diluting or dissolving with water so as to obtain a desired hydrogen peroxide concentration upon addition.

Hydrogen peroxide is preferably added in the form of an aqueous solution. The hydrogen peroxide concentration may be determined in consideration of workability when added to the wastewater, reactivity between the cyanide and the added compound, and the like, and is specifically 30 mg/L or more. The upper limit value is about 30 g/L.
Further, the amount of hydrogen peroxide added varies depending on the total content of cyanide and thiocyanic acid contained in the target wastewater. The amount of hydrogen peroxide to be added may be determined based on the measured value. The added amount of hydrogen peroxide is preferably 0.05 molar equivalent or more with respect to the total content. More preferably, it is 0.1 molar equivalent or more with respect to the total content of cyanide and thiocyanic acid in the waste water.
The upper limit of the amount of hydrogen peroxide added is about 25 molar equivalents.
The total content of cyanide and thiocyanic acid in the wastewater can be measured by a known method, for example, JIS K 0102 or ion chromatography.

By bringing wastewater into the presence of hydrogen peroxide, the effect of the present invention is easily exhibited. However, even if the wastewater is not present in the presence of hydrogen peroxide, the pH of the wastewater should be adjusted to 12 or more. Thereby, the effect of the present invention is exhibited.

(Injection of chlorine-based oxidizer)
The chlorine-based oxidizing agent used in the present invention is not particularly limited as long as it acts as an oxidizing agent in the present invention and does not inhibit the effects of the present invention, and examples thereof include sodium hypochlorite and potassium hypochlorite. , Calcium hypochlorite, magnesium hypochlorite and N-chlorosulfamate.
Among the above-mentioned alkali metal salts and alkaline earth metal salts of hypochlorous acid, sodium hypochlorite and potassium hypochlorite are industrially easily available and are preferably used in the present invention.

Further, N-chlorosulfamate can be prepared by a known method, for example, the method described in JP-A-2003-503323, JP-A-2006-022097 or the like, and for example, sulfamate and hypochlorous acid. It can be prepared by reaction with an aqueous solution of sodium chlorate.
As the chlorine-based oxidizing agent used in the present invention, sodium hypochlorite, potassium hypochlorite, and N-chlorosulfamate, which can be easily handled, are particularly preferable in terms of the effect of suppressing the volatilization of cyanogen chloride. ..

The chlorine-based oxidant is preferably injected in the form of an aqueous solution. The concentration of the chlorine-based oxidant may be determined in consideration of the workability at the time of injecting it into wastewater, the reactivity between cyanide and the infused compound, and specifically, it is 10 mg/L or more as effective chlorine. The upper limit value is about 30 g/L.
The injection amount of chlorine-based oxidizer varies depending on the total content of cyanide and thiocyanic acid contained in the target wastewater. It may be measured in advance and the amount of the chlorine-based oxidizing agent added may be determined based on the measured value. The injection amount of the chlorine-based oxidizing agent is preferably 0.01 molar equivalent or more as effective chlorine determined by the iodometric titration method with respect to the total content. More preferably, it is 0.1 molar equivalent or more with respect to the total content of cyanide and thiocyanic acid in the waste water.
The upper limit of the injection amount of the chlorine-based oxidizing agent is about 5.5 molar equivalents, preferably about 2.0 molar equivalents.

(Stirring)
In order to improve the reaction efficiency, it is preferable to stir the mixed solution at the time of adding (injecting) each of the above compounds and at the time of reacting these added (injected) compounds with cyan. This stirring should always be performed especially during the injection of the chlorine-based oxidant.
Furthermore, the time required for the reaction during stirring varies depending on the amount of wastewater, the type and concentration of cyanide, the form and scale of the processing equipment, etc., but it is necessary to ensure that the cyanide and the added (injected) compound are in sufficient contact. It may be determined appropriately. Usually, the stirring time may be 10 minutes or longer, and more preferably 20 to 60 minutes.

(Treatment and sedimentation)
The cyanate-containing wastewater treated by the method for suppressing volatilization of cyanogen chloride of the present invention can be separated by sedimentation in a sedimentation tank or the like by adding a surfactant, a coagulant or the like. Further, the treatment can be carried out through a step of oxidative decomposition (neutral) or acid hydrolysis (acidic).
Known devices such as an additive tank, a reaction treatment tank, a thickener, and a turbidity settling tank can be used for these series of operations, and existing equipment may be used.
In the method for suppressing volatilization of cyanogen chloride of the present invention, a known agent such as an antifoaming agent, a rust preventive, a corrosion inhibitor, a scale dispersant, and a slime control agent may be used in combination within a range that does not impair the effects of the present invention. Good.

The present invention will be specifically described with reference to test examples, but the present invention is not limited to these test examples.

(Test Example 1)
A thiocyanic acid-containing water was prepared, and this was used as a pseudo-wastewater to carry out a confirmation test of the effect of suppressing the volatilization of cyanogen chloride.
A thiocyanic acid-containing water was prepared by dissolving calculated amounts of potassium thiocyanate, an alkali or a buffer in 1000 g of water so that the concentrations and pHs of potassium thiocyanate shown in Table 1 were obtained. If necessary, 48% sodium hydroxide was used as an alkali and phosphate was used as a buffer.

200 mL of thiocyanate-containing water prepared was added to a 1 L capacity plastic bottle having a hole of about 9 mm (inner diameter of about 90 mm x inner height of about 160 mm), 0.4 mL of 30% hydrogen peroxide solution was further added, and the lid was closed. And the liquid in the plastic bottle was mixed by shaking.
Then, using a 0.5 ml volumetric pipette, 0.4 mL of a 12% sodium hypochlorite aqueous solution is injected into the bottom of the plastic bottle (35 mm below the liquid surface of the mixed solution) through the hole in the lid, or the mixed solution is used. It was dropped from a height of 130 mm from the liquid surface.
After that, the hole in the lid is sealed and the mixed solution is left to stand for 5 minutes. Then, a detection tube for measuring the concentration of cyanogen chloride (Dragel Safety Japan KK, product number: CH19811) is inserted through the hole in the lid, and The cyanogen chloride concentration (ppm) in the headspace of the bottle was measured.

When hydrogen peroxide was not added, an aqueous sodium hypochlorite solution was injected or dropped in the same manner as above except for the operation of mixing hydrogen peroxide, and the cyanogen chloride concentration (ppm) was measured.
The obtained results are shown in Table 1 together with the potassium thiocyanate concentration (mass %), the pH of thiocyanate-containing water, the presence/absence of hydrogen peroxide mixing, and the type of sodium hypochlorite injection or dropping.

The following can be seen from the results in Table 1.
When the sodium hypochlorite is injected after mixing hydrogen peroxide with thiocyanic acid-containing water (Examples 1 to 4 and Examples 6 to 8), volatilization of cyanogen chloride is suppressed. When sodium hypochlorite is injected after adjusting the pH of the acid-containing water to 12 or more (Example 5), volatilization of cyanogen chloride is suppressed.-Sodium hypochlorite is added dropwise to thiocyanic acid-containing water. In the case of (Comparative Example 1 and Comparative Examples 3 to 8), volatilization of cyanogen chloride is not suppressed regardless of whether hydrogen peroxide is mixed or not.-When the thiocyanic acid-containing water is adjusted to have a pH of less than 12, Even if sodium hypochlorite is injected without mixing hydrogen peroxide (Comparative Example 2), volatilization of cyanogen chloride is not suppressed.

(Test Example 2)
Cyan-containing water was prepared, and this was used as a pseudo-wastewater to carry out a confirmation test of the effect of suppressing the volatilization of cyanogen chloride.
Cyanide chloride was prepared in the same manner as in Test Example 1 except that the calculated amount of potassium cyanide, an alkali or a buffering agent was dissolved in 1000 g of water to prepare the cyanide-containing water so that the potassium cyanide concentration and pH shown in Table 2 were obtained. The concentration (ppm) was measured.
The obtained results are shown in Table 2 together with the potassium cyanide concentration (mass %), the pH of cyanide-containing water, the presence/absence of hydrogen peroxide mixing, and the type of injection or dropping of sodium hypochlorite.

The following can be seen from the results in Table 2.
When cyanogen-containing water is mixed with hydrogen peroxide and then sodium hypochlorite is injected (Examples 9, 10, 12 and 13), volatilization of cyanogen chloride is suppressed. When sodium hypochlorite is injected after adjusting the pH to 12 or more (Example 11), volatilization of cyanogen chloride is suppressed.-When sodium hypochlorite is dropped into cyanide-containing water (Comparative Example). 9 and Comparative Examples 11 to 13), volatilization of cyanogen chloride is not suppressed. When the pH of cyanide-containing water was adjusted to less than 12, hydrogen peroxide was not mixed and sodium hypochlorite was injected. Also (Comparative Example 10), volatilization of cyanogen chloride is not suppressed.

(Test Example 3)
A mixed-containing water containing cyan and thiocyanic acid was prepared, and this was used as a pseudo-waste water to carry out a confirmation test of the cyanide chloride volatilization suppressing effect.
Tests were conducted except that the calculated amounts of potassium cyanide, potassium thiocyanate, alkali or buffer were dissolved in 1000 g of water so as to obtain the potassium cyanide concentration, potassium thiocyanate concentration and pH shown in Table 3 to prepare a mixed-containing water. The cyanogen chloride concentration (ppm) was measured in the same manner as in Example 1.
The obtained results are shown together with the concentration of potassium cyanide (% by mass), the concentration of potassium thiocyanate (% by mass), the pH of the mixed contained water, the presence or absence of mixing of hydrogen peroxide, and the type of injection or dropping of sodium hypochlorite. 3 shows.

The following can be seen from the results in Table 3.
-When sodium hypochlorite is injected after mixing hydrogen peroxide into the mixed-containing water (Examples 14 to 16), volatilization of cyanogen chloride is suppressed-hypochlorous acid in the mixed-containing water When sodium is added dropwise (Comparative Examples 14 and 15 and Comparative Examples 17 to 19), volatilization of cyanogen chloride is not suppressed regardless of whether hydrogen peroxide is mixed. In this case, even if sodium hypochlorite is injected without mixing hydrogen peroxide (Comparative Example 16), the volatilization of cyanogen chloride is not suppressed.

Claims (2)

0.05 mol with respect to cyan and / or measured in advance the total content of the cyan and / or thiocyanate in the waste water containing thiocyanate, after adjusting the waste water over pH12 and / or the total content An equivalent amount or more of hydrogen peroxide is added, and a chlorine-based oxidizer having an effective chlorine concentration of 0.01 molar equivalent or more with respect to the total content is poured or sent into the wastewater without contact with the atmosphere. Te, volatilization suppression method of cyanogen chloride, characterized in that to suppress the volatilization of cyanogen chloride from the waste water. The method for suppressing volatilization of cyanogen chloride according to claim 1, wherein the chlorine-based oxidizing agent is sodium hypochlorite, potassium hypochlorite, or N-chlorosulfamate.