TWI613154B - Treatment method for cyanide and ammonia drainage - Google Patents

Abstract

The present invention provides a method for treating water containing cyanide and ammonia, which can sufficiently decompose cyanide and ammonia even when the concentration of dissolved iron is high. It is a treatment method for cyanide and ammonia-containing wastewater having the steps of adding a chemical solution containing hypobromous acid and / or hypochlorous acid to cyanide and ammonia-containing wastewater and oxidatively decomposing cyanide and ammonia. A solution in which a bromide aqueous solution and a hypochlorite aqueous solution are mixed to generate hypobromous acid and / or hypobromite is added to cyanide and ammonia-containing wastewater. An aqueous solution of sodium bromide and an aqueous solution of sodium hypochlorite are mixed at an equal molar ratio or added so that sodium hypochlorite becomes excessive.

Description

Treatment method for cyanide and ammonia drainage

The present invention relates to a method for treating cyanide and ammonia-containing wastewater, and in particular, to a method for treating cyanide and ammonia-containing wastewater containing dissolved iron by an improved method of the alkali-chlorine method.

As the treatment method for cyanide-containing wastewater discharged from industrial facilities such as plating plants, iron smelters, refineries, power plants, and coke manufacturing plants, the most widely used method is the alkali-chlorine method. In this method, a chlorine source such as sodium hypochlorite is added to cyanide-containing wastewater under alkaline conditions to oxidize cyanide in the wastewater (Patent Documents 1 and 2).

In the alkali-chlorine method of Patent Document 1, a cyanide compound is oxidatively decomposed by a two-stage reaction at a pH and an ORP (redox potential) control value as shown below.

One stage reaction: above pH 10, ORP control value 300 ~ 350mV

NaCN + NaOCl → NaCNO + NaCl ... (1)

Two-stage reaction: pH 7 ~ 8, ORP control value 600 ~ 650mV

2NaCNO + 3NaClO + H ₂ O → N ₂ + 3NaCl + 2NaHCO ₃ … (2)

Patent Document 2 describes the treatment of cyanide-containing wastewater containing free cyanide, mixed cyanide, and ammonia by an alkali-chlorine method having a two-stage step of a first oxidation step up to 80 ° C and a second oxidation step up to 80 ° C. Methods.

Patent Document 3 describes a method for treating wastewater containing cyanide and ammonium ions by an alkali-chlorine method at pH 11 or higher. In the method of this patent document 3, after the decomposition reaction of the cyanide compound, a chlorine source is also added so that the concentration of free residual chlorine becomes 0.1 mg / L or more. Patent Document 3 describes that most of the soluble iron in wastewater containing cyanide and ammonium ions exists as a ferricyanide complex. This ferricyanide complex is difficult to decompose in the alkali-chlorine method. Therefore, it contains cyanide. The concentration of dissolved iron in ammonium ion drainage should be 0.4 mg / L or less (paragraph 0025).

Patent Document 1: Japanese Patent Laid-Open No. 2001-269674

Patent Document 2: Japanese Patent Application Laid-Open No. 2006-334508

Patent Document 3: Japanese Patent Laid-Open No. 2013-208550

As described in Patent Document 3, when the dissolved iron concentration in the cyanide and ammonium ion-containing wastewater is high, conventional cyanide methods cannot sufficiently decompose cyanide by oxidation.

In the method of the above-mentioned Patent Document 3, in order to make the cyanide and ammonium ion-containing wastewater to have a pH of 11 or higher, there is a problem that the cost of the alkali medicine increases. Furthermore, depending on the amount of chlorine source added, there is a possibility that chlorine gas may be generated.

A first object of the present invention is to provide a treatment method for cyanide and ammonia-containing wastewater, which can sufficiently decompose cyanide even when the concentration of dissolved iron in the wastewater is high.

A second object of the present invention is to provide a treatment method for cyanide and ammonia-containing wastewater, which can sufficiently oxidize and decompose cyanide even at pH 11 or lower.

The method for treating cyanide-containing and ammonia-containing wastewater according to the present invention includes the step of adding a chemical solution containing hypobromous acid and / or hypochlorous acid to the cyanide- and ammonia-containing wastewater to oxidatively decompose cyanide. In the present invention, the "ammonia" includes "ammonium ions". The "cyan" means "cyanide ion" and "cyano compound such as cyano complex".

In one aspect of the present invention, the medicinal solution substantially only contains hypobromous acid and / or hypobromite as an oxidizing agent component. In another aspect of the present invention, the medicinal solution includes hypobromous acid and / or hypobromite and hypochlorous acid and / or hypochlorite as oxidant components.

In the method for treating cyanide and ammonia-containing wastewater of the present invention, ammonia is oxidatively decomposed by a reaction according to the following formula by using hypobromite ion.

_{^{OBr - + NH 4 + → NH}} 3 Br + + OH - .............................. (3)

_{^{2NH 3 Br + + OBr - →}} N 2 + 3Br - + H 2 O + 2H + ......... (4)

_{^{2NH 4 + + 3OBr - → N}} 2 + 3Br - + 3H 2 O + 2H + ......... (5)

In addition, cyanide is decomposed by the oxidizing power of hypobromous acid.

In the method of the present invention, as shown in formula (3), the bromide ion system and ammonia generate bromoamine, but the bromineamine system has a stronger oxidizing power than the chloramine produced by the chlorine agent. Therefore, cyanogen may be decomposed by the bromine amine system.

In the present invention, since no chlorine agent is added or the amount thereof is small, it is possible to prevent or suppress the generation of cyanide due to the reaction of the combined chlorine and organic matter, and to perform treatment in a manner that the cyanide concentration is sufficiently low.

In the present invention, the ferrocyano complex is decomposed by strong oxidation of hypobromite ion or bromineamine. Therefore, even when the dissolved iron concentration in the cyanide-containing and ammonia-containing wastewater is higher than 0.1 mg / L, cyanide is sufficiently decomposed. In addition, cyanide can be sufficiently decomposed even at a pH of 11 or less.

Implementation of the invention

Hereinafter, the present invention will be described in more detail.

In the present invention, although the cyanide and ammonia-containing drainage to be treated are exemplified by cyanide and ammonia-containing drainage such as ironworks drainage, plating factory drainage, electronics industry drainage, petroleum refining factory drainage, and the like, they are not limited thereto.

Under normal circumstances, the total cyanide concentration of such cyanide and ammonia-containing wastewater is about 0.1 to 400 mg / L, and the ammonia concentration is more than 10 mg / L in terms of ammonium ions, for example, about 10 to 10,000 mg / L. The pH is about 6 to 10.

Cyanide and ammonia-containing wastewaters may contain organic matter such as coal or coke. The concentration of organic matter is usually 1 mg / L or more, for example, about 1 to 1500 mg / L.

Most of the dissolved iron contained in factory wastewater with neutral pH or higher containing cyanide compounds exists as ferric cyanide complexes. In the oxidative decomposition reaction of the cyanide compound in the method of the present invention, since the ferrocyanide complex is also decomposed, the method of the present invention is that even if the cyanide-containing wastewater of the treatment target contains more than 0.1 mg / L of soluble iron, for example, 0.1 to 5 mg / L , Especially 1 ~ 3mg / L, can also fully decompose and treat cyanide and ammonia.

From the viewpoint of avoiding the occurrence of HCN gas, the pH of the cyanide and ammonia-containing wastewater treated by adding hypobromous acid and / or hypobromite is preferred. on.

The ORP of cyanide and ammonia-containing drainage water after the addition of hypobromous acid and / or hypobromite is 400 mV or more, preferably 500 mV or more. By setting the ORP at 400 mV or more, the oxidizing power in the water system can be maintained, and the hardly decomposable ferrocyano complex can be decomposed. On the other hand, the upper limit of the ORP is 800 mV or less from the viewpoint of the cost of the drug, and preferably 650 mV or less.

In the present invention, a medicinal solution containing hypobromous acid and / or hypobromite is added to such cyanide and ammonia-containing wastewater to decompose cyanide.

In one aspect of the present invention, the medicinal solution substantially only contains hypobromous acid and / or hypobromite as an oxidizing agent component. In another aspect of the present invention, the medicinal solution includes hypobromous acid and / or hypobromite and hypochlorous acid and / or hypochlorite as oxidant components.

Examples of the salts include sodium salts and potassium salts, and sodium salts are particularly preferred.

Hypobromite or hypobromite is preferably formed by reacting hypochlorous acid or a salt thereof (preferably sodium hypochlorite) with bromine and / or a bromide, preferably sodium bromide. Hypochlorous acid and sodium bromide are reacted according to the following formula to produce hypobromous acid.

HOCl + NaBr → HOBr + NaCl

Sodium hypochlorite and sodium bromide are reacted in accordance with the following formula to produce sodium hypobromite.

NaOCl + NaBr → NaOBr + NaCl

In addition, hypochlorous acid that reacts with bromine and / or bromide may be chlorine-dissolved water in which chlorine is dissolved in water to generate hypochlorous acid.

For cyanide and ammonia-containing wastewater, containing hypobromous acid and / or hypobromite or The amount of hypochlorous acid and / or hypochlorite-containing solution (medicine solution) to be added in one step can be determined while measuring the ORP value of the water system. Specifically, as described above, it is added before the ORP value reaches 400 mV or more, preferably 500 mV or more.

For cyanide and ammonia-containing wastewater, when adding hypobromous acid and / or hypobromite and hypochlorous acid and / or hypochlorite, the molar amount of hypobromite and / or hypobromite is preferably less The added amount of chloric acid and / or hypochlorite is 0.1 to 1.0 times, and particularly preferably 0.3 to 0.5 times.

The treatment of cyanide and ammonia-containing drainage can be carried out in batches in the tank, or the cyanide and ammonia-containing drainage can be continuously flowed into the reaction tank, and continuous outflow from the reaction tank can be performed in the reaction tank. In the cyanolysis reaction, cyanide and ammonia-containing wastewater may be flowed to a pipe, and a chemical solution may be added to the pipe to perform pipeline treatment.

In the present invention, the temperature of the water containing cyanide and ammonia drainage is set above 40 ° C, for example, 40 ~ 80 ° C, especially about 50 ~ 70 ° C, thereby increasing the reaction rate of cyanolysis. In order to suppress heating costs, the water temperature is preferably 80 ° C or lower, and particularly preferably 70 ° C or lower.

Examples

Examples and comparative examples are described below. In the following examples and comparative examples, the dissolved iron concentration, ammonium ion concentration, and total cyanide analysis were measured in accordance with JIS K 0102. All residual chlorine and free residual chlorine were measured using a DPD reagent and a residual chlorine meter manufactured by HACH.

[Example 1 (Treatment with a solution containing sodium hypobromite)]

As the test water, the ironworks of the following water quality were used for drainage.

pH: 8.3,

Total cyanide concentration: 0.8mg / L,

Ammonium ion concentration: 532mg / L,

TOC: 22mg / L,

Soluble iron: 1.3mg / L

ORP: 90mV

As a solution containing sodium hypobromite, a solution containing 40% by weight sodium bromide solution and 12% by weight sodium hypochlorite solution is mixed with NaBr: NaOCl = 1: 1 (molar ratio) to generate hypobromous acid. Sodium hypobromite and aqueous sodium hypochlorite.

1000 mL of test water was held in a glass container, the temperature of the water was maintained at 50 ° C., and the pH was set to 12 with NaOH, and then the above-mentioned chemical solution (sodium hypobromite and sodium hypochlorite aqueous solution) was added under the conditions of Table 1. The reaction time of the cyanolysis reaction was 1 hour. Table 1 shows the amount of added chemicals (but converted to NaBr addition rate and NaOCl addition rate to the test water), free residual chlorine concentration after the reaction time has elapsed, ORP, total cyanide concentration, total cyanide decomposition rate, and ammonium ion concentration. And ammonium ion decomposition rate.

[Example 2]

As the test water, the ironworks of the following water quality were used for drainage.

pH: 8.15,

Total cyanide concentration: 0.7mg / L,

Ammonium ion concentration: 354mg / L,

TOC: 17mg / L,

Soluble iron: 1.4mg / L

ORP: 230mV

As the solution containing sodium hypobromite as the chemical solution, the same solution as in Example 1 was used. Then, it processed similarly to Example 1 except having changed pH to 9 with NaOH. Table 1 shows the amount of the added agent, the free residual chlorine concentration after the elapse of the reaction time, the ORP, the total cyanide concentration, the total cyanide decomposition rate, the ammonium ion concentration, and the ammonium ion decomposition rate.

[Example 3]

As the test water, the ironworks of the following water quality were used for drainage.

pH: 8.6,

Total cyanide concentration: 1.2mg / L,

Ammonium ion concentration: 410mg / L,

TOC: 18mg / L,

Soluble iron: 1.0mg / L

ORP: 264mV

The test water was treated in the same manner as in Example 2 except that NaOH was added so as to have a pH of 9.6. The results are shown in Table 1.

[Comparative Example 1 (Treatment with sodium hypochlorite)]

As the test water, the ironworks of the following water quality were used for drainage.

pH: 8.7,

Total cyanide concentration: 0.7mg / L,

Ammonium ion concentration: 451mg / L,

TOC: 13mg / L,

Soluble iron: 1.3mg / L

ORP: 230mV

The test water was treated in the same manner as in Example 1 except that instead of the solution containing sodium hypobromite, sodium hypochlorite (12 wt% aqueous solution) was used, NaOH was added to pH 11.1, and NaOCl was added in the amount shown in Table 1. The results are shown in Table 1.

[Comparative Example 2 (treatment with sodium hypochlorite)]

As the test water, the ironworks of the following water quality were used for drainage.

pH: 8.7,

Total cyanide concentration: 3.0mg / L,

Ammonium ion concentration: 120mg / L,

TOC: 10mg / L,

Soluble iron: 0.1mg / L

ORP: 210mV

The test water was treated in the same manner as in Example 1 except that sodium hypobromite (12 wt% aqueous solution) was used instead of the solution containing sodium hypobromite, NaOH was added to pH 11.3, and NaOCl was added in the amount shown in Table 1. The results are shown in Table 1.

As shown in Table 1, according to Examples 1 to 3 using a solution containing sodium hypobromite, compared with Comparative Examples 1 and 2 using only sodium hypochlorite, the cyanide system was sufficiently decomposed. Furthermore, in Comparative Example 1 in which the dissolved iron concentration was high and only sodium hypochlorite was used, the result of the treatment was that the total cyanide concentration was higher than that of the test water. In the present invention, cyanide is sufficiently decomposed even under the condition that the dissolved iron concentration is high and the pH is less than 11.

[Example 4 (Treatment with a solution containing sodium hypobromite)]

As the test water, the ironworks of the following water quality were used for drainage.

pH: 8.2

Ammonium ion concentration: 410mg / L

TOC: 21mg / L

Soluble iron: 0.8mg / L

ORP: 187mV

As a chemical solution (a solution containing sodium hypobromite and sodium hypochlorite), a 40% by weight sodium bromide solution and a 12% by weight sodium hypochlorite aqueous solution were mixed with NaBr: NaOCl = 1: 1 (molar ratio) to form a secondary solution. Liquid sodium bromide.

1000 mL of test water was contained in a glass container, the temperature of the water was maintained at 50 ° C., and the pH was 9.6 with NaOH, and then the above-mentioned chemical solution was added. The reaction time was 5 min.

Table 2 shows the amount of chemicals added (but converted into NaBr addition rate and NaOCl addition rate to the test water) and the residual chlorine concentration after the reaction time has elapsed.

[Comparative Example 3 (Treatment with sodium hypochlorite)]

The same test water was treated in the same manner as in Example 4 except that only sodium hypochlorite (12 wt% aqueous solution) as a chemical solution was added in the amount shown in Table 2. The results are shown in Table 2.

[Examples 5 to 9 (treatment with liquid containing sodium hypobromite)]

As the test water, the ironworks of the following water quality were used for drainage.

pH: 8.3

Ammonium ion concentration: 532mg / L

TOC: 22mg / L

Soluble iron: 1.3mg / L

ORP: 90mV

As a medicinal solution (a solution containing sodium hypobromite, or sodium hypobromite and sodium hypochlorite), a 40% by weight sodium bromide solution and a 12% by weight sodium hypochlorite aqueous solution were mixed at a compounding amount in Table 2 to generate hypobromous acid. Sodium liquid.

1000 mL of test water was stored in a glass container, the water temperature was maintained at 50 ° C., and the pH was adjusted to 9.7 (Example 5) or 9.6 (Examples 6 to 9) with NaOH, and then an aqueous sodium hypobromite solution was added. The reaction time was 5 min.

Table 2 shows the amount of chemicals added (but converted into NaBr addition rate and NaOCl addition rate to the test water) and the residual chlorine concentration after the reaction time has elapsed.

[Table 2]

<Inspection>

As shown in Table 2, according to Examples 4 to 9 in which a solution containing sodium hypobromite and sodium hypochlorite was added, even if the dissolved iron concentration was high, the residual chlorine was less than that in Comparative Example 3 where only sodium hypochlorite was added. Therefore, it was found that the occurrence of halogen gas can be suppressed in the present invention.

The present invention has been described in detail using specific aspects, but those skilled in the art will recognize that various changes can be made without departing from the spirit and scope of the present invention.

This application is based on Japanese Invention Patent Application 2014-084692 filed on April 16, 2014, and the entire system is incorporated by reference.

Claims (7)

A treatment method for cyanide and ammonia-containing wastewater, which comprises the steps of adding a chemical solution containing hypobromous acid and / or hypobromite to cyanide and ammonia-containing wastewater, and oxidizing and decomposing cyanide at a pH of 9 or less and 11 or less. The treatment method for cyanide and ammonia-containing wastewater according to claim 1, wherein the aforementioned chemical solution is a mixture of bromine and / or bromide aqueous solution and hypochlorous acid and / or hypochlorite aqueous solution to generate hypobromous acid and / or hypobromide Salt solution For example, the treatment method for cyanide and ammonia-containing wastewater according to claim 2, wherein the mixed amount of bromine and / or bromide and hypochlorous acid and / or hypochlorite is an equal molar amount. For example, the treatment method for cyanide and ammonia-containing wastewater according to claim 1, wherein the aforementioned medicinal solution is mixed with hypochlorous acid and / or hypochlorite for bromine and / or bromide in an amount more than equal molar amount, and contains A solution prepared by the method of hypobromous acid and / or hypobromite and hypochlorous acid and / or hypochlorite. The treatment method for cyanide and ammonia-containing wastewater according to any one of claims 2 to 4, wherein the bromide is sodium bromide and the hypochlorite is sodium hypochlorite. The treatment method for cyanide and ammonia-containing wastewater according to any one of claims 1 to 4, wherein the dissolved iron concentration in the cyanide and ammonia-containing wastewater is 0.1 mg / L or more. The treatment method for cyanide and ammonia-containing wastewater according to any one of claims 1 to 4, wherein the ORP (redox potential) is set to 400 mV or more.