KR20140138173A - Method for treating cyanogen-containing waste water - Google Patents

Abstract

The present invention also provides a method for treating cyanide-containing wastewater, which can sufficiently oxidatively decompose the cyanide compound even when the cyanide-containing wastewater contains ammonium ions and organic matter, and also prevents scaling. A method for treating cyanide wastewater, which decomposes a cyanide compound by adding a chlorine source to cyanide wastewater containing cyanide compound, characterized in that the cyanide wastewater contains ammonium ions and organic matter and the pH of the cyanide wastewater is 11 , And a phosphonic acid-based scale inhibitor is added while the chlorine source is added so that the free residual chlorine concentration is not less than 0.1 mg / liter even after the cyanide decomposition reaction.

Description

METHOD FOR TREATING CYANOGEN-CONTAINING WASTE WATER [0002]

The present invention relates to a method for treating cyanide-containing wastewater, and more particularly to a method for treating cyanide-containing wastewater by an alkali chlorine method.

As a method for treating cyanide wastewater discharged from industrial facilities such as a plating plant, a steel mill, a smeltering plant, a power plant, and a coke manufacturing plant, the most widely adopted method at present is the alkali chlorine method. In this method, a chlorine source (e.g., sodium hypochlorite) is added to the cyanide-containing wastewater under alkaline conditions to oxidize the cyanide being drained (Patent Documents 1 and 2).

In the alkali chlorine method of Patent Document 1, the cyanide compound is oxidatively decomposed by a two-step reaction in the following pH and ORP control values.

1 reaction: pH 10 or higher, ORP control value 300 ~ 350 ㎷

NaCN + NaOCl? NaCNO + NaCl ... (One)

2-step reaction: pH 7 ~ 8, ORP control value 600 ~ 650 ㎷

2NaCNO + 3NaClO + H ₂ O? N ₂ + 3NaCl + 2NaHCO ₃ ... (2)

Patent Document 2 discloses a method of treating cyanide wastewater containing ammonia by a two-step reaction in an alkali chlorine method.

Japanese Patent Laid-Open No. 2001-269674 Japanese Patent Application Laid-Open No. 2006-334508

As a result of the research conducted by the present inventors, it has been found that when the alkali chlorine method is applied when cyanide-containing wastewater contains ammonium ions and organic matter, the cyanide compound is not sufficiently oxidized in the first stage reaction.

That is, when cyanide containing ammonium ions and organic substances is treated at pH 10 to 10.5, which is a general pH range in the first-stage reaction of the conventional alkali chlorination method, and ORP 300 to 350 ° C, decomposition of the cyanide compound is insufficient . In addition, when NaClO is added and the ORP is increased to 400 ㎷ or more, the total cyanide concentration does not decrease. Control over ORP of 300 to 350 pH at pH 11 or higher requires an extra chlorine source, which may increase the cost and corrosion of the steel.

If the cyanide compound is not sufficiently oxidized in the first-stage reaction of the alkali chlorine method as described above, not only the second-step reaction proceeds but also the cyanide compound reacts with sodium hypochlorite in the second- CNCl) may occur.

Further, when a chlorine source is added to cyanide-containing wastewater containing ammonium ions and organic matter, if the pH is less than 11, ammonium ion and chlorine source react with each other to produce bonded chlorine. This combined chlorine reacts with the organic matter to generate cyanide, so that the cyanide concentration of the cyanide-containing wastewater may not decrease or may rise inversely.

It is an object of the present invention to solve the above-mentioned conventional problems and to provide a method for treating cyanide-containing wastewater which can sufficiently oxidatively decompose a cyanide compound even when cyanide-containing wastewater contains ammonium ions and organic matter. It is another object of the present invention to provide a method of treating cyanide-containing wastewater in which scaling is prevented in the one embodiment.

A method of treating cyanide wastewater according to the present invention is a method for treating cyanide wastewater that decomposes a cyanide compound by adding a chlorine source to cyanide wastewater containing a cyanide compound wherein the cyanide wastewater contains ammonium ions and organic matter , And the chlorine source is added so that the pH of the cyanide-containing wastewater is 11 or more and the free residual chlorine concentration is 0.1 mg / liter or more even after the cyanide decomposition reaction.

As the chlorine source, at least one kind of sodium hypochlorite, chlorine and bleaching powder is preferable.

In one embodiment of the present invention, a phosphonic acid-based scale inhibitor is further added to the cyanide-containing wastewater.

As the phosphonic acid-based scale inhibitor, at least one species selected from 1-hydroxyethylidene-1,1-diphosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid and salts thereof is preferable .

In the present invention, it is preferable to add the chlorine source so that the free residual chlorine concentration is 0.1 to 1 mg / l.

It is also preferable to add an alkali agent to the cyanide-containing wastewater to adjust the pH to 11 to 12.5. In this case, it is preferable that the alkali agent and the anti-scale agent are mixed and liquefied.

The concentration of soluble iron in the cyanide-containing wastewater is preferably 0.4 mg / liter or less.

The water temperature of the cyanide-containing wastewater is preferably 40 ° C or higher, for example, 40 to 80 ° C, particularly preferably 50 to 70 ° C.

In the method of treating cyanide wastewater of the present invention, a chlorine source is added at a pH of 11 or higher to cyanide wastewater containing ammonium ions and organic matter. When the pH is higher than 11, the reaction between the chlorine source and the ammonium ion is inhibited, thereby inhibiting the formation of bound chlorine, and as a result, the cyanogenesis due to the reaction between bound chlorine and the organic matter is also suppressed.

The addition of the phosphonic acid-based scale inhibitor to the cyanide-containing wastewater prevents (suppresses) the generation of scale.

To adjust the pH to 11 or more, it is preferable to add an alkali agent. When this alkaline agent and the anti-scale agent are mixed and added in one liquor, scale trouble can be prevented in the drug infusion pump and the medicine infusion line.

Further, in the present invention, it is preferable that the pH is 11 or higher even after completion of the decomposition reaction of the cyanide compound.

Further, by adding a chlorine source to the ammonium ion and the organic substance-containing wastewater at a pH of 11 or more, and after the reaction, the free residual chlorine concentration is made to be 0.1 mg / liter or more, whereby cyanide is sufficiently oxidized, .

By controlling the free residual chlorine concentration after the reaction to 1 mg / liter or less, the corrosion of the liquid contact member made of steel or the like is suppressed.

When the water temperature at the time of the reaction is 40 占 폚 or higher, the efficiency of the cyanide decomposition reaction is improved, and the cyanide concentration is lowered in a short time. Further, when the reaction time is short, the contact time between the water to be treated containing free residual chlorine and the liquid contact member is shortened, and the corrosion of the liquid contact member made of a steel material or the like is suppressed.

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

In the present invention, the cyanide wastewater to be treated is a cyanide complex of metal, such as Ni, Ag, Cu, or the like, which is discharged from an industrial facility such as a plating plant, a power plant, a steel mill, a smelter, Zn, Cd, and the like, but the present invention is not limited thereto.

Normally, the cyanide concentration of such cyanide-containing wastewater is about 0.1 to 100 mg / L, and the pH is about 6 to 10.

In the present invention, the cyan-containing waste water containing ammonium ions and organic substances is treated. The concentration of the ammonium ion is preferably 5 mg / L or more, for example, about 5 to 250 mg / L. Examples of the organic substance include those derived from coal or coke, and the concentration thereof is preferably 1 mg / L or more, for example, about 1 to 30 mg / L.

Most of the soluble iron contained in the factory wastewater having pH neutral defects containing the cyanide compound is present as an iron cyanocomplex. In the cyanide compound oxidative decomposition reaction by the alkali chlorine method of the method of the present invention, the iron cyano complex is not decomposed well. Therefore, the cyanide-containing wastewater to be treated by the method of the present invention is preferably such that the total cyanide concentration of the iron cyano complex is 1.0 mg / liter or less and the soluble iron concentration is less than 0.4 mg / liter.

Examples of the chlorine source to be added to the cyanide-containing wastewater include chlorine, bleaching powder, sodium hypochlorite and the like. Examples of the phosphonic acid-based scale inhibitor added to the cyanide-containing wastewater include 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), 2-phosphonobutane-1,2,4-tricarboxyl (PBTC), and salts thereof. Examples of the salt include sodium salt, potassium salt and the like, among which 1-hydroxyethylidene-1,1-diphosphonic acid is preferable.

When adding a chlorine source to the cyanide-containing wastewater, the pH of the cyanide-containing wastewater is adjusted to 11 or more, preferably 11 to 12.5, especially 11 to 12, by adding an alkali such as NaOH and / or KOH, if necessary. The alkali addition may be carried out before or after the addition of the chlorine source, or simultaneously. If the pH of the cyanide-containing wastewater is 11 or more, the alkali may not be added. It is also preferable that the pH of the water after the treatment is 11 or higher.

When the alkali agent and the scale inhibitor are added to the cyanide-containing wastewater, the alkaline agent and the anti-scale agent may be mixed and liquefied. In this way, scale generation in the medicine infusion pump and the medicine infusion line is prevented. The amount of the anti-scale agent to be added is preferably determined empirically according to the quality of the cyanide-containing wastewater, but is usually about 1 to 100 mg / l, particularly about 5 to 30 mg / l.

The addition amount of the chlorine source is controlled so that the free residual chlorine concentration after the reaction is 0.1 mg / liter or more, preferably 0.1 to 1 mg / liter, particularly 0.1 to 0.5 mg / liter.

When the treatment of the cyanide wastewater is carried out in a batch manner in the tank, the free residual chlorine concentration of the liquid in the bath is measured over time, and when the rate of decrease of the free residual chlorine concentration is zero or below a predetermined value The reaction may be terminated. The preferred value is a value selected from 0 to 0.1 mg / l / min.

When the cyanide-containing wastewater is continuously introduced into the reaction tank and continuously flowed out from the reaction tank, and the cyanide decomposition reaction is carried out in the reaction tank, the residence time in the bath is made longer than the reaction termination time, It is preferable to treat the residual chlorine concentration as the free residual chlorine concentration after the reaction.

When cyanide-containing wastewater is caused to flow into a pipe, and a chlorine source and, if necessary, a scale inhibitor and an alkali are added to the pipe and subjected to a line treatment, the free residual chlorine concentration is measured at a plurality of points downstream of the line, , It can be regarded that the reaction is terminated at the measurement point or upstream of the measurement point. It is preferable that the measurement point is spaced by 5 m or more, particularly 10 to 30 m.

When cyanide wastewater is treated under such conditions, the formation of bound chlorine is suppressed and the cyanogenesis due to the reaction of bound chlorine and organic matter is also suppressed by setting the pH to 11 or more. Further, by adding a scale inhibitor, scale adhesion is prevented, and the cyan-containing wastewater can be stably treated.

Cyanide is sufficiently decomposed by adding a chlorine source so that the concentration of free residual chlorine after completion of the reaction is 0.1 mg / L or more. By making the free residual chlorine concentration after completion of the reaction not more than 1 mg / L, excessive addition of the chlorine source is prevented, and the chlorine source cost is suppressed. In addition, corrosion of a metal material such as a steel material constituting the electrode member is also suppressed.

In the present invention, it is preferable to set the water temperature of the cyanide-containing wastewater to 40 ° C or higher, for example, about 40 to 80 ° C, particularly about 50 to 70 ° C, thereby increasing the cyanide decomposition reaction rate. When the decomposition rate of cyanide is increased, the contact time between the for-treatment water containing free residual chlorine and the liquid contact member made of steel or the like is shortened, and corrosion of the liquid contact member is suppressed. In order to suppress the heating cost, the water temperature is preferably 80 占 폚 or lower, particularly 70 占 폚 or lower.

Example

Examples and Comparative Examples are described below. In the following examples and comparative examples, a NaCl aqueous solution (concentration of 12 wt%) was used as a chlorine source as an aqueous solution of NaOH (concentration of 48 wt%) as an alkali agent and HEDP, PBTC and an acrylic acid polymer Sodium acrylate (weight average molecular weight: 3500)) or a maleic acid polymer (sodium salt of isobutylene / maleic anhydride copolymer (weight average molecular weight: 15000)) was used. The total CN analysis was carried out by adding L (+) - ascorbic acid to reduce the residual chlorine, adjusting the pH to 12 with NaOH, and filtering according to JIS K 0102 according to the 4-pyridine-pyrazolone spectrophotometry Respectively. The scale prevention effect was judged based on the calcium ion concentration and the presence or absence of scale attachment to the test piece made of SUS in the reaction vessel.

[Examples 1 to 7 and Comparative Examples 1 to 9]

As the test water, the following water quality power generation facilities were used.

pH: 8.7,

Total cyan: 3 mg / l,

Ammonium ion: 120 mg / l,

TOC: 10 mg / l,

Soluble iron: less than 0.1 mg / l

50 ml of the test water was contained in a glass container with a cover and the water temperature was maintained at 20 캜, 40 캜, 50 캜 or 60 캜, and the alkaline agent and the chlorine source were added so as to meet the conditions shown in Table 1. The reaction time was as follows.

120 minutes at a water temperature of 20 ° C

90 minutes for water temperature 40 ℃

Water temperature 50, 60 minutes at 60 ℃

Table 5 shows the pH, the amount of NaClO added, the residual chlorine concentration after the elapse of the reaction time, the ORP and the total cyanide concentration after elapse of 5 minutes from the addition of the reagent and after each of the above elapsed time. In Table 1 and Tables 2 and 3 to be described later, "free" represents free residual chlorine.

As shown in Table 1, it can be seen that the total cyan concentration is lowered in each Example of pH > 11 even after the completion of the reaction, and the total cyan concentration is lowered by increasing the water temperature .

[Examples 8 and 9]

As the test water, the following water quality power generation facilities were used.

pH: 8.2,

Total cyan: 3 mg / l,

Ammonium ion: 100 mg / l,

TOC: 8 mg / l,

Soluble iron: less than 0.1 mg / l

An alkaline agent and a chlorine source were added under the conditions shown in Table 2, and an iron test piece was added. The mixture was stirred for 3 days with a stirrer (rotation number: 150 rpm) Lt; / RTI > The results are shown in Table 2. In Examples 8 and 9, as described above, a test piece made of iron (SPCC) was put in each beaker, and after 3 days, the water quality and the corrosion amount were measured and the corrosion rate was measured. Respectively.

As shown in Table 2, the corrosion rate of Example 8 in which the free residual chlorine concentration is low is lower than that in Example 9.

[Examples 10 to 15]

As the test water, the following water quality power generation facilities were used.

pH: 8,

Total cyan: 3 mg / l,

Ammonium ion: 130 mg / l,

TOC: 7 mg / l,

Soluble iron: less than 0.1 mg / l

500 ml of the test water was placed in a cover attachment beaker and the water temperature was kept at 25 캜, 40 캜, 50 캜, 60 캜 or 80 캜, and the alkaline agent and the chlorine source were added under the conditions shown in Table 3. The measured water quality after 60 minutes is shown in Table 3.

As shown in Table 3, the higher the water temperature, the lower the cyanide concentration after the reaction.

[Examples 16 to 19]

A ferric chloride aqueous solution was added to the same power generation facility collection water as in Example 1 to prepare a test water having a soluble iron concentration of 0.1 mg / l, 0.3 mg / l, 0.4 mg / l or 0.5 mg / l. 500 ml of each test water was collected in a glass container with a cover and the water temperature was maintained at 60 ° C and the chlorine source was added so that the concentration after the addition was 33.5 mg / And reacted for 60 minutes. Table 4 shows the measured water quality after 60 minutes.

As shown in Table 4, the higher the concentration of soluble iron, the higher the cyanide concentration after the reaction.

[Examples 20 to 22, Comparative Examples 10 to 13]

As the test water, we use the following water quality water collection facilities.

pH: 8.7,

Total cyan: 3 mg / l,

Ammonium ion: 120 mg / l,

TOC: 10 mg / l,

Soluble iron: less than 0.1 mg / l

500 ml of the test water was placed in a glass container with a lid, the water temperature was maintained at 60 캜, and an anti-scale agent, an alkali agent and a chlorine source were added so as to meet the conditions shown in Table 1. Further, a test piece made of SUS was placed in the container. The reaction time was 60 minutes.

Table 5 shows the pH, the amount of NaClO added, the calcium ion concentration after the elapse of the reaction time, the presence or absence of scale adhesion to the test piece, and the total cyan concentration after 5 minutes from the addition of the drug and after 60 minutes elapsed.

As shown in Table 5, according to the present invention, cyan can be sufficiently decomposed, and scale can be prevented. In Comparative Example 10, since the pH is less than 11, the residual cyanide concentration is high. In Comparative Example 11, no scale inhibitor was added and scale was generated. In Comparative Examples 12 and 13, an anti-scale agent was added, but a scale was attached because it was not a phosphonic acid-based anti-scale agent.

While the invention has been described in detail with reference to specific embodiments thereof, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.

 The present application is based on Japanese patent application (special license 2012-080437) filed on March 30, 2012 and Japanese patent application (special license 2012-080438) filed on March 30, 2012, all of which are incorporated herein by reference. Quot;

Claims (10)

A method of treating cyanide wastewater for decomposing a cyanide compound by adding a chlorine source to cyanide wastewater containing a cyanide compound,
The cyanide-containing wastewater contains ammonium ions and organic matter,
Wherein the chlorine source is added so that the pH of the cyanide-containing wastewater is 11 or more and the free residual chlorine concentration is 0.1 mg / liter or more even after the cyanide decomposition reaction. The method according to claim 1,
Characterized in that a phosphonic acid-based scale inhibitor is further added to the cyan containing wastewater. 3. The method of claim 2,
Wherein the phosphonic acid-based scale inhibitor is at least one selected from 1-hydroxyethylidene-1,1-diphosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, and salts thereof Characterized in that the cyanide-containing waste water is treated. The method according to claim 2 or 3,
Wherein the alkaline source and the anti-scale agent are mixed and liquefied and added. 3. The method according to claim 1 or 2,
Wherein the chlorine source is added so that the free residual chlorine concentration is 0.1 to 1 mg / l. 3. The method according to claim 1 or 2,
Wherein the alkaline agent is added to the cyan containing wastewater to adjust the pH to 11 to 12.5. The method according to claim 6,
Wherein the alkaline agent is added so that the pH after the cyanide decomposition reaction is 11 or higher. 3. The method according to claim 1 or 2,
Wherein the concentration of soluble iron in the cyanide-containing wastewater is 0.4 mg / liter or less. 3. The method according to claim 1 or 2,
Wherein the water temperature of the cyanide-containing wastewater is 40 占 폚 or higher. 3. The method according to claim 1 or 2,
Wherein the chlorine source is at least one of sodium hypochlorite, chlorine and bleaching powder.