TW201339105A - Method for treating cyanide-containing wastewater - Google Patents

Abstract

A method for treating cyanide-containing wastewater is provided. Even when the cyanide-containing wastewater includes an ammonia ion and organic substances, the method fully oxidatively decomposes a cyanide compound and additionally avoids scales. The method for treating cyanide-containing wastewater adds a chlorine source in the cyanide-containing wastewater containing the cyanide compound to decompose the cyanide compound, and the method is characterized in that the cyanide-containing wastewater includes an ammonia ion and organic substances; pH value of the cyanide-containing wastewater is set to 11 or more; the chlorine source is added in a way that free residual chlorine concentration becomes 0.1 mg/L or more even after decomposing reaction of the cyanide compound; and a phosphonic acid-based scale inhibitor is added.

Description

Cyanide-containing drainage treatment method

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

As a treatment method for cyanide-containing drainage discharged from industrial facilities such as a plating plant, a steel mill, a smelting plant, a power generation plant, and a coke manufacturing plant, the most widely used method is the alkali chloride method. In this method, a chlorine source such as sodium hypochlorite is added to the cyanide-containing drainage under alkaline conditions, and the cyanide in the drainage is oxidized (Patent Document 1 and Patent Document 2).

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

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

NaCN+NaOCl→NaCNO+NaCl...(1)

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

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

Patent Document 2 describes a method in which a cyanide-containing drainage containing ammonia is treated by a two-stage reaction of an alkali chloride method.

Prior technical literature Patent literature

Patent Document 1: Japanese Patent Laid-Open 2001-269674

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

As a result of investigations by the inventors of the present invention, it has been found that when the cyanide-containing drainage contains ammonium ions and organic substances, when the alkali chloride method is applied, the cyanide compound is not sufficiently oxidized in the first-stage reaction.

That is, the cyanide containing ammonium ions and organic substances is treated under the conditions of a normal pH range of 10 to 10.5 and an ORP of 300 mV to 350 mV in the first-stage reaction of the conventional alkali chloride method. In the case, the decomposition of the cyanide compound is insufficient. Further, even if NaClO is added and the ORP is increased to 400 mV or more, the total cyanide concentration is not lowered. In order to control the pH value of 11 or more and the ORP to be 300 mV to 350 mV, an excessive chlorine source is required, which may increase the cost and corrosion of the steel.

If the cyano compound is not sufficiently oxidized in the first-stage reaction of the alkali chloride method, not only the second-stage reaction does not proceed, but also the cyanide compound may react with sodium hypochlorite in the second-stage reaction to produce cyanogen chloride (CNCl). ).

In addition, a chlorine source is added to the cyanide-containing wastewater containing ammonium ions and organic matter. In the case where the pH is less than 11, the ammonium ion reacts with the chlorine source to form bound chlorine. Since the combined chlorine reacts with the organic substance to form cyanide, the cyanide concentration of the cyanide-containing drainage does not decrease, but may increase.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and to provide a method for treating cyanide-containing drainage, which can sufficiently oxidize and decompose a cyano compound even when the cyanide-containing drainage contains ammonium ions and organic substances. Further, in one embodiment of the present invention, an object of the invention is to provide a method for treating cyanide-containing drainage which prevents scale formation.

The cyanide-containing drainage treatment method of the present invention adds a chlorine source to the cyanide-containing drainage containing a cyanide compound to decompose the cyanide compound, and the cyanide-containing drainage treatment method is characterized in that the cyanide-containing drainage contains ammonium ions and organic substances, and The pH of the cyanide-containing water is adjusted to 11 or more, and the chlorine source is added so that the free residual chlorine concentration becomes 0.1 mg/L or more even after the decomposition reaction of the cyanide compound.

The chlorine source is preferably at least one of sodium hypochlorite, chlorine, and bleaching powder.

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

The phosphonic acid scale inhibitor is preferably selected from the group consisting of 1-hydroxyethylidene-1,1-diphosphonic acid, 2-phosphoniumbutane-1,2,4-tricarboxylic acid and the like. At least one.

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

Further, it is preferred to add an alkali agent to the cyanide-containing drainage to adjust the pH to 11 to 12.5. In this case, it is preferred to mix the alkali agent with the scale inhibitor and add it as a liquid.

Preferably, the concentration of the soluble iron containing the cyanide-containing water is 0.4 mg/L or less.

Preferably, the water temperature of the cyanide-containing drainage water is set to 40 ° C or higher, for example, 40 ° C to 80 ° C, and particularly preferably 50 ° C to 70 ° C.

In the method for treating cyanide-containing wastewater of the present invention, a cyanide-containing water containing ammonium ions and an organic substance is added to a chlorine source at a pH of 11 or more. When the pH is 11 or more, the reaction between the chlorine source and the ammonium ion is suppressed, whereby the formation of the bound chlorine is suppressed, and as a result, the cyanide formation by the reaction of the combined chlorine with the organic substance is also suppressed.

The formation of scale is prevented (including suppressed) by adding a phosphonic acid-based scale inhibitor to the cyanide-containing drainage.

In order to adjust the pH to 11 or more, it is preferred to add an alkali agent. When the alkaline agent is mixed with the scale inhibitor and added as one liquid, the scale in the injection (chemical injection) pump or the injection pipe is prevented from being troubled.

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

In addition, a chlorine source is added to a drain containing ammonium ions and an organic substance at a pH of 11 or more, and even if the residual residual chlorine concentration is 0.1 mg/L or more after the reaction, the cyanide is sufficiently oxidized and treated. The cyanide concentration in the drainage is sufficiently reduced.

By setting the free residual chlorine concentration after the reaction to 1 mg/L or less, corrosion of the liquid contact member including the steel material or the like is suppressed.

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

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

In the present invention, the cyanide-containing water to be treated may be exemplified by industrial facilities such as a plating plant, a power station, a steel mill, a smelting plant, and a coke manufacturing plant, and a metal cyanide complex such as Ni or Ag. The cyanide-containing cyanide-containing water is contained in the form of a cyanide complex of a metal such as Cu, Zn or Cd, but is not limited thereto.

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

In the present invention, a cyanide-containing drainage containing ammonium ions and an organic substance is treated. The concentration of the ammonium ion is preferably 5 mg/L or more, for example, about 5 mg/L to 250 mg/L. Further, the organic substance may be exemplified by coal or coke, and the concentration thereof is preferably 1 mg/L or more, for example, about 1 mg/L to 30 mg/L.

The pH of the cerium-containing compound contained in the factory wastewater above neutral Most of the dissolved iron is in the form of a ferricyanide complex. In the oxidative decomposition reaction of a cyanide compound using an alkali chloride method in the method of the present invention, it is difficult to decompose the ferricyanide complex. Therefore, the cyanide-containing water to be treated as the method of the present invention preferably has a total cyanide concentration of 1.0 mg/L or less and a dissolved iron concentration of less than 0.4 mg/L.

Chlorine, bleaching powder, sodium hypochlorite and the like can be exemplified as the chlorine source added to the cyanide-containing drainage. Further, the phosphonic acid-based scale inhibitor added to the cyanide-containing drainage can be exemplified by 1-hydroxyethylidene-1, 1-diphosphonic acid (HEDP), 2- At least one of 2-phosphonobutane-1, 2,4-tricarboxylic acid (PBTC) and the salts thereof, the salt may be exemplified by sodium salt, potassium salt, etc. Among them, 1-hydroxyethylidene-1,1-diphosphonic acid is preferred.

In the case of adding a chlorine source to the cyanide-containing drainage, the pH of the cyanide-containing drainage is adjusted to 11 or more, preferably 11 to 12.5, particularly preferably 11 by adding a base such as NaOH and/or KOH as needed. 12. The base addition can be carried out before or after the addition of the chlorine source, or simultaneously. If the pH of the cyanide-containing drainage is 11 or more, the alkali may not be added. Further, it is preferred that the pH of the water after the treatment is 11 or more.

When the alkali agent and the scale inhibitor are added to the cyanide-containing drainage, the alkali agent and the scale inhibitor may be mixed in advance to form a single liquid. If so, the scale in the injection pump or the injection pipe is prevented from being generated. The amount of the scale inhibitor added is preferably determined experimentally according to the water quality of the cyanide-containing drainage, and is usually preferably 1 mg/L to 100 mg/L, and particularly preferably 5 mg/L to 30 mg/L. .

The amount of the chlorine source to be added is controlled such that the free residual chlorine concentration after the reaction becomes 0.1 mg/L or more, preferably 0.1 mg/L to 1 mg/L, and particularly preferably 0.1 mg/L to 0.5 mg/L.

In the case where the cyanide-containing drainage treatment is carried out in a batch in a tank, the time at which the rate of decrease in the free residual chlorine concentration is zero or a predetermined value or less is determined as long as the free residual chlorine concentration of the solution in the tank is measured over time. The end time is fine. The predetermined value is preferably set to a value selected from the range of 0 mg/L/min to 0.1 mg/L/min.

When the cyanide-containing drainage is continuously introduced into the reaction tank and continuously flows out from the reaction tank, and the cyanide decomposition reaction is carried out in the reaction tank, it is preferred that the residence time in the tank is longer than the reaction end time. The concentration of free residual chlorine measured at the outlet of the reaction tank is regarded as the concentration of free residual chlorine after the reaction.

When the cyanide-containing water is circulated in the pipe and the chlorine source and the required scale inhibitor and alkali are added to the pipe for line treatment, the free residue can be measured at a plurality of locations on the downstream side of the line. When the chlorine concentration is substantially the same as the measured value of the free residual chlorine concentration at two or more sites, it is considered that the reaction is completed in the measurement site or a region higher than the upstream. Preferably, the measurement site is separated by more than 5 m, and particularly preferably from about 10 m to 30 m.

When the cyanide-containing drainage is treated under such conditions, by adjusting the pH to 11 or more, the formation of bound chlorine is suppressed, and cyanogenesis due to the reaction of the combined chlorine with the organic substance is also suppressed. Further, by adding a scale inhibitor to prevent scale adhesion, the treatment of cyanide-containing drainage can be stably performed.

By the concentration of free residual chlorine after the end of the reaction is 0.1 mg / L The chlorine source is added in the above manner, and the cyanogen is sufficiently decomposed. By setting the free residual chlorine concentration after the completion of the reaction to 1 mg/L or less, excessive addition of the chlorine source is prevented, and the cost of the chlorine source is suppressed. Further, corrosion of a metal material such as a steel material constituting the liquid contact member is also suppressed.

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

Example

Hereinafter, examples and comparative examples will be described. Further, in the following examples and comparative examples, an aqueous NaOH solution (concentration: 48 wt%) was used as an alkali agent, and an aqueous NaClO solution (concentration: 12 wt%) was used as a chlorine source, and HEDP, PBTC, and an acrylic polymer were used. (Sodium polyacrylate (weight average molecular weight: 3,500)) or a maleic acid polymer (sodium salt of an isobutylene-maleic anhydride copolymer (weight average molecular weight: 15,000)) is used as a scale inhibitor. In addition, the total CN analysis is the addition of L(+)-ascorbic acid (L(+)-ascorbic acid) to reduce residual chlorine, using NaOH to adjust the pH to 12, without filtration by Japanese Industrial Standards. , JIS) K 0102 was determined by 4-pyridine-pyrazolone spectrophotometry. Regarding the scale resistance effect, depending on the calcium ion concentration and the test piece on stainless steel (Stainless Steel, SUS) in the reaction vessel The scale is attached to judge.

[Example 1 to Example 7, Comparative Example 1 to Comparative Example 9]

The dust collecting water of the power generation equipment of the following water quality is used as the test water.

pH: 8.7, total cyanide: 3 mg/L, ammonium ion: 120 mg/L, total organic carbon (TOC): 10 mg/L, soluble iron: less than 0.1 mg/L

50 mL of test water was placed in a glass container with a lid, and the water temperature was maintained at 20 ° C, 40 ° C, 50 ° C or 60 ° C, and an alkali agent and a chlorine source were added so as to be in the conditions of Table 1. The reaction time is set as follows.

Water temperature is 20 ° C: 120 minutes

Water temperature is 40 ° C: 90 minutes

Water temperature is 50 ° C, 60 ° C: 60 minutes

The pH value, the amount of NaClO added, the residual chlorine concentration after the above reaction time, the ORP and the total cyanide concentration after 5 minutes from the addition of the chemical agent are shown in Table 1. In Table 1 and Tables 2 and 3 to be described later, free means free residual chlorine.

As shown in Table 1, the total cyanide concentration of each of the examples set to pH ≧11 after the completion of the reaction was lower than the comparative examples of pH <11, and the water temperature was further increased, and the total cyanide concentration was increased. The lower it becomes.

[Embodiment 8, Example 9]

The dust collecting water of the power generation equipment of the following water quality is used as the test water.

pH: 8.2, total cyanide: 3 mg/L, ammonium ion: 100 mg/L, TOC: 8 mg/L, soluble iron: less than 0.1 mg/L

100 mL of test water was stored in a 1000 mL beaker, and the water temperature was maintained at 60 ° C. Under the conditions of Table 2, an alkali agent and a chlorine source were added, and an iron test piece was placed, and the rotor (rotation speed of 150 rpm) was stirred. day. The results are shown in Table 2. In Example 8 and Example 9, as described above, a test piece containing iron (Steel Plate Cold Rolled Commercial (SPCC)) was placed in each beaker, and water quality and corrosion amount were measured after 3 days. And the corrosion rate was measured, and the results are shown in Table 2.

As shown in Table 2, the etching rate of Example 8 having a low free residual chlorine concentration was lower than that of Example 9.

[Example 10 to Example 15]

The dust collecting water of the power generation equipment of the following water quality is used as the test water.

pH: 8, total cyanide: 3 mg/L, ammonium ion: 130 mg/L, TOC: 7 mg/L, soluble iron: less than 0.1 mg/L

500 mL of test water was placed in a beaker with a lid, and the water temperature was maintained at 25 ° C, 40 ° C, 50 ° C, 60 ° C or 80 ° C, and an alkali agent and a chlorine source were added under the conditions of Table 3. The water quality measurement values after 60 minutes passed are 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]

An aqueous solution of ferric chloride was added to the dust collecting water of the same power generation facility as in Example 1 to prepare test water having a dissolved 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 into a glass container with a lid, the water temperature was maintained at 60 ° C, and the alkaline agent was added so that the pH after the reaction became 11, and the concentration immediately after the addition was 33.5 mg/L. The way to add chlorine source, the reaction is 60 minutes. The water quality measurement values after 60 minutes are shown in Table 4.

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

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

The dust collecting water of the power generation equipment of the following water quality is used as the test water.

pH: 8.7, total cyanide: 3 mg/L, ammonium ion: 120 mg/L, TOC: 10 mg/L, soluble iron: less than 0.1 mg/L

Store 500 mL of test water in a glass container with a lid to warm the water The scale inhibitor, the alkali agent, and the chlorine source were added at 60 ° C to achieve the conditions of Table 1. Furthermore, a test piece made of SUS was placed in the container. The reaction time was set to 60 minutes.

The pH value after 5 minutes from the addition of the chemical agent, the pH after the above 60 minutes, the amount of NaClO added, the calcium ion concentration after the above reaction time, the adhesion of the test piece to the anhydrous scale, and the total cyanide concentration are shown in Table 5.

As shown in Table 5, according to the present invention, cyanogen can be sufficiently decomposed and scale is also prevented. In Comparative Example 10, since the pH was set to be less than 11, the residual cyanide concentration was high. In Comparative Example 11, no scale inhibitor was added, and scale was generated. In Comparative Example 12 and Comparative Example 13, although a scale inhibitor was added, it was not a phosphonic acid scale inhibitor, so scale adhered.

The present invention has been described in detail with reference to the preferred embodiments thereof, and various modifications may be made without departing from the spirit and scope of the invention.

Further, the present application is based on a Japanese patent application filed on March 30, 2012 (Japanese Patent Application No. 2012-080437) and Japanese Patent Application No. 2012-080438 filed on March 30, 2012. ), all of its contents are referred to in this article by reference.

Claims (10)

A method for treating cyanide-containing drainage, which comprises adding a chlorine source to a cyanide-containing drainage containing a cyanide compound to decompose the cyanide compound, and the cyanide-containing drainage treatment method is characterized in that the cyanide-containing drainage contains ammonium ions and organic substances, and The pH of the cyanide-containing water is adjusted to 11 or more, and the chlorine source is added so that the free residual chlorine concentration becomes 0.1 mg/L or more even after the decomposition reaction of the cyanide compound. The method for treating cyanide-containing drainage according to claim 1, wherein a phosphonic acid-based scale inhibitor is further added to the cyanide-containing drainage. The method for treating cyanide-containing drainage according to claim 2, wherein the phosphonic acid-based scale inhibitor is selected from the group consisting of 1-hydroxyethylidene-1,1-diphosphonic acid and 2-phosphonium butane. -1,2,4-tricarboxylic acid and at least one of the salts. The method for treating cyanide-containing drainage according to the second or third aspect of the invention, wherein the alkali source is mixed with the scale inhibitor and added as a liquid. The method for treating cyanide-containing wastewater according to the first or second aspect of the invention, wherein the chlorine source is added so that the free residual chlorine concentration is 0.1 mg/L to 1 mg/L. The method for treating cyanide-containing drainage according to the first or second aspect of the invention, wherein an alkali agent is added to the cyanide-containing drainage to adjust the pH to 11 to 12.5. The method for treating a cyanide-containing wastewater according to the sixth aspect of the invention, wherein the pH value after the decomposition reaction of the cyanide compound is 11 or more Alkaline agent. The method for treating cyanide-containing drainage according to the first or second aspect of the invention, wherein the concentration of the dissolved iron containing the cyanide-containing water is 0.4 mg/L or less. The method for treating cyanide-containing drainage according to claim 1 or 2, wherein the water temperature of the cyanide-containing drainage is set to 40 ° C or higher. The method for treating cyanide-containing drainage according to claim 1 or 2, wherein the chlorine source is at least one of sodium hypochlorite, chlorine and bleaching powder.