JP2005254046A - Method for treating cyanogen in organic matter-containing sludge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treating cyanogen in organic matter-containing sludge, by which the cyanogen being a toxic substance, can be efficiently decomposed and detoxified without using chemicals, as regards the organic matter-containing sludge containing the cyanogen produced when a nitrogen-containing organic compound is heated or oxidized. <P>SOLUTION: This method for treating cyanogen in organic matter-containing sludge comprises a step to add water to the organic matter-containing sludge containing cyanogen to obtain slurry and a step to warm the obtained slurry at 130-210°C while adjusting the pH of the slurry to ≥9. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for treating cyan in organic matter-containing sludge. More specifically, the present invention efficiently decomposes cyanide, which is a toxic substance, without using chemicals against organic matter-containing sludge containing cyanide that is produced when a nitrogen-containing organic compound is heated or oxidized. The present invention relates to a method for treating cyan in organic matter-containing sludge that can be rendered harmless.

Nitrogen-containing organic compounds such as imidazolidinone compounds are used as organic solvents, and wastes containing this nitrogen-containing organic compound are heat-treated or oxidized in chemical plants, etc., or during solvent extraction. During the heating process, organic sludge containing cyanide generated by decomposition of the nitrogen-containing organic compound is generated. Cyan is extremely toxic and is not detected as an environmental standard for the protection of human health. For this reason, it is necessary to treat the nitrogen-containing organic compound so that cyan in the organic substance-containing sludge produced during the thermal decomposition or oxidation treatment is less than the detection limit.
Conventionally, cyanide has been decomposed into nitrogen and carbon dioxide by carrying out an oxidation treatment under alkaline conditions because cyanide ions (CN ⁻ ) are reducing substances. On the acidic side, since poisonous hydrogen cyanide is generated, the treatment is performed on the alkaline side. As the oxidation treatment method, treatment using an oxidizing agent is performed. As the oxidizing agent, sodium hypochlorite, hydrogen peroxide, ozone or the like is used. In particular, the alkali chlorine method using sodium hypochlorite is often employed.
First stage reaction: Treat at pH 10 or higher.
NaCN + NaOCl → NaCNO + NaCl
Two-stage reaction: pH 7.5 to 8.0.
2NaCNO + 3NaOCl + H ₂ O
→ 2CO ₂ + N ₂ + 2NaOH + 3NaCl
As another treatment method, there is a method in which an iron salt or a copper salt is added to form a hardly soluble salt of cyanide.
Furthermore, a thermal hydrolysis method is also known as a method for treating cyan-containing waste liquid. JP-A-8-71588 and the like describe that the thermal hydrolysis treatment method decomposes cyanide into ammonia and formic acid by thermal hydrolysis of the waste liquid to 140 ° C. or higher in a pressurized container.
JP, 8-71588, A The above processing methods are mainly processing methods of cyanide in water, and since it is difficult to mix a medicine equally in sludge, application to processing of cyanide in sludge was difficult. It was. Further, even when sludge is slurried and applied to the cyan treatment in organic matter-containing sludge, the oxidizing agent addition method consumes a large amount of oxidizing agent for the oxidation of organic matter, and cyan cannot be effectively treated. Further, the method of adding an iron salt or a copper salt is a method of fixing cyan by using cyan as a hardly soluble salt, and cyan is not completely decomposed and removed from sludge. Furthermore, even when the thermal hydrolysis method is applied to organic matter-containing sludge, cyan in the sludge is hardly decomposed and has not been adopted as a practical treatment method.

  The present invention is an organic substance capable of efficiently decomposing and detoxifying cyanide, which is a poisonous substance, without using chemicals, with respect to an organic substance-containing sludge containing cyanide produced when a nitrogen-containing organic compound is treated. The object of the present invention is to provide a method for treating cyan in contained sludge.

As a result of intensive research to solve the above problems, the present inventors have added water to an organic matter-containing sludge containing cyan to form a slurry, and heated to 130 ° C. or higher under alkaline conditions. The present inventors have found that cyanide is hydrolyzed to ammonia and formic acid, and the present invention has been completed based on this finding.
That is, the present invention
(1) A method for treating cyan in organic matter-containing sludge, characterized in that water is added to an organic matter-containing sludge containing cyan to form a slurry and heated at 130 to 210 ° C. at a pH of 9 or more, and
(2) The method for treating cyan in organic matter-containing sludge according to item 1, wherein the amount of water added is 0.5 to 10 times the weight of the organic matter-containing sludge,
Is to provide.

  According to the method for treating cyan in organic matter-containing sludge according to the present invention, cyanide, which is a poisonous substance, is efficiently hydrolyzed into ammonia and formic acid, without using chemicals such as an oxidant, for organic matter-containing sludge. Can be processed.

  In the method for treating cyan in organic matter-containing sludge of the present invention, water is added to an organic matter-containing sludge containing cyan that is produced when a nitrogen-containing organic compound is heated or oxidized to form a slurry, and the pH is 9 or more. , Heat treatment at 130-210 ° C. The method of the present invention is suitably applied to the treatment of sludge containing organic matter containing cyan produced when, for example, a nitrogen-containing organic compound such as an imidazolidinone compound that is an aprotic solvent is heated at 150 to 300 ° C. be able to.

Before discharging such organic matter-containing sludge containing cyan as industrial waste, it is necessary to treat the contained cyan. The amount of organic matter contained in the organic matter-containing sludge is often 10 to 30% by weight, and cyan is often 0.03 to 0.3% by weight as cyanide ions. Moreover, this sludge shows almost no fluidity.
In the method of the present invention, water is added to an organic substance-containing sludge containing cyan to form a slurry. The amount of water to be added is preferably 0.5 to 10 times by weight of the organic substance-containing sludge, and more preferably 1 to 5 times by weight. When the amount of water added is less than 0.5 times the weight of the organic substance-containing sludge, the viscosity of the slurry is not sufficiently lowered, the fluidity is poor, and the handling workability may be deteriorated. If the amount of water added exceeds 10 times the weight of the organic substance-containing sludge, the amount of slurry to be processed increases, the apparatus becomes too large, and the amount of waste becomes too large, which may reduce the economic efficiency.

In the method of the present invention, the pH of the slurry obtained by adding water to the organic substance-containing sludge is adjusted to 9 or more, more preferably 10 to 13. If the pH of the slurry is less than 9, the reactivity is lowered, the reaction time is prolonged, or the decomposition rate of cyan may be lowered. If the pH of the slurry exceeds 13, the amount of alkali to be added increases, which may impair economic efficiency.
In the method of the present invention, the slurry whose pH is adjusted to 9 or more is heated at 130 to 210 ° C., more preferably 150 to 180 ° C. When the temperature of the heating treatment is less than 130 ° C., the reaction rate is low, the reaction takes a long time, the reactor becomes large, and the cyan decomposition rate may be lowered. When the reaction temperature exceeds 210 ° C., a pressure exceeding 2 MPa is required to suppress gasification and maintain the liquid phase, which may increase the cost required for ensuring safety.

In the method of the present invention, the pressure during the heating treatment is preferably a pressure at which the gasification can be suppressed and the liquid phase can be maintained at the heating treatment temperature. That is, it is preferably 0.27 to 2 MPa, and more preferably 0.48 to 1 MPa. In the method of the present invention, the heating treatment time is not particularly limited, but is preferably 0.5 to 10 hours, and more preferably 1 to 4 hours. If the heating treatment time is less than 0.5 hour, the decomposition and removal of cyan may be insufficient. According to the method of the present invention, the rate of the decomposition reaction of cyan is fast, and it is usually unnecessary to perform the heating treatment for more than 10 hours. In the method of the present invention, it is preferable to stir the slurry during the heating treatment to make the treatment uniform.
According to the method of the present invention, it is considered that the cyanide ions contained in the organic matter-containing sludge are hydrolyzed according to the following formula to change into ammonia and formate ions.
CN ⁻ + 2H ₂ O → NH ₃ + HCOO ⁻

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
In Examples and Comparative Examples, the cyanide ion concentration was measured according to JIS K 0102 38.3 4-pyridinecarboxylic acid-pyrazolone spectrophotometry. Further, according to the Ministry of the Environment Notification No. 13 dissolution test, 50 g of a sample and 500 mL of water were mixed, shaken and filtered, and then the eluted cyanate concentration of the filtrate was measured in the same manner.
Example 1
Waste containing a high concentration imidazolidinone compound was heat-treated at 200 ° C., and the organic matter-containing sludge discharged at that time was treated. This organic matter-containing sludge had an organic matter content of 13% by weight and a cyanide ion concentration of 500 mg / kg.
750 g of water was added to 250 g of organic substance-containing sludge and stirred to form a slurry. This slurry had a pH of 12. This slurry was charged into a pressure vessel 4 equipped with a stirrer 1, a thermometer 2 and a pressure gauge 3 shown in FIG. The slurry was treated at a temperature of 140 ° C. and a pressure of 430 kPa for 4 hours while stirring.
The cyanide ion concentration of the slurry after the treatment was 3 mg / L, and the eluted cyanide concentration was 0.3 mg / L.
Example 2
The same treatment as in Example 1 was performed except that the treatment temperature was 150 ° C. and the treatment pressure was 570 kPa. The treated slurry had a cyanide ion concentration of less than 1 mg / L and an eluted cyanide concentration of less than 0.1 mg / L.
Example 3
The same treatment as in Example 1 was performed except that the treatment temperature was 160 ° C. and the treatment pressure was 740 kPa. The treated slurry had a cyanide ion concentration of less than 1 mg / L and an eluted cyanide concentration of less than 0.1 mg / L.
Example 4
The same treatment as in Example 1 was performed except that the treatment temperature was 170 ° C. and the treatment pressure was 950 kPa. The treated slurry had a cyanide ion concentration of less than 1 mg / L and an eluted cyanide concentration of less than 0.1 mg / L.
Comparative Example 1
The same treatment as in Example 1 was performed except that the treatment temperature was 120 ° C. and the treatment pressure was 240 kPa. The cyanide ion concentration of the slurry after treatment was 19 mg / L, and the eluted cyanide concentration was 1.4 mg / L.
Comparative Example 2
The same treatment as that in Example 1 was performed without adding water to the organic sludge, except that the treatment temperature was 160 ° C. and the treatment pressure was 740 kPa. The cyanide content in the sludge after the treatment was 500 mg / kg, and the eluted cyanide concentration was 23 mg / L.
The results of Examples 1 to 4 and Comparative Examples 1 and 2 are shown in Table 1.

As can be seen in Table 1, by adding 3 times the weight of water to the organic substance-containing sludge containing cyan to form a slurry of pH 12, and heating, the decomposition rate of cyanide ions is about 85% at 120 ° C. However, it can be seen that by increasing the treatment temperature, the decomposition rate of cyanide ions is improved, and cyan can be decomposed and removed without using a chemical such as an oxidizing agent.
Further, when no water was added (Comparative Example 2), cyan could not be decomposed.
Example 5
The water 333g was added to 667g of organic substance containing sludge containing the same cyan as Example 1, and it stirred and made it into a slurry form, and prepared to the pressure | voltage resistant container. This slurry had a pH of 13. The slurry was treated for 4 hours at a temperature of 160 ° C. and a pressure of 740 kPa while stirring.
The treated slurry had a cyanide ion concentration of less than 1 mg / L and an eluted cyanide concentration of less than 0.1 mg / L.
Example 6
The same treatment as in Example 5 was performed, except that 500 g of water was added to 500 g of organic matter-containing sludge to obtain a slurry having a pH of 12.5. The treated slurry had a cyanide ion concentration of less than 1 mg / L and an eluted cyanide concentration of less than 0.1 mg / L.
Example 7
The same treatment as in Example 5 was performed except that 667 g of water was added to 333 g of organic matter-containing sludge to obtain a slurry having a pH of 12.5. The treated slurry had a cyanide ion concentration of less than 1 mg / L and an eluted cyanide concentration of less than 0.1 mg / L.
Example 8
The same treatment as in Example 5 was performed except that 833 g of water was added to 167 g of organic matter-containing sludge to obtain a slurry having a pH of 12. The treated slurry had a cyanide ion concentration of less than 1 mg / L and an eluted cyanide concentration of less than 0.1 mg / L.
The results of Examples 5-8 are shown in Table 2.

As can be seen in Table 2, by adding 0.5 to 5 times by weight of water to organic matter-containing sludge containing cyan to form a slurry of pH 12-13, heat treatment at 160 ° C. It can be seen that cyan can be decomposed and removed without using chemicals.
Comparative Example 3
The same cyanide-containing sludge containing cyan as in Example 1 was treated by the alkali chlorine method.
The organic substance containing sludge containing the same cyan as Example 1 was put into the beaker, 600 g of water was added, and it stirred and made into the slurry form. This slurry had a pH of 12. Next, 27 g of an aqueous sodium hypochlorite solution containing 10% by weight of effective chlorine was added and stirred for 1 hour at room temperature to carry out the first stage reaction. Furthermore, it adjusted to pH 8 with hydrochloric acid, 41 g of sodium hypochlorite aqueous solution of 10 weight% of effective chlorine was added, and it stirred at room temperature for 1 hour, and performed the 2nd step | paragraph reaction. The sodium hypochlorite used is 10 times the theoretical chemical equivalent. The cyanide ion concentration of the slurry after the treatment was 26 mg / L.
Comparative Example 4
The organic substance containing sludge containing the same cyan as Example 1 was put into the beaker, 450 g of water was added, and it stirred and made into the slurry form. This slurry had a pH of 12. Next, 308 g of an aqueous solution of sodium hypochlorite containing 10% by weight of effective chlorine was added and stirred for 1 hour at room temperature to carry out the first stage reaction. Further, the pH was adjusted to 8 with hydrochloric acid, 460 g of an aqueous sodium hypochlorite solution containing 10% by weight of effective chlorine was added, and the mixture was stirred at room temperature for 1 hour to carry out the second reaction. The sodium hypochlorite used is 150 times the chemical equivalent. The cyanide ion concentration of the slurry after the treatment was 15 mg / L.
Comparative Example 5
The organic substance containing sludge containing the same cyan as Example 1 was put into the beaker, 300 g of water was added, and it stirred and made into the slurry form. This slurry had a pH of 12. Next, 411 g of an aqueous sodium hypochlorite solution containing 10% by weight effective chlorine was added, and the mixture was stirred at room temperature for 1 hour to carry out the first stage reaction. Furthermore, the pH was adjusted to 8 with hydrochloric acid, 615 g of an aqueous sodium hypochlorite solution containing 10% by weight effective chlorine was added, and the mixture was stirred at room temperature for 1 hour to carry out the second stage reaction. The sodium hypochlorite used is 300 times the theoretical chemical equivalent. The cyanide ion concentration of the slurry after the treatment was 12 mg / L.
The results of Comparative Examples 3 to 5 are shown in Table 3.

  As shown in Table 3, in the treatment by the alkali chlorine method, even if a large excess of sodium hypochlorite is added to cyanide contained in the organic matter-containing sludge, the cyanide ion concentration of the slurry after the treatment Is difficult to reduce to less than 10 mg / L.

  According to the method for treating cyan in organic matter-containing sludge of the present invention, an organic agent-containing sludge containing cyanide discharged when a nitrogen-containing organic compound is decomposed by heating, oxidation, or the like is used with an agent such as an oxidizing agent. It is possible to reduce the cyan density to less than 1 mg / L as a criterion for landfill disposal.

It is explanatory drawing of the pressure vessel used in the Example.

Explanation of symbols

1 Stirrer 2 Thermometer 3 Pressure gauge 4 Pressure vessel

Claims (2)

  A method for treating cyan in organic matter-containing sludge, characterized in that water is added to an organic matter-containing sludge containing cyan to form a slurry, followed by heating at 130 to 210 ° C at pH 9 or higher.   The method for treating cyan in organic matter-containing sludge according to claim 1, wherein the amount of water added is 0.5 to 10 times the weight of the organic matter-containing sludge.

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