JP4639309B2 - Treatment method of wastewater containing cyanide - Google Patents

Description

  The present invention relates to a method for treating cyan-containing wastewater discharged from various factories, in which cyan can be reliably removed by a simple operation so that the cyan concentration of the treated wastewater can satisfy the wastewater standard.

  Cyan has a strong negative impact on ecosystems, and cyanide-containing wastewater (hereinafter referred to as “cyan wastewater”) cannot be released into nature as it is. For cyanide, drainage standards are established based on the Water Pollution Control Law, and cyan removal processing is performed to satisfy this standard (1 mg / L or less), and wastewater cannot be discharged unless it is detoxified wastewater. ing. In addition, there are many areas that have established additional drainage standards that are even lower than the above-mentioned drainage standards due to regulations.

As a method for removing cyan from cyan wastewater,
(1) Alkaline chlorine method in which cyanate wastewater is adjusted to alkaline, then chlorine is injected to oxidatively decompose cyanide,
(2) Ozone oxidation method that oxidizes and decomposes cyanide into nitrogen gas and bicarbonate with strong ozone oxidizing power,
(3) Electrolytic oxidation method in which cyanide is electrolyzed using an insoluble electrode and an oxidation reaction is performed.
(4) A bitumen method in which, for example, ferrous sulfate is added as an iron ion supply compound to cyanine wastewater to form a poorly soluble ferriferrocyanide, and this is precipitated and removed.
(5) A biological treatment method for decomposing cyanide into a microorganism (cyanolytic bacteria) acclimatized to cyanide (see Non-Patent Document 1).

  However, each of the above methods has the following drawbacks. The alkali chlorine method is the most common cyan removal treatment method, but this method is a two-stage treatment, and pH values suitable for the reaction in each stage (first reaction: pH 10 or more, second reaction: pH 7. 5 to 8.0), and the amount of oxidant added and the amount of residual chlorine must be constantly monitored. Also, the alkali chlorine method tends to make it difficult to remove cyanide complex salts.

  The ozone oxidation method has advantages such as that no harmful compounds are generated by this treatment, and that even if the ozone itself used is decomposed, only harmless oxygen is produced, but this treatment is a gas-liquid reaction, so it is complicated and large-scale. Equipment is required. Moreover, since the manufacturing cost of ozone is high, the device on the apparatus for making ozone react effectively is required. For example, two oxidation towers are provided, a packing is placed in the first oxidation tower, cyan waste water and ozone are efficiently contacted countercurrently, and exhaust from the first oxidation tower is discharged to the second oxidation tower. Used in the oxidation tower to fully utilize residual ozone. Furthermore, it is necessary to carry out a coagulation precipitation treatment of metal hydroxide generated by the decomposition of cyanide.

  The electrolytic oxidation method has an advantage that cyan concentrated waste liquid can be processed efficiently and economically, but requires a large amount of electric power and increases the processing cost. In addition, there is a method of removing cyan by using an electrolytic oxidation method and another treatment method in combination, but in any case, the treatment becomes complicated and the treatment cost increases.

  The bitumen method is suitable for the treatment of cyanide wastewater, which is difficult to oxidize and decompose cyanide by other treatment methods. However, if there are few iron ions, the complex salt that is produced remains in the cyanate wastewater in a soluble state, and the treated water is colored. Therefore, it is necessary to add a large amount of an iron ion supply compound, and the amount of complex salt (waste) produced is enormous. In addition, when the pH of the treated water is higher than 6 or when the complex salt formed is easily oxidized with oxygen in the air, it becomes a ferriferro type and redissolves. It is difficult to do below.

  Biological treatment methods involve complicated operations such as maintaining pH suitable for microbial treatment, which is a drawback inherent to microbial reactions, adding nutrient substances (nitrogen, phosphorus, etc.), adjusting activated sludge concentration (MLSS), and treating excess sludge. In addition, if the treatment time (contact time between cyan and microorganisms) is long and the cyan concentration in the cyan waste water is high, the waste water to be treated must be diluted in advance. is doing.

  The applicant of the present invention provides a method of treating cyan wastewater by a simple operation and a treating agent used therefor, containing a reducing substance capable of reducing the failing solution in a cuprous halide solution. A treatment agent for wastewater containing cyanide and / or thiocyanate with improved treatment efficiency has been proposed (see Patent Document 1).

  Further, a method for treating iron cyanide complex-containing water in which iron cyanide complex-containing water is reacted with ferrous salt and copper salt to form a hardly soluble salt under alkalinity and solid-liquid separation (see Patent Document 2). Furthermore, the iron cyanide which keeps the pH of the aqueous solution at 7 or less in an aqueous solution containing an iron cyanide complex, adds an equimolar amount or more of copper (II) ions to the cyan complex, and separates the generated precipitate. A method for removing a complex (see Patent Document 3) has been proposed.

  However, in the above prior art, complicated processes and operations are necessary, and it is difficult to reduce the cyan concentration of the treated water to the drainage standard (1 mg / L or less). However, it was necessary to process again or dilute with water.

  In addition, considering the impact on the environment, there are many areas where additional drainage standards are set, so the cyan concentration of wastewater after treatment is lower than the drainage standard (1 mg / L or less), which satisfies the additional drainage standard. It is hoped that.

Moreover, the drainage standard of hydrogen ion concentration (pH) based on the Water Pollution Control Law is set as 5.0 to 9.0 in the sea area and 5.8 to 8.6 outside the sea area. If the pH of the wastewater needs to be adjusted to acidic or alkaline during the above prior art treatment, not only the cyan concentration of the wastewater but also the pH is adjusted within the drainage standard range before being discharged into sewage. Necessary and must be neutralized.

Japanese Patent Publication No. 63-1919 (Claim 1) JP-A 64-30693 (Claim 1) JP-A-1-171690 (Claim 1) Yasuhiko Miyoshi, “Chemical Fundamentals and Wastewater Treatment Technology”, Information Research Laboratory, Inc., November 10, 1996, second edition, p. 152-158

  The present invention reliably removes cyan by a simple operation so that the cyan concentration of the wastewater after treatment satisfies the drainage standard, and does not require neutralization treatment of the wastewater after treatment. It is an object of the present invention to provide a method for treating cyanide-containing wastewater that can be discharged into sewage or the like.

  Inventors of the present invention have conducted intensive research in view of such a situation, and as a result, after adding an amount of ferric salt and cuprous salt capable of removing cyan contained in the wastewater containing cyanide. The fact that by adjusting the pH of the wastewater to 6-8 and removing the generated water-insoluble salt from the wastewater, the cyan concentration in the wastewater can be reduced to a concentration that can meet the drainage standard by adding it. The headline and the present invention have been completed.

Thus, according to this invention, after adding ferric salt and cuprous salt in an amount capable of removing cyan contained in the waste water containing cyan at a weight ratio of 16: 1 to 1: 1 , adjust the pH of the wastewater to 6-8, and the generated water insoluble salts were removed from the wastewater treatment method of the cyan-containing waste water and removing the cyan in said waste water is provided.

  According to the present invention, cyan is surely removed by a simple operation, the cyan concentration of the treated wastewater is increased to a concentration that can satisfy the drainage standard, and the neutralization treatment of the treated wastewater is not required. A method for treating cyanide-containing wastewater can be provided. Therefore, even if the wastewater treated by the method of the present invention is released to nature as it is, there is very little influence on the environment, and the amount of water-insoluble salt (waste) generated after the treatment can be reduced. It is extremely useful in industry.

  Examples of cyan wastewater to be treated in this invention include metal cyanide compounds, cyan ions, cyanide complex salts, and cyano complex ions discharged from steel factories, chemical factories, plating factories, coke production factories, metal surface treatment factories, and the like. Examples include cyan wastewater. In particular, treatment of cyan wastewater having a strong buffering action, such as coke oven wastewater, can be suitably performed.

  The ferric salt used in the present invention may be any compound that is soluble in water and can form trivalent iron ions in water, and examples thereof include ferric chloride, ferric sulfate, and iron alum. It is done. Among these, ferric chloride is particularly preferable in terms of the effect of removing cyanide and the cost of treating cyanide wastewater.

  The cuprous salt used in the present invention may be any compound that is soluble in water and can form monovalent copper ions in water. Cuprous chloride, cuprous fluoride, cuprous bromide Examples include copper and cuprous iodide. Among these, cuprous chloride is particularly preferable in terms of the effect of removing cyanide and the cost of treating cyanide wastewater. Moreover, it is preferable from the stability point of a cuprous salt that these cuprous salt solutions are made into the cuprous salt solution which uses hydrogen chloride water, alkali metal halide aqueous solution, or ethanol as a solvent.

According to the method of the present invention, an amount of ferric salt and cuprous salt capable of removing cyan contained in cyan waste water is added to cyan waste water simultaneously or separately.
Each of the ferric salt and the cuprous salt is preferably added in the form of an aqueous solution. The concentration of each aqueous solution may be determined in consideration of the workability when adding them to the cyan waste water, the reactivity between cyan and the added compound, etc.

  Since the addition amounts of the ferric salt and the cuprous salt are affected by the type and concentration of cyan contained in the cyan wastewater, these addition amounts may be appropriately determined according to the conditions. Specifically, the cyan concentration or the like of cyan waste water before treatment may be measured in advance, and the amount of each additive added may be determined based on the measured value.

  The cyan content in the cyan wastewater to be treated in this invention is not particularly limited, but 2-100 mg / L of wastewater with a total cyan concentration can be suitably treated. When treating such cyan wastewater, the ferric salt is 40 to 1000 mg / L, preferably 40 to 300 mg / L, and the cuprous salt is 3 to 1000 mg / L, preferably It is good to add to cyan waste water so that it may become 3-100 mg / L. Furthermore, the addition ratio of the ferric salt and the cuprous salt is 12: 1 to 1: 1, preferably 10: 1 to 2: 1.

When adding the ferric salt and the cuprous salt, and when reacting these added compounds with cyanide, it is preferable to stir the mixed solution from the viewpoint of the effect of removing cyanide. The mixed solution is preferably heated to some extent in the sense of promoting the reaction during stirring, but a liquid temperature of about 20 to 60 ° C. is sufficient. The time required for the reaction during stirring varies depending on the amount of cyan waste water, the type and concentration of cyan, the form and scale of the treatment apparatus, but is determined so that cyan and the added compound are in sufficient contact. Usually, stirring time should just be 10 minutes or more, and it is preferable to set it as 20-30 minutes.

Moreover, in the method of this invention, after adding a ferric salt and a cuprous salt, pH of process wastewater is adjusted to 6-8, Preferably it is 6-7.
The water-insoluble salt generated in the treated wastewater is removed from the wastewater by a known method.

Thus, by carrying out the cyan removal treatment from the cyan waste water by the method of the present invention, the cyan concentration (total cyan content (mg / L)) before the treatment is below the drainage standard value and added to the drainage standard. Can be significantly reduced to a concentration that can satisfy the above.
Therefore, even when the method of the present invention is applied to waste water after being treated by a known cyan removal method for cyan waste water, the waste water can be discharged into sewage as it is.

The cyan wastewater treatment method of the present invention will be specifically described with reference to a schematic diagram (FIG. 1) showing an example of a cyan wastewater treatment apparatus, but the present invention does not limit the present invention.
The cyan waste water to be treated (indicated by the solid arrow in the figure) is measured for cyan concentration at point A and sent to the reaction treatment tank 1, and based on the measured values such as cyan concentration, the additive first tank 2. And the ferric salt aqueous solution and the cuprous salt aqueous solution are respectively added from the additive 2nd tank 3. The cyan waste water is allowed to stay for a predetermined time while stirring the cyan waste water in the reaction treatment tank 1, and then the cyan waste water containing the generated water-insoluble salt is sent to the thickener 4 from below the reaction treatment tank 1. In the thickener 4, the formation reaction of the water-insoluble salt is advanced, and the solid content is recovered from below the thickener 4. On the other hand, the supernatant is discharged from above the thickener 4, the cyan concentration of the supernatant is measured at point B, and it is confirmed that the measured value is the drainage standard value or the added drainage standard value or less. Drain the water. In addition, there is no problem in reusing the treated waste water.

  That is, a cyan waste water treatment apparatus that can be used in the treatment method of the present invention basically includes an additive tank for adding a ferric salt aqueous solution and a cuprous salt aqueous solution, and a water insoluble salt. It comprises a reaction tank, a precipitation tank for recovering the water-insoluble salt, piping connecting them, stirring means, a pump, and the like. The reaction tank and the precipitation tank can also be used together. In such a case, an apparatus such as a thickener can be used.

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

Test example 1
Test water collected from a steel factory (total cyanide concentration (T-CN): 4.2 mg / L, pH: 7.79) was dispensed into a 500 mL beaker and supplied to the concentrations shown in Table 1. After adding the reagent and adjusting to a predetermined pH with sodium hydroxide, the obtained test water was stirred for 1 minute each. The water-insoluble product in the test water is filtered off, the state of the filtrate is observed, and the total cyan concentration (T-CN) in the filtrate is measured according to JIS K0102, and the removal of cyanide compounds in each test water. The effect was evaluated.
The obtained results are shown in Table 1 together with the amount of reagent reagent added and the adjusted pH value. In the table, reagent A is ferric chloride aqueous solution (ferric chloride content: 38% by weight), and reagent B is cuprous chloride hydrogen chloride aqueous solution (cuprous chloride content: 20% by weight). ), Reagent Agent C represents a ferrous chloride aqueous solution (ferrous chloride content: 30% by weight), and Reagent Agent D represents a cupric chloride aqueous solution (cupric chloride content: 50% by weight).

From the results in Table 1, it can be seen that in Examples 1 to 9, transparent treated water having a very low total cyan density (T-CN) is obtained as compared with Comparative Examples 1 to 7. That is, it can be seen that the cyanide can be reliably removed from the cyan wastewater only when the pH is adjusted to 6 to 8 after adding the ferric salt and the cuprous salt.

Test example 2
The test water collected from the plating factory (total cyanide concentration (T-CN): 50 mg / L, pH: 8.21) was dispensed into a 500 mL beaker, and the reagent was used so that the concentrations shown in Table 2 were obtained. The test was conducted in the same manner as in Test Example 1.
The obtained results are shown in Table 2 together with the amount of reagent reagent added and the adjusted pH value.

From the results in Table 2, even in cyan wastewater with a high initial cyan concentration, the cyanide can be reliably removed when the pH is adjusted to 6-8 after adding ferric salt and cuprous salt. I understand.

It is a schematic diagram which shows an example of the processing apparatus of the cyan waste water used for the processing method of the cyan waste water of this invention.

Explanation of symbols

1 Reaction treatment tank 2 Additive first tank 3 Additive second tank 4 Thickener

Claims (4)

After adding ferric salt and cuprous salt in an amount capable of removing cyan contained in the wastewater containing cyan at a weight ratio of 16: 1 to 1: 1, the pH of the wastewater is adjusted to 6-8. adjusting the generated insoluble salt was removed from the wastewater treatment method of the cyan-containing waste water and removing the cyan in said wastewater. The amount of ferric salt and cuprous salt, processing method according to claim 1 respectively a 40~1000mg / L and 3~1000mg / L. The processing method according to claim 1 or 2, wherein the ferric salt is ferric chloride. The method according to the cuprous salt is any one of claims 1 to 3 cuprous chloride.

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