JP4656379B2 - Method of treating wastewater containing iron cyanide - Google Patents

Description

The present invention relates to a method of processing an iron cyanide-containing waste water.

  Cyanogen-containing compounds are generated in chemical factories, plating factories and coke factories. Among them, with regard to cyanide ions, alkali chlorine methods and methods of adding organic chemicals have been reported as treatment methods. However, for wastewater containing cyanide, especially cyanide complex, especially iron cyanide complex that is difficult to treat, various treatment methods have been proposed, but new sludge derived from the treatment agent is generated and the cost increases. There are problems such as.

  Conventional processing techniques are disclosed in more detail below.

  In Patent Document 1, ferrous compound is added to wastewater containing low-concentration cyanide, then alkali is added, the pH is adjusted to be alkaline (for example, pH 7 to 8.4), and then ferric compound is added, A method is disclosed in which the pH is adjusted (for example, to pH 6.5 to 7.3), and cyanide is precipitated and separated as an iron compound. However, this method requires complicated pH adjustment and generates sludge derived from the added ferrous compound.

  Patent Document 2 discloses a method in which a copper salt and a reducing agent are added to waste water containing free cyanide and a cyanate complex salt to form a hardly soluble precipitate and separated. By this method, free cyanide and cyanide complex can be treated, and the operation is simple. However, sludge is generated by the copper salt added in this method.

  Patent Document 3 discloses a method of adding hypochlorite and a manganese compound to cyanide-containing wastewater and removing the produced manganese salt from the wastewater. This method similarly generates sludge derived from the added manganese salt.

  In Patent Document 4, an alkali agent and an oxidizing agent are added in advance to an iron cyanide complex compound-containing cyan wastewater, the pH is adjusted to alkalinity, and then the wastewater is irradiated with ultraviolet to visible light to decompose the iron cyanide complex compound. There is disclosed a method of oxidizing free cyanide while separating and removing precipitates such as hydroxides generated from iron ions dissociated by the above as necessary from the waste water. However, this method is a very complicated processing method and is expensive.

  Further, in the conventionally known alkali chlorine method, free cyanide is the main object, and iron cyanide complex cannot be removed.

Summarizing the above problems of the prior art,
(1) Only free cyan can be processed,
(2) Even when iron cyanide can be treated, the method is complicated.
(3) Sludge derived from the treatment chemical is generated,
(4) High cost required for processing equipment,
Etc. are listed.
Japanese Patent Publication No. 56-51835 JP-A-2-48315 JP 2001-300553 A Japanese Patent Laid-Open No. 10-57974

  An object of the present invention is a method that overcomes the above-mentioned problems, is inexpensive, and can be treated easily, and treats cyanide-containing wastewater without generating sludge derived from a cyan treating agent. It is to provide a method.

Therefore, in the method for treating iron cyanide-containing wastewater of the present invention, sodium hypochlorite , which is an oxidizing agent , is added to the iron cyanide-containing wastewater for reaction, followed by formaldehyde and reduction in the cyanide-containing water after the reaction. It is characterized in that cyanide contained in the water is reduced without adding sodium bisulfite as an agent to generate sludge derived from the sodium hypochlorite, formaldehyde, and sodium bisulfite . In the present invention, cyanide means a free cyanide compound and / or a cyanide complex.

  A preferred embodiment of this method is as follows.

  The oxidizing agent is at least one selected from the group consisting of sodium hypochlorite, sodium hypobromite, hydrogen peroxide, calcium hypochlorite, and isocyanuric chloride.

  The reducing agent is preferably sodium bisulfite.

  After reacting by adding an oxidant to the cyanide-containing wastewater, if a residual oxidant is detected in the cyanide-containing wastewater, a reducing agent is added to exhaust the residual oxidant, and then the formaldehyde And adding a reducing agent.

  An inexpensive and simple treatment method for cyanide-containing wastewater is established without generating sludge due to cyanide treatment chemicals.

  In the present invention, cyanide-containing wastewater generated in chemical factories, petroleum factories, gas factories, plating factories, coke factories, metal surface treatment factories, and the like is targeted for treatment.

  This cyan is in the form of (1) free cyan (also called cyanide), (2) cyan complexes such as zinc, copper, cadmium, etc. (3) cyan complexes such as iron, nickel, cobalt or gold, silver, etc. There is. An example of the complex is an iron cyanide compound.

  Hereinafter, a cyan complex will be described as an example.

  First, an oxidizing agent is added to this cyanate complex-containing wastewater. The oxidizing agent to be added is at least one selected from the group consisting of sodium hypochlorite, sodium hypobromite, hydrogen peroxide, calcium hypochlorite and isocyanuric chloride. A plurality of kinds of oxidizing agents may be added in combination. The amount added is about 10 to 15% by weight of the total cyan as an oxidizing agent (pure component). However, in order to increase the reaction efficiency, more oxidizing agent may be added.

  The reaction time between cyanide and the oxidizing agent in the cyanide-containing wastewater is usually 1 to 60 minutes. The reaction is preferably carried out with stirring.

  Following this oxidation reaction, formaldehyde and a reducing agent are added. When the oxidant remains after the oxidation reaction, formaldehyde is consumed and the amount of use increases, so a reducing agent is added in advance to exhaust the remaining oxidant. Whether or not the oxidant remains can be easily checked with a residual chlorine meter. Examples of the reducing agent used here include sodium bisulfite, sodium sulfite, and sodium metabisulfite. The amount added is the amount at which residual chlorine disappears. The amount of formaldehyde added is preferably equimolar or more with respect to all cyan. In this step, the time for performing the treatment is usually 1 to 60 minutes, and it is preferable to proceed the reaction with stirring as described above.

  Next, a reducing agent is added. As the reducing agent to be used, those described above can be used. At this time, formaldehyde and the reducing agent may be added simultaneously, or formaldehyde may be added first, and then the reducing agent may be added.

  The amount of reducing agent added is about 1.1 to 1.5 times the amount of formaldehyde added.

  When the amount of cyanide-containing wastewater is small, it can be treated in a batch-type treatment tank, but when the amount is large, it is preferable to dispose the treatment tank in a cascade manner.

  FIG. 1 is a diagram showing an outline of a process for treating cyanate-containing wastewater when treatment tanks are arranged in a cascade manner. Cyanide complex-containing waste water (raw water) is guided to the first treatment tank 2 through the waste water inflow pipe 1. Necessary oxidizing agent is put into the first treatment tank 2. Stir with a stirrer if necessary. An agitation effect can also be imparted by blowing air.

  The treated water treated by the oxidation reaction is guided to the second treated layer 4 through the treated water transfer pipe 3. Necessary formaldehyde and a reducing agent are put into the second treatment tank. Stir with a stirrer if necessary.

  The treated water treated as described above is discharged out of the system through the treatment discharge pipe 5.

  In order to treat the residual oxidant in the treated water discharged from the first treatment tank 2, an intermediate tank is provided between the first treatment tank 2 and the second treatment tank 4 to reduce the residual oxidant. An agent can be added. This reducing agent may be of the same type or different type as the reducing agent added in the second treatment tank.

  In the present invention, after this, a polymer flocculant or the like may be further added to cause agglomeration to separate the solid matter. In this case, since the polymer flocculant is not a cyan treating agent, the generated solid matter is not derived from the cyan treating agent.

  Treatment was performed using cyanide complex-containing wastewater.

Wastewater quality used:
pH 9.0
T-CN: 30 mg / L
CN ion: 10mg / L
T-Fe: 50 mg / L
This waste water was dispensed as sample water into a beaker having a volume of 1 liter, and chemicals as shown in Table 1 were added. Sodium hypochlorite was added and stirred for 5 minutes. When residual chlorine was detected using a residual chlorine meter, sodium bisulfite was added to consume the residual chlorine. Next, formaldehyde and sodium bisulfite were added and stirred for another 5 minutes. Finally, this sample water is No. It was filtered through 5 filter papers and then analyzed for total and free cyan concentrations. The total cyan density-free cyan density = cyan complex density was calculated.

  The concentration of cyanide complex and free cyanide could be significantly reduced without generating sludge due to the treatment chemical.

  According to the present invention, since cyanide-containing wastewater can be treated inexpensively and easily without generation of sludge derived from the cyan treating agent, its utility value is extremely high.

It is a figure which shows the outline | summary of the process of processing the cyanide containing waste water of this invention.

Explanation of symbols

1 Wastewater inflow pipe 2 First treatment tank 3 Treated water transfer pipe 4 Second treatment layer 5 Treated water discharge pipe

Claims (2)

Addition of sodium hypochlorite as an oxidizer to waste water containing iron cyanide , followed by addition of formaldehyde and sodium bisulfite as a reducing agent to the cyanide-containing water after the reaction, and said hypochlorous acid A process for treating iron cyanide-containing wastewater , wherein cyanide contained in the water is reduced without generating sludge derived from soda, the formaldehyde and the sodium bisulfite . After reaction by adding the oxidant to the iron cyanide-containing waste water, if the residual oxidizing agent is detected in the cyanide-containing water, with the addition of sodium bisulfite depleted the residual oxidizing agent, Then, the formaldehyde and the sodium bisulfite which is the said reducing agent are added , The processing method of the iron cyanide containing wastewater of Claim 1 characterized by the above-mentioned.

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