JPH0483592A - Treatment of waste chemical washing solution - Google Patents

Abstract

PURPOSE:To easily remove COD by oxidative decomposition by together adding an alkali agent and activated carbon to a waste solution in the first treatment process. CONSTITUTION:The total amount of a waste acid washing solution and waste washing water whose quantity is twice that of said waste acid washing solution in quantity are received in a waste solution storage tank and an alkali agent and activated carbon are together added to said tank while air bubbling is carried out not only to remove hydrazine and an inhibitor at pH11 or more but also to precipitate an iron ion as hydroxide. The obtained supernatant solution is transferred to a separate waste solution tank and sulfuric acid is added to said tank while air bubbling is carried out to adjust pH to 1-2.5 to crystallize and precipitate EDTA. Subsequently, the supernatant solution is transferred to a separate waste solution tank in which waste washing water whose quantity is 6-8 times that of the waste acid washing solution is received and an alkali agent is added to said tank while air bubbling is carried out to adjust pH to 2-3.5 and, thereafter, ferrous sulfate is added thereto so that the concn. of a ferrous ion becomes about 100-200ppm and, next, hydrogen peroxide is added to COD in the waste solution.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a method for treating chemical cleaning waste liquid, and when discharging chemical cleaning liquid and washing water waste liquid after chemical cleaning, heavy metals, COD, SS ( This invention relates to a method for removing harmful substances such as solid suspended solids) and colored substances.

[Conventional technology]

Steam oxidation scale (main component: Fe5Oa, minor component: Cr2O5,
MO02 etc.) to ethylenediaminetetraacetic acid (hereinafter referred to as EDT)
In chemical cleaning, in which ammonia, hydrazine, and a corrosion inhibitor (hereinafter abbreviated as inhibitor) are added to A), the types of chemical cleaning waste liquid when applied to the main steam pipe of a thermal power plant, for example, are as follows: As shown in Table 1, in addition to the acid washing waste liquid, there is also a washing water waste liquid for completely discharging and removing the acid liquid remaining in the pipe after acid washing. The amount of washing water waste liquid is 8 to 10 volumes per 1 volume of acid washing waste liquid, but the initial 2 volumes are generally sent to a storage tank for treatment of acid washing waste liquid.
The remaining 6 to 8 volumes contain a very small amount of acid washing waste liquid components, so they are received in another storage tank for treatment.

As can be seen from Table 1, the mixed waste liquid before treatment contains wastewater standard items such as pH, CODSFe ion, Cr ion, S
Because it contains a large amount of S and the like, such chemical cleaning waste liquid cannot be discharged as is to prevent pollution. When discharging wastewater, it is necessary to purify it to a standard value determined by a pollution prevention agreement with the local government, as shown in Table 2.

Table 2 Effluent standard values (quoted from examples in various regions) Conventionally, such chemical cleaning waste liquid treatment methods include incineration treatment or wet chemical treatment.

Incineration treatment is outsourced to an industrial waste disposal company and incineration is carried out outside the premises, but wet chemical treatment is preferable from the viewpoint of high processing costs and prevention of troubles when transporting waste liquid outside the premises.

On the other hand, as a wet chemical treatment method, an alkaline agent (
A first step treatment in which heavy metal ions are precipitated and separated at pH 10 or above by adding caustic soda, slaked lime, etc., and EDTA is added to the separated liquid obtained in the first step by adding acid (hydrochloric acid or sulfuric acid).
A second step of crystallizing, separating and recovering the crystals, and adding hydrogen peroxide to the separated liquid from which the crystals have been separated,
A method is known that includes a third step treatment for reducing OD (Japanese Unexamined Patent Publication No. 59-76593). [Problems to be Solved by the Invention] In the method described above, Since the chemical cleaning solution shown in Table 1 has almost no effect in removing hydrazine and inhibitors, which are COD loading components, the oxidative decomposition of COD is not sufficient in the third step of COD oxidation treatment, and the excess Due to problems with the hydrogen oxide addition procedure, the oxidative decomposition of EDTA is insufficient, and chromium ions (which are chelated with unoxidized and undecomposed EDTA)
There are problems such as making it impossible to remove Cr34).

In view of the above-mentioned state of the art, the present invention aims to provide a method for treating chemical cleaning waste liquid that does not have the problems encountered in the conventional methods.

[Means to solve the problem]

The present invention consists of metal ions (main component: iron ion, minor component nichrome ion), ammonia,
In the chemical cleaning waste liquid treatment method for acid washing waste liquid containing hydrazine and inhibitors and washing water waste liquid after acid washing, after receiving the washing water waste liquid equivalent to the entire amount of the acid washing waste liquid and twice the amount of the acid washing waste liquid into the waste liquid storage tank, A first step treatment of removing hydrazine and inhibitors at pH 11 or higher by adding an alkaline agent and activated carbon together while air bubbling, and precipitating iron ions as hydroxide, followed by sedimentation and separation of the precipitate; After transferring the supernatant liquid obtained from the process treatment to another waste liquid storage tank, sulfuric acid or hydrochloric acid is added while air bubbling to adjust the pH to within the range of 1 to 2.5 and ED.
The second step treatment in which TA is crystallized and separated by sedimentation, and the supernatant liquid obtained in the second step treatment, are added in advance to 6 to 8 times the amount of acid washing waste liquid.
After transferring the washing water waste liquid equivalent to twice the amount to another waste liquid storage tank, the pH was adjusted to within the range of 2 to 3.5 by adding an alkaline agent while air bubbling, and then the ferrous ion (Fe ”) Add ferrous sulfate or ferrous chloride to a concentration of 100 to 200 ppm, then add 2.5 equivalents or more of hydrogen peroxide to the COD in the waste liquid in 4 parts, The second and subsequent additions are made every 3 days, during which air bubbling is stopped to oxidize and decompose COD, and then, while air bubbling, an alkaline earth metal is added to the waste liquid to adjust the pH to within the range of 6 to 8.6. This method of treating chemical cleaning waste liquid is characterized by comprising three steps: a third step treatment in which metal ions (iron ions, chromium ions, etc.) are precipitated and separated as hydroxides.

The method of the present invention will be explained in more detail below.

First, in the first step, sodium hydroxide, sodium hydroxide, and
Add alkaline agents such as potassium hydroxide and calcium hydroxide to 1
A combination of seeds and activated carbon (preferably powdered) is added to adjust the pH to 11 or more, preferably in the range of 11.5 to 12, and stirring is performed by air bubbling for about 4 hours to eliminate hydrazine and inhibitors in the waste liquid. After the iron ions are removed and the iron ions are completely precipitated, air bubbling is stopped and the precipitate is separated by sedimentation.

Next, the supernatant liquid obtained in the first step treatment is transferred to another storage tank for the second step treatment via a submersible pump, etc., and then sulfuric acid or hydrochloric acid is added while air bubbling to bring the pH to 1 to 2.5.
It is preferably adjusted to around 1.7, and after promoting crystallization of EDTA by air bubbling and stirring for about 1 hour, air bubbling is stopped and crystal precipitates are separated by sedimentation.

Next, the supernatant liquid obtained in the second step treatment is sent to another storage tank for the third step treatment, which receives the washing water waste liquid (6 to 8 times the volume of the acid washing waste liquid volume) after being pickled in advance using an ice pump. After the mixture is transferred and mixed through a filter or the like, one or more alkaline agents such as sodium hydroxide, potassium hydroxide, calcium hydroxide, etc. are added while air bubbling to bring the pH to 2 to 3.5, preferably 2.
After adjusting to the range of 5 to 3, ferrous ion (pe2+)
Add ferrous sulfate or ferrous chloride so that the concentration is 100 to 200 ppm, and then add 2.5 equivalents or more, preferably 3 equivalents, of hydrogen peroxide to the COD in the waste liquid, approximately equally divided four times. The second and subsequent additions are made every three days, during which time air bubbling is stopped except for stirring when hydrogen peroxide is added, and COD is oxidized and decomposed in a stationary state. Next, while air bubbling, one or more alkaline agents such as sodium hydroxide, potassium hydroxide, calcium hydroxide, etc. are added to the waste liquid to adjust the pH to within the range of 6 to 8.6, and the mixture is stirred by air bubbling for about 2 hours. After the metal ions (iron ions, chromium ions) are precipitated as hydroxides, air bubbling is stopped and the precipitates are separated by sedimentation.

The supernatant obtained in the third step can be discharged as is, and the precipitates and EDTA crystal precipitates generated during the first to third steps are dehydrated using an appropriate dehydration device. .

[Effect]

The mechanism or action by which hydrazine (N2H,), which is a COD loading component, and the inhibitor are effectively removed in the first step treatment of the present invention is considered to be due to the following.

That is, for N and H, N is produced by the chemical reaction shown in the first equation between ferric hydroxide [Fe(DH)3], which is precipitated by adding an alkali agent, and oxygen by air bubbling.
It is thought that the activated carbon added together with the alkaline agent acts as a reaction catalyst to promote the oxidative decomposition reaction.

2Fe(OH)a 10N2 +382[] '-""
""' (Formula 1) Fe(DH)2, which is produced by reduction with hydrazine, is oxidized to Fe(DH)s again by oxygen from air bubbling.

On the other hand, the inhibitor removal effect is due to the adsorption effect of activated carbon, but it is also thought that there is a synergistic effect of ferric hydroxide, which is precipitated by the addition of an alkaline agent. The amount of activated carbon added is sufficient in the range of 1 to 1.5 kg per waste liquid 1 to 3.

Further, in order to completely precipitate the EDTARe-chelated iron as hydroxide by adding an alkaline agent to the waste liquid, it is necessary to adjust the pH to 11 or more, preferably about 1.5 to 12. EDTA-F at pH 11 or below
e' + chelate formation constant is iron hydroxide [Fe([]H)
s], iron ions (Fe'') cannot be completely separated by precipitation.

95% of the COD loading components in the second step treatment of the present invention
It is extremely important to effectively remove EDTA, which accounts for the above loading rate, and there are known methods for removing it, but since the solubility of EDTA greatly depends on pH,
As a result of examining the optimum pH, it was found that the minimum solubility of EDTA is at pH 1 to 2.5, preferably around 1.7, and insoluble components are crystallized and all precipitated. Sulfuric acid or hydrochloric acid may be used as the pH adjuster, but E
The sedimentation volume of the DTA crystal precipitate varies greatly.

That is, a method in which the pH adjuster is added over a short period of time is preferable in terms of the method of adding the pH adjuster over a long period of time, since the sedimentation volume of the crystal precipitate becomes approximately 2, which is preferable for the dehydration treatment of the precipitate.

As described above, approximately 2000 ppm of COD remains in the waste liquid obtained by the first and second step treatments of the present invention. Most of this residual COD component is EDTA-Cr3
+ chelate compound f7) EDTA component and free EDTA.

Therefore, in order to effectively remove the residual COD component EDTA (C1, HI6N20B) in the third step of the present invention, it is necessary to oxidize and decompose it with hydrogen peroxide (I(,0,). It is thought that the oxidative decomposition effect is due to the chemical reaction of the second formula shown below.

10CO2+28)+20 +N2 +Fe3+
Hydrogen peroxide and ferrous ion (Fe2+) in the acidic region of the second formula
It is known that a mixed solution of E with hydrogen peroxide has a high oxidizing effect as Fenton's reagent.
It has been found that a major factor in effectively promoting the oxidative decomposition of DTA is the manner in which hydrogen peroxide is added.

In other words, when adding 2.5 equivalents or more of hydrogen peroxide to COD, if the entire amount is added at once, the COD removal effect will be small and the wastewater standard value will be far exceeded, but as an optimal addition method for hydrogen peroxide, For example, when adding 2.5 equivalents or more of hydrogen peroxide to COD, it is added in 4 equal parts, and the second and subsequent additions are made every 3 days, during which time COD is oxidized while standing still. According to the decomposition method, EDTA, which is a COD component, can be effectively removed. The reason why the method of adding hydrogen peroxide several times at intervals increases the COD removal effect is considered to be as follows.

That is, in order to oxidatively decompose COD components with hydrogen peroxide, active species (HD radicals, HD2
・Radicals) are required. As shown in the reactions of equations 3 and 4, ferrous ion (F
C”) of the present invention is essential.
In order to oxidize and decompose the OD component and further increase the removal rate of COD, it is necessary to reduce the oxidized ferric ions (Fe'') to ferrous ions (Fe'').

Fe"+)+202 →Fe"+〇ft-+H
D. 3rd formula HD・+H2O2→H,0+HD・
Equation 4 reduction reaction (p e 3 + → p e
2 + ) was found to occur when the waste liquid was allowed to stand while the COD component remained, and it was confirmed that 85 to 100% reduction was achieved by allowing the waste liquid to stand for 2 to 3 days.

By further adding hydrogen peroxide after reduction to ferrous ions (Fe2") in this way, the COD components that were not decomposed in the previous addition are effectively oxidized and decomposed and removed by the reaction of the second equation. To go.

In addition, the appropriate p)l range during oxidative decomposition treatment of COD components is 2
~3.5 is preferable, and COD removal rate deteriorates when outside this range. Ferrous ion (Fe”) concentration is 100-2
Approximately 0.00 ppm is sufficient, and even if more than 0.00 ppm is added, C
There is no change in the OD removal effect.

〔Example〕

Metal ion (Re”[:r3+
) The following tests were conducted in a chemical cleaning waste liquid treatment method for acid washing waste liquid containing ammonia, hydrazine, and inhibitors and washing water waste liquid after acid washing. This test was conducted using chemical cleaning waste liquids with the composition and properties shown in Table 1. (C) Mixed waste liquid 11 was received in a bee force and hydroxylated with 1 g of powdered activated carbon while air bubbling). After adjusting the pH to 11.5 to 12 by adding IJum, the mixture was stirred for 4 hours, air bubbling was stopped, and iron hydroxide (precipitate) was separated by sedimentation. The supernatant (alkaline) after separation of the precipitate had a green color due to EDTA-Cr'+ chelation.

This supernatant liquid was taken as a waste liquid for the second step in another beer, and while air bubbling, 97% sulfuric acid was added to adjust the pH.
After adjusting the temperature to 1.9, the mixture was stirred for 1 hour, air bubbling was stopped, and the ESTA crystal precipitate was separated by sedimentation. Crystal precipitate (white) The supernatant liquid (acidic) after sedimentation separation is E D T
The color was purple due to A-C,r'' chelation.

The properties of this treatment liquid are as shown in the supernatant liquid after the second step treatment in Table 3 (D).
, Pe 0.2 mg/1 or less, Cr 3493m
g/l. For comparison, the conventional method without the addition of activated carbon in the first step treatment had a COD of 2650 mg/i',
The Fe content was 1 mg/l or less, and the Cr value was 94■/I!.

The above (D) waste liquid 150- is mixed with (E) waste liquid 300- (washing water after pickling, equivalent to 6 times the waste liquid in Table 1 (A)). (F) mixed waste liquid 450- is used in the third step. The ferrous ion (Fe'") concentration was adjusted to 100 to 3.5 by adding 48% sodium hydroxide solution while air bubbling.
Ferrous sulfate was added to give a concentration of 200 ppm, and then 2.5 to 3 equivalents of 35% hydrogen peroxide was added to the COD in the waste liquid in four equal portions. However, the second and subsequent additions were made every three days, during which time air bubbling was stopped except for stirring when hydrogen peroxide was added, and the COD was oxidized and decomposed in a stationary state. Then, while air bubbling, the waste liquid was heated for 48 hours.
% sodium hydroxide solution to adjust the pH to 6 to 8.6 to precipitate metal ions (iron ions, chromium ions) as hydroxides, stir by air bubbling for about 2 hours, then air bubbling. The precipitate was separated by sedimentation. The COD, dissolved iron, total chromium and SS of the supernatant liquid after sedimentation separation were measured, and the test number (2) in Table 4 Example was measured.
~αQ results were obtained. For comparison, we also conducted a conventional method in which hydrogen peroxide was added all at once during COD oxidation treatment in the third step and left for static oxidation treatment.
I got results like this.

Test number (1) and (Company) are mixed waste liquid (F) shown in Table 3.
), and the properties before the third step treatment by the method of the present invention and the conventional method are shown as reference examples.

〔Effect of the invention〕

(1) By adding an alkaline agent and activated carbon together to the waste liquid in the first step treatment, not only iron ions in the waste liquid are precipitated and removed as ferric hydroxide, but also hydrazine and inhibitors are effectively removed. Since it became possible to remove the COD, it became easy to remove it by oxidation and decomposition of COD in the third step treatment.

(2) In the third step of COD oxidative decomposition treatment, when hydrogen peroxide is used to oxidize and decompose the COD component (EDTA), when adding 2.5 equivalents or more of hydrogen peroxide to COD, According to a method in which COD is oxidized and decomposed by adding it in 4 parts per minute, and the second and subsequent additions are made every 3 days, and COD is oxidized and decomposed while standing, EDTA is added to chromium ions ([r
3+) and chelated (EDTA-Cr”) ED
Since TA is also effectively oxidized and decomposed, the chelated chromium becomes free chromium ions (Cr"), and the chromium ions are converted to chromium hydroxide [Cr" by neutralization treatment with an alkaline agent after COD oxidation treatment. 0)1)s ]
It became possible to remove the precipitate as

(3) Since the treated water after the third step, which is the final treatment step, fully satisfies the wastewater standard values for all items in Table 2, it can be discharged as is without any adjustment.

Claims (1)

[Claims] In a chemical cleaning waste liquid treatment method for pickling waste liquid containing metal ions, ammonia, hydrazine, and corrosion inhibitors reactively bound to ethylenediaminetetraacetic acid and washing water waste liquid after acid washing, the total amount of pickling waste liquid and twice the amount of pickling waste liquid are used. After receiving a considerable amount of washing water waste liquid into a waste liquid storage tank, alkali agent and activated carbon are added together while air bubbling is performed to remove the hydrazine corrosion inhibitor at pH 11 or higher and to precipitate iron ions as hydroxide. , a first step treatment in which the precipitate is separated by sedimentation, the supernatant liquid obtained in the first step treatment is transferred to another waste liquid storage tank, and then sulfuric acid or hydrochloric acid is added while air bubbling to adjust the pH to 1 to 2.5. The second step is to crystallize ethylenediaminetetraacetic acid and separate it by precipitation.
The supernatant obtained in the step treatment and the second step treatment,
After receiving washing water waste liquid in an amount equivalent to 6 to 8 times the amount of acid washing waste liquid in advance and transferring it to another waste liquid storage tank, an alkaline agent is added while air bubbling to adjust the pH to within the range of 2 to 3.5. After that, the ferrous ion concentration is 100-20
Add ferrous sulfate or ferrous chloride so that the concentration is 0 ppm, and then add 2.5 equivalents or more of hydrogen peroxide to the COD in the waste liquid in 4 parts. Every 3 days, air bubbling is stopped and COD is oxidized and decomposed, and then, while air bubbling, an alkaline agent is added to the waste liquid to adjust the pH within the range of 6 to 8.6, and metal ions are converted into hydroxides. A method for treating chemical cleaning waste liquid, comprising a third step of precipitation separation.