JPS59222292A - Treatment of waste liquid of chemical cleaning containing ethylenediamine tetraacetate - Google Patents

Abstract

PURPOSE:To remove heavy metals bonded to EDTA efficiently by precipitating heavy metal ions by adjusting the pH of the waste liquid to >=10, removing fine particles by passing separated liquid through a filtration layer comprising active carbon, then adjusting the pH to 1.3-1.8. CONSTITUTION:After receiving the waste liquid 7 in a separation and treatment tank 1 for heavy metal ions, the waste liquid is stirred thoroughly with air, etc. after injecting an alkaline agent 8 such as NaOH, and the pH of the waste liquid is adjusted to >=10. After separation by precipitation, the waste liquid is transferred to a filtration tank 2 comprising active carbon with a transporting pump 9 through a transfer pipe 10, further to a crystallization reaction tank 3 for EDTA through a transfer pipe 11, through a transfer pipe 14 to a separation apparatus 5, and then to a receiving tank 6 through a transfer pipe 15, successively. Inorg. acid 12 is added to the crystallization reaction tank 3 under stirring to adjust the pH to 1.3-1.8. The crystal of EDTA separated in the separating apparatus 5 is washed with water and crystals having high purity are easily recovered after removing water contained therein.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating chemical cleaning waste liquid, particularly a method for treating chemical cleaning waste liquid containing heavy metal ions combined with ethylenediaminetetraacetic acid (hereinafter abbreviated as rEDTAJ).

Conventionally, EDTA has been widely used as a chelate cleaning agent to remove scale from boilers, heat exchangers, piping, etc. This washing waste liquid contains a large amount of heavy metal ions combined with EDTA during the washing process and a high concentration of COD, and there has been a demand for the development of an efficient waste liquid treatment method.

As a result of extensive research, the present invention has made it possible to recover and reuse EDTA from waste liquid.

That is, the present invention provides a method for treating chemical cleaning waste liquid containing heavy metal ions combined with EDTA, a first step of adding an alkali to the waste liquid and precipitating and separating the heavy metal ions at a pH of 10 or higher, and a step of separating the separated liquid of the first step. A second step in which fine particles and inhibitors are removed from the separated liquid by passing it through an activated carbon filtration layer, and an acid is added to the filtrate from the second step to remove EDTA at a pH in the range of 1.3 to 1.8. This method of treating chemical cleaning waste liquid containing EDTA is characterized by comprising a third step of generating crystals and separating and recovering the crystals.

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

The treatment method of the present invention includes: - First, an alkali is added to the waste liquid to remove the heavy metal ions chelated with EDTA from the EDTA.
Separate from. In the separation step, it is necessary to inject an alkaline agent such as caustic soda to bring the pH of the solution to 10 or more, but if the solution contains copper ions or nickel ions, the pH should be 12 or more, preferably 12.5. Furthermore, if iron (U) ions are contained, it is desirable to oxidize them into iron (2) ions by aeration with air or the like.

If it is an iron (IT) ion, it is necessary to set the pH to 12.5 or higher, but if it is an iron (IT) ion, the pH will be
12 is sufficient, which means that the amount of alkali agent added is small and is economical.

Note that any method can be used to oxidize iron (II) ions (for example, using an oxidizing agent), but
Aeration using air is simple and economical.

When the waste liquid contains ammonia, copper ions and nickel ions cannot be dissociated even at pH 12.5. This □
In order to dissociate, the pH must be 14 or higher.

Therefore, for copper ions, sodium sulfide as an alkali,
Add an alkali sulfide such as ammonium sulfide to copper ion of 1.0~
By adding 1.1 equivalent, it can be separated as copper sulfide. In this case, the pH of the solution only needs to be alkaline, so the amount of alkaline agent used can be saved and it is economical.

In addition to caustic soda and alkali sulfide, slaked lime and caustic potash can also be used as the alkali.

In addition, when separating heavy metals, they are separated by leaving them as they are, but adding a polymer flocculant has the effect of increasing the separation speed and reducing the volume of the precipitate.
It is valid.

Next, fine particles in the separated liquid in which heavy metal ions were precipitated and separated in the first step are removed by passing it through an activated carbon filtration layer. The microparticles in the separation liquid are mainly composed of colloidal iron hydroxide, and cannot be sufficiently separated only by standing still. These fine particles adhere to the EDTA crystals produced in the next third step and cause significant contamination. Further, the precipitate is subjected to dehydration treatment, and EDTA is also separated from this desorbed liquid, but in this case as well, the desorbed liquid contains more microparticles than the separated supernatant liquid. Therefore, it is necessary to remove the microparticles.

As a removal treatment method for this purpose, filtration using activated carbon is the most effective method, and microparticles are completely removed.

There is also a sand filtration method as a similar filtration method, but it is practically difficult to completely remove these microparticles.Although it can be completely removed using a filter method using particles of 1 μm or less, the amount of captured particles is small. Poor practicality. Therefore, the best method is to filter using activated carbon.

Furthermore, activated carbon has a high adsorptive property, and therefore has the effect of removing high molecular weight inhibitors contained in the cleaning liquid, so it has both effects.

Next, an acid is added to the filtrate filtered in the second step to make EDT.
Crystals of A are generated and the crystals are separated and collected. The EDTA
The pH range of the liquid during crystal formation varies depending on the concentration of EDTA, but is from pH 4.0 to 1.0.

FIG. 1 shows the results of a detailed investigation of the relationship between EDTA crystallization and pH. This is a result of crystallizing a 4% aqueous solution of EDTA at each pH, and examining the amount of EDTAO remaining in the solution after precipitation and separation over time at each pH.

This figure shows that at pH 1.3 or lower or pH 1.8 or higher, the rate of crystallization gradually slows down and the solubility of EDTA also decreases.Therefore, the best condition is a pH range of 1.3 to 1.8. It turns out that there is something.

In addition, when separating and recovering El:DTA from the filtrate continuously, it is more advantageous to connect two or more crystal formation reaction tanks in series than to perform the process using a single tank with the same residence time. be. If this is done continuously in a single tank, there is a certain probability that a short pass will occur and unreacted EDTA will flow out.
If this is done in two or more tanks in series, the probability of a short pass will be extremely small, and it will be possible to reach the solubility of EDTA, that is, to completely crystallize it, which will lead to an improvement in the recovery rate. be.

Furthermore, among the conditions for crystallization, a peripheral stirring speed of about 1.2 m/sae is sufficient for stirring the liquid, but if this speed is extremely high, the crystals will become fragmented or a large number of crystal nuclei will be generated. Become. Therefore, the specific volume of the crystal is large, which makes it difficult to separate and recover the crystal. It goes without saying that if the stirring circumferential speed is extremely slow, the liquids will not be mixed uniformly and crystallization will be insufficient.

An embodiment of the present invention will be described below with reference to FIG.

After receiving the waste liquid 7 into the heavy metal ion separation treatment tank 1,
An alkaline agent 8 such as caustic soda is injected as a heavy metal separation chemical and stirred well with air to adjust the pH to 1011 or higher, preferably 12 or higher. Next, in the case of waste liquid containing copper ions, add alkali sulfide to 1.0 to 1
．． Add 1 equivalent to separate copper ions. In addition, waste liquid containing iron (U) ions is agitated with air, oxidized, and iron [
[phase] ionize. The heavy metal ions separated here precipitate into insoluble substances such as hydroxides or sulfides, but in this case, the addition of an auxiliary agent such as a polymer flocculant enhances the separation effect.

After precipitation and separation, the mixture is transferred to the activated carbon filtration tank 2 via the transfer pipe 10 using the transfer pump 9, further to the EDTA crystal reaction tank 3 via the transfer pipe 11, to the EDTA crystal reaction tank 4 via the transfer pipe 13, and then via the transfer pipe 14. The separated liquid in the separation treatment tank 1 is continuously transferred to the separation device 5 through the transfer pipe 15 to the tank 6 17, and the separated liquid in the separation treatment tank 1 is processed. Further, the precipitate generated in the separation treatment tank 1 is treated by a dehydrator or the like, and the separated liquid is also recovered into crystals using the same route.

The flow from the crystal reaction tank 6 to the receiving tank 6 can also be carried out by a gravity flow method by providing a height difference, and the power of pumps and the like can be saved.

In the crystal reaction tank 6, acid 12 was added while stirring to bring the pH to 1.
, 3 to 1.8. The acid used here is an inorganic acid such as sulfuric acid or hydrochloric acid, and when the waste liquid 7 contains 1000 ppm or more of calcium ions, hydrochloric acid is used. The reaction time in crystal reaction vessels 3 and 4 was 15 minutes, respectively.
A total of about 30 minutes is sufficient.

The separation device 5 separates the EDTA crystals, and the separated liquid is transferred to the receiving tank 6 through the transfer pipe 15.
By providing a residence time of more than 1 minute, the crystals can further grow and the concentration of dissolved EDTA can be reduced.

The EDTA crystals separated by the separator 5 can be easily recovered as highly pure crystals by removing contaminated water by washing with water. As shown in Examples and Comparative Examples, the recovery rate and purity of llmDTA were good enough to allow sufficient reuse.

As described above, the present invention can efficiently recover and reuse EDTA from waste liquid containing heavy metal ions combined with EDTA, and the present invention has made it possible to rationally treat chemical cleaning waste liquid. .

Next, examples of the present invention will be described.

Example: 230% caustic soda was added to the solution having the above composition while stirring with air.
When Or was added and sufficiently oxidized, the pH became 12.6.

To this, 2080 f of sodium sulfide (Na2S.9H20) corresponding to 1.1 equivalents of copper ions was added. The pH at this time was 12.7.

When 5 ppm of a polymer flocculant was added to this and the precipitate was separated, the supernatant liquid was colorless, but the presence of suspended microparticles was observed. The water quality was as follows.

Using 20 tons of the first step treatment liquid, it was passed through an activated carbon filter tank and then poured into a reaction tank 3.4 while proportionally injecting 75 tons of sulfuric acid.
A residence time of 15 minutes was given for each treatment, and the treatment was continued. At this time, the pH of the liquid was 1.70, and white EDTA crystals were formed, which were separated using a separator. A residence time of 30 minutes was allowed in the separator.

The liquid at the outlet of reaction tank 3.4 was completely filtered to remove crystals using filter paper No. 5, and the EDTA concentration of the filtrate was measured to be 0.14% and 0.06%, respectively. Further, the concentration of EDTA in the liquid at the outlet of the separation device 5 was 0.05%. The EDTA recovered in this process is a white crystalline powder, and the amount is 7802.

Comparative Example-1 An experiment was conducted using the first step treatment liquid of the above example in the same manner as in this example. However, the proportional injection amount of sulfuric acid was increased and the treatment was carried out at pH 1.1. The EDTA crystals at that time were still white and crystalline powder.

The liquid at the outlet of reaction tank 6.4 was completely filtered to remove crystals using a 5A filter paper, and the concentrations of dissolved EDTA were measured to be 0.36% and 0.27%, respectively. In addition, the concentration of EDTA in the liquid at the outlet of the separation device 5 is 0.25.
%Met. EDTA was recovered as a result.

The amount is 740? Met.

Comparative Example 2 An experiment was conducted using the first step treatment liquid of the above example in the same manner as in this example. However, it was carried out without passing through an activated carbon filtration tank. At this time, the pH of the EDTA reaction tank was 1.7.
It was 5. Ocher-colored turbidity originating from SS was observed inside the reaction tank, and although the liquid at the outlet of the separation device 5 was clear, it was observed to have a slightly yellow color.

Moreover, the EDTA recovered here had a remarkable ocher color. The amount of EDTA recovered was 7752.

The EDTA separated and recovered in the above examples and comparative examples was
Each was washed with 3 tons of pure water (1 μs^ or less). The quality of the washing water was determined to be as shown in the table below, and the values are as shown above. The impurities in the recovered EDTA and the purity of the EDTA were measured and were as shown in the following table.

From this value, the recovery rate of EDTA was calculated using the following formula.

100 From the above results, it is clear that the Examples of the present invention had excellent EDTA concentration (purity) and high EDTA recovery rate, indicating good treatment results.

[Brief explanation of the drawing]

FIG. 1 is a solubility curve of EDTA, and FIG. 2 is a flow sheet showing M4 implementation of the present invention. 1... Separation treatment tank, 2... Activated carbon filtration tank, 6, 4.
...Crystal reaction tank, 5... Separation device, 6... Receiving tank,
7... Waste liquid, 8... Alkaline agent, 9... Transfer pump, 10, 11°13, 14, 15... Transfer pipe,
12...acid. Patent applicant Ebara Infilco Corporation Representative Patent Attorney 11) Twisting Takao Maruyama 15-

Claims (1)

[Claims] 1. A method for treating chemical cleaning waste liquid containing heavy metal ions combined with ethylenediaminetetraacetic acid, comprising: a) a first step of adding an alkali to the waste liquid to precipitate and separate heavy metal ions at a pH of 10 or higher; b) ) A second step of removing fine particles and inhibitors in the separated liquid by passing the separated liquid of the first step through an activated carbon filtration layer; C) Adding an acid to the filtrate of the second step to adjust the pH to 1.3.
A method for treating chemical cleaning waste liquid containing ethylenediaminetetraacetic acid, comprising: a third step of generating crystals of ethylenediaminetetraacetic acid in a range of 1.8 to 1.8, and separating and recovering the crystals. 2. The method according to claim 1, wherein the waste liquid contains at least one of iron ions and copper ions as heavy metal ions combined with ethylenediaminetetraacetic acid. 3. The method according to claim 2, wherein the iron ions are iron (m ions, in which case they are oxidized in advance to become iron-faced ions, and then the alkali is added. 4. In the first step) The method according to claim 1, wherein the alkali added is an alkali sulfide. 5. When the filtrate in the second step contains calcium ions, hydrochloric acid is added as the acid. The method described in paragraph 1.