JPS5836695A - Treatment of waste liquid of chemical washing - Google Patents

Abstract

PURPOSE:To recover iron and citric acid efficiently by controlling waste liquid of chemical washing contg. chelate of iron and citric acid to pH higher than specific values with caustic soda, settling iron as hydroxide, and adding a soluble Ca compd. to the filtrate. CONSTITUTION:If the pH of waste liquid of chemical washing contg. chelate of iron and citric acid is controlled to >=11.5 (more particularly 11.5-13) by adding an about 10% aq. caustic soda soln. thereto, the iron settles as hydroxide. After iron content is recovered by filtering out the sediment, a soluble Ca compd. such as CaCl2, Ca(NO3)2 or the like is added. The citric acid in the liquid reacts with the Ca compd. thereof and settles as calcium citrate which is recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating chemical cleaning liquid, and more specifically, to
This invention relates to a method for separately recovering iron and citric acid from chemical cleaning waste liquid containing chelates of iron and citric acid.

The inventors first developed a method for treating a chemical cleaning solution containing citric acid, and filed a patent application No. 48-62515 (Japanese Patent Application Laid-Open No. 50-198-1999).
0780), the content of which is that by adding an excessive amount of calcium compound to chemical cleaning waste liquid, the metal content and citric acid content in the waste liquid are simultaneously separated as poorly soluble calcium salts as precipitates. This is a method in which the supernatant liquid is oxidized with an oxidizing agent such as hydrogen peroxide or perchloride to decompose and render harmless COD components, and the purpose is to highly clarify the waste liquid. However, as mentioned above, this method precipitates the citric acid component together with the coexisting metal components.

Since it is a method of collecting sediment, it is extremely difficult to reuse the collected sediment, and disposal costs of approximately 20,000 to 30,000 yen per cubic meter are required for dewatering, incineration, landfilling, etc. This has been a major bottleneck in the industrialization of this process.

The inventors focused on the fact that these problems could be solved by recovering citric acid and iron separately, and conducted research that led to the invention.

That is, the method of the present invention adds caustic soda to the waste liquid and
is 11.5 or more, the iron content is precipitated as hydroxide, which is recovered, and then a soluble calcium compound is added to the waste liquid from which the iron content has been recovered, and the citric acid content is precipitated and recovered as calcium citrate.

The feature of this method is that most of the citric acid becomes sodium citrate when the pH is raised to 11.5 or higher by the addition of caustic soda in the first stage, but because this has extremely high solubility, it does not precipitate at the same time as the iron. This is because it takes advantage of the property that it can be effectively separated. It is well known to those skilled in the art that metals dissolved in water are easily precipitated as hydroxides by making the pH pH 8 to 9 alkaline, but when forming a chelate with citric acid, It has been said that almost no precipitation occurs at this level of alkalinity, and that it is extremely difficult to recover only the complexed metal.

The inventors discovered that the chelate of iron and citric acid in wastewater has a pH of 1.
Decomposition was observed from around 0, and almost all decomposition occurred at around pH 12, confirming that almost complete iron content could be recovered. Therefore, the higher the pH, the more purified citric acid can be recovered, and it is necessary to set the recovery conditions depending on the use of the recovered citric acid.

On the other hand, as p becomes higher, the amount of iron remaining in the waste liquid decreases, but from an industrial perspective, a value that satisfies the permissible amount of iron in the waste liquid (current emission standard 10 ppm) k is sufficient, and from that point of view, recognized that a pH of 11.5 or higher is required.

As mentioned above, the higher the pi, the higher the recovery rate of metals, but excessive addition increases the processing load of the final waste liquid, and as shown in Figure 1, the metal removal efficiency decreases as the amount of addition increases. The rise has reached a plateau, which is not very favorable economically. For this reason, an upper limit of about pH 13-. is sufficient.

By the way, if the pH of the wastewater is raised to about 12, most of the iron citrate chelate will be decomposed and the metal will precipitate as hydroxide, reducing the iron content remaining in the wastewater to about 1.5 ppm. I can do it. Furthermore, if the pH is raised to about 13, the iron citric acid chelate is almost completely decomposed, the remaining iron content is reduced to a trace amount, and the recovery rate of calcium citrate can be improved to almost the upper limit.

If the waste liquid recovered in this way is used for cleaning equipment in the petroleum industry, petrochemical industry, or general chemical industry, the metal content recovered in this way is mostly iron, and the hydroxide of Geitai i. After it is made into a material, it can be oxidized in air at about 600°C to be reused as red red iron.

On the other hand, in terms of the citric acid content, in the method of the present invention in which the metal is recovered as a calcium salt, pi is 10
It is known that the recovery rate is almost constant if it is above. Therefore, based on the requirements from the point of view of metal recovery, p
If H is set, a sufficiently satisfactory result can be obtained in terms of citric acid recovery. The recovered calcium citrate can be converted to citric acid by a conventionally widely used industrial method.

For example, a theoretical amount of sulfuric acid is added to calcium citrate to liberate citric acid, impurities are adsorbed and removed using activated carbon, etc., and then concentrated and recovered as citric acid crystals.

Although the concentration of the caustic soda aqueous solution used in the treatment of the present invention is not particularly limited, an approximately 10% aqueous solution is most desirable for the purpose of pH adjustment.

Moreover, as a soluble galcium compound, Cac4. Ca
There is no particular restriction as long as it can easily generate Ca ions in solution, such as (NOx)2.

The supernatant after recovering metals and citric acid in this way is disposed of, but this contains COD components of 500 to 500%, mainly consisting of corrosion inhibitors, surfactants, etc.
Since about 1.000 ppm remains, the content can be reduced to 20 ppm or less by treatment with an oxidizing agent such as bleaching powder, and then discharged into rivers and the like.

Next, the method of the present invention will be explained in more detail with reference to Examples.

Example 10% Na was added to the waste liquid of the following components obtained by pickling the oil refinery equipment.
OH aqueous solutions were added in the respective amounts shown in Table 1 below, and the iron content was precipitated and recovered, then CaCt2 was added and the citric acid content was precipitated and recovered as calcium citrate. The results are shown in Table 1.

The citric acid recovery rate shown in Table 1 indicates the percentage of citric acid recovered by the second stage treatment to the citric acid in the stock solution.

Stock liquid properties *1 Iron content 1.450 ppm *2 Citric acid content: 1.76 chi pH8,74 Appearance Yellowish brown Table 1

[Brief explanation of drawings]

FIG. 1 shows the change in metal removal efficiency with respect to the amount of 10 NaOH added to the waste liquid. Procedural amendment October 20, 1980 Haruki Shimada, Commissioner of the Japan Patent Office] Indication of the case 1981 Patent Application No. 154229 2,
Name of the invention Method for treating chemical cleaning waste liquid 3 Relationship with the case of the person making the amendment Patent applicant 1″r 2-12-1 Tsurumi Chuo, Tsurumi-ku, Yokohama, Kanagawa Prefecture
(328) Chiyoda Corporation (Name) 4 Agent 5, Subject of amendment (1) "Detailed description of the invention" column of the specification (1) "In the 18th line of page 1 of the specification""Chemical cleaning liquid" is corrected to "Chemical cleaning waste liquid." (2) "Chemical cleaning liquid" in the second line of page 2 of the above is corrected to "chemical cleaning waste liquid." (3) In the 14th line of page 5 of the same document, "It's iron." is corrected to "It's iron." (4) In the second line of Nis et al., page 8 of the same cylinder, "1ONaOHJ is corrected to [10%Na0HJ.

Claims (1)

[Claims] 1. A chemical cleaning waste solution containing a chelate of iron and citric acid is adjusted to a pg of 11.5 or more with caustic soda, and the iron content is precipitated as a hydroxide. After recovering this, further soluble A method for treating chemical cleaning waste liquid, characterized by adding a calcium compound and recovering the citric acid content by precipitation as calcium citrate. 2. The method according to claim 1, in which pn adjustment by caustic soda is adjusted to 11.5 to 13. 3. CaC4, Ca as soluble calcium compounds
Claim 1 or 2 using (No.)2
Section method.