JPS6111193A - Treatment of waste liquid of chemical cleaning - Google Patents

Abstract

PURPOSE:To permit the easy treatment by adding an alkali agent to waste liquid to form the precipitate of hydroxide of heavy metal, etc. and blowing air to the liquid to oxidize the liquid then adding active carbon thereto. CONSTITUTION:A calcium compd. such as calcium hydroxide is added to the waste liquid under stirring to adjust the pH to >=7 and to precipitate phosphoric acid and heavy metal ions in the form of calcium phosphate and the hydroxide of heavy metal. The formed ferrows hydroxide is oxidized to ferric hydroxide by blowing air and thereafter sodium peroxide is added to the waste liquid at the equiv. of COD in said liquid or above under blowing of air together with >=0.05 kg active carbon for each 1m<3> of the waste liquid to oxidize and decompose the COD component.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for treating chemical cleaning waste liquid containing a hydrochloric acid cleaning liquid and a phosphoric acid-based rust preventive liquid.

(Prior art) In the past, oxide scale mainly composed of iron that adhered or accumulated on the metal surfaces of boilers, heat exchangers, etc. in thermal power plants, chemical plants, etc., or oxide scale containing copper content such as in operating boilers, etc. Chemical cleaning is carried out to remove these substances and ensure the safe operation and maintenance of plants. As an example of a chemical cleaning composition, an acid corrosion inhibitor (inhibitor) is added to hydrochloric acid, or for scale containing copper, thiourea is added to hydrochloric acid to dissolve and sequester the inhibitor and copper. Surface 1 In the rust prevention treatment that temporarily prevents rust,
An example of the composition and properties of the waste liquid after chemical cleaning is shown in Table 1. In addition, wastewater standard values are determined by pollution prevention agreements with local governments, and examples are shown in Table 2.

As can be seen from Table 1, both the chemical cleaning waste for scale that does not contain copper and the chemical cleaning waste for scale that contains copper contain harmful components such as free acid, COD, iron, and copper (containing copper). Since a large amount of chemical scale cleaning waste liquid (only chemical scale cleaning waste liquid) and phosphates are dissolved, it is absolutely unacceptable to discharge such chemical cleaning waste liquid in its entirety due to pollution concerns.

On the other hand, as shown in Table 2, it is necessary to purify the quality of the discharged water to the regulatory values determined by pollution prevention agreements with local governments.

Conventionally, in the treatment process of such chemical cleaning waste liquid.

(1) Add an alkaline agent such as sodium hydroxide or calcium hydroxide to adjust the pH to 11 or higher to precipitate heavy metals.

(2) After adding a flocculant and settling the precipitate while aerating, the supernatant liquid is pumped to another storage tank.

(3) A I COD removal: While aerating, hydrogen peroxide is added in an amount equivalent to or more relative to kcOD, and treatment is carried out to a CODk level of approximately 1100 pp.

(4) A 2 COD removal: Add persulfate while aerating to treat COD to about 10 ppm.

(5) PH readjustment: Discharge after neutralizing with acid such as hydrochloric acid.

(Problems to be Solved by the Invention) According to the treatment method described above, the COD can certainly be lowered to within the wastewater standard value, but there are the following problems.

(1) The waste liquid treatment process is very complicated and takes a long time to process, resulting in high costs.

(2) The amount of chemical cleaning waste liquid is 800 to 1 bM @Q1
m', so in the case of a plant with only one waste liquid storage tank, a temporary waste liquid storage tank is required, which is a cause of high costs.

(3) When a COD remover of 1°A2 is added to the supernatant liquid from which the precipitated product has been separated, thiourea [(NH2)2CS, 1, which is a copper sequestering agent in the waste liquid, is oxidized and decomposed to form sulfur S. Precipitates out and becomes cloudy.

Problems remain when releasing water.

Table 1 Table 2 Examples of standard values for wastewater discharged into the sea and other areas (excerpts from examples from various regions) In addition to the methods mentioned above, COD can also be removed by making all wastewater alkaline with an alkaline agent.

There is also a method of oxidizing and decomposing COI by adding an oxidizing agent such as sodium hypochlorite, bleaching powder, or hydrogen peroxide.9
According to the experiments conducted by the present inventors, the oxidizing agent of the present invention also had a weak oxidizing power and far exceeded the wastewater standard value shown in Table 2, and no satisfactory results were obtained.

In order to solve the above-mentioned problems, the present invention removes harmful substances such as heavy metals, 9-phosphates, and COD from wastewater to within the wastewater standard values shown in Table 2, and produces relatively clear and colorless treated water. The object of the present invention is to provide a method for treating chemical cleaning waste liquid that can be easily obtained.

(Means for Solving the Problems) The present invention provides a method for treating chemical cleaning waste liquid containing a hydrochloric acid cleaning liquid and a phosphoric acid-based rust preventive liquid, by adding calcium hydroxide, calcium oxide, calcium chloride, etc. to the waste liquid. A calcium compound and an alkaline agent such as sodium hydroxide or potassium hydroxide are added to adjust the pH to 7 or higher to obtain an alkaline waste liquid, and the heavy metals and phosphates in this waste liquid are precipitated as heavy metal hydroxide and calcium phosphate. ,
After the generated ferrous hydroxide is oxidized to ferric hydroxide by air blowing.

This is a method for treating chemical cleaning waste liquid in which the COD component is oxidized and decomposed by adding at least an equivalent amount of sodium peroxide to the COD in the waste liquid and 0.05 kg or more of granular activated carbon to the waste liquid in'.

(Function) The following description deals with chemical cleaning waste liquid having the composition and properties shown in Table 1. First, a calcium compound such as calcium hydroxide, calcium oxide, or calcium chloride is added in an amount of 1 equivalent or more based on phosphate ion (PO4) in the waste liquid while forcibly stirring the waste liquid by blowing air, and then sodium hydroxide or Add an alkaline agent such as potassium hydroxide to adjust the pH to 7 or higher to precipitate cynic acid and heavy metal ions as calcium phosphate and heavy metal hydroxide, and then hydrate the ferrous hydroxide by blowing air. After oxidizing to ferric oxide, peroxidize while continuing to blow air) Add IJum in an amount equivalent to or more than the COD in the waste liquid and granular activated carbon to 1rr of the waste liquid. 0.0 against
5 K9 or higher is added in combination to oxidize and decompose COD components.

Then, the air blowing is stopped, and the supernatant liquid is completely separated into the precipitate using IJ.The supernatant liquid is neutralized with hydrochloric acid or sulfuric acid, etc., and discharged as it is using a pump, and the precipitate is removed. is dehydrated using a centrifuge or press filter machine.

Treat as a solid. In addition, when separating a supernatant liquid and a precipitate in the above-mentioned waste liquid treatment, a polymer flocculant may be added to promote coagulation and sedimentation of the precipitate.

Calcium compounds such as calcium hydroxide, calcium oxide, and calcium chloride, as well as alkaline agents such as potassium hydroxide and calcium hydroxide, are added to the chemical cleaning waste liquid shown in Table 1 to prevent phosphorus from being dissolved in the waste liquid. Salts and heavy metals such as iron and copper can be almost completely removed by precipitation of calcium phosphate (Ca5(PO4)zl and iron and copper hydroxides CFe(OH)z, Cu(OH)z). This is because it generates. Next, ferrous hydroxide C precipitated
F e(OH)z') by blowing air into the following (
1) As shown in the chemical reaction of formula, ferric hydroxide CFe(O
H) Oxidation to 3) reduces dissolved iron in waste liquid.

This is to prevent sodium peroxide, which will be added later, from being consumed by ferrous hydroxide.

2Fe(OH)z+1/202+H2O-+2Fe(O
H)3 (1) In addition, it is thought that this is due to the chemical reaction of the following formula (2), taking thiourea as an example, due to the oxidative decomposition of thiourea, which is a COD loading component in the waste liquid, and the inhibitor (organic amine type). Since the chemical formula of the inhibitor is not clear, the oxidative decomposition reaction associated with COD reduction is also unclear.

(NH2)2C8+7NazOz+4H20-+Na2
SO4 + 12NaOH + N2 +C02 (2) (peroxidation) The oxidation reaction of formula (2) using only IJ has the drawback of requiring a long time, but by adding 9 grains of activated carbon together, the oxidative decomposition reaction of formula (2) is effective. It has been confirmed through experiments that it promotes

The synergistic effect of oxidative decomposition due to the combined use of activated carbon is thought to be due to the catalytic action.

(Effects of the Invention) As described above, the present invention uses a combination of sodium peroxide and granular activated carbon to the alkaline waste liquid that has been produced by adding alkaline agents such as calcium hydroxide and sodium hydroxide to generate precipitates of heavy metals and phosphates. Adding it may have the advantage of effectively promoting the oxidative decomposition of COD components, but it also satisfies the wastewater standard values, so there is no need to dilute or adjust the pH of the treated liquid when discharging it. It can be released as is.

INDUSTRIAL APPLICATION This invention can be utilized for the treatment of the chemical cleaning waste liquid containing the hydrochloric acid cleaning liquid and rust prevention liquid of the boiler of thermal power plants, chemical plants, etc., heat exchangers, and other metal products.

(Example) This was carried out using chemical cleaning waste liquids having the composition and properties shown in Table 1. To 1 ton of these waste liquids, calcium hydroxide was added in an amount of 11 equivalents to the phosphate ions in the waste liquid, and 40% water was added. A sodium oxide solution was added to adjust the pH to 7 or higher to form precipitates of calcium phosphate, ferrous hydroxide, and copper hydroxide.

Next, the liquid is forcibly stirred together with the precipitate by blowing air to sufficiently oxidize the ferrous hydroxide to ferric hydroxide.
The equivalent ratio of sodium peroxide added to the COD in the waste liquid and the amount of granular activated carbon added were varied, and the mixture was forcibly stirred for 2 hours by air blowing, and then the air blowing was stopped to allow the precipitate to settle. , COD, dissolved iron, and copper of treated water whose supernatant was neutralized with sulfuric acid solution.

Measure phosphate ions and SS (solid suspended solids).

The results shown in Table 3 were obtained. In Table 3, test number 1
The first block up to 8 is a chemical cleaning mixed waste solution of scale that does not contain copper as shown in Table 1, and the second block of test numbers 9 to 16 is a chemical cleaning mixture of scale containing copper as shown in Table 1. It is waste liquid. In addition, test number 1.9 is the untreated chemical cleaning waste liquid from each block above, and is the mixed waste liquid 4 in Table 1.
The properties are shown for reference.

In addition, the inhibitor of hydrochloric acid cleaning solution is Hibilon A-1.
00 (amine-based pickling anticorrosive agent, manufactured by Sugimura Chemical Industry Co., Ltd., trade name) is used.

Results similar to those in Table 3 were obtained even when other companies' products were used, and the degreaser used was Plysurf A215C (polyethylene glycol ether, manufactured by Dai-Kogyo Seiyaku Co., Ltd., trade name); Results equivalent to those in Table 3 were obtained even when the product was used.

From Table 3 of the test results, the following was found.

(1) Chemical cleaning waste liquid of test numbers 2 to 8 and test number 1
For the collapse of chemical cleaning waste liquids of 0 to 16, calcium hydroxide is added in an amount equivalent to or more than the phosphate ions in the waste liquid, and sodium hydroxide solution is further added to adjust the pH to 7 or higher, and the COD in the waste liquid is adjusted to pH 7 or higher. By adding an equivalent amount of sodium oxide and granular activated carbon to the waste liquid IR, the COD, dissolved iron, and copper of the treated water can be reduced.

Both phosphate ions and SS fully satisfy the wastewater standard values in Table 2, so the treated liquid must be diluted and pH adjusted before discharging.
It can be released into the ocean as is without the need for adjustment.

Kazeta Nahaku

Claims (1)

[Claims] When treating chemical cleaning waste liquid containing hydrochloric acid cleaning liquid and phosphoric acid-based rust preventive liquid, calcium compounds and alkaline agents are added to the waste liquid to adjust the pH to 7 or higher, and heavy metals and phosphates in the waste liquid are removed by heavy metal hydroxide. C in the waste liquid is precipitated as carbon and calcium phosphate, and the generated ferrous hydroxide is oxidized to ferric hydroxide by air blowing.
C
A method for treating chemical cleaning waste liquid characterized by oxidizing and decomposing OD.