JPS59196796A - Treatment of liquid waste - Google Patents

Abstract

PURPOSE:To obtain treated water of good quality, by adding the specified amount of a calcium compound to the liquid waste of a citric acid washing solution or the like containing a fluoric compound, holding a pH below a specified value, and then adding aluminum and ferrous salts. CONSTITUTION:After a calcium compound is added to the liquid waste of a citric acid washing solution and/or a neutralized corrosion preventive solution containing a fluoric compound in a manner such that calcium content is at least 1 equivalent or more based on the total of citric acid and a fluorine part, a pH is adjusted to 11.5-13.0 to precipitately separate citric acid and the fluorine part existent in the liquid waste as relevant calcium salts. Thereafter, the pH of a separated supernatant liquid is adjusted to 4 or lower, aluminum and ferrous salts are added, hydrogen peroxide is further added to perform oxidation, and then the pH is readjusted to 6-8 to solid-liquid separate insoluble substance.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating a citric acid cleaning waste liquid and/or a neutralized rust prevention waste liquid containing a fluorine compound after pickling the inside of a pipe pink such as a pipette or equipment.

For example, in the case of a boiler for thermal power generation, steam generators, evaporator pipes, and pipes are removed from the steam generator, evaporator pipes, and pipes when newly installed and at an appropriate time after operation.

Chemical cleaning of the inner surface is required for the purpose of removing rust, and in some cases a fluorine compound is added to the citric acid cleaning solution to enhance the cleaning effect.

Table 1 shows an example of citric acid cleaning waste liquid from a boiler for thermal power generation.

(Varnish 1/Te Ywo) Table 1 *Iron oxide scale eluted into the acid solution by iron separation in the waste solution and acid washing.

To treat waste liquids such as IrTb to 1IIJ, add citric acid, fluorine, and calcium hydroxide.

After adding a calcium compound such as carnoum chloride so that the concentration of carnoum ions is equivalent or higher,
plI adjustment is carried out, and the PIIL-soluble substances calcium fluoride and calcium citrate are produced by the reactions of the following equations (1) and (2), and solid-liquid separation is performed to calculate the chemical oxygen demand (COD) in the waste liquid. Citric acid and fluorine components, which have a high loading rate, were removed.

N114■F→-On (01() 2→CaF2↓→
-NII, oti tenn,,,o =-Q)206H7
07NH4+ 8CIL(OH)2-+ C118(C
6H507) 2↓→-2NII40Ii + 4112
0...(2)F e (NH4) 2I-((061
1507)2 + 80a (OII)2→cnH(C
6H507)2+Fc(0)])3↓→-2NH40H
+ 020 ・---=-(3) However, in this treatment method, -L clear water after solid-liquid separation contains C
OD value 500-900ppm Fluorine content 15-30pp
The fluorine concentration remained in the effluent, and it was not possible to reduce the fluorine concentration to below the effluent standards shown in Table 2.

Table 2 The present invention eliminates the above-mentioned drawbacks in the treatment of conventional citric acid cleaning waste liquid containing fluorine compounds, owl or neutralized anti-corrosion waste liquid, removes harmful substances in the waste liquid, and improves the wastewater standard value. The purpose is to provide waste liquid treatment that reduces the citric acid content and fluorine content of citric acid cleaning waste liquid and O//or neutralized rust prevention waste liquid containing fluorine compounds. After adding a calcium compound so that the degree of calcification is at least equivalent to that of the waste liquid, the pif of the waste liquid is adjusted to 11.5 using a pH adjuster.
Adjust within the range of ~130.

The citric acid content and fluorine content in the waste liquid are removed as precipitates of calcium citrate and fluorine, respectively, and iron ammonium citrate is removed.

The first step is to remove the iron content in iron fluoride ammonium as a precipitate of iron hydroxide, and after adjusting the PII of the clean water separated in the first step to 4 or less, aluminum salt and ferrous salt are added. The waste liquid treatment method comprises a second step of further adding hydrogen peroxide to perform oxidation treatment, adjusting the pH to 6 to 8, and separating solid and liquid insoluble substances.

The present invention provides water in such a way that the concentration of carnoium ion is 1 equivalent or more, preferably 3 times as much as the citric acid content and fluorine content in the citric acid cleaning waste liquid and/or the neutralized rust prevention waste liquid containing fluorine compounds. Add calcium compounds such as calcium oxide, chloride, etc. Unless the amount of the calcium compound added is equal to or higher than the carnoum ion concentration relative to the citric acid and fluorine, the citric acid and fluorine will remain in the treated water and COD and fluorine cannot be reduced. Moreover, if the amount added is increased beyond the necessary level, the amount of sludge will increase in the subsequent sedimentation separation process, which is not preferable. In the experimental examples conducted by the present inventors, the appropriate amount of the calcium compound to be added was 8 times the carnoum ion concentration relative to the citric acid content and fluorine content in the waste liquid.

Then, the treated water is treated with an alkaline RU regulator such as caustic sorter, calcium hydroxide, carbonate sorter, etc.
5 to] 3, and precipitate carnoium fluoride and carnoum citric acid produced by the reactions of equations (1) and Q and (2) above, and iron ions coexisting in the treated water are
Solid-liquid separation is performed in the reaction of equation 3) as iron hydroxide is precipitated, and the COD component and most of the fluorine content in the J-δ solution and the metal ions, which are mainly occupied by iron ions, are removed as precipitates.

In the reaction of formula (2), the range of J and H in which a precipitate of calcium fluoride is formed is 2 to 13, but in the reaction of formula (2), a precipitate of calcium citrate is formed in the range J,,I.
Because the range of I is within the range of 115-130.

The pII adjustment of the treated water was limited to a range of 115 to 130 as a condition for effectively solid-liquid separation of the fluorinated and citric acid components (OI) in the treated water. Acceleration of reaction in this treatment step.

In order to improve the separability of the precipitate, oxidation treatment, etc., air spraying is performed, or to coarsen the fine particle precipitate and remove the precipitate by sedimentation +<r.
A flocculant may be added.

- In the first step of Section F, most of the citric acid content and fluorine content, which are the COD components in the waste liquid, are removed as precipitates. 00 D of solubility is 500-900 pp
Furthermore, since 15-30 ppln of fluorine is present and cannot be immediately discharged, the supernatant water separated in the first step is subsequently treated in the second step to reduce the fluorine content of COD component 7.

That is, the 1F clear water separated in the first step is adjusted to a pH of J'114 or less, preferably 3, using an inorganic acid such as 2 sulfuric acid, nitric acid, or hydrochloric acid.

Aluminum salts such as aluminum sulfate and aluminum chloride should be added to a small amount (preferably 3 to 3 to
5 (Add F4 current scene.

Note that below II 4, aluminum hydroxide flocs are not generated even if aluminum salt is added, and aluminum is dissolved in ptB and above, but aluminum compounds are not added in this PI region. It also has no effect on removing fluorine.

Next, oxidation treatment is performed by adding ferrous salts such as ferrous sulfate and ferrous chloride and hydrogen peroxide. The amount of the ferrous salt to be added is preferably at the equivalent level in iron ion concentration relative to the citric acid content of the treated water.

It is necessary to add 12 to 15 times equivalent (i), and the amount of hydrogen peroxide added is 171, which is necessary to sufficiently oxidize the ferrous salt. This is not preferable because in the next solid-liquid separation step, dregs will be mixed in the precipitate, impairing separation performance.

Approximately twice the equivalent amount of iron is suitable.

In addition, the pH range of the treated water in the oxidation treatment is preferably 3 to 4 in the treatment containing citric acid due to the efficiency of the oxidizing agent.

After the oxidation treatment is completed, an alkali such as caustic meter 2 hydroxide is added to neutralize the pH to 6 to 8, and the ferric hydroxide and ferric hydroxide generated in the oxidation treatment are The remaining fumes in the treated water are removed by precipitating the oxidation reaction product with aluminum as a MIA-soluble compound.

The solid l+ is further separated by adsorption coprecipitation. In order to promote the oxidation reaction, it is also good to add a polymer coagulant during precipitation and separation.

The precipitate separated in the first culm 7 and the second step is dehydrated by vacuum dehydration, a dehydration treatment device such as a PiEJ machine, or a filter press, and then treated by incineration or other methods.
The supernatant water separated in the process has a water quality that fully satisfies the above-mentioned water standard value, so it can be discharged as is.

Example: 2% citric acid discharged from acid cleaning of power generation boiler
, acidic ammonium fluoride 1%.

Sulfuric acid 15%, Inohichita 03%, iron ion 5.000
The acid cleaning solution containing ppm was washed with water and diluted by approximately 4 times i1i, Z with neutralized anti-corrosion solution, resulting in a COD of 8,500 ppm.
Calcium hydroxide + 7.00011 pm was added to the citric acid cleaning waste solution containing 840 ppm of fluorine.
was added to the mixture, and the reaction was accelerated by performing an air injection for 7 to 1 hours, and 20 ppm of a polymer flocculant was added and set-linked for about 12 hours to precipitate insoluble substances. In addition, the treated water after addition of lucium hydroxide p1. (was +2.2, so using pI-1 adjuster 0) J-,11
No adjustments were made.

Separation occurred in this first step. ”-Fluorine + 6p for clear water
p+n, COD 660 ppm remained.

-1- After transferring clear water to another treatment tank, add sulfuric acid to J
・Adjust to ■3, add 50 ppm of aluminum using aluminum sulfate, and 300 ppm of iron ions using ferrous sulfate.
pm, 85% hydrogen peroxide solution 681/treated instant water 1- were sequentially added, followed by aerating for about 5 hours, adding hydroxide to adjust the PI of the treated water to 7, and then solid-liquid. separated. The separated precipitate was treated by dehydration.

Fluorine in the treated water obtained in the first and second steps below was 8.8 ppm, and COD was 27 ppm.

Claims (1)

[Claims] After adding a carunium compound so that the calcium concentration is at least equivalent to the citric acid content and fluorine content of the citric acid cleaning waste liquid and/or neutralized rust prevention waste liquid containing fluorine compounds, using a pH adjuster. Adjusting the PII of the waste liquid within the range of 11.5 to 130,
A first step of removing citric acid and fluorine in the waste liquid as precipitates of calcium citrate and carnoium fluoride, respectively, and removing iron in ammonium iron citrate and ammonium iron fluoride as precipitates of iron hydroxide; 2 After adjusting the pII of the supernatant water separated in the first step to 4 or less, add aluminum salt and ferrous salt, and then perform oxidation treatment by adding hydrogen peroxide, and then adjust the pH. 6～
8 and a second step of separating the insoluble 1'I substance from solid to liquid.