JPS59196797A - Treatment of liquid waste - Google Patents

Abstract

PURPOSE:To treat liquid waste of high COD into a low-COD state, by adding the specified amount of a calcium compound to a washing solution containing citric acid, further adjusting a pH to a specified range, lowering the pH of a separated supernatant liquid below a specified value, and then adding a cupric compound. CONSTITUTION:The liquid waste of a chemical washing solution in which a corrosion inhibitor, a rust preventive agent, mainly ferric ion, etc. in addition to the mixture of citric acid and an ammonium salt are coexistent is introduced into a treating tank, wherein a calcium compound such as calcium hydroxide is added in a manner such that the concentration of calcium ion is 1 equivalent or more based on a citric acid part in the treating tank. Thereafter, a pH is adjusted to 11.5-13 using alkali such as caustic soda, to precipitate the citric acid part as calcium citrate. Cupric sulfate or the like is further added in a manner such that the concentration of cupric ion is 1 equivalent or more based on the calcium citrate part in a separated supernatant liquid, to form insoluble cupric sulfate. Then, the pH is readjusted to 5.8-8.6, and solid-liquid separation is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides various power generation systems 1-1 and chemical systems 1-1 and 7-1.
- Concerning a method for treating the inside of pipes and equipment and waste liquid in chemical cleaning using acid.

For example, in the case of a thermal power boiler, chemical cleaning is carried out for the purpose of descaling/l/rusting the inner surface of the boiler for the purpose of safe operation, 11.7) power...? In order to prevent intergranular cracking phenomena for boilers containing Autenai 1-stainless steel in the cleaning system, use a cleaning solution containing an organic acid, especially citric acid and iJL acid of ammonia, with a corrosion inhibitor added. Cars are common. This type of cleaning waste liquid contains various metal ions (mainly iron ions) eluted during cleaning and has a high 00D value, so it cannot be discharged as it is due to power and pollution, so it must be treated in some way. is required.

Conventionally, as a treatment method for such waste liquid, calcification of an amount equal to or greater than the citric acid content in the waste liquid is added, the pH is further adjusted to 11.5 to 13 using a pH adjuster, and the above-mentioned When the citric acid content in the waste liquid is precipitated as calcium citrate, the metal ions in the liquid are converted into hydroxides and the oxidizer is transferred to another treatment tank. Add 5 and wait for oxidation treatment, C0I
) After reducing the components, it was neutralized and discharged. However, with such treatment methods, there is a limit to the reduction of the Con component, and there is a risk that secondary pollution may occur due to excessively added oxidizing agent remaining in the Con component. Ta.

The present invention eliminates the drawbacks of the conventional method described above, and eliminates the high COD value (e.g. 8500 ppm)17) Low COD value! 0Dft1
(Example t is below 50 ppmlJ).

The present invention provides citric acid washing waste liquid and/or neutralization (lJ
j 7. For citric acid of rust waste liquid. t, then add at least an equivalent amount of calcium compound, and then reduce the amount of waste Kf to
A first step in which citric acid is precipitated as calcium citrate and metal ions in the waste liquid are precipitated as hydroxides by adjusting LI to 115 to 13 to perform solid-liquid separation.

Add acid to the supernatant liquid separated in the first culm to pH 7L':
This method is characterized by a second step in which, after adjusting the amount of liquid under L, a key compound is added to generate insoluble copper citrate and solid-liquid separation is performed.

The present invention is a chemical treatment method for treating abandoned hoofs using a mixture of citric acid and anomonium salt, a corrosion inhibitor, a rust preventive agent, and jF containing iron ions. Place the receiver on the side.

Calcium compounds such as calcium hydroxide and calcila chloride A are added so that the concentration of calcium ions is 1 times M or more, preferably 3 times M, relative to the citric acid content in the treatment solution. This is because unless the amount of calcium ions added is equal to or greater than the citric acid content, the citric acid content of the treated water becomes large and COD cannot be reduced. Moreover, if the amount added is increased unilaterally, the amount of sludge in the subsequent sedimentation separation process will increase, which is not preferable.

From experimental examples of the present invention, etc., it was found that a three-fold equivalent amount was suitable for this addition amount.

Next, process D11 water using alkaline pH adjusters such as caustic soda, calcium hydroxide, and carbonate sorter.
Adjust LI to 115 to 13, convert citric acid in the treated water into calcium citrate sediment, and perform solid-liquid separation by converting iron ions coexisting in the treated water into iron mercury sediment.
Most of the CO2) components in the treated water and metal ions, mainly iron ions, are removed as sediment. Separated sink hooks.

After dehydration using dehydration equipment such as vacuum dehydration, filters, and filter breaths, it is incinerated or treated by other methods. The chemical reaction equations for producing calcium citrate and iron hydroxide in this treatment are shown in the following equations (]) and (21).

2C6n707-Nl14 +30a(Oll,)2-
+ ca3(c6Il++07h +2NH4(for (-
4112Q ・= −(1)Fe(N114)211
(C(,n5o7)2 + aca (oII)2−)
0a3(c6Hr,07)2]doe (Oll)3
1,000 2NIT4011 +II20 ・Mountain...(2)(
]) The calcium citrate produced by the reaction of the formula is pHl+
From the above, a precipitate will be produced, and if the pH exceeds 118.5, no stagnation will be produced, so in order to produce sufficient precipitate, the pH must be adjusted to between 115 and 3.

Also, the hydroxide number produced by the reaction of formula (2) is.

111 pTI range for treating citric acid (pfl
11.5 to 13), it can be removed simultaneously as a precipitate of iron hydroxide. In this reaction, aeration may be performed to promote the reaction and improve sedimentation separation, or a polymer flocculant may be added to coarsen the sedimentation of fine particles to hasten sedimentation separation.

In the above first step, most of the citric acid, which is the 0OI) component in the waste liquid, is removed as a precipitate, or
After solid-liquid separation, the clear liquid contains 500 to 900 ppm of solubility as calcium citrate as a Con component.
Since it cannot be discharged as it is, the Con component in the second culm is reduced by the next second culm. After the supernatant liquid is transferred to another treatment tank, the pLI is adjusted to a range of 7 sts using an inorganic acid such as sulfuric acid or nitric acid. This pH adjustment is preferably about pII3 in view of the effectiveness of the subsequent oxidation treatment and the economy of the amount of acid used. Then 10 Kf
Silver sulfate,
After adding copper compounds such as copper nitrate and silver chloride to produce insoluble copper citrate, use calcium hydroxide as a pH adjuster to adjust the pII of the supernatant to par 5, which is the legal wastewater standard value. Solid-liquid separation is performed by adjusting the temperature within the range of .8 to 86.

The C0I) value of the separated supernatant liquid can be reduced to 20 ppm culm degree when treated by adding copper ion A equivalent to 1 mJ of egg treatment. In this second step, in order to make the precipitation and separation of copper citrate effective, aeration and the addition of a polymer flocculant are carried out in the same way as in the first step! -Good.

As mentioned above, the present invention uses 20pp of waste liquid with a high 001.1 value.
The mPI'' is effectively reduced, and no secondary pollution is caused due to the addition of excessive oxidizing agent.

Example 3% citric acid, corrosion inhibitor (manufactured by Sugizai Chemical ■).

Crack 07 K ~4) 0.8%, A7mo = 70.25
% ((78NH3) Waste i'fl mixed in the ratio of 11 volumes of acid i'j containing 8000 ppm of ferrous ions, 2 volumes of washing water, and 1 volume of neutralized rust prevention axil (COD 8.500
ppm) to 71.

Calcium hydroxide was added so that the equivalent ratio of citric acid content and calcium ion concentration was three times.

After performing aeration for about 5 hours, 20 ppm of a polymer flocculant was added, and the mixture was left to stand for about 2 hours to perform solid-liquid separation.

In addition, since the pIi of the waste liquid was 124 by using calcium hydroxide as the calcium compound, it was not necessary to adjust the ptr using a pH adjuster. C of the supernatant liquid separated! Or) value was 680 ppm, and no iron ions were detected. Subsequently, nitric acid was added to this supernatant liquid to adjust the pH to 118, and then copper nitrate (cu(No3)2) was added as a copper compound so that the copper ion concentration was 5 times equivalent to that of citric acid. The treatment was carried out for about 5 hours and then treated with calcium hydroxide.

The pII was adjusted to 65 (and then solid-liquid separation was carried out after being left for about 2 hours). The COD concentration of the double m solution was 20 ppm.

Claims (1)

[Scope of Claims] An acid washing waste solution containing citric acid and . At least an equivalent amount of a calcium compound is added to the citric acid of the neutralized anti-corrosion waste solution.1. Next, the pIl of the waste solution is adjusted to 115 to 13 using a pH adjuster.1. The first culm is where citric acid is precipitated as calcium citrate, metal ions in the waste liquid are converted into hydroxides, and solid-liquid separation is performed. ] After adding an acid to the clear liquid separated by the culm and condensing it, a copper compound is added to form an insoluble copper phosphate to form a solid-liquid fraction. A method for treating waste liquid characterized by forming two culms.