JPS5929082A - Treatment of waste water of stack gas scrubbing in refuse incineration plant - Google Patents

Abstract

PURPOSE:To remove effectively mercury and other heavy metals by adding an S compd. and an Fe compd. at the vicinity of neutrality to the waste water of stack gas scrubbing in a refuse incineration plant to cause reaction then adding an alkali agent to the water to adjust the same basic and subjecting the water to a solid-liquid sepn. CONSTITUTION:An S compd. (e.g.; Na2S) and an Fe compd. (e.g.; FeCl3) are added under 6-8pH conditions to the above-described waste water of stack gas scrubbing to cause reaction. The S compd. in this case is added for the purpose of removing mercury and other heavy metals, and the Fe compd. for the purpose of removing unreacted S ions. An alkali agent such as slaked lime is added to the waste water of stack gas scrubbing subjected to the above-described treatment to adjust the pH thereof to 9-11 and the water is subjected to a solid- liquid sepn. with heavy metals except mercury as insoluble hydroxides. If it is desired to remove F as well, a Ca compd. such as CaCl2 or the like is added to the water in the fore stage (6-8pH) and a good result is obtd. if Ca(OH)2 is used as the alkali agent in the post stage.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating smoke washing wastewater generated at a dust JF incinerator.

Since combustion gas cannot be directly discharged at garbage incinerators, smoke cleaning is performed, and there are two methods for cleaning smoke: dry and wet. The dry method produces flaky Ca (OHJffi
Gas is released into I@ etc. for treatment, but the mercury is not captured and is emitted into the atmosphere.

In contrast, wet methods can remove mercury, but require treatment of smoke washing wastewater.

Smoke washing is performed using an alkaline absorption liquid such as a sodium hydroxide solution, and hydrogen chloride in the combustion gas is absorbed, so the amount of smoke washing wastewater is high (1 g).

It also contains organic matter and various submetals.

The treatment method for this smoke washing wastewater is r r; I, chelate (
☆A method in which water is passed through a column filled with fat and activated carbon to remove it, and a precipitation method in which sulfur compounds, water-soluble cleating agents, etc. are added to form heavy compounds with mercury at °C and solid-liquid separation is carried out. It has been known. However, in the Maedagi filler method, not only is it necessary to remove the turbidity Hrlt as a pretreatment, but also several
The VL that removes mercury from pHl to several ppb is 1 of the filler.
It is difficult because you have to add a lot to the 1st replacement girl K'.

On the other hand, in the latter precipitation method using a sulfur compound, rice ion is added several times as much as mercury, and two times or before and after, the precipitation is carried out under conditions of pH 6 to 8 to remove excess sulfur-f-ion. Fully added with 2 iron ions.

A method has been adopted in which these insoluble products are separated by precipitation. , ferric ions f pll 6 to 8 are used under the conditions because this pH range is good for removing 71'C silver, and excess iron ions become hydroxide precipitates, making them easy to remove. However, this @11Z material method applies to other 11■ metals (
(Zn, PB, Cd, etc.), so if all of these are removed, it will be difficult to remove them.1. Te nail metal chito;
It is necessary to add 1 ton of sulfide, which is several times that of Mori.

Therefore, an excessive amount of 11 um (for example, sulfide) is added to mercury, causing cloudiness in the treated water (in addition, iron and daffodil are removed).
It has the disadvantage of poor exfoliability. On the other hand, this method p, H9
~11 "C treatment cannot remove mercury sufficiently. The reason for this is obvious. S/H, 9
This is thought to be due to the fact that when the ratio is high or when pIl is high, all polysulfides are produced, and the ferric iron is reduced to produce a rich amount of ferrous iron.

SUMMARY OF THE INVENTION An object of the present invention is to overcome the above-mentioned disadvantages and provide a method for treating smoke washing wastewater from a garbage incinerator, in which mercury and other heavy metals can be effectively removed.

As a result of studies by the present inventors, it was found that iodine compounds and iron compounds were added to wastewater under conditions of pH 6 to B.

Afterwards, it was discovered that mercury and heavy metals did not dissolve even if the pH was raised to 9 to 11. Therefore, the present invention was temporarily abolished. At pII G~8, an iron compound is added to the water side for the purpose of removing other heavy alloy silk, and an iron compound is added for the purpose of removing unreacted sulfur ions, and the mixture is reacted.

Next, an alkaline agent is added to adjust the pH to 9 to 11, and other heavy metals are separated from the insoluble hydroxide and solid-liquid. Therefore, 1) Two-stage treatment based on the findings of iJ.
! There are 9 lines in row 11r, 1 is mercury, and 1 is due to the effective removal of both metals.

Sulfur compounds (as used in the present invention)

Sodium sulfide (Na2S), sodium sulfide (NallS)
) etc. Iron compounds include NA2iron chloride, jjf
Ferric flate and the like can be used.

If you want to remove fluorine as well, add a calcium compound such as 1.kr CnCl, 2. C
Add u(OH)v, etc., and add C as an alkaline agent in the latter stage.
It is better to use A(O)lJtk. Aluminum compounds have also been considered for fluorine removal; however, calcium compounds are more expensive because their adsorption capacity is low and they are economically disadvantageous.

Note that solid-liquid separation is performed by known means such as filtration and coagulation and precipitation. Hereinafter, the effects of the present invention will be clarified through examples.

Example L'>S Smoke washing wastewater from waste incineration plant (pH 8.6, H mites 11
．． 40g/), fluorine: 1106ffi/no+] l'lead: 8.81 t1g/no, lead: 380 t1g/no, cadmium 1.0 m'j/horn (soda fluid exchanged with sulfur in 1 part) hg/j!added, ferric chloride i30t
Add lν/1 and add 2000 ha9/Jl of slaked lime p
I adjusted it to 6 to 8 in the order of H excitation and pressed 15 volts for 15 minutes. Add 400-800MS//i of slaked lime to adjust pH'
Adjust the temperature to 19-11 and stir for 15 minutes.
It was filtered through A p paper. The quality of treated water is shown in the table below. For comparison, the amount of sodium sulfide added is 5 m9/), the amount of ferric oxide added is 3QQmg/, and γt'q lime: 28
Add 00+IIg/no and further adjust the pH with sulfuric acid to 6-8 (comparative example) or pll 9-11 (comparative example 2) to 117
The table also shows the case where the mixture was stirred for 30 minutes after being adjusted.

From the results shown in the table, it will be seen that the λit property of the present invention is effective.

Claims (1)

[Scope of Claims] ], A sulfur compound and an iron compound are added to 7K of smoke washing waste from garbage incineration Jha at pH 6 to 8, the reaction is caused, and then an alkaline agent is added to adjust the pH to 9 to 11. The previous minute! 'i
Disposal of smoke washing wastewater of 0-waste incinerator characterized by #1
IJj method. 2. Claim 1J that the alkaline agent is slaked lime
The processing method described in Ji.