JPS59166290A - Method for removing harmful component in waste water of smoke scrubbing - Google Patents

Abstract

PURPOSE:To remove efficiently and simultaneously harmful components by adding a sulfide chemical and a magnesium chemical to the waste water of smoke scrubbing from a refuse incineration plant, etc. to insolubilize harmful components such as heavy metals, flourines, or the like then subjecting the same to a solid-liquid sepn. CONSTITUTION:Waste water of smoke scrubbing of 70-80 deg.C from a refuse incineration plant or the like which scrubs waste gas with an aq. alkaline soln. and discharges the waste water is cooled preferably to 30-40 deg.C in a cooling tower or heat exchanger and thereafter a sulfide chemical is added thereto to insolubilize mainly the heavy metals in the waste water. Said sulfide chemical is exemplified by sodium sulfide, sodium polysulfide, etc. A magnesium chemical is then added to the waste water to insolubilize mainly fluorine and boron. The magnesium chemical is exemplified by magnesium oxide, magnesium hydroxide, etc. The insolubilized heavy metals, etc. are subjected to a solid-liquid sepn. by settling, filtering, dehydrating, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing harmful components contained in smoke washing wastewater discharged from garbage incinerators and the like.

In recent years, hydrogen chloride, ionic oxides, and double heavy metals have been found in the exhaust gas from factories that incinerate municipal garbage and industrial waste.

It contains components such as fluorine and boron that hinder the growth of the human body, animals and plants, and is a cause of environmental pollution.

For this reason, a method of cleaning and treating the exhaust gas with an alkaline aqueous solution such as caustic soda is widely used. However, the smoke washing wastewater discharged after this treatment still contains mercury, cadmium, lead, and zinc.

Because it contains heavy metals such as chromium and copper, as well as harmful components such as fluorine and boron, it cannot be discharged into rivers as is.

This is why 64. Conventionally, the heavy metal hydroxide method, which involves adding ferric chloride, etc., and the heavy metal sulfide method, which involves adding sodium sulfide, etc., have been generally used to remove heavy metals contained in smoke washing wastewater. It has been adopted and is almost technically established. For the removal of fluorine components, there is a fluoroapatite method (Japanese Patent Application No. 147263/1983) in which phosphoric acid and calcium chloride are added, and for the removal of boron components, a chelate resin having an aminopolyol group is used. Adsorption method (see Japanese Patent Application No. 57-124845)
and so on. However, if such conventional methods were to be used to remove components such as heavy metals, fluorine, and boron contained in smoke washing wastewater, each of the above-mentioned methods would have to be combined, making the process extremely complicated. It has the following drawbacks.

The inventors of the present invention have conducted intensive research with the aim of establishing a method for removing harmful components from smoke washing wastewater that can eliminate the above-mentioned drawbacks and efficiently remove the various harmful components at the same time. The present invention was completed based on the discovery that the above object can be achieved by skillfully treating the product by adding a drug and a magnesium drug.

That is, the present invention is applicable to smoke cleaning wastewater from garbage incinerators, etc., where exhaust gas is washed with an alkaline aqueous solution and then discharged.

This is a method for removing harmful components from smoke washing wastewater, which is characterized by adding sulfide chemicals and magnesium chemicals to insolubilize the harmful components contained in heavy metals, fluorine, boron, etc., and then performing solid-liquid separation.

The method of the present invention will be explained in detail below.

In order to treat smoke washing wastewater from a garbage incinerator using the removal method of the present invention, the following methods can be used, for example. First, drain the smoke washing water at a temperature of 70 to 80°C, preferably in a cooling tower or heat exchanger, to a temperature of 30 to 40°C.
After cooling to °C, a sulfide agent is added to insoluble mainly heavy metals in the wastewater as sulfides. Sulfide agents used in this case include, for example, sodium sulfide and sodium polysulfide.

Examples include calcium polysulfide, but sodium sulfide and sodium hydrogen sulfide are particularly effective. The amount used is preferably 0.1 to 3 moles based on the total number of moles of heavy metal ions contained in the smoke washing wastewater, and if it is less than 0.1 mole, the insolubilization rate of heavy metal ions tends to be poor. On the other hand, if the amount is more than 3 moles, an excess of the sulfide agent remains in the liquid, which tends to cause problems with color and odor. Next, a magnesium agent is added to the waste water to insolubilize mainly fluorine and boron. Although this reaction is not clear, it is thought that the magnesium drug, fluorine, and boron probably form an insoluble complex compound with a relatively high molecular weight. Examples of magnesium drugs used here include magnesium oxide, magnesium hydroxide, magnesium sulfate, magnesium chloride, magnesium carbonate, magnesium silicate, magnesium phosphate, and magnesium nitrate.

Of these, magnesium oxide and magnesium hydroxide are preferred. The amount used is 100 to +' Mg based on the total amount of fluorine and boron ions contained in the smoke washing wastewater.
1000 times the amount (weight) is preferable; if the amount is less than 100 times, the insolubilization rate of fluorine and boron ions tends to deteriorate, while if the amount is more than 1000 times, the amount of sludge generated will be significantly large, making solid-liquid separation difficult. There is a tendency to In the present invention, the method of adding the magnesium agent after adding the sulfide agent as described above is preferably employed, but the order of addition of the agents may be reversed or both agents may be added at the same time.

The pH of the solution for insolubilizing harmful components is preferably 9 or higher. When the pH is lower than 9, the insolubilization rate of fluorine ions and boron ions tends to be low.
The pH may be adjusted to 9 or higher using an alkaline agent such as caustic soda.

In the present invention, in order to aggregate the insolubilized components and facilitate solid-liquid separation, an inorganic flocculant such as ferric chloride or polyaluminum chloride is added in an amount of 100 to 500 mg/min as necessary.
E, a polymer flocculant such as polyacrylamide, can also be added at r~5 mg/β.

The above drugs are injected as a liquid using a pump, and the two reactions are carried out while being mixed using a stirrer, etc. Each reaction time is 5 to 3 minutes.
In 0 minutes, the heavy metal ions and boron compounds that were insolubilized at the end are precipitated.

Solid-liquid separation is performed by filtration 5 dehydration treatment, etc.

Since the method of the present invention has the above-mentioned configuration, it is possible to efficiently remove harmful components contained in heavy metals such as 1-fluorine and boron in smoke washing wastewater, which have been difficult to remove in the past, by simple treatment.

The present invention will be specifically explained below with reference to Examples.

Example 1 As a result of measuring smoke washing wastewater obtained by washing exhaust gas from a garbage incinerator with a caustic soda aqueous solution, zinc was found to be 260 mg/12 (3,9
77m mol/ (!), lead 38mg/II
(0,183m mol/p), cadmium 3.9mg
/β(0,035mmol/II).

Total mercury 10 mg/β (0,050 m mol/II
), iron 12mg/A (0,215m mof/E
), copper 6.7 mg/ (! (0,105 m mol
/β), and the total number of moles of these is 4,565X 10' mol/β, and 62 mg/β of fluorine, 25 mg/β5 of boron, and 62,000 mg/(t, potassium 110 mg/β) of sodium.
00mg/β, calcium 4f30mg/II, magnesium 63mg/β, suspended solids 2100mg/β, etc., pH was 7.0, and temperature was 28°C.

1 ρ of this smoke washing waste water was collected in a heater and an experiment was conducted using a jar tester. First, 200 mg/β (approximately 0.23 mol/total number of moles of heavy metal ions) of 30% sodium hydrogen sulfide was added as a sulfide agent to the amount of smoke washing waste water to mainly insolubilize heavy metal ions. The reaction was carried out with stirring for 10 minutes, resulting in a pH of 7.3.

Next, as a magnesium drug, 95% magnesium oxide 5
0g/II (approximately 329 g as Mg/amount of fluorine and boron in smoke washing waste water) was added to mainly insolubilize fluorine and boron. This reaction was carried out with stirring for 20 minutes, and the pH at this time was 10.4.

Roughly, polyaluminum chloride 300 as an inorganic flocculant
mg/β, polyacrylamide polymer flocculant 3 mg/
ff was added to form a floc that facilitates solid-liquid separation of insolubilized substances such as heavy metals, fluorine, and boron. This reaction was carried out with stirring for 20 minutes, and the pH at this time was
became 10.3.

Finally, the insolubilized heavy metals, fluorine, and boron compounds were allowed to settle for 1 hour and separated into solid and liquid. Table 1 shows the analysis results of the wastewater.

What is clear from Table 1 <Example 1 has a fluorine removal rate of approximately 99%.
It has an excellent boron removal rate of approximately 93%, and satisfies the wastewater standards of Osaka and Shiga prefectures.

Furthermore, the removal rate of heavy metals was also good and satisfied the wastewater standards.The reason why such good results were obtained was that the heavy metals, fluorine, boron, etc. in the wastewater were removed by hydrosulfide sorter, stable insoluble substances such as magnesium sulfide, etc. It is thought that they form a complex compound.

Comparative Example 1 The process was carried out in exactly the same manner as in Example 1, except that the addition of 30% sodium hydrogen sulfide in Example 1 was omitted.

The results are also shown in Table 1. From Table 1, Comparative Example 1 has a fluorine removal rate of about 90%, which satisfies the wastewater standards, but it is a little worse than Example 1, and the boron removal rate has decreased to about 64%, which means that the wastewater It exceeds the standard. Furthermore, the removal rate of heavy metals has decreased, and lead, cadmium, and total mercury exceed wastewater standards. The reason for this poor result is considered to be that the addition of sodium hydrogen sulfide was omitted, so that no insoluble composite compound was formed.

Comparative example 2 The addition of magnesium oxide in Example 1 was omitted.

After adding 300 mg/β of polyaluminum chloride.

The treatment was performed in exactly the same manner as in Example 1, except that the pI was adjusted to 10.0 with 24% caustic soda.

The results are also shown in Table 1. From Table 1, Comparative Example 2 has a fluorine removal rate of about 8% and a boron removal rate of about 4% compared to Example 1, which is extremely low for both removal rates and greatly exceeds the wastewater standards, and also removes heavy metals. Cadmium and total mercury have fallen slightly and exceed wastewater standards. The reason for such a poor result is considered to be that the addition of magnesium oxide was omitted, so that an insoluble composite compound was not formed.

Comparative Example 3 After adding polyaluminum chloride in Example 1, 35
The treatment was carried out in exactly the same manner as in Example 1, except that the pH was adjusted to 6.0 with % hydrochloric acid. The results are also shown in Table 1.

As is clear from Table 1 (Comparative Example 3 is compared to Example 1).

The fluorine removal rate was approximately 3%, and the boron removal rate was 4%, both significantly lower than the wastewater standards, and the removal of heavy metals was also reduced, with cadmium and total mercury exceeding the wastewater standards. ing.

The reason for such poor results is thought to be that the pH was as low as 6.0, making it difficult to form an insoluble complex compound.

Example 2 Adding 100 g/β of 30% magnesium hydroxide (approximately 1 g/β as Mg) in place of 50 g/β of 95% magnesium oxide in Example 1, and adding polyaluminum chloride and polyacrylamide polymer flocculant. without adding.

It was treated in the same manner as in Example 1, except that 24% caustic soda was added to adjust the pi (pi) to 12.0, and instead of static precipitation, it was filtered using Toyo Roshi C-Main No. 2 qualitative filter paper.

The results are shown in Table 1. In Example 2, the fluorine removal rate was approximately 9.
9% and boron removal rate of approximately 96%, both removal rates are extremely excellent.Furthermore, the removal rate of heavy metals is also good, and both residual contents can satisfy the drainage standards. These excellent results were obtained for heavy metals, fluorine, and
It is thought that boron, etc., forms a stable insoluble complex compound with sodium hydrogen sulfide, magnesium hydroxide, etc., as in the previous example.

(Margin below) Table 1

Claims (3)

[Claims] (1) Wash the exhaust gas with an alkaline aqueous solution and discharge it. Sulfide chemicals and magnesium chemicals are added to smoke washing wastewater from garbage incinerators, etc. to eliminate heavy metals. A method for removing harmful components from smoke washing wastewater, which is characterized by solid-liquid separation after insolubilizing harmful components such as fluorine and boron. (2) The method for removing harmful components according to claim 1, wherein the magnesium agent is magnesium oxide. (3) The method for removing harmful components according to claim 1, wherein the magnesium agent is magnesium hydroxide.