JPH0252558B2 - - Google Patents

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, the exhaust gas from factories that incinerate municipal garbage and industrial waste has become a cause of environmental pollution because it contains components that hinder the growth of the human body, animals and plants, such as hydrogen chloride, sulfur oxides, heavy metals, fluorine, and boron. ing. 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 water discharged after this treatment still contains mercury, cadmium, lead, etc.
In addition to heavy metals such as zinc, chromium, and copper, it also contains harmful components such as fluorine and boron.
It cannot be discharged into rivers as is. For this reason, the conventional methods for removing heavy metals contained in smoke washing wastewater have been the heavy metal hydroxide method, which involves adding ferric chloride, etc., and the heavy metal sulfide method, which involves adding sodium sulfide, etc. It has been widely adopted and is almost technically established. To remove fluorine components, the fluorine apatite method (patent application filed in 1983) is used to remove fluorine components by adding phosphoric acid, calcium chloride, etc.
For the removal of boron components, there is a chelate resin adsorption method having an aminopolyol group (see Japanese Patent Application No. 124845/1983). However, if such conventional methods are used to remove components such as heavy metals, fluorine, and boron contained in smoke washing wastewater, the above-mentioned methods must be combined, making the process extremely complicated. It has its 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 has been completed based on the discovery that the above object can be achieved by skillfully processing by adding a drug and a magnesium drug. That is, the present invention adds a sulfide agent and a magnesium agent to the smoke washing wastewater of a garbage incinerator, which washes exhaust gas with an alkaline aqueous solution and discharges it, to insolubilize harmful components such as heavy metals, fluorine, and boron. This is a method for removing harmful components from smoke washing wastewater, which is characterized by 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 method can be adopted, for example. First, the smoke washing wastewater, which is at a temperature of 70 to 80℃, is preferably cooled to 30 to 40℃ using a cooling tower or heat exchanger, and then a sulfide agent is added to convert the heavy metals mainly in the wastewater into sulfides. Make it insolubilized. Examples of sulfide agents used in this case include sodium sulfide, sodium polysulfide,
Examples include calcium polysulfide, among which sodium sulfide and sodium hydrogen sulfide are preferred. 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, whereas if it is more than 3 moles. Excess sulfide chemicals remain 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. Magnesium drugs used here include magnesium oxide, magnesium hydroxide, magnesium sulfate, magnesium chloride, magnesium carbonate, magnesium silicate, magnesium phosphate, and magnesium nitrate, of which magnesium oxide and magnesium hydroxide are preferred. . The amount used is based on the total amount of fluorine and boron ions contained in smoke washing wastewater.
The amount (weight) of Mg is preferably 100 to 1000 times,
If the amount is less than 100 times, the insolubilization rate of fluorine and boron ions tends to be poor, while if the amount is more than 1000 times, the amount of sludge produced is significantly increased, and solid-liquid separation tends to be difficult. 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 liquid that insolubilizes 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, so 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, dichlorochloride is added as necessary.
Inorganic flocculants such as iron and polyaluminum chloride
It is also possible to add 100 to 500 mg/2 to 5 mg/of a polymer flocculant such as polyacrylamide. The above chemicals are injected as a liquid using a pump, and the reaction is carried out while being mixed using a stirrer, etc. The reaction time may be 5 to 30 minutes each, and finally the insolubilized heavy metals, fluorine, boron compounds, etc. are precipitated. ,
Separate solid and liquid by filtration, dehydration, etc. Since the method of the present invention has the above-mentioned structure, heavy metals in smoke washing wastewater, which were difficult to remove in the past, can be removed.
Harmful components such as fluorine and boron can be efficiently removed with simple treatment. The present invention will be specifically explained below using 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/day.
(3.977m mol/), lead 38mg/(0.183m
mol/), cadmium 3.9mg/(0.035m
mol/), total mercury 10 mg/(0.050 m mol/
), iron 12 mg/(0.215 m mol/), copper 6.7
Contains heavy metal ions of mg/(0.105m mol/), and the total number of moles of these is 4.565×
10 ^-3 mol/, fluorine 62 mg/, boron 25 mg/, others, sodium 62000 mg/,
It contained 11,000 mg of potassium, 460 mg of calcium, 63 mg of magnesium, and 2,100 mg of suspended solids, and the pH was 7.0 and the temperature was 28°C. This smoke washing waste water 1 was collected in a beaker and tested using a jar tester. First, 200 mg of 30% sodium hydrogen sulfide was used as a sulfide agent for the amount of smoke washing wastewater.
(approximately 0.23 mol/total number of moles of heavy metal ions) was added to mainly insolubilize heavy metal ions. This reaction was carried out with stirring for 10 minutes, resulting in a pH of
It became 7.3. Next, 50 g of 95% magnesium oxide (approximately 329 times the amount of Mg/amount of fluorine and boron in the smoke washing wastewater) was added as a magnesium agent 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. Further, 300 mg of polyaluminum chloride and 3 mg of a polyacrylamide polymer flocculant were added as an inorganic flocculant 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 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. As is clear from Table 1, Example 1 has a significantly superior fluoride removal rate of approximately 99%, which fully satisfies the wastewater standards, and an excellent boron removal rate of approximately 93%. Satisfies prefectural wastewater standards. 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 heavy metals such as fluorine and boron in the wastewater were removed by stable substances such as sodium hydrogen sulfide and magnesium sulfide. It is thought that they form an insoluble complex compound. Comparative Example 1 The same procedure as in Example 1 was carried out except that the addition of 30% sodium hydrogen sulfide was omitted. The results are also shown in Table 1. From Table 1, Comparative Example 1 has a fluorine removal rate of approximately 90%, which satisfies the wastewater standards, but it is slightly worse than Example 1, and the boron removal rate has decreased to approximately 64%. Exceeds wastewater standards. 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 same procedure as in Example 1 was carried out except that the addition of magnesium oxide in Example 1 was omitted, 300 mg of polyaluminum chloride was added, and the pH was adjusted to 10.0 with 24% caustic soda. The results are also shown in Table 1. From Table 1, compared to Example 1, Comparative Example 2 had a fluorine removal rate of about 8% and a boron removal rate of about 4%, both of which were extremely low and far exceeding the wastewater standards. Removal has also decreased slightly, and cadmium and total mercury exceed wastewater standards. The reason for this 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 The same process as in Example 1 was carried out except that after adding polyaluminum chloride in Example 1, the pH was adjusted to 6.0 with 35% hydrochloric acid. The results are also shown in Table 1. As is clear from Table 1, compared to Example 1, Comparative Example 1 had a fluorine removal rate of about 3% and a boron removal rate of 4%.
% and both have decreased significantly, exceeding the wastewater standards.Furthermore, removal of heavy metals has also decreased, and cadmium and total mercury exceed the wastewater standards. The reason for this poor result was the PH.
It is thought that the low value of 6.0 made it difficult to form an insoluble complex compound. Example 2 30% magnesium hydroxide 100g/instead of 95% magnesium oxide 50g/in Example 1
(approximately 144 times the amount of Mg/amount of fluorine and boron in waste water) and 24% caustic soda without adding polyaluminum chloride or polyacrylamide-based polymer flocculants to achieve a pH of 12. The treatment was carried out in exactly the same manner as in Example 1, except that the concentration was adjusted to 0 and that filtration was performed using No. 2 qualitative filter paper manufactured by Toyo Roshi Co., Ltd. instead of static precipitation. The results are shown in Table 1. In Example 2, the fluorine removal rate was approximately 99%, the boron removal rate was approximately 96%, and both removal rates were extremely excellent. Furthermore, the removal rate of heavy metals was also good, and both residual contents satisfied the wastewater standards. It is possible. The reason why such excellent results were obtained is thought to be that heavy metals, fluorine, boron, etc. in the wastewater form stable insoluble complex compounds with sodium hydrogen sulfide, magnesium hydroxide, etc., as in the previous example. .

[Table] (Note) Columns marked with *1 are 2 or less for Osaka and Shiga prefectures, and 1 or less for Kyoto prefecture.

Claims (1)

[Scope of Claims] 1. Sulfide chemicals and magnesium chemicals are added to smoke washing wastewater from garbage incinerators, etc., where flue gas is washed with an alkaline aqueous solution and then discharged to remove heavy metals, fluorine,
A method for removing harmful components from smoke washing wastewater, which is characterized by solid-liquid separation after insolubilizing harmful components such as boron. 2. The method for removing harmful components according to claim 1, wherein the magnesium drug is magnesium oxide. 3. The method for removing harmful components according to claim 1, wherein the magnesium agent is magnesium hydroxide.