JPH0256959B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for removing trace amounts of mercury in waste liquid,
More specifically, the present invention relates to a method for removing trace amounts of mercury contained in waste liquid by generating a spinel compound in the waste water after stripping the mercury in waste liquid, particularly incinerator waste water, and completely rendering the waste liquid harmless. Waste gas from incinerators, especially municipal waste incinerators, contains various harmful substances, so these waste gases are normally cleaned and then released into the atmosphere. The problem is how to dispose of the used cleaning waste liquid. For example, when municipal waste containing garbage, rubber, plastics, and other combustible materials is incinerated, the waste gas contains carbon dioxide, water vapor, and sulfur oxides, nitrogen oxides, chlorine, hydrogen chloride, etc. In addition to the harmful gases of It is included as a compound with. Although waste gases can be purified by treating them with a cleaning liquid such as water or an alkaline solution, it is difficult to detoxify cleaning waste liquids that have absorbed harmful substances. General sulfur oxides, sulfides, chlorides, etc. contained in waste liquid are separated and recovered by chemical or physical means to return them to safe and harmless substances.
Alternatively, it is relatively easy to perform dilution and discharge treatment, but harmful heavy metal compounds are not allowed to be discharged into sea areas, rivers, etc. even at dilute concentrations.Therefore, harmful heavy metals must be separated and recovered. Making wastewater harmless has been an extremely difficult problem. Many methods have been proposed to fix and separate heavy metals, especially mercury, from mercury-containing wastewater, but methods that can be implemented on an industrial scale have various problems and have yet to be fully established. It's not on. When the present inventors treat incinerator waste gas cleaning waste liquid using a spinel reaction, when air is blown in for the oxidation reaction, most of the mercury contained in the liquid turns into vapor and enters the air. After discovering that mercury is present in wastewater, he conducted further detailed studies and discovered a method to actively recover mercury in wastewater and make wastewater harmless. ” and applied for a patent. That is, the present invention is a method for recovering mercury in wastewater, which is characterized by treating mercury-containing wastewater at a temperature of 15° C. or higher in the presence of ferrous ions to separate mercury. In the invention, the wastewater after stripping is
After neutralizing with caustic alkali in the presence of 0.02 to 1.0 mol/NO ₃ ^- , maintain the pH between 6.5 and 11.5, and if necessary keep the temperature above 50°C to generate a spinel compound and separate the product. It is also possible to do so. Incinerator waste gas cleaning wastewater usually contains this amount of NO ₃ ^- , so there is no need to add it again.
When treating wastewater that does not contain NO ₃ ^- , nitrates such as sodium nitrate are added. At this time,
If the wastewater is acidic, neutralize it with a caustic alkali such as caustic soda or caustic potash to maintain the pH between 6.5 and 11.5.
If necessary, it is heated and kept at 50° C. or above, and further oxidized by blowing in an oxygen-containing gas to perform a spinelization reaction to produce a spinel compound, and the resulting precipitate is separated by a conventional method. Conditions at this time should be selected appropriately depending on the types of heavy metals other than mercury contained in the wastewater, such as cadmium, chromium, cobalt, tin, lead, nickel, manganese, zinc, and copper, as well as hazardous substances such as arsenic. Of course, the Fe ⁺⁺ used to remove mercury can be used as is for the spinelization reaction, but if it is still insufficient, it is necessary to add ferrous salts such as ferrous sulfate and ferrous chloride. . Also, stripping to recover mercury may be useful as a pretreatment for spinelization, and may require less subsequent oxidation. Therefore, in many cases, the method of continuously performing a combination of the mercury removal and recovery method in wastewater and the heavy metal detoxification treatment of the present invention is efficient and economical. In this way, harmful heavy metals such as chromium, cobalt, nickel, lead, zinc, arsenic, silver, cadmium, and tin contained in various wastewaters are transferred all at once into the spinel compound, forming water-insoluble precipitates. In this case, even if other miscellaneous salts were present in the solution, they not only did not substantially impede the spinelization reaction, but also expanded the operating range and made it possible to carry out the process on an industrial scale. This is also an effect of the invention. The spinel compound precipitate thus produced is separated from the liquid by filtration or centrifugation, and can be effectively used as a radio interference prevention material, a landfill material, and the like. The waste liquid from which the spinel compound precipitate is separated is rendered harmless and can normally be discharged as is, but if the amount of mercury needs to be further reduced, for example to 0.0001mg/or less, , the waste liquid after separation as described above is PH4
~5. While adjusting the temperature to 70±5℃, add ozone-containing air to 50 to 120 mg of ozone per 1 of the waste liquid.
Then, add hydrazine in the range of 30 to 80 mg while adjusting the pH of the liquid to 9.5 to 10.5 and the temperature of 70 ± 5°C, and react by blowing air. For example, the mercury contained in the liquid can be reduced to 0.0001 mg/or less. If the amount of ozone added is less than 50 mg, a sufficient effect will not be obtained, and even if more than 120 mg is added, the amount of blow-through will only increase and no commensurate effect will be obtained, which is not a good idea. Regarding the amount of hydrazine added, if the amount is less than 30 mg, a sufficient effect will not be obtained, and if it is added in an amount greater than 80 mg, a commensurate effect will not be obtained, and on the contrary, an ammonia odor will be emitted, which is not a good idea. The hydrazine used in the present invention is not particularly limited, such as hydrochloride or hydrate, but it is generally preferable to use an aqueous solution commercially available as a hydrate. According to the present invention, the process for removing trace amounts of mercury from wastewater from cleaning smoke from municipal waste incinerators can be industrialized very effectively without increasing the size of the equipment, and its industrial value is great. Hereinafter, the present invention will be specifically explained based on Examples. Comparative Example 1 Waste gas of 70000Nm ³ /H (dry gas) from a municipal waste incinerator with an incineration capacity of 300T/D was circulated with a cleaning solution of 70000Kg/H, and the pH was adjusted to around 7 with a 24% caustic soda aqueous solution. It was sent to the bottom of a wet cleaning device for cleaning. As a result of this cleaning, hydrogen chloride in the waste gas was reduced from 1000ppm to 10ppm. While most of the cleaning solution was being circulated, a portion of it was extracted. The salt concentration in the liquid is 18%, and the amount of liquid extracted is 1005 kg/
It is H. In addition to this washing wastewater, ash wastewater 50kg/
100Kg/H of boiler cleaning wastewater and 200Kg/H of ion exchange resin regeneration wastewater mixed in, totaling 1355Kg/H
of wastewater was discharged as incinerator wastewater. This wastewater contained 89mg/mercury. This was led to a continuous adjustment tank, where ferrous sulfate heptahydrate was added at a rate of 35 kg/h, the pH was adjusted to 10 with a 24% caustic soda aqueous solution, and the temperature was maintained at 70°C for about 1 hour with stirring. Processed. After that, it is introduced into the reaction tank, and from the blower.
Air was blown at 41 Nm ³ /H. In the exit air
Saturated water vapor at 70°C and metallic mercury turn into steam and produce 11.5
g/H. This is heated to 10℃ using a cooler.
11.2 g/H of liquid metallic mercury was recovered by cooling to 11.2 g/H. On the other hand, incinerator wastewater from which mercury has been removed contains various harmful heavy metals other than mercury, so sodium nitrate is added to it at a rate of 1 kg/H, and the pH is 10.
While maintaining the temperature at 70°C, air was blown into the solution to generate a spinel compound, which was filtered out. In this way, as shown in Table 1, the heavy metals in the incinerator wastewater were reduced as shown in the treated filtrate column, and the residual heavy metal concentration in the treated filtrate fully satisfied the legal regulations.

【table】

[Table] Regarding the treated filtrate shown in this Table 1, in order to further remove and recover all the mercury contained, PH11, temperature 70℃
While adding hydrazine dihydrochloride at a rate of 230g/H, air was blown at 50Nm ³ /H using a blower.
The mercury content in the liquid was reduced to 0.0005 mg/ml. Comparative Example 2 To the treated filtrate shown in Table 1 of Comparative Example 1, sodium hypochlorite was added as an oxidizing agent at a rate of 500 g/H, the pH was adjusted to 10, the temperature was adjusted to 70°C, and the mixture was stirred and mixed to react. Next, sodium sulfite was added to adjust the redox potential to ±0, and treatment was continued by blowing air at a rate of 50Nm ³ /H while adding hydroxylamine hydrochloride at a rate of 680g/H. We were able to reduce the mercury content to 0.0004mg/. Example 1 60 mg of ozone was added to Comparative Example 1, filtrate 1 in Table 1, and an oxidation reaction was carried out at pH 5 and temperature of 70°C.
10. Add 120 mg of 54% hydrated hydrazine (equivalent to 41.5 mg of hydrazine) at a temperature of 70°C, and reduce the air to 1/2.
When the reaction was carried out while blowing at a rate of min., the Hg content in the treated solution was 0.0001 mg/min.

Claims (1)

[Claims] 1 Waste liquid obtained by ferrite treatment of smoke washing water from a municipal waste incinerator and separation of the spinel compound produced, which contains a trace amount of mercury of at most 0.01 mg/ml, at a pH of 4 to 5 and a temperature of 70 ± 5°C. Ozone-containing air is added to the waste liquid 1 so that the ozone concentration is in the range of 50 to 120 mg while adjusting the temperature to react.Then, the liquid is heated to a pH of 9.5 to 10.5 and a temperature of 70±5.
Removal of trace amounts of mercury in waste liquid, characterized by adding hydrazine in the range of 30 to 80 mg while controlling the temperature at °C, and performing a reaction treatment by blowing air to reduce the mercury contained in the liquid to 0.0001 mg/or less. Method.