JP2003117538A - Treating method and treating equipment for soil, or the like, contaminated with hexavalent chromium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique of cost-effectively decomposing soil, or the like, contaminated with hexavalent chromium and making the same harmless down to the level of such a low hexavalent chromium level which is accepted in environmental quality standards relating to soil pollution or environmental quality standards relating to dumping at sea. SOLUTION: The method for treating the soil, or the like, contaminated with the hexavalent chromium comprises adding an alkaline material of at least one kind selected from the group consisting of calcium oxide, magnesium oxide and their precursor materials to the soil, or the like, contaminated with the hexavalent chromium, then treating the soil, or the like, at a temperature within a range from 500 to 1,000 deg.C while bringing the soil, or the like, into contact with a gaseous atmosphere of <=2.5% in oxygen content.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a treatment method capable of achieving environmental standards by decomposing / insolubilizing / detoxifying soil or the like contaminated with hexavalent chromium.

[0002]

[Table 1]

Related environmental standards are as shown in Table 1 above. There are various environmental standards for heavy metals, but here we show three environmental standards: soil, ocean dumping, and industrial waste landfill disposal. Environmental standard 1 concerning soil pollution is stipulated in the Environmental Agency Notification No. 46 (August 23, 1991).
Environmental standards related to ocean dumping and industrial waste landfill 2,
3 is specified in Prime Minister's Office Ordinance No. 5 (February 17, 1973). The numerical value is the concentration (mg / L) in the eluate extracted from the sample according to the analysis method specified in each notification or Cabinet Order. The detection limit of analysis is set to 1/10 of the environmental standard. The detection limit of alkyl mercury was 0.00 in the Environmental Agency Notification No. 59 and the Environmental Agency Notification No. 64.
It is set to 05 mg / L.

[0004]

2. Description of the Related Art Recently, the problem of hexavalent chromium has arisen as one of the soil contaminations in the former sites of factories. On the other hand, when the incineration ash of general waste is dried or heat-treated, it is heated to 300 ° C or higher in the air to generate hexavalent chromium. It was found to dissolve hexavalent chromium that exceeds the relevant Environmental Agency Notification No. 46) or the above Environmental Standard 2 (see Prime Minister's Ordinance No. 5 concerning ocean dumping). Under the circumstances described above, there is an increasing need for a technology for decomposing and detoxifying hexavalent chromium in soil or ash contaminated with these hexavalent chromium as an environmental measure. However, conventionally, no technology has been known for economically decomposing / detoxifying hexavalent chromium-contaminated soil, incinerated ash, or the like to a level of low hexavalent chromium that passes these environmental standards. .

[0005]

The present inventor has conducted research to solve this problem by various methods.
It didn't work. For example, a method of treating with air containing carbon monoxide or ammonia which is a reducing gas, a method of treating with an aqueous solution containing reducing hydrazine, and the like were tried, but all of them were treated with particulate matter contaminated with hexavalent chromium. It has been found difficult to render it harmless until it meets the above environmental standards. The present inventor, on the other hand, has found that the incineration ash in which hexavalent chromium exceeding the above environmental standards is eluted can be economically rendered harmless by contacting atmospheric gas with a low oxygen content at a high temperature. . The present inventor attempted to detoxify soil and the like contaminated with hexavalent chromium on the basis of these findings relating to incinerated ash, but the attempt was initially unsuccessful. Further, by continuing the test, it was found that calcium oxide or the like, which is usually contained in incineration ash, plays a large role in the decomposition, insolubilization and detoxification of hexavalent chromium, and the present invention was reached.

[0006]

That is, the gist of the present invention is that at least one alkaline substance selected from the group consisting of calcium oxide, magnesium oxide and their precursors is added to soil or the like contaminated with hexavalent chromium. Of the hexavalent chromium-contaminated soil or the like, which is treated at a treatment temperature in the range of 500 to 1000 ° C. while being brought into contact with an atmospheric gas having an oxygen content of 2.5% or less. It depends on the processing method. Hereinafter, the present invention will be described in detail.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Soil Contaminated with Hexavalent Chromium "Soil contaminated with Hexavalent Chromium" which is the object to be treated in the method of the present invention includes a factory site contaminated with Hexavalent chromium. In addition to soil, it includes incineration ash of general waste or industrial waste that does not sufficiently contain alkaline substances such as calcium oxide. Here, "contaminated with hexavalent chromium" means that the content of hexavalent chromium in the object exceeds the environmental standard value, and specifically, the Environmental Agency Notification No. 4
The concentration of hexavalent chromium in the eluate obtained from the sample by the method specified in No. 6 exceeds 0.05 mg / L, or in the eluate obtained from the sample by the method specified by Environmental Agency Notification No. 13. It means that the concentration of hexavalent chromium of is over 0.5 mg / L.

Further, "not sufficiently containing an alkaline substance" means that the concentration of at least one alkaline substance selected from the group consisting of calcium oxide, magnesium oxide and their precursors is 100 parts by weight of the object to be treated. Medium 3
Means less than weight. If this concentration is too low, the decomposition of hexavalent chromium will not proceed sufficiently even if the treatment according to the present invention is carried out. Specific examples of the precursors of calcium oxide and magnesium oxide include calcium and magnesium hydroxide compounds and carbonates. They are,
Within the treatment temperature range of the present invention, it is converted into calcium oxide and magnesium oxide, respectively. In order to carry out the method of the present invention, the amount of the alkaline substance added is preferably such that the concentration is at least 3 parts by weight in 100 parts by weight of the object to be treated, and at least 5 parts by weight in 100 parts by weight of the object to be treated. More preferably, the amount will be at least 10 parts by weight in 100 parts by weight of the object to be treated. When the concentration of the alkaline substance is low, the decomposition rate of hexavalent chromium is slow, which is economically disadvantageous. On the other hand, if the concentration of the alkaline substance is high, it is advantageous in terms of the decomposition rate of hexavalent chromium, but the cost of the alkaline substance required for the treatment increases, which is economically disadvantageous. From this point of view, the most appropriate addition amount is selected within a range in which the concentration of the alkaline substance is 100 parts by weight at maximum in 100 parts by weight of the object to be treated.

In the method of the present invention, the object to be treated is treated at a treatment temperature in the range of 500 to 1000 ° C. while being brought into contact with an atmospheric gas having an oxygen content of 2.5% or less. At that time, if the treatment temperature is lower than or equal to the lower limit, the oxygen content in the atmosphere gas is low, for example, 0.2% or less,
Degradation and detoxification of hexavalent chromium does not proceed. Decomposition / detoxification of hexavalent chromium requires 500 ° C or higher, preferably 5
It proceeds suitably at 50 ° C. or higher, more preferably 610 ° C. or higher. On the other hand, in general, the incineration ash of soil or general waste or industrial waste is solidified at 1000 ° C or higher, so that the upper limit of the temperature when the present invention is applied industrially is 1000 ° C, more preferably 980 ° C or lower. Is. The oxygen content in the atmospheric gas in contact with the object to be processed also controls the decomposition and formation of hexavalent chromium. That is, when the oxygen content is 3% or more, the rate of hexavalent chromium generation exceeds the rate of decomposition, and the amount of hexavalent chromium increases as a whole. on the other hand,
When the oxygen content is 2.5% or less, the rate of decomposition is higher than the rate of generation of hexavalent chromium, and the amount of hexavalent chromium decreases to a low level. In order to keep the amount of hexavalent chromium at a lower level, the oxygen content is preferably 1.5% or less, more preferably 0.6% or less.

The size of the particles to be treated is preferably 10 mm or less. When it contains a large lump to some extent, it is preferably crushed to a size of 10 mm or less. It is more preferably 2.5 mm or less, and even more preferably 1 mm or less. The atmosphere gas having an oxygen content of 2.5% or less used in the treatment of the present invention is preferably one containing nitrogen as a main component. Industrial nitrogen gas can be effectively used for this purpose. Combustion gas of oil and LPG can also be used effectively. In this case, carbon dioxide gas and water vapor are contained in addition to the atmospheric gas nitrogen, and one of them is the main component. The gas other than oxygen may be carbon dioxide only or water vapor only. Furthermore, it is more effective that the atmosphere gas contains a small amount of reducing gas. As the reducing gas, at least one selected from the group consisting of ammonia, hydrogen and carbon monoxide is effective, and a mixed gas thereof is also effective.

When treating soil or the like contaminated with hexavalent chromium according to the present invention, the apparatus is preferably an apparatus capable of assisting contact between atmospheric gas having a low oxygen content and particles such as soil. For example, a rotary kiln is one of the engineeringly effective devices, and a rotary kiln type reaction device is suitable as the processing reaction device of the present invention. By providing the lifter inside the rotary kiln, the contact between the atmospheric gas and particles such as soil can be further improved. In addition, a moving bed type reactor and a fluidized bed type reactor which can easily increase the residence time of the incinerated ash while improving the contact between the atmosphere gas and the particles of the incinerated ash can be preferably used.

The present invention will be described below with reference to examples. In addition, unless otherwise specified, parts are parts by weight and% is% by volume.

[Examples] Raw Soil The iron content was removed from the soil contaminated with hexavalent chromium with a magnet, and the product dried at 120 ° C. for 3 hours was pulverized with a test vibration mill to obtain a raw soil sample for this test. The grain size of the raw soil sample was 1 mm or less. As a result of performing an elution test of heavy metals on this raw soil in accordance with the Environmental Agency Notification No. 46, the eluent analysis results of hexavalent chromium and lead were 45 mg / L and 0.003 mg / L, respectively. In addition, calcium oxide (Ca
The content of O) was 1.5% by weight. Main test (common items) This test has a structure in which a ceramic inner cylinder is inserted into a batch rotary electric furnace made of SUS310, and an atmospheric gas of a predetermined composition is supplied from one end and discharged from the other end. Soil treatment was performed using a test device (called a batch-type rotary test device).

Example 1 100 parts of the above-mentioned raw soil sample was added with 20 parts of calcium oxide and mixed well, and the mixture was charged into a batch-type rotary tester (electric furnace), and nitrogen gas (oxygen content of about 5%) was used as an atmosphere gas. 0.01%),
Treatment was performed at 850 ° C. for 90 minutes to obtain treated soil. When the eluate of hexavalent chromium was analyzed for this treated soil in accordance with Notification No. 46 of the Environment Agency, it was 0.005 mg / L or less. This has passed the environmental standard for hexavalent chromium of the Environmental Agency Notification No. 46 concerning soil pollution.

Comparative Example 1 : A treated soil was obtained in the same manner as in Example 1 except that calcium oxide was not added to the raw soil sample. The hexavalent chromium eluate analysis result for the treated soil was 44 mg / L. Hexavalent chromium has hardly decomposed and has not passed the environmental standard.

Example 2 : In Example 1, 50 parts of calcium oxide was added in place of 20 parts of calcium oxide, and the treatment condition was 850 ° C. instead of 90 minutes and 750 ° C.
The treated soil was obtained in the same manner as in Example 1 except that the treatment time was 90 minutes. The eluent analysis result of hexavalent chromium in the treated soil was 0.005 mg / L or less. It has passed the environmental standards for soil pollution.

Example 3 : In Example 1, 50 parts of calcium oxide was added instead of 20 parts of calcium oxide, and oxygen, nitrogen, and nitrogen were added instead of nitrogen gas as the atmosphere gas.
A mixed gas of carbon dioxide and steam (O _2: 0.6%, C
Treated soil was obtained in the same manner as in Example 1 except that O _{2 was} about 8%, water vapor was about 5%, and the remaining nitrogen). Hexavalent chromium eluate analysis result for treated soil was 0.0
It was 07 mg / L. It has passed the environmental standards for soil pollution.

Comparative Example 2 : In Example 3, except that the atmosphere gas was changed to air (O ₂ : 21% and remaining nitrogen) instead of the mixed gas of oxygen, nitrogen, carbon dioxide and steam.
A treated soil was obtained in the same manner as in Example 3. Hexavalent chromium eluate analysis result for treated soil was 51 mg / L
And it has not passed the environmental standard. This indicates that although the calcium oxide was added, the oxygen content of the atmospheric gas was high, so that the substantial decomposition of hexavalent chromium did not proceed.

Example 4 In Example 3, the atmosphere gas was replaced with a mixed gas of oxygen, nitrogen, carbon dioxide and water vapor, and a mixed gas of oxygen and nitrogen (O ₂ : 2.0% and remaining nitrogen) was used. A treated soil was obtained in the same manner as in Example 3 except for the above. The hexavalent chromium eluate analysis result for the treated soil was 0.35 mg / L. It has passed the environmental standards for hexavalent chromium of Prime Minister's Ordinance No. 5 concerning marine pollution.

Examples 5 to 7 and Comparative Examples 3 to 4 : Treated soil was treated in the same manner as in Example 3 except that the treatment conditions and the oxygen content of the atmosphere gas were changed as shown in Table 2. Obtained. As shown in Table 2, the results of the hexavalent chromium elution analysis for the treated soil show that Example 6 passed the environmental standards for soil pollution, and Examples 5 and 7 passed the environmental standards for ocean dumping. In contrast, Comparative Examples 3 to 4 do not pass any environmental standard.

[0020]

[Table 2]

[0021]

According to the present invention, among the heavy metals (lead, cadmium, total mercury, alkylmercury, arsenic, selenium, and hexavalent chromium) which are environmentally problematic, the method is economically advantageous. Since the hexavalent chromium can be thoroughly decomposed and detoxified, it is possible to sufficiently and economically respond to the needs for detoxifying the soil or the like contaminated with hexavalent chromium.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shingo Sato             Shinjuku-ku, Tokyo Shinjuku 1-4-13 Stock Association             Company Japan Environmental System F-term (reference) 2E191 BA02 BB01 BC01 BD11                 4D004 AA36 AA41 AB03 CA22 CA37                       CB08 CB09 CC01 CC11 DA03                       DA06 DA10 DA20

Claims (14)

[Claims] 1. A soil or the like contaminated with hexavalent chromium (hereinafter,
It is called the "processing object." ), At least one alkaline substance selected from the group consisting of calcium oxide, magnesium oxide and their precursors is added, and then 500 to 1000 while contacting this with an atmospheric gas having an oxygen content of 2.5% or less. A method for treating soil or the like contaminated with hexavalent chromium, which comprises treating at a treatment temperature within a range of ℃. 2. The object 1 to be treated has a concentration of the alkaline substance.
The method for treating soil or the like contaminated with hexavalent chromium according to claim 1, wherein the alkaline substance is added in an amount of at least 3 parts by weight in 00 parts by weight. 3. The material to be treated 1 has a concentration of the alkaline substance.
The method for treating soil or the like contaminated with hexavalent chromium according to claim 2, wherein the alkaline substance is added in an amount of at least 5 parts by weight in 00 parts by weight. 4. The object 1 to be treated has a concentration of the alkaline substance.
The method for treating soil or the like contaminated with hexavalent chromium according to claim 3, wherein the alkaline substance is added in an amount of at least 10 parts by weight in 00 parts by weight. 5. The method for treating soil or the like contaminated with hexavalent chromium according to any one of claims 1 to 4, wherein the oxygen content is 1.5% or less. 6. The method for treating soil or the like contaminated with hexavalent chromium according to claim 5, wherein the oxygen content is 0.6% or less. 7. The method for treating soil or the like contaminated with hexavalent chromium according to any one of claims 1 to 6, wherein the treatment temperature is in the range of 550 ° C to 980 ° C. 8. The method for treating soil or the like contaminated with hexavalent chromium according to claim 7, wherein the treatment temperature is in the range of 610 ° C. to 980 ° C. 9. The method according to claim 1, wherein the main component of the atmosphere gas is at least one selected from the group consisting of water vapor, carbon dioxide gas and nitrogen. A method for treating soil contaminated with valent chromium. 10. The method for treating soil or the like contaminated with hexavalent chromium according to claim 9, wherein the main component of the atmospheric gas is nitrogen. 11. The method for treating soil or the like contaminated with hexavalent chromium according to any one of claims 1 to 10, wherein the atmospheric gas contains a reducing gas. 12. The hexavalent chromium-contaminated soil or the like according to claim 11, wherein the reducing gas is at least one selected from the group consisting of ammonia, hydrogen and carbon monoxide. Processing method. 13. The method for treating soil or the like contaminated with hexavalent chromium according to any one of claims 1 to 12, wherein the object to be treated has a particle size of 10 mm or less. 14. A hexavalent compound characterized in that the treatment device for performing the treatment according to any one of claims 1 to 10 is a rotary kiln type reactor, a moving bed type reactor or a fluidized bed reactor. Equipment for treating soil contaminated with chromium.