JP2005138065A - Method of cleaning contaminated soil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means of cleaning contaminants such as VOC and oil contained in contaminated soil without making a heavy metal elute even in a small-scale plant which can be installed in an excavation site or the vicinity. <P>SOLUTION: In order to clean the contaminated soil using the method of cleaning the contaminated soil according to the embodiments of the present invention, first quick lime is added to the contaminated soil with contaminants mixed in to form primary treatment soil (Step 101). Next, the primary treatment soil is thrown in a rotary kiln and heated in an airtight state to form secondary treatment soil (Step 102). In the heating process, the contaminants volatilize and the oxidation reaction is carried out within the range of temperatures which can be controlled. Further, the secondary treatment soil after the heat-treatment is discharged from the rotary kiln, and a hardening material such as quick lime is added as needed, and thereafter, it is recycled as general soil(Step 3). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention mainly relates to a method for purifying contaminated soil for purifying oil and volatile organic compounds contained in excavated soil.

  When foundation work is carried out at a factory site, fuel oil and machine oil may be mixed with excavated soil. If such oil-contaminated soil is left as it is, the oil contained in the soil will volatilize and diffuse to the surroundings, which will interfere with the lives of the residents of the surroundings. It becomes a cause to contaminate the water quality by mixing with water. Therefore, for such oil-contaminated soil, it is necessary to remove the oil by, for example, incineration to prevent diffusion to the environment.

  In addition, the soil of the factory site may be contaminated with volatile organic compounds (VOC) typified by trichlorethylene and tetrachlorethylene, and sufficient measures are required to prevent the diffusion of such contaminants.

JP 2002-119952 A JP 2001-205248 A

  Contaminated soil contaminated with such pollutants has been subjected to purification treatment by various methods in the past, and a typical example is volatilization treatment by heating.

  In such a treatment method, the contaminated soil is heated to volatilize contaminants such as oil and trichlorethylene contained in the contaminated soil, and adsorbed onto activated carbon or the like to purify the contaminated soil.

  However, it has been found that when such a volatilization treatment is performed, a situation occurs in which harmful heavy metals that have remained below the environmental standard before heating are eluted after the heating, exceeding the environmental standard.

  Of course, such a situation cannot be left unattended, and it is necessary to insolubilize heavy metals to the treated soil after heating. However, insolubilization is not regarded as purification and is treated as industrial waste. Another problem is that the original contaminated soil cannot be effectively used as general soil.

  On the other hand, if the contaminated soil is incinerated in a rotary combustion furnace known as a means for disposing of waste, for example, a rotary kiln, the combustion furnace is 850 ° C in order to prevent synthesis of dioxins. As described above, since incineration is usually performed at about 1000 ° C, it is possible to prevent elution of heavy metals as well as oil and VOC, but the disposal method itself of incineration is treated as industrial waste. It is difficult to adopt as soil purification means.

  In addition, even if the soil treated by incineration of contaminated soil is not treated as industrial waste, in other words, it can be regarded as purified soil, of course, in order to achieve the high temperature heating described above, the specifications of the burner are of course Higher heat resistance will be required for the combustion furnace as well, and the contaminated soil purification plant will naturally have to be scaled up.

  In addition, when contaminated soil is generated at an actual excavation site, in order to incinerate the contaminated soil, it must be transported to the above-mentioned large-scale plant. Depending on the transport distance, the contaminant purification efficiency is extremely high. There was also a problem of lowering.

  The present invention has been made in consideration of the above-described circumstances, and even in a small-scale plant that can be installed at or near an excavation site, VOC and oil contained in contaminated soil without eluting heavy metals. It aims at providing the purification method of the contaminated soil which can purify a pollutant.

  In order to achieve the above object, according to the method for purifying contaminated soil according to the present invention, as described in claim 1, a contaminated soil in which a contaminant composed of at least one of a volatile organic compound and oil and a heavy metal are mixed. Quick lime is added to primary treated soil, and the primary treated soil is heated in an airtight state within a temperature range where the contaminants volatilize and the oxidation reaction can be controlled to form secondary treated soil, and the secondary treated soil Is reused as general soil.

  In order to remove the pollutants from contaminated soil containing volatile organic compounds and oil as pollutants, the present applicant uses a small-scale plant to set the heating temperature to 200 ° C to 800 ° C for purification. When treatment was attempted, but volatile organic compounds and oils volatilized, but heavy metals were included in the contaminated soil, heavy metals that would not have eluted before heating were eluted at a high concentration after heating. The applicant's experiments and investigations revealed that the situation would change.

  The reason for this is that arsenic and lead adsorbed with hydrated oxides such as iron and aluminum in the soil have weakened the adsorption power due to iron and aluminum becoming oxides by heat treatment, and the amount of elution increased. It is conceivable that the amount of elution increased due to volatilization of the organic matter adsorbed until then by the heat treatment.

  In such a situation, after the volatilization process by heating, not only the process of insolubilizing heavy metals has to be performed, but even if insolubilized, the current soil pollution countermeasures were not recognized as purification and were insolubilized. The treated soil cannot be effectively used as general soil.

  Therefore, the present applicant focused on how to remove volatile organic compounds and oils in a small-scale plant without eluting heavy metals, and as a result of repeating various experiments, If quick lime is added to make the primary treated soil, and then the primary treated soil is heated in an airtight state within a temperature range where the pollutants are volatilized and the oxidation reaction can be controlled, heavy plants can be used without making the plant large-scale. Thus, the present inventors have obtained very useful knowledge in the industry that oil and VOC can be removed without eluting oil.

  That is, in order to purify contaminated soil using the method for purifying contaminated soil according to the present invention, first, quick lime is added to the contaminated soil in which the pollutant is mixed to obtain primary treated soil.

  Contaminants consist of at least one of volatile organic compounds (VOC) typified by trichlorethylene and tetrachlorethylene, and oil. In addition to these pollutants, harmful heavy metals such as arsenic, mercury and lead are mixed in the contaminated soil. ing.

  The contaminated soil includes excavated soil generated by excavation from the former factory site.

  Quick lime may be put into a mixer together with contaminated soil, for example, and stirred and mixed in the mixer.

  Next, the primary treated soil is heated in an airtight state, and this is used as the secondary treated soil.

  Here, the heating step is performed in a temperature range in which contaminants are volatilized and the oxidation reaction can be controlled.

  Next, the secondary treated soil is reused as general soil. In addition, what is necessary is just to incinerate, for example about the pollutant which volatilized from the primary treatment soil. In such incineration, it is desirable to burn at a temperature of, for example, about 850 ° C. in order to suppress the generation of dioxins. In incineration, for example, a known combustion furnace can be diverted.

  The temperature range in which the oxidation reaction can be controlled refers to a temperature range in which the temperature rise due to the oxidation reaction, that is, even if combustion occurs, specifically, for example, the upper limit temperature is 700 ° C. or less. Preferably, the temperature is set to 600 ° C. or lower, and the lower limit temperature is set to a volatilizable temperature corresponding to the pollutant. This temperature range naturally includes the case where no combustion occurs.

  The method for controlling the oxidation reaction within the above-described temperature range is arbitrary. For example, adjustment of heating time, adjustment of intermittent setting, adjustment of flow rate of heated air, adjustment of soil volume of contaminated soil, and the like can be considered.

  Hereinafter, an embodiment of a purification method for contaminated soil according to the present invention will be described with reference to the accompanying drawings. Note that components that are substantially the same as those of the prior art are assigned the same reference numerals, and descriptions thereof are omitted.

  FIG. 1 is a flowchart showing the procedure of the contaminated soil purification method according to this embodiment. As can be seen from the figure, in order to purify the contaminated soil using the method for purifying contaminated soil according to the present embodiment, first, quick lime is added to the contaminated soil mixed with the pollutant to form a primary treated soil. (Step 101).

  Contaminants consist of at least one of volatile organic compounds (VOC) typified by trichlorethylene and tetrachlorethylene, and oil. In addition to these pollutants, harmful heavy metals such as arsenic, mercury and lead are mixed in the contaminated soil. ing. In this embodiment, the excavated soil generated by excavation from the factory site is used as contaminated soil.

  Quick lime may be put into the mixer together with the contaminated soil, and stirred and mixed in the mixer.

  Next, the primary treated soil is put into a rotary kiln rotary furnace, and then the primary treated soil is heated in an airtight state to form secondary treated soil (step 102).

  Here, the heating step is performed in a temperature range in which contaminants are volatilized and the oxidation reaction can be controlled.

  The temperature range in which the oxidation reaction can be controlled means a temperature range in which the temperature rise due to the oxidation reaction, that is, combustion, can be controlled. For example, the upper limit temperature is 700 ° C. or less, preferably 600 ° C. C or less, and the lower limit temperature is a volatilizable temperature corresponding to the pollutant. This temperature range naturally includes the case where no combustion occurs.

  Such a temperature range is appropriately selected in consideration of the volatilization temperature corresponding to the contaminant. For example, depending on the type, it may be set to about 200 ° C. to 500 ° C. for VOC and about 200 ° C. to 600 ° C. for oil.

  In order to control the oxidation reaction below the above-mentioned upper limit temperature, for example, the heating time and the intermittent setting thereof, the flow rate of heated air, the amount of soil of contaminated soil, etc. may be appropriately adjusted. Specifically, it is conceivable to adjust the input amount of the primary treated soil according to the oil content of the contaminated soil, for example, to reduce the input amount of the primary treated soil if the oil content is high.

  In this way, quick lime is added to the contaminated soil to form a primary treated soil, and after the primary treated soil is put into a rotary kiln rotary furnace, the primary treated soil is heated as described above. Volatilizes and prevents the elution of heavy metals in the primary treated soil.

  This is considered to be because, when the heavy metal is, for example, arsenic, the quick lime added first causes a chemical reaction with arsenic to form a hardly soluble substance such as calcium arsenate. In addition, when the heavy metal is lead, in addition to the formation of the above-mentioned difficult-tolerance substance, it is considered that the pH of the primary treated soil is increased to about 9 and the solubility of lead is lowered by quick lime.

  Next, the secondary treated soil after the heat treatment is discharged from the rotary kiln rotary furnace, and a solidifying material such as quick lime and cement is added as necessary, and then reused as general soil (step 103). It should be noted that such a solidified material is for improving the strength, and it goes without saying that the purpose and action effect are completely different from the quick lime in step 101.

  Contaminants volatilized from the primary treated soil may be treated by, for example, a known procedure. For example, first, in order to suppress the generation of dioxins, combustion is performed at a temperature of 850 ° C. or higher, for example, about 1000 ° C. For this combustion step, for example, a known combustion furnace can be diverted.

  Next, in order to prevent recombination of dioxins, the exhaust gas from the combustion furnace is cooled to about 200 ° C at once, separated by a dry cyclone and collected as under-dust, and handled as specially controlled industrial waste. The over portion may be released to the atmosphere through a bag filter.

  As described above, according to the method for purifying contaminated soil according to the present embodiment, quick lime is added to the contaminated soil to make a primary treated soil, and after the primary treated soil is put into a rotary kiln rotary furnace, the pollutant is volatilized. In addition, since the primary treated soil is heated in a temperature range in which the oxidation reaction can be controlled, it becomes possible to suppress elution of heavy metals in the primary treated soil while volatilizing oil and VOC as contaminants. Not only is the insolubilization treatment of heavy metals unnecessary, but the purified secondary treated soil can be effectively used as civil engineering materials such as embankment materials, backfill materials, and landfill materials, as with general soil.

  On the other hand, the heating process of the primary treated soil is performed in a temperature range in which the oxidation reaction can be controlled, in other words, in a temperature range suppressed to a low temperature. Therefore, a small burner is sufficient, and a rotary kiln rotary furnace has high heat resistance. Thus, the scale of the entire plant can be reduced and installed at the excavation site.

  In this embodiment, the contaminated soil is heated using the rotary kiln rotary furnace, but it goes without saying that the heating means is arbitrary.

  In order to confirm the purification action of the contaminated soil by heating after the addition of quicklime, a purification test was conducted as follows, and the outline and test results will be described.

  Regarding the contaminated soil, waste white soil H containing oil, arsenic and lead was used as the sample soil.

The properties of the waste clay H are as follows, and arsenic and lead have already exceeded the environmental standards before the test.
Water content: 61.5%
Oil content: 90000 mg / kg-dry
Heavy metal elution amount (announcement method 46):
Arsenic: 0.065 (mg / L)
Lead: 0.015 (mg / L)
Soil environmental standard value is 0.01 (mg / L) or less.

  As a test procedure, after adding quick lime powder to waste white clay H which is a sample soil and mixing it with a mixer while crushing the soil to a particle size of 5 mm or less, each room is kept indoors for 6 hours or more. Then, the sample soil was heated at various temperatures using a small kiln, an electric muffle furnace and a pilot plant, and finally the sample soil subjected to the heat treatment was analyzed.

  The test results for arsenic are shown in Table 1.

  Table 1 shows the following.

(1) From the small kiln test cases No. 1 and No. 2 and the electric muffle furnace test cases No. 1 and No. 2, oil odor remains at the set temperature of 200 ° C to 300 ° C or less. Cannot be volatilized sufficiently.

(2) In other test cases in which oil can be sufficiently volatilized, in the following test cases where quick lime was not added, the arsenic elution amount exceeded the environmental standard in all cases.
Small kiln No.3, 7-10
Electric muffle furnace No.3,4,7,10,13-15
Pilot plant No.1

On the other hand, in the following test cases in which quicklime was added, the arsenic elution amount was lower than the environmental standard in almost all cases.
Small kiln No.5-6,12,13
Electric muffle furnace No.5,6,8,9,11,16
Pilot plant No.2

  The small kiln No. 4 is 0.016 and No. 11 is 0.023. This is probably because the amount of quicklime added was as small as 5%.

(3) Consideration Waste white clay H contained arsenic in the amount of elution exceeding the environmental standard from the beginning. However, the amount of elution was almost the same as that of the original muffle furnace due to heating. From the results, it can be seen that the initial elution amount is greatly exceeded by heating.

  Therefore, it can be seen that the arsenic elution amount does not decrease or increases only by heating, but if quicklime is added in advance, the arsenic elution amount can be suppressed to 0.01 or less, which is the environmental standard.

  A purification test was conducted in the same manner as in Example 1 to confirm the purification effect on lead.

  The test result for the small kiln is shown in FIG. 2, and the test result for the electric muffle furnace is shown in FIG.

  As can be seen in Fig. 2 (a), when the amount of quicklime added is in the range of 5 to 10%, the amount of lead elution is suppressed and is below the environmental standard of 0.01. It can be seen that the amount increases. This phenomenon is consistent with the relationship between the elution amount of lead and pH shown in FIG.

  Therefore, in the case of lead, it can be said that a moderate increase in pH due to quick lime greatly contributes to suppression of elution after heating.

  FIG. 3 shows almost the same tendency, and it can be seen that the amount of lead elution is suppressed in the pH range of 9 to 11, which is below the environmental standard of 0.01.

  As in Example 1, since the purification test was performed as follows in order to confirm the purification action of the contaminated soil by heating after the addition of quicklime, the outline and test results will be described.

  As the contaminated soil, waste white soil E containing oil and arsenic was used as sample soil.

The properties of the waste clay E are as follows. Arsenic is below the environmental standard 0.01 in the state before the test.
Water content: 63.7%
Oil content: 336000 mg / kg-dry
Heavy metal elution amount (announcement method 46):
Arsenic: 0.0052 (mg / L)
Soil environmental standard value is 0.01 (mg / L) or less.

  Since the test procedure is the same as in Example 1, the description thereof is omitted here. In this embodiment, a pilot plant is used as the heating means.

  The test results are shown in Table 2.

  Table 2 shows the following.

  Test No.2-0 shows the properties of the test soil before treatment, and the arsenic elution amount is 0.0052 (mg / L), which is lower than the soil environmental standard 0.01 (mg / L).

  However, when this sample soil is simply heated, it can be seen that the elution amount of arsenic is increased to 0.16, which is 30 times as shown in Test No. 2-1.

  On the other hand, in the case where quick lime is added to the sample soil in advance (No.2-2 to 2-7), not only when post-treatment is performed, but also after treatment (No.2-7), The amount of arsenic elution is controlled below the environmental standard.

  From the above test results, it can be seen that the elution amount of arsenic, which was initially lower than the environmental standard, is greatly increased by heating, but can be suppressed to 0.01 or lower, which is the environmental standard, by adding quick lime in advance.

The flowchart which showed the procedure of the purification method of the contaminated soil which concerns on this embodiment. The graph which showed the effect | action of the purification method of the contaminated clay soil which concerns on this embodiment. The graph which showed the effect | action of the purification method of the contaminated clay soil which concerns on this embodiment.

Claims (1)

Quick lime is added to a contaminated soil in which a contaminant consisting of at least one of a volatile organic compound and oil and heavy metal are mixed to form a primary treated soil, and the contaminant is volatilized and oxidized by the primary treated soil. A method for purifying contaminated soil, comprising heating in an airtight state within a controllable temperature range to obtain secondary treated soil, and reusing the secondary treated soil as general soil.

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