JP6213105B2 - Cyanide-containing soil treatment method - Google Patents

Description

  The present invention relates to a method for treating cyan-containing soil, and more specifically, by injecting an alkali agent and a chlorine-based oxidant into cyan-containing soil and heating as necessary, all cyan in the soil is efficiently removed. The present invention relates to a decomposition method.

  Conventionally, as a method for treating soil contaminated with cyanide, the slurry solution of cyan contaminated soil is adjusted to pH 10 to 13 with alkali, heated and stirred for 30 minutes or more, and hypochlorite is added separately to the slurry solution to obtain the pH. A method of reacting with free cyanide, complex cyanide and a hardly soluble cyanide compound in a temperature range of 80 to 100 ° C. has been proposed (Patent Document 1).

JP 2004-58011 A

However, the method described in Patent Document 1
-In order to disperse the contaminated soil in water to form a slurry, a large-scale processing device such as a kneading machine for slurrying, a slurry liquid storage tank, and a processing liquid storage tank is required.
-Since the slurry is handled, the maintenance cost of the processing equipment becomes high.
・ For the above reasons, it is difficult to treat a large amount of contaminated soil.
There is a problem.

  The present invention solves the above-mentioned conventional problems, and efficiently decomposes all cyan in the cyan-containing soil with a simple operation without slurrying the cyan-containing soil and without requiring a large-scale apparatus. It is an object of the present invention to provide a method for treating cyan-containing soil that can be used.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention do not slurry the cyan-containing soil as it is, but only an alkali agent and a chlorine-based oxidizing agent, or in some cases, a chlorine-based oxidizing agent. It was found that all cyan in the cyan-containing soil can be efficiently decomposed including the difficult-to-decompose iron cyano complex by injecting and heating the mixture as needed and holding it for a predetermined time. .

  The present invention has been achieved on the basis of such findings, and the gist thereof is as follows.

[1] A chlorinated oxidizer, or an alkali agent and a chlorinated oxidizer are added to a soil containing a cyanide compound , and the soil is heated to a temperature of 20 ° C to 100 ° C by blowing steam. After adding the chlorine-based oxidant, or the alkali agent and the chlorine-based oxidant so that the pH of the leachate collected from the water is 11 to 13 and the free chlorine concentration is 10 mg / L or more, it is performed at the soil temperature for a predetermined time. A method of treating cyan-containing soil that decomposes cyanide in the soil by holding , wherein the predetermined time is any one of the following (1) to (3) depending on the soil temperature A method for treating cyan-containing soil.
(1 ) 2000 hours or more when soil temperature is 20 ℃ or more and less than 40 ℃
(2) 300 hours or more when the soil temperature is 40 ° C or more and less than 60 ° C
(3) 24 hours or more when soil temperature is 60 ℃ or more and 100 ℃ or less

[2] Oite to [1], the processing method of the cyan-containing soil in which the cyanide is characterized by including iron cyano complexes.

According to the present invention, an alkali agent and a chlorine-based oxidizer, or in some cases only a chlorine-based oxidizer, are injected without using a slurry containing cyan as a slurry, and a heat source is used as necessary. By heating in this manner, it is possible to efficiently decompose all cyan in the cyan-containing soil including the hardly decomposable iron cyano complex.
In the present invention, since it is not necessary to slurry contaminated soil, a large-scale processing device such as a kneading machine for slurrying, a slurry liquid storage tank, and a processing liquid storage tank is unnecessary, and can be implemented with a simple apparatus. Maintenance costs can be kept low.
In the case of soil treatment, it may be allowed to react for a long time, and it is possible to perform treatment only by injecting a medicine without heating, and the cost can be reduced.
For this reason, it can fully cope with the treatment of a large amount of contaminated soil.

It is a schematic diagram which shows the processing method of the slag in an Example, (a) A figure is a side view, (b) A figure is a top view.

  Hereinafter, embodiments of the method for treating cyan-containing soil of the present invention will be described in detail.

  In the method for treating cyan-containing soil according to the present invention, a chlorine-containing oxidizing agent, or an alkali agent and a chlorine-containing oxidizing agent are added to soil containing a cyanide, and a heating steam is blown as necessary. The cyanide compound in the soil is decomposed by heating.

The treatment of the cyan-containing soil according to the present invention uses a heat source such as steam to maintain the soil at a temperature of 20 ° C. or higher and 100 ° C. or lower, preferably 40 ° C. or higher and lower than 80 ° C., more preferably 60 ° C. or higher and lower than 80 ° C. In addition, it is difficult to add a chlorine-based oxidizing agent, or an alkali agent and a chlorine-based oxidizing agent so that the pH of soil leachate is 11 to 13 and the free chlorine concentration is 10 mg / L or more. A decomposable iron cyano complex is also preferable for efficient decomposition treatment. This is presumably due to the fact that cyan oxidative decomposition reaction becomes active under the conditions of pH 11 or more and free chlorine concentration of 10 mg / L or more, and the hardly decomposable iron cyano complex in the soil is gradually decomposed. .

In the present invention, the soil to be treated is soil or slag containing a cyanide compound, and examples include ferrocyan complex such as a site of a plating plant, soil containing iron cyano complex such as ferricyan complex, and slag. Although there is no restriction | limiting in particular as the total cyan density | concentration of the eluate, The total cyan density | concentration of the eluate by the soil elution test described in the term of the below-mentioned Example is about 0.5-10 mg / L normally. In particular, when the basicity (mass% CaO / mass% SiO ₂ ) is a basic slag of 1.2 or more, an alkali agent is unnecessary or the amount of the alkali agent required is small, and chlorine-based oxidation It is also possible to treat only with an agent and steam, or a chlorine-based oxidizing agent, which is suitable for the present invention.
Moreover, from the point which is excellent in the permeability | transmittance of the inject | poured chemical | medical agent, it is preferable that a process target soil is soil with high water permeability, for example, the water permeability coefficient in the state piled up freely and piled up is 1 * 10 ^<-2 > ^-1 *. The thing of about 10 cm / s is preferable. Also in terms of the water permeability coefficient, the civil engineering material using slag is suitable for the present invention because the water permeability coefficient is relatively high.

In the present invention, as the alkaline agent to be injected into the soil, sodium hydroxide (NaOH), potassium hydroxide (KOH) and the like used in usual water treatment can be used, and the alkaline agent is usually 10 to 48 weights. % Aqueous solution.
The alkaline agent is added so that the pH of the soil leachate is preferably 11 to 13, more preferably 11 to 12.5, and particularly preferably 11 to 12. If the pH of the leachate is less than 11, cyan compounds such as iron cyano complexes may not be sufficiently decomposed and removed, and if the pH exceeds 13, the effect of improving the decomposition effect corresponding to that cannot be obtained. Problems such as an increase in the amount, alkali resistance of the equipment used, and handleability of high pH soil arise, which is practically disadvantageous in terms of economy and safety.

Moreover, sodium hypochlorite (NaClO), bleaching powder, chlorine gas, chlorine dioxide, etc. can be used as the chlorine-based oxidant added to the soil, and the chlorine-based oxidant is usually in an aqueous solution of 10 to 20% by weight. Used. Of these chlorinated oxidants, NaClO is preferred because it is inexpensive. These chlorine-based oxidants may be used alone or in combination of two or more, such as using NaClO and other chlorine-based oxidants.
The chlorinated oxidant is added so that the free chlorine concentration of the soil leachate is 10 mg / L or more, preferably 10 to 1000 mg / L. If the free chlorine concentration of the leachate is less than 10 mg / L, cyan compounds such as iron cyano complexes may not be sufficiently decomposed and removed. However, even if the concentration of free chlorine is excessively high, the effect of improving the decomposition effect can not be obtained, resulting in problems such as an increase in the amount of chlorinated oxidant used and the oxidant resistance of the equipment used. It is disadvantageous in terms of sex.

  In the present invention, the temperature of the soil is 20 ° C. or higher and 100 ° C. or lower, preferably 40 ° C. or higher and lower than 80 ° C., more preferably 60 ° C., by heating using a heat source such as steam as necessary. Heat to above 80 ° C. If the soil temperature is less than 20 ° C., cyan compounds such as iron cyano complexes may not be sufficiently decomposed and removed. Although the soil temperature may be 80 ° C. or higher, the soil temperature is preferably less than 80 ° C. from the viewpoint of economy, safety, and the like. In addition, after the predetermined time has elapsed from the start of the treatment, after the temperature of the leachate has stabilized, the temperature of the leachate can be regarded as almost equal to the soil temperature, and therefore the soil temperature can be confirmed by the temperature of the leachate. .

  As a specific treatment method of the present invention, a chlorinated oxidant, or an alkaline agent and a chlorinated oxidant (hereinafter sometimes referred to as “medicine”) are used so that the drug is distributed throughout the soil. What is necessary is just to add, For example, the method of inserting the hose in the several places of soil and inject | pouring the aqueous solution of a chemical | medical agent, the method of spraying the aqueous solution of a chemical | medical agent on soil like a shower, etc. are mentioned. At this time, when the amount of water in the soil gap is small, it is possible to increase the saturation (water content) of the water in advance by adding water to the soil. It is preferable in terms of enhancing the properties.

The steam blowing method, which is one of the heating methods, may be any method that warms the entire soil, and is not particularly limited. For example, a method of blowing steam by inserting steam blowing nozzles at a plurality of locations in the soil can be mentioned.
At this time, it is also preferable to take a heat retaining measure to prevent a temperature drop due to heat radiation from the soil surface by covering the surface of the soil to be treated with a vinyl sheet.

  At the start of the treatment according to the present invention, if necessary, the soil to be treated is first heated to the above-mentioned predetermined temperature by a heat source, and then the addition of the chemical is started. The drug is added so that the pH of the leachate and the free chlorine concentration are stabilized in this range, and the addition of the drug is stopped and maintained in this state.

  This treatment time varies depending on the permeability of the soil to be treated, but if the soil is relatively highly permeable, if the soil temperature is 20 ° C. or more and less than 40 ° C., 2000 hours or more, preferably 2000 to 4000 hours, When it is 40 ° C. or more and less than 60 ° C., it may be set for 300 hours or more, preferably 300 to 2000 hours, and when it is 60 ° C. or more and 100 ° C. or less, it may be set for 24 hours or more, preferably 24 to 1440 hours.

The processing according to the present invention is not limited to the case where the buried soil is transferred to another place for processing, and processing at the current position is also possible. In the case of processing at the current position, a groundwater sampling well is provided, and groundwater is sampled as leachate, and the pH and free chlorine concentration are measured.
When a well is provided, since the flow of groundwater becomes faster, it is more preferable to treat the groundwater around the well.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

  In the following Examples and Comparative Examples, slag (water permeability 10 cm / s) containing a cyanide compound (free cyan, iron cyano complex) is used as the soil to be treated, and a 48 wt% NaOH aqueous solution is used as the alkali agent. Was treated using a 12 wt% NaClO aqueous solution as the chlorine-based oxidant and industrial water as the water for injection.

  The analysis method of total cyanide and free chlorine concentration is as follows.

All cyanides in slag elution water: Using the treated slag, the eluate obtained by the soil elution test specified in the Environmental Agency Notification No. 46 (August 23, 1991) was compliant with JIS K0102. -Measured by pyridine-pyrazolone spectrophotometry.
Total cyanide in leachate: Measured by a 4-pyridine-pyrazolone spectrophotometric method according to JIS K0102, without filtering leachate.
The measurement of all cyan was performed after adding L (+)-ascorbic acid to reduce residual chlorine in water.
Free chlorine in leachate: The leachate was filtered through filter paper made of glass filter, diluted with pure water to a predetermined concentration, and measured by the DPD method according to JIS K0102.

[Examples 1 to 5]
As shown in FIG. 1, in a plastic (heat-resistant) storage tank (inner dimensions: 1 m × 1 m × 0.3 m) 1, a slag 2 peak containing cyanide is formed, and the upper part of the slag ridge is flattened. It was made into a substantially pyramidal trapezoidal shape, and a place for injecting steam and medicine was provided. In FIG. 1 (a), A indicates the injection point of chemicals (alkali agent and chlorine-based oxidant), and B indicates the injection point of steam. In FIG. 1B, C indicates the positions of A and B together.
In addition, a thermometer (not shown) was provided at a position where the steam did not directly hit at a position 3 cm deep from the upper surface of the slag mountain.
First, the slag pile was heated by blowing in steam, and after confirming that the temperature measured by the thermometer was equal to or higher than the set temperature, the drug was injected. When leachate could not be collected from the valve at the bottom of the storage tank, water mixed with a predetermined concentration of drug was injected from the upper center of the slag mountain until the amount of leachate required for analysis could be collected.
The pH of the leachate, the water temperature, and the free chlorine concentration were examined, and the amounts of drug and vapor injected were adjusted so that the water temperature would be a predetermined temperature at pH 11-12, free chlorine concentration of 10 mg / L or more, and maintained for the reaction time.
Table 1 shows the average temperature of the slag, the average pH and the free chlorine concentration of the leachate, the treatment time, and the total cyan concentration of the leachate and slag elution water after the treatment.

[Examples 6 to 12]
In Example 1, the treatment was carried out in the same manner except that the treatment conditions shown in Table 1 were changed by changing the amount of steam blown and the amount of medicine injected. The total cyan concentration of the leachate and slag elution water after the treatment was as shown in Table 1.

[Comparative Example 1]
With respect to the cyanide-containing slag, the total cyan density was measured by the above method without any treatment, and the results are shown in Table 1.

  From Table 1, according to the present invention, it is difficult to prevent all cyanides in the soil by injecting an alkali agent and a chlorine-based oxidizing agent into the soil and blowing it with steam for heating as necessary. Decomposable iron cyano complex can be efficiently decomposed, and injecting chemicals and injecting steam so that the free chlorine concentration is 10 mg / L or more when the temperature is 60 ° C. or higher and the pH of leachate is 11 or higher. It can be seen that it is preferable to perform. In this range of conditions, when the soil temperature is 20 ° C., the treatment time is 2160 hours, and when the soil temperature is 40 ° C., the treatment time is extended to 360 hours, thereby increasing the total cyanide content of the leachate or elution water. It can be seen that can be decomposed below the detection limit value, which is the environmental standard.

1 Storage tank 2 Slag

Claims (2)

Chlorine oxidizer or alkali agent and chlorine oxidizer are added to the soil containing cyanide , and the soil is heated to a temperature of 20 ° C. or higher and 100 ° C. or lower by steam blowing, and water is collected from the soil. After adding the chlorinated oxidant, or the alkali agent and the chlorinated oxidant so that the pH of the leached water is 11 to 13 and the free chlorine concentration is 10 mg / L or more, hold it at the soil temperature for a predetermined time. A process for treating cyanide-containing soil that decomposes cyanide in the soil,
The method for treating cyan-containing soil, wherein the predetermined time is any one of the following (1) to (3) according to the soil temperature .
(1 ) 2000 hours or more when soil temperature is 20 ℃ or more and less than 40 ℃
(2) 300 hours or more when the soil temperature is 40 ° C or more and less than 60 ° C
(3) 24 hours or more when soil temperature is 60 ℃ or more and 100 ℃ or less Oite to claim 1, the processing method of the cyan-containing soil in which the cyanide is characterized by including iron cyano complexes.

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