TWI673096B - Method for detoxifying polluted soil - Google Patents

Abstract

The invention is a method for detoxifying contaminated soil. The method includes the step of adding iron powder to adding to contaminated soil containing at least one pollutant selected from arsenic, lead, hexavalent chromium, cadmium, selenium, mercury, cyanide, fluorine, and boron. Iron powder; moisture content adjustment step, adjusting the moisture content of contaminated soil before magnetic separation to 36% by mass or less; dry magnetic separation step, recovering and removing iron powder by dry magnetic selection from polluted soil having a moisture content of 36% by mass or less.

Description

Detoxification method for contaminated soil

The invention relates to a method for detoxifying contaminated soil.

In recent years, with the economic recovery, the construction of tunnels or redevelopment has increased. Ensuring the dumping ground of the remaining soil becomes a problem. The leftover soil also includes contaminated soil caused by natural-based pollutants such as arsenic, and a method for coping with the leftover soil is a problem. As a characteristic of the contaminated soil, the content of the contaminated substance is relatively small compared with the content standard prescribed by the Soil Pollution Countermeasures Law, and on the other hand, it tends to exceed the elution amount standard of several to several tens of times.

It is reported that a water-repellent sheet is installed near a place where such contaminated soil is generated, for example, on a road body during road construction, or a water-blocking facility is provided by concrete, etc., and the facility is directly filled with the contaminated soil and managed. (Refer to the Research Manual on the Handbook for Coping with Soil and Sand Containing Heavy Metals from Nature in Building Construction (2010): "Manual for Coping with Rock and Soil Containing Heavy Metals from Nature in Building Construction (tentative version)". However, in the above method, regular monitoring and facility management must be performed, which is not a fundamental countermeasure. In addition, there is a problem that it is difficult to secure the installation place and obtain understanding from the surrounding residents. Moreover, the following problems arise: The pollution infiltrates from the temporary field of the contaminated soil, and the surrounding groundwater is polluted.

In addition, it describes a method of finding poison by insolubilizing contaminated substances by kneading various insolubilizing agents in contaminated soil (refer to "Guidelines for Investigation and Measures by the Soil Pollution Countermeasures Law (Revised 2nd Edition)" (2012.8) (Ministry of the Environment, Water, Atmospheric Environment Bureau, Soil Environment Section, and Japanese Patent Laid-Open No. 2003-290757). The insolubilized soil is operated as soil that must be continuously managed in the same way as the blockade measure, and in the Soil Pollution Countermeasures Act, it is stipulated that the subject is to secure the place where the insolubilized soil is managed.

In addition, methods for treating contaminated soil as a cement auxiliary material and methods for landfill disposal at a managed disposal site have been reported (see "Guidelines for Investigation and Measures by the Soil Pollution Countermeasures Law (Revised 2nd Edition)" 2012.8): Ministry of the Environment, Water and Soil Environment Section, Bureau of Atmospheric Environment). However, in the method of reporting, the status quo is that processing capacity or capacity cannot keep up with the amount generated.

As a method for detoxifying the contaminated soil to obtain purified soil, a method of performing a cleaning classification process is reported (refer to "About the purification of heavy metal polluted soil based on the soil cleaning method": Resources. Raw Materials Volume: 2000: 117-120 (2010)). However, since the method of the report is a wet process, it is necessary to increase the capacity of equipment for slurrying and dewatering equipment, and it is currently difficult to implement simple and large-scale processing inexpensively.

In addition, a method of concentrating a contaminated substance into a magnetic substance and separating it using at least one of a wet magnetic separator and a dry magnetic separator has been proposed (see Japanese Patent Laid-Open No. 10-71387). However, the proposed method to reduce pollutants For the purpose of quality, there is a problem that the removal ability of dissolvable pollutants is insufficient.

In addition, after adding iron powder to the polluted soil slurry to adsorb pollutants, a method of recovering and removing the iron powder adsorbing the pollutants by magnetic separation is proposed (see Japanese Patent Laid-Open No. 2000-51835). Bulletin). In the proposal, dissolvable pollutants can also be removed. However, since the proposed method is a wet process, it is necessary to increase the capacity of equipment for slurrying and dewatering equipment using a large amount of water, and it is currently difficult to implement simple and large-scale processing at low cost.

Therefore, it is desirable to provide a method for detoxifying contaminated soil that can be used to purify the soil simply and efficiently by using dry treatment without using a large amount of water.

An object of the present invention is to solve the aforementioned problems and achieve the following objects. That is, an object of the present invention is to provide a method for detoxifying contaminated soil which can be used to purify soil simply and effectively by using dry treatment without using a large amount of water.

As a means to solve the said problem, it is as follows. which is,

<1> A method for detoxifying contaminated soil, comprising the step of adding iron powder to contaminate at least one pollutant selected from the group consisting of arsenic, lead, hexavalent chromium, cadmium, selenium, mercury, cyanide, fluorine, and boron Iron powder is added to the soil; the water content adjustment step adjusts the water content of the polluted soil before magnetic separation to 36% by mass or less; In the dry magnetic separation step, iron powder is recovered and removed by using the dry magnetic material selected from polluted soil having a moisture content of 36% by mass or less.

<2> The method for detoxifying contaminated soil according to <1>, wherein iron powder is added to the contaminated soil in an amount of 0.05% by mass or more and 10% by mass or less.

<3> The method for detoxifying contaminated soil according to any one of <1> to <2>, wherein the moisture content of the contaminated soil before iron powder is added is 60% by mass or less.

<4> The method for detoxifying contaminated soil according to any one of <1> to <3>, wherein in the iron powder adding step, any one of sulfuric acid and hydrochloric acid is added.

<5> The method for detoxifying contaminated soil according to any one of the above <1> to <4>, wherein the contaminated soil is a contaminated soil containing a pollutant derived from nature.

According to the present invention, the previous problems can be solved, and a method for detoxifying contaminated soil which can be used to purify the soil can be simply and effectively utilized by dry treatment without using a large amount of water, and can be provided.

FIG. 1 is a flowchart of a method for detoxifying contaminated soil according to the present invention.

FIG. 2 is a flow chart of an apparatus for detoxifying contaminated soil according to the present invention.

FIG. 3 is a flow chart of an apparatus for detoxifying a contaminated soil as described in Japanese Patent Laid-Open No. 2000-51835.

Fig. 4 (a) shows the water content before magnetic separation and the recovery rate of magnetic objects in soil A And the relationship between As recovery rate.

FIG. 4 (b) is a graph showing the relationship between the water content before magnetic separation in soil A and the amount of As eluted out.

FIG. 5 (a) is a graph showing the relationship between the water content before magnetic separation in soil B, the recovery rate of magnetic objects, and the recovery rate of F. FIG.

FIG. 5 (b) is a graph showing the relationship between the water content before magnetic separation in soil B and the amount of F eluted.

FIG. 6 (a) is a graph showing the relationship between the hardening time after the addition of iron powder in the soil A, the recovery rate of the magnetite, and the recovery rate of As.

FIG. 6 (b) is a graph showing the relationship between the hardening time after adding iron powder in soil A and the amount of As eluted out.

FIG. 7 (a) is a graph showing the relationship between the hardening time after the iron powder is added to the soil C, the recovery rate of the magnetite, and the recovery rate of Se.

FIG. 7 (b) is a graph showing the relationship between the hardening time after the iron powder was added to the soil C and the amount of Se eluted out.

FIG. 8 (a) is a graph showing the relationship between the hardening time after the iron powder is added to the soil D, the recovery rate of the magnetite, and the recovery rate of Pb and Cr.

FIG. 8 (b) is a graph showing the relationship between the hardening time after the iron powder is added to the soil D and the amount of Pb and Cr ⁶⁺ eluted.

FIG. 9 (a) is a graph showing the relationship between the amount of iron powder added to the soil A, the recovery rate of the magnetic particles, and the recovery rate of As.

Figure 9 (b) shows the relationship between the amount of iron powder added in soil A and the amount of As eluted out. chart.

FIG. 10 (a) is a graph showing the relationship between the amount of iron powder added to the soil C, the recovery rate of the magnetite, and the recovery rate of Se.

FIG. 10 (b) is a graph showing the relationship between the amount of iron powder added to the soil C and the amount of Se eluted out.

FIG. 11 (a) is a graph showing the relationship between the amount of iron powder added to the soil D, the recovery rate of magnetic particles, and the recovery rate of Pb and Cr.

FIG. 11 (b) is a graph showing the relationship between the amount of iron powder added to the soil D and the amount of Pb and Cr eluted.

FIG. 12 (a) is a graph showing the relationship between the amount of sulfuric acid added to soil A, the recovery rate of magnetic particles, and the recovery rate of As.

FIG. 12 (b) is a graph showing the relationship between the amount of sulfuric acid added to the soil A and the amount of As eluted out.

FIG. 13 (a) is a graph showing the relationship between the amount of sulfuric acid added to the soil C, the recovery rate of the magnetite, and the recovery rate of Se.

FIG. 13 (b) is a graph showing the relationship between the amount of sulfuric acid added to the soil C and the amount of Se eluted out.

FIG. 14 (a) is a graph showing the relationship between the amount of sulfuric acid added to the soil D, the recovery rate of the magnetite, and the recovery rate of Pb and Cr.

14 (b) is a graph showing the relationship between the amount of sulfuric acid added to the soil D and the amount of Pb and Cr ⁶⁺ eluted.

Fig. 15 is a graph showing the relationship between the moisture content before magnetic separation and the quality of magnetite recovery table.

16 is a photograph showing differences in soil properties due to changes in water content in contaminated soil before magnetic separation in Examples 6, 8, 8, and Comparative Example 1. FIG.

FIG. 17 is a five-stage sequential extraction flowchart.

FIG. 18 is a graph showing changes in the revenue and expenditure ratio of the pre-treatment soil, the iron powder mixed soil, and the post-treatment soil in Test 1. FIG.

FIG. 19 is a graph showing changes in the revenue and expenditure ratio of the pre-treatment soil, the iron powder mixed soil, and the post-treatment soil in Test 2. FIG.

(Detoxification method for contaminated soil)

The method for detoxifying contaminated soil of the present invention includes: an iron powder adding step, a moisture content adjusting step, and a dry magnetic separation step, and further includes other steps as required.

<Iron powder adding procedure>

The iron powder adding step is a step of adding iron powder to a contaminated soil containing at least one pollutant selected from the group consisting of arsenic, lead, hexavalent chromium, cadmium, selenium, mercury, cyanide, fluorine, and boron.

The contaminated soil is, for example, leftover soil generated along with various construction works such as road construction, tunnel construction construction, and redevelopment construction, and refers to soil containing the contaminated substance derived from nature.

Examples of the pollutant include arsenic (As), lead (Pb), hexavalent chromium (Cr (VI)), cadmium (Cd), selenium (Se), mercury (Hg), cyanide (CN), Fluorine (F), Boron (B) and the like. The polluted substance is a substance that is derived from nature and exists in rocks or soil among the target substances for environmental pollution caused by soil pollution.

The moisture content of the contaminated soil before the iron powder is added is preferably 60% by mass or less, more preferably 0% by mass or more and 45% by mass, and even more preferably 10% by mass or more and 35% by mass or less. If it is the range of the water content of the contaminated soil, the water content adjustment in the water content adjustment step to be described later is small (may also be omitted). Although it also depends on the soil quality, it is also advantageous in terms of transportability in terms of loading It is in a state capable of being transported without liquefaction, such as a dump truck.

The added amount of the iron powder is preferably 0.05% by mass or more and 10% by mass or less, more preferably 0.05% by mass or more and 1% by mass or less with respect to the contaminated soil. Within the range of the amount of the iron powder added, pollutants can be recovered and removed by dry magnetic separation efficiency.

The type of the iron powder is not particularly limited, and may be appropriately selected according to the purpose, and examples thereof include reduced iron powder, cutting scrap iron powder (using scrap iron as a raw material), and atomized iron powder. Among the iron powders, reduced iron powder is preferred.

Preferably, the acid is added while the iron powder is added to the contaminated soil. The acid is added to promote the movement of the pollutant.

The acid is preferably any of hydrochloric acid and sulfuric acid.

The amount of the acid to be added is not particularly limited, and may be appropriately selected according to the purpose, and is preferably 0% by mass or more and 1% by mass or less relative to the contaminated soil.

The pH value of the acid-treated contaminated soil is preferably 4.0 to 9.0, and more preferably 6.0 to 8.0. If the pH is in the range, the polluting substance does not become dissolvable And safe. In addition, when the purified soil is made from the treated soil, since the normal soil is in a neutral region, the pH range is also preferred.

When the acid is used, it is preferable not to perform dilution with water in order to perform a moisture content adjustment step thereafter. The reason is that any of the addition amount of the dehydrating agent, the drying time, and the drying temperature required for the moisture content adjustment must be increased.

For the excavated contaminated soil having a moisture content before the iron powder is added, at least any one of the iron powder and the acid is put into a mixer and fully kneaded. At this time, when coarse gravel or the like enters the contaminated soil, it may cause obstacles to the kneading, so it is preferable to perform pretreatment such as sieving and pulverization in advance.

The kneading method is not particularly limited, and can be appropriately selected according to the purpose. When considering the effect of finely dividing the pellets, it is more preferable to use a shear mixer as compared to the impact mixer. Examples of the shear mixer include a biaxial stirring mixer and the like.

<Moisture content adjustment procedure>

The water content adjustment step is a step of adjusting the water content of the contaminated soil before magnetic separation to 36% by mass or less.

In addition, when the moisture content of the contaminated soil before magnetic separation is 36% by mass or less, the dry magnetic separation step described below may be performed without performing the moisture content adjustment step.

The moisture content of the contaminated soil before the magnetic separation is 36% by mass or less, preferably 22% by mass or less, and more preferably 14% by mass or less. If the moisture content of the contaminated soil before the magnetic separation is 36% by mass or less, the aggregates will generally become soil particle monomers, which is easy to be magnetically separated, and dry magnetic separation can be performed efficiently.

The moisture content of the contaminated soil can be determined, for example, by measuring the quality of the contaminated soil (wet soil quality w1), drying the contaminated soil using a drying oven, etc., and then measuring the soil quality (dry soil quality w2) according to the following formula.

Water content (%) = [1- (mass of dry soil w2 / mass of wet soil w1)] × 100

The method for adjusting the moisture content in the moisture content adjustment step is not particularly limited and may be appropriately selected according to the purpose, and examples thereof include a method of adding a hygroscopic agent, and drying using a dryer.

The moisture absorbent is not particularly limited. Generally, materials such as quicklime or cement are also considered. However, since the materials are strongly alkaline materials, the pH range must be controlled, so neutral curing materials are more preferred.

Examples of the neutral curing material include a material containing hemihydrate gypsum as a main component and a material containing magnesium oxide as a main component. Among the neutral curing materials, in terms of economic efficiency, a material mainly composed of calcined gypsum is preferred.

In addition, when the moisture content of the contaminated soil after the iron powder is added is 36% by mass or less, no agglomerates are formed, the state is finely divided, and the dry magnetic separation is not an obstacle, the addition of the hygroscopic agent may be omitted.

The dryer used for the drying is not particularly limited and may be appropriately selected depending on the purpose, and examples thereof include a biaxial kneading drying furnace, a rotary dryer, a tunnel furnace, and the like. In the dryer, in terms of the effect of subdividing the pellets, It is preferably a double-shaft kneading drying furnace and a rotary dryer.

<Dry Magnetic Separation Procedure>

The dry magnetic separation step is a step of recovering and removing iron powder from the polluted soil by adjusting the moisture content of the contaminated soil before magnetic separation to 36% by mass or less by using the dry magnetic selection.

Here, as shown in FIG. 15, there are two areas in which the iron powder can be magnetically separated from the contaminated soil according to the moisture content of the contaminated soil before magnetic separation.

One of them is a low-moisture content region with a moisture content of 36% by mass or less before magnetic separation, and the other is a high-moisture content region with a moisture content of 45% by mass or more before magnetic separation.

The method for detoxifying contaminated soil according to the present invention performs dry magnetic separation in the low moisture content region.

On the other hand, in the method described in Japanese Patent Laid-Open No. 2000-51835, wet magnetic separation is performed in the high water content containing region. In the method described above, iron powder can be magnetically separated from polluted soil, but in order to slurry the polluted soil, a large amount of water is required, and drainage is also necessary, and it is difficult to implement simple and large-scale treatment at low cost.

The moisture content of the contaminated soil before magnetic separation is in a range of 38% by mass or more and 43% by mass or less, and it is a region where the separation efficiency of both dry magnetic separation and wet magnetic separation is significantly poor (magnetic separation difficult area).

The dry magnetic separation is not particularly limited, and can be appropriately selected according to the purpose. For example, the contaminated soil with a moisture content of 36% by mass or less before the magnetic separation is put into a magnetic separator and separated into magnets by magnet Objects and non-magnetic objects. The magnetic force of the magnetic sorter is not particularly limited, and may be appropriately selected according to the purpose, preferably 1,500 G or more, 12,000 G or less, and more preferably 1,500 G Above and below 7,000 G.

The purpose of the dry magnetic separation step is to reduce the elution amount of harmful substances by magnetism by separating and removing iron powder adsorbed with pollutants, and it can be fully separated and recovered by a magnetic force of 1,500 G or more and 7,000 G or less. . If the magnetic force is higher than the magnetic force, the weakly magnetic soil particles pre-existing in the contaminated soil are also recovered, and the amount of the magnetite becomes larger. The magnetite must be disposed of as another contaminated concentrated soil, so it is not economical to recover it in large quantities unnecessarily.

Here, FIG. 1 is a flowchart of a method for detoxifying contaminated soil according to the present invention.

First, at least any one of iron powder and acid is poured into a mixer and thoroughly mixed in excavated contaminated soil. In this case, when coarse gravel or the like enters the contaminated soil, mixing may be hindered. Therefore, it is preferable to perform pretreatment such as sieving and pulverization in advance.

Then, iron powder is added to a predetermined amount of contaminated soil (iron powder adding step). The contaminated soil mixed with iron powder and the acid as required is hardened for more than 0 minutes, preferably about 10 minutes, and then mixed with a neutral curing material as a hygroscopic agent, if necessary, from 0 kg to 200 kg. The water content in the contaminated soil before magnetic separation is adjusted to 36% by mass or less by performing sufficient mixing in a machine or removing water by a dryer (water content adjustment step).

Then, iron powder having adsorbed pollutants was recovered and removed by a dry magnetic separation with a magnetic force of 1,500 G or more and 7,000 G or less (dry magnetic separation step).

In addition, FIG. 2 shows a device flow chart of the method for detoxifying contaminated soil by dry magnetic separation according to the present invention. For comparison, FIG. 3 shows Japanese Patent Laid-Open An apparatus flow chart of an example of a method for detoxifying contaminated soil by wet magnetic separation described in Japanese Patent Publication No. 2000-51835.

Comparing FIG. 2 and FIG. 3, in the detoxification method described in Japanese Patent Laid-Open No. 2000-51835, the processing flow is complicated, and operation management is difficult. For example, the kneading machine in FIG. 2 may be substituted by a soil improving machine or the like as a general-purpose rental machine, and detoxification may be performed by a simple equipment procedure. In addition, since the flow of FIG. 3 is a wet type, it is necessary to treat it with water or spray water.

[Example]

Hereinafter, examples of the present invention will be described, but the present invention is not limited in any way by the examples.

<Sample used for test>

Five kinds of soils A to E shown in Table 1 below were used as samples. In addition, soil D is man-made contaminated soil, and others are contaminated soil caused by nature.

(Examples 1 to 11 and Comparative Example 1)

-The effect of moisture content-

The effects of moisture content were investigated using soil A and soil B.

First, the soil A and the soil B were air-dried in advance, and then any amount of ion-exchanged water was added to adjust the moisture content of the soil shown in Tables 2 and 3.

Next, 100 g of soil A or soil B with adjusted water content was taken into a polypropylene cup, and 1 g of reduced iron powder (special iron powder E200, manufactured by DOWA IP Creation) was added, and 0.3 mL of concentrated sulfuric acid (0.1 N / kg in terms of acid concentration) was added to soil A, and 5 mL of a 10% by mass aqueous hydrochloric acid solution (0.1 N / kg in terms of acid concentration) was added to soil B, and mixed with a medicine spoon for 1 minute. After hardening for 10 minutes, a neutral curing material (Gypsander C, manufactured by Ishihara Industries Co., Ltd.) containing gypsum as a main component was added within a range of 0 g to 20 g, and mixed for about 1 minute.

Then, the soil was opened in the vat and evenly spread, and the surface magnetic force was applied. A 1,500 G magnet was used to scan the surface of the uniform soil, magnetically separate the magnetic particles from the non-magnetic particles (purified soil), and analyze the content of pollutants in the soil (for soil A according to the substrate Survey method, according to Ministry of the Environment Notice No. 19 for soil B), and analysis of dissolution amount for non-magnetic particles (Ministry of the Environment Notice No. 18).

In addition, regarding the moisture content of contaminated soil before iron powder addition and after treatment (before magnetic separation), after measuring the quality of the contaminated soil (wet soil quality w1), the contaminated soil is dried using a drying oven or the like, and the soil quality is then measured (Dried soil mass w2) was calculated according to the following formula.

Water content (%) = [1- (mass of dry soil w2 / mass of wet soil w1)] × 100

The test results of soil A and soil B are shown in Table 2 and Table 3, respectively.

In addition, regarding soil B, the soil properties were shown in Example 6, Example 8, Example 11, and Comparative Example 1 in which the moisture content before the magnetic separation was 10.4% by mass, 20.0% by mass, 35.5% by mass, and 41.7% by mass. Figure 16. From the results of FIG. 16, it was found that until the moisture content before the magnetic separation was 35.5 mass%, the soil had no fluidity and was solid.

<Test Results of Soil A>

<Test Results of Soil B>

By applying the method for detoxifying contaminated soil of the present invention, in the test range, regardless of the water content before magnetic separation, the amount of pollutants in the purified soil is greater than that in the soil before treatment. reduce.

For soil A, if the moisture content of the contaminated soil before iron powder addition is 10 mass % Or less, it does not form agglomerates and magnetic separation is relatively easy, without the need to add a neutral curing material. When the moisture content of the contaminated soil before iron powder addition is 20% by mass or more, since the contaminated soil forms aggregates, it is necessary to add a neutral solidified material. When the moisture content before iron powder addition is 30% by mass, although the contaminated soil before magnetic separation is in a fluidized state, magnetic separation can be performed by adding a neutral solidified material. The moisture content before magnetic separation at this time was 25.0% by mass.

For soil B, similar to soil A, if the moisture content of the contaminated soil before iron powder addition is 24.1% by mass or less, magnetic separation is easy, and it is not necessary to add a neutral solidified material. When the moisture content is 34.8% by mass or more before the iron powder is added, a neutral curing material must be added. When the moisture content before the iron powder was added was 41.7% by mass, 15% by mass of the neutral solidified material was added to make the pellets magnetically separable. However, the moisture content before the magnetic separation was 35.5% by mass. When the moisture content before the iron powder was added was 41.7% by mass and the neutral curing material was not added, magnetic separation could not be performed (Comparative Example 1).

Fig. 4 (a) shows the relationship between the water content before magnetic separation in soil A, the recovery rate of magnetic objects, and the As recovery rate, and Fig. 4 (b) shows the relationship between the water content before magnetic separation in soil A and the amount of As eluted. FIG. 5 (a) shows the relationship between the water content before magnetic separation in soil B and the recovery rate and F recovery rate of magnetic objects, and FIG. 5 (b) shows the relationship between the water content before magnetic separation and F elution amount in soil B.

According to the results of FIG. 4 and FIG. 5, as the moisture content before magnetic separation increases, there is a tendency that the amount of recovered magnetic particles and the amount of recovered pollutants increase. The reason for this is considered that, when the water content is increased, the aggregates of the soil particles increase slightly. On the other hand, about The amount of elution tends to decrease if the moisture content increases before magnetic separation. The reason is considered that if the moisture content before the magnetic separation is large, the adsorption of As on the iron powder easily proceeds. In addition, it can be seen that in any of the ranges of moisture content before magnetic separation in the test range, the amount of dissolved pollutants was sufficiently reduced, which was effective.

(Example 12 to Example 39)

<Hardening time after iron powder addition, influence of iron powder addition amount and acid addition amount>

Use soil A, soil C, and soil D to confirm the effects of hardening time, iron powder addition, and acid addition after iron powder addition.

An amount of 100 g of each soil sample was taken into a polypropylene cup, an arbitrary amount of reduced iron powder similar to that in Example 1 was added, and an arbitrary amount of concentrated sulfuric acid was added, and mixed with a medicine spoon for 1 minute. After hardening at any time, 10 g of a neutral curing material (Gypsander C, manufactured by Ishihara Sangyo Co., Ltd.) containing gypsum as a main component was added and mixed for about 1 minute. Then, the soil was opened in the tank and spread evenly. The magnetic particles with a surface magnetic force of 1,500 G were used to magnetically separate the magnetic particles from the non-magnetic particles (purified soil), and the content of pollutants in the soil was separately implemented. Analysis (substrate survey method), and analysis of dissolution of non-magnetic matter (Ministry of the Environment Notice No. 18). The results of soil A, soil C, and soil D are shown in Tables 4 to 6 and Figs. 6 to 14, respectively.

<Result of Soil A>

<Result of Soil C>

<Result of Soil D>

<Effect of hardening time after iron powder is added>

According to the results of Tables 4 to 6, in the range of the test, no correlation was found between the magnetite recovery rate, the polluted substance recovery rate, and the dissolved amount of the polluted substance in the hardening time after the iron powder was added in any of the soils. From this, it can be seen that the mixing time of the iron powder is about 1 minute is sufficient.

<Influence of iron powder addition amount>

According to the results of Tables 4 to 6, in the range of the test, as the amount of iron powder was increased in any of the soils, it was found that the recovery rate of the magnetic particles and the recovery rate of the pollutants increased. In addition, with regard to the amount of pollutants eluted, with the exception of Cr ^{6+ in} soil D, the amount of iron powder added tended to decrease. In addition, at any level, it was judged that the amount of dissolution before treatment was greatly reduced, and it had the effect of removing the eluted components. In the range of the test, the minimum amount of iron powder added was 0.05% by mass in soil A, but it was also found that the effect was sufficiently reduced when the amount of iron powder was added.

<Effect of Acid Addition>

According to the results of Tables 4 to 6, in the range of the test, no correlation was found between the magnetic substance recovery rate and the polluted substance recovery rate for the acid addition amount in any of the soils. In addition, with the exception of soil D, no correlation was found between the amount of dissolved pollutants and the amount of acid added. In soil D, with the increase of acid addition, the amount of Pb dissolution showed a slight increase, and Cr ⁶⁺ showed a slight decrease. However, at any level, the amount of dissolution before treatment significantly decreased. .

In addition, in any kind of soil, it can be removed sufficiently when the acid addition amount is 0N / kg. In consideration of the economic effect of the dissolvable contaminating component, it is not necessary to add an acid.

(Comparative example 2)

<When the moisture content is not adjusted>

The same as in Example 1 was used except that the soil B whose iron content was adjusted to 41.3% by mass before the addition of iron powder, without using a neutral solidified material, and whose water content was not adjusted (the moisture content before magnetic separation was 41.3% by mass). Way, try magnetic separation. As a result, the soil has high viscosity and large aggregates, so that magnetite cannot be obtained. Then, using a magnet with a surface magnetic force of 12,000 G, magnetic separation was attempted. As a result, the soil was completely attached to the magnet, and it was impossible to separate magnetic and non-magnetic objects.

(Example 40 to Example 42)

<Comparison of magnetic separation by different iron powders>

100g of Se-contaminated soil (Se content: 0.75mg / kg ~ 0.86mg / kg, Se dissolution amount: 0.013m / L) at the same site (site) as soil C was taken into a polypropylene cup and prepared Three.

Add 1 g of reduced iron powder, chip iron powder (CC-1004, manufactured by Connelly), or atomized iron powder (-180 μm, Wako Pure Chemical Industries, Ltd.) to each cup. (Manufactured by the company), and 0.07 N / kg hydrochloric acid was added and mixed for 1 minute. After hardening for 30 minutes, 10 g of a neutral curing material (Gypsander C, manufactured by Ishihara Industry Co., Ltd.) containing gypsum as a main component was added and mixed for about 1 minute.

Then, open the soil in the tank and spread it evenly. Use the surface magnetic force to A 7,000 G magnet separates magnetic particles and non-magnetic particles (purified soil) magnetically, measures the content of pollutants in the soil (substrate survey method), and measures the amount of dissolution of non-magnetic materials (environment) Provincial Notice No. 18). The results are shown in Table 7.

<Results of magnetic separation by different iron powders>

According to the results of Table 7, the treatment tests were performed with different iron powders. As a result, the reduced iron powder had the highest recovery rate of the magnetic particles and the Se recovery rate, followed by chip iron powder and atomized iron powder in this order. The difference in the magnetite recovery rate is considered to be a result of the relatively small particle size of the reduced iron powder, which forms aggregates, and the increase in the Se recovery rate due to the large amount of soil attached. On the other hand, when the amount of dissolution of non-magnets is compared, it is a degree where a slight difference occurs.

(Comparative Example 3 to Comparative Example 4)

-Result of performing only magnetic separation without adding iron powder (the method described in Japanese Patent Laid-Open No. 10-71837)-

For the air-dried soil A and the soil samples used in Examples 40 to 42, 100 g of each was thinly spread in a cylinder, and a magnet with a surface magnetic force of 7,000 G was used to deposit the magnetic particles and non-magnetic Particles (purified soil) are magnetically separated, The analysis of the content of pollutants in the soil (substrate survey method) and the analysis of the dissolution amount of non-magnetic matter (Ministry of the Environment Notice No. 18) were carried out. The results are shown in Tables 8 and 9.

<Magnetic separation result of soil A>

<Results of Magnetic Separation of Soil Samples Used in Examples 40 to 42>

According to the results of Tables 8 and 9, as a result of magnetic separation of soil A, 10.4% by mass of magnetite can be obtained, and As can be recovered by 10.3% by mass. However, no reduction in the amount of As eluted was found. From this, it was determined that the dissolvable As was adsorbed on the iron powder and recovered. On the other hand, in the soil samples used in Examples 40 to 42, almost no magnetite was obtained by magnetic separation. It can be seen from Japanese Patent Laid-Open No. 10-71837 Compared with the method described in the publication, the method for detoxifying contaminated soil of the present invention is effective in recovering and removing dissolvable pollutants.

(Comparative experiment of the method for detoxifying contaminated soil of the present invention (dry magnetic separation) and the method described in Japanese Patent Laid-Open No. 2000-51835 (wet magnetic separation))

<Comparative example 5>

100 g of Se-contaminated soil (Se content: 0.75 mg / kg to 0.86 mg / kg, Se dissolution amount: 0.013 mg / L) at the same position as the soil C used in Examples 40 to 42 was taken to 1.0 L. In a Poly Bottle, 1 g of the same reduced iron powder as in Example 1, 400 mL of ion-exchanged water, and 0.5 mL of concentrated sulfuric acid were added for sealing, and the flask was shaken at 200 reciprocating / minutes for 30 minutes to contaminate Se. Soil slurry.

After shaking, the slurry in the Polaroid bottle was opened in a polypropylene cylinder, and the surface magnetic force of 0.7T was scanned in the slurry to separate the magnetic objects. When the slurry was transferred to another container or the like, 100 mL of ion-exchanged water was used in order to recover the attached soil particles.

The non-magnetic deposits remaining in the polypropylene cylinder were suction filtered using 5C filter paper to obtain non-magnetic deposits and treated water.

The obtained non-magnets and magnets were subjected to content analysis based on the substrate survey method and dissolution analysis based on the Ministry of the Environment Notice No. 18. The treated water is analyzed for the concentration of the target pollutant.

In addition, the "content before adding iron powder" and "the amount of pollutants in the magnetic substance" in the following table were obtained by the following formula.

． Content before adding iron powder (mg / kg) = (soil content after treatment × soil weight distribution after treatment + magnetite content × magnetite weight distribution) / (treatment soil weight distribution + magnetite weight distribution)

． Revenue and Expenditure of Pollutants in Magnetic Substances (%) = (Magnetic Substance Content × Magnetic Substance Weight Distribution) / (Soil Content Before Iron Powder Addition × Soil Weight Distribution Before Iron Powder Addition) × 100

The results of Comparative Example 5 are shown in Table 10.

<Example 43>

Using the contaminated soil of Example 40, the detoxification method (dry magnetic separation) of the contaminated soil of the present invention was performed.

The moisture content of the soil C before the iron powder was added was 15.0% by mass.

The magnetic force of the magnet used is 0.15T (1,500 Gauss)

According to the results of Table 10, the soil (non-magnetic matter) after the treatment was reduced to the same extent as the result of Example 43 of Table 11 with respect to the soil before the iron powder was added. However, in the contaminated soil of Comparative Example 5 with a large water content, the results were as follows: the Se budget in the magnetite was significantly lower than that in Example 43 of Table 11, but Se was distributed in the treated water to obtain the same results. Example 43 of 11 has different results. From this, it can be seen that when wet magnetic separation is performed on Se-contaminated soil, Se is transferred to the treated water, and the amount of Se that can be recovered as magnetite is reduced compared to the case where dry magnetic separation is performed.

That is, from the results of Tables 10 and 11, it can be seen that in the soil C, the amount of Se eluted from the treated soil was the same as that of Comparative Example 5 in Example 43, but the Se budget in the magnetite was the same as that in Comparative Example. Compared with the wet magnetic separation of Example 5, in the method of detoxifying the contaminated soil of Example 43, the Se budget in the magnetite was greatly increased, and the transfer of Se to the magnetite was greatly increased (the amount of Se that can be recovered is greatly increased) ) (0.2% vs. 23.4%).

In addition, in the above comparative experiments, compared with the wet magnetic separation process described in Japanese Patent Laid-Open No. 2000-51835, the examples of the present invention both perform dry magnetic separation with a magnetic force of about 1/5. Processing of the magnetic force, of course foreseeable More significant increase in the amount of magnetization and the effect of suppressing the amount of dissolution.

In addition, the Se content of the treated water of Comparative Example 5 was 0.022 mg / kg, and because it exceeded the environmental standard, a separate drainage treatment was required.

Next, in the soil samples described in Table 1, the same test as in Comparative Example 5 was performed using soil A (As contaminated soil) and soil B (F contaminated soil).

(Result of soil A)

<Comparative Example 6>

Method described in Japanese Patent Laid-Open No. 2000-51835 (wet magnetic separation)

The magnetic force of the magnet used is 0.7T (7,000 Gauss)

<Example 44>

Using the contaminated soil of Example 4, the detoxification method (dry magnetic separation) of the contaminated soil of the present invention was performed.

The moisture content of the soil A before the iron powder was added was 20.0% by mass.

The magnetic force of the magnet used is 0.15T (1,500 Gauss)

From the results of Tables 12 and 13, it can be seen that, in the soil A, the amount of As dissolved in the soil after the treatment was relatively lower than that in Comparative Example 6 in Example 44 (0.002 mg / L vs. 0.00001 mg / L). In addition, as for the As balance in the magnetite, compared with Comparative Example 6, the As balance in the magnetite in Example 44 becomes larger, and As is more transferred to the magnetite (recyclable As substance). More) (6.2% vs. 15.8%).

(Result of soil B)

<Comparative Example 7>

Method described in Japanese Patent Laid-Open No. 2000-51835 (wet magnetic separation)

The magnetic force of the magnet used is 0.7T (7,000 Gauss)

<Example 45>

Using the contaminated soil of Example 10, the detoxification method (dry magnetic separation) of the contaminated soil of the present invention was performed.

The moisture content of the soil B before the iron powder was added was 34.8% by mass.

The magnetic force of the magnet used is 0.15T (1,500 Gauss)

From the results of Tables 14 and 15, it can be seen that in soil B, the amount of F dissolved in the treated soil was the same as that of Comparative Example 7 in Example 45, but the balance of F in the magnetite was the same as that in Comparative Example 7. In contrast, the F balance in the magnetite in Example 45 becomes larger, and the transfer of F to the magnetite is larger (the mass of the recyclable F material is greater) (7.0% vs. 10.8%).

In addition, the experimental results when magnetic separation processing is performed by the same magnetic force are shown below.

[Test Method 1 (Example of Detoxification Method of Contaminated Soil by the Present Invention)]

In the soil sample described in Table 1, 100 g of soil A (As contaminated soil) was weighed into a polypropylene cup, and 1 g of reduced iron powder (special iron powder E200, manufactured by DOWAIP Manufacturing Co., Ltd.) and concentrated sulfuric acid were added. 0.1mL, mixed with medicine spoon 1 minute. After hardening for 10 minutes, 10 g of a neutral curing material was added and mixed for about 1 minute.

Then, the soil was opened in the tank and spread evenly, and the surface magnetic force of 7,000 G was scanned on the surface of the uniform soil to magnetize the magnetic particles and non-magnetic particles (purified soil). Separate to obtain non-magnetism (treated soil) and magnetism.

The moisture content of the soil A before the iron powder was added was 18.0% by mass.

[Test method 2 (comparative example of wet magnetic separation described in Japanese Patent Laid-Open No. 2000-51835)]

Among the soil samples described in Table 1, the same test as in Comparative Example 5 was performed on soil A (As contaminated soil) as described below.

Measure 100g of soil into a 1.0L wide-mouth Polaroid bottle, add 1g of reduced iron powder (special iron powder E200, manufactured by DOWAIP Manufacturing Co., Ltd.), 400mL of ion-exchanged water, and 0.5mL of concentrated sulfuric acid, and seal. The machine was shaken at 200 reciprocations / minute for 30 minutes.

After shaking, the slurry in the Polaroid bottle was opened in a polypropylene cylinder, and the surface magnetic force of 0.7T (7,000 Gauss) was scanned in the slurry to separate the magnetic objects. When the slurry was transferred to another container or the like, 100 mL of ion-exchanged water was used in order to recover the attached soil particles.

The non-magnetized slurry remaining in the polypropylene cylinder was suction-filtered using 5C filter paper to obtain non-magnetized materials (treated soil) and treated water.

[Analysis of As Chemical Form of Treated Soil]

Before treatment, each product obtained in the soil A, the test 1, and the test 2 was subjected to a five-stage sequential extraction method (refer to A. Tesir, PGC Campbell, and M. Bison, "Score Steps of Extracting Species of Metal Particles in Order ", Analytical Chemistry, 51, 844-851 (1979). (A. Tessier, PGCCampbell and M. Bisson," Sequential extraction procedure for the speciation of particulate trace metals ", Analytical chemistry , 51,844-851 (1979).)), And the morphology of As in each product was confirmed. The extraction process is shown in FIG. 17.

According to the chemical speciation analysis, As in the soil is fractionated into an exchange state, a carbonate-bound state, and iron. Five fractions of manganese bound, organic bound, and residue. The extraction solvent is acidic and oxidatively becomes stronger gradually, and thus indicates a fraction that is easily soluble in water in the exchanged state and most difficult to dissolve in water in the residue state.

[Test Results 1 Material Revenue and Expenditure]

Table 16 shows the results of the material balance of the test 1 and Table 17 shows the results of the material balance of the test 2.

Table 16 shows the results of the test 1.

The magnetic force of the magnet used is 0.7T (7,000 Gauss)

Table 17 shows the results of the test 1.

The magnetic force of the magnet used is 0.7T (7,000 Gauss)

From Tables 16 and 17, it can be seen that if Test 1 and Test 2 are compared, the amount of As dissolved in the treated soil is compared with the wet magnetic separation described in Japanese Patent Laid-Open No. 2000-51835. In the method for detoxifying contaminated soil, it is a low-digit value (0.002 mg / L vs. 0.0002 mg / L). As for the balance of As in the magnetite, it is described in Japanese Patent Laid-Open No. 2000-51835 Compared with wet magnetic separation, in the detoxification method of this application, the As balance of the magnetite becomes larger. As is transferred to the magnetic substance more (recyclable As substance has more mass) (6.4% to 17.9%).

[Test Results 2As Chemical Form Analysis Results]

Table 18 shows the results of chemical form analysis of each product in Test 1 and Table 19 shows the results of chemical form analysis of each product in Test 2.

In addition, the content of the soil after the iron powders in Tables 18 and 19 were mixed was determined by the following formula.

Content of each fraction of soil after iron powder mixing [mg / kg] = (content of each fraction of treated soil × distribution of soil weight after treatment + content of each fraction of magnetite × weight distribution of magnetite) / (distribution of soil weight after treatment + (Magnetite weight distribution)

As shown in Table 16 and Table 17, the As dissolution test value of soil A is 0.028 mg / L, and if converted to the content, it is 0.28 mg / kg (the solid-liquid ratio of the dissolution test is soil: water = 1: 10 ).

As shown in Tables 18 and 19, regarding the soil before treatment, the total of the exchanged state and the carbonate-bound state was 0.27 mg / kg (Table 18) and 0.25 mg / kg (Table 19). Content conversion values are almost equivalent. Therefore, it can be seen that the water-soluble As of the soil before the treatment corresponds to the fraction in the exchanged state and the carbonate-bound state. It can be seen from the above description that when the total As content of soil A is about 2% of 12.3 mg / kg, the dissolvable As content is extremely small.

In addition, the value of each fraction of the soil before treatment was the largest in the residue state, and the other fractions were relatively small. From the viewpoint of soil purification, the content of As is based on 150 mg / kg of As content and 0.01 mg of As is based on the amount of As dissolved. / mL, it can be seen that the soil A is a soil that satisfies the content criterion and exceeds the dissolution amount criterion. It is particularly important to remove the exchanged state and carbonate-bound state.

In any of the test results, exchange states and carbonate junctions were found after the iron powder was mixed. The reduction in the number of morphologies is apparent, but it can be seen that the method for detoxifying contaminated soil of the present invention significantly reduces the morphology. In addition, in the magnetite, in the method for detoxifying contaminated soil of the present invention, there is less As in the fractions that are fractionated into exchange-organic bound fractions and more As in the residue fractions. It can be said that As is more strongly adsorbed to iron powder.

Next, the As budget of each fraction in the test 1 is shown in Table 20, and the As budget of each fraction in the test 2 is shown in Table 21.

Next, based on the results of Tables 20 and 21, the ratios of revenues and expenditures of the pre-treatment soil, iron powder mixed soil, and post-treatment soil (purified soil) when the As budget of each fraction of the soil before the treatment was set to 1 were set. These are shown in Fig. 18 and Fig. 19 respectively.

Comparing FIG. 18 and FIG. 19, it can be seen that, in the test 1 (the method for detoxifying contaminated soil of the present invention), As in the exchange state to the organic binding state was significantly reduced and transferred to the residue state. In Experiment 2 (wet magnetic separation described in Japanese Patent Laid-Open No. 2000-51835), although the exchange state was reduced, each fraction changed from a carbonate-bound state to a residue state.

Therefore, it can be seen that the method for detoxifying contaminated soil of the present invention is more effective in terms of removing dissolvable pollutants in soil than the wet magnetic separation described in Japanese Patent Laid-Open No. 2000-51835, and it is more effective More stable morphology was obtained after treatment of the soil.

Claims (5)

A method for detoxifying contaminated soil, comprising: an iron powder adding step, adding iron to a contaminated soil containing at least one pollutant selected from the group consisting of arsenic, lead, hexavalent chromium, cadmium, selenium, mercury, cyanide, fluorine, and boron Powder; a moisture content adjustment step to adjust the moisture content of the contaminated soil before magnetic separation to 36% by mass or less; a dry magnetic separation step to recover and remove iron powder from the contaminated soil treated by the moisture content adjustment step by the dry magnetic separation. The method for detoxifying contaminated soil as described in item 1 of the scope of the patent application, wherein the contaminated soil is added with iron powder of 0.05% by mass or more and 10% by mass or less. The method for detoxifying contaminated soil according to item 1 of the scope of patent application, wherein the moisture content of the contaminated soil before iron powder is added is 60% by mass or less. The method for detoxifying contaminated soil according to item 1 of the scope of the patent application, wherein in the iron powder adding step, any one of sulfuric acid and hydrochloric acid is added. The method for detoxifying contaminated soil according to any one of claims 1 to 4, wherein the contaminated soil is contaminated soil containing a contaminated substance from nature.