TW201545796A - Method for detoxifying polluted soil - Google Patents

Abstract

The invention is a method for detoxification of contaminated soil, including: an iron powder addition step, in which iron powder is added to contaminated soil that contains at least one contaminant selected from arsenic, lead, hexavalent chromium, cadmium, selenium, mercury, cyan, fluorine and boron; a water content adjustment step, in which a water content of the contaminated soil prior to magnetic separation is adjusted to 36% by mass or less; and a dry magnetic separation step, in which the iron powder is recovered and removed from the contaminated soil that has the water content of 36% by mass or less by dry magnetic separation.

Description

Detoxification method for contaminated soil

The present invention relates to a detoxification method for contaminated soil.

In recent years, with the economic recovery, the construction of tunnel construction or redevelopment has increased. The assurance of the dumping field of the remaining soil that comes with it becomes a problem. The remaining soil also includes contaminated soil due to natural pollutants represented by arsenic, and a countermeasure is a problem. As a characteristic of the contaminated soil, the content of the pollutant is relatively small compared with the content standard defined by the soil pollution countermeasure method, and on the other hand, there is a tendency that the amount of dissolution exceeds several times to several tens of times.

It is reported that in the vicinity of the place where the contaminated soil is produced, for example, in the road body during road construction, a water-blocking sheet is provided or a water-blocking facility is provided by concrete or the like, and the facility is directly landfilled with contaminated soil for management. The method (refer to the Handbook for the Handling of Soils and Soils containing natural heavy metals in construction (2010): "Handbook for the treatment of rocks and soils containing heavy metals from nature (tentative version)"). However, in the 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 an installation place and to obtain an understanding of the surrounding residents. Moreover, the following problems arise: Contamination from the temporary field of contaminated soil infiltration, resulting in surrounding groundwater pollution.

In addition, it is described that a method of solving the problem is based on the "Guidelines for Investigation and Measures Based on the Soil Pollution Control Law (Revised 2nd Edition)" (2012.8) by mixing various insolubilizers in contaminated soils to incinerate pollutants. : Environment and Water Conservation. Department of Soil and Environmental Engineering, Atmospheric Environment Bureau, and Japanese Patent Laid-Open Publication No. 2003-290757. In the same manner as the above-described blocking measures, the insoluble soil is treated as a soil that must be continuously managed, and it is prescribed in the soil pollution countermeasure method that the site is managed to ensure that the insoluble soil is returned.

In addition, it is reported that there is a method of treating contaminated soil as a cement raw material, and a method of landfill disposal in a management type disposal site (refer to "Guidelines for Investigations and Measures Based on Soil Pollution Countermeasures (Revised 2nd Edition)" ( 2012.8): Environmental Water Conservation. Department of Soil and Environment, Atmospheric Environment Bureau). However, in the reported method, the current situation is that the processing power or capacity cannot keep up with the amount generated.

As a method of detoxifying the contaminated soil to obtain purified soil, a method of performing washing and grading treatment is reported (refer to "Remediation of Heavy Metal Contaminated Soil Based on Soil Cleaning Method": Resources. Raw Material Volume: 2000: Page 117 - Page 120 (2010)). However, since the reported method is a wet process, it is necessary to increase the capacity of the apparatus for performing slurrying and the dewatering equipment, and it is difficult to carry out a simple and large-scale treatment at a low cost.

In addition, a method of concentrating a contaminant into a magnetic substance using at least one of a wet magnetic separator and a dry magnetic separator is proposed (see Japanese Patent Laid-Open No. Hei 10-71387). However, the proposed method is to reduce pollutants For the purpose of the amount of the substance, there is a problem that the ability to remove the eluting pollutants is insufficient.

In addition, it is proposed to remove the iron powder adsorbed by the magnetic material by adding iron powder to the contaminated soil slurry and adsorbing the pollutants, thereby obtaining a method for purifying the soil (refer to Japanese Patent Laid-Open No. 2000-51835). Bulletin). In the proposal, the eluting contaminant can also be removed. However, since the proposed method is a wet process, it is necessary to increase the capacity of a device and a dewatering device that use a large amount of water for slurrying, and it is difficult to carry out a simple and large-scale process at a low cost.

Therefore, it is desirable to provide a detoxification method in which contaminated soil can be easily and efficiently utilized to make contaminated soil for purifying soil by dry treatment without using a large amount of water.

An object of the present invention is to solve the above problems and achieve the following objects. That is, an object of the present invention is to provide a detoxification method which can easily and efficiently utilize contaminated soil to make contaminated soil for purifying soil by using a large amount of water without using a large amount of water.

As a method for solving the above problem, it is as follows. which is,

<1> A method for detoxifying contaminated soil, characterized by comprising: an iron powder addition step of contaminating at least one pollutant selected from the group consisting of arsenic, lead, hexavalent chromium, cadmium, selenium, mercury, cyanide, fluorine, and boron Adding iron powder to the soil; adjusting the moisture content to adjust the moisture content of the contaminated soil before magnetic separation to 36% by mass or less; In the dry magnetic separation step, iron powder is recovered by dry magnetic separation from contaminated soil having a moisture content of 36% by mass or less.

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

The detoxification method of the contaminated soil as described in any one of <1> to <2>, wherein the water content of the contaminated soil before the addition of the iron powder is 60% by mass or less.

The detoxification method of the contaminated soil as described in any one of <1> to <3> which added the sulfuric acid and hydrochloric acid in the iron powder addition step.

<5> The detoxification method of the contaminated soil according to any one of <1> to <4> wherein the contaminated soil is a contaminated soil containing contaminants derived from nature.

According to the present invention, the prior problems can be solved, and a detoxification method which can easily and efficiently utilize the treated soil to make contaminated soil for purifying soil by dry treatment can be provided without using a large amount of water.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a flow chart showing the detoxification method of the contaminated soil of the present invention.

2 is a flow chart of the apparatus for detoxifying a contaminated soil of the present invention.

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

Figure 4 is a graph showing the moisture content before magnetic separation and the recovery rate of magnetic material in soil A and The relationship between the recovery rate of As [a)], the relationship between the moisture content before magnetic separation and the amount of As dissolved [b)].

Fig. 5 is a graph showing the relationship between the moisture content before magnetic separation in the soil B and the recovery rate of the magnetic material and the F recovery rate [a)], and the relationship between the moisture content before magnetic separation and the amount of F elution [b).

Fig. 6 is a graph showing the relationship between the hardening time after the addition of iron powder in the soil A and the recovery rate of the magnetic material and the As recovery rate [a)], and the relationship between the hardening time after the addition of the iron powder and the amount of As dissolved [b)] Chart.

Fig. 7 is a graph showing the relationship between the hardening time after the addition of iron powder in the soil C and the recovery rate of the magnetic material and the Se recovery rate [a)], and the relationship between the hardening time after the addition of the iron powder and the amount of Se dissolved [b)] Chart.

Fig. 8 is a graph showing the relationship between the hardening time after the addition of iron powder in the soil D and the recovery rate of the magnetic material, the recovery rate of Pb and Cr [a)], the hardening time after the addition of the iron powder, and the amount of Pb and Cr ⁶⁺ eluted. The relationship [b)] of the chart.

Fig. 9 is a graph showing the relationship [a)] between the amount of iron powder added in the soil A and the recovery rate of the magnetic material and the As recovery rate, and the relationship between the amount of iron powder added and the amount of eluted As [b).

Fig. 10 is a graph showing the relationship [a)] between the amount of iron powder added in the soil C and the recovery rate of the magnetic material and the Se recovery rate, and the relationship between the amount of the iron powder added and the amount of Se eluted [b).

Fig. 11 is a graph showing the relationship between the amount of iron powder added in the soil D and the recovery rate of the magnetic material and the Pb and Cr recovery rate [a)], the relationship between the amount of iron powder added and the amount of Pb and Cr elution [b)]. .

Figure 12 is a graph showing the amount of sulfuric acid added in the soil A and the recovery of the magnetic material and As The relationship between the recovery rate [a)], the relationship between the amount of acid added and the amount of As dissolved [b)].

FIG. 13 is a graph showing the relationship [a)] between the amount of sulfuric acid added in the soil C, the recovery rate of the magnetic material, and the Se recovery rate, and the relationship between the amount of acid added and the amount of Se dissolved [b).

Fig. 14 is a graph showing the relationship between the amount of acid added in the soil D and the recovery rate of the magnetic material, the relationship between the Pb and the Cr recovery rate [a)], the relationship between the amount of acid added and the amount of Pb and Cr ⁶⁺ elution [b)]. .

Fig. 15 is a graph showing the relationship between the moisture content before magnetic separation and the mass of magnetic material recovered.

16 is a photograph showing a difference in soil properties due to a change in moisture content of contaminated soil before magnetic separation in Example 6, Example 8, Example 11, and Comparative Example 1. FIG.

Figure 17 is a flow chart of the five-stage sequential extraction.

Fig. 18 is a graph showing changes in the ratio of the balance of the soil and the soil after the treatment of the soil before the treatment in the test 1.

Fig. 19 is a graph showing changes in the ratio of the balance of the soil and the treated soil after the treatment of the soil and the iron powder before the treatment in the test 2.

(Detoxification method for contaminated soil)

The detoxification method of the contaminated soil of the present invention includes an iron powder addition step, a moisture content adjustment step, and a dry magnetic separation step, and further includes other steps as needed.

<Iron powder addition step>

The iron powder addition step is a step of adding iron powder to 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 by various constructions such as road construction, tunnel construction, and redevelopment, and refers to soil containing the pollutants from nature.

Examples of the contaminant include arsenic (As), lead (Pb), hexavalent chromium (Cr(VI)), cadmium (Cd), selenium (Se), mercury (Hg), and cyanide (CN). Fluorine (F), boron (B), and the like. The pollutants are substances derived from nature and present in rocks or soils in the target substance of the environmental pollution of the soil.

The moisture content of the contaminated soil before the addition of the iron powder is preferably 60% by mass or less, more preferably 0% by mass or more and 45% by mass or less, and particularly preferably 10% by mass or more and 35% by mass or less. In the range of the moisture content of the contaminated soil, the water content adjustment in the water content adjustment step described later is small (may be omitted), and depending on the soil quality, it is also advantageous in terms of transportability. A state in which it can be transported without liquid, such as a dump truck.

The amount of the iron powder added 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 based on the contaminated soil. In the range of the amount of the iron powder added, the pollutants can be recovered and recovered efficiently by dry magnetic separation.

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

It is preferred to add an acid while the iron powder is added to the contaminated soil. The acid is added to promote the movement of the contaminant.

As the acid, any of hydrochloric acid and sulfuric acid is preferred.

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 based on the contaminated soil.

The pH of the contaminated soil after the acid treatment is preferably from 4.0 to 9.0, more preferably from 6.0 to 8.0. When the pH is in the above range, the contaminant does not become soluble and is safe. Further, when the treated soil is made into purified soil, since the usual soil is in a neutral region, the pH range is also preferable.

Further, when the acid is used, it is preferred not to carry out dilution by water in order to carry out the moisture content adjusting step thereafter. The reason is that any one of the amount of the dehydrating agent added, the drying time, and the drying temperature which are required for the adjustment of the moisture content must be increased.

At least one of the iron powder and the acid is put into the mixer and thoroughly kneaded in the excavated contaminated soil having the moisture content before the iron powder is added. At this time, when entering the coarse gravel or the like in the contaminated soil, since the kneading is hindered, it is preferable to perform pretreatment such as sieving and pulverization in advance.

The kneading method is not particularly limited, and may be appropriately selected according to the purpose. When considering the subdividing effect of the agglomerates, the shear mixer is preferable to the striking mixer. As the shear mixer, for example, a biaxial stirring mixer or the like can be mentioned.

<Moisture content adjustment step>

The moisture content adjustment step is to adjust the moisture content of the contaminated soil before the magnetic separation The whole step is 36% by mass or less.

In addition, when the moisture content of the contaminated soil before the magnetic separation is 36% by mass or less, the dry magnetic separation step described later 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. When the moisture content of the contaminated soil before the magnetic separation is 36% by mass or less, the agglomerates are substantially changed into soil particle monomers, and the magnetic separation is easy, and the 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 mass w1), drying the contaminated soil using a drying oven or the like, and then measuring the soil quality (dry soil mass w2), and calculating according to the following formula.

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

The method of adjusting the moisture content in the moisture content adjusting step is not particularly limited, and may be appropriately selected depending on the purpose, and examples thereof include a method of adding a moisture absorbent, and drying using a dryer.

The moisture-absorbing agent is not particularly limited, and materials such as quicklime or cement are generally considered. However, since the material is a strong alkaline material, it is necessary to control the pH range, and thus it is more preferably a neutral curing material.

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 economy, it is preferred to use calcined gypsum as a main component. s material.

In addition, when the moisture content of the contaminated soil after the addition of the iron powder is 36% by mass or less, the agglomerates are not formed, and the state is subdivided, and the dry magnetic separation is not hindered, the addition of the moisture absorbent may be omitted.

The dryer to be used for the drying is not particularly limited, and may be appropriately selected according to the purpose, and examples thereof include a biaxial kneading drying furnace, a rotary dryer, and a tunnel furnace. In the dryer, in terms of the effect of subdividing the pellets, a biaxial kneading drying oven and a rotary dryer are preferred.

<Dry magnetic separation step>

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

Here, as shown in Fig. 15, the range of the magnetically-selected iron powder from the contaminated soil may exist, and there are two regions depending on the moisture content of the contaminated soil before the magnetic separation.

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

The detoxification method of the contaminated soil of the present invention performs dry magnetic separation in the low moisture content region.

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

The moisture content of the contaminated soil before magnetic separation is 38% by mass or more and 43% by mass. The lower range is a region in which the separation efficiency of each of the dry magnetic separation and the wet magnetic separation is significantly inferior (magnetically difficult region).

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

The purpose of the dry magnetic separation step is to reduce the amount of harmful substances eluted by the magnetic material by separating and removing the iron powder to which the pollutant is adsorbed, and to sufficiently separate and recover the magnetic force by 1,500 G or more and 7,000 G or less. . If it is a magnetic force higher than the magnetic force, the weak magnetic soil particles previously present in the contaminated soil are also recovered, and the amount of the magnetic material is increased. The magnetaceous material must be disposed of as another contaminated concentrated soil, so it is not economical to unnecessarily recycle it in large quantities.

Here, Fig. 1 is a flow chart of a detoxification method of the contaminated soil of the present invention.

First, at least one of iron powder and acid is put into a mixer for thorough mixing in the contaminated soil that has been excavated. At this time, when coarse gravel or the like enters the contaminated soil, the mixing may be hindered. Therefore, it is preferred to perform pretreatment such as sieving and pulverization in advance.

Then, iron powder is added to the specified amount of contaminated soil (iron powder addition step). After adding the iron powder and the contaminated soil containing the acid according to the need for curing for 0 minutes or longer, preferably for about 10 minutes, the neutral solidified material as a moisture absorbent is added as needed. The water content of the contaminated soil before the magnetic separation is adjusted to 36% by mass or less (moisture content adjustment step), and the water content of the contaminated soil before the magnetic separation is adjusted to be sufficiently mixed with the mixture of 0 kg or more and 200 kg or less.

Then, the iron powder to which the pollutant is adsorbed is recovered by dry magnetic separation using a magnetic force of 1,500 G or more and 7,000 G or less (dry magnetic separation step).

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

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

[Examples]

Hereinafter, the embodiments of the present invention will be described, but the present invention is not limited to the examples.

<sample used for the test>

Five soils A to soil E shown in Table 1 below were used as samples. In addition, soil D is artificially polluted soil, and other soils are naturally polluted.

(Example 1 to Example 11 and Comparative Example 1)

- the effect of moisture content -

Soil A and soil B were used to investigate the effects of moisture content.

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

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

Then, the soil is opened in the vat and thinly applied, and the surface magnetic force is applied. The 1,500 G magnet was scanned on the surface of the soil, and the magnetic particles and non-magnetic particles (purified soil) were magnetically separated to analyze the content of pollutants in the soil (for soil A according to the substrate). The investigation method, the soil B according to the Ministry of the Environment, No. 19), and the analysis of the amount of dissolution for the non-magnetic particles (Environmental Protection Notice No. 18).

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

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

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

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

<Test results of soil A>

<Test results of soil B>

By applying the detoxification method of the contaminated soil of the present invention, and any of the soil A and the soil B, regardless of the moisture content before the magnetic separation in the range of the test, the amount of the pollutant dissolved in the purified soil is higher than that before the treatment. reduce.

For soil A, if the moisture content of the contaminated soil before the addition of iron powder is 10 mass Below %, no agglomerates are formed and magnetic separation is relatively easy without the need to add a neutral curing material. When the moisture content of the contaminated soil before the addition of the iron powder is 20% by mass or more, since the contaminated soil forms agglomerates, it is necessary to add a neutral solidified material. When the moisture content before the addition of the iron powder is 30% by mass, although the contaminated soil before the magnetic separation is in a fluidized state, the 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.

In the case of the soil B, as in the case of the soil A, if the moisture content of the contaminated soil before the addition of the iron powder 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 before the addition of the iron powder is 34.8% by mass or more, it is necessary to add a neutral solid material. When the moisture content before the addition of the iron powder was 41.7% by mass, a 15% by mass of a neutral solidified material was added to form a pellet which was magnetically separable, but the moisture content before magnetic separation at this time was 35.5% by mass. When the moisture content before the addition of the iron powder was 41.7% by mass and the neutral solidified material was not added, magnetic separation could not be performed (Comparative Example 1).

Figure 4 shows the relationship between the moisture content before magnetic separation in the soil A and the recovery of the magnetic material and the As recovery rate [a)], the relationship between the moisture content before magnetic separation and the amount of As dissolved [b)]. Fig. 5 is a graph showing the relationship between the moisture content before magnetic separation in the soil B and the recovery rate of the magnetic material and the F recovery rate [a)], the relationship between the moisture content before magnetic separation and the amount of F elution [b)].

According to the results of FIG. 4 and FIG. 5, as the moisture content before the magnetic separation increases, the amount of magnetic material recovered and the amount of pollutants recovered tend to increase. The reason is considered to be that if the moisture content is increased, the agglomerates of the soil particles are slightly increased. On the other hand, regarding the elution amount, if the moisture content before magnetic separation increases, the amount of elution tends to decrease. Think that the reason is If the moisture content is large before magnetic separation, the adsorption of As on the iron powder is easy to proceed. In addition, it can be seen that in the range of the moisture content before any of the magnetic separation ranges in the range of the test, the elution amount of the pollutants is sufficiently lowered, which is effective.

(Examples 12 to 39)

<Effect of hardening time after iron powder addition, amount of iron powder added and amount of acid added>

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

100 g of each soil sample was weighed into a polypropylene cup, and any amount of the reduced iron powder as in Example 1 was added, and any amount of concentrated sulfuric acid was added thereto, and the mixture was mixed for 1 minute. After being hardened at any time, 10 g of a neutral solid material (Gypsander C, manufactured by Ishihara Sangyo Co., Ltd.) containing gypsum as a main component was added, and the mixture was mixed for about 1 minute. Then, the soil is opened in a cylinder and thinly applied, and magnetic particles of magnetic particles having a surface magnetic force of 1,500 G are used to magnetically separate magnetic particles and non-magnetic particles (purified soil) to perform soil contamination. Material content analysis (primary quality investigation method), and analysis of dissolution amount for non-magnetic materials (Environmental Protection Notice No. 18). The results of soil A, soil C, and soil D are shown in Tables 4 to 6 and Figures 6 to 14, respectively.

<Results of soil A>

<Results of soil C>

<Results of soil D>

<Impact of hardening time after iron powder addition>

According to the results of Tables 4 to 6, in the range of the test, in any of the soils, no correlation was found between the magnetic recovery rate, the pollutant recovery rate, and the amount of the pollutants eluted in the hardening time after the addition of the iron powder. From this, it is understood that it is sufficient that the iron powder mixing time is about 1 minute.

<Impact of iron powder addition amount>

According to the results of Tables 4 to 6, in the range of the test, in any soil, as the amount of iron powder added increased, the recovery rate of the magnetic material and the recovery rate of the pollutants were found to increase. Further, regarding the amount of the pollutants eluted, in addition to Cr ⁶⁺ in the soil D, the amount of the iron powder added tends to decrease as the amount of the iron powder added increases. Further, at any of the levels, it was judged that the amount of elution before the treatment was greatly reduced, and the effect of removing the eluted component was obtained. In the range of the test, the minimum amount of iron powder added was 0.05% by mass in the soil A, but it was found to be sufficiently reduced in the amount of the iron powder added.

<Impact of acid addition amount>

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 pollutant recovery rate in any of the soils. In addition, in addition to the soil D, no correlation was found between the amount of pollutants eluted relative to the amount of acid added. In soil D, as the amount of acid added increased, the amount of Pb dissolved showed a slight increase tendency, and Cr ⁶⁺ showed a slight tendency to decrease, but at any level, the amount of dissolution was greatly reduced for the amount of dissolution before treatment. .

In addition, in any soil, when the amount of acid added is 0N/kg, it can be fully removed. When the degraded contaminated component is removed, if it is considered to have an economic effect, it is considered that it is not necessary to add an acid.

(Comparative Example 2)

<The case where the moisture content is not adjusted>

The soil B having a moisture content adjusted to 41.3% by mass before the addition of the iron powder was used, and the same as in Example 1, except that the neutral solidified material was not used and the moisture content was not adjusted (the moisture content before magnetic separation was 41.3 mass%). Way, try magnetic separation. As a result, the soil has high viscosity and large aggregates, so magnetic materials cannot be obtained. Then, using a magnet having a surface magnetic force of 12,000 G, magnetic separation was attempted, and as a result, all of the soil adhered to the magnet, and separation of the magnetic material from the non-magnetic material could not be performed.

(Examples 40 to 42)

<Comparison of magnetic separation by different iron powders>

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

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

Then, the soil is opened in the cylinder and thinly applied, using the surface magnetic force. 7,000G magnet magnetically separates magnetic particles from non-magnetic particles (purified soil) to measure the content of pollutants in the soil (substrate investigation method) and the amount of dissolved matter on 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 test was carried out by using different iron powders. As a result, with respect to the magnetic material recovery rate and the Se recovery rate, the reduced iron powder was the highest, followed by the swarf powder and the atomized powder. The difference in the recovery rate of the magnetic material is considered to be due to the fact that the particle size of the reduced iron powder is relatively fine to form agglomerates, and the Se recovery rate is increased due to the large amount of attached soil. On the other hand, if the amount of elution of the non-magnetic material is compared, it is slightly different.

(Comparative Example 3 to Comparative Example 4)

- a result of magnetic separation only without adding iron powder (method described in Japanese Patent Laid-Open No. Hei 10-71837) -

For the air-dried soil A and the soil samples used in Examples 40 to 42, 100 g of each of the soil samples were thinly applied in a cylinder, and magnets of magnets having a surface magnetic force of 7,000 G were used to magnetize the particles and non-magnetic particles. Magnetic particles (purified soil) for magnetic Sexual separation, respectively, the analysis of the content of pollutants in the soil (the sedimentation method), and the analysis of the dissolution of the non-magnetic materials (Environmental Protection Notice No. 18). The results are shown in Tables 8 and 9.

<Magnetic selection results of soil A>

<Magnetic selection results of soil samples used in Examples 40 to 42>

According to the results of Table 8 and Table 9, as a result of the magnetic separation of the soil A, 10.4% by mass of the magnetic material was obtained, and As was recoverable by 10.3% by mass, but the decrease in the amount of eluted As was not observed. From this, it was judged that the eluted As was adsorbed to the iron powder and recovered. On the other hand, in the soil samples used in Examples 40 to 42, almost no magnetic material separated by magnetic separation was obtained. It can be seen that, with Japanese Patent Laid-Open No. 10-71837 Compared with the method described in the publication, the detoxification method of the contaminated soil of the present invention has an effect of recovering and removing the eluted pollutant.

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

<Comparative Example 5>

The amount 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 measured to be 1.0 L wide. In the Poly Bottle, 1 g of the reduced iron powder, 400 mL of ion-exchanged water, and 0.5 mL of concentrated sulfuric acid were added and sealed, and the mixture was shaken by a shaker at 200 reciprocating/min for 30 minutes to contaminate Se. Soil slurrying.

After shaking, the slurry in the Polaroid bottle was opened in a polypropylene cylinder, and a magnetic field of 0.7 T was scanned in the slurry to separate the magnetic material. Further, when the slurry was transferred to another container or the like, 100 mL of ion-exchanged water was used in order to recover the adhered soil particles.

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

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

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

. Content before iron powder addition (mg/kg) = (soil content after treatment × soil weight distribution after treatment + magnetic content × magnetic weight distribution) / (post soil weight distribution + magnetic weight distribution after treatment)

. Contaminant balance in magnetic material (%) = (magnetic content × magnetic 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>

The detoxification method (dry magnetic separation) of the contaminated soil of the present invention was carried out using the contaminated soil of Example 40.

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

The magnet used is 0.15T (1,500 Gauss)

According to the results of Table 10, the treated soil (non-magnetic material) was reduced to the same extent as in 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 having a large water content, the Se balance in the magnetic material was significantly lower than that in Example 43 of Table 11, and Se was distributed in the treated water, and the obtained table was obtained. Example 43 of 11 has different results. From this, it is understood that when the Se-contaminated soil is subjected to wet magnetic separation, it is seen that Se is transferred to the treated water, and the amount of Se which can be recovered as the magnetic material is reduced as compared with the case of performing dry magnetic separation.

In other words, according to the results of Tables 10 and 11, it is found that in the soil C, the amount of Se eluted in the soil after the treatment was the same as that of the comparative example 5, but the Se revenue in the magnetic material was compared with the comparative example. Compared with the wet magnetic separation of 5, in the detoxification method of the contaminated soil of Example 43, the Se balance in the magnetic material is greatly increased, and the transfer of Se to the magnetic material is greatly increased (the mass of the Se material recoverable is much larger) ) (0.2% vs. 23.4%).

Further, in the above comparative experiment, the embodiment of the present invention performs dry magnetic separation with a magnetic force of about 1/5 as compared with the wet magnetic separation treatment described in Japanese Laid-Open Patent Publication No. 2000-51835, The magnetic force is processed, of course, foreseeable A more significant increase in the amount of magnetic charge and an inhibitory effect on the amount of dissolution.

Further, the Se content of the treated water of Comparative Example 5 was 0.022 mg/kg, and since it exceeded the environmental standard, it was necessary to additionally treat the wastewater.

Then, in the soil samples described in Table 1, soil A (As contaminated soil) and soil B (F contaminated soil) were used, and the same test as in Comparative Example 5 was carried out.

(Results of soil A)

<Comparative Example 6>

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

The magnet used is 0.7T (7,000 Gauss)

<Example 44>

The detoxification method (dry magnetic separation) of the contaminated soil of the present invention was carried out using the contaminated soil of Example 4.

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

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 eluted in the soil after the treatment was considerably lower than that in Comparative Example 6 (0.002 mg/L vs. 0.00001 mg/L). In addition, as for the As balance in the magnetic material, as in Comparative Example 6, the As balance in the magnetic material in Example 44 becomes large, and the transfer of As to the magnetic material is large (Recoverable As substance) A large amount) (6.2% vs. 15.8%).

(Results of soil B)

<Comparative Example 7>

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

The magnet used is 0.7T (7,000 Gauss)

<Example 45>

The detoxification method (dry magnetic separation) of the contaminated soil of the present invention was carried out using the contaminated soil of Example 10.

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

The magnet used is 0.15T (1,500 Gauss)

From the results of Tables 14 and 15, it can be seen that in the soil B, the amount of F eluted in the soil after the treatment was the same as that of the comparative example 7, but the F balance in the magnetic body was compared with that of the comparative example 7. In contrast, in Example 45, the F-retraction in the magnetic material became large, and the transfer of F to the magnetic material was large (the mass of the recoverable F-mass was large) (7.0% vs. 10.8%).

Further, the results of the experiment when the magnetic separation treatment 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 shown in Table 1, 100 g of soil A (As contaminated soil) was taken into a cup made of polypropylene, and 1 g of reduced iron powder (special iron powder E200, manufactured by DOWAIP Co., Ltd.) and concentrated sulfuric acid were added. 0.1mL, mixed with a spoon 1 minute. After hardening for 10 minutes, 10 g of a neutral solidified material was added and mixed for about 1 minute.

Then, the soil is opened in the cylinder and thinly applied, and a magnet having a surface magnetic force of 7,000 G is scanned on the surface of the applied soil to magnetically magnetize the magnetic particles and the non-magnetic particles (purified soil). Separate to obtain non-magnetic objects (treated soil) and magnetic objects.

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

[Test Method 2 (Comparative Example of Wet Magnetic Separation as described in JP-A-2000-51835)]

In the soil samples shown in Table 1, the same test as in Comparative Example 5 was carried out for soil A (As contaminated soil) as described below.

The amount of soil 100g was taken into a 1.0L wide-mouth bottle, and the reduced iron powder (special iron powder E200, manufactured by DOWAIP Manufacturing Co., Ltd.), ion-exchanged water 400mL, and concentrated sulfuric acid 0.5mL were added for sealing. The oscillation was carried out for 30 minutes at 200 reciprocating/min.

After the shaking, the slurry in the bottle was opened in a polypropylene cylinder, and a magnetic field of 0.7 T (7,000 gauss) was scanned in the slurry to separate the magnet. Further, when the slurry was transferred to another container or the like, 100 mL of ion-exchanged water was used in order to recover the adhered soil particles.

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

[Analysis of As Chemical Forms for Treatment of Soil]

The soil A before treatment, the test 1, and the products obtained in the test 2 were respectively subjected to a five-stage sequential extraction method (refer to A. Tessil, PGC Campbell, and M. Bissen, "The mark Steps for sequential extraction of species of metal particles", 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).)) Chemical morphology analysis, and confirmed the morphology of As in each product. The extraction process is shown in Fig. 17.

According to the chemical morphological analysis, the As fraction in the soil is divided into exchange state, carbonate bound state, and iron. Five fractionation of manganese bound state, organic bound state, and residual state. Since the extraction solvent is gradually increased in acidity and oxidizing property, it indicates that it is easily dissolved in water in the exchange state, and is the most difficult to dissolve in water in the residue state.

[Test result 1 Material income and expenditure]

The results of the substance balance of the test 1 are shown in Table 16, and the results of the substance balance of the test 2 are shown in Table 17.

Table 16 shows the results of the test 1.

The magnet used is 0.7T (7,000 Gauss)

Table 17 shows the results of the test 1.

The magnet used is 0.7T (7,000 Gauss)

According to Tables 16 and 17, it is understood that the test 1 is compared with the test 2, and the amount of As eluted in the soil after the treatment is compared with the wet magnetic separation described in JP-A-2000-51835. In the detoxification method of the contaminated soil, the value is as low as one digit (0.002 mg/L vs. 0.0002 mg/L), and the As balance in the magnetic material is described in Japanese Patent Laid-Open Publication No. 2000-51835. Compared with wet magnetic separation, in the detoxification method of the present application, the As revenue in the magnetic object becomes larger, The transfer of As to the magnetic material is much (the quality of the recoverable As is high) (6.4% vs. 17.9%).

[Test result 2 Chemical analysis results of As]

The results of chemical speciation analysis of each product in the test 1 are shown in Table 18, and the results of chemical speciation analysis of each product in the test 2 are shown in Table 19.

Further, the contents of the soil after mixing the iron powders in Tables 18 and 19 were obtained by the following formula.

The content of each fraction of the soil after iron powder mixing [mg/kg] = (the content of each fraction of soil after treatment × the weight distribution of soil after treatment + the content of each fraction of magnetic material × the weight distribution of magnetic material) / (the weight distribution of soil after treatment + Magnetic object weight distribution)

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

As shown in Tables 18 and 19, the total of the exchange state and the carbonate-bound state of the soil before treatment was 0.27 mg/kg (Table 18) and 0.25 mg/kg (Table 19), which was the amount of the dissolution. The content conversion value is almost the same value. Therefore, it is understood that the water-soluble As of the soil before the treatment corresponds to the fraction of the exchanged state and the carbonate-bound state. In the above case, when the total As content of the soil A is about 2% of 12.3 mg/kg, the elutive As is extremely small.

In addition, the value of each fraction of the soil before treatment is the largest, and the other fractions are relatively small. From the viewpoint of soil purification, the content of As is 150 mg/kg, and the amount of As is 0.01 mg. /mL, it can be seen that the soil A is a soil which satisfies the content standard and exceeds the basis of the dissolution amount, and it is particularly important to carry out the removal of the exchange state and the carbonate-bound state.

In any of the test results, exchanged and carbonated knots were found after mixing the iron powder. The decrease in the state of conformation is known, but it is known that the detoxification method of the contaminated soil of the present invention significantly reduces the morphology. Further, in the magnetic material, in the detoxification method of the contaminated soil of the present invention, the fraction fractionated into the exchange-organic-bound state is small, and the fraction of the fraction in the residual state is large, and it can be said that As is more strongly adsorbed to the iron. powder.

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

Then, according to the results of Tables 20 and 21, the ratio of the amount of the pre-treatment soil, the iron-mixed soil, and the treated soil (purified soil) when the As balance of each fraction of the soil before treatment is set to 1 These are shown in Fig. 18 and Fig. 19, respectively.

18 and FIG. 19, it is understood that in the test 1 (the detoxification method of the contaminated soil of the present invention), the As in the exchanged state to the organically bound state is remarkably reduced, and is transferred to the residue state. In the test 2 (wet magnetic separation described in JP-A-2000-51835), although the exchange state is reduced, the fraction from the carbonate-bound state is changed to the residue in the residue state.

Therefore, it is understood that the detoxification method of the contaminated soil of the present invention is more effective than the wet magnetic separation described in Japanese Laid-Open Patent Publication No. 2000-51835, in terms of the removal of the eluting contaminant in the soil, and A more stable morphology is obtained after treatment of the soil.

Claims (5)

A detoxification method for polluted soil, characterized by comprising: an iron powder addition step of adding iron to 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 moisture content adjusting step adjusts the moisture content of the contaminated soil before the magnetic separation to 36% by mass or less; and the dry magnetic separation step recovers the iron powder by dry magnetic separation from the contaminated soil having a moisture content of 36% by mass or less. The detoxification method of the contaminated soil according to the first aspect of the invention, wherein the iron powder is added in an amount of 0.05% by mass or more and 10% by mass or less to the contaminated soil. The detoxification method of the contaminated soil according to the first aspect of the patent application, wherein the moisture content of the contaminated soil before the addition of the iron powder is 60% by mass or less. The detoxification method of the contaminated soil according to claim 1, wherein in the iron powder addition step, any one of sulfuric acid and hydrochloric acid is added. A method for detoxifying contaminated soil as described in claims 1 to 4, wherein the contaminated soil is a contaminated soil containing contaminants from nature.