JP6118571B2 - Treatment method of contaminated soil - Google Patents

Description

  The present invention efficiently removes pollutants from soil, groundwater, river water, lake water, various industrial wastewater, etc. contaminated with pollutants such as arsenic, selenium, lead, cadmium and chromium heavy metals, fluorine and boron. The present invention relates to a method and a treating agent used therefor. In the present invention, “the heavy metals of arsenic, selenium, lead, cadmium and chromium” is intended to include simple metals, compounds (particularly oxides), salts and ions of arsenic, selenium, lead, cadmium and chromium. .

  Heavy metals such as arsenic, selenium, lead, cadmium and chromium, and pollutants such as fluorine and boron are harmful to the human body and cause health problems. Therefore, environmental pollution caused by these pollutants becomes a problem. Yes. Among these, heavy metals are contained in soil, groundwater, river water, lake water, various industrial wastewater, etc., and environmental standards and drainage standards are established. When the heavy metals in water exceed these water quality standards, it is necessary to remove these heavy metals from the water.

  As a method of continuously purifying water contaminated with these pollutants (hereinafter sometimes referred to as “polluted water”), various methods of adsorbing and removing pollutants using an adsorbent (adsorption method) Has been proposed. In this adsorption method, contaminated water containing contaminants is continuously passed through an adsorption tower filled with an adsorbent, and the contaminated water is brought into contact with the adsorbent to remove it by adsorption.

  Known adsorbents used in the above adsorption method include activated carbon, activated alumina, zeolite, titanic acid, zirconia hydrate and the like. In the method using these adsorbents, excellent removal efficiency can be achieved by selecting the type of adsorbent according to the type of contaminant, but since these adsorbents are generally expensive, their adsorption If the treatment is carried out with only the agent, there is a disadvantage that the treatment cost becomes high.

As a method for treating contaminated water, it is known to adsorb arsenic in water with iron powder, and various proposals have been made to improve the adsorption capacity of iron powder. For example, Patent Document 1 discloses iron powder whose surface is coated with iron hydroxide as an arsenic removing agent. Further, in Patent Documents 2 to 4, by using iron powder containing a predetermined amount of S, the iron anode reaction (Fe → Fe ²⁺ + 2e ⁻ ) is promoted by the addition of sulfur. As a result, heavy metals There has been proposed a method for improving the purification performance by a mechanism that promotes the reduction reaction or insolubilization reaction. Furthermore, Patent Document 5 also proposes a method of adsorbing and removing arsenic in water on acid-treated iron powder obtained by bringing iron powder into contact with an acidic solution.

  The development of these technologies has improved the ability of the adsorbent to remove heavy metals, but it is actually desired to develop a technology that exhibits even higher adsorption efficiency.

  By the way, in the method using an adsorbent, it is desirable that the water resistance to the packed bed of adsorbent is low in terms of equipment cost and operation efficiency. For these reasons, the adsorbent is not a fine powder but is often granulated to a particle diameter of a certain level or more.

  As a technique relating to the granulated adsorbent, for example, Patent Document 6 discloses, “Fibrous activated carbon, activated carbon obtained by molding a mixture of a fine particle inorganic compound having a heavy metal adsorption performance: 0.1 to 90 μm and a binder. "Molded bodies" have been proposed. In this technique, a fiber-bonded activated carbon and a fine particle inorganic compound are molded as a granulated product using microfibrillated fibers, heat-bonded fibers, heat-bonded resin powder or thermosetting resin powder as a binder.

  As another technique related to the granulated adsorbent, for example, a technique such as Patent Document 7 has been proposed. According to this technique, “a synthetic zeolite and activated carbon in which 10 mol% or more of the total exchangeable cation amount is replaced by magnesium ion and 60 mol% or more is replaced by magnesium ion and calcium ion, 2:98 to 50: It is referred to as a heavy metal removal agent in water containing at a weight ratio of 50 ”. In this technology, “synthetic zeolite is preferably a powdered synthetic zeolite molded with an appropriate binder and pulverized.” Or “activated carbon is made from coconut shell as a raw material and crushed. Is preferable. "

  On the other hand, a method of increasing the contact efficiency with contaminated water using a powdery adsorbent without granulation is also conceivable. However, when such a method is adopted, it is expected that the water flow resistance to the adsorbent packed bed will be excessive, and the equipment and operating costs will increase, so that treatment will be performed at a practical water flow rate. There may be another problem that becomes difficult.

  As contaminants other than heavy metals, fluorine is particularly mentioned, but it is also necessary to remove and purify fluorine from contaminated water and soil (hereinafter sometimes referred to as “contaminated soil”) contaminated by fluorine. For example, Patent Document 8 discloses a heavy metal-contaminated soil composed of a rare earth hydroxide formed by adding an aqueous solution of a rare earth salt containing cerium as a main component and an alkali and an inorganic ore to inorganic minerals. Insolubilizers "have been proposed. This technique insolubilizes heavy metals such as arsenic, chromium, lead, and boron, including fluorine. However, this technique uses expensive cerium, and an increase in processing cost is inevitable.

Patent Document 9 discloses that “a porous maghemite having a specific surface area measured by a nitrogen gas adsorption method of 50 m ² / g or more” as a treatment agent (recovery agent) for recovering environmental load components such as arsenic and fluorine. Has been proposed. However, this technique uses a porous compound, which inevitably increases manufacturing effort and cost.

JP 2006-272260 A JP 2006-312163 A JP 2008-043921 A JP 2009-082818 A JP 2008-207071 A JP 2003-334543 A JP 2004-912 A JP 2009-249554 A JP 2010-83719 A

  The present invention has been made paying attention to the circumstances as described above, and its purpose is to use heavy metals selected from arsenic, selenium, lead, cadmium and chromium from contaminated water and soil, fluorine, boron A treatment agent capable of exhibiting high removal efficiency and satisfying required characteristics such as practical equipment scale, water flow conditions and long-term durability, and such a treatment agent. It is to provide a useful processing method used.

  The treatment agent of the present invention capable of achieving the above-mentioned object includes at least one heavy metal selected from arsenic, selenium, lead, cadmium and chromium, and / or from contaminated water or soil containing fluorine. It is a treatment agent for removing heavy metals and / or fluorine, and has a gist in that iron powder and metal chloride coexist. Examples of the “metal chloride” used in the present invention include ferrous chloride, ferric chloride, magnesium chloride, tin chloride, manganese chloride, zinc chloride, copper chloride, nickel chloride and the like. Of these, at least one selected from the group consisting of ferrous chloride, ferric chloride, tin chloride and manganese chloride is preferable.

  Further, in addition to the heavy metals and / or fluorine, from at least one heavy metal selected from arsenic, selenium, lead, cadmium and chromium and / or contaminated water or soil containing boron in addition to fluorine When removing boron, a treatment agent in which at least one of slaked lime and quicklime and aluminum sulfate is coexisted in addition to iron powder and metal chloride may be used.

  In the treatment agent of the present invention, (a) the iron powder is produced by the atomizing method, (b) the iron powder contains sulfur, and (c) (b), the sulfur content is 0. Those satisfying the requirements such as .6 to 5% by mass are preferable.

  Using the treatment agent as described above, contamination is caused by bringing the treatment agent into contact with contaminated water containing at least one heavy metal selected from arsenic, selenium, lead, cadmium and chromium and / or fluorine. It can effectively remove heavy metals and fluorine in water.

  In addition, the heavy metal or fluorine in the contaminated soil is brought into contact with the contaminated soil containing at least one heavy metal selected from arsenic, selenium, lead, cadmium and chromium and / or fluorine and the treatment agent. Can be effectively removed.

  When contaminated water or contaminated soil contains boron in addition to heavy metals and fluorine, contact treatment with iron powder and metal chloride as well as at least one of slaked lime and quicklime and aluminum sulfate. As a result, boron can be effectively removed together with heavy metals and fluorine in the contaminated water.

  According to the present invention, heavy metal such as arsenic, selenium, lead, cadmium and chromium and fluorine are efficiently removed from contaminated water and contaminated soil by using iron powder and a metal chloride as a treatment agent. If necessary, arsenic, selenium, lead, cadmium and arsenic, selenium, lead, cadmium Boron can be removed together with chromium heavy metals and fluorine.

  The treating agent of the present invention has a basic gist in that a metal chloride coexists with iron powder. The type of iron powder used as a raw material for the treatment agent in the present invention is not particularly limited, and any industrially available iron powder can be used. Examples of the iron powder include atomized iron powder, cast iron powder and sponge iron powder, and these iron-based complete alloy powders (prealloy alloy powders) or partial alloys (premix alloy powders). Among these, the atomized iron powder manufactured by the atomization method is preferable from the viewpoint that mass production is possible and the components and particle sizes can be uniformed.

  The iron powder used in the present invention has a larger surface area (specific surface area) as its particle size (average particle size) is smaller, and it is represented by contaminants such as heavy metals and fluorine (hereinafter referred to as “heavy metals”). The removal performance of (some) increases. On the other hand, the larger the particle size of the iron powder, the higher the yield and the easier the handling, but the lower the removal rate of heavy metals. For these reasons, the preferable average particle diameter of the raw iron powder is 1000 μm or less (more preferably 100 μm or less). In the present invention, the “average particle diameter of iron powder” means the percentage of particle size distribution obtained by a dry sieving test using a sieve (screen) specified in JIS Z 8801, or the percentage under the cumulative sieve. Means a particle diameter of 50 mass%.

  It is also useful that the iron powder used as a raw material for the treatment agent in the present invention contains sulfur (S) as necessary. By including sulfur in the iron powder, it is possible to further improve the performance of removing heavy metals such as arsenic and selenium from contaminated water and contaminated soil. That is, it has been found that the performance of removing heavy metals such as selenium from contaminated water is improved by containing a predetermined amount of S in the iron powder, and its technical significance has been recognized. (Japanese Unexamined Patent Application Publication Nos. 2006-312163, 2008-143921, and 2009-82818). By using such iron powder as a raw material for the treatment agent, the removal performance of the treatment agent to heavy metals is improved.

  In removing heavy metals, the sulfur content in the raw iron powder is preferably 0.6% by mass or more. The sulfur content is more preferably 0.7% by mass or more, and still more preferably 0.8% by mass or more.

  On the other hand, the higher the sulfur content in the iron powder, the better the removal performance of heavy metals in the iron powder. However, if the sulfur content is excessively increased, the iron metal inherent heavy metal adsorption activity may be inhibited. Moreover, it leads to the cost increase by an unnecessary care agent more than necessary. For these reasons, the sulfur content in the iron powder is preferably 5% by mass or less (more preferably 4% by mass or less, and still more preferably 3% by mass or less).

The reason why the removal performance of heavy metals is improved by adding sulfur to the iron powder is that the oxidation of the iron powder surface is promoted by the action of sulfur contained in the iron powder (iron anode reaction: Fe → Fe ²⁺ + 2e ⁻ ), iron ions that are efficiently generated on the surface of the iron powder, and heavy metals that exist in the form of metal ions and compound ions in contaminated water and soil due to rapidly growing iron oxides and hydroxides It is considered that the adsorption of the metal to the iron powder is promoted, and the removal of heavy metals proceeds efficiently accordingly.

  The inventors further studied to further improve the performance of the treatment agent. As a result, if iron chloride or iron powder containing sulfur (sulfur-containing iron powder) coexists with metal chloride, the removal performance for heavy metals in contaminated water or soil will be significantly improved. The present invention was completed.

The basic presumed mechanism by which each heavy metal is adsorbed on iron can be considered as follows. First, arsenic and selenium are dissolved in water in the form of arsenate ions (AsO ₄ ³⁻ ) and selenate ions (SeO ₄ ²⁻ ). In order to remove these arsenate ions and selenate ions, these ions may be reacted with iron ions to form a compound. And iron ion can be efficiently discharge | released in water by using iron powder or sulfur containing iron powder. As a result, insoluble iron arsenate or iron selenate (arsenic acid or a compound of selenate and iron) is precipitated on the surface of the iron powder (that is, heavy metal is adsorbed to the iron powder), and arsenate ions from water. And selenate ions can be efficiently removed.

Lead and cadmium are dissolved in water in the form of lead ions (Pb ²⁺ ) and cadmium ions (Cd ²⁺ ), respectively. Since the iron anodic reaction is promoted by iron powder containing sulfur, lead ions and cadmium ions are efficiently reduced to metal cadmium and metal lead, respectively, and are deposited on the surface of the iron powder (that is, heavy metals are converted into iron powder). Adsorb). As a result, cadmium ions and lead ions can be efficiently removed from the water.

Chromium is dissolved in water in the form of chromium ions (Cr ³⁺ , Cr ⁶⁺ ). The iron powder containing sulfur supplies electrons to water by an anodic reaction of iron, and efficiently generates hydroxide ions. These chromium ions and hydroxide ions react to precipitate insoluble chromium hydroxide on the surface of the iron powder (that is, heavy metal is adsorbed to the iron powder). As a result, chromium ions can be efficiently removed from the water.

  The mechanism of adsorption and adsorption of fluorine has not been clarified, but it can probably be considered as follows. By analyzing the iron powder immersed in fluorine contamination by XPS (X-ray photoelectron spectroscopy), the peak of iron ion and the peak of fluoride can be confirmed, so it is considered that the iron powder is adsorbed in the form of iron fluoride. be able to.

  For contaminated water and contaminated soil containing boron, it is useful to use a treatment agent in which at least one of slaked lime and quicklime and aluminum sulfate is used in addition to iron powder and metal chloride, and the adsorption mechanism is Although it is not known, it can probably be considered as follows. This is because, in addition to iron powder and metal chloride, at least one of coexisting slaked lime and quicklime and aluminum sulfate form a hardly soluble calcium sulfoaluminate hydrate. It can be considered that boron is removed by incorporation into the crystal structure.

  By the way, the pH of groundwater and the like contaminated with heavy metals varies depending on the surrounding environment. For example, some groundwater in which sodium bicarbonate and other alkali components are dissolved exhibits weak alkalinity of about pH 8. Moreover, some waste water and the like exhibit higher alkalinity. However, it has been found that when the pH of these contaminated waters is increased, there is a problem that the amount of heavy metal adsorbed on the iron powder decreases (Patent Document 5).

In the treating agent of the present invention, a metal chloride coexists in order to increase the reactivity of heavy metals selected from arsenic, selenium, lead, cadmium and chromium, contaminants such as fluorine, and iron powder. By producing chlorides that are highly reactive with iron powder, pollutants can be efficiently adsorbed and removed from contaminated water and soil. In addition, when metal chloride is added, the contaminated water is shifted to the acidic side (ie, less than pH 7), becomes a corrosive region of iron, increases the supply capacity of divalent iron ions (Fe ²⁺ ), and heavy metal ions It can be expected that the purification performance is further improved by promoting the reaction with. In addition, by increasing the supply capacity of divalent iron ions, it can be oxidized to trivalent iron ions in the presence of dissolved oxygen, so that the reduction capacity can be improved at the same time, and the reaction with heavy metal ions, Can also be expected to generate heavy metals by the reduction of heavy metal ions and adsorb them on the surface.

The reason why the adsorption efficiency of heavy metals is improved by the coexistence of metal chloride is that metal chloride has the effect of reducing the oxidation-reduction potential (OPR) in the solution and increasing the reducibility. It is believed that there is. That is, the effect of accelerating the adhesion (precipitation) to iron powder can be expected by facilitating reduction of various heavy metal ions dissolved in the contaminated water. In particular, selenium is effective because it has a low redox potential and is difficult to precipitate.

  The mechanism described above is not limited to contaminated water, but contains water (chemical water, hygroscopic water, capillary water, gravity water, rainwater inflow, etc.) in the soil, so it can be considered similarly in contaminated soil. .

  Examples of the metal chloride used in the present invention include ferrous chloride, ferric chloride, magnesium chloride, tin chloride, manganese chloride, zinc chloride, copper chloride, nickel chloride, etc., and use one or more of these. Can do. Among these, at least one selected from the group consisting of ferrous chloride, ferric chloride, tin chloride and manganese chloride is preferable from the viewpoint of an inexpensive material.

  In the treatment agent of the present invention, the coexistence ratio (mass ratio) of iron powder and metal chloride should be in a range in which the adsorption efficiency of either iron powder or metal chloride is improved more than alone, specifically, Is preferably metal chloride: 80 to 5 with respect to iron powder: 20 to 95 (total ratio is 100; the same shall apply hereinafter). More preferably, it is metal chloride: 60-10 with respect to iron powder: 40-90.

  By using iron powder and metal chloride as well as at least one of slaked lime and quick lime, and aluminum sulfate, a treatment agent that coexists with arsenic, selenium, lead, cadmium, and chronous heavy metals from contaminated water and contaminated soil. When removing boron as well as fluorine, the coexistence ratio (mass ratio) of aluminum sulfate and slaked lime and / or quick lime is slaked lime and / or quick lime: 80 to 20 with respect to aluminum sulfate: 20 to 80. Is preferred. More preferably, it is slaked lime and / or quicklime: 60-30 with respect to aluminum sulfate: 40-70.

  The mixing ratio (mass%) of (a) iron powder and metal chloride, (b) slaked lime and / or quicklime, and (c) aluminum sulfate can be appropriately set depending on the concentration of heavy metal or boron to be purified. When the concentration of any of the components is 1% by mass or less, it is difficult to mix uniformly, and the purification performance may not be stable. It is recommended to do.

  High contact efficiency can be achieved by contacting contaminated water or soil containing boron with at least one of heavy metals such as arsenic, selenium, lead, cadmium and chromium, or fluorine together with these treatment agents. It can be demonstrated.

  The treatment agent of the present invention is also useful in the form of a granulated product through a binder if necessary, and in addition to the effect of exhibiting high adsorption efficiency by adopting such a form, a practical apparatus scale. In addition, the effect of satisfying required characteristics such as water flow conditions and long-term durability can be exhibited.

  As the binder used when the treating agent of the present invention is in the form of a granulated product, various materials such as an organic or inorganic polymer binder or a hydraulic binder can be used. However, depending on the binder to be applied, there is a tendency to increase the pH, or there is a case where the strength is not developed. Therefore, a binder that maintains the pH below 7 and specified in JIS K 1474. Any of the above binders can be used as long as it exhibits 90% or more (preferably 95% or more) in the strength test of the granulated product according to the “activated carbon test method”. The above “activated carbon test method” is a method in which the mass ratio (mass% relative to the whole) of the sample remaining on the sieve is used as an index of strength (hardness), and the greater the measured value, the higher the strength. Is shown.

  It is preferable that the average particle diameter when it is in the form of a granulated product is about 0.1 to 4.0 mm. When the average particle diameter of the granulated product is less than 0.1 mm, the water flow resistance of the packed bed filled with the granulated product increases. On the other hand, when the average particle size of the granulated product exceeds 4.0 mm, the voids in the packed bed become large, and the adsorption efficiency with respect to the volume of the packed bed decreases. In the present invention, the “average particle diameter of the granulated product” has the same definition as the above-mentioned “average particle diameter of iron powder”.

  The present invention also provides a method for removing heavy metals and the like from contaminated water and contaminated soil by bringing the contaminated water or contaminated soil containing heavy metals such as selenium into contact with the treatment agent of the present invention. In the present invention, there is no particular limitation on the method of bringing the contaminated water or soil into contact with the treatment agent (iron powder) of the present invention. For example, (1) the treatment agent is filled in a suitable container, (2) A method in which the treatment agent is added to the contaminated water and then stirred and dispersed to capture heavy metals, etc. (3) A treatment agent is added to the contaminated soil and mixed. And a method of capturing heavy metals and the like. In addition, it has been confirmed that the iron powder from which heavy metals have been adsorbed and removed does not cause re-elution of heavy metals and the like, and may be left in the soil without being recovered. However, when collecting intentionally, collection by magnetic separation is possible and preferable.

  EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited by the following examples, and appropriate modifications are made within a range that can meet the above and the following purposes. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

[Example 1]
<Iron powder>
As raw material iron powder, iron powder (average particle size: 70 μm) having a sulfur content of 1 mass% produced by a water atomization method was used.

<Metal chloride>
Ferric chloride (commercially available reagent)
<Target substances>
Sodium selenate (Se (VI): commercially available reagent)

  An example in which the amount of the metal chloride and iron powder coexisting is changed is shown in Table 1 below together with the experimental conditions.

<Experimental conditions>
250 mL of a solution of sodium selenate (adjusted with a 0.2 mol / L NaCl solution) adjusted to a concentration of 1 mg / L was taken into a polyethylene container with an internal volume of 500 mL, and the solid-liquid ratio (g / L) The iron powder and the metal chloride were coexistingly added at the ratio shown in Table 1 so that the ratio was 1: 1000. After measuring the pH, the mixture was shaken for 24 hours at a rotation speed of 140 rpm and a shaking width of 4 cm with a horizontal shaker at room temperature of 25 ° C. Then, after shaking was stopped and pH was measured, the test water was suction filtered through a membrane filter having a pore size of 0.45 μm, and the residual selenium concentration in the solution was measured by atomic absorption method. The results are shown in Table 2 below together with the iron powder / metal chloride ratio and the pH values before and after the test.

  From the results in Table 2, it can be considered as follows. When ferric chloride coexisted with iron powder, particularly in iron powder: metal chloride = 88: 12, the selenium concentration after the test was lower than the environmental standard value (0.010 mg / L). From this, it can be seen that the coexistence of iron powder and metal chloride at an appropriate ratio indicates the possibility of processing below the environmental standard value.

  In this experiment, severe experimental conditions were used in order to clarify the degree of decrease in residual selenium concentration due to the coexistence of metal chloride. For this reason, not all experiments are below the environmental standard value. Actually, in order to cope with the actual situation, it is possible to lower the environmental standard value and the emission standard value by processing such as lowering the solid-liquid ratio (for example, 1/100, etc.) and increasing the shaking time. is there.

[Example 2]
<Iron powder>
As raw material iron powder, iron powder (average particle size: 70 μm) having a sulfur content of 1 mass% produced by a water atomization method was used.

<Metal chloride>
Ferric chloride (commercially available reagent)
<Target substances>
(A) Sodium hydrogen arsenate (As (V): commercially available reagent)
(B) Sodium selenate (Se (VI): commercially available reagent)
(C) Potassium dichromate (Cr (VI): commercially available reagent)
(D) Lead nitrate (Pb: commercially available reagent)
(E) Cadmium nitrate (Cd (VI): commercially available reagent)
(F) Sodium fluoride (F: commercially available reagent)

  Examples of various target substance solutions are shown in Table 3 below along with experimental conditions.

<Experimental conditions>
Adjust the sodium hydrogen arsenate, sodium selenate, cadmium nitrate, lead nitrate (adjusted with ion-exchanged water) to a concentration of 5 mg / L in a polyethylene container with an internal volume of 500 mL. 250 mL of each solution of potassium dichromate (adjusted with ion-exchanged water) and sodium fluoride (adjusted with ion-exchanged water) adjusted to a concentration of 10 mg / L was taken, and the solid-liquid ratio (g / L ) Was 1: 1000 so that iron powder and metal chloride coexisted (coexistence ratio 90:10) and added at the ratio shown in Table 3 above. After measuring the pH, the mixture was shaken for 24 hours at a rotation speed of 140 rpm and a shaking width of 4 cm with a horizontal shaker at room temperature of 25 ° C. Then, after shaking was stopped and the pH was measured, the test water was suction filtered through a membrane filter having a pore size of 0.45 μm, and the residual concentration in the solution was determined by atomic absorption method for selenium and arsenic, and IPC emission method for chromium. , Lead and cadmium were measured by IPC mass spectrometry, and fluorine was measured by absorptiometry using a lanthanum-alizarin complexone method. The results are shown in Table 4 below together with the iron powder / metal chloride ratio and the pH values before and after the test.

  From the results in Table 4, it can be seen that for any heavy metal, the concentration is much lower than the initial concentration.

[Example 3]
<Iron powder>
As raw material iron powder, iron powder (average particle size: 70 μm) having a sulfur content of 1 mass% produced by a water atomization method was used.

<Metal chloride>
(A) Ferrous chloride (iron (I) chloride: a commercially available reagent)
(B) Ferric chloride (commercially available reagent)
(C) Manganese chloride (commercially available reagent)
(D) Dose (II) chloride (commercially available reagent)

<Target substances>
Sodium selenate (Se (VI): commercially available reagent)

  Examples of coexistence of the various metal chlorides and iron powder are shown in Table 5 below together with the experimental conditions.

<Experimental conditions>
250 mL of a solution of sodium selenate (adjusted with a 0.2 mol / L NaCl solution) adjusted to a concentration of 1 mg / L was taken into a polyethylene container with an internal volume of 500 mL, and the solid-liquid ratio (g / L) The iron powder and the metal chloride were coexistent at a ratio shown in Table 5 (coexistence ratio 50:50) so that the ratio was 1: 1000. After measuring the pH, the mixture was shaken for 24 hours at a rotation speed of 140 rpm and a shaking width of 4 cm with a horizontal shaker at room temperature of 25 ° C. Then, after shaking was stopped and pH was measured, the test water was suction filtered through a membrane filter having a pore size of 0.45 μm, and the residual selenium concentration in the solution was measured by atomic absorption method. The results are shown in Table 6 below together with the iron powder / metal chloride ratio and the pH values before and after the test.

  From the results in Table 6, it can be considered as follows. When ferrous chloride, ferric chloride, manganese chloride, and tin chloride coexist with iron powder, the selenium concentration must be lower than iron powder alone (Test No. 10 in Tables 1 and 2). I understand. This confirmed the usefulness of coexisting various metal chlorides.

[Example 4]
<Iron powder>
As raw material iron powder, iron powder (average particle size: 70 μm) having a sulfur content of 1 mass% produced by a water atomization method was used.

<Metal chloride>
Ferrous chloride tetrahydrate (commercially available reagent)
<Target substances>
(A) Sodium hydrogen arsenate (As (V): commercially available reagent)
(B) Sodium selenate (Se (VI): commercially available reagent)
(C) Potassium dichromate (Cr (VI): commercially available reagent)
(D) Lead nitrate (Pb: commercially available reagent)
(E) Cadmium nitrate (Cd (VI): commercially available reagent)
(F) Sodium fluoride (F: commercially available reagent)

  Table 7 below shows examples in which the coexistence amount of the metal chloride and iron powder is changed together with the experimental conditions.

<Experimental conditions>
Adjust the sodium hydrogen arsenate, sodium selenate, cadmium nitrate, lead nitrate (adjusted with ion-exchanged water) to a concentration of 5 mg / L in a polyethylene container with an internal volume of 500 mL. 250 mL of each solution of potassium dichromate (adjusted with ion-exchanged water) and sodium fluoride (adjusted with ion-exchanged water) adjusted to a concentration of 1 mg / L or 3 mg / L, and the solid-liquid ratio Iron powder and metal chloride were coexistently added at the ratio shown in Table 7 so that (g / L) was 1: 1000. After measuring the pH, the mixture was shaken for 24 hours at a rotation speed of 140 rpm and a shaking width of 4 cm with a horizontal shaker at room temperature of 25 ° C. Then, after shaking was stopped and pH was measured, the test water was suction filtered through a membrane filter having a pore size of 0.45 μm, and the residual selenium concentration in the solution was measured by atomic absorption method. The results are shown in Table 8 below together with the iron powder / metal chloride ratio and the pH values before and after the test.

  From the results in Table 8, it can be considered as follows. It can be seen that when ferrous chloride tetrahydrate coexists with the iron powder, it is much lower than the initial concentration for any heavy metal. From this, it can be seen that the coexistence of iron powder and metal chloride at an appropriate ratio indicates the possibility of processing below the environmental standard value.

[Example 5]
<Iron powder>
As raw material iron powder, iron powder (average particle size: 70 μm) having a sulfur content of 1 mass% produced by a water atomization method was used.

<Metal chloride>
Ferric chloride (commercially available reagent)
<Aluminum sulfate, slaked lime, quicklime>
Aluminum sulfate (commercially available reagent)
Slaked lime (commercially available reagent)
<Target substances>
(A) Sodium hydrogen arsenate (As (V): commercially available reagent)
(B) Sodium selenate (Se (VI): commercially available reagent)
(C) Sodium fluoride (F: commercially available reagent)
(D) Boric acid H ₃ BO ₃ (B: commercially available reagent)

  Examples of various target substance solutions are shown in Table 9 below together with experimental conditions.

<Experimental conditions>
Sodium hydrogen arsenate, sodium selenate adjusted to a concentration of 0.1 mg / L, sodium fluoride and boric acid (ion-exchanged water adjusted to a concentration of 10 mg / L) in a polyethylene container having an internal volume of 500 mL 250 ml of each of the solutions prepared in (5), and the iron powder, ferric chloride, slaked lime, and aluminum sulfate in the proportions shown in Table 9 so that the solid-liquid ratio (g / L) is 1:50. Were added together. After measuring the pH, the mixture was shaken for 24 hours at a rotation speed of 140 rpm and a shaking width of 4 cm with a horizontal shaker at room temperature of 25 ° C. Then, after shaking was stopped and the pH was measured, the test water was suction filtered through a membrane filter having a pore size of 0.45 μm, and the residual concentration in the solution was determined by atomic absorption method for selenium and arsenic, and lanthanum-alizarin for fluorine. Absorption photometry by the complexone method and boron were measured by the carmine method (measurement of the reaction product with carminic acid under sulfuric acid acidity). The results are shown in Table 10 below together with the ratio of each compound (ratio of iron powder, ferric chloride, slaked lime, and aluminum sulfate) and the pH values before and after the test.

  From the results of Table 10, it can be seen that for any heavy metal, the concentration is much lower than the initial concentration. In this example, slaked lime was used. However, quick lime changes to slaked lime as soon as it is put in water. Therefore, it is judged that the effect of the present invention can be exhibited even if quick lime is used instead of slaked lime. In the results shown in Table 10, the pH before and after the test is high, but the absolute amount of iron used is high (the solid-liquid ratio is small), so the performance of the iron powder is reduced by alkali. Even so, heavy metals can be removed.

Claims (2)

Contaminated soil containing boron in addition to at least one heavy metal selected from arsenic, selenium, lead, cadmium and chromium and / or fluorine;
A treatment agent for removing boron together with the heavy metals and / or fluorine from the contaminated soil, wherein iron sulfate and metal chloride as well as at least one of slaked lime and quicklime and aluminum sulfate coexist. A method for treating contaminated soil , wherein the iron powder is atomized iron powder and is contacted with a treatment agent containing 0.6 to 5% by mass of sulfur . The method for treating contaminated soil according to claim 1, wherein the metal chloride is at least one selected from the group consisting of ferrous chloride, ferric chloride, tin chloride and manganese chloride.