JP2018047397A - Heavy metal immobilization method and method for inhibiting migration of heavy metal to plant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heavy metal immobilization method and a method for inhibiting migration of heavy metals to plants whereby it is possible to sufficiently immobilize and insolubilize heavy metals included in the soil and the like.SOLUTION: A heavy metal immobilization method is characterized by immobilizing heavy metals by using neutralized schwertmannite, obtained by the reaction of calcium carbonate with schwertmannite showing the structure of FeO(OH)(SO)(where, x is 1≤x≤1.75).SELECTED DRAWING: Figure 1

Description

  The present invention relates to, for example, a method for immobilizing heavy metals in soil and a method for suppressing the migration of heavy metals to plants.

For example, Patent Document 1 describes a method for purifying contaminated soil using Schwertmannite to passivate arsenic and heavy metals contained in the contaminated soil to purify the contaminated soil.
Further, for example, Patent Document 2 discloses a Schwbert having a stabilized arsenic sorption ability by substituting sulfate ions present in the structure of Schwbertmannite with silicate ions to stabilize the structure of Schwertmannite. Manite has been proposed.

JP 2003-112162 A Japanese Patent No. 3895001

  However, although the method of Patent Document 1 discloses that heavy metal can be adsorbed and supplemented to a certain extent in Schwertmannite, it is not clear to what extent it can be immobilized or insolubilized. Then, when the present inventors examined, the further improvement was calculated | required. On the other hand, the method of Patent Document 2 requires a mixing treatment step of Schwertmannite and a silicate compound, but has a problem that its practicality is low from the viewpoint of production efficiency and cost.

  The present invention has been made under the above-mentioned circumstances, and the problem to be solved is a method for immobilizing heavy metals contained in soil or the like, a method for immobilizing heavy metals capable of insolubilization, and suppression of heavy metal migration to plants. It is to provide a method, and to provide a heavy metal immobilizing agent that enables immobilization and insolubilization, and a method for producing the same.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have come up with a neutralized schwertmannite obtained by reacting schwertmannite with calcium carbonate. And the neutralized Schwertmannite is chemically stable, knowing that it is excellent in immobilization of heavy metals in the environment including soil, insolubilization, immobilization method of heavy metals using the neutralized Schwertmannite, The present invention was completed by conceiving a method for suppressing the migration of heavy metals to plants.

That is, the first invention for solving the above-described problem is:
Fe ₈ O ₈ (OH) _8-2x (SO ₄ ) _x (where x is 1 ≦ x ≦ 1.75) Neutralized Schwbertma obtained by reacting calcium carbonate with Schwbertmannite showing the structure of Fe ₈ O ₈ (OH) _8-2x (SO ₄ ) _x A heavy metal immobilization method characterized by immobilizing heavy metal using knight.
The second invention is
A method for immobilizing heavy metal, comprising adding the neutralized schwertmannite according to the first invention to soil containing heavy metal to immobilize the heavy metal.
The third invention is
The method for immobilizing heavy metals according to the second invention, wherein the concentration of neutralized schwertmannite to the soil containing the heavy metals is 0.1% by mass or more.
The fourth invention is:
The heavy metal immobilization method according to any one of the first to third aspects, wherein the heavy metal is arsenic.
The fifth invention is:
A method for inhibiting heavy metal migration to a plant, comprising inhibiting the migration of heavy metal from soil to a plant using the method for immobilizing heavy metal according to any one of the first to fourth inventions.
The sixth invention is:
The method for inhibiting heavy metal migration to a plant according to the fifth invention, wherein the plant is a gramineous plant.
The seventh invention
It is a heavy metal transfer suppression method to a plant according to the fifth aspect of the invention, wherein the heavy metal transfer to the seed or fruit of the plant is suppressed.

  According to the present invention, heavy metals in the environment such as soil can be sufficiently fixed and insolubilized by adding neutralized schwertmannite.

It is a graph which shows the verification result of the arsenic absorption suppression effect in brown rice. It is a graph which shows the verification result of the arsenic absorption suppression effect in a rice husk. It is a graph which shows the verification result of the arsenic absorption suppression effect in rice straw. It is a graph which shows the verification result of the arsenic absorption suppression effect in the field test of brown rice. It is a graph which shows the verification result of the arsenic absorption suppression effect in the field test of rice straw.

  Hereinafter, embodiments for carrying out the present invention will be described. 1. Neutralized Schwertmannite, 2. Neutralized schwertmannite as a fixing agent for heavy metals; 3. Construction method of neutralized Schwermannite The summary will be described in the order.

1. Neutralized _{Schwermannite Neutralized Schwermannite according to the} present invention has a structure of Fe ₈ O ₈ (OH) _8-2x (SO ₄ ) _x (where x is 1 ≦ x ≦ 1.75). Calcium carbonate is reacted with schwertmannite, and at least a part of sulfate ions present in the molecular structure of the schwertmannite is substituted with calcium ions.

Here, the example of a manufacturing method of neutralization schwertmannite is demonstrated.
Ferric salt is added to the wastewater obtained from the mine of the iron sulfide deposit, and alkali is further added to adjust the pH to a range of 3-4. And after forming the precipitation of ferric hydroxide, the said waste_water | drain is isolate | separated into the porcelain slurry and supernatant water (removal process).
Iron-oxidizing bacteria are added to the supernatant water obtained in the removing step, and divalent iron contained in the supernatant water is oxidized to trivalent iron to obtain a treatment liquid (oxidation step).
The treatment solution after the oxidation step is separated into bacterial oxide slurry and supernatant water, and neutralized by adding calcium carbonate to the resulting supernatant water after the oxidation step, so that the pH is in the range of 4-5. (First neutralization step). And neutralized schwertmannite is obtained by adding slaked lime to the liquid after said 1st neutralization process, and neutralizing and making pH into the range of 7-9 (2nd neutralization process). .

  Schwertmannite has a high adsorption capacity for heavy metals including arsenic. However, the schwertmannite is easily dissolved in water or the like, and easily mutated to goethite through dissolution and reprecipitation. As a result, when the Schwertmannite is added to low-concentration heavy metal-contaminated water or heavy metal-contaminated soil, or when stored or transported for a long period of time, mutation to goethite occurs and the adsorption capacity for heavy metals is increased. I couldn't do it.

Here, as described above, it is known that at least a part of sulfate ions present in Schwertmannite is substituted with silicate ions to suppress the mutation to goethite.
However, according to the study by the present inventors, substitution of at least a part of sulfate ions present in Schwertmannite with silicate ions is a process of adding a silicate to the Schwertmannite, and product recovery. For this, a process such as solid-liquid separation is required. And in the addition process of a silicate, adjustment of addition conditions is calculated | required, and a solid-liquid separation process is unsuitable for mass synthesis. As a result, it was considered that it was difficult to replace at least a part of sulfate ions present in Schwertmannite with silicate ions from the viewpoint of production efficiency and cost. Furthermore, Schwertmannite is an acidic substance even if it is partially silicified. As a result, it was thought that use as environmental conservation materials, especially agricultural materials, was difficult to use due to the concern of acidification of the soil.

  In contrast, the present invention neutralizes the acidic compound Schwertmannite with calcium carbonate and makes it exist as a calcium salt. The reaction proceeds easily, and is easy to implement from the viewpoint of production efficiency and cost. It is. Furthermore, the calcium salt of Schwertmannite is neutral. As a result, particularly when used as an agricultural material, there is no need to consider adverse effects on the acidification of soil, which is preferable.

2. Neutralized Schwermannite as a fixing agent for heavy metals The neutralized Schwermanite according to the present invention can sufficiently immobilize and insolubilize heavy metals.
Here, the heavy metals contained in the soil include arsenic (As), lead, mercury, cadmium, chromium, tin, zinc, barium, bismuth, nickel, cobalt, manganese, vanadium, cesium, strontium, And uranium.
Then, as the calcium compound to obtain the calcium _{salt, CaO, Ca (OH) 2} , it is preferable that CaCO ₃ and CaSO ₄ any one or more selected from.

  Neutralized Schwertmannite exhibits excellent heavy metal adsorption ability. This mechanism is currently being confirmed, but it is not due to the synergistic effects of heavy metal adsorption ability and calcium salt of Schwertmannite, the further stabilization effect of neutralized Schwermanite by added calcium salt, etc. I can guess that it is not.

  From the above knowledge, it is also preferable to preliminarily mix Schwertmannite and the calcium salt to obtain a neutralized Schwertmannite, which is a heavy metal fixing agent according to the present invention, and to apply the heavy metal fixing agent. It is a configuration.

3. Method of applying neutralized chevertmannite The amount of neutralized chevertmannite added to the soil containing heavy metals may be 0.1% by mass or more with respect to the amount of soil. preferable.

  It is because the heavy metal in the soil can be sufficiently fixed and insolubilized if the added amount of neutralized schwertmannite is 0.1% by mass or more. On the other hand, the upper limit of the amount added depends on the heavy metal concentration contained in the soil. For example, if the heavy metal concentration in the soil is about 50 mg / kg, the heavy metal in the soil can be sufficiently fixed and insolubilized by adding 0.1% by mass to 1% by mass of the neutralized schbertmannite.

Furthermore, when the target heavy metal contained in the soil is an arsenic compound, neutralized Schwertmannite is mixed with the soil as a heavy metal fixing agent, and arsenic acid and calcium ions, which are one form of the arsenic compound, are mixed. It is preferable to react to produce calcium arsenate (Ca ₃ (AsO ₄ ) ₂ ). As a result, arsenic is immobilized and insolubilized not only by adsorption of arsenic by neutralized Schwermannite but also by calcium arsenate, and further arsenic immobilization and insolubilization effects are obtained. The solubility of calcium arsenate is 0.00363 g / 100 g-H ₂ O, which is extremely difficult to water. Arsenic acid or the like is known as a form of arsenic compound in the environment, but since conversion reaction to arsenic acid also occurs, the above-described immobilization and insolubilization effects are obtained as a result.

4). Summary The method for inhibiting the migration of heavy metals including arsenic from soil to plants by the construction of the neutralized Schwertmannite according to the present invention is the method for immobilizing heavy metals described above, and plants typified by grasses and the like are cultivated. Can be used in the soil. By this construction, it is possible to suppress the heavy metal in the soil from being taken into plants such as Gramineae, their seeds, and their fruits, thereby realizing safe cultivation. That is, it is possible to suppress the transfer of heavy metals to seeds or fruits of plants such as Gramineae.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the embodiment.
In addition, as for the quantitative analysis of arsenic in a crop sample, the lower limit of analysis is 0.1 mg / kg by atomic absorption spectrum measurement at Japan Food Analysis Center. Moreover, the arsenic density | concentration analysis of soil used the inductively coupled plasma emission analysis (ICP-AES), and measured the analysis lower limit at 0.1 mg / kg.

(Manufacture of neutralized schwertmannite)
First, a specific example of a method for producing neutralized schwertmannite will be described.
The wastewater obtained from the mine of the iron sulfide deposit is set to 28 ° C., and the ferric sulfate as a ferric salt (Bioferric manufactured by Sonekura Mining Co., Ltd.) is added to the wastewater to a concentration of 7 g / L. Added. And the wastewater containing the said ferric sulfate was stirred, and then 24 mass% caustic soda solution was added, and pH was set to 3.6.
A ferric hydroxide precipitate was formed while maintaining the pH of the waste water at 3.6. And the said waste water was isolate | separated into the porcelain slurry and the supernatant water using the thickener (removal process). The pH of the wastewater was measured using a pH meter (HORIBA 9625-10D, manufactured by Horiba, Ltd.).

To the supernatant water obtained in the removal step, Thiobacillus ferrooxidans was added as an iron-oxidizing bacterium, and divalent iron contained in the supernatant water was oxidized to trivalent iron to obtain a treatment solution ( Oxidation process). Therefore, using a thickener, the treatment liquid after the oxidation step was separated into bacterial oxidation residue slurry and supernatant water.
The obtained supernatant water after the oxidation step was neutralized with calcium carbonate to adjust the pH to a range of 4.0 to 4.5 (first neutralization step). Thereafter, slaked lime was added to the liquid after the first neutralization step to neutralize it, and the pH was adjusted to a range of 7.3 to 8.3 (second neutralization step). Therefore, using a thickener, the liquid after the second neutralization step was subjected to solid-liquid separation to obtain a solid.
The obtained solid was passed through a filter press to obtain a neutralized schwertmannite having a water content of 60% or less and containing a solid content containing iron hydroxide and sulfate.

(A) Pot test paddy rice cultivation arsenic migration suppression test To a pot with an area of 0.75 m ² and a depth of 0.5 m, 90 kg of soil and sodium arsenate were added and mixed to make the soil arsenic concentration 50 mg / kg. Six pots were prepared.
Neutralized Schwertmannite produced by the above production method (may be described as “NS” in this example) was prepared.

Example 1
0.9 kg of NS was added to the pot described above and cultivated to prepare NS so that NS in the soil (specific gravity about 1) was 1% by mass.
Next, 12 bundles of rice (variety: Hinohikari) were seeded in a pot (one bundle of three rice seedlings), and the bundles were sowed in two rows at intervals of 0.2 m and cultivated. Fertilization was performed as appropriate, rice was harvested after about 4 months, dried for about 2 weeks, and after threshing and graining, a brown rice sample according to Example 1 was obtained.
The brown rice yield was 0.33 kg / m ² . The arsenic concentration contained in the brown rice sample is shown in FIG.

(Example 2)
A husk sample according to Example 2 was obtained by performing the same operation as in Example 1 except that the husk sample was obtained after threshing and rice hulling as described in Example 1. The arsenic concentration contained in the rice husk sample is shown in FIG.

(Example 3)
The rice straw sample according to Example 3 was obtained by performing the same operation as in Example 1 except that the rice straw sample was obtained after the threshing and hulling described in Example 1. The arsenic concentration contained in the rice straw sample is shown in FIG.

Example 4
The same operation as in Example 1 was performed except that 2.7 kg of NS was added to the above-mentioned pot and cultivated, and NS was adjusted to 3% by mass in soil (specific gravity about 1). A sample of brown rice according to 4 was obtained.
The brown rice yield was 0.30 kg / m ² . The arsenic concentration contained in the brown rice sample is shown in FIG.

(Example 5)
The same operation as in Example 2 was performed except that 2.7 kg of NS was added to the above-mentioned pot and cultivated, and NS was adjusted to 3% by mass in soil (specific gravity about 1). A sample of rice husk according to 5 was obtained. The arsenic concentration contained in the rice husk sample is shown in FIG.

(Example 6)
The same operation as in Example 3 was performed except that 2.7 kg of NS was added to the above-mentioned pot and cultivated, and NS was adjusted to 3% by mass in soil (specific gravity about 1). A rice straw sample according to 6 was obtained. The arsenic concentration contained in the rice straw sample is shown in FIG.

(Comparative Example 1)
A brown rice sample according to Comparative Example 1 was obtained in the same manner as in Example 1 except that NS was not added to the pot.
The brown rice yield was 0.30 kg / m ² . The arsenic concentration contained in the brown rice sample is shown in FIG.

(Comparative Example 2)
A rice husk sample according to Comparative Example 2 was obtained in the same manner as in Example 2 except that NS was not added into the pot. The arsenic concentration contained in the rice husk sample is shown in FIG.

(Comparative Example 3)
A rice straw sample according to Comparative Example 3 was obtained in the same manner as in Example 3 except that NS was not added into the pot. The arsenic concentration contained in the rice straw sample is shown in FIG.

(Summary of Example 1-6 and Comparative Example 1-3)
From the data of arsenic content in brown rice, rice husk and rice straw shown in the graph of Fig. 1-3, there is a statistically significant difference between NS non-application and NS 1 mass%, 3 mass% application Was recognized.
In particular, in brown rice, NS 1% by mass and 3% by mass application data were obtained that suppressed arsenic migration by about 80% compared to NS non-application.
On the other hand, in the brown rice yield, 0.33 kg ^/ m 2 with NS1 wt% application, NS3 wt% application, a 0.30 kg / ^{m 2} with no application, NS1 mass% application was also obtained as a result of high yields.

(B) Arsenic migration inhibition test by paddy rice cultivation (Tsuyama city field)
(Example 7)
A test field having an area of about 14 m ² was prepared. The arsenic concentration in the soil of the test field was 10 mg / kg. In the test field, ² kg of NS was applied per 1 m ² and cultivated at a depth of 0.2 m to prepare a NS 1 mass% application zone in the soil (specific gravity about 1).
0.4 kg of mixed fertilizer of the registered trademark “Swallow Coat” (San Agro Co., Ltd.) and the registered trademark “SR Coat” (Sumitomo Chemical Co., Ltd.), which is a fertilizer, was sprayed on each field before rice planting.
The cultivated rice variety was “Akitakomachi”.
Rice planting was carried out with a rice transplanter, and about 7 ml of the registered trademark “shinobi” (Sumitomo Chemical Co., Ltd.), a herbicide, was dropped onto each field immediately after rice transplanting. Two months and 2.5 months after rice planting, an appropriate amount of a registered trademark “Sumithion” (Sumitomo Chemical Co., Ltd.) as a herbicide was sprayed.
Five months after rice planting, each plot was harvested (n = 3 for each), allowed to dry naturally for about 3 weeks, and then threshing and mashing were carried out, and samples of brown rice and rice straw were collected.
FIG. 4 shows the arsenic concentration contained in the brown rice sample, and FIG. 5 shows the arsenic concentration contained in the rice straw sample.

(Comparative Example 4)
Except that NS was not applied, the same operation as in Example 7 was performed to collect brown rice and rice straw samples.
FIG. 4 shows the arsenic concentration contained in the brown rice sample, and FIG. 5 shows the arsenic concentration contained in the rice straw sample.

(Summary of Example 7 and Comparative Example 4)
From the results of the arsenic content in the brown rice sample shown in the graph of FIG. 4, data for suppressing arsenic migration by about 20% was obtained by applying NS 1% by mass.
In the yield of brown rice, there was no significant difference between NS application and non-application areas.
From the result of the arsenic content in the rice straw sample shown in the graph of FIG. 5, the rice straw in the NS 1 mass% application area was reduced to an arsenic concentration below the reference value. On the other hand, it was found that the non-application area exceeded the standard value and was not suitable as feed.

Claims (7)

Fe ₈ O ₈ (OH) _8-2x (SO ₄ ) _x (where x is 1 ≦ x ≦ 1.75) Neutralized Schwbertma obtained by reacting calcium carbonate with Schwbertmannite showing the structure of Fe ₈ O ₈ (OH) _8-2x (SO ₄ ) _x A method for immobilizing heavy metals, characterized in that heavy metals are immobilized using knight.   A method for immobilizing heavy metal, comprising adding the neutralized schwertmannite according to claim 1 to soil containing heavy metal to immobilize the heavy metal.   The method for immobilizing heavy metal according to claim 2, wherein the concentration of neutralized schwertmannite in the soil containing the heavy metal is 0.1 mass% or more.   The heavy metal immobilization method according to claim 1, wherein the heavy metal is arsenic.   A method for inhibiting heavy metal migration to a plant, comprising inhibiting the migration of heavy metal from soil to a plant using the method for immobilizing heavy metal according to any one of claims 1 to 4.   The said plant is a gramineous plant, The heavy metal transfer suppression method to the plant of Claim 5 characterized by the above-mentioned.   6. The method for inhibiting heavy metal migration to a plant according to claim 5, wherein heavy metal migration to seeds or fruits of the plant is suppressed.