JP2014150754A - Rice growing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rice growing method which makes it possible to grow rice without flooding management, can be conducted at low cost, and can also reduce the cadmium content of rice without inhibiting rice growth.SOLUTION: This invention provides a rice growing method in which a cadmium absorption inhibitor of an iron precipitate composed of an iron hydroxide is applied to a field and rice is grown. In preferable embodiments, the iron hydroxide (Fe(OH)) content of the cadmium absorption inhibitor is 25 mass% or more, and the cadmium absorption inhibitor is applied to a field at the rate of 25 kg/50 mor more.

Description

  The present invention relates to a method for growing rice.

Cadmium (Cd) is in the mountains as a natural resource and may be contained in rivers. Rice grown in agricultural water and soil may contain a small amount of cadmium. For this reason, as a method for reducing the content of cadmium in rice, for example, water level management is performed to adjust the water falling time when cultivating rice in paddy fields. However, it is difficult to manage flooding during the harvest season.
Further, as means for reducing cadmium accumulation in rice, for example, artificial zeolite (see Patent Document 1), cadmium absorption suppression material mainly composed of molasses (see Patent Document 2), and the like have been proposed. However, artificial zeolite and molasses are methods that increase costs, and it is difficult to adopt them in general because the cost to farmers for cadmium control is considerably reduced.
Therefore, it is desired to provide a technique that is inexpensive and that can reduce the cadmium content in rice without inhibiting the growth of rice.

JP 2009-278881 A JP 2011-83194 A

  An object of the present invention is to solve the above-described problems and achieve the following objects. That is, the present invention provides a rice growth method that can cultivate rice without performing flooding management, is inexpensive, and can reduce the cadmium content in the rice without inhibiting rice growth. For the purpose.

Means for solving the problems are as follows. That is,
<1> A method for growing rice characterized by cultivating rice by spraying a cadmium absorption inhibitor of iron glaze made of iron hydroxide on rice fields.
<2> The iron spray (Fe (OH) ₃ ) content in the cadmium absorption inhibitor is 25% by mass or more, and the cadmium absorption inhibitor is sprayed on the rice field so as to be 25 kg / 50 m ² or more. The method for growing rice according to <1>.
<3> The cadmium absorption inhibitor is
After adding a ferric salt to a liquid containing ferrous metal and heavy metals other than the ferrous iron, an alkali is added to adjust the pH to 3.2 or higher, while maintaining the pH 3.2 or higher. Removing the heavy metal other than the ferrous iron by forming a ferric precipitate and removing the hydroxide precipitate by solid-liquid separation;
An oxidation step of oxidizing divalent iron contained in the treatment liquid after removing heavy metals other than ferrous iron using an oxidizing agent into trivalent iron;
A first neutralization step of neutralizing the liquid after the oxidation step with a first neutralizer to a pH of 4.0 to 4.5;
A second neutralization step of neutralizing the liquid after the first neutralization step to a pH of 7.3 to 8.3 with a second neutralizing agent;
The method for growing rice according to any one of <1> to <2>, which is produced by a method for producing a cadmium absorption inhibitor comprising
<4> The method for growing rice according to <3>, including a solid-liquid separation step in which the liquid after the second neutralization step is subjected to solid-liquid separation to obtain an iron cake.

  According to the present invention, the conventional problems described above can be solved, rice can be cultivated without flooding management, it is inexpensive, and the cadmium content in rice is reduced without inhibiting rice growth. A method of growing rice that can be provided can be provided.

FIG. 1 is a process diagram showing an example of a method for producing a cadmium absorption inhibitor used in the present invention. FIG. 2 is a process diagram showing a method for analyzing cadmium content in rice in Example 1. FIG. 3 is a graph showing the results of cadmium content in rice of Examples 2 to 3 and Comparative Example 1.

(How to grow rice)
The method for growing rice according to the present invention is characterized in that an iron cadmium absorption inhibitor comprising iron hydroxide is sprayed on rice fields and the rice is cultivated.

  The iron cadmium, which is a cadmium absorption inhibitor used in the rice growth method, is an iron hydroxide. It is a composite with other sulfates. A production method for producing such a cadmium absorption inhibitor for iron products will be described below.

<Method for producing cadmium absorption inhibitor>
The method for producing the cadmium absorption inhibitor includes a removal step, an oxidation step, and a neutralization step (first neutralization step and second neutralization step) for a liquid containing ferrous metal and heavy metals other than the ferrous iron. Neutralization step), preferably a solid-liquid separation step, and further includes other steps as necessary.

In the present invention, as a method of reducing cadmium accumulation in rice, iron hydroxide Fe (OH) ₃ obtained by subjecting a liquid containing ferrous metal and a heavy metal other than ferrous iron to a predetermined treatment is used. It was found that the content of cadmium in rice can be reduced by spraying iron-containing products containing 25% by mass or more on the soil of rice fields. As a result, iron waste generated from processing wastewater from the iron mine and the wastewater from the iron smelting plant is used, so the cost is low and the wastewater from the iron mine and the wastewater from the iron smelting plant can be recycled. It becomes.

<< Removal process >>
In the removing step, a ferric salt is added to a liquid containing ferrous metal and heavy metals other than the ferrous iron, and then an alkali is added to adjust the pH to 3.2 or higher, and the pH of 3.2 or higher is maintained. This is a step of removing heavy metals other than ferrous iron by forming a precipitate of ferric hydroxide while removing the hydroxide precipitate by solid-liquid separation.

-Liquid containing ferrous metal and heavy metals other than ferrous iron-
The liquid containing the ferrous metal and the heavy metal other than the ferrous iron is not particularly limited as long as it contains at least the ferrous metal and the heavy metal other than the iron, and can be appropriately selected according to the purpose. , For example, various waters existing in the natural environment (for example, river water, lake water, hot spring drainage, geothermal water, drainage from mine sites), industrial drainage (for example, agricultural chemical factory, chemical factory, sulfuric acid refining factory, Wastewater generated in wood preservative treatment facilities, glass manufacturing plants, metal smelting plants, non-ferrous smelting plants, electronic component manufacturing facilities, garbage processing facilities, or geothermal power plants), chemical laboratories, biological laboratories, etc. , Etc. Among these, the wastewater from the iron mine and the wastewater from the iron smelting factory are acidic water, and the amount is large and must be treated semipermanently. Therefore, it is desired to treat it safely and effectively.

There is no restriction | limiting in particular as a density | concentration of the bivalent iron ion contained in the liquid containing heavy metals other than said ferrous iron and this ferrous iron, Although it can select suitably according to the objective, 500 ppm-3, 000 ppm is preferred.
Examples of the heavy metal other than the ferrous iron contained in the liquid containing the ferrous iron and heavy metals other than the ferrous iron include, for example, oxyacid anions such as arsenic acid, arsenous acid, selenic acid, selenous acid, and chromic acid, Copper, zinc, manganese, cadmium, etc. are mentioned.

-Ferric salt-
There is no restriction | limiting in particular as said ferric salt, Although it can select suitably according to the objective, Poly ferric sulfate is preferable.
The polyferric sulfate has the formula: [Fe ₂ (OH) _n (SO ₄ ) _{3 -n / 2} ] _m [wherein n <2 and m> 10. It is a compound represented by this.
As said polyferric sulfate, what was synthesize | combined suitably may be used and a commercial item may be used. Examples of the commercially available products include Polytetsu R (manufactured by Nippon Steel Mining Co., Ltd.), Bioferric (manufactured by Sonekura Mining Co., Ltd.), and the like.
When the ferric polysulfate is added to the liquid containing the ferrous metal and the heavy metal other than the ferrous iron, ferric hydroxide precipitates, and the precipitated ferric hydroxide aggregates and settles. . When ferric hydroxide precipitates and aggregates, it is considered that heavy metals other than ferrous iron in a liquid containing ferrous metal and heavy metals other than ferrous iron are captured.

The amount of polyferric sulfate added as the ferric salt is not particularly limited and may be appropriately selected according to the purpose. However, the liquid contains heavy metal other than the ferrous iron and the ferrous iron. On the other hand, 10 g / L or less is preferable, 0.5 g / L to 10 g / L is more preferable, and 1 g / L to 5 g / L is more preferable.
If the amount added is less than 0.5 g / L, the effect of removing heavy metals other than ferrous iron may be reduced. If it exceeds 10 g / L, the amount of alkali consumption increases and the cost is high. turn into.

-Alkali-
There is no restriction | limiting in particular as said alkali, According to the objective, it can select suitably, For example, caustic soda (NaOH), caustic potash (KOH); lime, quicklime (CaO), slaked lime (Ca (OH) ₂ ), carbonic acid Examples include calcium (Ca) -based alkali agents such as calcium; magnesium (Mg) -based alkali agents such as magnesium oxide and magnesium hydroxide. These may be used individually by 1 type and may use 2 or more types together.

-PH adjustment-
After adding ferric sulfate as a ferric salt to the liquid containing heavy metal other than the ferrous iron and the ferrous iron, an alkali is added and the pH is preferably 3.2 or more. It is more preferable to adjust to 3.6-4.5. A ferric hydroxide precipitate is formed while maintaining the pH of 3.2 or higher, and the hydroxide precipitate is removed by solid-liquid separation.
If the pH is less than 3.2, the ability to remove heavy metals other than ferrous iron may decrease. If the pH exceeds 4.5, the amount of ferrous iron gradually increases. When the pH is increased to 6 or more, the amount of the residue is rapidly increased. Therefore, pH 3.6 to 4.5 is more preferable. When the pH is in the more preferable range, it is advantageous from the viewpoint of removing heavy metals other than ferrous iron.
The pH can be measured by, for example, a commercially available pH meter.

<< Oxidation process >>
The oxidation step is a step of oxidizing divalent iron contained in the treatment liquid after removing heavy metals other than ferrous iron to trivalent iron using an oxidizing agent.
The ferrous iron oxidation method is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include iron-oxidizing bacteria, hypochlorite, hydrogen peroxide, air, oxygen gas, ozone gas, and ozone. Water, etc. Among these, iron-oxidizing bacteria are particularly preferable from the viewpoint of drug cost and oxidation efficiency.

As the iron-oxidizing bacteria, not as long as it has an oxidizing power particularly limited in the treatment solution after said removing step, may be appropriately selected depending on the intended purpose, for example, Thiobacillus Ferro oxidant (Thiobachillus ferrooxidans) Etc. Among these, thiobacillus ferrooxidant is particularly preferable. Thiobacillus ferrooxidant lives at pH 2 to 3 and has oxidative activity. Therefore, divalent iron can be rapidly oxidized to trivalent iron in an environment having a low pH.
The oxidation reaction of divalent iron by the iron-oxidizing bacteria is represented by the following formula.
Fe ²⁺ + H ⁺ +1/4 O ₂ → Fe ³⁺ + 1/2 H ₂ O
The addition of the iron-oxidizing bacteria to the treatment solution after the removing step may be performed at once, or may be performed in several times. When continuous oxidation treatment is performed, it is preferable to appropriately supplement iron-oxidizing bacteria.
The amount of the iron-oxidizing bacteria added to the treatment solution after the removal step can be appropriately selected according to the concentration of divalent iron in the treatment solution after the removal step.

<< First neutralization step >>
The first neutralization step is a step of neutralizing the liquid after the oxidation step to pH 4.0 to 4.5 with a first neutralizing agent.
There is no restriction | limiting in particular as said 1st neutralizing agent, Although it can select suitably according to the objective, From the point of chemical | medical agent cost, a calcium carbonate is preferable.
The addition of the first neutralizing agent to the solution after the oxidation step may be performed at once, or may be performed in several steps.

<< Second neutralization step >>
The second neutralization step is a step of neutralizing the liquid after the first neutralization step to a pH of 7.3 to 8.3 with a second neutralizing agent. The pH is defined by the drainage standard for neutralized treated water.
There is no restriction | limiting in particular as said 2nd neutralizing agent, Although it can select suitably according to the objective, Slaked lime is preferable from the point of the sedimentation property of a generated residue.
The addition of the second neutralizing agent to the liquid after the first neutralization step may be performed at once, or may be performed in several steps.

<< Solid-liquid separation process >>
The solid-liquid separation step is a step in which the liquid after the second neutralization step is subjected to solid-liquid separation to obtain an iron product.
There is no restriction | limiting in particular as said solid-liquid separation, According to the objective, it can select suitably, For example, membrane filtration, suction filtration, pressure filtration, sedimentation separation, centrifugation, etc. are mentioned.
In the solid-liquid separation step, specifically, after solid-liquid separation with a thickener, moisture is removed by a filter press, and an iron product having a moisture content of 60% or less is obtained.

The content of iron hydroxide (Fe (OH) ₃ ) in the obtained iron temple is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 25% by mass or more, and 50% by mass or more. Is more preferable. When the content of the iron hydroxide is less than 25% by mass, a sufficient cadmium absorption suppression effect may not be obtained. That is, the iron temple may be iron hydroxide alone, or may be in a state in which iron hydroxide is contained and is not decomposed after being spread on the rice field.
In addition to iron hydroxide, the iron temple contains CaSO ₄ , CaO, aluminum hydroxide, SiO ₂ and the like, but does not contain heavy metals such as Cd, Cr, As.

  The obtained iron porcelain has an excellent cadmium absorption inhibitory effect, and can be used as it is as a cadmium absorption inhibitor in the rice growth method of the present invention.

According to the rice growth method of the present invention, the cadmium absorption inhibitor is sprayed on the rice field, and the rice is grown without irrigation management, so that the rice is grown inexpensively and without inhibiting rice growth. Thus, the cadmium-free rice can be produced. The rice may be brown rice or white rice.
Here, “does not contain cadmium” in the cadmium-free rice is 0.04 mass ppm or less as measured by using an inductively coupled plasma mass spectrometer (Agilent 7500 ICP-MS, manufactured by Agilent). Means that.

Cultivation of the rice can be performed by a usual method without performing water level management for adjusting the water falling time.
There is no restriction | limiting in particular in the dispersion | distribution of the said cadmium absorption inhibitor in a rice field, Although it can select suitably according to the objective, The method of raising a rice field and spraying on the soil of a rice field, etc. are mentioned.
The amount of the cadmium absorption inhibitor sprayed onto the rice field is not particularly limited and can be appropriately selected according to the purpose, but if the cadmium absorption inhibitor is an iron hydroxide content of 25% by mass or more, 25 kg / 50 m ² or more is preferable, and 50 kg / 50 m ² or more is more preferable. When the amount of the cadmium absorption inhibitor applied to the rice field is less than 25 kg / 50 m ² , a sufficient cadmium absorption inhibitory effect may not be obtained.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

Example 1
-Production of cadmium absorption inhibitor-
Using the mine wastewater of the iron sulfide deposit having the composition shown in Table 1 below, an iron temple as a cadmium absorption inhibitor was produced by the method shown in FIG.

  First, 0.7 g / L of polyferric sulfate (Bioferric, manufactured by Sonekura Mining Co., Ltd.) as a ferric salt was added to the mine wastewater of the iron sulfide deposit at 28 ° C. The waste water containing ferric sulfate was stirred and then the pH was adjusted to 3.6 while adding 24% caustic soda. While maintaining the pH of 3.6, a ferric hydroxide precipitate was formed and separated into a slurry slurry and a supernatant by a thickener (removal step). In addition, pH was measured using the pH meter (HORIBA, Ltd. make, HORIBA 9625-10D).

Next, using the iron Thiobacillus-ferrooxidans as oxidizing bacteria (Thiobachillus ferrooxidans), it was oxidized divalent iron contained in the filtrate after the removing step trivalent iron (oxidation step).
Next, the treatment liquid after the oxidation step was separated into bacterial oxide slurry and supernatant water by a thickener.
Next, the supernatant water after the oxidation step was neutralized with calcium carbonate to pH 4.0 to 4.5 (first neutralization step).
Next, the liquid after the first neutralization step was neutralized with slaked lime to pH 7.3-8.3 (second neutralization step).
Next, after the liquid after the second neutralization step was subjected to solid-liquid separation with a thickener, an iron product having a moisture content of 60% or less was obtained by a filter press.
Table 2 below shows the composition of the iron product as the obtained cadmium absorption inhibitor.

From the results shown in Table 2, it was found that the obtained iron cadmium as a cadmium absorption inhibitor contained 52% by mass of iron hydroxide (Fe (OH) ₃ ) and no heavy metals such as Cd, Cr and As. It was. In addition, the unit of content of Cd, Cr, As is mass ppm.

<Cultivation of rice>
Rice cultivation was carried out in domestic test fields. This rice field was sprayed with fertilizer containing nitrogen, potassium, and phosphoric acid at 0.25 kg / m ² .

(Example 2)
After raising 50 m ² of the test paddy field and spraying 0.5 kg / m ² of the iron porcelain of Example 1 as a cadmium absorption inhibitor, cultivating rice without water level control did. The test paddy was dropped in summer. Rice harvesting was carried out 42 days later. The harvested rice was dried and the yield of brown rice was measured as follows and found to be 0.55 kg / m ² . Moreover, the cadmium content in brown rice was measured as follows. The results are shown in Table 3 and FIG.

<Measurement of the yield of brown rice>
The brown rice harvested in the examples was air-dried and then weighed to calculate the yield per unit area.

<Measurement of cadmium content in brown rice>
The analysis method of cadmium content contained in the harvested brown rice is shown in FIG.
2 g of brown rice was weighed and added with aqua regia [mixed hydrochloric acid for measuring harmful metals (manufactured by Kanto Chemical Co., Ltd.) and nitric acid for measuring hazardous metals (manufactured by Kanto Chemical Co., Ltd.) at a ratio of 3: 1 (volume ratio)] Wet and wet decomposition. The residue after decomposition was dissolved with nitric acid for measuring harmful metals (manufactured by Kanto Chemical Co., Inc.). For the measurement of cadmium, an inductively coupled plasma mass spectrometer (manufactured by Agilent, Agilent 7500 ICP-MS) was used. Note that cadmium nuclides used were z / m = 110, 111, 112, and 114.

(Example 3)
After raising 50 m ² of the test paddy field and spraying 1 kg / m ² of the iron porcelain of Example 1 as a cadmium absorption inhibitor, paddy cutting was performed, and rice was grown without water level control. The test paddy was dropped in summer. Rice harvesting was carried out 42 days later. The harvested rice was dried and the yield of brown rice was measured in the same manner as in Example 2. The yield was 0.55 kg / m ² . Further, the cadmium content in the brown rice was measured in the same manner as in Example 2. The results are shown in Table 3 and FIG.

(Comparative Example 1)
In the same manner as before, the test rice field of 50 m ² was raised, and after pricking, the water level was controlled and rice was cultivated. The falling water of the test paddy field was carried out in the fall in order to carry out water level management. Rice harvesting was carried out 30 days later. The harvested rice was dried and the yield of brown rice was measured in the same manner as in Example 2. The yield was 0.55 kg / m ² . Further, the cadmium content in the brown rice was measured in the same manner as in Example 2. The results are shown in Table 3 and FIG.

From the results of Table 3 and FIG. 3, in Examples 2 and 3, the cadmium content in the brown rice decreased by 34% to 68% compared to Comparative Example 1 although the water level was not managed.
Moreover, the yield of the brown rice of Examples 2 and 3 was equivalent to the yield of Comparative Example 1, and the inhibitory effect on the cultivation of rice by the spraying of iron koji as a cadmium absorption inhibitor was not confirmed.

<Measurement of absorption behavior of cadmium>
About the said Example 3 and the said comparative example 1, cadmium content contained in the rhizosphere of a rice, a panicle, etc. was measured by changing collection days. The results are shown in Table 4. Note that the number of days of collection means the number of days that have elapsed since the first date of collection.

From the results in Table 4, in both Comparative Example 1 and Example 3, there was a tendency for the cadmium content to increase after the rice field fell. Cadmium contained in the rice rhizosphere is then absorbed and accumulated in the rice ear. From the results of Example 3, it was confirmed that the absorption of cadmium into the rhizosphere of rice was suppressed to 25% to 45% when the iron deposit as a cadmium absorption inhibitor was added to the soil. This indicates that the cadmium uptake suppression effect in the rhizosphere of rice is effective in suppressing cadmium absorption into the harvested brown rice.

Claims (4)

  A method for growing rice, characterized by cultivating rice plants by spraying a cadmium absorption inhibitor of iron-containing products made of iron hydroxide on rice fields. The content of iron hydroxide (Fe (OH) ₃ ) in the cadmium absorption inhibitor is 25% by mass or more, and the cadmium absorption inhibitor is sprayed on rice fields so as to be 25 kg / 50 m ² or more. The rice growth method described. The cadmium absorption inhibitor is
After adding a ferric salt to a liquid containing ferrous metal and heavy metals other than the ferrous iron, an alkali is added to adjust the pH to 3.2 or higher, while maintaining the pH 3.2 or higher. Removing the heavy metal other than the ferrous iron by forming a ferric precipitate and removing the hydroxide precipitate by solid-liquid separation;
An oxidation step of oxidizing divalent iron contained in the treatment liquid after removing heavy metals other than ferrous iron using an oxidizing agent into trivalent iron;
A first neutralization step of neutralizing the liquid after the oxidation step with a first neutralizer to a pH of 4.0 to 4.5;
A second neutralization step of neutralizing the liquid after the first neutralization step to a pH of 7.3 to 8.3 with a second neutralizing agent;
The method for growing rice according to claim 1, which is produced by a method for producing a cadmium absorption inhibitor comprising   The method for growing rice according to claim 3, further comprising a solid-liquid separation step of solid-liquid separation of the liquid after the second neutralization step to obtain an iron cake.