Heavy metal absorption inhibitors, soil and crop cultivation methods

Abstract

This invention relates to a heavy metal absorption inhibitor, soil, and a method for cultivating crops. One type of heavy metal absorption inhibitor is a heavy metal absorption inhibitor that is mixed in soil to inhibit the absorption of heavy metals by crops in the soil. It contains a plurality of granules, wherein the average content of 0-valent Fe in the granules is 80% by mass or more, the combined average content of CaCO3 (converted from Ca) and SiO2 (converted from Si) in the granules is 30% by mass or less, and the combined average content of S and P is 1% by mass or less. At least a portion of the granules has a coating layer composed of CaCO3, SiO2, or both on its surface.

Description

Technical Field

[0001] This invention relates to heavy metal absorption inhibitors, soil, and cultivation methods for crops. Background Technology

[0002] Soil used for growing crops sometimes contains high levels of heavy metals such as arsenic and cadmium, which can have adverse effects on both crops and humans. If these heavy metals are present in the soil, crops grown in that soil will absorb them along with any nutrients they require for growth. Therefore, taking safety measures to prevent crops from absorbing these heavy metals is crucial in crop cultivation.

[0003] For example, arsenic, one of the aforementioned heavy metals, is known not to dissolve in the presence of iron, and iron-containing absorption inhibitors are well-known (e.g., International Publication No. 2010 / 117222). These absorption inhibitors, for example, when mixed into the soil, can effectively absorb and remove arsenic from the soil.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2019 / 117222 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] The absorption inhibitor described in Patent Document 1 utilizes iron powder containing phosphorus and sulfur, which increases the solubility of Fe ions and achieves the immobilization of heavy metals. However, the presence of phosphorus and sulfur makes it more prone to rusting than ordinary iron powder. Especially during crop cultivation, soil tends to become acidic due to the application of fertilizers. In acidic soil, dissolved iron is more easily oxidized. Therefore, the aforementioned absorption inhibitor may not be able to maintain a stable immobilization effect of heavy metals for a long period (e.g., more than one year).

[0009] Based on the above-mentioned circumstances, the present invention aims to provide a heavy metal absorption inhibitor and soil that can maintain the inhibitory effect of crops on heavy metal absorption for a long period of time, as well as a method for cultivating crops using the heavy metal absorption inhibitor of the present invention.

[0010] Problem-solving methods

[0011] One aspect of the present invention is a heavy metal absorption inhibitor that is mixed into soil to inhibit the absorption of heavy metals by crops in the soil. The inhibitor comprises a plurality of granules, wherein the average content of 0-valent Fe in the granules is 80% by mass or more, the combined average content of CaCO3 (converted from Ca) and SiO2 (converted from Si) in the granules is 30% by mass or less, and the combined average content of S and P is 1% by mass or less. At least a portion of the granules has a coating layer composed of CaCO3, SiO2, or both on its surface.

[0012] This heavy metal absorption inhibitor ensures that the content of 0-valent Fe in the aforementioned granules is at least above the lower limit. In this heavy metal absorption inhibitor, when the granules come into contact with moisture in the soil, the 0-valent Fe dissolves appropriately in the moisture as divalent Fe ions. The dissolved Fe ions cause heavy metals to precipitate as insoluble substances on the surface of the granules and adsorb onto them. Furthermore, this heavy metal absorption inhibitor ensures that the average total content of CaCO3 (calculated from the Ca content of the granules) and SiO2 (calculated from the Si content) is at least below the upper limit, and at least a portion of the granules have a coating layer composed of CaCO3, SiO2, or both on their surface. Therefore, when the granules come into contact with moisture in the soil, the dissolution of Fe is appropriately delayed, and the heavy metal absorption inhibition effect is maintained for a long time. Additionally, the CaCO3 and SiO2 on the coating surface dissolve in the moisture, exhibiting weak alkalinity, thus inhibiting the oxidation of Fe. Furthermore, sulfur (S) and phosphorus (P) elements accelerate the dissolution of iron (Fe), thus ensuring that the average total content of S and P elements in the aforementioned particulate matter is below the upper limit mentioned above. This extends the duration of the heavy metal absorption inhibitor's effect. Therefore, this heavy metal absorption inhibitor can maintain its inhibitory effect on heavy metal absorption by crops for a long period.

[0013] The aforementioned particulate matter can be steelmaking furnace dust. Steelmaking furnace dust is generated during the steelmaking process. If this steelmaking furnace dust is utilized, the aforementioned particulate matter can be easily obtained. Therefore, by making the particulate matter steelmaking furnace dust, costs and environmental burden can be reduced.

[0014] The aforementioned heavy metals may include arsenic. This heavy metal absorption inhibitor is particularly effective in inhibiting the absorption of arsenic by crops.

[0015] Another embodiment of the present invention involves soil mixed with the heavy metal absorption inhibitors of the present invention.

[0016] The soil, using the heavy metal absorption inhibitor of this invention, can inhibit the long-term absorption of heavy metals by crops.

[0017] The content of the above-mentioned heavy metal absorption inhibitor is preferably 0.1% by mass or more. By ensuring that the content of the above-mentioned heavy metal absorption inhibitor is above the lower limit, the absorption of heavy metals by crops can be effectively inhibited.

[0018] Another aspect of the present invention provides a method for cultivating crops, comprising the following steps: a mixing step of mixing the heavy metal absorption inhibitor of the present invention into soil; and a planting step of planting crops in the soil after the mixing step, repeating the planting step for many years.

[0019] The cultivation method for this crop, because the heavy metal absorption inhibitor of this invention is mixed into the soil, allows the heavy metal absorption inhibition effect to last for many years. Therefore, without the need to remix the heavy metal absorption inhibitor, crops with reduced heavy metal absorption can be harvested even after many years of cultivation.

[0020] Here, "average content of 0-valent Fe" refers to the value obtained by dividing the total content of 0-valent Fe in the multiple particles constituting the heavy metal absorption inhibitor by the total mass of the multiple particles. The average content of other substances such as CaCO3 and SiO2 is calculated in the same way. Furthermore, "content of 0-valent Fe" is measured according to the quantitative method for metallic iron described in JIS-M-8213:1995 "Iron Ore - Quantitative Method for Oxidized Soluble Iron (II)". "CaCO3 converted from the Ca content in the particles" means that all Ca in the particles is considered to be in the form of CaCO3. The same applies to "SiO2 converted from Si".

[0021] Invention Effects

[0022] As explained above, the heavy metal absorption inhibitor of the present invention, the soil of the present invention, and the cultivation method of crops using the heavy metal absorption inhibitor of the present invention can maintain the inhibitory effect of crops on heavy metal absorption for a long time. Attached Figure Description

[0023] Figure 1 This is a schematic cross-sectional view illustrating a heavy metal absorption inhibitor according to one embodiment of the present invention.

[0024] Figure 2 This is a flowchart illustrating the steps of a method for cultivating crops according to one embodiment of the present invention.

[0025] Figure 3 This is a diagram showing the total arsenic concentration of brown rice harvested in the first year of planting in the example.

[0026] Figure 4This is a diagram showing the total arsenic concentration of brown rice harvested in the second year of planting in the example.

[0027] Symbol Explanation

[0028] 1. Heavy metal absorption inhibitors

[0029] 10 granular bodies

[0030] 11. Covering layer Detailed Implementation

[0031] The following describes a heavy metal absorption inhibitor, soil, and crop cultivation method according to one embodiment of the present invention. Furthermore, in this specification, it is suitable to combine one of the plurality of upper limit values ​​and one of the plurality of lower limit values ​​described in any of the above-mentioned matters. The numerical range between the combined upper and lower limit values ​​is recorded in this specification as a preferred numerical range for any of the above-mentioned matters.

[0032] [Heavy metal absorption inhibitors]

[0033] Figure 1 The heavy metal absorption inhibitor 1 shown is a heavy metal absorption inhibitor that is mixed into the soil to inhibit the absorption of heavy metals by crops in the soil.

[0034] The aforementioned heavy metals include selenium, mercury, arsenic, lead, cadmium, and chromium, but only arsenic is considered a heavy metal. This heavy metal absorption inhibitor 1 is particularly effective in inhibiting the absorption of arsenic.

[0035] <granular bodies>

[0036] This heavy metal absorption inhibitor 1 contains multiple granules 10.

[0037] The lower limit for the average particle size of the granules 10 is preferably 1 μm, more preferably 5 μm, even more preferably 10 μm, and particularly preferably 50 μm. On the other hand, the upper limit for the average particle size of the granules 10 is preferably 1000 μm, more preferably 500 μm, and even more preferably 100 μm. If the average particle size of the granules 10 is lower than the above-mentioned lower limit, the manufacturing yield may decrease, or the processability may decrease. Conversely, if the average particle size of the granules 10 is higher than the above-mentioned upper limit, the specific surface area becomes too small, and the adsorption rate of heavy metals described later may decrease. Furthermore, the term "average particle size" refers to the particle size distribution obtained by dry sieving test as specified in JIS-Z-8801:2006, under which the cumulative mass of the particle size distribution is 50%.

[0038] (Fe element)

[0039] Granule 10 contains Fe (iron). Specifically, granule 10 contains Fe with a valence of 0. This 0-valent Fe exists in granule 10 in the form of metallic iron. Granule 10 may also contain Fe with a valence of 2.

[0040] When soil contains moisture, heavy metals in the soil, such as arsenic, dissolve in the moisture in the form of arsenopyrite or arsenite ions. Conversely, when soil is dry, if it comes into contact with moisture, arsenic dissolves in the contacting moisture in the form of arsenopyrite or arsenite ions. If moisture containing dissolved arsenopyrite or arsenite ions comes into contact with particulate matter 10—that is, if arsenopyrite or arsenite ions come into contact with particulate matter 10 in the presence of moisture—the arsenopyrite or arsenite ions do not dissolve under the influence of Fe. The mechanism will be explained using arsenopyrite as an example. The same applies to arsenite ions and other heavy metals.

[0041] If water containing dissolved arsenate ions is brought into contact with granules 10, the 0-valent Fe element contained in granules 10 will be oxidized, resulting in an anodic reaction (oxidation reaction) that emits electrons (Fe→Fe). 2+ +2e － Through this oxidation reaction, divalent Fe ions from the zero-valent Fe element dissolve into the water. At this time, arsenate ions in the water are reduced to zero-valent arsenic.

[0042] In addition, the divalent Fe ions dissolved by the above oxidation reaction react with arsenate ions to form an insoluble salt.

[0043] Thus, arsenate ions become insoluble through the aforementioned reduction reaction and salt formation. Furthermore, the mechanism by which iron insolubles arsenic is known to be due to the co-precipitation of arsenic caused by the formation of scorodite and the adsorption effect of goethite. In addition, because iron also has the function of insolubleting substances such as cadmium, lead, chromium, selenium, mercury, fluorine, and cyanide contained in the soil, it can also simultaneously insoluble these harmful substances.

[0044] Because this insolubility occurs on the surface of the particles 10, the 0-valent arsenic and its salts, as precipitates, can be adsorbed onto the particles 10. Therefore, through this insolubility and adsorption, arsenic, as a heavy metal, can be removed from the components absorbed by crops from the soil. Thus, the absorption of arsenic by crops growing in this soil can be inhibited. Furthermore, this heavy metal absorption inhibitor 1 is an absorption inhibitor that inhibits the absorption of arsenic by crops; it does not mean that the arsenic compounds will disappear from the soil.

[0045] The lower limit for the average content of 0-valent Fe in the granular material 10 is 80% by mass, more preferably 85% by mass. If the average content of 0-valent Fe is lower than the lower limit, the amount of divalent Fe ions dissolved from the granular material 10 becomes too small, and the absorption inhibition effect of heavy metals may be insufficient or the effect may not be long-lasting. On the other hand, all the elements other than CaCO3 and SiO2 can be 0-valent Fe, or all the elements other than CaCO3 and SiO2 can be both 0-valent and divalent Fe.

[0046] (CaCO3 and SiO2)

[0047] Granular particles 10, which contain part or all of C a The heavy metal absorption inhibitor contains calcium, silicon, and oxygen. Some or all of these elements may be present in the form of CaCO3 and SiO2. This heavy metal absorption inhibitor 1 contains CaCO3, SiO2, or both.

[0048] Heavy metal absorption inhibitors 1, such as Figure 1 As shown, at least a portion of the granular body 10 has a coating layer 11 composed of CaCO3, SiO2, or both on at least a portion of its surface. Specifically, CaCO3, SiO2, or both components coat the surface of the granular body 10 as layered crystals or as an amorphous coating. This is also evident from the analysis results of the surface of the granular body 10 using X-ray diffraction (XRD) (Table 1). Furthermore, this layer has the effect of delaying the dissolution of Fe element from the surface of the granular body 10.

[0049] Table 1

[0050] Fe Iron 10.77 <![CDATA[Fe3O4 Magnetite]]> 4.90 FeO Wuestite 5.00 α-FeOOH Goethite 2.67 γ-FeOOH Lepidocrocite 1.20 <![CDATA[CaCO3 Calcite]]> 2.00 <![CDATA[SiO2 Quartz]]> 3.41

[0051] Table 1 shows the semi-quantitative analysis results performed using the WPF method with the SmartLab X-ray diffraction apparatus manufactured by Rigaku Corporation. The results are displayed in the RIR column as simplified quantitative values ​​of the reference intensity ratio; a higher value indicates a higher mass ratio. The parameters were: target: Cu, target output power: 45kV-200mA, monochromator entrance slit: 0.8mm, detector: scintillation counter, scan rate: 2° / min, sampling width: 0.02°, measurement range (2θ): 5–90°.

[0052] like Figure 1 As shown, in the heavy metal absorption inhibitor 1, the particles 10 can be completely covered by the coating layer 11 (lower right) or the particles 10 without the coating layer 11 (upper left). In addition, they can be mostly covered by the coating layer 11 (lower left), but only a small part can be covered (center), or they can be intermittently covered in multiple places (upper right).

[0053] The lower limit of the ratio of the total coverage area of ​​the coating layer 11 to the total surface area of ​​the plurality of particles 10 is preferably 0.1%, more preferably 1%, and even more preferably 5%. On the other hand, the upper limit of the ratio of the total coverage area of ​​the coating layer 11 is not particularly limited, but it is preferable that there is at least an uncovered exposed portion, for example, it can be 99%.

[0054] The proportion of particles 10 having a coating layer 11 (the ratio of the total mass of particles 10 having a coating layer 11 to the total mass of particles 10) is higher than 0% by mass, but as a lower limit of the above proportion, it is preferably 1% by mass, more preferably 5% by mass, further preferably 10% by mass, and particularly preferably 30% by mass. If the above proportion is lower than the above lower limit, the absorption inhibition effect of heavy metals may not be sufficiently durable. On the other hand, the upper limit of the above proportion is not particularly limited and can also be 100% by mass. Furthermore, whether the particles 10 have a coating layer 11 can be classified, for example, by visual observation of multiple particles 10 using an electron microscope. In addition, the mass of each particle 10 can be calculated, for example, by conversion based on the area of ​​each particle 10 observed in the visual observation using an electron microscope.

[0055] If soil moisture comes into contact with granular material 10, CaCO3 and SiO2 dissolve in the moisture. Since CaCO3 and SiO2 are alkaline components, they form a ferric hydroxide coating on the surface of Fe, inhibiting excessive dissolution of Fe. Furthermore, they inhibit Fe oxidation. Therefore, the heavy metal absorption inhibitor 1 can maintain its effect of inhibiting the absorption of heavy metals by crops for a long period.

[0056] To explain in more detail the inhibition of excess Fe dissolution, the aforementioned alkaline components form a layered coating of Goethite (FeOOH) and Lepidocrocite (FeOOH: fibrous iron oxide) on the surface of the particles 10. This layered coating inhibits the excess dissolution of divalent Fe ions, maintaining this dissolution over a longer period. Through this prolonged dissolution of divalent Fe ions, the heavy metal absorption inhibitor 1 can exert a longer-lasting effect in inhibiting heavy metal absorption.

[0057] The upper limit for the total average content of CaCO3 (calculated from Ca in the granules) and SiO2 (calculated from Si) is 30% by mass, preferably 10% by mass, and more preferably 5% by mass. Conversely, the lower limit for the total average content is preferably 0.1% by mass, and more preferably 1% by mass. If the total average content is higher than the upper limit, the dissolution of Fe becomes too slow, and the absorption inhibition effect of heavy metals may not be sufficiently achieved. Conversely, if the total average content is lower than the lower limit, the dissolution or oxidation of Fe accelerates, and the absorption inhibition effect of heavy metals may not be durable enough.

[0058] (S elements and P elements)

[0059] The upper limit of the total average content of S and P elements in the granules 10 is 1% by mass, more preferably 0.5% by mass. S and P elements accelerate the dissolution of Fe, improving the insolubility of heavy metals by supplying Fe ions; however, if ionization occurs too early, the duration of the effect is shorter. In this case, the frequency of application to farmland increases, potentially increasing fertilizer costs. Therefore, slowing down the dissolution rate of iron, i.e., slow release, is important. Structures exhibiting good slow-release effects are CaCO3 and SiO2 present on the surface of the granules 10, and the content of S and P elements contained in the granules 10 is also important. The lower limit of the total average content of S and P elements is not particularly limited; except for unavoidable contamination, it can also be 0% by mass.

[0060] (Heavy metal elements)

[0061] Granular particles 10 themselves sometimes inevitably contain heavy metal elements. Examples of such heavy metal elements include Hg (mercury), Pb (lead), As (arsenic), and Cr. 6+ (Hexavalent chromium), etc. If the content of heavy metals in the granules 10 is high, heavy metal ions that should have been excluded from the granules 10 may dissolve. Therefore, the lower the content of heavy metals, the better. In particular, the total average content of Hg, Pb, As, and Cr in the granules 10 is preferably less than 0.1% by mass. Furthermore, the total average content of these heavy metals can be calculated based on the "Test Methods for Fertilizers, etc. (2020)" stipulated by the independent administrative agency "Farmers, etc. Test Methods (2020)". Specifically, for example, Hg can be calculated according to 5.1.a of the Test Methods for Fertilizers, etc. (2020), Pb can be calculated according to 5.6.d, As can be calculated according to 5.2.a, and Cr can be calculated according to 5.5.f.

[0062] (Other elements)

[0063] Furthermore, elements that may be included in the particulate matter 10 include, for example, Al (aluminum), Mg (magnesium), K (potassium), Na (sodium), and C (carbon). Al, Mg, K, and Na can be included in the particulate matter 10 in the form of oxides or compounds, while C can be included in the particulate matter 10 in the form of a solid solution dissolved in metallic iron or in the form of a compound. A lower content of these elements is preferred. Specifically, the upper limit of the average content of the other elements in the particulate matter 10, excluding Fe, CaCO3, SiO2, and heavy metals, is preferably 5% by mass, more preferably 2% by mass, and even more preferably 1% by mass.

[0064] The granular material 10 can be steelmaking furnace dust. Steelmaking furnace dust is generated during the steelmaking process. If this steelmaking furnace dust is used, the granular material 10 can be easily obtained. Therefore, by using steelmaking furnace dust as the granular material 10, costs and environmental burden can be reduced. Furthermore, the steelmaking furnace dust selected above has an average content of 0-valent Fe of 80% by mass or more, an average total content of CaCO3 (converted from Ca) and SiO2 (converted from Si) of 30% by mass or less, an average total content of S and P of 1% by mass or less, and at least a portion of the steelmaking furnace dust has a coating layer composed of CaCO3, SiO2, or both on its surface.

[0065] <Advantages>

[0066] This heavy metal absorption inhibitor 1 ensures that the content of 0-valent Fe element in the granules 10 is 80% by mass or more. In this heavy metal absorption inhibitor 1, when the granules 10 come into contact with moisture in the soil, the 0-valent Fe element dissolves appropriately in the moisture as divalent Fe ions. Utilizing the dissolved Fe ions, heavy metal elements can precipitate as insoluble substances on the surface of the granules 10 and be adsorbed onto the granules 10. Furthermore, the heavy metal absorption inhibitor 1 has an average total content of CaCO3 (converted from Ca) and SiO2 (converted from Si) of granules 10 of 10% by mass or less, and at least a portion of the granules 10 has a coating layer 11 composed of CaCO3, SiO2, or both on its surface. Therefore, when the granules 10 come into contact with moisture in the soil, the dissolution of Fe element can be appropriately delayed, maintaining the heavy metal absorption inhibition effect for a long period. Furthermore, the CaCO3 and SiO2 on the surface dissolve in the aforementioned moisture, exhibiting weak alkalinity, thus inhibiting the oxidation of Fe. In addition, because S and P elements accelerate the dissolution of Fe, the average combined S and P content of the granules 10 in this heavy metal absorption inhibitor 1 is less than 1% by mass. This prolongs the duration of the effect of the heavy metal absorption inhibitor 1. Therefore, this heavy metal absorption inhibitor 1 can maintain its inhibitory effect on heavy metal absorption by crops for a long period.

[0067] 〔soil〕

[0068] Another embodiment of the soil of the present invention is mixed with the heavy metal absorption inhibitor 1 of the present invention. This soil is suitable for planting and cultivating crops such as rice.

[0069] As described above with the heavy metal absorption inhibitor 1, Fe ions dissolve from the granules 10 into the soil moisture. Their solubility affects the pH value of the soil moisture. The pH value of the soil moisture depends on the pH value of the soil. A lower limit for the soil pH value is preferably 3, more preferably 4. On the other hand, an upper limit for the soil pH value is preferably 9.5, more preferably 9. Furthermore, the pH value may temporarily increase due to fertilizer addition, or temporarily decrease due to reaction with CO2 in the air; the pH value referred to here is a constant pH value excluding such temporary states.

[0070] The lower limit for the content of the heavy metal absorption inhibitor 1 in the soil is preferably 0.1% by mass, more preferably 0.3% by mass, and even more preferably 0.5% by mass. On the other hand, the upper limit for the content of the heavy metal absorption inhibitor 1 is preferably 10% by mass, more preferably 5% by mass, and even more preferably 1% by mass. If the content of the heavy metal absorption inhibitor 1 is lower than the above-mentioned lower limit, the amount of divalent Fe ions dissolved becomes too small, and the absorption inhibition effect of heavy metals may be insufficient. Conversely, if the content of the heavy metal absorption inhibitor 1 is higher than the above-mentioned upper limit, the cultivation cost of crops may increase unnecessarily relative to the obtained effect.

[0071] <Advantages>

[0072] The soil, using the heavy metal absorption inhibitor 1 of the present invention, can inhibit the long-term absorption of heavy metals by crops.

[0073] [Cultivation methods for crops]

[0074] Figure 2 The cultivation method for the crops shown includes a mixing process S1 and a planting process S2.

[0075] <Mixed Process>

[0076] In the mixing process S1, the heavy metal absorption inhibitor 1 of the present invention is mixed into the soil.

[0077] There are no particular limitations on the soil used as the base for mixing this heavy metal absorption inhibitor 1, as long as it can be used to cultivate crops, such as paddy soil.

[0078] The heavy metal absorption inhibitor 1 can be mixed using a known mixer. There are no particular limitations on the mixing method; the heavy metal absorption inhibitor 1 can be sprinkled on the prepared soil before mixing with the mixer, or the soil can be pre-mixed with the heavy metal absorption inhibitor 1 before being laid out using the mixer. Alternatively, fertilizers or other similar substances can be mixed together with the heavy metal absorption inhibitor 1.

[0079] As described above, the amount of the heavy metal absorption inhibitor 1 in the mixture is preferably 0.1% by mass or more and 10% by mass or less relative to the mixed soil.

[0080] <Planting Process>

[0081] In planting step S2, crops are planted in the soil after mixing step S1. Specifically, crops are planted in soil that has been mixed with the heavy metal absorption inhibitor 1 and is in a laid-out state.

[0082] Crop planting can be done using well-known agricultural machinery such as rice transplanters, or it can be done manually.

[0083] In the cultivation method of this crop, this planting process S2 is repeated for many years. Because the heavy metal absorption inhibitor 1 has an inhibitory effect on heavy metal absorption that lasts at least until the second year of planting, the soil can be used for many years even without repeating the mixing process S1.

[0084] <Advantages>

[0085] The cultivation method of this crop, because the heavy metal absorption inhibitor 1 of the present invention is mixed into the soil, allows the heavy metal absorption inhibition effect to last for many years. Therefore, even if the heavy metal absorption inhibitor 1 is not remixed and the crop is planted for many years, it is possible to harvest a crop with reduced heavy metal absorption.

[0086] [Other Implementation Methods]

[0087] Furthermore, the present invention is not limited to the embodiments described above.

[0088] Example

[0089] The present invention will now be described in more detail by way of examples, but the present invention is not limited to these examples.

[0090] [First Year]

[0091] <No.1>

[0092] As a heavy metal absorption inhibitor, steelmaking furnace dust (steelmaking furnace dust produced by Kafurukawa Ironworks at Kobe Steel) equivalent to the heavy metal absorption inhibitor of this invention was prepared. In a crucible, 20g of the above-mentioned heavy metal absorption inhibitor was mixed with 2kg of soil equivalent to dry soil. The steelmaking furnace dust had an average content of 86.28% by mass of 0-valent Fe, an average total content of 2.20% by mass of CaCO3 (converted from Ca) and SiO2 (converted from Si), and an average total content of 0.037% by mass of S and P.

[0093] Next, a mixed liquid fertilizer containing 0.2g each of nitrogen (N), phosphorus (P2O5 conversion), and potassium (K2O conversion) was applied to the soil as a base fertilizer, and then stirred with a hand drill. After the suspended soil settled, three Koshihikari rice seedlings were transplanted.

[0094] Approximately two and three months after transplanting, ammonium sulfate solution containing 0.08 g of nitrogen was applied as top dressing to the aforementioned crucibles. About four months later, mature rice was harvested, threshed, and hulled to obtain brown rice. The brown rice was then decomposed by heating with concentrated nitric acid and hydrogen peroxide. The arsenic concentration in the decomposition solution was measured by inductively coupled plasma mass spectrometry (ICP-MS) to determine the total arsenic concentration in the brown rice. The results showed... Figure 3 middle.

[0095] <No.2>

[0096] As a heavy metal absorption inhibitor, iron powder containing 1% by mass of sulfur (S) was used. Brown rice was harvested in the same manner as No. 1, and the total arsenic concentration in the brown rice was measured. Results showed... Figure 3 middle.

[0097] <No.3>

[0098] No heavy metal absorption inhibitors were used; in other words, the soil consisted only of soil. Brown rice was harvested in the same manner as in No. 1, and the total arsenic concentration in the brown rice was measured. The results showed... Figure 3 middle.

[0099] [Second Year]

[0100] In cases No. 1 through No. 3 above, for soils where brown rice was harvested in the first year, without re-mixing heavy metal absorption inhibitors, three Koshihikari rice seedlings were transplanted in the second year. Brown rice was harvested using the same procedures as in the first year, and the total arsenic concentration in the brown rice was measured. The results showed... Figure 4 middle.

[0101] [result]

[0102] From the results of the first year Figure 3 It can be seen that in soil No.3, where no heavy metal absorption inhibitors were used, the total arsenic concentration in brown rice was high. In contrast, in soils No.1 and No.2, where heavy metal absorption inhibitors were added, the arsenic concentration in brown rice was lower.

[0103] In addition, the results from the second year Figure 4 It can be seen that the total arsenic content in brown rice using No. 1, which uses the heavy metal absorption inhibitor of the present invention, is lower than that in No. 3, which does not use the heavy metal absorption inhibitor, and the effect of reducing the total arsenic concentration continues. On the other hand, No. 2, which uses iron powder containing 1% by mass of sulfur, shows a smaller reduction in total arsenic concentration and a smaller effect in inhibiting arsenic absorption.

[0104] If observed in greater detail, then... Figure 3The results for the first year show that No. 2 has a higher arsenic absorption inhibition effect than No. 1, but this effect reverses in the second year. In No. 1, which uses the heavy metal absorption inhibitor of this invention, the effect is correspondingly suppressed in the first year because the dissolution of Fe is moderately delayed, and the effect can be maintained for a long time. In contrast, because No. 2 does not delay the dissolution of Fe, it shows a correspondingly high absorption inhibition effect in the first year, but its effect declines significantly in the second year and cannot be maintained for a long time.

[0105] In conclusion, the heavy metal absorption inhibitor of the present invention can maintain the inhibitory effect of crops on the absorption of heavy metals for a long time.

[0106] Industrial availability

[0107] The heavy metal absorption inhibitor of the present invention, the soil of the present invention, and the cultivation method of crops using the heavy metal absorption inhibitor of the present invention can maintain the inhibitory effect of crops on heavy metal absorption for a long time.

Claims

1. A heavy metal absorption inhibitor, which is a heavy metal absorption inhibitor that is mixed into the soil to inhibit the absorption of heavy metals by crops in the soil, wherein, It contains multiple granular particles, and the average content of 0-valent Fe element in the granular particles is more than 80% by mass. The combined average content of CaCO3 (calculated from Ca content in the granules) and SiO2 (calculated from Si content) is less than 30% by mass. The combined average content of sulfur (S) and phosphorus (P) is less than 1% by mass. At least a portion of the granules has a coating layer formed by CaCO3, SiO2 or both of them as layered crystals or as an amorphous coating on at least a portion of its surface.

2. The heavy metal absorption inhibitor according to claim 1, wherein, The granular material is steelmaking furnace dust.

3. The heavy metal absorption inhibitor according to claim 1, wherein, The heavy metal in question is arsenic.

4. A type of soil, in which, It contains a heavy metal absorption inhibitor as described in claim 1, claim 2 or claim 3.

5. The soil according to claim 4, wherein, The content of the heavy metal absorption inhibitor is 0.1% by mass or more.

6. A method for cultivating a crop, wherein, It has the following processes: The mixing process of mixing the heavy metal absorption inhibitors described in claim 1, claim 2 or claim 3 into the soil; The planting process of planting crops in the soil after the mixing process. The planting process was repeated for many years.

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