JP2019149963A - Ferrous ion controlled release unglazing and manufacturing method thereof, and bivalve farming tool and aquatic environment maintenance method using the unglazing - Google Patents

Abstract

To provide a ferrous ion controlled release unglazing and a manufacturing method thereof, and a bivalve farming tool and an aquatic environment maintenance method using the unglazing which can release ferrous ion controlling and for a long term, can promote growth of phytoplankton, can raise amount of production of aquatic biology including bivalve, can suppress a reduction layer and can neutralize underwater acidic substances.SOLUTION: A ferrous ion controlled release unglazing 10 that solidified waste containing shell powder as a chief ingredient, clay as a binder and citric acid iron are burnt and the surface is porous can release ferrous ion controlling and for a long term, can promote growth of phytoplankton, can raise amount of production of aquatic biology including bivalve such as shor-necked clam 16, can suppress a reduction layer and can neutralize underwater acidic substances.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a bivalent iron ion sustained release clay, a method for producing the same, and a method for producing the same, by gradually releasing divalent iron ions into seawater or fresh water over a long period of time. The present invention relates to a bivalve farming tool used and a water environment conservation method.

In recent years, in sea areas and river areas, the amount of iron necessary for plants that carry out photosynthesis in water is insufficient, and the production of aquatic organisms is decreasing. For example, in the vicinity of the coast, rocky seaweeds have died, and in addition to shellfish such as clams and clams, coastal fishery resources such as kelp and sea urchins have declined significantly.
The main iron content in the vicinity of the Gulf is the water-soluble fulvic acid iron chelated with fulvic acid and divalent iron ions (Fe ²⁺ ) in the humus soil of the forest, which flows out from the river to the sea. In recent years, forests have been devastated, and the amount of this fulvic acid fertilizer dissolved in seawater has decreased, and soot burning has occurred.

Therefore, as a conventional technique for solving this problem, for example, as disclosed in Patent Document 1, an iron component containing divalent iron ions existing on the surface of a concrete block is submerged in the sea floor to promote the growth of seaweed. Has been developed.
In addition, as in, for example, Patent Document 2, a water permeable bag material is filled with a humus-containing substance containing fulvic acid and humic acid and a divalent iron-containing substance to produce an aquatic environment conservation material, It is known that, by submerging in water, a substance containing divalent iron (FeO, Fe ₃ O ₄ ) and a substance containing humus (fulvic acid, etc.) are combined in the sea to produce iron fulvic acid. ing.

JP-A-5-268854 JP 2006-212036 A

However, in Patent Document 1, a concrete block is used as an iron carrier. For this reason, it is basically difficult to produce divalent iron ions in a strong alkali environment of concrete. Even if divalent iron ions that can be ingested by photosynthetic organisms are eluted from the surface of the concrete block, the divalent iron ions are easily oxidized by oxygen in the water and become trivalent iron ions (Fe ³⁺ ) immediately. It precipitates as iron (Fe ₂ O ₃ ). For this reason, phytoplankton and the like cannot take it, and the supply of divalent iron ions to aquatic organisms is not efficient.
Further, according to Patent Document 2, when the water-permeable bag material is installed in water, the contents (iron) may be eluted to the surroundings in a short time. As a result, there is a possibility that water pollution caused by this may be caused, and it is unclear whether divalent iron ions can be supplied continuously for a long time.
Furthermore, in the muddy tidal flats in the estuary area, many microorganisms that decompose organic matter are generated. Therefore, an oxygen-free reduction layer is easily formed in the thickness area from the surface of the tidal flat to several centimeters. In Sludge), sulfate ions contained in the soil were reduced by bacteria such as sulfate-reducing bacteria, generating hydrogen sulfide and producing a foul odor, and worsening the aquatic environment in which aquatic organisms live.

  Thus, as a result of earnest research, the inventor has focused on, for example, shells discarded in large quantities from bivalve farms such as oysters. The main component is powdered shells, and iron-containing clay (binder), citric acid and water are added and stirred. After shaping into a shape or the like, a porous unglazed product is produced by firing the shaped product at a predetermined temperature. For example, by immersing this in water in an estuary area, divalent iron ions are gradually released below the surface of the water, and the micropores on the surface become a place for phytoplankton. When used in, hydrogen sulfide is chemically immobilized by the eluted divalent iron ions, and it is possible to suppress sludge malodor and the like, and further, by shell powder mainly composed of alkaline calcium carbonate, For example, the inventors have found that neutralization of acidic substances in mud mudflats can be achieved, and the present invention has been completed.

  The present invention has been made in view of such problems, and can gradually release divalent iron ions into seawater and fresh water over a long period of time, thereby promoting the growth of phytoplankton and the like, and aquatic organisms including bivalves. Divalent iron ion sustained release clay that can increase the production volume, suppress the generation of a reduced layer containing hydrogen sulfide, and also neutralize various acidic substances present in sea areas and river areas It is an object of the present invention to provide a bivalve farming tool and a water environment conservation method using the clay, its manufacturing method, and the clay.

  The present invention according to claim 1 is a bivalent iron ion sustained-release element characterized in that it has shell powder as a main component, clay as a binder, and iron citrate, and has a porous surface. It is a pottery.

The shell used as the raw material for the shell powder is not limited. For example, oyster shells, clams, red shells, scallop shells, etc. can be employed. These shells are disposed of in large quantities after shellfish are collected and processed, and are readily available.
Although the kind of clay is not limited, one containing iron is preferable. For example, Seiwa clay (red clay) is preferable.
The iron citrate contained in the solidified body is, for example, produced by adding citric acid to the main component shell powder and iron-containing clay and stirring them to obtain a solidified body, so that iron citrate is generated. May be. In addition, when stirring the shell powder and the clay not containing iron, it may be added to the solidified body as iron citrate.
The shape of the bivalent iron ion sustained release clay is arbitrary. For example, a spherical shape (uncooked ball) or a piece shape such as an abacus may be used.

The size of the bivalent iron ion sustained release clay is not limited. For example, when the shape is spherical, the bottom of the bivalve larvae is higher when the diameter is 8 mm to 15 mm. Moreover, the bivalent iron ion sustained release clay is more likely to be submerged in bivalves that have the habit of submerging in the sand after growth when the shape is uneven and the sizes are not uniform.
The pH of the bivalent iron ion sustained release clay is not limited. However, since oyster shell powder is the main component, it is generally weakly alkaline (pH 7.8 to pH 8.2).
As a method of using the bivalent iron ion sustained release clay, for example, it is possible to employ a method in which a bivalent iron ion sustained release clay is enclosed in a water-permeable bag and immersed in seawater or fresh water. In addition, for example, it may be sprayed on a muddy tidal flat in the estuary area. In this case, in order to prevent the divalent iron ion sustained release clay from flowing due to the tide, the upper area of the divalent iron ion sustained release clay is covered with a flat mesh, and the flat mesh is covered with an anchor pin. It is better to fix.

  Further, in the present invention according to claim 2, the divalent iron ion sustained release clay is (a) 20-30% by weight of clay containing iron, (b) 70-80% by weight of shell powder (provided that ( a) + (b) = 100% by weight) The iron citrate hydrate obtained by reacting this iron content with the iron content in terms of solid content and this molar amount of citric acid with respect to the main raw material 2. The bivalent iron ion sustained-release clay according to claim 1, comprising iron citrate obtained by calcining.

  Among these, when the blending amount of the shell powder with respect to 100% by weight of the main raw material of the clay is less than 70% by weight, it is difficult to form pores serving as a place for phytoplankton on the entire surface of the bivalent iron ion sustained release ceramic For example, it cannot prevent solidification of mud mudflats and neutralize acidic substances by making the soil pH alkaline. Moreover, if it exceeds 80 weight%, the compounding ratio of the clay which is a binder will reduce, and the shape of the obtained bivalent iron ion slow release clay will be easy to collapse.

Moreover, when the blending amount of the clay with respect to 100% by weight of the main body of the clay is less than 20% by weight, the ratio of the clay is reduced, and the obtained divalent iron ion sustained release clay is easily broken. On the other hand, if it exceeds 30% by weight, the amount of shell powder is reduced, and it is difficult to form pores serving as a place for phytoplankton on the entire surface of the bivalent iron ion sustained-release porcelain. It cannot prevent solidification and neutralize acidic substances by making the soil pH alkaline.
The amount of iron citrate (C ₆ H ₅ O ₇ Fe; 208.1 g / mol) contained in 100% by weight of the bivalent iron ion sustained release clay is the iron content (Fe; 19.00 g / mol) contained in the clay. Is approximately 11.0 times that.

  The present invention described in claim 3 is characterized in that the iron content in the clay is 2 to 10% by weight with respect to 100% by weight of the clay. It is an iron ion sustained release clay.

  If the proportion of iron contained in the clay is less than 2% by weight based on 100% by weight of clay, the amount of iron citrate contained in the bivalent iron ion sustained-release clay is too small and becomes a phytoplankton nutrient. The amount of divalent iron ions released is reduced. On the other hand, if it exceeds 10% by weight, the binder effect of the clay on the shell powder is lowered, and there is a possibility that protrusions called “Odeki” appear on the surface of the fired bivalent iron ion sustained release clay. In addition, the amount of iron citrate released from the bivalent iron ion slow-release clay is excessive, which may cause red tide and blue sea urchin. A preferable proportion of iron contained in the clay is 2.5 to 5% by weight, more preferably 3 to 4% by weight.

  Furthermore, in the present invention according to claim 4, pores having a macropore diameter of 10 μm to 60 μm and a micropore diameter of 3 μm to 5 μm are formed over the entire surface of the divalent iron ion sustained release ceramic. The bivalent iron ion sustained-release clay according to any one of claims 1 to 3.

When the diameter of the pore macropore is less than 10 μm, the number of nanoplankton (2 μm to 20 μm) such as diatoms is reduced because the macropore is too narrow. Therefore, the bottoming rate of floating larvae (100 μm to 230 μm) of bivalves that feed on this decreases. On the other hand, if it exceeds 60 μm, the macropores are too wide, the surface of the bivalent iron ion sustained release clay becomes rough, the nanoplankton is easily washed away, and the bottoming rate of the bivalve floating larvae decreases. A preferable diameter of the macropore is 20 μm to 50 μm.
In addition, when the diameter of the micropores of the pores is less than 3 μm, the micropores are too narrow, and picoplankton (0.2 μm to 2 μm) such as cyanobacteria are not easily picked up. On the other hand, if it exceeds 5 μm, the micropores are too wide and the picoplankton is likely to be washed away, and it is difficult to fix. The preferred diameter of the micropore is around 4 μm.

  Furthermore, the present invention according to claim 5 is a method for producing a bivalent iron ion sustained release clay, using a clay containing iron, (a) 20-30 wt% clay, (b) shell Based on 70 to 80% by weight of the powder (however, (a) + (b) = 100% by weight), the iron content, equimolar amount of citric acid and a predetermined amount of water in terms of solid content And stirring to make a suspension, and then the suspension is allowed to stand for a predetermined period of time to react iron contained in the clay with citric acid. An iron hydrate is produced, and then the produced precipitate is taken out, shaped, dried, and calcined.

If the amount of citric acid added to the unglazed main material is less than the equivalent of the iron content in the clay in terms of solid content, the amount of citric acid is insufficient relative to the iron content in the clay, and divalent iron The amount of released divalent iron ions, which are nutrients of phytoplankton, from the slow-release ion-fired product is reduced.
The amount of citric acid (C ₆ H ₅ O ₇ ; 192.125 g / mol) added to the iron content (Fe; 19.00 g / mol) in the clay is approximately 10.1 times the iron content in terms of solid content. It is.
Moreover, the amount of the obtained iron citrate hydrate (C ₆ H ₅ O ₇ .3H ₂ O.Fe (chemical formula; C ₆ H ₅ FeO ₇ .nH ₂ O); 262.148 g / mol) It is about 13.8 times the iron content contained in.
As water, for example, tap water can be used. The amount of water added is not limited as long as a suspension of clay, shellfish powder and citric acid is obtained.

The suspension time (precipitation time) is arbitrary. During this standing, iron contained in the clay reacts with citric acid to produce iron citrate hydrate.
The taken-out precipitate is made into a hardness suitable for shaping by, for example, dehydration, and shaped into a predetermined shape including a spherical shape or a piece shape by using various shaping (molding) devices.

  In the present invention according to claim 6, the average particle diameter of the shell powder is 10 μm to 30 μm, the firing temperature is 400 ° C. to 750 ° C., and after firing, the surface of the bivalent iron ion sustained release clay is applied to the surface. 6. The method for producing a bivalent iron ion sustained release clay according to claim 5, wherein pores having a macropore diameter of 10 μm to 60 μm and a micropore diameter of 3 μm to 5 μm are formed.

If the average particle size of the shell powder is less than 10 μm, the surface of the obtained bivalent iron ion sustained release clay is too dense, and the bottoming rate of the bivalve floating larvae decreases. On the other hand, if it exceeds 30 μm, the surface of the bivalent iron ion sustained release clay is too rough, and the bottoming rate of the bivalve floating larvae decreases. The preferred average particle size of the shell powder is around 20 μm.
If the calcination temperature of the solidified body is less than 400 ° C., the calcination temperature is too low, and the bivalent iron ion sustained release clay becomes brittle. Moreover, when it exceeds 750 ° C., the firing temperature is too high, and the divalent iron ion sustained release clay is shrunk to a high density, and the surface porosity of the divalent iron ion sustained release clay is reduced (the pores are reduced). To do. A preferable firing temperature of the solidified body is 600 ° C to 700 ° C.

The firing time is, for example, 12 to 24 hours. If it is less than 12 hours, the firing becomes insufficient, and the bivalent iron ion sustained release clay may be brittle. On the other hand, if it exceeds 24 hours, the firing time is too long, and the surface of the bivalent iron ion sustained release clay becomes rough and may be deformed.
When firing, the firing temperature is gradually increased from a low temperature to a predetermined temperature, so that the formation rate of pores of the above-mentioned size on the surface of the bivalent iron ion sustained release ceramic product is increased (divalent iron ion slow release element). Pores are formed on the entire surface of the ceramic).

  Further, the present invention according to claim 7 is the method for producing a bivalent iron ion sustained release clay, wherein the suspension is left for 24 to 48 hours.

  If the suspension time for accelerating the production of iron citrate is less than 24 hours, iron citrate cannot be produced sufficiently. In addition, if it exceeds 48 hours, the standing time becomes longer than necessary, and the productivity of the bivalent iron ion sustained release clay is reduced. The preferred standing time for the suspension is 30 to 40 hours.

  Furthermore, the present invention according to claim 8 is characterized in that the clay containing iron contains 2 to 10% by weight of iron with respect to 100% by weight of the clay. Item 8. The method for producing a bivalent iron ion sustained release clay according to any one of Items 7 above.

  Furthermore, in the present invention described in claim 9, the bivalent iron ion sustained-release clay according to any one of claims 1 to 4 is enclosed in a water-permeable bag. This is a bivalve farming tool.

As a bag body which has water permeability, a net bag can be adopted, for example. In addition, the bag body obtained from the nonwoven fabric bag body, the plastic sheet in which the water-permeable hole was formed, etc. may be sufficient.
The shape of the bag is arbitrary. For example, a rectangular bag, a circular bag, an oval bag, a triangular bag, etc. are employable.
The size of the bag is arbitrary.
The size of the hole diameter (mesh size) of the bag body is arbitrary. However, if it is less than 1 mm, dust, mud, etc. are likely to adhere, and the water permeability may be reduced. Moreover, if it exceeds 8 mm, when a divalent iron ion sustained release clay with a suitable diameter of 8 mm to 15 mm is adopted, the divalent iron ion sustained release clay may be discharged from the bag. A preferable bag body has a hole diameter of 3 mm to 5 mm.
The place where the bivalve farming equipment is used is arbitrary. It may be a predetermined place in seawater or freshwater. Specific examples include estuaries of tidal flats.

  Moreover, this invention of Claim 10 encloses the bivalent iron ion slow release clay of any one of Claims 1-4 in a water-permeable bag body, and is a water environment. By providing a maintenance material, and then leaving the water environment protection material immersed in seawater or fresh water, the divalent iron ions are gradually added to the seawater or fresh water over a long period of time from the bivalent iron ion slow release clay. It is a water area environmental preservation method characterized by preserving the surrounding water area environment.

The water environment conservation material here is composed of the same structure as that of the bivalve culture tool, and is used not for the cultivation of bivalve but for the conservation of the aquatic environment.
The place where the water environment environmental protection material is used is arbitrary. It may be a predetermined place in seawater or freshwater. Specific examples include the seabed in the estuary.

  According to the bivalent iron ion sustained release clay of the present invention described in claim 1, for example, the divalent iron ion slow release clay is immersed in seawater or fresh water and left to stand. Divalent iron ions are gradually (stablely) released over a long period of time from the iron citrate contained in the released clay. For phytoplankton, iron is a substance necessary for electron transfer in photosynthesis and respiration. Therefore, it is possible to compensate for the diminished amount of iron fulvic acid dissolved in seawater and fresh water due to devastation of the forest by divalent iron ions from iron citrate, which has the same function as iron fulvic acid. it can.

As a result, the amount of phytoplankton that performs photosynthesis in water increases, and the growth of aquatic organisms that feed on the phytoplankton, such as bivalves, is promoted, and the production amount can be increased. Moreover, hydrogen sulfide generated in the eutrophied bottom mud can be chemically fixed by divalent iron ions, and generation of blue tide can be suppressed.
As a mechanism of chemical fixation of hydrogen sulfide by divalent iron ions, a mechanism represented by the following formula (1) has been proposed.
Fe ²⁺ + HS ⁻ → FeS · nH ₂ O + H ⁺ (1)

  Further, the divalent iron ion binds to phosphorus in water to become iron phosphate. As a result, this eutrophication, which causes blue sea bream and red tide, can also be prevented.

Furthermore, this bivalent iron ion sustained release clay is mainly composed of shell powder containing alkaline calcium carbonate. Therefore, it is possible to neutralize various acidic substances existing in the sea area, river area, etc., and further maintain the water environment where aquatic organisms live.
In addition, the elution of calcium from shellfish powders can also prevent the sulfate reduction of sulfides by sulfate-reducing bacteria, and the chemical fixation effect of phosphorus. As a mechanism of chemical fixation of phosphorus by calcium, the one represented by the following formula (2) has been proposed.
5Ca ²⁺ + OH ⁻ + 3PO ₄ ³⁻ → Ca ₅ (OH) (PO ₄ ) ₃ ↓ (2)

  Moreover, the bivalent iron ion sustained release clay is a clay obtained by baking at high temperature. Therefore, in the case of conventional fulvic acid iron, etc. originating from forest humus soil, it is burned down by the heat during firing, but the iron citrate contained in the divalent iron ion slow release clay of the present invention Does not disappear with baking heat. Moreover, the germs and shellfish corrosive substances adhering to the shell powder etc. are incinerated by this baking heat.

In particular, according to the bivalent iron ion sustained release clay according to claim 2, (a) 20-30 wt% clay, (b) 70-80 wt% shell powder, , (Where (a) + (b) = 100% by weight), obtained by reacting this iron content with iron content in terms of solid content and this mole or more of citric acid, in terms of solid content A material containing iron citrate obtained by firing iron citrate hydrate was employed. As a result, a bivalent iron ion sustained release clay having the preferred effect of the invention of claim 1 can be obtained.
In particular, the content of iron citrate is obtained by firing iron citrate hydrate obtained by reacting iron contained in clay with this iron content in an amount equivalent to or higher than this mole in terms of solid content. Therefore, the amount of divalent iron ions released from the bivalent iron ion sustained release clay is suitable.

  Moreover, according to the manufacturing method of the bivalent iron ion slow release clay of Claim 3, and the divalent iron ion slow release clay of Claim 8, the iron content in clay is reduced to 100% by weight of clay. On the other hand, since the content is 2 to 10% by weight, divalent iron ions serving as a nutrient for phytoplankton can be sufficiently released into water without lowering the binder effect of clay on the main component shell powder.

  In addition, according to the method for producing a bivalent iron ion sustained release clay of the present invention according to claim 4, the diameter of the macropores is 10 μm to 60 μm and the diameter of the micropores over the entire surface of the bivalent iron ion sustained release clay. Provided pores of 3 μm to 5 μm. This increases the bottoming rate of the bivalve floating larvae (100 μm to 230 μm). That is, nanoplankton (2 μm to 20 μm) such as diatoms is likely to bite into macropores, and picoplankton (0.2 μm to 2 μm) such as cyanobacteria is likely to bite into micropores.

Furthermore, according to the method for producing a bivalent iron ion sustained release clay of the present invention according to claim 5, (a) 20 to 30% by weight of clay containing iron as a binder, (b) shell powder 70 to 80 And (b) = 100% by weight), and the iron content, equivalent mole or more citric acid, and a predetermined amount of water in terms of solid content To give a suspension.
Thereafter, this suspension is allowed to stand for a predetermined time, and iron contained in the clay is reacted with citric acid to produce iron citrate hydrate. At this time, since the amount of citric acid is equal to or more than that of iron, all iron contained in the clay reacts with citric acid to become iron citrate hydrate.

Next, the precipitate is taken out from the water (in the supernatant liquid) and shaped into a predetermined shape including a spherical shape or a piece shape. The shaped precipitate is dried and fired.
Thereby, the bivalent iron ion slow release clay having the effect of claim 1 can be manufactured.

  Furthermore, according to the method for producing a bivalent iron ion sustained release clay according to claim 6, the average particle diameter of the shell powder is 10 μm to 30 μm, and the firing temperature is 400 ° C. to 750 ° C. Thus, after firing, pores having a macropore diameter of 10 μm to 60 μm and a micropore diameter of 3 μm to 5 μm can be formed on the surface of the bivalent iron ion sustained release clay.

  According to the seventh aspect of the present invention, the suspension is allowed to stand for 24 to 48 hours after stirring the material. Thereby, the production | generation reaction of iron citrate can be accelerated in the time which is necessary and does not reduce productivity.

  Furthermore, according to the bivalve farming tool of the present invention described in claim 9, the bivalent iron ion sustained-release clay according to any one of claims 1 to 4, in a water-permeable bag. And soaked in, for example, a muddy tidal flat. As a result, divalent iron ions are gradually released from the iron citrate contained in the bivalent iron ion slow-release clay in a long time under the water surface. As a result, the amount of phytoplankton that performs photosynthesis in water increases, and the production of aquatic organisms such as bivalves that use this phytoplankton as a feed can be increased.

In particular, since the bivalent iron ion sustained release clay is a porous material, various phytoplankton stagnate on its surface, and the floating larvae of the bivalves that feed on it are drawn through the holes of the bag. Then, it settles on the surface of the clay and grows into bivalves. Thereafter, the bivalve that grows larger than this hole diameter in the bag cannot go out of the bag. As a result, for example, it is possible to harvest (culture) a large amount of bivalves that have become adult shells of 25 mm or more without escaping them.
In addition, in order to use a bivalve culture tool in which a plurality of bivalent iron ion sustained release ceramics are packed in a bag in this way, the mass and quantity of the bivalent iron ion sustained release ceramics filled in the bag are adjusted. Thus, it can be stably placed on the bottom of the water without being swept away by the tide.

Furthermore, according to the water area environmental conservation method of the present invention described in claim 10, first, the divalent iron ion according to any one of claims 1 to 4 is formed on the water-permeable bag body. Enclose the slow-release clay and provide water environment conservation material. Then, this water area environmental conservation material is left in the state immersed in seawater or fresh water. As a result, divalent iron ions are gradually released over a long period of time from the iron citrate contained in the divalent iron ion slow-release porcelain to the seawater or fresh water, thereby protecting the surrounding water environment.
That is, first of all, phytoplankton such as cyanobacteria and diatoms that perform photosynthesis in water and rocky seaweeds grow by the slow release of divalent iron ions. This will increase the production of coastal fishery resources such as kelp and sea urchins, as well as shellfish such as clams and clams.
Secondly, hydrogen sulfide generated in the eutrophic bottom mud can be chemically immobilized by divalent iron ions. Thereby, generation | occurrence | production of a blue tide can be suppressed. Moreover, the divalent iron ions are combined with phosphorus in water to form iron phosphate. As a result, this eutrophication, which causes blue sea bream and red tide, can also be prevented.

Thirdly, this bivalent iron ion sustained release clay is mainly composed of shell powder containing alkaline calcium carbonate. Therefore, it is possible to neutralize various acidic substances present in the sea area, river area, etc., and maintain the water environment where aquatic organisms live.
Moreover, the bivalent iron ion sustained release clay is a porous clay that has a large surface area. Therefore, a large amount of an oxygen-free reducing layer can be attached to the surface. Therefore, the generated amount of the reducing layer can be reduced by, for example, periodically pulling out the water environment protection material from water and exposing it to the air.
Furthermore, in order to use the aquatic environment conservation material in which the divalent iron ion sustained release clay is packed in the bag as described above, the mass and quantity of the divalent iron ion sustained release clay filled in the bag are adjusted. Thus, the water area environmental conservation material can be stably installed on the bottom of the water (such as a tidal flat) without being washed away by the tide.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a bivalent iron ion sustained release clay according to Example 1 of the present invention. It is a principal part expanded sectional view of the use condition which shows the pore part of the bivalent iron ion slow-release ceramics which concern on Example 1 of this invention. It is a flow sheet which shows the manufacturing method of the bivalent iron ion slow release unglazed article concerning Example 1 of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a top view of the use condition of the bivalve culture tool or water area environmental conservation material which packed the bivalent iron ion slow-release ceramics concerning Example 1 of this invention. It is a principal part enlarged view which shows the state of the clam cultivated in the bivalve cultivation tool which packed the bivalent iron ion slow-release clay according to Example 1 of the present invention.

  Examples of the present invention will be specifically described below. Here, oyster shell powder is used as the shell powder, and clam culture in estuarine mudflats using divalent iron ion sustained-release porcelain and water environment conservation in the estuary are taken as examples.

In FIG. 1, reference numeral 10 denotes a divalent iron ion sustained release clay of the present invention. This divalent iron ion sustained release clay 10 is composed of oyster shell powder (shell powder) as a main component, clay as a binder, and quencher. The entire surface obtained by firing the solidified body containing iron oxide is a porous unglazed ball.
The divalent iron ion slow release clay 10 has a spherical shape with a diameter of 8 to 12 mm, and a large number of pores 13 having a diameter of the macropore 11 of 50 μm and a diameter of the micropore 12 of 4 μm are formed over the entire surface. (FIG. 2). In addition, the reason why the sizes of the bivalent iron ion sustained release clay 10 are irregularly set to 8 to 12 mm is that bivalves that have the habit of diving into sand after growth tend to submerge. Further, for the same reason, it is preferable that the divalent iron ion sustained release clay 10 has an irregular shape (for example, a piece shape).

Hereinafter, with reference to FIGS. 1-5, the manufacturing method of the bivalent iron ion slow release clay is demonstrated.
As shown in the flow sheet of FIG. 3, in the rotating drum of the stirring apparatus, 75% by weight (7,500 g) of oyster shell powder having an average particle diameter of 20 μm and 25% by weight of clay containing iron as a binder (2,500 g) ) And 100% by weight (10,000 g) of the main product of the unglazed product obtained from the citric acid, 7.575% by weight (757.5 g) in terms of solid content, and a predetermined amount of water (100 liters) Are stirred for 30 minutes to form a suspension (material stirring step).
As the clay containing iron, Moriwa clay (red clay) containing 3% by weight (75 g) of iron with respect to 100% by weight (2,500 g) of clay is used.
Then, this suspension is left for 30 hours to react iron in the soil with citric acid to produce iron citrate hydrate (iron citrate hydrate production step). As a result, 10.35% by weight (1,035 g) of iron citrate hydrate is generated with respect to 100% by weight of the main product of the clay (refer to paragraph number 0019 for the calculation method).

Next, the precipitate is taken out from the suspension in which the production of iron citrate is promoted, dehydrated by a dehydrator, and then formed into a spherical shape having a diameter of 8 to 12 mm using a press molding apparatus ( Shaping process).
Next, the shaped spherical product is charged into a hot air drying apparatus, and hot air drying is performed at 50 ° C. for 8 hours. Thereby, a spherical solid body having a diameter of 8 to 12 mm is obtained (drying step).

Next, the solidified body is charged into a firing apparatus and fired at 700 ° C. for 20 hours. As a result, a divalent structure containing iron citrate and having a diameter of 8 to 12 mm and a weight of 3 to 3.5 g in which a large number of pores 13 having a diameter of the macropore 11 of 50 μm and a diameter of the micropore 12 of 4 μm exists over the entire surface. An iron ion sustained release clay 10 is produced (firing step, FIGS. 1 and 2). It should be noted that iron citrate is 7.67% by weight (825 g) with respect to 100% by weight of the bivalent iron ion slow release clay 10 because the amount of iron citrate is the iron content in the clay ( 3 wt% (75 g)), which is 11.0 times (see paragraph 0013).
The divalent iron ion sustained-release ceramic product 10 thus produced is about 4 in a plastic net bag (water-permeable bag) 14 having a bag size of 50 cm x 35 cm and a mesh size of 4 mm x 4 mm. .051 kg (1,266 pieces / bag) is enclosed (FIG. 4). The obtained bagging body becomes the clam culture tool 15 for clam culture or the water environment protection material 15A for preserving the environment of the mud tidal flat. These will be described later.

  In Example 1, the oyster shell powder was 69.77% by weight with respect to 100% by weight of the divalent iron ion sustained release clay (the ratio of each contained in the divalent iron ion sustained release clay 10). In order to obtain a bivalent iron ion slow release clay 10 comprising Moriwa clay (iron removed by the production of iron citrate) of 22.56% by weight and iron citrate of 7.67% by weight (825 g), For example, by leaving it on the mud bottom of a muddy tidal flat, divalent iron ions can be gradually released into seawater over a long period of time. As a result, the growth of phytoplankton and the like can be promoted around the bivalent iron ion slow release clay (FIG. 2), and the production of aquatic organisms including bivalves such as clams 16 can be increased (FIG. 5). In addition, it is possible to suppress the generation of a reduced layer containing hydrogen sulfide, and it is also possible to neutralize various acidic substances present in sea areas, river areas, and the like.

  Moreover, the bivalent iron ion slow release clay 10 is a clay that is obtained by baking at a high temperature. Therefore, when the conventional iron fulvic acid generated from the humus soil of the forest is adopted, it is burned out (evaporated) by the baking heat at 700 ° C. in the baking process. However, the iron citrate of the bivalent iron ion sustained release clay 10 is not lost by the heat of firing at this time. Therefore, it functions as a slow release material for divalent iron ions. Moreover, the germs and shellfish corrosive substances adhering to the oyster shell powder etc. are incinerated by heat at 700 ° C.

In particular, since iron citrate was 7.67% by weight (825 g) with respect to 100% by weight of the bivalent iron ion sustained release clay, the amount of divalent iron ions released from the bivalent iron ion slow release clay. Is preferred.
In addition, since there are a large number of pores 13 composed of a macropore 11 having a diameter of 50 μm and a micropore 12 having a diameter of 4 μm over the entire surface of the bivalent iron ion sustained release clay 10 which is an unglazed product, for example, cyanobacteria Picoplankton P1 (0.2 μm to 2 μm) such as moss can be found in the micropore 12, and nanoplankton P2 (2 μm to 20 μm) such as diatom can be found in the macropore 11 (FIG. 2).

Furthermore, by using the bivalve culture tool 15 having such a structure, the mass and quantity of the bivalent iron ion sustained release clay 10 filled in the net bag 14 can be adjusted. Thus, the bivalve farming tool 15 can be stably left on the tidal flat without being swept away by the tide (FIG. 4).
Further, in the production of the bivalent iron ion sustained release clay 10, 75% by weight of oyster shell powder having an average particle diameter of 20 μm, 25% by weight of Siwa clay containing 3% by weight of iron, and elements obtained therefrom. Add 7.575% by weight of citric acid to 100% by weight of the main material of the pottery and stir to produce iron citrate (material stirring step), and then shape this suspension into a spherical shape (shaped) Step), the shaped suspension was dried with hot air to obtain a solidified body (drying step), and then the solidified body was fired at 700 ° C. for only 20 hours (firing step) (a firing process). Flow sheet of FIG. 3). As a result, one of the features of the bivalent iron ion sustained release clay 10 of Example 1 is that the pores 13 having a diameter of the macropore 11 of 50 μm and a diameter of the micropore 12 of 4 μm are formed on the surface of the clay 10. The divalent iron ion sustained release clay 10 that can be formed over the entire region (FIG. 2) and has the above-described effects can be produced efficiently and stably.

Furthermore, immediately after the material stirring step, an iron citrate hydrate production step is provided in which the suspension is allowed to stand for 30 hours, so that the production reaction of iron citrate hydrate can be promoted. As a result, the amount of iron citrate produced can be increased as compared with the case of simply stirring oyster shell powder, iron-containing clay, and citric acid.
Moreover, since the iron content in the clay (Moriwa clay) was 3% by weight with respect to 100% by weight of the clay, an excess of divalent iron ions serving as nutrients for the phytoplankton from the bivalent iron ion sustained release clay It can be released for a long time without becoming.

Next, a clam culture method using the bivalve culture tool 15 will be described with reference to FIGS.
As shown in FIG. 4, when clams 16 are cultivated using the bivalve cultivation tool 15, they are left in the mud flats in the estuary.
Thereby, divalent iron ions are gradually released into the seawater over a long period of time from iron citrate (chelate) contained in the bivalent iron ion slow release clay 10. Therefore, it is possible to compensate for the “decrease in the amount of fulvic acid leaching into seawater caused by devastation of the forest”, which has become a problem in recent years, with divalent iron ions from iron citrate, which has the same function as fulvic acid iron. it can.

As a result, phytoplankton such as cyanobacteria, which are picoplanktons that carry out photosynthesis in water, and diatoms, which are nanoplanktons, are present on the surface of the bivalent iron ion sustained release clay 10 (macropores 11 or micropores). 12) Grows in 13. As a result, the floating larvae (100 μm to 230 μm) 16 a of the clams 16 drifting in the seawater that feed on the phytoplankton are attracted, and they pass through a mesh of 4 mm in length and width, and the bivalent iron ion slow release clay It settles on the surface of 10 and grows into a clam 16.
That is, fertilized eggs of clams 16 are from floating larvae (trochophore, D upper stage (100 μm to 110 μm) 16 a, ampo stage (130 μm to 180 μm), full-growing period (180 μm to 230 μm)), 300 μm), early larvae (300 μm to 1000 μm), larvae (1 to 15 mm), early adult shellfish (15 mm to 25 mm), and adult shellfish (25 mm or more).

  Thus, the clams 16 that have grown larger than 4 mm (mesh size) in the mesh bag 14 cannot pass through the meshes, and can be harvested (cultured) without letting the clams 16 escape until they become adult shellfish. In addition, the clam 16 culture period (the period until it becomes an adult clam of 30 mm or more) takes more than a year and a half in the case of a natural clam 16, whereas the clam culture tool 15 is used. For example, it can be shortened to about 6 months, and it is possible to harvest clams 16 twice a year.

Next, with reference to FIG. 1, FIG. 2, FIG. 4 and FIG. 5, the water area environmental preservation method of the estuary area by this water area environmental preservation material 15A will be described.
When water area environmental conservation material 15A, which is the same as the bivalve farming tool 15 shown in FIG. 4, is used to protect the water area environment in the estuary area, a predetermined number of the water area environment conservation material 15A is placed on the seabed of the estuary coast. Just leave them side by side. Thereby, divalent iron ions are gradually released from the iron citrate contained in the bivalent iron ion slow release clay 10 into seawater over a long period of time. Thereby, the decrease in the elution amount of fulvic acid iron in the conventional method can be compensated by divalent iron ions from iron citrate.

As a result, phytoplankton that performs photosynthesis in water, seaweed in the rocks, and the like grow around the bivalent iron ion sustained release clay 10. Therefore, in addition to shellfish such as clams 16 and clams, production of coastal fishery resources such as kelp and sea urchins can be increased.
Moreover, the bivalent iron ion sustained release clay 10 can chemically fix the hydrogen sulfide generated in the eutrophic bottom mud by the gradually released divalent iron ions and suppress the generation of blue tide. .
The mechanism of chemical fixation of hydrogen sulfide by the divalent iron ions is shown in the following formula (1).
Fe ²⁺ + HS ⁻ → FeS · nH ₂ O + H ⁺ (1)

Furthermore, since the divalent iron ion sustained release clay 10 is mainly composed of oyster shell powder containing alkaline calcium carbonate, it can neutralize various acidic substances present in the sea area. Thereby, the water environment where aquatic organisms live can be preserved. That is, the elution of calcium from the oyster shell powder of the bivalent iron ion sustained release clay 10 also has the effect of inhibiting sulfate reduction of sulfide by sulfate-reducing bacteria and the chemical fixing effect of phosphorus. For example, about 12 mg of hydrogen sulfide (as S) is adsorbed per 1 g of oyster shell powder, and the effect of suppressing the poor oxygenation of the upper layer water can be obtained. The mechanism of chemical fixation of phosphorus by calcium is as shown in the following formula (2).
5Ca ²⁺ + OH ⁻ + 3PO ₄ ³⁻ → Ca ₅ (OH) (PO ₄ ) ₃ ↓ (2)

  Furthermore, this divalent iron ion combines with phosphorus in water to form iron phosphate. As a result, this eutrophication that causes water melon and red tide can be prevented.

In addition, the oyster shell powder has an effect of removing total nitrogen, and most of ammonia nitrogen is removed by digestion.
Moreover, as shown in FIG. 1 and FIG. 2, the bivalent iron ion sustained release clay 10 is a porous clay having a large surface area. Therefore, a large amount of an oxygen-free reduced layer (sludge) can be adhered to the surface (for example, 5 to 10 times the purification action of silica sand). As a result, the generated amount of the reduced layer can be reduced by periodically pulling up the water area environmental conservation material 15A from the water and exposing the attached reduced layer to air to inactivate anaerobic bacteria.

  Here, in a muddy tidal flat, a bivalve cultivation tool 15 (test example) in which a bivalent iron ion sustained release clay 10 having an iron citrate content of Example 1 of 7.67% by weight is packed in a net bag 14 1), a bivalve culture tool 15 (Test Example 2) in which a bivalent iron ion sustained release clay 10 having an iron citrate content of 5.3 wt% is packed in a net bag 14, and an iron citrate content A bivalve cultivation tool 15 (Test Example 3) in which a 22% by weight divalent iron ion sustained release clay 10 is packed in a net bag 14, iron fulvicate instead of iron citrate, oyster shell powder, iron content A bivalve culture tool 15 (Comparative Example 1) in which a spherical unglazed product kneaded and baked in clay containing no sachet is packed in a net bag 14, and a slow release of divalent iron ions having an iron citrate content of 4% by weight A bivalve culture tool 15 (Comparative Example 2) in which the unglazed product 10 is packed in a net bag 14 and containing iron citrate A bivalve cultivation tool 15 (Comparative Example 3) in which a 30% by weight divalent iron ion sustained release clay 10 was packed in a net bag 14 was left to stand, and a clam 16 aquaculture test and a water environment conservation test were conducted. Report the results.

  In Test Examples 1 to 3, oyster powder is 7,500 g and Siwa clay is 2500 g under the same conditions. Among these, in the case of 2% by weight of iron with respect to 100% by weight of clay, the iron citrate produced is 5.24% by weight with respect to 100% by weight of the bivalent iron ion sustained release clay. When the iron content is 10% by weight with respect to 100% by weight of the clay, the iron citrate produced is 22% by weight with respect to 100% by weight of the bivalent iron ion sustained release clay.

(Test Example 1)
First, test conditions common to Test Examples 1 to 3 and Comparative Examples 1 to 3 will be described.
The bivalve farming tool 15 (water environment conservation material 15A) to be used is a plastic mesh bag 14 having a bag size of 50 cm x 35 cm and a mesh size of 4 mm x 4 mm. About 4 kg (1,266 pieces / bag) of ~ 3.5 g of spherical divalent iron ion sustained release clay 10 is enclosed. The weight ratio of the oyster shell powder is about 70% by weight with respect to 100% by weight of the bivalent iron ion sustained release clay. Therefore, the total weight of the oyster powder in the bag is about 2.8 kg.
The test site is Sone Tidal Flat in Kitakyushu City, Fukuoka Prefecture. The test period is from April 12, 2015 to February 10, 2016. Moreover, the test method leaves the bivalve culture tool 15 on the mud of the tidal flat under the sea surface at the time of low tide.

  Under these conditions, the clam culture device 15 (water area environmental conservation material 15A) of Test Example 1 was used, and the clam 16 culture test and water area environmental conservation test were performed. At the beginning of the test, the floating larvae 16a of clams 16 attached to the surface of each bivalent iron ion slow release clay 10 of the bivalve farming tool 15 grew to 10 mm clams 16 after 92 days. Generally, the period during which the clam 16 grows to 10 mm is about 180 days (half year). The number of days in parentheses indicates a general period required for the clam 16 to grow to the corresponding size.

After that, the clam 16 was 15 mm after 110 days (after about 273 days), 20 mm after 136 days (after about 318 days), 25 mm after 168 days (after about 365 days (one year)), and 30 mm after 197 days (after about 498 days ( After one and a half years)) 226 days later, it grew to 35 mm (approximately 730 days later (two years later)) and 267 days later to 40 mm (approximately 1,095 days later).
Moreover, when it reached 30 mm size (about 7 g), which is the shipping time of the clams 16, the average number of clams 16 harvested from one net bag 14 was 93 and the weight was 651 g. When converted to this population density of 1 m ² per clam 16, it was 300 to 600 pieces / ^{m 2.} The average population density of clams 16 in the Sone tidal flat in 2004 was about 2.5 per 1 m ² , which was about 120 to 240 times the yield.

The average yield of clams per net bag 14 by year is July 31, 2015 (85 pieces / bag, 485 pieces / m ² ), September 26, 2015 (85 pieces / piece). Bag, 485 pieces / m ² ), July 31, 2015 (85 pieces / bag, 485 pieces / m ² ), July 31, 2015 (73 pieces / bag, 417 pieces / m ² ), Heisei October 27, 2015 (82 / bag, 469 / m ² ), December 28, 2015 (78 / bag, 445 / m ² ), April 22, 2016 (70 / bag) Bag, 399 / m ² ), December 15, 2016 (77 / bag, 439 / m ² ), February 27, 2017 (70 / bag, 399 / m ² ), Heisei It was April 12, 2017 (83 pieces / bag, 473 pieces / m ² ). In addition, in this result of April 12, 2017, 83 clams are harvested in one net bag 14 containing 1,266 divalent iron ion sustained release clay 10. That is, about 15 divalent iron ion sustained release clays 10 were required for each clam.

Incidentally, the average population density of clam 16 in 1985 and earlier Sone flats was 430 per 1 m ² (Mikawa estimated harvest amount of clam 16 in color flats). From this, it was found that if the bivalve farming tool 15 of Test Example 1 was used, a harvest of clams 16 corresponding to before 1985 was obtained.
Generally, clams 16 are 25 mm in size and lay eggs, and the laying season is twice a year in spring (April to May) and autumn (September to October).

Thus, the cultivation period in which the clam 16 grows to 30 mm or more requires one and a half years in the case of the natural clam 16, whereas in Test Example 1, it could be shortened to about 6 months. This made it possible to harvest clams 16 twice a year.
In addition, as described above, the bivalve farming tool 15 also serves as the water area environmental conservation material 15A. Therefore, by leaving it in the Sone tidal flat, about 12 mg / day of hydrogen sulfide per 1 g of oyster shell powder could be removed. Since there is 2.8 kg of oyster shell powder in one bivalve farming tool 15, 33.6 g per bag of bivalve farming tool 15 and about 27.3 kg of hydrogen sulfide per 1 m ² from the following calculation formula every day. It was found that can be processed.
2.8 kg (powder powder) / bag × 12 mg / day = 33.6 g

Furthermore, it is possible to purify (filter) water at a rate of 4 tons or 1 liter / h per clam 16 and use one bivalve farming tool 15 (an average of 93 clams 16 are harvested). It was found that it was possible to purify water at 372 t / year or 2,232 liters / h.
One clam has the ability to filter about 1 liter of water per hour. Therefore, for example, in the case of 419 clams, it is possible to improve the water quality by filtering 3,670,440 liters of seawater per year from the following formula.
419 pieces x 24 hours = 10,056 liters / day 10,056 liters / day x 365 days = 3,670,440 liters / year

Further, the next harvest forecast when using 13 bags of the bivalve farming tool 15 is obtained by the following equation.
16,458 pieces (1,266 divalent iron ion sustained release ceramics 10 × 13 bags) ÷ 15 pieces (number of divalent iron ion slow release ceramics 10 required for one clam adult) = 1, 098 (next harvest expected value)
The harvest weight here is 1098 × 7 g = 7,686 g because one 30 mm adult shellfish is 7 g. The amount of seawater filtered in this case is 9,618,480 liters per year from the following formula.
1,098 x 24 hours = 26,352 liters / day 26,352 liters / day x 365 days = 9,618,480 liters / year

(Test Example 2)
A clam similar to that of Test Example 1 except that a bivalve culture tool 15 (water area environmental conservation material 15A) packed with a bivalent iron ion sustained release clay 10 having an iron citrate content of 5.3% by weight is used. Sixteen aquaculture tests were conducted. As a result, substantially the same effect as in Test Example 1 was obtained.

(Test Example 3)
The clam 16 of the same clam 16 as in Test Example 1 is used except that a bivalve culture tool 15 (aquatic environment conservation material 15A) packed with a bivalent iron ion sustained release clay 10 having an iron citrate content of 22% by weight is used. An aquaculture test was conducted. As a result, substantially the same effect as in Test Example 1 was obtained.

(Comparative Example 1)
Instead of using iron citrate, use a bivalve culture tool (15) in which iron fulvic acid is kneaded into oyster shell powder and clay that does not contain iron, and then baked globular clay (10). The clam 16 was cultured using the same method as in Test Example 1. In Comparative Example 1, since fulvic acid iron was employed instead of iron citrate as described above, when producing divalent iron ion sustained release clay (10), fulvic acid iron evaporated and disappeared during the firing step. I have. As a result, even when the bivalve culture tool (15), which is the water area environmental conservation material (15A), was immersed in seawater, divalent iron ions were not gradually released from the spherical unglazed product (10). As a result, the harvest of clams 16 was drastically reduced and the water environment conservation was insufficient.

(Comparative Example 2)
Similar to Test Example 1 except that the bivalve cultivation tool (15), which is a water environment conservation material (15A) packed with a divalent iron ion slow release clay 10 having an iron citrate content of 4% by weight, is used. The clam 16 was cultured. As a result, as compared with the case of Test Example 1, the amount of phytoplankton that clings to the pores 13 of the bivalent iron ion sustained-release porcelain (10) is reduced, and the harvest of clams is slightly reduced, and until it becomes an adult shellfish The period has also become somewhat longer. On the other hand, the water quality improvement effect also decreased slightly.

(Comparative Example 3)
Test Example 1 except that the bivalve cultivation tool (15), which is a water environment conservation material (15A) packed with a bivalent iron ion sustained release clay (10) having an iron citrate content of 30% by weight, is used. The same clam 16 aquaculture test was conducted. As a result, the amount of iron contained in the clay increased, the clay binder effect on the shell powder decreased slightly, and the amount of citric acid used increased. Further, some protrusions called “Odeki” appeared on the surface of the fired bivalent iron ion sustained release clay (10) after firing, and the water quality improving effect was slightly reduced.

  INDUSTRIAL APPLICABILITY The present invention is useful as a technique for cultivating bivalve molluscs that promote the growth of phytoplankton and the like and for protecting the water environment by gradually releasing divalent iron ions into seawater and fresh water over a long period of time.

10 Divalent iron ion slow release clay 11 Macropore 12 Micropore 13 Pore 14 Mesh bag (water-permeable bag)
15 Bivalve farming tool 15A Water environment conservation material 16 Clam (Bivalve)

Claims (10)

  A bivalent iron ion sustained-release clay comprising a shell powder as a main component, clay as a binder, and iron citrate, and having a porous surface.   The divalent iron ion sustained release clay is (a) 20-30% by weight of clay containing iron, (b) 70-80% by weight of shell powder (provided that (a) + (b) = 100% by weight). It contains iron citrate obtained by calcining iron citrate hydrate obtained by reacting this iron content with an equivalent mole of citric acid in terms of solid content with respect to the raw material of the raw material The bivalent iron ion sustained-release clay according to claim 1.   The iron content contained in the clay is 2 to 10% by weight with respect to 100% by weight of the clay, and the bivalent iron ion sustained release clay according to claim 1 or 2.   The pores having a macropore diameter of 10 μm to 60 μm and a micropore diameter of 3 μm to 5 μm are formed over the entire surface of the divalent iron ion sustained release clay. 5. Among them, the bivalent iron ion sustained-release clay according to any one of the above. A method for producing a divalent iron ion sustained release clay,
A clay containing iron is used as a main raw material for clay, consisting of (a) 20-30% by weight of clay and (b) 70-80% by weight of shell powder (however, (a) + (b) = 100% by weight). On the other hand, the above-mentioned iron content in terms of solid content, equimolar amount of citric acid, and a predetermined amount of water are added and stirred to form a suspension.
Then, by allowing this suspension to stand for a predetermined time, the iron content contained in the clay reacts with citric acid, and iron citrate hydrate is generated in the raw clay main material,
Thereafter, the produced precipitate is taken out, shaped, dried and fired, and a method for producing a bivalent iron ion sustained release clay. The average particle size of the shell powder is 10 μm to 30 μm,
The baking temperature is 400 ° C. to 750 ° C.
6. The pores having a macropore diameter of 10 μm to 60 μm and a micropore diameter of 3 μm to 5 μm are formed on the surface of the bivalent iron ion sustained release clay after firing. A method for producing a bivalent iron ion sustained release clay.   The method for producing a bivalent iron ion sustained-release clay according to claim 5 or 6, wherein the suspension is left for 24 to 48 hours.   8. The clay according to claim 5, wherein the iron-containing clay contains 2 to 10% by weight of iron with respect to 100% by weight of the clay. 9. A method for producing a bivalent iron ion sustained release clay.   A bivalve culture tool, wherein the bivalent iron ion sustained-release clay according to any one of claims 1 to 4 is enclosed in a water-permeable bag. In the water-permeable bag body, the water-based environment conservation material is provided by enclosing the bivalent iron ion sustained release clay of any one of claims 1 to 4,
Then, by leaving the water environment environmental preservation material in a state immersed in seawater or fresh water, the divalent iron ions are gradually released over a long period of time into the seawater or fresh water from the bivalent iron ion slow release clay. Water area environmental preservation method characterized by preserving the water area environment.