JP7136670B2 - Structure for algal growth and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a structure for algae colonization and a method for producing the same.

Rare earths are essential elements in cutting-edge technology industries as raw materials used in neodymium/iron/boron magnets, LED light bulbs, fuel cells, and the like, and their demand has increased rapidly in recent years. On the other hand, there are concerns about supply shortages and soaring prices of rare earths, and securing new supply sources of rare earths has become an issue.
Under these circumstances, deep-sea mud containing a high content of rare earths widely distributed in the Pacific Ocean is attracting attention as a new supply source of rare earths.
Mud containing a high content of rare earths (for example, deep-sea mud in the Pacific Ocean) has a huge amount of resources, can be extracted by a simple method of immersing in dilute acid for 1 to 3 hours, and contains thorium. It has many advantages such as containing almost no radioactive elements such as uranium.

On the other hand, the ratio of the mass of rare earths to the dry mass of mud containing rare earths is only 0.3% by mass or less even in the deep seabed of the Pacific Ocean, which is known for its high rare earth content. Therefore, there is a problem that a large amount of acidic residue (mud) is generated when rare earths are extracted from rare earth-containing mud using dilute acid.
As a technique for using the above acidic residue as a raw material for useful products, Patent Document 1 discloses a method of baking a dewatered cake or slurry, which is the residue generated after treating rare earth-containing mud with an acid. A characterized granular earthworking material is described.

JP 2017-164705 A

Since a large amount of residue is generated after treating mud containing rare earths with acid, effective utilization of the residue is desired.
SUMMARY OF THE INVENTION An object of the present invention is to provide a structure for algae colonization that can effectively utilize the residue generated after treating mud containing rare earths with an acid, and that has little adverse effect on the environment.

As a result of intensive studies to solve the above problems, the present inventors have found algae containing granular materials obtained by baking a dehydrated cake or slurry consisting of the residue generated after treating rare earth-containing mud with acid. The inventors have found that the above object can be achieved by the settlement structure, and completed the present invention.
That is, the present invention provides the following [1] to [6].
[1] A structure for algae colonization for installation in water, containing granular materials, wherein the granular materials are dehydrated cakes consisting of residues generated after treating mud containing rare earths with acid. Alternatively, a structure for growing algae is obtained by firing a slurry.
[2] The structure for algae growth according to [1] above, which includes water-permeable storage means for storing the granular material.
[3] The structure for algae colonization according to [2] above, which includes a plurality of the above-described storage means, and a connection means for connecting these storage means.
[4] The structure for algae colonization according to any one of [2] or [3], including a movement suppressing means for suppressing movement of the containing means on the bottom of the water.

[5] A method for producing an algae-adhering structure according to any one of [1] to [4] above, comprising a baking step of baking the dehydrated cake or slurry to obtain a baked product; and a granulation step of crushing, cutting, or classifying the fired product to obtain the granular material.
[6] A method for growing algae using the structure for growing algae according to any one of the above [1] to [4], wherein a place for installing the structure for growing algae is selected. A method for colonization of algae, comprising: a site selection step; and a structure installation step of installing the structure for algae colonization in the selected location.

According to the structure for algae growth of the present invention, it is possible to effectively utilize a large amount of residue generated after treating mud containing rare earths with an acid.
In addition, according to the structure for algae growth of the present invention, it has little adverse effect on the environment, allows algae to grow thereon, forms fish reefs and algae reefs where aquatic organisms grow, and improves the underwater environment. can contribute to

The figure (1-a) on the left is a photograph showing an example of the structure for algae adherence of the present invention before installation, and the figure (1-b) on the right is a photograph of the algae adherence of the present invention collected after installation. It is a photograph which shows an example of a living structure. FIG. 2 is a diagram showing an example of a structure for algae colonization of the present invention, which includes a plurality of housing means and also includes connecting means and movement suppressing means.

The structure for algae growth of the present invention is a structure for algae growth for installation in water containing granular materials, wherein the granular materials are generated after treating mud containing rare earths with an acid. It is obtained by calcining a dehydrated cake or slurry consisting of a residue that
In the present invention, the "residue generated after treating mud containing rare earths with acid" (hereinafter sometimes abbreviated as "residue") means that mud containing rare earths is treated with acid (for example, diluted hydrochloric acid). It is an acidic residue generated after extracting rare earths into liquid.
Rare earth refers to 17 elements including Sc (scandium) and Y (yttrium) in addition to the lantaloids of Group 3 of the periodic table (La (lanthanum) to Lu (lutetium)).

As an example of rare earth-containing mud, it is distributed in stratified layers (for example, the ground from the seabed to a depth of several tens of meters) on the deep seabed (for example, an area of 3,500 to 6,000m as the depth of the sea). and mud with a high content of rare earths.
In the present invention, the rare earth content (mass basis) in the rare earth-containing mud (dry state; solid content) is preferably 1, 1, 2 from the economic point of view when mining rare earth resources. 000 ppm or more, more preferably 2,000 ppm or more.

The water content ratio of the residue (ratio of water to 100% by mass of the solid content of the residue) is not particularly limited, but from the viewpoint of reducing the load on heating means such as a heating furnace, it is preferably 200% by mass or less, more preferably 150% by mass. % or less, particularly preferably 120 mass % or less.
Methods (methods) for reducing the water content of the residue include a sedimentation method in which mud is stored in a container such as a tank, the solid content of the mud is precipitated, and the supernatant is collected, and a centrifugal method using a device such as a screw decanter. Examples include a separation method and a pressurized dehydration method using a device such as a filter press.
Among them, the sedimentation method and the centrifugal separation method are preferable, and the sedimentation method is more preferable, because dehydration can be easily performed at a low cost.
The degree of dehydration increases in the order of the sedimentation method, the centrifugal separation method, and the pressurized dehydration method.

In the present invention, "a dehydrated cake or slurry consisting of a residue" means (a) a dehydrated cake or slurry consisting only of a residue, (b) a residue, and a small amount that does not adversely affect the effect of the present invention. means either a dewatered cake or a slurry, which consists of a mixture of ingredients other than residue, which is formulated in the
In the case of (b) above, examples of materials other than the residue include sodium hydroxide, calcium hydroxide, fly ash, and the like.
Examples of forms of materials other than residues include aqueous solutions, suspensions, powders, granules, and the like.
Materials other than residues (including water) for the total amount of 100 parts by mass of the residue and materials other than the residues (moisture contained in the residue and the weight including water in the aqueous solution when using an aqueous solution as a material other than the residue) solid content) is preferably less than 5 parts by mass, more preferably 3 parts by mass or less, still more preferably 2 parts by mass or less, from the viewpoint of increasing the lightness of the granular material used in the present invention. Particularly preferably, it is 1 part by mass or less.
In the present invention, "a product obtained by baking a dehydrated cake or slurry consisting of a residue" means that by heating at a moderately high temperature that is not excessively high such that the baked product is reduced in volume by melting due to heating, It is partially or wholly melted.

Granular materials may be used without adjusting the particle size (particle size if the material is spherical, longitudinal dimension if the material is rod-shaped), or may be used with a specific particle size depending on the purpose and means of storage. You may adjust and use it so that it may be in the range. The particle size is preferably 0.2 to 60 mm, more preferably 1 to 50 mm, particularly preferably 4 to 40 mm. If the particle size is 0.2 mm or more, the granular material is less likely to flow out from the place where it is installed or the storage means, and the particle size can be adjusted more easily. If the particle size is 60 mm or less, the granular materials can be more easily stored in the storage means, and small aquatic organisms (for example, crustaceans such as crabs, small animals such as small fish, Benthic organisms such as lugworms) can easily enter the gaps between the contained granular materials and settle there.

The algae settlement structure of the present invention prevents the above-mentioned granular materials from flowing out in water and accommodates the granular materials from the viewpoint of facilitating the installation and recovery of the algae settlement structure. It may also include a water-permeable containing means for.
Specifically, organic fibers such as cellulose fiber, polyamide fiber, vinylon fiber, polyester fiber, polyolefin fiber, rayon fiber, aramid fiber, polypropylene fiber, polyethylene fiber, glass fiber, ceramic fiber, silica fiber, alumina fiber, lock Bags made of woven fabric or non-woven fabric using fibers such as inorganic fibers such as wool and slag wool; storage spaces formed using hydraulic compositions such as iron, plastic, wood, stone, ceramics, and cement as raw materials and the like.
The water-permeable portion of the containing means may be a part (one region) or the entirety (entire region) of the containing means. As an example of a storage means that is partially (one region) permeable to water, the lower part of the storage means is impervious to water from the viewpoint of preventing outflow of granular material with a small particle size (about 0.2 to 1 mm). and whose upper part is water-permeable.

The opening size of the water permeable portion is preferably 1 to 25 mm, more preferably 3 to 20 mm, particularly preferably 5 to 15 mm. If the opening dimension is 1 mm or more, small aquatic organisms (for example, crustaceans such as crabs, small animals such as small fish, and benthic organisms such as lugworms) can freely enter and exit the housing means. It becomes easy to get into the gaps between the stored granular materials and settle in. If the size of the opening is 25 mm or less, the granular material is less likely to flow out from the opening of the containing means, and large aquatic organisms that feed on small aquatic organisms can enter the inside of the containing means. Intrusion can be prevented.
Moreover, from the viewpoint of preventing outflow of the granular materials, it is preferable that the size of the opening is such that the granular materials stored in the storage means cannot pass through.

The accommodation means may be one or plural. The number of storage means varies depending on the size of the storage means, the amount of granular material to be stored, the place where the algae settlement structure is installed, etc., but is usually 1 to 100, preferably 3 to 50, More preferably 5-20.
The number of granular materials to be stored in the storage means varies depending on the size and shape of the granular materials and the capacity of the storage means. is.
The amount of the granular material contained in the algae settlement structure (the total amount of the granular material contained in each containing means in the case of having a plurality of containing means) varies depending on the capacity of the containing means, but is preferably 0.5 to 50 kg, more preferably 1 to 30 kg, particularly preferably 2 to 10 kg. If the amount is 0.5 kg or more, a larger amount of residue generated after acid treatment of rare earth-containing mud can be effectively utilized, and a larger amount of algae can be implanted. If the amount is 50 kg or less, installation work and removal work of the structure for algae settlement can be carried out without requiring a large amount of labor.

The structure for algae colonization of the present invention will be described below with reference to FIGS. 1 and 2. FIG.
In addition, in FIGS. 1 and 2, the same reference numerals are assigned to the parts having the same names.
In FIG. 1, the algae settlement structure 6 is formed by storing a plurality of granular materials 1 inside one storage means 2 .
In "1-a" of FIG. 1, the housing means 2 is formed by processing a plastic net into a bag shape. The granular material 1 has a grain size larger than the opening size of the plastic mesh forming the containing means 2, and is placed inside the containing means 2 so as not to flow out of the internal space of the containing means 2 to the outside. are housed in
"1-b" in FIG. 1 shows that the algae settlement structure 6 installed in the water in the state "1-a" causes algae to adhere to the containing means 2 and the granular material 1 over time. It shows the state of
In FIG. 2 , the algae settlement structure 6 includes a plurality of housing means 2 . Granular material (not shown) is stored inside each storage means 2 .
The plurality of storage means 2 are connected to each other by connection means 3 from the viewpoint of preventing the storage means 2 from flowing out in the water 8 and facilitating the installation and recovery of the algae settlement structure 6. .
The connecting means 3 may be any means that can fix the plurality of housing means 2 to each other, and examples thereof include binding bands, ropes, wires, and the like. Moreover, the plurality of storage means 2 may be arranged in a horizontal direction and connected, or may be stacked and connected in a vertical direction.

A movement restraining means 4 may be provided at one end of the connecting means 3 for the purpose of restraining the movement of the containing means 2 on the bottom 7 . The movement suppressing means 4 is not particularly limited as long as it can fix the algae settlement structure 6 to the water bottom 7 or its vicinity. and sandbags. Alternatively, the end of the connecting means 3 may be directly fixed to the bottom of the water 7, a quay wall, or the like using an anchor or the like.
At the other end of the connecting means 3, a buoyant body 5 may be provided for the purpose of facilitating the removal of the algae-growth structure 6 as a reference for the installation location of the algae-growth structure. Examples of the buoyant body 5 include buoys and rafts.

Next, a method for producing a structure for algae colonization of the present invention will be described.
The method for producing a structure for algae growth of the present invention comprises a baking step of obtaining a baked product by baking a dehydrated cake or slurry consisting of a residue generated after treating rare earth-containing mud with an acid, and the baking step. and a granulation step of crushing, cutting or classifying the material to obtain granulated materials. Each step will be described below.

[Baking process]
In the calcination step, a dehydrated cake or slurry (hereinafter also referred to as “calcination raw material”) consisting of a residue (usually acidic) generated after treating mud containing rare earth with acid is calcined to produce a calcined product. is the process of obtaining
As described above, the residue is desirably treated in advance to reduce the water content.
When a material other than the residue is used, the residue is mixed with the material other than the residue to prepare a mixture before granulation.
Also, the firing raw material may be dried before heating.

The heating temperature for obtaining the fired product (maximum temperature during heating) is preferably 1,070 to 1,130° C., more preferably 1,080 to 1,120° C., particularly preferably 1,090 to 1,110. °C. When the temperature is 1,070° C. or higher, the heating time required to obtain a baked product can be shortened. A larger amount of reduction in the volume of the residue can be achieved. When the temperature is 1,130° C. or less, it is possible to prevent excessive melting and volume reduction, resulting in a high-density baked product. Moreover, it is possible to prevent an excessive increase in energy required for heating and an increase in cost.
The heating time at the highest temperature in the firing step is preferably 15 to 40 minutes, more preferably 15 to 30 minutes, particularly preferably 20 to 25 minutes. If the heating time is 15 minutes or longer, more sufficient baking can be achieved. When the heating time is 40 minutes or less, the processing efficiency (production efficiency of granular materials) can be further improved.

The heating means for obtaining the baked product is not particularly limited, and both continuous means and batch-type means can be used.
Examples of continuous heating means include a rotary kiln and a tunnel furnace.
Batch-type heating means include, for example, an incinerator (using gas or the like as fuel), an electric furnace, a microwave heating device, and the like.
Among them, it is preferable to use a rotary kiln from the viewpoint of improving the efficiency of the treatment.
The sintered product obtained in the sintering step is usually a mixture of independent granules and lumps in which a plurality of granules are linked together (two or more lumps bonded together via a fused portion). The proportion of independent grains in the total amount of the fired product is usually 20% by mass or less. Therefore, in the present invention, a granulation step is required after the firing step.

[Granulation step]
The granulation step is a step of crushing, cutting, or classifying the fired product obtained in the firing step to obtain a granular material.
The means for crushing or cutting is not particularly limited as long as it can crush or cut the fired product obtained in the firing step. Examples of means for crushing include a jaw crusher and an impact crusher. etc., and means for cutting include a wire saw, a diamond cutter, and the like.
Moreover, a sieve etc. are mentioned as a means for classification. The coarse particles obtained by the classification are further crushed or cut to obtain granular materials, which can be used as the granular material in the present invention.

One or more of the granular materials obtained in the granulation step may be placed in water as they are as a structure for algae colonization. From the viewpoint of facilitating installation and recovery of the settlement structure, it may be used by being housed in a housing means by the following housing process.
[Accommodation process]
The accommodating step is a step of accommodating the granular materials obtained in the granulating step in the above-described accommodating means.
The storage means in which the granular material is stored may be used as it is as a structure for algae settlement, or may be connected via the above-described connection means (see No. 3 in FIG. 2). Alternatively, the movement suppressing means (see No. 4 in FIG. 2) or the buoyant body (see No. 5 in FIG. 2) may be provided at both ends of the connecting means.

By installing the structure for algae growth of the present invention in water (seawater, fresh water or brackish water), algae grow on the structure for algae growth (for example, the surface portion of a granular material), A fish reef or an algae reef can be created.
In addition, the structure for growing algae of the present invention has little adverse effect on the environment because it causes little excessive fluctuation of the pH of the water area in which it is installed and elution of heavy metals and the like from the structure for growing algae. be.
The place where the algae settlement structure is to be installed is not particularly limited, but any place in the shallow sea area of the coast where there are no fish reefs or algae reefs may be selected.

EXAMPLES The present invention will be specifically described below by way of examples, but the present invention is not limited to these examples.
[Materials used]
(1) Mud containing rare earths (deep-sea mud in the Pacific Ocean at a depth of 4,000 m or more; content of rare earths in the solid content of the mud: 2,000 ppm or more on a mass basis)
[Example 1]
Mud containing rare earths was immersed in 0.5N hydrochloric acid for 1 hour and then dehydrated with a centrifuge to a water content of 100% by mass to obtain a residue.
This residue was granulated (molded) using a plurality of types of ice trays having different recess sizes to obtain granules (particle size: 5 to 30 mm).
After drying the granules at 105° C. for 12 hours, the temperature was raised at a rate of 10° C./min in an electric furnace, and the maximum temperature was 1,100° C. for 20 minutes.
By crushing the obtained fired product with a crushing means (hammer), the lumps in which a plurality of granules are connected, contained in the fired product, are made into independent granules, and the particle size is 5 to 30 mm. A certain granular material was obtained.

Regarding the obtained granular materials, metals contained in wastes to be discharged to landfill sites, etc. prescribed in Article 5, Paragraph 1 of the Order for Enforcement of the Law Concerning the Prevention of Marine Pollution and Maritime Disasters in Public Notice 14 of the Environment Agency Mercury or its compounds (shown as "Hg" in Table 1), cadmium or its compounds (shown as "Cd" in Table 1), lead or its compounds (shown as "Pb" in Table 1), hexavalent chromium compounds (shown as "Cr ⁶⁺ " in Table 1), arsenic or its compounds (shown as "As" in Table 1), cyanide compounds (indicated by "CN" in Table 1), selenium or its compound (indicated by "Se" in Table 1), and fluoride (indicated by "F" in Table 1) were measured. . Table 1 shows the results.
Table 1 also shows the standard values for each elution amount stipulated in the "Prime Minister's Office Ordinance No. 6 of 1973".

Also, 15 liters of fresh water and 1,000 g of the obtained granular materials were placed in a tank, and then 15 goldfish were bred in the tank for one year. In rearing, circulation pumps and aeration were used. In addition, every 7 days, water equivalent to 10% by mass of 100% by mass of water in the water tank was replaced with fresh fresh water. Aside from this every 7 days, fresh water was added as needed to compensate for the evaporated water.
[Comparative Example 1]
Fifteen goldfish were bred for one year in the same manner as in Example 1, except that instead of 1,000 g of the granular material, an aquarium material (porous filter material having a pH-adjusting function) was added.
Table 2 shows the number of surviving goldfish and Table 3 shows the pH value of the water in the aquarium after each time (month) has elapsed.

From Table 1, it can be seen that the amount of heavy metals eluted from the granular material is below the standard value.
Moreover, from Table 2, it can be seen that the use of granular materials does not adversely affect the growth of goldfish.
Furthermore, from Table 3, even if the granular material is placed in water, the pH fluctuation (6.5 to 9.5) in one year is the same as the pH fluctuation (6.1 to 9.0) in Comparative Example 1. It turns out that it is about the same as
From these facts, it can be seen that the granular material used in the present invention has little adverse effect on the environment.

[Example 2]
As shown in FIGS. 1 and 2, inside a bag-shaped storage means 2 made by processing a plastic net, which is 11 cm long, 14 cm wide, 5 cm high, and has an opening size of 13 mm, Of the granular material 1 obtained in Example 1, about 500 g of the granular material 1 having a particle size of about 20 mm or more was prepared (see "1-a" in Fig. 1). Next, using a connecting means 3 made of a 16 m rope, the containing means 2 are connected in a row in the horizontal direction, and a weight of 8 kg is installed as a movement suppressing means 4 at one end of the connecting means 3, A polystyrene float was installed as the buoyant body 5 at the other end of the connecting means to complete the algae culture structure 6 .
The algae culture structure 6 was installed in a sea area with a water depth of 10 m and left for five months. When the algae culture structure 6 was recovered after 5 months, it was found that algae had adhered to the surfaces of the granular materials 1 and the containing means 2 (see "1-b" in Fig. 1). In addition, it was found that various aquatic organisms grow in the algae culture structure 6 (especially in the gaps between the granular materials 2).
The confirmed aquatic organisms are: aquatic organisms of the family Lutaceae (41 bodies), aquatic organisms of the lugworm family (19 bodies), a colony of aquatic organisms of the order Tustoptera, a colony of aquatic organisms of the family Kobkochemidae, and aquatic organisms of the family Lithoceridae. (4 bodies).

1 granular material 2 storage means 3 connecting means 4 movement suppressing means (weight)
5 buoyant body 6 structure for algal growth 7 bottom 8 water

Claims (6)

A structure for algae settlement for installation in water, comprising a granular material and a partially or wholly water-permeable housing means for containing the granular material ,
The granular material has a particle size of 4 to 40 mm and is obtained by baking a dehydrated cake or slurry, which is the residue generated after treating mud containing rare earths with acid.
A structure for algae settlement, wherein a water-permeable portion of the containing means has an aperture size of 3 to 15 mm, and is a size that does not allow the granular material to pass through . 2. The structure for algae colonization according to claim 1 , comprising a plurality of said containing means and connecting means for connecting said containing means. 3. The structure for algae growth according to claim 1 or 2 , further comprising a movement suppressing means for suppressing movement of the containing means on the bottom of the water. A method for producing the structure for algae colonization according to any one of claims 1 to 3 ,
A baking step of baking the dehydrated cake or slurry to obtain a baked product;
a granulation step of crushing, cutting or classifying the fired product to obtain the granular material;
A method for producing a structure for algae colonization, comprising: The method for producing a structure for algae growth according to claim 4, wherein the baking in the baking step is performed by heating the dehydrated cake or slurry at 1,070 to 1,130°C for 15 to 40 minutes. A method for growing algae using the structure for growing algae according to any one of claims 1 to 3 ,
a location selection step of selecting a location for installing the algae settlement structure;
A structure installation step of installing the algae settlement structure at the selected location;
A method for growing algae, comprising:

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