JP7393751B2 - Rare earth mud collection method and environmental load reduction method - Google Patents

Description

The present invention relates to a method for collecting rare earth mud and a method for reducing environmental load.

There are many liquid and gaseous natural resources, including oil and natural gas, on the ocean floor around the world. Furthermore, the existence of solid mineral resources such as manganese nodules has also become clear. Patent Documents 1 to 4 disclose a method for extracting liquid or gaseous natural resources, or a method for lifting mineral resources in a relatively shallow seabed.

Japanese Patent Application Publication No. 2012-172418 JP 2019-120063 Publication JP 2019-011568 Publication Special Publication No. 8-26740

It has been confirmed that there is a layer of mud containing rare earths beneath the ocean floor in the deep sea. This mud is called rare earth mud and is attracting attention as a new resource. However, the technology to efficiently extract rare earth mud from such deep seabeds has not yet been established.

The present invention provides a method for collecting rare earth mud that can also be applied to layers beneath the ocean floor in the deep sea. The present invention also provides a method for reducing the environmental burden caused by collecting rare earth mud from below the seabed.

The method for collecting rare earth mud according to the present invention includes the steps of (A) forming a depression on the seabed by excavating a layer under the seabed containing rare earth mud, and making a slurry containing rare earths contained in the depression; and (B) a step of injecting a replacement material having a higher density than the slurry into the depression, and in the step (B), the slurry is pushed up to a mud lifting mechanism located above the depression.

According to the above slurry sampling method, the slurry is pushed up to the pumping mechanism using a replacement material that has a higher density than the slurry containing rare earths, so slurry containing rare earths can be efficiently sampled without using large-scale underwater equipment. can. In addition, "slurry containing rare earths" as used in the present invention means rare earth mud having fluidity, or a mixed fluid containing at least rare earth mud and seawater.

The environmental load reduction method according to the present invention includes the steps of: (A) forming a depression on the seabed by excavating a sub-seafloor layer containing rare earth mud, and making a slurry containing rare earths contained in the depression; (B) a step of injecting a replacement material with a higher density than the slurry into the depression; in the (B) step, the slurry is pushed up to a mud pumping mechanism located above the depression, and after the (B) step, By maintaining the depression filled with the replacement material, formation of a low-oxygen region of seawater within the depression is suppressed. This environmental load reduction method is useful for reducing the environmental load caused by collecting rare earth mud from beneath the seabed.

Preferably, the replacement material includes cement. By solidifying the replacement material due to the hydration reaction of cement, after the above step (B) (after replacing the slurry with the replacement material), the state in which the depression is filled with the replacement material can be stably maintained for a sufficiently long period of time. I can do it. When the replacement material contains cement, it is preferable to further contain an admixture from the viewpoint of improving workability. The replacement material may include mud produced by the excavation in step (A) (for example, the remaining soil after removing the rare earth-enriched area). By using such mud, the amount of residual soil that must be disposed of as waste can be reduced.

The replacement material preferably has a viscosity of 40 to 500 mPa·s measured at a temperature of 20° C. and a shear rate of 100 s ⁻¹ . When the viscosity is 40 mPa·s or more, the state in which the depression is filled with the replacement material tends to be easily maintained. On the other hand, when the viscosity is 500 mPa·s or less, pressure loss when transferring the replacement material tends to be reduced. It is preferable that the density A (unit: g/cm ³ ) of the replacement material under atmospheric pressure and the density B (unit: g/cm ³ ) of the slurry under atmospheric pressure satisfy the condition expressed by the following inequality.
A-B≧0.03
In other words, if the difference between density A and density B is 0.03 g/ ^cm3 or more, the replacement material will settle under the slurry containing rare earths in a short time even in depressions under the seabed, and the replacement material will reduce the slurry. can be pushed up stably.

According to the present invention, there is provided a method for collecting rare earth mud that can be applied to layers below the seabed in the deep sea. Further, according to the present invention, a method is provided for reducing the environmental load caused by collecting rare earth mud from below the seabed.

FIG. 1 is a sectional view schematically showing an embodiment of a rare earth mud collecting system according to the present invention. FIG. 2 is a cross-sectional view schematically showing how a mud collection pipe is penetrated into the layer below the seabed. FIG. 3 is a cross-sectional view schematically showing how the slurry in the mud collecting pipe is transferred to the mud pumping pipe. FIG. 4 is a cross-sectional view schematically showing how the slurry in the slurry pumping pipe is transferred upward by the circulation flow. FIG. 5 is a plan view schematically showing the apparatus used in elemental experiments regarding the replacement behavior of replacement materials.

Embodiments of the present invention will be described below with reference to the drawings. The present invention is not limited to the following embodiments.

<Rare earth mud recovery system>
FIG. 1 is a cross-sectional view schematically showing a rare earth mud recovery system according to the present embodiment. The recovery system 10 is for recovering rare earth mud existing in a layer L under the seabed in the deep sea exceeding 5000 meters in the form of a slurry. FIG. 1 shows how rare earth mud is desilted by the stirring device 3. The recovery system 10 includes a mud collecting pipe 1 penetrated into the layer L under the seabed, a stirring device 3, a mud lifting pipe 5 (sludge lifting mechanism) connected to the mud collecting pipe 1, and an annulus switching mechanism 7. Equipped with.

The mud collecting pipe 1 is for removing rare earth mud near the seabed. Furthermore, a slurry S containing rare earth mud is prepared in the mud collecting pipe 1. The mud collecting pipe 1 includes a cylindrical portion 1a, an upper plate 1b that closes the upper end of the cylindrical portion 1a, and an opening 1c passing through the upper plate 1b. The mud collecting pipe 1 in FIG. 1 has its tip penetrated from the seabed F to the layer L.

The stirring device 3 includes a drill pipe 3a extending from a ship on the sea (not shown), and a blade 3b provided on the lower end side and outside of the drill pipe 3a. The blade 3b is configured to rotate as the drill pipe 3a rotates, and to move vertically as the drill pipe 3a moves vertically. As the blade 3b rotates and moves downward in the mud collecting pipe 1, a depression C is formed in the layer L, and the rare earth mud is mixed with seawater to obtain a fluid slurry S.

The annulus switching mechanism 7 includes an annulus closing mechanism 7a, a drill pipe closing valve 7b, and a shutter mechanism 7c. The mud lifting pipe 5 is connected to the opening 1c of the mud collecting pipe 1 via an annulus closing mechanism 7a. The mud pumping pipe 5 can generate a circulating flow together with the drill pipe 3a. Specifically, the mud lifting pipe 5 constitutes a double pipe together with the drill pipe 3a, and the drill pipe 3a (inner pipe) and the annulus portion 5a (the outer surface of the drill pipe 3a and the inner surface of the mud lifting pipe 5) The defined area) can be communicated with each other at a position above the upper plate 1b (see FIG. 4).

The annulus closing mechanism 7a is operated from the ship or by an ROV. The drill pipe 3a is closed with a drill pipe closing valve 7b as required. Further, the shutter mechanism 7c allows communication between the inside of the drill pipe 3a and the annulus portion 5a as necessary. A subsea control device (not shown) controls these. Further, a subsea accumulator (not shown) is a power source for operating these mechanisms. The drill pipe closing valve 7b is provided at a position corresponding to the lower end of the mud lifting pipe 5 in the drill pipe 3a, and by operating this valve, the mud lifting pipe 5 can be brought out of communication with the mud collecting pipe 1. It is possible. The shutter mechanism 7c is provided at a higher position than the drill pipe closing valve 7b in the drill pipe 3a, and by operating the shutter mechanism 7c, the inside of the drill pipe 3a and the annulus portion 5a can be communicated at that position. .

<How to collect rare earth mud>
A method for recovering rare earth mud using the recovery system 10 will be described with reference to FIGS. 1 to 4. The rare earth mud recovery method according to this embodiment includes the following steps.
(a) Step of penetrating the mud collecting pipe 1 into the layer L under the seabed containing rare earth mud (see FIG. 2).
(b) Step of preparing slurry S containing rare earths by desilting rare earth mud in the mud collection pipe 1 (see Figure 1)
(c) Step of pushing up the slurry S in the mud collecting pipe 1 into the mud lifting pipe 5 by injecting the replacement material R into the mud collecting pipe 1 (see FIG. 3)
(d) Process of transferring the slurry S to a ship on the sea using the slurry pump 5 (see Figure 4)

As shown in FIG. 2, step (a) is a step in which the mud collection pipe 1 is penetrated into the layer L under the seabed. With the mud collection pipe 1 attached to the tip of the mud collection pipe 5, the mud collection pipe 5 is lowered from the ship, and the tip side of the mud collection pipe 1 is pierced into the seabed F. The mud collecting pipe 1 sinks into the layer L due to its own weight.

Step (b) is a step of preparing slurry S in the mud collecting pipe 1 by desilting the rare earth mud with the blade 3b (see FIG. 1). For example, the blade 3b is attached to the tip of the drill pipe 3a and descends inside the mud lifting pipe 5, and reaches the inside of the mud collecting pipe 1. Seawater is supplied from the ship through the drill pipe 3a, and the blade 3b is rotated and gradually lowered while spouting the seawater from the opening (not shown) of the blade 3b. As a result, the rare earth mud is loosened in the mud collecting pipe 1 and becomes fine particles. A slurry S is prepared in the mud collecting pipe 1 by desilting the rare earth mud. The concentration of slurry S can be adjusted by adjusting the amount of seawater supplied from the ship. Note that the physical properties of the slurry S, such as the density, can be measured with a sensor placed or dropped into the slurry pipe 1.

Step (c) is a step in which the slurry S in the mud collecting pipe 1 is pushed up into the mud lifting pipe 5 by injecting the replacement material R into the mud collecting pipe 1 (see FIG. 3). A replacement material R having a higher density than the slurry S is supplied into the mud collection pipe 1 through the drill pipe 3a. As a result, the slurry S in the mud collecting pipe 1 is pushed up into the mud lifting pipe 5. This process is called sludge extraction.

The replacement material R will be explained. The replacement material R is a fluid with a higher density than the slurry S. It is preferable that the density A (unit: g/cm ³ ) of the replacement material R under atmospheric pressure and the density B (unit: g/cm ³ ) of the slurry S under atmospheric pressure satisfy the condition expressed by the following inequality.
A-B≧0.03
In other words, since the difference between density A and density B is 0.03 g/cm3 ^or more, the replacement material R settles under the slurry S in a short time even in the depression C under the seabed, and the replacement material R The slurry S can be stably pushed up toward the slurry pumping pipe 5. The difference between density A and density B is more preferably 0.05 g/cm ³ or more, and even more preferably 0.08 g/cm ³ or more. Note that the upper limit of the difference between density A and density B is, for example, 2.0 g/cm ³ .

It is preferable that the replacement material R contains cement. As the replacement material R solidifies due to the hydration reaction of cement, after the above step (c) (after replacing the slurry S with the replacement material R), the depression C is stably and sufficiently filled with the replacement material R. Can be maintained over a long period of time. As the type of cement, for example, Portland cement or alumina cement can be used, and early-strength Portland cement is preferred because it is economical and hardens in a relatively short period of time. When the replacement material R contains cement, it is preferable to further contain an admixture from the viewpoint of improving workability. Examples of admixtures that can be used include thickeners, separation reducing agents, water reducing agents, AE water reducing agents, high performance AE water reducing agents, and fluidizing agents.

The replacement material R may include mud produced by the excavation in step (a) (for example, the remaining soil after removing the rare earth-enriched area). By using such mud, the amount of residual soil that must be disposed of as waste can be reduced.

The replacement material R preferably has a viscosity of 40 to 500 mPa·s, more preferably 80 to 400 mPa·s, and even more preferably 100 to 300 mPa·s, as measured at a temperature ^of 20°C and a shear rate of 100 s −1. It is s. When this viscosity is 40 mPa·s or more, the state in which the depression C is filled with the replacement material tends to be easily maintained. On the other hand, when the viscosity is 500 mPa·s or less, the pressure loss when transferring the replacement material R tends to be reduced.

The step (d) is a step in which the slurry S transferred into the slurry pumping pipe 5 through the step (c) is transferred toward a ship on the sea (see FIG. 4). By supplying seawater from the drill pipe 3a, a circulation flow can be generated in the mud lifting pipe 5 (see the arrow in FIG. 4). This process is called pumping. Note that the destination of the slurry S is not limited to a ship on the sea, but may be, for example, a treatment facility in the sea or on the sea.

According to the embodiment described above, since sludge removal and slurry preparation are performed within the sludge collecting pipe 1, slurry having a concentration suitable for sludge removal can be stably prepared. Further, after the step (c), by maintaining the state in which the depression C is filled with the replacement material R, it is possible to suppress the formation of a low-oxygen region of seawater in the depression C. It is possible to reduce the environmental burden caused by extracting rare earth mud from beneath the seabed.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments. For example, in the above embodiment, the case where rare earth mud is collected from under the seabed in a deep sea exceeding 5,000 m in depth is illustrated, but the present invention may be applied to shallower sea areas (for example, in a water depth of 1,000 to 3,000 m or 3,000 to 5,000 m). May be applied.

In order to prepare two types of replacement materials (seafloor clay replacement material and simulated clay replacement material), the following materials were prepared.
(1) Early strength Portland cement (manufactured by Ube Mitsubishi Cement Co., Ltd.)
(2) Artificial seawater (tetramarine salt, manufactured by GEX)
(3) Cellulose thickener (Metrose 3403Q, manufactured by Shin-Etsu Chemical Co., Ltd.)
(4) Seabed clay off the coast of Minamitorishima (5) Bentonite (Kunigel V1, manufactured by Kunimier Kogyo Co., Ltd.)

<Preparation of submarine clay replacement material>
The above materials were mixed in the proportions shown in Table 1, and a submarine clay replacement material was prepared as follows. That is, artificial seawater was added to the seabed clay off the coast of Minamitorishima, and the mixture was stirred for 2 minutes using a hand mixer. Thereafter, cement and a thickener were added, and the mixture was again stirred for 2 minutes using a hand mixer to obtain a submarine clay replacement material. The blending ratio of cement and admixtures in Table 1 is based on the total mass of the replacement material, and the water content of clay is the value before adding cement and admixtures (water mass/clay mass) (Table 2 (The same applies to

<Preparation of simulated clay replacement material>
The above materials were blended in the proportions shown in Table 2, and a simulated clay replacement material was prepared as follows. That is, after artificial seawater was added to bentonite and stirred for 2 minutes with a hand mixer, cement and a thickener were added, and the mixture was stirred again with a hand mixer for 2 minutes to obtain a simulated clay replacement material.

<Measurement of material properties of replacement materials>
(1) Viscosity Using a rheostress meter (manufactured by Anton Paar, MCR102), the viscosity of the replacement material was measured at a temperature of 20° C. and a shear rate of 100 s ⁻¹ .
(2) Dimensional stability A 300 cc cup was filled with artificial seawater, 300 cc of replacement material was poured into it, and the volume of the replacement material 24 hours later was measured. The dimensional change rate (volume change rate) was calculated by substituting the measured values into the following formula.
Dimensional change rate (%) = [300 - (volume of replacement material after 24 hours)] / 300 × 100
(3) Density Pour the replacement material into a 30cc capacity mass until it wears out, and apply a light impact from a height of 5cm 4 to 5 times to remove air bubbles, then calculate the density from the measured mass. did.

From the results shown in Tables 1 and 2, it is useful to adjust the viscosity of the replacement material to 40 mPa·s or more in order to reduce the dimensional change rate of the replacement material. At least one of the following methods may be employed to adjust the viscosity of the replacement material to 40 mPa·s or more.
- Lower the moisture content of clay to less than 88% by mass.
- Set the amount of cement as the replacement material to 5% by mass or more.
- Add a thickener to the replacement material.

<Elemental experiments on replacement behavior of replacement materials>
Three types of simulated slurries (simulating slurries containing rare earths) shown in Table 3 were prepared.

An experiment was conducted as follows to evaluate whether the slurries A to C, which imitate slurries containing rare earths, can be replaced by a replacement material due to density differences.
(Experimental device)
We prepared experimental equipment with the following sizes that imitated a mud collection pipe and a drill pipe (see Figure 5).
・Size of two formworks (made of transparent resin): width 60cm, height 54cm
・Distance between two formworks: 2cm
- Shape of the top of the simulated mud collection pipe: roof-like - Simulated drill pipe: rubber hose (diameter 2cm)

(Injection method of replacement material)
・Toremi type: A method in which replacement material is injected while a simulated drill pipe is installed at the bottom of the simulated mud collection pipe.
・Free-fall method: A method in which replacement material is poured into a simulated mud collection pipe while a simulated drill pipe is installed at the top of the pipe.

(Evaluation of recovery rate of simulated slurry)
A photograph of the simulated slurry before the replacement material was injected and a photograph of the remaining portion of the simulated slurry at the time when the replacement material was injected until the replacement between the replacement material and the simulated slurry apparently stopped were taken. The injection time of the replacement material was 12 minutes at maximum. Using image analysis software Image-J, the area of the simulated slurry before and after injection of the replacement material was determined, and the recovery rate of the simulated slurry was calculated from the ratio. Table 4 shows the results of the experiment.

1... Sludge collection pipe, 1a... Cylindrical part, 1b... Upper plate, 1c... Opening, 3... Stirring device, 3a... Drill pipe, 3b... Blade, 5... Sludge lifting pipe (sludge lifting mechanism), 5a... Annulus part, 7... Annulus section switching mechanism, 7a... Annulus section closing mechanism, 7b... Drill pipe closing valve, 7c... Shutter mechanism, 10... Recovery system, C... Depression, F... Seabed, L... Layer

Claims (8)

(A) forming a depression on the seabed by excavating a layer beneath the seabed containing rare earth mud, and causing a slurry containing rare earths to be accommodated in the depression;
(B) injecting a replacement material having a higher density than the slurry into the depression;
including;
The replacement material has a viscosity of 40 to 500 mPa·s measured at a temperature of 20° C. and a shear rate of 100 s ⁻¹ ,
A method for collecting rare earth mud, in which the slurry is pushed up to a mud pumping mechanism located above the depression in the step (B). (A) forming a depression on the seabed by excavating a layer beneath the seabed containing rare earth mud, and causing a slurry containing rare earths to be accommodated in the depression;
(B) injecting a replacement material having a higher density than the slurry into the depression;
including;
Density A (unit: g/cm ³ ) of the replacement material under atmospheric pressure and density B (unit: g/cm ³ ) of the slurry under atmospheric pressure satisfy the condition expressed by the following inequality,
A-B≧0.03
A method for collecting rare earth mud, in which the slurry is pushed up to a mud pumping mechanism located above the depression in the step (B). The method for collecting rare earth mud according to claim 1 or 2 , wherein the replacement material contains cement. The method for collecting rare earth mud according to claim 3 , wherein the replacement material further includes an admixture. The method for collecting rare earth mud according to any one of claims 1 to 4 , wherein the replacement material includes mud produced by excavation in the step (A). (A) forming a depression on the seabed by excavating a layer beneath the seabed containing rare earth mud, and causing a slurry containing rare earths to be accommodated in the depression;
(B) injecting a replacement material having a higher density than the slurry into the depression;
including;
The replacement material has a viscosity of 40 to 500 mPa·s measured at a temperature of 20° C. and a shear rate of 100 s ⁻¹ ,
In the step (B), the slurry is pushed up to a mud lifting mechanism located above the depression, and
After the step (B), the depression is maintained in a state filled with the replacement material, thereby suppressing the formation of a low-oxygen region of seawater in the depression. (A) forming a depression on the seabed by excavating a layer beneath the seabed containing rare earth mud, and causing a slurry containing rare earths to be accommodated in the depression;
(B) injecting a replacement material having a higher density than the slurry into the depression;
including;
Density A (unit: g/cm ³ ) of the replacement material under atmospheric pressure and density B (unit: g/cm ³ ) of the slurry under atmospheric pressure satisfy the condition expressed by the following inequality,
A-B≧0.03
In the step (B), the slurry is pushed up to a mud lifting mechanism located above the depression, and
After the step (B), the depression is maintained in a state filled with the replacement material, thereby suppressing the formation of a low-oxygen region of seawater in the depression. The environmental load reduction method according to claim 6 or 7, wherein the replacement material contains cement.

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