WO2012033083A1 - Magnesium recovery method and magnesium recovery apparatus - Google Patents

Abstract

In this magnesium recovery method and this magnesium recovery apparatus, anodically electrolyzed water (7a) and cathodically electrolyzed water (7b) both generated by the electrolysis of seawater are separated from each other, an alkaline material is introduced into the anodically electrolyzed water to adjust the pH value of the anodically electrolyzed water, magnesium is allowed to precipitate in the cathodically electrolyzed water in the form of magnesium hydroxide and is then recovered, the pH-adjusted anodically electrolyzed water and the cathodically electrolyzed water after the fixing of a carbonate salt are joined together, and the joined solution is adjusted to the same pH value as that of seawater and is then discharged. In this manner, magnesium can be recovered from seawater while minimizing an environmental load.

Description

Magnesium recovery method and magnesium recovery device

The present invention relates to a method for recovering magnesium from seawater by electrolysis of seawater and an apparatus therefor.
This application claims priority based on Japanese Patent Application No. 2010-203353 for which it applied to Japan on September 10, 2010, and uses the content here.

In recent years, magnesium with high specific strength has been attracting attention as a next-generation structural material, and demand is expected to increase in the future. However, magnesium smelted mainly from minerals is unevenly distributed in a limited area, and in order to secure a stable supply together in the future, it is desirable to establish a procurement method other than importing magnesium.

As is well known, magnesium exists as a mineral and also in seawater. Therefore, if magnesium can be recovered from seawater, it will greatly contribute to the stable supply of magnesium. On the other hand, when a large amount of magnesium is recovered from seawater, there is a possibility of placing a burden on the environment, such as changing the composition of seawater. Therefore, the recovery of magnesium from seawater must be done without burdening the environment.

Patent Document 1 discloses an electrolytic cell that obtains fresh water, chlorine gas, and magnesium hydroxide from seawater. Patent Document 2 electrolyzes the pH of deep ocean water or adds an alkali to adjust the pH. A method is shown in which a hydroxide such as Mg and Ca is precipitated and recovered as a precipitate.

JP-A-51-77586 JP 2007-167786 A

In view of such circumstances, the present invention provides a magnesium recovery method and a magnesium recovery apparatus that can recover magnesium from seawater without imposing a burden on the environment.

The present invention electrolyzes seawater, separates anode electrolyzed water and cathode electrolyzed water generated by electrolysis of seawater, adjusts the pH by introducing an alkaline material into the anode electrolyzed water, and magnesium in the cathode electrolyzed water Is collected as magnesium hydroxide, recovered, and the anode electrolyzed water after pH adjustment and the cathode electrolyzed water after magnesium hydroxide recovery are merged to release the same pH as seawater.

In this case, the alkali material is preferably waste concrete. Moreover, it is desirable to use iron, which is a soluble metal, for the anode-side electrode, and to dissolve iron ions in the anode electrolyzed water during the seawater electrolysis process.

Further, the present invention is produced by an electrolytic cell having an anode and a cathode, a diaphragm partitioning the inside of the electrolytic cell into an anode side region including the anode and a cathode side region including the cathode, and the anode side region. A first treatment tank for storing the anode electrolyzed water, a second treatment tank for storing the cathode electrolyzed water generated in the cathode side region, a power supply device for supplying power to the anode and the cathode, and the first treatment An alkali material charging device for charging an alkali material into the tank; and a recovery means for recovering the magnesium hydroxide precipitated in the second processing tank. The drainage from the first processing tank and the second processing tank The present invention relates to a magnesium recovery apparatus that joins drainage and discharges it with a pH equivalent to that of seawater.

In this case, it is desirable that the power supply device has at least one of a solar cell, a fuel cell, a wind power generator, a wave power generator, an ocean temperature difference power generation device, and a solar thermal power generation device. The power supply device preferably includes a fuel cell that uses hydrogen gas generated on the cathode side and oxygen gas generated on the anode side. Moreover, it is desirable that the alkali material input from the alkali material input device is waste concrete. Furthermore, it is preferable that the anode contains iron as a consumable electrode, and the consumable electrode dissolves iron ions.

According to the magnesium recovery method of the present invention, seawater is electrolyzed, anode electrolyzed water and cathode electrolyzed water generated by seawater electrolysis are separated, and an alkaline material is added to the anode electrolyzed water to adjust the pH, Magnesium is precipitated and recovered as magnesium hydroxide in the cathode electrolyzed water, and the anode electrolyzed water after pH adjustment and the cathode electrolyzed water after magnesium hydroxide recovery are combined and discharged at a pH equivalent to seawater. Therefore, according to the present invention, magnesium can be recovered from seawater without placing a burden on the environment.

Moreover, in the magnesium recovery method of the present invention, industrial waste can be treated together by using the alkali material as waste concrete.

Further, in the magnesium recovery method of the present invention, by using iron which is a soluble metal for the anode side electrode, iron ions are dissolved in the anode electrolyzed water during the seawater electrolysis process, and iron ions which are phytoplankton nutrients are submerged in the sea. To be supplied. As a result, reproduction of phytoplankton is promoted, and carbon dioxide gas can be fixed by phytoplankton.

Further, according to the magnesium recovery apparatus of the present invention, an electrolytic cell having an anode and a cathode, a diaphragm partitioning the inside of the electrolytic cell into an anode side region including the anode and a cathode side region including the cathode, A first treatment tank for storing anode electrolyzed water generated in the anode side region, a second treatment tank for storing cathode electrolyzed water generated in the cathode side region, and a power supply device for supplying power to the anode and cathode And an alkali material charging device for charging an alkali material into the first treatment tank, and a recovery means for collecting magnesium hydroxide precipitated in the second treatment tank, and the waste water from the first treatment tank, By combining the waste water from the second treatment tank, waste water having a pH equivalent to that of seawater is discharged. Therefore, magnesium can be recovered from seawater without placing a burden on the environment.

Further, in the magnesium recovery apparatus of the present invention, the power supply apparatus has at least one of a solar cell, a fuel cell, a wind power generator, a wave power generator, an ocean temperature difference power generation device, and a solar thermal power generation device. Magnesium can be recovered without imposing a burden.

In the magnesium recovery apparatus of the present invention, the power supply device includes a fuel cell that uses hydrogen gas generated on the cathode side and oxygen gas generated on the anode side. The part is again used for seawater electrolysis. Therefore, energy saving can be achieved.

Also, in the magnesium recovery apparatus of the present invention, waste concrete that is industrial waste can be treated together by using waste alkali as the alkali material thrown from the alkali material throwing device.

Moreover, in the magnesium recovery apparatus of the present invention, when the anode contains iron as a consumable electrode, the consumable electrode dissolves iron ions, so iron ions that are phytoplankton nutrients are supplied into the sea. As a result, the reproduction of phytoplankton is promoted, and the excellent effect that carbon dioxide gas can be fixed by phytoplankton is exhibited.

It is a conceptual diagram of the Example of this invention. The present embodiment is a graph showing the in cathode current density and CaCO ₃ and Mg _{(OH) 2} precipitation ratio. It is a block diagram which shows the material balance in the Example of this invention. It is a schematic block diagram which shows the magnesium collection | recovery apparatus based on the Example of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

First, the principle of the embodiment of the present invention will be described with reference to FIG.

In FIG. 1, 1 is an electrolytic cell, 2 is a first treatment tank, and 3 is a second treatment tank.

The electrolytic cell 1 has an electrolytic treatment container 4 made of a corrosion resistant material such as stainless steel, and the electrolytic treatment container 4 has an inlet 5 at the upstream end and an outlet 6 at the downstream end. Seawater 7 flowing in from the inflow port 5 flows uniformly through the inside of the electrolytic treatment container 4 and flows out from the outflow port 6.

As the means for forming the flow of the seawater 7, various means are adopted. For example, the electrolytic treatment container 4 may be submerged in water, and the seawater 7 may be circulated inside the electrolytic treatment container 4 by using a sea current, or a screw or the like is provided at the inlet 5 and the screw is rotated by a motor. The seawater 7 may be formed by using a pump or the like and supplied to the inlet 5.

A diaphragm 8 is provided inside the electrolytic treatment container 4 along the flow direction of seawater. The diaphragm 8 partitions the inside of the electrolytic treatment container 4 into two, and as a result, a flow of seawater 7 separated by the diaphragm 8 is formed in the electrolytic treatment container 4.

The diaphragm 8 is made of a material and a structure through which an electric current is passed so that the separated flows do not mix or the mixing is suppressed. For example, a tiled unglazed plate or a synthetic resin porous sheet is used.

When the inside of the electrolytic treatment container 4 is partitioned by the diaphragm 8, various forms such as partitioning up and down, partitioning left and right, and concentric circles are conceivable. However, the inside of the electrolytic treatment container 4 is partitioned vertically by the diaphragm 8 below. The case will be described.

A positive electrode (anode) 9 is provided along the upper wall surface of the electrolytic treatment container 4, a negative electrode (cathode) 11 is provided along the lower wall surface, and the anode 9 and the cathode 11 are connected to the positive electrode and the negative electrode of the power supply device 12, respectively. Connecting. Therefore, the inside of the electrolytic processing container 4 is partitioned by the diaphragm 8, so that the anode side region 9 a and the cathode side region 11 a are formed in the electrolytic processing container 4.

Although the power supply source of the power supply device 12 is arbitrary, the power supply source using natural energy, such as solar power generation, wind power generation, wave power generation, ocean temperature difference power generation, solar thermal power generation, or fuel in which emissions are harmless A battery is preferred. Moreover, a composite apparatus using two or more of power generation sources such as solar power generation, wind power generation, wave power generation, ocean temperature difference power generation, solar thermal power generation, and fuel cell may be used. Further, when power can be supplied from the power plant, the surplus power at night may be used.

As the anode 9, an insoluble metal such as titanium or a porous plate bucket (consumable electrode storage container) in which a soluble metal is charged as the consumable electrode material 13 is used. Note that iron is preferable as the consumable electrode material 13 to be charged. Not only is iron readily available as a waste material, but dissolved iron ions are nutrients for the growth of phytoplankton. As a result, phytoplankton is propagated by supplying iron ions into seawater, and carbon dioxide fixation by phytoplankton can also be expected.

The cathode 11 is made of titanium plated with platinum. Further, a hydrogen recovery device 14 is provided in the vicinity of or opposite to the cathode 11, and the hydrogen recovery device 14 recovers hydrogen gas generated on the cathode 11 side. Seawater (anode electrolyzed water 7a) flowing through the anode 9 side (anode side region 9a) is guided to the first treatment tank 2, and seawater (cathode electrolyzed water 7b) flowing through the cathode 11 side (cathode side region 1 1 a). ) Is guided to the second treatment tank 3.

The first treatment tank 2 has a waste concrete charging device 15, and concrete, which is a waste, is charged into the first treatment tank 2 by the waste concrete charging device 15. The waste concrete to be added is preferably pulverized and has a large surface area, and further preferably is one from which aggregates such as sand and stone have been removed.

Hydrogen gas recovered in the seawater 7 is supplied to the second treatment tank 3 as a reducing agent for the fuel cell. Further, in the second treatment tank 3, precipitated Mg (OH) ₂ is precipitated, and the precipitated Mg (OH) ₂ is recovered. The anode electrolyzed water 7a flowing out from the first treatment plant 2 and the cathode electrolyzed water 7b flowing out from the second treatment tank 3 are merged, and after pH is adjusted, discharged into the sea.

Hereinafter, the operation of this embodiment will be described.

By applying a voltage between the anode 9 and the cathode 11 and energizing between the anode 9 and the cathode 11, seawater electrolysis occurs, and the following reactions (1) and (2) mainly occur on the cathode 11 side. .

_{H 2 O + 1 / 2O 2} + 2e - → 2OH - (1)
2H ₂ O + 2e ⁻ → 2OH ⁻ + H ₂ (2)

Therefore, since OH ⁻ (hydroxide ion) is generated, the pH of seawater (cathode electrolyzed water 7b) rises on the cathode side, and CaCO ₃ and Mg (OH) ₂ are generated as shown in FIG. Further, when the current amount per unit area of the cathode 11 and the cathode current density Dk (A / ^{m 2),} cathode - de current density Dk and CaCO ₃ and Mg _{(OH) 2} precipitation ratios are shown in Figure 2 It becomes like. That is, as the cathode current density Dk increases, the deposition ratio of Mg (OH) ₂ increases, and the deposition of Mg (OH) ₂ occurs when the cathode current density Dk exceeds 2 (A / m ² ). It becomes saturated. Note that, until the cathode current density Dk is 2 (A / m ² ), the precipitation of CaCO ₃ gradually decreases and the precipitation of Mg (OH) ₂ gradually increases. Therefore, cathode - by controlling the de current density Dk, CaCO ₃ and Mg _{(OH) 2} precipitation ratio control, or it is possible to CaCO ₃ and Mg _{(OH) 2} selective precipitation.

Therefore, by performing electrolysis with the cathode current density Dk set high, that is, according to FIG. 2, by performing electrolysis of seawater with a cathode current density Dk of 2 [A / m ² ] or more, precipitates Most of this can be made approximately Mg (OH) ₂ .

The cathode electrolyzed water 7b is stored in the second treatment tank 3 with Mg (OH) ₂ precipitated. The precipitated Mg (OH) ₂ is precipitated in the second treatment tank 3, and the precipitate is recovered by the precipitate recovery means 16.

In the seawater electrolysis process, oxygen gas is generated on the anode 9 side and hydrogen gas is generated on the cathode 11 side. The generated hydrogen gas is recovered by the hydrogen recovery device 14, and when a fuel cell is used for the power supply device 12, it is supplied to the fuel cell as a reducing agent.

Next, when iron is used as the consumable electrode material 13 on the anode 9 side, the following reaction occurs and iron is dissolved. Furthermore, hydrolysis of iron ions produces ferrous hydroxide and H ⁺ , thereby lowering the pH of seawater (anode electrolyzed water 7a) on the anode 9 side.

Fe → Fe ²⁺ + 2e ⁻ (3)
Fe ²⁺ + 2H ₂ O → Fe (OH) ₂ + 2H ⁺ (4)

The anode electrolyzed water 7a flowing into the first treatment tank 2 is acidified by 2H ⁺ . Therefore, when waste concrete (Ca (OH) ₂ ) is introduced into the first treatment tank 2, the acid seawater is neutralized by the waste concrete as shown in the following formula.
Ca (OH) ₂ + 2H ⁺ → Ca ²⁺ + 2H ₂ O (5)

When an insoluble metal is used for the anode 9 or when electrolysis of seawater is performed at a high current density, chlorine Cl ₂ is generated, and HCl and HClO are generated as Cl ₂ is generated. Since HCl is strongly acidic and HClO is a harmful substance to living organisms, it is electrolyzed with a current density that suppresses the generation of HCl and HClO as much as possible. However, as described above, since the waste concrete (Ca (OH) ₂ ) is put into the anode electrolyzed water 7a,

Ca (OH) ₂ + HC1 → CaC1 ₂ + 2H ₂ O (6)
HCl is neutralized by this reaction.

And the seawater neutralized in the 1st processing tank 2 joins the seawater which flows out of the 2nd processing tank 3, and is discharged in the sea. In this case, by controlling the amount of concrete dissolved in the anode electrolyzed water 7a and the amount of carbon dioxide gas blown into the cathode electrolyzed water 7b, the pH of the seawater after merging is about 8.0, that is, equivalent to the pH of the seawater. It is adjusted so that

Therefore, according to the present invention, Mg (OH) ₂ can be recovered continuously, and since waste concrete is used in the fixing process, industrial waste can be processed in parallel. Furthermore, since the seawater discharged after the recovery of Mg (OH) ₂ is equivalent to the pH of natural seawater, there is no burden on the environment. In addition, iron ions dissolved in the electrolysis process propagate phytoplankton, which contributes to fixation of carbon dioxide.

As described above, oxygen gas is generated on the anode 9 side and hydrogen gas is generated on the cathode 11 side in the process of seawater electrolysis. When a fuel cell is used for the power supply device 12, oxygen gas and hydrogen gas are supplied to the fuel cell and used as fuel for power generation.

Next, an example of material balance in the above embodiment will be described with reference to FIG. In FIG. 3, the same components as those shown in FIG.

The electrolytic reaction is changed by changing the cathode current density Dk, and the electrolytic reaction is promoted by increasing the cathode current density Dk. Therefore, by controlling the cathode current density Dk, it is possible to control the pH on the anode 9 side and the cathode 11 side in the process of recovering Mg (OH) ₂ .

First, the pH of the cathode electrolyzed water 7b is adjusted to about 10 to 11 by electrolysis, and all Ca ²⁺ and Mg ²⁺ in seawater are precipitated. At this time, the pH of the anode electrolyzed water 7a is about 3 to 4. In order to efficiently recover Mg (OH) ₂ , the cathode current density Dk is set to 2 [A / m ² ] or more.

Further, Mg (OH) ₂ precipitated in the second treatment tank 3 is collected. The pH of the cathode electrolyzed water 7b flowing out from the second treatment tank 3 is about 10-11. In the first treatment tank 2, waste concrete is introduced, and the pH of the anode electrolyzed water 7 a flowing out from the first treatment tank 2 is adjusted to about 4 to 5. The pH of the anodic electrolyzed water 7a flowing out is an example, and when the anodic electrolyzed water 7a and the cathodic electrolyzed water 7b are merged, the amount of the waste concrete input is set so that the pH becomes 8.0 to 8.2. adjust. By setting the pH of the discharged wastewater to 8.0 to 8.2, Mg (OH) ₂ can be recovered while discharging the wastewater without changing the physical characteristics of the seawater. Therefore, there is no load on the environment.

By refining the collected Mg (OH) ₂ , Mg metal can be produced.

In the above embodiment, waste concrete is used as the neutralizing agent for the anode electrolyzed water 7a. However, the neutralizing agent may be any waste having an alkaline property such as coal ash generated at a thermal power plant.

In the above embodiment, seawater electrolysis was performed while flowing seawater in the electrolytic cell 1, but an open / close valve was provided at each of the inlet 5 and outlet 6, and seawater electrolysis was performed with the inlet 5 and outlet 6 closed. It is good also as a batch type which replaces the seawater in the electrolytic cell 1 after electrolytic treatment.

FIG. 4 shows an outline of the Mg (OH) ₂ recovery apparatus according to the embodiment of the present invention.

In FIG. 4, the same components as those shown in FIG. In the embodiment shown in FIG. 4, a fuel cell 18 is shown as a power generation source.

This apparatus is provided with a hydrogen gas recovery line 21 that recovers hydrogen gas generated on the hydrogen recovery device 14 side of the electrolytic cell 1 and supplies it to the fuel cell 18, and oxygen generated on the anode 9 side of the electrolytic cell 1. An oxygen gas recovery line 22 that recovers gas and supplies it to the fuel cell 18 is provided. The hydrogen gas recovery line 21 and the oxygen gas recovery line 22 have gas flow rate adjusting blowers 23 and 24, respectively, to adjust the flow rates of oxygen gas and hydrogen gas supplied to the fuel cell 18.

The power generated by the fuel cell 18 is stored in the power supply device 12, and the supply of the stored power is controlled so that the cathode 11 has a predetermined cathode current density Dk. Note that the power shortage in the amount of power generated by the fuel cell 18 is supplemented by power from solar power generation, power from wind power generation or wave power generation, or power from a power plant.

The electrolysis tank 1 is connected with a seawater supply line 25, a waste concrete tank 26 (corresponding to the first treatment tank 2), and a recovery tank 27 (corresponding to the second treatment tank 3).

The waste concrete tank 26 is supplied with acidic water which is the anode electrolyzed water 7a, and the waste concrete is supplied, and the pH is adjusted so as to be weakly acidic water, and then discharged.

The recovery tank 27 is supplied with alkaline water that is cathode electrolyzed water 7b containing Mg (OH) ₂ . The Mg (OH) ₂ precipitated in the collection tank 27 is collected, and the cathode electrolyzed water 7b (alkali water) from which the Mg (OH) ₂ has been removed is discharged from the collection tank 27.

The acid water discharged from the waste concrete tank 26 and the alkaline water discharged from the recovery tank 27 are merged and then discharged from the recovery device to the ocean. The pH of the wastewater is adjusted by combining the acidic water and the alkaline water. As a result, the pH of the wastewater is equivalent to the pH of the seawater when it is finally discharged from the recovery device, which places a burden on the environment. There is nothing.

In FIG. 4, 31 is a pump for feeding seawater to the electrolytic cell 1, 32 is a pump for feeding the cathode electrolyzed water 7b to the recovery tank 27, 33 is a pump for draining from the waste concrete tank 26, 34 is Pumps for draining from the collection tank 27 are shown.

According to the present invention, it is possible to provide a magnesium recovery method and a magnesium recovery apparatus that can recover magnesium from seawater while minimizing the burden on the environment.

1 electrolysis tank, 2 first treatment tank, 3nd treatment tank, 4 electrolysis treatment vessel, 5 inlet, 7 seawater, 7a anode electrolyzed water, 7b cathode electrolyzed water, 8 diaphragm, 9 anode, 9a anode side region, 11 Cathode, 11a cathode side region, 12 power supply device, 13 consumable electrode material, 14 hydrogen recovery device, 15 waste concrete charging device, 16 carbon dioxide gas blowing device, 18 fuel cell, 21 hydrogen gas recovery line, 22 oxygen gas recovery line, 26 Waste concrete tank, 27 recovery tower

Claims (8)

1. Seawater is electrolyzed, anode electrolyzed water and cathode electrolyzed water generated by seawater electrolysis are separated, an alkaline material is added to the anode electrolyzed water, pH is adjusted, and magnesium is converted into magnesium hydroxide in the cathode electrolyzed water. A magnesium recovery method in which the anode electrolyzed water after pH adjustment and the cathode electrolyzed water after magnesium hydroxide recovery are merged and discharged as a pH equivalent to seawater.
2. The magnesium recovery method according to claim 1, wherein the alkali material is waste concrete.
3. The magnesium recovery method according to claim 1, wherein iron, which is a soluble metal, is used for the anode side electrode, and iron ions are dissolved in the anode electrolyzed water during the seawater electrolysis process.
4. An electrolytic cell having an anode and a cathode, a diaphragm partitioning the inside of the electrolytic cell into an anode side region including the anode and a cathode side region including the cathode, and anode electrolyzed water generated in the anode side region A first processing tank for storing; a second processing tank for storing the cathode electrolyzed water generated in the cathode side region; a power supply for supplying power to the anode and the cathode; and an alkali material for the first processing tank. An alkali material charging device to be charged; and a recovery means for recovering magnesium hydroxide precipitated in the second treatment tank. The waste water from the first treatment tank and the waste water from the second treatment tank are joined together. , A magnesium recovery device that discharges as pH equal to that of seawater.
5. The magnesium recovery apparatus according to claim 4, wherein the power supply device includes at least one of a solar cell, a fuel cell, a wind power generator, a wave power generator, an ocean temperature difference power generation device, and a solar thermal power generation device.
6. The magnesium recovery apparatus according to claim 4, wherein the power supply device includes a fuel cell using hydrogen gas generated on the cathode side and oxygen gas generated on the anode side.
7. The magnesium recovery apparatus according to claim 4, wherein the alkali material input from the alkali material input apparatus is waste concrete.
8. The magnesium recovery apparatus according to claim 4, wherein the anode contains iron as a consumable electrode, and the consumable electrode dissolves iron ions.

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