JPH0557285A - Method for removing silica in aqueous solution and recovering valuable element - Google Patents

Abstract

PURPOSE:To continuously remove silica (SiO2) from an aq. soln. contg. silica such as geothermal hot water, to prevent the formation of silica scales in the soln. passage and to separate and recover various valuable elements dissolved in the soln. CONSTITUTION:The geothermal hot water 1 separated from steam in a separation tank 3 is passed through a reaction passage 4, a current is intermittently applied between the electrodes 5A and 5B set in the passage 4 at regular time intervals, and the hydroxide of the metal constituting the anode between the electrodes 5A and 5B is repeatedly formed and removed. Since silica and various valuable elements are occluded in the hydroxide, the hydroxide is recovered by a filter 11, and the valuable elements are recovered from the hydroxide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention separates silica from an aqueous solution containing silica (SiO ₂ ) such as geothermal hot water to prevent the formation of silica scale in the flow path of the aqueous solution, and The present invention relates to a method for removing silica from an aqueous solution for separating and recovering various valuable elements dissolved in the aqueous solution, and a method for recovering the valuable element.

[0002]

2. Description of the Related Art In geothermal power generation, high-temperature geothermal fluid in the ground is jetted to generate electric power using separated steam.
Geothermal hot water containing 0 mg / l is emitted. The ejected geothermal hot water is returned to the ground through an underground reduction valve, but the temperature of the geothermal fluid is 250 ° C to 350 ° C, whereas the temperature of the geothermal hot water is as low as 97 ° C to 98 ° C. Because
Since the solubility of silica in the geothermal hot water is relatively reduced and the silica is concentrated as it is separated from the steam, a part of the silica contained in the geothermal hot water becomes supersaturated.

This supersaturated silica is likely to be deposited as silica scale on the hot water passage in the geothermal power plant, the inner wall of the underground reduction well, etc., and as a result, the thermal efficiency of the heat exchanger is reduced, the hot water passage is blocked, or the underground reduction well is formed. Is causing the decrease in capacity. Moreover, since the deposited silica adheres strongly to the inner wall and the like and is difficult to remove, when the silica deposition proceeds, the operation of the power plant is stopped and the hot water path or the underground reduction well is removed. Must be replaced. As described above, the presence of silica in the geothermal hot water is a major obstacle in using the geothermal hot water.

Therefore, if silica in the geothermal hot water is removed in advance, the precipitation of silica scale in the hot water passage and the underground reduction valve can be prevented.

Here, these conventional silica recovery methods are roughly classified into the following three types. (1) Ultrafiltration membrane method: JP-A-60-94198, JP-A-63-1496, and JP-A-63-
According to the method disclosed in Japanese Patent No. 2805, etc., a chemical solution such as silica seed is added to silica in the geothermal hot water to form a colloidal form, which is then filtered using an ultrafiltration membrane made of polyvinyl chloride or the like. The silica is removed by collecting the residue on the filtration membrane.

(2) Adsorption method: JP-A-59-16588
Japanese Patent Publication No. 60-114391 and Japanese Patent Publication No. 59-13919.
An adsorbent (an organic solvent such as a thioether polymer, or a metal compound containing calcium, magnesium, etc., activated alumina, etc.) is added to the geothermal hot water. In this method, the additive and the silica are polymerized or the precipitated silica is removed together with the hydroxide of the secondary product resulting from the hydrolysis of the additive.

(3) Floating separation method: a method in which a foaming liquid agent containing a silica collector is added to the geothermal hot water, fine silica particles are adsorbed on the surface of the generated bubbles, and removed as a foam layer. is there.

[0008]

However, among the above-mentioned methods, in the ultrafiltration method, since the filtration membrane is easily clogged, it is necessary to wash or replace it each time, and the removal rate is only a few percent. Therefore, there is a problem that the removal efficiency is low and the cost required for the removal increases.

In addition, although the adsorption method has a high removal rate of silica, it requires the use of a special chemical agent. Particularly, when an organic solvent is used, the organic solvent to be added is expensive, which is economical. I had a problem with. Furthermore, in the flotation method, in order to improve the removal efficiency, pH adjustment and other methods
It is necessary to promote the polymerization and aggregation of silica in advance, which complicates the process.

On the other hand, when an electrode is brought into contact with an aqueous solution containing silica and a current of about several hundred mA is applied between the electrodes, the anode among the electrodes is dissolved to form a hydroxide, and this water It is known that silica in the aqueous solution coagulates together with the oxide. According to this method, the concentration of silica in the aqueous solution can be lowered relatively easily, but the surface of the anode is covered with the hydroxide along with the energization, and the removal efficiency is gradually lowered. Since there is a case where the conduction between the electrodes becomes impossible, it is necessary to periodically remove the hydroxide covering the surface of the anode, and silica cannot be continuously removed. There was a problem.

[0011]

Means for Solving the Problems The present invention provides an anode of the electrodes by bringing the electrodes into contact with an aqueous solution containing silica such as geothermal hot water and intermittently energizing the electrodes at regular intervals. Silica, and a hydroxide of the substance forming the electrode together with silica and a group I, III, V or V
A method of removing silica from the aqueous solution and a method of recovering valuable element, in which the valuable element in the aqueous solution selected from Group I elements is aggregated and the valuable element is further recovered from the hydroxide.

[0012]

According to the present invention, when an electrode is brought into contact with a silica-containing aqueous solution such as geothermal hot water, and the electrode is energized, silica is aggregated in the secondary generated hydroxide, As a result, silica in the aqueous solution is efficiently removed.

[0013]

Embodiments of the present invention will now be described in more detail with reference to the drawings. The basic structure of the silica removing equipment according to the present invention is shown in FIGS. 1 to 3
In FIG. 3, reference numeral 3 is a cylindrical separation tank, and the introduction pipe 2 is connected to the side surface thereof. Further, a vapor transfer pipe 10 is inserted from the lower side to the upper side in the center of a circular portion forming the lower end of the separation tank 3, and one end of the steam transfer tube 10 is opened in the separation tank 3 at a position where the geothermal water 1 is not mixed. .. The other end of the vapor transfer pipe 10 is connected to a power generation facility (not shown).

The separation tank 3 is connected to the tip of a reaction channel 4 having a U-shaped groove, and in the reaction channel 4, a pair of electrodes 5A and 5B each having a rectangular flat plate-shaped anode and cathode are provided. Has been done. Further, the positions of the electrodes 5A and 5B are such that the lower portions of the electrodes 5A and 5B are immersed in the geothermal hot water 1 when the geothermal hot water 1 flows into the reaction channel 4.

A power source 8 is connected to the upper ends of the electrodes 5A and 5B via a switch 7, and the switch 7 is provided with an automatic opening / closing mechanism (not shown). This automatic opening / closing mechanism automatically energizes at regular intervals, and the energization and de-energization times can be set arbitrarily. And
A reduction pipe 9 is connected to the rear end of the reaction channel 4, and the reduction pipe 9 is further connected to an underground reduction well (not shown) via a filtration device 11.

The geothermal hot water 1 ejected from the ground is stored in the separation tank 3 through the introduction pipe 2 and then becomes a vortex flow into the reaction flow path 4 to form electrodes 5A and 5B in the reaction flow path 4. A flow toward the reduction tube 9 is formed while making contact. When the switch 7 is turned on in this state, the current supplied from the power source 8 causes conduction between the electrodes 5A and 5B via the geothermal hot water 1 to form a circuit between the power source 8 and the electrodes 5A and 5B. Of the electrodes 5A and 5B, the anode is dissolved, and a precipitate made of a hydroxide of a substance forming the electrode is formed on the surface of the anode. In addition, silica and other valuable elements contained in the geothermal hot water 1 coagulate with this hydroxide together with the hydroxide.

By the way, since the switch 7 is provided with the automatic opening / closing mechanism as described above, the energization is automatically stopped by the action of the automatic opening / closing mechanism after a lapse of a certain time after the switch 7 is turned on. .. Then, the entrapment generated on the surface of the anode causes the reaction flow path 4 to stop when electricity is stopped.
It is separated from the surface of the anode by the flow of the geothermal hot water 1 therein, and further flows into the reduction pipe 9 through the reaction flow path together with the geothermal hot water 1 and is separated from the geothermal hot water 1 in the filtering device 11.

When a certain period of time elapses after the power supply is stopped,
Energization is restarted by the action of the automatic opening / closing mechanism, and a precipitate made of a hydroxide of the substance forming the electrode is formed around the anode again. In this way, when the switch 7 is turned on, the energization of the electrodes 5A and 5B is repeated intermittently at regular intervals, and accordingly, the generation and removal of hydroxide is repeated on the surface of the anode.

As a result, most of the silica dissolved in the geothermal hot water 1 is agglomerated by the impurities and separated in the filtering device 11, so that the geothermal hot water 1 discharged from the filtering device 11 contains silica. It is returned to the ground from the above-mentioned underground reduction well through the reduction pipe 9 in a state where it is hardly contained. Therefore, silica scale is not generated in the hot water path or the underground reduction well. On the other hand, as described above, various valuable elements other than silica are agglomerated in the recovered starch, and thus a method such as a melt electrolysis method is used to recover and utilize these elements from the starch. be able to.

Moreover, since the energization is intermittently performed and the formation and removal of the hydroxide is repeated on the surface of the anode, the surface of the anode is not covered with the hydroxide. Therefore, even if the silica removing equipment is continuously operated for a long time, the conduction between the electrodes 5A and 5B does not become impossible.

The steam ejected together with the geothermal hot water 1 is separated from the geothermal hot water 1 in the separation tank 3 and then transferred to the power generation facility through the steam transfer pipe 9 and used for power generation.

The material used for the electrodes 5A and 5B is a metal selected from aluminum, copper, iron, zinc, lead, nickel, cobalt, titanium, calcium, and magnesium, or an alloy thereof.
Other materials may be used if necessary.

In addition, the magnitude of the current during energization and the interval between energization / non-energization are set so that the above-mentioned substance is generated, and the shapes and sizes of the electrodes 5A and 5B are set as follows.
The conditions such as the distance between the electrodes 5A and 5B, the volume of the reaction channel 4 and the like are determined by the flow velocity of the geothermal hot water 1 in the reaction channel 4, the temperature of the geothermal hot water 1, and the concentration of silica in the geothermal hot water 1. In addition, it is arbitrarily set depending on conditions such as the presence or absence of a mixture including other metal ions.

In the silica removing equipment shown in FIG. 1,
Although the cross-sectional shape of the reaction channel 4 is U-shaped as shown in FIG. 2, the cross-sectional shape of the channel is tubular as shown in FIG. 3, and the electrodes 5A and 5B are provided in the reaction channel 4A. May be installed. Further, a plurality of removing parts 6 may be provided, and the silica in the geothermal hot water 1 may be removed stepwise as the geothermal hot water 1 sequentially passes through the removing parts 6.
The electrodes 5A and 5B may be directly installed in the column to energize in the separation tank 3. Further, in order to accelerate the production of the above-mentioned starch, it is possible to provide a large settling tank or to use a settling accelerator together.

On the other hand, as the anode is melted, the electrodes 5A, 5
When the conduction between B becomes impossible, the electrodes 5A and 5B
By replacing the, it is possible to conduct again.

[0026]

As described above, according to the present invention, a secondary hydroxide is formed by simply contacting an electrode with a silica-containing aqueous solution such as geothermal hot water and energizing this electrode. Silica aggregates in the solution, and as a result, silica in the aqueous solution is efficiently removed. Therefore, the operation of collection is simple, the cost required for collection is greatly reduced, and moreover,
Since no special chemicals are used, economic efficiency and safety are improved. That is, by utilizing the present invention, the production of silica scale in geothermal water in geothermal power generation,
It can be easily and inexpensively and reliably prevented.

In particular, by intermittently energizing the electrode, it is possible to prevent the reduction of silica removal efficiency due to the coating of the electrode with the hydroxide, so that the silica in the aqueous solution can be efficiently treated for a long time. Can be removed.

Further, in the aqueous solution, together with silica, I
In the case where various valuable elements selected from Group III, Group III, Group V and Group VI elements are dissolved, these various valuable elements can also be aggregated in the hydroxide. Moreover, any of these valuable elements can be recovered from the hydroxide and effectively utilized.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a basic configuration of silica removal equipment in the present invention.

FIG. 2 is a transverse cross-sectional view of a silica removal portion showing an example of the shape of a reaction channel in the present invention.

FIG. 3 is a transverse cross-sectional view of a silica removing portion showing an example of the shape of a reaction channel in the present invention.

[Explanation of symbols]

 1 Geothermal hot water 2 Introducing pipe 3 Separation tank 4, 4A Reaction channel 5A, 5B Electrode 7 Switch 8 Power supply 9 Reduction pipe 10 Steam transfer pipe 11 Filtration device

Claims (3)

[Claims] 1. At least a pair of electrodes are brought into contact with an aqueous solution containing silica, and the electrodes are intermittently energized at regular intervals to coagulate with a hydroxide of a substance forming the electrodes. Method for removing silica in aqueous solution. 2. The aqueous solution according to claim 1, wherein a metal selected from aluminum, copper, iron, zinc, lead, titanium, nickel, and cobalt or an alloy thereof is used as a material used for the electrode. Method of removing silica in. 3. Along with the hydroxide, in addition to silica,
A method for recovering a valuable element in an aqueous solution, which comprises aggregating the valuable element in the aqueous solution selected from Group I, Group III, Group V and Group VI elements.