JPH05131194A - Recovery of silica from aqueous solution - Google Patents

Abstract

PURPOSE:To prevent a silica scale from generating in an aqueous solution flow path and utilize the recovered silica as a silicon resource by separating and recovering silica from geothermal water as well as from an aqueous solution containing silica. CONSTITUTION:Geothermal water 1 separated from vapor in a separation tank 3 is allowed to run through a reaction flow path 4, and at the same time, an alternating current is applied to an area between electrodes 5A, 5B installed in the reaction flow path 4. Thus silica is allowed to deposit alternately on the surface of the electrodes 5A, 5B, and the deposited silica is permitted to precipitate to the bottom of the reaction flow path 4 for recovery.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention separates and recovers silica from an aqueous solution containing silica (SiO ₂ ) such as geothermal hot water, prevents the formation of silica scale in the flow path of the aqueous solution, and recovers the recovered silica. The present invention relates to a method for recovering silica in an aqueous solution which utilizes as a silicon resource.

[0002]

2. Description of the Related Art In geothermal power generation, high-temperature geothermal fluid in the ground is jetted to generate electric power by utilizing separated steam.
Geothermal hot water containing at a concentration of 000 mg / l erupts. The ejected geothermal hot water is returned to the ground through an underground reduction well,
Since the temperature of the geothermal fluid is 250 ° C to 350 ° C, whereas the temperature of the geothermal water is low at 97 ° C to 98 ° C, the solubility of silica in the geothermal water is relatively lowered, Moreover, since silica is concentrated as it is separated from the water vapor, some of the silica contained in the geothermal hot water becomes supersaturated. This supersaturated silica is likely to precipitate as a silica scale in the hot water path in the geothermal power plant, the underground reduction well, etc., and causes problems such as a decrease in heat efficiency of the heat exchanger and blockage of the hot water path, or a decrease in the capacity of the underground reduction well. This is a major obstacle to the utilization of the geothermal hot water.

On the other hand, high-purity silica is used as a raw material for metallic silicon used for semiconductor devices and the demand for it has increased significantly in recent years, but most of it depends on imports from overseas. Therefore, it must be said that it is an unstable resource in terms of supply.

Therefore, if silica in the geothermal hot water is recovered in advance, precipitation of silica scale in the hot water passage and the underground reduction well can be prevented, and moreover, silicon resources can be utilized. Research is being done.

Here, these conventional silica recovery methods are roughly classified into the following three types.

(1) Ultrafiltration membrane method: JP-A-60-94
198, JP-A-63-1496, JP-A-63-2805, and the like.
A chemical solution such as silica seed is added to silica of the geothermal hot water to form a colloidal form, which is then collected by filtration using an ultrafiltration membrane made of polyvinyl chloride or the like.

(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 the same method, silica is polymerized with the additive or the precipitated silica is recovered together with a hydroxide of a secondary product formed as a result of 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, and fine silica particles are adsorbed on the surface of the generated bubbles to collect as a foam layer. is there.

[0009]

However, among the above methods, in the ultrafiltration method, the filtration membrane is easily clogged, so that the filtration membrane needs to be washed or replaced each time, and the recovery rate is several%. However, there is a problem that the cost required for recovery increases.

On the other hand, although the adsorption method has a high recovery 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, so that it is economical. There was a problem in terms. When a metal compound is used, silica is Ca (OH) ₂ or Mg.
Since it is adsorbed by sludge (precipitate) containing a large amount of metal hydroxide added with (OH) _2, etc., it was necessary to use a means such as filtration again for its recovery.

Further, in the flotation separation method, since metals such as aluminum and arsenic in the geothermal hot water are mixed in the recovered silica, the purity is lowered and the recovery efficiency is improved. It is necessary to promote the polymerization and aggregation of silica in advance, which complicates the process.

[0012]

The present invention has been made to solve the above-mentioned problems, and at least a pair of electrodes is brought into contact with an aqueous solution containing silica such as geothermal hot water, and an alternating current is applied between these electrodes. Is applied to cause the silica to deposit on the surface of the electrode, and at the same time, the deposited silica is removed from the surface of the electrode to recover the silica in the aqueous solution.

The means of the present invention will be described below in more detail with reference to the drawings. The basic structure of the silica recovery facility in the present invention is shown in FIGS. 1, 3 and 4. In FIG. 1, reference numeral 3 is a cylindrical separation tank, and the introduction pipe 2 is connected to the side surface thereof. The separator 3 is connected to the tip of the U-shaped reaction channel 4 by a pipe or the like.

A pair of electrodes 5A and 5B each having a rectangular flat plate shape are installed in the reaction channel 4, and the positions of the electrodes 5A and 5B are 5A, 5B when the geothermal hot water 1 is flown into the reaction channel 4.
The lower part of 5B is located so as to be immersed in the geothermal hot water 1. Further, an AC power supply 8 is connected to the upper ends of the electrodes 5A and 5B via a switch 7, and a silica recovery part 6 is formed together with the reaction channel 4. Then, 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).

On the other hand, one end of the steam transfer pipe 10 is inserted at a position where the geothermal water 1 is not mixed in the upper part of the separation tank 3, and the other end of the steam transfer pipe 10 is connected to a power generation facility (not shown). It is connected.

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 electrodes 5A and 5B are electrically connected via the geothermal hot water 1 by the AC current supplied from the AC power source 8, and a circuit is formed between the AC power source 8 and the electrodes 5A and 5B. At the same time, silica contained in the geothermal hot water 1 is deposited on the surface of the anode of the electrodes 5A and 5B.

Then, the geothermal hot water 1 discharged from the reaction channel 4 contains the reduction tube 9 in a state where it contains almost no supersaturated silica.
Via the underground return well. Therefore,
No silica scale is generated in the hot water path or the underground reduction well.

On the other hand, 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.

Here, in the case of the present invention, since the AC power source 8 is used, the anode and the cathode are continuously alternated between the electrodes 5A and 5B at a cycle corresponding to the frequency during energization. Therefore, silica is deposited on both the electrodes 5A and 5B during energization, but when the electrode becomes a cathode, the deposited silica is spontaneously exfoliated from the surface of the electrode without being redissolved in the geothermal hot water 1. . That is, the electrode 5 is energized.
Deposition of silica and peeling thereof between A and 5B are alternately repeated at a cycle corresponding to the frequency, and as a result, the surfaces of the electrodes 5A and 5B are always kept clean due to the peeling of deposited silica. The separated silica precipitates on the bottom of the reaction channel 4. Therefore, in the present invention, for the purpose of recovering silica and ensuring conduction between the electrodes 5A, 5B, the electrodes 5A,
It is not necessary to artificially remove the silica deposited on 5B from the electrodes 5A and 5B.

The silica recovered here is SiO 2.
The purity as ₂ is very high and contains almost no impurities other than the above-mentioned electrodes, so that it can be used for semiconductor devices and the like, and in addition, it has an even particle size, which is advantageous in handling. Further, by performing operations such as washing with water, silica with higher purity can be obtained.

Moreover, by using the AC power supply 8, the power consumption is greatly reduced as compared with the case of the DC power supply normally used for electrolysis, and the electricity supplied from the power company is converted. Since it can be used directly without using a device, it is possible to simplify the power supply equipment.

On the other hand, the materials used for the electrodes 5A and 5B are aluminum, copper, iron, zinc, lead, nickel,
A metal selected from cobalt, titanium, calcium, and magnesium or an alloy thereof is used, but other materials can be used if necessary. Moreover, the magnitude of the current during energization, the frequency and the energizing time are set so that the above-mentioned precipitates are produced. Good. In this case, since the maximum amplitude maintaining time and the energizing time at the time of energizing are almost equal, the efficiency of collecting the deposit by energizing is improved.

Further, conditions such as the shape and size of the electrodes 5A and 5B, 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 water 1 in the reaction channel 4 and the geothermal water. 1 and the concentration of silica in the geothermal hot water 1, the presence or absence of a mixture including other metal ions, and the concentration thereof. Specifically, it is determined by experiment.

Incidentally, in the silica recovery equipment of FIG.
Although the cross-sectional shape of the reaction flow path 4 is U-shaped as shown in FIG. 3, the cross-sectional shape of the flow path is tubular as shown in FIG.
The electrodes 5A and 5B may be installed in the reaction channel 4A. Alternatively, a plurality of recovery parts 6 may be provided so that the silica in the geothermal hot water 1 is removed stepwise as the geothermal hot water 1 passes through the recovery parts 6 in sequence. The electrodes 5A and 5B may be installed and electricity may be supplied in the separation tank 3.

[0025]

EXAMPLES Next, the effects of the present invention will be described with reference to examples. Geothermal hot water containing silica at an average concentration of 868.4 ppm was used, and the volume was 304 cm ³ and the cross-sectional area was 16 cm ^2.
While being made to flow down into the gutter-shaped reaction tank, ^two aluminum electrode plates having a surface area of the immersed portion of 71.25 cm ² were immersed in this reaction tank, and an alternating current having a frequency of 50 Hz was applied.

[0026] The flow conditions and energization conditions of the geothermal hot water,
Table 1 shows the silica concentrations of the geothermal hot water flowing out of the reaction tank.

[0027]

[Table 1] However, the water temperature in Table 1 shows the water temperature at the time of flowing into the reaction vessel.

As a result, in each case, a deposit was formed on both electrode plates, and this deposit was deposited at the bottom of the reaction vessel after deposition. Further, as a result of further investigation, this precipitate was high-purity silica containing only a small amount of aluminum as a contaminant.

Further, when the silica concentration of the geothermal hot water flowing out from the reaction tank was measured, the results shown in Table 2 were obtained.

[0030]

[Table 2]

As is clear from the numerical values shown in Table 2, in all cases, the silica concentration in the geothermal hot water after energization decreased. This indicates that the silica in the geothermal hot water was removed by applying electricity.

[0032]

As described above, according to the present invention,
By simply passing an alternating current through a silica-containing liquid such as geothermal hot water, high-purity silica can be easily recovered from the contained liquid. Therefore, not only the operation of collection is simplified, but also the cost required for collection is significantly reduced. Moreover, since no special chemicals are used, economic efficiency and safety are further enhanced. That is, by utilizing the present invention, the recovery of silica in geothermal water in geothermal power generation and the prevention of silica scale production can be performed easily and inexpensively and reliably, and
The recovered silica can be utilized as a silicon resource.

Further, by using the AC power source, the power consumption is greatly reduced as compared with the case of using the DC power source, and the electricity supplied from the power company is directly used without using a converter or the like. Therefore, there is an advantage that the power supply equipment is simplified.

[Brief description of drawings]

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

FIG. 2 is a diagram showing an example of a waveform of an energizing current in the present invention.

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

FIG. 4 is a cross-sectional view of a silica recovery part showing an example of the shape of a reaction channel in the present invention.

[Explanation of symbols]

 1 Geothermal hot water 2 Introduction pipe 3 Separation tank 4, 4A Reaction channel 5A, 5B Electrode 6 Silica recovery part 7 Switch 8 AC power supply 9 Reduction pipe 10 Steam transfer pipe

Claims (3)

[Claims] 1. At least a pair of electrodes are brought into contact with an aqueous solution containing silica, and an alternating current is applied between the pair of electrodes to deposit silica on the surface of the electrodes, and at the same time deposit the deposited silica. A method for recovering silica in an aqueous solution, which comprises removing the silica from the surface of the electrode. 2. A material selected from aluminum, platinum, copper, iron, zinc, lead, nickel, cobalt, titanium, calcium, and magnesium or an alloy thereof is used as a material used for the electrode. The method for recovering silica in an aqueous solution according to claim 1. 3. The method for recovering silica in an aqueous solution according to claim 1, wherein a current having a rectangular wave is passed as the alternating current.