JP2017071527A - Method for producing silica using geothermal brine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing colloidal silica with high concentration, which does not cause clogging of geothermal brine piping with silica scale, prevents agglomeration of silica particles, provides a uniform particle diameter, and does not cause lowering of a passage speed of a filtrate when filtering.SOLUTION: The method for producing silica using geothermal brine comprises: a seed formation step of adding an additive 2 containing salts or ions to a portion 1a of geothermal brine 1, followed by cooling to obtain a seed solution 3 containing precipitated supersaturated silica; a particle growth and concentration step of making the particle size of silica grow by mixing another portion 1b of the geothermal brine and the seed solution, followed by filtering and concentrating the mixture to obtain a silica sol 5 with high concentration containing a filtrate and silica particles having a grown particle size; and an RO treatment step of filtering the filtrate 4 by using a reverse osmosis membrane 18 to obtain a concentrated salt-containing liquid 7 and purified water 6. In the particle growth step, another portion 1b of the geothermal brine is used instead of and/or together with the additive containing salts or ions as a seed liquid, and the purified water 6 is also mixed into the grown silica sol.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing silica using geothermal hot water.

Conventionally, several methods have been proposed for recovering silica from geothermal hot water or treating silica when recovering heat from geothermal hot water.
Examples of such conventional methods include the methods described in Patent Documents 1 to 5.

Japanese Patent Publication No. 2-7882 Japanese Examined Patent Publication No. 2-15279 Japanese Examined Patent Publication No. 6-94952 JP-A-8-276191 JP 2002-167213 A

  However, in the conventional method, since nucleation, particle growth, and concentration are simultaneously performed, the quality is not stable. In addition, silica may agglomerate or it may be difficult to control the degree of supersaturation, resulting in an increase in particle size distribution or thickening when concentrated. Moreover, it was difficult to increase the concentration of silica.

An object of the present invention is to solve the above problems.
That is, in the present invention, since nucleation and particle growth are separated, silica particles are prevented from agglomerating in order to promote silica particle growth, the particle diameter is relatively uniform, and the filtration membrane is difficult to block. In addition, the concentration of colloidal silica with reduced salt content can be reduced by using purified water obtained by filtration using a reverse osmosis membrane in the particle growth and concentration process. An object of the present invention is to provide a method for producing silica in which

The inventor has intensively studied to solve the above-mentioned problems, and has completed the present invention.
The present invention includes the following (1) to (6).
(1) A seed for obtaining a seed solution containing precipitated supersaturated silica by cooling after adding an additive containing salts or ions to a part of the geothermal hot water or after adding the additive to a part of the geothermal hot water. Forming process;
Particle growth to obtain a high-concentration silica sol containing the filtrate and silica particles having a grown particle size by mixing another part of the geothermal hot water with the seed solution to grow the particle size of silica and then filtering. A concentration process;
RO treatment step of filtering the filtrate using a reverse osmosis membrane to obtain a concentrated salt-containing solution and purified water;
And in the particle growth / concentration step, another purified part of the geothermal hot water and the seed solution are mixed with the purified water.
(2) The method for producing silica according to (1), wherein the concentrated salt-containing liquid is used as the additive.
(3) The production of silica according to the above (1) or (2), wherein the additive contains at least one selected from the group consisting of a metal oxide that lowers the solubility of silica, its ions, and anions. Method.
(4) The additive according to any one of (1) to (3), wherein the additive includes at least one selected from the group consisting of Na, Ca, Mg, Al, Ti, Si, Cl, and SO ₄ . A method for producing silica.
(5) The method for producing silica according to any one of the above (1) to (4), wherein in the particle growth / concentration step, filtration is performed using an ultrafiltration membrane having a fractional molecular weight of 4,000 to 100,000.
(6) In the seed formation step, the geothermal hot water is cooled to {X-{(X / 100-1) × 100}} ° C. or lower, where X is the temperature of the geothermal hot water or the sampling site. The method for producing silica according to any one of (1) to (5) above.

[Comparison with conventional technology]
In conventional processes, nucleation and particle growth occur at the same time or concentrate in a salt-rich system, so silica is likely to agglomerate, and silica is deposited at the inlet and membrane surface of the reduced filtration membrane and backwashed. However, since it cannot be removed, the permeation rate of the filtrate is lowered, and eventually membrane clogging occurs.
Therefore, when growing into uniform silica particles as in the present invention, silica deposited on the film surface can be easily removed by backwashing, so that the permeation rate of filtrate is high or maintained at a high level for a long time. Can withstand wide usage.

  According to the present invention, separation of nucleation and particle growth promotes the growth of silica particles, prevents agglomeration, makes the particle size relatively uniform, and prevents the filtration membrane from being clogged. Furthermore, by using purified water obtained by filtration using a reverse osmosis membrane in particle growth, a method for producing silica can be provided in which high-concentration colloidal silica with reduced salts can be obtained. it can.

It is the schematic of the manufacturing apparatus of the silica which can perform the suitable example of the manufacturing method of this invention.

The present invention will be described.
In the present invention, a seed solution containing precipitated supersaturated silica is obtained by adding an additive containing salts or ions to a part of the geothermal hot water or after adding the additive to a part of the geothermal hot water. The seed formation step, another part of the geothermal hot water and the seed solution are mixed to grow the particle size of silica, and then filtered to obtain a high concentration containing the filtrate and silica particles having a grown particle size A particle growth / concentration step for obtaining a silica sol, and a RO treatment step for filtering the filtrate using a reverse osmosis membrane to obtain a concentrated salt-containing solution and purified water. In the particle growth / concentration step, the geothermal heat This is a method for producing silica using geothermal hot water, wherein the purified water is mixed together with another part of water and the seed solution.
Hereinafter, such a method for producing silica is also referred to as “the production method of the present invention”.

The manufacturing method of this invention is demonstrated using FIG.
FIG. 1 shows a silica production apparatus 20 (hereinafter also simply referred to as “apparatus 20”) that can carry out a preferred example of the production method of the present invention.
As shown in FIG. 1, the apparatus 20 includes a seed tank 12, a particle growth tank 22, concentration tanks 24 and 29, filtration apparatuses 25 and 30, and an RO membrane 18.

In the apparatus 20, the geothermal hot water 1 is processed. The geothermal hot water 1 may be, for example, a conventionally known one. For example, the temperature is about 60 to 100 ° C., 0.04 to 0.15 mass% of silica is contained, and ions (metal ions or anions (for example, Na, Ca, Mg, Al, Ti, Si, Cl and SO _4)), include those containing 0.05 mass% in total.

  In the apparatus 20, the additive 2 is added to a part (1a) of the geothermal hot water 1. Additive 2 contains salts or ions (metal ions or anions) (which may of course include both), and precipitates or aggregates silica components contained in part (1a) of geothermal hot water 1 It has a function to do. When the salt concentration contained in the geothermal hot water 1 is increased by adding the additive 2, the solubility of the silica is decreased (the degree of supersaturation of the silica is increased) and the silica is likely to be precipitated.

The additive 2 preferably contains at least one selected from the group consisting of Na, Ca, Mg, Al, Ti, Si, Cl, and SO ₄ . Such additive 2 includes CaCl ₂ ,
MgCl ₂ , AlCl ₃ , Ti (SO ₄ ) ₂ may be mentioned.

The additive 2 may be an inorganic cationic additive such as alumina sol or cationic silica sol, or an organic cationic additive such as (CH ₃ ) ₄ NOH.

Moreover, it is preferable to use the concentrated salt containing liquid 7 obtained by the RO process mentioned later as the additive 2. In this case, since no additive is used and an apparatus for diluting salts is not required, the cost is low. Moreover, you may carry out by using an additive together with a concentrated salt containing liquid newly.
The additive 2 may be only the concentrated salt-containing liquid 7 obtained by the RO treatment described later, or the other additive 2 and the concentrated salt-containing liquid 7 may be used together.

In the apparatus 20, the additive 2 may be added to a part (1a) of the geothermal hot water 1 at the time of flushing or after flushing.
Moreover, in the apparatus 20, after adding the additive 2 to a part (1a) of the geothermal hot water 1, it cools using the cooling device 11.
The cooling device 11 is not particularly limited, and can be cooled using, for example, a water cooling or a wind cooling heat exchanger. Moreover, it is preferable to cool to {X-{(X / 100-1) * 100}} degrees C or less with respect to the temperature (X) of the geothermal hot water (geothermal reservoir) 1 before cooling. Moreover, it is preferable to cool to {X-{(X / 100-1) * 100}} degrees C or less rather than the temperature (X) of the sampling site of the geothermal hot water 1 before cooling. By cooling, the degree of supersaturation of silica increases, so that silica precipitates from the liquid phase and forms nuclei. Here, if a poorly soluble salt or the like that plays the role of a nucleus coexists in advance, it becomes a nucleus, and silica is likely to precipitate in the nucleus.

In addition, in the apparatus 20 shown in FIG. 1, after adding the additive 2 to a part (1a) of the geothermal hot water 1, it cools using the cooling device 11, but the additive 2 is the geothermal hot water 1 You may cool using the cooling device 11, adding to a part (1a).
Moreover, it can also cool by adding the cooled additive 2 and the concentrated salt containing liquid 7 to a part (1a) of the geothermal hot water 1, for example, without using the cooling device 11.
Furthermore, since the temperature of the concentrated salt-containing liquid 7 is lower than that of the geothermal hot water 1, the temperature of the geothermal hot water is decreased by adding it to a part of the geothermal hot water 1, and the degree of supersaturation of silica. Therefore, silica precipitates from the liquid phase and is easily generated as nuclei.

  The additive 2 as described above is added to a part (1a) of the geothermal hot water 1 (or while being added), cooled, and then introduced into the seed tank 12. Silica particles are deposited inside the seed tank 12 to form seeds. The residence time in the seed tank 12 is preferably 0.1 to 1.0 hour.

  After a certain residence time has elapsed, the seed solution 3 is discharged from the seed tank 12.

  In this manner, in the seed tank 12, a seed formation is obtained in which a seed liquid 3 containing precipitated supersaturated silica is cooled while adding or adding an additive containing salts or ions to a part of the geothermal hot water. A process can be performed.

  Next, the seed solution 3 is sent to the particle growth tank 22.

  Further, the concentrated salt-containing water 7 obtained by the treatment with the RO membrane, which will be described later, can be combined with another part (1a) of the geothermal hot water 1 to form the seed solution (3). In addition, the silica particles can be purified by mixing together in the concentration tank 29 together with the purified water 6 obtained by the treatment with the RO membrane described later. Thereby, the silica particle in the high concentration silica sol 5 obtained can be stabilized more and can be highly purified.

  In the apparatus 20, the seed solution 3 is mixed with a part (1 b) of the geothermal hot water 1 in the particle growth tank 22. And the particle size of a silica particle grows. The residence time in the particle growth tank 1 is preferably 0.25 to 3.0 hours, and more preferably about 1.0 hour.

Thereafter, the silica sol 23 discharged from the lower part of the particle growth tank 22 is sent to the concentration tank A (24).
Silica produced in the concentration tank A (24) is extracted from the lower part of the tank and filtered by the ultrafiltration device 25. Then, the concentrated liquid 26 is returned again to the concentrated tank A (24), and the filtrate is discharged to the reducing well 27.

  The portion (28) where the sol is concentrated is sent to the next concentration tank B (29). The silica concentration in the liquid (28) sent to the concentration tank B (29) is preferably 0.5 to 9% by mass, and more preferably about 2% by mass.

  Here, in the concentration tank B (29), the liquid (28) sent from the concentration tank A (24) is stored, and the generated silica is extracted from the lower part of the tank and filtered by the ultrafiltration device 30. Is done. The concentrated liquid portion 31 is returned to the concentration tank B (29) again. A part of the filtrate 4 (filtrate 32) is discharged to the next step (treatment by the RO membrane), and the remaining part (filtrate 33) is discharged to the reduction well (34).

Then, by filtering and concentrating using the filtration devices 25 and 30, it is possible to obtain the high-concentration silica sol 5 containing the filtrate 4 and silica particles having a grown particle size.
The silica concentration in the recovered high-concentration silica sol is preferably 10 to 40% by mass, and more preferably about 15% by mass.
Here, it is preferable to use an ultrafiltration membrane for filtration, and it is more preferable to perform filtration using an ultrafiltration membrane having a molecular weight cutoff of 4000 to 100,000.

  In this way, in the particle growth tank 22, the concentration tanks 24 and 29, and the filtration devices 25 and 30, another part of the geothermal hot water and the seed solution are mixed to grow the particle size of silica, and then filtered. -By concentrating, a particle growth / concentration step for obtaining a high-concentration silica sol containing silica particles having a grown particle diameter can be performed.

Next, the filtrate 4 is filtered using a reverse osmosis membrane (RO membrane) 18 to obtain a concentrated salt-containing solution 7 and purified water 6.
The reverse osmosis membrane 18 is not specifically limited, For example, a conventionally well-known heat resistant thing can be used.

The purified water 6 obtained here is introduced into the particle growth / concentration tank 29 as described above.
In addition, as described above, the concentrated salt-containing liquid 7 is preferably used as at least a part or all of the additive 2 and added to a part (1a) of the geothermal hot water 1.

  Thus, in the reverse osmosis membrane 18, the filtrate can be filtered using a reverse osmosis membrane, and the RO treatment process which obtains a concentrated salt containing liquid and purified water can be performed.

<Example 1>
A high-concentration silica sol 5 was obtained from the geothermal hot water 1 using the apparatus shown in FIG.
This will be specifically described below.
The geothermal hot water 1 contains 580 g of SiO ₂ and 3000 g of salts (total amount of Na, K, Ca, Al, Cl) per 1000 L, and the cooled geothermal water temperature is 99 ° C. (The geothermal reservoir temperature X is 200 ° C.) The composition of the geothermal hot water 1 was based on the composition of the Otake geothermal hot water.
Such geothermal hot water 1 was supplied to the apparatus 20 shown in FIG. 1 in an amount of 1000 L / Hr.
Of these, 10% (1a: 100 L / Hr) was adjusted to be supplied to the seed tank 12. Further, the remainder (90%: 1b: 900 L / Hr) was adjusted to be supplied to the particle growth tank 22.

Next, CaCl ₂ was added as an additive to 150 ppm of part (1a) of the geothermal hot water 1 supplied to the seed tank 12. Moreover, the concentrated salt containing water 7 obtained by filtration using the reverse osmosis membrane 18 mentioned later was also supplied.
And it cooled so that it might become 80 degreeC using the large sized electric fan (cooling device 11).
Additive 2 (salt concentration: about 3%) is added at 0.6 L / Hr, and the cooled geothermal hot water 1 stays in the seed tank 12. The residence time is 0.5 hours. Thereafter, the seed solution 3 discharged from the seed tank 12 is supplied to the particle growth tank 22.

  The seed solution 3 is mixed with another part (1 b) of the geothermal hot water 1 in the particle growth tank 22. And the particle size of a silica particle grows. The residence time in the particle growth tank 22 is 1.0 hour.

Thereafter, the silica produced in the concentration tank A (24) is extracted from the lower part of the tank and filtered by the ultrafiltration device 25. The amount returned to the concentration tank A (24) (circulation flow rate) was 5 m ³ / Hr, and the amount discharged to the reduction well (27) (drainage flow rate) was 0.99 m ³ / Hr. Further, the portion where the particle diameter has grown is sent to the next concentration tank B. The silica concentration in the liquid (silica sol) sent to the concentration tank B was 2% by mass, and the amount was 991 L / Hr.

In the concentration tank B (29), the liquid (silica sol 28) sent from the concentration tank A (24) is stored and then filtered by the ultrafiltration device 30. Then, the concentrate is returned again to the concentration tank B (29). A part (32) of the filtrate 4 is discharged to the RO membrane 18 which is the next process, and the remaining part (33) is discharged to the reduction well (34). The amount (circulation flow rate) of the liquid (31) returned to the concentration tank B (29) was 5 m ³ / Hr. The amount of the filtrate 4 discharged to the next step (32) is 5.9 L / Hr, the amount of the remainder (33) of the filtrate 4 discharged to the reduction well (34) (flow rate of filtrate). Was 1.9 L / Hr.
Further, the portion where the particle diameter has grown is recovered as a high concentration silica sol 5. The recovered high-concentration silica sol 5 had a silica concentration of 15% by mass and an amount of 1.2 L / Hr.
Further, purified water 6 obtained by filtration using a reverse osmosis membrane 18 described later was also supplied to the concentration tank B (29).

A portion (32) of the filtrate is treated with a reverse osmosis membrane. Then, it is separated into concentrated salt-containing water 7 and desalted purified water 6.
As described above, the concentrated salt-containing water 7 was added to the geothermal hot water 1 as a part of the additive 7 at an addition amount of 0.6 L / Hr. And the purified water 6 was supplied to the concentration tank B (29) by the supply amount of 5.3 L / Hr as mentioned above.

Although the high concentration silica sol 5 was manufactured by such a method, the stability of the recovered sol (high concentration silica sol) in such a manufacturing method was evaluated. The evaluation was performed by measuring the viscosity after 150 g of high-concentration silica sol was collected in a 200 g glass container, hermetically sealed so that the evaporated water did not volatilize, immersed in a constant temperature bath at 70 ° C., and immersed and cooled for 12 days. . In addition, when immersed in a thermostat, the silica sol liquid level in the glass container was made higher than the liquid level of the thermostat in order to prevent scaling due to drying of the silica sol. And as a result, compared with the viscosity of unimmersed silica sol, the viscosity change rate within 30% is evaluated as “◯”, 30-100% as “Δ”, and 100% or more as “×”. did. The viscosity was measured by a method called a capillary viscometer method.
Each processing condition and evaluation results are shown in Table 1.

<Example 2>
In Example 1, an additive (CaCl ₂ ) was added to geothermal hot water so as to be 150 ppm, but in Example 2, this was added so as to be 500 ppm, and everything else was the same as Example 1. The process was performed and evaluated.
Each processing condition and evaluation results are shown in Table 1.

<Example 3>
In Example 1, CaCl ₂ was used as an additive to geothermal hot water, and this was added to 150 ppm. In Example 3, AlCl ₃ was used as an additive and added to 10 ppm. The other processes were the same as in Example 1 and evaluated.
Each processing condition and evaluation results are shown in Table 1.

<Example 4>
In Example 1, CaCl ₂ was used as an additive to geothermal hot water and added to 150 ppm. In Example 4, Ti (SO ₄ ) ₂ was used as an additive, and this was 3 ppm. The other treatments were the same as in Example 1 and evaluated.
Each processing condition and evaluation results are shown in Table 1.

<Example 5>
In Example 1, CaCl ₂ was used as an additive to geothermal hot water and added to 150 ppm. In Example 3, 10% alumina sol was used as an additive and added to 100 ppm. However, the other processes were the same as in Example 1 and evaluated.
Each processing condition and evaluation results are shown in Table 1.

<Example 6>
In Example 1, CaCl ₂ was used as an additive to geothermal hot water and added to 150 ppm. In Example 6, 20% cationic silica sol was used as an additive so that this became 50 ppm. In addition, the other processes were the same as in Example 1 and evaluated.
Each processing condition and evaluation results are shown in Table 1.

<Example 7>
In Example 1, CaCl ₂ was used as an additive to geothermal hot water and added so as to be 150 ppm. In Example 7, (CH ₃ ) ₄ NOH was used as an additive, and this was 10 ppm. The other treatments were the same as in Example 1 and evaluated.
Each processing condition and evaluation results are shown in Table 1.

<Example 8>
In Example 1, CaCl ₂ was used as an additive to geothermal hot water, and this was added to 150 ppm. In Example 8, the additive was not used, and everything else was the same as Example 1. Processed and evaluated.
Each processing condition and evaluation results are shown in Table 1.

<Comparative Example 1>
In Example 1, CaCl ₂ was used as an additive to geothermal hot water, and this was added to 150 ppm. In Comparative Example 1, it was obtained by filtration using a reverse osmosis membrane without using the additive. Concentrated salt was not fed either. In Example 1, purified water was supplied to the concentration tank B at a supply amount of 5.3 L / Hr, but in Comparative Example 1, this was not supplied.
The other processes were the same as in Example 1 and evaluated.
Each processing condition and evaluation results are shown in Table 1.

<Comparative example 2>
In Example 1, an additive (CaCl ₂ ) was added to geothermal hot water so as to be 150 ppm. In Comparative Example 2, this was added so as to be 500 ppm, but it was obtained by filtration using a reverse osmosis membrane. No concentrated salt was supplied. In Example 1, purified water was supplied to the concentration tank B at a supply amount of 5.3 L / Hr, but in Comparative Example 2, this was not supplied.
The other processes were the same as in Example 1 and evaluated.
Each processing condition and evaluation results are shown in Table 1.

  For Examples 1 to 8, the stability of the recovered sol was good.

  In Comparative Example 1, the stability of the recovered sol was Δ. This is probably because the additive and the concentrated salt were not used, and the purified water was not supplied to the concentration tank B.

  In Comparative Example 2, the stability of the recovered sol was Δ. This is probably because the additive was not used and the purified water was not supplied to the concentration tank B.

1, 1a, 1b: Geothermal hot water 2: Additive 3: Seed water 4: Filtrate 5: High concentration silica sol 6: Purified water 7: Concentrated salt-containing water 11: Cooling device 12: Seed tank 18: RO membrane 20: Device 22: Particle growth tank 24: Concentration tank A
25: Filtration device 27: Reduction well 29: Concentration tank B
30: Filtration device 34: Reduction well

Claims (6)

A seed formation step of obtaining a seed solution containing precipitated supersaturated silica while adding an additive containing salts or ions to a part of the geothermal hot water or after adding the additive to a part of the geothermal hot water; ,
A concentration step of obtaining a high-concentration silica sol containing silica particles having a grown particle size by mixing another part of the geothermal hot water with the seed solution to grow the particle size of silica, and then filtering and concentrating. When,
The filtrate is filtered using a reverse osmosis membrane to obtain a concentrated salt-containing solution and purified water, and in the particle growth step, another part of the geothermal hot water contains the salts or ions. A method for producing silica using geothermal hot water, wherein the seed liquid is used instead of and / or at the same time as the additive, and the purified water is also mixed with the grown silica sol.   The method for producing silica according to claim 1, wherein the concentrated salt-containing liquid is used as the additive.   The method for producing silica according to claim 1 or 2, wherein the additive contains at least one selected from the group consisting of a metal oxide that lowers the solubility of silica, its ions, and anions. It said additive, Na, Ca, Mg, Al , Ti, Si, containing at least one selected from the group consisting of Cl and SO _4, the method of producing the silica according to any one of claims 1 to 3.   The method for producing silica according to any one of claims 1 to 4, wherein in the particle growth / concentration step, filtration is performed using an ultrafiltration membrane having a molecular weight cut-off in the range of 4000 to 100,000.   In the seed formation step, the geothermal hot water is cooled to {X-{(X / 100-1) × 100}} ° C. or lower, where X is the temperature of the geothermal hot water or a sampling place thereof. Item 6. The method for producing silica according to any one of Items 1 to 5.

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