JP2000093705A - Activated silica, its preparation and preservation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an activated silica wherein gelation trouble is almost not generated in preparation or in preservation, there is no polymerization process, measurement of a limiting viscosity is not required, a preparation process is remarkably simpler than traditionally, a preparation-required time is short, and an alkali is not used in preparation; its preparation; its preservation; and further a flocculation treating method and apparatus for which they are used. SOLUTION: In the preparation of the activated silica, a water glass aqueous solution (sodium silicate aqueous solution) 4 is added while a mineral acid aqueous solution 3 of at most 1 in pH is stirred, and a silicate aqueous solution of at most 3 in pH and to 12% in SiO2 concentration is generated. On presevation, the obtained silicate aqueous solution is diluted with water. Further, for a highly concentrated activated silica for water treatment, the sodium silicate aqueous solution 4 and the mineral acid aqueous solution 3 are mixed, and an aqueous solution set at 5 to 10% in silicate concentration and 1.1 to 2.8 in pH is maintained at 8 deg.C or lower water temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to activated silica, a method for producing the same, and a method for storing the same. More particularly, the present invention relates to an activated silica used for coagulation treatment such as water purification, a novel method for producing the same, and a method for storing the same.

[0002]

2. Description of the Related Art In a water purification treatment, there is a coagulation treatment step as one of the treatment steps. In the coagulation treatment, a coagulant is used, and as the coagulant, aluminum sulfate and polyaluminum chloride (PAC) are mainly used. The aggregation treatment includes an aggregation precipitation step, a sand filtration step, an aggregation separation step, and the like. The above inorganic coagulants such as aluminum sulfate and polyaluminum chloride generally do not form sufficiently large flocs when used alone. Therefore, the solid-liquid separation speed is low in the coagulation sedimentation step and the sand filtration step. The sludge discharged from the coagulation / separation step also has poor sedimentation, concentration, and dewatering properties. In particular, in raw water in which the eutrophication of the raw water in the water purification treatment is advanced and algae such as microcystis are contained in a large amount, only the PAC or the sulfate band forms only flocs having extremely poor sedimentation. There, flocs with poor sedimentation may come up, making it impossible to remove algae effectively. The flocculant is not limited to aluminum sulfate or polyaluminum chloride. In the field of wastewater treatment other than water purification, various synthetic polymer flocculants are frequently used to promote floc formation. However, the use of the synthetic organic polymer flocculant for water purification is concerned about its safety and has not been approved.

[0003] In the field of water treatment, the use of "active silica" discovered by Baylis of the United States in the 1950's was examined in Japan as a highly safe coagulation aid in the 1950s. Activated silica refers to silica in a state where a silica monomer is polymerized to be a polymer. Although monomeric silica has no coagulation promoting effect, active silica has a pronounced coagulation effect and is so named. The “activity” of activated silica refers to the flocculation activity. The Baylis method refers to a method for obtaining activated silica as follows. That is, water glass is diluted with water to obtain an aqueous solution having a silica (SiO ₂ ) concentration of 1.5%, and the pH is adjusted to 8.5 by adding sulfuric acid, followed by stirring at room temperature for 2 hours to polymerize the silica monomer. . This is a method of obtaining silica in a polymer state by polymerizing, that is, active silica. Baylis
In the method, gelation during the production and storage of active silica (a phenomenon in which the whole liquid solidifies in a jelly state) frequently occurred, and it was very difficult to stably produce and store active silica. Therefore, it was not put to practical use in Japan.

Recently, however, there has been a movement to re-evaluate activated silica. For example, Japanese Patent Publication No. 4-75796 "Water treatment method and coagulant for water treatment" discloses the following coagulation treatment method. That is, "a polymerized silica having an intrinsic viscosity of about twice or more the intrinsic viscosity of a silica monomer, and a soluble salt of a metal capable of forming a hydroxide in water are mixed under the condition that the molar ratio of silicon to the metal is 2 or more. And agitating the water into the water to be treated ”. This polymerized silica is another name for “active silica”. FIG. 3 shows a method for producing activated silica disclosed in Japanese Patent Publication No. 4-75796. This conventional method is shown in FIG.
As shown in (1), a “water glass acidifying step” and a “monomer silica polymerization step” are required. In the water glass acidifying step, a diluted water glass aqueous solution is added to and mixed with a mineral acid aqueous solution such as sulfuric acid or hydrochloric acid, and the SiO ₂ is adjusted to 3.2% and the pH to 2 or less. In the monomer silica polymerization step, after the water glass acidification step, the pH is increased to 4 by adding caustic soda, and the silica monomer is polymerized for 2 to 6 hours while measuring the intrinsic viscosity.

[0005]

The inventors of the present invention have studied the method for producing activated silica in detail and found that there are the following problems. Since the required polymerization time greatly changes due to subtle variations in silica concentration, pH, water temperature, etc., it is very difficult to set the polymerization time. If the polymerization time is set incorrectly, a gelation trouble of silica is caused, and the silica cannot be used as a flocculant. In particular, when the silica concentration is increased to 4% or more, a gelation trouble of silica during the production becomes extremely easy to occur. It is difficult to store for more than one day and gels in tens of minutes. The time required to polymerize the silica monomer at a pH of 4 to adjust the intrinsic silica of the required intrinsic viscosity is 2 to 6 hours. Therefore, it takes a long time to prepare activated silica. The polymerization tank volume also increases.

The measurement of the intrinsic viscosity takes one hour or more even for a skilled person. The method of controlling the polymerization time while measuring the intrinsic viscosity in the field is not practically possible. An alkaline agent such as NaOH is indispensable. When the produced active silica has poor storage stability and the silica concentration is 4% or more, the whole liquid gels in several tens of minutes after the production and becomes unusable. Therefore, it was impossible to produce activated silica at a factory and transport it to a water purification plant for use. It was necessary to produce activated silica on-site at a water purification plant and use it immediately. Therefore, activated silica could not be used in a water purification plant where there is no skilled engineer for producing activated silica. The present invention considers the above-mentioned drawbacks of the conventional active silica production technology, and hardly causes gelation trouble during production or storage, has no polymerization step, does not require measurement of the intrinsic viscosity, and has a manufacturing process. Another object of the present invention is to provide an active silica which is significantly simpler than the conventional one, requires a short production time and does not use an alkali during the production, a method for producing the same, and a method for storing the same.

[0007]

The present invention has solved the above-mentioned problems by the following means. (1) It is obtained by adding a water glass aqueous solution while stirring a mineral acid aqueous solution having a pH of 1 or less to generate a silicic acid aqueous solution having a silica concentration of 5 to 12% and a pH of 3 or less. Activated silica. (2) Activated silica for water treatment wherein an aqueous solution having a silicic acid concentration of 5 to 10% and a pH of 1.1 to 2.8 mixed with a sodium silicate aqueous solution and a mineral acid aqueous solution is maintained at a water temperature of 8 ° C. or lower. (3) A method for producing active silica, comprising adding a water glass aqueous solution while stirring a mineral acid aqueous solution having a pH of 1 or less to produce a silicic acid aqueous solution having a silica concentration of 5 to 12% and a pH of 3 or less. (4) A method for preserving active silica, comprising diluting the aqueous solution of silicic acid obtained by the method for producing active silica according to (3) with water and storing the diluted silica. (5) A method of coagulating water, comprising coagulating water using the activated silica according to (1). (6) An apparatus for coagulating water, comprising a supply apparatus for adding the activated silica according to (1) to the tank for coagulating water.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. FIG.
FIG. 2 is a view showing a method for producing the activated silica of the present invention. In a mixing tank 2 provided with a stirrer 1, for example, pH
A strong acid aqueous solution 3, which is an aqueous solution of a strongly acidic mineral acid of 1 or less, is added, and a strong alkaline aqueous glass solution 4 is stirred while stirring.
Are added and mixed, and the pH after the mixing is 3 or less, and the silica concentration is 5 or less.
Prepare a ~ 12% aqueous solution of acidic silicic acid.

The present inventor has found that an active silica having a large aggregation effect can be produced by such an extremely simple method without gelling trouble during the production. Therefore, activated silica can be easily and continuously produced at the water purification plant according to the flow shown in FIG. 2, and the produced activated silica can be injected into raw water without preservation. In FIG. 2, water 6 and sulfuric acid 7 are added to an acid adjusting tank 8 to continuously prepare a sulfuric acid aqueous solution 9 having a pH of 1 or less, and it is continuously sent to the stirring tank 2.
An aqueous silica glass aqueous solution 4 is added to the stirring tank 2 and reacted to form an activated silica 10. The activated silica is continuously added to the raw water 5 to be supplied, sent to the floc forming and stirring tank 11, and stirred to form flocs. Set it in the sedimentation tank 12
To purify the water by settling the flocs. If necessary, when storing the manufactured active silica, gelation can be prevented for 10 days or more by diluting with water and reducing the silica concentration to about 1% or less.

Further, in the production of this activated silica,
A method for producing a high-concentration active silica for water treatment, which has an extended gelation time of the obtained active silica and has good storage stability, will be described. As shown in FIG. 1, while stirring a strongly acidic mineral acid aqueous solution 3 having a pH of 1 or less in a mixing tank 2 having a stirrer 1, a strongly alkaline sodium silicate aqueous solution 4 (preferably a water glass aqueous solution) is added and mixed. The pH after the mixing is 1.2 to 2.
An acidic aqueous solution having a silicic acid concentration of 5 to 10% is prepared. Thereafter, the water temperature is cooled to 8 ° C. or lower, transported to a water purification plant, and used as a coagulation aid. As a result, it is possible to produce high-concentration active silica in a short time (about 10 minutes) having an extremely large aggregation effect and no gelation trouble during production and storage. Conventionally, there is no research example which investigated the effect of water temperature on the gelation time of activated silica. We have studied in detail the effect of water temperature on the gelation time of activated silica. As a result, it was surprisingly found that at a water temperature of 8 ° C. or lower, the gelation time of the activated silica was drastically increased, and the storage stability was significantly improved. As a result, high-concentration activated silica with a silica concentration of 5% or more, which has been impossible to produce due to gelling in an extremely short time, can now be produced at the factory and transported to the water purification plant, and the complicated activity at the water purification plant can be achieved. This eliminates the need for on-site production of silica.

The important findings discovered during the research process of the present inventor are summarized below. As a result of pursuing the cause of the gelling trouble during the production of the activated silica by the conventional method (FIG. 3), the biggest problem is that the step of adjusting the pH to 4 and proceeding the polymerization of the silica monomer for 2 hours or more is the biggest problem. found. As a result, it has been found that the best solution is to find a method for producing active silica having a good coagulation effect even if the silica polymerization step is omitted. For that purpose, various investigations revealed that the silica concentration at the time of mixing the acidic aqueous solution and the sodium silicate aqueous solution was 5-12.
%, It has been found that an active silica having a large aggregation effect can be produced even if the step of polymerizing the silicate monomer for 2 hours or more is omitted. The reason that it is not necessary to set the pH of the mixture of the water glass and the acidic aqueous solution to 4 and proceed with the polymerization of the silica monomer for 2 hours or more is that the silica concentration is set to a high concentration, so that the polymerization of silica is performed even at a low pH of 3 or less. Is to proceed effectively. That is, high concentration active silica having a silica concentration of 5% or more has a pH of 3 or less, preferably 2.4.
Below, it was discovered that the lower the pH, the faster the gelation.

If the silica concentration is 5% or less, the polymerization rate of the silica monomer is low, and active silica having a good aggregation effect cannot be produced. If the silica concentration exceeds 12%, the entire liquid is likely to gel during production and become unusable, so it is better to avoid it. In the present invention, it is important to set the pH during production of the active silica to 3 or less, and if the pH exceeds 3, the polymerization rate of silica becomes too large, and gelling trouble tends to occur during the production. If the water temperature falls below about 10 ° C. in the cold season, the polymerization rate of the silicate monomer during the production of activated silica decreases, and it is not possible to produce active silica having a large coagulation effect. preferable.

The following can be said regarding the means for storing the produced active silica at a low temperature. In relation to the silica concentration and the water temperature, the silica concentration is 10%
In the case of pH 1.0, gelation occurs after 9 hours at 5 ° C. On the other hand, at pH 2, it does not gel for 73 hours. However, at pH 2.8 or higher, gelation occurs in a very short time, and p
In the case of H4.0, gelation occurs at a water temperature of 5 ° C. for 4 hours. In other words, it was found that the gelation time of the high-concentration active silica was good when the pH was in the range of 1.1 to 2.8. It is important to maintain the water temperature at 8 ° C. or less while the high-concentration activated silica of the present invention is produced at the factory and transported to the water purification plant.
% Does not cause gelation trouble for about one week. Therefore, cooling and preservation at a water purification plant is not an essential condition. Addition of any of ferric salts, aluminum salts, and titanium salts to the manufactured high-concentration active silica can prolong the gelation time and reduce or eliminate the injection rate of inorganic flocculants such as sulfate bands and PAC at water purification plants. This is convenient.

The aqueous solution of water glass used for producing the activated silica according to the present invention is usually prepared from commercially available water glass, and the concentration varies depending on the concentration of the aqueous mineral acid solution. A range in which a 12% aqueous solution of silicic acid having a pH of 3 or less is obtained is selected. Preferred is 5-10%. Sulfuric acid, hydrochloric acid, and the like are used as the mineral acid of the mineral acid aqueous solution having a pH of 1 or less, and sulfuric acid is preferable. In addition, it is necessary to use not only the pH value of the mineral acid aqueous solution but also an amount such that a predetermined pH and a silica concentration are obtained when the water glass aqueous solution is added.

When the active silica of the present invention is injected into raw water for coagulation treatment at a water purification plant together with an inorganic metal coagulant such as a sulfuric acid band, PAC, ferric chloride, and polyiron sulfate, and the mixture is stirred in a coagulation stirring tank. Micro flocs are quickly formed (about 40 seconds). After that, when a slow stirring is performed, a very large floc is formed in about 2 minutes, and the solid-liquid separation can be performed at a high speed. In the case of water purification treatment, the appropriate injection rate of the active silica composite of the present invention is ₁ to 8 mg as SiO ₂ .
Per liter in many cases.

[0016]

EXAMPLES Examples will be described below, but the present invention is not limited to these examples. Example 1 (Example of producing high-concentration active silica of the present invention) JIS
No. 3 water glass stock solution (silica concentration 30%) was diluted with tap water (water temperature 25 ° C) to prepare a water glass aqueous solution (pH 11.5) having a silica concentration of 16%. 100 g of this solution was mixed with 100 g of an aqueous sulfuric acid solution to prepare an active silica solution having a silica concentration of 8% and a pH of 3 or less (pH 1.6). The flocculation effect of the activated silica by this method is very good. When used together with an inorganic flocculant such as PAC, sulfate band and ferric chloride, the sedimentation speed is 5 to 10 times as shown in Table 1 compared to the case of adding the inorganic pseudo-absorbent alone. Produced a large floc.

(Coagulation test conditions) Raw water: A water purification plant intake river water (pH 7.4, water temperature 27 ° C, turbidity 2)
Jar test conditions: Rapid stirring 50 rpm, 3 minutes, slow stirring 50 rpm, 10 minutes Inorganic flocculant type: ferric chloride

[0018]

[Table 1]

Example 2 (Production example of high-concentration active silica of the present invention) An acidic silica solution having a silica concentration of 8% and a pH of 1.6 was prepared in the same manner as in Example 1. Thereafter, the temperature was cooled to 5 ° C.
The active silica in this state has a very good preservability of about 169.
It did not gel for a time and the aggregation effect did not deteriorate. Table 2 shows the gelation time at various water temperatures of activated silica having a silica concentration of 8% and a pH of 1.6 prepared according to the above method.

[0020]

[Table 2]

As is apparent from Table 2, the silica concentration of 8
% Of conventional active silica (silica concentration about 1-2%)
The gelation time of high-concentration active silica having a much higher silica concentration is greatly affected by the water temperature.
It has been found that the gelation time is rapidly increased at a temperature of not more than 0 ° C, and that the gelation can be prevented for 169 hours at a water temperature of 5 ° C.

Example 3 (Effect of pH on Gelation Time of Activated Silica) Activated silica having a silica concentration of 8% was prepared according to the method of Example 1, and the pH of the solution was varied and maintained at a temperature of 5 ° C. The gelation time was measured. Table 3 shows the results.
As shown in Table 3, the conditions under which gelation does not occur after storage at 5 ° C. for 1 day are in the range of pH 1.1 to 2.8. did.

[0023]

[Table 3]

[0024]

The present invention has the following effects. Since silica is not polymerized at pH 4, gelation trouble during production of active silica can be reliably prevented. That is, B
A high-concentration active silica having a silica concentration of 5% or more, which was impossible with the aylis method and the conventional active silica production method (FIG. 3), can be produced without gelation. Further, the measurement of the intrinsic viscosity of the polymerized silica is not required, and the process for producing the activated silica can be significantly simplified. The time required for the production of active silica, which was required for two hours or more in the conventional method, can be reduced to a very short time of about 10 minutes. Since the caustic soda that was required by the conventional method is unnecessary,
Manufacturing costs are reduced and work safety is improved. In the case of the low-temperature preservation method, a silica concentration of 5 which was impossible with the Baylis method and the conventional method for producing activated silica (FIG. 2).
% Or more of the active silica can be stored for a long time without gelation. Further, the measurement of the intrinsic viscosity of the polymerized silica is not required, and the process for producing the activated silica can be significantly simplified. In the conventional method for producing activated silica, gelation was extremely liable to occur and it was impossible to store the activated silica for a long time, so that activated silica could not be produced in a factory and transported to a water purification plant.
However, according to the present invention, high-concentration active silica can be stored for a long time, so that active silica can be produced at a factory and transported to a water purification plant, and the on-site production of active silica at the water purification plant is eliminated. Since the silica concentration of the activated silica liquid is much higher than before, the transportation cost is greatly reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a method for producing activated silica of the present invention.

FIG. 2 is a flow chart for continuously producing activated silica of the present invention.

FIG. 3 is a diagram showing a conventional method for producing activated silica.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Stirrer 2 Mixing tank 3 Strong acid aqueous solution 4 Sodium silicate aqueous solution 5 Raw water 6 Water 7 Sulfuric acid 8 Acid adjusting tank 9 Sulfuric acid aqueous solution 10 Activated silica 11 Flock formation stirring tank 12 Precipitation tank

Claims (6)

[Claims] An aqueous solution of a mineral glass having a pH of 1 or less is obtained by adding a water glass aqueous solution while stirring the aqueous solution of a mineral acid having a pH of 1 or less to produce a silicic acid aqueous solution having a silica concentration of 5 to 12% and a pH of 3 or less. Activated silica. 2. Activated silica for water treatment, wherein an aqueous solution of sodium silicate and an aqueous solution of mineral acid are mixed, and an aqueous solution having a silicic acid concentration of 5 to 10% and a pH of 1.1 to 2.8 is maintained at a water temperature of 8 ° C. or lower. 3. A method for producing activated silica, comprising adding a water glass aqueous solution while stirring a mineral acid aqueous solution having a pH of 1 or less to produce a silicic acid aqueous solution having a silica concentration of 5 to 12% and a pH of 3 or less. 4. A method for preserving activated silica, comprising diluting the aqueous solution of silicic acid obtained by the method for producing activated silica according to claim 3 with water and storing. 5. A method for coagulating water, comprising coagulating water using the activated silica according to claim 1. 6. An apparatus for coagulating water, comprising a supply apparatus for adding the activated silica according to claim 1 to a tank for coagulating water.