JPH0252559B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for reducing the content of dissolved silica by polymerizing supersaturated silica from an aqueous solution containing supersaturated dissolved silica and separating it out of the system. Although an aqueous solution containing supersaturated dissolved silica appears to be stable at first glance, it is difficult to handle because it causes scale adhesion to the equipment in which it is handled. For example, underground silica is dissolved in geothermal hot water after steam separation at a geothermal power plant, and its concentration reaches 400ppm to 100ppm. Then, when the liquid is released to atmospheric pressure or heat is recovered, the temperature of the liquid decreases, and the dissolved silica content exceeds its solubility at that temperature, that is, it is in a supersaturated state. By the way, amorphous silica has a concentration of several tens of ppm in water at 20°C to 100°C.
It has a solubility of ~300 ppm. Therefore, a considerable amount of supersaturated silica is present in the liquid, and since this supersaturated silica is unstable and has a strong adhesive force, it will precipitate as scale on the parts of the equipment that come into contact with the liquid. In the past, research to solve scale problems was conducted in the Miscellaneous Test "Ceramics" Vol. 15 No. 2, pages 100 to 104, "Geothermal Power Generation and Hot Water Utilization," and the Miscellaneous Test "Shimadzu Review Vol. 28," 2 reprint, pages 107 to 120 (first report), pages 121 to 127 (second report), or Nihon Kagaku Miscellaneous Examination Vol. 91, No. 12, pages 39 to 46, etc. These reports revealed that there is a mutual relationship between the colloidalization process of supersaturated silica in hot water and the adhesion of silica, and that under conditions where the formation rate of silica colloid is high, silica adheres to the tube wall. It is said that the adhesion of colloids is noticeable.Reducing the temperature to 50℃, stirring, filtering, and filtering after mixing with river water all have the effect of suppressing colloid formation. Furthermore, the particle size of silica colloid was measured using a light scattering method to be approximately 0.3μ, and it was stated that under conditions that are effective in suppressing colloids, there is little adhesion.However, the adhesion of silica is Although there is an effect of suppressing this, and although it has been reduced, the problem of adhesion has not been eliminated, and it still remains a major problem. As a result of repeated research on the polymerization of supersaturated silica, we found that rather than suppressing the polymerization of supersaturated silica,
Based on the idea of forcibly polymerizing in a short time and separating the polymerized silica, the present invention was completed by further discovering factors and conditions for increasing the polymerization rate. That is, in the present invention, a liquid to be treated containing supersaturated dissolved silica and silica seeds are mixed, and the total amount of silica is
This mixture, which is in the range of 0.05% to 5%, has a pH of 6.
~10. The solution temperature is maintained at 40°C or higher to promote polymerization of dissolved silica, and then an ultramembrane is used to separate the silica polymer. In the polymerization reaction of supersaturated dissolved silica, the originally contained dissolved silica alone cannot trigger the reaction, so polymerization does not occur easily. Even if polymerization occurs, the content of dissolved silica in the supersaturated portion cannot be reduced in a short time. Especially silica concentration
An aqueous solution with a concentration of 400 to 500 ppm causes almost no reaction. At a silica concentration higher than this, although a polymerization reaction occurs, the rate is slow, and the precipitated polymerized silica is unstable and cannot be separated. Therefore, in the present invention, another silica source (silica seed) is mixed with the liquid to be treated to promote the polymerization of silica, and it acts as a seed that causes the polymerization of the dissolved silica in the liquid to be treated. ing. As a result of many experiments, the properties that can be the seeds that cause the polymerization of dissolved silica have been found to be a group of substances with small particle sizes, and some are in the range where particle sizes can be measured. This ranges from fine particles that cannot be removed. Furthermore, there are silicas whose properties are still difficult to understand, such as those immediately after hydrolysis of alkali silicate, and it is not easy to define the same properties for their characterization. A specific list of silica seeds in the present invention is as follows. () When an alkaline silicate solution is mixed with an acid, or a silica solution that has been previously neutralized with an acid or dealkalized with an ion exchange resin is mixed with the liquid to be treated, the total silica concentration after mixing is
Effectiveness was observed at 500ppm (0.05%) or higher. It exhibits excellent effects especially when it is 1000ppm (0.1%) or more. () Silica polymer that can be fractionated with an ultramembrane with a molecular weight cutoff of 5000 (particle size is too small to be measured by other methods)
When the silica liquid containing the silica liquid is mixed with the liquid to be treated,
The concentration of supersaturated silica decreases, and in particular, the greater the amount of silica liquid, the faster the rate of decrease in the concentration of supersaturated silica. () Although it is difficult to understand the colloidal diameter and molecular weight of low-molecular-weight silica polymers, it is difficult to determine the colloidal diameter and molecular weight of low-molecular-weight silica polymers, but it is possible to use silica liquids for which a concentration peak of polymerized silica was clearly observed in addition to the concentration peak of dissolved silica when measured using gel chromatography. When mixed with the liquid to be treated, the effect was observed when the total silica concentration was 500 ppm or higher. () Industrially synthesized primary average particle diameter is 4m
When using a silica solution containing a silica colloid of μ or more, a total silica concentration of 500 ppm or more contributes to the reduction of supersaturated silica, and the larger the amount of the silica solution is, the faster the rate of reduction becomes. () Using a silica source whose specific surface area can be measured for non-precipitating silica polymers, the amount added and the amount of decrease in supersaturated silica were investigated, and the results shown in Figure 1 were obtained.
As a result ^, it was found that there is a close relationship between the specific surface area of the added silica colloid group and the amount of reduction in supersaturated silica. I learned something. Note that FIG. 1 is a plot of Examples 7 to 11 described later. Comparing and explaining () ~ () and (),
() to () are silica polymers that can be measured as molecular weights rather than particle diameters, and these are low molecular weight polymers (about 500 to 5000). () is a commercially available colloidal silica liquid that has been grown to a thickness of 4 mμ or more in order to obtain a highly concentrated liquid due to the problem of hand linkage, and is generally denser than the silica polymers () to (). It has a particle shape. It is important that the total amount of silica in the mixed liquid after mixing the silica seeds and the liquid to be treated as described above is within the range of 0.05% to 5%. The larger the amount of silica seeds is, the more the reaction is accelerated, the less the amount of supersaturated silica is, and the closer it is to saturation at that temperature. In addition, in promoting the reaction rate after mixing, pH6~
It is important to keep the temperature above 40°C between 10 and 10 minutes. Preferably, the pH is between 7 and 9 and the temperature is 60°C or higher to further promote the reaction. The silica polymer thus precipitated is separated from the mixed solution using an ultramembrane. The ultra membrane can be made of cellulose, polyimide, polyolefin, polysulfonate, etc., and it is possible to use a wide range of membranes with a molecular weight cut-off of about 5,000 to 300,000. The method of use is not particularly limited and may be carried out under the usual conditions of use of ultramembranes. According to the present invention, since the precipitated silica polymer is stable and difficult to re-dissolve, supersaturated silica can be effectively separated. It was also found that the separated liquid did not contain any silica polymer, but contained dissolved silica in an amount slightly higher than its solubility at that temperature. Next, Examples and Comparative Examples will be shown to clarify the effects of the present invention. Preparation method of hot water simulated coagulation Dissolve 263 g of sodium silicate with 24 wt% silica concentration in 100 kg of pure water to make diluted sodium silicate with 0.063 wt% silica concentration, and pre-regenerate cation exchange resin (SK-IB). 10cm in diameter filled with 5.
The above solution was passed through a column with a length of 200 cm at a speed of SV5 to prepare a 0.06 wt% silicic acid solution 100. In this 0.06wt% silicic acid liquid 100

After adding [Table] and heating at 80°C for 10 minutes, a simulated hot water coagulant with a pH of 7.5 was prepared using 6N hydrochloric acid. The dissolved silica concentration of this solution was 600 ppm. Hereinafter, it will be referred to as liquid A. Example 1 212.5 g of sodium silicate having a silica concentration of 24 wt% was added to 100 of Solution A to make the total silica concentration 1100 ppm. The pH at this time was 7.8. Thereafter, the temperature was maintained at 80°C for 60 minutes. Next, 90 of this liquid was separated using an ultramembrane with a molecular weight cutoff of 6000 to obtain 89 liquid. Example 2 1620.5 g of a 1% silica concentration solution in which 1138 ml of 1.4N-HC was added to a solution of 67.5 g of sodium silicate with a 24 wt% silica concentration diluted in 1415 g of pure water to adjust the pH to 7.0.
was prepared, and this solution was added to 100% of solution A to make the total silica concentration 750 ppm. The pH at this time was 7.3. Thereafter, the temperature was maintained at 80°C for 60 minutes. Next, 90 of this liquid was separated using an ultramembrane with a molecular weight cutoff of 6000 to obtain 89 liquid. Example 3 135g of sodium silicate with 24wt% silica concentration was diluted with 1415g of pure water to prepare 1620.5g of 2% silica concentration solution with pH 7.1 by adding 70ml of 5N-HCI, and this solution was added to A solution 100. was added to bring the total silica concentration to 1500 ppm. The pH at this time was 7.2.
Thereafter, the temperature was maintained at 80°C for 60 minutes. Next, 90% of this liquid was separated using an ultramembrane with a molecular weight cutoff of 5000 to obtain a concentrated liquid of 1 with a silica concentration of 7.5% by weight. Next, 0.5 of this solution was added to 100 of solution A and kept at 80° C. for 60 minutes. Next, 90% of this liquid was separated using an ultramembrane with a molecular weight cutoff of 6000, and the liquid was reduced to 89%.
Obtained. Example 4 588 g of 99.5% sodium chloride was dissolved in 100 g of pure water. While stirring the solution, 416.7 g of sodium silicate having a silica concentration of 24 wt % was added, heated to 80° C., and held at that temperature for 10 minutes. then 6
Normal hydrochloric acid was added to adjust the pH to 7.5, and the mixture was allowed to cool at room temperature for 12 hours. It was determined by gel chromatography that this solution contained 143 ppm of dissolved silica as well as colloidal substances (see Figure 2). 42.9 kg of this solution was added to 100 kg of solution A to make the total silica concentration 720 ppm. The pH at this time was 7.4. This solution was then kept at 80°C for 60 minutes, and then
Liquid 120 was obtained by separating 121 using an ultramembrane with a molecular weight cutoff of 6000. Example 5 25 g of a solution containing silica colloid with a silica concentration of 40 wt% and an average particle diameter of 16 mμ was added to 100 of Solution A to make the total silica concentration 700 ppm. The pH at this time was 7.7. Then, after being kept at 80°C for 60 minutes,
This liquid 90 was separated using an ultramembrane having a molecular weight cut off of 6000 to obtain liquid 89. Example 6 20 g of a solution containing silica colloid with a silica concentration of 30 wt% and an average particle diameter of 7 mμ was added to 100 g of solution A to give a total silica concentration of 660 ppm. The pH at this time was 7.8. Next, after being maintained at 80° C. for 60 minutes, this liquid 90 was separated using an ultramembrane having a molecular weight cut off of 6000 to obtain liquid 89. Example 7 SiO ₂ at a silica concentration of 30 wt% for 100 of solution A
A colloidal liquid containing a silica colloid group having a specific surface area per gram of 227 m ² is mixed with a colloidal liquid containing a silica colloid group having a specific surface area of 680 m ² (6.8 m ² per 1 mixed liquid).
The total silica concentration was 630 ppm.
The pH at this time was 7.7. Next, after maintaining the temperature at 80℃ for 60 minutes, this liquid 90 was
Separation was performed using a 6000 ultra membrane to obtain liquid 89. Example 8 Instead of the colloidal liquid of Example 7, a colloidal liquid containing a silica colloid group with a silica concentration of 20 wt% and a specific surface area of 634 m ² per ₂ grams of SiO was used, and this was surface area
Solution 89 was obtained in the same manner as in Example 7, except that 7600 m ² (76 m ² per mixed solution) was added and the total silica concentration was 720 ppm. Example 9 Instead of the colloidal liquid of Example 7, a colloidal liquid containing a silica colloid group with a silica concentration of 40 wt% and a specific surface area of 61 m ² per ₂ grams of SiO was used, and this was surface area
Solution 89 was obtained in the same manner as in Example 7, except that 720 m ² (7.2 m ² per mixed solution) was added to make the total silica concentration 718 ppm. Example 10 Instead of the colloidal liquid of Example 7, a colloidal liquid containing a silica colloid group with a silica concentration of 40 wt% and a specific surface area of 34 m ² per ₂ grams of SiO was used, and this was surface area
Solution 89 was obtained in the same manner as in Example 7, except that 400 m ² (4.0 m ² per mixed solution) was added to make the total silica concentration 717 ppm. Example 11 Instead of the colloidal liquid of Example 7, a colloidal liquid containing a silica colloid group with a silica concentration of 30 wt% and a specific surface area of 227 m ² per ₂ grams of SiO was used, and this was surface area
Example 7 except that 13600 m ² (136 m ² per mixed solution) was added and the total silica concentration was 1197 ppm.
Liquid 89 was obtained in the same manner as above. Example 12 Instead of the colloidal liquid of Example 7, a colloidal liquid containing a silica colloid group with a silica concentration of 30 wt% and a specific surface area of 390 m ² per ₂ grams of SiO was used, and this was surface area
Solution 89 was obtained in the same manner as in Example 7, except that 4200 m ² (42 m ² per mixed solution) was added to make the total silica concentration 707 ppm. Example 13 Instead of the colloidal liquid of Example 7, a colloidal liquid containing a silica colloid group with a silica concentration of 5 wt% and a specific surface area of 1174 m ² per ₂ grams of SiO was used, and this was surface area
Example 7 except that 70000 m ² (700 m ² per mixed solution) was added and the total silica concentration was 1182 ppm.
Liquid 89 was obtained in the same manner as above. Comparative Example 1 Liquid A 100 was heated to 80°C while stirring. 20
After maintaining the temperature at 80℃ for a minute, this liquid was added to the molecular weight cutoff 90.
Separation was performed using a 6000 ultra membrane to obtain liquid 89. Comparative Example 2 Liquid 89 was obtained in the same manner as Comparative Example 1 except that the temperature was maintained at 80°C for 60 minutes. Comparative Example 3 50 g of quartz powder (specific surface area: 1 m ² /g) with a silica concentration of 99 wt% was added to Solution A 100, and then heating was continued for 60 minutes while maintaining the temperature at 80°C. This liquid mixture required constant mixing and stirring because the crystal powder would settle. 90 of this liquid was separated using an ultramembrane with a molecular weight cutoff of 6000 to obtain liquid 89. Comparative Example 4 50 g of silica powder (specific surface area: 620 m ² /g) with a silica concentration of 98 wt% was added to Solution A 100, and then heating was continued for 60 minutes while maintaining the temperature at 80°C. This liquid mixture required constant mixing and stirring because the silica powder would settle. 90 of this liquid was separated using an ultramembrane with a molecular weight cutoff of 6000 to obtain liquid 89. Examples 1 to 13 and Comparative Examples 1 to 4 obtained above
The amount of silica in the liquid was determined and the results are shown in Tables 1 and 2.

【table】

[Table] In Comparative Examples 1 to 4, some dissolved silica could be precipitated, but since the precipitated silica was unstable, it was redissolved during ultrafiltration and could hardly be removed. In contrast, Example 1
In samples 1 to 13, the amount of silica precipitated was large and the silica was stable, so silica could be effectively removed. The data obtained by gel chromatography method is provided by T. Tarutani, J. Chromatogr., 50 , 523.
(1970). Further, the dissolved silica concentration was determined by the following method. Dissolved silica analysis method (industrial water test method)
(According to JISK0101) Quantify the total SiO ₂ in the sample in advance, and convert it to 0.05 as SiO ₂ .
Collect a sample so that the amount of Dilute to 50 ml with distilled water and adjust the pH to 1.0 with 2N-HCl. Transfer to a 250 ml volumetric flask and dilute to approximately 230 ml. Add 10 ml of ammonium molybdate solution (10%) and make up to 250 ml with distilled water and mix. 420 after leaving for 20 minutes
Measure the absorbance at a wavelength of mμ. The amount of dissolved silica was determined using a calibration curve prepared in advance from the absorbance of the sample (dissolved silica in this method refers to monosilicic acid and disilicic acid).

[Brief explanation of drawings]

FIG. 1 illustrates the relationship between the specific surface area of the silica colloid group in the silica seed and the amount of reduction in supersaturated silica. FIG. 2 illustrates a case in which the presence of polymerized silica was recognized by gel chromatography.

Claims (1)

[Claims] 1. A liquid to be treated containing supersaturated dissolved silica and silica seeds are mixed, and this mixed liquid with a total silica content in the range of 0.05% to 5% is heated at a pH of 6 to 10 and a liquid temperature of 40°C.
A method for reducing supersaturated dissolved silica in which the polymerization of dissolved silica is promoted by maintaining the above temperature, and then the silica polymer is separated using an ultramembrane. 2. The silica seed is an alkali silicate solution or a silica solution obtained by neutralizing an alkali silicate solution or dealkalizing it with an ion exchange resin. Claim 1
The method described in section. 3. The method according to claim 1, wherein the silica seed is a silica liquid containing a silica polymer that can be fractionated with an ultramembrane having a molecular weight cut off of 5000. 4. The method according to claim 1, wherein the silica seed is a silica liquid in which the presence of polymerized silica is confirmed by gel chromatography. 5. The method according to claim 1, wherein the silica seed is a silica liquid containing a silica colloid having a primary average particle diameter of 4 mμ or more. 6. The silica seed contains a non-sedimentable silica polymer that gives the silica colloid group in the mixed liquid a specific surface area of 1 m ² or more per mixed liquid when the silica seed is mixed with the liquid to be treated containing supersaturated dissolved silica. The method according to claim 1, which is a silica liquid.