JP2001179007A - Flocculant for water treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flocculant for water treatment hard to gel over a long time and enhanced in storage stability. SOLUTION: A flocculant for water treatment is a polymerized silicic acid solution containing water-soluble alcohol and has a SiO2 concentration of 0.1-10weight% and pH of 1-4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water treatment coagulant used for coagulation treatment of various kinds of wastewater,
More specifically, the present invention relates to a flocculant for water treatment containing a polymerized silicic acid having improved storage stability.

[0002]

2. Description of the Related Art Conventionally, agglomeration of water has been widely performed in order to remove suspended solids, dissolved organic substances, and phosphate ions in various wastewaters. In these water coagulation treatments, aluminum sulfate, polyaluminum chloride,
Aluminum-based or iron-based inorganic metal salt coagulants such as ferric sulfate, polyferric sulfate, and ferric chloride are used. On the other hand, when these inorganic metal salt coagulants are used alone, sufficient cohesive strength cannot be obtained, and therefore, a polymer coagulant is often used. The use of a polymerized silicic acid solution as an agent has been studied, but a flocculant using a polymerized silicic acid solution has a drawback that it is extremely easy to gel, and has not been put to practical use. Therefore, various attempts have been made to solve the problem of gelation and to provide a flocculant that can be stored for a long time.

[0003] For example, Japanese Patent No. 2,732,067 discloses that ferric ion is contained as a stabilizer and pH 1.
A coagulant for water treatment comprising a silicic acid solution of 5 or less is disclosed. The coagulant disclosed in this publication aims to stabilize by polymerizing a silicic acid solution obtained by dissolving water glass in an acidic solution, and then adding an iron salt such as ferric chloride. Things.

[0004] Also, Japanese Patent No. 2759853 discloses that
A coagulant for water treatment obtained by subjecting an aqueous solution of an alkali metal silicate to a de-alkali metal treatment, intentionally gelling the resulting solution, and liquefying it again is disclosed. The coagulant disclosed here is a substance that can be stored for a long period of time by gelling by bringing the pH of the silicic acid solution with reduced alkali metal concentration to near neutrality once and then liquefying it again. is there.

[0005]

However, when the present inventors examined these techniques in detail, it was found that there were the following problems.

The coagulant disclosed in Japanese Patent No. 27332067 increases the gelation time by adding a large amount of a ferric salt to a polymerized silicate solution having a low Si concentration of 0.5 to 2% by weight. This coagulant is stable while maintaining the Si concentration at a low concentration, but becomes unstable when it is higher than 2% by weight and easily gels. Become. Further, there is disclosed an example in which a long-term storage of 5,000 hours or more was made possible by adding a large amount of ferric salt, but gelation immediately occurred when the iron concentration was lowered, which was very unstable. It was also found that it was in a state. Further, at the time of use, it is necessary to adjust the concentrations of silica and iron according to the composition of the wastewater. However, if the iron content is too large, such adjustment becomes difficult.

[0007] The coagulant disclosed in Japanese Patent No. 2759853 is obtained by polymerizing water alkali glass which has been subjected to a dealkalization metal treatment, gelling it once, and then redissolving it by heating to obtain a polymerized silicic acid solution in a stable state. In Although,
Since a three-stage manufacturing process is required, the operation is very complicated and the manufacturing cost is high. Further, once the gelation step is performed in the polymerization apparatus, there is a problem in handling the equipment, and it is difficult to industrially produce the equipment.

[0008] The present invention has been made in view of the above problems, and an object of the present invention is to provide a coagulant for water treatment which is hardly gelled for a long time and has improved storage stability.

[0009]

In view of the situation of the prior art described above, as a result of various studies, the present inventors have found that a coagulant containing polymerized silicic acid can be obtained by adding a water-soluble alcohol. The present inventors have found that a stable state hardly occurs in gelation, and completed the present invention.

That is, the present invention provides a water treatment flocculant comprising:
A polymerized silicic acid solution containing a water-soluble alcohol,
The first feature is that the concentration of SiO ₂ is 0.1 to 10% by weight and the pH is 1 to 4, and the second feature is that it contains 1 to 50% by volume of a water-soluble alcohol,
A third feature is that the water-soluble alcohol is at least one selected from the group consisting of ethanol, methanol, propanol and ethylene glycol. A fourth feature is that the coagulant for water treatment contains 0.1 to 10% by weight of a metal salt, and a fifth feature is that the metal salt is a ferric salt. And

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the coagulant for water treatment in the present invention will be described in detail.

The water treatment flocculant of the present invention is characterized in that it is a polymerized silicic acid solution containing a water-soluble alcohol.

The polymerized silicic acid solution is not particularly limited. For example, the polymerized silicic acid solution in an acidic solution (a strong acid such as hydrochloric acid, sulfuric acid, etc.)
A solution obtained by adding an aqueous solution of sodium silicate obtained by diluting a water glass stock solution, a sodium silicate powder or the like with water can be used.

The water-soluble alcohol is not particularly limited, but a lower alcohol having 1 to 6 carbon atoms is preferable.
Particularly, methanol, ethanol, propanol and ethylene glycol are preferred. These water-soluble alcohols may be used alone or in combination of two or more.

The content of the water-soluble alcohol is not particularly limited, but is preferably 1 to 50 vol%, more preferably 5 to 30 vol% in the coagulant. 1v
If the amount is less than 50% by volume, the effect of stabilization tends to be hardly seen.

Although the reason why the water-soluble alcohol contributes to the stabilization of the flocculant is not clear, the water-soluble alcohol reduces the polarity of the solvent, thereby alleviating the interaction between the silica particles and reducing the cohesive force between the silica particles. This is presumed to be due to the fact that it was made smaller and hardly gelled.

Further, the coagulant for water treatment of the present invention comprises SiO 2
₂ It is characterized in that the concentration is in the range of 0.1 to 10% by weight and the pH is in the range of 1 to 4.

If the SiO ₂ concentration is less than 0.1% by weight, the cohesive force is too small to be used for practical use. If the SiO ₂ concentration exceeds 10% by weight, gelation is liable to occur, making it difficult to store for a long period of time. In the region where the pH of the flocculant is less than 1 or greater than 4, the pH of the flocculant must be adjusted to a range of 1 to 4 because the reactivity of the silicic acid is so high that the gel is easily formed.

The coagulant for water treatment of the present invention can be used alone, but when used for wastewater treatment, sufficient cohesion is exhibited by using it together with a metal salt.

The metal salt used in combination is aluminum sulfate,
Aluminum salts such as polyaluminum chloride and ferric salts such as ferric sulfate, ferric polysulfate, and ferric chloride are preferable, and among them, ferric salts are particularly preferable.

The metal salt is preferably contained in the flocculant in an amount of 0.1 to 10% by weight. If the amount is less than 0.1% by weight, the cohesive force is not sufficient, and it tends to be difficult to put into practical use. If the amount exceeds 10% by weight, the charge state of the suspended substance in the wastewater changes, and This is because they tend to be lost.

The metal salt may be added when the coagulant is used, or may be stored in a state where the metal salt is previously added to the coagulant. In particular, the ferric salt has an action of stabilizing the polymerized silicic acid solution, and a better storage stability can be obtained by a synergistic effect with the stabilizing action of the water-soluble alcohol.

The method for producing the coagulant for water treatment in the present invention is described below.

First, a polymerized silicic acid solution is produced. The polymerized silicic acid solution is obtained by adding an aqueous solution of sodium silicate to an acidic solution and stirring the mixture at room temperature to 60 ° C.

The aqueous sodium silicate solution is prepared by diluting a water glass stock solution or a sodium silicate powder with water, and forming an SiO ₂ concentration of 0.2.
It is good to use what was adjusted so that it might be -20% by weight. If the SiO ₂ concentration is less than 0.2% by weight, the polymerization tends to require a long time, and if it exceeds 20% by weight, it tends to gel during the polymerization.

The kind of the acidic solution is not particularly limited, but it is preferable to use a strong acid such as hydrochloric acid and sulfuric acid.

In the polymerization process of silicic acid, the pH rises as an alkaline aqueous solution of sodium silicate is added to the acidic solution. At this time, if the aqueous solution of sodium silicate is rapidly added, the reaction proceeds due to a local increase in pH and gelation is likely to occur.

The water-soluble coagulant of the present invention is completed by adding a water-soluble alcohol to the polymerized silicic acid solution thus obtained.

The water-soluble alcohol may be added after the polymerization of the silicic acid solution, or may be added in the acidic solution. In the former case, the storage and stabilization of the flocculant is achieved by the action of delaying the gelation of the polymerized silicic acid solution,
In the latter case, there is an effect that gelation hardly occurs during polymerization. Further, if the water-soluble alcohol is added both before and after the polymerization of the silicic acid, it is possible to avoid a gelling trouble during the polymerization, and it is possible to stabilize the storage of the obtained flocculant, which is more effective. .

[0030]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples.

The value of the intrinsic viscosity in the present embodiment is calculated from the specific viscosity measured by using an Ubbelohde viscometer based on the Huggi value.
It was calculated using the ns formula.

(Example 1) Water glass stock solution No. 4 (manufactured by Nippon Chemical Industry) was diluted with tap water, and SiO ₂ concentration was 14% by weight.
A 500 ml aqueous solution of sodium silicate was prepared. 500 ml of this aqueous sodium silicate solution was added to 500 ml of 1.3N HCl.
The mixture was stirred and mixed at room temperature while being added dropwise over 30 minutes to obtain 1,000 ml of a polymerized silicic acid solution having a pH of 1.5 and a SiO ₂ concentration of 7% by weight. This is designated as solution (A).

[0033] were collected 100ml partial solution (A) in a beaker, water 80ml of ethanol 20ml addition, SiO ₂
Concentration 3.5% by weight, ethanol 10% by volume, pH 1.
8. 200 ml of flocculant having an intrinsic viscosity of 0.11 was obtained.

Example 2 Solution (A) was added to a beaker at 10
0 ml was taken, 40 ml of water and 60 ml of ethanol were added, SiO ₂ concentration was 3.5% by weight, and ethanol was 30 vol.
%, PH 1.8, intrinsic viscosity 0.18 200ml flocculant
I got

Example 3 Solution (A) was added to a beaker at 10
Take out 0 ml, water 80 ml and ethylene glycol 20 m
was added to obtain 200 ml of a coagulant having a SiO ₂ concentration of 3.5% by weight, ethylene glycol of 10 vol%, a pH of 1.8 and an intrinsic viscosity of 0.09.

(Embodiment 4) S formed in the same manner as in Embodiment 1
100 ml of an aqueous solution of sodium silicate having an iO ₂ concentration of 14% by weight
With 1.3N-HC containing 20% by volume of ethanol
The mixture was stirred and mixed at room temperature while being dropped into 100 ml of the solution over 30 minutes, pH 1.5, SiO ₂ concentration 7% by weight.
200 ml of a polymerized silicic acid solution was prepared.

90 ml of water and 10 ml of ethanol were added to 100 ml of this solution to obtain 200 ml of a flocculant having a SiO ₂ concentration of 3.5% by weight, ethanol of 10 vol%, a pH of 1.8 and an intrinsic viscosity of 0.07.

Example 5 9 g of ferric chloride was added to 200 ml of the flocculant obtained in the same manner as in Example 1,
₂ concentration 3.5% by weight, ethanol 10% by volume, pH
1.8, coagulant 2 with intrinsic viscosity of 0.13 and iron concentration of 1% by weight
00 ml were obtained.

(Comparative Example 1) Solution (A) was added to a beaker at 10
0 ml was taken, 100 ml of water was added, and the SiO ₂ concentration was 3.
5% by weight, pH 1.8, intrinsic viscosity 0.02 flocculant 20
0 ml was obtained.

(Comparative Example 2) 9 g of ferric chloride was added to 200 ml of the flocculant obtained in the same manner as in Comparative Example 1,
₂ concentration 3.5% by weight, pH 1.8, intrinsic viscosity 0.04,
200 ml of a flocculant having an iron concentration of 1% by weight was obtained.

Each of the coagulants obtained as described above was subjected to a stabilization test and a cohesion test by the following methods.

<Stability Test> In order to evaluate the storage stability of the flocculant, the following stability test was performed. Example 1
Each of the flocculants obtained in Comparative Examples 1 to 5 and Comparative Example 1 was stored in a thermostat at 25 ° C., and the gelation time and the limiting viscosity at each fixed time were measured. The gelation time was defined as the time until the flocculant solidified in a jelly state and lost its fluidity. The results are shown in Table 1 and further graphed in FIG.

[0043]

[Table 1]

As shown in Table 1, while the gel time of Comparative Example 1 was 139 hours, Examples 1 to 5 all had a remarkably long gel time exceeding 200 hours. . In addition, as is apparent from FIG. 1, in Comparative Example 1, the intrinsic viscosity rapidly increased and the gelation occurred, whereas in Examples 1 to 5, the intrinsic viscosity changed very slowly and was stable. You can see that there is. From these results, it was confirmed that the water-soluble alcohol acts on the stabilization of the polymerized silicic acid solution, and the flocculant can be stored in a stable state for a long time.

The intrinsic viscosity immediately after production of Examples 1 to 5 was higher than that of Comparative Example 1, because the apparent intrinsic viscosity was increased by the addition of the water-soluble alcohol. Silica has the same molecular weight.

<Cohesion Test> The cohesion of the water treatment flocculants obtained in Example 5 and Comparative Example 2 was evaluated by a jar test. The raw water to be treated was prepared by adding kaolin to tap water to make the raw water turbidity 100 °, and the coagulant addition rate was 0.5 ml /
L, the mixture was stirred at a water temperature of 21 ° C. and 120 rpm for 3 minutes, and the floc appearance time, floc particle size and supernatant turbidity were measured. Table 2 shows the results of these tests.

[0047]

[Table 2]

From Table 2, it was also confirmed that the coagulant of the present invention had sufficient cohesive force as the conventional coagulant in each of the items of floc appearance time, floc particle size and supernatant turbidity.

[0049]

According to the present invention, by adding a water-soluble alcohol, a polymerized silicic acid solution can be stabilized, and a coagulant for water treatment which can be stored for a long time can be obtained. Therefore, it becomes possible to easily mass-produce the flocculant containing the polymerized silicic acid.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between elapsed time of a flocculant and intrinsic viscosity.

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Claims (5)

[Claims] 1. A polymerized silicic acid solution containing a water-soluble alcohol, wherein the SiO ₂ concentration is 0.1 to 10% by weight,
H is 1 to 4. A water treatment flocculant, wherein H is 1 to 4. 2. The coagulant for water treatment according to claim 1, wherein the coagulant contains 1 to 50 vol% of a water-soluble alcohol. 3. The coagulant for water treatment according to claim 1, wherein the water-soluble alcohol is at least one selected from the group consisting of methanol, ethanol, propanol and ethylene glycol. 4. The coagulant for water treatment according to claim 1, which contains 0.1 to 10% by weight of a metal salt. 5. The coagulant for water treatment according to claim 4, wherein the metal salt is a ferric salt.