JP3751779B2 - Production method of flocculant for water treatment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a flocculant for water treatment for removing impurities from water.
[0002]
[Prior art]
In recent years, due to the progress of organic pollution in water supply sources, high-performance flocculants for coagulation removal of pollutants are required. Polyaluminum chloride (PAC) and sulfuric acid widely used in Japan It has been pointed out that aluminum flocculants such as aluminum may cause neurological diseases such as Alzheimer's disease if they remain in the treated water. In addition, the use of inorganic flocculants containing metals other than aluminum, such as ferric chloride and ferric sulfate, is also expected, but there are drawbacks such that the agglomeration effect is inferior to PAC.
[0003]
On the other hand, a method of improving the aggregation effect by using a synthetic organic polymer flocculant such as polyacrylamide in combination with an iron salt flocculant is also considered, but the monomer contained in the synthetic organic polymer flocculant has toxicity. Therefore, in Japan, it is not permitted to use in waterworks.
[0004]
The present applicant has already proposed a flocculant containing polymerized silicic acid and an iron salt as an inorganic polymer flocculant having no concern about safety and having a high flocculation effect (Japanese Patent No. 1783473, Patent No. 1). No. 2732067 and Japanese Patent No. 2,759,853), and the technology related to these patents is also of great interest from the viewpoint of the advantage of utilizing silicon-containing resources available everywhere on the earth.
[0005]
[Problems to be solved by the invention]
Regarding the technologies proposed in the above patents, the flocculant tends to be inherently unstable, so that it can be transported and stored between the production site and the use location, or in mass production. From the point of view, problems still remain.
[0006]
That is, when the active ingredient concentration such as Si concentration is increased in order to make the flocculating effect of flocculating agent the same as PAC, the period of storage in a stable state is relatively short. There was a risk that it would have to be manufactured at a remote manufacturing plant and transported immediately to the water treatment site. On the other hand, if the concentration of the active ingredient is lowered so that it can be stored for a relatively long period of time at the water treatment site, the amount of the production flocculant increases significantly, transportation costs increase, and a remarkably large storage tank is constructed at the water treatment site. It may be necessary to keep it.
[0007]
In the aforementioned 2775953 patent, a high concentration and high stability flocculant is proposed, but it is necessary to perform treatment using an ion exchange resin in the production process, which may cause an increase in production cost. . Further, as a problem in mass production, in general, in order to perform polymerization treatment so that the raw material does not gel during the production of the flocculant using a silicic acid solution, it is necessary to always maintain an appropriate pH value. In the case of production, strict control of the pH value may not always be easy.
[0008]
Furthermore, the optimum value of the content ratio of both (silicon and iron) in the flocculant composed of polymerized silicic acid and iron salt varies depending on the properties and properties of the water to be treated. Therefore, a coagulant produced at a manufacturing factory with a constant ratio may not always produce the best coagulation effect for water to be treated at the site of use.
[0009]
The present invention provides a method for producing a coagulant for water treatment that avoids the above-mentioned difficulties in the prior art and that provides a coagulant having the best effect on the water to be used even at the site of use. The purpose is to do.
[0010]
[Means for Solving the Problems]
In the present invention, a silicic acid solution having a low pH value, usually treated as a non-polymerization zone, and having a strongly acidic pH of 1 to 2, is heated to 50 ° C. to 80 ° C., which is significantly higher than room temperature, A means for polymerizing by stirring in that state is used. That is, in the method of the present invention, an acidic silicic acid solution having a pH value of about 1.0 to 2.0 is stirred in a state heated to about 50 ° C. to 80 ° C. to obtain polymerized silicic acid. A method for producing a flocculant for water treatment comprising adding ferric chloride (Claim 1). In the above-mentioned production method, the concentration of silicon (Si) in the acidic silicic acid solution is about 2 A method for producing a flocculant for water treatment, wherein the content is from 5 to 3.5% by weight (Claim 2).
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Conventionally, when a silicic acid solution is polymerized to form a flocculant, it has been constrained by how to set the Si concentration and pH value at room temperature to perform the polymerization operation. In view of the conventional preconception that polymerization is carried out while maintaining a low pH value, which was thought to be unsuitable for polymerization treatment, while being heated to a temperature significantly higher than room temperature, an unexpected means is used. Therefore, it is possible to install a production apparatus that can be easily polymerized at a water treatment site, thereby always allowing an optimum specification of the flocculant to be produced and used immediately.
[0012]
【Example】
The flocculant was manufactured using the apparatus shown in the flow sheet of FIG. In FIG. 1, 1 is a water glass reservoir (100 l), 2 is a hydrochloric acid reservoir (50 l), 3 is a ferric chloride reservoir (100 l), 4 is a dilution water reservoir (100 l), and 5 is a flocculant dilution. A storage tank (300 l) and 6 are stirring polymerization reaction tanks (internal volume 75 l). In the initial stage, all the valves V1 to V9 are closed, the metering pumps P1 to P6 are stopped, the stirrers 7 and 8 are stopped, and the heater 10 is stopped. Filled with chemicals or tap water.
[0013]
(1) Valves V1 and V4 are opened, and the discharge rates of metering pumps P1 and P4 are simultaneously operated at 605 ml / min and 1140 ml / min for 10 minutes, respectively, and the dilute hydrochloric acid solution stirred and mixed by in-line mixer 9 is stirred for polymerization reaction Transfer to tank 6. After the transfer, the valves V1 and V4 are closed, and the stirrer 7 of the stirring polymerization reaction tank 6 is started.
[0014]
(2) Next, the valves V2 and V5 are opened, the discharge rates of the metering pumps P2 and P4 are respectively operated at 110 ml / min and 292 ml / min, and stirred and mixed by the in-line mixer 10 so that the Si concentration is 4.6%. The diluted water glass solution prepared in the above step is dropped at a rate of 402 ml / min into 10% hydrochloric acid stirred in the stirring polymerization reactor 6 for 120 minutes. After the dropping, the operation of the metering pumps P2 and P4 is stopped, and the valves V2 and V5 are closed. The content after completion of the dropping was an acidic silicic acid solution having a pH of 1.3 to 1.5 and a Si concentration of about 3.4%.
[0015]
(3) Next, while stirring in the stirred polymerization reactor 6 was continued, the heater 11 was heated to 60 ° C., and the state was continued for 90 minutes to promote polymerization, thereby preparing a polymerized silicic acid.
[0016]
(4) After completion of the polymerization, the heating in the heater 11 is stopped, the valve V3 is opened, and 9.38 l of ferric chloride is introduced into the stirred polymerization reactor 6 using the metering pump P3. After the ferric chloride solution is added, the metering pump P3 is stopped, the valve V3 is closed, the polymerized silicic acid solution and the ferric chloride aqueous solution are sufficiently stirred and mixed to obtain a flocculant, and the production of the flocculant is completed. After that, the stirrer was shut down. The flocculant produced here has an Si concentration of 2.9%, an iron concentration of 1.9% (as Fe), a molar ratio of 3: 1 (Si: Fe), and an intrinsic viscosity of 0.38 (100 ml / g). ) And high agglomeration performance.
[0017]
{Circle around (5)} When the produced flocculant is used as it is, the valve V6 is opened, and a predetermined amount is injected into the raw water by the metering injection pump P5 to agglomerate. When the produced flocculant is temporarily stored, the valve V7 is opened and the flocculant is transferred to the flocculant dilution storage tank 5 by the metering injection pump P5. Next, the valve 8 is opened, and the metering pump 4 is used to inject tap water twice the amount of the flocculant and stir to dilute the flocculant to a concentration of 1/3. If necessary, the valve V9 is opened and metered. A predetermined amount is injected into the raw water to be treated by the injection pump P6.
[0018]
【The invention's effect】
According to the production method of the present invention, a water treatment flocculant containing polymerized silicic acid and an iron salt, which has high safety and agglomeration effect and is easily available for raw materials, is a troublesome operation of strict control of pH value. The flocculant can be produced by a simple device installed at the water treatment site, so that the required amount of coagulation that always has the component specifications suitable for the water to be treated can be produced. This makes it possible to produce an agent.
[Brief description of the drawings]
FIG. 1 is a flow sheet of an embodiment of the method of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Water glass storage tank 2 ... Hydrochloric acid storage tank 3 ... Ferric chloride storage tank 4 ... Dilution water storage tank 5 ... Coagulant dilution Storage tank 6 ... Stir polymerization reaction tank 7.8 ... Stirrer 9.10 ... In-line mixer 11 ... Heaters V1 to V9 ... Valves P1 to P6 ... Metering pump M1. M2 ... Motor

Claims (1)

An acidic silicic acid solution having a pH of 1.3 to 1.5 and a silicon concentration (Si concentration) of 2.5 to 3.5% is installed at a water treatment site, and the flocculant is used as water to be treated. In a stirred polymerization reaction vessel provided with a pipe that can be directly injected, after stirring into a polymerized silicic acid under heating at 50 ° C. to 80 ° C., ferric chloride is added thereto , A method for producing a flocculant for water treatment, which comprises producing a flocculant for water treatment that can be directly injected into water to be treated.

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