JPH1034161A - Treatment of silica-containing waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide treating SiO2 -containing waste water capable of efficiently removing SiO2 -containing waste water in cost lower than conventional cost. SOLUTION: In a method for treating SiO2 -containing waste water to separate SiO2 by flocculation, an aluminum compd. and sulfuric acid are added to waste water to hold the pH of waste water to 3.8-4.8 for several min to flocculate SiO2 particles so as to have a particle size of several-several ten μm. Next, an alkali agent is added to this waste water to adjust the pH thereof to 6-8 and, thereafter, flocculation sedimentation separation by the addition of a polymeric flocculant or solid-liquid separation using a membrane with a pore size of 1μm or less is performed. It is pref. to preliminarily add. fine particles with a particle size of 0.03-0.6μm to waste water to be treated as pretreatment and, as fine particles to be added, colloidal SiO2 is pref. and, when treated water by this method is further treated with an RO membrane and/or an ion exchange, SiO2 can be removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a processing method of SiO ₂ containing wastewater, in particular, from groundwater and industrial waste etc. containing SiO _2, relates to a method for separating and removing by agglomerating SiO ₂ efficiently is there.

[0002]

_2. Description of the Related Art As a method for removing SiO ₂ from wastewater, two types of soluble SiO ₂ are generally used, namely, membrane separation and removal using an RO membrane and adsorption and removal using an anion exchange resin. ₂ has a pore size of 0.01μ
Solid-liquid separation with an ultrafiltration membrane (hereinafter referred to as a UF membrane) of m or less was common. Among the above conventional methods, in the case of adsorption by an anionic resin, other ionic substances besides soluble SiO ₂ are adsorbed, so these methods are suitable when used for pure water production, Soluble SiO
_{When the} main purpose was to remove only ₂ , it was not very efficient, and in some cases, it was necessary to add the adsorbed useful ions again. Also, when the concentration of soluble SiO ₂ is high, there are problems such as a large required resin capacity, frequent regeneration, and high cost. RO
In membranes and UF membranes, it is necessary to frequently replace the membrane unit in order to gradually deposit SiO ₂ particles on the membrane surface and form a dense layer to deteriorate the filtration efficiency, which is costly. There was a problem in maintenance such as difficulty in specifying the frequency of replacing the membrane.

[0003]

SUMMARY OF THE INVENTION In view of the above-mentioned drawbacks of the prior art, the present invention provides a treatment method capable of removing SiO ₂ -containing wastewater at a lower cost and more efficiently. Make it an issue.

[0004]

In order to solve the above problems SUMMARY OF THE INVENTION In the present invention, SiO ₂ from the waste water containing SiO ₂
In the treatment method of coagulating and separating the wastewater, an aluminum compound and sulfuric acid are added to the wastewater to adjust the pH to 3.8 to 4.
8 for several minutes to reduce the SiO ₂ particles
m, then adjust the pH to 6 to 8 by adding an alkali agent, and then perform coagulation sedimentation separation using a polymer coagulant, or solid-liquid separation using a 1 μm or less pore size membrane. And a method for treating wastewater containing SiO ₂ . In the treatment method, in the solid-liquid separation using the membrane, the thickness of the cake layer formed on the membrane surface is 1 to 1
It is preferable to use a membrane separation device provided with a mechanism for controlling the distance to 0 mm. Further, fine particles having a particle size of 0.03 to 0.6 μm are preferably added to the wastewater treated by the treatment method in advance as a pre-treatment, and the added fine particles are preferably colloidal SiO _2. . Further, in the present invention, the aforementioned SiO ₂
The treated water treated by the treatment method for wastewater containing water is further treated with an RO membrane and / or an ion-exchange resin to obtain S
iO ₂ can be removed to a trace amount.

[0005]

Next, the present invention will be described in detail.
The aluminum compound to be added to the SiO ₂ containing waste water used in the present invention, poly aluminum chloride, is effective sulfate or the like, when the addition rate of the poly aluminum chloride, Al ₂ O ₃ with respect to SiO ₂ in the solution 0 in conversion.
An appropriate range is 5 to 3.0% by weight. The aggregates have grown to a size of several to several tens of μm when sulfuric acid is added to adjust the pH to 3.8 to 4.8, but the mechanical strength is small and the aggregates are broken by a large stirring force. Tends to be easy.
When the pH becomes 3.8 or less, the particle size of the aggregate tends to decrease again.

As the alkaline agent, sodium hydroxide, calcium hydroxide, magnesium hydroxide and the like are all effective. Judging from the strength of the aggregate, the aggregate made of magnesium hydroxide is the most excellent. At the time when the alkali agent is added, the aggregate has changed to particles having such a strength as not to be broken by the stirring force of the stirrer, having excellent filterability, and being difficult to form scale. This aggregate is hereinafter referred to as aggregate A. Aggregate A can be aggregated and precipitated by a polymer flocculant. In particular, the aggregation performance of the anionic polymer is high, and the addition rate of 0.2 (% to-TS),
Agglomerated flocs having a sedimentation speed of 10 mm or more and a sedimentation speed of 100 mm / min or more are formed. The aggregate A can be subjected to membrane separation by a microfiltration method, a dynamic filtration method, or vacuum filtration. In particular, by performing an operation method of controlling the cake layer deposited on the membrane surface to a constant thickness, a reduction in filtration efficiency is prevented, and a long-term continuous operation becomes possible.

[0007] Further, SiO _{2 in} the waste liquid is soluble SiO ₂
Only, and when the concentration is high, the particle size is from 0.03 to 0.03.
By performing the above aggregation operation after adding the 0.6 μm fine particles, the aggregation of the soluble SiO _{2 on} the surface of the fine particles is promoted, and the processing efficiency is increased. In particular, when 0.1 to 0.4 μm colloidal SiO ₂ is used as the added fine particles, the agglutination reaction speed of SiO ₂ is increased, and the particle diameter of the formed aggregate is uniform and the property of easy separation by filtration is obtained. I will have it. The range of the appropriate amount of colloidal SiO ₂ varies depending on the concentration of soluble SiO ₂ . When the soluble SiO ₂ is several tens mg / liter, 1/10
It is effective to add a certain amount of colloidal SiO ₂ .
When removing SiO _{2 in} a solution to a very small level of ppb or less, a method using an RO membrane or an anion exchange resin is generally used. Also in this case, when the concentration of the undiluted solution is high, it is effective to adopt the above-mentioned processing method as the pre-processing.

[0008]

The present invention will be described below in more detail with reference to examples. Example 1 According to a conventional method and an example, the same continuous treatment of wastewater containing SiO ₂ was performed. Colloidal silica-based semiconductor factory wastewater with an average TS concentration of 14.5 g / liter,
A solution in which the content of colloidal SiO ₂ having a particle size of 0.4 μm or less in the total evaporation residue was 95% or more was used as raw water.
The processing speed was 124 liters / h on average, and continuous operation was performed for 30 days. Table 1 shows the processing conditions.

[0009]

[Table 1] In Example 1, polyaluminum chloride was prepared by using SiO ₂ in a solution.
Was added at 2.0% by weight in terms of Al ₂ O ₃ , the pH was adjusted to 4.0 with sulfuric acid, and the pH was adjusted with magnesium hydroxide.
After adjusting to H7.0, the mixture was supplied to a concentrator loaded with a rotating flat membrane type MF membrane to perform membrane separation. This device has a mechanism for controlling the thickness of the cake layer formed on the film surface to 6 mm. In the conventional example, the raw water is supplied to the membrane module loaded with the capillary type UF membrane without chemical injection, the concentrated water is returned to the raw water tank again, and a part of the concentrated water is periodically discharged.

Table 2 shows the processing results. In Table 2, the clarity of the treated water is a suspended substance (hereinafter referred to as SS ^0.1 ) obtained by filtration through a 0.1 μm filter, and the concentration of the concentrated water is evaluated by the TS concentration. Shows the average value of the processing results.

[Table 2]

In the conventional example, the treated water is clear, but as the concentration concentration increases, the amount of permeated water decreases, and the inside of the capillary membrane tends to be clogged. In order to maintain a constant processing speed, it was difficult to increase the concentration to 80 g / liter or more. At the time of 96 hours, the throughput decreased rapidly and continuous operation could not be continued. In the first embodiment, the treated water is clear and the concentration can be concentrated to about twice the concentration of the conventional example.
The S concentration was 143.1 g / liter. Continuous operation for 700 hours or more was possible.

Example 2 Next, an example of coagulation precipitation separation to which a polymer coagulant is added will be described. To the same SiO ₂ -containing wastewater as in Example 1, 2.0% by weight of polyaluminum chloride (PAC) was added with Al ₂ O ₃ , the pH was adjusted to 4.0 with sulfuric acid, and the pH was adjusted to 7.0 with magnesium hydroxide. After setting to 0, 2.0 mg / liter of an anionic polymer coagulant was added to perform coagulation sedimentation separation. The water area load of the settling tank was 2 m / h, and the concentrated liquid was continuously discharged. Table 3 shows the average value of the processing results.

[0013]

[Table 3] With a simple coagulation / sedimentation / separation apparatus such as this one, concentration can be made about 4-fold, maintenance-free, and not so bright compared to conventional examples.

[0014]

As described above, according to the present invention, in the wastewater containing colloidal SiO ₂ , the addition of an aluminum compound and the control of the pH twice allow the colloidal Si 2 to be added.
It is possible to grow or aggregate O ₂ and convert it into an aggregate having a particle size and strength that facilitates membrane separation, and this aggregate can be precipitated and separated by a polymer flocculant and colloidal. SiO ₂ -containing wastewater can be efficiently removed. As a result, solid-liquid separation can be performed by the MF membrane having a large permeated water amount, instead of the UF membrane having a relatively small permeated water amount in the conventional method, and the concentration of the concentrated water is increased by about two times, so that the recovery efficiency of the treated water is increased. .

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication location C02F 1/44 ZAB C02F 1/44 ZABE 1/56 ZAB 1/56 ZABK

Claims (5)

[Claims] 1. A processing method of separating from the waste water containing SiO ₂ by agglomerating SiO _2, the waste water, an aluminum compound and sulfuric acid was added, the pH 3.8 to 4.8
For several minutes to reduce the size of the SiO ₂ particles to several tens μm.
And then, after adjusting the pH to 6 to 8 by adding an alkali agent, performing coagulation sedimentation separation using a polymer coagulant, or solid-liquid separation using a membrane having a pore size of 1 μm or less. SiO ₂ content processing method of wastewater. 2. The solid-liquid separation using the membrane, wherein a membrane separation device having a mechanism for controlling the thickness of a cake layer formed on the membrane surface to 1 to 10 mm is used. SiO ₂ content processing method of waste water according to. 3. The treatment of SiO ₂ -containing waste water according to claim 1, wherein the waste water to be treated is added with fine particles having a particle size of 0.03 to 0.6 μm as pre-treatment. Method. 4. The method according to claim 1, wherein the fine particles to be added are colloidal S particles.
4. The SiO according to claim 3, wherein the SiO ₂ is iO _2.
Processing method ₂ containing wastewater. 5. A method for treating wastewater containing SiO ₂ , wherein the treated water treated by the method according to claim 1 is further treated with an RO membrane and / or an ion exchange resin.