JPS62760B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for solid-liquid separation of muddy water derived from civil engineering work.

Mud water is generated in civil construction work that involves driving underground walls, piling, digging tunnels, shield construction, etc., but recently, in an effort to streamline construction and reduce costs, muddy water produced during construction has been circulated. It's here. As muddy water is repeatedly used, its slurry concentration increases and its viscosity increases, so that it does not settle easily, so it is transported to a final treatment plant by vacuum car or muddy pump for treatment. Since solid-liquid separation of muddy water as it is in a final treatment plant is extremely difficult, a solid-liquid separation agent is usually used to promote solid-liquid separation.

Conventionally, polyacrylamide and/or its hydrolyzed product, or a combination thereof with an inorganic salt, particularly a polyvalent metal salt, has been used as the solid-liquid separating agent.
This solid-liquid separation agent can efficiently perform solid-liquid separation of muddy water, but recently the toxicity of the acrylamide monomer contained in polyacrylamide and its partial hydrolyzate has become a problem.
There has been a demand for the development of non-toxic solid-liquid separation agents other than polyacrylamide.

In response to this demand, sodium alginate, starch chemicals, mannan gum, etc. have been proposed, but even when used in combination with polyvalent metal salts, their solid-liquid separation performance is extremely low compared to polyacrylamide. It has its drawbacks.

The present invention is non-toxic and allows solid-liquid separation of muddy water to the same extent as when polyacrylamide or its hydrolyzate is used, and the muddy water can be added to the muddy water not as a solution but as a powder. This method provided a solid-liquid separation method.

According to the present invention, when a mixed composition consisting of polyaluminum chloride and sodium polyacrylate is used as a solid-liquid separator for muddy water, the polyaluminum chloride is involved in the flocculation effect and clarity of the solid components of the muddy water, and the sodium polyacrylate is The solid components in the mud have a bridging compaction and agglomeration effect, and the mutual replenishment and synergistic effect of the two separates the mud into a solid phase and a liquid phase, and polyaluminum chloride and polyacrylic When a mixed composition formed by adding a zinc salt to the two components of sodium chloride is used as a solid-liquid separator for muddy water, in addition to the flocculating and clarifying effects of the solid component of the muddy water, the three components replenish each other. This is based on the knowledge that due to the synergistic effect, the solid-liquid separation of muddy water is better than that of the two-component separating agent, and the separated liquid phase is clarified.

The gist of the present invention is a solid-liquid separation method for muddy water, which is characterized by adding polyaluminum chloride, sodium polyacrylate, a PH regulator, and a zinc salt to muddy water to cause the solid components to coagulate and settle.

Sodium polyacrylate has a polymerization degree of 20,000~
100000 is used.

In the present invention, polyaluminum chloride is 40% by weight or less and 10% by weight or more, and sodium polyacrylate is 90% by weight based on the total amount of the mixture added to muddy water.
Hereinafter, it is preferably 60% by weight or more.

The amount of a solid-liquid separator made of polyaluminum chloride and sodium polyacrylate added to muddy water varies depending on the concentration of solid components in the muddy water, its components, and the components of the solid-liquid separator, and the optimum amount to be added depends on the site. Although it is determined, the standard is 0.05 to 1.0% by weight based on the weight of muddy water.

After adding solid-liquid separator to muddy water, the pH of muddy water is 5~
10, preferably 6 to 9. To maintain the pH of muddy water within this range, an aqueous solution of pH adjusters such as sodium carbonate, sodium hydroxide, and calcium hydroxide is used.

A solid-liquid separation agent for muddy water that uses zinc salt in addition to sodium polyacrylate and polyaluminum chloride has much improved solid-liquid separation properties of muddy water and clarity of the resulting separated liquid compared to those that do not use these agents together. do. The optimum blending ratio of polyaluminum chloride, zinc salt, and sodium polyacrylate in this case varies depending on the components and properties of muddy water, just as in the case of two-component solid-liquid separation agents, but polyaluminum chloride If the amount is 40% by weight or more based on the total amount, the agglomeration of solid components of muddy water by sodium polyacrylate will be delayed, and if it is less than 10% by weight, the clarity, which is a characteristic of polyaluminum chloride, will be significantly reduced. . The sodium polyacrylate content is preferably 60% by weight or more and 80% by weight or less, and the zinc salt content is preferably 1% by weight or more and 20% by weight or less. If it is 20% by weight or more, the agglomeration of the solid components of muddy water by sodium polyacrylate will be inhibited, and if it is 1% by weight or more,
The following has no effect.

Zinc chloride, zinc sulfate, zinc nitrate, etc. are used as the zinc salt. When carrying out the present invention, it does not deviate from the present invention even if a flocculant, a crosslinking agent, and a surfactant are added in addition to the solid-liquid separating agent described above.

When a solid-liquid separation agent consisting of polyaluminum chloride, zinc salt, and sodium polyacrylate is added to muddy water to perform solid-liquid separation of muddy water according to the present invention, the pH of the muddy water is 5 to 10, preferably 6 to 9. It is desired that Depending on the type of muddy water, the pH when adding a solid-liquid separation agent may be outside the above range, but in that case, add a pH adjuster such as sodium carbonate, sodium hydroxide, or calcium hydroxide. , it is necessary to adjust.

When carrying out the present invention, in addition to the above-mentioned solid-liquid separating agent, a flocculant, a crosslinking agent, and a surfactant can be used in combination.

The amount of solid-liquid separating agent added to muddy water varies depending on the concentration of solid components in muddy water, its components, and the components of solid-liquid separating agent.The optimal amount to be added is determined depending on the site, but it is 0.05 to 0.05 to the weight of muddy water. The standard is 1.0% by weight.

To add a solid-liquid separator to muddy water, mix the powdered components that make up the solid-liquid separator at a predetermined ratio.
Furthermore, if necessary, add sodium carbonate, etc.
By mixing a PH adjuster, adding the resulting mixed composition to muddy water, and stirring the muddy water to disperse the solid-liquid separation agent well, the muddy water will be separated into solid-liquid in a short time, and the upper layer of clear supernatant water will be In addition, sludge is obtained in the lower layer. The supernatant water is discharged, the sludge is drained with a screen, and further dehydrated as necessary.

Each component of the solid-liquid separating agent may be mixed in a predetermined ratio as powder or an aqueous solution, and the resulting aqueous solution of the solid-liquid separating agent may be added to the muddy water.

According to the method of the present invention, not only the solid-liquid separating agent used but also the supernatant liquid and sedimented sludge after adding it to muddy water are free from toxicity, and the resulting sludge has excellent solid-liquid separation ability. The water content of the sludge is as low as 70%, and the dehydration rate is 85-90% when using other inorganic flocculants. The liquid separating agent is universal for the types and properties of muddy water, and the purpose of the present invention can be achieved by simply changing the amount of solid-liquid separating agent used for muddy water, and the solid-liquid separating agent of the present invention can also be used. If each component is in powder form, it can be added to muddy water as a single mixed composition, so unlike conventional methods, each component such as a solid-liquid separator, crosslinking agent, PH adjuster, etc. can be added separately to a constant concentration. Adjust,
It has the advantage of not requiring a complicated process of adding these.

Next, the present invention will be explained with reference to Examples, but the present invention is not limited thereto.

Comparative Example 1 The muddy water used in the comparative example was that discharged during tunnel excavation work using the shield method.
This muddy water is a silty clay with relatively little organic matter, suspended solids content is 21.5% by weight, fine particles of 74 microns or less account for 98% of the total solids, and the pH of the muddy water is
It was 8.7.

Take this muddy water 1 in a beaker and add polyaluminum chloride (powder, apparent specific gravity 0.83, Al ₂ O ₃ content
30% by weight) and 200 ppm of sodium polyacrylate (powder, degree of polymerization: 80000) were added to the muddy water, and the resulting mixed composition was rapidly stirred at 120 rpm for 20 seconds. The pH at that time was 6.4.

The contents of the beaker were then stirred by reducing the stirring speed to 75 rpm. Flocks began to form at a deceleration rate of 40 seconds, and the generation of flocs was completed in 1 minute and 30 seconds.

After the reaction product was allowed to stand for 3 minutes, the transparency of the supernatant water was measured and found to be 25.

The sedimented flocs were solidified to a particle size of approximately 10 mm. As a result of passing this floc through a screen with an opening of 1 mm using only gravity, the slag on the screen had a moisture content of 70%, and the SS (suspended solids) in the liquid at that time was 80 ppm. .

Example 1 Take the muddy water 1 used in Comparative Example 1 into a beaker,
To this, 110 ppm of polyaluminum chloride, the same as used in Comparative Example 1, and sodium polyacrylate were added.
As a result of adding 200 ppm of zinc chloride and further adding 70 ppm of zinc chloride and treating the mixed composition according to Comparative Example 1, the transparency of the supernatant water after allowing the reaction product to stand was 30, and the settled flocs were passed through a screen with an opening of 1 mm. The moisture content of the slag was 70% when it was left to dry naturally, and the SS content in the solution was 60 ppm.

Comparative Example 2 Take muddy water 1 used in Comparative Example 1 into a beaker,
To this were added 110 ppm of polyaluminum chloride and 200 ppm of polyacrylamide (added as a 0.1% by weight aqueous solution) with a degree of hydrolysis of 25% and a degree of polymerization of 100,000, and stirred rapidly at 120 rpm for 20 seconds in the same manner as in Comparative Example 1. . At that time, the PH of the mixed composition is
It was 6.4. When this was further stirred at a reduced speed in the same manner as in Comparative Example 1, flocs were formed 1 minute after deceleration, and the formation of flocs was completed in 1 minute and 50 seconds.

After the obtained reaction product was allowed to stand for 3 minutes, the transparency of the supernatant liquid was 25, and the settled flocs had solidified to a particle size of 8 mm. Open the settling floc 1
When the flocs were naturally filtered through a mm screen, the moisture content of the flocs was 72%, but compared to Comparative Example 1 and Example 1, it was found that the sedimented flocs were difficult to drain and were sticky.

Example 2 The muddy water used in this example was discharged from a construction site where an underground wall construction method was implemented, and the SS concentration was
17%, silt and clay with a diameter of 74μ or less account for 98% of the solid content, and also contain polymer stabilizers (polysaccharides) used in excavation, calcium ligninsulfonate, Telstop (humate), etc. was.

Take this muddy water 1 in a beaker, add 150 ppm of polyaluminum chloride as a 5% aqueous solution, 60 ppm of zinc chloride as a 1% aqueous solution, and 180 ppm of sodium polyacrylate as a 0.1% aqueous solution, and mix the resulting mixed composition at 120 rpm. After stirring for 20 seconds with
A 5% slaked lime aqueous solution was added while stirring at 120 rpm until the pH of the contents of the beaker reached 8.2.
Then, when the stirring speed was reduced to 75 rpm and stirred, flocs were generated 25 seconds after the speed was reduced.
As the flocs continue to be stirred, their particle size increases, and approximately 1 minute 20 minutes after the start of deceleration.
It grows to 7 mm in seconds, and the generation and agglomeration of flocs are completed in 1 minute and 50 seconds, and the diameter of the flocs is approximately
It was 10mm.

Stop stirring 2 minutes after starting deceleration, then 3 minutes.
When the reaction product was allowed to stand for 3 minutes, it was separated into a floc layer of 10 parts by volume and a supernatant water of 90 parts by volume in the beaker. The pH of the obtained supernatant water was 8.2, and the transparency was about 30. When the obtained floc layer was placed on a 1 mm aperture screen to a thickness of 30 mm and left to dry, the flocs remained for about 2 minutes and 10 seconds. The water content was 70% and it was easily peeled off from the screen. The liquid SS separated by the screen is
It was found that the concentration was 80ppm and the pH was 8.2, which means that it is safe to discharge into rivers.

Example 3 The muddy water used in Example 2 was taken into a beaker and treated in the same manner as in Example 2 except that zinc chloride was not used. The clarity of clear water is about 23
It was hot.

In addition, the obtained floc layer was placed on a screen with a 1 mm opening to a thickness of 30 mm in the same manner as in Example 2, and the water was drained in about 2 minutes and 30 seconds, and the moisture content of the slag was 71. It was %.

Comparative Example 3 Mud water 1 used in Examples 2 and 3 was taken in a beaker, and polyaluminum chloride was added to it.
60ppm in a 5% aqueous solution and a partial hydrolyzate of polyacrylamide (molecular weight 100000 hydrolysis rate)
25%) was added as a 0.1% aqueous solution, and in the same manner as in Example 2, a 5% slaked lime aqueous solution was added while stirring the contents of the beaker to adjust the pH to 8.2.

Then, as in Example 2, the stirring speed was reduced and stirring was continued, and the formation of flocs was observed in about 30 seconds, the flocs grew to a particle size of 7 mm in about 1 minute and 30 seconds, and the flocs disappeared in about 2 minutes. Generation and agglomeration have been completed.

Further, stirring was stopped, and the contents of the beaker were allowed to stand still for 3 minutes, resulting in separation into a floc layer of 10 parts by volume and a supernatant water layer of 90 parts by volume. The pH of the supernatant water was 8.2 and the transparency was about 20.

When the obtained floc layer was placed on a screen with a 1 mm opening to a thickness of 30 mm and allowed to evaporate naturally, the water was drained in about 2 minutes and 30 seconds, and the dehydration rate of the obtained slag was 72%. It was observed that the releasability from the film was inferior to that of Examples 2 and 3.

As is clear from the above examples and comparative examples,
According to the present invention, unlike conventional methods, polyacrylamide, which has a high toxicity concern, is not used, so the wastewater obtained by treatment is completely harmless, and the resulting floc has good permeability and dehydration rate, and is screened. It was recognized that the separability from the

Claims (1)

[Scope of Claims] 1. A solid-liquid separation method for muddy water, which comprises adding polyaluminum chloride, sodium polyacrylate, a PH adjuster, and a zinc salt to muddy water to cause the solid components to coagulate and settle. 2. In claim 1, polyaluminum chloride accounts for 40% by weight or less and 10% by weight based on the total amount of polyaluminum chloride and sodium polyacrylate and zinc salt.
Above, sodium polyacrylate is 80% by weight or less
A solid-liquid separation method for muddy water in which the content is 60% by weight or more, and the zinc salt content is 20% by weight or more and 1% by weight or more. 3. In either claim 1 or 2, the sodium polyacrylate is 20,000 to 20,000
Solid-liquid separation method for muddy water with a degree of polymerization of 100,000. 4. In any one of claims 1 to 3, the total amount of polyaluminum chloride, zinc salt, and sodium polyacrylate is not very large in muddy water.
Solid-liquid separation method for muddy water that is 0.05-1.0% by weight. 5 In any one of claims 1 to 4, the pH of muddy water after adding polyaluminum chloride, zinc salt, and sodium polyacrylate is 5 to 5.
10, preferably 6 to 9, solid-liquid separation method for muddy water.