JPS6020074B2 - How to treat grout wastewater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating wastewater in grouting methods, particularly wastewater generated during grouting methods using water glass-based chemicals.

As is well known, the method of injecting water, glass, and cement-based suspended or semi-suspended chemicals, known as the LW construction method, is used to stabilize soil quality and prevent spring water by injecting water glass chemicals.
There is a solution-type injection method that does not use cement, and each method stabilizes the soil and stops water depending on the properties of the soil and the strength of the spring water. However, in such a grouting method, a large amount of civil engineering drainage (hereinafter referred to as grout drainage) is generated due to the construction of water conveyance, water flow, and other civil engineering works.

This grout drainage, ranging from suspension to solution, is a big problem at construction sites.In particular, grout drainage in the water glass chemical injection method is contaminated with limescale sand and is accompanied by the chemical, which makes it highly alkaline. This makes the process even more difficult. For example, if the concentration of sodium silicate in wastewater is high, simply neutralizing it will result in gelation and result in a sludge with a high water content that is difficult to separate, whereas if the concentration is low, it will dissolve without gelling. However, in many cases, such grout drainage is neutralized with sulfuric acid and separated by precipitation, but in addition to the above, if cement particles are suspended, this is also Not only does it require a large amount of sulfuric acid because it is consumed by neutralization, but it also results in sludge that is difficult to separate. In addition, this is particularly likely to occur with wastewater in the LW construction method, but depending on the wastewater, the silicic acid content in the sodium silicate turns into colloid, causing a white cloudy phenomenon, which can hardly be agglomerated by the above-mentioned neutralization treatment or flocculant. , cannot be removed by normal separation operations. In view of the above-mentioned issues, the inventors of the present invention have made a decision regarding grout wastewater treatment.As a result of extensive research,
The cloudy phenomenon is caused by silicate ions and divalent intestinal ions, especially C, in the wastewater.
The present invention was completed based on the fact that this occurs when there is a certain relationship between 10 and 10, and that it does not occur if this relationship is removed, and that more effective neutralization treatment can be achieved.

That is, the gist of the present invention is that one or more soluble calcium-containing substances selected from quicklime, slaked lime, cement, and calcined dolomite are added to wastewater in the water glass injection method in a molar ratio of at least Ca0/Si02. 0. This is a method for treating grout wastewater, which is characterized in that it is added to the wastewater at a pH of 8.5 or higher, and then a flocculant is added to coagulate and separate the suspended matter.

Among grout wastewater, wastewater that is particularly difficult to treat has an appearance that is not cloudy due to kaolin or cement particles but is cloudy overall, has a high pH, and has a large amount of settled sludge.

This kind of drainage depends on the circumstances at the site, but in many cases,
Appears during construction where a large amount of water glass is used. According to the results of numerous experiments conducted by the present inventors, such a cloudy phenomenon is related to the balance between the concentrations of sodium silicate, Mg++, and C in the wastewater, and occurs particularly when the concentration of sodium silicate is higher than the CaH concentration. I understand.

The reason for this is probably that the concentration of salts that promote gelation is low relative to the dissolved amount of sodium silicate, and together with the influence of pH in the wastewater, silicate ions colloidize and form fine silicate gel particles. This seems to be due to the fact that it does not grow until it becomes a gel. For example, in the case of sodium silicate aqueous solution and cement, or seawater + sodium silicate + cement, if mixed regardless of the order of addition, they will gel and form a precipitate, but if the amount of C is small compared to the sodium silicate The top solution becomes milky and cloudy, which not only cannot be separated by sedimentation or filtration, but also does not coagulate even if a coagulant is added.

However, when Ca++ is added to such cloudy water to change the concentration relationship between the two, precipitation occurs and the cloudiness is removed. The reason for this is probably that there are active silica colloid particles and fine calcium silicate particles, and silicate ions are dissolved in dissolved Ca.
This is thought to be due to reaction with H to produce coarse calcium silicate particles.

From the above, it has been found that a calcium-containing material that releases 10 carbon atoms is suitable for cleaning water glass grout drainage.

Examples of such substances include quicklime, slaked lime, cements, and calcined dolomite. When added, these are used in the form of solid powder or slurry, but in most cases, a slurry of slaked lime is suitable.

When a water-dropping calcium compound is used in place of the above-mentioned elutriation-soluble calcium-containing substance, it cannot be applied in the present invention because there is substantially no turbidity removal effect on opalescent grout wastewater.

On the other hand, flocculants used in combination with this include known inorganic flocculants such as basic aluminum chloride, aluminum sulfate, iron sulfate, or iron chloride, and a typical organic flocculant is poly-1'acrylamide. , a copolymer of acrylic acid and acrylamide, etc., and one or a mixture of two or more of them is used.

In this reaction, it is desirable that the pH in the waste water is at least 8.5 or higher, and particularly preferably in the range of 90 to 11.0.

The reason for this is that when the pH is below 85, it is difficult to generate insoluble silicates. However, since the water glass grout drainage generally has a pH within the above-mentioned pH range, it is often not necessary to adjust the pH of the drainage especially when carrying out this reaction, and it may be done as necessary.

Next, the amount of the Ca-containing substance added must be such that the molar ratio CaC/Si02 is at least 0.5 with respect to the total silicic acid content in the wastewater, and the upper limit is not particularly limited and is set based on economic conditions. However, in most cases, a range of 1 to 4 is appropriate.

The total silicic acid content in wastewater mainly refers to the silicic acid content of dissolved sodium silicate in the wastewater, but if colloidal silica or fine calcium silicate are present, the silicic acid content also includes them. shall mean.

Due to the nature of wastewater, it constantly changes depending on the construction method, quality, water leakage, etc., so before adding calcium-containing substances, set up equipment in the treatment system to easily monitor the total silicic acid content. This is desirable.

This reaction proceeds after adding the above calcium-containing substance to the grout drainage and, if appropriate filtration is carried out, produces insoluble calcium silicate, which then improves the separation of suspended matter such as this product and carrions. To make it better, add a flocculant. The calcium silicate produced by this reaction acts very sensitively with a flocculant and tends to flocculate, and easily forms coarse flocs and settles, so only a small amount of flocculant is needed. Next, the wastewater treated as described above becomes treated water that does not substantially contain silicate ions and is purified, and can be discharged as it is, but if the pH of the wastewater is high, it should be neutralized. It is necessary.

In the present invention, this neutralization treatment can be effectively performed by introducing CO2 gas.

That is, in this reaction, CaH resulting from the added excess calcium-containing substance can be easily insolubilized by introducing CO2 gas, so that it can be made substantially harmless by this treatment. This introduction of C02 gas may be carried out as it is regardless of the separation of the precipitate generated after the above reaction, or even after the precipitate separation, it can be set depending on the circumstances at the site, but generally speaking The latter is preferable. Note that if neutralization by introducing this CQ gas is insufficient, further neutralization may be performed with sulfuric acid if necessary. Thus, according to the invention:
Grout waste water using water glass, which is considered difficult to treat, can be economically and advantageously rendered harmless by using a simple chemical and a simple operation.

In particular, silicate ions in treated wastewater are added with 5p as Si02.
It is of great significance to lower it to a level below m. Example 1 970 parts of water, 2 parts of water glass (No. 3) and 2 parts of kaolin
Light the mixture equivalent to 0 cough pm at 150 Rpm for 5 minutes.

Next, a predetermined amount of CaC12 solution was added and the engine was heated at 40 Rpm.
, after 15 minutes of worship, after leaving it for 30 minutes, apply 500 ml of Kamedou liquid.
is used as the model wastewater and the test solution. All of these test solutions are milky white liquids (pH 10 to 12). A predetermined amount of slaked lime slurry (1000 pm) was added to this test solution, and it was lit with a candle.
After standing for 0 minutes, the top lighting solution was measured and the results shown in Table 1 were obtained. When the treated water of test solutions A and B of Experiment No. 6 in Table 1 was added with 1 ml of sulfuric acid band solution (loo0 ypm), the floc volume was 6.9, and the turbidity was 7.3. Also 0
．． 3. Dissolved oxalic acid content is 45ppm and 35p as Sj02
It became pm.

(Note) Test solution A: Milky white liquid prepared by adding CaC12 as Ca++ equivalent to 10 cape blood Test solution B: CaC12 as Ca++
Milky white liquid prepared by adding 20 pm equivalent of CaC12 as a+1 Test solution C: Milky white liquid prepared by adding 30 pm equivalent of CaC12 as Ca++ Example 2 Bortland cement in JIS sodium silicate No. 3 aqueous solution When the relationship between the turbidity and the amount of cement added at each concentration was examined, the results shown in Table 2 were obtained.

Table 2 As shown above, it is estimated that milky white turbidity in wastewater occurs over a wide range and at high concentrations as the concentration of sodium silicate increases.

Take 500 supernatant samples each showing the highest turbidity, and
Add slaked lime slurry with a concentration of 1000 pm so that the molar ratio of ○/Si02 is 4, and heat at 150 Rpm for 1 minute.
Next, a basic aluminum chloride solution of 2 pm was added and allowed to stand in the same manner. The flocs settled and the supernatant solution became clear. When this upper phosphor solution was measured, the turbidity was 0.5 or less, and the dissolved silicic acid content was Si02
It was 20-4 Cape pm. Incidentally, a similar problem was observed when 5 ppm of a polyacrylamide flocculant was added.

Example 3 Grout drainage by LW method (pH: 11.6, turbidity:
Sodium silicate (Si02): 176 pm), even if the suspension is separated, the separated liquid shows milky turbidity, and the turbidity is 1.
It was 60.

A slaked lime slurry (1000 pm concentration) was added to 500% of this solution to make the molar ratio Ca○/Si023.8, and then a small amount of basic aluminum chloride solution was added and allowed to react. , C02 gas was introduced for 2 minutes at a flow rate of 500 desk/min. When the suspended matter was then separated by a furnace, the separation was good and the liquid became transparent. The dissolved silicic acid content of this solution was 3 pm as Si02, and the pH was 7.
5 The koji level was 0.4, and it was purified to the point where there was almost no actual damage. Example 4 Dissolved silicic acid is 365 ppm as Si02
To 500 g of grout waste water containing 230 ppm of kaolin in water glass, 20 g of a slurry of 50% partial decomposition of alumina cement with hydrochloric acid (1,000 pm) and 30 g of slaked lime slurry (1,000 pm) were added. When it was allowed to fly, it formed flocs and coagulated and settled.

Moreover, the phosphorous solution had a turbidity of 0.3, a phosphoric acid content of 3 kpm as Si02, and a pH' of 10.2. This liquid contains C02
When neutralized by introducing gas at 500 I/min for 2 minutes,
The pH was 7.4, and free CaH could also be substantially removed, rendering it harmless.

Comparative Example 1 Same as Example 1, 1 standard for 1 night of milky white water.
When the specific S04 solution was added until neutralization, the relationship between pH and turbidity was as follows, and the milky turbidity could hardly be eliminated. Table 3 shows the results. Table 3 Comparative Example 2 Aluminum sulfate solution (
When a predetermined amount of 1000 pm) was added and each treatment liquid was measured, the results shown in Table 4 were obtained.

Table 4

Claims (1)

[Claims] 1. One or more poorly soluble calcium-containing substances selected from quicklime, slaked lime, cement, or calcined dolomite are added to the wastewater in the water glass grout injection method so that the molar ratio CaO/SiO_2 is at least 0.5 and the pH is 8.
．． A method for treating water glass-based grout wastewater, which comprises adding a coagulant to the wastewater at a temperature of 5 or more, and then adding a flocculant to coagulate and separate the suspended matter.