JP2001190902A - Method for removing fine sand from sludge water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently remove fine sand in sludge water, in a method for reusing ready-mixed concrete sludge. SOLUTION: In method for reusing cement by recovering aggregate from wastewater, which is generated by washing an equipment to which concrete or mortar is adhered, with sludge water containing a coagulation retarder and delaying the hydration of cement, fresh water is injected in the sludge water layer within a fine aggregate recovery equipment to form a fresh water thin layer and a high performance cement water reducing agent or an oxycarboxylic acid coagulation retarder is preferably added to this fresh water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reusing raw concrete sludge, and more particularly, to a method for removing fine sand from sludge water by quickly sedimenting and collecting fine sand in the sludge water.

[0002]

2. Description of the Related Art In recent years, sludge water containing cement and retarder that has not yet set has been used to wash equipment such as drums of agitator trucks on which concrete or mortar has adhered, and aggregate has been separated from the wash water to calculate the cement concentration. A method of reusing it as mixing water for fresh concrete is being adopted. This method has an effect of improving the quality of the fresh concrete without lowering the quality of the fresh concrete since the cement in the washing water is kept unhydrated and active.
Furthermore, it is a desirable method for maintaining the global environment in which all components in the sludge water obtained by washing the apparatus can be reused.

[0003]

However, by repeatedly washing the apparatus on which concrete or cement adheres using sludge water containing a setting retarder, the sludge water becomes high in concentration and viscosity increases, and as a result, The sedimentation speed of fine sand in the aggregate tends to decrease. In particular, when treated water such as a return condenser and a residual condenser flows in, the solid concentration temporarily reaches 30 to 60%. On the other hand, the method for removing aggregate that has settled due to the difference in specific gravity has been adopted for the aggregate separation device, but fine sand having a particle size of 1.5 mm or less has a further reduced sedimentation speed and passes through the fine aggregate separation device. However, the fine sand was not sufficiently separated, and the fine sand tended to be mixed into the sludge water containing the cement and the retarder.

It has been found that the fine sand mixed into the sludge water binds to the cement in the sludge water and has an effect of promoting the hydration of the cement. If the hydration of the cement is promoted, the consumption of the setting retarder increases. Since the setting retarder is a consumable in a cement factory where the cement is recovered and reused, the amount of the setting retarder to be used should be reduced as much as possible. Therefore, there has been a demand for a method of segregating the aggregate in the sludge water in a small amount at high speed in a large amount in the aggregate separating apparatus.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems, and an object of the present invention is to use a sludge water containing a setting retarder to wash aggregates from concrete or mortar-applied effluent to aggregate. In the method of recovering the cement, delaying the hydration of the cement and reusing the cement, fresh water is poured into the sludge water layer in the fine aggregate recovery device to form a thin layer of the fresh water, and preferably, It is characterized by adding a performance cement water reducing agent or an oxycarboxylic acid-based setting retarder.

That is, according to the present invention, fresh water or fresh water added with a cement dispersant such as an oxycarboxylic acid-based setting retarder or a high-performance water reducing agent is injected into sludge water containing aggregate flowing into the aggregate separating apparatus. A thin layer of fresh water is formed in the sludge water containing fine aggregate, and the presence of this thin layer promotes the sedimentation of the aggregate, especially fine sand, and suppresses the subsequent consumption of the setting retarder in the sludge water. It was found and completed. Generally, the residence time of the sludge water containing fine aggregate in the aggregate separation apparatus is 2 to 4 minutes, and in the present invention, the sedimentation of fine sand is remarkably promoted within this time. In addition, simply mixing fresh water with sludge water containing fine sand has no effect, but the present invention is presumed that the expected effect can be obtained by contact between the rich sludge water layer and the fresh water layer. Is done.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The sludge water in the present invention is water containing cement, and the cement is maintained in an unhydrated active state by adding a setting retarder. Aggregate is separated from the sludge water, and a device such as a drum of an agitator wheel to which cement adheres is washed. By repeating this operation, the sludge water that has reached a high concentration is reused as mixing water for fresh concrete from the next day. In separating the aggregate, the coarse aggregate is first separated, and then the fine aggregate is separated from the sludge water containing the fine aggregate. In the present invention, fresh water is injected into a device for removing fine aggregate from sludge water containing the fine aggregate.

Although there is no particular limitation on the fine aggregate removing device, FIG.
As shown in FIG. 2, a spiral rod 2 is provided obliquely from the deepest part of the sedimentation tank 1 to the outside of the sedimentation tank 1, and a rotating shaft 5 of the spiral rod 2 is rotated via a rotation transmission mechanism 4 by a motor 3 provided outside the sedimentation layer 1. Is to rotate. Fine aggregate that has settled at the deepest part of the settling tank rises by the rotation of the spiral rod 2 and falls from the upper part. Reference numeral 6 denotes sludge water, and reference numeral 7 denotes a cyclone for supplying sludge water containing fine aggregate.
Although a cyclone is shown in FIG. 1, a flow rate adjusting tank may be provided instead of the cyclone. The inside of the sedimentation layer 1 is gently stirred by the rotation of the helical rod 2, and the sludge water from which fine aggregate has been removed is discharged from the portion indicated by the arrow in FIG.

In the present invention, since the high-concentration sludge water has a high viscosity, sedimentation of fine sand is hindered. Therefore, the solid content concentration of the sludge water is 15% by weight or more, preferably 25% by weight or more. More preferably, when the content is 35% by weight or more, a remarkable effect is exhibited. Fine sand is fine sand that tends to remain without being removed by the fine aggregate removing device. In the present invention, sand having a particle size of 1.2 mm or less was selected and tested.

Examples of the cement dispersant include an oxycarboxylic acid-based setting retarder and a high-performance water reducing agent.
Examples of oxycarboxylic acid-based setting retarders include gluconic acid,
Examples thereof include citric acid and tartaric acid. Examples of the high-performance water reducing agent include a naphthalenesulfonic acid-based water reducing agent and a polycarboxylic acid-based water reducing agent. The amount of the cement dispersant used varies depending on the type of the dispersant, but is generally 0.01 to 1.0%, preferably 0.02 to 0.1%, based on the sludge water. No effect was observed in the case of the lignin sulfonic acid type water reducing agent.

[0011] The method of injecting fresh water into the fine aggregate recovery device is as follows.
There are a method of injecting into the upper surface of the aqueous layer, a method of injecting into the middle of the aqueous layer, and a method of injecting into the lower part of the aqueous layer. The method of injecting water into the upper surface of the water layer is practical because the difference in the specific gravity of water gradually disappears and the effect appears because the inside of the fine aggregate recovery device is in a gentle stirring state by the rotation of the helical rod. When the residence time of the fine aggregate recovery device becomes short, a method of injecting into the lower part of the aqueous layer is preferable.

[0012]

Experimental method A measuring cylinder having a volume of 10 liters or more and a height of about 70 cm with a scale of 10 liters was used. The sludge water prepared by adding water to the specified concentration with the used materials and mixing ratios shown in Table 1 was constantly stirred with a stirrer, and an experiment was performed within 3 hours after the preparation of the sludge water. 10 liters of sludge water was poured into the measuring cylinder, and after confirming that there was no sediment, the resulting cylinder was allowed to stand. The amount of sedimentation after each hour from the standing was read from the scale of the measuring cylinder.

[0013]

[Table 1]

Example 1 and Comparative Example 1 Sodium gluconate as a drug A was added to sludge water having a concentration of 50% so as to be 0.03% of the sludge water. The amount of sedimentation of the sand was indicated in (ml) as a graduated cylinder reading and shown in Table 2. As Comparative Example 1, the amount of sludge settling was also shown in Table 2 in the same manner as in Example 1 except that sodium gluconate was not added. According to Table 2, the addition of water containing an oxycarboxylic acid-based retarder such as sodium gluconate accelerates the sedimentation of sand, especially after 2 to 4 minutes, which is the residence time of a practical fine aggregate separator. The sedimentation rate was high and it was confirmed that it was effective.

[0015]

[Table 2]

Examples 2 to 3 and Comparative Examples 2 to 3 Sludge water was prepared in the same manner as in Example 1 except that the sludge concentration was 40%, and as it was (Comparative Example 2), a lignin sulfonate-based water reducing agent was used. WRDA (Comparative Example 3) manufactured by Grace Chemicals, Super 20 (Example 2) manufactured by Grace Chemicals as a naphthalene sulfonate-based high-performance water reducing agent, and Super 200 (Super 200) as a polycarboxylic acid-based high-performance water reducing agent. The elapsed time after the addition of Example 3) was measured, and the reading of the measuring cylinder was measured in (ml). As is evident from Table 3, the naphthalene-based water reducer and the polycarboxylic acid-based water reducer, which are high-performance water reducers, exhibited remarkable effects, but the lignin-based water reducer had no effect even when the added amount was increased. .

[0017]

[Table 3]

Examples 4-5 and Comparative Examples 4-5 Examples 4 and 5 were obtained by pouring fresh water into sludge water having the concentration shown in Table 4 and pouring it into the sludge water having the concentration shown in Table 4 for dilution. In the case of water injection, the specific gravity of the sludge water was measured with a pycnometer, and the amount to be 10 liters after water injection was calculated and poured into the graduated cylinder in advance. The calculation formula is 40
% → 35%, specific gravity of 40% sludge water 1.27,
Assuming that the injection amount of the 40% sludge water is X ml and the injection amount is Y ml, 1.27 × 0.4 = 0.35 × 10000. Therefore, X = 6890 ml, where X + Y
= 10000, so that Y = 3110 ml.

In the measuring cylinder used in the first embodiment,
Extend pipes that can be filled with water at 5 and 8 liter scales, connect hoses to these pipes and always close them,
Water can be injected when needed. When injecting water into a measuring cylinder, Xml calculated by the above formula was injected, and after confirming that there was no sediment, a specified amount of cement dispersant was added from one of 2, 5, and 8 liter nozzles. Shimizu Y
ml of water for 3 minutes, and after the start of water injection, the amount of sedimentation after each hour was read from the scale of the measuring cylinder in the same manner as in Example 1. In the fifth embodiment, the sedimentation rate seems to be poor at first glance, but this is because water is injected into the lower part. However, after three minutes of water injection, sedimentation was quickly performed, and as a result, fine sand was efficiently separated. Unlike a laboratory cylinder, a real apparatus is more efficient because it has gentle stirring as a whole. As Comparative Examples 4 and 5, the settling velocities of sludge water of the same concentration without addition of water or cement dispersant from the beginning were measured, and are also shown in Table 4.

[0020]

[Table 4]

Examples 6 to 7 and Comparative Example 6 When pouring water, water was poured in the same manner as in Example 4 except that the upper part and the middle part of the sedimentation tank were used, and the sludge water concentration was changed to 35%. 5 is shown. According to Table 5, water injection from the top is not large at the beginning, but the effect appears when the difference in specific gravity of water gradually disappears. Since sludge water is also gently stirred by the spiral rod 2 in an actual facility, it is preferable to inject water from above for practical effects.

[0022]

[Table 5]

Example 8 In a cement plant, the content of one return condenser was discharged and washed, so that the concentration of sludge water in the fine aggregate recovery device reached 48 W / V%. At this time, fresh water was continuously sprinkled on the water surface of the fine aggregate recovery device. The amount of fresh water was about 6% of the amount of sludge flowing into the fine aggregate recovery device. Aggregate was effectively separated, and the solids concentration of the effluent from the fine aggregate recovery device became 30 W / V%. On the other hand, in the same device, when watering is not performed, when the concentration of sludge water in the fine aggregate recovery device is about 50 W / V%, the discharged water from the fine aggregate recovery device is about 36 to 37 W / V%. Met. When watering was performed, fine sand was well separated, so that the amount of the setting retarder used thereafter was significantly reduced.

[0024]

According to the present invention, fine sand is efficiently removed in the settling tank, and as a result, the consumption of the setting retarder can be reduced. Furthermore, the removal of fine sand increases the fluidity of the concrete, and has the effect of increasing the strength.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a fine aggregate recovery device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sedimentation tank 2 Spiral rod 3 Motor 4 Rotation transmission mechanism 5 Rotation shaft 6 Sludge water 7 Cyclone

Claims (6)

[Claims] 1. A method for recovering aggregate from wastewater obtained by washing an apparatus to which concrete or mortar adheres with sludge water containing a setting retarder, delaying hydration of cement, and reusing cement. A method for removing fine sand from sludge water, wherein fresh water is injected into the aggregate recovery device. 2. The method according to claim 1, wherein a cement dispersant is added to the fresh water. 3. The method for removing fine sand from sludge water according to claim 2, wherein the cement dispersant is a high-performance cement water reducing agent or an oxycarboxylic acid-based setting retarder. 4. The method for removing fine sand from sludge water according to claim 1, wherein the concentration of the sludge water is 15% by weight or more. 5. The method for removing fine sand from sludge water according to claim 1, wherein fresh water is injected into an upper portion of the water surface in the fine aggregate recovery device. 6. The method for removing fine sand from sludge water according to claim 1, wherein fresh water is injected into a lower part of a water layer in the aggregate collecting device.