Carbonization and reuse method of wastewater and waste slurry from concrete premix plant without precipitation

Abstract

This application discloses a method for the non-precipitation carbonization and reuse of wastewater and slurry from ready-mixed concrete plants. The method includes the following steps: A) Wet grinding 1000-1200 parts by weight of alkaline wastewater and 5-10 parts by weight of calcium hydroxide under carbon dioxide gas conditions. The alkaline wastewater is generated during concrete production at the ready-mixed concrete plant; B) When the pH of the grinding environment reaches neutral, the wet grinding is stopped, resulting in enhanced mixing water. This application achieves green utilization of alkaline wastewater from ready-mixed concrete plants and high-value-added utilization of carbon dioxide. After reducing the pH of the alkaline wastewater to neutral, it can be directly used to completely replace tap water in the preparation of ready-mixed concrete. The preparation process is simple and low-cost, and has promising applications in the actual production of ready-mixed concrete.

Description

Technical Field

[0001] The present application relates to the technical field of wastewater resource recovery and reuse, and in particular to a method for carbonizing and reusing wastewater and waste slurry from a concrete premix plant without precipitation. Background Art

[0002] With the rapid development of the construction industry, the use of ready-mixed concrete has increased, while also reducing the impact on environmental pollution at construction sites. In the process of producing concrete at commercial concrete mixing stations, a large amount of alkaline waste slurry and wastewater is generated, mainly from cleaning mixers, mixer trucks, pumping pipelines, commercial concrete mixing station sites and other facilities, resulting in increased treatment costs. However, the process of treating alkaline waste slurry and wastewater at commercial concrete mixing stations is still mainly based on discharge, resulting in the inability to effectively solve the pollution problem.

[0003] Domestic mixing plants mainly treat commercial concrete wastewater by replacing part of the mixing water with admixture water and using it in the production of ready-mixed concrete. Recycling commercial concrete wastewater will help reduce its treatment costs and reduce its impact on the environment. However, there are still problems such as complex processes and high alkalinity of mixing water, which leads to reduced concrete structure strength.

[0004] For example, the wastewater treatment equipment for a concrete mixing station described in patent number CN202220199424.5, the wastewater treatment method described in this invention patent classifies, collects and treats the sand, gravel and slurry water in the wastewater of a concrete mixing station, saving resources while reducing damage to the natural environment. However, the pH of the commercial mixed wastewater is weakly alkaline, the process is complicated, and it is not suitable for application in the actual production of ready-mixed concrete. Summary of the invention

[0005] In view of this, the present application provides a method for carbonizing and reusing wastewater and waste slurry from a concrete ready-mix plant without precipitation, which can completely replace the tap water required for preparing ready-mixed concrete while obtaining better compressive strength.

[0006] Based on the technical difficulties found in the previous article, the inventors used alkaline wastewater collected from commercial mixing stations as raw materials, and used the violent mechanical force of the wet grinding process to ultrafine the active calcium particles such as fly ash, mineral powder, silica fume, cement particles, etc. in the alkaline wastewater, thereby increasing the specific surface area of ​​the calcium particles. In addition, CO2 gas was introduced during the wet grinding process to reduce the Ca dissolved in the calcium-based particles. 2+ and the added calcium hydroxide and CO3 2- The reaction generates nano-scale stable calcite calcium carbonate seeds and reduces the pH of the alkaline wastewater to neutral, thereby obtaining enhanced mixing water for commercial mixing stations.

[0007] Here, the main reaction equations involved are as follows:

[0008]

[0009]

[0010] Based on the above unexpected discovery, the inventors have created the present invention.

[0011] In a first aspect, the present application provides a method for carbonizing and recycling wastewater and waste slurry from a concrete premix plant without precipitation, comprising the following steps:

[0012] A. Wet grinding 1000-1200 parts by mass of alkaline wastewater and 5-10 parts by mass of calcium hydroxide under the condition of introducing carbon dioxide gas, wherein the concentration of carbon dioxide gas is>70%, and the introduction rate of carbon dioxide gas is 10-15 parts by mass / min, wherein the alkaline wastewater is generated by concrete production of a commercial mixing station;

[0013] B. When the pH of the grinding environment is neutral, stop the wet grinding to obtain enhanced mixing water.

[0014] Suitably but not restrictively, the solid particles in the alkaline wastewater are at least one of unhydrated fly ash, silica fume, mineral powder, and cement particles.

[0015] Suitable but not restrictive, the alkaline wastewater has a solid content of 5-7%, a median particle size of 18 μm, and a pH value of 10-11.2.

[0016] Suitable but not limiting, the particle size of the calcium hydroxide is 0.8-2 μm.

[0017] Suitable but not limiting, the wet grinding speed is 400-500r / min, and the wet grinding medium is 0.25-1.2mm zirconia ball.

[0018] Suitable but not limiting, the grinding environment pressure is maintained at 2.5-3.5 MPa, and the grinding environment temperature is maintained at 30-40°C.

[0019] Suitable but not limiting, the median particle size of the slurry formed after the wet milling is 0.6-1 μm.

[0020] Suitably but not limitingly, the pH of the acid-base environment is 7-7.5.

[0021] Suitable but not limiting, the amount of the wet grinding media is 500-800 parts by mass.

[0022] In a second aspect, the present application provides a concrete composition comprising the reinforced mixing water obtained by the above method.

[0023] This application has the following beneficial effects:

[0024] (1) This application utilizes alkaline wastewater collected from commercial concrete mixing stations as raw material, and after treatment, it is used as mixing water to replace tap water. Compared with the method of using chemical reagents and sand and gravel filtration and precipitation to treat alkaline wastewater from commercial concrete mixing stations, it is beneficial to solve the environmental pollution problem caused by commercial concrete mixing station wastewater from the root, and realize the green and high utilization of commercial concrete mixing station wastewater resources.

[0025] (2) The CO2 mixed gas introduced during the wet grinding process reduces the pH value of the alkaline wastewater. After the wastewater is reduced to neutral, it is used to prepare ready-mixed concrete, which solves the problem of reduced concrete structural strength caused by weak alkaline wastewater as mixing water, and realizes the high added value utilization of CO2 gas.

[0026] (3) The alkaline wastewater from commercial mixing stations is combined with a wet grinding process to stimulate the activity of unhydrated calcium-based particles in the alkaline wastewater. In addition, the solubility of CO2 can be greatly increased by increasing the grinding environment pressure and reducing the grinding environment temperature. As the dissolved calcium ions and the added calcium hydroxide react with the dissolved CO2, nano-scale stable calcite calcium carbonate seeds are generated. The calcium carbonate seeds can be used as nucleation sites to promote cement hydration. DETAILED DESCRIPTION

[0027] The technical solution of the present application will be described clearly and completely in conjunction with the embodiments below. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0028] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application may be combined with each other.

[0029] The present application is further described below in conjunction with specific embodiments, but is not intended to be a limitation of the present application.

[0030] The sources of the raw materials involved in this article are as follows:

[0031] The alkaline wastewater comes from China Resources concrete ready-mixing plant, and its pH value is 10-11.2. Other raw materials not mentioned are commercially available.

[0032] The raw materials and their mass fractions involved in Examples 1-6 of the present application are shown in Table 1 below:

[0033] Table 1

[0034]

[0035] Example 1

[0036] Step 1: Take 500 parts by mass of grinding media and put them in a grinding tank, mix 1000 parts by mass of alkaline wastewater A and 5-10 parts of calcium hydroxide and pump them into the grinding tank through a high-pressure pump, and introduce CO2 mixed gas after the grinding starts, the gas introduction rate is 10 parts by mass / min, the wet mill speed is 400r / min, and the grinding environment pressure is maintained stable at 5-6MPa;

[0037] Step 2: By observing the pH meter, when the pH reaches 7-7.5, stop grinding, and pump out the slurry B obtained by wet grinding by high pressure, and pump out the enhanced mixing water with a median particle size of 0.6-1 μm.

[0038] Example 2

[0039] Step 1: Take 800 parts by mass of grinding media and put them in a grinding tank, mix 1000 parts by mass of alkaline wastewater A and 10 parts of calcium hydroxide and pump them into the grinding tank through a high-pressure pump, and introduce CO2 mixed gas after the grinding starts, the gas introduction rate is 11 parts by mass / min, the wet mill speed is 500r / min, and the grinding environment pressure is maintained stable at 5-6MPa;

[0040] Step 2: By observing the pH meter, when the pH reaches 7-7.5, stop grinding, and pump out the slurry B obtained by wet grinding by high pressure, and pump out the enhanced mixing water with a median particle size of 0.6-1 μm.

[0041] Example 3

[0042] Step 1: Take 750 parts by mass of grinding media and put them in a grinding tank, mix 1200 parts by mass of alkaline wastewater A and 7 parts of calcium hydroxide and pump them into the grinding tank through a high-pressure pump, and introduce CO2 mixed gas after the grinding starts, the gas introduction rate is 15 parts by mass / min, the wet mill speed is 450r / min, and the grinding environment pressure is maintained stable at 5-6MPa;

[0043] Step 2: By observing the pH meter, when the pH reaches 7-7.5, stop grinding, and pump out the slurry B obtained by wet grinding by high pressure, and pump out the enhanced mixing water with a median particle size of 0.6-1 μm.

[0044] Example 4

[0045] Step 1: Take 650 parts by mass of grinding media and put them in a grinding tank, mix 1200 parts by mass of alkaline wastewater A and 5 parts of calcium hydroxide and pump them into the grinding tank through a high-pressure pump, and introduce CO2 mixed gas after the grinding starts, the gas introduction rate is 10 parts by mass / min, the wet mill speed is 500r / min, and the grinding environment pressure is maintained stable at 5-6MPa;

[0046] Step 2: By observing the pH meter, when the pH reaches 7-7.5, stop grinding, and pump out the slurry B obtained by wet grinding by high pressure, and pump out the enhanced mixing water with a median particle size of 0.6-1 μm.

[0047] Example 5

[0048] Step 1: Take 700 parts by mass of grinding media and put them in a grinding tank, mix 1100 parts by mass of alkaline wastewater A and 6 parts of calcium hydroxide and pump them into the grinding tank through a high-pressure pump, and introduce CO2 mixed gas after the start of grinding, the gas introduction rate is 14 parts by mass / min, the speed of the wet mill is 480r / min, and the grinding environment pressure is maintained stable at 5-6MPa;

[0049] Step 2: By observing the pH meter, when the pH reaches 7-7.5, stop grinding, and pump out the slurry B obtained by wet grinding by high pressure, and pump out the enhanced mixing water with a median particle size of 0.6-1 μm.

[0050] Example 6

[0051] Step 1: Take 600 parts by mass of grinding media and put them in a grinding tank, mix 1150 parts by mass of alkaline wastewater A and 8 parts of calcium hydroxide and pump them into the grinding tank through a high-pressure pump, and introduce CO2 mixed gas after the grinding starts, the gas introduction rate is 12 parts by mass / min, the wet mill speed is 420r / min, and the grinding environment pressure is maintained stable at 5-6MPa;

[0052] Step 2: By observing the pH meter, when the pH reaches 7-7.5, stop grinding, and pump out the slurry B obtained by wet grinding by high pressure, and pump out the enhanced mixing water with a median particle size of 0.6-1 μm.

[0053] Comparative Example 1

[0054] 100 parts by mass of alkaline wastewater A were taken as mixing water.

[0055] Comparative Example 2

[0056] Take 100 mass points of tap water as mixing water

[0057] The mixing water in Examples 1-6 and Comparative Examples 1-2 was used to prepare C30 concrete compression test blocks in the following proportions:

[0058] Table 2

[0059]

[0060] The test results are shown in Table 3.

[0061] Table 3

[0062]

[0063] From the comparison of the results in Table 3, it can be seen that the mixing water prepared by the method of the present application has improved the compressive strength of the concrete test blocks (150×150×150mm) at 7d and 28d. Compared with Example 2 and Comparative Example 2, the enhanced mixing water prepared in Example 2 has improved the compressive strength of 7d and 28d by more than 15%. Compared with Comparative Example 1, the untreated commercial alkaline wastewater directly used as mixing water weakens the compressive strength of concrete at 7d and 28d, and the enhanced mixing water helps to improve the development of early strength and has the effect of an early strength agent.

[0064] This fully demonstrates that the commercial concrete station reinforced mixing water prepared in this application can completely replace water while improving the compressive strength of concrete to varying degrees.

[0065] The above is only a preferred specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed in the present application should be covered within the protection scope of the present application.

Claims

1. A method for preparing enhanced mixing water by carbonizing and reusing wastewater and waste slurry from a concrete premix plant without precipitation, characterized in that: The following steps are involved: A. Wet grinding 1000-1200 parts by mass of alkaline wastewater and 5-10 parts by mass of calcium hydroxide under the condition of introducing carbon dioxide gas, wherein the concentration of carbon dioxide gas is>50%, and the introduction rate of carbon dioxide gas is 10-15 parts by mass / min, and the alkaline wastewater is generated by concrete production of a commercial mixing station; B. When the pH of the grinding environment is neutral, stop the wet grinding to obtain enhanced mixing water; The solid particles in the alkaline wastewater are at least one of unhydrated fly ash, silica fume, mineral powder and cement particles; The solid content of the alkaline wastewater is 5-7%, the median particle size of the alkaline wastewater is 18 μm, and the pH value of the alkaline wastewater is 10-11.2; The grinding environment temperature was maintained at 30-40°C.

2. The method according to claim 1, characterized in that The particle size of the calcium hydroxide is 0.8-2 μm.

3. The method according to claim 1, characterized in that The wet grinding speed is 400-500 r / min, and the wet grinding medium is 0.25-1.2 mm zirconia balls.

4. The method according to claim 1, characterized in that: The pressure of the grinding environment is maintained at 2.5-3.5 Mpa.

5. The method according to claim 1, characterized in that The median particle size of the slurry formed after the wet grinding is 0.6-1 μm.

6. The method according to claim 1, characterized in that The amount of the wet grinding medium is 500-800 parts by mass.

7. A concrete composition, characterized in that: The invention comprises the fortified mixing water obtained by the method according to claim 1.

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