A process for recycling waste slurry water of a concrete mixing plant

Abstract

The present application relates to the technical field of concrete, in particular to a recycling process of waste slurry water of a concrete mixing plant, which comprises the following steps: (1) sending the waste slurry water of the concrete mixing plant into a hydrocyclone for treatment to obtain sludge and overflow slurry water; (2) performing pressure filtration treatment on the sludge to obtain filter residue and pressure filtration slurry water; mixing the filter residue and coal gangue powder, placing them in a roasting furnace for roasting, cooling to room temperature with the furnace, ball milling to obtain roasted powder; (3) mixing the overflow slurry water and the pressure filtration slurry water, adjusting the pH value to 8-8.5, adding a dispersant, stirring and dispersing to obtain a slurry treatment liquid; the dispersant is made by mixing the following raw materials in percentage by weight: 95-100% polycarboxylic acid dispersant and 0-5% dispersing aid; (4) using the roasted powder and the slurry treatment liquid to prepare concrete; the present application can realize the full recycling of waste slurry water in a short time, and has good application effect when preparing concrete.

Description

Technical Field

[0001] This invention relates to the field of concrete technology, specifically to a process for recycling waste slurry from concrete mixing plants. Background Technology

[0002] Concrete is an important building material, and concrete mixing plants generate a large amount of waste slurry during the concrete production process. This waste slurry contains fine aggregates such as cement, mineral powder, fly ash, and admixtures, and is highly alkaline.

[0003] Currently, the main methods for treating wastewater from concrete mixing plants are sedimentation and filtration. The former involves passing the waste slurry through a three-stage sedimentation tank, recycling the purified water, and treating the solid waste separately. The latter involves filtration of the wastewater and slurry from the sedimentation tank to obtain purified water and waste residue, then recycling the purified water. Both methods are difficult to fully reuse the waste slurry, and the recycling process is time-consuming. Furthermore, as cement in the waste slurry continues to hydrate, the composition of the solid components changes. The main hydration products, such as CSH colloid, calcium hydroxide, and ettringite, change with the extended storage time of the waste slurry. Therefore, it is necessary to reuse the waste slurry within an appropriate timeframe; otherwise, it will adversely affect the performance of the concrete. Summary of the Invention

[0004] The purpose of this invention is to provide a process for recycling waste slurry from concrete mixing plants, which can achieve complete reuse of waste slurry in a short time and has a good application effect in concrete preparation.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A process for recycling wastewater from a concrete mixing plant includes the following steps:

[0007] (1) The waste slurry from the concrete mixing plant is sent into a hydrocyclone for treatment to obtain sediment and overflow slurry.

[0008] (2) The slurry is subjected to pressure filtration to obtain filter residue and pressure slurry water; the filter residue and coal gangue powder are mixed to obtain a mixture, and then the mixture is placed in a calcining furnace and heated to 800-900℃ for calcination. After calcination, it is cooled to room temperature with the furnace and then ball-milled to obtain calcined powder.

[0009] (3) After mixing the overflow slurry and the filter press slurry, a mixed slurry is obtained; a pH adjuster is added to the mixed slurry to adjust the pH value to 8-8.5, and then a dispersant is added. After stirring and dispersing, a slurry treatment liquid is obtained; the dispersant is made by mixing the following raw materials in the following weight percentages: 95-100% polycarboxylate dispersant and 0-5% dispersing aid.

[0010] (4) The calcined powder and slurry treatment liquid are used to prepare concrete.

[0011] Preferably, in step (1), the waste slurry from the concrete mixing plant is the waste slurry after sand and gravel separation, and the solid content of the waste slurry from the concrete mixing plant is below 50%.

[0012] The pressure at the feed inlet of the hydrocyclone is 0.45-0.8 MPa.

[0013] Preferably, in step (2), the mass ratio of the filter residue to the coal gangue powder is 1:0.2-0.35; and the roasting time is 70-100 min.

[0014] Preferably, in step (3), the polycarboxylic acid dispersant is prepared by the following method:

[0015] 1) Mix 100 parts water, 60-75 parts allyl polyoxyethylene ether, 12-16 parts hydroxyethyl cashew ether, 2-5 parts methacrylate, and 0.5-1 parts polyoxyethylene alkyl ether to obtain mixture A; mix 50 parts water, 15-20 parts methacrylic acid, 8-15 parts maleic anhydride, 2.5-3.5 parts mercaptoethylamine, and 0.1-0.3 parts vitamin C to obtain mixture B; mix 20 parts water, 1-1.5 parts ammonium persulfate, and 0.3-0.6 parts benzoyl peroxide to obtain mixture C.

[0016] 2) Add mixture A to the reactor. Under nitrogen protection, simultaneously add mixture B and mixture C to the reactor for reaction. The reaction temperature is 55-63℃, and the adding time is 3.5-5h. After the adding is complete, raise the temperature to 70-75℃, seal the reactor and continue stirring at a constant temperature for 3-5h. Then lower the temperature to below 50℃ and adjust the pH value to 7-7.5 with sodium hydroxide solution to obtain the polycarboxylic acid dispersant.

[0017] Preferably, in step (1), the dispersant is prepared by mixing the following raw materials in weight percentages: 95-98% polycarboxylic acid dispersant and 2-5% dispersing aid.

[0018] Preferably, the pH adjuster is citric acid; the amount of dispersant added is 0.3-0.5% of the mass of the mixed slurry.

[0019] Preferably, the dispersing agent is benzohydroxyxamic acid.

[0020] Preferably, the concrete is foamed concrete; the foamed concrete comprises the following raw materials in parts by weight: 100 parts cement, 1.2-2 parts silica aerogel, 1-1.6 parts modified glass fiber, 30-40 parts calcined powder, 2-3 parts EVA emulsion, 0.43-0.51 parts foaming agent, 0.04-0.06 parts foam stabilizer, 0.45-0.55 parts water-reducing agent, 35-45 parts slurry treatment liquid, and 20-30 parts water.

[0021] Preferably, the modified glass fiber includes the following steps: adding 100 parts of DMF to a reaction vessel, then adding 10 parts of glass fiber with a length of 0.5-3 mm and 1-3 parts of cobalt chloride in sequence. After sealing the reaction vessel, the temperature is raised to 80-85°C while stirring, and kept at this temperature for 3-4 hours. Then, 1.5-2.5 parts of triethylamine are added, and the temperature is raised to 105-115°C while stirring, and kept at this temperature for 6-8 hours. After cooling to room temperature, the modified glass fiber is obtained by centrifugation and washing.

[0022] Preferably, the cement is 42.5 grade ordinary Portland cement; the silica aerogel has an average particle size of 25-40 μm and a specific surface area of ​​650-820 m². 2 / g; the solid content of the EVA emulsion is 68-75%; the foaming agent is prepared by mixing sodium ethoxylated alkyl sulfate and ammonium dodecyl sulfate in a mass ratio of 1:1-2; the foam stabilizer is prepared by mixing ethanolamine and alkylphenol oxyethylene ether in a mass ratio of 1:3-6; the water-reducing agent is a naphthalene-based high-efficiency water-reducing agent or a polycarboxylic acid high-efficiency water-reducing agent.

[0023] The beneficial effects of this invention are:

[0024] 1. This invention sends waste slurry from a concrete mixing plant into a hydrocyclone for treatment. The centrifugal force field of the hydrocyclone accelerates the sedimentation of solid components in the waste slurry. Compared to a sedimentation tank, this effectively shortens the solid-liquid separation time and allows the solid content in the resulting overflow slurry to be controlled below 6%, with the particle size of solid particles below 0.2 mm. This allows the overflow slurry, after dispersion treatment, to be directly used as mixing water in concrete preparation, effectively maintaining the concrete's workability. Simultaneously, the shorter separation time of the hydrocyclone enables the waste slurry to be reused in a shorter time, with minimal changes in the composition of hydration products, reducing the adverse effects of the waste slurry on concrete performance.

[0025] 2. The modified polycarboxylic acid dispersant prepared in this invention introduces hydroxyethyl cashew ether monomer, which can introduce a sterically hindered benzene ring structure and a long carbon chain. As a result, the modified polycarboxylic acid dispersant has a high steric hindrance effect, which makes the fine particles of the overflow slurry have a strong repulsive force, and makes the particles in the obtained slurry treatment liquid have high dispersibility, are not easy to agglomerate and settle, have high uniformity, and have better effect in the preparation of concrete.

[0026] In treating overflow slurry, this invention selectively adds the dispersing aid benzoyl hydroxamic acid in addition to the addition of a modified polycarboxylic acid dispersant, which can further enhance the dispersion effect and improve the performance of the prepared concrete.

[0027] 3. This invention involves mixing and calcining the filter residue obtained from pressure filtration with coal gangue powder, and then grinding the resulting calcined powder. This calcined powder is then applied to concrete preparation, demonstrating good performance. Furthermore, the filter residue and coal gangue powder exhibit a synergistic effect; the combination of the two, compared to using filter residue calcined powder alone, results in concrete with higher performance.

[0028] 4. The calcined powder and slurry treatment liquid of this invention are highly applicable in the preparation of foamed concrete. With the addition of appropriate modified glass fiber reinforcement, specific foaming agents, silica aerogel, and EVA emulsion, foamed concrete with good mechanical and thermal insulation properties can be prepared.

[0029] 5. The process of this invention for treating waste slurry from concrete mixing plants can achieve complete reuse of the waste slurry in a short time and has a good application effect in concrete preparation. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] The recycling process for waste slurry from concrete mixing plants described in this invention uses waste slurry from concrete mixing plants that has undergone sand and gravel separation, and the solid content of the waste slurry is 41.3%.

[0032] The polycarboxylate dispersant prepared using the method of the present invention is as follows:

[0033] ① Preparation of polycarboxylate dispersant I:

[0034] The preparation method of polycarboxylate dispersant I includes the following steps:

[0035] 1) Mix 100 parts water, 70 parts allyl polyoxyethylene ether, 16 parts hydroxyethyl cashew ether, 3 parts methacrylate, and 1 part polyoxyethylene alkyl ether to obtain mixture A; mix 50 parts water, 18 parts methacrylic acid, 15 parts maleic anhydride, 3.5 parts mercaptoethylamine, and 0.2 parts vitamin C to obtain mixture B; mix 20 parts water, 1.5 parts ammonium persulfate, and 0.5 parts benzoyl peroxide to obtain mixture C.

[0036] 2) Add mixture A to the reactor. Under nitrogen protection, simultaneously add mixture B and mixture C to the reactor for reaction. The reaction temperature is 60℃ and the adding time is 4h. After the adding is complete, raise the temperature to 75℃, seal the reactor and continue stirring at a constant temperature for 5h. Then lower the temperature to below 50℃ and adjust the pH value to 7-7.5 with sodium hydroxide solution to obtain polycarboxylic acid dispersant I.

[0037] ② Preparation of polycarboxylate dispersant II:

[0038] The preparation method of polycarboxylate dispersant II includes the following steps:

[0039] 1) Mix 100 parts water, 60 parts allyl polyoxyethylene ether, 13 parts hydroxyethyl cashew ether, 2 parts methacrylate, and 0.8 parts polyoxyethylene alkyl ether to obtain mixture A; mix 50 parts water, 15 parts methacrylic acid, 12 parts maleic anhydride, 2.5 parts mercaptoethylamine, and 0.1 parts vitamin C to obtain mixture B; mix 20 parts water, 1 part ammonium persulfate, and 0.6 parts benzoyl peroxide to obtain mixture C.

[0040] 2) Add mixture A to the reactor. Under nitrogen protection, simultaneously add mixture B and mixture C to the reactor for reaction. The reaction temperature is 55℃ and the adding time is 5h. After the adding is complete, raise the temperature to 70℃, seal the reactor and continue stirring at a constant temperature for 3h. Then lower the temperature to below 50℃ and adjust the pH value to 7-7.5 with sodium hydroxide solution to obtain polycarboxylic acid dispersant II.

[0041] ③ Preparation of polycarboxylic acid dispersant III:

[0042] The preparation method of polycarboxylate dispersant III includes the following steps:

[0043] 1) Mix 100 parts water, 75 parts allyl polyoxyethylene ether, 12 parts hydroxyethyl cashew ether, 5 parts methacrylate, and 0.5 parts polyoxyethylene alkyl ether to obtain mixture A; mix 50 parts water, 20 parts methacrylic acid, 8 parts maleic anhydride, 3 parts mercaptoethylamine, and 0.3 parts vitamin C to obtain mixture B; mix 20 parts water, 1.2 parts ammonium persulfate, and 0.3-0.6 parts benzoyl peroxide to obtain mixture C.

[0044] 2) Add mixture A to the reactor. Under nitrogen protection, simultaneously add mixture B and mixture C to the reactor for reaction. The reaction temperature is 63℃ and the adding time is 3.5h. After the adding is complete, raise the temperature to 75℃, seal the reactor and continue stirring at a constant temperature for 4h. Then lower the temperature to below 50℃ and adjust the pH value to 7-7.5 with sodium hydroxide solution to obtain polycarboxylic acid dispersant III.

[0045] Example 1:

[0046] A process for recycling wastewater from a concrete mixing plant includes the following steps:

[0047] (1) The waste slurry from the concrete mixing plant is sent to a hydrocyclone for treatment. The pressure at the inlet of the hydrocyclone is 0.6 MPa, and sediment and overflow slurry are obtained.

[0048] (2) The sediment is subjected to pressure filtration to obtain filter residue and pressure slurry water; the filter residue and coal gangue powder are mixed at a mass ratio of 1:03 to obtain a mixture. The mixture is then placed in a roasting furnace and heated to 860℃ for roasting for 100 minutes. After roasting, it is cooled to room temperature with the furnace and then ball-milled to obtain roasted powder.

[0049] (3) After mixing the overflow slurry and the filter press slurry, a mixed slurry is obtained; citric acid is added to the mixed slurry to adjust the pH value to 8-8.5, and then 0.37% of the mass of the mixed slurry dispersant is added. After stirring and dispersing, the slurry treatment liquid is obtained; the dispersant is made by mixing the following raw materials in the following weight percentages: polycarboxylic acid dispersant I 97% and benzoyl hydroxyacid 3%.

[0050] (4) Use calcined powder and slurry treatment liquid to prepare concrete.

[0051] Example 2:

[0052] A process for recycling wastewater from a concrete mixing plant includes the following steps:

[0053] (1) The waste slurry from the concrete mixing plant is sent to a hydrocyclone for treatment. The pressure at the inlet of the hydrocyclone is 0.8 MPa, and sediment and overflow slurry are obtained.

[0054] (2) The slurry is subjected to pressure filtration to obtain filter residue and pressure slurry water; the filter residue and coal gangue powder are mixed at a mass ratio of 1:0.2 to obtain a mixture. The mixture is then placed in a roasting furnace and heated to 830℃ for roasting for 100 minutes. After roasting, it is cooled to room temperature with the furnace and then ball-milled to obtain roasted powder.

[0055] (3) After mixing the overflow slurry and the filter press slurry, a mixed slurry is obtained; citric acid is added to the mixed slurry to adjust the pH value to 8-8.5, and then 0.42% of the mass of the mixed slurry dispersant is added. After stirring and dispersing, the slurry treatment liquid is obtained; the dispersant is made by mixing the following raw materials in the following weight percentages: 95% polycarboxylic acid dispersant II and 5% benzoyl hydroxamic acid.

[0056] (4) Use calcined powder and slurry treatment liquid to prepare concrete.

[0057] Example 3:

[0058] A process for recycling wastewater from a concrete mixing plant includes the following steps:

[0059] (1) The waste slurry from the concrete mixing plant is sent to a hydrocyclone for treatment. The pressure at the inlet of the hydrocyclone is 0.7 MPa, and sediment and overflow slurry are obtained.

[0060] (2) The slurry is subjected to pressure filtration to obtain filter residue and pressure slurry water; the filter residue and coal gangue powder are mixed at a mass ratio of 1:0.35 to obtain a mixture. The mixture is then placed in a roasting furnace and heated to 900℃ for roasting for 70 minutes. After roasting, it is cooled to room temperature with the furnace and then ball-milled to obtain roasted powder.

[0061] (3) After mixing the overflow slurry and the filter press slurry, a mixed slurry is obtained; citric acid is added to the mixed slurry to adjust the pH value to 8-8.5, and then 0.5% of the mass of the mixed slurry dispersant is added. After stirring and dispersing, the slurry treatment liquid is obtained; the dispersant is made by mixing the following raw materials in the following weight percentages: polycarboxylic acid dispersant III 98% and benzoyl hydroxyacid 2%.

[0062] (4) Use calcined powder and slurry treatment liquid to prepare concrete.

[0063] Example 4:

[0064] A process for recycling wastewater from a concrete mixing plant includes the following steps:

[0065] (1) The waste slurry from the concrete mixing plant is sent to a hydrocyclone for treatment. The pressure at the inlet of the hydrocyclone is 0.45 MPa, resulting in sediment and overflow slurry.

[0066] (2) The sediment is subjected to pressure filtration to obtain filter residue and pressure slurry water; the filter residue and coal gangue powder are mixed at a mass ratio of 1:0.25 to obtain a mixture. The mixture is then placed in a calcining furnace and heated to 800℃ for calcination for 100 minutes. After calcination, the mixture is cooled to room temperature with the furnace and then ball-milled to obtain calcined powder.

[0067] (3) After mixing the overflow slurry and the filter press slurry, a mixed slurry is obtained; citric acid is added to the mixed slurry to adjust the pH value to 8-8.5, and then 0.3% of the mass of the mixed slurry dispersant is added. After stirring and dispersing, the slurry treatment liquid is obtained; the dispersant is made by mixing the following raw materials in the following weight percentages: polycarboxylic acid dispersant I 96% and benzoyl hydroxyacid 4%.

[0068] (4) Use calcined powder and slurry treatment liquid to prepare concrete.

[0069] Example 5:

[0070] A process for recycling waste slurry from a concrete mixing plant, which differs from Example 4 in that the dispersant is polycarboxylate dispersant I.

[0071] Example 6:

[0072] The calcined powder and slurry treatment liquid obtained in Example 1 were used to prepare foamed concrete.

[0073] Foamed concrete comprises the following raw materials in parts by weight: 100 parts of 42.5 grade ordinary Portland cement, 1.2 parts of silica aerogel, 1.6 parts of modified glass fiber, 30 parts of calcined powder, 2.6 parts of EVA emulsion, 0.51 parts of foaming agent, 0.05 parts of foam stabilizer, 0.55 parts of naphthalene-based high-efficiency water-reducing agent, 40 parts of slurry treatment liquid, and 26 parts of water.

[0074] The modified glass fiber described above includes the following steps: 100 parts of DMF are added to the reactor, followed by 10 parts of glass fiber with a length of 0.5-3 mm and 3 parts of cobalt chloride. After sealing the reactor, the temperature is raised to 80°C while stirring, and the temperature is maintained for 4 hours. Then, 2.5 parts of triethylamine are added, and the temperature is raised to 105°C while stirring, and the temperature is maintained for 8 hours. After cooling to room temperature, the modified glass fiber is obtained by centrifugation and washing.

[0075] The silica aerogel has an average particle size of 30 μm and a specific surface area of ​​710 m². 2 / g; the solid content of the EVA emulsion is 75%; the foaming agent is prepared by mixing sodium ethoxylated alkyl sulfate and ammonium dodecyl sulfate in a mass ratio of 1:2; the foam stabilizer is prepared by mixing ethanolamine and alkylphenol oxyethylene ether in a mass ratio of 1:5.

[0076] The preparation method of foamed concrete includes the following steps:

[0077] First, dilute the foaming agent with 45 times its weight of water, then add a foam stabilizer and mix to prepare foam; then mix the remaining raw materials evenly to obtain a mixed slurry; then add the prepared foam to the mixed slurry and stir, then pour, demold, and cure to obtain foamed concrete.

[0078] Example 7:

[0079] The calcined powder and slurry treatment liquid obtained in Example 2 were used to prepare foamed concrete.

[0080] Foamed concrete comprises the following raw materials in parts by weight: 100 parts of 42.5 grade ordinary Portland cement, 16 parts of silica aerogel, 1 part of modified glass fiber, 35 parts of calcined powder, 2 parts of EVA emulsion, 0.43 parts of foaming agent, 0.04 parts of foam stabilizer, 0.45 parts of naphthalene-based high-efficiency water-reducing agent, 35 parts of slurry treatment liquid, and 30 parts of water.

[0081] The modified glass fiber described above includes the following steps: 100 parts of DMF are added to a reaction vessel, followed by 10 parts of glass fiber with a length of 0.5-3 mm and 1 part of cobalt chloride. After sealing the reaction vessel, the temperature is raised to 85°C while stirring, and the temperature is maintained for 3 hours. Then, 1.5 parts of triethylamine are added, and the temperature is raised to 115°C while stirring, and the temperature is maintained for 6 hours. After cooling to room temperature, the modified glass fiber is obtained by centrifugation and washing.

[0082] The silica aerogel has an average particle size of 40 μm and a specific surface area of ​​650 m². 2 / g; the solid content of the EVA emulsion is 68%; the foaming agent is prepared by mixing sodium ethoxylated alkyl sulfate and ammonium dodecyl sulfate in a mass ratio of 1:2; the foam stabilizer is prepared by mixing ethanolamine and alkylphenol oxyethylene ether in a mass ratio of 1:3.

[0083] The preparation method of foamed concrete is the same as in Example 6.

[0084] Example 8:

[0085] The calcined powder and slurry treatment liquid obtained in Example 3 were used to prepare foamed concrete.

[0086] Foamed concrete comprises the following raw materials in parts by weight: 100 parts of 42.5 grade ordinary Portland cement, 2 parts of silica aerogel, 1.2 parts of modified glass fiber, 40 parts of calcined powder, 2 parts of EVA emulsion, 0.43 parts of foaming agent, 0.06 parts of foam stabilizer, 0.52 parts of naphthalene-based high-efficiency water-reducing agent, 45 parts of slurry treatment liquid, and 20 parts of water.

[0087] The modified glass fiber described above is the same as the modified glass fiber prepared in Example 6.

[0088] The silica aerogel has an average particle size of 25 μm and a specific surface area of ​​820 m². 2 / g; the solid content of the EVA emulsion is 71%; the foaming agent is prepared by mixing sodium ethoxylated alkyl sulfate and ammonium dodecyl sulfate in a mass ratio of 1:1; the foam stabilizer is prepared by mixing ethanolamine and alkylphenol oxyethylene ether in a mass ratio of 1:6.

[0089] The preparation method of foamed concrete is the same as in Example 6.

[0090] Example 9:

[0091] The calcined powder and slurry treatment liquid obtained in Example 4 were used to prepare foamed concrete.

[0092] Foamed concrete comprises the following raw materials in parts by weight: 100 parts of 42.5 grade ordinary Portland cement, 1.5 parts of silica aerogel, 1.2 parts of modified glass fiber, 37 parts of calcined powder, 2 parts of EVA emulsion, 0.45 parts of foaming agent, 0.04 parts of foam stabilizer, 0.5 parts of naphthalene-based high-efficiency water-reducing agent, 42 parts of slurry treatment liquid, and 23 parts of water.

[0093] The modified glass fiber described above is the same as the modified glass fiber in Example 7; the silica aerogel has an average particle size of 30 μm and a specific surface area of ​​710 m². 2 / g; the solid content of the EVA emulsion is 71%; the foaming agent is prepared by mixing sodium ethoxylated alkyl sulfate and ammonium dodecyl sulfate in a mass ratio of 1:1; the foam stabilizer is prepared by mixing ethanolamine and alkylphenol oxyethylene ether in a mass ratio of 1:6.

[0094] The preparation method of foamed concrete is the same as in Example 6.

[0095] Example 10:

[0096] The calcined powder and slurry treatment liquid obtained in Example 5 were used to prepare foamed concrete.

[0097] Foamed concrete comprises the following raw materials in parts by weight: 100 parts of 42.5 grade ordinary Portland cement, 1.5 parts of silica aerogel, 1.2 parts of modified glass fiber, 37 parts of calcined powder, 2 parts of EVA emulsion, 0.45 parts of foaming agent, 0.04 parts of foam stabilizer, 0.5 parts of naphthalene-based high-efficiency water-reducing agent, 42 parts of slurry treatment liquid, and 23 parts of water.

[0098] The preparation methods of the modified glass fiber, silica aerogel, EVA emulsion, foaming agent, foam stabilizer, and foamed concrete are all the same as in Example 9.

[0099] Comparative Example 1:

[0100] The calcined powder and mixed slurry (replacing the slurry treatment liquid) obtained in Example 4 were used to prepare foamed concrete.

[0101] Foamed concrete comprises the following raw materials in parts by weight: 100 parts of 42.5 grade ordinary Portland cement, 1.5 parts of silica aerogel, 1.2 parts of modified glass fiber, 37 parts of calcined powder, 2 parts of EVA emulsion, 0.45 parts of foaming agent, 0.04 parts of foam stabilizer, 0.5 parts of naphthalene-based high-efficiency water-reducing agent, 42 parts of mixed slurry, and 23 parts of water.

[0102] The preparation methods of the modified glass fiber, silica aerogel, EVA emulsion, foaming agent, foam stabilizer, and foamed concrete are all the same as in Example 9.

[0103] Comparative Example 2:

[0104] First, a carboxylic acid dispersant IV is prepared. The preparation method of this polycarboxylic acid dispersant IV differs from that of polycarboxylic acid dispersant I in that 16 parts of hydroxyethyl cashew ether are replaced with 16 parts of allyl polyoxyethylene ether in the preparation method of polycarboxylic acid dispersant I.

[0105] Subsequently, in the recycling process of waste slurry from concrete mixing plants, the difference from Example 4 is that the polycarboxylate dispersant I used is replaced with the aforementioned carboxylate dispersant IV.

[0106] Then, the calcined powder and slurry treatment liquid obtained from the above-mentioned process of recycling the waste slurry from the concrete mixing plant are used to prepare foamed concrete.

[0107] Foamed concrete comprises the following raw materials in parts by weight: 100 parts of 42.5 grade ordinary Portland cement, 1.5 parts of silica aerogel, 1.2 parts of modified glass fiber, 37 parts of calcined powder, 2 parts of EVA emulsion, 0.45 parts of foaming agent, 0.04 parts of foam stabilizer, 0.5 parts of naphthalene-based high-efficiency water-reducing agent, 42 parts of slurry treatment liquid, and 23 parts of water.

[0108] The preparation methods of the modified glass fiber, silica aerogel, EVA emulsion, foaming agent, foam stabilizer, and foamed concrete are all the same as in Example 9.

[0109] Comparative Example 3:

[0110] In the recycling process of waste slurry from concrete mixing plants, unlike in Example 4, the filter residue is placed directly in a calcining furnace, heated to 830°C for calcination, and calcined for 100 minutes. After calcination, it is cooled to room temperature with the furnace and then ball-milled to obtain calcined powder.

[0111] Then, the calcined powder and slurry treatment liquid obtained from the above-mentioned process of recycling the waste slurry from the concrete mixing plant are used to prepare foamed concrete.

[0112] Foamed concrete comprises the following raw materials in parts by weight: 100 parts of 42.5 grade ordinary Portland cement, 1.5 parts of silica aerogel, 1.2 parts of modified glass fiber, 37 parts of calcined powder, 2 parts of EVA emulsion, 0.45 parts of foaming agent, 0.04 parts of foam stabilizer, 0.5 parts of naphthalene-based high-efficiency water-reducing agent, 42 parts of slurry treatment liquid, and 23 parts of water.

[0113] The preparation methods of the modified glass fiber, silica aerogel, EVA emulsion, foaming agent, foam stabilizer, and foamed concrete are all the same as in Example 9.

[0114] Performance testing:

[0115] The dry density, 28-day compressive strength, and thermal conductivity of the foamed concrete in Examples 6-10 and Comparative Examples 1-3 were tested. The dry density and compressive strength tests were conducted according to JG / T 266-2011 "Foamed Concrete". The test specimens were all 100mm × 100mm × 100mm in size. Curing for compressive strength and dry density tests was performed in a standard curing room for 28 days, followed by drying to constant weight. The thermal conductivity test was conducted according to GB / T 10294-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Insulation Materials - Protective Hot Plate Method". The test specimens were 300mm × 300mm × 30mm in size, cured in a standard curing room for 28 days, and then dried to constant weight. The test results for 28-day compressive strength, dry density, and thermal conductivity are shown in Table 1.

[0116] Table 1. Concrete performance test results

[0117] Example 6 467 2.55 0.131 Example 7 449 2.43 0.125 Example 8 434 2.35 0.111 Example 9 441 2.39 0.118 Example 10 445 2.28 0.116 Comparative Example 1 438 1.91 0.145 Comparative Example 2 443 2.03 0.133 Comparative Example 3 451 2.08 0.122

[0118] As shown in Table 1, the calcined powder and slurry treatment liquid obtained by using the recycling process of this invention to treat the waste slurry from concrete mixing plants can produce foamed concrete with high strength and excellent thermal conductivity, demonstrating good application results. Specifically, as shown in Examples 9 and 10, the addition of the dispersant benzoyl hydroxamic acid to the dispersant improves the mechanical properties of the foamed concrete prepared with the obtained slurry treatment liquid. However, a comparison between Comparative Example 1 and Example 9 shows that mixing the overflow slurry and filter slurry, adjusting the pH, and using it directly without adding a dispersant significantly reduces the strength and thermal insulation performance of the resulting foamed concrete. A comparison between Comparative Example 2 and Example 9 shows that without the addition of hydroxyethyl cashew ether, the strength and thermal insulation performance of the obtained foamed concrete are also reduced when using the prepared polycarboxylate dispersant. A comparison between Comparative Example 3 and Example 9 shows that calcining the filter residue separately and using the resulting calcined powder to prepare foamed concrete reduces the strength of the foamed concrete.

[0119] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A process for recycling wastewater from a concrete mixing plant, characterized in that, Includes the following steps: (1) The waste slurry from the concrete mixing plant is sent to a hydrocyclone for treatment to obtain sediment and overflow slurry; (2) The slurry is subjected to pressure filtration to obtain filter residue and pressure slurry water; the filter residue and coal gangue powder are mixed to obtain a mixture, and then the mixture is placed in a calcining furnace and heated to 800-900℃ for calcination. After calcination, it is cooled to room temperature with the furnace and then ball-milled to obtain calcined powder. (3) After mixing the overflow slurry and the filter press slurry, a mixed slurry is obtained; a pH adjuster is added to the mixed slurry to adjust the pH value to 8-8.5, and then a dispersant is added. After stirring and dispersing, a slurry treatment liquid is obtained; the dispersant is made by mixing the following raw materials in the following weight percentages: 95-100% polycarboxylate dispersant and 0-5% dispersing aid; The polycarboxylic acid dispersant was prepared by the following method: 1) Mix 100 parts water, 60-75 parts allyl polyoxyethylene ether, 12-16 parts hydroxyethyl cashew ether, 2-5 parts methacrylate, and 0.5-1 parts polyoxyethylene alkyl ether to obtain mixture A; mix 50 parts water, 15-20 parts methacrylic acid, 8-15 parts maleic anhydride, 2.5-3.5 parts mercaptoethylamine, and 0.1-0.3 parts vitamin C to obtain mixture B; mix 20 parts water, 1-1.5 parts ammonium persulfate, and 0.3-0.6 parts benzoyl peroxide to obtain mixture C. 2) Add mixture A to the reaction vessel. Under nitrogen protection, simultaneously add mixture B and mixture C to the reaction vessel for reaction. The reaction temperature is 55-63℃, and the adding time is 3.5-5h. After the adding is completed, raise the temperature to 70-75℃, seal the reaction vessel and continue to stir at a constant temperature for 3-5h. Then lower the temperature to below 50℃ and adjust the pH value to 7-7.5 with sodium hydroxide solution to obtain the polycarboxylic acid dispersant. (4) The calcined powder and slurry treatment liquid are used to prepare concrete.

2. The process for recycling wastewater from concrete mixing plants according to claim 1, characterized in that, In step (1), the waste slurry from the concrete mixing plant is the waste slurry after sand and gravel separation, and the solid content of the waste slurry from the concrete mixing plant is below 50%. The pressure at the feed inlet of the hydrocyclone is 0.45-0.8 MPa.

3. The process for recycling wastewater from concrete mixing plants according to claim 1, characterized in that, In step (2), the mass ratio of the filter residue to the coal gangue powder is 1:0.2-0.35; the roasting time is 70-100 min.

4. The process for recycling wastewater from concrete mixing plants according to claim 1, characterized in that, In step (1), the dispersant is made by mixing the following raw materials in weight percentages: 95-98% polycarboxylic acid dispersant and 2-5% dispersing aid.

5. The process for recycling wastewater from concrete mixing plants according to claim 1, characterized in that, The pH adjuster is citric acid; the amount of dispersant added is 0.3-0.5% of the mass of the mixed slurry.

6. The process for recycling wastewater from concrete mixing plants according to claim 1, characterized in that, The dispersing agent is benzohydroxyoxime acid.

7. The process for recycling wastewater from a concrete mixing plant according to claim 1, characterized in that, The concrete is foamed concrete; the foamed concrete comprises the following raw materials in parts by weight: 100 parts cement, 1.2-2 parts silica aerogel, 1-1.6 parts modified glass fiber, 30-40 parts calcined powder, 2-3 parts EVA emulsion, 0.43-0.51 parts foaming agent, 0.04-0.06 parts foam stabilizer, 0.45-0.55 parts water-reducing agent, 35-45 parts slurry treatment liquid, and 20-30 parts water.

8. The process for recycling wastewater from a concrete mixing plant according to claim 7, characterized in that, The modified glass fiber comprises the following steps: adding 100 parts of DMF to a reaction vessel, followed by 10 parts of glass fiber with a length of 0.5-3 mm and 1-3 parts of cobalt chloride. After sealing the reaction vessel, the temperature is raised to 80-85°C while stirring, and the temperature is maintained for 3-4 hours. Then, 1.5-2.5 parts of triethylamine are added, and the temperature is raised to 105-115°C while stirring, and the temperature is maintained for 6-8 hours. After cooling to room temperature, the modified glass fiber is obtained by centrifugation and washing.

9. The process for recycling wastewater from a concrete mixing plant according to claim 7, characterized in that, The cement is 42.5 grade ordinary Portland cement; the silica aerogel has an average particle size of 25-40 μm and a specific surface area of ​​650-820 m². 2 / g; the solid content of the EVA emulsion is 68-75%; the foaming agent is prepared by mixing sodium ethoxylated alkyl sulfate and ammonium dodecyl sulfate in a mass ratio of 1:1-2; the foam stabilizer is prepared by mixing ethanolamine and alkylphenol oxyethylene ether in a mass ratio of 1:3-6; the water-reducing agent is a naphthalene-based high-efficiency water-reducing agent or a polycarboxylate high-efficiency water-reducing agent.