Carbon-silicon skeleton regulation and multi-mechanism complex flocculation synergistic mud dewatering method

Abstract

The present application is suitable for the field of slurry dewatering, and provides a slurry dewatering method with carbon-silicon skeleton regulation and multi-mechanism compound flocculation synergy, which comprises the following steps: (1) carbon-silicon composite skeleton material premixing modification: constructing multi-layer drainage channels through wood sawdust-rice husk carbon-fly ash composite skeleton; (2) PAC-APAM compound gradient flocculation regulation: combining the electric neutralization of polyaluminum chloride (PAC) and the adsorption-bridging effect of anionic polyacrylamide (APAM); (3) magnetized biochar enhanced dewatering synergy: assisting the physical interception effect of the magnetically modified biochar to realize more than 50% improvement of the slurry flocculation structure stability; (4) dynamic filter pressing parameter optimization: after gradient dewatering control, the solid content of the slurry cake reaches 55%-62%, the dewatering efficiency is increased by 45%-60% compared with the traditional process, and the COD reduction rate of the filter pressing filtrate reaches 80%. The present application is suitable for high clay shield slurry, and has the dual advantages of environmental protection and economy.

Description

Technical Field

[0001] This invention relates to the field of mud dewatering, and more particularly to a mud dewatering method that combines carbon-silicon framework regulation with multi-mechanism compound flocculation synergy. Background Technology

[0002] Currently, tunnel boring machines (TBMs) have become one of the main methods for subway construction. However, the excavated soil produced by TBMs exists in the form of slurry, and its disposal has become a major problem restricting TBM construction. Improper treatment of the excavated soil, especially insufficient dewatering, can significantly affect its resource utilization and even lead to dangers. The construction of the Changchun Metro project faces the same problem. Taking the Changchun Airport Line as an example, all tunnel sections are constructed using the TBM method, generating a large amount of excavated soil during construction. In addition, the lake above the tunnel sections further contributes to the high moisture content of the excavated soil, which greatly affects its subsequent transportation, storage, and secondary utilization. Therefore, research on the dewatering treatment of TBM slurry is urgently needed. Summary of the Invention

[0003] This invention provides a mud dewatering method that combines carbon-silicon framework regulation with multi-mechanism compound flocculation synergy to solve the technical problems mentioned in the background art.

[0004] A method for sludge dewatering that combines carbon-silicon framework regulation with multi-mechanism compound flocculation synergy, the method comprising the following steps:

[0005] S1. The sawdust is crushed, washed and dried; the rice husks are calcined, cooled and sieved into homogeneous particles to obtain calcined rice husk char; the sawdust, calcined rice husk char and fly ash are mixed in a mass ratio of 1:1:1, and a 5% (w / w) silane coupling agent solution is added for impregnation for ≥15 minutes, followed by drying and curing at 80℃ to form a hydrophobic reinforced composite skeleton material.

[0006] S2. Prepare a 5% mass concentration solution of polyaluminum chloride (PAC, Al2O3 content ≥28%) and add it at 0.2% to 0.4% of the dry weight of the mud; prepare a 0.1% concentration solution of anionic polyacrylamide (APAM, molecular weight ≥12 million) and add it at 0.15% to 0.25% of the dry weight of the mud.

[0007] S3. Mix rice husk biochar with Fe3O4 nanoparticles (mass ratio 10:1) and pyrolyze at 500℃ for 1 hour under nitrogen protection to obtain magnetized biochar (specific surface area ≥120m²). 2 / g), add magnetized biochar at 3% to 5% of the dry weight of the mud, stir at a medium speed of 110-130 r / min for 10 minutes, and use the magnetic field effect to physically retain particles with a diameter <10μm, while improving the shear stability of the flocs.

[0008] S4. Add the composite skeleton material obtained in step S1 at 20% of the dry weight of the mud, and stir at 110-130 r / min for 10 minutes to form a dual-effect drainage system of "pipeline-interlayer".

[0009] S5. Implement gradient pressurization control to increase the solid content of the mud cake to 55%–62%;

[0010] S6. The filtrate from the pressure filter flows through the magnetized biochar (Fe3O4 supported) adsorption tower (residence time ≥10 minutes), and the COD decreases from the initial 800-1200 mg / L to ≤200 mg / L, with a reduction rate ≥80%.

[0011] Preferably, in step S1, the sawdust is crushed to a target particle size of 0.52 mm, washed with deionized water to remove surface impurities, and then dried, resulting in calcined rice husk charcoal with a specific surface area ≥ 200 m². 2 / g.

[0012] Preferably, the calcination conditions in step S1 are calcination at 300°C for 2 hours, silane coupling agent concentration of 5% (w / w), and impregnation time ≥15 minutes.

[0013] Preferably, in step S1, fly ash with a particle size ≤12μm is selected, and its CaO content ≥52.3% and MgO ≥23.4% are selected.

[0014] Preferably, in step S2, the order of adding PAC solution and APAM solution is as follows: first, PAC solution is quantitatively injected using a peristaltic pump, while stirring at high speed of 200 r / min for 1 minute to break the double electric layer of mud colloid, achieve charge neutralization, and destabilize fine particles. After a 30-second interval, APAM solution is added, and stirring is switched to low speed of 40-60 r / min for 4-6 minutes to achieve the synergistic effect of "charge neutralization-adsorption bridging".

[0015] Preferably, in step S5, gradient pressure control is performed. In the initial stage, low-pressure dewatering at 0.5 MPa is carried out for 5 minutes to quickly discharge free water and form an initial filter cake. In the intermediate stage, the pressure is increased to medium-pressure dewatering at 1.5 MPa for 10 minutes, and the filtration rate is adjusted to 0.8–1.2 m using an online viscosity sensor. 3 / h, to avoid filter cake pore closure, during the final pressure stage, 3.0MPa high pressure is maintained for 15 minutes, combined with temperature control (40~60℃), to destroy the bound water structure and increase the solid content of the sludge cake to 55%~62%.

[0016] The beneficial effects achieved by this invention are as follows:

[0017] (1) The method of the present invention can significantly improve the dewatering efficiency. Through the synergistic effect of PAC (charge neutralization) and APAM (adsorption-bridging) compound flocculation, the flocculation and settling time is shortened and the moisture content of the bottom sediment is reduced to ≤55%. The wood chip-rice husk charcoal-fly ash composite skeleton constructs a dual-effect drainage system of "pipeline-interlayer channel", and the moisture content of the filter cake is reduced by 45% to 60% compared with the traditional process.

[0018] (2) The method of the present invention can ensure stability through multiple mechanisms. Magnetized biochar enhances physical retention, and combined with the compressive strength of the composite skeleton (porous structure retention rate ≥80%), the stability of the floc structure is improved by more than 50%. Dynamic pressure gradient pressurization (0.5~3.0MPa) avoids filter cake pore blockage and achieves uniform dewatering.

[0019] (3) The method of the present invention can reduce pollutants in the filtrate. The compound flocculant works synergistically with magnetized biochar to efficiently intercept fine particles, and the COD reduction rate of the filtrate reaches more than 80%, which meets the environmental protection emission requirements.

[0020] (4) The method of the present invention can reuse solid waste. The compressive strength of the filter cake after pressing is ≥500kPa. It can be directly used as roadbed filler or sintered building material to realize the resource utilization of shield tunneling mud. The low-cost composite application of biomass materials such as wood chips and rice husk charcoal with fly ash (industrial waste) reduces the treatment cost by 30% to 40%.

[0021] (5) The method of the present invention is more economical and adaptable. The compound flocculant (PAC-APAM) saves 20% to 30% of the dosage compared with the single flocculant. It also adapts to different water content mud (100% to 400%) through "gradient addition", reducing the cost of chemical consumption. When the amount of skeleton material added is 20% of the dry weight, the dewatering efficiency and cost are optimally balanced. It is also suitable for shield tunneling mud with high clay content, especially for the problem of high water content (≥65%) in the center of the filter cake. Deep dewatering is achieved through multi-level drainage channels. It supports dynamic adjustment of filter press parameters (pressure, time) to adapt to complex working conditions.

[0022] (6) The core technology of the method of this invention is more innovative. The hydrophobic treatment of wood chips-rice husk charcoal (300℃ + silane coupling agent) increases the compressive strength of the skeleton material by 20%. Fly ash assists in the construction of a three-dimensional drainage network to overcome the defect of wood chips absorbing water and rebounding. Staged pressurization and temperature control (25~60℃) synergistically optimize the dehydration rate and the density of the mud cake. Attached Figure Description

[0023] Figure 1 The image shows a scanning electron microscope (SEM) image of a filter cake formed by pressing fly ash with a dry weight content of 20% after compound flocculation conditioning.

[0024] Figure 2The image shows a scanning electron microscope (SEM) image of a filter cake formed by pressing rice husk ash with a dry weight content of 20% after compound flocculation conditioning.

[0025] Figure 3 Scanning electron microscope image of filter cake formed by pressing sawdust with 20% dry weight content after compound flocculation conditioning.

[0026] Figure 4 The moisture content of the dewatered cake under different amounts of composite skeleton material added in Example 1 and Comparative Examples 1-4 is shown.

[0027] Figure 5 The moisture content of the filter cake in Example 1 is measured under different filtration pressures during the initial, intermediate, and final stages of the composite skeleton.

[0028] Figure 6 This is a diagram showing the influence of compound flocculation on sediment height.

[0029] Figure 7 The graph shows the effect of compound flocculants on the turbidity of the supernatant.

[0030] Figure 8 The flowchart of a mud dewatering method based on carbon silicon framework regulation and multi-mechanism compound flocculation synergy provided by the present invention is shown. Detailed Implementation

[0031] 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 with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to represent selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0032] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0033] Example 1, please refer to Figure 8 This invention provides a method for dewatering mud based on carbon-silicon framework regulation and multi-mechanism compound flocculation synergy, applied to shield tunneling mud (silty clay) of Changchun Metro Airport Line, specifically including the following steps:

[0034] (1) The sawdust was crushed to the target particle size of 0.52 mm, and after washing with deionized water to remove surface impurities, it was dried. The rice husk char was placed in a muffle furnace and calcined at 300°C for 2 hours with a heating rate of 5°C / min. After cooling, it was sieved into homogeneous particles to obtain calcined rice husk char. 1250 mesh (particle size ≤12 μm) fly ash was selected with CaO content ≥52.3% and MgO ≥23.4%. The sawdust, calcined rice husk char and fly ash were mixed in a mass ratio of 1:1:1. A 5% (w / w) silane coupling agent solution was added and impregnated for 15 minutes. Then it was dried and cured at 80°C to form a hydrophobic reinforced composite skeleton material.

[0035] (2) Prepare a 5% mass concentration solution of polyaluminum chloride (PAC, Al2O3 content ≥28%) and add it at 0.35% of the dry weight of the mud, i.e., 14 ml; prepare a 0.1% concentration solution of anionic polyacrylamide (APAM, molecular weight ≥12 million) and add it at 0.15% of the dry weight of the mud, i.e., 0.6 ml. Inject the PAC solution quantitatively with a peristaltic pump, and stir at high speed of 200 r / min for 1 minute to break the colloidal double layer of the mud, achieve charge neutralization, and destabilize the fine particles. After a 30-second interval, add the APAM solution and switch to low speed stirring at 50 r / min for 5 minutes to destabilize the particles through the adsorption of long-chain molecules, forming dense flocs with a diameter ≥2 mm.

[0036] (3) Rice husk biochar (purchased from Henan Puze Environmental Protection Co., Ltd., produced in Henan Province, with a mesh size of 4 mesh) was mixed with Fe3O4 nanoparticles (mass ratio 10:1) and pyrolyzed at 500℃ for 1 hour under nitrogen protection to obtain magnetized biochar (specific surface area ≥120m²). 2 / g), add magnetized biochar at 4% of the dry weight of the mud, stir at 120r / min for 10 minutes, and use the magnetic field effect to physically retain fine particles (<10μm) and improve the shear stability of the flocs.

[0037] (4) Add the composite skeleton material obtained in step 1 at 20% of the dry weight of the mud (excessive addition will increase transportation costs, while insufficient addition will affect the channel construction), stir at 120 r / min for 10 minutes to make the skeleton evenly dispersed, wood chips to construct vertical pipe network channels (pore diameter 0.5-1 mm), rice husk charcoal to enhance interlayer lateral permeability (permeability coefficient increased by 3 times), and fly ash to fill micropores to form a dense support layer, thus forming a "pipe network-interlayer" dual-effect drainage system;

[0038] (5) Gradient pressurization control is implemented. In the initial stage, low-pressure dewatering at 0.5 MPa is used for 5 minutes to quickly discharge free water and form an initial filter cake. In the intermediate stage, the pressure is increased to medium-pressure dewatering at 1.5 MPa for 10 minutes. The filter press rate is adjusted to 1.0 m using an online viscosity sensor (dynamically monitoring mud rheology). 3 / h, to avoid filter cake pore closure, during the final pressure stage, 3.0MPa high pressure is maintained for 15 minutes, combined with temperature control (50℃), to destroy the bound water structure and increase the solid content of the sludge cake to 60%.

[0039] (6) When the filter press filtrate flows through the magnetized biochar adsorption tower (residence time ≥ 10 minutes), the COD drops from the initial 800-1200 mg / L to ≤ 200 mg / L, with a reduction rate ≥ 80%.

[0040] Comparative Example 1 differs from Example 1 only in that, in step 4, the composite skeleton material is added at 0% of the dry weight of the slurry, while the other steps and conditions remain the same.

[0041] Comparative Example 2 differs from Example 1 only in that, in step 4, the composite skeleton material is added at 10% of the dry weight of the slurry, while the other steps and conditions remain the same.

[0042] Comparative Example 3 differs from Example 1 only in that, in step 4, the composite skeleton material is added at 30% of the dry weight of the slurry, while the other steps and conditions remain the same.

[0043] Comparative Example 4 differs from Example 1 only in that, in step 4, the composite skeleton material is added at 40% of the dry weight of the slurry, while the other steps and conditions remain the same.

[0044] Comparative Example 5 uses fly ash as a raw material to prepare a skeleton material instead of the composite skeleton material in Example 1. The only difference from Example 1 is that only 20% fly ash is added as the skeleton material, and scanning electron microscopy experiments are performed.

[0045] Comparative Example 6 uses rice husk ash as a raw material to prepare a skeleton material instead of the composite skeleton material in Example 1. The only difference from Example 1 is that only 20% rice husk ash is added as the skeleton material, and scanning electron microscopy experiments are performed.

[0046] Comparative Example 7 uses wood chips as raw material to prepare a skeleton material instead of the composite skeleton material in Example 1. The only difference from Example 1 is that only 20% wood chips are added as the skeleton material, and scanning electron microscopy experiments are performed.

[0047] Figure 1 The image shows a scanning electron microscope (SEM) image of the filter cake formed by pressing fly ash with a dry weight content of 20% after compound flocculation conditioning, which is the SEM image of the filter cake of Comparative Example 5.

[0048] Figure 2 The image shows a scanning electron microscope (SEM) image of the filter cake formed by pressing rice husk ash with a dry weight content of 20% after compound flocculation conditioning, which is the SEM image of the filter cake of Comparative Example 6.

[0049] Figure 3 The image shows a scanning electron microscope (SEM) image of the filter cake formed by pressing sawdust with a dry weight content of 20% after compound flocculation conditioning, which is the SEM image of the filter cake of Comparative Example 7.

[0050] Figure 4 The moisture content of the dewatered cake under different amounts of composite skeleton material added in Example 1 and Comparative Examples 1-4 is shown.

[0051] pass Figure 4 It can be seen that when 20% composite skeleton is added, the moisture content of the filter cake decreases from the initial 60% to 14.15%, and the stability is improved by 52%, which verifies that the drainage channel constructed by the skeleton material effectively solves the problem of high moisture content (≥65%) in the center of the filter cake.

[0052] Figure 5 The moisture content of the filter cake in Example 1 is measured under different filtration pressures during the initial, intermediate, and final stages of the composite skeleton.

[0053] pass Figure 5 It can be seen that when the pressure increases from 0.1 MPa to 0.5 MPa, the moisture content of the filter cake decreases by 13%. When the pressure increases from 0.5 MPa to 0.9 MPa, the moisture content of the filter cake decreases by 3%.

[0054] Figure 6 This is a diagram showing the influence of compound flocculation on sediment height.

[0055] Figure 7 The graph shows the effect of compound flocculants on the turbidity of the supernatant.

[0056] pass Figure 6 , 7 It can be seen that the dewatering performance of the tunnel boring machine (TBM) slurry has been further improved, demonstrating a good flocculation and conditioning effect on reducing bottom mud height, and also showing significant advantages in reducing supernatant. This is because the slurry exists as a highly dispersed mixed suspension under high water content conditions, and the Al produced by PAC hydrolysis... 3+The negative charge of PAC and APAM neutralizes the negative charge of clay particles, thereby lowering the potential of the clay particles and reducing the repulsion between adjacent particles, thus increasing the probability of contact. The long chains of PAC and APAM adhere to the surface of soil particles through a series of processes including dissolution, bonding, and connection. After connecting several soil particles into bridges, the floc weight increases, the settling speed accelerates, and thus achieves rapid settling. PAC hydrolysis produces positively charged hydroxides, which, together with the polar groups in the APAM molecular weight, adsorb clay particles. During rapid settling, it also adsorbs suspended particles, while APAM surrounds the particles. The dosage of PAC is much greater than that of APAM; the large amount of hydroxides produced by its hydrolysis adheres to each other, forming a network structure. Through a sweeping effect, the flocs and bridge-like connectors generated in the first two stages are connected, ultimately causing these large molecules to co-aggregate and settle.

[0057] This invention focuses on the shield tunneling slurry (silty clay) of the Changchun Metro Airport Line. Flocculation and settling experiments were conducted on the slurry to establish the optimal ratio of PAC-APAM compound flocculant and the relationship between relevant control factors. Based on the optimal flocculation dosage, further plate-and-frame filter press model tests will be carried out after conditioning with the optimal flocculation scheme, using its treatment capacity as a characterizing indicator. The invention systematically studies and reveals the influence of changes in the content of the skeleton material and the filter press pressure on the dewatering performance of the slurry after optimal flocculation conditioning. A quantitative relationship between the plate-and-frame filter press treatment capacity of the slurry after optimal flocculation conditioning and the control factors of plate-and-frame filter press will be established. This provides theoretical support for the optimization and control of mechanical dewatering technology in slurry reduction treatment processes and offers technical reference for projects such as river dredging.

[0058] It should be noted that, in this document, the term "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0059] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A method for mud dewatering that combines carbon-silicon framework regulation with synergistic multi-mechanism compound flocculation, characterized in that, The method includes the following steps: S1. Crush, wash and dry the wood chips; calcine and cool the rice husks and sieve them into homogeneous particles to obtain calcined rice husk char; mix the wood chips, calcined rice husk char and fly ash, add silane coupling agent solution and impregnate for ≥15 minutes, then dry and solidify to form a hydrophobic reinforced composite skeleton material. S2. Prepare a 5% (w / w) polyaluminum chloride solution and add it at 0.2%–0.4% of the dry weight of the mud; prepare a 0.1% (w / w) anionic polyacrylamide solution and add it at 0.15%–0.25% of the dry weight of the mud. S3. Mix rice husk biochar with Fe3O4 nanoparticles and pyrolyze at 500℃ for 1 hour under nitrogen protection to obtain magnetized biochar. Add magnetized biochar at 3% to 5% of the dry weight of mud and stir at a medium speed of 110-130 r / min for 10 minutes. The magnetic field effect physically retains particles with a diameter <10μm and improves the shear stability of the flocs. S4. Add the composite skeleton material obtained in step S1 at 20% of the dry weight of the mud, and stir at 110-130 r / min for 10 minutes to form a "pipeline-interlayer" dual-effect drainage system. S5. Implement gradient pressurization control to increase the solid content of the mud cake to 55%–62%; S6. The filtrate from the pressure filter flows through the magnetized biochar adsorption tower, and the COD is reduced from the initial 800-1200 mg / L to ≤200 mg / L, with a reduction rate of ≥80%.

2. The method for mud dewatering based on carbon-silicon framework regulation and multi-mechanism compound flocculation synergy as described in claim 1, characterized in that, In step S1, the sawdust is crushed to the target particle size of 0.52 mm, washed with deionized water to remove surface impurities, and then dried. The specific surface area of ​​the calcined rice husk charcoal is ≥200 m². 2 / g.

3. The method for mud dewatering based on carbon-silicon framework regulation and multi-mechanism compound flocculation synergy as described in claim 1, characterized in that, In step S1, sawdust, calcined rice husk charcoal, and fly ash are mixed in a mass ratio of 1:1:

1.

4. The method for mud dewatering based on carbon-silicon framework regulation and multi-mechanism compound flocculation synergy as described in claim 1, characterized in that, The calcination conditions described in step S1 are: calcination at 300°C for 2 hours, silane coupling agent concentration of 5% (w / w), and impregnation time ≥15 minutes.

5. The method for slurry dewatering based on carbon-silicon framework regulation and multi-mechanism compound flocculation synergy according to claim 1, characterized in that, In step S1, fly ash with a particle size ≤12μm is selected, and its CaO content ≥52.3% and MgO ≥23.4% are selected.

6. The method for mud dewatering based on carbon-silicon framework regulation and multi-mechanism compound flocculation synergy as described in claim 1, characterized in that, In step S2, the order of adding PAC solution and APAM solution is as follows: first, PAC solution is quantitatively injected using a peristaltic pump while stirring, and then APAM solution is added after a 30-second interval. Then, the stirring is switched to a low speed of 40-60 r / min for 4-6 minutes to achieve the synergistic effect of "charge neutralization-adsorption bridging".

7. The method for mud dewatering based on carbon-silicon framework regulation and multi-mechanism compound flocculation synergy according to claim 1, characterized in that, In step S5, gradient pressurization control is implemented. In the initial stage, low-pressure dewatering at 0.5 MPa is used for 5 minutes to quickly discharge free water and form an initial filter cake. In the intermediate stage, the pressure is increased to 1.5 MPa for 10 minutes for dewatering, and the filtration rate is adjusted to 0.8–1.2 m using an online viscosity sensor. 3 / h, to avoid filter cake pore closure, during the final pressure stage, 3.0MPa high pressure is maintained for 15 minutes, combined with temperature control, to destroy the bound water structure and increase the solid content of the filter cake to 55%~62%.

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