Red mud-based ceramic membrane for oil-water separation and preparation method thereof

Abstract

The invention relates to a ceramic membrane based on red mud and used for oil-water separation and a preparation method thereof, and belongs to the technical field of inorganic non-metallic materials, the ceramic membrane is prepared by taking red mud (16%-20%), fly ash (16%-20%), Al2O3 (6%-7.5%) and SiO2 (2%-2.5%) as main raw materials, polyethersulfone PESf (6.5%) as a binder, polyvinylpyrrolidone (PVP) (2%) as a dispersant and N-methyl pyrrolidone (NMP) (41.5%-51.5%) as an organic solvent through a hydrothermal method. The material is prepared by a tape casting method. The preparation method is simple and low in cost, the three-layer asymmetric pore structure of the membrane ensures that the interior of the membrane has higher water flux, and the prepared ceramic membrane has the characteristics of hydrophilicity, underwater lipophobicity, stable performance, reusability and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of inorganic non-metallic materials, and specifically to a ceramic membrane for oil-water separation prepared by a tape casting method using red mud as a raw material. Background Art

[0002] Red mud is a solid waste produced after alumina is extracted from bauxite. In 2023, the global alumina production was 141.9 million tons. Extracting 1 ton of alumina will produce at least 1-1.5 tons of red mud waste, which is mainly stored in open-pits and tailings dams. Because it contains a large amount of alkali metal ions, it will cause a series of environmental problems such as soil alkalinization, water pollution, and air pollution when stored. The resource utilization of red mud has become a difficult problem.

[0003] Marine oil spills occur frequently, and the production of oil / water mixtures has increased dramatically due to the development of industries such as food, steel, petroleum, and manufacturing. Large oil spills and direct discharge of oily wastewater not only destroy the balance of the ecosystem and threaten human health, but also cause a waste of precious resources. The effective separation of oil / water mixtures has become an urgent challenge for researchers around the world.

[0004] Tape casting is an important technology for preparing ceramics. Different from the common dry pressing molding, it has the characteristics of continuous operation and high degree of automation. The prepared porous ceramic membrane has a three-layer asymmetric structure of skin layer, finger-like pore layer and sponge layer. The pores are connected up and down, which can effectively improve the porosity.

[0005] Existing ceramic membranes face problems such as expensive raw materials, complex preparation methods, and the use of chemical reagents that cause certain environmental pollution. Therefore, using solid waste red mud as raw material to prepare ceramic membranes that can be used for oil-water separation has important environmental significance and practical application value. Summary of the invention

[0006] In order to solve the above-mentioned deficiencies and shortcomings of the existing problems, the present invention discloses an environmentally friendly, simple and easy preparation method of red mud-based porous ceramic membrane. Red mud is not only low-cost as solid waste, but also has a composition similar to that required for ceramics. A red mud-based porous ceramic membrane with an excellent three-layer asymmetric pore structure can be obtained by a tape casting method.

[0007] The present invention is carried out according to the following steps

[0008] Step 1, ceramic ingredients: red mud, fly ash, SiO2, Al2O3 are mixed into ceramic raw materials according to a certain mass ratio; then all the prepared raw materials are transferred to an alumina ball mill, a certain amount of anhydrous ethanol is added, and the ceramic raw materials are ball milled for a certain number of hours to obtain a uniform ceramic slurry.

[0009] Step 2, vacuum drying and sieving: the ceramic slurry obtained in step 1 is sieved, and the filtered slurry is fully dried. The obtained powder is filtered through a sieve to obtain a red mud-based ceramic raw material.

[0010] Step 3, preparing an organic mixture solution: mixing a binder polyethersulfone (PESf), a dispersant polyvinylpyrrolidone (PVP) and an organic solvent N-methylpyrrolidone (NMP) in a certain mass ratio, placing them in a planetary ball mill and stirring them at a constant speed for several hours to obtain a uniformly mixed and stable polymer mixture.

[0011] Step 4, prepare ceramic slurry: add the ceramic raw material prepared in step 2 to the polymer mixture obtained in step 3 according to a certain mass ratio, continue ball milling for a certain period of time to obtain a uniform and stable mixed ceramic slurry, put it into a vacuum drying oven for vacuum degassing until there are no bubbles, and obtain a uniformly mixed and dense ceramic slurry.

[0012] Step 5, tape casting and phase inversion to prepare a ceramic film body: put the slurry obtained in step 4 into the slurry tank of the tape casting machine, use PET polyester film as a carrier, and evenly apply the slurry on the carrier. Slowly put the tape-cast body into a coagulation bath, take it out and dry it at room temperature for a certain period of time, and cut the dried ceramic film body into discs.

[0013] Step 6, solid phase sintering: the ceramic membrane is calcined in air atmosphere according to the designed sintering system to obtain a porous ceramic membrane. After being cleaned by alternating ultrasonic vibration with deionized water and anhydrous ethanol, it is transferred to a constant temperature blast drying oven, dried for a certain period of time, and then packaged for use.

[0014] The raw material red mud described in step 1 is characterized in that it is a solid waste and its composition is similar to that of ceramics.

[0015] The method for preparing a ceramic membrane based on red mud and used for oil-water separation described in step 1 is characterized in that the ratio of raw materials in step (1) is red mud: fly ash: SiO2: Al2O3 mass fraction ratio 40:40:15:5. The ball milling speed is 300r / min, the time is 5h, and the amount of anhydrous ethanol added is 100ml.

[0016] The method for preparing a ceramic membrane based on red mud for oil-water separation described in step 2 is characterized in that the drying temperature in step (2) is 80° C. and the drying time is 12 hours. The powder is filtered with a 300-mesh sieve to obtain a red mud-based ceramic raw material with a particle size of less than 48 μm.

[0017] . The method for preparing a ceramic membrane based on red mud and used for oil-water separation described in step 3 is characterized in that the mass ratio of polyethersulfone: polyvinylpyrrolidone: N-methylpyrrolidone in step (3) is 6.5:2:41.5-51.5, and the stirring time is 2h

[0018] .The method for preparing a ceramic membrane based on red mud and used for oil-water separation described in step 4 is characterized in that the mass ratio of raw material: polymer solution in step (4) is 40-50:60-50, the ball milling time is 20 hours, and the rotation speed is 400r / min.

[0019] The method for preparing a ceramic membrane based on red mud for oil-water separation in step 5 is characterized in that the scraper height during coating in step (5) is 2 mm and the push rod movement rate is 5 mm / s. The coagulation bath is deionized water, and the mixture is immersed in the coagulation bath for 12 hours and dried at room temperature for 48 hours.

[0020] The method for preparing a ceramic membrane based on red mud for oil-water separation described in step 6 is characterized in that the calcination rate in step (6) is 1°C / min, the temperature is kept at 600°C for 180min, and the temperature is kept at 1000°C for 60min. After drying at 100°C for 24h, the membrane is packaged for standby use.

[0021] Compared with the prior art, this application has the following beneficial effects:

[0022] .Using solid waste red mud and fly ash as raw materials, it reduces pollution while greatly reducing costs. The ceramic membrane has low cost and simple preparation process, does not require modification, is green and environmentally friendly, has good anti-fouling ability and can be reused. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a SEM image of the red mud-based ceramic membrane provided by the present invention, where (a) is a cross section, (b) is a layered pore, and (f) is a sponge layer.

[0024] Figure 2 Schematic diagram of the characterization of the water contact angle in air and the underwater oil contact angle of the red mud-based ceramic membrane provided by the present invention, wherein (a) water contact angle and (b) underwater oil contact angle

[0025] Figure 3 The red mud-based ceramic membrane provided by the present invention has the performance of separating oil-water emulsions. DETAILED DESCRIPTION

[0026] The following is a clear and complete description of the scheme in the implementation of the present invention, and a presentation of some characterization results.

[0027] Example 1

[0028] Red mud, fly ash, Al2O3, and SiO2 are prepared into ceramic raw materials in a mass ratio of 40:40:15:5, 100 ml of ethanol is added as a ball milling medium, and the ceramic slurry is obtained at 300 r / min for 5 hours. Then it is dried, and the obtained powder is filtered with a 300 mesh screen. The obtained ceramic raw material is mixed with a binder polyethersulfone (PESf), a dispersant polyvinylpyrrolidone (PVP), and an organic solvent N-methylpyrrolidone (NMP) in a mass ratio of 40:6.5:2:51.5, and then put into a ball mill and ball milled at a speed of 400 r / min for 20 hours to obtain a uniformly mixed slurry, which is placed in a vacuum drying oven for vacuum degassing until there are no bubbles, and then placed in the slurry tank of the tape casting machine, and the PET polyester film is used as a carrier, and the slurry is evenly and evenly coated on the carrier. During coating, the scraper height is 2 mm and the push rod movement rate is 5 mm / s. The green body after tape casting is slowly placed in a deionized water coagulation bath and soaked. After being taken out, it is dried at room temperature for 48 hours. The dried ceramic membrane green body is cut into discs. The ceramic membrane is calcined in an air atmosphere at a calcination rate of 1°C / min, and a porous ceramic membrane is obtained after being kept at 600°C for 180 minutes and 1000°C for 60 minutes. After being cleaned 3-5 times (10 minutes each time) by alternating ultrasonic vibration with deionized water and anhydrous ethanol, it is transferred to a constant temperature blast drying oven, dried at 100°C for 24 hours, and then packaged for use. 1g vacuum pump oil, 0.005g sodium dodecyl sulfate, and 1L deionized water are stirred at high speed at 12000r / min for one hour to form a stable emulsion. The encapsulated ceramic membrane is installed on a homemade cross-flow circulation device, and the oil-water emulsion enters the membrane assembly from the storage tank and contacts the surface of the ceramic membrane. Under the action of 0.2bar pressure, the feed liquid is selectively screened by the membrane and permeates out, and the permeate is collected in a glass bottle. The pure water permeability of the ceramic membrane was measured using a homemade membrane assembly and filtration device, as shown in Equation 1 Where J(L / m 2 h) is the pure water flux of the membrane, V(L) is the permeate volume, A(m 2 ) is the effective membrane area of ​​the ceramic membrane, t(h) is the test time

[0029] Implementation Example 2

[0030] Red mud, fly ash, Al2O3, and SiO2 are prepared into ceramic raw materials in a mass ratio of 40:40:15:5, 100 ml of ethanol is added as a ball milling medium, and the ceramic slurry is obtained at 300 r / min for 5 hours. Then it is dried, and the obtained powder is filtered with a 300 mesh screen. The obtained ceramic raw material is mixed with a binder polyethersulfone (PESf), a dispersant polyvinylpyrrolidone (PVP), and an organic solvent N-methylpyrrolidone (NMP) in a mass ratio of 45:6.5:2:46.5, and then put into a ball mill and ball milled at a speed of 400 r / min for 20 hours to obtain a uniformly mixed slurry, which is placed in a vacuum drying oven for vacuum degassing until there are no bubbles, and then placed in the slurry tank of the tape casting machine, and the PET polyester film is used as a carrier. The slurry is evenly and evenly coated on the carrier. During coating, the scraper height is 2 mm and the push rod movement rate is 5 mm / s. The green body after tape casting is slowly placed in a deionized water coagulation bath and soaked. After being taken out, it is dried at room temperature for 48 hours. The dried ceramic membrane green body is cut into discs. The ceramic membrane is calcined in an air atmosphere at a calcination rate of 1°C / min, and a porous ceramic membrane is obtained after being kept at 600°C for 180 minutes and 1000°C for 60 minutes. After being cleaned 3-5 times (10 minutes each time) by alternating ultrasonic vibration with deionized water and anhydrous ethanol, it is transferred to a constant temperature blast drying oven, dried at 100°C for 24 hours, and then packaged for use. 1g vacuum pump oil, 0.005g sodium dodecyl sulfate, and 1L deionized water are stirred at high speed at 12000r / min for one hour to form a stable emulsion. The encapsulated ceramic membrane is installed on a homemade cross-flow circulation device, and the oil-water emulsion enters the membrane assembly from the storage tank and contacts the surface of the ceramic membrane. Under the action of 0.2bar pressure, the feed liquid is selectively screened by the membrane and permeates out, and the permeate is collected in a glass bottle. The pure water permeability of the ceramic membrane was measured using a homemade membrane assembly and filtration device, as shown in Equation 1 Where J(L / m 2 h) is the pure water flux of the membrane, V(L) is the permeate volume, A(m 2 ) is the effective membrane area of ​​the ceramic membrane, t(h) is the test time

[0031] Implementation Example 3

[0032] Red mud, fly ash, Al2O3, and SiO2 are prepared into ceramic raw materials in a mass ratio of 40:40:15:5, 100 ml of ethanol is added as a ball milling medium, and the ceramic slurry is obtained at 300 r / min for 5 hours. Then it is dried, and the obtained powder is filtered with a 300 mesh screen. The obtained ceramic raw material is mixed with a binder polyethersulfone (PESf), a dispersant polyvinylpyrrolidone (PVP), and an organic solvent N-methylpyrrolidone (NMP) in a mass ratio of 50:6.5:2:41.5, and then put into a ball mill and ball milled at a speed of 400 r / min for 20 hours to obtain a uniformly mixed slurry, which is placed in a vacuum drying oven for vacuum degassing until there are no bubbles, and then placed in the slurry tank of the tape casting machine, and the PET polyester film is used as a carrier. The slurry is evenly and evenly coated on the carrier. During coating, the scraper height is 2 mm and the push rod movement rate is 5 mm / s. The green body after tape casting is slowly placed in a deionized water coagulation bath and soaked. After being taken out, it is dried at room temperature for 48 hours. The dried ceramic membrane green body is cut into discs. The ceramic membrane is calcined in an air atmosphere at a calcination rate of 1°C / min, and a porous ceramic membrane is obtained after being kept at 600°C for 180 minutes and 1000°C for 60 minutes. After being cleaned 3-5 times (10 minutes each time) by alternating ultrasonic vibration with deionized water and anhydrous ethanol, it is transferred to a constant temperature blast drying oven, dried at 100°C for 24 hours, and then packaged for use. 1g vacuum pump oil, 0.005g sodium dodecyl sulfate, and 1L deionized water are stirred at high speed at 12000r / min for one hour to form a stable emulsion. The encapsulated ceramic membrane is installed on a homemade cross-flow circulation device, and the oil-water emulsion enters the membrane assembly from the storage tank and contacts the surface of the ceramic membrane. Under the action of 0.2bar pressure, the feed liquid is selectively screened by the membrane and permeates out, and the permeate is collected in a glass bottle. The pure water permeability of the ceramic membrane was measured using a homemade membrane assembly and filtration device, as shown in Equation 1 Where J(L / m 2 h) is the pure water flux of the membrane, V(L) is the permeate volume, A(m 2 ) is the effective membrane area of ​​the ceramic membrane, t(h) is the test time

[0033] Implementation Example 4

[0034] Red mud, fly ash, Al2O3, and SiO2 are prepared into ceramic raw materials in a mass ratio of 40:40:15:5, 100 ml of ethanol is added as a ball milling medium, and the ceramic slurry is obtained at 300 r / min for 5 hours. Then it is dried, and the obtained powder is filtered with a 300 mesh screen. The obtained ceramic raw material is mixed with a binder polyethersulfone (PESf), a dispersant polyvinylpyrrolidone (PVP), and an organic solvent N-methylpyrrolidone (NMP) in a mass ratio of 45:6.5:2:46.5, and then put into a ball mill and ball milled at a speed of 400 r / min for 20 hours to obtain a uniformly mixed slurry, which is placed in a vacuum drying oven for vacuum degassing until there are no bubbles, and then placed in the slurry tank of the tape casting machine, and the PET polyester film is used as a carrier. The slurry is evenly and evenly coated on the carrier. During coating, the scraper height is 2 mm and the push rod movement rate is 5 mm / s. The green body after tape casting is slowly placed in a deionized water coagulation bath and soaked. After being taken out, it is dried at room temperature for 48 hours. The dried ceramic membrane green body is cut into discs. The ceramic membrane is calcined in an air atmosphere at a calcination rate of 1°C / min, and a porous ceramic membrane is obtained after being kept at 600°C for 180 minutes and 1000°C for 60 minutes. After being cleaned 3-5 times (10 minutes each time) by alternating ultrasonic vibration with deionized water and anhydrous ethanol, it is transferred to a constant temperature blast drying oven, dried at 100°C for 24 hours, and then packaged for use. 1g vacuum pump oil, 0.005g sodium dodecyl sulfate, and 1L deionized water are stirred at high speed for one hour at 12000r / min to form a stable emulsion. The encapsulated ceramic membrane is installed on a homemade cross-flow circulation device, and the oil-water emulsion enters the membrane assembly from the storage tank and contacts the surface of the ceramic membrane. Under the action of 0.1bar pressure, the feed liquid is selectively screened by the membrane and permeates out, and the permeate is collected in a glass bottle. The pure water permeability of the ceramic membrane was measured using a homemade membrane assembly and filtration device, as shown in Equation 1 Where J(L / m 2 h) is the pure water flux of the membrane, V(L) is the permeate volume, A(m 2 ) is the effective membrane area of ​​the ceramic membrane, t(h) is the test time

[0035] Implementation Example 5

[0036] Red mud, fly ash, Al2O3, and SiO2 are prepared into ceramic raw materials in a mass ratio of 40:40:15:5, 100 ml of ethanol is added as a ball milling medium, and the ceramic slurry is obtained at 300 r / min for 5 hours. Then it is dried, and the obtained powder is filtered with a 300 mesh screen. The obtained ceramic raw material is mixed with a binder polyethersulfone (PESf), a dispersant polyvinylpyrrolidone (PVP), and an organic solvent N-methylpyrrolidone (NMP) in a mass ratio of 45:6.5:2:46.5, and then put into a ball mill and ball milled at a speed of 400 r / min for 20 hours to obtain a uniformly mixed slurry, which is placed in a vacuum drying oven for vacuum degassing until there are no bubbles, and then placed in the slurry tank of the tape casting machine, and the PET polyester film is used as a carrier. The slurry is evenly and evenly coated on the carrier. During coating, the scraper height is 2 mm and the push rod movement rate is 5 mm / s. The green body after tape casting is slowly placed in a deionized water coagulation bath and soaked. After being taken out, it is dried at room temperature for 48 hours. The dried ceramic membrane green body is cut into discs. The ceramic membrane is calcined in an air atmosphere at a calcination rate of 1°C / min, and a porous ceramic membrane is obtained after being kept at 600°C for 180 minutes and 1000°C for 60 minutes. After being cleaned 3-5 times (10 minutes each time) by alternating ultrasonic vibration with deionized water and anhydrous ethanol, it is transferred to a constant temperature blast drying oven, dried at 100°C for 24 hours, and then packaged for use. 1g vacuum pump oil, 0.005g sodium dodecyl sulfate, and 1L deionized water are stirred at high speed for one hour at 12000r / min to form a stable emulsion. The encapsulated ceramic membrane is installed on a homemade cross-flow circulation device, and the oil-water emulsion enters the membrane assembly from the storage tank and contacts the surface of the ceramic membrane. Under the action of 0.3bar pressure, the feed liquid is selectively screened by the membrane and permeates out, and the permeate is collected in a glass bottle. The pure water permeability of the ceramic membrane was measured using a homemade membrane assembly and filtration device, as shown in Equation 1 Where J(L / m 2 h) is the pure water flux of the membrane, V(L) is the permeate volume, A(m 2 ) is the effective membrane area of ​​the ceramic membrane, t(h) is the test time

[0037] Figure 1It is the surface morphology observed by scanning electron microscope. Figure a is the overall membrane cross-section of the ceramic membrane. It can be seen from the figure that the ceramic membrane has a three-layer asymmetric structure of skin layer, finger-like pore layer and sponge layer. The top is the skin layer, which is about 5 microns thick; the middle is the finger-like pore layer, which is composed of many channels that are wide at the bottom and narrow at the top, with a thickness of about 600 microns. Figure b is the SEM image of the surface of the finger-like pore layer exposed after grinding off the surface skin layer. The finger-like channels are distributed very evenly in the ceramic membrane; the bottom is the sponge layer, which is about 20 microns thick. Its surface morphology is shown in Figure c. The sponge layer structure is very loose, and there are a large number of evenly distributed and interconnected pores. During the phase inversion process, the skin layer on the top of the ceramic membrane is the first to come into contact with the coagulation bath, so it is formed in the early stage of the phase inversion process, providing a small pore filtration channel for the ceramic membrane and serving as the separation layer of the membrane; the middle finger-like pore layer is formed due to the viscous fingering phenomenon of mutual diffusion between the solvent and the non-solvent during the phase inversion process, and it occupies a large proportion in the membrane and plays a supporting role; the bottom sponge layer is formed in the late stage of the phase inversion due to the slowed exchange between the solvent and the non-solvent and the deposition of ceramic particles at the bottom, and the sponge layer has a certain mass transfer resistance. Figure 2 The surface wettability of the ceramic membrane is that the membrane is hydrophilic in air with a water contact angle of 0°, and oleophobic underwater with an oil contact angle of 125.5°. Figure 3 Table 1 shows the oil-water separation performance of the ceramic membrane when the emulsion concentration is 1000 ppm. Table 1. Ceramic membrane oil-water separation performance

Claims

1. A method for preparing a ceramic membrane based on red mud for oil-water separation, characterized in that: The following steps are included: (1) Ceramic ingredients: Red mud, fly ash, SiO2, and Al2O3 are mixed into ceramic raw materials; then all the prepared raw materials are transferred into an alumina ball mill, anhydrous ethanol is added, and the ceramic raw materials are ball milled to obtain a uniform ceramic slurry; The mass ratio of red mud: fly ash: SiO2: Al2O3 is 40:40:15:5; (2) Vacuum drying and sieving: sieving the obtained ceramic slurry, and fully drying the filtered slurry; filtering the obtained powder with a sieve to obtain a red mud-based ceramic raw material; filtering the powder with a 300-mesh sieve to obtain a red mud-based ceramic raw material with a particle size of less than 48 μm; (3) Preparation of organic mixture solution: Mix the binder polyethersulfone (PESf), the dispersant polyvinylpyrrolidone (PVP) and the organic solvent N-methylpyrrolidone (NMP), put them into a planetary ball mill and stir them at a constant speed to obtain a uniform and stable polymer mixture; the ratio of polyethersulfone: polyvinylpyrrolidone: N-methylpyrrolidone is 6.5:2:41.5-46.5 (4) preparing a ceramic slurry: adding the ceramic raw material prepared in step (2) to the polymer solution obtained in step (3) at a ceramic raw material: polymer solution mass ratio of 40-50:60-50, continuing ball milling to obtain a uniform and stable mixed ceramic slurry, placing the mixed slurry in a vacuum drying oven for vacuum degassing until there are no bubbles, and obtaining a uniformly mixed and dense ceramic slurry; (5) Preparing a ceramic film body by tape casting and phase inversion: placing the slurry obtained in step (4) into the slurry tank of a tape casting machine, using a PET polyester film as a carrier, and evenly coating the slurry on the carrier; placing the tape-cast body into a coagulation bath for immersion, taking it out and drying it at room temperature, and cutting the dried ceramic film body into discs; (6) Solid-phase sintering: The ceramic membrane is calcined in an air atmosphere to obtain a porous ceramic membrane at a calcination rate of 1°C / min. The membrane is kept at 600°C for 180 min and at 1000°C for 60 min. The membrane is cleaned with alternating ultrasonic vibrations of deionized water and anhydrous ethanol and then transferred to a constant temperature forced air drying oven. After drying, it is packaged for standby use.

2. The preparation method according to claim 1, characterized in that: The ball milling speed was 300 r / min and the time was 5 h.

3. The preparation method according to claim 1, characterized in that: The drying temperature in step (2) is 80° C. and the drying time is 12 h.

4. The preparation method according to claim 1, characterized in that: The stirring time in step (3) is 2 h.

5. The preparation method according to claim 1, characterized in that: In step (4), the ball milling time is 20 h and the rotation speed is 400 r / min.

6. The preparation method according to claim 1, characterized in that: During coating in step (5), the scraper height is 2 mm and the push rod movement rate is 5 mm / s.

7. The preparation method according to claim 1, characterized in that: The coagulation bath described in step (5) is deionized water. The samples are immersed in the coagulation bath for 12 hours and dried at room temperature for 48 hours.

8. The preparation method according to claim 1, characterized in that: In step (6), the product is dried at 100° C. for 24 hours and then packaged for later use.

9. The ceramic membrane prepared according to any one of claims 1 to 8.

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