Method for ultrasonic-microwave synergistic pretreatment to strengthen dewatering of red mud

Abstract

The present application relates to a kind of ultrasonic-microwave collaborative pretreatment methods for strengthening red mud dewatering, and more particularly to the field of red mud solid waste treatment technology.The present application constructs a composite pretreatment system of "ultrasonic-microwave collaboration+precise temperature control+alkaline regulation", and the synergistic effect of ultrasonic-microwave collaborative treatment, alkaline regulation and composite filter aid can quickly destroy the agglomerate structure and water combination form of red mud particles, achieve efficient removal of free water and bound water, and finally achieve efficient removal of red mud moisture with a moisture content of ≤4%.The present application also improves the characteristics of red mud particles, reduces the energy consumption of subsequent dewatering, solves many limitations of existing technologies, and promotes the large-scale resource utilization of red mud.

Description

Technical Field

[0001] This invention relates to the field of red mud solid waste treatment technology, and in particular to a method for enhancing red mud dewatering through ultrasonic-microwave synergistic pretreatment. Background Technology

[0002] Red mud is an industrial solid waste generated during alumina production. Its high alkalinity and high water content severely restrict its utilization. Currently, red mud dewatering technologies mainly rely on mechanical pressure filtration, natural air drying, and hot air drying, supplemented by chemical filter aids for conditioning. However, these methods generally have many shortcomings.

[0003] Mechanical filtration is ineffective at removing free and bound water from red mud, resulting in a filter cake moisture content exceeding 30%. Natural drying is heavily influenced by weather and causes significant environmental pollution. Hot air drying is energy-intensive and prone to causing red mud agglomeration. Chemical filter aids introduce secondary pollution to some extent and have limited dewatering effects. Furthermore, existing red mud dewatering technologies do not take into account the strong alkalinity of red mud, which easily leads to agglomeration, increases water binding force, and makes dewatering more difficult. Summary of the Invention

[0004] In view of this, the present invention provides a method for enhancing red mud dewatering through ultrasonic-microwave synergistic pretreatment. This invention achieves efficient removal of moisture from red mud by constructing a composite pretreatment system of "ultrasonic-microwave synergy + precise temperature control + alkaline regulation," while simultaneously improving the particle characteristics of red mud, reducing subsequent dewatering energy consumption, overcoming many limitations of existing technologies, and promoting the large-scale resource utilization of red mud.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a method for enhancing red mud dewatering through ultrasonic-microwave synergistic pretreatment, comprising the following steps: Add an alkaline regulator to the homogeneous red mud slurry to adjust the pH value to 8.5-10.5, and stir. The pH-adjusted red mud slurry was subjected to ultrasonic-microwave synergistic treatment to control the slurry temperature at 45-65℃. A composite filter aid was added to the red mud slurry after ultrasonic-microwave synergistic treatment, stirred, and filtered under pressure to obtain red mud filter cake; The red mud filter cake is dried to obtain dehydrated red mud.

[0006] Furthermore, the method also includes a pretreatment step, specifically: stirring the red mud slurry evenly to obtain a homogeneous red mud slurry; the red mud slurry has a water content of 60-80%.

[0007] Furthermore, the alkaline regulator is a compound system of sodium bicarbonate and potassium dihydrogen phosphate; the amount of alkaline regulator added is 0.5-1.2 wt% of the dry weight of red mud.

[0008] Furthermore, the mass ratio of sodium bicarbonate to potassium dihydrogen phosphate is 2-3:1.

[0009] Further, adjust the pH value to 8.5-10.5 and stir for 10-20 minutes.

[0010] Furthermore, the ultrasonic power is 180-320 W, the ultrasonic frequency is 20-40 kHz; the microwave power is 200-400 W, the microwave frequency is 2400-2500 MHz; and the ultrasonic-microwave co-processing time is 8-25 min.

[0011] Furthermore, the ultrasound-microwave synergistic processing adopts a synergistic mode of "intermittent ultrasound operation and continuous microwave operation", with ultrasound working for 30-60 seconds, followed by an interval of 10-20 seconds, and the cycle continues until the synergistic effect time ends.

[0012] Furthermore, the composite filter aid is composed of polyaluminum chloride, modified fly ash, and sodium carboxymethyl cellulose; the amount of composite filter aid added is 1.5-3.0 wt% of the dry weight of red mud.

[0013] Furthermore, the mass ratio of polyaluminum chloride, modified fly ash, and sodium carboxymethyl cellulose is 3-5:8-12:1.

[0014] Furthermore, the modified fly ash is obtained by calcining fly ash at 800-900 ℃ for 2-3 h and then pulverizing it to a particle size ≤ 100 mesh.

[0015] Furthermore, after adding the composite filter aid, the stirring time is 15-30 min; the filtration pressure is 1.2-2.0 MPa, and the filtration time is 30-60 min.

[0016] Furthermore, the drying operation involves drying at 80-120 ℃ to constant weight for 2-3 hours.

[0017] Furthermore, the moisture content of the dehydrated red mud is ≤ 4%.

[0018] Compared with the prior art, the present invention has achieved the following beneficial effects: The red mud dewatering method provided by this invention has high dewatering efficiency and significant effect. Through the synergistic effect of ultrasonic-microwave synergistic pretreatment, alkaline regulation, and composite filter aid, it can rapidly destroy the agglomeration structure and water binding form of red mud particles, achieving efficient removal of free and bound water, with the final red mud moisture content ≤4%. The synergistic mode of "intermittent ultrasound + continuous microwave" reduces energy consumption by more than 30% compared to microwave pretreatment alone. The amount of alkaline regulator and composite filter aid used is small, and the modified fly ash can be prepared from industrial solid waste fly ash, further reducing raw material costs. The energy-saving agent adopts a mild compound system to avoid wastewater pollution caused by strong acid neutralization; the modified fly ash in the composite filter aid is an industrial solid waste resource utilization, without the introduction of harmful components; no toxic or harmful substances are generated in the entire treatment process, and the red mud can be directly used for resource utilization after dewatering, realizing the green development of "solid waste treatment - resource recycling"; the whole method is simple and the parameters are easy to control, and the ultrasonic-microwave synergistic reaction device can realize continuous production, adapt to the transformation and upgrading of existing red mud treatment production lines, without the need for large-scale new equipment, with low investment costs, and is easy to promote and apply on an industrial scale. Detailed Implementation

[0019] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0020] This invention provides a method for enhancing red mud dewatering through ultrasonic-microwave synergistic pretreatment, comprising the following steps: Add an alkaline regulator to the homogeneous red mud slurry to adjust the pH value to 8.5-10.5, and stir. The pH-adjusted red mud slurry was subjected to ultrasonic-microwave synergistic treatment to control the slurry temperature at 45-65℃. A composite filter aid was added to the red mud slurry after ultrasonic-microwave synergistic treatment, stirred, and filtered under pressure to obtain red mud filter cake; The red mud filter cake is dried to obtain dehydrated red mud.

[0021] The pretreatment, pH adjustment, pressure filtration, and drying processes are optimized in a coordinated manner. The treatment temperature (45-65 ℃) and the subsequent low-temperature drying temperature are connected in a gradient to avoid energy waste. At the same time, the characteristics of red mud particles are improved during the treatment process, reducing the pressure of subsequent pressure filtration and drying energy consumption. Moreover, the moisture content of the red mud after dehydration is ≤ 4%, which fully meets the requirements for the resource utilization of red mud-based cementitious materials, etc., and realizes the synergistic promotion of "dehydration-resource utilization".

[0022] Furthermore, the method also includes a pretreatment step, specifically: stirring the red mud slurry evenly to obtain a homogeneous red mud slurry; the red mud slurry has a water content of 60-80%; the red mud is Bayer process red mud.

[0023] Furthermore, the alkaline regulator is a compound system of sodium bicarbonate and potassium dihydrogen phosphate; the amount of alkaline regulator added is 0.5-1.2 wt% of the dry weight of red mud. The amount of alkaline regulator added can be any value between 0.5-1.2 wt% of the dry weight of red mud, such as 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, etc.

[0024] Furthermore, the mass ratio of sodium bicarbonate to potassium dihydrogen phosphate is 2-3:1. The mass ratio of sodium bicarbonate to potassium dihydrogen phosphate can be any value between 2 and 3:1, such as 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, or 2.9:1.

[0025] Further, adjust the pH value to 8.5-10.5 and stir for 10-20 minutes.

[0026] This invention addresses the problems of particle agglomeration and strong water binding caused by the strong alkalinity of red mud. It innovatively uses a compound alkaline regulator of sodium bicarbonate and potassium dihydrogen phosphate, instead of the traditional strong acid neutralization (which easily causes secondary pollution). By gently adjusting the pH of the slurry to 8.5-10.5, it can reduce the strong alkalinity of the red mud, break the hydrogen bonding between particles, reduce water binding, and avoid equipment corrosion and red mud mineral phase damage caused by excessively low slurry pH. At the same time, the compound regulator can also form a weak charge barrier on the surface of red mud particles, further preventing particle agglomeration and laying the foundation for subsequent dewatering.

[0027] Furthermore, the ultrasonic power is 180-320 W, and the ultrasonic frequency is 20-40 kHz; the microwave power is 200-400 W, and the microwave frequency is 2400-2600 MHz; the ultrasonic-microwave co-processing time is 8-25 min. The ultrasonic power can be any value between 180-320 W, the ultrasonic frequency can be any value between 20-40 kHz, and the microwave power can be any value between 200-400 W.

[0028] Furthermore, the ultrasound-microwave synergistic processing adopts a synergistic mode of "intermittent ultrasound operation and continuous microwave operation", with ultrasound working for 30-60 seconds, followed by an interval of 10-20 seconds, and the cycle continues until the synergistic effect time ends.

[0029] The ultrasonic-microwave synergistic treatment is carried out in an ultrasonic-microwave synergistic reaction device. In this device, ultrasonic transducers and microwave radiation sources are staggered, with ultrasonic frequencies of 20-40 kHz and microwave frequencies of 2400-2500 MHz (2450 MHz), ensuring that the ultrasonic and microwave signals form a uniformly superimposed physical field in the slurry. The ultrasonic-microwave synergistic reaction device includes a reaction vessel, ultrasonic transducers, microwave radiation sources, a temperature sensor, and a stirring assembly. The ultrasonic transducers are evenly distributed on the sidewalls of the reaction vessel, and the microwave radiation sources are installed at the top and bottom. The stirring assembly rotates at 60-120 r / min to ensure uniform contact between the slurry and the ultrasonic and microwave signals, avoiding localized overheating or uneven ultrasonic action.

[0030] Both ultrasonic and microwave treatments have significant drawbacks. Ultrasonic treatment alone primarily disrupts the surface structure of red mud particles through cavitation, but its penetration is limited, making it difficult to reach the water trapped inside the red mud. Furthermore, energy consumption is dispersed, resulting in poor dehydration enhancement. While microwave treatment alone can rapidly heat the internal water in the red mud and promote evaporation, it easily leads to localized overheating and agglomeration, creating a phenomenon of "dry outer shell and water-containing interior," which hinders water migration. Additionally, microwave energy utilization is low, resulting in high processing costs. This invention employs a combined synergistic mode of "intermittent ultrasonic operation and continuous microwave operation," solving the problems of insufficient penetration by ultrasonic treatment alone and the tendency for localized agglomeration caused by microwave treatment alone. The cavitation effect of ultrasound can disrupt the hydration film and agglomeration structure on the surface of red mud particles, forming micropores that provide channels for microwave energy penetration. Microwaves, through molecular polarization, rapidly heat the free and bound water inside the red mud, increasing its kinetic energy and causing it to migrate rapidly to the particle surface. The two methods work synergistically, reducing the moisture content of the red mud filter cake by 15-25% compared to ultrasonic or microwave treatment alone.

[0031] Furthermore, the composite filter aid is composed of polyaluminum chloride, modified fly ash, and sodium carboxymethyl cellulose; the amount of composite filter aid added is 1.5-3.0 wt% of the dry weight of red mud. The amount of composite filter aid added can be any value between 1.5-3.0 wt% of the dry weight of red mud, for example, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2.0 wt%, 2.5 wt%, 2.6 wt%, 2.7 wt%, 2.8 wt%, and 2.9 wt%.

[0032] Furthermore, the mass ratio of polyaluminum chloride, modified fly ash, and sodium carboxymethyl cellulose is 3-5:8-12:1.

[0033] Furthermore, the modified fly ash is obtained by calcining fly ash at 800-900℃ for 2-3 hours and then pulverizing it to a particle size ≤ 100 mesh. The calcination temperature can be any temperature between 800-900℃, such as 810℃, 820℃, 830℃, 840℃, 850℃, 860℃, 870℃, 880℃, or 890℃; the calcination time can be any value between 2-3 hours, such as 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, or 2.9 hours.

[0034] By combining the flocculation effect of polyaluminum chloride, the adsorption and porosity of modified fly ash, and the binding and dispersing effect of sodium carboxymethyl cellulose, a synergistic filter aid system is formed. The modified fly ash, after high-temperature calcination, has a richer pore structure, which can adsorb free moisture on the surface of red mud particles and act as a skeletal support, reducing filter cake clogging. Sodium carboxymethyl cellulose further disperses the red mud particles, preventing filter cloth clogging during pressure filtration. Compared to a single filter aid, the filter cake filtration speed is increased by 40-60%, the filter cake moisture content is further reduced by 5-8%, and the amount of filter aid used is reduced, lowering treatment costs.

[0035] Furthermore, after adding the composite filter aid, the stirring time is 15-30 min; the filtration pressure is 1.2-2.0 MPa, and the filtration time is 30-60 min. The stirring time can be any value between 15-30 min, such as 20 min, 25 min, etc.; the filtration pressure can be any value between 1.2-2.0 MPa, such as 1.3 MPa, 1.4 MPa, 1.5 MPa, 1.6 MPa, 1.7 MPa, 1.8 MPa, 1.9 MPa; and the filtration time can be any value between 30-60 min, such as 35 min, 40 min, 45 min, 50 min, 55 min, etc.

[0036] Furthermore, the drying operation involves drying at 80-120 ℃ to constant weight for 2-3 hours.

[0037] Furthermore, the moisture content of the dehydrated red mud is ≤ 4%.

[0038] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0039] Example 1 This embodiment provides a method for enhancing red mud dewatering through ultrasonic-microwave synergistic pretreatment, including the following steps:

[0040] 1. Red mud pretreatment: Take Bayer process red mud slurry with a water content of 70%, put it into a mixing device, and stir it evenly to obtain homogeneous red mud slurry; then add an alkaline regulator (sodium bicarbonate to potassium dihydrogen phosphate mass ratio 2.5:1) to the homogeneous red mud slurry, the amount of which is 0.8 wt% of the dry weight of red mud, adjust the pH value of the slurry to 9.5, stir for 15 min, and complete the red mud preconditioning.

[0041] 2. Ultrasonic-microwave synergistic treatment: The pre-conditioned red mud slurry was fed into an ultrasonic-microwave synergistic reaction device. The ultrasonic power was set to 250 W, the ultrasonic frequency to 30 kHz, the microwave power to 320 W, the microwave frequency to 2450 MHz, and the synergistic reaction time to 15 min. During the treatment, the slurry temperature was maintained at 55 ℃. A cycle mode of 45 s ultrasonic operation followed by 15 s intermittent operation was adopted, and the stirring component speed was 90 r / min.

[0042] 3. Auxiliary conditioning: Add a composite filter aid (polyaluminum chloride, modified fly ash, and sodium carboxymethyl cellulose in a mass ratio of 4:10:1) to the co-treated red mud slurry. The amount added is 2.2 wt% of the dry weight of the red mud. The modified fly ash is obtained by calcining at 850 ℃ for 2.5 h and then crushing it to a particle size ≤ 100 mesh. Stir for 25 min.

[0043] 4. Filtration and dewatering: The red mud slurry after auxiliary conditioning is fed into a plate and frame filter press. The filtration pressure is set to 1.6 MPa and the filtration time is 45 min to obtain red mud filter cake.

[0044] 5. Low-temperature drying: The red mud filter cake is sent to a low-temperature drying equipment and dried at 100 ℃ for 2.5 h to constant weight to obtain the final dehydrated red mud. The moisture content is 3.2%.

[0045] Example 2 This embodiment provides a method for enhancing red mud dewatering through ultrasonic-microwave synergistic pretreatment, including the following steps:

[0046] 1. Red mud pretreatment: Take red mud slurry with a water content of 80%, put it into a mixing device, and stir it evenly to obtain homogeneous red mud slurry; then add an alkaline regulator (sodium bicarbonate to potassium dihydrogen phosphate mass ratio 3:1) to the homogeneous red mud slurry, the amount of which is 1.0 wt% of the dry weight of red mud, adjust the pH value of the slurry to 10.5, stir for 20 min, and complete the red mud preconditioning.

[0047] 2. Ultrasonic-microwave synergistic treatment: The pre-conditioned red mud slurry was fed into an ultrasonic-microwave synergistic reaction device. The ultrasonic power was set to 280 W, the ultrasonic frequency to 35 kHz, the microwave power to 350 W, the microwave frequency to 2450 MHz, and the synergistic reaction time to 20 min. During the treatment, the slurry temperature was maintained at 60 ℃. A cycle mode of 60 s ultrasonic operation followed by 20 s intermittent operation was adopted, and the stirring component speed was 120 r / min.

[0048] 3. Auxiliary conditioning: Add a composite filter aid (polyaluminum chloride, modified fly ash, and sodium carboxymethyl cellulose in a mass ratio of 5:12:1) to the co-treated red mud slurry. The amount added is 2.5 wt% of the dry weight of the red mud. The modified fly ash is obtained by calcining at 900 ℃ for 3 h and then crushing it to a particle size ≤100 mesh. Stir for 30 min.

[0049] 4. Filtration and dewatering: The red mud slurry after auxiliary conditioning is fed into a plate and frame filter press. The filtration pressure is set to 1.8 MPa and the filtration time is 50 min to obtain red mud filter cake.

[0050] 5. Low-temperature drying: The red mud filter cake is sent to a low-temperature drying equipment and dried at 110 ℃ for 2 hours to constant weight to obtain the final dehydrated red mud. The moisture content is 2.8%.

[0051] Example 3 This embodiment provides a method for enhancing red mud dewatering through ultrasonic-microwave synergistic pretreatment, including the following steps:

[0052] 1. Red mud pretreatment: Take red mud slurry with a water content of 60%, put it into a mixing device, and stir it evenly to obtain homogeneous red mud slurry; then add an alkaline regulator (sodium bicarbonate to potassium dihydrogen phosphate mass ratio 2:1) to the homogeneous red mud slurry, the amount of which is 0.5wt% of the dry weight of red mud, adjust the pH value of the slurry to 8.5, stir for 10 min, and complete the red mud preconditioning.

[0053] 2. Ultrasonic-microwave synergistic treatment: The pre-conditioned red mud slurry was fed into the ultrasonic-microwave synergistic reaction device. The ultrasonic power was set to 180 W, the ultrasonic frequency to 20 kHz, the microwave power to 200 W, the microwave frequency to 2450 MHz, and the synergistic reaction time to 8 min. During the treatment, the slurry temperature was maintained at 45 ℃. The ultrasonic operation mode was 30 s followed by 10 s intervals. The stirring component speed was 60 r / min.

[0054] 3. Auxiliary conditioning: Add a composite filter aid (polyaluminum chloride, modified fly ash, and sodium carboxymethyl cellulose in a mass ratio of 3:8:1) to the co-treated red mud slurry. The amount added is 1.5 wt% of the dry weight of the red mud. The modified fly ash is obtained by calcining at 800 ℃ for 2 h and then crushing it to a particle size ≤ 100 mesh. Stir for 15 min.

[0055] 4. Filtration and dewatering: The red mud slurry after auxiliary conditioning is fed into a plate and frame filter press. The filtration pressure is set to 1.2 MPa and the filtration time is 30 min to obtain red mud filter cake.

[0056] 5. Low-temperature drying: The red mud filter cake is sent to a low-temperature drying equipment and dried at 80 ℃ for 3 hours until constant weight is obtained, and the final dehydrated red mud is obtained. The moisture content is 3.8%.

[0057] Example 4 This embodiment provides a method for enhancing red mud dewatering through ultrasonic-microwave synergistic pretreatment, including the following steps:

[0058] 1. Red mud pretreatment: Take red mud slurry with a water content of 75%, put it into a mixing device, and stir it evenly to obtain homogeneous red mud slurry; then add an alkaline regulator (sodium bicarbonate to potassium dihydrogen phosphate mass ratio 2.5:1) to the homogeneous red mud slurry, the amount of which is 0.9 wt% of the dry weight of red mud, adjust the pH value of the slurry to 10.0, stir for 15 min, and complete the red mud preconditioning.

[0059] 2. Ultrasonic-microwave synergistic treatment: The pre-conditioned red mud slurry was fed into the ultrasonic-microwave synergistic reaction device. The ultrasonic power was set to 240 W, the ultrasonic frequency to 32 kHz, the microwave power to 300 W, the microwave frequency to 2450 MHz, and the synergistic reaction time to 18 min. During the treatment, the slurry temperature was maintained at 58 ℃. The ultrasonic operation mode was 45 s followed by 15 s intervals. The stirring component speed was 100 r / min.

[0060] 3. Auxiliary conditioning: Add a composite filter aid (polyaluminum chloride, modified fly ash, and sodium carboxymethyl cellulose in a mass ratio of 4:10:1) to the co-treated red mud slurry. The amount added is 2.3 wt% of the dry weight of the red mud. The modified fly ash is obtained by calcining at 850 ℃ for 2.5 h and then crushing it to a particle size ≤ 100 mesh. Stir for 28 min.

[0061] 4. Filtration and dewatering: The red mud slurry after auxiliary conditioning is fed into a plate and frame filter press. The filtration pressure is set to 1.7 MPa and the filtration time is 48 min to obtain red mud filter cake.

[0062] 5. Low-temperature drying: The red mud filter cake is sent to a low-temperature drying equipment and dried at 105 ℃ for 2.2 h to constant weight to obtain the final dehydrated red mud. The moisture content is 3.0%.

[0063] Example 5 This embodiment provides a method for enhancing red mud dewatering through ultrasonic-microwave synergistic pretreatment, including the following steps:

[0064] 1. Red mud pretreatment: Take red mud slurry with a water content of 75%, put it into a mixing device, and stir it evenly to obtain homogeneous red mud slurry; then add an alkaline regulator (sodium bicarbonate to potassium dihydrogen phosphate mass ratio 2.8:1) to the homogeneous red mud slurry, the amount of which is 0.95 wt% of the dry weight of red mud, adjust the pH value of the slurry to 10.2, stir for 18 min, and complete the red mud preconditioning.

[0065] 2. Ultrasonic-microwave synergistic treatment: The pre-conditioned red mud slurry was fed into the ultrasonic-microwave synergistic reaction device. The ultrasonic power was set to 260 W, the ultrasonic frequency to 33 kHz, the microwave power to 330 W, the microwave frequency to 2450 MHz, and the synergistic reaction time to 16 min. During the treatment, the slurry temperature was maintained at 56 ℃. The ultrasonic operation mode was 50 s followed by 15 s intervals. The stirring component speed was 110 r / min.

[0066] 3. Auxiliary conditioning: Add a composite filter aid (polyaluminum chloride, modified fly ash, and sodium carboxymethyl cellulose in a mass ratio of 4.5:11:1) to the co-treated red mud slurry. The amount added is 2.4 wt% of the dry weight of the red mud. The modified fly ash is obtained by calcining at 880 ℃ for 2.6 h and then crushing it to a particle size ≤ 100 mesh. Stir for 26 min.

[0067] 4. Filtration and dewatering: The red mud slurry after auxiliary conditioning is fed into a plate and frame filter press. The filtration pressure is set to 1.75 MPa and the filtration time is 46 min to obtain red mud filter cake.

[0068] 5. Low-temperature drying: The red mud filter cake is fed into a low-temperature drying device and dried at 108 ℃ for 2.1 h to constant weight to obtain the final dehydrated red mud. The moisture content is 2.9%.

[0069] Example 6 This embodiment provides a method for enhancing red mud dewatering through ultrasonic-microwave synergistic pretreatment, including the following steps:

[0070] 1. Red mud pretreatment: Take red mud slurry with a water content of 65%, put it into a mixing device, and stir it evenly to obtain homogeneous red mud slurry; then add an alkaline regulator (sodium bicarbonate to potassium dihydrogen phosphate mass ratio 2.2:1) to the homogeneous red mud slurry, the amount of which is 0.7wt% of the dry weight of red mud, adjust the pH value of the slurry to 9.0, stir for 12 min, and complete the red mud preconditioning.

[0071] 2. Ultrasonic-microwave synergistic treatment: The pre-conditioned red mud slurry was fed into the ultrasonic-microwave synergistic reaction device. The ultrasonic power was set to 200 W, the ultrasonic frequency to 28 kHz, the microwave power to 250 W, the microwave frequency to 2450 MHz, and the synergistic reaction time to 10 min. During the treatment, the slurry temperature was maintained at 48 ℃. The ultrasonic operation mode was 35 s followed by 12 s intervals. The stirring component speed was 80 r / min.

[0072] 3. Auxiliary conditioning: Add a composite filter aid (polyaluminum chloride, modified fly ash, and sodium carboxymethyl cellulose in a mass ratio of 3.5:9:1) to the co-treated red mud slurry. The amount added is 1.8 wt% of the dry weight of the red mud. The modified fly ash is obtained by calcining at 820 ℃ for 2.2 h and then crushing it to a particle size ≤ 100 mesh. Stir for 18 min.

[0073] 4. Filtration and dewatering: The red mud slurry after auxiliary conditioning is fed into a plate and frame filter press. The filtration pressure is set to 1.4 MPa and the filtration time is 35 min to obtain red mud filter cake.

[0074] 5. Low-temperature drying: The red mud filter cake is sent to a low-temperature drying equipment and dried at 88 ℃ for 2.8 h to constant weight to obtain the final dehydrated red mud. The moisture content is 3.5%.

[0075] Comparative Example 1 Using Bayer red mud from Example 1 as raw material, mechanical pressure filtration and dewatering were performed without any pretreatment, and other conditions were the same as in Example 1.

[0076] 1. Take Bayer red mud with a moisture content of 70% and put it into a mixing device, mix it evenly to obtain a homogeneous red mud slurry;

[0077] 2. No pH adjustment, ultrasonic-microwave synergistic treatment, or filter aid addition is performed on the red mud slurry; mechanical filtration is carried out directly: the red mud slurry is fed into a plate and frame filter press, the filtration pressure is set to 1.6 MPa, and the filtration time is 45 min to obtain red mud filter cake.

[0078] 3. The red mud filter cake was dried at 100 ℃ for 2.5 h until constant weight was obtained to obtain dehydrated red mud. The water content of the red mud was found to be 38.2%.

[0079] Comparative Example 2 This comparative example only uses ultrasonic pretreatment, without microwave synergy and alkaline regulation. Other conditions are the same as in Example 1. The specific steps are as follows:

[0080] 1. Take Bayer red mud with a moisture content of 70% and put it into a mixing device. Mix it evenly to obtain a homogeneous red mud slurry.

[0081] 2. Add an alkaline conditioner (sodium bicarbonate to potassium dihydrogen phosphate mass ratio 2.5:1) to the homogeneous red mud slurry. The amount added is 0.8 wt% of the dry weight of the red mud. Adjust the pH of the slurry to 9.5 and stir for 15 min to complete the red mud preconditioning.

[0082] 3. Ultrasonic pretreatment only: ultrasonic power 250 W, frequency 30 kHz, treatment time 15 min, temperature 55 ℃, ultrasonic 45 s / intermittent 15 s, stirring speed 90 r / min; no microwave co-treatment.

[0083] 4. Add a composite filter aid (polyaluminum chloride: modified fly ash: sodium carboxymethyl cellulose = 4:10:1) to the ultrasonically treated red mud slurry. The amount added is 2.2 wt% of the dry weight of the red mud. The modified fly ash is obtained by calcining at 850 ℃ for 2.5 h and then crushing it to a particle size ≤ 100 mesh. Stir for 25 min.

[0084] 5. Mechanical filtration: The red mud slurry after auxiliary conditioning is fed into a plate and frame filter press. The filtration pressure is set to 1.6 MPa and the filtration time is 45 min to obtain red mud filter cake.

[0085] 6. Low-temperature drying: The red mud filter cake is fed into a low-temperature drying device and dried at 100 ℃ for 2.5 h to constant weight to obtain the final dehydrated red mud. The final red mud moisture content is 22.6%.

[0086] Comparative Example 3 This comparative example only used microwave pretreatment (320 W power, 15 min time), without ultrasonic synergy and alkaline regulation. Other conditions were the same as in Example 1. The specific steps were as follows:

[0087] 1. Take red mud with a moisture content of 70% and put it into a mixing device. Mix it evenly to obtain a homogeneous red mud slurry.

[0088] 2. Add an alkaline conditioner (sodium bicarbonate to potassium dihydrogen phosphate mass ratio 2.5:1) to the homogeneous red mud slurry. The amount added is 0.8 wt% of the dry weight of the red mud. Adjust the pH of the slurry to 9.5 and stir for 15 min to complete the red mud preconditioning.

[0089] 3. Microwave pretreatment only: microwave power 320 W, frequency 2450 MHz, treatment time 15 min, temperature 55℃, stirring speed 90 r / min; no ultrasonic synergistic treatment.

[0090] 4. Auxiliary conditioning: Add a composite filter aid (polyaluminum chloride: modified fly ash: sodium carboxymethyl cellulose = 4:10:1) to the microwave-treated red mud slurry at a dosage of 2.2 wt%. The modified fly ash is obtained by calcining at 850 ℃ for 2.5 h and then pulverizing it to a particle size ≤ 100 mesh. Stir for 25 min.

[0091] 5. Mechanical filtration: The red mud slurry after auxiliary conditioning is fed into a plate and frame filter press. The filtration pressure is set to 1.6 MPa and the filtration time is 45 min to obtain red mud filter cake.

[0092] 6. Low-temperature drying: The red mud filter cake is sent to a low-temperature drying equipment and dried at 100 ℃ for 2.5 h to constant weight to obtain the final dehydrated red mud. The moisture content is 20.3%.

[0093] Comparative Example 4 This comparative example uses ultrasonic-microwave synergistic pretreatment, but without the addition of an alkaline modifier. Other conditions are the same as in Example 1. The specific steps are as follows:

[0094] 1. Take red mud with a moisture content of 70% and put it into a mixing device. Mix it evenly to obtain a homogeneous red mud slurry.

[0095] 2. Without adding alkaline regulators, direct ultrasonic-microwave synergistic treatment is carried out: The pre-conditioned red mud slurry is fed into the ultrasonic-microwave synergistic reaction device, the ultrasonic power is set to 250 W, the ultrasonic frequency is 30 kHz, the microwave power is 320 W, the microwave frequency is 2450 MHz, the synergistic reaction time is 15 min, the slurry temperature is controlled at 55 ℃ during the treatment, and a cycle mode of ultrasonic operation for 45 s and intermittent operation for 15 s is adopted, and the stirring component speed is 90 r / min.

[0096] 3. Auxiliary conditioning: Add a composite filter aid (polyaluminum chloride, modified fly ash, and sodium carboxymethyl cellulose in a mass ratio of 4:10:1) to the co-treated red mud slurry. The amount added is 2.2 wt% of the dry weight of the red mud. The modified fly ash is obtained by calcining at 850 ℃ for 2.5 h and then crushing it to a particle size ≤ 100 mesh. Stir for 25 min.

[0097] 4. Filtration and dewatering: The red mud slurry after auxiliary conditioning is fed into a plate and frame filter press. The filtration pressure is set to 1.6 MPa and the filtration time is 45 min to obtain red mud filter cake.

[0098] 5. Low-temperature drying: The red mud filter cake is sent to a low-temperature drying equipment and dried at 100 ℃ for 2.5 h to constant weight to obtain the final dehydrated red mud. The moisture content is 9.1%.

[0099] Comparative Example 5 This comparative example uses ultrasonic-microwave synergistic pretreatment and alkaline regulation, but uses polyaluminum chloride as a single filter aid. Other conditions are the same as in Example 1. The specific steps are as follows:

[0100] 1. Take red mud with a moisture content of 70% and put it into a mixing device. Mix it evenly to obtain a homogeneous red mud slurry.

[0101] 2. Add an alkaline conditioner (sodium bicarbonate to potassium dihydrogen phosphate mass ratio 2.5:1) to the homogeneous red mud slurry. The amount added is 0.8 wt% of the dry weight of the red mud. Adjust the pH of the slurry to 9.5 and stir for 15 min to complete the red mud preconditioning.

[0102] 3. Ultrasonic-microwave synergistic treatment: The pre-conditioned red mud slurry was fed into an ultrasonic-microwave synergistic reaction device. The ultrasonic power was set to 250 W, the ultrasonic frequency to 30 kHz, the microwave power to 320 W, the microwave frequency to 2450 MHz, and the synergistic reaction time to 15 min. During the treatment, the slurry temperature was maintained at 55 ℃. A cycle mode of 45 s ultrasonic operation followed by 15 s intermittent operation was adopted, and the stirring component speed was 90 r / min.

[0103] 4. Auxiliary conditioning: Add polyaluminum chloride to the co-treated red mud slurry at a rate of 2.2 wt% of the dry weight of the red mud, and stir for 25 min.

[0104] 5. Mechanical filtration: The red mud slurry after auxiliary conditioning is fed into a plate and frame filter press. The filtration pressure is set to 1.6 MPa and the filtration time is 45 min to obtain red mud filter cake.

[0105] 6. Low-temperature drying: The red mud filter cake is sent to a low-temperature drying equipment and dried at 100 ℃ for 2.5 h to constant weight to obtain the final dehydrated red mud. The moisture content is 6.3%.

[0106] Comparative experimental results show that the ultrasonic-microwave synergistic pretreatment enhanced red mud dewatering method of the present invention has a significantly better dewatering effect than existing technologies, which are single mechanical pressure filtration and single ultrasonic / microwave pretreatment. At the same time, through the synergistic effect of alkaline regulation and composite filter aid, the water content of red mud is further reduced.

[0107] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for enhancing red mud dewatering through ultrasonic-microwave synergistic pretreatment, characterized in that, Includes the following steps: Add an alkaline regulator to the homogeneous red mud slurry to adjust the pH value to 8.5-10.5, and stir. The pH-adjusted red mud slurry was subjected to ultrasonic-microwave synergistic treatment to control the slurry temperature at 45-65 ℃. A composite filter aid was added to the red mud slurry after ultrasonic-microwave synergistic treatment, stirred, and filtered under pressure to obtain red mud filter cake; the ultrasonic power was 180-320 W and the ultrasonic frequency was 20-40 kHz; the microwave power was 200-400 W and the microwave frequency was 2400-2500 MHz. The red mud filter cake is dried to obtain dehydrated red mud; The alkaline regulator is a compound system of sodium bicarbonate and potassium dihydrogen phosphate, and the amount of alkaline regulator added is 0.5-1.2 wt% of the dry weight of red mud.

2. The method as described in claim 1, characterized in that, The method also includes a pretreatment step, specifically: stirring the red mud slurry evenly to obtain a homogeneous red mud slurry; the red mud slurry has a water content of 60-80%.

3. The method as described in claim 1, characterized in that, The mass ratio of sodium bicarbonate to potassium dihydrogen phosphate is 2-3:

1.

4. The method as described in claim 1, characterized in that, The ultrasound-microwave co-processing time is 8-25 min.

5. The method as described in claim 4, characterized in that, The ultrasound-microwave synergistic treatment adopts a synergistic mode of "intermittent ultrasound operation and continuous microwave operation". The ultrasound works for 30-60 seconds, with an interval of 10-20 seconds, and the cycle continues until the synergistic effect time ends.

6. The method as described in claim 1, characterized in that, The composite filter aid is composed of polyaluminum chloride, modified fly ash, and sodium carboxymethyl cellulose; the amount of composite filter aid added is 1.5-3.0 wt% of the dry weight of red mud.

7. The method as described in claim 6, characterized in that, The mass ratio of polyaluminum chloride, modified fly ash, and sodium carboxymethyl cellulose is 3-5:8-12:

1.

8. The method as described in claim 6, characterized in that, Modified fly ash is obtained by calcining fly ash at 800-900 ℃ for 2-3 hours and then pulverizing it to a particle size ≤ 100 mesh.

9. The method as described in claim 1, characterized in that, After adding the composite filter aid, stir for 15-30 minutes; the filtration pressure is 1.2-2.0 MPa, and the filtration time is 30-60 minutes.

10. The method as described in claim 9, characterized in that, The drying process involves drying at 80-120 ℃ to constant weight for 2-3 hours; or, the moisture content of the dehydrated red mud is ≤ 4%.