Method for preparing geopolymer ecological alien soil through red mud-gypsum synergistic curing
By combining red mud-gypsum synergistic solidification with a geopolymer system, the problems of long solidification cycle and limited large-scale production in the preparation of topsoil from red mud are solved. This achieves efficient and harmless treatment of red mud and preparation of ecological topsoil, which is suitable for scenarios such as sandy soil improvement, compacted soil remediation, slope ecological greening and mining area reclamation.
Patent Information
- Application Number
- CN202512051047.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-31
- Publication Date
- 2026-04-14
AI Technical Summary
Existing red mud preparation technologies for topsoil have problems such as long curing cycles, low efficiency, limited large-scale production, and complex industrial processes with high equipment requirements, making them difficult to promote and apply.
A red mud-gypsum synergistic solidification method is adopted, in which red mud and gypsum are initially rendered harmless by compounding, and then combined with a geopolymer system to form a slurry. Combined with open-air stacking and curing or subcritical pressure vessel solidification mode, geopolymer ecological topsoil is prepared.
It achieves efficient and harmless treatment of red mud, shortens the solidification cycle, reduces production costs, is suitable for production of different scales, and the prepared topsoil has good ecological performance and compressive strength, making it suitable for multiple soil improvement and ecological restoration scenarios.
Smart Images
Figure CN121850469A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of soil improvement technology, and in particular to a method for preparing geopolymer ecological topsoil through synergistic solidification of red mud and gypsum. Background Technology
[0002] Red mud is an industrial solid waste generated during the production of alumina from bauxite, including sintering red mud and Bayer process red mud. my country's cumulative stockpiles have reached over 1 billion tons. Long-term stockpiling not only occupies large amounts of land but also poses ecological and environmental risks such as high alkalinity, heavy metal leaching, and fluoride ion leaching. Existing technologies for preparing topsoil from red mud mostly employ a single open-air curing model, which suffers from long curing cycles, low efficiency, and limitations in large-scale production. Furthermore, some industrial processes are complex and require sophisticated equipment, making widespread application difficult. Summary of the Invention
[0003] In view of this, the present invention aims to provide a method for preparing geopolymer ecological topsoil through synergistic solidification of red mud and gypsum, in order to solve or alleviate the technical problems existing in the prior art, and at least provide a beneficial alternative.
[0004] The technical solution of this invention is implemented as follows: a method for preparing geopolymer ecological topsoil through synergistic solidification of red mud and gypsum, comprising the following steps: S1. Raw material preparation: Select red mud that has been stockpiled for ≥30 days, including sintered red mud or Bayer process red mud. After crushing, pass it through a 10mm sieve to remove large impurities. Adjust the moisture content to 15%~20%. Select phosphogypsum or desulfurized gypsum, let it age naturally for 7~10 days, crush it, and pass it through a 5mm sieve to control the free water content ≤5%. Select geopolymer composed of highly active raw materials and composite alkaline activators. The highly active raw materials are a mixture of Grade I F type fly ash and S95 grade mineral powder at a mass ratio of 2:1. The composite alkaline activator is a mixture of water glass and quicklime at a mass ratio of 3:1. The water glass modulus is 1.0~1.5. S2. Solidified red mud-gypsum: Weigh the raw materials according to the mass ratio of red mud:gypsum = 6~10:1, dry mix for 3~4 minutes to mix evenly, adjust the moisture content to 15%~20%, and let it age naturally for 7~15 days, turning it over once every 2~3 days during the period to achieve acid-base neutralization and initial solidification of heavy metals. The pH at the end of aging should be controlled at 7.0~8.5. S3. Geopolymer Composite Slurry Preparation: Weigh the raw materials according to the following mass percentages: 30%~50% red mud-gypsum solidified material, 40%~60% high-activity raw materials of geopolymer system, and 3%~6% composite alkaline activator, with a total mass percentage of 100%. First, dry mix all solid raw materials for 3~4 minutes, then add water at 20%~25% of the total raw material mass, and wet mix for 4~5 minutes to form a uniform topsoil slurry. S4. Curing and shaping, prepared using any of the following methods: Method 1: Spread or compact the topsoil slurry naturally and cure it for 7 to 14 days at 20-25℃ and 60%-80% humidity, spraying water regularly to keep it moist during the period; Method 2: The imported soil slurry is fed into a pressure vessel and solidified for 2 to 4 hours under subcritical conditions of 120~160℃ and 0.8~1.2MPa (preferably 1MPa). After discharge, it is naturally cooled to room temperature and crushed to a particle size ≤5mm. S5. Finished product aging: Method 1: Geopolymer ecological topsoil is obtained directly after curing; Method 2: After crushing, it is piled up in the open air for aging for 3-7 days. After the topsoil properties are stable, geopolymer ecological topsoil is obtained.
[0005] In some embodiments: In S1, if the red mud is Bayer process red mud, an additional 0.1% to 0.3% of sodium tripolyphosphate dispersant by weight of the red mud is added, and the mixture is stirred and dispersed for 10 to 15 minutes.
[0006] In some embodiments: In S2, if the pH of the aged red mud-gypsum solidified product is ≥9.0, the gypsum content is increased, wherein the ratio of red mud to gypsum is 5~6:1; if the pH is <7.0, the gypsum content is reduced, wherein the ratio of red mud to gypsum is 9~10:1.
[0007] In some embodiments: In step S3, if the heavy metal content of the red mud exceeds the standard, 2% to 3% iron powder is added to the solid raw material during the dry mixing stage.
[0008] In some embodiments: In step S3, if the red mud is Bayer process red mud, 3% to 5% bentonite is added to the solid raw material to enhance the adsorption and fixation effect of fluoride ions.
[0009] In some embodiments: In the second method of S4, nitrogen gas at 0.1~0.2MPa is introduced as a protective gas during the curing process of the pressure vessel to prevent the slurry from oxidizing.
[0010] In some embodiments: the performance indicators of the imported soil are: pH 6.5~8.5, Cr leaching content ≤0.15mg / L, Leaching concentration ≤ 0.05 mg / L Leaching concentration ≤ 0.05 mg / L Leaching amount ≤1.0mg / L, compressive strength 0.5~2.0MPa, 0.5~5cm agglomerate ratio ≥60%, porosity 30%~40%.
[0011] In some embodiments, the imported soil is used for sandy soil improvement, compacted soil remediation, slope ecological greening, or mining area reclamation.
[0012] The embodiments of the present invention have the following advantages due to the adoption of the above technical solutions: I. This invention does not require a complicated pretreatment process. It achieves preliminary harmlessness only through the compound aging of red mud and gypsum, and then combines it with a geopolymer system to make pulp. The steps are few and easy to master, making it suitable for production of different scales.
[0013] Second, the open-air storage curing mode of this invention has low cost and is suitable for small and medium scale; the subcritical pressure autoclave curing mode has high efficiency (cycle shortened by more than 60%) and is suitable for large-scale production. The two modes can be flexibly selected and are highly practical.
[0014] III. The soil prepared by this invention achieves acid-base neutralization and initial solidification of heavy metals through red mud-gypsum compounding, further deep encapsulation and fixation of the geological polymer network, more thorough solidification under subcritical environment, complete compliance of harmful element leaching, and harmlessness rate ≥95%.
[0015] Fourth, the imported soil prepared by this invention contains 30% to 50% red mud, which can digest the old red mud stored in red mud dams on a large scale, effectively reduce the risk of solid waste storage, and has ecological benefits.
[0016] V. The topsoil prepared by this invention has a stable pH of 6.5~8.5 (suitable for crop growth), stable granular structure (0.5~5cm granules account for ≥60%), good air and water permeability, water and fertilizer retention capacity, compressive strength of 0.5~2.0MPa, and root penetration capability, thus meeting the needs of soil improvement and ecological restoration.
[0017] VI. The raw materials for the topsoil prepared by this invention are all industrial solid waste or conventional materials, which are readily available. Although the subcritical mode requires a pressure vessel, the production efficiency is significantly improved and the overall cost is controllable. The topsoil can be used in multiple scenarios such as sandy soil improvement, compacted soil remediation, slope ecological greening, and mining area reclamation.
[0018] The above overview is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features of the invention will become readily apparent from the accompanying drawings and the following detailed description. Attached Figure Description
[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0020] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation
[0021] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.
[0022] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
[0023] like Figure 1 As shown, this invention provides a method for preparing geopolymer-based ecological topsoil through the synergistic solidification of red mud and gypsum. The method simplifies the process, establishes two industrial solidification modes, achieves initial harmlessness through the compounding of red mud and gypsum, and then combines the geopolymer system with different solidification modes to form high-quality topsoil. This method balances practicality, economy, and the needs of large-scale production, and includes the following steps: S1. Raw material preparation: Red mud: Priority should be given to old red mud that has been stored in the red mud dam for ≥30 days (either sintering method or Bayer method is acceptable). After crushing and screening, large impurities should be removed and the moisture content adjusted to 15%~20%. The old red mud has undergone long-term natural leaching, and the alkalinity has been initially reduced. The heavy metal forms are more stable, the treatment effect is better, and it can digest existing solid waste.
[0024] Gypsum: Phosphogypsum or desulfurized gypsum is crushed and screened after natural aging for 7-10 days, with free water content controlled to ≤5% to avoid excessive reaction with red mud, while ensuring mild acidity to facilitate acid-base neutralization.
[0025] Geopolymer system: The highly active raw material is a 2:1 mixture of Grade F fly ash and Grade S95 mineral powder to ensure sufficient silicon and aluminum activity, providing a material basis for the formation of the geopolymer network; the composite alkaline activator is a 3:1 mixture of water glass and quicklime, with a water glass modulus of 1.0~1.5, to gently activate the reaction and avoid alkalinity rebound.
[0026] S2. Solidified Red Mud-Gypsum: Dry-mix red mud and gypsum at a mass ratio of 6-10:1 for 3-4 minutes. After thorough mixing, adjust the moisture content to 15%-20% and allow to age naturally for 7-15 days, stirring every 2-3 days. The acidity of gypsum neutralizes the alkalinity of red mud, stabilizing the pH of the mixture at 7.0-8.5; simultaneously, the gypsum releases... With red mud , , The formation of stable calcium salt precipitates by heavy metal ions achieves preliminary solidification of heavy metals, with a fixation rate of 60% to 80%.
[0027] S3. Geopolymer Composite Slurry Preparation: Weigh out the red mud-gypsum solidified material, highly active raw materials of the geopolymer system, and composite alkaline activator at mass percentages of 30%~50%, 40%~60%, and 3%~6%, respectively. First, dry mix all solid raw materials for 3~4 minutes, then add water at 20%~25% of the total raw material mass and wet mix for 4~5 minutes to form a uniform topsoil slurry. Dry mixing ensures uniform dispersion of solid particles, while wet mixing ensures that the activator fully contacts the highly active raw materials, laying the foundation for the subsequent solidification reaction.
[0028] S4. Curing and shaping, prepared using any of the following methods: Method 1 (Open-air curing): Suitable for small to medium-scale production or scenarios with ample space. Spread the topsoil slurry naturally (10-20cm thick) or compact it, and cure it for 7-14 days at 20-25℃ and 60%-80% humidity, spraying water regularly to maintain moisture and ensure sufficient geopolymer reaction. This method requires no complex equipment, is simple to operate, and is inexpensive. Method 2: (Subcritical Pressure Vessel Curing): Suitable for large-scale industrial production with higher efficiency. The topsoil slurry is fed into a pressure vessel, and nitrogen gas at 0.1~0.2MPa is introduced as a protective gas to prevent oxidation. Curing is carried out for 2~4 hours under subcritical conditions at 120~160℃ and 0.8~1.2MPa (preferably 1MPa). The subcritical environment accelerates the aluminosilicate polymerization reaction, shortens the curing cycle, and makes the geopolymer network denser, resulting in better heavy metal curing. After discharge, the material is naturally cooled to room temperature and then crushed to a particle size ≤5mm for easy subsequent aging and use. S5. Finished Product Aging: Method 1: Geopolymer ecological topsoil is obtained directly after the curing process is completed; Method 2 involves storing the crushed material in the open for 3-7 days to further stabilize the properties of the topsoil, balance the pH, and ultimately form a geopolymer ecological topsoil that meets the requirements.
[0029] Specifically: In S1, if the red mud is Bayer process red mud, add an additional 0.1% to 0.3% of sodium tripolyphosphate dispersant by weight of the red mud, and stir and disperse for 10 to 15 minutes.
[0030] Specifically: In S2, if the pH of the aged red mud-gypsum solidified product is ≥9.0, increase the gypsum content, where the ratio of red mud to gypsum is 5~6:1; if the pH is <7.0, reduce the gypsum content, where the ratio of red mud to gypsum is 9~10:1.
[0031] Specifically: In step S3, if the heavy metal content of the red mud exceeds the standard, 2% to 3% iron powder is added to the solid raw material during the dry mixing stage.
[0032] Specifically: In S3, if the red mud is Bayer process red mud, 3% to 5% bentonite is added to the solid raw material to enhance the adsorption and fixation effect of fluoride ions.
[0033] Specifically: In the second method of S4, nitrogen gas at 0.1~0.2MPa is introduced as a protective gas during the curing process of the pressure vessel to prevent the slurry from oxidizing.
[0034] Specifically, the performance indicators of the imported soil are: pH 6.5~8.5, Cr leaching content ≤0.15mg / L. Leaching concentration ≤ 0.05 mg / L Leaching concentration ≤ 0.05 mg / L Leaching amount ≤1.0mg / L, compressive strength 0.5~2.0MPa, 0.5~5cm agglomerate ratio ≥60%, porosity 30%~40%.
[0035] Specifically, this topsoil is used for improving desertified soil, repairing compacted soil, ecological greening of slopes, or reclamation of mining areas.
[0036] The present invention also provides examples of preparing imported soil according to the method of the present invention: Example 1: Sintering method red mud + open-air curing mode 1. Raw material preparation: Select sintered red mud that has been stored in the red mud dam for 35 days, crush it and pass it through a 10mm sieve, and adjust the moisture content to 18%; desulfurized gypsum aged for 8 days, crushed it and pass it through a 5mm sieve, with a free water content of 4%; the high-activity raw material is a mixture of fly ash and mineral powder in a 2:1 ratio, and the composite activator is a mixture of water glass and quicklime in a 3:1 ratio (water glass modulus 1.1).
[0037] 2. Red mud-gypsum co-curing: Weigh the raw materials according to the mass ratio of red mud:gypsum = 8:1, dry mix for 3 minutes, adjust the moisture content to 18%, and let it age naturally for 10 days, turning it over once every 2 days. The pH after aging is 7.8.
[0038] 3. Geopolymer composite slurry preparation: Weigh the raw materials according to the following mass percentages: 40% red mud-gypsum solidified material, 55% high-activity raw material, and 5% composite activator. Dry mix for 3 minutes, add water at 22% of the total raw material mass, and wet mix for 4 minutes to form the topsoil slurry.
[0039] 4. Curing and shaping: Spread the topsoil slurry into shape (15cm thick) and cure it for 10 days at 23℃ and 75% humidity, spraying water once a day during the period.
[0040] 5. Finished product aging: The finished product is obtained directly after curing. The pH of the topsoil is 7.5, the Cr leaching amount is 0.12 mg / L, the As leaching amount is 0.03 mg / L, the compressive strength is 1.2 MPa, the particle size ratio is 65%, and the porosity is 35%.
[0041] Example 2: Bayer process red mud + subcritical pressure vessel solidification mode 1. Raw material preparation: Bayer red mud stored in the red mud dam for 40 days was selected, crushed and passed through a 10mm sieve, 0.2% sodium tripolyphosphate dispersant was added and stirred for 12 minutes, and the moisture content was adjusted to 17%; phosphogypsum was aged for 9 days, crushed and passed through a 5mm sieve, with a free water content of 3%; the high-activity raw material was a mixture of fly ash and mineral powder in a 2:1 ratio, and the composite activator was a mixture of water glass and quicklime in a 3:1 ratio (water glass modulus 1.3).
[0042] 2. Red mud-gypsum co-curing: Weigh the raw materials according to the mass ratio of red mud:gypsum = 7:1, dry mix for 3 minutes, adjust the moisture content to 17%, and let it age naturally for 12 days, turning it over once every 3 days. The pH after aging is 7.9.
[0043] 3. Geopolymer composite slurry preparation: Weigh the raw materials according to the following mass percentages: 40% red mud-gypsum solidified material, 52% high-activity raw material, 5% composite activator, and 3% bentonite. Dry mix for 4 minutes, add water at 23% of the total raw material mass, and wet mix for 5 minutes to form the topsoil slurry.
[0044] 4. Curing and molding: The imported soil slurry is fed into a pressure vessel, and nitrogen gas of 0.15MPa is introduced. It is cured for 3 hours at a temperature of 140℃ and a pressure of 1MPa. After discharge, it is naturally cooled to room temperature and crushed to a particle size of ≤5mm.
[0045] 5. Finished product aging: After crushing, the soil is piled up in the open air for 5 days to obtain a finished topsoil with a pH of 7.7 and F. - The leaching amount is 0.7 mg / L, the Pb leaching amount is 0.04 mg / L, the compressive strength is 1.5 MPa, the agglomerate ratio is 68%, and the porosity is 38%.
[0046] The scope of protection of this invention is not limited to the above embodiments. Any adjustments made to the raw material ratio, aging time, curing temperature and pressure, and curing conditions within the spirit and principles of this invention, as long as they achieve the harmlessness of red mud and the performance of the imported soil meet the standards, fall within the scope of protection of this invention. For example, the temperature of the subcritical pressure vessel can be adjusted to 120~160℃, the pressure to 0.8~1.2MPa, and the curing time to 2~4 hours, all according to the equipment capacity, to achieve similar effects.
[0047] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various variations or substitutions within the technical scope disclosed in the present invention, and these should all be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.
Claims
1. A method for preparing geopolymer ecological topsoil through synergistic solidification of red mud and gypsum, characterized in that, Includes the following steps: S1. Raw material preparation: Select red mud that has been stockpiled for ≥30 days, including sintered red mud or Bayer process red mud. After crushing, pass it through a 10mm sieve to remove large impurities. Adjust the moisture content to 15%~20%. Select phosphogypsum or desulfurized gypsum, let it age naturally for 7~10 days, crush it, and pass it through a 5mm sieve to control the free water content ≤5%. Select geopolymer composed of highly active raw materials and composite alkaline activators. The highly active raw materials are a mixture of Grade I F type fly ash and S95 grade mineral powder at a mass ratio of 2:
1. The composite alkaline activator is a mixture of water glass and quicklime at a mass ratio of 3:
1. The water glass modulus is 1.0~1.
5. S2. Solidified red mud-gypsum: Weigh the raw materials according to the mass ratio of red mud:gypsum = 6~10:1, dry mix for 3~4 minutes to mix evenly, adjust the moisture content to 15%~20%, and let it age naturally for 7~15 days, turning it over once every 2~3 days during the period to achieve acid-base neutralization and initial solidification of heavy metals. The pH at the end of aging should be controlled at 7.0~8.
5. S3. Geopolymer Composite Slurry Preparation: Weigh the raw materials according to the following mass percentages: 30%~50% red mud-gypsum solidified material, 40%~60% high-activity raw materials of geopolymer system, and 3%~6% composite alkaline activator, with a total mass percentage of 100%. First, dry mix all solid raw materials for 3~4 minutes, then add water at 20%~25% of the total raw material mass, and wet mix for 4~5 minutes to form a uniform topsoil slurry. S4. Curing and shaping, prepared using any of the following methods: Method 1: Spread or compact the topsoil slurry naturally and cure it for 7 to 14 days at 20-25℃ and 60%-80% humidity, spraying water regularly to keep it moist during the period; Method 2: The imported soil slurry is fed into a pressure vessel and solidified for 2 to 4 hours under subcritical conditions of 120~160℃ and 0.8~1.2MPa (preferably 1MPa). After discharge, it is naturally cooled to room temperature and crushed to a particle size ≤5mm. S5. Finished product aging: Method 1: Geopolymer ecological topsoil is obtained directly after curing; Method 2: After crushing, it is piled up in the open air for aging for 3-7 days. After the topsoil properties are stable, geopolymer ecological topsoil is obtained.
2. The method for preparing geopolymer ecological topsoil through synergistic solidification of red mud and gypsum according to claim 1, characterized in that: In step S1, if the red mud is Bayer process red mud, an additional 0.1% to 0.3% of sodium tripolyphosphate dispersant by weight of the red mud is added, and the mixture is stirred and dispersed for 10 to 15 minutes.
3. The method for preparing geopolymer ecological topsoil through synergistic solidification of red mud and gypsum according to claim 1, characterized in that: In S2, if the pH of the aged red mud-gypsum solidified product is ≥9.0, the gypsum content is increased, wherein the ratio of red mud to gypsum is 5~6:1; if the pH is <7.0, the gypsum content is reduced, wherein the ratio of red mud to gypsum is 9~10:
1.
4. The method for preparing geopolymer ecological topsoil through synergistic solidification of red mud and gypsum according to claim 1, characterized in that: In step S3, if the heavy metal content of the red mud exceeds the standard, 2% to 3% iron powder is added to the solid raw material during the dry mixing stage.
5. The method for preparing geopolymer ecological topsoil through synergistic solidification of red mud and gypsum according to claim 1, characterized in that: In step S3, if the red mud is Bayer process red mud, 3% to 5% bentonite is added to the solid raw material to enhance the adsorption and fixation effect of fluoride ions.
6. The method for preparing geopolymer ecological topsoil through synergistic solidification of red mud and gypsum according to claim 1, characterized in that: In the second method of S4, nitrogen gas at 0.1~0.2MPa is introduced as a protective gas during the curing process of the pressure vessel to prevent the slurry from oxidizing.
7. The method for preparing geopolymer ecological topsoil through synergistic solidification of red mud and gypsum according to claim 1, characterized in that: The performance indicators of the imported soil are: pH 6.5~8.5, Cr leaching content ≤0.15mg / L. Leaching concentration ≤ 0.05 mg / L Leaching concentration ≤ 0.05 mg / L Leaching amount ≤1.0mg / L, compressive strength 0.5~2.0MPa, 0.5~5cm agglomerate ratio ≥60%, porosity 30%~40%.
8. A method for preparing geopolymer ecological topsoil through synergistic solidification of red mud and gypsum according to claims 1-7, characterized in that, This topsoil can be used for improving desertified soil, repairing compacted soil, ecological greening of slopes, or reclamation of mining areas.