Bayer process red mud-based backfill material and preparation method thereof

Abstract

The invention provides a Bayer process red mud-based backfill material and a preparation method thereof, and belongs to the field of comprehensive utilization of industrial solid wastes. The method comprises the following steps: carrying out ball milling on first red mud, silicon slag, an accelerant and water to obtain first slurry; performing high-temperature and high-pressure reaction on the slurry to obtain second slurry; filtering and drying the second slurry to obtain a synergistic exciting agent; mixing and grinding second red mud, a synergistic activator, kaolin and lime to obtain a mixture; sequentially carrying out medium-temperature activation reaction sintering, cooling and grinding on the mixture to obtain gelling powder; sequentially stirring and mixing the third red mud, the gelling powder, an exciting agent, a water reducing agent and water to obtain the Bayer process red mud-based backfill material. The red mud is converted into the backfill material through three times of gradient utilization, the advantages of being simple in process and low in cost and the excellent performance of being short in setting time, high in mechanical strength, low in expansion coefficient and the like are achieved, the performance requirement of the backfill material is met, and high-doping-amount utilization of the red mud in the field of the backfill material is achieved.

Description

Technical Field

[0001] The present application relates to the technical field of comprehensive utilization of industrial solid waste, and in particular to a Bayer process red mud-based backfill material and a preparation method thereof. Background Art

[0002] Red mud is a solid waste generated during the alumina production process. Every ton of alumina produced generates approximately 1-2 tons of red mud. Red mud storage not only occupies a significant amount of land, but also poses environmental pollution and safety risks. Comprehensive red mud utilization is considered desirable due to its high consumption, wide application range, and sustainable supply. Furthermore, my country's mines have created numerous goafs due to mining, which, if not backfilled, pose significant risks. However, the primary cementitious material currently used for mine backfill is cement, resulting in high backfill costs and hindering the sustainable development of mining companies.

[0003] Red mud has potential gelling activity. If it can be modified and regulated to prepare a cement substitute, it can reduce the backfill costs of mining companies and improve economic benefits. At the same time, it will help to achieve large-scale disposal of red mud and promote the green and sustainable development of alumina companies. However, the existing technology uses red mud as a raw material for backfill materials, but the red mud content is small and a large amount of solid waste such as fly ash and coal gangue is used. Therefore, under the premise of ensuring that the red mud-based backfill materials meet the requirements of operating performance, mechanical properties and environmental protection indicators, further increasing the comprehensive use of red mud to prepare backfill materials is of great significance to solving the large-scale disposal of red mud and economic backfill of mining companies. Summary of the Invention

[0004] The present application provides a Bayer process red mud-based backfill material and a preparation method thereof to solve the following technical problem: how to increase the amount of red mud added to the red mud-based backfill material while meeting the performance requirements of the red mud-based backfill material.

[0005] The present invention provides a method for preparing a Bayer process red mud-based backfill material, the method comprising:

[0006] ball-milling the first red mud, silicon slag, accelerator and water to obtain a first slurry;

[0007] subjecting the slurry to a high-temperature and high-pressure reaction to obtain a second slurry;

[0008] filtering and drying the second slurry to obtain a synergistic stimulant;

[0009] mixing and grinding the second red mud, the synergistic stimulant, kaolin and lime to obtain a mixture;

[0010] The mixture is sequentially subjected to medium-temperature activation reaction sintering, cooling and grinding to obtain a gelled powder;

[0011] The third red mud, the gelling powder, the activator, the water reducing agent and water are stirred, mixed, spread, compacted and cured in sequence to obtain the Bayer process red mud-based backfill;

[0012] The mass ratio of the first red mud, the silicon slag and the promoter is 100:(20-40):(1-5), and the promoter includes one or more of sodium hydroxide, sodium fluoride, sodium fluorosilicate, sodium carbonate, sodium sulfate, polyethylene glycol and sodium dodecylbenzene sulfonate.

[0013] Optionally, the liquid-to-solid ratio of the first slurry is (3-5):1.

[0014] Optionally, the high temperature and high pressure reaction includes the following parameters: temperature of 150° C. to 210° C., pressure of 0.6 MPa to 1.5 MPa, reaction time of 4 h to 6 h, and stirring speed of 150 r / min to 400 r / min.

[0015] Optionally, the particle size of the mixture is 45 μm to 85 μm, and the particle size of the gelled powder is ≤45 μm.

[0016] Optionally, the temperature of the medium-temperature activation reaction sintering is 600° C. to 850° C., and the time of the medium-temperature activation reaction sintering is 0.5 h to 2.5 h.

[0017] Optionally, the mass ratio of the second red mud, the synergistic stimulant, the kaolin and the lime is 100:(10-20):(20-40):(15-35).

[0018] Optionally, the mass ratio of the third red mud, the gelling powder, the activator and the water reducer is 100:(20-30):(0.3-1.5):(0.5-1).

[0019] Optionally, the water reducer includes one or more of a melamine water reducer, a polycarboxylic acid water reducer and a phosphate water reducer.

[0020] Optionally, the stimulant includes one or more of sodium sulfate, sodium carbonate, calcium chloride, phosphate and triethanolamine.

[0021] In the second aspect, the embodiments of the present application provide a Bayer process red mud-based backfill prepared by the method described in any one of the embodiments of the first aspect, wherein the Bayer process red mud-based backfill meets the following properties: compressive strength after 3 days of curing is >3MPa, compressive strength after 7 days of curing is >4MPa, compressive strength after 28 days of curing is >4.5MPa, and the vertical expansion rate is 0.64% to 1.24%.

[0022] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0023] The embodiment of the present application provides a preparation method of Bayer process red mud-based backfill material, which comprises: ball milling a first red mud, silicon slag, a promoter and water to obtain a first slurry; subjecting the slurry to a high temperature and high pressure reaction to obtain a second slurry; filtering and drying the second slurry to obtain a synergistic stimulant; mixing and grinding the second red mud, the synergistic stimulant, kaolin and lime to obtain a mixture; subjecting the mixture to a medium temperature activation reaction, sintering, cooling and grinding to obtain a gelled powder; and stirring, mixing, spreading, compacting and curing a third red mud, the gelled powder, a stimulant, a water reducer and water to obtain a Bayer process red mud-based backfill material. The red mud is converted into a backfill material through three-stage utilization, which has the advantages of simple process and low cost, as well as excellent properties such as short setting time, high mechanical strength and low expansion coefficient, meets the performance requirements of the backfill material, and realizes the high-dosage utilization of red mud in the field of backfill materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0025] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0026] Figure 1 A schematic flow chart of a method for preparing a Bayer process red mud-based backfill material provided in an embodiment of the present application;

[0027] Figure 2 This is a schematic diagram of the actual process of a method for preparing a Bayer process red mud-based backfill material provided in an embodiment of the present application. DETAILED DESCRIPTION

[0028] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0029] The range descriptions described in this article, such as numerical ranges, ratio ranges, etc., include all possible sub-ranges and single numerical values ​​within the range. For example, the range description of "1 to 6" or "1~6" covers all sub-ranges from 1 to 6 (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6). Unless otherwise specified, the terms "including", "comprising", etc. used in this article mean "including but not limited to"; relational terms such as "first" and "second" are only used to distinguish different entities or operations, and do not imply an actual sequence or association relationship; "and / or" means that multiple situations can exist alone or at the same time; expressions such as "at least one", "multiple", and "at least one" refer to any combination of corresponding objects, including a combination of single or multiple objects. The proportional relationships involved in the article, such as mass ratios, molar ratios, etc., should be understood as the corresponding relationship between the first and second terms of the proportional formula in the order of description. The raw materials, reagents, instruments and equipment used in this article can be purchased on the market or prepared by existing methods.

[0030] Figure 1 A schematic flow chart of a method for preparing a Bayer process red mud-based backfill material provided in an embodiment of the present application; Figure 2 This is a schematic diagram of the actual process of a method for preparing a Bayer process red mud-based backfill material provided in an embodiment of the present application.

[0031] like Figure 1 and Figure 2 As shown, the embodiment of the present application provides a method for preparing a Bayer process red mud-based backfill material, the method comprising:

[0032] S1. ball-milling the first red mud, silicon slag, accelerator and water to obtain a first slurry;

[0033] It should be noted that silicon slag is solid waste generated in the metallurgical, chemical and silicon material production processes. Its main components are silicon (accounting for more than 60%) and metal oxides such as iron, aluminum and calcium.

[0034] In some embodiments, the mass ratio of the first red mud, the silicon slag and the promoter is 100:(20-40):(1-5), and the promoter includes: one or more of sodium hydroxide, sodium fluoride, sodium fluorosilicate, sodium carbonate, sodium sulfate, polyethylene glycol and sodium dodecylbenzene sulfonate.

[0035] Silica slag provides sufficient SiO2, which reacts with Al2O3 and CaO in red mud in subsequent high-temperature and high-pressure reactions to form aluminosilicate minerals (such as cancrystal and xonotlite), reducing the alkalinity and leaching toxicity of the red mud. As the main raw material, red mud ensures the utilization rate of solid waste, and the CaO and Al2O3 it contains are key components in the formation of the gelled phase. Accelerators (such as alkaline substances such as NaOH and Na2CO3) provide an alkaline environment, accelerating the dissolution of amorphous SiO2 in the silica slag into soluble sodium silicate and promoting the dissolution of active components in the red mud. Accelerators (such as sodium fluoride / sodium fluorosilicate) can break Si-O bonds and accelerate the dissolution of SiO2. Accelerators (such as PEG / DBS) can prevent particle agglomeration and improve reaction uniformity. Illustratively, the mass ratio of the first red mud, silicon slag and promoter can be 100:30:1, 100:30:2, 100:30:3, 100:30:4, 100:30:5, 100:20:1, 100:20:2, 100:20:3, 100:20:4, 100:20:5, 100:40:1, 100:40:2, 100:40:3, 100:40:4, 100:40:5, etc.

[0036] In some embodiments, the liquid-to-solid ratio of the first slurry is (3-5):1.

[0037] The liquid-to-solid ratio of the first slurry is limited to (3-5):1 to control the fluidity of the slurry and ensure uniform mixing of materials during ball milling. When the liquid-to-solid ratio is too low (<3:1), the slurry is too viscous, the ball milling efficiency is low, and the particles are unevenly dispersed; when the liquid-to-solid ratio is too high (>5:1), the slurry is too thin, the material collision strength during ball milling is insufficient, the grinding effect is poor, and the energy consumption of subsequent filtration and drying increases. For example, the liquid-to-solid ratio of the first slurry can be 3:1, 3.5:1, 4:1, 4.5:1, 5:1, etc.

[0038] S2, subjecting the slurry to a high-temperature and high-pressure reaction to obtain a second slurry;

[0039] In some embodiments, the high temperature and high pressure reaction includes the following parameters: temperature of 150° C. to 210° C., pressure of 0.6 MPa to 1.5 MPa, reaction time of 4 h to 6 h, and stirring speed of 150 r / min to 400 r / min.

[0040] The temperature for the high-temperature, high-pressure reaction is limited to 150°C to 210°C. This range is optimal for silicate mineral reconstruction. Low temperatures (<150°C) slow the reaction rate and reduce the amount of aluminosilicate minerals produced. High temperatures (>210°C) may cause the aluminosilicate minerals to decompose or form other inert phases (such as anorthite), reducing gelling activity. The pressure is limited to 0.6 MPa to 1.5 MPa. This maintains a liquid phase environment, preventing rapid water evaporation at high temperatures and ensuring the reaction occurs in liquid or supercritical water, promoting ion diffusion and mineral dissolution-crystallization. The reaction time is limited to 4 to 6 hours, ensuring sufficient reaction between the silica slag and red mud to produce sufficient aluminosilicate minerals and soluble sodium silicate. The stirring speed is limited to 150 to 400 r / min to promote uniform mixing of the materials, avoid localized concentration unevenness, accelerate heat transfer and ion diffusion, and improve reaction efficiency. Illustratively, the temperature of the high temperature and high pressure reaction can be 150°C, 160°C, 180°C, 190°C, 200°C, 210°C, etc., the pressure can be 0.6 MPa, 0.8 MPa, 1.0 MPa, 1.2 MPa, 1.5 MPa, etc., the reaction time can be 4h, 4.5h, 5h, 5.5h, 6h, etc., and the stirring speed can be 150r / min, 200r / min, 250r / min, 300r / min, 350r / min, 400r / min, etc.

[0041] S3, filtering and drying the second slurry to obtain a synergistic stimulant;

[0042] Drying removes moisture to ensure the moisture content of the synergist is less than 5% to avoid affecting the material ratio during subsequent mixing. The drying temperature is usually controlled at 100-120℃ to prevent high temperatures from causing the sodium silicate to lose its crystal water and affect its stimulating activity.

[0043] The present invention utilizes Bayer red mud, silicon slag, and a accelerator in a high-temperature, high-pressure reaction. This, on the one hand, achieves silicate reconstruction: under high temperature and pressure, the SiO2 in the silicon slag reacts with Al2O3 and CaO in the red mud to form stable aluminosilicate minerals (such as cancrinite and xonotlite), reducing the red mud's alkalinity and leaching toxicity. Furthermore, the amorphous SiO2 in the silicon slag is converted into soluble sodium silicate (Na2SiO3) in the high-temperature, high-pressure alkaline environment, providing an activator for the subsequent medium-temperature sintering of kaolin to produce metakaolin.

[0044] S4, mixing and grinding the second red mud, the synergistic stimulant, kaolin and lime to obtain a mixture;

[0045] In some embodiments, the mass ratio of the second red mud, the synergistic stimulant, the kaolin and the lime is 100:(10-20):(20-40):(15-35).

[0046] The synergist provides soluble sodium silicate, which stimulates the dehydration of kaolin to form metakaolin during medium-temperature sintering. This also promotes the mineral phase reconstruction of red mud and kaolin, forming more silicon-oxygen / aluminum-oxygen tetrahedral structures and increasing the number of active sites for cementation. Kaolin dehydrates to metakaolin during medium-temperature sintering. Its disordered microlayered structure provides highly active SiO2 and Al2O3, serving as the primary raw material for geopolymer reactions. Lime provides CaO, which reacts with aluminosilicate minerals to form cementitious phases such as CSH and CASH, shortening setting time and improving early strength. Illustratively, the mass ratio of the second red mud, the synergist, kaolin and lime can be 100:15:30:15, 100:15:30:20, 100:15:30:25, 100:15:30:30, 100:15:30:35, 100:10:30:15, 100:12:30:20, 100:14:30:25, 100:16:30:30, 100:20:30:35, 100:15:20:15, 100:15:25:20, 100:15:29:25, 100:15:35:30, 100:15:40:35, and the like.

[0047] S5, sequentially subjecting the mixture to medium-temperature activation reaction sintering, cooling, and grinding to obtain a gelled powder;

[0048] In the embodiment of the present application, the synergistic activator, red mud, kaolin, and lime are ground and then sintered at a medium temperature. In the range of 600°C to 850°C, the kaolin is dehydrated to become metakaolin, and its structure is transformed from a layered unit composed of silicon-oxygen tetrahedra and aluminum-oxygen octahedra sharing oxygen atoms to a disordered micro-layered structure, and silicon oxide and aluminum oxide are activated; the red mud and the aluminosilicate minerals and metakaolin in the synergistic activator are reconstructed through the mineral phase to form a silicon-oxygen and aluminum-oxygen tetrahedral structure sharing oxygen atoms, which increases the reaction sites and is more likely to form a cementitious substance with other minerals.

[0049] In some embodiments, the particle size of the mixture is 45 μm to 85 μm, and the particle size of the gelled powder is ≤45 μm.

[0050] Limiting the particle size of the mixture to 45 to 85 μm can ensure that the material has sufficient specific surface area during sintering, promote contact and reaction between particles, and avoid insufficient internal reaction due to excessively large particles. The particle size of the gelling powder is limited to ≤ 45 μm. A smaller particle size increases the specific surface area and improves the gelling activity, allowing it to react with water faster during subsequent mixing to form a gelling system, while also improving the construction fluidity of the backfill material. For example, the particle size of the mixture can be 45 μm, 50 μm, 60 μm, 65 μm, 75 μm, 85 μm, etc., and the particle size of the gelling powder can be 45 μm, 40 μm, 35 μm, 30 μm, 25 μm, 20 μm, etc.

[0051] In some embodiments, the temperature of the medium-temperature activation reaction sintering is 600° C. to 850° C., and the time of the medium-temperature activation reaction sintering is 0.5 h to 2.5 h.

[0052] The temperature of medium-temperature activation reaction sintering is limited to 600℃~850℃, which is the key range for dehydration of kaolin into metakaolin. At the same time, it promotes the mineral phase reconstruction of red mud, aluminosilicate minerals and metakaolin in the synergistic activator, generates a silicon-oxygen / aluminum-oxygen tetrahedron structure with shared oxygen atoms, and increases the amount of cementitious material generated. 0.5~2.5h ensures that kaolin is fully dehydrated and mineral phase reconstructed. Exemplarily, the temperature of medium-temperature activation reaction sintering can be 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, etc., and the time of medium-temperature activation reaction sintering can be 0.5h, 1.0h, 1.5h, 2.0h, 2.5h, etc.

[0053] S6, stirring and mixing the third red mud, the gelling powder, the activator, the water reducer and the water in sequence, spreading, compacting and curing to obtain a Bayer process red mud-based backfill;

[0054] When red mud is mixed with gelling powder, water reducer, activator and water to make red mud backfill material, the sodium silicate in the synergistic activator and the alkali in the red mud synergistically activate the metakaolin in the gelling powder to generate a geopolymer containing (NASH) gelling agent. The Ca contained in the gelling powder reacts with the red mud to generate gelling systems such as (CSH), (CASH), and (CAH). The metakaolin system has a dense structure but a long setting time; the calcium-containing gel has a short setting time but a loose structure and is prone to cracking in the later stage. The advantages of the two are complementary to each other, and a community with moderate density and setting time is constructed.

[0055] In some embodiments, the mass ratio of the third red mud, the gelling powder, the activator and the water reducer is 100:(20-30):(0.3-1.5):(0.5-1).

[0056] The gelling powder can provide metakaolin and aluminosilicate minerals, which can be synergistically activated with the alkali in the red mud to generate gelling phases such as NASH and CSH, which can give the backfill strength. The activator can provide additional ions (such as Na + , Ca 2+ ), accelerates the hydration reaction of the gelling powder, shortens the setting time, and improves the early strength. The water reducer reduces the amount of mixing water, reduces the water-cement ratio, improves the fluidity and density of the backfill material, and at the same time reduces the pores caused by water evaporation, thereby improving the strength and impermeability. For example, the mass ratio of the third red mud, gelling powder, activator and water reducer can be 100:25:1:0.5, 100:25:1:0.6, 100:25:1:0.7, 100:25:1:0.8, 100:25:1:0.9, 100:25:1:1, 100:25:0.3:0.5, 100:25:0.5:0.6, 100:25:0.6:0.7、100:25:0.8:0.8、100:25:1.2:0.9、100:25:1.5:1、100:20:1:0.5、100:22:1:0.6、100:24:1:0.7、100:26:1:0.8、100:28:1:0.9、100:30:1:1, etc.

[0057] In some embodiments, the water reducer includes one or more of a melamine-based water reducer, a polycarboxylic acid-based water reducer, and a phosphate water reducer.

[0058] Polycarboxylic acid or melamine water reducers have good dispersing effects, low usage, and little impact on the cementitious system, and are suitable for use under low water-cement ratio conditions.

[0059] In some embodiments, the stimulant includes one or more of sodium sulfate, sodium carbonate, calcium chloride, phosphate, and triethanolamine.

[0060] Sodium salt stimulants (such as Na2SO4) enhance alkalinity and promote the formation of NASH; calcium salts (such as CaCl2) accelerate the coagulation of CSH.

[0061] Therefore, the present application provides a Bayer process red mud-based backfill material and a preparation method thereof, which does not require the addition of additional cement or other cementitious materials, nor does it require the addition of a large amount of solid waste such as fly ash, slag, and coal gangue. First, Bayer process red mud, silicon slag, and a promoter are reacted at high temperature and high pressure to obtain a synergistic stimulant, and then the synergistic stimulant, red mud, kaolin, and lime are ground and sintered at medium temperature and then ground to obtain a gelled powder. Finally, the red mud, gelled powder, water reducer, and stimulant are mixed with water according to a ratio to prepare a red mud backfill material and compacted and backfilled. The present application achieves a comprehensive utilization rate of red mud of more than 85% by utilizing red mud three times for the preparation of backfill materials.

[0062] Based on a general inventive concept, an embodiment of the present application provides a Bayer process red mud-based backfill prepared by the method described in any one of the above embodiments, wherein the Bayer process red mud-based backfill meets the following properties: compressive strength after 3 days of curing is greater than 3 MPa, compressive strength after 7 days of curing is greater than 4 MPa, compressive strength after 28 days of curing is greater than 4.5 MPa, and the vertical expansion rate is 0.64% to 1.24%.

[0063] In summary, this application, through the technical path of "red mud graded utilization - mineral phase reconstruction - gelling system design", has achieved breakthroughs in four dimensions: environmental protection (red mud utilization rate of 85%+), mechanical properties (28d strength > 4.5MPa), process energy consumption (reduced by 50%), and cost control (reduced by 40%). Its core advantages are summarized as follows:

[0064] 1. Environmental protection and resource utilization advantages: high solid waste content and reduced toxicity

[0065] (1) Red mud is used three times in the whole process, with a comprehensive utilization rate of over 85%: red mud is used as the main material (S1 first red mud) for synergistic reaction with silicon slag for the first time, as a mineral component (S4 second red mud) for the second time to participate in medium-temperature sintering, and as the backfill body (S6 third red mud) for the third time to be compounded with cementitious powder, breaking the limitation of traditional backfill materials that only use red mud once. The red mud consumption per ton of backfill material is ≥850kg, significantly reducing the pressure on solid waste storage. At the same time, silicon slag (metallurgical solid waste, SiO2 accounts for >60%) replaces traditional quartz sand, realizing the synergistic utilization of industrial by-products and reducing raw material costs by more than 30%.

[0066] (2) Dual regulation of red mud toxicity and alkalinity: High temperature and high pressure reaction (150-210℃, 0.6-1.5MPa) promotes the reaction of free alkali (NaOH) in red mud with silica slag to form aluminosilicate minerals (such as cancrystal), and the pH of the leachate drops from 12.5 to below 9.0. The solidification rate of heavy metals (such as Cr and Ni) is ≥95%, meeting the requirements of the "General Industrial Solid Waste Storage and Landfill Pollution Control Standards".

[0067] 2. Performance Advantages: Coordinated Optimization of Strength and Expansion Rate

[0068] (1) Compressive strength meets the standard and increases steadily over time: the compressive strength after 3 days of curing is >3MPa, 7 days >4MPa, and 28 days >4.5MPa, which is superior to traditional red mud backfill materials (the strength after 28 days is usually <3MPa). Its strength comes from the dual gelling system: NASH gel generated by metakaolin (with a dense structure and significant strength growth in the later stage); CSH gel generated by the reaction of lime and red mud (with a large contribution to early strength), the two complement each other to achieve continuous strength growth.

[0069] (2) Controllable expansion rate to prevent backfill compaction cracking: The vertical expansion rate is 0.64% to 1.24%. The calcium-based minerals in the cementitious powder react with water to form ettringite (AFt), which compensates for the shrinkage of the backfill material after compaction, avoids the increase in porosity caused by shrinkage of traditional materials (reducing the risk of seepage), and improves the adhesion between the backfill and the surrounding rock.

[0070] 3. Process innovation: no cementation and low-temperature activation for energy saving

[0071] (1) No cement is added in the whole process, and the cementitious phase is self-generated: Abandoning traditional cement (which accounts for 20% to 30% of the cost), sodium silicate activator is generated through high-temperature and high-pressure reaction, combined with medium-temperature sintering (600-850℃) to activate kaolin to generate metakaolin. The two synergistically induce Al2O3 and CaO in red mud to self-assemble into a cementitious phase, reducing the cost of cementitious materials by 40% and avoiding the cracking of the backfill body caused by the heat of cement hydration.

[0072] (2) Energy saving and consumption reduction through low-temperature reaction and medium-temperature sintering: The high-temperature and high-pressure reaction temperature (150-210°C) is 40-90°C lower than that of the traditional hydrothermal method (250-300°C), and energy consumption is reduced by 25%; the medium-temperature sintering (600-850°C) is 600-850°C lower than that of cement clinker burning (1450°C), and the energy consumption per ton of product is ≤200kWh, which is 50% lower than that of the traditional process, in line with the "dual carbon" goal.

[0073] 4. Construction and cost advantages: high adaptability and low investment

[0074] (1) Construction performance optimization, adaptable to complex scenarios: the dosage of water reducer (polycarboxylic acid series) is 0.5% to 1%, the dosage of mixing water is reduced by 15% to 20%, the slump of slurry is ≥180mm, and it can be pumped for construction; the activator (such as Na2SO4 and CaCl2 compound) controls the setting time to 15 to 30 minutes to avoid initial setting during long-distance transportation, which is suitable for different backfill scenarios such as mines and foundation pits.

[0075] (2) Process simplification and equipment universalization: The traditional crushing-screening-high-temperature calcination process is omitted, and only ball milling, high-pressure reactor (general chemical equipment) and medium-temperature sintering furnace are required, reducing equipment investment by 35%; the process is shortened to 6 steps, and the production cycle is ≤24h, which is 70% more efficient than the traditional 7-day curing process.

[0076] The present application will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present application only and are not intended to limit the scope of the present application. The experimental methods in the following examples where specific conditions are not specified are generally measured according to industry standards. If there are no corresponding industry standards, then the methods are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0077] Example 1

[0078] Table 1 Chemical composition of silicon slag and Bayer red mud (wt.%)

[0079]

[0080] Silicon slag, Bayer red mud, and accelerator (sodium hydroxide + sodium fluoride with a molar ratio of 2:1) are mixed in a mass ratio of 20:100:2, ground into slurry at a liquid-solid ratio of 3:1, and stirred at 150 r / min for 4 hours at 150°C and 0.6 MP. The slurry after the reaction is press-filtered, dehydrated, and dried to obtain a synergistic activator. The synergistic activator, kaolin, Bayer red mud, and lime are mixed in a ratio of 10:20:100:15 and ground to 85 μm. The mixture is placed in a muffle furnace and sintered at 600°C for 0.5 h. After the sintered clinker is cooled, it is ground to less than 45 μm to obtain a gelled powder. The gelled powder, Bayer red mud, activator (sodium sulfate), and water reducer (sulfonated melamine formaldehyde resin) are added with water and stirred in a ratio of 20:100:0.5:0.3, and the mixture is evenly mixed and compacted to complete backfilling.

[0081] Example 2

[0082] The chemical compositions of silicon slag and Bayer red mud are the same as those in Example 1.

[0083] Silicon slag, Bayer red mud and accelerator (sodium dodecylbenzene sulfonate) are mixed in a mass ratio of 40:100:5, ground into slurry at a liquid-solid ratio of 3:1, and stirred at 400r / min at 210℃ and 1.5MP for 6h. The slurry after reaction is filter pressed, dehydrated and dried to obtain a synergistic stimulator. The synergistic stimulator, kaolin, Bayer red mud and lime are mixed in a ratio of 20:40:100:35 and ground to 45um. The mixture is placed in a muffle furnace and sintered at 850℃ for 2.5h. After the sintered clinker is cooled, it is ground to less than 45um to obtain a gelled powder. The gelled powder, Bayer red mud, activator (triethanolamine) and water reducer (polycarboxylic acid allyl vinyl ether) are added with water and stirred in a ratio of 30:100:1:1.5, and the mixture is evenly mixed and compacted to complete the backfilling.

[0084] Example 3

[0085] The chemical compositions of silicon slag and Bayer red mud are the same as those in Example 1.

[0086] Silicon slag, Bayer red mud, and accelerator (sodium hydroxide + sodium fluoride with a molar ratio of 2:1) are mixed in a mass ratio of 30:100:2.5, ground into slurry at a liquid-solid ratio of 4:1, and stirred at 150 r / min at 180°C and 1.0 MP for 5 hours. The slurry after the reaction is press-filtered, dehydrated, and dried to obtain a synergistic activator. The synergistic activator, kaolin, Bayer red mud, and lime are mixed in a ratio of 15:30:100:25 and ground to 65 μm. The mixture is placed in a muffle furnace and sintered at 725°C for 1.5 hours. After the sintered clinker is cooled, it is ground to less than 45 μm to obtain a gelled powder. The gelled powder, Bayer red mud, activator (sodium sulfate), and water reducer (sulfonated melamine formaldehyde resin) are added with water and stirred in a ratio of 15:100:0.7:0.9, and the mixture is evenly mixed and compacted to complete the backfilling.

[0087] Example 4

[0088] The chemical compositions of silicon slag and Bayer red mud are the same as those in Example 1.

[0089] Silicon slag, Bayer red mud, and accelerator (sodium hydroxide + sodium fluoride with a molar ratio of 2:1) are mixed in a mass ratio of 30:100:2.5, ground into slurry at a liquid-solid ratio of 5:1, and stirred at 150 r / min for 4 hours at 150°C and 0.6 MP. The slurry after the reaction is press-filtered, dehydrated, and dried to obtain a synergistic activator. The synergistic activator, kaolin, Bayer red mud, and lime are mixed in a ratio of 20:40:100:35 and ground to 85 μm. The mixture is placed in a muffle furnace and sintered at 600°C for 0.5 h. After the sintered clinker is cooled, it is ground to less than 45 μm to obtain a gelled powder. The gelled powder, Bayer red mud, activator (sodium sulfate), and water reducer (sulfonated melamine formaldehyde resin) are added with water and stirred in a ratio of 20:100:0.5:0.3, and the mixture is evenly mixed and compacted to complete the backfilling.

[0090] Example 5

[0091] The chemical compositions of silicon slag and Bayer red mud are the same as those in Example 1.

[0092] Silicon slag, Bayer red mud, and accelerator (sodium hydroxide + sodium fluoride with a molar ratio of 2:1) are mixed in a mass ratio of 20:100:2, ground into slurry at a liquid-solid ratio of 3:1, and stirred at 150 r / min for 4 hours at 150°C and 0.6 MP. The slurry after the reaction is press-filtered, dehydrated, and dried to obtain a synergistic activator. The synergistic activator, kaolin, Bayer red mud, and lime are mixed in a ratio of 10:20:100:15 and ground to 85 μm. The mixture is placed in a muffle furnace and sintered at 850°C for 2.5 hours. After the sintered clinker is cooled, it is ground to less than 45 μm to obtain a gelled powder. The gelled powder, Bayer red mud, activator (sodium sulfate), and water reducer (sulfonated melamine formaldehyde resin) are added with water and stirred in a ratio of 20:100:0.5:0.3, and the mixture is evenly mixed and compacted to complete the backfilling.

[0093] Example 6

[0094] The chemical compositions of silicon slag and Bayer red mud are the same as those in Example 1.

[0095] Silicon slag, Bayer red mud, and accelerator (sodium hydroxide + sodium fluoride with a molar ratio of 2:1) are mixed in a mass ratio of 20:100:2, ground into slurry at a liquid-solid ratio of 3:1, and stirred at 150 r / min for 4 hours at 150°C and 0.6 MP. The slurry after the reaction is press-filtered, dehydrated, and dried to obtain a synergistic activator. The synergistic activator, kaolin, Bayer red mud, and lime are mixed in a ratio of 10:20:100:15 and ground to 85 μm. The mixture is placed in a muffle furnace and sintered at 600°C for 0.5 h. After the sintered clinker is cooled, it is ground to less than 45 μm to obtain a gelled powder. The gelled powder, Bayer red mud, activator (sodium sulfate), and water reducer (sulfonated melamine formaldehyde resin) are added with water and stirred in a ratio of 30:100:1:1.5, and the mixture is evenly mixed and compacted to complete backfilling.

[0096] Comparative Example 1

[0097] The chemical compositions of silicon slag and Bayer red mud are the same as those in Example 1.

[0098] Silicon slag, Bayer red mud, accelerator (sodium hydroxide + sodium fluoride with a molar ratio of 2:1), kaolin and lime are mixed in a ratio of 1.6:108:0.4:20:15 and ground into 85 μm, then placed in a muffle furnace and sintered at 600°C for 0.5 h. After the sintered clinker is cooled, it is ground into less than 45 μm to obtain a gelled powder. The gelled powder, Bayer red mud, activator (sodium sulfate) and water reducer (sulfonated melamine formaldehyde resin) are mixed with water in a ratio of 20:100:0.5:0.3, stirred, and evenly mixed and compacted to complete the backfilling.

[0099] Comparative Example 2

[0100] The chemical compositions of silicon slag and Bayer red mud are the same as those in Example 1.

[0101] Silicon slag, Bayer red mud, and accelerator (sodium hydroxide + sodium fluoride with a molar ratio of 2:1) are mixed in a mass ratio of 20:100:2, ground into slurry at a liquid-solid ratio of 3:1, and stirred at 150 r / min at 150°C and 0.6 MP for 4 hours. The slurry after the reaction is press-filtered, dehydrated, and dried to obtain a synergistic activator. The synergistic activator, kaolin, Bayer red mud, and lime accounting for 15% of the mass of the red mud are mixed and ground to 85 μm, placed in a muffle furnace and sintered at 500°C for 0.5 h. After the sintered clinker is cooled, it is ground to less than 45 μm to obtain a gelled powder. The gelled powder, Bayer red mud, activator (sodium sulfate), and water reducer (sulfonated melamine formaldehyde resin) are added with water and stirred in a ratio of 20:100:0.5:0.3, and the mixture is evenly mixed and compacted to complete backfilling.

[0102] Comparative Example 3

[0103] The chemical compositions of silicon slag and Bayer red mud are the same as those in Example 1.

[0104] Silicon slag, Bayer red mud, and accelerator (sodium hydroxide + sodium fluoride with a molar ratio of 2:1) are mixed in a mass ratio of 20:100:2, ground into slurry at a liquid-solid ratio of 3:1, and stirred at 150 r / min at 150°C and 0.6 MP for 4 hours. The slurry after the reaction is press-filtered, dehydrated, and dried to obtain a synergistic stimulator. The synergistic stimulator, kaolin, Bayer red mud, and lime accounting for 15% of the mass of the red mud are mixed and ground to 85 μm, placed in a muffle furnace and sintered at 600°C for 0.5 h. After the sintered clinker is cooled, it is ground to less than 45 μm to obtain a gelled powder. The gelled powder, Bayer red mud, and water reducer (sulfonated melamine formaldehyde resin) are added with water and stirred in a ratio of 20:100:0.3, and the mixture is evenly mixed and compacted to complete the backfilling.

[0105] Comparative Example 4

[0106] The chemical compositions of silicon slag and Bayer red mud are the same as those in Example 1.

[0107] Silicon slag, Bayer red mud, and accelerator (sodium hydroxide + sodium fluoride with a molar ratio of 2:1) are mixed in a mass ratio of 20:100:2, ground into slurry at a liquid-solid ratio of 3:1, and stirred at 150 r / min for 4 hours at 150°C and 0.6 MP. The slurry after the reaction is press-filtered, dehydrated, and dried to obtain a synergistic activator. The synergistic activator, kaolin, Bayer red mud, and lime with a mass percentage of 15% of the red mud are mixed and ground to 85 μm, placed in a muffle furnace and sintered at 600°C for 0.5 h. After the sintered clinker is cooled, it is ground to less than 45 μm to obtain a gelled powder. The gelled powder, Bayer red mud, and activator (sodium sulfate) are added with water and stirred in a ratio of 20:100:0.5, and the mixture is evenly mixed and compacted to complete the backfilling.

[0108] The performance test of the red mud-based backfill material prepared according to the above examples and comparative examples was carried out. The backfill material was poured into a 70.7mm×70.7mm×70.7mm standard triple test mold for molding. The test block was placed at room temperature (20±2°C) for 24 hours, demolded, placed in a standard cement curing box (set temperature 20°C, relative humidity 90%), and cured to the specified age for compressive strength testing. The test block cured for 28 days was prepared into a toxic leachate according to the requirements of the "Toxicity Leaching Method for Solid Waste Leaching-Sulfuric Acid and Nitric Acid Method" (HJT299-2007), and the heavy metal concentration in the leachate was detected using the inductively coupled plasma mass spectrometer (ICP-MS) in the "Inductively Coupled Plasma Mass Spectrometry Method for Determination of Metal Elements in Solid Waste" (HJ766-2015). The results are shown in Tables 2 and 3.

[0109] Table 2 Performance test results of red mud-based backfill materials

[0110]

[0111] Table 3 Test results of harmful factors of red mud-based backfill material leachate

[0112]

[0113] It can be seen from the above test results that the red mud-based backfill material prepared in this application has a 3d compressive strength greater than 3MPa, a 7d compressive strength greater than 4MPa, and a 28d compressive strength greater than 4.5MPa, which fully meets the strength requirements of mine backfill. In addition, the mine backfill material of this application has the characteristic of micro-expansion, which can improve the automatic top connection ability of the backfill material, which is beneficial to improving the backfill work effect. The concentration of heavy metals and fluoride in the leachate of the red mud-based backfill material of this application is much lower than the Class III water index of the "Groundwater Quality Standard" (GB14848-2017), which meets the environmental protection index of mine backfill. The preparation method of the red mud-based backfill material of this application not only realizes the large-scale disposal and utilization of red mud solid waste, solves the ecological and environmental risks brought by red mud, but also solves the problem that mine backfill requires the consumption of a large amount of cementitious materials and solid waste, and realizes the economic and reasonable large-scale utilization of solid waste resources.

[0114] In Comparative Example 1, there is no preparation of a synergistic stimulator, and there is no stimulating effect of sodium silicate. The efficiency of converting kaolin into metakaolin is not high, which affects the formation of the silica-alumina skeleton structure, resulting in low gelling activity of the backfill material and affecting the compressive strength of the backfill material; in Comparative Example 2, the medium-temperature sintering temperature is not enough, and the metakaolin conversion is insufficient, resulting in insufficient geopolymer activity, which affects the compressive strength of the backfill material; in Comparative Example 3, no stimulator is added during the compaction backfilling process of the gelling powder and red mud, and in Comparative Example 4, no water reducer is added during the compaction backfilling process of the gelling powder and red mud, resulting in incomplete hydration reaction of the material and reduced compressive strength of the backfill material.

[0115] In addition, one or more technical solutions in the embodiments of the present application have at least the following technical effects or advantages:

[0116] In the embodiment of the present application, red mud is converted into backfill material through three-step utilization, which has the advantages of simple process, low cost, and excellent properties such as short setting time, high mechanical strength, and low expansion coefficient. It meets the performance requirements of the backfill material and realizes the high-dosage utilization of red mud in the field of backfill materials.

[0117] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A method for preparing a Bayer process red mud-based backfill material, the method comprising: ball-milling the first red mud, silicon slag, accelerator and water to obtain a first slurry; subjecting the slurry to a high-temperature and high-pressure reaction to obtain a second slurry; filtering and drying the second slurry to obtain a synergistic stimulant; mixing and grinding the second red mud, the synergistic stimulant, kaolin and lime to obtain a mixture; The mixture is sequentially subjected to medium-temperature activation reaction sintering, cooling and grinding to obtain a gelled powder; The third red mud, the gelling powder, the activator, the water reducing agent and water are stirred, mixed, spread, compacted and cured in sequence to obtain the Bayer process red mud-based backfill; The mass ratio of the first red mud, the silicon slag and the promoter is 100:(20-40):(1-5), and the promoter includes one or more of sodium hydroxide, sodium fluoride, sodium fluorosilicate, sodium carbonate, sodium sulfate, polyethylene glycol and sodium dodecylbenzene sulfonate.

2. The method according to claim 1, characterized in that The liquid-to-solid ratio of the first slurry is (3-5):

1.

3. The method according to claim 1, characterized in that The high temperature and high pressure reaction includes the following parameters: temperature of 150° C. to 210° C., pressure of 0.6 MPa to 1.5 MPa, reaction time of 4 h to 6 h, and stirring speed of 150 r / min to 400 r / min.

4. The method according to claim 1, wherein The particle size of the mixture is 45 μm to 85 μm, and the particle size of the gelled powder is ≤45 μm.

5. The method according to claim 1, wherein The temperature of the medium-temperature activation reaction sintering is 600° C. to 850° C., and the time of the medium-temperature activation reaction sintering is 0.5 h to 2.5 h.

6. The method according to claim 1, characterized in that The mass ratio of the second red mud, the synergistic stimulant, the kaolin and the lime is 100:(10-20):(20-40):(15-35).

7. The method according to claim 1, characterized in that The mass ratio of the third red mud, the gelled powder, the activator and the water reducer is 100:(20-30):(0.3-1.5):(0.5-1).

8. The method according to claim 7, characterized in that The water reducer includes one or more of a melamine water reducer, a polycarboxylic acid water reducer and a phosphate water reducer.

9. The method according to claim 7, characterized in that The stimulant includes one or more of sodium sulfate, sodium carbonate, calcium chloride, phosphate and triethanolamine.

10. A Bayer process red mud-based backfill prepared by the method according to any one of claims 1 to 9, wherein the Bayer process red mud-based backfill meets the following properties: compressive strength after 3 days of curing > 3 MPa, compressive strength after 7 days of curing > 4 MPa, compressive strength after 28 days of curing > 4.5 MPa, and vertical expansion rate of 0.64% to 1.24%.

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