Geopolymer-based rare earth tailing curing material and preparation method thereof

Abstract

The invention relates to the technical field of industrial solid waste resource utilization, and particularly discloses a geopolymer-based rare earth tailing curing material and a preparation method thereof, the geopolymer-based rare earth tailing curing material comprises 8%-15% of mineral powder, 20%-25% of fly ash, 20%-35% of rare earth tailings, 0.5%-3% of fiber, 0.5%-1% of nano oxide, 15%-20% of an alkaline activator and 15%-36% of water. The geopolymer-based rare earth tailing curing material provided by the invention has the advantages of excellent mechanical properties, good fluidity, appropriate curing time, environmental friendliness and the like, and is suitable for ecological restoration of mines, treatment of tailings ponds and preparation of road base materials; according to the invention, industrial wastes (such as fly ash, slag and rare earth tailings) are used, so that resource recycling is realized; the carbon emission is low in the production and use process of the material, and the sustainable development requirement is met.

Description

Technical Field

[0001] This application relates to the technical field of industrial solid waste resource utilization, and particularly to a geopolymer-based rare earth tailing solidification material and a preparation method thereof. Background Art

[0002] Rare earth tailings are the main solid waste after rare earth ore processing, and their stacking causes problems such as land occupation and heavy metal pollution. The current rare earth tailing solidification technology faces systematic technical bottlenecks, which are prominently manifested as the dual imbalance between material system design and environmental adaptability. Traditional solidification methods mostly adopt a single solid waste treatment mode, and fail to construct a synergistic mechanism between bulk industrial solid wastes such as fly ash and slag and rare earth tailings, resulting in that the solidification system can neither give full play to the complementary effects of different solid waste components nor achieve the organic unity of high solid sealing performance and low environmental load. At the same time, due to insufficient regulation of the microstructure of existing solidified bodies, there are generally defects in crack resistance: under the action of wet-dry alternation or freeze-thaw cycles, microcracks inside the material continuously expand and cause structural disintegration, seriously restricting the reliability of engineering applications. The superposition effect of the short board of this material durability and environmental pollution risk makes the development of a new solidification system with a three-dimensional network densification structure, multi-scale crack suppression ability and long-term heavy metal stabilization function the key path to break through the technical bottleneck of rare earth tailing treatment, which has an urgent practical significance for promoting mine ecological restoration and solid waste resource utilization. Summary of the Invention

[0003] In order to improve the deficiencies of the current rare earth tailing solidification technology, this application provides a geopolymer-based rare earth tailing solidification material and a preparation method thereof.

[0004] A geopolymer-based rare earth tailing solidification material provided by this application adopts the following technical scheme: A geopolymer-based rare earth tailing solidification material, by mass percentage, comprises the following components: 8%-15% mineral powder, 20%-25% fly ash, 20%-35% rare earth tailings, 0.5%-3% fiber, 0.5%-1% nano-oxide, 15%-20% alkaline activator and 15%-36% water.

[0005] The mineral powder provides active SiO2 and Al2O3 components, and the fly ash improves the workability of the mixture by virtue of its spherical particle characteristics, while the trace rare earth elements remaining in the rare earth tailings can play a nucleation effect during the reaction process. A binary activator system composed of sodium silicate and sodium hydroxide is used to prepare a geopolymer with a three-dimensional network structure by regulating the 4- polycondensation reaction of [SiO4] 5- and [AlO4]. Incorporating fibers can significantly improve the mechanical properties of the composite material, and its bridging effect effectively inhibits the expansion of microcracks.

[0006] The rare earth elements remaining in rare earth tailings (such as La 3+ , Ce 3+ ) are adsorbed on the gel surface through coordination, acting as mineralizers to promote the orderly arrangement of oligomeric silicon-aluminum units, thus enhancing the compressive strength. In the material system, different particle gradations have a significant impact on strength. The coarse particles (>30μm) in rare earth tailings serve as the skeleton support, reducing the hardening shrinkage rate and providing a stable support for the overall structure, avoiding early damage due to stress concentration and laying the foundation for strength. The fine particles (<10μm) fill the pores formed by the coarse particles, making the structure more dense, enhancing the interaction force between particles and improving the overall strength. The unreacted quartz particles in tailings with different particle gradations form a "mechanical interlock" structure at the interface, enhancing the interfacial bonding strength with fibers.

[0007] Rare earth tailings are rich in amorphous SiO2 (content 30 - 45%) and Al2O3 (15 - 25%). Under the action of alkaline activators, they are gradually dissociated, releasing soluble silicon-aluminum substances (such as [SiO(OH)3] - , [Al(OH)4] - ), which participate in the geopolymerization reaction to form a three-dimensional [-Si-O-Al-O-] network skeleton. Compared with the pure slag system, the slow-release characteristics of tailings (the dissolution rate is reduced by 20 - 30%) can effectively delay the polycondensation reaction process, extend the initial setting time, and provide a wider time window for construction operations.

[0008] Furthermore, the alkaline activator is a solution prepared by compounding water glass with a modulus of 0.6 - 1.2 and sodium hydroxide.

[0009] The modulus of the alkaline activator (i.e., the molar ratio of SiO2 to Na2O in water glass) is a key parameter controlling the geopolymer reaction kinetics and microstructure. When the modulus is large, the SiO2 content is high, the solution viscosity is large, resulting in a reduced dissociation rate of silicon-aluminum raw materials and a slow polycondensation reaction, and it is easy to form a loose network structure with limited mechanical properties; when the modulus is small, the alkaline environment is strong, accelerating the dissolution and polycondensation reaction of silicon-aluminum components, and promoting the formation of a dense three-dimensional network structure.

[0010] The low-modulus activator (when the modulus is 0.6 - 1.2) reduces the solution viscosity and, combined with the "ball bearing effect" of fly ash, enables the slurry to meet the pumping requirements. At the same time, the ratio of free [SiO4] 4- and [AlO4] 5- units in the activator reaches the optimal balance, which is beneficial to the formation of a high cross-linking degree -Si-O-Al-O- skeleton, reducing pore defects, improving the material density and mechanical strength, and overcoming the defects of poor fluidity or insufficient early strength of traditional materials.

[0011] In addition, the low-modulus activator forms a coordination interaction with trace rare earth elements in the rare earth tailings, acting as a "mineralizer" to promote the orderly arrangement of the gel phase. Further, the low-modulus activator can delay the dissolution rate of heavy metal ions in the rare earth tailings and improve the heavy metal fixation rate through the dual mechanisms of chemical bonding and physical adsorption.

[0012] Furthermore, the liquid-solid ratio of all components is 0.3 - 0.5. The liquid-solid ratio = mass of liquid / mass of solid, where the mass of liquid is the sum of the mass of the alkaline activator solution and water, and the mass of solid is the sum of the mass of mineral powder, fly ash, rare earth tailings, fiber, and nano-oxide.

[0013] When the liquid-solid ratio is low, the viscosity of the slurry is high and the fluidity is poor, which may lead to insufficient filling or residual bubbles, reducing the density. When the liquid-solid ratio is high, the slurry is too thin, with good fluidity but prone to segregation or sedimentation, resulting in uneven distribution of components and a decrease in strength. When the liquid-solid ratio is within the range of 0.3 - 0.5, it balances the fluidity and density, ensuring that the slurry evenly fills the mold and forms a dense structure after vibration.

[0014] On the other hand, the liquid-solid ratio directly affects the contact efficiency between the alkaline activator and the solid components. When the liquid-solid ratio is too low, the activator cannot fully wet the solid particles, and the dissolution and polycondensation reactions of the aluminosilicate components are limited. When the liquid-solid ratio is too high, it dilutes the reaction concentration and delays the formation of the gel network. When the liquid-solid ratio is within the appropriate range, it can quickly dissociate the aluminosilicate components and avoid excessive dilution, achieving an optimal balance between the polycondensation reaction rate and the crosslinking degree of the three-dimensional network structure.

[0015] A suitable liquid-solid ratio combined with a specific activator modulus can significantly reduce the free water content, inhibit drying shrinkage, avoid the expansion of microcracks, and improve durability. The synergistic effect of the liquid-solid ratio and the fiber / nano-oxide enables the material to still have high fluidity at a low liquid-solid ratio, overcoming the defect of poor fluidity of traditional low liquid-solid ratio materials.

[0016] In this application, through the combination of a low modulus (0.6 - 1.2) and a low liquid-solid ratio (0.3 - 0.5), the reaction rate and the rheology of the slurry reach the best match, and the high activity of the activator and the appropriate fluidity jointly promote the formation of a dense gel network.

[0017] Furthermore, the fiber is selected from at least one of polypropylene fiber, glass fiber, carbon fiber, polyvinyl alcohol fiber, aramid fiber, or cellulose fiber.

[0018] Furthermore, the nano-oxide is selected from at least one of nano-aluminum oxide, nano-silicon dioxide, nano-titanium oxide, nano-zinc oxide, or nano-iron oxide.

[0019] Furthermore, the length of the fiber is 2 - 10 mm, and the diameter is 10 - 50 μm.

[0020] Furthermore, the particle size of the nano-oxide is 10 - 100 nm, and it is a hydrophilic or surface-modified particle.

[0021] Introducing the synergistic reinforcement effect of fibers and nano-oxides into the geopolymer material system, the mechanism of compressive strength improvement can be explained from two aspects: multi-scale structure regulation and energy dissipation mechanism. When the geopolymer matrix is damaged under compression, nano-oxide particles first play a role at the microscale: their high specific surface area and surface hydroxyl activity enable them to tightly adsorb on the pore surface of the geopolymer gel, effectively reducing 10 - 100 nm micropore defects through the dual mechanisms of "physical filling - chemical bonding". At the same time, metal ions on the surface of the nano-particles form bonds with [SiO4] in the geopolymer, enhancing the cross-linking degree of the gel network. When the load further increases to the critical value, the macro-mesoscopic reinforcement effect of the fibers begins to appear. The interface between the fibers and the geopolymer matrix forms a strong bond through van der Waals forces and mechanical interlocking, and its bridging effect deflects the crack propagation path. This multi-scale synergistic reinforcement mechanism is ultimately reflected in a significant increase in compressive strength. 4- This multi-scale synergistic reinforcement mechanism is ultimately reflected in a significant increase in compressive strength.

[0022] The present application also provides a preparation method of a rare earth tailing solidification material based on geopolymer, comprising the following steps: Prepare an alkaline activator: Gradually add solid sodium hydroxide to the water glass solution to adjust the modulus to 0.6 - 1.2, mix well and then let it stand. Stir and mix the alkaline activator with water to obtain a liquid mixture; Stir and mix ore powder, fly ash, rare earth tailings, fibers and nano-oxides to obtain a solid mixture; Add the liquid mixture to the solid mixture, stir and mix, then pour it into a mold and vibrate and compact it, and place it in a constant temperature environment for curing.

[0023] Furthermore, in the step of preparing the alkaline activator, the standing temperature is room temperature and the standing time is not less than 24 hours.

[0024] The present application also provides an application of a rare earth tailing solidification material based on geopolymer in mine backfilling.

[0025] Due to its excellent mechanical properties, good fluidity and appropriate setting time, the rare earth tailing solidification material based on geopolymer provided by the present application has sufficient compressive strength to support the overlying strata and prevent the collapse of the goaf; has a certain fluidity to be transported to the goaf through pipelines or boreholes and evenly fill the voids; has reasonable initial and final setting times, which can not only ensure the construction efficiency but also quickly form strength, and is suitable for mine backfilling.

[0026] In summary, the present application includes the following beneficial technical effects: The rare earth tailings solidification material based on geopolymers provided by this application has excellent mechanical properties, good fluidity, appropriate solidification time, environmental friendliness, etc., and can be used for mine ecological restoration, tailings pond treatment, and the preparation of road base materials. It needs to have sufficient compressive strength to support the overlying rock strata and prevent the collapse of the goaf; have a certain fluidity to be transported to the goaf through pipelines or boreholes and evenly fill the voids; have reasonable initial setting and final setting times, which can not only ensure the construction efficiency but also quickly form strength; use industrial wastes (such as fly ash, slag, rare earth tailings, etc.) as backfill materials to achieve resource recycling; have low carbon emissions during the production and use of the materials, meeting the requirements of sustainable development. Replacing traditional silica-aluminum raw materials (such as metakaolin) with rare earth tailings can reduce the raw material cost of geopolymer production by about 35%, and at the same time reduce the land occupation and ecological restoration costs caused by tailings stacking, realizing the multi-objective coordination of "solid waste value-added - pollution control - engineering applicability", providing an innovative solution for the sustainable development of mining areas. Detailed implementation mode

[0027] Example 1 The following method is used to prepare a rare earth tailings solidification material based on geopolymers: Prepare an alkaline activator: According to the ratio of adding 51.1 g of sodium hydroxide to 100 g of water glass with a modulus of 2.4 in portions, add the solid sodium hydroxide to the water glass solution to adjust the modulus to 0.6. After mixing evenly, let it stand at room temperature for 24 hours.

[0028] Stir and mix 40 g of the alkaline activator with 40 g of water to obtain a liquid mixture; stir and mix 24 g of mineral powder, 40 g of fly ash, 52 g of rare earth tailings, 2 g of polypropylene fiber (fiber length is 5 mm, diameter is 20 μm), and 2 g of nano-aluminum oxide (particle size is 50 nm) to obtain a solid mixture; add the liquid mixture to the solid mixture, stir and mix, then pour it into a mold and vibrate and compact it, and cure it in a constant temperature environment of 35°C.

[0029] Example 2 The difference from Example 1 is that in Example 2, the modulus of the alkaline activator is 1.2.

[0030] Comparative example 1 The difference from Example 1 is that in Comparative example 1, the modulus of the alkaline activator is 0.5.

[0031] Comparative example 2 The difference from Example 1 is that in Comparative example 2, the modulus of the alkaline activator is 1.3.

[0032] Comparative example 3 The difference from Example 1 is that in Comparative example 3, the addition amount of mineral powder is 10 g.

[0033] Comparative Example 4 The difference from Example 1 is that polypropylene fibers and nano-aluminum oxide are not added in Comparative Example 4.

[0034] The geopolymer-based rare earth tailings solidification materials obtained in Examples 1-2 and Comparative Examples 1-4 were tested for compressive strength, slump, initial setting time, and porosity. Among them, the compressive strength was tested in accordance with GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)", the slump was tested in accordance with GB / T 50080-2016 "Standard Test Method for Properties of Ordinary Concrete Mixtures", the initial setting time was tested in accordance with GB / T 1346-2011 "Test Method for Standard Consistency Water Requirement, Setting Time and Soundness of Cement", and the porosity was tested in accordance with GB / T 50082-2009 "Standard Test Method for Long-Term Performance and Durability of Ordinary Concrete".

[0035] The test results are as follows:

[0036] The test results show that selecting an appropriate modulus of the activator can not only provide a sufficient alkaline environment to accelerate the dissolution of siliceous and aluminous components (slag powder, fly ash), but also release an appropriate amount of SiO4 4- and AlO4 5- units, promote the rapid polycondensation of the three-dimensional network structure, so as to improve the compressive strength and reduce the porosity. With the ball-bearing effect of fly ash, the appropriate liquid-solid ratio, and the synergistic effect with fibers / nano-oxides, the cured material has both high strength and good fluidity, improving the contradiction between "strength-fluidity" in traditional materials, and the obtained material can be used for mine backfilling.

[0037] The above are all the preferred embodiments of this application, and the protection scope of this application is not limited accordingly. Therefore, all equivalent changes made according to the structure, shape, and principle of this application should be covered within the protection scope of this application.

Claims

1. A geopolymer-based solidification material for rare earth tailings, characterized in that: By mass percentage, it includes the following components: 8% - 15% mineral powder, 20% - 25% fly ash, 20% - 35% rare earth tailings, 0.5% - 3% fiber, 0.5% - 1% nano - oxide, 15% - 20% alkaline activator and 15% - 36% water.

2. The geopolymer-based rare earth tailings solidification material according to claim 1, characterized in that: The alkaline activator is a solution prepared by compounding sodium silicate with a modulus of 0.6 - 1.2 and sodium hydroxide.

3. The geopolymer-based rare earth tailings solidification material according to claim 1, characterized in that: The liquid - solid ratio of all components is 0.3 - 0.5, and the liquid - solid ratio = liquid mass / solid mass, where the liquid mass is the sum of the masses of the alkaline activator solution and water, and the solid mass is the sum of the masses of the mineral powder, fly ash, rare earth tailings, fiber and nano - oxide.

4. The geopolymer-based rare earth tailings solidification material according to claim 1, wherein: The fiber is selected from at least one of polypropylene fiber, glass fiber, carbon fiber, polyvinyl alcohol fiber, aramid fiber or cellulose fiber.

5. A geopolymer-based rare earth tailing solidification material according to claim 1, characterized in that: The nano - oxide is selected from at least one of nano - aluminum oxide, nano - silicon dioxide, nano - titanium oxide, nano - zinc oxide or nano - iron oxide.

6. The geopolymer-based rare earth tailing solidification material according to claim 1, wherein: The length of the fiber is 2 - 10 mm, and the diameter is 10 - 50 μm.

7. A geopolymer-based rare earth tailings solidification material according to claim 1, characterized in that: The particle size of the nano - oxide is 10 - 100 nm, and it is a hydrophilic or surface - modified particle.

8. A preparation method of a rare earth tailing solidification material based on geopolymer, which is used to prepare a rare earth tailing solidification material based on geopolymer according to any one of claims 1-7, and is characterized in that: It includes the following steps: Prepare the alkaline activator: Gradually add solid sodium hydroxide to the sodium silicate solution to adjust the modulus to 0.6 - 1.2, mix well and then let it stand. Stir - mix the alkaline activator and water to obtain a liquid mixture; stir - mix the mineral powder, fly ash, rare earth tailings, fiber and nano - oxide to obtain a solid mixture; add the liquid mixture to the solid mixture, stir - mix, pour it into a mold, vibrate and compact it, and place it in a constant - temperature environment for curing.

9. The preparation method of a rare earth tailing solidification material based on geopolymers according to claim 8, characterized in that: In the step of preparing the alkaline activator, the standing temperature is room temperature, and the standing time is not less than 24 hours.

10. Application of a rare - earth - tailing solidification material based on geopolymers according to any one of claims 1 - 7 in mine backfill.

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