A subgrade water-stable layer prepared by synergistically activating and pressing fine mud with lithium slag and a preparation method thereof

Abstract

The present invention provides a subgrade water-stable layer prepared by synergistically activating and pressing fine mud with lithium slag. By weight, the subgrade water-stable layer is prepared from the following raw materials: 15-20 parts of lithium slag, 20-30 parts of activated pressed fine mud, 45-55 parts of graded aggregate, 0-5 parts of regulator, and 9-13 parts of water; the activated pressed fine mud is obtained by mixing the by-product tail mud of spodumene concentrate and metakaolin, followed by high-temperature alkali activation and grinding. After activation treatment, the pressed fine mud forms new active reaction gel components such as calcium silicate, sodium silicate, and aluminosilicate. The present invention also provides a method for preparing a subgrade water-stable layer by using a large amount of lithium slag and pressed fine mud. Using the method of the present invention to prepare the subgrade water-stable layer can stably solidify sulfates, prevent the phenomenon of long hair and salting out, improve the activation of the pressed fine mud, realize the valuable utilization of lithium slag and pressed fine mud in the cement-based water-stable layer, prepare low-carbon engineering building materials, and solve the pollution problem and resource utilization problem of solid waste.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid waste treatment and resource utilization, and particularly relates to a method for synergistically preparing a roadbed water-stable layer by activating and stimulating fine slime from spodumene beneficiation pressing and then combining with lithium slag. Background Art

[0002] The lithium mica to lithium carbonate industry produces a large amount of by-product pressing fine slime and lithium slag, which have problems such as large scale quantity, serious stacking pollution, and high sulfur and alkali content. The content of sulfate ions in lithium slag is relatively high, making it difficult to develop and utilize on a large scale. A large amount of long-term stacking leads to problems such as the dissolution and leakage of harmful ions, which seriously endanger the surrounding ecological safety and cause pollution of soil and water flow and damage to the ecological environment. Under the strict environmental protection pressure, it severely restricts the orderly development of the lithium battery industry and the local economic development. Therefore, vigorously developing and utilizing lithium slag and by-product tail mud has important economic value and ecological and environmental protection effects.

[0003] With the rapid development of urbanization and new rural construction, as well as the need for local ecological civilization construction, it is an inevitable demand to develop low-carbon and green ecological building materials. Therefore, for road engineering paving projects with low strength requirements, it is more inclined to use solid waste materials to replace natural sand and soil and cement for preparation. However, various types of construction waste have different physical and chemical characteristics and hazards. Lithium slag and by-product pressing fine slime have the characteristics of polysilicate-aluminate minerals. After spodumene is leached by sulfate roasting, a large amount of lithium slag is produced. Therefore, lithium slag has the characteristic of relatively high sulfate content. Using the traditional strong alkali chemical activation method can improve the gelling activity of silicate-aluminate minerals, but it is prone to problems such as sulfate crystallization and hair growth and the expansion and cracking of hardened components.

[0004] What is disclosed in CN114031341A is a scheme for preparing non-fired and non-steamed solidified bricks using lithium slag and fine slime from spodumene beneficiation pressing. Traditional alkali activation components (such as water glass, sodium sulfate, etc.) are used to activate the activity of lithium slag. In view of the problem that lithium slag is rich in sulfate, a carbon curing method is adopted to reduce the problem of efflorescence (i.e., sulfate crystallization) on the surface of non-fired and non-steamed solidified bricks. The limitation of this scheme is that it improves the curing requirements, increases the curing cost, and it is difficult to effectively solidify the sulfate inside the solidified bricks.

[0005] In order to further effectively improve the gelling property of lithium slag products and fundamentally solve the environmental pollution caused by sulfate crystallization and hair growth and the problems such as the expansion and cracking of hardened components, it is necessary to propose a new method for applying lithium slag and pressing fine slime to prepare building materials. Summary of the Invention

[0006] To better solve the above problems, the main measures adopted in the present invention include: adjusting the mixing ratio of lithium slag and pressed sludge used as raw materials simultaneously, appropriately reducing the dosage of lithium slag and increasing the dosage of pressed sludge, and at the same time controlling the content of sulfur trioxide in the incorporated lithium slag, that is, controlling the content of sulfate radical in the raw materials from the source; on this basis, using a calcium-containing alkali activator to activate the pressed sludge with a large dosage under high-temperature conditions to fully improve the hydration reaction activity of the silicate in the pressed sludge. By adopting the above measures, the present invention can finally stably solidify sulfates, prevent the phenomenon of hair growth and salting out, realize the valuable utilization of lithium slag and pressed sludge in the cement-based water-stable layer, prepare low-carbon engineering building materials, and solve the pollution problem and resource utilization problem of solid waste.

[0007] Based on the above ideas, the present invention adopts the following technical solutions:

[0008] First, a roadbed water-stable layer prepared by synergistically activating pressed sludge with lithium slag is provided. Calculated by weight, the roadbed water-stable layer is prepared from the following raw materials: 15-20 parts of lithium slag, 20-30 parts of activated pressed sludge, 45-55 parts of graded aggregate, 0-5 parts of regulator, and 9-13 parts of water; preferably, it is prepared from the following raw materials: 15-18 parts of lithium slag, 20-26 parts of activated pressed sludge, 45-55 parts of graded aggregate, 2-4 parts of regulator, and 9-10 parts of water.

[0009] In the roadbed water-stable layer of the present invention, the lithium slag is the tail slag obtained by extracting lithium from lepidolite by the sulfate roasting process. Specifically, it is the leaching residue remaining after the lepidolite concentrate powder is mixed evenly with sulfate and fluorine-fixing agent, and then subjected to roasting - grinding - leaching - filtration. As Figure 1 shown, the main phases in the lithium slag are wollastonite, hemihydrate gypsum, quartz, fluorite, and albite. The main chemical components and contents of the lithium slag are: SiO2 content of 28-47%, Al2O3 content of 16-22%, CaO content of 11-14%, SO3 content of 15-20%, and Na2O and K2O content of 1-12%, showing the characteristics of high sulfur and high alkali. The SO3 in the lithium slag mainly exists in the form of hemihydrate gypsum and sodium sulfate, and Na2O and K2O mainly exist in the form of feldspar minerals. Wollastonite is a high-sulfate product (Na,Ca) 4-8 [AlSiO4]6(SO4) 1-2 .

[0010] In the preferred roadbed water-stable layer of the present invention, the specific surface area of the lithium slag is 100-500m 2 / kg; the further preferred lithium slag is a coarse slag with a specific surface area of 200-300m 2 / kg and a fine slag with a specific surface area of 300-500m 2A mixture of fine slag at / kg; in the more preferably lithium slag, the mixing ratio of the coarse slag to the fine slag is 6:2 to 2:6, more preferably 5:3 to 2:5.

[0011] In the subgrade water-stable layer of the present invention, the activated pressed fine mud is obtained by mixing the by-product tail mud of selected lepidolite concentrate and metakaolin and then subjecting it to calcium-containing alkali activation and grinding at high temperature. After the activation treatment, the pressed fine mud forms new active reaction gel components such as calcium silicate, sodium silicate and aluminosilicate.

[0012] The by-product tail mud of the selected lepidolite concentrate is characterized by quartz, albite and mica as the main minerals, and its main chemical components and contents are: SiO2 content 68 - 72%, Al2O3 content 16 - 18%, CaO content 1 - 3%, Na2O and K2O content 7 - 10%, having the characteristics of high silicon and aluminum and low calcium.

[0013] In the preferably subgrade water-stable layer of the present invention, the activation step of the activated pressed fine mud is: by weight, mixing 70 - 77 parts of the by-product tail mud of selected lepidolite concentrate and 15 - 20 parts of metakaolin evenly to obtain a solid mixture, preparing a suspension of 5 - 10 parts of calcium hydroxide and 3 - 5 parts of sodium hydroxide, mixing it evenly with the solid mixture, heating to 400 - 600 °C, keeping warm for 90 min, then cooling and grinding.

[0014] In the further preferably subgrade water-stable layer of the present invention, the specific surface area of the activated pressed fine mud is 400 - 700 m 2 / kg.

[0015] In the preferably subgrade water-stable layer of the present invention, the particle size of the graded aggregate is 0.075 - 31.5 mm.

[0016] In the subgrade water-stable layer of the present invention, the regulator can be any one or a mixture of two of a water reducer or a curing agent; the water reducer is a polycarboxylic acid water reducer, and the curing agent is one of cement or mineral powder.

[0017] On this basis, the present invention also provides a method for preparing a subgrade water-stable layer by using a large amount of lithium slag and pressed fine mud, including the following steps:

[0018] (1) By weight, mixing 70 - 77 parts of the by-product tail mud of selected lepidolite concentrate and 15 - 20 parts of metakaolin evenly to obtain a solid mixture, preparing a suspension of 5 - 10 parts of calcium hydroxide and 3 - 5 parts of sodium hydroxide, mixing it evenly with the solid mixture, heating to 400 - 600 °C, keeping warm for 90 min, then cooling and grinding to obtain activated pressed fine mud containing new phases such as calcium silicate, calcium aluminosilicate, aluminosilicate minerals, etc.;

[0019] (2) Mix 15-20 parts by weight of lithium slag and 20-30 parts of the activated pressed fine mud obtained in (1), stir well, and then mix with 45-55 parts of graded aggregate, 0-5 parts of regulator and 9-13 parts of water, and stir strongly to make the slurry and lithium slag completely wrap around the aggregate to obtain a mixture.

[0020] (3) Use the mixture obtained in (2) to lay the roadbed to obtain a uniform roadbed water-stable layer structure.

[0021] In the method for preparing the roadbed water-stable layer according to the present invention, in (1), the selected lithium mica concentrate by-product tail mud has quartz, albite and mica as the main mineral characteristics, and its main chemical components and contents are: SiO2 content 68-72%, Al2O3 content 16-18%, CaO content 1-3%, Na2O and K2O content 7-10%, with high silicon-aluminum and low activity characteristics.

[0022] In the method for preparing the roadbed water-stable layer by using a large amount of lithium slag and pressed fine mud according to the present invention, in (2), the lithium slag is the tail slag obtained by extracting lithium from lithium mica by the sulfate roasting process. Specifically, it is the leaching residue remaining after the lithium mica concentrate powder is mixed with sulfate and fluorine-fixing agent, and then roasted, ground, leached and filtered. As Figure 1 shown, the main phases in the lithium slag are nosean, hemihydrate gypsum, quartz, fluorite and albite. The main chemical components and contents of the lithium slag are: SiO2 content 28-47%, Al2O3 content 16-22%, CaO content 11-14%, SO3 content 15-20%, Na2O and K2O content 1-12%, with high sulfur and high alkali characteristics. The SO3 in the lithium slag mainly exists in the form of hemihydrate gypsum, and Na2O and K2O mainly exist in the form of feldspar minerals. Nosean is a high-sulfate product (Na,Ca) 4-8 [AlSiO4]6(SO4) 1-2 .

[0023] In the preferred method for preparing the roadbed water-stable layer according to the present invention, in (2), the specific surface area of the lithium slag is 100-500m 2 / kg; further preferably, in (2), the lithium slag is a mixture of coarse slag with a specific surface area of 200-300m 2 / kg and fine slag with a specific surface area of 300-500m 2 / kg; even more preferably, in (2), in the lithium slag, the mixing ratio of the coarse slag to the fine slag is 6:2 to 2:6, and more preferably 5:3 to 2:5.

[0024] In the further preferred method for preparing the roadbed water-stable layer according to the present invention, in (1), the grinding is to grind the cooled activated pressed fine mud to a specific surface area of 400-700m 2 / kg.

[0025] In the preferred method for preparing the subgrade water-stable layer of the present invention, the particle size of the graded aggregate described in (2) is controlled to be 0.075 - 31.5 mm.

[0026] In the method for preparing the subgrade water-stable layer of the present invention, the regulator described in (2) can be any one or a mixture of two of a water reducer or a curing agent; the water reducer is a polycarboxylic acid water reducer, and the curing agent is one of cement or mineral powder.

[0027] In the preferred method for preparing the subgrade water-stable layer of the present invention, it further includes: (4) covering the subgrade water-stable layer laid in (3) with cotton binding cloth and then watering in time, the watering frequency is not less than 4 times a day, and the curing time is not less than 7 days.

[0028] Compared with the prior art, by adopting the above technical solution, the beneficial effects that can be obtained by the present invention include:

[0029] 1. By formula design, the sulfate content in the water-stable layer mixture is controlled, the generation of Na2SO4·10H2O caused by alkali activation is reduced, and the salting-out phenomenon is controlled.

[0030] In the prior art, when high-sulfur and high-alkali lithium slag is used in large amounts for building material preparation, the sulfate it is rich in also enters the raw material mixture in large amounts. When conventional alkali activators such as water glass and sodium hydroxide are used to activate lithium slag, a large amount of sulfate in the raw materials will precipitate in the form of sulfate to generate Na2SO4·10H2O, resulting in the phenomenon of crystal precipitation and hair growth on the surface of building materials. By adjusting the mixing ratio of lithium slag and pressed fine mud, the designed mixing ratio of lithium slag rich in sulfate is reduced, and instead, a large amount of tantalum-niobium ore dressing lithium mica concentrate by-product tail mud, that is, pressed fine mud, is used in large amounts. Since the pressed fine mud basically does not contain sulfate, the amount of SO3 or sulfate introduced into the raw materials is controlled at a relatively low level from the source in the present invention. Therefore, less Na2SO4·10H2O is generated during the alkali activation of the raw materials for the subgrade water-stable layer of the present invention.

[0031] 2. Using a calcium-containing alkali activator to activate the pressed fine mud at high temperature can provide a calcium source while increasing the number of active silicon-aluminum-oxygen bonds, generating new biological phases such as calcium silicate, and improving the hydration reaction activity of the raw materials and the strength of the product.

[0032] Although the pressed fine mud used in large amounts in the present invention does not introduce a large amount of sulfate radicals, it is still an inert material. After direct use or treatment according to the conventional alkali activation method, its hydration reaction activity of silicate is insufficient, and the strength of the prepared roadbed water-stabilized layer is relatively low. However, the pressed fine mud also has the characteristics of high silicon and aluminum. The present invention makes full use of this characteristic and adopts a specific activation treatment method, including using a mixed suspension mainly composed of calcium hydroxide as an alkali activator, and uniformly mixing the mixture of the pressed fine mud and metakaolin, and performing high-temperature heat preservation treatment at a specific temperature, which can activate the high-silicon-aluminum minerals in the pressed fine mud to generate active silicon-aluminum bonds. The active silicon-aluminum bonds are re-polymerized to form a geopolymer precursor with hydraulic function. After adding water and stirring for curing, C(N)-S-A-H gel can be formed, and at the same time, new phases such as calcium silicate, calcium aluminosilicate, and silicon-aluminum minerals are generated (see Figure 2 ), thereby improving the hydration reaction activity of the low-activity pressed fine mud of silicate and further promoting the stability and solidification of the water-stabilized layer. After the pressed fine mud is activated, the crystallinity of mica and albite is reduced, and the alkaline activator and the active silicon-aluminum phase generate new mineral structures such as calcium silicate, kyanite, and calcium aluminosilicate. In addition, the alkali activator mainly composed of calcium hydroxide can more greatly limit the generation and crystallization hair growth phenomenon of Na2SO4·10H2O, so that more sulfate radicals in the raw materials are converted into gypsum and ettringite, further improving the strength of the water-stabilized layer.

[0033] 3. The lithium slag in the present invention can be adjusted and optimized for the particle gradation of the water-stabilized material and the pore structure after being mixed with coarse and fine particles. The hemihydrate gypsum component in the lithium slag gradually dissolves and generates dihydrate gypsum after adding water, and the hydration reaction of the dihydrate gypsum colloid can increase the hardening process of the water-stabilized material. After adding the curing agent cement or mineral powder, the gypsum, as a sulfate, can promote the formation of the early hydration product ettringite, further increasing the early strength of the water-stabilized layer. The 7-day and 28-day activity indexes of the fine lithium slag can reach 90%.

[0034] 4. The present invention uses the mixture of lithium slag and activated pressed fine mud to prepare the water-stabilized layer, which can consume a large amount of solid waste by-products in the lithium carbonate industry, reduce stacking and environmental pollution, and effectively ensure the green and sustainable development of the lithium battery industry.

[0035] In summary, by adjusting the lithium slag content, controlling the lithium slag gradation, changing the type and excitation method of the alkali activator, the present invention not only solves the problem of crystallization hair growth on the material surface, but also realizes the synergistic effect of the calcium source alkali activation of the pressed fine mud and the hydration hardening microstructure, so that the hydrated product such as dihydrate gypsum, ettringite, hydrated calcium silicate gel, and aluminosilicate can be effectively generated from the formula raw material mixture, making the 7-day compressive strength of the water-stabilized material greater than 4.5 Mpa and the 28-day compressive strength greater than 6.9 Mpa. Brief Description of the Drawings

[0036] Figure 1Characterizes the mineral properties of lepidolite slag.

[0037] Figure 2 Characterizes the phase transformation of the activated pressing sludge excited by the activator containing calcium hydroxide in the present invention, where the activated pressing sludges 1 and 2 correspond to the activated pressing sludges in Example 1 and Example 2 respectively.

[0038] Figure 3 Is a photograph of the appearance of the water-stable layer test block prepared in Example 1 of the present invention.

[0039] Figure 4 Is a photograph of the appearance of the water-stable layer test block prepared in Example 2 of the present invention.

[0040] Figure 5 Characterizes the new biological phase of the activated pressing sludge excited by sodium hydroxide in Comparative Example 1.

[0041] Figure 6 Reflects the salting-out phenomenon of the high-amount lithium slag water-stable material excited by sodium hydroxide in Comparative Example 1.

[0042] Figure 7 Is the analysis result of the salting-out and hair-growing phase of the test block in Comparative Example 1.

[0043] Figure 8 Reflects the phenomenon of expansion and cracking caused by high sulfate in the high-amount lithium slag water-stable material in Comparative Example 1. Detailed implementation manners

[0044] The technical solution of the present invention will be further described in detail below by listing examples and comparative examples, but the scope of the present invention is not limited to the listed examples.

[0045] The lithium slag used in the examples listed in the present invention is the tail slag obtained by extracting lithium from lepidolite by the sulfate roasting process. Specifically, the lepidolite concentrate powder is mixed evenly with sulfate and fluorine-fixing agent, and the leaching residue remaining after roasting - grinding - leaching - filtering. As Figure 1 shown, the main phases in the lithium slag are nosean, hemihydrate gypsum, quartz, fluorite and albite. The main chemical components and contents of the lithium slag are: SiO2 content 28 - 47%, Al2O3 content 16 - 22%, CaO content 11 - 14%, SO3 content 15 - 20%, Na2O and K2O content 1 - 12%. The SO3 in the lithium slag mainly exists in the form of hemihydrate gypsum, and Na2O and K2O mainly exist in the form of feldspar minerals. Nosean is a high-sulfate product (Na,Ca) 4-8 [AlSiO4]6(SO4) 1-2 .

[0046] The pressed fine mud used in the examples listed in the present invention is the by-product tail mud from the selection of lithium mica concentrate from tantalum-niobium ore, with quartz, albite and mica as the main mineral characteristics. Its main chemical components and contents are: SiO2 content 68 - 72%, Al2O3 content 16 - 18%, CaO content 1 - 3%, Na2O and K2O content 7 - 10%.

[0047] The aggregate used in the examples listed in the present invention is graded aggregate with a particle size of 0.075 - 31.5 mm. Example 1

[0048] A method for preparing a subgrade water-stable layer using lithium slag and pressed fine mud includes the following steps:

[0049] By mass percentage, 50% of coarse lithium slag (specific surface area of 200 - 300 m 2 / kg) and 38% of fine lithium slag (specific surface area of 300 - 500 m 2 / kg) are mixed evenly with 12% of mineral powder regulator to obtain a lithium slag mixture with regulated gradation;

[0050] By weight, 70 parts of pressed fine mud and 20 parts of metakaolin are taken and mixed as powder material. A compound alkali activator suspension prepared by mixing 7 parts of calcium hydroxide and 3 parts of sodium hydroxide is mixed evenly with the powder material, heated to 600 °C and kept warm for 90 min, and then ground to a specific surface area of 500 m 2 / kg after cooling to obtain activated pressed fine mud. It can be known from XRD test (as shown by "activated pressed fine mud 1" in Figure 2 ), after the above activation treatment of the pressed fine mud, the crystallinity of mica and albite decreases, and the alkaline activator and the active silica-alumina phase generate mineral structures such as calcium silicate, kyanite, and calcium aluminosilicate.

[0051] By mass percentage, 21% of the obtained activated pressed fine mud, 55% of the aggregate and 15% of the lithium slag mixture obtained in 1 are mixed evenly to obtain a solid mixture; the remaining water and an additional 0.2% of polycarboxylate superplasticizer are mixed and added to the solid mixture, and forced to stir evenly until the slurry fully wraps the aggregate.

[0052] Use the material obtained in 3 to lay the subgrade to obtain a uniform subgrade water-stable layer structure, cover it with plastic film and sprinkle water for curing. The frequency of sprinkling water is not less than 4 times a day, and the curing time is not less than 7 days.

[0053] For the water-stable layer prepared in this example, when tested according to the national standard, the 7-day compressive strength is 5.3 Mpa, and the 28-day compressive strength is 7.7 Mpa. As shown in Figure 3 , no crystallization phenomenon was observed on the appearance of the test block prepared in this example. Example 2

[0054] A method for preparing a subgrade water-stable layer using lithium slag and pressed fine mud, comprising the following steps:

[0055] By mass percentage, mix 60% of coarse lithium slag (specific surface area of 200 - 300 m 2 / kg) and 20% of fine lithium slag (specific surface area of 300 - 500 m 2 / kg) with 20% of P.O 52.5 cement regulator evenly to obtain a lithium slag mixture with regulated gradation;

[0056] By weight, take 74 parts of pressed fine mud and 18 parts of metakaolin and mix them to obtain a powder material. Then, make 8 parts of calcium hydroxide into a suspension and mix it evenly with the powder material, heat it to 500 °C and keep it warm for 90 min, and grind it to a specific surface area of 600 m 2 / kg after cooling to obtain activated pressed fine mud; as known from XRD test (as shown by "activated pressed fine mud 2" in Figure 2 ), the crystallinity of mica and albite minerals in the activated pressed fine mud is significantly reduced, generating more active silicon-aluminum valence bonds, and new mineral phases such as calcium silicate aluminate, calcium silicate, and silicon-aluminum minerals are formed under the action of an alkali activator;

[0057] By mass percentage, mix 26% of the obtained activated pressed fine mud, 46% of aggregate, and 18% of the lithium slag mixture obtained in 1 evenly to obtain a solid mixture; add the remaining water and an additional 0.3% of polycarboxylate superplasticizer to the solid mixture and stir it forcibly until the slurry fully wraps the aggregate.

[0058] Use the material obtained in 3 to lay the subgrade to obtain a uniform subgrade water-stable layer structure, cover it with cotton cloth and sprinkle water for curing. The frequency of sprinkling water is not less than 4 times a day, and the curing time is not less than 7 days.

[0059] For the water-stable layer prepared in this example, it is tested according to the national standard. The 7-day compressive strength is 6.3 Mpa, and the 28-day compressive strength is 8.2 Mpa; as shown in Figure 4 , no crystallization phenomenon is observed on the appearance of the test blocks prepared in this example. Comparative Example 1

[0060] A method for preparing a subgrade water-stable layer using lithium slag and pressed fine mud, comprising the following steps:

[0061] 1. By weight percentage, mix 43% of coarse lithium slag (specific surface area of 200 - 300 m 2 / kg) and 46% of fine lithium slag (specific surface area of 300 - 500 m 2 / kg) with 11% of fly ash regulator evenly to obtain a lithium slag mixture;

[0062] 2. Mix 70 parts of pressed fine mud and 20 parts of metakaolin evenly, and then mix them with a solution prepared from 10 parts of sodium hydroxide. Heat the mixture to 600 °C and keep it warm for 90 min. After cooling, grind it to a specific surface area of 500 m 2 / kg to obtain activated pressed fine mud. As shown by XRD test (as Figure 5 shown), after activation, new biophases such as sodium silicate and lazulite are generated in the pressed fine mud.

[0063] 3. By weight percentage, take 17% of the activated pressed fine mud obtained in 2, 48% of the aggregate, and 24% of the lithium slag mixture obtained in 1, and mix them evenly to obtain a solid mixture. Then, take the remaining water, 0.3% of the polycarboxylate superplasticizer by weight of the solid mixture, and mix them with 11% of the water, and add them to the solid mixture. Stir forcefully until the slurry fully wraps the aggregate to obtain a sodium hydroxide-activated high-volume lithium slag water-stable material.

[0064] 4. Use the material obtained in 3 to lay the roadbed to obtain a uniform roadbed water-stable layer structure, cover it with a plastic film, and sprinkle water for curing. The frequency of sprinkling water is not less than 4 times a day, and the curing time is not less than 7 days.

[0065] The water-stable layer prepared in this comparative example was tested according to the national standard. The 7-day compressive strength was 5.7 Mpa, and the 28-day compressive strength was 9.6 Mpa. However, the sodium sulfate content of the water-stable layer test block obtained in this comparative example was relatively high, and surface salting-out was serious, as Figure 6 shown. After testing, the precipitated crystalline salts were Na2SO4 and Na2SO4·10H2O, as Figure 7 shown. In addition, as Figure 8 shown, the test block was also prone to cracking. Comparative Example 2

[0066] 1. By weight percentage, take 43% of the coarse lithium slag (specific surface area is 200 - 300 m 2 / kg) and 45% of the fine lithium slag (specific surface area is 300 - 500 m 2 / kg), and mix them evenly with 12% of the P.O 52.5 cement regulator to obtain a lithium slag mixture;

[0067] 2. By weight, take 74 parts of pressed fine mud and 18 parts of fly ash, mix them evenly to obtain a powder material. Prepare a suspension of 8 parts of calcium hydroxide and mix it evenly with the powder material. Heat it to 500 °C, keep it warm for 90 min, and after cooling, grind it to a specific surface area of 600 m 2 / kg; obtain the calcium hydroxide-activated fly ash pressed fine mud powder material.

[0068] 3. By weight percentage, take 10% of the activated pressed fine mud obtained from 2, 50% of the aggregate and 26% of the lithium slag mixture obtained from 1, and mix them evenly to obtain a solid mixture. Then, take the remaining water and an additional polycarboxylate superplasticizer accounting for 0.3% of the weight of the solid mixture and add them to the solid mixture, and stir forcibly until the slurry fully wraps the aggregate to obtain a calcium hydroxide-activated high-volume lithium slag water-stable material.

[0069] 4. Use the material obtained in 3 to lay the roadbed to obtain a uniform roadbed water-stable layer structure, cover it with cotton fabric and then sprinkle water for curing. The frequency of sprinkling water is not less than 4 times a day, and the curing time is not less than 7 days.

[0070] The water-stable layer prepared in this comparative example was tested according to the national standard. The 7-day compressive strength was 1.2 Mpa, and the 28-day compressive strength was 2.3 Mpa. It can be seen that although calcium hydroxide was also used to activate the pressed fine mud in this comparative example, since the material added before activation was fly ash instead of metakaolin, the activation effect was poor and the strength of the water-stable layer was insufficient. Since metakaolin can provide more stable and larger amounts of reactive silicon and aluminum than fly ash, and can also adjust the silicon-aluminum ratio and product structure, the activation effect of fly ash is much lower than that of metakaolin.

Claims

1. A subgrade water-stable layer prepared by synergistically activating and pressing fine mud with lithium slag, characterized in that The subgrade water-stable layer is prepared from the following raw materials by weight: 15-20 parts of lithium slag, 20-30 parts of activated pressed fine mud, 45-55 parts of graded aggregate, 0-5 parts of regulator, and 9-13 parts of water; the activated pressed fine mud is a powder containing new active reaction gel components calcium silicate, sodium silicate and aluminosilicate obtained by mixing the by-product tail mud of spodumene concentrate and metakaolin in a weight ratio of 70-77:15-20, activating with a calcium-containing alkali activator and grinding at high temperature.

2. The subgrade water-stable layer according to claim 1, characterized in that The subgrade water-stable layer is prepared from the following raw materials: 15-18 parts of the lithium slag, 20-26 parts of the activated pressed fine mud, 45-55 parts of the graded aggregate, 2-4 parts of the regulator, and 9-10 parts of water.

3. The subgrade water-stable layer described in claim 1, characterized in that The lithium slag contains the following chemical components in percentage by mass: SiO2 content is 28 - 47%, Al2O3 content is 16 - 22%, CaO content is 11 - 14%, SO3 content is 15 - 20%, and Na2O and K2O content is 1 - 12%; the specific surface area of the lithium slag is 100 - 500 m 2 / kg.

4. The subgrade water-stable layer according to claim 3, characterized in that The lithium slag described above is a mixture of coarse slag with a specific surface area of 200 - 300 m 2 / kg and fine slag with a specific surface area of 300 - 500 m 2 / kg.

5. The subgrade water-stable layer according to claim 4, characterized in that In the lithium slag, the mixing ratio of the coarse slag to the fine slag is 6:2 to 2:

6.

6. The subgrade water-stable layer according to claim 4, characterized in that In the lithium slag, the mixing ratio of the coarse slag to the fine slag is 5:3 to 2:

5.

7. The subgrade water-stable layer described in claim 1, characterized in that The by-product tail mud of spodumene concentrate contains the following chemical components by weight percentage: 68-72% of SiO2, 16-18% of Al2O3, 1-3% of CaO, and 7-10% of Na2O and K2O.

8. The subgrade water-stable layer described in claim 1, characterized in that The activated pressed fine mud is activated according to the following steps: By weight, 70-77 parts of the by-product tail mud of spodumene concentrate and 15-20 parts of metakaolin are mixed evenly to obtain a solid mixture, 5-10 parts of calcium hydroxide and 3-5 parts of sodium hydroxide are made into a suspension, mixed evenly with the solid mixture, heated to 400-600 °C, kept warm for 90 min, then cooled and ground.

9. The subgrade water-stable layer described in claim 1, characterized in that The specific surface area of the activated pressing fine mud is 400-700m 2 / kg.

10. A method for preparing a subgrade water-stable layer by using a large amount of lithium slag and pressed fine mud, comprising the following steps: (1) By weight, mix 70-77 parts of the tail mud produced as a by-product of selected spodumene concentrate with 15-20 parts of metakaolin to obtain a solid mixture. Prepare a suspension of 5-10 parts of calcium hydroxide and 3-5 parts of sodium hydroxide, mix it with the solid mixture, heat it to 400-600 °C, keep it warm for 90 min, then cool and grind it to obtain activated pressed fine mud containing calcium silicate, calcium aluminosilicate and aluminosilicate minerals; (2) By weight, mix 15-20 parts of lithium slag and 20-30 parts of the activated pressed fine mud obtained in (1), stir well, then mix it with 45-55 parts of graded aggregate, 0-5 parts of regulator and 9-13 parts of water, and stir strongly to make the slurry and lithium slag completely wrap around the aggregate to obtain a mixture; (3) Use the mixture obtained in (2) to lay the subgrade to obtain a uniform subgrade water-stable layer structure.

11. The method according to claim 10, characterized in that: (1) The by-product tail mud of spodumene concentrate contains the following chemical components by weight percentage: 68-72% of SiO2, 16-18% of Al2O3, 1-3% of CaO, and 7-10% of Na2O and K2O.

12. The method according to claim 10, characterized in that: (2)The lithium slag contains the following chemical components in percentage by mass: SiO2 content is 28 - 47%, Al2O3 content is 16 - 22%, CaO content is 11 - 14%, SO3 content is 15 - 20%, Na2O and K2O content is 1 - 12%; the specific surface area of the lithium slag is 100 - 500 m 2 / kg.

13. The method according to claim 12, characterized in that: The lithium slag described above is a mixture of coarse slag with a specific surface area of 200 - 300 m 2 / kg and fine slag with a specific surface area of 300 - 500 m 2 / kg.

14. The method according to claim 13, characterized in that: In the lithium slag, the mixing ratio of the coarse slag to the fine slag is 6:2 to 2:

6.

15. The method according to claim 13, characterized in that: In the lithium slag, the mixing ratio of the coarse slag to the fine slag is 5:3 to 2:

5.

16. The method according to claim 10, characterized in that: (1) The grinding described above is to grind the activated pressed fine mud after cooling to a specific surface area of 400 - 700 2 m² / kg.

17. The method according to claim 10, characterized in that: It also includes (4): After covering the subgrade water-stable layer laid in (3) with cotton cloth, sprinkle water in time. The frequency of sprinkling water is not less than 4 times a day, and the curing time is not less than 7 days.

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