Soft soil solidifying agent based on waste lithium iron phosphate cathode powder, preparation method and application

Abstract

The present invention relates to the field of recycling of waste batteries containing lithium iron phosphate, in particular to a soft soil solidifying agent based on waste lithium iron phosphate cathode powder, a preparation method and an application thereof. The soft soil solidifying agent comprises, by mass parts: 10-30 parts of waste lithium iron phosphate cathode powder, 10-75 parts of silica fume, 50-80 parts of slag, 10-20 parts of fly ash cenospheres, and 1-3 parts of water glass. Under the synergistic action of each component, the soft soil solidifying agent has a relatively high unconfined compressive strength. The 7-day unconfined compressive strength of the solidified soil is 0.75-4.96 MPa, and the 28-day unconfined compressive strength of the solidified soil is 2.07-7.63 MPa. The soft soil solidifying agent of the present invention realizes the high-value utilization of waste lithium iron phosphate, reduces the cost of the soft soil solidifying agent, and reduces the environmental pollution caused by waste batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of soft soil solidification, and in particular to a soft soil solidifying agent based on waste lithium iron phosphate cathode powder, a preparation method and an application thereof. Background Art

[0002] In the coastal areas of our country, soft soil foundations with high water content, low bearing capacity and strong thixotropy generally exist. These soft soil foundations cannot provide sufficient foundation bearing capacity, so foundation treatment is particularly important. Among many treatment methods, using soil solidifying agents to reinforce soft soil has become a widely used preferred solution. While ensuring that the engineering design standards and requirements are met, how to further reduce the cost of soft soil foundation treatment is one of the important exploration directions for the current development of soil solidifying agent technology. Patent CN202311093071.6 discloses a soft soil solidifying agent produced from industrial solid waste. On the one hand, it can effectively reduce the cement dosage, realize the recycling of solid waste resources, be conducive to reducing solid waste emissions, and achieve energy conservation and environmental protection; at the same time, it can also effectively improve the mechanical properties of solidified soil and ensure the solidification effect of the solidifying agent.

[0003] Industrial solid waste refers to solid waste generated in industrial production activities, which are various waste residues, dusts and other wastes discharged into the environment during the industrial production process. Some industrial solid wastes such as slag and fly ash will be activated in an alkaline environment and have a certain gelling ability, so they can be used for soft soil solidification. However, due to the low activity of industrial solid waste, a high-concentration activator is required to activate its activity, resulting in a high cost and low economic benefits.

[0004] Due to the relatively early promotion and use of lithium iron phosphate batteries in China, compared with other types of batteries, they have faced the challenges of retirement and scrapping earlier. It is worth noting that waste lithium iron phosphate batteries can obtain waste lithium iron phosphate cathode powder after being disassembled. There are no rare metals in the waste lithium iron phosphate cathode powder, and at the same time, the separation and purification cost is relatively high, and the economic benefits of recycling are not obvious. After appropriate process processing, the waste lithium iron phosphate cathode powder can obtain auxiliary cementitious materials such as lithium silicate, and applying it to the production of soft soil solidifying agents helps to realize the high-value utilization of waste lithium iron phosphate cathode powder.

[0005] Currently, the application of waste lithium iron phosphate cathode powder in the field of building materials is less. In patent CN202210081430.5, sodium hydroxide is used to dissolve the waste lithium iron phosphate cathode powder to obtain a solution containing aluminum element, and calcium aluminate is synthesized for use in concrete. This method actually utilizes the impurity aluminum element in the waste lithium iron phosphate cathode powder, rather than directly using the waste lithium iron phosphate cathode powder. The soft soil solidifying agent produced by using various compounds such as lithium silicate in patent CN202110996674.1 has the advantages of fast solidification speed, higher strength after solidification, and greater compactness of the subgrade after solidification. Therefore, lithium silicate has the potential to be used in the field of soft soil solidification technology.

[0006] In summary, the existing technology discloses less application of waste lithium iron phosphate cathode powder in the field of soft soil solidification. Processing waste lithium iron phosphate cathode powder into lithium silicate through a simple process for use in the field of soft soil solidification technology can effectively reduce the cost of soft soil solidifying agent, reduce the environmental pollution of waste batteries, and realize the high-value application of waste batteries. For this reason, the present invention provides a soft soil solidifying agent based on waste lithium iron phosphate cathode powder, a preparation method and an application thereof. Summary of the Invention

[0007] The purpose of the present application is to provide a soft soil solidifying agent based on waste lithium iron phosphate cathode powder, a preparation method and an application thereof, aiming to solve the above problems in the existing technology.

[0008] The present application provides a soft soil solidifying agent based on waste lithium iron phosphate cathode powder. The soft soil solidifying agent includes, by mass: 10 - 30 parts of waste lithium iron phosphate cathode powder, 10 - 75 parts of silica fume, 50 - 80 parts of slag, 10 - 20 parts of fly ash cenospheres, and 1 - 3 parts of water glass.

[0009] Furthermore, under the synergistic effect of each component of the soft soil solidifying agent of the present invention, it has a relatively high unconfined compressive strength. The 7-day unconfined compressive strength of the solidified soil is 0.75 - 4.96 MPa, and the 28-day unconfined compressive strength of the solidified soil is 2.07 - 7.63 MPa. Moreover, the soft soil solidifying agent of the present invention realizes the high-value utilization of waste lithium iron phosphate cathode powder and reduces the cost of the soft soil solidifying agent.

[0010] Furthermore, the soft soil solidifying agent of the present invention includes, by mass: 10 - 30 parts of waste lithium iron phosphate cathode powder, such as 10 parts, 15 parts, 20 parts, 25 parts or 30 parts, etc., but is not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0011] Further, the soft soil solidifying agent of the present invention, by mass, comprises 10 - 75 parts of waste silica fume, such as 10 parts, 20 parts, 30 parts, 50 parts or 75 parts, etc., but not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0012] Further, the soft soil solidifying agent of the present invention, by mass, comprises 50 - 80 parts of slag, such as 50 parts, 60 parts, 70 parts or 80 parts, etc., but not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0013] Further, the soft soil solidifying agent of the present invention, by mass, comprises 10 - 20 parts of fly ash cenospheres, such as 12 parts, 14 parts, 16 parts, 18 parts or 20 parts, etc., but not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0014] Further, the source of the waste lithium iron phosphate cathode powder is: the waste lithium iron phosphate cathode powder is obtained after disassembling, crushing and screening waste lithium iron phosphate batteries.

[0015] Further, the SiO₂ content in the silica fume is ≥97wt%, and the particle size of the silica fume is 3000 mesh.

[0016] Further, the grade of the slag is not lower than S95. It should be noted that, according to different activity indexes, slag can be divided into three grades: S75, S95 and S105. The larger the number, the higher the grade, indicating better activity and better strength when used as a cementitious material.

[0017] Further, the particle size of the fly ash cenospheres is 2000 mesh. It should be noted that fly ash is a solid residue generated during coal combustion. After sorting fly ash, spherical fly ash cenospheres can be obtained. Fly ash cenospheres can be used as a filler for cementitious materials, improving the fluidity and impermeability of the mixture, etc., and having excellent durability.

[0018] Further, the modulus of the water glass is 1.0. It should be noted that when the modulus of the water glass is 1.0, the excitation effect of the activator is the best.

[0019] The second object of the present invention is to provide a preparation method of a soft soil solidifying agent based on waste lithium iron phosphate cathode powder, comprising the following steps:

[0020] 1. Obtain waste lithium iron phosphate cathode powder by crushing and screening waste lithium iron phosphate old batteries, and calcine the waste lithium iron phosphate cathode powder at 500 - 550 °C for 4 - 6 h to remove fluorine-containing impurities to obtain waste lithium iron phosphate powder.

[0021] II. After the lithium iron phosphate waste powder is cooled, it is ground by a horizontal ball mill to obtain a precursor of the auxiliary cementitious material. The grinding is carried out by a horizontal ball mill, the grinding time is 2 - 5 h, such as 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h or 5 h, etc., the rotation speed is 30 - 50 revolutions per minute, such as 30 revolutions per minute, 31 revolutions per minute, 33 revolutions per minute, 35 revolutions per minute, 38 revolutions per minute, 40 revolutions per minute, 42 revolutions per minute, 45 revolutions per minute, 46 revolutions per minute, 48 revolutions per minute or 50 revolutions per minute, etc., but not limited to the listed values, and other unlisted values within the above value range are equally applicable. The specific surface area of the precursor of the auxiliary cementitious material is 350 - 400 m 2 / kg, such as 350 m 2 / kg, 355 m 2 / kg, 360 m 2 / kg, 365 m 2 / kg, 370 m 2 / kg, 375 m 2 / kg, 380 m 2 / kg, 385 m 2 / kg, 390 m 2 / kg, 395 m 2 / kg or 400 m 2 / kg, etc., but not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0022] III. Silica fume is added to the precursor of the auxiliary cementitious material to adjust the silicon-lithium ratio, and oxygen is added for melting and oxidation in a high-temperature furnace at 700 - 900 °C to obtain an auxiliary cementitious material such as lithium silicate. In a high-temperature environment, lithium ions in lithium iron phosphate are removed and combined with oxygen and silicon dioxide to form lithium silicate. The chemical reaction formula is as follows:

[0023] 4LiFePO4 + 6SiO2 + O2 = 2Li2SiO3 + 2Fe2O3 + 4P2O5 (1)

[0024] IV. The slag, fly ash cenospheres and the auxiliary cementitious material are mixed to form a soft soil curing agent cementitious material. It should be noted that due to the quick-setting phenomenon of the slag, the activator should not be mixed with the soft soil curing agent cementitious material before transportation. Therefore, the activator and the soft soil curing agent cementitious material should be separately packed and transported to the construction site for use.

[0025] V. The soil to be cured, the soft soil curing agent cementitious material, polypropylene fiber, water glass and water are mixed and stirred evenly, and the curing is completed after 24 hours.

[0026] Further, polypropylene fibers with a length of 6 ± 1 mm are incorporated in an amount of 0 - 1.5% of the mass of the soft soil curing agent. When the soft soil curing agent of the present invention is used for soil curing and fibers are further added, it can effectively inhibit shrinkage cracking and is beneficial to achieving a relatively high unconfined compressive strength.

[0027] The third object of the present invention is to provide an application of a soft soil curing agent based on waste lithium iron phosphate cathode powder, and the soft soil curing agent is applied to soft soil curing treatment, especially suitable for the reinforcement of clay or silt foundations with high water content.

[0028] Further, the addition amount of the soft soil curing agent is 10 - 20% of the mass of the soft soil, such as 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%, etc., but is not limited to the listed values, and other unlisted values within the above value range are equally applicable. It should be noted that in order to achieve a better curing effect, when the soft soil curing agent of the present invention is mixed with the soil to be cured, an additional 30% - 50% of water equivalent to the mass of the curing agent needs to be added to make the cured soil have sufficient fluidity; the fluidity is preferably between 150 mm and 200 mm during soft soil curing. When the soft soil curing agent of the present invention is applied, the activator is first mixed with the additional water and then added to the gelling particle part of the soft soil curing agent and stirred evenly, and then mixed with the soft soil. This belongs to a common soil reinforcement method and will not be elaborated here. The above addition amount of the soft soil curing agent and the additional added water will affect the strength of the cured soft soil, so it needs to be added according to the actual engineering needs.

[0029] The strength of the cured soft soil can refer to Formula 2 to predict the strength of the soft soil after 7 days of curing, and can refer to Formula 3 to predict the strength of the soft soil after 28 days of curing.

[0030]

[0031] σ 7d is the predicted value of the unconfined compressive strength of the soil after 7 days of curing, σ 28d is the predicted value of the unconfined compressive strength of the soil after 28 days of curing, ω p is the ratio of the doping amount of lithium iron phosphate to the total amount of the soft soil curing agent, ω b is the ratio of the doping amount of silica fume to the total amount of the soft soil curing agent, ω g is the ratio of the doping amount of slag to the total amount of the soft soil curing agent, ω f is the ratio of the doping amount of fly ash to the total amount of the soft soil curing agent, ω z is the ratio of the doping amount of the soft soil curing agent to the mass of the soft soil, ω x is the ratio of the doping amount of fibers to the total amount of the soft soil curing agent, ω s is the ratio of the activator to the total amount of the soft soil curing agent, and q is the mass ratio of water to soft soil.

[0032] Compared with the existing technical solutions, the present invention has the following beneficial effects:

[0033] (1) The soft soil solidifying agent of the present invention is prepared based on waste lithium iron phosphate cathode powder. Under the synergistic action of each component, it has a high unconfined compressive strength. The 7-day unconfined compressive strength of the solidified soil is 0.75 - 4.96 MPa, and the 28-day unconfined compressive strength of the solidified soil is 2.07 - 7.63 MPa;

[0034] (2) The soft soil solidifying agent of the present invention realizes the high-value utilization of waste lithium iron phosphate cathode powder and reduces the cost of the soft soil solidifying agent;

[0035] (3) The soft soil solidifying agent of the present invention enables the 28-day target strength of the solidified soil to reach 2.07 - 7.63 MPa, while the 28-day target strength of the commonly used cement-based solidifying agent or industrial waste-based solidifying agent in engineering is often only 1 - 5 MPa. The present invention has a greater advantage in the target strength of the solidified soil, so it can scale up the utilization of waste lithium iron phosphate cathode powder and facilitate industrialization. Specific Embodiments

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0037] Example 1

[0038] This example provides a soft soil solidifying agent based on waste lithium iron phosphate cathode powder. The soft soil solidifying agent includes, by mass: 30 parts of waste lithium iron phosphate cathode powder, 75 parts of silica fume, 80 parts of slag, 20 parts of fly ash cenospheres, and 3 parts of water glass.

[0039] Among them, the source of the waste lithium iron phosphate cathode powder includes: obtained by crushing and screening waste lithium iron phosphate old batteries; the waste lithium iron phosphate cathode powder is calcined at 500 °C for 4 h to remove fluorine-containing impurities, and after cooling, it is ground by a horizontal ball mill with a grinding time of 5 h and a rotation speed of 50 r / min; the specific surface area of the waste lithium iron phosphate cathode powder is 400 m 2 / kg, the waste lithium iron phosphate cathode powder is in the form of black particles, and more than 95% of the particles have a particle size less than 0.1 mm; the silica fume is 3000-mesh white silica fume with a SiO2 content ≥ 97 wt%; the waste lithium iron phosphate cathode powder and silica fume are mixed evenly and melted in a high-temperature furnace at 900 °C for 4 h by introducing oxygen.

[0040] The slag used is S95 grade slag; the fly ash cenospheres used are 2000-mesh fly ash cenospheres; the water glass modulus is 1.0.

[0041] The soft soil stabilizer described in this example is used to solidify the soft soil from a certain subway line in Nansha District, Guangzhou. The water content of the soft soil to be solidified is 33.57%. The engineering requirement is that the unconfined compressive strength of the soft soil after 7 days of solidification is not less than 1.5 MPa, and the unconfined compressive strength of the soft soil after 28 days of solidification is not less than 4.0 MPa.

[0042] The dosage of the soft soil stabilizer is selected as 20% of the mass of the soft soil to be solidified.

[0043] According to the on-site mixing situation, an additional amount of water equivalent to 40% of the mass of the stabilizer is added to make the fluidity of the solidified soil reach 185 mm. According to Formula 2, the predicted value of the 7-day unconfined compressive strength of the solidified soil is 1.99 MPa, and the unconfined compressive strength of the solidified soil after 7 days of solidification is 2.01 MPa. The prediction error of Formula 2 is 0.97%. According to Formula 3, the predicted value of the 28-day unconfined compressive strength of the solidified soil is 4.50 MPa, and the unconfined compressive strength of the soft soil after 28 days of solidification is 4.65 MPa. The prediction error of Formula 3 is 3.23%, meeting the engineering requirements.

[0044] Example 2

[0045] This example provides a soft soil stabilizer based on waste lithium iron phosphate cathode powder. The soft soil stabilizer includes, by mass: 30 parts of waste lithium iron phosphate cathode powder, 50 parts of silica fume, 50 parts of slag, 20 parts of fly ash cenospheres, and 2 parts of water glass;

[0046] Among them, the source of the waste lithium iron phosphate cathode powder includes: obtained by crushing and screening waste lithium iron phosphate old batteries; the waste lithium iron phosphate cathode powder is calcined at 500 °C for 6 h to remove fluorine-containing impurities, and after cooling, a horizontal ball mill is used with a grinding time of 4 h and a rotation speed of 30 revolutions per minute; the specific surface area of the waste lithium iron phosphate cathode powder is 350 m 2 / kg, the waste lithium iron phosphate cathode powder is in black granular form, and more than 95% of the particles have a particle size less than 0.1 mm; the silica fume is 3000-mesh white silica fume, and the SiO2 content ≥ 97 wt%; after the waste lithium iron phosphate cathode powder and silica fume are mixed evenly, they are melted in a high-temperature furnace at 900 °C with oxygen for 4 h.

[0047] The slag used is S95 grade slag; the fly ash cenospheres used are 2000-mesh fly ash cenospheres; the water glass modulus is 1.0, and it is packed separately from the gelling material of the soft soil stabilizer.

[0048] The soft soil solidifying agent described in this embodiment is used to solidify the soft soil from a subway line in Nansha District, Guangzhou. The water content of the soft soil to be solidified is 23.5%. The engineering requirement is that the unconfined compressive strength of the soft soil after 7 days of solidification is not less than 1.0 MPa, and the unconfined compressive strength of the soft soil after 28 days of solidification is not less than 2.5 MPa.

[0049] Polypropylene fibers with a length of 6 ± 1 mm are selected and incorporated at 0.5% of the mass of the soft soil solidifying agent. The dosage of the soft soil solidifying agent is selected as 20% of the mass of the soft soil to be solidified.

[0050] According to the on-site preparation situation, an additional amount of water equivalent to 50% of the mass of the solidifying agent is added to make the fluidity of the solidified soil reach 160 mm. According to Formula 2, the predicted value of the 7-day unconfined compressive strength of the solidified soil is 1.58 MPa. After 7 days of solidification, the unconfined compressive strength of the solidified soil is 1.51 MPa, and the prediction error of Formula 2 is 4.57%. According to Formula 3, the predicted value of the 28-day unconfined compressive strength of the solidified soil is 2.65 MPa. After 28 days of solidification, the unconfined compressive strength of the soft soil is 2.65 MPa, and the prediction error of Formula 3 is 0.11%, meeting the engineering requirements.

[0051] Example 3

[0052] This embodiment provides a soft soil solidifying agent based on waste lithium iron phosphate cathode powder. The soft soil solidifying agent includes, by mass: 10 parts of waste lithium iron phosphate cathode powder, 10 parts of silica fume, 80 parts of slag, 10 parts of fly ash cenospheres, and 3 parts of water glass;

[0053] Among them, the source of the waste lithium iron phosphate cathode powder includes: obtained by crushing and screening waste lithium iron phosphate old batteries; the waste lithium iron phosphate cathode powder is calcined at 500 °C for 6 h to remove fluorine-containing impurities, and after cooling, a horizontal ball mill is used with a grinding time of 4 h and a rotation speed of 40 revolutions per minute; the specific surface area of the waste lithium iron phosphate cathode powder is 380 m 2 / kg. The waste lithium iron phosphate cathode powder is in the form of black particles, and more than 95% of the particles have a particle size less than 0.1 mm; the silica fume is 3000-mesh white silica fume, and the SiO2 content is ≥ 97 wt%; after the waste lithium iron phosphate cathode powder and silica fume are mixed evenly, they are melted in an oxygen-containing high-temperature furnace at 900 °C for 4 h.

[0054] The slag selected is S95 grade slag; the fly ash cenospheres selected are 2000-mesh fly ash cenospheres; the water glass has a modulus of 1.0 and is packaged separately from the gelling material of the soft soil solidifying agent.

[0055] The soft soil solidifying agent described in this embodiment is used to solidify the soft soil of a residential foundation in Nansha District, Guangzhou. The water content of the soft soil to be solidified is 49.5%. The engineering requirement is that the unconfined compressive strength of the soft soil after 7 days of solidification is not less than 1.0 MPa, and the unconfined compressive strength of the soft soil after 28 days of solidification is not less than 3 MPa.

[0056] The dosage of the soft soil solidifying agent is selected as 20% of the mass of the soft soil to be solidified.

[0057] According to the on-site preparation situation, an additional amount of water equivalent to 30% of the mass of the solidifying agent is added to make the fluidity of the solidified soil reach 160 mm. The predicted value of the 7-day unconfined compressive strength of the solidified soil calculated according to Formula 2 is 4.94 MPa, and the unconfined compressive strength of the solidified soil after 7 days of solidification is 4.96 MPa. The prediction error of Formula 2 is 0.45%. The predicted value of the 28-day unconfined compressive strength of the solidified soil calculated according to Formula 3 is 7.65 MPa, and the unconfined compressive strength of the soft soil after 28 days of solidification is 7.63 MPa. The prediction error of Formula 3 is 0.32%, meeting the engineering requirements.

[0058] Example 4

[0059] This embodiment provides a soft soil solidifying agent based on waste lithium iron phosphate cathode powder. The soft soil solidifying agent includes, by mass: 30 parts of waste lithium iron phosphate cathode powder, 10 parts of silica fume, 50 parts of slag, 10 parts of fly ash cenospheres, and 1 part of water glass;

[0060] Among them, the source of the waste lithium iron phosphate cathode powder includes: obtained by crushing and screening waste lithium iron phosphate old batteries; the waste lithium iron phosphate cathode powder is calcined at 500 °C for 6 h to remove fluorine-containing impurities, and after cooling, a horizontal ball mill is used with a grinding time of 5 h and a rotation speed of 50 revolutions per minute; the specific surface area of the waste lithium iron phosphate cathode powder is 400 m 2 / kg. The waste lithium iron phosphate cathode powder is in the form of black particles, and more than 95% of the particles have a particle size less than 0.1 mm; the silica fume is 3000-mesh white silica fume, and the SiO2 content ≥ 97 wt%; after the waste lithium iron phosphate cathode powder and silica fume are mixed evenly, they are melted in an oxygen-containing atmosphere in a high-temperature furnace at 900 °C for 4 h.

[0061] The slag selected is S95 grade slag; the fly ash cenospheres selected are 2000-mesh fly ash cenospheres; the water glass has a modulus of 1.0 and is packed separately from the cementitious materials of the soft soil solidifying agent.

[0062] The soft soil solidifying agent described in this embodiment is used to solidify the soft soil of a foundation pit in Huangpu District, Guangzhou. The water content of the soft soil to be solidified is 10.4%. The engineering requirement is that the unconfined compressive strength of the soft soil after 7 days of solidification is not less than 1.0 MPa, and the unconfined compressive strength of the soft soil after 28 days of solidification is not less than 3.5 MPa.

[0063] Select the mass of the soft soil to be solidified with a soft soil solidifying agent dosage of 20%.

[0064] According to the on-site preparation situation, add an additional amount of water equivalent to 50% of the mass of the solidifying agent to make the fluidity of the solidified soil reach 180 mm. According to Formula 2, the predicted value of the unconfined compressive strength of the solidified soil after 7 days is 1.72 MPa. After solidifying for 7 days, the unconfined compressive strength of the solidified soil is 1.74 MPa, and the prediction error of Formula 2 is 1.32%. According to Formula 3, the predicted value of the unconfined compressive strength of the solidified soil after 28 days is 5.07 MPa. After solidifying for 28 days, the unconfined compressive strength of the soft soil is 4.98 MPa, and the prediction error of Formula 3 is 1.74%, meeting the engineering requirements.

[0065] Example 5

[0066] This example provides a soft soil solidifying agent based on waste lithium iron phosphate cathode powder. The soft soil solidifying agent includes, by mass: 30 parts of waste lithium iron phosphate cathode powder, 50 parts of silica fume, 50 parts of slag, 20 parts of fly ash cenospheres, and 1 part of water glass;

[0067] Among them, the source of the waste lithium iron phosphate cathode powder includes: obtained by crushing and screening waste lithium iron phosphate old batteries; the waste lithium iron phosphate cathode powder is calcined at 500 °C for 6 h to remove fluorine-containing impurities, and after cooling, a horizontal ball mill is used with a grinding time of 5 h and a rotation speed of 50 revolutions per minute; the specific surface area of the waste lithium iron phosphate cathode powder is 400 m 2 / kg, the waste lithium iron phosphate cathode powder is in the form of black particles, and more than 95% of the particles have a particle size less than 0.1 mm; the silica fume is 3000-mesh white silica fume, and the SiO2 content ≥ 97 wt%; after the waste lithium iron phosphate cathode powder and silica fume are mixed evenly, oxygen is introduced into a high-temperature furnace at 900 °C and melted for 4 h.

[0068] The slag selected is S95 grade slag; the fly ash cenospheres selected are 2000-mesh fly ash cenospheres; the water glass has a modulus of 1.0 and is packed separately from the soft soil solidifying agent binder.

[0069] Use the soft soil solidifying agent in this example to solidify the soft soil in the foundation of the subway line in Panyu District, Guangzhou. The water content of the soft soil to be solidified is 5.76%. The engineering requirements are that the unconfined compressive strength of the soft soil after solidifying for 7 days is not less than 0.5 MPa, and the unconfined compressive strength of the soft soil after solidifying for 28 days is not less than 1.5 MPa.

[0070] Select the mass of the soft soil to be solidified with a soft soil solidifying agent dosage of 10%.

[0071] According to the on-site mixing situation, adding an additional amount of water equivalent to 50% of the mass of the curing agent makes the fluidity of the solidified soil reach 180 mm. According to Formula 2, the predicted value of the 7-day unconfined compressive strength of the solidified soil is 0.62 MPa. After curing for 7 days, the unconfined compressive strength of the solidified soil is 0.75 MPa, and the prediction error of Formula 2 is 16.84%. According to Formula 3, the predicted value of the 28-day unconfined compressive strength of the solidified soil is 1.36 MPa. After curing for 28 days, the unconfined compressive strength of the soft soil is 1.57 MPa, and the prediction error of Formula 3 is 13.26%, meeting the engineering requirements.

[0072] Comparative Example 1

[0073] This comparative example provides a soft soil curing agent. Compared with the soft soil curing agent described in Example 1, the only difference is: 20 parts of waste lithium iron phosphate cathode powder.

[0074] Comparative Example 2

[0075] This comparative example provides a soft soil curing agent. Compared with the soft soil curing agent described in Example 1, the only difference is: 10 parts of waste lithium iron phosphate cathode powder.

[0076] Comparative Example 3

[0077] This comparative example provides a soft soil curing agent. Compared with the soft soil curing agent described in Example 1, the only difference is: 50 parts of silica fume.

[0078] Comparative Example 4

[0079] This comparative example provides a soft soil curing agent. Compared with the soft soil curing agent described in Example 1, the only difference is: 25 parts of silica fume.

[0080] Comparative Example 5

[0081] This comparative example provides a soft soil curing agent. Compared with the soft soil curing agent described in Example 1, the only difference is: 10 parts of silica fume.

[0082] Comparative Example 6

[0083] This comparative example provides a soft soil curing agent. Compared with the soft soil curing agent described in Example 1, the only difference is: 70 parts of slag.

[0084] Comparative Example 7

[0085] This comparative example provides a soft soil curing agent. Compared with the soft soil curing agent described in Example 1, the only difference is: 60 parts of slag.

[0086] Comparative Example 8

[0087] This comparative example provides a soft soil curing agent. Compared with the soft soil curing agent described in Example 1, the only difference is: 50 parts of slag.

[0088] Comparative Example 9

[0089] This comparative example provides a soft soil solidifying agent. Compared with the soft soil solidifying agent described in Example 1, the only difference is that there are 15 parts of fly ash cenospheres.

[0090] Comparative Example 10

[0091] This comparative example provides a soft soil solidifying agent. Compared with the soft soil solidifying agent described in Example 1, the only difference is that there are 10 parts of fly ash cenospheres.

[0092] Comparative Example 11

[0093] This comparative example provides a soft soil solidifying agent. Compared with the soft soil solidifying agent described in Example 1, the only difference is that there are 2 parts of water glass.

[0094] Comparative Example 12

[0095] This comparative example provides a soft soil solidifying agent. Compared with the soft soil solidifying agent described in Example 1, the only difference is that there is 1 part of water glass.

[0096] Comparative Example 13

[0097] This comparative example provides a soft soil solidifying agent. Compared with the soft soil solidifying agent described in Example 1, the only difference is that an additional 50% of the mass of the solidifying agent of water is added.

[0098] Comparative Example 14

[0099] This comparative example provides a soft soil solidifying agent. Compared with the soft soil solidifying agent described in Example 1, the only difference is that an additional 30% of the mass of the solidifying agent of water is added.

[0100] Comparative Example 15

[0101] This comparative example provides a soft soil solidifying agent. Compared with the soft soil solidifying agent described in Example 1, the only difference is that the dosage of the soft soil solidifying agent is selected as 15% of the mass of the soft soil to be solidified.

[0102] Comparative Example 16

[0103] This comparative example provides a soft soil solidifying agent. Compared with the soft soil solidifying agent described in Example 1, the only difference is that the dosage of the soft soil solidifying agent is selected as 10% of the mass of the soft soil to be solidified.

[0104] Comparative Example 17

[0105] This comparative example provides a soft soil solidifying agent. Compared with the soft soil solidifying agent described in Example 1, the only difference is that polypropylene fibers with a length of 6 ± 1 mm are selected and incorporated at 1.5% of the mass of the soft soil solidifying agent.

[0106] Comparative Example 18

[0107] This comparative example provides a soft soil solidifying agent. Compared with the soft soil solidifying agent described in Example 1, the only difference is that polypropylene fibers with a length of 6 ± 1 mm are selected and incorporated at 1.0% of the mass of the soft soil solidifying agent.

[0108] Comparative Example 19

[0109] This comparative example provides a soft soil solidifying agent. Compared with the soft soil solidifying agent described in Example 1, the only difference is that polypropylene fibers with a length of 6 ± 1 mm are selected and incorporated at 0.5% of the mass of the soft soil solidifying agent.

[0110] The soft soil solidifying agent described in the above comparative example was used to solidify the same soft soil as in Example 1, and the unconfined compressive strength of the solidified soil at 7 days and the unconfined compressive strength of the solidified soil at 28 days were measured respectively. The specific measurement results are shown in the following table:

[0111]

[0112]

[0113] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be encompassed within the present invention. Any reference signs in the claims should not be construed as limiting the claimed rights.

Claims

1. A soft soil solidifying agent based on waste lithium iron phosphate cathode powder, characterized in that, The soft soil solidifying agent comprises, by mass parts: 10 - 30 parts of waste lithium iron phosphate cathode powder, 10 - 75 parts of silica fume, 50 - 80 parts of slag, 10 - 20 parts of fly ash cenospheres, and 1 - 3 parts of water glass; The lithium iron phosphate cathode powder is calcined at high temperature to remove fluorine - containing impurities to obtain lithium iron phosphate waste powder; after the lithium iron phosphate waste powder is cooled, it is ground by a horizontal ball mill to obtain a precursor of the auxiliary cementitious material; silica fume is added to the precursor of the auxiliary cementitious material to adjust the silicon - lithium ratio, and oxygen is added to the high - temperature furnace for melting and oxidation to obtain lithium silicate auxiliary cementitious material.

2. The soft soil solidifying agent based on waste lithium iron phosphate cathode powder according to claim 1, characterized in that The source of the waste lithium iron phosphate cathode powder is: the waste lithium iron phosphate cathode powder is obtained by disassembling, crushing, and screening waste lithium iron phosphate batteries.

3. The soft soil solidifying agent based on waste lithium iron phosphate cathode powder according to claim 1, wherein The SiO₂ content in the silica fume is ≥97wt%, and the particle size of the silica fume is 3000 mesh.

4. A soft soil solidifying agent based on waste lithium iron phosphate cathode powder according to claim 1, characterized in that The grade of the slag is not lower than S95.

5. The soft soil solidifying agent based on waste lithium iron phosphate cathode powder according to claim 1, characterized in that, The particle size of the fly ash cenospheres is 2000 mesh.

6. The soft soil solidifying agent based on waste lithium iron phosphate cathode powder according to claim 1, wherein The modulus of the water glass is 1.

0.

7. A method for using the soft soil solidifying agent based on waste lithium iron phosphate cathode powder as described in claim 1, characterized in that, It includes the following steps:

1. The lithium iron phosphate cathode powder is obtained by crushing and screening waste lithium iron phosphate old batteries, and the lithium iron phosphate cathode powder is calcined at high temperature to remove fluorine - containing impurities to obtain lithium iron phosphate waste powder; 2. After the lithium iron phosphate waste powder is cooled, it is ground by a horizontal ball mill to obtain a precursor of the auxiliary cementitious material; 3. Silica fume is added to the precursor of the auxiliary cementitious material to adjust the silicon - lithium ratio, and oxygen is added to the high - temperature furnace for melting and oxidation to obtain lithium silicate auxiliary cementitious material; 4. The slag, fly ash cenospheres, and lithium silicate auxiliary cementitious material are mixed in proportion to form the cementitious material of the soft soil solidifying agent; 5. The soil to be solidified, the cementitious material of the soft soil solidifying agent, polypropylene fiber, water glass with a modulus of 1.0, and water are mixed and stirred evenly, and the solidification is completed after 24 hours.

8. The using method of a soft soil solidifying agent based on waste lithium iron phosphate cathode powder according to claim 7, characterized in that, Polypropylene fibers with a length of 6 ± 1mm are incorporated in an amount of 0 - 1.5% of the mass of the soft soil solidifying agent.

9. The application of a soft soil solidifying agent as described in claim 1, characterized in that, The soft soil solidifying agent is applied to soft soil solidification treatment and is suitable for the reinforcement of clay or silt foundations with high water content.

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