Method for disposing and utilizing large particle waste sand in ammonia-soda process alkali waste liquid

Abstract

The application discloses a method for treating and utilizing large-particle waste sand in ammonia-alkali method alkali waste liquid, and the process is as follows: treating the large-particle waste sand, reducing the content of soluble salt in the waste sand through water washing, controlling the content of soluble salt in the waste sand to be less than or equal to 2%, designing the mixing proportion of the waste sand lime cement soil, replacing the soil in the cement lime soil with different amounts of waste sand, keeping the mass ratio of the admixture lime and cement unchanged in each test, and decreasing the content of the soil corresponding to the waste sand proportion gradient; carrying out the compaction test on the materials in each group under different target moisture contents, obtaining the maximum dry density and the optimum moisture content of the sample; determining the waste sand replacement interval of the waste sand lime cement soil meeting the strength and the optimum proportion of the waste sand lime cement soil material; and preparing the waste sand lime cement soil for paving the roadbed or the base of the road. The application solves the phenomenon of pipe grinding in the process of filling the well with the alkali waste liquid, prepares the road material according to the designed proportion of the large-particle waste sand and the lime soil, reduces the cost of the alkali waste liquid, and changes the large-particle waste sand into the road raw material.

Description

Technical Field

[0001] This invention relates to the field of replacing and preparing roadbed filling with large-particle waste sand, and particularly to a method for disposing of and utilizing large-particle waste sand in ammonia-soda process alkali production waste liquid. Background Technology

[0002] The soda ash industry, often referred to as the "mother of industries," plays a vital role in economic development. Approximately 45% of soda ash production utilizes the ammonia-soda process, with an annual production capacity of 30 million tons. This process generates a significant amount of waste liquid; statistics show that approximately 10 cubic meters of waste liquid are discharged for every ton of soda ash produced. 3 Waste liquid. The "New Technology for Rock Salt Resource Filling-Type Water-Based Mining" proposes to mix the waste liquid produced during the alkali production process with alkali residue and desulfurized gypsum according to a designed liquid-solid weight ratio to form a mixed filling slurry. This slurry is then filled into underground rock salt cavities through pipelines. This process treats both the waste liquid and alkali residue while effectively filling the underground rock salt cavities using the precipitated alkali residue, eliminating potential geological hazards associated with the salt mining cavities. This process requires transporting the waste liquid from the alkali plant to the vicinity of the rock salt mining area via pipelines. The ammonia-soda process waste liquid contains a certain amount of large-particle waste sand, with particle sizes ≥0.075mm. These large particles severely erode the waste liquid transport pipelines, causing wear and blockages at bends and joints, affecting waste liquid transportation and posing significant safety risks. How to dispose of the large-particle waste sand in the ammonia-soda process waste liquid is a major challenge for enterprises.

[0003] To address the issue of large-particle waste sand in the wastewater discharged from the ammonia-soda process, the company proposed adding a ball mill grinding process to the ammonia-soda alkali production equipment system. This process would grind and pulverize the large-particle waste sand in the wastewater, reducing the particle size to <0.2mm, eliminating the potential for pipeline erosion, and ensuring the operation of well injection in the mining area. However, this method requires a large initial investment, generates significant noise during ball mill operation, creating a new noise source, and incurs substantial annual costs in manpower, materials, and electricity during the sand grinding process. Annual expenses for waste sand disposal and ball mill maintenance reach as high as 4 million yuan. This method only addresses the wear and tear on equipment and the impact on well injection caused by waste sand, without generating economic benefits.

[0004] Given the aforementioned background, how to reduce the waste liquid treatment cost of alkali production enterprises, transform solid waste large-particle waste sand into road construction raw materials, address the tight supply of environmental road materials, realize the resource utilization of large-particle waste sand and prepare new road construction materials have become urgent technical problems to be solved. Summary of the Invention

[0005] Objective: To address the shortcomings of existing technologies, this invention proposes a method for the disposal and utilization of large-particle waste sand from ammonia-soda process alkali production wastewater. This method solves the "pipe grinding" phenomenon during the injection, filling, and transportation of alkali production wastewater. The disposal method involves extracting large-particle waste sand from the ammonia-soda process wastewater using sedimentation and a sand separator, followed by water washing to reduce the chloride ion content and control the soluble salt content to ≤2%, thus preventing efflorescence and corrosion in later engineering projects. This invention recycles the large-particle waste sand for use in road materials, using it as filler to replace part of the soil in lime-cement soil materials. Through mechanical performance testing, a suitable replacement ratio is selected. This method meets road load-bearing requirements while solving the land occupation and environmental protection problems associated with solid waste dumping, reducing road raw material costs, and bringing economic benefits.

[0006] Technical solution: The method for treating and utilizing large-particle waste sand in the waste liquid from the ammonia-soda process of alkali production of this invention includes the following steps:

[0007] (1) Disposal of large-particle waste sand in the waste liquid from the ammonia-soda process.

[0008] In the ammonia-soda process for producing soda ash, the mother liquor after carbonization filtration is decomposed with lime slurry. The resulting NH3 is recovered by distillation in a distillation tower, generating a large amount of waste liquid. The main solid components of this waste liquid are CaCO3, CaCl2, and Mg(OH)2, including large particles of waste sand. To extract these large particles, a neutralization tower is added to the existing equipment. The distillation waste liquid from the ammonia-soda process is fed to the bottom of the neutralization tower for sedimentation. Large solid particles are discharged from the bottom of the tower and separated by a spiral sand separator to obtain waste sand. A spraying device is added at an appropriate location on the equipment to spray the large particles of waste sand with clean water, dissolving the soluble salts in the waste sand. The soluble salt content in the waste sand is tested to be ≤2%, reducing the soluble salt content in the large particles of waste sand and preventing potential hazards from lime cement soil corrosion and salinization in the later stages. The waste sand is then fed into a return sand bin via a spiral feeder.

[0009] (2) Design the mix proportions of waste sand, lime, cement, and soil.

[0010] (2.1) Selecting test materials and obtaining their basic properties

[0011] The materials required for the experiment were waste sand, lime, cement, and soil, with plain soil being selected. Ordinary silicate commercial cement and anhydrous lime powder (for industrial use) were purchased, respectively. The waste sand and plain soil were obtained from the alkali plant's return sand storage and the roadbed borrow pit, respectively. The waste sand and plain soil were air-dried, then crushed, ground, and passed through a 2mm sieve. Samples of the waste sand and soil were then tested for their natural moisture content in an oven.

[0012] (2.2) Design the mix proportions of waste sand, lime, cement and soil.

[0013] A section of road was selected as the test section. The planned lime-cement-soil mix ratio for the test road was used as the reference mix ratio. The reference mix ratio was assumed to be a set value a:b:c, such as 2:4:100. Four to six test groups were designed, with the first group serving as a control. The material ratio was waste sand:lime:cement:soil = 0:a:b:c = 0:2:4:100. Different amounts of waste sand were used to replace the soil in the reference material, and the group numbers were designated 1, 2, 3, 4 (or 1, 2, 3, 4, 5, 6). In each test group, the mass ratio of the admixtures lime and cement remained constant, while the waste sand percentage was 0%, x%, 2x%, 3x%, 4x% (or 0%, x%, 2x%, 3x%, 4x%, 5x%, 6%). The soil content corresponds to the waste sand ratio decreasing sequentially in a gradient manner, namely 100%, (100-x%), (100-2x%), (100-3x%), (100-4x%) or (100%, (100-x%), (100-2x%), (100-3x%), (100-4x%), (100-5x%), (100-6x%).

[0014] (2.3) Determine the optimal moisture content of waste sand, lime, cement and soil.

[0015] Compaction tests were conducted on materials at different target moisture contents for each group, and the optimum moisture content was calculated. Assuming the optimum moisture content of the reference group (lime-cement soil) is known to be y%, 4-6 target moisture contents were designed for each experimental group. The target moisture contents were set based on y%, fluctuating up or down by 2-3 units, i.e., (y-2)%, (y-1)%, y%, (y+1)%, and (y+2)% (rounded to the nearest integer). Based on the target moisture content requirements, light compaction tests were conducted according to the "Test Procedures for Inorganic Binder Stabilized Materials in Highway Engineering." The maximum dry density and optimum moisture content of the samples were calculated and fitted based on the different dry densities corresponding to different target moisture contents.

[0016] (2.4) Mechanical property test of waste sand-lime-cement soil

[0017] (2.4.1) The preparation of UCS specimens was carried out in accordance with the T0805—2018 Test Method for Unconfined Compressive Strength of Inorganic Binder Stabilized Materials in the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" (JTG E51-2009). Based on the mix design and the optimum moisture content and maximum dry density of the materials, the required material quantity for specimen preparation was calculated. According to the requirements of the unconfined compressive strength test, the specimens should have small size and good uniformity. Cylindrical unconfined compressive strength specimens with a diameter × height of 50 × 50 mm were prepared.

[0018] (2.4.2) Refer to the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" (JTG E51-2009) T0805-2018, "Test Method for Unconfined Compressive Strength of Inorganic Binder Stabilized Materials". Strength test: Turn on the press switch, connect the computer and the press, place the specimen on the press base, and use the handle to control the upper platen of the press to almost contact the specimen, but not completely, maintaining a loading rate of 1 mm / min. Record the maximum pressure P at the time of specimen failure.

[0019] (2.5) Select the optimal mix ratio of waste sand, lime, cement and soil

[0020] Based on the mechanical test results of each group, unconfined compressive strength curves under different replacement amounts were plotted, and curve fitting was performed to obtain a complete curve. Waste sand-lime-cement soil is used for Class II and lower-grade highways. 0.7 MPa was selected as the minimum screening standard for the 7-day unconfined compressive strength of the waste sand-lime-cement soil material. The minimum requirement was the unconfined compressive strength of the material under the first mix proportion (i.e., waste sand: lime: cement: soil = 0:2:4:100). Mix proportions with strengths greater than both the minimum screening standard and the 7-day unconfined compressive strength under the first mix proportion were considered acceptable. Sand replacement amounts lower than these two strengths were deemed unacceptable. From the fitting results, mix proportions that met the requirements were selected, and the mix proportion with the highest strength was chosen. Finally, the waste sand replacement range that met the strength requirements of the waste sand-lime-cement soil material and the optimal mix proportion of the waste sand-lime-cement soil material were determined.

[0021] (3) Utilization of large-particle waste sand

[0022] Based on the particle characteristics of large-particle waste sand, a certain proportion of soil components in road lime-cement soil are replaced by large-particle waste sand. Road waste sand lime-cement soil is prepared by using large-particle waste sand, cement, lime and soil to pave roadbed or base course.

[0023] In step (2.3), the sample is divided into multiple parts and added into the compaction cylinder for compaction. Then, the cylindrical ring cutter sample is taken out from the compacted sample and the maximum dry density and optimum moisture content of the sample are calculated.

[0024] In step (2.4.1), the process of preparing the cylindrical sample includes weighing, curing, molding, compaction, demolding, and curing.

[0025] In step (2.4.2), the unconfined compressive strength of the specimen is calculated using formulas (1) and (2):

[0026]

[0027] In the formula: R c—Unconfined compressive strength of the specimen (MPa); P—Maximum pressure at which the specimen fails (N); A—Cross-sectional area of ​​the specimen (mm2);

[0028]

[0029] D — Diameter of the sample (mm).

[0030] Working Principle: This invention proposes a sand-liquid separation treatment for waste liquid, and reduces the soluble salt content in the waste sand by spraying water, controlling the soluble salt content of the waste sand to not exceed 2%. Large-particle waste sand is then mixed with lime and soil in a certain designed ratio, and the separated large-particle waste sand is used to prepare road construction materials. This reduces the waste liquid treatment cost of alkali production enterprises, transforms solid waste large-particle waste sand into road construction raw materials, addresses the problem of tight supply of environmental road materials, realizes the resource utilization of large-particle waste sand, and prepares new road construction materials.

[0031] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0032] (1) This invention solves the problem of grinding tubes in waste liquid transportation by treating the waste liquid with sand-liquid separation, and reduces the content of easily soluble salts in alkali sand by water washing, effectively avoiding the potential danger of efflorescence in the later stage of alkali sand preparation material engineering.

[0033] (2) This invention uses large-particle waste sand, lime, and soil in a certain design ratio to prepare road construction materials by separating large-particle waste sand, thereby reducing the waste liquid treatment cost of alkali production enterprises, turning solid waste large-particle waste sand into road construction raw materials, solving the problem of tight supply of environmental road materials, realizing the resource utilization of large-particle waste sand, and preparing new road construction materials. Attached Figure Description

[0034] Figure 1 This is a diagram illustrating the method for extracting large-particle waste sand from waste liquid produced by the ammonia-soda process of the present invention.

[0035] Figure 2 This is a roadmap for the method of utilizing large-particle waste sand according to the present invention;

[0036] Figure 3 This is a test diagram showing the optimal moisture content of the materials used in this invention.

[0037] Figure 4 This is a diagram illustrating the sample preparation process of the present invention;

[0038] Figure 5 This is the unconfined compressive strength test in this invention;

[0039] Figure 6 This is a graph showing the unconfined compressive strength and fitting curve of the experimental group in this invention. Detailed Implementation

[0040] Example:

[0041] The method for treating and utilizing large-particle waste sand in the waste liquid from the ammonia-soda process of alkali production of this invention includes the following steps:

[0042] (1) Extraction of large-particle waste sand from waste liquid produced by the ammonia-soda process

[0043] Distillation waste liquid from the evaporation process is sent to the bottom of the waste liquid neutralization tower for sedimentation. Larger solid particles are discharged from the bottom of the tower, separated by a spiral sand separator and treated with water spray. The waste sand is then loaded onto trucks and transported out as a by-product.

[0044] (2) Experimental materials and treatment

[0045] The waste sand source was the return sand from the spiral sand separator of an alkali plant. In this embodiment, the neutralized sand from the return sand was selected. The soil used for the test was taken from about 20m south of the intersection of Keji Avenue and Tianjin Road in Qingjiangpu District, Huai'an City, at a depth of 1-2 meters. The soil was crushed according to the requirements for soil samples in the "Specifications for Geotechnical Testing of Highways" (JTG 3430-2020). The cement used for the test was Conch brand ordinary Portland cement, grade 42.5. The main mineral components of Portland cement are: 3CaO·SiO2, 3CaO·SiO2, 3CaO·Al2O3, and C4AF. The lime used for the test was gray-white industrial anhydrous lime powder, a white powdery substance with calcium carbonate as the main component and a calcium and magnesium content of over 80%.

[0046] Moisture content tests were conducted on waste sand and native soil sequentially. Six waste sand samples and six soil samples were tested. The soil samples were extracted from soil samples at different depths. After extraction, the moisture content of the waste sand and soil was found to be significantly high, which could not meet the subsequent mix design requirements. To meet the calculation conditions, the waste sand and soil were first dried for two days. The test was conducted when the samples turned bluish-green and powdery. Before the test, representative samples were separated from the samples using the quartering method. During the test, the weight of the aluminum box was first weighed, recorded, and zeroed. Then, 20 grams of test sample were added, and the total weight was weighed. The test was repeated six times, and the data were recorded. The six aluminum boxes were then placed in an oven for baking. The temperature was set at 110 degrees Celsius, and the baking time was 8 hours. After baking, the samples were removed, the remaining mass was weighed, and the moisture content was calculated according to the formula.

[0047] (3) Compaction test

[0048] According to the "Test Procedures for Inorganic Binder Stabilized Materials in Highway Engineering" (JTGE51-2009), compaction tests are necessary for materials to plot dry density-moisture content curves, thereby determining their optimum moisture content and maximum dry density.

[0049] In this embodiment, waste sand with an intermediate replacement amount of 9% was selected, and the ratio of waste sand:cement:lime:soil = 9:2:4:91 was used. The designed target moisture content was 17%, 18%, 19%, 20%, and 21%. The total mass of the specimen was set at 2000g.

[0050] Substitute the moisture content obtained from the test into the formula to calculate the material. Weigh the corresponding weight of material according to the calculation results. Repeat the experiment five times. In the experiment, after putting all the materials into a plastic bag, stir them evenly to mix the materials. Then add water and soak for two hours before compacting.

[0051] After sample preparation, the samples were divided into three portions. One-third of the sample was added to the compaction cylinder each time, and the cylinder was compacted 27 times with a compactor. The surface was then roughened to prevent delamination before adding the next portion of sample. This process was repeated three times until all samples were compacted. After compaction, a weighed ring cutter was used to remove cylindrical samples from the compacted specimens. The results showed that, with a 9% waste sand replacement rate, the specimens achieved a maximum dry density of 1.75 g / cm³ at an optimum moisture content of 18.39%.

[0052] (4) Experimental Design

[0053] According to the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" (JTGE51-2009), this invention conducts a 7-day unconfined compressive strength test on waste sand specimens in order to study the compressive strength of waste sand under different mix proportions.

[0054] This invention designs cement and lime as external admixtures at dosages of 2% and 4%, respectively. Under the premise of maintaining the same admixture ratio, waste sand is used to replace soil. Five sets of waste sand replacement amounts are designed: 3%, 6%, 9%, 12%, and 15% of the total mass of waste sand and soil. Experiments are conducted to determine the optimal mix ratio. The optimal mix ratios are shown in Table 1 below.

[0055] Table 1 Scheme Proportions

[0056]

[0057] According to the "Test Procedure for Inorganic Binder Stabilized Materials", after the soil sample passes through a 2mm sieve, based on the maximum moisture content and maximum dry density of the sample obtained from previous basic experiments, the required amount of material for different waste sand replacement amounts is designed, as shown in Table 2 below.

[0058] Table 2 Material Usage Table

[0059]

[0060] (5) Sample preparation

[0061] During sample preparation, the high moisture content of the soil prevented subsequent mix design. Therefore, before preparing the samples, the soil was spread out and dried for two days. The moisture content was then remeasured. Once the average moisture content of the soil had dropped to a suitable range, the soil was broken up, small stones and debris were removed, and the soil was sieved through a 2mm sieve and stored in a bucket for later use.

[0062] Select a clean workbench and place the soil, waste sand, lime, cement, and water raw materials on one side, and an electronic balance, beakers, and dropper measuring equipment on the other side. According to the experimental proportions, use the electronic balance to measure the mass of the soil, waste sand, lime, cement, and water in sequence. The order of the dry materials can be changed during the measurement process, but water should be weighed last. After all the dry materials are placed in a plastic bag, shake the bag to mix them evenly, and add water in three batches. Shake well after each addition of water. Repeat the above preparation steps until all specimens are prepared. Since cement-stabilized materials are used in this experiment, specimen molding should begin immediately after specimen preparation is completed, and all work should be completed within one hour.

[0063] The sample was slowly poured into a small compaction cylinder, ensuring both the upper and lower iron blocks were sealed tightly. The oil pump was turned on, lowering the press. The specimen was placed under the press and compacted until the iron blocks on both sides were parallel to the sides of the compaction cylinder. During the test, some iron blocks in the compaction cylinder could not be pressed down. Analysis revealed this was due to aging and internal corrosion of the compaction cylinder. The problem was resolved by repositioning and repressurizing. After compacting the specimen, the press pressure was maintained for one minute to achieve the predetermined 95% compaction requirement.

[0064] After compacting the specimen, place it on the demolding machine to demold. During demolding, be careful to handle the specimen gently if its strength is too low, and be careful not to let the corners of the specimen fall off.

[0065] Repeat the above steps to demold all 18 specimens of the prepared mix. After demolding, wrap each specimen with plastic wrap to prevent direct water exposure. Prepare a standard curing chamber, setting the curing temperature to 20℃ and the relative humidity to above 95%. Before curing, first check that the curing chamber is functioning properly and fill the water tank with water. Place the specimens in the chamber and check again that the wrapping is complete. Studies have shown that alkaline soil specimens soften significantly when cured in an exposed state.

[0066] Curing in a standard curing chamber for 6 days, constantly monitoring the water level in the tank and the sealing condition of the specimen. After 6 days, remove the specimen and immerse it in water at 20°±2°, with the water level 2.5cm above the top of the specimen. After soaking for one day, wipe off the surface moisture and remove it for later use.

[0067] (6) Unconfined compressive strength test

[0068] According to the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" (JTGE51-2009), the retrieved samples were tested using an electronic universal testing machine.

[0069] The universal testing machine should be checked to ensure the specimen's failure load is greater than 20% and less than 80% of the measuring range. Oil should be applied to the spherical support to allow for smooth rotation. The surface of the removed specimen should be wiped dry with a soft cloth, and the height and width of the specimen should be precisely measured again using vernier calipers, accurate to 1 mm.

[0070] Using the DSP operating platform, input the specimen size as 50mm × 50mm and set the descent speed as 1mm / min. Place the specimen on the pre-placed spherical support and manually fine-tune the testing machine to ensure the pressure-bearing surface of the specimen contacts the machine. Start the machine; the specimen will rise under pressure until all specimens fail. Record the maximum pressure at failure of each specimen.

[0071] After the test, the unconfined compressive strength of the specimen was calculated by substituting the values ​​into formulas (1) and (2) according to the specifications.

[0072]

[0073] In the formula: R c —Unconfined compressive strength of the specimen (MPa); P—Maximum pressure at specimen failure (N); A—Cross-sectional area of ​​the specimen (mm2);

[0074]

[0075] D—Diameter of the specimen (mm).

[0076] (7) Data fitting and analysis

[0077] Unconfined compressive strength of road waste sand cement lime soil under different waste sand replacement amounts, such as Figure 6 As shown.

[0078] Experimental Results Analysis: When the waste sand replacement rate was 0%, the strength of the road waste sand specimen reached 0.8 MPa. With the increase in waste sand replacement rate, the average unconfined compressive strength of the waste sand gradually increased, reached a peak, and then gradually decreased. When the waste sand replacement rate was 3%, 6%, and 9%, the unconfined compressive strength was greater than the minimum requirements of the control group and the roadbed. When the waste sand replacement rate was greater than 12%, the strength requirement was not met. Since the data trend showed an initial increase followed by a decrease with continuous variation, a polynomial function was used for fitting. The cubic function used for fitting was y = (0.79651) + (0.00816)x + (0.00117)x. 2 +(-1.50892E-4)x 3According to this function, y = (0.79651) + (0.00816)x + (0.00117)x 2 +(-1.50892E-4)x 3 Analysis showed that as the amount of waste sand replaced increased, the strength of the road waste sand-lime-cement soil specimen reached its maximum of 0.86 MPa when the waste sand replacement rate reached 7.56%. Further increasing the waste sand replacement rate, when it reached 12.07%, the strength of the road waste sand-lime-cement soil specimen dropped to 0.8 MPa. This strength is below 0.8 MPa and does not meet the unconfined compressive strength value of the control group. In other words, waste sand with a replacement rate exceeding this threshold does not meet the strength requirements of this test. The waste sand replacement range that meets the strength requirements is 0%-12.07%.

[0079] Under the premise of meeting the strength requirements, the optimal mix ratio of waste sand, lime, cement, and soil was selected based on the highest unconfined compressive strength of the specimens. According to the functional trend, the road waste sand and soil specimens reached their highest strength of 0.86 MPa when the waste sand replacement amount was 7.56%. Therefore, the amount of waste sand replacing soil at this point is 7.56%. That is, the optimal mix ratio is waste sand:cement:lime:soil = 7.56:2:4:92.44. Rounding to the nearest integer, the ratio is 8:2:4:92.

Claims

1. A method for the treatment and utilization of large-particle waste sand in ammonia-soda process alkali production waste liquid, characterized in that: include: (1) Extract large-particle waste sand from the waste liquid of ammonia-soda process alkali production. Add a neutralization tower device to the process equipment. Send the distillation waste liquid from the ammonia-soda process evaporation process to the bottom of the neutralization tower for sedimentation. The solids are discharged from the bottom of the tower. After sand separation, waste sand is obtained. Add a spraying device to the process equipment to spray water on the large-particle waste sand so that the soluble salts in the waste sand dissolve in the water. Detect the soluble salt content in the waste sand ≤2%. Then the waste sand enters the return sand bin for storage. (2) Design the mix proportions of waste sand, lime, cement and soil; (2.1) The waste sand and soil were dried in the sun, crushed and ground after drying, and then sieved. A portion of the waste sand and soil was taken out for natural moisture content testing. (2.2) Based on the original planned cement-lime-soil mix ratio of the test road, the reference mix ratio was used. Assuming the mass ratio of lime, cement, and soil in the reference group was a:b:c, 4-6 test groups were designed. The first group was the control test, with a material ratio of waste sand:lime:cement:soil = 0:a:b:c. Different amounts of waste sand were used to replace the soil in the reference material, and the group numbers were marked. In each test group, the mass ratio of the external admixtures lime and cement remained unchanged, and the proportion of waste sand was 0%, x%, and so on. %, 2x%, 3x%, 4x% or 0%, x%, 2x%, 3x%, 4x%, 5x%, 6%; the soil content corresponds to a decreasing proportion of waste sand in a gradient, namely 100%, (100-x)%, (100-2x)%, (100-3x)%, (100-4x)% or 100%, (100-x)%, (100-2x)%, (100-3x)%, (100-4x)%, (100-5x)%, (100-6x)%; (2.3) Determine the optimal moisture content of waste sand, lime, cement, and soil; Compaction tests were conducted on materials at different target moisture contents for each group, and the optimum moisture content was calculated. Assuming that the optimum moisture content of the reference group lime-cement soil was y%, 4-6 target moisture contents were designed for each experimental group. The target moisture contents were set based on y%, fluctuating up or down by 2-3 units of moisture content, namely (y-2)%, (y-1)%, y%, (y+1)%, and (y+2)%, respectively. Based on the target moisture content requirements, compaction tests were conducted, and the maximum dry density and optimum moisture content of the sample were calculated and fitted. (2.4) Mechanical property test of waste sand, lime, cement and soil; (2.4.1) Based on the optimum moisture content and maximum dry density of the sample, calculate the amount of material required for sample preparation and prepare a cylindrical unconfined compressive strength sample. (2.4.2) Perform an unconfined compressive strength test on the specimen and record the maximum pressure P when the specimen fails; The unconfined compressive strength of the specimen is calculated using formulas (1) and (2): （1）； In the formula: —Unconfined compressive strength of the specimen, MPa; P—Maximum pressure at specimen failure, N; A—Cross-sectional area of ​​the specimen, mm 2 ; （2）； D—Diameter of the sample, mm; (2.5) Select the optimal mix ratio of waste sand, lime, cement and soil. Based on the mechanical test results of each group, plot the corresponding unconfined compressive strength curves under different replacement amounts and perform curve fitting to obtain the complete curve. Select the minimum screening standard for the 7-day unconfined compressive strength of waste sand, lime, cement and soil materials. Take the unconfined compressive strength of the materials under the first group of material ratios in step (2.2) as the minimum requirement. The mix ratio with conditional strength greater than the minimum screening standard and the minimum requirement is the selectable mix ratio. Select the mix ratio that meets the requirements from the fitting results and select the mix ratio with the highest strength. Finally, determine the waste sand replacement range and the optimal mix ratio of waste sand, lime, cement and soil that meet the strength requirements. (3) Use large-particle waste sand, lime, cement and soil to prepare road waste sand lime cement soil for paving roadbed or base course.

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