High-water-content ardealite soil curing agent and preparation method thereof

Abstract

The invention relates to the technical field of ardealite resource utilization, in particular to a high-water-content ardealite soil curing agent and a preparation method thereof. The high-water-content ardealite soil curing agent is prepared from the following raw materials: ardealite, a modifier, a composite active mineral admixture and a reinforcing agent. The ardealite with high water content is mainly used as a raw material, the steps of drying and calcining are not needed in the curing agent preparation process, the ardealite is processed by the modifier and then mixed with other raw materials, the curing agent can be prepared, the preparation process is simple, and the energy consumption is low.

Description

Technical Field

[0001] The invention relates to the technical field of phosphogypsum resource utilization, and specifically relates to a high-water content phosphogypsum soil curing agent and a preparation method thereof. Background Art

[0002] Phosphogypsum is a solid waste discharged when wet phosphoric acid is produced. Its main component is calcium sulfate dihydrate (CaSO4·2H2O), and it also contains incompletely decomposed phosphate rock, fluoride, phosphoric acid, organic matter, etc. Usually, about 4-5 tons of phosphogypsum are produced as by-products for every ton of phosphoric acid produced. At present, the annual emission of phosphogypsum worldwide is about 100-280 million tons, and the utilization rate is only about 15%. The annual emission of phosphogypsum in my country has exceeded 50 million tons. Due to the bottleneck of resource utilization technology, the cumulative stockpile exceeds 200 million tons. The open-air storage of phosphogypsum not only occupies a large amount of land, pollutes water bodies, and harms the surrounding atmosphere, soil and groundwater. In order to alleviate this environmental crisis, water-washed phosphogypsum or lime-washed phosphogypsum is the most commonly used method for resource utilization of phosphogypsum, which can eliminate most of the harmful substances in phosphogypsum. However, the water content of water-washed phosphogypsum is generally around 20%, or even higher, which limits the application scope of phosphogypsum and is not conducive to the promotion and application of phosphogypsum. The resource utilization of phosphogypsum has important practical significance. It can achieve efficient utilization and disposal of stockpiled phosphogypsum, develop a circular economy, and restore industrial solid waste resources to industrial construction. It can solve the environmental pollution problem of the phosphating industry from the source and realize the construction of a beautiful China.

[0003] At present, some studies have tried to use phosphogypsum as raw material, supplemented with industrial waste residue to prepare curing agent, which is used to solidify poor soil, construction or industrial solid waste. However, phosphogypsum has 20%-30% free water and about 20% crystal water, which has high viscosity and is not easy to transport. Most of the water can be removed by drying and calcining, but low-temperature drying is inefficient and difficult to adapt to large-scale production. High-temperature drying can easily cause dehydration of dihydrate gypsum; calcining into building gypsum or anhydrous gypsum consumes a lot of energy and has high cost, making it difficult to apply and absorb in large quantities.

[0004] For example, the prior art CN115286344B discloses a method for preparing a curing agent using phosphogypsum and its application. In this patent, the curing agent includes independently packaged dry materials and wet materials. The dry materials are phosphogypsum, lime-like substances and volcanic ash-like substances, and the wet materials are aqueous solutions of anionic surfactants and emulsifiers. The two are compounded and used. The curing process requires three mixing and stirring processes: (1) the dry materials are mixed with the curing materials, (2) the wet materials are mixed with water, and (3) the dry-based mixture and the wet-based mixture are mixed again to obtain a hardened body. The phosphogypsum needs to be dried and ground at a drying temperature of 45°C and a drying time of up to 48 hours. Large-scale production is difficult. During use, the dry materials and wet materials need to be compounded and used. The wet materials contain a variety of polymer substances and the composition is relatively complex.

[0005] CN113716927A discloses a phosphogypsum-based soil curing agent, a preparation method, a curing sample and a preparation method thereof. The phosphogypsum-based soil curing agent in the patent includes modified phosphogypsum and an active component. The preparation process is to stir the original phosphogypsum and carbide slag in a ratio of 1: (1-4) for 30-45 minutes, and calcine at 800-900℃ for 1.5-2.5 hours to obtain the modified phosphogypsum; the modified phosphogypsum and the active component are mixed in a mass ratio of 45:55, and stirred again for 30-45 minutes to obtain the phosphogypsum-based soil curing agent. The phosphogypsum has a high moisture content, the material is sticky, and calcination and drying often cause agglomeration. The curing agent has a complex production process, high energy consumption, a long production process, and a low phosphogypsum consumption.

[0006] CN115724629A discloses a solidifying agent for silty slag and a preparation method thereof. In the patent, the solidifying agent is made of silicate cement, steel slag powder, industrial by-product gypsum, mineral admixtures, surfactants, etc. as raw materials, wherein silicate cement: 15-30 parts, steel slag powder 15-30 parts, industrial by-product gypsum accounts for 20-30 parts, composite admixtures: 30-50 parts, surfactant: 0.01-0.8 parts. Industrial by-product gypsum can be selected from one or more of desulfurized gypsum, phosphogypsum, titanium gypsum, and fluorinated gypsum, preferably phosphogypsum, and its water content is limited to less than 5%. The proportion of phosphogypsum in the solidifying agent is relatively low, and there are certain requirements for the water content, and it is difficult to absorb a large amount of phosphogypsum with high water content.

[0007] In summary, phosphogypsum has been studied and applied in the field of curing agents, but most of them still need drying or calcination for pretreatment, or their moisture content must be strictly controlled. The preparation process needs to go through calcination, drying and other processes, which consumes a lot of energy. Summary of the invention

[0008] In view of this, the present invention aims to provide a high-water content phosphogypsum soil curing agent and a preparation method thereof.

[0009] A first aspect of the present invention provides a high-water content phosphogypsum soil curing agent, comprising phosphogypsum, a modifier, a composite active mineral admixture, and a reinforcing agent.

[0010] The soil solidifying agent comprises the following raw materials in percentage by weight: 20%-55% phosphogypsum, 5%-20% modifier, 25%-65% composite active mineral admixture, and 0-10% reinforcing agent; unless otherwise specified, the contents described in the present invention are all percentages by weight, and the sum of the contents of each component is 100%.

[0011] In one embodiment, the soil solidifying agent is divided into material A and material B, wherein material A comprises phosphogypsum and a modifier, and material B comprises a composite active mineral admixture and a reinforcing agent. Further, the mass ratio of material A to material B is 70:30 to 35:65, preferably 60:40 to 40:60, and most preferably 55:45.

[0012] Further preferably, the phosphogypsum is selected from washed phosphogypsum with a moisture content of 15%-30% and a dry basis CaSO4·2H2O content ≥65%; preferably, the phosphogypsum has a moisture content of 15%-25%, and a dry basis CaSO4·2H2O ≥80%; further preferably, the phosphogypsum has a moisture content of 15%-20%, and a dry basis CaSO4·2H2O ≥90%.

[0013] Further preferably, the modifier is selected from at least two of lime kiln tail ash, desulfurization ash, cement kiln ash, calcium quicklime, and carbide slag, and the CaO content of the modifier is ≥50%; preferably, the CaO content is ≥60%, and further preferably, the CaO content is ≥75%; preferably, the specific surface area of ​​the modifier is 800-2000cm 2 / g; further preferably, the specific surface area of ​​the modifier is 1000-2000cm 2 / g.

[0014] Further preferably, the activity index of the slag powder in the composite active mineral admixture is ≥95; the activity index of the steel slag powder, copper slag powder, phosphorus slag powder and lithium slag powder is ≥65.

[0015] Further preferably, the composite active mineral admixture comprises the following raw materials in the following mass proportions: 80-100% slag powder; the remainder is one or more of steel slag powder, copper slag powder, phosphorus slag powder, and lithium slag powder; more preferably, the composite active mineral admixture includes 80-90% slag powder and 10-20% steel slag powder.

[0016] Further preferably, the reinforcing agent includes one or more of ultrafine steel slag powder, ultrafine slag powder, ordinary Portland cement, sulphoaluminate cement, nano-hydrated calcium silicate, and nano-calcium carbonate.

[0017] The second aspect of the present invention provides a method for preparing a high-water content phosphogypsum soil curing agent, comprising the following steps:

[0018] S1, phosphogypsum and a modifier are mixed and aged to obtain material A;

[0019] S2, mixing the composite active mineral admixture with the reinforcing agent to obtain material B;

[0020] S3, mix material A and material B to obtain.

[0021] Beneficial Effects

[0022] (1) The present invention mainly uses high-water content phosphogypsum as raw material. In the process of preparing the curing agent, no drying and calcining steps are required. After being processed by a modifier and then mixed with other raw materials, the curing agent can be prepared. The preparation process is simple and the energy consumption is low.

[0023] (2) In the soil solidifying agent provided by the present invention, the proportion of phosphogypsum is more than 40%, and the solid waste utilization rate is as high as 90%, which can still meet the performance requirements in subsequent applications, is conducive to the large-scale disposal of phosphogypsum resources, and meets the requirements of low-carbon environmental protection.

[0024] (3) In the present invention, phosphogypsum with a moisture content of 15%-30% and a dry basis CaSO4·2H2O ≥ 65% is preferred. Compared with traditional cement mortar, gypsum mortar made of phosphogypsum can save material costs and construction costs during construction. However, since it contains a certain amount of moisture, the mechanical properties of the material are poor, and it is easy to absorb moisture and peel off. Currently, steel slag is often used to modify the water-containing phosphogypsum on the market. However, the density and porosity of steel slag are low. After being used in the curing agent, the thermal insulation, corrosion resistance, seismic resistance and frost resistance of the curing agent may be affected to a certain extent. The inventors unexpectedly discovered that by using at least two of lime kiln tail ash, desulfurization ash, cement kiln dust, calcium quicklime and carbide slag as modifiers for high-water-content phosphogypsum, the high-water-content phosphogypsum can be modified. Under the condition of ensuring that it has a certain water content, since the lime kiln tail ash and other materials themselves have the characteristics of low density, high cylinder pressure strength and high porosity, the thermal insulation, corrosion resistance, earthquake resistance and frost resistance of the curing agent can be effectively guaranteed. However, the single-component modifier has a higher porosity and stronger water absorption. Therefore, in order to further reduce the water absorption performance of the curing agent, the inventors preferably use a compound of at least two of lime kiln tail ash, desulfurization ash, cement kiln dust, calcium quicklime and carbide slag as modifiers for high-water-content phosphogypsum, which can effectively reduce the water absorption performance of the curing agent and ensure the stability of the material to be processed and cured after its use.

[0025] (4) Although the modified phosphogypsum has certain thermal insulation, corrosion resistance, earthquake resistance and frost resistance, its mechanical properties are relatively poor. The inventors found that the use of steel slag powder in the curing agent system can effectively improve the mechanical properties of the curing agent, but the defects of steel slag powder mainly include: causing a significant decrease in the early strength of concrete, cement coagulation too fast and no strength, and stability problems. Therefore, the inventors selected slag powder and steel slag powder as a composite active mineral admixture, which can improve the defects of the above-mentioned single-component steel slag powder. At the same time, slag powder also has certain anti-corrosion properties, significantly reducing the amount of water seepage of cement concrete, improving the workability of concrete, improving the density of cement concrete, improving the impermeability, and improving the stability and application range of the soil curing agent.

[0026] (5) The present invention achieves a high utilization rate of solid waste and can ensure the solidification effect of the soil solidifier by rationally selecting raw materials, and has certain unconfined compressive strength, anti-permeability and water stability; the obtained soil solidifier can be used in engineering fields such as sludge solidification disposal, solidification disposal of engineering waste soil, roadbed filling, tidal flat solidification, and poor soil improvement. DETAILED DESCRIPTION

[0027] Example 1 Curing agent formulation selection experiment

[0028] The test method refers to the "DG_TJ08-2082-2023 Technical Standard for the Application of Soil Hardeners" for molding, curing, and testing of 7d and 28d compressive strength.

[0029] In the curing agent described in this example, the moisture content of phosphogypsum PG1 is 15%, and the CaSO4·2H2O content is 85.6%; the moisture content of PG2 is 25%, and the CaSO4·2H2O content is 97.2%;

[0030] Modifier: Modifier 1 is prepared from lime kiln tail ash, desulfurization ash and calcium quicklime, wherein the CaO content of modifier 1 is 70% and the specific surface area is 800cm 2 / g; Modifier 2 is prepared from desulfurized ash and calcium quicklime, wherein the CaO content of modifier 2 is 55% and the specific surface area is 2000cm 2 / g.

[0031] Composite active mineral admixture: slag powder accounts for 90% by mass, and steel slag powder accounts for 10% by mass.

[0032] Reinforcement agent: PO 42.5 cement and ultrafine slag powder in a ratio of 50:50.

[0033] The experimental proportions of phosphogypsum modification are shown in Table 1.

[0034] Table 1 Phosphogypsum modified test ratio

[0035]

[0036] From the above test results, it can be seen that the pH value, moisture content and CaSO4·2H2O content of A2 material all have certain advantages, so A2 is selected as the curing agent for A material.

[0037] The test soil selected was silty clay (natural moisture content 36%), the soil solidifier was added at a ratio of 20% of the wet soil mass, the water-cement ratio was 1.5, and the detailed formula is shown in Table 2 below.

[0038] Table 2 Compressive strength test of different curing agent formulations

[0039]

[0040] The preparation method of the curing agent is:

[0041] S1, phosphogypsum and modifier are mixed and aged for 24 hours to obtain material A;

[0042] S2, mixing the composite active mineral admixture with the reinforcing agent to obtain material B;

[0043] S3, mix material A and material B to obtain.

[0044] Example 2 Experiment on the recycling of soil solidifying agent for engineering waste soil disposal

[0045] The test method refers to the "T / CECS1037-2022 Technical Standard for Premixed Fluidized Solidified Soil Filling" to conduct slump, setting time and compressive strength tests, and the amount of water is dynamically adjusted according to the fluidity.

[0046] The curing agents G1 and G2 in the aforementioned Example 1 were selected to carry out the engineering slag curing test. The specific formula of the soil curing agent in the test is shown in Table 3. The test soil is the silty silt soil in the engineering slag described in Example 1, with a moisture content of 36%. The test formulas with different dosages are shown in Table 4.

[0047] Table 3 Curing agent formula

[0048]

[0049] Table 4 Compressive strength and fluidity test under different curing agents and different dosages

[0050]

[0051] According to the above test results, when the construction waste is mixed with water and the two soil solidifying agents are added at a dosage of 10% and 20%, backfill materials that meet the technical requirements of "T / CECS1037-2022JGJ / T 70-2009 Technical Standard for Ready-Mixed Fluidized Solidified Soil Filling" can be prepared. This material can be used in different backfill fields to realize the resource utilization of construction waste.

[0052] Example 3 Roadbed filling test

[0053] The application of soil solidifying agent in the field of roadbed filling, the test method refers to "JTG E51 Highway Engineering Inorganic Binder Stabilization Material Test Procedure", and the test of solidifying agent for roadbed filling material is carried out. The silty silt soil with a moisture content of 21% is used in the test. G2 and G4 solidifying agents in Example 1 are selected, and the dosage is selected to be 15% and 20%.

[0054] Table 5 Curing agent formula

[0055]

[0056] Table 6 Test of different curing agents for roadbed filling

[0057]

[0058] It can be seen from the test in Table 6 that according to the standard "CJJT-286 Technical Standard for the Application of Soil Stabilizers", when the mass content of G2 is 15% and 20%, and the mass content of G2 is 20%, it can meet the requirements of the first-level stabilized soil grade, and can be used in the subbase of light traffic, and can also be used in the field of roadbed reinforcement.

Claims

1. A high-water content phosphogypsum soil curing agent, characterized in that: The raw materials include phosphogypsum, a modifier, a composite active mineral admixture, and a reinforcing agent; the composite active mineral admixture includes the following raw materials in mass proportion: 80-100% slag powder; the remainder is one or more of steel slag powder, copper slag powder, phosphorus slag powder, and lithium slag powder; The phosphogypsum is selected from washed phosphogypsum, with a moisture content of 15%-30% and a dry basis CaSO4·2H2O content of ≥65%; The modifier is selected from at least two of lime kiln tail ash, desulfurization ash, cement kiln ash, calcium quicklime, and carbide slag; The CaO content of the modifier is greater than 50%, and the specific surface area is 800-2000cm 2 / g; The reinforcing agent includes one or more of ultra-fine steel slag powder, ultra-fine slag powder, ordinary silicate cement, sulphoaluminate cement, nano-hydrated calcium silicate and nano-calcium carbonate.

2. The high-water content phosphogypsum soil curing agent according to claim 1, characterized in that: The soil solidifying agent comprises, by mass percentage, 20%-55% of phosphogypsum, 5%-20% of a modifier, 25%-65% of a composite active mineral admixture, and 0-10% of a reinforcing agent.

3. The high-water content phosphogypsum soil curing agent according to claim 1, characterized in that: The soil solidifying agent is divided into material A and material B, wherein material A contains phosphogypsum and a modifier; material B contains a composite active mineral admixture and a reinforcing agent; and the mass ratio of material A to material B is 70:30 to 35:

65.

4. The high-water content phosphogypsum soil curing agent according to claim 1, characterized in that: The activity index of the slag powder is ≥95.

5. The high-water content phosphogypsum soil curing agent according to claim 1, characterized in that: The activity index of the steel slag powder, copper slag powder, phosphorus slag powder and lithium slag powder is ≥65.

6. A method for preparing a high-water content phosphogypsum soil curing agent according to any one of claims 3 to 5, characterized in that: The following steps are involved: S1, phosphogypsum and modifier are mixed and aged to obtain material A; S2, mixing the composite active mineral admixture with the reinforcing agent to obtain material B; S3, mix material A and material B to obtain.

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