A fluidized solidified soil with phosphogypsum as main raw material and a special solidifying agent

Abstract

A fluidized solidified soil and a special curing agent using phosphogypsum as the main raw material, which relate to the technical field of fluidized solidified soil, wherein the special curing agent comprises an early strength curing component and a gelling component, wherein the early strength curing component is composed of a water-soluble aluminum salt and sodium silicate; the fluidized solidified soil comprises slag, phosphogypsum, a curing agent and water, wherein the phosphogypsum accounts for 20-30 wt% by mass, and the curing agent is a special curing agent. The present invention uses phosphogypsum as the main raw material to prepare fluidized solidified soil, which is conducive to the resource recovery of phosphogypsum solid waste, and the amount of phosphogypsum used is large, which can be used as the main way to resource recovery of phosphogypsum solid waste, and solves the problems of environmental pollution, long coagulation time and reduced strength when exposed to water caused by the large amount of phosphogypsum used.

Description

Technical Field

[0001] The invention relates to the technical field of fluidized solidified soil, in particular to fluidized solidified soil with phosphogypsum as main raw material and a special curing agent. Background Art

[0002] Fluidized solidified soil is a mixture of various discarded slag, curing agent and water mixed in a certain ratio to achieve certain performance indicators. It can replace traditional concrete, lime soil foundation and crushed stone concrete in some areas, and has great social significance for energy conservation, emission reduction and comprehensive utilization of industrial solid waste. Phosphogypsum is a by-product of the preparation of phosphoric acid and phosphate fertilizer. Its main component is calcium sulfate dihydrate, and it also contains a small amount of soluble phosphorus, fluorine, organic matter, oxides and heavy metals. The resource utilization of phosphogypsum is a global difficulty. Large amounts of phosphogypsum are stored as solid waste, which not only occupies a large area of ​​land, but also poses certain environmental and safety risks.

[0003] At present, the resource utilization of phosphogypsum has developed relatively maturely in related industries such as construction and agriculture. Among them, the most widely used is the building materials industry, where it can be used as a cement additive, road construction or filling material, etc. However, phosphogypsum is mostly used as an additive, while it is rarely used as a main material, and the consumption is relatively small for the huge stockpile of phosphogypsum. The application of phosphogypsum in fluidized solidified soil is also relatively small. For example, Chinese patent CN115974515A discloses a fluidized solidified soil based on clay and a preparation method thereof, and Chinese patent CN113402228A discloses a liquefied consolidated soil and a preparation method thereof, in which phosphogypsum is only used as a curing agent, and the amount used is relatively small, with the highest mass percentage being only in the single digit. Phosphogypsum also needs to be pre-treated for harmlessness before use.

[0004] This is because the soluble phosphorus in phosphogypsum will make phosphogypsum acidic, corroding gypsum products and equipment. During hydration, soluble phosphorus, eutectic phosphorus and calcium ions will generate Ca3(PO4)2, which will prevent the hydration reaction, prolong the hydration reaction time, and make the structure of the solidified product loose. Soluble fluorine will also prevent the hydration reaction. Soluble phosphorus entering the water body will cause eutrophication, and the penetration and precipitation of impurities such as soluble fluorine and heavy metals will also cause environmental pollution. Calcium sulfate dihydrate itself does not have gelling properties and does not dissolve in water, resulting in reduced strength. When the amount of phosphogypsum increases, the content of the above impurities will also increase, which will lead to problems such as longer material coagulation time, greater risk of environmental pollution, and lower strength when in contact with water. Summary of the invention

[0005] In view of the problems in the prior art that large amounts of phosphogypsum are used, such as long setting time, high risk of environmental pollution, and reduced strength when exposed to water, the present invention provides a fluidized solidified soil and a special curing agent using phosphogypsum as a main raw material.

[0006] The present invention provides the following technical solution: a special curing agent for fluidized solidified soil with phosphogypsum as main raw material, comprising an early strength curing component and a gelling component, wherein the early strength curing component is composed of water-soluble aluminum salt and sodium silicate.

[0007] Preferably, the water-soluble aluminum salt is one or more of aluminum nitrate, aluminum chloride, aluminum sulfate, and aluminum hydroxide.

[0008] Preferably, the sodium silicate is low modulus sodium silicate.

[0009] Preferably, the weight ratio of the water-soluble aluminum salt to sodium silicate is 1:0.1-0.2.

[0010] Preferably, the gelling component is one of ordinary Portland cement and sulphoaluminium cement.

[0011] Preferably, a water reducing component is also included.

[0012] Preferably, the water reducing component is one of a naphthalene-based high-efficiency water reducing agent, a melamine water reducing agent, and a polycarboxylic acid high-performance water reducing agent.

[0013] A fluidized solidified soil with phosphogypsum as the main raw material comprises slag soil, phosphogypsum, a curing agent and water, wherein the phosphogypsum accounts for 20-30 wt% by weight and the curing agent is a special curing agent.

[0014] Preferably, the weight ratio of the early strength curing component to the phosphogypsum in the special curing agent is 1:10-30.

[0015] Preferably, the weight ratio of the early strength curing component to phosphogypsum is 1:25.

[0016] The beneficial effects of the present invention are as follows: phosphogypsum and slag are used as main raw materials to prepare fluidized solidified soil, which is beneficial to the resource recovery of phosphogypsum solid waste. Compared with the prior art, phosphogypsum does not require harmless pretreatment and is used in large amounts, and can be used as the main method for resource recovery of phosphogypsum solid waste; water-soluble aluminum salts and sodium silicates are used as early strength curing components, and soluble phosphorus, fluorine and heavy metal ions in phosphogypsum are complexed and solidified with gelling components to form aluminate and silicate complexes, which can stabilize the soluble phosphorus, fluorine and heavy metal impurities in phosphogypsum, and prevent the fluidized solidified soil using a large amount of phosphogypsum as raw material from causing environmental pollution; the special curing agent can also significantly shorten the coagulation time of the fluidized solidified soil, and solve the problem of reduced strength of phosphogypsum when it comes into contact with water. Implementation

[0017] The following is a more detailed description of the embodiments of the present invention so that those skilled in the art can implement the embodiments after reading this specification. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Example

[0018] The invention provides a special curing agent for fluidized solidified soil with phosphogypsum as main raw material, comprising an early strength curing component, a water reducing component and a gelling component.

[0019] The early strength curing component is composed of a water-soluble aluminum salt and sodium silicate, wherein the water-soluble aluminum salt is one or more of aluminum nitrate, aluminum chloride, aluminum sulfate, and aluminum hydroxide, and the sodium silicate is a low modulus sodium silicate, and its modulus n is less than 1.0. The weight ratio of the water-soluble aluminum salt to the sodium silicate is 1:0.1-0.2.

[0020] The gelling component is one of ordinary silicate cement and sulphoaluminium cement.

[0021] The water reducing component is one of a naphthalene-based high-efficiency water reducing agent, a melamine water reducing agent, and a polycarboxylic acid high-performance water reducing agent. Example

[0022] The present invention provides a special curing agent for fluidized solidified soil with phosphogypsum as main raw material, comprising an early strength curing component, a water reducing component and a gelling component, wherein the weight proportion of the early strength curing component is 10 parts, and the weight proportions of the water reducing component and the gelling component are 6 and 100 parts respectively.

[0023] The early strength curing component is composed of water-soluble aluminum salt and sodium silicate, the water-soluble aluminum salt is aluminum nitrate, and the sodium silicate is low modulus sodium silicate. The weight ratio of the water-soluble aluminum salt to the sodium silicate is 1:0.1.

[0024] The gelling component is ordinary Portland cement.

[0025] The water reducing component is a naphthalene-based high-efficiency water reducing agent. Example

[0026] The present invention provides a special curing agent for fluidized solidified soil with phosphogypsum as main raw material, comprising an early strength curing component, a water reducing component and a gelling component, wherein the weight proportion of the early strength curing component is 20 parts, the weight proportion of the water reducing component and the weight proportion of the gelling component are 6 and 100 parts respectively.

[0027] The early strength curing component is composed of water-soluble aluminum salt and sodium silicate, the water-soluble aluminum salt is aluminum nitrate, and the sodium silicate is low modulus sodium silicate. The weight ratio of the water-soluble aluminum salt to the sodium silicate is 1:0.1.

[0028] The gelling component is ordinary Portland cement.

[0029] The water reducing component is a naphthalene-based high-efficiency water reducing agent. Example

[0030] The present invention provides a special curing agent for fluidized solidified soil with phosphogypsum as main raw material, comprising an early strength curing component, a water reducing component and a gelling component, wherein the weight proportion of the early strength curing component is 30 parts, and the weight proportions of the water reducing component and the gelling component are 6 and 100 parts respectively.

[0031] The early strength curing component is composed of water-soluble aluminum salt and sodium silicate, the water-soluble aluminum salt is aluminum nitrate, and the sodium silicate is low modulus sodium silicate. The weight ratio of the water-soluble aluminum salt to the sodium silicate is 1:0.1.

[0032] The gelling component is ordinary Portland cement.

[0033] The water reducing component is a naphthalene-based high-efficiency water reducing agent. Example

[0034] A fluidized solidified soil with phosphogypsum as the main raw material, including 20-50% slag, 20-30% phosphogypsum, 1-10% curing agent and 10-50% water, in terms of mass percentage, and the sum of the mass percentages of each component is 100%. Phosphogypsum is used directly as a raw material without the need for harmless pretreatment. The curing agent is one of the special curing agents described in Examples 1 to 4. The weight ratio of the early strength curing component to the phosphogypsum in the special curing agent is 1:10-30, and a preferred ratio is 1:25.

[0035] Embodiment 6-8

[0036] A fluidized solidified soil with phosphogypsum as the main raw material comprises slag soil, phosphogypsum, a curing agent and water in a mass ratio of 49:29:7:15. The phosphogypsum is from Dazhou Wengfu Chemical Co., Ltd., and the curing agent is the special curing agent described in Examples 2 to 4.

[0037] The present invention has a solidifying and stabilizing effect on harmful impurities in phosphogypsum. The present invention uses early strength solidifying components and gelling components to carry out complex solidification of soluble phosphorus, fluorine and heavy metal ions in phosphogypsum to form aluminate and silicate complexes, which have cementing properties, making them stable in the solidified body and not easily leached by water, thereby achieving the purpose of not polluting the environment.

[0038] The fluidized solidified soil in Example 8 was added into a 70.7×70.7×70.7 mm cubic test mold, and placed in a standard curing box (20°C±2°C, relative humidity ≥95%) for curing for 28 days to obtain a plurality of test specimens.

[0039] According to the national standard "GB 5085.3-2007 Identification Standard of Hazardous Waste Leaching Toxicity Identification", the horizontal oscillation method (HJ 557-2010) was used to obtain the leachate of the sample and phosphogypsum raw material. The sample cured for 28 days was dried and crushed, placed in a mortar for grinding and sieved, the sieve hole diameter was 3 mm, and the sieve was placed in a drying oven to dry to constant weight. 100 g of the sample was weighed and poured into a 2 L extraction bottle, and 1000 mL of deionized water was added at a solid-liquid ratio of 1:10 (g / mL) and shaken well. It was fixed vertically on a reciprocating horizontal oscillation device for 8 h and then allowed to stand for 16 h, and then filtered with a filter device with a 0.45 μm microporous filter membrane. The filtrate was the leachate.

[0040] The heavy metal content in the leachate was determined by inductively coupled plasma mass spectrometry (HJ 766-2015) and microwave digestion / atomic fluorescence spectrometry (HJ 702-2014), the phosphate content in the leachate was determined by ion chromatography (GB 5085.3-2007), and the fluoride content in the leachate was detected by ion selective electrode method (GB / T 15555.11-1995), and the test results are shown in Table 1. As shown in Table 1, the content of heavy metals and fluoride in the sample leachate made of fluidized solidified soil provided in Example 8 is lower than the concentration limit specified in "GB 5085.3-2007 Hazardous Waste Identification Standard Leaching Toxicity Identification"; the phosphate content is also much lower than that of phosphogypsum raw materials, and is lower than the first-level standard specified in "GB 8978-1996 Sewage Comprehensive Discharge Standard", indicating that the curing agent provided by the present invention has a good stabilizing effect on heavy metals, soluble fluorine, and soluble phosphorus.

[0041]

[0042] The present invention can significantly shorten the setting time of fluidized solidified soil. Prepare a comparative example, which is the same as Example 5, but the curing agent does not contain an early strength curing component; add the fluidized solidified soil provided by the comparative example and Examples 6 to 8 into a Φ140mm×H70mm cylindrical container respectively, and test according to the setting time test method specified in the "JGJ / T 70-2009 Standard for Basic Performance Test Methods of Building Mortar", record the setting time, and the results are shown in Table 2; the curing agents used in Examples 6 to 8 are the special curing agents provided in Examples 2 to 4 respectively. It can be seen that with the increase of the content of the early strength curing component in the curing agent, the setting time of the fluidized solidified soil is significantly shortened, which can meet the construction requirements for rapid setting. The reason may be that Al 3+ And sodium silicate can promote cement hydration and shorten the setting time.

[0043]

[0044] The present invention can significantly improve the strength of fluidized solidified soil. The fluidized solidified soil provided in Examples 6 to 8 and the comparative example described above was added to a 70.7×70.7×70.7 mm cubic test mold, and placed in a standard curing box (20°C±2°C, relative humidity ≥90%) for curing for 28 days to obtain multiple samples. The multiple samples were tested for strength according to the cubic compressive strength test method specified in the "JGJ / T 70-2009 Standard for Basic Performance Test Methods of Building Mortar"; the samples were placed in a container and immersed in water for 48 hours, and then their cubic compressive strength was tested. The results are shown in Table 3. It can be seen that the compressive strength of the samples made of the fluidized solidified soil provided in Examples 6 to 8 did not decrease after being immersed in water for 48 hours, while the compressive strength of the control sample decreased significantly, indicating that the present invention solves the problem of reduced strength when exposed to water. The reason may be that the hydration products of aluminum salt and sodium silicate in the fluidized solidified soil reacting with cement and phosphogypsum can fill the pores, reduce the migration of solutes and the penetration of water, and increase the density of the fluidized solidified soil, thereby improving the water resistance of the fluidized solidified soil.

[0045]

[0046] The above are one or more embodiments of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A fluidized solidified soil with phosphogypsum as the main raw material, comprising slag, phosphogypsum, a curing agent and water, characterized in that: In terms of mass percentage, it comprises 20-50% of slag, 20-30% of phosphogypsum, 1-10% of a curing agent and 10-50% of water, the sum of the mass percentages of each component being 100%, and the curing agent is a special curing agent; The special curing agent comprises an early strength curing component, a gelling component and a water reducing component, wherein the early strength curing component is composed of a water-soluble aluminum salt and sodium silicate; The water-soluble aluminum salt is one or more of aluminum nitrate, aluminum chloride, aluminum sulfate, and aluminum hydroxide; The sodium silicate is low modulus sodium silicate; The weight ratio of the water-soluble aluminum salt to sodium silicate is 1:0.1-0.2; The gelling component is one of ordinary silicate cement and sulphoaluminium cement.

2. The fluidized solidified soil with phosphogypsum as the main raw material according to claim 1, characterized in that: The water reducing component is one of a naphthalene-based high-efficiency water reducing agent, a melamine water reducing agent, and a polycarboxylic acid high-performance water reducing agent.

3. The fluidized solidified soil with phosphogypsum as the main raw material according to claim 1, characterized in that: The weight ratio of the early strength curing component to the phosphogypsum in the special curing agent is 1:10-30.

4. The fluidized solidified soil with phosphogypsum as the main raw material according to claim 3, characterized in that: The weight ratio of the early strength curing component to the phosphogypsum is 1:25.

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