High-consumption phosphogypsum filling material and application thereof

Abstract

The application discloses a high-consumption phosphogypsum filling material and application thereof, and relates to the field of road materials.The raw materials of the application include 50-60 parts of phosphogypsum powder, 5-10 parts of a cementing component, 25-35 parts of recycled aggregate, 5-10 parts of industrial solid waste powder, 1-2 parts of a microcapsule consolidating agent and 3-5 parts of a complex water-resistance enhancing agent, wherein the microcapsule consolidating agent is prepared by spray drying of starch, sodium metaaluminate, aluminum chloride and sodium bicarbonate.The application adopts phosphogypsum and recycled aggregate with a single particle size, and the recycled aggregate with a single particle size can play a role of "reverse impact breaking" and "ball milling", so that the phosphogypsum lumps which are not easy to disperse are dispersed, and the phosphogypsum lumps are fully contacted with the cementing component, thereby improving the water damage resistance, strength and modulus of the filling material.The 7d strength of the filling material can reach 9.2MPa, the 28d strength can reach 18.7MPa, and the dynamic compression elastic modulus can reach 32500MPa.

Description

Technical Field

[0001] This invention relates to the field of road materials, and in particular to a high-absorption phosphogypsum filling material and its application. Background Technology

[0002] Phosphogypsum is a byproduct of the sulfuric acid decomposition of phosphate rock and the extraction of phosphoric acid. Approximately 5 tons of phosphogypsum are produced to produce 1 ton of phosphoric acid. Phosphogypsum contains harmful substances such as phosphate rock, phosphoric acid, and iron-aluminum compounds, with a pH of approximately 4-5. Without strict management and preventative measures, long-term accumulation of phosphogypsum can disrupt the soil's acid-base balance, affecting crop growth, or causing large-scale damage to arable land, thus limiting agricultural production and development. Specifically, when soluble fluoride in phosphogypsum is absorbed and utilized by plants and animals and enters the human body through the food chain, excessive fluoride ions can cause tooth decay, osteoporosis, and even paralysis. Phosphate ions seep into rivers and lakes with rainwater, causing severe eutrophication and destroying aquatic ecosystems. Environmental and economic pressures are driving the accelerated upgrading of the comprehensive utilization of phosphogypsum. In the past 30 years, with the rapid development of urbanization in my country and the continuous expansion of construction scale, a large amount of construction waste has been generated. The landfilling and dumping of this construction waste occupies a significant amount of land resources. Therefore, it would be of great significance to use phosphogypsum and recycled aggregates from construction waste as raw materials in highway engineering construction to prepare a new material with better performance for highway engineering construction.

[0003] Numerous studies and practices have shown that high phosphogypsum content can affect the early and late strength of cement hydration, as well as the setting time of cement. This results in phosphogypsum, when used as a stabilized material, severely impacting the construction quality and efficiency of road subgrade and base course. When phosphogypsum powder is mixed with cementitious materials, it is difficult to achieve uniform dispersion, and aggregate-free mixtures often have a low modulus of elasticity. When stabilized materials with low modulus are used as road fill materials, the strain caused by external forces under traffic loads is large, leading to significant pavement deflection and a substantial reduction in road load-bearing capacity and durability. Furthermore, when phosphogypsum is used as a stabilized material, its slightly soluble nature poses certain risks to the water stability coefficient and durability of the stabilized material. To address these issues, Chinese patent CN 109467379A discloses a phosphogypsum roadbed material that solves the problems of phosphogypsum's water sensitivity and dispersion by adding construction adhesive powder; however, its 7-day and 28-day compressive strengths are relatively low. Summary of the Invention

[0004] To address the shortcomings of the existing technologies, this invention provides a high-absorption phosphogypsum filler material and its application. By simultaneously using phosphogypsum and recycled aggregate as stabilized materials, the strength and elastic modulus of the filler material are significantly improved. Its 7-day strength can reach 9.2 MPa, its 28-day strength can reach 18.7 MPa, and its dynamic compressive elastic modulus can reach 57,500 MPa. This is achieved through the following techniques:

[0005] In a first aspect, the present invention provides a high-absorption phosphogypsum filling material, the raw materials of which, by weight, include: 50-60 parts phosphogypsum powder, 5-10 parts cementing components, 25-35 parts recycled aggregate, 5-10 parts industrial solid waste powder, 1-2 parts microcapsule binder, and 3-5 parts complexed water-resistant reinforcing agent.

[0006] The preparation method of the above microcapsule consolidating agent is as follows: dissolve starch, sodium aluminate, aluminum chloride and sodium bicarbonate in water, mix well and spray dry, and the dried particles obtained are the microcapsule consolidating agent;

[0007] The preparation method of the above-mentioned complexed water-resistant reinforcing agent is as follows:

[0008] S1. Add 4.5 to 6.5 parts of sodium hydroxide and 3 to 4 parts of sodium carbonate to 300 to 400 parts of water at 60 to 65°C. Mix well and then quickly add 45 to 55 parts of oleic acid. Mix well until the oleic acid is completely dissolved. Add 500 to 700 parts of water and mix well.

[0009] S2. After the solution in S1 has cooled to below 35°C, add 26-32 parts of ammonia water, 5-10 parts of complexing agent, and 50-100 parts of water glass. The resulting water emulsion is the complexed water-resistant reinforcing agent emulsion.

[0010] If the prepared complexed water-resistant reinforcing agent needs to be stored for a long time, the emulsion can be evaporated and dried at an environment below 35°C, then ground into powder with a particle size of <0.075mm and stored in a dry environment.

[0011] Furthermore, the above-mentioned raw materials, by weight, include: 50 parts phosphogypsum powder, 5 parts cementing components, 35 parts recycled aggregate, 10 parts industrial solid waste powder, 2 parts microcapsule binder, and 4 parts complexed water-resistant reinforcing agent.

[0012] The above-mentioned phosphogypsum powder has a pH of 7.5–8 and a particle size ≤2.36 mm. Phosphogypsum powder can be obtained by adjusting the pH of phosphogypsum to 7.5–8 using carbide slag, calcium hydroxide, or sodium hydroxide.

[0013] The above-mentioned recycled aggregate is a construction waste recycled aggregate with a single particle size of 4.75 to 31.5 mm; the industrial solid waste powder is a mixture of 6 to 9 parts blast furnace slag, 2 to 4 parts aluminum slag, 0 to 6 parts red mud powder, and 0 to 2 parts fly ash.

[0014] Furthermore, the above-mentioned cementitious component is at least one of limestone and cement.

[0015] Furthermore, the preparation method of the above-mentioned microcapsule consolidating agent is as follows: by weight, 300 parts of starch, 4-16 parts of sodium aluminate, 10-25 parts of aluminum chloride, and 2-4 parts of sodium bicarbonate are dissolved in 1000 parts of water at 40-45°C, mixed well, and then added to a spray dryer. The inlet temperature is adjusted to 130°C and the outlet temperature is adjusted to 80°C. The resulting dried microparticles are the microcapsule consolidating agent.

[0016] Furthermore, the complexing agent is one or more selected from ethylenediaminetetraacetic acid, dihydroxyethylglycine, aminotriacetic acid, and tartaric acid. The water glass modulus is 3.1–3.3, and the effective solid content is 28–32%.

[0017] The preparation method of the above-mentioned high-absorption phosphogypsum filling material is as follows: accurately weigh the above-mentioned raw materials, add them into an intermittent forced mixer, and wet or dry mix the phosphogypsum powder, cement, recycled aggregate, industrial solid waste powder, microcapsule binder, and complexed water-resistant reinforcing agent for 60 seconds to obtain the final product.

[0018] Secondly, this invention also provides applications of the above-mentioned filling material. The high-absorption phosphogypsum filling material prepared can be used in road subgrades or road base courses. When used in road subgrades, the filling material is leveled with a grader, initially compacted with a sheep's foot roller, and then compacted with a heavy roller. When used in road base courses, the filling material is spread with a paver, and if necessary, leveled with a grader. Then, it is compacted by static initial compaction with a double-drum roller, vibratory secondary compaction with a single-drum roller, and final compaction with a rubber-tired roller. Expansion joints are set every 100-200m.

[0019] The working principle of each raw material in this invention is as follows: phosphogypsum and recycled aggregate are used as stabilized materials at the same time. The recycled aggregate with a single particle size can act as a "impact crusher" and "ball mill", dispersing the phosphogypsum lumps that are not easy to disperse, allowing them to fully contact the cementitious components, improving the water damage resistance and strength of the filling material. In addition, the internal curing effect of the continuously released water by the recycled aggregate can reduce the plasticity of the filling material, making it easier to construct.

[0020] Aluminum-rich industrial waste red mud powder, Class C fly ash, granulated blast furnace ore powder, and aluminum slag are mixed to form industrial solid waste powder, which is then added as an admixture to the cementitious components. This not only improves the strength of the hydration products of the cementitious components, but also allows some phosphogypsum to participate in the reaction of the cementitious materials. Under the premise of keeping the amount of phosphogypsum unchanged, the actual amount of stabilized phosphogypsum is reduced, thereby significantly improving the strength of the filling material.

[0021] The highly surface-active complexing water-resistant reinforcing agent further improves the dispersion performance of phosphogypsum and cementitious components. The alkali and siliceous components in the agent stimulate the formation of calcium sulfoaluminate hydration products from the aluminum phase of the cementitious material and the sulfur phase of the phosphogypsum, thus enhancing the performance of the fill material. The non-polar groups of the complexing water-resistant reinforcing agent can adsorb and encapsulate unreacted phosphogypsum particles, significantly improving the water permeability resistance of the fill material and substantially increasing its water stability coefficient.

[0022] The microcapsule binder uses starch as the microcapsule wall material to encapsulate other components. When added to the mixture, it is evenly dispersed. During transportation, the microcapsule walls remain intact. After being transported to the paving site, the microcapsule walls are broken down and the binder is released through rolling, kneading, and chemical hydrolysis of the alkaline components in the complexing water-resistant reinforcing agent. This increases the free active aluminum phase in the mixture and destroys the surface of the passivated cement hydration products, thereby accelerating cement hydration. This achieves the "vibration pressure-sensitive strength formation" of the phosphogypsum subgrade material, avoiding losses such as water loss and external force damage caused by the slow setting of the filling material.

[0023] Compared with the prior art, the advantages of the present invention are:

[0024] 1. The high-absorption phosphogypsum filling material of the present invention has a content of phosphogypsum powder, recycled aggregate, and industrial solid waste powder of up to 85-95%, realizing the large-scale resource recycling of phosphogypsum and other wastes. Moreover, its 7-day strength can reach 9.2 MPa, its 28-day strength can reach 18.7 MPa, and its dynamic compressive elastic modulus can reach 32500 MPa, solving the problems of phosphogypsum being difficult to mix and disperse evenly with cementitious materials and the mixture often having a low elastic modulus.

[0025] 2. The complexing water-resistant reinforcing agent further improves the dispersion performance of phosphogypsum and cementitious components, stimulates the hydration reaction of aluminum phase substances in cementitious materials and sulfur phase substances in phosphogypsum, and the non-polar groups of the complexing water-resistant reinforcing agent can adsorb and encapsulate unreacted phosphogypsum particles, which greatly improves the water permeability resistance of the filling material and significantly increases the water stability coefficient of the stabilized material, solving the problem of low water stability coefficient caused by the micro-dissolution characteristics of phosphogypsum.

[0026] 3. The consolidation aid is a slow-release microcapsule. It is not released during the mixing process, allowing the subgrade material to be transported or stored for a relatively long time before vibration compaction. The consolidation aid works rapidly during the vibration compaction of the subgrade material to improve its strength. At the same time, it avoids the problem of excessively fast cement hydration during the mixing process caused by the use of quick-setting agents, which makes it difficult to meet the requirements of the mixing-transportation-construction time. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] In the following specific implementation methods, the model and / or procurement source of each raw material are shown in Table 1 below:

[0029] Table 1. Types and / or Sources of Raw Materials

[0030] cement Ordinary silicate 42.5 cement phosphogypsum Yichang Xingfa Group phosphogypsum tailings dam Oleic acid Commercially available chemically pure EDTA-1,5-diaminetetraacetic acid Commercially available chemically pure Dihydroxyethylglycine Commercially available chemically pure aminotriacetic acid Commercially available chemically pure tartaric acid Commercially available chemically pure Sodium aluminate Commercially available chemically pure Aluminum chloride Commercially available chemically pure

[0031] The chemical compositions of the following raw materials are shown in Table 2:

[0032] Table 2 Chemical composition of each raw material

[0033]

[0034]

[0035] Unless otherwise specified, the preparation method of the filling material in the following embodiments and comparative examples is as follows: accurately weigh each raw material according to the specific proportions of each embodiment and comparative example, add it to an intermittent forced mixer, and wet mix phosphogypsum powder, cement, recycled aggregate, industrial solid waste powder, microcapsule binder, and complexed water-resistant reinforcing agent for 60 seconds to obtain the filling material.

[0036] For the preparation of filling materials, microcapsule binders, and complexed water-resistant reinforcing agents, the proportions of each raw material disclosed in this invention are quite effective. The raw materials for the filling materials, by mass, include: 50-60 parts phosphogypsum powder, 5-10 parts cementitious components, 25-35 parts recycled aggregate, 5-10 parts industrial solid waste powder, 1-2 parts microcapsule binder, and 3-5 parts complexed water-resistant reinforcing agent. To simplify the steps, Examples 1-3 and Comparative Examples 1-4 use the following proportions. The raw material composition of each example and comparative example, by mass fraction, is shown in Table 3 below:

[0037] Table 3. Raw material composition of the examples and comparative examples

[0038]

[0039] The composition of the industrial solid waste powder in each embodiment and comparative example, by mass fraction, is shown in Table 4 below:

[0040] Table 4. Composition of industrial solid waste powder in the examples and comparative examples.

[0041]

[0042] The preparation methods of the microcapsule consolidating agents in Examples 1-2 and Comparative Examples 1 and 3 are as follows: 300 parts by mass of starch, 4 parts by mass of sodium aluminate, 10 parts by mass of aluminum chloride, and 2 parts by mass of sodium bicarbonate are dissolved in 1000 parts by mass of water at 40°C. After mixing, the mixture is added to a spray dryer, the inlet temperature is adjusted to 130°C, the outlet temperature is adjusted to 80°C, and the microcapsule consolidating agent is obtained after spray drying.

[0043] The preparation methods of the complexed water-resistant reinforcing agent in Examples 1-2 and Comparative Examples 1 and 2 are as follows: 4.5 parts of sodium hydroxide and 3 parts of sodium carbonate are dissolved in 300 parts of water at 60°C. After mixing, 45 parts of oleic acid are quickly added and mixed until the oleic acid is completely dissolved. Then, 500 parts of water at 25°C are added and mixed. After the solution is cooled to below 35°C, 26 parts of ammonia, 5 parts of ethylenediaminetetraacetic acid, and 50 parts of water glass are added and stirred evenly to obtain an emulsion, which is the complexed water-resistant reinforcing agent.

[0044] The preparation method of the microcapsule consolidating agent in Example 3 is as follows: 300 parts by weight of starch, 16 parts by weight of sodium aluminate, 25 parts by weight of aluminum chloride, and 4 parts by weight of sodium bicarbonate are dissolved in 1000 parts by weight of water at 45°C. After mixing, the mixture is added to a spray dryer, the inlet temperature is adjusted to 130°C, the outlet temperature is adjusted to 80°C, and the microcapsule consolidating agent is obtained by spray drying.

[0045] The preparation method of the complexed water-resistant reinforcing agent in Example 3 is as follows: 6.5 parts of sodium hydroxide and 4 parts of sodium carbonate are dissolved in 400 parts of water at 65°C. After mixing, 55 parts of oleic acid are quickly added and mixed until the oleic acid is completely dissolved. Then, 700 parts of water at 25°C are added and mixed. After the solution is cooled to below 35°C, 32 parts of ammonia, 10 parts of dihydroxyethylglycine, and 100 parts of water glass are added and stirred evenly to obtain an emulsion, which is the complexed water-resistant reinforcing agent.

[0046] The filling materials prepared in the above embodiments and comparative examples were spread using a paver, and leveled using a grader if necessary. Then, they were compacted using a double-drum roller for initial static compaction, a single-drum roller for vibratory compaction, and a rubber-tired roller for final compaction, thus obtaining a road base course with high phosphogypsum absorption capacity. After 7 days of natural curing, core samples were taken using a core extractor and cured for 28 days under standard curing conditions and water-soaked curing conditions, respectively. Simultaneously, the mixture was compacted into cylindrical test blocks, which were cured for 28 days under standard curing conditions and under standard curing conditions followed by water-soaked curing conditions, respectively. The compressive strength and harmful substance concentration of the core samples and test blocks under different conditions were tested. The testing methods were based on the "Highway Geotechnical Testing Procedures" (JTG 3430-2020) (T0148) and ion chromatography, respectively. The results of the compressive strength test are shown in Table 5, and the concentration of harmful substances in the leachate is shown in Table 6.

[0047] Table 5. Test results of uncompacted compressive strength of each embodiment and comparative example.

[0048]

[0049]

[0050] Table 6. Test results of harmful substance concentration in leachates of each embodiment and comparative example.

[0051]

[0052] The above examples demonstrate that the high-absorption phosphogypsum filling material of this invention possesses excellent mechanical properties, water resistance, and freeze-thaw resistance. Its 7-day strength reaches 9.2 MPa, its 28-day strength reaches 18.7 MPa, its resilient modulus reaches 32.5 GPa, and its 28-day water-soaked strength and freeze-thaw strength residual rates are 98.8% and 95.9%, respectively. This high-absorption phosphogypsum filling material of the present invention exhibits good early strength and water permeability resistance, solving the problems of phosphogypsum's difficulty in uniformly mixing and dispersing with cementitious materials and its low water stability coefficient due to its slight solubility.

[0053] From the test results in Table 5, the performance data of Examples 1-3 show that the compressive strength of the fill material increases to a certain extent with the increase of recycled aggregate, indicating that the amount of recycled aggregate can be appropriately increased in actual construction. Compared to Example 1, Comparative Example 1 lacks the synergistic reaction between industrial solid waste and cementitious materials, resulting in a significant decrease in the strength and modulus of the fill material. Simultaneously, its water permeability resistance and freeze-thaw resistance are also affected to varying degrees. Compared to Example 1, Comparative Example 2 does not use a microencapsulated binder, leading to a significant increase in the setting time of the fill material and a slight decrease in strength and elastic modulus, but with little impact on the material's water resistance and freeze-thaw resistance. Compared to Example 1, Comparative Example 3 does not use a complexing water-resistant reinforcing agent, resulting in a significant decrease in the strength and modulus of the fill material, and a decrease in the residual water strength and freeze-thaw strength by approximately 15%. Compared to Example 1, Comparative Example 4 does not use a microencapsulated binder or a complexing water-resistant reinforcing agent, and the strength, water resistance, freeze-thaw resistance, and setting ability of the fill material are all greatly affected.

[0054] As can be seen from the test results in Table 6, the leachate of the high-sodium phosphogypsum filler material of this invention contains very few harmful substances and has good environmental performance. Compared with Example 1, Comparative Examples 3 and 4 have higher concentrations of harmful substances, and arsenic, lead, chromium, copper, zinc, and nickel were also detected. This is because Comparative Examples 3 and 4 did not incorporate a complexing water-resistant reinforcing agent, and heavy metal ions in the filler material were not adsorbed, thus arsenic, lead, chromium, copper, zinc, and nickel were still widely distributed in the material.

[0055] The above detailed embodiments describe the implementation of the present invention; however, the present invention is not limited to the specific details described in the above embodiments. Within the scope of the claims and technical concept of the present invention, various simple modifications and changes can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A high-sodium phosphogypsum filler material, characterized in that, Its raw materials, by weight, include: 50-60 parts phosphogypsum powder, 5-10 parts cementing components, 25-35 parts recycled aggregate, 5-10 parts industrial solid waste powder, 1-2 parts microcapsule binder, and 3-5 parts complexed water-resistant reinforcing agent. The preparation method of the microcapsule consolidating agent is as follows: 300 parts of starch, 4-16 parts of sodium aluminate, 10-25 parts of aluminum chloride, and 2-4 parts of sodium bicarbonate are dissolved in water, mixed evenly, and then spray-dried. The dried particles obtained are the microcapsule consolidating agent. The preparation method of the complexed water-resistant reinforcing agent is as follows: S1. Add 4.5 to 6.5 parts of sodium hydroxide and 3 to 4 parts of sodium carbonate to 300 to 400 parts of water at 60 to 65°C. Mix well and then quickly add 45 to 55 parts of oleic acid. Mix well until the oleic acid is completely dissolved. Add 500 to 700 parts of water and mix well. S2. After the solution in S1 has cooled to below 35°C, add 26-32 parts of ammonia water, 5-10 parts of complexing agent, and 50-100 parts of water glass. The resulting water emulsion is the complexed water-resistant reinforcing agent emulsion.

2. The high-sodium phosphogypsum filling material according to claim 1, characterized in that, The raw materials, by weight, include: 50 parts phosphogypsum powder, 5 parts cementing components, 35 parts recycled aggregate, 10 parts industrial solid waste powder, 2 parts microcapsule binder, and 4 parts complexed water-resistant reinforcing agent.

3. The high-sodium phosphogypsum filling material according to any one of claims 1-2, characterized in that, The phosphogypsum powder has a pH of 7.5~8 and a particle size of ≤2.36mm.

4. The high-sodium phosphogypsum filling material according to any one of claims 1-2, characterized in that, The recycled aggregate is a construction waste recycled aggregate with a single particle size of 4.75~31.5mm.

5. The high-sodium phosphogypsum filling material according to any one of claims 1-2, characterized in that, The industrial solid waste powder is composed of 6-9 parts blast furnace slag, 2-4 parts aluminum slag, 0-6 parts red mud powder, and 0-2 parts fly ash.

6. The high-sodium phosphogypsum filling material according to any one of claims 1-2, characterized in that, The cementitious component is cement.

7. The high-sodium phosphogypsum filling material according to claim 1, characterized in that, The complexing agent is one or more of ethylenediaminetetraacetic acid, dihydroxyethylglycine, aminotriacetic acid, and tartaric acid.

8. The high-sodium phosphogypsum filling material according to claim 1, characterized in that, The water glass has a modulus of 3.1 to 3.3 and an effective solid content of 28% to 32%.

9. The application of the high-sodium phosphogypsum filling material according to any one of claims 1-2 in road subgrade or road base.

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