A kind of phosphogypsum neutron ray shielding aggregate and a preparation method thereof

Abstract

The application discloses a kind of phosphogypsum neutron ray shielding aggregate, each component and its content include: phosphogypsum 70~90%, ultrafine active admixture 2~5%, industrial waste residue 1~5%, functional component 0~30%, cement 5~10%, alkaline activator 0.5~5%, pore-forming agent 1~5%;Water-binder ratio 0.16~0.45.The application uses phosphogypsum as main raw material, further combines cement, ultrafine active admixture, activator, pore-forming agent and the like to carry out composite excitation hydration reaction, forms the light aggregate system with abundant micro fine connected hole, simultaneously utilizes cementation reaction to carry out spatial crosslinking to the component with shielding effect of boron, lead, can further significantly improve the shielding capacity to neutron ray.The phosphogypsum aggregate described in the application has good mechanical properties, water storage and release properties and anti-neutron ray performance, and can realize high value utilization of phosphogypsum;And the preparation method is simple and controllable, with low energy consumption, suitable for popularization and application.

Description

Technical Field

[0001] This invention belongs to the field of building materials, specifically relating to a phosphogypsum neutron radiation shielding aggregate and its preparation method. Background Technology

[0002] Phosphogypsum is an industrial waste residue produced by treating phosphate rock with sulfuric acid to extract phosphoric acid. Its main component is calcium sulfate (CaSO4·2H2O), and it also contains pollutants such as phosphorus, fluorides, cadmium, mercury, arsenic, lead, and thallium. Phosphoric acid is one of the main raw materials for producing high-concentration phosphate compound fertilizers; approximately 5 tons of phosphogypsum are produced to produce 1 ton of phosphoric acid (calculated as 100% P2O5). Therefore, the large-scale resource utilization of phosphogypsum is urgently needed.

[0003] Currently, some research is applying phosphogypsum to the preparation of recycled aggregates to achieve high-value-added resource utilization of phosphogypsum. For example, patent CN114956628 discloses a high-strength phosphogypsum-based recycled aggregate, using phosphogypsum, slag powder, cement clinker, steel slag powder, fly ash, silica fume, and residual slurry from pipe piles as main raw materials to prepare a high-strength, non-fired phosphogypsum-based recycled aggregate with good water resistance. This aggregate can replace natural crushed stone and be applied in areas such as permeable bricks for sponge cities, wall blocks, and road water-stabilized materials. Patent CN115572089A discloses a phosphogypsum ceramsite for ultra-high performance concrete. It uses core-shell modification methods combined with optimized calcination processes to prepare phosphogypsum aggregate, which replaces traditional high-density ore aggregates, solving problems such as weak radiation areas caused by poor homogeneity in traditional radiation-shielding concrete, while improving the mechanical properties and durability of the resulting ultra-high performance radiation-shielding concrete. However, this approach mainly targets gamma rays for radiation protection and has some neutron shielding performance, but its neutron shielding effect is limited. Summary of the Invention

[0004] The main objective of this invention is to address the problems and shortcomings of existing technologies by providing a phosphogypsum neutron radiation shielding aggregate. While ensuring the compressive strength of the cylinder, this invention maximizes the content of crystal water and light elements such as boron and be in the phosphogypsum aggregate, resulting in an aggregate with excellent neutron radiation shielding performance. At the same time, it also takes into account good water absorption and slow water release performance, realizing the high-value (high absorption and harmless) utilization of phosphogypsum. Furthermore, the preparation method involved is relatively simple and low-cost, making it suitable for widespread application.

[0005] To achieve the above-mentioned objectives, the technical solution provided by this invention is as follows:

[0006] A phosphogypsum neutron radiation shielding aggregate, comprising the following components and their contents: 70-90% phosphogypsum, 2-5% ultrafine active admixture, 1-5% industrial waste residue, 0-30% functional component, 5-10% cement, 0.5-5% alkaline activator, and 1-5% pore-forming agent; water-cement ratio (cementing materials are phosphogypsum, ultrafine active admixture, and cement) 0.16-0.45.

[0007] According to the above scheme, the phosphogypsum is an industrial solid waste with a free water content of 6-18%, and its main component is CaSO4·2H2O with a content of more than 90wt%; the pH value is 4-6; and the particle size is less than 1.18mm.

[0008] According to the above scheme, the ultrafine active admixture is one or a mixture of ultrafine mineral powder and active silica fume.

[0009] Furthermore, the ultrafine mineral powder is grade S95 or higher; the SiO2 content in the active silica fume is 94wt% or higher.

[0010] According to the above scheme, the industrial waste includes boron slag, beryllium slag and lead slag; its particle size is less than 4.75 mm.

[0011] Preferably, the mass ratio of the boron slag, beryllium slag, and lead slag is 1:(1.6-2.5):(3.0-4.0).

[0012] Furthermore, the boron slag is the waste residue generated during the borax production process, with the boron content adjusted to 5.9 wt% using borax (when the original waste residue has insufficient boron content); the beryllium slag is the waste residue (acid-soluble slag) generated during the beryllium extraction process, with the beryllium content adjusted to 4.6 wt% using beryl (when the original waste residue has insufficient beryllium content); and the lead slag is the waste residue generated during the lead smelting process, with its main chemical components being SiO2, FeO, CaO, and ZnO.

[0013] Furthermore, the boron slag contains no less than 5 wt% B, the beryllium slag contains no less than 4 wt% Be, and the lead slag contains no less than 8 wt% Pb; other major components in the boron slag, beryllium slag, and steel slag are clay and rock components, etc.

[0014] According to the above scheme, the functional component is one or more of spodumene powder, lithium carbonate, and boron carbide powder.

[0015] According to the above scheme, the alkaline activator is one or more of sodium hydroxide, sodium aluminate, sodium carbonate, sodium sulfate, and sodium silicate.

[0016] According to the above scheme, the pore-forming agent can be one or a mixture of CaCO3 and MgCO3, with a purity ≥99.7%.

[0017] According to the above scheme, the strength grade of the cement is 52.5 or higher.

[0018] The preparation method of the above-mentioned phosphogypsum neutron radiation shielding aggregate includes the following steps:

[0019] 1) Weigh each raw material according to the proportion. The components and their contents include: 70-90% phosphogypsum, 2-5% ultrafine active admixture, 1-5% industrial waste residue, 0-30% functional components, 5-10% cement, 0.5-5% alkaline activator, 1-5% pore-forming agent; water-cement ratio 0.16-0.45;

[0020] 2) Weigh out the phosphogypsum powder, cement, ultrafine active admixture, industrial waste residue and functional components and mix them evenly. Put the evenly mixed powder into the pelletizer, and then add a mixed solution of water, pore-forming agent and alkaline activator into the pelletizer for granulation, and control the particle size of the pellet to be less than 4.75 mm.

[0021] 3) After solidifying the spherical preforms obtained in step 2), steam curing is performed to obtain the phosphogypsum aggregate.

[0022] In the above scheme, the steam curing temperature is 45-90℃, the relative humidity is above 90%, and the time is 22-26h.

[0023] Furthermore, after steam curing, standard curing or natural curing shall be carried out for a period of not less than 14 days.

[0024] The apparent density of the phosphogypsum aggregate obtained by this invention is 900–1300 kg / m³. 3 The cylinder compressive strength can reach 6.5 to 12 MPa, the micro-fine interconnected pores <0.1 μm account for more than 50% of the total porosity, and the water absorption rate is 15 to 20%, which shows excellent water storage and release performance and has important practical application value.

[0025] The principle employed in this invention is as follows:

[0026] This invention employs a composite activating hydration reaction based on cement, ultrafine active admixtures, industrial waste, alkaline activator, and phosphogypsum to significantly improve the strength of phosphogypsum aggregates, meeting the strength requirements of high-strength and ultra-high-strength radiation-resistant concrete. The composite activating hydration reaction products contain 2-32 water molecules of crystallization and can spatially crosslink phosphogypsum and industrial waste, which possess neutron radiation protection properties, to form dense, water-rich, micro-expanding hydration products, significantly improving the radiation protection (neutron radiation protection) performance of the aggregates. Through the volume changes of phosphogypsum and gel during the composite activation process, and the chemical reaction between phosphogypsum and pore-forming agents at room temperature, the aggregates are encouraged to form numerous interconnected micropores, effectively improving aggregate strength while imparting an "internal curing effect" to the concrete, thus significantly increasing the concrete strength. The pore-forming reaction products can also act as activators to further promote the composite activating hydration reaction of cementitious materials, phosphogypsum, and waste.

[0027] 1) This invention adopts a structured design concept with high micro-fine interconnected porosity. High-strength phosphogypsum aggregate is prepared by using cement, ultrafine active admixtures and alkaline activators. By designing the raw material composition and controlling the pore structure characteristics, the proportion of macropores and closed pores in the aggregate is reduced, so that the resulting high-strength phosphogypsum aggregate has the characteristics of high micro-fine interconnected pores, high water absorption and slow water release.

[0028] 2) The phosphogypsum used in this invention has a crystal water content of 20-25%. The application of large-volume phosphogypsum can not only reduce phosphogypsum inventory and realize the resource utilization of phosphogypsum, but also enable the prepared aggregate to have good neutron radiation shielding ability, thereby realizing the high-value and harmless utilization of phosphogypsum. Furthermore, by combining cement, ultrafine active admixtures and activators to carry out a composite activating hydration reaction, the resulting reaction product contains a single amount of Aft with a high crystal water content, which further increases the crystal water content of the obtained aggregate. At the same time, through the cementation reaction, the boron and lead components with shielding effect are spatially cross-linked, which can further significantly improve the shielding ability against neutron radiation (stronger radiation protection effect than dispersed shielding components).

[0029] 3) This invention uses pore-forming agents such as CaCO3 and MgCO3. On the one hand, these agents can decompose and release CO2 gas at room temperature (reacting with acidic phosphogypsum at room temperature) or under steam curing conditions, forming micropores. On the other hand, the decomposed CaO and MgO can appropriately increase the viscosity of the low-temperature liquid phase, reduce the ion migration and pore discharge rate, and to a certain extent hinder the densification of lightweight aggregates, which helps lightweight aggregates form micro-interconnected pores. At the same time, combined with the hydration process based on the composite adhesive and activator described in this invention, the industrial waste residue is cemented while further promoting the generation of micro-interconnected pores, ultimately obtaining high-strength lightweight aggregates with micro-interconnected pores.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] 1) The phosphogypsum aggregate prepared by the present invention has the characteristics of high strength, high water absorption and high micro-fine interconnected pores, which can effectively solve the problem that it is difficult for lightweight aggregates to have both high strength and high water absorption.

[0032] 2) This invention uses phosphogypsum as the main raw material to prepare neutron radiation protection aggregate, making full use of the high crystal water characteristics of phosphogypsum, and supplementing it with light elements such as boron and beryllium to prepare high-strength phosphogypsum concrete with tiny interconnected pores, which can exhibit excellent water storage and release capacity and neutron ray protection performance, realizing the high-value utilization of phosphogypsum.

[0033] 3) The preparation process of the phosphogypsum aggregate described in this invention is simple and controllable, with low energy consumption and easy to achieve industrial production; in addition, the phosphogypsum content can reach 70-90%, which can effectively reduce the stockpiling of phosphogypsum and reduce its pollution to the environment, thus having important economic and environmental benefits. Attached Figure Description

[0034] Figure 1 This is a morphological diagram of the phosphogypsum neutron radiation shielding aggregate obtained in this invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be noted that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0036] In the following examples, Huaxin P·O52.5 ordinary Portland cement was used; the active silica fume was produced by Sichuan Langtian Resource Comprehensive Utilization Company, with a SiO2 content of 95% and a specific surface area of ​​19000 m². 2 / kg, 28-day activity index 105%; ultrafine mineral powder produced by Tuyun Mineral Products Processing Plant, Lingshou County, Shijiazhuang City, Hebei Province, grade S95, density 2.92g / cm³. 3 Specific surface area is 450m² 2 / kg; the industrial waste residues were obtained from a company in Liaoning (boron slag, particle size ≤4.75mm), a company in Hubei (beryllium slag, particle size ≤4.75mm), and a company in Hunan (lead slag, particle size ≤4.75mm); among them, the boron slag contained 5.9wt% boron, and the remaining main components were clay and rock components, which were waste residues generated from the borax production process; the beryllium slag contained 4.6wt% beryllium, and the remaining main components were clay and rock components, which were waste residues (acid-soluble slags) generated during the beryllium extraction process, and the beryllium content was adjusted to 4.6wt%; the lead slag contained 9.3% phosphorus, which were waste residues generated during the lead smelting process.

[0037] The phosphogypsum used was supplied by Yichang Yihua Phosphogypsum Warehouse. Its free water content was 11%, CaSO4·2H2O content was 97wt%, pH value was 5, and particle size was <1.18mm.

[0038] The fly ash microspheres used in the application example were provided by Tianjin Zhucheng New Material Technology Co., Ltd., with a specific surface area of ​​1200 m². 2 / kg, 28d activity index >90%, amorphous state; copper-plated steel fiber is produced by Wuhan Xintu Engineering New Material Technology Co., Ltd., nominal length 13mm±1, equivalent diameter 0.20±0.02mm, tensile strength approximately 3500MPa, elastic modulus approximately 52GPa; the expanding agent is HME type expanding agent produced by Jiangsu Bote New Material Co., Ltd., with a density of 3220kg / m³. 3 The 7-day restricted expansion rate in water is 0.062%; the water-reducing agent is a polycarboxylate high-performance water-reducing agent produced by Jiangsu Subote New Material Co., Ltd., with a solid content of 50%, a water reduction rate of 60%, and an air entrainment of <5%; CaCO3, MgCO3, and Li2CO3 are all chemically analytical grade and produced by Sinopharm Group; the water is ordinary tap water.

[0039] Examples 1-2

[0040] The preparation steps of the phosphogypsum neutron radiation shielding aggregate described in Examples 1 and 2 are as follows:

[0041] 1) Weigh each raw material according to the proportions described in Table 1, wherein the total amount of phosphogypsum, ultrafine mineral powder, industrial waste residue (the mass ratio of boron slag, beryllium slag and lead slag is 1:2:3), cement and lithium carbonate is 100 parts;

[0042] 2) First, mix the weighed phosphogypsum, ultrafine mineral powder, industrial waste residue, cement and other raw materials for 3 minutes. Then, put the evenly mixed powder into the pelletizing machine. Then, add a mixed solution of water, pore-forming agent and alkaline activator into the pelletizing machine to granulate, and control the particle size of the pellet to be less than 4.75 mm.

[0043] 3) The phosphogypsum ceramsite balls produced in step 2) are subjected to initial and final setting at 20°C. After initial and final setting, they are placed in a steam curing equipment with a temperature of 65°C and a humidity of over 90% for 1 day, and then cured for 15 days according to standard; the phosphogypsum neutron radiation shielding aggregate is obtained. The specific performance test results are shown in Table 2.

[0044] Comparative Example 1

[0045] 1) Weigh each raw material according to the proportions described in Table 1;

[0046] 2) Phosphogypsum lightweight aggregate was prepared using the same process as in the above embodiments. The specific performance test results are shown in Table 2.

[0047] Table 1. Formulation composition (parts by weight) of the phosphogypsum aggregates described in Examples 1 and 2.

[0048]

[0049] Table 2. Performance test results of the phosphogypsum aggregates obtained in Examples 1-2 The above results indicate that the phosphogypsum aggregate obtained by this invention has advantages such as high strength, high water absorption (the high water absorption rate of Comparative Example 1 is mainly achieved by large-sized pores, but directly affects the strength), and high crystal water content. The apparent density of the obtained phosphogypsum aggregate is 900–1300 kg / m³. 3 The compressive strength of the aggregate can reach 6.5 to 12 MPa. The micro-interconnected pores (pores smaller than 100 μm are usually interconnected pores) have a size of 0.01 to 100 nm and account for more than 50% of the total porosity, which makes the aggregate have high strength, high water absorption, and excellent water storage and release capacity, and has important practical application value.

[0050] Application examples

[0051] The phosphogypsum aggregates obtained in Example 2 and Comparative Example 1, as well as traditional shale ceramsite, were respectively applied to prepare ultra-high performance concrete. The specific preparation methods include the following steps:

[0052] 1) Weigh each raw material according to the proportions described in Tables 3 and 4. Phosphogypsum aggregates 1 and 2 are the phosphogypsum aggregates prepared in Example 2 and Comparative Example 1, respectively. The shale ceramsite is commercially available spherical shale ceramsite with a particle size of 3–5 mm and a density of 1050 kg / m³. 3 The water absorption rate is 16.8%;

[0053] 2) Soak the phosphogypsum aggregate and shale ceramsite in water until saturated. Add the pre-wetted phosphogypsum aggregate (or ceramsite), cement, silica fume, and fly ash microspheres to a concrete mixer and premix for 1-3 minutes until visually uniform. Then add water and polycarboxylate superplasticizer and wet mix for 3-5 minutes. Finally, sprinkle copper-plated steel fibers and mix evenly. After molding, vibration, and shaping, cover the surface with an impermeable film for film curing. After demolding, perform standard curing until the specified age to obtain the radiation-resistant ultra-high performance concrete.

[0054] The obtained radiation-resistant ultra-high performance concrete was tested for its workability, mechanical properties, impermeability and shrinkage properties. The results are shown in Table 6.

[0055] Table 3. Mix proportions of radiation-resistant ultra-high performance concrete (kg / m³) 3 )

[0056]

[0057] Table 3 Aggregate and filler ratios for radiation-shielding ultra-high performance concrete (kg / m³) 3 )

[0058]

[0059] Table 5 Performance test results of radiation-resistant ultra-high performance concrete

[0060]

[0061] Table 6. Shielding effect of ultra-high performance radiation-resistant concrete against DT source neutron rays.

[0062]

[0063]

[0064] The above results demonstrate that the neutron-shielding ultra-high performance concrete obtained by this invention possesses excellent workability, mechanical properties, and neutron-shielding performance: the compressive strength grade of the obtained ultra-high performance concrete is all above C120, the scalar extension is above 600 mm, and the apparent density is above 2150 kg / m³. 3 It exhibits excellent crack resistance and impermeability; and its linear attenuation coefficient μ is greater than 0.1 (up to 0.11371), allowing the half-value layer thickness to be reduced to 6.10cm.

[0065] The above embodiments are merely illustrative examples and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations; therefore, any obvious variations or modifications derived therefrom remain within the scope of protection of this invention.

Claims

1. A phosphogypsum neutron radiation shielding aggregate, characterized in that, The components and their contents include: 70-90% phosphogypsum, 2-5% ultrafine active admixture, 1-5% industrial waste residue, 0-30% functional components, 5-10% cement, 0.5-5% alkaline activator, and 1-5% pore-forming agent; water-cement ratio 0.16-0.45; The main component of the phosphogypsum is CaSO4·2H2O, its free water content is 6~18%, and its pH value is 4~6. The industrial waste residue includes boron slag, beryllium slag, and lead slag, with a mass ratio of 1:(1.6~2.5):(3.0~4.0). The pore-forming agent includes one or a mixture of CaCO3 and MgCO3, with a purity ≥99.7%; The apparent density of the phosphogypsum neutron radiation shielding aggregate is 900~1300 kg / m³. 3 The compressive strength of the cylinder can reach 7.5~12MPa, the micro-fine interconnected pores <0.1μm account for more than 50% of the total porosity, and the water absorption rate is 15~20%.

2. The phosphogypsum aggregate according to claim 1, characterized in that, The ultrafine active admixture is one or a mixture of ultrafine mineral powder and active silica fume.

3. The phosphogypsum aggregate according to claim 1, characterized in that, The functional component is one or more of spodumene powder, lithium carbonate, and boron carbide powder.

4. The phosphogypsum aggregate according to claim 1, characterized in that, The alkaline activator is one or more of sodium hydroxide, sodium aluminate, sodium carbonate, sodium sulfate, and sodium silicate.

5. The method for preparing the phosphogypsum neutron radiation shielding aggregate according to any one of claims 1 to 4, characterized in that, Includes the following steps: 1) Weigh each raw material according to the proportion. The components and their contents include: 70-90% phosphogypsum, 2-5% ultrafine active admixture, 1-5% industrial waste residue, 0-30% functional components, 5-10% cement, 0.5-5% alkaline activator, 1-5% pore-forming agent; water-cement ratio 0.16-0.

45. 2) Weigh out phosphogypsum, cement, ultrafine active admixture, industrial waste residue and functional components and mix them evenly. Add a mixed solution of water, pore-forming agent and alkaline activator to the obtained powder and granulate to obtain spherical green bodies. 3) After the obtained spherical preform is solidified, it is steam cured to obtain the phosphogypsum neutron radiation shielding aggregate.

6. The preparation method according to claim 5, characterized in that, The steam curing temperature is 45~90℃, and the relative humidity is above 90%.

7. The preparation method according to claim 5, characterized in that, The particle size of the spherical preform is less than 4.75 mm.

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