A method for preparing lightweight phosphogypsum thermal insulation material by using waste polyurethane foam

Abstract

The application provides a method for preparing lightweight phosphogypsum thermal insulation material by using waste polyurethane foam. The method is that: first, the crushed waste polyurethane powder and dry phosphogypsum powder are added into a mill type force chemical reactor for co-milling and crushing, after the milling is completed, the polyurethane-phosphogypsum composite powder is collected, then the dry phosphogypsum powder is added and mixed in the composite powder, and the lightweight phosphogypsum mortar is obtained according to the conventional building mortar preparation process. The method uses waste polyurethane foam and waste phosphogypsum as main raw material components, and innovatively mixes the two kinds of raw material powders uniformly through co-milling, so that the premixed mortar meeting the standard can be prepared, and the stratification defect is not easy to occur.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal insulation building materials and waste phosphogypsum recycling, and relates to a method for preparing lightweight phosphogypsum thermal insulation material by using waste polyurethane foam, in particular, the method is directed to the preparation using a mechanochemical reactor disclosed in Chinese authorized invention patent ZL95111258.9. Background Art

[0002] Phosphogypsum is a solid waste produced in the wet phosphoric acid process, and its main component is calcium sulfate dihydrate. At present, the resource utilization of phosphogypsum in my country is mainly concentrated in the building materials industry, including its use in construction materials, thermal insulation materials, and decorative materials. However, building materials using phosphogypsum as the main material usually have the defects of poor thermal insulation and limited application range, resulting in large amounts of phosphogypsum being stored and unable to be effectively utilized as a resource for a long time. It is stored in large quantities in major production areas such as Yunnan, Guizhou and Sichuan. While occupying land space, it also pollutes soil and groundwater resources. While causing waste of land resources, the acidic substances, fluorides, and organic matter it contains also pollute the soil and groundwater, causing serious damage to the ecological environment.

[0003] Foam materials are porous composite materials based on plastics such as PU, PET, and PA, produced with the action of various additives such as catalysts and foaming agents. They have functions such as heat preservation, sound insulation, and cushioning. Polyurethane (PU) foam uses isocyanate and polyether as main raw materials. It is light in weight, simple to process, has thermal insulation, low thermal conductivity, and acoustic insulation properties, and is corrosion-resistant, water-resistant, and aging-resistant. It is widely used in construction, automobiles, ships, electrical appliances, and other fields. Due to the large-scale application of polyurethane foam, a large amount of waste polyurethane foam is generated. In addition, the production process of polyurethane foam also produces a large amount of scraps, mold overflow, waste products, etc., which need to be dealt with urgently. Currently, the commonly used treatment methods are landfill and incineration. The landfill method occupies a large amount of land, and the incineration method requires strict process conditions and is difficult to be widely promoted. Its high-value and efficient resource utilization has become a bottleneck problem that needs to be solved in the industry.

[0004] Therefore, if phosphogypsum could be combined with waste polyurethane foam, leveraging the thermal insulation properties of polyurethane foam to improve the thermal insulation performance of phosphogypsum building materials, creating a high-value recycled material from these two wastes, this would have significant technical value and market potential. It could also become an important alternative for developing high-value-added thermal insulation phosphogypsum building materials and achieving resource utilization. However, during our research, we found no technical literature documenting the combined use of phosphogypsum and waste polyurethane foam alone. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems in the above-mentioned background technology and provide a method for preparing lightweight phosphogypsum thermal insulation material using waste polyurethane foam. The method utilizes waste polyurethane foam and waste phosphogypsum as the main raw material components, and innovatively mixes the two raw material powders evenly through co-grinding, so as to prepare a premixed mortar that meets the standards and is not prone to stratification defects.

[0006] To achieve the above objectives, the present invention is implemented by adopting a technical solution consisting of the following technical measures.

[0007] A method for preparing lightweight phosphogypsum mortar using waste polyurethane foam comprises the following steps:

[0008] (1) Selecting waste polyurethane foam materials or products, and after pretreatment including cleaning, crushing them into waste polyurethane powder with an average particle size of not more than 0.3 mm;

[0009] (2) mixing the waste polyurethane powder obtained in step (1) with the dry phosphogypsum powder in a mass ratio of (0.9-1.1):1, and then adding the mixture into a grinding disc type mechanochemical reactor for co-grinding and pulverization. After the grinding is completed, collecting the polyurethane-phosphogypsum composite powder; wherein the process parameters of the grinding disc type mechanochemical reactor are as follows: a grinding pressure of 3-6 MPa, a grinding disc surface temperature controlled by passing a constant temperature circulating liquid medium with a temperature below 10° C., a grinding disc speed of 50-100 rpm, and cyclic grinding for 1-3 times;

[0010] (3) adding dry phosphogypsum powder to the polyurethane-phosphogypsum composite powder obtained in step (2) and mixing to obtain a mixed powder having a polyurethane content of 3 to 20 wt%;

[0011] (4) The mixed powder obtained in step (3) is subjected to a conventional construction mortar preparation process to obtain a lightweight phosphogypsum mortar. The lightweight phosphogypsum mortar can be directly solidified and formed as a thermal insulation building material, or as a premixed mortar.

[0012] Herein, the waste polyurethane foam material or product in step (1) is selected from various conventional polyurethane foam types, such as soft polyurethane foam, semi-rigid polyurethane foam, rigid polyurethane foam, etc.

[0013] Generally speaking, the waste polyurethane foam materials or products described in step (1) include industrial waste with a large amount of waste, such as scraps and waste materials generated during the synthesis and production process of polyurethane foam, and waste products using polyurethane foam materials, such as insulation pipes and insulation building materials. Those skilled in the art can check the specifications of the waste polyurethane foam materials or products to determine whether they meet the requirements for selection as raw materials of the present invention.

[0014] In this article, the pretreatment including washing described in step (1) is mainly to remove impurities on the surface of the waste polyurethane foam material or product. If necessary, the non-polyurethane foam part needs to be removed. Those skilled in the art can carry out specific treatment according to the actual conditions of the waste polyurethane foam material or product to be recycled and based on the existing technology.

[0015] Generally, the waste polyurethane foam powder processed and crushed to an average particle size of not more than 0.3 mm in step (1) can be processed by existing conventional crushing equipment such as a jaw crusher, a planetary ball mill, and a frozen ball mill.

[0016] In one preferred technical solution, the waste polyurethane powder processed and crushed to an average particle size of not more than 0.3 mm in step (1) is preferably crushed using a grinding disc type force chemical reactor; wherein the process parameters of the grinding disc type force chemical reactor are: grinding pressure of 3 to 6 MPa, the grinding disc surface temperature is controlled by passing a constant temperature circulating liquid medium with a temperature below 10°C, the grinding disc speed is 50 to 100 rpm, and the cycle grinding is 0 to 1 times.

[0017] In this article, the dry phosphogypsum powder in step (2) has been dehydrated and is in a dry powder form, which is consistent with the commonly available phosphogypsum powder on the market.

[0018] In this context, the grinding disc type mechanochemical reactor in step (2) is the mechanochemical reactor disclosed in the previously authorized patent ZL95111258.9 of the present applicant, and the temperature of the grinding disc is controlled by introducing a constant temperature circulating liquid medium into the grinding disc. Generally speaking, the liquid medium is water.

[0019] Typically, the cyclic milling process described in step (2) is performed by milling the mixed material in a disc-type mechanochemical reactor, collecting the product at the discharge end, and then milling it again in a disc-type mechanochemical reactor. This process is considered to be 1 round of cyclic milling. It should be noted that when the cyclic milling is 0 times, it is sufficient to mill the mixed material in a disc-type mechanochemical reactor and collect the product at the discharge end.

[0020] In this article, the polyurethane content of the mixed powder in step (3) is 3 to 20 wt%, and the polyurethane content is calculated based on the total amount of the waste polyurethane powder obtained in step (1) and the dry phosphogypsum powder added in steps (2) and (3).

[0021] In this article, the step (4) is to obtain a lightweight phosphogypsum mortar by using the mixed powder obtained in step (3) according to a conventional construction mortar preparation process. This is a conventional construction mortar preparation method in the common knowledge in this technical field. The mixed powder obtained in step (3) and a conventional mortar adhesive are used as dry materials and mixed with water to prepare the mortar. The specific process method and process parameters can be directly referred to the standard method in the prior art, preferably, the mortar preparation process in the prior art using phosphogypsum as the main raw material can be referred to.

[0022] The main invention of the present invention is that the inventors discovered during the project research on the recycling of phosphogypsum that phosphogypsum itself has a certain thermal insulation ability. After searching, it was found that its thermal conductivity is about 0.275W / mk, but compared with the thermal conductivity of 0.022W / mk of polyurethane foam material, one of the mainstream choices of thermal insulation materials on the market, there is still a huge gap. This greatly affects the market value and competitiveness of the thermal insulation recycled materials prepared by recycling phosphogypsum.

[0023] At the same time, polyurethane foam, as a mainstream insulation material, produces a large amount of waste during its production and use. If the thermal insulation properties of polyurethane foam could be used to improve the insulation performance of phosphogypsum building materials, and high-value recycled materials could be produced from these two wastes, this would have great technical value and market potential. It could also become an important alternative for developing high-value-added insulating phosphogypsum building materials and achieving resource utilization. However, during the research, a search revealed no technical literature documenting the combination of phosphogypsum and waste polyurethane foam alone.

[0024] In the process of developing a combination of waste phosphogypsum and waste polyurethane foam materials, the inventors discovered that due to the microscopic porous structure of the polyurethane foam material, when the phosphogypsum powder and the polyurethane foam powder were used as dry materials to prepare mortar, the two showed a very serious stratification phenomenon. Therefore, the mortar premix obtained by the preparation could not form a suspension and was difficult to use as mortar. At the same time, the thermal insulation layer formed after curing could not well combine with the thermal insulation properties of the polyurethane foam material.

[0025] During a serendipitous experiment, the inventors surprisingly discovered that by co-grinding waste phosphogypsum and waste polyurethane foam in a disc-type solid-phase mechanochemical reactor, they could form a composite powder from waste phosphogypsum. This composite powder, when blended with waste phosphogypsum powder, formed a mortar premix that formed a suspension suitable for use as a building material. Furthermore, when the resulting mortar premix was cured with only a small amount of polyurethane foam, the thermal conductivity of the resulting building material was reduced by up to 50% compared to phosphogypsum, significantly improving its thermal insulation properties.

[0026] However, while the co-milling process allows the polyurethane-phosphogypsum composite powder to form a suspension system after blending with the waste phosphogypsum powder, the inventors found that as the number of co-milling cycles increased, the thermal conductivity of the building material formed by the cured mortar increased significantly. This is presumably because co-milling also destroys the porous structure of the polyurethane foam to a certain extent. As the number of milling cycles increases, the polyurethane foam is further pulverized, its porous structure is also destroyed, resulting in a decrease in its thermal insulation performance, resulting in poor related properties of the final product. Based on this, when using a grinding wheel type mechanochemical reactor for co-grinding, it is necessary to ensure that the ground composite powder and the waste phosphogypsum powder can form a suspension that is not easy to stratify, and it is necessary to retain the porous structure characteristics of the polyurethane foam as much as possible to ensure the thermal insulation performance of the product. Through control experiments, the present invention finally determined that when the process parameters of the grinding wheel type mechanochemical reactor are selected as a grinding pressure of 3 to 6 MPa, the grinding wheel surface temperature is controlled by passing a constant temperature circulating liquid medium with a temperature below 10°C, the grinding wheel speed is 50 to 100 rpm, and the grinding is circulated for 1 to 3 times, while meeting the requirements of being able to form a suspension that is not easy to stratify with the waste phosphogypsum powder, it has excellent thermal insulation properties.

[0027] In one of the technical solutions, in step (4), the mixed powder obtained in step (3) is subjected to a conventional construction mortar preparation process to obtain a lightweight phosphogypsum mortar. It is further preferred that the mixed powder is used as the main dry material, and a polyvinyl alcohol aqueous solution with a polyvinyl alcohol content of 1 to 2 wt% is used as the wet material, and the dry material and the wet material are stirred and mixed to obtain the lightweight phosphogypsum mortar.

[0028] In this preferred technical solution, the inventors discovered that limiting the use of polyvinyl alcohol as a binder can further enhance the mechanical properties of the phosphogypsum-polyurethane composite material, improving its practicality. Furthermore, the use of polyvinyl alcohol as a binder has a good combination effect with conventional building mortar components such as borax, promoting further cross-linking of the polyvinyl alcohol, thereby further improving the mechanical properties of the product. Furthermore, polyvinyl alcohol is a water-soluble binder and can be prepared into an aqueous solution, facilitating subsequent mixing and processing. Furthermore, polyvinyl alcohol is a green and environmentally friendly binder. In addition to its inherent performance advantages, it does not produce toxic or harmful substances, is healthy and environmentally friendly, and does not affect the applicability of the final product.

[0029] It is worth noting that because the composition of waste phosphogypsum is relatively complex and contains harmful substance components, the prepared product of the present application is recommended for application in the building material field, and those skilled in the art can perform the same harmless treatment according to the reports of the application of phosphogypsum in the building material field in the prior art. For example, the treatment method in the paper published by Zhang Zhenhuan et al. (Zhang Zhenhuan, Ma Hang, Wan Banglong, Yang Xiaolong. Preparation process of phosphogypsum-based building gypsum powder and its retarding performance research [J]. Phosphate and compound fertilizer, 2021, 36(09): 22-24.).

[0030] The present application has the following beneficial effects:

[0031] 1. The technical scheme of the present application utilizes waste polyurethane foam and waste phosphogypsum as main raw material components, and innovatively mixes the two raw material powders uniformly through co-milling, so that pre-mixed mortar meeting the standard can be prepared, and stratification defects are not easy to occur.

[0032] 2. The technical scheme of the present application has simple process, environmentally friendly raw materials, low cost, and significantly improved product thermal insulation effect, and is expected to be popularized in the field of building materials, especially thermal insulation building materials.

[0033] 3. Through market research, it is known that waste phosphogypsum is currently in the stage of paid treatment by production enterprises, and the treatment cost of each ton of waste phosphogypsum is 30-50 yuan, so the present application not only saves material cost, but also has income space. Giving these two materials with no value the ability to be processed into high-value products not only solves the environmental problem of waste materials on a large scale, but also can improve the value of products to obtain unexpected profits, and greatly reduce the industrial cost. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 A photo of the cured sample prepared in Example 1 of the present application.

[0035] Figure 2 A photo of the mixed mortar prepared in Comparative Example 3 of the present application. DETAILED DESCRIPTION

[0036] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than for limiting the claims of the invention. Those skilled in the art can refer to the contents of this article and appropriately improve the process parameters for implementation. It is particularly important to point out that all similar replacements and modifications are obvious to those skilled in the art, and they are all considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention. Although it is believed that those of ordinary skill in the art fully understand the following terms, the following definitions are still stated to help illustrate the subject matter disclosed by the present invention.

[0037] A method for preparing lightweight phosphogypsum mortar using waste polyurethane foam comprises the following steps:

[0038] (1) Selecting waste polyurethane foam materials or products, and after pretreatment including cleaning, crushing them into waste polyurethane powder with an average particle size of not more than 0.3 mm;

[0039] (2) mixing the waste polyurethane powder obtained in step (1) with the dry phosphogypsum powder in a mass ratio of (0.9-1.1):1, and then adding the mixture into a grinding disc type mechanochemical reactor for co-grinding and pulverization. After the grinding is completed, collecting the polyurethane-phosphogypsum composite powder; wherein the process parameters of the grinding disc type mechanochemical reactor are as follows: a grinding pressure of 3-6 MPa, a grinding disc surface temperature controlled by passing a constant temperature circulating liquid medium with a temperature below 10° C., a grinding disc speed of 50-100 rpm, and cyclic grinding for 1-3 times;

[0040] (3) adding dry phosphogypsum powder to the polyurethane-phosphogypsum composite powder obtained in step (2) and mixing to obtain a mixed powder having a polyurethane content of 3 to 20 wt%;

[0041] (4) The mixed powder obtained in step (3) is subjected to a conventional construction mortar preparation process to obtain a lightweight phosphogypsum mortar. The lightweight phosphogypsum mortar can be directly solidified and formed as a thermal insulation building material, or as a premixed mortar.

[0042] Herein, the waste polyurethane foam material or product in step (1) is selected from various conventional polyurethane foam types, such as soft polyurethane foam, semi-rigid polyurethane foam, rigid polyurethane foam, etc.

[0043] Generally speaking, the waste polyurethane foam materials or products described in step (1) include industrial waste with a large amount of waste, such as scraps and waste materials generated during the synthesis and production process of polyurethane foam, and waste products using polyurethane foam materials, such as insulation pipes and insulation building materials. Those skilled in the art can check the specifications of the waste polyurethane foam materials or products to determine whether they meet the requirements for selection as raw materials of the present invention.

[0044] In this article, the pretreatment including washing described in step (1) is mainly to remove impurities on the surface of the waste polyurethane foam material or product. If necessary, the non-polyurethane foam part needs to be removed. Those skilled in the art can carry out specific treatment according to the actual conditions of the waste polyurethane foam material or product to be recycled and based on the existing technology.

[0045] Generally, the waste polyurethane foam powder processed and crushed to an average particle size of not more than 0.3 mm in step (1) can be processed by existing conventional crushing equipment such as a jaw crusher, a planetary ball mill, and a frozen ball mill.

[0046] In one embodiment, the waste polyurethane foam powder processed and pulverized to an average particle size of not more than 0.3 mm in step (1) may have an average particle size of 0.05 mm, 0.1 mm, 0.15 mm, 0.2 mm, 0.25 mm, 0.3 mm, or any range or point value therebetween. Further preferably, the waste polyurethane foam material or product may be processed and pulverized to a waste polyurethane powder having an average particle size that is consistent with or similar to the average particle size of the waste phosphogypsum powder, based on the average particle size of the selected waste phosphogypsum.

[0047] In one preferred embodiment, the waste polyurethane powder processed and crushed to an average particle size of not more than 0.3 mm in step (1) is preferably crushed using a grinding disc type mechanochemical reactor; wherein the process parameters of the grinding disc type mechanochemical reactor are: grinding pressure of 3 to 6 MPa, grinding disc surface temperature is controlled by passing a constant temperature circulating liquid medium with a temperature below 10°C, grinding disc speed is 50 to 100 rpm, and cycle grinding is 0 to 1 times.

[0048] In this article, the dry phosphogypsum powder in step (2) has been dehydrated and is in a dry powder form, which is consistent with the commonly available phosphogypsum powder on the market.

[0049] In one embodiment, the step (2) comprises mixing the waste polyurethane powder obtained in the step (1) with the dry phosphogypsum powder in a mass ratio of (0.9 to 1.1): 1, and the mass ratio can be 0.9: 1, 0.91: 1, 0.92: 1, 0.93: 1, 0.94: 1, 0.95: 1, 0.96: 1, 0.97: 1, 0.98: 1, 0.99: 1, 1.01: 1, 1.02: 1, 1.03: 1, 1.04: 1, 1.05: 1, 1.06: 1, 1.07: 1, 1.08: 1, 1.09: 1, 1.1: 1 or any range or point value therebetween.

[0050] In this context, the grinding disc type mechanochemical reactor in step (2) is the mechanochemical reactor disclosed in the previously authorized patent ZL95111258.9 of the present applicant, and the temperature of the grinding disc is controlled by introducing a constant temperature circulating liquid medium into the grinding disc. Generally speaking, the liquid medium is water.

[0051] Typically, the cyclic milling process described in step (2) is performed by milling the mixed material in a disc-type mechanochemical reactor, collecting the product at the discharge end, and then milling it again in a disc-type mechanochemical reactor. This process is considered to be 1 round of cyclic milling. It should be noted that when the cyclic milling is 0 times, it is sufficient to mill the mixed material in a disc-type mechanochemical reactor and collect the product at the discharge end.

[0052] In one embodiment, the process parameters of the grinding disc type mechanochemical reactor in step (2) are as follows: the grinding pressure is 3 to 6 MPa, for example, 3 MPa, 3.5 MPa, 4 MPa, 4.5 MPa, 5 MPa, 5.5 MPa, 6 MPa or any range or point value therebetween; the grinding disc surface temperature is controlled by passing a constant temperature circulating liquid medium with a temperature below 10°C; the grinding disc speed is 50 to 100 rpm, for example, 50 rpm, 55 rpm, 60 rpm, 65 rpm, 70 rpm, 75 rpm, 80 rpm, 85 rpm, 90 rpm, 95 rpm, 100 rpm or any range or point value therebetween; and the grinding is cyclically performed 2 to 4 times, for example, 2 times, 3 times, or 4 times.

[0053] In this article, the polyurethane content of the mixed powder in step (3) is 3 to 20 wt%, and the polyurethane content is calculated based on the total amount of the waste polyurethane powder obtained in step (1) and the dry phosphogypsum powder added in steps (2) and (3).

[0054] In one embodiment, the polyurethane content in step (3) is 3 to 20 wt% of the mixed powder, wherein the polyurethane content can be selected as 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt% or any range or point value therebetween.

[0055] In this article, the step (4) is to obtain a lightweight phosphogypsum mortar by using the mixed powder obtained in step (3) according to a conventional construction mortar preparation process. This is a conventional construction mortar preparation method in the common knowledge in this technical field. The mixed powder obtained in step (3) and a conventional mortar adhesive are used as dry materials and mixed with water to prepare the mortar. The specific process method and process parameters can be directly referred to the standard method in the prior art, preferably, the mortar preparation process in the prior art using phosphogypsum as the main raw material can be referred to.

[0056] The main invention of the present invention is that the inventors discovered during the project research on the recycling of phosphogypsum that phosphogypsum itself has a certain thermal insulation ability. After searching, it was found that its thermal conductivity is about 0.275W / mk, but compared with the thermal conductivity of 0.022W / mk of polyurethane foam material, one of the mainstream choices of thermal insulation materials on the market, there is still a huge gap. This greatly affects the market value and competitiveness of the thermal insulation recycled materials prepared by recycling phosphogypsum.

[0057] At the same time, polyurethane foam, as a mainstream insulation material, produces a large amount of waste during its production and use. If the thermal insulation properties of polyurethane foam could be used to improve the insulation performance of phosphogypsum building materials, and high-value recycled materials could be produced from these two wastes, this would have great technical value and market potential. It could also become an important alternative for developing high-value-added insulating phosphogypsum building materials and achieving resource utilization. However, during the research, a search revealed no technical literature documenting the combination of phosphogypsum and waste polyurethane foam alone.

[0058] In the process of developing a combination of waste phosphogypsum and waste polyurethane foam materials, the inventors discovered that due to the microscopic porous structure of the polyurethane foam material, when the phosphogypsum powder and the polyurethane foam powder were used as dry materials to prepare mortar, the two showed a very serious stratification phenomenon. Therefore, the mortar premix obtained by the preparation could not form a suspension and was difficult to use as mortar. At the same time, the thermal insulation layer formed after curing could not well combine with the thermal insulation properties of the polyurethane foam material.

[0059] In a casual experimental exploration, the inventors surprisingly found that by using the co-milling pulverization of the millstone type solid phase force chemical reactor, the waste phosphogypsum and the waste polyurethane foam material can form a composite powder, and the composite powder can form a suspension system after being blended with the waste phosphogypsum powder, and can be used as a building material. At the same time, the building material formed by curing the prepared mortar premix with the addition of a small amount of polyurethane foam has a thermal conductivity that is 50% lower than that of phosphogypsum, greatly improving its thermal insulation.

[0060] However, at the same time, although the addition of co-milling operation enables the polyurethane-phosphogypsum composite powder to form a suspension system after being blended with the waste phosphogypsum powder, the inventors found that as the number of cycles of co-milling increases, the thermal conductivity of the building material formed by curing the prepared mortar increases significantly. It is speculated that this is because co-milling also destroys the foam porous structure of the polyurethane foam to some extent, and as the number of milling increases, the polyurethane foam is further pulverized, and its porous structure is also destroyed, reducing its thermal insulation performance, resulting in poor performance of the final product. Based on this, when co-milling is performed using the millstone type force chemical reactor, it is necessary to ensure that the milled composite powder and the waste phosphogypsum powder can form a suspension that is not easily layered, and at the same time, the porous structure characteristics of the polyurethane foam should be preserved as much as possible to ensure the thermal insulation performance of the product. Through comparative experiments, the inventors ultimately determined that when the process parameters of the millstone type force chemical reactor are selected as a milling pressure of 3-6 MPa, the millstone disc surface temperature is controlled by passing a constant temperature circulating liquid medium with a temperature of 10°C or lower, the millstone rotation speed is 50-100 rpm, and the cycle milling is 1-3 times, the suspension formed with the waste phosphogypsum powder is not easily layered, and at the same time, it has excellent thermal insulation performance.

[0061] In one embodiment, the mixed powder obtained in step (3) is used to prepare a lightweight phosphogypsum mortar according to the conventional building mortar preparation process in step (4). Further preferably, the mixed powder is used as the main dry material, and a polyvinyl alcohol solution with a polyvinyl alcohol content of 1-2 wt% is used as the wet material. After stirring and mixing the dry material with the wet material, a lightweight phosphogypsum mortar is obtained.

[0062] In this preferred embodiment, the inventors discovered that limiting the use of polyvinyl alcohol as a binder can further enhance the mechanical properties of the phosphogypsum-polyurethane composite material, improving its practicality. Furthermore, the use of polyvinyl alcohol as a binder has a good combination with conventional building mortar components such as borax, promoting further cross-linking of the polyvinyl alcohol, thereby further improving the mechanical properties of the product. Furthermore, polyvinyl alcohol is a water-soluble binder and can be prepared as an aqueous solution, facilitating subsequent mixing and processing. Furthermore, polyvinyl alcohol is a green and environmentally friendly binder. In addition to its inherent performance advantages, it does not produce toxic or harmful substances, is healthy and environmentally friendly, and does not affect the applicability of the final product.

[0063] It is worth noting that because the components of waste phosphogypsum are relatively complex and contain harmful substances, the product prepared by the present invention is recommended for application in the field of building materials. Those skilled in the art can perform the same harmless treatment based on the reports on the application of phosphogypsum in the field of building materials in the prior art. For example, the treatment method in the paper published by Zhang Zhenhuan et al. (Zhang Zhenhuan, Ma Hang, Wan Banglong, Yang Xiaolong. Preparation process of phosphogypsum-based building gypsum powder and study on its retarding properties [J]. Phosphate Fertilizers and Compound Fertilizers, 2021, 36(09): 22-24.)

[0064] The present invention will be further explained in detail below with reference to the examples. However, it will be appreciated by those skilled in the art that these examples are provided for illustrative purposes only and are not intended to limit the present invention.

[0065] Example

[0066] The embodiments of the present application will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are merely illustrative of the present application and should not be considered as limiting the scope of the present application. In the examples, if no specific conditions are indicated, the conditions are carried out according to normal conditions or manufacturer recommendations. The reagents used or the instruments that are not indicated by the manufacturer are conventional products that can be obtained commercially. The application should not be construed as being limited to the specific examples described.

[0067] 1. Raw materials

[0068] Waste phosphogypsum: a by-product provided by an industrial phosphate fertilizer manufacturer;

[0069] Waste polyurethane foam material: waste insulation foam generated by dismantling discarded refrigerators.

[0070] 2. Preparation method

[0071] (1) treating and crushing the waste polyurethane foam material into waste polyurethane powder with an average particle size not exceeding 0.3 mm;

[0072] (2) mixing the waste polyurethane powder obtained in step (1) with the dry phosphogypsum powder in a mass ratio of 1:1, and then adding the mixture into a grinding disc type mechanochemical reactor for co-grinding and pulverization. After the grinding is completed, collecting the polyurethane-phosphogypsum composite powder; wherein the process parameters of the grinding disc type mechanochemical reactor are as follows: the grinding pressure is 3 MPa, the grinding disc surface temperature is controlled by passing a constant temperature circulating liquid medium at a temperature of 4° C., the grinding disc speed is 100 rpm, and the grinding cycle is repeated 1 to 3 times;

[0073] (3) adding dry phosphogypsum powder to the polyurethane-phosphogypsum composite powder obtained in step (2) and mixing to obtain a mixed powder having a polyurethane content of 3 to 20 wt%;

[0074] (4) A 2 wt% polyvinyl alcohol aqueous solution was prepared, and the mixed powder obtained in step (3) was mixed with the polyvinyl alcohol aqueous solution in a mass ratio of 1:1 to obtain a lightweight phosphogypsum mortar, which was then further solidified to obtain a sample.

[0075] 3. Test methods

[0076] Thermal conductivity test: Various samples were made into sheet samples with a diameter of about 47 mm and a thickness of 6-8 mm. The surface of the samples was polished flat, and then the thermal conductivity of the obtained sheet samples was tested using the HS-DR-5 thermal conductivity analyzer (Hesheng Technology).

[0077] Examples 1 to 3

[0078] Examples 1 to 3 are based on the above preparation method, and the cyclic milling is fixed at 1 time. The thermal insulation properties of the samples obtained by curing with the polyurethane content in the mixed powder as a variable are studied, as shown in Table 1 below:

[0079] Table 1 Effect of different polyurethane contents on thermal conductivity of final products

[0080]

[0081] The table above clearly demonstrates that, even with the addition of a small amount of polyurethane foam, the samples prepared according to the technical solution of the present invention all exhibited excellent thermal insulation performance. Specifically, the thermal conductivity of the sample in Example 1 decreased by approximately 22% compared to 0.275 W / mk of phosphogypsum, the thermal conductivity of the sample in Example 2 decreased by approximately 39% compared to 0.275 W / mk of phosphogypsum, and the thermal conductivity of the sample in Example 3 decreased by approximately 53% compared to 0.275 W / mk of phosphogypsum. Even with the smallest addition of polyurethane foam in Example 1, the reduction in thermal conductivity achieved with each 1 wt% addition of polyurethane foam reached the highest level, significantly exceeding the theoretical thermal conductivity of a mixture of two materials with different thermal conductivities. Furthermore, a large amount of waste phosphogypsum was utilized as the primary raw material, significantly reducing costs.

[0082] It is worth noting that the actual sample thermal conductivity is smaller than the theoretical thermal conductivity calculated by mixing the thermal conductivity of phosphogypsum and the thermal conductivity of polyurethane according to the mixing ratio (for example, the theoretical thermal conductivity of the sample with 5% polyurethane content in Example 1 is calculated to be about 0.262 W / mk, but the actual thermal conductivity is 0.2146 W / mk, which is significantly higher than the theoretical value), so that the obtained material has a thermal insulation capacity significantly higher than the theoretical case of simply mixing the two substances.

[0083] Examples 4-6, Comparative Examples 1-2

[0084] Examples 4-6, Comparative Examples 1-2 Based on the above preparation method, and the polyurethane content is fixed at 5wt%, the thermal insulation performance of the sample prepared with the number of cycles as a variable is studied, as shown in Table 2 below:

[0085] Table 2: Effect of the number of cycles on the thermal conductivity of the final product

[0086] Comparative Example 1 Example 4 Example 5 Example 6 Comparative Example 2 Circulation grinding (times) 0 1 2 3 4 Average thermal conductivity (W / mk) 0.2673 0.2522 0.2769 0.2861 0.2960

[0087] It should be noted that in Examples 4-6, Comparative Examples 1-2, the raw material of the experimental sample is another batch of phosphogypsum powder produced by the factory, which is tested to have a thermal conductivity of 0.3076 W / mk.

[0088] It is worth noting that in the case of 0 cycles, the prepared mortar shows a slight stratification, which is manifested as a lighter color on the surface of the sample and more pores, and its practical stability is questionable.

[0089] As can be seen from the above table, with the increase of the number of cycles in the examples, the thermal conductivity of the samples prepared in Examples 4-6 increases significantly, which is speculated to be due to the destruction of the porous structure of the polyurethane foam material with the multiple cycles of co-milling, resulting in an increase in the thermal conductivity of the material and a decrease in the thermal insulation property.

[0090] Comparative Example 3

[0091] In Comparative Example 3, based on the same raw materials and proportions as Examples 4-6, the waste polyurethane powder and dry phosphogypsum powder are separately milled and crushed instead of co-milling. The milling and crushing process also uses a mill-type chemical reactor, and the process parameters are consistent with those of Examples 4-6, with 1 cycle of co-milling.

[0092] The final prepared mixed mortar is shown in the attached Figure 2 As can be seen, the mixed mortar shows obvious stratification after standing, with a higher content of polyurethane in the upper layer and a lower content of polyurethane in the lower layer, making it difficult for the sample to become a qualified mixed material and not having practical value.

Claims

1. A method for preparing lightweight phosphogypsum mortar using waste polyurethane foam, characterized in that The following steps are involved: (1) Select waste polyurethane foam materials or products, and after pretreatment including cleaning, crush them into waste polyurethane powder with an average particle size not higher than 0.3 mm; (2) The waste polyurethane powder obtained in step (1) is mixed with the dry phosphogypsum powder in a mass ratio of (0.9-1.1):1, and then added to a grinding disc type mechanochemical reactor for co-grinding and pulverization. After the grinding is completed, the polyurethane-phosphogypsum composite powder is collected; wherein the process parameters of the grinding disc type mechanochemical reactor are: grinding pressure of 3-6 MPa, the grinding disc surface temperature is controlled by passing a constant temperature circulating liquid medium with a temperature below 10°C, the grinding disc speed is 50-100 rpm, and the grinding cycle is 1-3 times; (3) adding dry phosphogypsum powder to the polyurethane-phosphogypsum composite powder obtained in step (2) and mixing to obtain a mixed powder having a polyurethane content of 3 to 20 wt%; (4) The mixed powder obtained in step (3) is subjected to a conventional construction mortar preparation process to obtain lightweight phosphogypsum mortar.

2. The method according to claim 1, wherein: The waste polyurethane powder processed and crushed to an average particle size of not more than 0.3 mm in step (1) is crushed using a grinding disc type mechanochemical reactor; wherein the process parameters of the grinding disc type mechanochemical reactor are: a grinding pressure of 3 to 6 MPa, a grinding disc surface temperature controlled by passing a constant temperature circulating liquid medium with a temperature below 10°C, a grinding disc speed of 50 to 100 rpm, and 0 to 1 cycle grinding.

3. The method according to claim 1, wherein: In step (4), the mixed powder obtained in step (3) is subjected to a conventional construction mortar preparation process to obtain a lightweight phosphogypsum mortar, wherein the mixed powder is used as a main dry material, and a polyvinyl alcohol aqueous solution with a polyvinyl alcohol content of 1 to 2 wt% is used as a wet material, and the dry material and the wet material are stirred and mixed to obtain the lightweight phosphogypsum mortar.

4. The method according to claim 1, wherein: In step (3), dry phosphogypsum powder is added to the polyurethane-phosphogypsum composite powder obtained in step (2) to obtain a mixed powder with a polyurethane content of 5 to 10 wt%.

5. A lightweight phosphogypsum mortar prepared by the method for preparing lightweight phosphogypsum mortar using waste polyurethane foam according to claim 1.

6. Use of the lightweight phosphogypsum mortar according to claim 5 as a building material.

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