All-solid wastewater hard cementing material based on phosphogypsum as well as preparation method and application of all-solid wastewater hard cementing material

Abstract

The invention discloses an all-solid waste water hard cementing material based on ardealite. The gelling material is prepared from the following components in parts by weight: 13.80 to 40.53 parts of modified phosphogypsum, 10.55 to 37.63 parts of mineral waste residue, 7.06 to 14.52 parts of steel slag, 1.35 to 2.67 parts of sodium hydroxide, 0.21 to 0.52 part of nano silica sol and 22.47 to 34.56 parts of water, wherein the modified phosphogypsum is modified phosphogypsum; the modified ardealite is obtained by using original ardealite produced by a wet-process phosphoric acid process as a raw material, calcining at 120-160 DEG C for 1-2 hours, screening, and calcining at 175-220 DEG C for 1.5-3 hours. The invention further discloses a preparation method and application of the cementing material. The method is simple, convenient and efficient, the prepared cementing material is large in solid waste proportion, high in strength and good in water resistance, the comprehensive performance of the cementing material is similar to that of cement, and therefore remarkable economical efficiency and environmental friendliness are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and in particular relates to a full-solid wastewater hardening gelling material based on phosphogypsum, and a preparation method and application thereof. Background Art

[0002] Phosphogypsum, steel slag, and mining slag are major industrial and municipal solid wastes that urgently need to be addressed. Currently, the national stockpile of phosphogypsum exceeds 820 million tons, with an annual increase of approximately 77 to 80 million tons. The comprehensive utilization rate is only around 50%. This massive stockpile of phosphogypsum not only depletes land resources but also poses significant risks to the safety of the aquatic environment, including the Yangtze River, due to the water-soluble phosphorus pentoxide and fluorine it contains. Furthermore, over 100 million tons of steel slag are discharged nationwide annually, and the accumulated stockpile has exceeded 1 billion tons. Due to its complex composition, high quality fluctuations, poor stability, and low reactivity, the comprehensive utilization rate of steel slag is currently less than 30%. Therefore, with national, provincial, and municipal governments issuing documents to promote the safe and resourceful utilization of major solid wastes, the reduction, harmlessness, and resourceful recycling of these major solid wastes, such as phosphogypsum, steel slag, and mining slag, is urgently needed.

[0003] At the same time, the use of traditional cementitious materials such as cement and natural gypsum, which are energy-intensive and carbon-intensive, remains high. For example, China's cement production accounts for approximately 50% of global production, and carbon dioxide emissions from cement production account for approximately 7% of total human emissions. In this context, and particularly considering that solid wastes vary in chemical composition, their primary components, such as SiO2, CaO, Al2O3, and Fe2O3, possess potential cementitious activity, the synergistic effects of solid wastes such as phosphogypsum, steel slag, and slag in the preparation of cementitious materials can not only achieve the resource utilization of bulk solid waste but also replace traditional cementitious materials such as cement and natural gypsum. This is an important direction for the future low-carbon and sustainable development of cementitious materials.

[0004] However, due to the air-hardening properties of phosphogypsum, its strong acidity and high impurities, and the complex mineral composition and low cementing activity of steel slag, all-solid waste cementitious materials prepared using phosphogypsum, steel slag, and ore slag have insufficient mechanical properties and durability (especially water resistance), severely restricting their widespread application. Therefore, cementitious materials prepared primarily from solid wastes such as phosphogypsum are currently primarily used in applications with lower mechanical performance and durability requirements, and their role in replacing cement is far less than expected. Summary of the Invention

[0005] A technical problem to be solved by the present invention is to provide a fully solid waste water-hardening cementitious material based on phosphogypsum, which has a large solid waste ratio, high strength, excellent water resistance, and comprehensive properties similar to cement.

[0006] Another technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned material.

[0007] To solve the first technical problem, the all-solid waste water-hardening cementitious material provided by the present invention comprises the following components per 100 parts by weight of raw materials: 13.80 to 40.53 parts of modified phosphogypsum, 10.55 to 37.63 parts of slag, 7.06 to 14.52 parts of steel slag, 1.35 to 2.67 parts of sodium hydroxide, 0.21 to 0.52 parts of nano-silica sol, and 22.47 to 34.56 parts of water; the modified phosphogypsum is obtained by using the original phosphogypsum produced by the wet phosphoric acid process as raw material, calcining at 120 to 160°C for 1 to 2 hours, screening, and then calcining at 175 to 220°C for 1.5 to 3 hours.

[0008] Furthermore, the particle size of the modified phosphogypsum is 200-250 meshes.

[0009] Furthermore, the slag is water-quenched granulated blast furnace slag produced by ironmaking, and the grade is S95.

[0010] Furthermore, the particle size of the steel slag is 200-300 meshes.

[0011] Furthermore, the sodium hydroxide is analytically pure and has a sodium hydroxide content of not less than 96%.

[0012] Furthermore, the pH value of the nano-silica sol is 7-11.5, and the SiO2 content is 20-30%.

[0013] Furthermore, the water is ordinary tap water.

[0014] In order to solve the above-mentioned second technical problem, the present invention provides a method for preparing a solid waste water-hardening gelling material, comprising the following steps: Taking modified phosphogypsum, slag, and steel slag in parts by weight, and mixing them uniformly to obtain a mixture A; Take sodium hydroxide, water and nano-silica sol by weight, first add sodium hydroxide to water and stir evenly to obtain mixture B, then add mixture B to mixture A and stir evenly to obtain mixture C, and then add nano-silica sol and stir evenly to obtain mixture D, that is, a full-solid wastewater hardening gelling material based on phosphogypsum is obtained.

[0015] Furthermore, in step (1), the mixture is mechanically stirred for 1 to 3 minutes to obtain a mixture A.

[0016] Furthermore, in step (2), mechanical stirring is performed for 1 to 2 minutes to obtain mixture B, mechanical stirring is performed for 3 to 5 minutes to obtain mixture C, and mechanical stirring is performed for 1 to 3 minutes to obtain mixture D.

[0017] The present invention also provides the application of the above-mentioned all-solid wastewater hardening cementitious material in foundation pit backfill, underground backfill, soft soil treatment, concrete and its products.

[0018] Compared with the prior art, the beneficial effects of the present invention include: The present invention is simple to operate and requires no new construction processes compared to conventional cement binders and concrete. Furthermore, the solid waste content is extremely high, enabling high-proportion and high-value utilization of industrial solid waste. Furthermore, the present invention fully leverages the "enhanced gelling activity of modified phosphogypsum and the synergistic effect of multi-source solid waste," resolving issues such as low strength, poor water resistance, and limited application of traditional solid waste-based binders. In particular, it overcomes the problem of traditional solid waste-based binders being unable to be used in humid environments, enabling the stable application of solid waste-based binders in a wide range of complex environments. DETAILED DESCRIPTION

[0019] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0020] The embodiment of the present invention provides a method for preparing a fully solid waste water-hardening cementitious material by modifying phosphogypsum by a double calcination method. The raw materials of each 100 parts by weight include the following components: 13.80 to 40.53 parts of modified phosphogypsum, 10.55 to 37.63 parts of slag, 7.06 to 14.52 parts of steel slag, 1.35 to 2.67 parts of sodium hydroxide, 0.21 to 0.52 parts of nano-silica sol, and 22.47 to 34.56 parts of tap water.

[0021] The modified phosphogypsum is prepared from raw phosphogypsum produced in a wet-process phosphoric acid process. The raw material is calcined at 120-160°C for 1-2 hours, sieved, and then calcined at 175-220°C for 1.5-3 hours. The particle size of the modified phosphogypsum is 200-250 mesh. The slag is water-quenched granulated blast furnace slag produced in ironmaking, grade S95. The particle size of the steel slag is 200-300 mesh. The sodium hydroxide is analytical grade, with a sodium hydroxide content of not less than 96%. The nano-silica sol has a pH of 7-11.5 (in the comparative examples and examples below, the specific nano-silica sol used has a pH of 9.5) and a SiO2 content of 20-30% (in the comparative examples and examples below, the SiO2 content is 25±1%).

[0022] In the above-mentioned material system, the modified phosphogypsum is obtained by two calcination modifications. Compared with the one-time calcination process, its advantages are mainly manifested in: on the one hand, the first calcination can reduce the free water content, thereby increasing the soluble impurity removal rate and the hemihydrate gypsum conversion rate after the second calcination. On the other hand, the residual phosphates, fluorides and organic matter in the original phosphogypsum will form a coating layer on the surface of the phosphogypsum particles after dissolution, hindering the growth of the hemihydrate gypsum hydration products. The twice-calcined modified phosphogypsum can reduce this adverse effect and is more conducive to the formation of strength of the cementitious material. Furthermore, the two-time calcination modification significantly weakens the acidity of the phosphogypsum, making it weakly acidic or even neutral. In addition, its reaction activity is greatly increased after the two-time calcination modification. Therefore, a large amount of SO4 can be dissociated in a weakly alkaline environment. 2- , and Al released from steel slag and slag 3+ and Ca 2+ The reaction generates ettringite (AFt), and the active SiO2 and Ca 2+ Combine to form CSH gel.

[0023] Second, the weakly alkaline environment created by an appropriate amount of sodium hydroxide can break the silicon-oxygen (Si-O-Si) and aluminum-oxygen (Al-O) bonds in steel slag and ore slag, releasing active SiO2 and Al2O3 components. It also accelerates the co-crystallization of AFt and CSH, forming a double network structure that increases the material's early strength by over 30% and inhibits later strength reduction. Compared to original phosphogypsum, which requires more sodium hydroxide to create an alkaline environment, modified phosphogypsum has significantly reduced acidity, achieving optimal results with less sodium hydroxide, thus avoiding the adverse effects of excessive sodium hydroxide addition, such as efflorescence.

[0024] Third, as a hydration regulating component, nano-silica sol can fill microscopic pores and promote secondary hydration reactions, accelerate the later hydration process of slag and steel slag, and enhance the density of the material.

[0025] Fourth, through the synergistic effect of multiple solid wastes, the crystal morphology and spatial distribution of the hydration products can be optimized, promoting the CSH gel to wrap the AFt crystals and fill the pores to form a densified matrix structure, whose porosity can be reduced to below 15%. At the same time, the chemical bonding between the products is enhanced, so the water resistance of the material system is significantly improved.

[0026] The above-mentioned method for preparing all-solid waste water-hardening cementitious material by modifying phosphogypsum by a double calcination method comprises the following steps: Modified phosphogypsum, slag, and steel slag are mixed according to weight, and mechanically stirred for 1 to 3 minutes to obtain a mixture A; Sodium hydroxide, tap water and nano-silica sol are taken by weight. First, sodium hydroxide is added to tap water and mechanically stirred for 1 to 2 minutes to obtain mixture B. Then, mixture B is added to mixture A and mechanically stirred for 3 to 5 minutes to obtain mixture C. Nano-silica sol is then added and mechanically stirred for 1 to 3 minutes to obtain mixture D, that is, a fully solid wastewater-hardening cementitious material prepared based on the double-calcination method to modify phosphogypsum is obtained.

[0027] In summary, the present invention uses a double calcination method to modify phosphogypsum to improve its reactivity, and designs a reasonable compounding scheme based on the physical and chemical properties of modified phosphogypsum, slag, and steel slag. It can not only utilize the interaction between solid waste materials to achieve the design goal of all-solid waste cementitious materials, but also fundamentally improve the problems of poor water resistance and limited application range of conventional solid waste-based cementitious materials. In scenarios such as foundation pit backfill, underground backfill, soft soil treatment, concrete and its products, it can be used as a cementitious material to bond other materials or all cementitious materials are used to prepare pure slurry for use, thereby achieving a comprehensive replacement of cement. Therefore, the economic, social and environmental benefits of the present invention are very outstanding.

[0028] The present invention is further described in detail below through specific examples.

[0029] Comparative Example A0: Modified phosphogypsum: tap water = 65.53 parts: 34.47 parts First, weigh the modified phosphogypsum and water according to the ingredient ratio, add them into the mixer and stir for 4 minutes, then fill the mold, naturally cure for 1 hour, demould, and place it under the conditions of temperature 20±1℃ and humidity 95%±1% for 12 hours.

[0030] Modified phosphogypsum is prepared by calcining raw phosphogypsum produced in a wet-process phosphoric acid process at 150°C for 1 hour, sieving to select material with a mesh size of 200-250 mesh, and further calcining it at 200°C for 2 hours. In the following comparative examples and examples, unless otherwise specified, all methods were obtained using the two-stage calcination method. In all the following comparative examples and examples, tap water was used. However, as is well known to those skilled in the art, river water, lake water, or stream water can also meet the requirements of the present invention.

[0031] Comparative Example A1: modified phosphogypsum: slag: water = 52.42 parts: 13.11 parts: 34.47 parts First, the modified phosphogypsum and slag were weighed according to the proportion of ingredients, added into a mixer and mechanically stirred for 2 minutes, then water was added and stirred for 4 minutes before filling into a mold. After natural curing for 1 hour, the mold was removed and placed under conditions of temperature 20±1°C and humidity 95%±1% for curing for 12 hours.

[0032] Comparative Example A2: Modified phosphogypsum: steel slag: water = 52.42 parts: 13.11 parts: 34.47 parts First, the modified phosphogypsum and steel slag were weighed according to the proportion of ingredients, added into a mixer and mechanically stirred for 2 minutes, then water was added and stirred for 4 minutes before filling into a mold. After natural curing for 1 hour, the mold was removed and cured at a temperature of 20±1°C and a humidity of 95%±1% for 12 hours.

[0033] Comparative Example A3: Modified phosphogypsum: slag: sodium hydroxide: water = 52.31 parts: 10.55 parts: 2.67 parts: 34.47 parts First, the modified phosphogypsum and slag were weighed according to the proportion of ingredients, added to the mixer and mixed and mechanically stirred for 2 minutes. Then, the weighed sodium hydroxide was added to the water and stirred for 1 minute. Then, the mixture was added to the mixer and stirred for 4 minutes before being molded. After natural curing for 1 hour, the molds were removed and cured at a temperature of 20±1°C and a humidity of 95%±1% for 12 hours.

[0034] Comparative Example A4: Modified phosphogypsum: steel slag: sodium hydroxide: water = 52.35 parts: 10.42 parts: 2.67 parts: 34.56 parts First, the modified phosphogypsum and steel slag were weighed according to the proportion of ingredients, added into the mixer and mixed and mechanically stirred for 2 minutes. Then, the weighed sodium hydroxide was added into the water and stirred for 1 minute. Then, the mixture was added into the mixer and stirred for 4 minutes before being molded. After natural curing for 1 hour, the molds were removed and cured for 12 hours under the conditions of temperature 20±1°C and humidity 95%±1%.

[0035] Comparative Example A5: Modified phosphogypsum: slag: steel slag: nano-silica sol: water = 26.52 parts: 29.63 parts: 8.77 parts: 0.52 parts: 34.56 parts First, the modified phosphogypsum, slag and steel slag were weighed according to the proportion of ingredients, added into the blender and mixed and mechanically stirred for 2 minutes, then the weighed sodium hydroxide was added into the water and stirred for 1 minute, then added into the blender and stirred for 4 minutes, and finally the weighed nano-silica sol was added and stirred for 2 minutes before filling the mold. After natural curing for 1 hour, the mold was removed and the mixture was placed under conditions of temperature 20±1°C and humidity 95%±1% for curing for 12 hours.

[0036] Comparative Example A6: Modified phosphogypsum: slag: steel slag: sodium hydroxide: water = 26.33 parts: 29.38 parts: 7.06 parts: 2.67 parts: 34.56 parts First, the modified phosphogypsum, slag and steel slag were weighed according to the proportion of ingredients, added into the mixer and mixed and mechanically stirred for 2 minutes. Then, the weighed sodium hydroxide was added into the water and stirred for 1 minute. Then, the mixture was added into the mixer and stirred for 4 minutes before being molded. After natural curing for 1 hour, the mold was removed and the mixture was placed under conditions of temperature 20±1°C and humidity 95%±1% for curing for 12 hours.

[0037] Comparative Example A7: Primary calcined phosphogypsum: slag: steel slag: sodium hydroxide: nano-silica sol: water = 25.10 parts: 28.82 parts: 8.83 parts: 2.67 parts: 0.21 parts: 34.37 parts First, uncooked phosphogypsum was calcined at 200°C for 2 hours and sieved to obtain primary calcined phosphogypsum with a particle size of 200-250 mesh. The primary calcined phosphogypsum, slag, and steel slag were weighed according to the proportions and added to a blender, where they were mechanically stirred for 2 minutes. The weighed sodium hydroxide was then added to water and stirred for 1 minute. The mixture was then stirred in the blender for another 4 minutes before being molded and naturally cured for 1 hour. The molds were then removed and cured for 12 hours at a temperature of 20±1°C and a humidity of 95%±1%.

[0038] Example B1: Modified phosphogypsum: slag: steel slag: sodium hydroxide: nano-silica sol: water = 25.10 parts: 28.82 parts: 8.83 parts: 2.67 parts: 0.21 parts: 34.37 parts Example B2: Modified phosphogypsum: slag: steel slag: sodium hydroxide: nano-silica sol: water = 28.23 parts: 20.91 parts: 14.62 parts: 1.35 parts: 0.52 parts: 34.37 parts Example B3: Modified phosphogypsum: slag: steel slag: sodium hydroxide: nano-silica sol: water = 25.86 parts: 29.14 parts: 7.25 parts: 2.67 parts: 0.52 parts: 34.56 parts Example B4: Modified phosphogypsum: slag: steel slag: sodium hydroxide: nano-silica sol: water = 25.97 parts: 29.59 parts: 8.05 parts: 1.35 parts: 0.52 parts: 34.52 parts Example B5: Modified phosphogypsum: slag: steel slag: sodium hydroxide: nano-silica sol: water = 25.86 parts: 29.14 parts: 7.25 parts: 2.67 parts: 0.21 parts: 34.87 parts Example B6: Modified phosphogypsum: slag: steel slag: sodium hydroxide: nano-silica sol: water = 37.12 parts: 10.98 parts: 14.24 parts: 2.67 parts: 0.52 parts: 34.47 parts Example B7: Modified phosphogypsum: slag: steel slag: sodium hydroxide: nano-silica sol: water = 15.90 parts: 37.63 parts: 8.72 parts: 2.67 parts: 0.52 parts: 34.56 parts The method for preparing all-solid waste water-hardening cementitious materials by modifying phosphogypsum by a double calcination method in Examples B1 to B7 is as follows: First, weigh modified phosphogypsum, slag, steel slag, sodium hydroxide, nano-silica sol, and water according to the ingredient ratio; mix the modified phosphogypsum, slag, and steel slag and mechanically stir for 2 minutes to obtain Mixture A. Then, add sodium hydroxide to the water and mechanically stir for 1 minute to obtain Mixture B. Then, add Mixture B to Mixture A and mechanically stir for 4 minutes to obtain Mixture C. Finally, add nano-silica sol and mechanically stir for 2 minutes to obtain Mixture D. Place Mixture D in a mold, naturally cure for 1 hour, then demold and cure at 20±1°C and 95%±1% humidity for 12 hours.

[0039] For the convenience of comparison, the raw material dosages of the above examples and comparative examples are listed in Table 1 below.

[0040] Table 1 Raw material dosage of each embodiment of the present invention and comparative example (parts by weight) The compressive strength and water resistance of the slurry test blocks (100 mm × 100 mm × 100 mm) of the above examples and comparative examples were tested, wherein: The compressive strength was obtained by calculating the average compressive strength of three test blocks of each group of neat slurry (excluding abnormal values ​​with deviation > 15%).

[0041] The water absorption rate was obtained by calculating the average water absorption rate of three test pieces in each group of pure slurry (excluding abnormal values ​​with deviation > 15%).

[0042] The softening coefficient is obtained by calculating the average softening coefficient of three test blocks in each group of pure slurry (excluding abnormal values ​​with deviation > 15%).

[0043] The test results of the 3d, 7d and 28d compressive strength, water absorption and softening coefficient of the slurry test blocks of the embodiments of the present invention and the comparative example are shown in Table 2.

[0044] Table 2 Compressive strength and durability test results of various embodiments of the present invention and comparative examples Comparative Examples A0-A2 show that the pure phosphogypsum system, due to its loose structure and single hydration product, has the highest water absorption and the lowest softening coefficient. Adding slag or steel slag reduces the water absorption of the cementitious material to a certain extent, while increasing its softening coefficient. This suggests that the combination of modified phosphogypsum with either slag or steel slag improves the durability of the cementitious material system. However, the synergistic effect between the two solid wastes is not significant, resulting in limited improvements in material performance.

[0045] It can be seen from Comparative Examples A3 to A4 that at the same sodium hydroxide dosage, the mechanical properties and water resistance of the cementitious material compounded with modified phosphogypsum and steel slag or slag are further improved compared with the cementitious material not activated by sodium hydroxide, but are still significantly lower than those in the examples.

[0046] It can be seen from Comparative Example A5 and Examples B3 and B4 that when modified phosphogypsum, steel slag and slag are compounded and nano-silica sol is added, the mechanical properties of the cementitious material without using a sodium hydroxide activator are significantly weaker than those of the examples, and the amount of sodium hydroxide added has a significant effect on the mechanical strength and water resistance of the cementitious material, among which Example B3 has the best mechanical properties and water resistance.

[0047] It can be seen from Comparative Example A6 and Examples B3 and B5 that when modified phosphogypsum, steel slag and slag are compounded and sodium hydroxide is added, the mechanical properties of the gelling material are significantly weaker than those of the Examples when nano-silica sol is not used.

[0048] It can be seen from Comparative Example A7 and Example B1 that, when the material composition is consistent, if only the original phosphogypsum modified by single calcination is used, the compressive strength and water resistance of the obtained cementitious material are weaker than the cementitious material prepared by the twice calcined modified phosphogypsum used in the examples of the present invention.

[0049] The present invention adopts modified phosphogypsum, slag, steel slag, sodium hydroxide, nano-silica sol and water in appropriate proportions, and the compressive strength is significantly improved, indicating that the cementitious material obtained in the embodiment of the present invention has the advantages of high strength and good durability. The 3d compressive strength is 23.42~32.78MPa, the 28d compressive strength can reach up to 54.79MPa, the softening coefficient is greater than 0.8, and the maximum can reach 0.95, which is significantly better than the comparative example and meets the standard for use in a humid environment.

[0050] The above-described embodiments merely illustrate the implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A fully solid waste water-hardening cementitious material based on phosphogypsum, characterized in that: The cementitious material is prepared from 100 parts by weight of the following components: 13.80 to 40.53 parts of modified phosphogypsum, 10.55 to 37.63 parts of slag, 7.06 to 14.52 parts of steel slag, 1.35 to 2.67 parts of sodium hydroxide, 0.21 to 0.52 parts of nano-silica sol, and 22.47 to 34.56 parts of water. The modified phosphogypsum is obtained by using original phosphogypsum produced by a wet phosphoric acid process as a raw material, calcining at 120 to 160° C. for 1 to 2 hours, screening, and then calcining at 175 to 220° C. for 1.5 to 3 hours.

2. The all-solid waste water-hardening cementitious material based on phosphogypsum according to claim 1, characterized in that: The particle size of the modified phosphogypsum is 200-250 meshes.

3. The all-solid waste water-hardening cementitious material based on phosphogypsum according to claim 1 or 2, characterized in that: The slag is water-quenched granulated blast furnace slag produced by ironmaking, and the grade is S95.

4. The all-solid waste water-hardening cementitious material based on phosphogypsum according to claim 1 or 2, characterized in that: The particle size of the steel slag is 200-300 meshes.

5. The all-solid waste water-hardening cementitious material based on phosphogypsum according to claim 1 or 2, characterized in that: The sodium hydroxide is analytically pure, and the sodium hydroxide content is not less than 96%.

6. The all-solid waste water-hardening cementitious material based on phosphogypsum according to claim 1 or 2, characterized in that: The pH value of the nano-silica sol is 7-11.5, and the SiO2 content is 20-30%.

7. The all-solid waste water-hardening cementitious material based on phosphogypsum according to claim 1 or 2, characterized in that: The water is ordinary tap water.

8. The method for preparing the all-solid waste water-hardening cementitious material based on phosphogypsum according to any one of claims 1 to 7, characterized in that: The method comprises the steps of: (1) Taking modified phosphogypsum, slag, and steel slag in parts by weight, and mixing them evenly to obtain a mixture A; (2) Sodium hydroxide, water and nano-silica sol are taken by weight. First, sodium hydroxide is added to water and stirred evenly to obtain mixture B. Then, mixture B is added to mixture A and stirred evenly to obtain mixture C. Then, nano-silica sol is added and stirred evenly to obtain mixture D. In this way, a fully solid wastewater hardening cementitious material based on phosphogypsum is obtained.

9. The method for preparing all-solid waste water-hardening cementitious materials based on double calcination modified phosphogypsum according to claim 8, characterized in that: In the step (1), the mixture is mechanically stirred for 1 to 3 minutes to obtain a uniform mixture A. In the step (2), the mixture is mechanically stirred for 1 to 2 minutes to obtain a mixture B. The mixture is mechanically stirred for 3 to 5 minutes to obtain a mixture C. The mixture is mechanically stirred for 1 to 3 minutes to obtain a mixture D.

10. Use of the all-solid wastewater hardening cementitious material based on phosphogypsum according to any one of claims 1 to 7 as a cementitious material to bond other materials in foundation pit backfill, underground backfill, soft soil treatment, concrete and its products or use cementitious materials to prepare pure slurry.

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