An alkali-activated slag-phosphogypsum solid waste cementitious material and its preparation method

Abstract

This invention provides an alkali-activated slag-phosphogypsum solid waste cementitious material and its preparation method, relating to the field of cementitious material technology. The preparation method includes the following steps: treating phosphogypsum with acid, filtering and hydrophobically treating the filter cake, drying, grinding, and calcining, followed by low-temperature aging to obtain pretreated phosphogypsum; grinding coal slag, soaking it in acid, filtering, and drying the filter cake to constant weight to obtain pretreated coal slag; mixing the pretreated phosphogypsum and pretreated coal slag in a certain proportion, then adding a water-reducing agent, a retarder, calcium oxide, and sodium hydroxide and mixing thoroughly to obtain the alkali-activated slag-phosphogypsum solid waste cementitious material. This invention uses phosphogypsum and coal slag to prepare the phosphogypsum-slag cementitious material, which can adsorb water-soluble phosphorus, fluorine, and other harmful substances in phosphogypsum, avoiding their impact on the hydration of phosphogypsum and reducing groundwater pollution, thus solving the problem of the difficulty in utilizing solid wastes such as phosphogypsum.

Description

Technical Field

[0001] This invention belongs to the field of cementitious materials technology, specifically relating to an alkali-activated slag-phosphogypsum all-solid waste cementitious material and its preparation method. Background Technology

[0002] Phosphogypsum, as an industrial byproduct, has become a significant factor restricting the development of the phosphate chemical industry. Currently, global phosphogypsum stockpiles exceed 6 billion tons, and continue to increase at a rate of approximately 200 million tons annually. However, the global comprehensive utilization rate of phosphogypsum is only around 25%, making the harmless treatment and resource utilization of phosphogypsum solid waste a global challenge. The application of phosphogypsum as a building material is the main way to utilize it on a large scale in the construction sector, and it is also one of the important topics for concentrated technical research. Phosphogypsum has a wide range of applications in roads, such as replacing natural gypsum as a cement retarder, replacing fine aggregates in concrete preparation after grinding, and replacing part of the cement as a cementitious material after calcination.

[0003] Currently, the main problems with the application of phosphogypsum as a cementing material in road engineering are as follows: First, there are few methods for homogenizing phosphogypsum, making it difficult to achieve large-scale utilization; second, the material contains harmful substances such as water-soluble phosphorus and water-soluble fluorine, which not only affect the hydration of gypsum but also pollute groundwater resources; third, the material is prone to cracks and pores during the hydration process, resulting in poor water resistance and mechanical properties.

[0004] Some studies have used acid leaching to remove most of the free phosphorus and fluoride from phosphogypsum, thereby reducing the release of water-soluble phosphorus and fluoride during use. However, acid leaching cannot completely remove free phosphorus and fluoride from phosphogypsum and exhibits a diminishing returns effect; the higher the removal rate, the greater the increase in the amount of acid consumed. Therefore, acid leaching alone cannot completely solve the problem of water-soluble phosphorus and fluoride release from materials containing phosphogypsum.

[0005] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0006] The purpose of this invention is to provide an alkali-activated slag-phosphogypsum all-solid waste cementitious material, made from phosphogypsum and other solid wastes, which can replace cement in the production of concrete and has the advantages of low release of water-soluble phosphorus and fluorine, thus solving the problem of the difficulty in utilizing solid wastes such as phosphogypsum.

[0007] The present invention also aims to provide a method for preparing the alkali-activated slag-phosphogypsum solid waste cementitious material.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for preparing an alkali-activated slag-phosphogypsum all-solid waste cementitious material includes the following steps:

[0010] S1. Mix the acid solution with phosphogypsum, react for a certain time, filter, hydrophobically treat the filter cake, dry to constant weight, grind the dried phosphogypsum into fine powder, then calcine it, and then age the calcined phosphogypsum at low temperature to obtain pretreated phosphogypsum.

[0011] S2. Grind the coal slag into fine powder, then mix it with acid solution, react for a certain time, filter it, and dry the filter cake to constant weight to obtain pretreated coal slag.

[0012] S3. The pretreated phosphogypsum and pretreated coal-fired slag are thoroughly mixed in a certain proportion to obtain phosphogypsum-slag cementitious material. Water-reducing agent, retarder, calcium oxide and sodium hydroxide are added to the phosphogypsum-slag cementitious material and then thoroughly mixed to obtain alkali-activated slag-phosphogypsum all-solid waste cementitious material.

[0013] Preferably, in step S1, the acid solution is an aqueous solution of hydrochloric acid or sulfuric acid, the concentration of the acid solution is 0.05-1.5 mol / L, the mass ratio of the acid solution to phosphogypsum is (4-6):1, and the reaction is stirred for 20-30 min.

[0014] Preferably, in step S1, a hydrophobic agent is used to treat the filter cake for hydrophobic treatment. By weight, the hydrophobic agent includes 0.5 to 1.0 parts of KH550, 4 to 5 parts of TEOS, and 90 to 95 parts of water.

[0015] In step S1, the drying temperature is 40-50℃.

[0016] Preferably, in step S1, the phosphogypsum is ground to a finer size than 0.075 mm and then calcined at 150–180 °C for 3–5 h.

[0017] Preferably, in step S1, the calcined phosphogypsum is aged at 2-5°C and 35%-45% humidity for 24 hours, and then aged at 8-12°C and 30%-40% humidity for 24-48 hours to obtain pretreated phosphogypsum.

[0018] Preferably, in step S2, the coal-fired slag is ground to below 0.075 mm, the concentration of the acid solution is 0.05-0.15 mol / L, the mass ratio of the acid solution to the coal-fired slag is (4-6):1, and the reaction is stirred for 20-30 min.

[0019] Preferably, in step S2, the drying temperature is 100-110°C.

[0020] Preferably, in step S3, the mass ratio of the pretreated phosphogypsum to the pretreated coal slag is (6-8):(2-4).

[0021] Preferably, in step S3, based on the mass ratio of phosphogypsum-slag cementitious material, the following are added: water-reducing agent 0.8%–1.2%, retarder 0.01%–0.03%, calcium oxide 1.0%–4.0%, sodium hydroxide 0.3%–0.9%, and water glass 0.1%–0.4%.

[0022] The present invention also provides an alkali-activated slag-phosphogypsum solid waste cementitious material, which is prepared by any of the above-described preparation methods.

[0023] Beneficial effects:

[0024] (1) Under the condition of acid leaching treatment of phosphogypsum, the present invention mixes phosphogypsum with coal slag to prepare phosphogypsum-slag cementitious material. The coal slag has a porous structure, which can adsorb water-soluble phosphorus, fluorine and other harmful substances in phosphogypsum, avoids the influence of them on the hydration of phosphogypsum, and reduces the pollution of groundwater. The coal slag has hydration activity and can react with phosphogypsum to generate ettringite and hydrated calcium silicate under the action of alkali activation. In the later stage of the hydration reaction, it can continuously improve the strength of the material.

[0025] (2) This invention improves the adsorption effect of water-soluble fluorine and phosphorus by acid leaching the coal-fired slag, thereby further reducing the release of water-soluble fluorine and phosphorus and reducing the impact on the environment.

[0026] (3) The alkali-activated slag-phosphogypsum all-solid waste cementitious material provided by the present invention uses phosphogypsum and coal slag to replace cement. The material cost is low and the preparation is simple. On the basis of consuming a large amount of phosphogypsum and slag, it can also reduce carbon emissions, which has obvious economic and environmental benefits. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0028] The present invention will now be described in detail with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0029] This invention addresses the current problem of the difficulty in utilizing phosphogypsum by providing a method for preparing an alkali-activated slag-phosphogypsum all-solid waste cementitious material. The alkali-activated slag-phosphogypsum all-solid waste cementitious material prepared by this method has extremely low water-soluble fluorine and phosphorus leaching content and high compressive and flexural strength, making it suitable for use as a cementitious material to replace cement.

[0030] The present invention provides a method for preparing an alkali-activated slag-phosphogypsum all-solid waste cementitious material, comprising the following steps:

[0031] S1. Mix the acid solution with phosphogypsum, react for a certain time, filter, hydrophobically treat the filter cake, dry to constant weight, grind the dried phosphogypsum into fine powder, then calcine it, and then age the calcined phosphogypsum at low temperature to obtain pretreated phosphogypsum.

[0032] S2. Grind the coal slag into fine powder, then mix it with acid solution, react for a certain time, filter it, and dry the filter cake to constant weight to obtain pretreated coal slag.

[0033] S3. The pretreated phosphogypsum and pretreated coal-fired slag are thoroughly mixed in a certain proportion to obtain phosphogypsum-slag cementitious material. Water-reducing agent, retarder, calcium oxide and sodium hydroxide are added to the phosphogypsum-slag cementitious material and then thoroughly mixed to obtain alkali-activated slag-phosphogypsum all-solid waste cementitious material.

[0034] This invention effectively reduces the release of water-soluble fluorine and phosphorus from phosphogypsum in cementitious materials by acid leaching and hydrophobic treatment of phosphogypsum; by grinding and acid leaching coal-fired slag, the adsorption capacity of coal-fired slag for water-soluble fluorine and phosphorus can be enhanced, further reducing the release of water-soluble fluorine and phosphorus, reducing the impact of water-soluble fluorine and phosphorus on the hydration process and the pollution to the environment.

[0035] In a preferred embodiment of the present invention, in step S1, the acid solution is an aqueous solution of hydrochloric acid or sulfuric acid, and the concentration of the acid solution is 0.05–1.5 mol / L (e.g., 0.06 mol / L, 0.07 mol / L, 0.09 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.5 mol / L, 0.7 mol / L, 0.9 mol / L, 1.0 mol / L, 1.4 mol / L). The mass ratio of the acid solution to phosphogypsum is (4–6):1, for example, 4.1:1, 4.5:1, 5.0:1, 5.5:1, 5.9:1. The reaction is stirred for 20–30 min (e.g., 21 min, 22 min, 23 min, 24 min, 25 min, 26 min, 27 min, 28 min, 29 min).

[0036] In a preferred embodiment of the present invention, in step S1, a hydrophobic agent is used to treat the filter cake with hydrophobicity. By weight, the hydrophobic agent includes 0.5 to 1.0 parts (e.g., 0.6, 0.7, 0.8, 0.9 parts) of KH550, 4 to 5 parts (e.g., 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9 parts) of TEOS, and 90 to 95 parts (e.g., 90.5, 91, 91.5, 92, 92.5, 93, 93.5, 94, 94.5 parts) of water.

[0037] In step S1, the drying temperature is 40-50℃ (e.g., 41℃, 42℃, 43℃, 44℃, 45℃, 46℃, 47℃, 48℃, 49℃).

[0038] In a preferred embodiment of the present invention, in step S1, phosphogypsum is ground to a fineness below 0.075 mm (e.g., 0.074 mm, 0.070 mm, 0.065 mm, 0.060 mm, 0.055 mm, 0.050 mm, 0.045 mm, 0.040 mm, 0.035 mm, 0.030 mm, 0.020 mm, 0.010 mm), and then calcined at 150–180°C (e.g., 151°C, 153°C, 155°C, 157°C, 159°C, 160°C, 165°C, 170°C, 175°C, 179°C) for 3–5 hours (e.g., 3.1 hours, 3.3 hours, 3.5 hours, 3.7 hours, 3.9 hours, 4.0 hours, 4.1 hours, 4.3 hours, 4.5 hours, 4.7 hours, 4.9 hours).

[0039] In a preferred embodiment of the present invention, in step S1, the calcined phosphogypsum is aged for 24 hours at 2–5°C (e.g., 2°C, 3°C, 4°C, 5°C) and 35%–45% humidity (e.g., 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%), and then aged at 8–12°C (e.g., 8.5°C, 9°C, 9.5°C, 10°C, 10.5°C). Pretreated phosphogypsum is obtained by aging it for 24–48 hours (e.g., 25h, 27h, 29h, 30h, 32h, 34h, 35%, 36%, 37%, 38%, 39%) at 11℃, 11.5℃ and 30%–40% humidity (e.g., 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%).

[0040] Under conditions of 2–5°C and 35%–45% humidity, the dihydrate gypsum in phosphogypsum can rapidly transform into hemihydrate gypsum, while under conditions of around 10°C and 30%–40% humidity, the anhydrous gypsum in phosphogypsum can rapidly transform into hemihydrate gypsum. This invention significantly increases the aging speed of phosphogypsum by controlling the temperature and humidity during the aging process, and can significantly shorten the time required to complete the aging process, thereby greatly shortening the production cycle of cementitious materials.

[0041] In a preferred embodiment of the present invention, in step S2, the coal-fired slag is ground to below 0.075 mm, the concentration of the acid solution is 0.05-0.15 mol / L (e.g., 0.06 mol / L, 0.07 mol / L, 0.09 mol / L, 0.10 mol / L, 0.11 mol / L, 0.13 mol / L, 0.14 mol / L), the mass ratio of the acid solution to the coal-fired slag is (4-6):1, for example 4.1:1, 4.5:1, 4.9:1, 5.0:1, 5.1:1, 5.5:1, 5.9:1, and the reaction is stirred for 20-30 min (e.g., 21 min, 22 min, 23 min, 24 min, 25 min, 26 min, 27 min, 28 min, 29 min).

[0042] In a preferred embodiment of the present invention, in step S2, the drying temperature is 100-110℃ (e.g., 101℃, 102℃, 103℃, 104℃, 105℃, 106℃, 107℃, 108℃, 109℃).

[0043] In a preferred embodiment of the present invention, in step S3, the mass ratio of the pretreated phosphogypsum to the pretreated coal slag is (6-8):(2-4), for example 6:4, 6.5:3.5, 7:3, 7.5:2.5, or 8:2.

[0044] In a preferred embodiment of the present invention, in step S3, based on the mass ratio of phosphogypsum-slag cementitious material, the following are added: 0.8%–1.2% (e.g., 0.85%, 0.9%, 0.95%, 1.0%, 1.05%, 1.1%, 1.15%) of water-reducing agent, 0.01–0.03% (e.g., 0.01%, 0.015%, 0.020%, 0.025%, 0.03%) of retarder, and 1.0–4.0% (e.g., calcium oxide) of phosphate rock. 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, sodium hydroxide 0.3%–0.9% (e.g., 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%), water glass 0.1%–0.4% (e.g., 0.15%, 0.20%, 0.25%, 0.30%, 0.35%).

[0045] The present invention also proposes an alkali-activated slag-phosphogypsum solid waste cementitious material, which is prepared by any of the above-described preparation methods.

[0046] The following detailed description of an alkali-activated slag-phosphogypsum solid waste cementitious material and its preparation method is provided through specific embodiments of the present invention.

[0047] The raw materials and reagents used in the following examples are from the following sources:

[0048] Phosphogypsum, purchased from Chongqing Huaqiang Fertilizer Co., Ltd., is a blackish-gray powder solid with a dihydrate gypsum content of 80-85% and a moisture content of 10-15%.

[0049] The coal-fired furnace slag, taken from the Huaneng Luohuang Power Plant furnace, is a black porous powder solid with a SiO2 content of 54.67%, an Al2O3 content of 20.45%, and a CaO content of 9.91%.

[0050] Black porous powder solid, with SiO2 content of 54.67%, Al2O3 content of 20.45%, and CaO content of 9.91%.

[0051] KH550 (γ-aminopropyltriethoxysilane), purity 95%, purchased from Chengdu Huaxia Chemical Reagent Co., Ltd.

[0052] TEOS (tetraethoxysilane), 99.5% purity, purchased from Chongqing Xingguang Chemical Glass Co., Ltd.

[0053] Hydrochloric acid, 36.5% purity, purchased from Chongqing Xingguang Chemical Glass Company;

[0054] The water-reducing agent is a polycarboxylate type water-reducing agent, purchased from Shanxi Feike New Material Technology Co., Ltd.

[0055] The retarder was a modified amino acid type retarder, purchased from Sika (China) Co., Ltd.

[0056] Calcium oxide, 65% purity, purchased from Chongqing Xingguang Chemical Glass Company;

[0057] Sodium hydroxide, purity 99.0%, purchased from Chongqing Xingguang Chemical Glass Company.

[0058] Water glass, Baume degree 40, purchased from Henan Luboshi New Materials Co., Ltd.

[0059] Example 1

[0060] This embodiment provides an alkali-activated slag-phosphogypsum all-solid waste cementitious material, and the preparation steps are as follows:

[0061] S1. Place the phosphogypsum in 4.0 times its mass of 0.1 mol / L hydrochloric acid solution, heat to 50°C, stir for 30 min, and then filter.

[0062] By weight, 0.7 parts KH550, 4.5 parts TEOS and 93 parts water were mixed to obtain a hydrophobic agent. The filter cake was washed with 1.0 times the weight of the filter cake of the hydrophobic agent and then dried at 50°C to constant weight.

[0063] The dried phosphogypsum was ground to a finer size than 0.075 mm and then calcined in an oven at 165°C for 3 hours.

[0064] The calcined phosphogypsum was placed in an environment of 2-5℃ and aged at 35%-45% humidity for 24 hours, and then aged in an environment of 8-12℃ and 30%-40% humidity for 24 hours to obtain pretreated phosphogypsum.

[0065] S2. Grind the coal slag to below 0.075 mm, place it in 4.0 times its mass of 1 mol / L hydrochloric acid solution and stir for 30 min. Then filter it and dry the filter cake at 105℃ to constant weight to obtain pretreated coal slag.

[0066] S3. The pretreated phosphogypsum prepared in step S1 and the pretreated coal slag prepared in step S2 are thoroughly mixed at a mass ratio of 7:3 to obtain phosphogypsum-slag cementitious material.

[0067] Based on the mass ratio of phosphogypsum-slag cementitious material, add 1.0% water-reducing agent, 0.02% retarder, 3.0% calcium oxide, 0.6% sodium hydroxide, and 0.25% water glass to the phosphogypsum-slag cementitious material prepared in step S6, and then mix thoroughly to prepare alkali-activated slag-phosphogypsum all-solid waste cementitious material.

[0068] Example 2

[0069] This embodiment provides an alkali-activated slag-phosphogypsum all-solid waste cementitious material, and the preparation steps are as follows:

[0070] S1. Place the phosphogypsum in 4.0 times its mass of 0.1 mol / L hydrochloric acid solution, heat to 50°C, stir for 30 min, and then filter.

[0071] By weight, 0.5 parts KH550, 4 parts TEOS and 90 parts water were mixed to obtain a hydrophobic agent. The filter cake was washed with 1.0 times the weight of the filter cake of the hydrophobic agent and then dried at 50°C to constant weight.

[0072] The dried phosphogypsum was ground to a finer size than 0.075 mm and then calcined in an oven at 165°C for 3 hours.

[0073] The calcined phosphogypsum was placed in an environment of 2-5℃ and aged at 35%-45% humidity for 24 hours, and then aged in an environment of 8-12℃ and 30%-40% humidity for 24 hours to obtain pretreated phosphogypsum.

[0074] S2. Grind the coal slag to below 0.075 mm, place it in 4.0 times its mass of 1 mol / L hydrochloric acid solution and stir for 30 min. Then filter it and dry the filter cake at 105℃ to constant weight to obtain pretreated coal slag.

[0075] S3. The pretreated phosphogypsum prepared in step S1 and the pretreated coal slag prepared in step S2 are thoroughly mixed at a mass ratio of 8:2 to obtain phosphogypsum-slag cementitious material.

[0076] Based on the mass ratio of phosphogypsum-slag cementitious material, add 1.2% water-reducing agent, 0.03% retarder, 2.0% calcium oxide, 0.30% sodium hydroxide, and 0.13% water glass to the phosphogypsum-slag cementitious material prepared in step S6, and then mix thoroughly to prepare alkali-activated slag-phosphogypsum all-solid waste cementitious material.

[0077] Example 3

[0078] This embodiment provides an alkali-activated slag-phosphogypsum all-solid waste cementitious material, and the preparation steps are as follows:

[0079] S1. Place the phosphogypsum in 4.0 times its mass of 0.1 mol / L hydrochloric acid solution, heat to 50°C, stir for 30 min, and then filter.

[0080] By weight, 1 part KH550, 5 parts TEOS and 95 parts water were mixed to obtain a hydrophobic agent. The filter cake was washed with 1.0 times the weight of the filter cake of the hydrophobic agent and then dried at 50°C to constant weight.

[0081] The dried phosphogypsum was ground to a finer size than 0.075 mm and then calcined in an oven at 165°C for 3 hours.

[0082] The calcined phosphogypsum was placed in an environment of 2-5℃ and aged at 35%-45% humidity for 24 hours, and then aged in an environment of 8-12℃ and 30%-40% humidity for 24 hours to obtain pretreated phosphogypsum.

[0083] S2. Grind the coal slag to below 0.075 mm, place it in 4.0 times its mass of 1 mol / L hydrochloric acid solution and stir for 30 min. Then filter it and dry the filter cake at 105℃ to constant weight to obtain pretreated coal slag.

[0084] S3. The pretreated phosphogypsum prepared in step S1 and the pretreated coal slag prepared in step S2 are thoroughly mixed at a mass ratio of 6:4 to obtain phosphogypsum-slag cementitious material.

[0085] Based on the mass ratio of phosphogypsum-slag cementitious material, add 0.8% water-reducing agent, 0.01% retarder, 4.0% calcium oxide, 0.9% sodium hydroxide, and 0.40% water glass to the phosphogypsum-slag cementitious material prepared in step S6, and then mix thoroughly to prepare alkali-activated slag-phosphogypsum all-solid waste cementitious material.

[0086] Comparative Example 1

[0087] This comparative example provides a slag-phosphogypsum cementitious material, and the preparation steps are as follows:

[0088] S1. Grind the dried phosphogypsum to below 0.075 mm and calcine it in an oven at 165℃ for 3 hours;

[0089] Calcined phosphogypsum was placed in an environment of 25°C and aged at 50% humidity for 30 days to obtain aged phosphogypsum.

[0090] S2. Grind the coal slag and pass it through a 0.0075 sieve to obtain refined coal slag;

[0091] S3. The aged phosphogypsum prepared in step S1 and the refined coal-fired slag prepared in step S2 are thoroughly mixed at a mass ratio of 7:3 to obtain phosphogypsum-slag cementitious material.

[0092] Based on the mass ratio of phosphogypsum-slag cementitious material, add 1.0% water-reducing agent, 0.02% retarder, 3.0% calcium oxide, 0.6% sodium hydroxide, and 0.25% water glass to the phosphogypsum-slag cementitious material prepared in step S6, and then mix thoroughly to prepare the slag-phosphogypsum cementitious material.

[0093] Comparative Example 2

[0094] This comparative example provides a slag-phosphogypsum cementitious material, and the preparation steps are as follows:

[0095] S1. Place the phosphogypsum in 4.0 times its mass of 0.1 mol / L hydrochloric acid solution, heat to 50°C, stir for 30 min, and then filter.

[0096] By weight, 0.7 parts KH550, 4.5 parts TEOS and 93 parts water were mixed to obtain a hydrophobic agent. The filter cake was washed with 1.0 times the weight of the filter cake of the hydrophobic agent and then dried at 50°C to constant weight.

[0097] The dried phosphogypsum was ground to a finer size than 0.075 mm and then calcined in an oven at 165°C for 3 hours.

[0098] Calcined phosphogypsum was placed in an environment of 25°C and aged at 50% humidity for 30 days to obtain aged phosphogypsum.

[0099] S2. Grind the coal slag to below 0.075 mm, place it in 4.0 times its mass of 1 mol / L hydrochloric acid solution and stir for 30 min. Then filter it and dry the filter cake at 105℃ to constant weight to obtain pretreated coal slag.

[0100] The pretreated phosphogypsum prepared in step S1 and the pretreated coal slag prepared in step S2 are thoroughly mixed at a mass ratio of 7:3 to obtain phosphogypsum-slag cementitious material.

[0101] S2. According to the mass ratio of phosphogypsum-slag cementitious material, add 1.0% water-reducing agent, 0.02% retarder, 3.0% calcium oxide, 0.6% sodium hydroxide, and 0.25% water glass to the phosphogypsum-slag cementitious material prepared in step S6, and then mix thoroughly to prepare alkali-activated slag-phosphogypsum cementitious material.

[0102] Comparative Example 3

[0103] This embodiment provides a slag-phosphogypsum all-solid waste cementitious material, and the preparation steps are as follows:

[0104] S1. Place the phosphogypsum in 4.0 times its mass of 0.1 mol / L hydrochloric acid solution, heat to 50°C, stir for 30 min, and then filter.

[0105] By weight, 0.7 parts KH550, 4.5 parts TEOS and 93 parts water were mixed to obtain a hydrophobic agent. The filter cake was washed with 1.0 times the weight of the filter cake of the hydrophobic agent and then dried at 50°C to constant weight.

[0106] The dried phosphogypsum was ground to a finer size than 0.075 mm and then calcined in an oven at 165°C for 3 hours.

[0107] The calcined phosphogypsum was placed in an environment of 25°C and aged at 50% humidity for 48 hours to obtain pretreated phosphogypsum.

[0108] S2. Grind the coal slag to below 0.075 mm, place it in 4.0 times its mass of 1 mol / L hydrochloric acid solution and stir for 30 min. Then filter it and dry the filter cake at 105℃ to constant weight to obtain pretreated coal slag.

[0109] S3. The pretreated phosphogypsum prepared in step S1 and the pretreated coal slag prepared in step S2 are thoroughly mixed at a mass ratio of 7:3 to obtain phosphogypsum-slag cementitious material.

[0110] Based on the mass ratio of phosphogypsum-slag cementitious material, add 1.0% water-reducing agent, 0.02% retarder, 3.0% calcium oxide, 0.6% sodium hydroxide, and 0.25% water glass to the phosphogypsum-slag cementitious material prepared in step S6, and then mix thoroughly to prepare slag-phosphogypsum all-solid waste cementitious material.

[0111] Comparative Example 4

[0112] This embodiment provides a slag-phosphogypsum all-solid waste cementitious material, and the preparation steps are as follows:

[0113] S1. Place the phosphogypsum in 4.0 times its mass of 0.1 mol / L hydrochloric acid solution, heat to 50°C, stir for 30 min, and then filter.

[0114] By weight, 0.7 parts KH550, 4.5 parts TEOS and 93 parts water were mixed to obtain a hydrophobic agent. The filter cake was washed with 1.0 times the weight of the filter cake of the hydrophobic agent and then dried at 50°C to constant weight.

[0115] The dried phosphogypsum was ground to a finer size than 0.075 mm and then calcined in an oven at 165°C for 3 hours.

[0116] The calcined phosphogypsum was placed in an environment of 10°C and aged at 50% humidity for 48 hours to obtain pretreated phosphogypsum.

[0117] S2. Grind the coal slag to below 0.075 mm, place it in 4.0 times its mass of 1 mol / L hydrochloric acid solution and stir for 30 min. Then filter it and dry the filter cake at 105℃ to constant weight to obtain pretreated coal slag.

[0118] S3. The pretreated phosphogypsum prepared in step S1 and the pretreated coal slag prepared in step S2 are thoroughly mixed at a mass ratio of 7:3 to obtain phosphogypsum-slag cementitious material.

[0119] Based on the mass ratio of phosphogypsum-slag cementitious material, add 1.0% water-reducing agent, 0.02% retarder, 3.0% calcium oxide, 0.6% sodium hydroxide, and 0.25% water glass to the phosphogypsum-slag cementitious material prepared in step S6, and then mix thoroughly to prepare slag-phosphogypsum all-solid waste cementitious material.

[0120] Comparative Example 5

[0121] This embodiment provides a slag-phosphogypsum all-solid waste cementitious material, and the preparation steps are as follows:

[0122] S1. Place the phosphogypsum in 4.0 times its mass of 0.1 mol / L hydrochloric acid solution, heat to 50°C, stir for 30 min, and then filter.

[0123] By weight, 0.7 parts KH550, 4.5 parts TEOS and 93 parts water were mixed to obtain a hydrophobic agent. The filter cake was washed with 1.0 times the weight of the filter cake of the hydrophobic agent and then dried at 50°C to constant weight.

[0124] The dried phosphogypsum was ground to a finer size than 0.075 mm and then calcined in an oven at 165°C for 3 hours.

[0125] The calcined phosphogypsum was placed in an environment of 5°C and aged at 50% humidity for 48 hours to obtain pretreated phosphogypsum.

[0126] S2. Grind the coal slag to below 0.075 mm, place it in 4.0 times its mass of 1 mol / L hydrochloric acid solution and stir for 30 min. Then filter it and dry the filter cake at 105℃ to constant weight to obtain pretreated coal slag.

[0127] S3. The pretreated phosphogypsum prepared in step S1 and the pretreated coal slag prepared in step S2 are thoroughly mixed at a mass ratio of 7:3 to obtain phosphogypsum-slag cementitious material.

[0128] Based on the mass ratio of phosphogypsum-slag cementitious material, add 1.0% water-reducing agent, 0.02% retarder, 3.0% calcium oxide, 0.6% sodium hydroxide, and 0.25% water glass to the phosphogypsum-slag cementitious material prepared in step S6, and then mix thoroughly to prepare slag-phosphogypsum all-solid waste cementitious material.

[0129] Comparative Example 6

[0130] This comparative example provides a cementitious material containing phosphogypsum. Based on Example 1, fly ash is used instead of coal-fired slag. The preparation steps are as follows:

[0131] S1. Place the phosphogypsum in 4.0 times its mass of 0.1 mol / L hydrochloric acid solution, heat to 50°C, stir for 30 min, and then filter.

[0132] By weight, 0.7 parts KH550, 4.5 parts TEOS and 93 parts water were mixed to obtain a hydrophobic agent. The filter cake was washed with 1.0 times the weight of the filter cake of the hydrophobic agent and then dried at 50°C to constant weight.

[0133] The dried phosphogypsum was ground to a finer size than 0.075 mm and then calcined in an oven at 165°C for 3 hours.

[0134] The calcined phosphogypsum was placed in an environment of 2-5℃ and aged at 35%-45% humidity for 24 hours, and then aged in an environment of 8-12℃ and 30%-40% humidity for 24 hours to obtain pretreated phosphogypsum.

[0135] S2. Grind the fly ash to below 0.075 mm, place it in 4.0 times its mass of 1 mol / L hydrochloric acid solution and stir for 30 min, then filter it, and dry the filter cake at 105℃ to constant weight to obtain pretreated fly ash.

[0136] S3. Mix the pretreated phosphogypsum prepared in step S1 and the pretreated fly ash prepared in step S2 at a mass ratio of 7:3. Then add 1.0% water-reducing agent, 0.02% retarder, 3.0% calcium oxide, 0.6% sodium hydroxide, and 0.25% water glass. Mix thoroughly to obtain phosphogypsum-fly ash cementitious material.

[0137] Comparative Example 7

[0138] This comparative example provides a cementitious material containing phosphogypsum. Based on Example 1, fly ash is used instead of coal-fired slag. The preparation steps are as follows:

[0139] S1. Place the phosphogypsum in 4.0 times its mass of 0.1 mol / L hydrochloric acid solution, heat to 50°C, stir for 30 min, and then filter.

[0140] By weight, 0.7 parts KH550, 4.5 parts TEOS and 93 parts water were mixed to obtain a hydrophobic agent. The filter cake was washed with 1.0 times the weight of the filter cake of the hydrophobic agent and then dried at 50°C to constant weight.

[0141] The dried phosphogypsum was ground to a finer size than 0.075 mm and then calcined in an oven at 165°C for 3 hours.

[0142] The calcined phosphogypsum was placed in an environment of 2-5℃ and aged at 35%-45% humidity for 24 hours, and then aged in an environment of 8-12℃ and 30%-40% humidity for 24 hours to obtain pretreated phosphogypsum.

[0143] S2. Grind the fly ash to below 0.075mm and set aside.

[0144] S3. Mix the pretreated phosphogypsum prepared in step S1 and the pretreated fly ash prepared in step S2 at a mass ratio of 7:3. Then add 1.0% water-reducing agent, 0.02% retarder, 3.0% calcium oxide, 0.6% sodium hydroxide, and 0.25% water glass. Mix thoroughly to obtain phosphogypsum-fly ash cementitious material.

[0145] Cementitious material performance testing:

[0146] Using the cementitious materials provided in the above examples and comparative examples, and referring to the "Test Method for Strength of Cement Mortar GB / T17671-2021", standard specimens were prepared without adding sand or gravel aggregates, at a water-cement ratio of 0.3, and cured for 7 days (curing temperature 20℃~25℃, humidity 50%~80%). Performance tests were then conducted, and the test results are shown in Table 1 below.

[0147] Table 1. Performance Tests of Cementitious Materials

[0148]

[0149] Comparing the test results of Example 1 and Comparative Example 1, it can be seen that the standard specimens made from the alkali-activated slag-phosphogypsum solid waste cementitious material prepared in Example 1 had water-soluble fluorine and phosphorus contents as low as 0.17 mg / L and 0.25 mg / L, respectively, while the standard specimens made from the cementitious material provided in Comparative Example 1 had water-soluble fluorine contents as high as 47.68 mg / L and water-soluble phosphorus contents as high as 23.2 mg / L. It is evident that the alkali-activated slag-phosphogypsum solid waste cementitious material prepared in Example 1 has a significant effect on fixing fluorine and phosphorus.

[0150] Furthermore, a comparison of the test results of Example 1 and Comparative Example 2 shows that acid leaching and hydrophobic treatment can significantly reduce the release of water-soluble fluorine and phosphorus in phosphogypsum, but it is still significantly higher than that of Example 1. Moreover, the compressive strength and flexural strength are significantly lower than those of Example 1. In Example 1, the standard specimens prepared by low-temperature aging, with an aging time much shorter than that of the comparative example, have higher strength and less release of water-soluble fluorine and phosphorus. This proves that low-temperature aging can significantly shorten the aging time, promote the conversion of anhydrous gypsum to hemihydrate gypsum, thereby improving the specimen strength and reducing the release of water-soluble fluorine and phosphorus. It has obvious advantages over conventional aging conditions.

[0151] The compressive and flexural strengths of Comparative Example 5 were significantly lower than those of other examples and comparative examples. Analysis revealed that a small amount of anhydrous gypsum was produced during the calcination of phosphogypsum. At a low temperature of around 5°C, this anhydrous gypsum could not be effectively converted into hemihydrate gypsum, and only the reaction of dihydrate gypsum to hemihydrate gypsum occurred, resulting in a significant decrease in the strength of the specimen. The strength of the specimen after low-temperature curing was much lower than that of specimens under other aging conditions. In addition, the strength of the specimen in Comparative Example 3 was also relatively low, indicating that the anhydrous gypsum in the specimen of Comparative Example 3 failed to be completely converted into hemihydrate gypsum even after aging at 25°C for 48 hours.

[0152] However, comparing the data from proportions 3, 4, and 5, it can be seen that the strength of the specimens aged at 10℃ for the same amount of time is actually higher than that at 25℃, indicating that a higher aging temperature is not necessarily better.

[0153] Comparing Example 1 and Comparative Example 6, it can be seen that when fly ash is used instead of coal slag, the strength of the specimens increases significantly. However, even after acid leaching, the adsorption capacity of the cementitious material made with fly ash for water-soluble fluorine and phosphorus is still significantly different from that of coal slag. The cementitious material prepared in Comparative Example 7, which was not acid leached, has almost no ability to adsorb water-soluble fluorine and phosphorus.

[0154] In summary:

[0155] This invention prepares a high-strength phosphogypsum-slag cementitious material by acid leaching of phosphogypsum and coal-fired slag, followed by mixing. This cementitious material exhibits extremely low release of water-soluble fluorine and phosphorus, minimizing their impact on the hydration of phosphogypsum and reducing groundwater pollution. Furthermore, by aging the acid-leached phosphogypsum at a temperature range from low to high, the conversion of dihydrate and anhydrous gypsum in the phosphogypsum to hemihydrate gypsum is promoted, significantly shortening the aging time of the phosphogypsum and substantially improving the production efficiency of the cementitious material.

[0156] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an alkali-activated slag-phosphogypsum all-solid waste cementitious material, characterized in that, Includes the following steps: S1. Mix the acid solution with phosphogypsum, react for a certain time, filter, hydrophobically treat the filter cake, dry to constant weight, grind the dried phosphogypsum into fine powder, then calcine it, and then age the calcined phosphogypsum at low temperature to obtain pretreated phosphogypsum. S2. Grind the coal slag into fine powder, then mix it with acid solution, react for a certain time, filter it, and dry the filter cake to constant weight to obtain pretreated coal slag. S3. The pretreated phosphogypsum and pretreated coal-fired slag are thoroughly mixed in a certain proportion to obtain phosphogypsum-slag cementitious material. Water-reducing agent, retarder, calcium oxide and sodium hydroxide are added to the phosphogypsum-slag cementitious material and then thoroughly mixed to obtain alkali-activated slag-phosphogypsum all-solid waste cementitious material.

2. The preparation method of an alkali-activated slag-phosphogypsum all-solid waste cementitious material as described in claim 1, characterized in that, In step S1, the acid solution is an aqueous solution of hydrochloric acid or sulfuric acid, the concentration of the acid solution is 0.05-1.5 mol / L, the mass ratio of the acid solution to phosphogypsum is (4-6):1, and the reaction is stirred for 20-30 min.

3. The preparation method of an alkali-activated slag-phosphogypsum all-solid waste cementitious material as described in claim 1, characterized in that, In step S1, the filter cake is treated with a hydrophobic agent. By weight, the hydrophobic agent includes 0.5 to 1.0 parts of KH550, 4 to 5 parts of TEOS, and 90 to 95 parts of water. In step S1, the drying temperature is 40–50°C.

4. The preparation method of an alkali-activated slag-phosphogypsum all-solid waste cementitious material as described in claim 1, characterized in that, In step S1, the phosphogypsum is ground to a finer size than 0.075 mm and then calcined at 150–180 °C for 3–5 h.

5. The preparation method of an alkali-activated slag-phosphogypsum all-solid waste cementitious material as described in any one of claims 1 to 4, characterized in that, In step S1, the calcined phosphogypsum is aged at 2-5°C and 35%-45% humidity for 24 hours, and then aged at 8-12°C and 30%-40% humidity for 24-48 hours to obtain pretreated phosphogypsum.

6. The preparation method of an alkali-activated slag-phosphogypsum all-solid waste cementitious material as described in any one of claims 1 to 4, characterized in that, In step S2, the coal-fired slag is ground to below 0.075 mm, the concentration of the acid solution is 0.05-0.15 mol / L, the mass ratio of the acid solution to the coal-fired slag is (4-6):1, and the reaction is stirred for 20-30 min.

7. The preparation method of an alkali-activated slag-phosphogypsum all-solid waste cementitious material as described in any one of claims 1 to 4, characterized in that, In step S2, the drying temperature is 100–110°C.

8. The preparation method of an alkali-activated slag-phosphogypsum all-solid waste cementitious material as described in any one of claims 1 to 4, characterized in that, In step S3, the mass ratio of the pretreated phosphogypsum to the pretreated coal slag is (6-8):(2-4).

9. A method for preparing an alkali-activated slag-phosphogypsum solid waste cementitious material as described in any one of claims 1 to 4, characterized in that, In step S3, based on the mass ratio of phosphogypsum-slag cementitious material, add 0.8%–1.2% water-reducing agent, 0.01%–0.03% retarder, 1.0%–4.0% calcium oxide, 0.3%–0.9% sodium hydroxide, and 0.1%–0.4% water glass.

10. An alkali-activated slag-phosphogypsum all-solid waste cementitious material, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 9.

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