Method for preparing efficient cement retarder by rapidly hydrating semi-hydrated phosphogypsum and application of efficient cement retarder

Abstract

The invention discloses a method for preparing an efficient cement retarder by rapidly hydrating semi-hydrated phosphogypsum and application of the efficient cement retarder, and belongs to the technical field of preparation of cement retarders. A composite fluorosilicone material and by-product fluorosilicone waste liquid are used as rapid hydrating agents, semi-hydrated phosphogypsum is rapidly hydrated, semi-hydrated phosphogypsum crystals are converted into dihydrate phosphogypsum crystals in an acid environment, and after aging is conducted at the normal temperature, the efficient retarding cement retarder is obtained. The problem that semi-hydrated phosphogypsum is difficult to be used as a raw material for producing the high-efficiency delayed-setting cement retarder is solved, and meanwhile, a new way is found for consumption of a byproduct composite fluorosilicone material and a byproduct fluorosilicone waste liquid in phosphorus and fluorine chemical enterprises.

Description

Technical Field

[0001] This invention belongs to the field of cement retarder preparation technology, specifically relating to a method for preparing a high-efficiency cement retarder by rapid hydration of hemihydrate phosphogypsum and its application. Background Technology

[0002] Phosphate byproducts, such as phosphogypsum, can be divided into dihydrate phosphogypsum and hemihydrate phosphogypsum. Since using hemihydrate phosphogypsum directly as a cement retarder presents a series of problems, all gypsum-based cement retarder uses must be dihydrate phosphogypsum. Traditionally, hemihydrate phosphogypsum is used as a cement retarder by modifying it with alkaline activators such as quicklime to solidify the free phosphorus and fluorine in the phosphogypsum, thus converting it into dihydrate phosphogypsum. However, the solidification of free phosphorus and fluorine in the modified phosphogypsum results in a cement retarder with a short setting time, failing to meet the needs of all cement plants for high-efficiency retarder cement. Therefore, it is necessary to find a rapid hydration agent that can convert hemihydrate phosphogypsum into dihydrate phosphogypsum while retaining free phosphorus and fluorine.

[0003] The solid composite fluorosilicone materials and by-product fluorosilicone waste liquid produced during the production of phosphate and fluorine chemical enterprises contain a large amount of soluble fluorine. Because the soluble fluorine adhering to and encapsulated in the ultrafine silica of these composite fluorosilicone materials is extremely difficult to extract, it is difficult to achieve harmless or comprehensive resource utilization, leading to resource waste. Furthermore, natural accumulation will continuously leach soluble phosphorus, fluorine, and other acidic impurities, causing serious environmental impact. Similarly, the by-product fluorosilicone waste liquid, due to its low concentration and complex impurities, lacks economic value for direct recycling, becoming a typical problem in the industry that combines resource waste and environmental risk.

[0004] This invention utilizes at least one of composite fluorosilicone materials and by-product fluorosilicone waste liquid as a rapid hydration agent to quickly hydrate hemihydrate phosphogypsum, transforming hemihydrate phosphogypsum crystals into dihydrate phosphogypsum crystals under acidic conditions. This solves the problem of hemihydrate phosphogypsum being difficult to use as a raw material for producing high-efficiency retarder cement retarders, and also provides a new approach for the disposal of composite fluorosilicone materials and fluorosilicone waste liquid produced by phospho-fluorochemical enterprises. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a high-efficiency cement retarder by rapidly hydrating hemihydrate phosphogypsum and its application. By using composite fluorosilicone materials and by-product fluorosilicone waste liquid as rapid hydration agents, the hemihydrate phosphogypsum is rapidly hydrated, causing the hemihydrate phosphogypsum crystals to transform into dihydrate phosphogypsum crystals under acidic conditions. After aging at room temperature, a high-efficiency retarder for cement is obtained. This invention addresses the difficulty of using hemihydrate phosphogypsum as a raw material for producing high-efficiency retarder for cement. It also provides a new approach for the disposal of composite fluorosilicone materials and fluorosilicone waste liquid by-products from phospho-fluorochemical enterprises.

[0006] To solve the above technical problems, the present invention adopts the following technical solution: A method for preparing a high-efficiency cement retarder by rapidly hydrating hemihydrate phosphogypsum involves using hemihydrate phosphogypsum, a byproduct of phosphate chemical industry, as raw material. After mixing with a rapid hydration agent and an acid-base regulator, the mixture is aged at room temperature for 3-7 days to obtain dihydrate phosphogypsum. The phosphogypsum is then crushed to a particle size of less than 10 cm to obtain a high-efficiency retarder for cement. The mass ratio of the rapid hydration agent, acid-base regulator, and hemihydrate phosphogypsum dry matrix is ​​2~8:0~1:91.0~98.0; The rapid hydration agent is a by-product composite fluorosilicone material or / and a by-product fluorosilicone waste liquid; The acid-base regulator is anhydrous sodium carbonate.

[0007] The aforementioned composite fluorosilicone material, on a dry basis, comprises 80-90 wt% SiO2 and 5-15 wt% total F, and has a BET specific surface area of ​​4-8 m². 2 / g, with an average particle size of 4~20um.

[0008] The aforementioned by-product fluorosilicone waste liquid consists of 4-6 wt% H2SiF6 and 94-96 wt% water.

[0009] The initial free water content of the aforementioned hemihydrate phosphogypsum is 5.0~25.0%, and the crystal water content is ≤9.0%.

[0010] The aforementioned hemihydrate phosphogypsum comprises: 42-54 wt% SO3, 31-36 wt% CaO, 0-6 wt% SiO2, 0.05-1.5 wt% Al2O3, 0-0.7 wt% Fe2O3, 0-0.5 wt% MgO, 0.3-1.3 wt% total P2O5, 0.01-1.0 wt% water-soluble P2O5, 0.1-1.3 wt% total F, 0.01-0.8 wt% water-soluble F, 0.001-0.3 wt% K2O, 0.01-0.6 wt% Na2O, and 0.005-0.015 wt% Cl. - .

[0011] When the aforementioned rapid hydration agent is a by-product composite fluorosilicone material, the mass ratio of the by-product composite fluorosilicone material, the acid-base regulator, and the hemihydrate phosphogypsum dry matrix is ​​2~4:0.5~1:96~97.5.

[0012] When the aforementioned rapid hydration agent is a by-product fluorosilicone waste liquid, the mass ratio of the by-product fluorosilicone waste liquid, the acid-base regulator, and the hemihydrate phosphogypsum dry matrix is ​​1~3:0.3~1:96~98.5.

[0013] When the aforementioned rapid hydration agent is a by-product composite fluorosilicone material and a by-product fluorosilicone waste liquid, the mass ratio of the by-product composite fluorosilicone material, the by-product fluorosilicone waste liquid, the acid-base regulator, and the hemihydrate phosphogypsum dry matrix is ​​1~3:1~3:0.3~1:93~97.5.

[0014] The aforementioned aging time is 5-7 days.

[0015] The aforementioned high-efficiency cement retarder is used in the preparation of silicate cement by mixing the high-efficiency cement retarder and cement clinker dry basis in a mass ratio of 3~6:94~97 and ball milling them. After ball milling, high-efficiency retarded silicate cement can be obtained. The initial setting time of the high-efficiency retarded silicate cement is not less than 35 min and the final setting time is not more than 600 min.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention utilizes at least one of composite fluorosilicone materials and by-product fluorosilicone waste liquid to rapidly hydrate hemihydrate phosphogypsum, and then adjusts the pH of the hemihydrate phosphogypsum with sodium carbonate. This solves the problems of difficulty in converting crystal water when hemihydrate phosphogypsum retains free phosphorus and fluorine, and loss of early strength of cement due to efficient slow setting. It significantly reduces the cost of rapid hydration agent for hemihydrate phosphogypsum, and further realizes the resource utilization of by-product composite fluorosilicone materials and fluorosilicone waste liquid.

[0017] 2. The solid composite fluorosilicone materials produced as a byproduct of phosphate and fluorine chemical production contain large amounts of soluble phosphorus and fluorine. The soluble fluorine adhering to and coating the surface of ultrafine silica is extremely difficult to extract, hindering its harmless or resource-based comprehensive utilization. This invention proposes adding a certain amount of composite fluorosilicone material to hemihydrate phosphogypsum to rapidly hydrate it. The composite fluorosilicone material reacts with the phosphogypsum in cement to form part of the cement product, harmlessly disposing of the solid waste. This solves the problem of the difficulty in harmlessly or resource-based comprehensive utilization of the solid composite fluorosilicone materials produced as a byproduct of phosphate and fluorine chemical enterprises, providing a pathway for the disposal and treatment of composite fluorosilicone materials.

[0018] 3. The by-product fluorosilicone waste liquid generated in the production of phospho-fluorine chemicals has extremely low resource value due to its low concentration of fluorosilicone components, complex and costly concentration and purification processes. It cannot be disposed of within the existing production system and incurs additional storage costs, becoming a key bottleneck restricting the closed-loop operation of phospho-fluorine chemical processes. This invention introduces this by-product fluorosilicone waste liquid into hemihydrate phosphogypsum, enabling rapid hydration of the hemihydrate phosphogypsum. This not only provides a reliable alternative technology route when the quality of composite fluorosilicone materials fluctuates or raw material shortages occur, but also achieves the in-process disposal of the by-product fluorosilicone waste liquid, fundamentally solving this industry-wide problem.

[0019] 4. Traditional rapid hydration agents for hemihydrate phosphogypsum are usually formed by combining certain soluble calcium salts or certain soluble sulfates, or by mixing the two in a certain proportion. However, this type of rapid hydration agent has problems such as high cost, excessive phosphorus and fluorine curing, and difficulty in large-scale use. This invention proposes a method to rapidly hydrate hemihydrate phosphogypsum using by-product solid slag composite fluorosilicone material and by-product fluorosilicone waste liquid, so that hemihydrate phosphogypsum naturally transforms into dihydrate gypsum, solving the problems of high cost, excessive phosphorus and fluorine curing, and difficulty in large-scale use of rapid hydration methods for hemihydrate phosphogypsum.

[0020] 5. In the process of producing high-efficiency retarded cement, phosphogypsum is used as a cement retarder. Along with the SO4 released from the dissolved gypsum... 2- The free phosphorus and fluorine form a more insoluble protective film on the cement surface, hindering the cement hydration process and thus extending the setting time to some extent. This retarding process is also accompanied by a loss of early cement strength. However, the addition of fine silica in the composite fluorosilicone material enhances the cement strength to a certain extent through the "micro-aggregate effect" and "potential pozzolanic activity effect," compensating for the strength loss caused by the efficient retarding of phosphogypsum.

[0021] 6. Among various agents, sodium carbonate was selected as the regulator. While ensuring that its cement retarder meets the pH>5 requirement of the standard "GBT21371-2019 Industrial By-product Gypsum for Cement", it can also meet the alkali content requirements of GB 175-2023 General Portland Cement. It does not solidify the free phosphorus and fluorine in phosphogypsum and raise the pH value of gypsum. Furthermore, the sodium sulfate (Na2SO4, sodium sulfate) generated after the addition of sodium carbonate to phosphogypsum is a soluble neutral salt. The sodium sulfate generated in the reaction also has a strong rapid hydration effect on hemihydrate phosphogypsum, further promoting the conversion of hemihydrate phosphogypsum to dihydrate phosphogypsum. Detailed Implementation

[0022] The present invention will be specifically described below through embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention.

[0023] Example 1: Raw Material Preparation The initial free water content of hemihydrate phosphogypsum is 5.0~25.0%, and the crystal water content is ≤9.0%. The components of hemihydrate phosphogypsum include: 42~54wt% SO3, 31~36wt% CaO, 0~6wt% SiO2, 0.05~1.5wt% Al2O3, 0~0.7wt% Fe2O3, 0~0.5wt% MgO, 0.3~1.3wt% total P2O5, 0.01~1.0wt% water-soluble P2O5, 0.1~1.3wt% total F, 0.01~0.8wt% water-soluble F, 0.001~0.3wt% K2O, 0.01~0.6wt% Na2O, and 0.005~0.015wt% Cl. - ; The rapid hydration agent is a composite fluorosilicone material, a solid composite fluorosilicone material obtained as a byproduct of hydrogen fluoride production. Its composition, calculated on a dry basis, includes: 80-90 wt% SiO2, 5-15 wt% total F, and 0.03-0.06 wt% Cl. - The BET specific surface area of ​​composite fluorosilicone materials is 4~8m². 2 / g, with an average particle size of 4~20um; The rapid hydration agent is a by-product fluorosilicone waste liquid, which is a by-product of the phosphorus and fluorine chemical production process. The components of this by-product fluorosilicone waste liquid include: 4~6wt% H2SiF6 and 94~96wt% water.

[0024] The acid-base regulator is anhydrous sodium carbonate (commercially available).

[0025] The raw materials used in Examples 2-6 below are the hemihydrate phosphogypsum, composite fluorosilicone material and anhydrous sodium carbonate prepared in Example 1.

[0026] Example 2 Process for producing anhydrous hydrogen fluoride: The direct method (concentrated sulfuric acid decomposition method) directly decomposes concentrated fluorosilicic acid with concentrated sulfuric acid, generating a mixed gas of HF and SiF4. After purification, condensation, and distillation, anhydrous hydrogen fluoride is obtained. Under the strong dehydrating and acidic environment of concentrated sulfuric acid, the silicon in the fluorosilicic acid rapidly forms silica gel (SiO2·nH2O). This silica gel encapsulates a certain amount of unreacted fluorosilicic acid and the generated fluorides, forming an amorphous composite fluorosilicone solid material with a large surface area and porous structure, containing a certain amount of fluorosilicic acid and fluorides.

[0027] Example 3: The process of generating fluorosilicone waste liquid in a semi-aqueous wet process. In wet-process phosphoric acid production, phosphate rock (fluorinated apatite) and sulfuric acid undergo a semi-aqueous acidolysis reaction in the reaction tank. Fluorine in the phosphate rock is released along with the phosphoric acid, mainly in the form of HF and SiF4 gas, which enter the tail gas of the reaction tank. The fluorinated silicon tail gas enters a multi-stage washing system in sequence. SiF4 undergoes a hydrolysis reaction with the washing water: 3SiF4 + 2H2O = 2H2SiF6 + SiO2↓. HF combines with SiF4 to generate fluorosilicic acid. At the same time, the washing process introduces phosphoric acid process dilution and makeup water to dilute the concentration of fluorosilicic acid waste liquid. The washing liquid that is not recovered by phosphoric acid and whose fluorosilicic acid concentration does not meet the industrial utilization standard (usually <10%) is separated into solid and liquid components to remove most of the silica gel and other impurities, which becomes the by-product fluorosilicic acid waste liquid.

[0028] Example 4: Preparation method of high-efficiency retarder for cement. Using hemihydrate phosphogypsum, a byproduct of phosphate chemical industry, as raw material, a mixture of composite fluorosilicone material, acid-base regulator, and hemihydrate phosphogypsum dry matrix in a mass ratio of 2:0.5:97.5 was added. The mixture was then aged at room temperature for 7 days to obtain dihydrate phosphogypsum, which was then crushed to a particle size of less than 10 cm to obtain a high-efficiency retarder for cement.

[0029] The high-efficiency retarding cement retarder prepared in Example 4 and the dry basis of cement clinker were mixed and ball-milled at a mass ratio of 5:95. After ball milling, silicate cement was obtained. The initial setting time of silicate cement was not less than 35 min and the final setting time was not more than 600 min.

[0030] Example 5: Preparation method of high-efficiency retarder for cement. Using hemihydrate phosphogypsum, a byproduct of phosphate chemical industry, as raw material, and following the principles of byproduct fluorosilicone waste liquid, acid-base regulator, and hemihydrate... The dry matrix of phosphogypsum is mixed with by-product rapid hydration agent (by-product fluorosilicone waste liquid) and anhydrous sodium carbonate in a mass ratio of 2:0.5:97.5. After aging at room temperature for 7 days, dihydrate phosphogypsum is obtained. The mixture is then crushed to a particle size of less than 10 cm to obtain a high-efficiency retarder for cement.

[0031] The high-efficiency retarding cement retarder prepared in Example 5 and the dry basis of cement clinker were mixed and ball-milled at a mass ratio of 5:95. After ball milling, silicate cement was obtained. The initial setting time of silicate cement was not less than 35 min and the final setting time was not more than 600 min.

[0032] Example 6: Preparation method of high-efficiency retarder for cement. Using hemihydrate phosphogypsum, a byproduct of phosphate chemical industry, as raw material, by-product composite fluorosilicone material, by-product fluorosilicone waste liquid, acid-base regulator and hemihydrate phosphogypsum dry matrix are mixed in a mass ratio of 2:1:0.5:96.5. By-product rapid hydration agent composite fluorosilicone material, by-product fluorosilicone waste liquid and anhydrous sodium carbonate are added and mixed. After aging at room temperature for 7 days, dihydrate phosphogypsum is obtained. It is then crushed to a particle size of less than 10 cm to obtain a high-efficiency retarder for cement.

[0033] The high-efficiency retarding cement retarder prepared in Example 6 and the dry basis of cement clinker were mixed and ball-milled at a mass ratio of 5:95. After ball milling, silicate cement was obtained. The initial setting time of silicate cement was not less than 35 min and the final setting time was not more than 600 min.

[0034] Example 7: Preparation method of high-efficiency retarder for cement setting Using hemihydrate phosphogypsum, a byproduct of phosphate chemical industry, as raw material, a mixture of composite fluorosilicone material, acid-base regulator, and hemihydrate phosphogypsum dry matrix in a mass ratio of 2:1:97 was added. The mixture was then mixed with byproduct rapid hydration agent, composite fluorosilicone material, and anhydrous sodium carbonate. After aging at room temperature for 7 days, dihydrate phosphogypsum was obtained. The mixture was then crushed to a particle size of less than 10 cm to obtain a high-efficiency retarder for cement.

[0035] The high-efficiency retarding cement retarder prepared in Example 7 and the dry basis of cement clinker were mixed and ball-milled at a mass ratio of 5:95. After ball milling, silicate cement was obtained. The initial setting time of silicate cement was not less than 35 min and the final setting time was not more than 600 min.

[0036] Example 8: Preparation method of high-efficiency retarder for cement. Using hemihydrate phosphogypsum, a byproduct of phosphate chemical industry, as raw material, by adding byproduct fluorosilicone waste liquid, acid-base regulator and hemihydrate phosphogypsum dry matrix in a mass ratio of 3:0.3:96.7, and mixing with byproduct rapid hydration agent fluorosilicone waste liquid and anhydrous sodium carbonate, and aging at room temperature for 7 days, dihydrate phosphogypsum is obtained. After crushing to a particle size of less than 10cm, a high-efficiency retarder for cement is obtained.

[0037] Example 9: Preparation method of high-efficiency retarder for cement. Using hemihydrate phosphogypsum, a byproduct of phosphate chemical industry, as raw material, a mixture of composite fluorosilicone material, acid-base regulator, and hemihydrate phosphogypsum dry matrix in a mass ratio of 4:1:95 was added. The mixture was then aged at room temperature for 3 days to obtain dihydrate phosphogypsum, which was then crushed to a particle size of less than 10 cm to obtain a high-efficiency retarding cement retarder.

[0038] Example 10: Preparation method of high-efficiency retarding cement retarder Using hemihydrate phosphogypsum, a byproduct of phosphate chemical industry, as raw material, a mixture of composite fluorosilicone material, acid-base regulator, and hemihydrate phosphogypsum dry matrix in a mass ratio of 2:1:97 was added. The mixture was then aged at room temperature for 5 days to obtain dihydrate phosphogypsum, which was then crushed to a particle size of less than 10 cm to obtain a high-efficiency retarder for cement.

[0039] Results: After aging at room temperature for 7 days, Examples 4-10 all yielded phosphogypsum dihydrate with a crystal water content of over 16%, meeting the requirements of GB / T23456-2018 "Phosphogypsum" for gypsum adhering water ≤25%, calcium sulfate dihydrate (CaSO4•2H2O) ≥65%, water-soluble phosphorus pentoxide (P2O5) ≤0.50%, and water-soluble fluoride ions (F... - ≤0.30%, chloride ions (Cl) - The gypsum dihydrate is further crushed by mechanical crushing to a particle size of less than 10cm, and can be used as a high-efficiency retarder for cement. The cement retarder meets the requirements of GB / T 21371-2019 "Industrial By-product Gypsum Used in Cement" for gypsum grade ≥75% and chloride ion content ≤0.50%.

[0040] To obtain the method for preparing the high-efficiency cement retarder of this invention and to verify the technical effect of this invention, the inventors conducted a large number of experimental studies, some of which are recorded below: 1. Comparison of the hydration-promoting effects of rapid hydration agents and conventional hydration-promoting agents 1.1 Comparison of the hydration-promoting effects of traditional alkaline modifiers The method for testing the conversion rate of water of crystallization is to take fresh hemihydrate phosphogypsum back, add different hydration agents, and then place it in a 60℃ constant temperature water bath for curing. After the curing period is reached, the water of crystallization content of the gypsum is tested using a Guanya moisture analyzer to analyze the storage time required for hemihydrate phosphogypsum to meet the water of crystallization requirements of cement retarder (cement manufacturers usually require a water of crystallization content >16%).

[0041] The cement setting time refers to the time taken when the cement retarder and cement clinker are mixed at a ratio of 1:19 and then placed in a small cement mill to prepare cement, with the specific surface area of ​​the cement after ball milling controlled to be 345~355 m². 2 / kg, the cement setting time is tested according to the standard "GBT 1346-2024 Cement Standard Consistency Water Requirement, Setting Time and Soundness Test Method".

[0042] Quicklime and hemihydrate phosphogypsum were mixed evenly at a certain ratio. The crystal water conversion rate of the mixed gypsum samples was monitored. Gypsum samples with a crystal water conversion value of more than 14% were used to prepare cement retarder and test the cement setting time. The hydration effect of hemihydrate phosphogypsum when the alkaline modifier was quicklime was compared (the effective calcium of lime was 70%).

[0043] Table 1. Hydration-promoting effect of traditional alkaline-modified hemihydrate phosphogypsum Note: The free water content of the hemihydrate gypsum is 23.00%. All gypsum was cured at 60℃. " / " indicates that the crystal water of the gypsum did not meet the requirements for cement retarder, so the cement setting time was not tested.

[0044] Based on the experimental data in the table above, the crystal water of hemihydrate gypsum without the addition of an alkaline modifier is difficult to convert. When the proportion of quicklime is 0.5%, the conversion of crystal water of hemihydrate gypsum is slow and cannot meet the requirements for producing cement retarder. When the proportion of quicklime is 1.0~2.0%, the crystal water reaches more than 15% after 7 days of storage, which can meet the crystal water requirements for producing cement retarder. However, the conversion rate of crystal water is slow in the early stage, and the cement setting time gradually shortens, which cannot meet the setting time requirements of cement plants that require high-efficiency retarding.

[0045] In summary, traditional alkaline modification promotes the hydration of hemihydrate phosphogypsum. A certain amount of low effective calcium lime can promote the conversion of crystal water in hemihydrate phosphogypsum. However, excessive dosage will affect the cement setting time of high-efficiency retarder cement. Furthermore, for industrial production, the accuracy of the feeding equipment needs to be controlled within ±0.5%. Otherwise, insufficient modification will result in an insignificant hydration promotion effect, or excessive modification will lead to a short cement setting time.

[0046] 1.2 Comparison of NaF's hydration-promoting effects NaF was mixed evenly with hemihydrate phosphogypsum in a certain proportion, and the crystal water conversion rate of the gypsum group sample after mixing was monitored. The gypsum group with crystal water of more than 14% was used to prepare cement retarder and the cement setting time was tested to observe the effect of NaF on cement setting time.

[0047] Table 2. Effect of NaF on promoting the hydration of hemihydrate phosphogypsum Note: The free water content of the hemihydrate gypsum is 23.00%. All gypsum was cured at 60℃. " / " indicates that the gypsum crystal water did not meet the requirements for cement retarder, so cement setting time was not tested.

[0048] The data above shows that NaF has an insignificant effect on promoting the hydration of hemihydrate phosphogypsum. The dosage needs to be increased to 0.6% to have a significant effect on accelerating the hydration of hemihydrate phosphogypsum. This will lead to a series of problems such as high cost of rapid hydration agents and excessive F in gypsum.

[0049] 1.3 Comparison of the hydration-promoting effects of sulfuric acid Sulfuric acid was mixed with hemihydrate phosphogypsum in a certain proportion and the crystal water conversion rate of the gypsum group sample was monitored. Gypsum group with crystal water of more than 14% was used to prepare cement retarder and the cement setting time was tested to observe the effect of sulfuric acid on cement setting time.

[0050] Table 3. Effect of sulfuric acid on promoting the hydration of hemihydrate phosphogypsum Note: The free water content of the hemihydrate gypsum is 23.00%. All gypsum was cured at 60℃. " / " indicates that the gypsum crystal water did not meet the requirements for cement retarder, so cement setting time was not tested.

[0051] The data above shows that sulfuric acid has a certain promoting effect on the hydration of hemihydrate phosphogypsum. The dosage needs to be adjusted to more than 0.4% to have a significant effect, which will increase the cost of rapid hydration agents. In addition, the strong acidity of sulfuric acid will reduce the early strength of cement, and there are no components in sulfuric acid that can compensate for the strength of cement.

[0052] 1.4 Comparison of the hydration-promoting effects of by-product fluorosilicone waste liquid A certain concentration of by-product fluorosilicone waste liquid was mixed with hemihydrate phosphogypsum in a certain proportion and the crystal water conversion rate of the gypsum group sample after mixing was monitored. The gypsum group with crystal water of more than 14% was used to prepare cement retarder and the cement setting time was tested to observe the effect of by-product fluorosilicone waste liquid on cement setting time.

[0053] Table 4. Effect of by-product fluorosilicone waste liquid on promoting the hydration of hemihydrate phosphogypsum Note: The free water content of the hemihydrate gypsum is 23.00%, the H2SiF6 content of the by-product fluorosilicone waste liquid is 5.0%, and the gypsum is cured at 60℃. " / " indicates that the gypsum crystal water did not meet the requirements for cement retarder, so the cement setting time was not tested.

[0054] The data above shows that adding by-product fluorosilicone waste liquid at a dosage of 1% to 3% to hemihydrate phosphogypsum, although the hydration promotion effect is relatively average after 3 days, the overall curing effect after 7 days is obvious in promoting the rapid hydration of hemihydrate phosphogypsum. A dosage of 1% by-product fluorosilicone waste liquid can also meet the crystal water requirements for cement retarder production after 7 days of storage. When the dosage is above 2%, the crystal water content of hemihydrate gypsum after 7 days of curing is about 17%.

[0055] The setting time of cement retarders increases with the addition of by-product fluorosilicone waste liquid, but the increase is small and the impact is still within the required range.

[0056] 1.5 Hydration-promoting effect of composite fluorosilicone materials The composite fluorosilicone material, a byproduct of hydrogen fluoride production, was mixed with hemihydrate phosphogypsum in a certain proportion. The crystal water conversion rate of the gypsum sample after mixing was monitored. The gypsum sample with a crystal water content of more than 14% was used to prepare cement retarder and the cement setting time was tested to observe the effect of the composite fluorosilicone material on the cement setting time.

[0057] Table 5. Effect of composite fluorosilicone materials on promoting the hydration of hemihydrate phosphogypsum Note: The free water content of the hemihydrate gypsum is 23.00%, the total F of the composite fluorosilicone material is 8%, and the gypsum is cured at 60℃. " / " indicates that the gypsum crystal water did not meet the requirements for cement retarder, so the cement setting time was not tested.

[0058] The data above shows that when the total F content of the composite fluorosilicone material is 8%, adding it to hemihydrate phosphogypsum at a dosage of 1% to 4% significantly promotes the rapid hydration of hemihydrate phosphogypsum. A 1% dosage of composite fluorosilicone material can meet the crystal water requirements for cement retarder production after 7 days of storage. A dosage of more than 2% of composite fluorosilicone material enables hemihydrate phosphogypsum to reach more than 17% crystal water in just 3 days, and the crystal water can reach more than 15% after 0.5 days of storage.

[0059] The increase in the dosage of composite fluorosilicone materials has a relatively small impact on the setting time of cement, and the dosage of rapid hydration agent can be between 1% and 4%, which greatly reduces the requirements for the accuracy of feeding equipment. It has a certain degree of production stability and inclusiveness in industrial applications, and compared with other rapid hydration agents, it does not require reagent costs. It can also help phosphate and fluorine chemical companies dispose of a certain amount of solid waste from composite fluorosilicone materials.

[0060] 1.6 Synergistic Hydration Effect of Composite Fluorosilicone Materials and By-product Fluorosilicone Waste Liquid By-product composite fluorosilicone material and by-product fluorosilicone waste liquid were mixed with hemihydrate phosphogypsum in a certain proportion and the crystal water conversion rate of the gypsum group sample after mixing was monitored. Gypsum group with crystal water of more than 14% was used to prepare cement retarder and the cement setting time was tested. The synergistic hydration promotion effect of by-product composite fluorosilicone material and by-product fluorosilicone waste liquid and the cement setting time were observed.

[0061] Table 6. Synergistic effect of composite fluorosilicone materials and fluorosilicone waste liquid on promoting the hydration of hemihydrate phosphogypsum. Note: The free water content of the hemihydrate gypsum is 23.00%, the H2SiF6 content of the by-product fluorosilicone waste liquid is 5.0%, the total F of the composite fluorosilicone material is 8%, and the gypsum is cured at 60℃. " / " indicates that the gypsum crystal water did not meet the requirements for cement retarder, so the cement setting time was not tested.

[0062] When by-product fluorosilicone waste liquid and composite fluorosilicone materials work synergistically on hemihydrate phosphogypsum, the two have a significant synergistic effect on accelerating the conversion of hemihydrate phosphogypsum crystal water, and do not cause significant fluctuations in the setting time of cement retarder. Therefore, when the quality of composite fluorosilicone materials is substandard or the output is insufficient, the rapid hydration agent can be replaced with by-product fluorosilicone waste liquid to promote the hydration of hemihydrate phosphogypsum through synergistic effect, effectively solving the application limitations of a single rapid hydration agent.

[0063] 2. Effects of different rapid hydration agents on the strength of cement mortar Agents that have a rapid hydration effect on hemihydrate phosphogypsum were selected and added to hemihydrate phosphogypsum at appropriate dosages. When the crystal water content of hemihydrate phosphogypsum was converted to more than 14%, it was prepared as a cement retarder. The effect of this cement retarder on the strength of cement mortar was tested and compared with cement retarder made from desulfurized gypsum and pure hemihydrate phosphogypsum.

[0064] Table 6. Influence of composite fluorosilicone materials on the strength of cement mortar Note: The content of gypsum in cement is 5%.

[0065] The data above shows that, compared with desulfurized gypsum, hemihydrate phosphogypsum reduces the early strength of cement to a certain extent when used as a cement retarder. Even after adding sulfuric acid and by-product fluorosilicone waste liquid, the early strength of cement still shows a certain degree of reduction. However, the addition of composite fluorosilicone materials compensates for a certain degree of reduction in early strength, and the strength increases to a certain extent at 28 days.

[0066] 3. pH adjustment and hydration promotion effects of acid-base regulators To meet the requirement of pH > 5 for cement retarders in the standard GB / T 21371-2019 "Industrial By-product Gypsum Used in Cement", a certain amount of acid-base adjuster needs to be added to the high-efficiency retarder. This acid-base adjuster should raise the pH value of the high-efficiency retarder to above 5 without affecting the cement setting time and crystal water conversion rate. Among many acid-base adjusters, sodium carbonate was selected as the pH adjusting agent. The crystal water conversion rate of hemihydrate phosphogypsum and the cement setting time data when adjusting the pH value with sodium carbonate are as follows: Table 7. Data on the effects of acid-base regulators Note: The free water content of the hemihydrate gypsum is 23.00%, the total F of the composite fluorosilicone material is 8%, and the gypsum is cured at 60℃.

[0067] The data above shows that adding sodium carbonate to adjust the pH of gypsum does not affect the rapid hydration effect of composite fluorosilicone materials. On the contrary, it further promotes the conversion of hemihydrate phosphogypsum to dihydrate phosphogypsum, reducing the risk of cement retarder clumping in the later stage. A dosage of 0.5~1.0% sodium carbonate can adjust the pH of gypsum to above 5, thereby meeting the requirement of pH>5 in the standard "GBT21371-2019 Industrial By-product Gypsum for Cement".

[0068] Sodium carbonate is added at 0.3-1% of the dry weight of gypsum, while cement retarder is usually added at 3-6% of the dry weight of cement clinker to adjust the cement setting time. The sodium introduced into the cement by sodium carbonate accounts for only 0.03-0.06% of the dry weight of cement, which can meet the sodium ion content limit requirements of various standards.

[0069] 4. Reaction Mechanism Analysis 4.1 Rapid hydration mechanism of composite fluorosilicone materials The fluorine in composite fluorosilicone materials mainly consists of fluorosilicates and fluorosilicic acid, and the composite fluorosilicone materials themselves contain 30-50% moisture, which causes the fluorosilicates and fluorosilicic acid to slowly hydrolyze. [SiF6] 2- + 2H₂O → SiO₂·nH₂O (silica gel) + 4H + + 6F - This hydrolysis reaction continues during the stacking, cooling, or washing of the composite fluorosilicone material. The resulting amorphous silica gel with high adhesion and a large surface area tightly encapsulates the undecomposed fluorosilicates and strongly adsorbs them through the silica gel surface with hydroxyl groups (-OH).

[0070] Due to the special structure of composite fluorosilicone materials, the active component (H) is realized. + [SiF6] 2 The slow and continuous release of ) can maintain an ideal high supersaturation environment during the hydration of gypsum, and in synergy with the efficient heterogeneous nucleation sites provided by the ultrafine silica particles, together greatly accelerate the hydration of hemihydrate gypsum to dihydrate gypsum.

[0071] 4.2 Mechanism of the effect of composite fluorosilicone materials on cement strength Fluoride ions in composite fluorosilicone materials are adsorbed and encapsulated by amorphous silica gel, and are slowly and continuously released during cement hydration. These fluoride ions can undergo a series of complex reactions with the aluminum phase and gypsum in the cement, promoting the rapid and abundant formation of ettringite, which has high early strength. The reaction pathway is as follows: F - + C3A + CaSO4·2H2O → hydrated calcium fluoroaluminate → AFt These early-formed, evenly distributed ettringite crystals interweave and overlap, forming a robust early-stage spatial network together with CSH gel, significantly enhancing the early strength of cement.

[0072] In composite fluorosilicone materials, amorphous SiO2 reacts with calcium hydroxide crystals (CH) which have low strength and poor stability through a pozzolanic reaction, producing high-strength, highly cementitious CSH gel. This not only reduces weak points in the system but also increases the total amount of cementitious material, making the cement stone structure denser and thus continuously improving strength. The pozzolanic reaction formula between SiO2 and CH in composite fluorosilicone materials is as follows: SiO2 + Ca(OH)2 + H2O → CSH gel Through the above reactions, the hydration products rapidly generated by the composite fluorosilicone material in cement effectively fill the original pores and capillaries between cement particles. The generated CSH gel and ettringite make the structure denser. This reduces harmful macropores and increases harmless or less harmful micropores, thereby increasing the early strength of cement and compensating for the loss of early strength caused by phosphogypsum as a cement retarder.

[0073] 4.3 Mechanism of Action of Acid-Base Regulators The addition of a pH adjuster (sodium carbonate) effectively increases the pH of phosphogypsum without solidifying the free phosphorus and fluorine in it, thus preserving the retarding components. Furthermore, sodium carbonate undergoes a series of reactions with hemihydrate gypsum, further accelerating the hydration of the hemihydrate phosphogypsum. The addition of sodium carbonate reacts with calcium ions in the gypsum: Na2CO3+CaSO4·0.5H2O+1.5H2O→CaCO3↓+Na2SO4+2H2O The generated sodium sulfate causes SO4 in the solution to rise. 2- The increase in ion concentration reduces the solubility of hemihydrate gypsum, allowing the solution system to reach and exceed the supersaturation of dihydrate gypsum more quickly, thereby further accelerating the hydration of hemihydrate phosphogypsum.

[0074] Furthermore, the generated sodium sulfate microcrystals can serve as "seeds" or "nucleation sites" for the precipitation of gypsum dihydrate crystals, reducing the nucleation barrier and enabling gypsum dihydrate crystals to be generated and grown simultaneously in more locations, thus accelerating the conversion of hemihydrate gypsum to dihydrate gypsum.

Claims

1. A method for preparing a high-efficiency cement retarder by rapid hydration of hemihydrate phosphogypsum, characterized in that: Using hemihydrate phosphogypsum, a byproduct of phosphate chemical industry, as raw material, a rapid hydration agent and an acid-base regulator are added and mixed. After aging at room temperature for 3-7 days, dihydrate phosphogypsum is obtained. It is then crushed to a particle size of less than 10cm to obtain a high-efficiency retarding cement retarder. The mass ratio of the rapid hydration agent, acid-base regulator, and hemihydrate phosphogypsum dry matrix is ​​2~8:0~1:91.0~98.0; The rapid hydration agent is a by-product composite fluorosilicone material or / and a by-product fluorosilicone waste liquid; The acid-base regulator is anhydrous sodium carbonate.

2. The method according to claim 1, characterized in that: The composite fluorosilicone material comprises, on a dry basis, 80-90 wt% SiO2 and 5-15 wt% total F, and has a BET specific surface area of ​​4-8 m². 2 / g, with an average particle size of 4~20um.

3. The method according to claim 1, characterized in that: The by-product fluorosilicone waste liquid consists of 4-6 wt% H2SiF6 and 94-96 wt% water.

4. The method according to claim 1, characterized in that: The initial free water content of the hemihydrate phosphogypsum is 5.0~25.0%, and the crystal water content is ≤9.0%.

5. The method according to claim 1, characterized in that: The hemihydrate phosphogypsum comprises: 42-54 wt% SO3, 31-36 wt% CaO, 0-6 wt% SiO2, 0.05-1.5 wt% Al2O3, 0-0.7 wt% Fe2O3, 0-0.5 wt% MgO, 0.3-1.3 wt% total P2O5, 0.01-1.0 wt% water-soluble P2O5, 0.1-1.3 wt% total F, 0.01-0.8 wt% water-soluble F, 0.001-0.3 wt% K2O, 0.01-0.6 wt% Na2O, and 0.005-0.015 wt% Cl. - .

6. The method according to claim 1, characterized in that: When the rapid hydration agent is a by-product composite fluorosilicone material, the mass ratio of the by-product composite fluorosilicone material, the acid-base regulator, and the hemihydrate phosphogypsum dry matrix is ​​2~4:0.5~1:96~97.

5.

7. The method according to claim 1, characterized in that: When the rapid hydration agent is a by-product fluorosilicone waste liquid, the mass ratio of the by-product fluorosilicone waste liquid, the acid-base regulator, and the hemihydrate phosphogypsum dry matrix is ​​1~3:0.3~1:96~98.

5.

8. The method according to claim 1, characterized in that: When the rapid hydration agent is a by-product composite fluorosilicone material and a by-product fluorosilicone waste liquid, the mass ratio of the by-product composite fluorosilicone material, the by-product fluorosilicone waste liquid, the acid-base regulator, and the hemihydrate phosphogypsum dry matrix is ​​1~3:1~3:0.3~1:93~97.

5.

9. The method according to claim 1, characterized in that: The aging time is 5-7 days.

10. The application of the high-efficiency cement retarder according to claim 1 in the preparation of silicate cement, characterized in that: The high-efficiency retarding cement retarder and cement clinker dry basis are mixed and ball-milled at a mass ratio of 3~6:94~97. After ball milling, high-efficiency retarding silicate cement can be obtained. The initial setting time of high-efficiency retarding silicate cement is not less than 35 min and the final setting time is not more than 600 min.

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