Fluidized bed slag modified ardealite-based cement retarder and preparation method thereof

Abstract

The invention relates to the field of solid waste resource utilization, and discloses a boiling furnace slag modified ardealite-based cement retarder and a preparation method thereof.The retarder is prepared from 10-15 parts of a base material and 0.5-3 parts of auxiliary materials, and the base material is prepared from, by weight, 65-71 parts of ardealite, 16-28 parts of boiling furnace slag and 10-100 parts of calcium hydroxide; the auxiliary material is prepared from the following components in parts by weight: 0.1 to 5 parts of sodium dodecyl benzene sulfonate, 2 to 10 parts of citric acid, 0.2 to 2 parts of lignosulfonate, 1 to 18 parts of anhydrous sodium sulfate and 0.1 to 10 parts of fly ash. According to the scheme, boiling furnace slag and calcium hydroxide are used as an exciting agent to be doped into phosphogypsum to excite the phosphogypsum, so that the strength of the hydrogel is favorably improved; the boiling slag is used for replacing conventional lime to serve as an exciting agent, so that the cost is saved, the boiling slag and the ardealite are effectively and comprehensively utilized, the problem of high resource utilization difficulty of the ardealite and the boiling slag is solved, and meanwhile, the property of the ardealite-based hydrogel is improved.

Description

Technical Field

[0001] The invention relates to the technical field of solid waste resource utilization, and in particular to a boiling furnace slag modified phosphogypsum-based cement retarder and a preparation method thereof. Background Art

[0002] Phosphogypsum is a solid waste produced in the wet phosphoric acid process, and its main component is calcium sulfate dihydrate. The composition of phosphogypsum is relatively complex. In addition to calcium sulfate, there are also incompletely decomposed phosphate ore, residual phosphoric acid, fluoride, acid insoluble matter, organic matter, etc. Among them, the presence of fluorine and organic matter has the greatest impact on the resource utilization of phosphogypsum. The random discharge and accumulation of phosphogypsum has seriously damaged the ecological environment, not only polluting groundwater resources, but also causing waste of land resources.

[0003] At present, the main application methods of phosphogypsum are: gypsum building materials, cement retarders, ammonium sulfate fertilizers, and soil conditioners. Portland cement is an important building cementitious material with a large application volume and a wide range of uses. Therefore, using PG as a cement retarder is considered to be one of the most promising ways to utilize PG resources. Cement retarders can delay the cement hydration reaction, thereby prolonging the setting time of concrete, allowing the freshly mixed concrete to maintain plasticity for a long time, facilitating pouring, and improving construction efficiency. C3A and C4AF in cement clinker react with gypsum to form hydrated calcium sulfoaluminate and hydrated calcium sulfoferrate. These hydration products adhere to the surface of the clinker particles to form a thin film, sealing the surface of the hydrated components, blocking the diffusion of water molecules and ions, thereby delaying the continued hydration of cement particles, especially C3A, until the crystallization pressure reaches a certain value to partially crack the calcium sulfonate film, and hydration can continue. The early hydration effect of gypsum on cement is particularly obvious. And the strength development is good, and the shrinkage and creep are small.

[0004] The use of phosphogypsum as a cement retarder is widely recognized, but because harmful impurities in phosphogypsum affect its performance and the use of powdered phosphogypsum is difficult to control, phosphogypsum needs to be pretreated before it can be used in cement processing. Phosphogypsum pretreatment generally uses processes such as water washing, neutralization with lime or alkaline calcium materials, and the phosphogypsum powder is pelletized to improve its ease of use in cement processing. However, existing production and disposal methods cannot effectively reduce the content of water-soluble phosphorus and other harmful impurities in phosphogypsum, which has a certain impact on cement performance, resulting in it not being used in large quantities and as widely as natural gypsum in cement industrial production. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a boiling slag modified phosphogypsum-based cement retarder and a preparation method thereof, so as to solve the problem of difficulty in resource utilization of phosphogypsum and boiling slag, and at the same time improve the performance of phosphogypsum-based hydraulic agents.

[0006] In order to achieve the above object, the present invention provides a boiling furnace slag modified phosphogypsum-based cement retarder, which is prepared from 10-15 parts of a base material and 0.5-3 parts of an auxiliary material.

[0007] The base material is composed of the following components by weight: 65-71 parts of phosphogypsum, 16-28 parts of boiling furnace slag, and 10-100 parts of calcium hydroxide;

[0008] The auxiliary materials are composed of the following components by weight: 0.1-5 parts of sodium dodecylbenzene sulfonate, 2-10 parts of citric acid, 0.2-2 parts of lignin sulfonate, 1-18 parts of anhydrous sodium sulfate, and 0.1-10 parts of fly ash.

[0009] The second aspect of the present invention provides a method for preparing a boiling furnace slag modified phosphogypsum-based cement retarder, comprising the following steps:

[0010] S1, ball-milling phosphogypsum, fly ash and anhydrous sodium sulfate to obtain a mixture;

[0011] S2, adding sodium dodecylbenzene sulfonate, citric acid, lignin sulfonate and water to the mixture, mixing and stirring, and then performing a hydrothermal reaction to recrystallize the phosphogypsum and complete the reaction and elimination of harmful impurities; the solid-liquid ratio of water to phosphogypsum is 0.2-2;

[0012] S3, adding calcium hydroxide and boiling slag as activators to the mixture in step S2, stirring at 20-60° C. to obtain a slurry to enhance the strength of the phosphogypsum;

[0013] S4, after the slurry solidifies, the slurry is piled up and aged for a predetermined time to obtain the retarder.

[0014] Preferably, in step S1, the ball-to-material ratio of ball milling is 2-10:1, the ball milling speed is 100-1000 r / min, and the ball milling time is 1-14 h.

[0015] Preferably, in step S2, the stirring time is 0.5-5 d.

[0016] Preferably, in step S3, calcium hydroxide is first added and stirred for 2-10 minutes to make the mixture alkaline, and then boiling slag is added and stirred for 2-200 minutes.

[0017] Preferably, the stirring in step S3 is carried out under normal pressure, and calcium hydroxide is added to make the pH of the mixture ≥10.

[0018] Preferably, in step S4, the stacking aging is carried out at a temperature of 15-30° C. for 2-20 days.

[0019] Preferably, in step S4, granulation is performed before stacking and aging, water is sprayed 3-5 times during the stacking and aging to make the moisture content of the solid particles 5-20%, and the solid particles are dried by autogenous air after the stacking and aging.

[0020] Preferably, the granulation is carried out using a disc granulator, and the particle size of the spherical particles is controlled to be 15-30 mm.

[0021] Preferably, the particle size of the boiling furnace slag is 1-6 mm and the density is 800-900 kg / m 3 The main chemical components of the boiling furnace slag are SiO2 and Al2O3, and the content of SiO2 and Al2O3 accounts for 51-80wt%.

[0022] The technical solution of the present invention has the following beneficial effects:

[0023] (1) Physical ball milling of phosphogypsum will expose the soluble phosphorus, soluble fluorine and harmful impurities in it, but it cannot be eliminated. The chemical method is used: sodium dodecylbenzene sulfonate is used as a surfactant, and citric acid and lignin sulfonate cooperate to convert the phosphorus, fluorine and other impurities in the phosphogypsum into citrate, removing most of the organic matter and some impurities such as phosphorus and fluorine, while facilitating the subsequent reaction of boiling furnace slag and calcium hydroxide doping.

[0024] (2) Using calcium hydroxide as an activator, the boiling slag reacts in an alkaline environment to generate a gelling hydration product, which can fill the pores of the phosphogypsum-based material, thereby improving the density and mechanical strength. At the same time, the gelling hydration product can not only wrap the calcium phosphate precipitate to form a dense structure to prevent the dissolution of phosphorus, but also use its nanoporous structure to physically intercept CaF2 particles or free F - , reducing its mobility, thereby solidifying the phosphorus and fluorine in the phosphogypsum, and further improving the performance of the phosphogypsum-based cement retarder.

[0025] (3) In an alkaline environment, the boiling slag partially dissolves to generate active silicate and aluminate, releasing more adsorption sites. The harmful metals in phosphogypsum are adsorbed through the synergistic effects of ion exchange and surface complexation / coprecipitation, effectively reducing the content of harmful impurities and thus improving the performance of phosphogypsum-based cement retarder.

[0026] (4) It effectively and comprehensively utilizes boiling slag and phosphogypsum, solving the problem of the difficulty in resource utilization of phosphogypsum and boiling slag. It is environmentally friendly and low-cost, and is suitable for large-scale solid waste treatment. DETAILED DESCRIPTION

[0027] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0028] The present invention will be described in detail below by way of examples. In the following examples, all reagents used are commercially available.

[0029] Embodiment 1:

[0030] A boiling furnace slag modified phosphogypsum-based cement retarder is prepared from 15 parts of a base material and 3 parts of an auxiliary material. The base material consists of the following components by weight: 71 parts of phosphogypsum, 28 parts of boiling furnace slag, and 100 parts of calcium hydroxide; the auxiliary material consists of the following components by weight: 5 parts of sodium dodecylbenzene sulfonate, 10 parts of citric acid, 0.2 parts of lignin sulfonate, 18 parts of anhydrous sodium sulfate, and 0.1 parts of fly ash. The particle size of the boiling furnace slag is 1-6 mm, and the density is 800-900 kg / m 3 The main chemical components of the boiling furnace slag are SiO2 and Al2O3, and the content of SiO2 and Al2O3 accounts for 51-80wt%; the preparation method comprises the following steps:

[0031] S1. Mix phosphogypsum, fly ash and anhydrous sodium sulfate and grind them into a mixture; the ball-to-material ratio of the ball mill is 10:1, the ball mill speed is 1000r / min, and the ball milling is performed for 1h;

[0032] S2, adding sodium dodecylbenzene sulfonate, citric acid, lignin sulfonate and water to the mixture, mixing and stirring, and then performing a hydrothermal reaction to recrystallize the phosphogypsum and complete the reaction and elimination of harmful impurities; the solid-to-liquid ratio of water to phosphogypsum is 2, and the stirring time is 0.5d;

[0033] S3, adding calcium hydroxide and boiling slag as activators to the mixture in step S2, stirring at 20° C. to obtain a slurry, specifically, first adding calcium hydroxide and stirring for 10 minutes to make the mixture alkaline, then adding boiling slag and continuing to stir for 200 minutes to enhance the strength of phosphogypsum, and adding calcium hydroxide to make the pH of the mixture 12;

[0034] S4. After the slurry solidifies, a disc granulator is used to granulate the slurry, and the particle size of the spherical particles is controlled to be 15-30 mm. The slurry is piled and aged at a temperature of 30° C. for 20 days. During the pile-aging period, water is sprayed 5 times to make the moisture content of the solid particles 20%. After the pile-aging period, the slurry is dried by autothermal air to obtain the retarder.

[0035] Embodiment 2:

[0036] A boiling furnace slag modified phosphogypsum-based cement retarder is prepared from 10 parts of a base material and 0.5 parts of an auxiliary material. By weight, the base material consists of the following components: 65 parts of phosphogypsum, 16 parts of boiling furnace slag, and 10 parts of calcium hydroxide; by weight, the auxiliary material consists of the following components: 0.1 parts of sodium dodecylbenzene sulfonate, 2 parts of citric acid, 0.2 parts of lignin sulfonate, 1 part of anhydrous sodium sulfate, and 10 parts of fly ash. The particle size of the boiling furnace slag is 1-6 mm, and the density is 800-900 kg / m 3 The main chemical components of the boiling furnace slag are SiO2 and Al2O3, and the content of SiO2 and Al2O3 accounts for 51-80wt%; the preparation method comprises the following steps:

[0037] S1. Mix phosphogypsum, fly ash and anhydrous sodium sulfate and grind them into a mixture; the ball-to-material ratio of the ball mill is 2:1, the ball mill speed is 100 r / min, and the ball milling is performed for 14 hours;

[0038] S2, adding sodium dodecylbenzene sulfonate, citric acid, lignin sulfonate and water to the mixture, mixing and stirring, and then performing a hydrothermal reaction to recrystallize the phosphogypsum and complete the reaction and elimination of harmful impurities; the solid-to-liquid ratio of water to phosphogypsum is 0.2, and the stirring time is 5d;

[0039] S3, adding calcium hydroxide and boiling slag as activators to the mixture in step S2, stirring at 60° C. to obtain a slurry, specifically, first adding calcium hydroxide and stirring for 2 minutes to make the mixture alkaline, then adding boiling slag and continuing to stir for 2 minutes to enhance the strength of phosphogypsum, and adding calcium hydroxide to make the pH of the mixture 10;

[0040] S4. After the slurry solidifies, a disc granulator is used to granulate the slurry, and the particle size of the spherical particles is controlled to be 15-30 mm. The slurry is piled and aged at a temperature of 15° C. for 2 days. During the pile-aging period, water is sprayed 3 times to make the moisture content of the solid particles 5%. After the pile-aging period, the slurry is dried by autothermal air to obtain the retarder.

[0041] Embodiment 3:

[0042] A boiling furnace slag modified phosphogypsum-based cement retarder is prepared from 12 parts of a base material and 1.5 parts of an auxiliary material. By weight, the base material consists of the following components: 68 parts of phosphogypsum, 21 parts of boiling furnace slag, and 30 parts of calcium hydroxide; by weight, the auxiliary material consists of the following components: 2.6 parts of sodium dodecylbenzene sulfonate, 6 parts of citric acid, 1.2 parts of lignin sulfonate, 9 parts of anhydrous sodium sulfate, and 5 parts of fly ash. The particle size of the boiling furnace slag is 1-6 mm, and the density is 800-900 kg / m 3The main chemical components of the boiling furnace slag are SiO2 and Al2O3, and the content of SiO2 and Al2O3 accounts for 51-80wt%; the preparation method comprises the following steps:

[0043] S1. Mix phosphogypsum, fly ash and anhydrous sodium sulfate and grind them into a mixture; the ball-to-material ratio of the ball mill is 6:1, the ball mill speed is 550r / min, and the ball milling is performed for 7h;

[0044] S2, adding sodium dodecylbenzene sulfonate, citric acid, lignin sulfonate and water to the mixture, mixing and stirring, and then performing a hydrothermal reaction to recrystallize the phosphogypsum and complete the reaction and elimination of harmful impurities; the solid-to-liquid ratio of water to phosphogypsum is 1.1, and the stirring time is 2d;

[0045] S3, adding calcium hydroxide and boiling slag as activators to the mixture in step S2, stirring at 30° C. to obtain a slurry, specifically, first adding calcium hydroxide and stirring for 6 minutes to make the mixture alkaline, then adding boiling slag and continuing to stir for 100 minutes to enhance the strength of phosphogypsum, and adding calcium hydroxide to make the pH of the mixture 12.5;

[0046] S4. After the slurry solidifies, a disc granulator is used to granulate the slurry, and the particle size of the spherical particles is controlled to be 15-30 mm. The slurry is piled and aged at a temperature of 18° C. for 11 days. During the pile-aging period, water is sprayed 4 times to make the moisture content of the solid particles 12%. After the pile-aging period, the slurry is dried by autothermal air to obtain the retarder.

[0047] Embodiment 4:

[0048] A boiling furnace slag modified phosphogypsum-based cement retarder is prepared from 10 parts of a base material and 2 parts of an auxiliary material. The base material consists of the following components by weight: 70 parts of phosphogypsum, 19 parts of boiling furnace slag, and 60 parts of calcium hydroxide; the auxiliary material consists of the following components by weight: 3 parts of sodium dodecylbenzene sulfonate, 4 parts of citric acid, 1.5 parts of lignin sulfonate, 10 parts of anhydrous sodium sulfate, and 2 parts of fly ash. The particle size of the boiling furnace slag is 1-6 mm, and the density is 800-900 kg / m 3 The main chemical components of the boiling furnace slag are SiO2 and Al2O3, and the content of SiO2 and Al2O3 accounts for 51-80wt%; the preparation method comprises the following steps:

[0049] S1. Mix phosphogypsum, fly ash and anhydrous sodium sulfate and grind them into a mixture; the ball-to-material ratio of the ball mill is 4:1, the ball mill speed is 750 r / min, and the ball milling is performed for 5 hours;

[0050] S2, adding sodium dodecylbenzene sulfonate, citric acid, lignin sulfonate and water to the mixture, mixing and stirring, and then performing a hydrothermal reaction to recrystallize the phosphogypsum and complete the reaction and elimination of harmful impurities; the solid-to-liquid ratio of water to phosphogypsum is 1.8, and the stirring time is 1.5d;

[0051] S3, adding calcium hydroxide and boiling slag as activators to the mixture in step S2, stirring at 45° C. to obtain a slurry, specifically, first adding calcium hydroxide and stirring for 4 minutes to make the mixture alkaline, then adding boiling slag and continuing to stir for 120 minutes to enhance the strength of phosphogypsum, and adding calcium hydroxide to make the pH of the mixture 11.5;

[0052] S4. After the slurry solidifies, a disc granulator is used to granulate the slurry, and the particle size of the spherical particles is controlled to be 15-30 mm. The slurry is piled and aged at a temperature of 20° C. for 7 days. During the pile-aging period, water is sprayed 4 times to make the moisture content of the solid particles 10%. After the pile-aging period, the slurry is dried by autothermal air to obtain the retarder.

[0053] Comparative Example 1:

[0054] A phosphogypsum-based cement retarder is prepared from 12 parts of a base material and 1.5 parts of an auxiliary material. The base material consists of the following components by weight: 68 parts of phosphogypsum and 30 parts of calcium hydroxide; the auxiliary material consists of the following components by weight: 2.6 parts of sodium dodecylbenzene sulfonate, 6 parts of citric acid, 1.2 parts of lignin sulfonate, 9 parts of anhydrous sodium sulfate, and 1 part of fly ash. The particle size of the boiling furnace slag is 1-6 mm, and the density is 800-900 kg / m 3 The main chemical components of the boiling furnace slag are SiO2 and Al2O3, and the content of SiO2 and Al2O3 accounts for 51-80wt%; the preparation method comprises the following steps:

[0055] S1. Mix phosphogypsum, fly ash and anhydrous sodium sulfate and grind them into a mixture; the ball-to-material ratio of the ball mill is 6:1, the ball mill speed is 550r / min, and the ball milling is performed for 7h;

[0056] S2, adding sodium dodecylbenzene sulfonate, citric acid, lignin sulfonate and water to the mixture, mixing and stirring, and then performing a hydrothermal reaction to recrystallize the phosphogypsum and complete the reaction and elimination of harmful impurities; the solid-to-liquid ratio of water to phosphogypsum is 1.1, and the stirring time is 2d;

[0057] S3. After the slurry solidifies, a disc granulator is used to granulate the slurry, and the particle size of the spherical particles is controlled to be 15-30 mm. The slurry is piled and aged at a temperature of 18° C. for 11 days. During the pile aging period, water is sprayed 4 times to make the moisture content of the solid particles 12%. After the pile aging period, the slurry is dried by autothermal air to obtain the retarder.

[0058] Comparative Example 1 has the same steps and experimental conditions as Example 3, except that no boiling furnace slag and calcium hydroxide are added in Comparative Example 1.

[0059] Comparative Example 2:

[0060] A phosphogypsum-based cement retarder is prepared from 12 parts of a base material and 1.5 parts of an auxiliary material. The base material consists of the following components by weight: 68 parts of phosphogypsum, 21 parts of boiling furnace slag, and 30 parts of calcium hydroxide; the boiling furnace slag has a particle size of 1-6 mm and a density of 800-900 kg / m 3 The main chemical components of the boiling furnace slag are SiO2 and Al2O3, and the content of SiO2 and Al2O3 accounts for 51-80wt%; the preparation method comprises the following steps:

[0061] S1. Ball milling the phosphogypsum to obtain a mixture; the ball-to-material ratio of the ball milling is 6:1, the ball milling speed is 550 r / min, and the ball milling is performed for 7 hours;

[0062] S2, adding water to the mixture, mixing and stirring, and then performing a hydrothermal reaction, the solid-liquid ratio of water to phosphogypsum is 1.1, and the stirring time is 2 days;

[0063] S3, adding calcium hydroxide and boiling furnace slag as activators to the mixture in step S2 and stirring to obtain a slurry, specifically, first adding calcium hydroxide and stirring for 6 minutes to make the mixture alkaline, then adding boiling furnace slag and continuing to stir for 100 minutes to enhance the strength of phosphogypsum, and adding calcium hydroxide to make the pH of the mixture 12.5;

[0064] S4. After the slurry solidifies, a disc granulator is used to granulate the slurry, and the particle size of the spherical particles is controlled to be 15-30 mm. The slurry is piled and aged at a temperature of 18° C. for 11 days. During the pile-aging period, water is sprayed 4 times to make the moisture content of the solid particles 12%. After the pile-aging period, the slurry is dried by autothermal air to obtain the retarder.

[0065] The steps and experimental conditions of Comparative Example 2 are the same as those of Example 3, except that fly ash and anhydrous sodium sulfate are not added in Comparative Example 2.

[0066] Comparative Example 3:

[0067] The steps and experimental conditions of Comparative Example 1 are the same as those of Example 3, except that no boiling slag is added in Comparative Example 1.

[0068] The performance of the phosphogypsum-based cement retarders of Examples 1-4 of the present invention were tested, and compared with the phosphogypsum-based cement retarders prepared in Comparative Examples 1-3. According to GB / T21371-2008 "Industrial By-product Gypsum for Cement Production", the comparison data of modified phosphogypsum cement retarders produced by different technical schemes are shown in Table 1.

[0069] Table 1

[0070]

[0071]

[0072] Physical ball grinding of phosphogypsum will expose the soluble phosphorus, soluble fluorine and harmful impurities in it, but it cannot be eliminated. The chemical method is used: sodium dodecylbenzene sulfonate is used as a surfactant, citric acid and lignin sulfonate cooperate to convert the phosphorus, fluorine and other impurities in the phosphogypsum into citrate, which removes most of the organic matter and part of the phosphorus, fluorine and other impurities, and is also beneficial to the subsequent reaction of boiling furnace slag and calcium hydroxide doping.

[0073] Boiling slag, also known as boiling slag, is the waste residue produced when boiling boilers are burned. It has stable chemical composition, is active, and is easy to grind. The main contents of boiling slag are SiO2 and Al2O3. Physical ball milling of phosphogypsum will expose the soluble phosphorus, soluble fluorine and harmful impurities, and the alkaline environment provided by calcium hydroxide will also release OH - , Ca 2+ Water-soluble PO4 exposed to phosphogypsum 3- and F - Forming insoluble compounds such as calcium phosphate and CaF2, OH - Attack the silicon-aluminum skeleton of boiling slag: On the one hand, it causes the Si-O-Si and Al-O-Si bonds to break, releasing active SiO2 and Al2O3, which further react with Ca(OH)2 at 20-60°C to generate gelling hydration products including hydrated calcium silicate and hydrated calcium aluminate. The gelling hydration products can fill the pores of phosphogypsum-based materials, thereby improving the density and mechanical strength. At the same time, the gelling hydration products can not only wrap the calcium phosphate precipitation to form a dense structure to prevent the dissolution of phosphorus, but also use their nanoporous structure to physically intercept CaF2 particles or free F - , reducing its mobility, thereby solidifying the phosphorus and fluorine in the phosphogypsum, further improving the performance of the phosphogypsum-based cement retarder; on the other hand, part of the solution is dissolved to generate active silicate (H4SiO4) and aluminate (Al(OH)4 - ), releasing more adsorption sites through ion exchange (for cationic metals, such as Pb 2+ 、Cd 2+ ) and surface complexation / coprecipitation (for anionic metals such as AsO4 3- ) work synergistically to adsorb harmful metals in phosphogypsum, effectively reducing the content of harmful impurities, thereby improving the performance of phosphogypsum-based cement retarder.

[0074] The performance of the phosphogypsum-based cement retarder obtained by the component configuration of Examples 1-4 and the corresponding preparation method is significantly better than that of the phosphogypsum-based cement retarder of Comparative Examples 1-3, and the setting performance and strength are significantly improved. When the phosphogypsum modified by the components in the technical solution of the present invention and the corresponding experimental conditions is applied to cement production, its material properties are fundamentally changed. In the process of changing the crystal structure of the phosphogypsum, the harmful impurities contained in the phosphogypsum are effectively removed and digested, thereby achieving the change of the material properties of the phosphogypsum material. Excessive phosphorus impurity content in the retarder will reduce the retarding effect and increase the retarding time. It can be seen from the comparison of Example 3 and Comparative Example 2 in Table 1 that the use of anhydrous sodium sulfate and fly ash in conjunction with boiling furnace slag and calcium hydroxide and other components can promote the solidification of phosphorus in phosphogypsum, reduce the phosphorus content, thereby shortening the setting time of the cement retarder and improving the compressive and flexural strengths. From the comparison between Example 3 and Comparative Example 1 and Comparative Example 3 in Table 1, it can be seen that calcium hydroxide is used as an activator to activate the boiling furnace slag modified phosphogypsum-based cement retarder to significantly improve the setting performance and strength.

[0075] In summary, the technical solution of the present invention uses boiling furnace slag and calcium hydroxide as an activator to be added into phosphogypsum to modify the phosphogypsum-based cement retarder, which has the following beneficial effects:

[0076] (1) Physical ball milling of phosphogypsum will expose the soluble phosphorus, soluble fluorine and harmful impurities in it, but it cannot be eliminated. The chemical method is used: sodium dodecylbenzene sulfonate is used as a surfactant, and citric acid and lignin sulfonate cooperate to convert the phosphorus, fluorine and other impurities in the phosphogypsum into citrate, removing most of the organic matter and some impurities such as phosphorus and fluorine, while facilitating the subsequent reaction of boiling furnace slag and calcium hydroxide doping.

[0077] (2) Using calcium hydroxide as an activator, the boiling slag reacts in an alkaline environment to generate a gelling hydration product, which can fill the pores of the phosphogypsum-based material, thereby improving the density and mechanical strength. At the same time, the gelling hydration product can not only wrap the calcium phosphate precipitate to form a dense structure to prevent the dissolution of phosphorus, but also use its nanoporous structure to physically intercept CaF2 particles or free F - , reducing its mobility, thereby solidifying the phosphorus and fluorine in the phosphogypsum, and further improving the performance of the phosphogypsum-based cement retarder.

[0078] (3) In an alkaline environment, the boiling slag partially dissolves to generate active silicate and aluminate, releasing more adsorption sites. The harmful metals in phosphogypsum are adsorbed through the synergistic effects of ion exchange and surface complexation / coprecipitation, effectively reducing the content of harmful impurities and thus improving the performance of phosphogypsum-based cement retarder.

[0079] (4) It effectively and comprehensively utilizes boiling slag and phosphogypsum, solving the problem of the difficulty in resource utilization of phosphogypsum and boiling slag. It is environmentally friendly and low-cost, and is suitable for large-scale solid waste treatment.

[0080] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A boiling furnace slag modified phosphogypsum-based cement retarder, characterized in that: It is prepared from 10-15 parts of base material and 0.5-3 parts of auxiliary materials. The base material is composed of the following components by weight: 65-71 parts of phosphogypsum, 16-28 parts of boiling furnace slag, and 10-100 parts of calcium hydroxide; The auxiliary materials are composed of the following components by weight: 0.1-5 parts of sodium dodecylbenzene sulfonate, 2-10 parts of citric acid, 0.2-2 parts of lignin sulfonate, 1-18 parts of anhydrous sodium sulfate, and 0.1-10 parts of fly ash.

2. A method for preparing the boiling furnace slag modified phosphogypsum-based cement retarder according to claim 1, characterized in that: The following steps are involved: S1, ball-milling phosphogypsum, fly ash and anhydrous sodium sulfate to obtain a mixture; S2, adding sodium dodecylbenzene sulfonate, citric acid, lignin sulfonate and water to the mixture, mixing and stirring, and then performing a hydrothermal reaction to recrystallize the phosphogypsum and complete the reaction and elimination of harmful impurities; the solid-liquid ratio of water to phosphogypsum is 0.2-2; S3, adding calcium hydroxide and boiling slag as activators to the mixture in step S2, stirring at 20-60° C. to obtain a slurry to enhance the strength of the phosphogypsum; S4, after the slurry solidifies, the slurry is piled up and aged for a predetermined time to obtain the retarder.

3. The method according to claim 2, characterized in that In step S1, the ball-to-material ratio of ball milling is 2-10:1, the ball milling speed is 100-1000 r / min, and the ball milling time is 1-14 h.

4. The method according to claim 2, characterized in that: In step S2, the stirring time is 0.5-5d.

5. The method according to claim 2, characterized in that: In step S3, calcium hydroxide is first added and stirred for 2-10 minutes to make the mixture alkaline, and then boiling slag is added and stirred for 2-200 minutes.

6. The method according to claim 5, characterized in that In step S3, stirring is carried out under normal pressure, and calcium hydroxide is added to make the mixture pH ≥ 10.

7. The method according to claim 2, characterized in that In step S4, the stacking aging is carried out at a temperature of 15-30° C. for 2-20 days.

8. The method according to claim 2, characterized in that: In step S4, granulation is performed before stacking and aging. During the stacking and aging, water is sprayed 3-5 times to make the moisture content of the solid particles 5-20%. After the stacking and aging, the solid particles are dried by self-heating.

9. The method according to claim 8, characterized in that The granulation is carried out using a disc granulator, and the particle size of the spherical particles is controlled to be 15-30 mm.

10. The method according to any one of claims 2 to 9, characterized in that: The particle size of the boiling furnace slag is 1-6 mm, and the density is 800-900 kg / m 3 The main chemical components of the boiling furnace slag are SiO2 and Al2O3, and the content of SiO2 and Al2O3 accounts for 51-80wt%.

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