Spherical cement retarder and preparation method thereof

Abstract

The invention provides a spherical cement retarder and a preparation method thereof, and belongs to the technical field of building materials.The spherical cement retarder is prepared from, by mass, 100 parts of gypsum powder, 10-20 parts of mother nucleus, 0.5-1.5 parts of alkaline excitant and 15-20 parts of water; wherein the raw materials of the gypsum powder comprise semi-hydrated gypsum and anhydrous gypsum, and the semi-hydrated gypsum accounts for 45-55% of the total mass of the gypsum powder; the mother nucleus is gypsum particles prepared by blending gypsum powder and water, mixing, granulating and screening. According to the spherical cement retarder and the preparation method thereof, the anhydrite with lower value is used for partially replacing the semi-hydrated gypsum, and the semi-hydrated gypsum and the anhydrite are mutually excited to form a relatively stable state, so that the obtained spherical cement retarder meets the use standard of the cement retarder, the aging time is shortened, and the production efficiency is improved.

Description

Technical Field

[0001] The present application belongs to the technical field of building materials, and in particular relates to a spherical cement retarder and a preparation method thereof. Background Art

[0002] Cement is one of the main raw materials in engineering construction and has been widely and extensively used. Gypsum is an indispensable retarder in the cement production process and has a very large market demand. Most of the retarders used in cement production are natural gypsum. With the development of industry, the use of cement is increasing, and the demand for natural gypsum will also increase accordingly, resulting in a shortage of natural gypsum resources. Phosphogypsum is an industrial waste residue discharged by phosphorus chemical enterprises in the production of wet phosphoric acid (i.e., phosphoric acid is prepared by the reaction of sulfuric acid and phosphate rock). It mainly exists in the form of calcium sulfate dihydrate (CaSO4·2H2O). It is used to replace natural gypsum as a cement retarder, which not only alleviates the problem of waste residue stacking in phosphorus chemical enterprises, improves the resource utilization rate of phosphogypsum, but also reduces dependence on natural gypsum. However, directly using phosphogypsum as a cement retarder will not only lead to unstable initial setting time of cement and reduced cement strength, but also pollute the environment.

[0003] Regarding the preparation method of cement retarder, in the prior art, phosphogypsum (a mixture of dihydrate gypsum and hemihydrate gypsum), alkaline additives and gelling agents are mixed, granulated and aged to obtain cement retarder. However, the aging time of this method is relatively long, requiring 10-30 days. In the prior art, cement retarder is also prepared by aging phosphogypsum, adding an alkaline activator and water, and mixing and granulating. However, this method also requires a relatively long aging time, and since the hemihydrate gypsum in the phosphogypsum is converted into dihydrate gypsum by aging, and the value of hemihydrate gypsum is much higher than that of dihydrate gypsum, this method cannot achieve high-value utilization of hemihydrate gypsum.

[0004] Therefore, it is necessary to propose a new preparation method of phosphogypsum ball cement retarder to solve the technical problems of long aging time and low preparation efficiency in the existing preparation process of cement retarder. Summary of the invention

[0005] In view of the technical problems existing in the background technology, the present application provides a spherical cement retarder and a preparation method thereof, aiming to solve the technical problems of long aging time and low preparation efficiency in the existing preparation process of cement retarder.

[0006] In a first aspect, an embodiment of the present application provides a spherical cement retarder. In terms of parts by mass, the raw materials for preparing the spherical cement retarder include: 100 parts of gypsum powder, 10 - 20 parts of mother nucleus, 0.5 - 1.5 parts of alkaline activator, and 15 - 20 parts of water; wherein, the raw materials of the gypsum powder include hemihydrate gypsum and anhydrous gypsum, and the hemihydrate gypsum accounts for 45% - 55% of the total mass of the gypsum powder; the mother nucleus is a gypsum particle obtained by blending gypsum powder and water, followed by mixing granulation and screening.

[0007] In the technical solution of the embodiment of the present application, by mixing and granulating hemihydrate gypsum, anhydrous gypsum, mother nucleus, alkaline activator, and water to prepare the cement retarder, on the one hand, the aging time in the process can be reduced; on the other hand, the hemihydrate gypsum can be directly applied, reducing the stacking pressure of the hemihydrate gypsum; in addition, replacing the hemihydrate gypsum that needs to be hydrated with low-cost anhydrous gypsum improves the effective utilization rate of the anhydrous gypsum and also reduces the stacking pressure of the anhydrous gypsum. Among them, if the proportion of anhydrous gypsum is too high, it will cause the product particle size to decrease and the strength to decrease; on the contrary, if the proportion of hemihydrate gypsum is too high, it will cause the product particle size to increase and the strength to increase; the proportion of anhydrous gypsum should not exceed 55% of the raw materials. If the proportion of anhydrous gypsum exceeds 55% of the raw materials, it will directly affect the pellet forming.

[0008] Specifically, in the present application, the mother nucleus provides the starting points for attachment and growth to form larger and more uniformly structured particles. If the proportion of the mother nucleus is too low, it will cause the product particle size to be too small and even directly affect the pellet forming; while if the proportion of the mother nucleus is too high, a large number of nucleation sites will form a large number of fine particles, which will also cause the product particle size to be too small and the strength to decrease. The alkaline activator is used to adjust the pH value and accelerate the hydration process by the heat released from the reaction with water, and can also solidify the soluble impurities that are difficult to remove by water washing. If the addition amount of the alkaline activator is too high, the hydration reaction will be too rapid and difficult to control, resulting in local premature setting or uneven hardening. At the same time, due to the generation of a large amount of calcium hydroxide, large internal stresses are generated inside the product, resulting in cracks or delamination, thereby affecting the structural integrity and strength of the product; if the addition amount of the alkaline activator is too low, the hydration speed will slow down, prolonging the time from the slurry to the hardened product, affecting the production efficiency. At the same time, it will also cause insufficient optimization and adjustment of the pH value and ineffective solidification of the soluble impurities, affecting the quality of the final product (such as the setting time, etc.) and environmental friendliness. Water, as the binder in the granulation process, can bond the reaction particles together to form pellets. At the same time, it can also be used as the reaction water for the hydration of hemihydrate gypsum and anhydrous gypsum. If the proportion of water is too low, the pellets cannot be formed; if the proportion of water is too high, the pellets will be severely bonded.

[0009] In some embodiments, the hemihydrate gypsum is α-hemihydrate gypsum, with a free water content of 9%-12% and a particle size of 20-30 μm; the anhydrite is type II anhydrite, with a free water content of 9%-12% and a particle size of 10-20 μm.

[0010] In this embodiment, α-hemihydrate gypsum has high strength and hardness, and at the same time has the characteristics of hemihydrate crystallization, and can harden rapidly after adding water. Type II anhydrite belongs to a kind of anhydrite, which is usually insoluble in water, has a slow hydration rate, poor setting ability or almost no setting, has no early strength, and has a low additional value utilization rate. By selecting type II anhydrite, its effective utilization rate can be improved and the stacking pressure can be reduced; by controlling the free water content of hemihydrate gypsum and anhydrite within the above range, the hemihydrate gypsum and anhydrite products obtained directly after filtration by the existing wet process of hemihydrate gypsum or anhydrite (the water content can be controlled at 12% and below after filtration) can be used as raw materials without an additional drying process, providing good conditions for reducing the aging time. By controlling the particle size of hemihydrate gypsum and anhydrite within the above range, it is not only beneficial to obtain products with high appearance quality and particle strength, but also beneficial to improve production efficiency.

[0011] Among them, if the particle size of hemihydrate gypsum and anhydrite is too high, on the one hand, the production efficiency is reduced due to the too slow hydration rate, and on the other hand, due to the large particle voids, the porosity inside the hardened gypsum product increases and the density decreases, resulting in a decrease in the strength of the product and a rougher surface; if the particle size of hemihydrate gypsum and anhydrite is too low, although the initial hydration rate is increased to some extent, too many fine particles will cause the internal water to be not easily discharged, and will also prolong the drying time and hardening time and reduce the production efficiency. At the same time, the tiny defects formed inside the hardened material may become stress concentration points and weaken the mechanical strength of the product.

[0012] In some embodiments, the mother nucleus is a gypsum particle with a particle size ≤ 5 mm.

[0013] In this embodiment, by controlling the particle size of the mother nucleus below 5 mm, products with excellent appearance and high mechanical strength can be obtained, avoiding problems such as rough product appearance and low mechanical strength caused by too high a particle size of the mother nucleus.

[0014] In some embodiments, the alkaline activator is at least one of calcium oxide, calcium hydroxide or carbide slag.

[0015] In this embodiment, the main component of the alkaline activator is calcium oxide or calcium hydroxide, and the regulation of pH is more gentle, which is beneficial to controlling the reaction rate.

[0016] In some embodiments, the particle size of the spherical cement retarder is 5 - 30 mm, and the proportion of particles with a particle size of 10 - 30 mm is ≥ 70%; the free water content of the spherical cement retarder is ≤ 10%, and the crystal water content is ≥ 10%.

[0017] In this embodiment, by controlling the particle size of the spherical cement retarder within the above range, the particles are uniform, the strength is moderate, meeting the standard requirements, and it is convenient for transportation, and the adverse effects of too high or too low particle size on properties such as the setting time and compressive strength of cement are avoided; by controlling the free water content within 10%, it helps to reduce the caking phenomenon of the material during storage and transportation, improve the fluidity and dispersibility of the product, and facilitate construction operations; by controlling the crystal water content above 10%, it helps to improve the overall hardness and mechanical strength of the material.

[0018] Second, the embodiments of the present application provide a preparation method of a spherical cement retarder, including the following steps: Mix and granulate gypsum powder, mother nucleus, alkaline activator and water to obtain pellets; Cure the pellets to obtain a spherical cement retarder.

[0019] In the technical solution of the embodiments of the present application, by mixing, granulating and curing gypsum powder, mother nucleus, alkaline activator and water to prepare a spherical cement retarder, the gypsum can form a denser structure, thereby increasing its mechanical strength and facilitating transportation, storage and use.

[0020] In some embodiments, in the step of mixing and granulating, it further includes: adding water and / or gypsum powder to the granulator.

[0021] In this embodiment, by adding water during the mixing and granulating process, the fluidity and processability of the material can be improved, and at the same time, it can participate in the hydration reaction and accelerate the process of chemical bonding; by adding gypsum powder during the mixing and granulating process, the fluidity and processability of the material can be improved.

[0022] In some embodiments, after the pellets are cured, it further includes: Screen the pellets to obtain a spherical cement retarder.

[0023] In this embodiment, by screening the cured pellets, a spherical cement retarder with a suitable particle size distribution can be obtained; at the same time, by recycling the small particle size particles screened out, they can be used as the mother nucleus for the second time, which is beneficial to the smooth progress of the granulation process on the one hand and avoids waste of raw materials on the other hand.

[0024] In some embodiments, a disk granulator is used for mixing and granulating, wherein the rotation speed of the disk granulator is 30 - 50 rpm, and the inclination angle of the disk granulator is 40° - 60°.

[0025] In this embodiment, by controlling the rotation speed and inclination angle of the disk granulator, the particle size distribution can be optimized, the particle quality can be improved, and spherical cement retarders meeting the standard requirements can be obtained. If the rotation speed is too high, problems such as too large particle size or easy fragmentation may occur; if the rotation speed of the disk granulator is too low, the product forming speed is slow and a large amount of materials remain. If the inclination angle of the disk granulator is too low, the pellets will stay in the machine for a long time and the pellet size will be too large; if the inclination angle of the disk granulator is too high, the pellets will break due to the force, forming a large number of fine particles. The fragments grow and round in the disk to generate new aggregate prototypes, and some fragments and powders do not grow well, forming small irregular aggregates.

[0026] In some embodiments, the curing method is natural curing, and the natural curing time is 2 - 24 h.

[0027] In this embodiment, spherical cement retarders meeting the standard requirements can be obtained by adopting the method of natural curing for 2 - 24 h, which greatly saves the production time.

[0028] The above description is only an overview of the technical solution of this application. In order to be able to understand the technical means of this application more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features and advantages of this application more obvious and understandable, the following specific embodiments of this application are specifically given. Specific Embodiments

[0029] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, so they are only examples and cannot be used to limit the protection scope of this application.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above description are intended to cover non-exclusive inclusion.

[0031] In the description of the embodiments of this application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "a plurality" is more than two, unless otherwise clearly and specifically defined.

[0032] References to "embodiments" in this specification mean that the specific features, structures, or characteristics described in connection with the embodiments can be included in at least one embodiment of the present application. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0033] In the description of the embodiments of the present application, the term "and / or" is merely a description of the association relationship between associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally represents an "or" relationship between the associated objects before and after.

[0034] In the description of the embodiments of the present application, the term "plurality" refers to two or more (including two). Similarly, "multiple groups" refers to two or more groups (including two groups), and "multiple pieces" refers to two or more pieces (including two pieces).

[0035] In the description of the embodiments of the present application, the orientation or positional relationship indicated by technical terms such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. is based on the indicated orientation or positional relationship, and is only for the convenience of describing the embodiments of the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the embodiments of the present application.

[0036] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installation", "connection", "connection", "fixation", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can also be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and can be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.

[0037] In the prior art, preparing a cement retarder requires aging the hemihydrate gypsum in phosphogypsum to convert it into dihydrate gypsum. The aging time is relatively long and the utilization value of the hemihydrate gypsum is reduced.

[0038] In order to solve the technical problems of long aging time required and low preparation efficiency in the existing preparation process of cement retarders, the present application provides a spherical cement retarder and its preparation method. By mixing hemihydrate gypsum, anhydrous gypsum, mother nucleus, alkaline activator and water for granulation to prepare the cement retarder, the present application can shorten the aging time and improve the production efficiency. By using anhydrous gypsum with relatively low value to partially replace hemihydrate gypsum and making hemihydrate gypsum and anhydrous gypsum mutually activate to form a relatively stable state, a spherical cement retarder meeting the use standard of cement retarder can be obtained.

[0039] In a first aspect, an embodiment of the present application provides a spherical cement retarder. Calculated by mass parts, the raw materials for preparing the spherical cement retarder include: 100 parts of gypsum powder, 10 - 20 parts of mother nucleus, 0.5 - 1.5 parts of alkaline activator and 15 - 20 parts of water; wherein, the raw materials of the gypsum powder include hemihydrate gypsum and anhydrous gypsum, and the hemihydrate gypsum accounts for 45% - 55% of the total mass of the gypsum powder; the mother nucleus is gypsum particles obtained by mixing and granulating the gypsum powder and water and then screening.

[0040] In the present application, by mixing hemihydrate gypsum, anhydrous gypsum, mother nucleus, alkaline activator and water for granulation to prepare the cement retarder, the aging time in the process will be reduced; at the same time, the hemihydrate gypsum can be directly applied, reducing the stacking pressure of hemihydrate gypsum; in addition, using low-cost anhydrous gypsum to replace the hemihydrate gypsum that needs to be hydrated improves the effective utilization rate of anhydrous gypsum and also reduces the stacking pressure of anhydrous gypsum. However, if the proportion of anhydrous gypsum is too high, it will cause the product particle size to decrease and the strength to decrease; on the contrary, if the proportion of hemihydrate gypsum is too high, it will cause the product particle size to increase and the strength to increase; the proportion of anhydrous gypsum shall not exceed 55% of the raw materials. If the proportion of anhydrous gypsum exceeds 55% of the raw materials, it will directly affect the pellet forming.

[0041] Specifically, the mother nucleus provides a starting point for attachment and growth to form larger and more structurally uniform particles. If the proportion of the mother nucleus is too low, it will result in too small product particle size and even directly affect pellet forming; if the proportion of the mother nucleus is too high, a large number of nucleation sites will form a large number of fine particles, which will also lead to too small product particle size and reduced strength. The alkaline activator is used to adjust the pH value, accelerate the hydration process by the heat released from the reaction with water, and can also solidify soluble impurities that are difficult to remove by water washing. If the addition amount of the alkaline activator is too high, it will cause the hydration reaction to be too rapid and difficult to control, resulting in local premature solidification or uneven hardening. At the same time, due to the generation of a large amount of calcium hydroxide, large internal stresses are generated inside the product, resulting in cracks or delamination, thereby affecting the structural integrity and strength of the product; if the addition amount of the alkaline activator is too low, it will cause the hydration rate to slow down, prolong the time from the slurry to the hardened finished product, affect the production efficiency, and at the same time, it will also lead to insufficient optimization of the pH value and ineffective solidification of soluble impurities, affecting the quality of the final product (such as setting time, etc.) and environmental friendliness. Water, as an adhesive in the granulation process, can bond the particles together to form pellets. At the same time, water can also be used as the reaction water for the hydration of hemihydrate gypsum and anhydrous gypsum. If the proportion of water is too low, the pellets cannot be formed; if the proportion of water is too high, the pellets will be severely bonded.

[0042] Further, in some embodiments, the hemihydrate gypsum is α-hemihydrate gypsum, and its free water content is 9%-12%, and the particle size is 20-30 μm.

[0043] In this application, α-hemihydrate gypsum has relatively high strength and hardness, and at the same time has the characteristics of hemihydrate crystallization and can rapidly harden after adding water. By controlling the free water content of the hemihydrate gypsum within the above range, the hemihydrate gypsum product obtained after filtration by the existing wet process of hemihydrate gypsum (the water content can be controlled at 12% and below after filtration) can be directly used as a raw material without an additional drying process, providing good conditions for reducing the aging time. By controlling the particle size of the hemihydrate gypsum within the above range, it is not only beneficial to obtain products with high appearance quality and particle strength, but also beneficial to improve production efficiency. If the particle size of the hemihydrate gypsum is too high, on the one hand, the production efficiency is reduced due to too slow hydration rate, and on the other hand, due to the large particle voids, the porosity inside the hardened gypsum product increases and the density decreases, resulting in a decrease in the strength of the product and a rougher surface; if the particle size of the hemihydrate gypsum is too low, although the initial hydration rate is increased to some extent, too many fine particles will cause the internal water to be not easily discharged, and it will also prolong the drying time and hardening time and reduce the production efficiency. At the same time, the tiny defects formed inside the hardened material may become stress concentration points, weakening the mechanical strength of the finished product.

[0044] Further, in some embodiments, the anhydrite is type II anhydrite, with a free water content of 9% - 12% and a particle size of 10 - 20 μm.

[0045] In the present application, type II anhydrite belongs to a kind of anhydrous gypsum, usually showing poor solubility in water, slow hydration rate, poor setting ability or almost no setting, no early strength, and low additional value utilization rate. By selecting type II anhydrite, its effective utilization rate can be improved and the stacking pressure can be reduced. By controlling the free water content of the anhydrite within the above range, the anhydrite product obtained directly after filtration by the existing anhydrous gypsum wet process (the water content can be controlled at 12% and below after filtration) can be used as the raw material without additional drying process, providing good conditions for reducing the aging time.

[0046] Among them, by controlling the particle size of the anhydrite within the above range, it is not only beneficial to obtain products with high appearance quality and particle strength, but also beneficial to improve production efficiency. If the particle size of the anhydrite is too high, on the one hand, the production efficiency is reduced due to the too slow hydration rate, and on the other hand, due to the large particle voids, the porosity inside the hardened gypsum product increases and the density decreases, resulting in a decrease in the strength of the product and a rougher surface; if the particle size of the anhydrite is too low, although the initial hydration rate is increased to some extent, too many fine particles will cause the internal water to be not easily discharged, also prolong the drying time and hardening time, reduce the production efficiency, and at the same time, the tiny defects formed inside the material after hardening may become stress concentration points, weakening the mechanical strength of the finished product.

[0047] Further, in some embodiments, the mother nucleus is a gypsum particle with a particle size ≤ 5 mm.

[0048] In the present application, by controlling the particle size of the mother nucleus below 5 mm, products with excellent appearance and high mechanical strength can be obtained, avoiding problems such as rough product appearance and low mechanical strength caused by too high particle size of the mother nucleus.

[0049] Further, in some embodiments, the alkaline activator is at least one of calcium oxide, calcium hydroxide or carbide slag.

[0050] In the present application, the main component of the alkaline activator is calcium oxide or calcium hydroxide, and the regulation of pH is milder, which is beneficial to controlling the reaction rate.

[0051] Further, in some embodiments, the free water content of the spherical cement retarder ≤ 10%, and the crystal water content ≥ 10%.

[0052] In this application, by controlling the free water content within 10%, it helps to reduce the caking phenomenon of the material during storage and transportation, improve the fluidity and dispersibility of the product, and facilitate construction operations; by controlling the crystal water content above 10%, it helps to enhance the overall hardness and mechanical strength of the material.

[0053] Further, in some embodiments, the particle size of the spherical cement retarder is 5 - 30 mm, and the proportion of particles with a particle size of 10 - 30 mm is ≥70%.

[0054] In this application, by controlling the particle size of the spherical cement retarder within the above range, the particles are uniform, which is convenient for transportation and avoids the adverse effects of too high or too low particle size on the properties such as the setting time and compressive strength of cement.

[0055] Further, in some embodiments, the 2 - hour cylinder compressive strength of the spherical cement retarder is ≥3 MPa, and the 1 - day cylinder compressive strength is ≥3.5 MPa.

[0056] In this application, by mixing and granulating hemihydrate gypsum, anhydrous gypsum, mother nucleus, alkaline activator and water, not only can the aging time be reduced, but also a spherical cement retarder that meets the standard requirements can be obtained.

[0057] In a second aspect, an embodiment of this application provides a preparation method of a spherical cement retarder, including the following steps: Mix and granulate gypsum powder, mother nucleus, alkaline activator and water to obtain pellets; Cure the pellets to obtain a spherical cement retarder.

[0058] In this application, by mixing, granulating and curing gypsum powder, mother nucleus, alkaline activator and water to prepare a spherical cement retarder, the gypsum can form a denser structure, thereby increasing its mechanical strength and facilitating transportation, storage and use.

[0059] Further, in some embodiments, in the step of mixing and granulating, it further includes: adding water and / or gypsum powder to the granulator.

[0060] In this application, by adding water during the mixing and granulating process, the fluidity and processability of the material can be improved; at the same time, it can also participate in the hydration reaction and accelerate the process of chemical bonding; by adding gypsum powder during the mixing and granulating process, the fluidity and processability of the material can be improved.

[0061] Further, in some embodiments, after the pellets are cured, it further includes: Screen the pellets to obtain a spherical cement retarder.

[0062] In this application, by screening the pelletized product after curing, spherical cement retarders with a suitable particle size distribution can be obtained. At the same time, by recycling the small-sized particles screened out, they can be reused as nuclei, which is beneficial to the smooth progress of the granulation process on the one hand and avoids waste of raw materials on the other hand.

[0063] Further, in some embodiments, a disk granulator is used for mixing granulation. Among them, the rotation speed of the disk granulator is 30 - 50 rpm, and the inclination angle of the disk granulator is 40° - 60°.

[0064] In this application, by controlling the rotation speed and inclination angle of the disk granulator, the particle size distribution can be optimized, the particle quality can be improved, and spherical cement retarders meeting the standard requirements can be obtained. If the rotation speed is too high, problems such as too large particle size or easy fragmentation of the particles will occur; if the rotation speed of the disk granulator is too low, the product molding is slow and a large amount of materials remain. If the inclination angle of the disk granulator is too low, the pellets will stay in the machine for a long time and the pellet size will be too large; if the inclination angle of the disk granulator is too high, the pellets will break due to the force, forming a large number of fine particles. The fragments grow and roll in the disk to form new aggregate prototypes, and some fragments and powders fail to grow well, forming small irregular aggregates.

[0065] Further, in some embodiments, the curing method is natural curing, and the natural curing time is 2 - 24 h.

[0066] In this application, by adopting the method of natural curing for 2 - 24 h, spherical cement retarders meeting the standard requirements can be obtained, which greatly saves the production time.

[0067] Some specific embodiments are listed below. It should be noted that the embodiments described below are exemplary and are only used to explain this application and should not be construed as a limitation to this application. For those technologies or conditions not specified in the embodiments, they shall be carried out according to the technologies or conditions described in the literature in this field or according to the product specifications. For the reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0068] In the following examples and comparative examples, to avoid unnecessary repetition, the preparation methods of hemihydrate gypsum and anhydrous gypsum are as follows: Preparation of α hemihydrate gypsum: Phosphogypsum (with CaSO4·2H2O content of 85% - 90%, free water content of 9% - 12%, and particle size of 5 - 25 μm) is put into an acid solution to prepare a suspension with a solid content of 0.05 g / mL; a stirring paddle is added to the suspension for stirring, and it is kept warm at 94°C for 4.5 hours; the reaction product is filtered while it is hot, washed with hot water and absolute ethanol, and then dried at 50°C to obtain hemihydrate gypsum (with CaSO4·1 / 2H2O content of 65% - 70%, free water content of 9% - 12%, and particle size of 20 - 30 μm). Among them, the acid solution is prepared by mixing concentrated phosphoric acid, concentrated sulfuric acid and water, and the mass concentration of sulfuric acid in the acid solution is 5%, and the mass concentration of phosphoric acid is 40%.

[0069] Preparation of type II anhydrous gypsum: Phosphogypsum (with CaSO4·2H2O content of 85% - 90%, free water content of 9% - 12%, and particle size of 5 - 25 μm) is put into an acid solution to prepare a suspension with a solid content of 0.1 g / mL; a stirring paddle is added to the suspension for stirring, and it is kept warm at 85°C for 3.5 hours; the reaction product is filtered while it is hot, washed with hot water and absolute ethanol, and then dried at 50°C to obtain anhydrous gypsum (with CaSO4 content of 85% - 90%, free water content of 9% - 12%, and particle size of 10 - 20 μm). Among them, the acid solution is prepared by mixing concentrated phosphoric acid, concentrated sulfuric acid and water, and the mass concentration of sulfuric acid in the acid solution is 35%, and the mass concentration of phosphoric acid is 20%.

[0070] I. Preparation method Example 1 A spherical cement retarder is prepared as follows: By mass, 45 parts of hemihydrate gypsum, 55 parts of anhydrous gypsum, 10 parts of mother nucleus, 1.0 part of calcium oxide and 20 parts of water are weighed. The hemihydrate gypsum, anhydrous gypsum and calcium oxide are mixed, and then poured into a disk granulator together with the mother nucleus for mixing granulation. The rotation speed of the disk granulator is set to 50 rpm, and the inclination angle is 60°. During the granulation process, water is sprayed while rotating, and it is judged whether to supplement raw materials according to the actual situation (i.e., the powder content and humidity during the granulation process); after the granulation is completed, the equipment is shut down and natural curing is carried out; after the natural curing is completed, the particles with a particle size > 5 mm are collected for use as the spherical cement retarder, and the fine particles with a particle size ≤ 5 mm are collected for recycling as the mother nucleus.

[0071] Example 2 A spherical cement retarder, by mass, includes: 50 parts of hemihydrate gypsum, 50 parts of anhydrous gypsum, 10 parts of mother nucleus, 1.0 part of calcium oxide and 20 parts of water. Its preparation method is the same as that of Example 1.

[0072] Example 3 A spherical cement retarder, by mass, includes: 55 parts of hemihydrate gypsum, 45 parts of anhydrous gypsum, 10 parts of mother nucleus, 1.0 part of calcium oxide, and 20 parts of water. Its preparation method is the same as that of Example 1.

[0073] Example 4 A spherical cement retarder, by mass, includes: 50 parts of hemihydrate gypsum, 50 parts of anhydrous gypsum, 10 parts of mother nucleus, 0.5 part of calcium oxide, and 20 parts of water. Its preparation method is the same as that of Example 2.

[0074] Example 5 A spherical cement retarder, by mass, includes: 50 parts of hemihydrate gypsum, 50 parts of anhydrous gypsum, 10 parts of mother nucleus, 1.5 parts of calcium oxide, and 20 parts of water. Its preparation method is the same as that of Example 2.

[0075] Example 6 A spherical cement retarder, by mass, includes: 50 parts of hemihydrate gypsum, 50 parts of anhydrous gypsum, 10 parts of mother nucleus, 1.0 part of calcium oxide, and 15 parts of water. Its preparation method is the same as that of Example 2.

[0076] Example 7 A spherical cement retarder, by mass, includes: 50 parts of hemihydrate gypsum, 50 parts of anhydrous gypsum, 15 parts of mother nucleus, 1.0 part of calcium oxide, and 20 parts of water. Its preparation method is the same as that of Example 2.

[0077] Example 8 A spherical cement retarder has the same raw material composition as Example 2. The difference in its preparation method from that of Example 2 is only that the inclination angle of the disk granulator is set to 40°.

[0078] Example 9 A spherical cement retarder has the same raw material composition as Example 2. The difference in its preparation method from that of Example 2 is only that the inclination angle is adjusted to 50°.

[0079] Example 10 A spherical cement retarder has the same raw material composition as Example 2. The difference in its preparation method from that of Example 2 is only that the rotation speed is adjusted to 30 rpm.

[0080] Example 11 A spherical cement retarder has the same raw material composition as Example 2. The difference in its preparation method from that of Example 2 is only that the rotation speed is adjusted to 40 rpm.

[0081] Comparative Example 1 A spherical cement retarder, by mass, includes: 20 parts of hemihydrate gypsum, 80 parts of anhydrous gypsum, 10 parts of mother nucleus, 1.0 part of calcium oxide, and 20 parts of water. Its preparation method is the same as that of Example 2.

[0082] Comparative Example 2 A spherical cement retarder, by mass, includes: 100 parts of hemihydrate gypsum, 0 parts of anhydrous gypsum, 10 parts of mother nucleus, 1.0 part of calcium oxide, and 20 parts of water. Its preparation method is the same as that of Example 2.

[0083] Comparative Example 3 A spherical cement retarder, by mass, includes: 50 parts of hemihydrate gypsum, 50 parts of anhydrous gypsum, 10 parts of mother nucleus, 0 part of calcium oxide, and 20 parts of water. Its preparation method is the same as that of Example 2.

[0084] Comparative Example 4 A spherical cement retarder, by mass, includes: 50 parts of hemihydrate gypsum, 50 parts of anhydrous gypsum, 10 parts of mother nucleus, 4 parts of calcium oxide, and 20 parts of water. Its preparation method is the same as that of Example 2.

[0085] Comparative Example 5 A spherical cement retarder, by mass, includes: 50 parts of hemihydrate gypsum, 50 parts of anhydrous gypsum, 10 parts of mother nucleus, 1.0 part of calcium oxide, and 10 parts of water. Its preparation method is the same as that of Example 2.

[0086] Comparative Example 6 A spherical cement retarder, by mass, includes: 50 parts of hemihydrate gypsum, 50 parts of anhydrous gypsum, 10 parts of mother nucleus, 1.0 part of calcium oxide, and 25 parts of water. Its preparation method is the same as that of Example 2.

[0087] Comparative Example 7 A spherical cement retarder, by mass, includes: 50 parts of hemihydrate gypsum, 50 parts of anhydrous gypsum, 5 parts of mother nucleus, 1.0 part of calcium oxide, and 20 parts of water. Its preparation method is the same as that of Example 2.

[0088] Comparative Example 8 A spherical cement retarder, by mass, includes: 50 parts of hemihydrate gypsum, 50 parts of anhydrous gypsum, 0 part of mother nucleus, 1.0 part of calcium oxide, and 20 parts of water. Its preparation method is the same as that of Example 2.

[0089] Comparative Example 9 A spherical cement retarder, by mass, includes: 50 parts of hemihydrate gypsum, 50 parts of anhydrous gypsum, 30 parts of mother nucleus, 1.0 part of calcium oxide, and 20 parts of water. Its preparation method is the same as that of Example 2.

[0090] Comparative Example 10 A spherical cement retarder has the same raw material composition as Example 2. The difference in its preparation method from that of Example 2 is only that the inclination angle is adjusted to 15°.

[0091] Comparative Example 11 A spherical cement retarder, having the same raw material composition as that of Example 2. The difference in its preparation method from that of Example 2 is only that the inclination angle is adjusted to 75°.

[0092] Comparative Example 12 A spherical cement retarder, having the same raw material composition as that of Example 2. The difference in its preparation method from that of Example 2 is only that the rotation speed is adjusted to 20 rpm.

[0093] Comparative Example 13 A spherical cement retarder, having the same raw material composition as that of Example 2. The difference in its preparation method from that of Example 2 is only that the rotation speed is adjusted to 60 rpm.

[0094] In the above-mentioned examples and comparative examples, the preparation parameters of the spherical cement coagulant are shown in Table 1.

[0095] Table 1 Preparation parameters of spherical cement retarder in each example and comparative example

[0096] II. Test methods Test for the cylinder compressive strength of spherical cement retarder: Sieving the test specimens with a particle size range of 5 - 30 mm to ensure that the volume content of particles with a particle size of 10 - 30 mm in the test specimens accounts for 70% - 80%. Conduct drying treatment on the test specimens to eliminate the influence of moisture on the test results. Load the test specimens into a bearing cylinder (with a bottom), measure the loose material weights three times respectively, and take the arithmetic mean. Multiply the measured average loose material weight value by the filling coefficient (the filling coefficient is taken as 1.10) to obtain the amount of test specimens. Weigh the test specimens according to the above amount of test specimens, load them into the bearing cylinder, and first gently tap the cylinder wall around with a wooden hammer several times to densify the aggregate. Install the guiding cylinder and the stamping die on the bearing cylinder to ensure that the upper edge of the guiding cylinder is aligned with the lower scale line of the stamping die. Place the bearing cylinder on the lower platen of the press and apply a load at a uniform speed of about 300 N / s per second. When the pressing depth of the stamping die is 20 mm, record the pressure value (N). The cylinder compressive strength, in MPa, is calculated according to the following formula: Cylinder compressive strength = Pressure value when the pressing depth is 20 mm / Bearing area (i.e., the area of the stamping die).

[0097] Test for the setting time of cement: Detect its initial setting time and final setting time in accordance with GB / T 1346 - 2011 "Test Methods for Water Requirement of Normal Consistency, Setting Time and Soundness of Cement".

[0098] Preparation of cement test blocks: Mix ordinary Portland cement, spherical cement retarder and water evenly according to a mass ratio of 100:3:25, then press them into shape. After curing at room temperature for 24 h, demold and cure at room temperature until the specified age (3 days or 28 days) to obtain cement test blocks.

[0099] Flexural Strength Test of Cement Specimens: The specimens are beam-shaped samples. The standard specimen length is 550 mm, a prism of 150 mm×150 mm×550 mm, with a length tolerance less than ±1 mm and width and thickness tolerances of ±0.05 mm. Place the specimen on the supporting fixture of the testing machine to ensure that the specimen is on the support and in close contact. Apply the load vertically on the specimen uniformly at a constant rate of 50 N / s through the loading cylinder until the specimen breaks. Record the maximum load and deformation data of the specimen before breaking. The flexural strength, in MPa, is calculated by the following formula: Flexural strength = maximum load / (specimen width × specimen height × specimen span).

[0100] Compressive Strength Test of Cement Specimens: The specimens are cube samples. The standard specimen size is a cube of 150 mm×150 mm×150 mm with a tolerance of ±2 mm. Place the specimen in the pressure fixture of the testing machine to ensure close contact between the specimen and the fixture. Detect the maximum resistance of the specimen by gradually increasing the load. The loading rate can be adjusted according to the test requirements. The loading rate for this test is set at 10 KN / S. Record the load and deformation data of the specimen during compression until the specimen fails. The compressive strength, in MPa, is calculated by the following formula: Compressive strength = failure load / specimen bearing area.

[0101] III. Analysis of Test Results of Each Example and Comparative Example Table 2 Effects of Different α-Hemihydrate Gypsum Dosages on Particle Size Distribution, Free Water, Crystal Water, 2h Cylinder Compressive Strength, and 1d Cylinder Compressive Strength

[0102] Table 3 Effects of Different α-Hemihydrate Gypsum Dosages on Cement Setting Time, 3d Strength, and 28d Strength

[0103] Table 4 Effects of Different Calcium Oxide Dosages on Particle Size Distribution, Free Water, Crystal Water, 2h Cylinder Compressive Strength, and 1d Cylinder Compressive Strength

[0104] Table 5 Effects of Different Calcium Oxide Dosages on Cement Setting Time, 3d Strength, and 28d Strength

[0105] Table 5 Effects of Different Water Dosages on Particle Size Distribution, Free Water, Crystal Water, 2h Cylinder Compressive Strength, and 1d Cylinder Compressive Strength

[0106] Table 7 Effects of Different Water Dosages on Cement Setting Time, 3d Strength, and 28d Strength

[0107] Table 8 Effects of Different Dosages of the Mother Nucleus on Particle Size Distribution, Free Water, Crystal Water, 2h Cylinder Compressive Strength and 1d Cylinder Compressive Strength

[0108] Table 9 Effects of Different Dosages of the Mother Nucleus on Setting Time, 3d Strength and 28d Strength of Cement

[0109] Table 10 Effects of Different Inclination Angles on Particle Size Distribution, Free Water, Crystal Water, 2h Cylinder Compressive Strength and 1d Cylinder Compressive Strength

[0110] Table 11 Effects of Different Inclination Angles on Setting Time, 3d Strength and 28d Strength of Cement

[0111] Table 12 Effects of Different Rotation Speeds on Particle Size Distribution, Free Water, Crystal Water, 2h Cylinder Compressive Strength and 1d Cylinder Compressive Strength

[0112] Table 13 Effects of Different Rotation Speeds on Setting Time, 3d Strength and 28d Strength of Cement

[0113] Please refer to Tables 1 - 13. It can be seen from Tables 1 - 13 that the particle size of the spherical cement retarder prepared in the embodiments of the present application is 5 - 30 mm, and the proportion of particles with a particle size of 10 - 30 mm is ≥70%; the free water content of the spherical cement retarder is ≤10%, and the crystal water content is ≥10%; the 2h cylinder compressive strength of the spherical cement retarder is ≥3 Mpa, and the 1d cylinder compressive strength is ≥3.5 Mpa.

[0114] Furthermore, after the spherical cement retarder prepared in the embodiments of the present application is used in cement products, the initial setting time is ≥130 min, the final setting time is ≤280 min, the 3d flexural strength of the cement specimen is ≥6 MPa, the 3d compressive strength is ≥30 MPa, the 28d flexural strength of the cement specimen is ≥7.5 MPa, and the 28d compressive strength is ≥38 MPa. It can be seen that the spherical cement retarder prepared by the method of the present application has a good retarding effect on the cement specimen, and the compressive strength of the cement specimen is high.

[0115] It can be seen from Examples 1 - 3 and Comparative Examples 1 - 2 that as the proportion of hemihydrate gypsum in the gypsum powder increases, the particle size, free water content, crystal water content, and cylinder compressive strength of the spherical cement retarder all show an upward trend. The proportion of hemihydrate gypsum in the gypsum powder is preferably in the range of 45% - 55%. If the proportion of hemihydrate gypsum in the gypsum powder is too low, the particle size of the spherical cement retarder will be too small, and properties such as crystal water content will not meet the requirements; if the proportion of hemihydrate gypsum in the gypsum powder is too high, the particle size of the spherical cement retarder will be too large. Although the cylinder compressive strength of the spherical cement retarder increases, properties such as free water content cannot meet the requirements, and the initial setting time of the cement products made with the above spherical cement retarder will also be significantly reduced.

[0116] It can be seen from Example 2, Examples 4 - 5 and Comparative Examples 3 - 4 that as the CaO content increases, the particle size and crystal water content of the spherical cement retarder both show an upward trend, and the free water content generally shows a downward trend. The content of CaO is preferably in the range of 0.5 parts - 1.5 parts. If no CaO is added, the particle size of the spherical cement retarder will be too small, and properties such as free water content will not meet the requirements, and the initial setting time of the cement products made with the above spherical cement retarder will also be significantly reduced; if the CaO content is too high, the particle size of the spherical cement retarder will be too large. Although the setting retardation performance of the cement products made with the above spherical cement retarder is improved, it will lead to a decrease in compressive strength.

[0117] It can be seen from Example 2, Example 6 and Comparative Examples 5 - 6 that the water content is preferably in the range of 15 parts - 20 parts. If the water content is too low, the pellets cannot be formed; if the water content is too high, the pellets will stick together seriously.

[0118] It can be seen from Example 2, Examples 7 and Comparative Examples 7 - 9 that as the mother nucleus content increases, the particle size of the spherical cement retarder shows a trend of first increasing and then decreasing. The content of the mother nucleus is preferably in the range of 10 parts - 15 parts. If no mother nucleus is added, the mother nucleus content is too low, or the mother nucleus content is too high, it will all lead to too small particle size of the spherical cement retarder, and a spherical cement retarder that meets the requirements cannot be obtained.

[0119] It can be seen from Example 2, Examples 8 - 9 and Comparative Examples 10 - 11 that as the inclination angle of the disk granulator increases, the particle size of the spherical cement retarder shows a downward trend. The inclination angle of the disk granulator is preferably in the range of 40° - 60°. If the inclination angle of the disk granulator is too low, the particle size of the spherical cement retarder will be too large; if the inclination angle of the disk granulator is too high, a large number of fine particles will be formed due to particle breakage, resulting in too small particle size of the spherical cement retarder, and a spherical cement retarder that meets the requirements cannot be obtained.

[0120] It can be seen from Example 2, Examples 10-11 and Comparative Examples 12-13 that as the rotational speed of the disk granulator increases, both the particle size and the cylinder compressive strength of the spherical cement retarder show an upward trend. The rotational speed of the disk granulator is preferably in the range of 30 rpm - 50 rpm. If the rotational speed of the disk granulator is too low, it will lead to slow product formation and a large amount of material remaining, affecting production efficiency; if the rotational speed of the disk granulator is too high, it will result in a relatively large particle size of the spherical cement retarder, and the initial setting time and final setting time of the cement products made with the above spherical cement retarder will also be significantly reduced.

[0121] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments having the same composition and the same effect within the technical scope of this application are included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways constructed by combining some of the constituent elements of the embodiments are also included in the scope of this application.

Claims

1. A spherical cement retarder, characterized in that, The raw materials for preparing the spherical cement retarder, by mass fraction, include: 100 parts of gypsum powder, 10 - 20 parts of mother nucleus, 0.5 - 1.5 parts of alkaline activator, and 15 - 20 parts of water; Among them, the raw materials of the gypsum powder include hemihydrate gypsum and anhydrous gypsum, and the hemihydrate gypsum accounts for 45% - 55% of the total mass of the gypsum powder; the mother nucleus is gypsum particles obtained by blending the gypsum powder and the water, followed by mixing granulation and screening.

2. The spherical cement retarder according to claim 1, wherein The hemihydrate gypsum is α-hemihydrate gypsum, with a free water content of 9% - 12% and a particle size of 20 - 30 μm; and / or, The anhydrous gypsum is type II anhydrous gypsum, with a free water content of 9% - 12% and a particle size of 10 - 20 μm.

3. The spherical cement retarder according to claim 1, characterized in that, The mother nucleus is gypsum particles with a particle size ≤ 5 mm.

4. The spherical cement retarder according to claim 1, wherein The alkaline activator is at least one of calcium oxide, calcium hydroxide, or carbide slag.

5. The spherical cement retarder according to claim 1, characterized in that, The spherical cement retarder has a particle size of 5 - 30 mm, and the proportion of particles with a particle size of 10 - 30 mm is ≥ 70%; and / or, The spherical cement retarder has a free water content ≤ 10% and a crystal water content ≥ 10%.

6. A method for preparing the spherical cement retarder according to any one of claims 1 - 5, comprising the following steps: Mixing and granulating the gypsum powder, mother nucleus, alkaline activator, and water to obtain pellets; Curing the pellets to obtain the spherical cement retarder.

7. The preparation method of the spherical cement retarder according to claim 6, characterized in that, In the step of mixing and granulating, it further includes: adding supplementary water and / or gypsum powder to the granulator.

8. The preparation method of the spherical cement retarder according to claim 6, characterized in that, After the pellets are cured, it further includes: Screening the pellets to obtain the spherical cement retarder.

9. The preparation method of the spherical cement retarder according to claim 6, characterized in that, Using a disk granulator for mixing and granulating, wherein the rotation speed of the disk granulator is 30 - 50 rpm, and the inclination angle of the disk granulator is 40° - 60°.

10. The preparation method of the spherical cement retarder according to claim 6, characterized in that, The curing method is natural curing, and the time for natural curing is 2 - 24 h.

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