Modified fluorine-containing gypsum, modified fluorine-containing gypsum product and its manufacturing method

Abstract

Modified fluorine-containing gypsum, modified fluorine-containing gypsum product and method for producing the same. [Solution] The manufacturing method of modified fluorine-containing gypsum includes a step of mixing and grinding quicklime and fluorine-containing gypsum, and a step of adding a naphthalene-based water reducing agent, in which the mass ratio of quicklime to fluorine-containing gypsum is (0.5-1.0):100, the mass ratio of the naphthalene-based water reducing agent to fluorine-containing gypsum is (0.3-0.9):100, and the mixing and grinding time is 15-45 minutes. In response to the problems that exist in directly using fluorine-containing gypsum as a gelling material, the present invention proposes a method of modifying it using quicklime and a naphthalene-based water reducing agent, which is low cost, easy to implement, suitable for industrialized production, and uses a single raw material with a small variety.

Description

[Technical Field]

[0001] The present invention belongs to the field of building materials technology, and specifically relates to modified fluorine-containing gypsum, modified fluorine-containing gypsum products and methods for producing the same. [Background technology]

[0002] Fluorine-containing gypsum is a slag generated when a fluoride salt factory uses fluorite and concentrated sulfuric acid to produce hydrofluoric acid. Its main chemical composition is anhydrous calcium sulfate (type 2), with a certain amount of residual calcium fluoride, sulfuric acid, hydrofluoric acid, a small amount of silica, and a trace amount of Na. + , K. + It contains impurities such as

[0003] Fluorine-containing gypsum has problems such as low grinding efficiency, strong acidity, and poor activity, which restrict its direct use as a gelling material, thereby limiting its large-scale use. The current treatment of fluorine-containing gypsum is still mainly carried out by stacking, which not only occupies a large amount of land but also is a huge waste of resources. In addition, the acidity and soluble F contained in fluorine-containing gypsum that has been stacked for a long time - Toxic and harmful substances such as fluorine-containing gypsum gradually leach out, causing serious pollution of the surrounding soil and groundwater. Fluorine-containing gypsum has a low density, and the dust blown by the wind also has a significant impact on the air and the environment. In recent years, standardized stacking has been adopted in most places, but the high maintenance costs of stacking sites not only reduce the economic benefits of companies, but also become a major constraint on the sustainable development of companies.

[0004] Currently, fluorine-containing gypsum is mainly used as an auxiliary gelling material or as a cement gelling inhibitor in place of natural gypsum dihydrate, and its resource utilization rate is relatively low.

[0005] Therefore, there is a need to provide an improved technical solution to address the shortcomings of the prior art. Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a modified fluorine-containing gypsum, a modified fluorine-containing gypsum product, and a method for producing the same, in order to solve or alleviate the problems existing in the prior art. [Means for solving the problem]

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A step of co-grinding quicklime and fluorine-containing gypsum; further adding a naphthalene-based water reducing agent; A method for producing a modified fluorine-containing gypsum, comprising: a mass ratio of the quicklime to the fluorine-containing gypsum is (0.5 to 1.0):100, and a mass ratio of the naphthalene-based water-reducing agent to the fluorine-containing gypsum is (0.3 to 0.9):100, The method for producing modified fluorine-containing gypsum, wherein the mixing and grinding time is 15 to 45 minutes.

[0009] A modified fluorine-containing gypsum produced by the above-described production method.

[0010] A modified fluorine-containing gypsum product, which is produced using the modified fluorine-containing gypsum.

[0011] The method for producing the above-mentioned modified fluorine-containing gypsum product includes the steps of: (1) stirring the modified fluorine-containing gypsum and water to uniformly mix them to obtain a modified fluorine-containing gypsum slurry; and (2) placing the modified fluorine-containing gypsum slurry in a mold and curing it to obtain the modified fluorine-containing gypsum product.

[0012] In response to the problems inherent in directly using fluorine-containing gypsum as a gelling material, the present invention proposes a method for modifying fluorine-containing gypsum using quicklime and a naphthalene-based water-reducing agent, which is low-cost, easy to implement, suitable for industrial production, and requires only a single raw material with a limited variety.

[0013] By mixing fluorine-containing gypsum with a certain proportion of quicklime and a naphthalene-based water-reducing agent and then grinding (polishing), not only can the grinding efficiency be improved, but the hydration activity of the fluorine-containing gypsum can also be increased, and the elution of fluoride ions can be effectively suppressed. The modified fluorine-containing gypsum of the present invention can be used directly as a gelling material, realizing large-scale resource utilization of fluorine-containing gypsum. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 2 is a diagram showing the effect of the amount of quicklime mixed in on the pH value of fluorine-containing gypsum provided by an embodiment of the present invention. [Figure 2] FIG. 1 is a diagram of the effect of grinding time on the particle size distribution of modified fluorine-containing gypsum particles, where (a) is the particle size distribution and (b) is the cumulative volume. [Figure 3] SEM images of fluorine-containing gypsum after 15 minutes of grinding, (a) without quicklime mixed in, and (b) with 0.75% quicklime mixed in. [Figure 4] FIG. 1 is a comparative XRD diagram of modified fluorine-containing gypsum obtained by pulverization for 15 minutes in Example 2 and pulverized fluorine-containing gypsum in Comparative Example 1. [Figure 5] This figure shows the effect of the amount of water-reducing agent mixed in on the particle size distribution of modified fluorine-containing gypsum, where (a) is the particle size distribution and (b) is the cumulative volume. [Figure 6] FIG. 1 is a graph showing the setting time and standard consistency water consumption results of modified fluorine-containing gypsum with different amounts of water-reducing agent mixed in. [Figure 7] FIG. 1 is a diagram of the transverse strength of modified fluorine-containing gypsum products with different hydration times. [Figure 8] FIG. 1 is a diagram of compressive strength of modified fluorine-containing gypsum products with different hydration times. [Figure 9]1 shows images of modified fluorine-containing gypsum products with different amounts of water-reducing agent after 3 days of hydration. [Figure 10] FIG. 1 is a graph showing the results of hydration rates of modified fluorine-containing gypsum with different amounts of water-reducing agent mixed in. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention provides a method for producing modified fluorine-containing gypsum, which addresses the problems of current fluorine-containing gypsum being inappropriate for use as a direct gelling material and difficult to utilize as a resource on a large scale. The method for producing modified fluorine-containing gypsum includes a step of co-grinding quicklime and fluorine-containing gypsum.

[0016] In the process of co-grinding quicklime and fluorine-containing gypsum, quicklime can play a grinding auxiliary role, which helps to improve the grinding effect of fluorine-containing gypsum, reduce the particle size of fluorine-containing gypsum, and make the particle size of the obtained modified fluorine-containing gypsum more uniform. Quicklime also adjusts the pH and free F. - By acting as setting ions, they also help improve the mechanical performance and hydration rate of modified fluorine-containing gypsum products.

[0017] The method further includes adding a naphthalene-based water reducing agent, which can also serve as a grinding aid in the grinding process of the fluorine-containing gypsum, shorten the setting time of the modified fluorine-containing gypsum, reduce the amount of water used at standard consistency, and help improve the mechanical properties and hydration rate of the modified fluorine-containing gypsum product.

[0018] The mass ratio of quicklime to fluorine-containing gypsum is (0.5 to 1.0):100 (e.g., 0.5:100, 0.6:100, 0.7:100, 0.8:100, 0.9:100, or 1.0:100). The mass ratio of naphthalene-based water-reducing agent to fluorine-containing gypsum is (0.3 to 1.5):100 (e.g., 0.3:100, 0.5:100, 0.7:100, 0.9:100, 1.1:100, 1.2:100, 1.3:100, 1.4:100, or 1.5:100).

[0019] The mass ratio of the naphthalene-based water-reducing agent to the fluorine-containing gypsum is (0.3~0.9):100 (for example, 0.4:100, 0.6:100, or 0.8:100). When the mass ratio of the naphthalene-based water-reducing agent to the fluorine-containing gypsum is (0.3~0.9):100, the modified fluorine-containing gypsum product has a flat surface, no obvious cracks, and good mechanical properties and volume stability.

[0020] The mass ratio of quicklime to fluorine-containing gypsum is 0.75:100, and the mass ratio of naphthalene-based water-reducing agent to fluorine-containing gypsum is 0.9:100.

[0021] Fluorine-containing gypsum is a by-product generated during the production of hydrogen fluoride. Its particle size is 0.3-1.5cm, pH is 2.3, and density is 2.59g / cm. 3 The main mineral composition of fluorine-containing gypsum is type 2 anhydrite, and fluorine-containing gypsum also contains fluorite.

[0022] The effective content of calcium oxide in the quicklime is 80 wt.% or more, and the naphthalene-based water-reducing agent is a commercially available naphthalene-based water-reducing agent.

[0023] The mixed-grinding is carried out in a ball mill, and the mixed-grinding time is 15 to 45 minutes (for example, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, or 45 minutes).

[0024] The ball mill is a Φ50cm×50cm ball mill.

[0025] A modified fluorine-containing gypsum produced by the above-described production method.

[0026] A modified fluorine-containing gypsum product, which is produced using the modified fluorine-containing gypsum.

[0027] A method for producing a modified fluorine-containing gypsum product, comprising: a step (1) of uniformly mixing modified fluorine-containing gypsum with water by stirring to obtain a modified fluorine-containing gypsum slurry; and a step (2) of placing the modified fluorine-containing gypsum slurry in a mold and curing the mold to obtain a modified fluorine-containing gypsum product.

[0028] Curing is performed at a temperature of 20±5°C (e.g., 15°C, 18°C, 20°C, 22°C, 24°C, or 25°C) and a relative humidity of 70%±4% (e.g., 66%, 68%, 70%, 72%, or 74%).

[0029] The modified fluorine-containing gypsum and its manufacturing method, and the modified fluorine-containing gypsum product and its manufacturing method of the present invention will be described in detail below with reference to specific examples.

[0030] In the following examples, the fluorine-containing gypsum used is a by-product generated during the production of hydrogen fluoride. The gray-white spherical particles have a particle size of 0.3 to 1.5 cm, a pH value of 2.3, and a density of 2.59 g / cm. 3 Its main mineral composition is type 2 anhydrite, with small amounts of residual fluorite.

[0031] Quicklime is quicklime powder, and its technical requirements meet the relevant requirements of the industry standard "Quicklime Powder for Construction" (JC / T480-92) and above.

[0032] The naphthalene-based water-reducing agent is a commercially available powder that is brown in color.

[0033] Example 1 The method for producing the modified fluorine-containing gypsum of this example includes the steps of mixing 100 parts by mass of fluorine-containing gypsum with 0.5 parts, 0.75 parts, 1.0 parts, and 1.5 parts by mass of quicklime, placing the mixture in a Φ50 cm×50 cm ball mill and pulverizing for 15 minutes to obtain the modified fluorine-containing gypsum of this example.

[0034] The method for producing the modified fluorine-containing gypsum product of this example is as follows: Step (1): Sequentially adding water and powdered modified fluorine-containing gypsum of this embodiment into a stirring kettle at a set water-to-material ratio, and uniformly mixing and stirring to obtain a modified fluorine-containing gypsum slurry; the amount of water used in the manufacturing process of the modified fluorine-containing gypsum slurry is determined based on the amount of water used for standard consistency; and when the amount of quicklime used is 0.5 parts, 0.75 parts, 1.0 parts, and 1.5 parts, the corresponding water-to-material ratios are 0.28, 0.31, 0.32, and 0.327, respectively; Step (2) of placing the modified fluorine-containing gypsum slurry in step (1) into a mold having predetermined specifications and conducting tests on the setting time and compressive strength, respectively; Step (3) involves testing the setting time and compressive strength of the gypsum slurry using a Vicat apparatus in accordance with the national standard "PLASTERER GYPSUM" (GB / T 28627-2012). The mechanical performance test specimens of the hardened slurry are 40mm x 40mm x 160mm, cured under the conditions of a temperature of 20±5°C and a relative humidity (RH) of 70%±4%. The flexural strength and compressive strength are tested after 3 days, 7 days, and 28 days, respectively, with three specimens tested for each group, and the average value is used as the final result.

[0035] The pH of the fluorine-containing gypsum and the modified fluorine-containing gypsum prepared in this example were measured to determine the effect of the quicklime content on the pH of the fluorine-containing gypsum. The experimental results are shown in FIG. 1.

[0036] As is clear from FIG. 1, quicklime was added from the outside in amounts of 0.5%, 0.75%, 1.0%, and 1.5% of the mass of the fluorine-containing gypsum, respectively. The pH of the modified fluorine-containing gypsum increased as the amount of quicklime added increased, and when the amount of quicklime added was 0.75%, the pH value reached a neutral value of 7.3.

[0037] Example 2 The method for producing the modified fluorine-containing gypsum of this example includes the steps of mixing 100 parts by mass of fluorine-containing gypsum with 0.75 parts by mass of quicklime, placing the mixture in a Φ50 cm×50 cm ball mill, and pulverizing the mixture for 15 minutes, 30 minutes, and 45 minutes, respectively, to obtain the modified fluorine-containing gypsum of this example.

[0038] The method for producing the modified fluorine-containing gypsum product of this example is as follows: Step (1): water and powdered modified fluorine-containing gypsum of this embodiment are sequentially charged into a stirring kettle at a set water / material ratio, and uniformly mixed and stirred to obtain a modified fluorine-containing gypsum slurry; the amount of water used in the manufacturing process of the modified fluorine-containing gypsum slurry is determined based on the amount of water used for standard consistency, and the water / material ratios corresponding to the grinding times of 15 minutes, 30 minutes, and 45 minutes are 0.31, 0.35, and 0.38, respectively; Step (2) of placing the modified fluorine-containing gypsum slurry in step (1) into a mold having predetermined specifications and conducting tests on the setting time and compressive strength, respectively; Step (3) involves testing the setting time and compressive strength of the gypsum slurry using a Vicat device in accordance with the national standard "Plastering Gypsum" (GB / T 28627-2012). The mechanical performance test specimens of the hardened slurry are 40mm x 40mm x 160mm, cured under the conditions of a temperature of 20±5°C and a relative humidity (RH) of 70%±4%. The flexural strength and compressive strength are tested after 3 days, 7 days, and 28 days, respectively. Each group tests three specimens, and the final result is the average value.

[0039] Example 3 The method for producing the modified fluorine-containing gypsum of this example includes the steps of mixing 100 parts by mass of fluorine-containing gypsum with 0.75 parts by mass of quicklime and 0.3 parts, 0.6 parts, 0.9 parts, 1.2 parts, and 1.5 parts by mass of a naphthalene-based water-reducing agent, placing the mixture in a Φ50 cm×50 cm ball mill, and pulverizing the mixture for 15 minutes to obtain the modified fluorine-containing gypsum of this example.

[0040] The method for producing the modified fluorine-containing gypsum product of this example is as follows: Step (1): Sequentially adding water and powdered modified fluorine-containing gypsum of this embodiment into a stirring vessel at a set water / material ratio, and uniformly mixing and stirring to obtain a modified fluorine-containing gypsum slurry; the amount of water used in the manufacturing process of the modified fluorine-containing gypsum slurry is determined based on the amount of water used for standard consistency; when the amount of naphthalene-based water reducer used is 0.3 parts, 0.6 parts, 0.9 parts, 1.2 parts, and 1.5 parts, the corresponding water / material ratios are 0.396, 0.382, 0.37, 0.312, and 0.232, respectively; Step (2) of placing the modified fluorine-containing gypsum slurry in step (1) into a mold having predetermined specifications and conducting tests on the setting time and compressive strength, respectively; Step (3) involves testing the setting time and compressive strength of the gypsum slurry using a Vicat device in accordance with the national standard "Plastering Gypsum" (GB / T 28627-2012). The mechanical performance test specimens of the hardened slurry are 40mm x 40mm x 160mm, cured under the conditions of a temperature of 20±5°C and a relative humidity (RH) of 70%±4%. The flexural strength and compressive strength are tested after 3 days, 7 days, and 28 days, respectively. Each group tests three specimens, and the final result is the average value.

[0041] Comparative Example 1 The method for producing the ground fluorine-containing gypsum of this comparative example includes the step of placing 100 parts by mass of fluorine-containing gypsum in a Φ50 cm × 50 cm ball mill and grinding for 15 minutes to obtain the ground fluorine-containing gypsum of this comparative example.

[0042] The method for producing the pulverized fluorine-containing gypsum product of this comparative example is as follows: Step (1): water and powdered fluorine-containing gypsum of this comparative example are sequentially added to a stirring vessel at a set water / material ratio (0.2), and then uniformly mixed and stirred to obtain a pulverized fluorine-containing gypsum slurry; Step (2) of placing the ground fluorine-containing gypsum slurry in step (1) into a mold of predetermined specifications and conducting tests on the setting time and compressive strength, respectively; Step (3) involves testing the setting time and compressive strength of the gypsum slurry using a Vicat device in accordance with the national standard "Plastering Gypsum" (GB / T 28627-2012). The mechanical performance test specimens of the hardened slurry are 40mm x 40mm x 160mm, cured under the conditions of a temperature of 20±5°C and a relative humidity (RH) of 70%±4%. The flexural strength and compressive strength are tested after 3 days, 7 days, and 28 days, respectively. Each group tests three specimens, and the final result is the average value.

[0043] Comparative Example 2 The comparative example includes a step of modifying fluorine-containing gypsum with a polycarboxylic acid-based water-reducing agent instead of a naphthalene-based water-reducing agent, mixing 100 parts by mass of fluorine-containing gypsum and 0.75 parts by mass of quicklime with 0.3 parts by mass of the polycarboxylic acid-based water-reducing agent, and pulverizing the mixture in a Φ50 cm×50 cm ball mill for 15 minutes to obtain the modified fluorine-containing gypsum of this comparative example.

[0044] The method for producing the modified fluorine-containing gypsum product of this comparative example is as follows: Step (1) of sequentially adding water and powdered modified fluorine-containing gypsum of this comparative example to a stirring vessel at a set water / material ratio (0.26, determined based on the amount of water used for standard consistency), and uniformly mixing and stirring them to obtain a modified fluorine-containing gypsum slurry; Step (2) of placing the modified fluorine-containing gypsum slurry in step (1) into a mold having predetermined specifications and conducting tests on the setting time and compressive strength, respectively; Step (3) involves testing the setting time and compressive strength of the gypsum slurry using a Vicat device in accordance with the national standard "Plastering Gypsum" (GB / T 28627-2012). The mechanical performance test specimens of the hardened slurry are 40mm x 40mm x 160mm, cured under the conditions of a temperature of 20±5°C and a relative humidity (RH) of 70%±4%. The flexural strength and compressive strength are tested after 3 days, 7 days, and 28 days, respectively. Each group tests three specimens, and the final result is the average value.

[0045] Experimental example 1. The particle size distribution of the modified fluorine-containing gypsum produced in Example 2 and the pulverized fluorine-containing gypsum produced in Comparative Example 1 was measured; The particle size distribution diagram is shown in FIG. 2, and the particle size characterization parameters are shown in Table 1 below.

[0046] [Table 1] Table 1: Particle size characterization of modified fluorine-containing gypsum and ground fluorine-containing gypsum

[0047] As can be seen from Figure 2 and Table 1, the addition of quicklime during the 15-minute grinding clearly reduced the particle size of the fluorine-containing gypsum, and the D v (90) decreased from 176 μm to 60.2 μm, improving the grinding efficiency. Quicklime exerted a good grinding-aid dispersion effect. However, with increasing grinding time, small particles gradually aggregated due to the collision extrusion of the grinding body, and the particle size gradually increased.

[0048] 2. The micromorphology of the modified fluorine-containing gypsum (with 0.75% quicklime content) produced by pulverizing for 15 minutes in Example 2 and the pulverized fluorine-containing gypsum (without quicklime content) produced by pulverizing for 15 minutes in Comparative Example 1 was observed, and the XRD patterns, main chemical compositions, and soluble F of both were analyzed. - The content was measured.

[0049] The SEM images of the modified fluorine-containing gypsum (with 0.75% quicklime content) produced by pulverization for 15 minutes in Example 2 and the pulverized fluorine-containing gypsum (without quicklime content) produced by pulverization for 15 minutes in Comparative Example 1 are shown in Fig. 3(b) and Fig. 3(a), respectively, and the XRD patterns are shown in Fig. 4. The chemical compositions and soluble F - The contents were as shown in Table 3 below.

[0050] [Table 3] Table 3: Main chemical composition / wt.% of modified fluorine-containing gypsum ground for 15 min in Example 2 and ground fluorine-containing gypsum ground for 15 min in Comparative Example 1

[0051] As can be seen from Figure 3, the addition of quicklime made the particle size of the fluorine-containing gypsum after grinding more uniform, the particle surface roughened, and the shape tended to become spherical.

[0052] As can be seen from Figure 4, the diffraction peaks of the fluorine-containing gypsum characterization after grinding were significantly enhanced, and the crystal grain size and structural regularity were also significantly improved by the grinding aid effect of quicklime. Furthermore, the diffraction peaks of fluorite were significantly enhanced, and the content of fluorite increased from 3.63% to 8.48%. The increase in the fluorite content was also beneficial to the grinding of fluorine-containing gypsum.

[0053] From Table 3, the soluble F of the modified fluorine-containing gypsum - The ion content decreased by 80.7%. The following reactions may occur during the milling process: CaO+2H + +2F - →CaF2↓+H2O (1)

[0054] 3. The effect of quicklime on the performance of fluoride-containing gypsum was considered. (1) The setting and hardening performance of the modified fluorine-containing gypsum in Example 2, which was produced by pulverizing for 15 minutes and contained 0.75% quicklime, was compared with that of the pulverized fluorine-containing gypsum in Comparative Example 1, which was produced by pulverizing for 15 minutes without adding quicklime. The test results are shown in Table 4 below.

[0055] [Table 4] Table 4: Comparison of the physical properties of fluorine-containing gypsum products obtained with and without quicklime mixing during grinding

[0056] Table 4 shows the effect of quicklime on the setting and hardening performance of fluorine-containing gypsum. The grinding aid of quicklime significantly reduced the particle size of the fluorine-containing gypsum, resulting in an increase in the amount of water used at standard consistency. Smaller particle size meant that the specific surface area of ​​the fluorine-containing gypsum was larger, which was beneficial for the progress of the hydration reaction, increasing the hydration and hardening rate and shortening the setting time. The mechanical performance of the fluorine-containing gypsum product also improved, and the effect of quicklime on improving the strength of the fluorine-containing gypsum product became more apparent after 28 days, preventing the occurrence of later strength regression in the fluorine-containing gypsum product.

[0057] (2) The hydration rates of the modified fluorine-containing gypsum produced by pulverizing for 15 minutes in Example 2, in which the amount of quicklime mixed was 0.75%, and the pulverized fluorine-containing gypsum produced by pulverizing for 15 minutes in Comparative Example 1, in which no quicklime was mixed, were measured, respectively. The hydration rate was measured using a muffle furnace in accordance with the national standard "Building Gypsum - Determination of Crystal Water Content" (GB / T17669.2-1999), and the dihydrate gypsum content and hydration rate of fluorine-containing gypsum were calculated. The test results are shown in Table 5 below.

[0058] [Table 5] Table 5: Comparison of hydration rates of fluorine-containing gypsum with and without quicklime mixing during grinding

[0059] The hydration rate of fluorine-containing gypsum also increased after adding quicklime grinding aid, as shown in Table 5. The increase in hydration rate was small within 1 day, and the hydration rate increased significantly after 1 day of solidification. This law was consistent with the mechanical performance.

[0060] 4. Water reducers are a common additive in the application of gelling materials. Although the particle size distribution of fluorine-containing gypsum after grinding is smaller, this increases the amount of standard consistency water used, which is detrimental to performance development. Grinding aids not only improve the grinding efficiency of materials during the grinding process, but also reduce energy consumption and improve powder performance. Therefore, we explored the effect of naphthalene-based water reducers as grinding aids on the performance of fluorine-containing gypsum and clarified the grinding aid modification mechanism.

[0061] The particle size distribution of the modified fluorine-containing gypsum of Example 3 was measured, and the effects of different water-reducing agent contents on the particle size distribution of the fluorine-containing gypsum after grinding were as shown in FIG. 5 and Table 6 below.

[0062] [Table 6] Table 6: Effect of water-reducing agents on the grinding aid effect of fluorine-containing gypsum

[0063] The results demonstrated that naphthalene-based water-reducing agents can play a "grinding aid" role in the grinding process of fluorine-containing gypsum. The particle size distribution of the fluorine-containing gypsum first gradually became finer and more concentrated with increasing amounts of water-reducing agent. When the amount of water-reducing agent was 0.6%, the particle size distribution reached a minimum, after which the particle size increased as excess particles gradually aggregated. The specific surface area of ​​the fluorine-containing gypsum particles also first increased and then decreased with increasing amounts of water-reducing agent.

[0064] According to the results in Table 6, when the amount of water-reducing agent mixed is 0.6%, the fluorine-containing gypsum particles have a median diameter D v (90) decreased to 37.8 μm, and D v (50) decreased to 3.76 μm, and D v (10) decreased to 0.394 μm and the specific surface area was 472.1 m 2 / kg.

[0065] The presence of an appropriate amount of water-reducing agent increases the mutual dispersion of fluorine-containing gypsum particles during the grinding process, and the water-reducing agent gradually adheres to the particle surface, reducing mutual extrusion collisions between particles and reducing the occurrence of particle agglomeration and grinding. However, if too much water-reducing agent is used within the same grinding time, the surface roughness increases, the specific surface area increases, and the surface energy increases, causing mechanical interlocking between particles and inducing agglomeration, which is detrimental to grinding efficiency.

[0066] 5. The effect of naphthalene-based water-reducing agents on the solidification and hardening performance of modified fluorine-containing gypsum was examined. (1) The standard consistency water requirement and setting time of the modified fluorine-containing gypsum with different amounts of water-reducing agent in Example 3 were measured; The grinding aid effect of water-reducing agents increases the grinding efficiency of fluorinated gypsum, so the standard consistency water requirement for fluorinated gypsum slurry first rises and then falls with increasing water-reducing agent content, as shown in Figure 6. When the amount of water-reducing agent is low, the fluorinated gypsum particles become more fragmented, and the water-reducing agent adheres to the particle surface, increasing the charge repulsion between particles, but the increase in specific surface area is the main factor, increasing the water requirement. As the amount of water-reducing agent gradually increases, the degree of dispersion between particles increases, and the water requirement decreases.

[0067] The setting time of fluorine-containing gypsum decreased with increasing water-reducing agent content. At low water-reducing agent content, the particle size of fluorine-containing gypsum became finer, thereby increasing the dissolution rate and nucleation rate of gypsum dihydrate, accelerating the precipitation and growth of gypsum dihydrate crystals, and accelerating the hydration process, resulting in shorter setting times. As the amount of water-reducing agent increased and the amount of standard consistency water used decreased, the spacing between slurry particles became smaller, making it easier for the gypsum dihydrate to form a hardened structure after the hydration reaction, shortening the setting time. The initial and final setting times of the slurry decreased from 421 and 554 min in the control group to 104 and 237 min, respectively, at a water-reducing agent content of 1.5%.

[0068] The water requirement and setting time were measured according to the national standard "Plastering Gypsum" (GB / T 28627-2012).

[0069] (2) Measuring the mechanical properties of the hardened fluorine-containing gypsum (modified fluorine-containing gypsum) for different times in Example 3; The mechanical properties of hardened fluorine-containing gypsum at different times tended to increase first and then decrease as the amount of water-reducing agent increased, and both reached a maximum when the amount of water-reducing agent was 0.9%.

[0070] In Figure 7, the flexural strength of the fluorine-containing gypsum with a mixing amount of 0.9% increased from 1.9 MPa for the control group (with no mixing amount of naphthalene-based water-reducing agent, i.e., the sample numbered 1 in Table 6) to 5.4 MPa after 3 days of hydration, an increase of 184.2%. The flexural strength after 7 days of hydration increased from 5.2 MPa for the control group to 9.1 MPa, an increase of 75.0%. The flexural strength after 28 days of hydration increased from 7.9 MPa for the control group to 11.2 MPa, an increase of 41.8%.

[0071] 8, the compressive strengths of the control group after 3 days, 7 days, and 28 days of hydration were 3.5 MPa, 7.6 MPa, and 10.0 MPa, respectively. When the amount of water-reducing agent mixed in was 0.9%, the compressive strengths of the fluoride-containing gypsum after 3 days, 7 days, and 28 days of hydration increased to 12.0 MPa, 21.1 MPa, and 28.9 MPa, respectively, which were increases of 243%, 178%, and 189%, respectively.

[0072] In Figure 9, for samples containing 0-0.9% water-reducing agent, the modified fluorinated gypsum products had a flat surface with no obvious cracks after 3 days of hydration. For samples containing 1.2% and 1.5% water-reducing agent, obvious cracks appeared on the surface of the modified fluorinated gypsum products after 3 days of hydration. The higher the water-reducing agent content, the shorter the setting time of the fluorinated gypsum slurry, making it easier for the fluorinated gypsum to form a hardened structure. However, because the volume of the dihydrate gypsum crystals generated by hydration is much larger than that of the fluorinated gypsum, after forming a stable hardened structure, as hydration continues, the dihydrate gypsum crystals continue to grow, causing their internal volume to expand, leading to the destruction of the hardened structure, a decrease in volume stability, and a significant decrease in the mechanical performance of the samples, until obvious cracks appeared on the sample surface. This was the main reason for the shorter setting time and decreased mechanical performance of the fluorinated gypsum after increasing the water-reducing agent content.

[0073] 6. The effect of different hydration times of naphthalene-based water reducers on the hydration rate of fluorine-containing gypsum was investigated. As shown in Figure 10, the effect of water-reducing agent on the hydration rate of fluorine-containing gypsum can be divided into two stages depending on the hydration time. Before 3 days of hydration, the hydration rate increased with increasing water-reducing agent content, from 37.68% in the control group to 66.81% when the water-reducing agent content was 0.9%, and peaked at 69.28% when the water-reducing agent content was 1.5%, which also conformed to the law of setting time. The increase in the hydration rate was primarily due to the increase in the dissolution rate of fluorine-containing gypsum and the nucleation rate of gypsum dihydrate.

[0074] After 3 days of hydration, the increase in the hydration rate of fluorinated gypsum with a water-reducing agent content above 0.9% slowed, while the hydration rate of fluorinated gypsum with a water-reducing agent content below 0.9% steadily increased. At 28 days, the hydration rate reached a maximum of 84.21% when the water-reducing agent content was 0.9%. The hydration rates for the control and 1.5% water-reducing agents were 45.37% and 75.71%, respectively. This result was consistent with the mechanical properties. After the water-reducing agent content exceeded 0.9%, cracks in the fluorinated gypsum specimens led to the dissipation of water from the specimens, disrupting the initial liquid phase environment and hindering the sustainability of the hydration reaction, which was unfavorable for improving the hydration rate.

[0075] 7. The particle size, mechanical properties and hydration rate of the product obtained by modifying the fluorine-containing gypsum with the polycarboxylic acid water-reducing agent in Comparative Example 2 were tested, and the test results are shown in Tables 7 to 9 below.

[0076] [Table 7] Table 7: Particle size characterization of modified fluorine-containing gypsum at 0.3% polycarboxylic acid water-reducing additive loading.

[0077] [Table 8] Table 8: Performance of modified fluorine-containing gypsum at 0.3% polycarboxylic acid water-reducing agent loading

[0078] [Table 9] Table 9: Hydration rate of modified fluorine-containing gypsum when the amount of polycarboxylic acid water-reducing agent mixed is 0.3%

[0079] From Tables 7 to 9 above, it can be seen that polycarboxylic acids have high water-reducing efficiency and can play an obvious role in the grinding-assisted modification of fluorine-containing gypsum, but they also have a suppression effect on the mechanical properties of the modified products, and the hydration rate is low.

Claims

1. A method for producing modified fluorine-containing gypsum, comprising a step of mixing and grinding quicklime, a naphthalene-based water-reducing agent, and fluorine-containing gypsum, a mass ratio of the quicklime to the fluorine-containing gypsum is 0.75:100, and a mass ratio of the naphthalene-based water-reducing agent to the fluorine-containing gypsum is (0.3 to 0.9):100, The fluorine-containing gypsum is a by-product generated during the production of hydrogen fluoride, the particle size of the fluorine-containing gypsum is 0.3 to 1.5 cm, the pH value is 2.3, and the density is 2.59 g / cm3, the main mineral composition of the fluorine-containing gypsum is type 2 anhydrite, and the fluorine-containing gypsum also contains fluorite, The effective content of calcium oxide in the quicklime is 80 wt. % or more, The method for producing modified fluorine-containing gypsum, wherein the mixing and grinding time is 15 minutes.

2. 2. The method for producing modified fluorine-containing gypsum according to claim 1, wherein the naphthalene-based water reducing agent is a commercially available naphthalene-based water reducing agent.

3. A method for producing a modified fluorine-containing gypsum product using the modified fluorine-containing gypsum produced by the production method according to claim 1 or 2, Step (1) of uniformly mixing the modified fluorine-containing gypsum and water by stirring to obtain a modified fluorine-containing gypsum slurry; Step (2) of placing the modified fluorine-containing gypsum slurry into a mold and curing it to obtain the modified fluorine-containing gypsum product; A method for producing a modified fluorine-containing gypsum product, comprising:

4. The curing is characterized by a temperature of 20±5°C and a relative humidity of 70%±4%. The method for producing a modified fluorine-containing gypsum product according to claim 3,

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