阅读说明：本技术 一种基准石膏的制备方法及其在检测外加剂中的应用 (Preparation method of reference gypsum and application of reference gypsum in detection of additives ) 是由 李泽钢 陈尚伟 朱国良 罗通 徐立斌 周灵 何信周 陈亦苏 廖昶 聂晓鹏 崔晨 于 2021-07-06 设计创作，主要内容包括：本发明属于石膏改性技术领域,具体涉及一种基准石膏的制备方法及其在检测外加剂中的应用；采用乙二胺四乙酸和硅酸酐制成一种改性剂,对天然石膏进行表面改性处理,使其物相构成为：半水相石膏(HH)含量≥75％,二水相石膏(DH)含量＜3％,可溶性无水相石膏(AⅢ)含量＜3％。且制备得到的石膏可作为基准石膏,对石膏外加剂的性能进行测试评价。(The invention belongs to the technical field of gypsum modification, and particularly relates to a preparation method of reference gypsum and application of the reference gypsum in detection of an additive; a modifier is prepared from ethylenediamine tetraacetic acid and silicic anhydride, and the natural gypsum is subjected to surface modification treatment to make the phase composition of the natural gypsum: the content of semi-aqueous phase gypsum (HH) is more than or equal to 75 percent, the content of two-aqueous phase gypsum (DH) is less than 3 percent, and the content of soluble anhydrous phase gypsum (AIII) is less than 3 percent. And the prepared gypsum can be used as reference gypsum for testing and evaluating the performance of the gypsum admixture.)

1. A preparation method of reference gypsum is characterized in that natural gypsum is used as a raw material and is prepared by pretreatment, dehydration, stir-frying in different times, aging and modification, and the fineness of the obtained reference gypsum is 200 meshes of screen residue and is less than or equal to 5%.

2. The method of claim 1, wherein the parching is performed in two steps, and the first parching and the second parching are performed after the dewatering and before the aging.

3. The method for preparing reference gypsum as claimed in claim 2, wherein the first parching is carried out at a temperature of 120 ℃ and 150 ℃ for 5-20 min.

4. The method as claimed in claim 2, wherein the second parching is carried out at 130-180 deg.C for 100-200 min.

5. The method of claim 1, wherein the modifying step is carried out by modifying the surface crystal form of the gypsum with a modifying agent.

6. The method of claim 5, wherein the modifier comprises, in percent: 0.20 to 0.45 percent of ethylenediamine tetraacetic acid, 0.15 to 0.20 percent of silicic anhydride and the balance of water.

7. The method of claim 1, comprising the steps of:

(1) pretreatment: selecting natural gypsum with the gypsum grade not lower than 85% to remove impurities and screen, screening out coarse particle impurities, and reserving fine particles;

(2) and (3) dehydrating: removing attached water by using hot flue gas or fried tail gas;

(3) frying for the first time: adopting a fluidization calciner to fry the gypsum obtained in the step (2);

(4) and (3) frying for the second time: then, the mixture is fried by adopting a fluidized calciner, enters a homogenizing bin for aging after being modified, ground and ground, and a vent pipe is arranged in the homogenizing bin;

so as to hydrate the anhydrous gypsum component contained in the gypsum powder and convert the anhydrous gypsum component into the semi-hydrated gypsum

(5) Modification treatment: and after aging, adding a modifier accounting for 3-5% of the weight of the gypsum for modification to obtain the reference gypsum.

8. The reference gypsum is characterized by comprising the following main chemical components: SO (SO)₃The content is more than or equal to 38 percent, the content of CaO is more than or equal to 26.6 percent, and Cl^-Less than or equal to 0.06 percent and less than or equal to 0.2 percent of water-soluble phosphorus pentoxide.

9. The reference gypsum of claim 8, wherein the phases are: the content of semi-aqueous phase gypsum (HH) is more than or equal to 75 percent, the content of two-aqueous phase gypsum (DH) is less than 3 percent, and the content of soluble anhydrous phase gypsum (AIII) is less than 3 percent.

10. An application of standard gypsum in performance detection of a gypsum admixture.

Technical Field

The invention belongs to the technical field of gypsum modification, and particularly relates to a preparation method of reference gypsum and application of the reference gypsum in detection of an additive.

Background

Gypsum is a monoclinic mineral and has a major chemical component of calcium sulfate (CaSO)₄) A hydrate of (1). Gypsum is a widely used industrial and building material. Can be used for cement retarders, gypsum building products, model making, medical food additives, sulfuric acid production, paper fillers, paint fillers and the like.

The general term gypsum can broadly refer to both raw gypsum and anhydrite minerals. The gypsum is calcium sulfate dihydrate (Ca [ SO ]₄〕·2H₂O), also called dihydrate gypsum, water gypsum or soft gypsum, is calcined and ground to obtain beta-type hemihydrate gypsum (2 CaSO)₄·H₂O), namely building gypsum, also called plaster and plaster.

Patent document CN201610357630.3 discloses a crystal transformation agent for producing alpha-type high-strength gypsum, which is prepared by mixing one or more of phthalic acid and its salt, phthalic acid derivative, phthalate derivative, and phthalic anhydride in any proportion. However, phthalic acid has certain toxicity, and the toxicity LD50(mg/kg) is that rats can take orally 7900.

Patent document CN201410721543.2 discloses a method and a device for preparing high-strength alpha hemihydrate gypsum by using phosphogypsum, wherein a crystal transformation agent prepared by compounding sodium citrate and aluminum sulfate is disclosed. However, the crystal transformation effect of sodium citrate is not ideal when phosphogypsum is treated and applied to natural gypsum.

Disclosure of Invention

The invention provides a preparation method of reference gypsum and application of the reference gypsum in detecting an additive, aiming at solving the problems.

The method is realized by the following technical scheme:

a preparation method of reference gypsum comprises the following steps:

1. pretreatment: selecting natural gypsum with the gypsum grade not lower than 85% to remove impurities and screen, screening out coarse particle impurities, and reserving fine particles;

2. and (3) dehydrating: removing attached water by using hot flue gas or fried tail gas;

3. frying for the first time: adopting a fluidization calciner to fry the gypsum obtained in the step (2);

further, the frying temperature for the first time is 120-.

4. And (3) frying for the second time: frying by adopting a fluidized calciner again;

further, the second stir-frying is carried out at the stir-frying temperature of 130-.

5. Aging: after being ground by a modifying mill, the gypsum powder enters a homogenizing chamber for aging, and a vent pipe is arranged in the homogenizing chamber so as to hydrate the anhydrous gypsum component contained in the gypsum powder and convert the anhydrous gypsum component into semi-hydrated gypsum;

6. modification treatment: and after aging, adding a modifier accounting for 3-5% of the weight of the gypsum for modification to obtain the reference gypsum.

Further, the modifier comprises the following components in percentage by weight: 0.20 to 0.45 percent of ethylenediamine tetraacetic acid, 0.15 to 0.20 percent of silicic anhydride and the balance of water.

Furthermore, the silicic anhydride can be replaced by acetic anhydride.

Further, preparing the resulting benchmarkThe gypsum comprises the following main chemical components: SO (SO)₃The content is more than or equal to 38 percent, the content of CaO is more than or equal to 26.6 percent, and Cl^-Less than or equal to 0.06 percent and less than or equal to 0.2 percent of water-soluble phosphorus pentoxide (dry basis). The phase composition is as follows: the content of semi-aqueous phase gypsum (HH) is more than or equal to 75 percent, the content of two-aqueous phase gypsum (DH) is less than 3 percent, and the content of soluble anhydrous phase gypsum (AIII) is less than 3 percent. The fineness is 200 meshes and the screen residue is less than or equal to 5 percent.

Further, the prepared reference gypsum can be used as a reference, and the performance of the gypsum admixture is tested and evaluated according to the following method:

(1) water reducing agent:

measuring the water consumption of the standard consistency of a sample by taking the reference gypsum according to GB/T17669.4-1999 Chapter 6, wherein when the expansion diameter of the slurry is 180mm +/-5 mm, the measured water consumption is the water consumption of the standard consistency;

adding a water reducing agent into the reference gypsum, uniformly stirring to obtain detected gypsum, measuring the detected gypsum according to a measuring method of GB/T17669.4-1999 Chapter 6, and calculating the water consumption when the extended diameter of the slurry is 180mm +/-5 mm;

the ratio of the difference between the water consumption of the standard phosphogypsum and the detected gypsum to the water consumption of the standard gypsum is the water reduction rate. Tests show that when the reference gypsum prepared by the method is used for testing the water reducing agent, when the mixing amount of the powder water reducing agent is 0.15-0.5%, the water reducing rate is not lower than 10%.

(2) Retarder:

measuring the setting time of the reference gypsum according to GB/T17669.4-1999 Chapter 7, forming 1 group of test pieces according to GB/T9776-2008, curing for 48h in the environment with the temperature of 20 +/-5 ℃ and the humidity of 65 +/-10%, and detecting the flexural strength and the compressive strength;

adding the reference gypsum into the retarder, uniformly stirring to obtain detected phosphogypsum, and correspondingly detecting the detected gypsum according to the steps of the reference gypsum setting time and the bending and compression resistance;

and calculating the difference of the setting time of the detected gypsum and the reference gypsum, calculating the ratio of the flexural strength of the detected gypsum to the reference gypsum, and calculating the ratio of the compressive strength of the detected gypsum to the reference gypsum, thereby comprehensively evaluating the retarding effect of the retarder. Tests show that when the retarder is tested by the reference gypsum prepared by the method, when the doping amount of the powder retarder is 0.15-0.5%, the retarding time is prolonged by 1 hour, and the strength is reduced by no more than 30%.

In conclusion, the beneficial effects of the invention are as follows: the invention adopts ethylene diamine tetraacetic acid and silicic anhydride to prepare a modifier, and carries out surface modification treatment on natural gypsum to ensure that the phase composition of the natural gypsum is as follows: the content of semi-aqueous phase gypsum (HH) is more than or equal to 75 percent, the content of two-aqueous phase gypsum (DH) is less than 3 percent, and the content of soluble anhydrous phase gypsum (AIII) is less than 3 percent. And the prepared gypsum can be used as reference gypsum for testing and evaluating the performance of the gypsum admixture.

Among them, those skilled in the art know that Ethylene Diamine Tetraacetic Acid (EDTA) is a crystallization agent with a good effect, but most of its surface crystal forms are monolayer flaky crystals when natural gypsum is subjected to crystallization, and organic acids have strong crystallization-converting capability to phosphogypsum and desulfurized gypsum, but the crystallization-converting effect to natural gypsum is still not ideal. According to the invention, silicic anhydride and EDTA are adopted in combination, and silicic anhydride and acetic anhydride are selected to effectively prevent most of anhydride from reacting with water to generate corresponding acid, and simultaneously, the gypsum can be ensured to generate long fibers more under hydrothermal conditions, so that the chemical components and phase composition of the gypsum are stable. In the prior art, the modification treatment of natural gypsum is mostly carried out by using a water washing and grinding mode, and the properties of the gypsum obtained by the modification method are easy to change along with the washing times and the grinding degree, so that the obtained gypsum cannot be used as reference gypsum and cannot specify a basic judgment standard for a gypsum admixture.

Detailed Description

The following is a detailed description of the embodiments of the present invention, but the present invention is not limited to these embodiments, and any modifications or substitutions in the basic spirit of the embodiments are included in the scope of the present invention as claimed in the claims.

Example 1

A preparation method of reference gypsum comprises the following steps:

1. selecting natural gypsum with the gypsum grade not lower than 85% to remove impurities and screen, screening out coarse particle impurities, and reserving fine particles;

2. and (3) dehydrating: removing attached water by using hot flue gas or fried tail gas;

3. frying for the first time: d, frying the gypsum obtained in the step 2 by adopting a fluidization calciner;

further, the first frying is carried out at the temperature of 135 ℃ for 12 min.

4. And (3) frying for the second time: frying by adopting a fluidized calciner again;

further, the second frying is carried out, wherein the frying temperature is 160 ℃, and the frying time is 150 min.

5. Aging: after being ground by a modifying mill, the gypsum powder enters a homogenizing chamber for aging, and a vent pipe is arranged in the homogenizing chamber so as to hydrate the anhydrous gypsum component contained in the gypsum powder and convert the anhydrous gypsum component into semi-hydrated gypsum;

6. modification treatment: and after aging, adding a modifier accounting for 4 percent of the weight of the gypsum for modification to obtain the reference gypsum.

Further, the modifier comprises the following components in percentage by weight: 0.35 percent of ethylenediamine tetraacetic acid, 0.17 percent of silicic anhydride and the balance of water.

Through detection, the prepared reference gypsum comprises the following main chemical components: SO (SO)₃40.5% of CaO, 28.1% of CaO, Cl^-The content is 0.04 percent, and the content of the water-soluble phosphorus pentoxide is 0.13 percent. The phase composition is as follows: the content of semi-aqueous phase gypsum (HH) was 80%, the content of two-aqueous phase gypsum (DH) was 2%, and the content of soluble anhydrous phase gypsum (AIII) was 2%. The fineness is 200 meshes and the screen residue is less than or equal to 5 percent.

Through tests, when the reference gypsum prepared by the method is used for testing the water reducing agent, the mixing amount of the powder water reducing agent is 0.3%, and the water reducing rate is 20%.

When the retarder is tested by the reference gypsum prepared by the method, the doping amount of the powder retarder is 0.4%, the retarding time is prolonged by 1 hour, and the strength is reduced by no more than 30%.

Example 2

A preparation method of reference gypsum comprises the following steps:

1. pretreatment: selecting natural gypsum with the gypsum grade not lower than 85% to remove impurities and screen, screening out coarse particle impurities, and reserving fine particles;

2. and (3) dehydrating: removing attached water by using hot flue gas or fried tail gas;

3. frying for the first time: d, frying the gypsum obtained in the step 2 by adopting a fluidization calciner;

further, the first frying is carried out, wherein the frying temperature is 120 ℃, and the frying time is 20 min.

4. And (3) frying for the second time: frying by adopting a fluidized calciner again;

further, the second frying is carried out, wherein the frying temperature is 130 ℃, and the frying time is 200 min.

5. Aging: after being ground by a modifying mill, the gypsum powder enters a homogenizing chamber for aging, and a vent pipe is arranged in the homogenizing chamber so as to hydrate the anhydrous gypsum component contained in the gypsum powder and convert the anhydrous gypsum component into semi-hydrated gypsum;

6. modification treatment: and after aging, adding a modifier accounting for 3 percent of the weight of the gypsum for modification to obtain the reference gypsum.

Further, the modifier comprises the following components in percentage by weight: 0.20 percent of ethylenediamine tetraacetic acid, 0.20 percent of acetic anhydride and the balance of water.

Further, the prepared reference gypsum comprises the following main chemical components: SO (SO)₃38.7 percent of CaO, 26.6 percent of CaO and Cl^-The content is 0.05 percent, and the content of the water-soluble phosphorus pentoxide is 0.11 percent. The phase composition is as follows: the content of semi-aqueous phase gypsum (HH) was 76%, the content of two-aqueous phase gypsum (DH) was 1.8%, and the content of soluble anhydrous phase gypsum (AIII) was 2%. The fineness is 200 meshes and the screen residue is less than or equal to 5 percent.

Through tests, when the reference gypsum prepared by the method is used for testing the water reducing agent, the mixing amount of the powder water reducing agent is 0.15%, and the water reducing rate is 12%.

When the retarder is tested by the reference gypsum prepared by the method, the doping amount of the powder retarder is 0.2%, the retarding time is prolonged by 1 hour, and the strength is reduced by no more than 30%.

Example 3

A preparation method of reference gypsum comprises the following steps:

1. pretreatment: selecting natural gypsum with the gypsum grade not lower than 85% to remove impurities and screen, screening out coarse particle impurities, and reserving fine particles;

2. and (3) dehydrating: removing attached water by using hot flue gas or fried tail gas;

3. frying for the first time: d, frying the gypsum obtained in the step 2 by adopting a fluidization calciner;

further, the first frying is carried out at the temperature of 150 ℃ for 5 min.

4. And (3) frying for the second time: frying by adopting a fluidized calciner again;

further, the second frying is carried out, wherein the frying temperature is 180 ℃, and the frying time is 100 min.

5. Aging: after being ground by a modifying mill, the gypsum powder enters a homogenizing chamber for aging, and a vent pipe is arranged in the homogenizing chamber so as to hydrate the anhydrous gypsum component contained in the gypsum powder and convert the anhydrous gypsum component into semi-hydrated gypsum;

6. modification treatment: and after aging, adding a modifier accounting for 5 percent of the weight of the gypsum for modification to obtain the reference gypsum.

Further, the modifier comprises the following components in percentage by weight: 0.45 percent of ethylenediamine tetraacetic acid, 0.15 percent of silicic anhydride and the balance of water.

Further, the prepared reference gypsum comprises the following main chemical components: SO (SO)₃41.2% of CaO, 27.0% of CaO, Cl^-The content is 0.06 percent, and the content of the water-soluble phosphorus pentoxide is 0.18 percent. The phase composition is as follows: the content of semi-aqueous phase gypsum (HH) was 79%, the content of two-aqueous phase gypsum (DH) was 2%, and the content of soluble anhydrous phase gypsum (AIII) was 1%. The fineness is 200 meshes and the screen residue is less than or equal to 5 percent.

Through tests, when the standard gypsum prepared by the method is used for testing the water reducing agent, the mixing amount of the powder water reducing agent is 0.28%, and the water reducing rate is 17%.

When the retarder is tested by the reference gypsum prepared by the method, the doping amount of the powder retarder is 0.5%, the retarding time is prolonged by 1 hour, and the strength is reduced by no more than 30%.

First, modifier screening experiment

Comparative example 1: in this experiment, the pretreatment was carried out by washing with water under the same conditions as in example 1;

comparative example 2: in this experiment, the modification treatment step was not performed under the same conditions as in example 1;

comparative example 3: in this experiment, the modifier was replaced with the crystal modifier of example 1 in application No. CN201610357630.3 under the same conditions as in example 1;

comparative example 4: in the experiment, under the same conditions as those in example 1, the use amount of the modifier EDTA is changed to 2 percent;

comparative example 5: in the experiment, under the same conditions as those of the example 1, the consumption of silicic anhydride is changed to 2 percent;

comparative example 6: in this experiment, under the same conditions as in example 1, the same amount of succinic anhydride was used instead of silicic anhydride.

The chemical components and phase composition of the gypsum obtained in the above experiment were measured and compared with those of the gypsum obtained in examples 1 to 3, and the results are shown in tables 1 and 2.

TABLE 1 Gypsum Fibrosum chemical composition content table

TABLE 2 Gypsum phase composition test results