A method for reducing the dehydration temperature when gypsum raw materials are converted into gypsum variants

Abstract

The present invention relates to the technical field of calcium sulfate chemical industry, and particularly relates to a method for reducing the dehydration temperature when gypsum raw materials are transformed into gypsum variants; by controlling the overall process parameters: the moisture content in the raw material system, the reaction temperature and reaction time, the stirring rate, the pH value of the reaction system, the addition amount of the crystal water destroyer and the crystal modifier, etc., the lowest temperature for the transformation of CaSO4·2H2O into β - hemihydrate gypsum can be 86.08°C, and the lowest temperature for the transformation of β - hemihydrate gypsum into type II anhydrous gypsum can be 146.95°C, that is, the dehydration temperature during phase change is significantly reduced; moreover, the present invention can also reduce the water requirement for standard consistency by regulating the crystal form of the gypsum variant, so as to obtain a gypsum-based product with better performance.

Description

Technical Field

[0001] The invention relates to the technical field of calcium sulfate chemical industry, and in particular to a method for reducing the dehydration temperature when gypsum raw materials are transformed into gypsum variants. Background Art

[0002] Industrial by-product gypsum refers to the by-product or waste residue with calcium sulfate as the main component generated by chemical reactions in industrial production. It is also called chemical gypsum or industrial waste gypsum, such as phosphogypsum, titanium gypsum, citric acid gypsum, etc. Its main component is calcium sulfate dihydrate (CaSO 4 ·2H 2 O), when losing 1.5 or 2 molecules of crystal water, it can be transformed into hemihydrate gypsum (β-hemihydrate gypsum) or anhydrous gypsum.

[0003] The main technical difficulties in the above methods are:

[0004] 1) CaSO 4 ·2H 2 When O is converted into hemihydrate gypsum or anhydrous gypsum, the calcination process consumes high energy and produces large emissions;

[0005] 2) When producing high-quality hemihydrate gypsum or anhydrous gypsum, due to different process parameters, the crystal forms of the obtained finished products vary greatly, and the yield of high-quality finished products is not high.

[0006] To solve the above problems, the inventors have designed a method for preparing different gypsum variants by lowering the calcination temperature / crystal transformation, aiming to reduce the energy consumption required for dehydration while preparing gypsum variant products with good performance. Summary of the invention

[0007] In order to solve the above problems, the present invention provides a method for reducing the dehydration temperature when the gypsum raw material is converted into a gypsum variant, which can significantly reduce the CaSO 4 ·2H 2 The invention discloses a method for preparing high-quality β-hemihydrate gypsum, ...

[0008] It is worth noting that the present invention does not protect the following CaSO 4 ·2H 2 The principle of O conversion into β-hemihydrate gypsum or type II anhydrous gypsum:

[0009] 1) The existing crystal water destroyer itself and its mechanism of promoting the formation of β-hemihydrate gypsum into type II anhydrous gypsum;

[0010] 2) The existing crystal-modifying agent itself and its principle of controlling grain growth;

[0011] The focus of the present invention is:

[0012] On the basis of obtaining high-quality β-hemihydrate gypsum and type II anhydrous gypsum, CaSO 4 ·2H 2 The invention discloses an overall process method for converting β-hemihydrate gypsum into 86.08°C, and converting β-hemihydrate gypsum into anhydrous gypsum at a minimum temperature of 146.95°C, including the moisture content in the raw material system, reaction temperature and reaction time, stirring rate, pH value of the reaction system, addition amount of crystal water destroying agent and crystal regulating agent, etc.

[0013] The present invention provides a method for reducing the dehydration temperature when gypsum raw materials are converted into gypsum variants, comprising the following steps:

[0014] S1, according to the quality of gypsum raw materials M 1 , water content a%, and CaSO in gypsum raw materials 4 ·2H 2 O content b%, add a crystal water destroying agent and a crystal adjusting agent to the gypsum raw material, mix them evenly to obtain a mixed system;

[0015] Among them, the mass of the crystal water destroyer is M 2 , the mass fraction of the solute in the crystal water destroyer is (1-c)%, and the mass fraction of water in the crystal water destroyer is c%;

[0016] The mass of the crystal modifier is M 3 , the mass fraction of solute in the crystal modifier is (1-d)%, and the mass fraction of water in the crystal water destroyer is d%;

[0017] S2, heat the mixed system to make CaSO 4 ·2H 2 O is transformed into a gypsum variant, and then the target product is obtained through cooling and screening, and the gypsum variants include β-hemihydrate gypsum and type II anhydrous gypsum;

[0018] Among them, CaSO 4 ·2H 2 The phase transition temperature when O transforms to β-hemihydrate gypsum is T β The phase transition temperature of β-hemihydrate gypsum to type II anhydrous gypsum is T Ⅱ ;

[0019] When the following is true:

[0020]

[0021] Can constrain T β and T Ⅱ Satisfy the following formula:

[0022]

[0023] Furthermore, the gypsum raw material is CaSO 4 ·2H 2 The gypsum of O includes one or more combinations of natural gypsum, phosphogypsum, titanium gypsum, desulfurized gypsum, boric gypsum, mirabilite gypsum or citric acid gypsum.

[0024] Furthermore, the particle size of the gypsum raw material is ≤2.36 mm. Controlling the particle size of the gypsum raw material not only helps to facilitate the subsequent mixing of raw materials, but also helps the gypsum to reach the required transition temperature faster during the calcination stage, and can improve the uniformity of the final product.

[0025] Furthermore, the crystal water destroying agent has an ionization constant Ka>10 -7 The acid includes an organic acid or an inorganic acid; the inorganic acid is any one of sulfuric acid, aminosulfonic acid, phosphoric acid, hydrochloric acid, nitric acid, etc.; the organic acid is any one of oxalic acid, citric acid, acetic acid, etc.

[0026] Furthermore, the crystal modifier is an organic crystal modifier and / or an inorganic crystal modifier; the organic crystal modifier is any one of maleic acid, tartaric acid, succinic acid, sodium citrate, etc.; the inorganic crystal modifier is any one of aluminum sulfate, calcium oxide, etc.

[0027] Furthermore, the crystal water destroying agent and the crystal modulating agent in S1 are added by external addition, and the adding method is: the gypsum raw material is stirred under set parameters, and the crystal water destroying agent and the crystal modulating agent are uniformly added at a frequency of 1 to 2 drops / 30s during stirring; the set parameters are: the self-rotating speed of the mixer is 140±2r / min, and the rotating speed is 62±2r / min.

[0028] Furthermore, the CaSO 4 ·2H 2 The heating parameters for the transformation of O into β-hemihydrate gypsum are: heating from 20°C to T at a rate of 5-10°C / min. β , keep warm for 2 to 2.5 hours, and finally cool to 30°C with the furnace.

[0029] Furthermore, the CaSO 4 ·2H 2 The heating parameters for the transformation of O into type II anhydrous gypsum are: first, the temperature is raised from 20°C to T at a rate of 5-10°C / min. β , keep warm for 3 to 5 minutes; then increase the temperature from T to β Heating to T Ⅱ , keep warm for 2 to 2.5 hours; finally cool to 30℃ with the furnace.

[0030] Compared with the existing gypsum variant preparation method, the present invention has the following beneficial effects:

[0031] (1) The design scheme of the present invention can significantly reduce CaSO 4 ·2H 2 The invention discloses a method for preparing high-quality β-hemihydrate gypsum, ...

[0032] (2) The design scheme of the present invention can reduce the water requirement of standard consistency by regulating the crystal form of gypsum variants, thereby obtaining gypsum-based products with better performance.

[0033] (3) The present invention reduces the dehydration temperature of gypsum, thereby significantly reducing production energy consumption and emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is the TG-DSC curve diagram of Example 1;

[0035] Figure 2 is the XRD pattern of Example 1;

[0036] Figure 3 is the XRD pattern of Example 2;

[0037] Figure 4 It is the TG-DSC curve diagram of Comparative Example 1;

[0038] Figure 5 is the XRD pattern of Comparative Example 1;

[0039] Figure 6 This is the XRD pattern of Comparative Example 2. DETAILED DESCRIPTION

[0040] In order to further illustrate the method and effect of the present invention, the technical solution of the present invention will be clearly and completely described in combination with experiments.

[0041] Example 1: This example describes a method for reducing the dehydration temperature when a gypsum raw material is converted into a gypsum variant. The target product in this example is type II anhydrous gypsum.

[0042] S1. The raw material of gypsum is: phosphogypsum, which is in the original state of dry irregular granules, with a moisture content of 0% and a content of calcium sulfate dihydrate of 89.60%;

[0043] S2, crystal water destroying agent: 40% sulfuric acid by mass;

[0044] S3-1, take 4kg of phosphogypsum and crush it to less than 2.36mm, seal and store for later use;

[0045] S3-2, take 200g of the above phosphogypsum into a stirring pot; take 8.78g of sulfuric acid with a mass fraction of 40%, stir at a speed of 142r / min and a rotational speed of 64r / min, and add dropwise at a frequency of 1 to 2 drops / 30s until the dropwise addition is complete and the components are uniform, to obtain a mixture;

[0046] S4-1, take 30 mg of the mixture in S3-2 for simultaneous thermal analysis test, and obtain the TG-DSC curve: heat the crucible containing the mixture in a muffle furnace, first increase the temperature from 20°C to 86.08°C at a rate of 5°C / min, and keep it warm for 3 minutes; then increase the temperature from 86.08°C to 280°C at a rate of 15°C / min, and keep it warm for 2 hours; finally cool it to 30°C in the furnace and take out the sample;

[0047] S4-2. Take 3 g of a sample with a constant weight and pass it through a 200-mesh sieve, and analyze its phase composition through XRD testing.

[0048] Example 2: This example describes a method for reducing the dehydration temperature when a gypsum raw material is converted into a gypsum variant. The target product in this example is a mixed phase of dihydrate gypsum and β-hemihydrate gypsum.

[0049] S1, gypsum raw materials: phosphogypsum, the original state is muddy, the water content is 13.92%, and the content of calcium sulfate dihydrate is 86.09%;

[0050] S2, crystal water destroying agent: 20% sulfuric acid by mass;

[0051] S3-1. Since the original state of gypsum raw materials is muddy, it does not need to be crushed and can be used directly;

[0052] S3-2, take 200g of the above phosphogypsum and transfer it to a stirring pot; take 7.26g of sulfuric acid with a mass fraction of 20%, stir it at a speed of 138r / min and a rotational speed of 60r / min, and add it dropwise at a frequency of 1 to 2 drops / 30s until the dripping is completed and the components are uniform, to obtain a mixture;

[0053] S4-1, take 30 mg of the mixture in S3-2 for simultaneous thermal analysis test, and obtain the TG-DSC curve: heat the crucible containing the mixture in a muffle furnace, first increase the temperature from 20°C to 86.08°C at a rate of 5°C / min, and keep it warm for 3 minutes; then increase the temperature from 86.08°C to 120°C at a rate of 15°C / min, and keep it warm for 2 hours; finally cool it to 30°C in the furnace and take out the sample;

[0054] S4-1. Take 3 g of a sample with a constant weight and pass it through a 200-mesh sieve, and analyze its phase composition through XRD testing.

[0055] Example 3: This example describes a method for reducing the dehydration temperature when gypsum raw materials are converted into gypsum variants. The target product in this example is type II anhydrous gypsum.

[0056] S1. The raw material of gypsum is: phosphogypsum, which is originally in the form of dry irregular granules, with a moisture content of 0% and a calcium sulfate dihydrate content of 89.60%;

[0057] S2, the crystal water destroying agent is 40% sulfuric acid by mass; the crystal regulating agent is aluminum sulfate;

[0058] S3-1. Weigh 4 kg of phosphogypsum and crush it to less than 2.36 mm, and seal it for later use;

[0059] S3-2, take 200g of the above phosphogypsum into a stirring pot; take 8.78g of sulfuric acid with a mass fraction of 40%, stir at a speed of 140r / min and a rotational speed of 62r / min, and add dropwise at a frequency of 1 to 2 drops / 30s until the dropwise addition is complete and the components are uniform, to obtain a mixture;

[0060] S3-3, on the basis of S3-2, 1.31 mL of 2 mol / L aluminum sulfate solution was uniformly dripped into the crucible at a frequency of 1 to 2 drops / 30 s to ensure uniform composition, thereby obtaining a mixture;

[0061] S4-1, take 30 mg of the mixture in S3-3 for synchronous thermal analysis test, and obtain the TG-DSC curve: heat the crucible containing the mixture in a muffle furnace, first increase the temperature from 20°C to 86.08°C at a rate of 5°C / min, and keep it warm for 3 minutes; then increase the temperature from 86.08°C to 280°C at a rate of 15°C / min, and keep it warm for 2 hours; finally cool it to 30°C in the furnace and take out the sample;

[0062] S4-2. Take 3 g of a sample with a constant weight and pass it through a 200-mesh sieve, and analyze its phase composition through XRD testing.

[0063] Example 4: The description of this example is based on the scheme in Example 3, and is intended to illustrate the scheme design under another parameter.

[0064] S1, gypsum raw material composition: water content 15%, calcium sulfate dihydrate content 60%;

[0065] S2, the crystal water destroying agent is oxalic acid with a mass fraction of 80%; the crystal adjusting agent is sodium citrate;

[0066] S3-1. Weigh 4 kg of gypsum raw material and crush it to less than 2.36 mm, and seal it for later use;

[0067] S3-2, take 200g of the above gypsum raw material into a stirring pot; take 0.128g of oxalic acid, stir at a speed of 140r / min and a rotational speed of 62r / min, and add at a constant speed of 1 to 2 drops / 30s until the dripping is completed and the components are uniform, to obtain a mixture;

[0068] S3-3, on the basis of S3-2, 0.173 mL of 2 mol / L sodium citrate solution was uniformly dripped into the crucible at a frequency of 1 to 2 drops / 30 s to ensure uniformity of the components, thereby obtaining a mixture;

[0069] S4-1. Heat the crucible containing the mixture in S3-3 in a muffle furnace. First, heat it from 20°C to 86.08°C at a rate of 5°C / min and keep it warm for 3 minutes. Then, heat it from 86.08°C to 280°C at a rate of 15°C / min and keep it warm for 2 hours. Finally, cool it to 30°C in the furnace and take out the sample.

[0070] Example 5: The description of this example is based on the scheme in Example 3, and is intended to illustrate the scheme design under another parameter.

[0071] S1, gypsum raw material composition: moisture content 0%, calcium sulfate dihydrate content 99.60%;

[0072] S2, the crystal water destroying agent is oxalic acid with a mass fraction of 80%; the crystal adjusting agent is sodium citrate;

[0073] S3-1. Weigh 4 kg of gypsum raw material and crush it to less than 2.36 mm, and seal it for later use;

[0074] S3-2, take 200g of the above gypsum raw material into a stirring pot; take 12.45g of oxalic acid, stir at a speed of 140r / min and a rotational speed of 62r / min, and add dropwise at a frequency of 1 to 2 drops / 30s until the dropwise addition is complete and the components are uniform, to obtain a mixture;

[0075] S3-3, based on S3-2, 10.16 mL of 2 mol / L sodium citrate mixture was dripped into the crucible at a rate of 1 to 2 drops / 30 s to ensure uniform composition, thereby obtaining a mixture;

[0076] S4-1. Heat the crucible containing the mixture in S3-3 in a muffle furnace. First, heat it from 20°C to 146°C at a rate of 10°C / min and keep it warm for 5 minutes. Then, heat it from 146°C to 440.85°C at a rate of 20°C / min and keep it warm for 2 hours. Finally, cool it to 30°C in the furnace and take out the sample.

[0077] Comparative Example 1: This comparative example describes a method for converting a gypsum raw material into a gypsum variant, and the target product is type II anhydrous gypsum.

[0078] S1. The raw material of gypsum is: phosphogypsum, which is originally in the form of dry irregular granules, with a moisture content of 0% and a calcium sulfate dihydrate content of 89.60%;

[0079] S2. Weigh 4 kg of phosphogypsum and crush it to less than 2.36 mm, and seal it for later use;

[0080] S3, directly weigh 200g of the crushed phosphogypsum without adding any components, and put it into a crucible;

[0081] S4, take 30 mg of the above phosphogypsum for synchronous thermal analysis test to obtain the TG-DSC curve, heat the crucible containing the phosphogypsum in a muffle furnace, and heat the temperature from 20°C to 400°C at a rate of 15°C / min for 2 hours. After the heating is completed, the temperature in the furnace drops to 30°C and then take out the sample;

[0082] S5. Take 3 g of a sample with a constant weight and pass it through a 200-mesh sieve, and analyze its phase composition through XRD testing.

[0083] Comparative Example 2: This comparative example describes a method for converting a gypsum raw material into a gypsum variant, and the target product is β-hemihydrate gypsum.

[0084] S1, gypsum raw materials: phosphogypsum, the original state is muddy, the water content is 13.92%, and the content of calcium sulfate dihydrate is 86.09%;

[0085] S2, because the original state is muddy, it does not need to be crushed and can be used directly;

[0086] S3. Weigh 200 g of original phosphogypsum directly without adding any components and put it into a crucible;

[0087] S4. Take 30 mg of the above phosphogypsum for simultaneous thermal analysis test to obtain TG-DSC curve. Heat the crucible containing the phosphogypsum in a muffle furnace, and heat the temperature from 20°C to 120°C at a rate of 15°C / min. The heating time is 2h. After the heating is completed, the temperature in the furnace drops to 30°C and then take out the sample.

[0088] S5. Take 3 g of a sample with a constant weight and pass it through a 200-mesh sieve, and analyze its phase composition through XRD testing.

[0089] Experimental Example: The description of this experimental example is based on the contents of the above-mentioned Examples 1 to 2 and Comparative Examples 1 and 2, and is intended to illustrate the actual performance of the product of the present invention.

[0090] 1. Performance test: In order to illustrate the actual performance of the products prepared by the present invention, the following performances in the above examples were tested:

[0091] Test the product in Example 1 and obtain Figure 1 The TG-DSC curves shown in Figure 2 XRD pattern shown;

[0092] Test the product in Example 2 and obtain Figure 3 XRD pattern shown;

[0093] Test the product in Comparative Example 1 and obtain Figure 4 The TG-DSC curves shown in Figure 5 XRD pattern shown;

[0094] Test the product in Comparative Example 2 and obtain Figure 6 XRD pattern shown.

[0095] 2. Performance Characterization

[0096] 2-1. Performance Characterization of Example 1

[0097] 2-1-1. TG-DSC test

[0098] The temperature for conversion into β-hemihydrate gypsum is 86.08℃; the temperature for conversion into type II anhydrous gypsum is 146.95℃.

[0099] The dehydration temperature of phosphogypsum for removing 1.5 or 2 molecules of crystal water was significantly reduced by adding 2% sulfuric acid with a concentration of 40%.

[0100] 2-1-2. XRD test

[0101] By analyzing the phase composition, Example 1 is composed of anhydrous gypsum and a small amount of silicon dioxide.

[0102] Comparing with the PDF card of type II anhydrous gypsum, the main peak formed near 2θ of 25.4° corresponds to the position of the PDF card of type II anhydrous gypsum; and except for a small amount of characteristic peaks of silica, the remaining peaks all correspond to type II anhydrous gypsum.

[0103] That is, at 280°C, adding 2% sulfuric acid with a concentration of 40% can achieve the preparation of single type II anhydrous gypsum.

[0104] 2-2. Performance Characterization of Example 2

[0105] 2-2-1. XRD test

[0106] By analyzing the phase composition, Example 2 is composed of dihydrate gypsum, β-hemihydrate gypsum and a small amount of silicon dioxide.

[0107] When 1% sulfuric acid with a concentration of 20% was added, β-hemihydrate gypsum was obviously generated, and the main peak intensity of dihydrate gypsum near 2θ of 12° was significantly weakened, indicating that sulfuric acid can promote the transformation of dihydrate phase to hemihydrate phase. A mixed phase of dihydrate gypsum and β-hemihydrate gypsum can be prepared under calcination conditions at 120°C.

[0108] 2-3. Performance Characterization of Comparative Example 1

[0109] 2-3-1. TG-DSC test

[0110] The temperature for conversion into β-hemihydrate gypsum is 149.98°C; the temperature for conversion into anhydrous phase is as follows: the DSC curve does not show an obvious endothermic peak. Compared with the XRD results, the conversion temperature is greater than 400°C.

[0111] It can be seen from this that the dehydration temperature of phosphogypsum without the addition of sulfuric acid to remove 1.5 or 2 molecules of crystal water is significantly higher.

[0112] 2-3-2. XRD test

[0113] By analyzing the phase composition, Comparative Example 1 is composed of anhydrous gypsum, β-hemihydrate gypsum and a small amount of silicon dioxide.

[0114] By comparing the PDF cards, it was found that the positions of 2θ of 14.7° and 29.7° still contained β-hemihydrate gypsum peaks; the main peak position was still near 2θ of 25.4°, corresponding to the position of the PDF card of type II anhydrous gypsum peak; the remaining peaks were consistent with Example 1.

[0115] This shows that in the absence of sulfuric acid, increasing the temperature to 400°C cannot achieve the preparation of a single type II anhydrous gypsum. It is worth noting that compared with Example 1, the intensity of the same characteristic main peak is significantly reduced, indicating that the crystallinity of type II anhydrous gypsum is relatively low.

[0116] 2-4. Performance Characterization of Comparative Example 1

[0117] 2-4-2. XRD test

[0118] By analyzing the phase composition, Comparative Example 2 is composed of dihydrate gypsum and a small amount of silicon dioxide.

[0119] This indicates that β-hemihydrate gypsum cannot be generated at 120°C when no sulfuric acid is added.

Claims

1. A method for reducing the dehydration temperature when gypsum raw materials are converted into gypsum variants, characterized in that: The following steps are involved: S1, according to the mass M1 of the gypsum raw material, the water content a%, and the content b% of CaSO4·2H2O in the gypsum raw material, adding a crystal water destroying agent and a crystal modulating agent to the gypsum raw material, and mixing them uniformly to obtain a mixed system; Wherein, the mass of the crystal water destroying agent is M2, the mass fraction of the solute in the crystal water destroying agent is 1-c%, and the mass fraction of water in the crystal water destroying agent is c%; The mass of the crystal modifier is M3, the mass fraction of the solute in the crystal modifier is 1-d%, and the mass fraction of water in the crystal water destroyer is d%; S2, heating the mixed system to convert CaSO4·2H2O into a gypsum variant, and then cooling and screening to obtain a target product, wherein the gypsum variant includes β-hemihydrate gypsum or type II anhydrous gypsum; Among them, the phase transition temperature when CaSO4·2H2O transforms into β-hemihydrate gypsum is T β The phase transition temperature when β-hemihydrate gypsum transforms to type II anhydrous gypsum is T Ⅱ ; When the following conditions are met: Can constrain T β and T Ⅱ Satisfy the following formula: The heating parameters for converting CaSO4·2H2O into β-hemihydrate gypsum are: heating from 20°C to T at a rate of 5-10°C / min. β , keep warm for 2-2.5h, and finally cool to 30℃ with the furnace; The heating parameters for converting CaSO4·2H2O into type II anhydrous gypsum are: first, heating from 20°C to T at a rate of 5-10°C / min. β , keep warm for 3 to 5 minutes; then increase the temperature from T to β Heating to T Ⅱ , keep warm for 2 to 2.5 hours; finally cool to 30°C with the furnace; The gypsum raw material is gypsum containing CaSO4·2H2O, and the crystal water destroying agent has an ionization constant Ka>10 -7 of acid.

2. A method for reducing the dehydration temperature when gypsum raw materials are converted into gypsum variants according to claim 1, characterized in that: The particle size of the gypsum raw material is ≤2.36 mm.

3. A method for reducing the dehydration temperature when gypsum raw materials are converted into gypsum variants as claimed in claim 1, characterized in that: The crystal modifier is an organic crystal modifier and / or an inorganic crystal modifier.

4. A method for reducing the dehydration temperature when gypsum raw materials are converted into gypsum variants according to claim 1, characterized in that: The crystal water destroyer and the crystal modifier in S1 are added by external addition, and the adding method is: the gypsum raw material is stirred under the set parameters, and the crystal water destroyer and the crystal modifier are uniformly added at a frequency of 1 to 2 drops / 30s during stirring; the set parameters are: the self-speed rate of the mixer is 140±2r / min, and the speed rate is 62±2r / min.

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