CN110156358B - Salt gypsum crystal transformation excitant, preparation method and application - Google Patents
Salt gypsum crystal transformation excitant, preparation method and application Download PDFInfo
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- CN110156358B CN110156358B CN201910285317.7A CN201910285317A CN110156358B CN 110156358 B CN110156358 B CN 110156358B CN 201910285317 A CN201910285317 A CN 201910285317A CN 110156358 B CN110156358 B CN 110156358B
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B11/00—Calcium sulfate cements
- C04B11/02—Methods and apparatus for dehydrating gypsum
- C04B11/024—Ingredients added before, or during, the calcining process, e.g. calcination modifiers
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- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
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- C04B11/00—Calcium sulfate cements
- C04B11/02—Methods and apparatus for dehydrating gypsum
- C04B11/028—Devices therefor characterised by the type of calcining devices used therefor or by the type of hemihydrate obtained
- C04B11/032—Devices therefor characterised by the type of calcining devices used therefor or by the type of hemihydrate obtained for the wet process, e.g. dehydrating in solution or under saturated vapour conditions, i.e. to obtain alpha-hemihydrate
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
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- C04B11/00—Calcium sulfate cements
- C04B11/26—Calcium sulfate cements strating from chemical gypsum; starting from phosphogypsum or from waste, e.g. purification products of smoke
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Abstract
The invention relates to a gypsum salt crystal transformation excitant, and a preparation method thereof, wherein maleic anhydride triethanolamine ester is grafted on acidolysis starch; the method specifically comprises the following steps: acid hydrolysis of starch; synthesizing maleic anhydride triethanolamine ester; grafting the starch after acidolysis to maleic anhydride triethanolamine ester by adopting a semidry method to prepare the gypsum salt crystal transformation excitant. And relates to a method for realizing crystal transformation of the salt gypsum by using the excitant. The excitant can directly carry out hydrothermal crystal transformation on the salt gypsum into alpha-type-high-strength semi-hydrated gypsum by a one-step method, greatly improves the competitive advantage of salt gypsum series products, and realizes large-scale and high-valued resource utilization of the byproduct salt gypsum.
Description
Technical Field
The invention relates to an excitant, in particular to a salt gypsum crystal transformation excitant, a preparation method and a method for realizing crystal form transformation of salt gypsum by using the crystal transformation excitant.
Background
The salt gypsum is a byproduct waste residue in salt manufacturing industry. The byproduct salt gypsum of China is 260 ten thousand tons every year, and is the first in the world. In order to promote the resource utilization of byproduct gypsum such as salt gypsum and the like and save precious natural resources.
Because salt gypsum has small granularity and low strength, is easy to adsorb water and impurities, has high salt content, can reduce the strength of cement if being directly used as a cement additive or a building material product, and can corrode reinforcing steel bars to a certain extent to influence the building safety. Therefore, the salt gypsum can not be directly used as a cement retarder and can not be directly used for preparing building gypsum, and the cost and difficulty of resource utilization of the salt gypsum are much higher than those of desulfurized gypsum and phosphogypsum which are two by-products. A large amount of salt gypsum is accumulated in a factory area or illegally discharged by a salinization enterprise for a long time, so that not only is the land resource waste and the stacking cost increased, but also certain pollution and damage are caused to the coastal environment, and the problem facing and urgently waiting to be solved by salt manufacturing enterprises and governments is formed.
The main raw material of the gypsum product is semi-hydrated gypsum, and the semi-hydrated gypsum is divided into alpha semi-hydrated gypsum and beta semi-hydrated gypsum. Due to the difference of the process conditions when the hemihydrate gypsum is formed, the strength of alpha-type hemihydrate gypsum is far stronger than that of beta-type hemihydrate gypsum. Beta hemihydrate forms when dehydrated in a dry environment, and alpha-hemihydrate forms in a non-dry environment. The beta-hemihydrate gypsum has poor crystallinity of crystal grains, is loose, fine and irregular, is mostly flaky in shape, and is a little sheet crystal form. The alpha-hemihydrate gypsum is relatively intact, coarse and dense in crystallization, so that the specific surface area of the alpha-hemihydrate gypsum is much worse than that of the beta-hemihydrate gypsum. The alpha-type semi-hydrated gypsum crystal forms a high-strength cementing material after being hardened, has the characteristics of strong anti-static medium corrosion effect, smooth surface, small volume change at high temperature and the like, and has less water requirement, higher compactness and strength compared with beta-type semi-hydrated gypsum.
The resource utilization of the overseas industrial byproduct gypsum is more in documents, but the amount of the byproduct salt gypsum is less and the resource utilization of the salt gypsum is not reported much because a vacuum salt making purification technology is adopted.
The hydrothermal excitation crystal transformation process of the common gypsum is simple, and the gypsum salt crystal transformation activator can be divided into inorganic salts and organic acids (salts), wherein the inorganic salts comprise aluminum sulfate, ferric sulfate, aluminum potassium sulfate dodecahydrate (alum) and the like, and the gypsum salt crystal transformation activator comprises anhydrous sodium acetate, sodium citrate, tartaric acid and the like.
The sodium chloride content has a large influence on crystal transformation, when the salt content exceeds 5%, the crystal transformation effect of the traditional gypsum crystal transformation activator is greatly reduced, the length-diameter ratio of crystal grains is gradually increased along with the increase of the salt content, coarse crystals are reduced, fine crystals are increased, the content of beta-type semi-hydrated gypsum in a product is increased, the water requirement of a gypsum product is large, and the final strength is low. Salt gypsum is used as a byproduct in the salt chemical industry, has a large amount of included salt and is not easy to remove, so that the difficulty in crystal transformation and utilization of the salt gypsum is high, and a special-effect salt gypsum crystal transformation excitant with strong salt adaptability and high tolerance needs to be developed.
The research progress at home and abroad is integrated, and the resource utilization of the salt gypsum has two problems, namely high salt content, small particle size and low strength. Aiming at the problem of chloride-containing salt, two means of water washing and recrystallization can be adopted, and because the salt gypsum has small particle size, large specific surface area and is easy to contain chloride, the capacity of directly removing chloride ions by the water washing method is limited; the recrystallization method can obviously increase the particle size of the salt gypsum, reduce the specific surface area, effectively reduce the adsorption and inclusion capacity of the gypsum raw material to the chloride, and reduce the residual content of the salt.
Patent CN101475328A describes a gypsum crystal transformation activator and application thereof in producing building gypsum from salt gypsum, wherein the salt gypsum is recrystallized into dihydrate gypsum by a hydrothermal method, and then the dihydrate gypsum product is calcined into beta-type hemihydrate gypsum which is used as a common gypsum building material. The method effectively reduces the salt content of the reduced salt gypsum through recrystallization, improves the crystal form of the dihydrate gypsum, is beneficial to improving the product quality, but has relatively longer process route and higher energy consumption, and the final product is the beta-type hemihydrate gypsum commonly used for common gypsum building materials, has relatively lower economic added value and unobvious competitive advantage.
Patent CN101734871A describes a method for growing short column-shaped alpha-type semi-hydrated gypsum crystals after the steps of purification treatment, crystal transformation reaction, directional crystallization, washing separation, drying and grinding of desulfurized gypsum; patent CN103011641A describes a method for preparing high-activity alpha-type hemihydrate gypsum cementing material by treating phosphogypsum with chlor-alkali waste liquid. The crystal forms of the desulfurized gypsum and the phosphogypsum are more regular and coarser than those of the salt gypsum, the impurities do not contain chloride salt, and the hydrothermal crystal transformation rule of the desulfurized gypsum and the phosphogypsum is more similar to that of the natural gypsum; however, due to the characteristics of the salt gypsum, the one-step hydrothermal crystal transformation of the salt gypsum into the alpha-type-high-strength semi-hydrated gypsum still has great difficulty, and the development of related research is urgently needed to solve the technical problem.
The one-step method for direct hydrothermal crystal transformation of the salt gypsum is an alpha-type-high-strength semi-aqueous gypsum process route, can greatly improve the competitive advantage of salt gypsum series products, realizes large-scale and high-valued resource utilization of the byproduct salt gypsum, and is beneficial to win-win of environmental protection and economic benefit.
Disclosure of Invention
Maleic anhydride and triethanolamine can be used as organic crystal modifiers for hydrothermal crystal transformation of gypsum, the mixing amount is generally 0.1-0.2%, and the two organic crystal modifiers are high in price, so that the application cost is high. However, like most of organic crystal transformation agents, the crystal transformation effect of maleic anhydride and triethanolamine is obviously reduced under the condition of high salt content, and a better effect can be obtained only by obviously increasing the doping amount, so that the application cost is obviously increased. The starch is used as a renewable resource, has wide source, low price and rich reserves and has a natural high molecular structure. The maleic anhydride triethanolamine ester is grafted to a starch macromolecular chain to form a regular and ordered three-dimensional comb-shaped structure, so that the embedding effect of a gypsum crystallization process on a crystal transfer agent can be reduced, the effective concentration of the crystal transfer agent in a solution is improved, the three-dimensional molecular structure improves the activity of maleic acid and triethanolamine, the crystal transfer efficiency is further improved, the using amount of the maleic anhydride and the triethanolamine is reduced, and the production cost is reduced. Moreover, starch molecules contain a large amount of hydroxyl groups, and the hydroxyl groups can generate complexation with calcium ions in gypsum, so that the synergistic effect with maleic anhydride and triethanolamine is realized, the composite synergistic effect is realized, and the tolerance of the crystal modifier to salt is improved. The hydrothermal crystal transformation is realized by adopting a one-step method, and the method has the advantages of simple and convenient process and short market flow. The method can greatly reduce the waste stone alpha-type high-strength building gypsum. The alpha-type semi-hydrated gypsum has thicker grain diameter and regular crystal form, reduces the adsorption and embedding effects of the gypsum on salt, and greatly reduces the content of the salt in the product.
The technical scheme adopted by the invention is as follows: a method for preparing gypsum salt crystal transformation excitant comprises grafting triethanolamine maleate on acidolysis starch; the method specifically comprises the following steps:
s01 acid hydrolysis of starch;
s02 synthesizing triethanolamine maleate;
s03, grafting the starch after acidolysis to maleic anhydride triethanolamine ester by a semi-dry method to prepare the gypsum salt crystal transformation activator.
Further, the acidolysis starch comprises the following specific processes:
a, adding water into starch to prepare starch milk with the mass content of starch being 40-50%;
b, adding concentrated sulfuric acid into the starch milk and reacting, wherein the mass of the concentrated sulfuric acid is 1-5% of the mass of the starch, the reaction temperature is 20-60 ℃, and the reaction time is 1-2 hours;
and c, after the reaction is finished, carrying out vacuum filtration, washing and drying on the reaction product, and then storing.
Further, the synthesis process of the maleic anhydride triethanolamine ester comprises the following steps: and adding triethanolamine and excessive maleic anhydride into a container, adding a catalyst for catalyzing the reaction of the maleic anhydride and the triethanolamine, and carrying out catalytic reaction for 5-6 h at the reaction temperature of 75-80 ℃ to obtain a maleic anhydride triethanolamine ester and maleic anhydride mixture.
Further, the step S03 is specifically:
a, preparing an aqueous solution of a penetrant, and adding acidolyzed starch into the aqueous solution of the penetrant to obtain a mixed solution I;
b, adding a mixture of maleic anhydride triethanolamine ester and maleic anhydride into the mixed solution I, and uniformly mixing to obtain a mixture II;
and c, putting the mixture II into an oven at the temperature of 70-90 ℃, reacting for 2-4 h, and drying and grinding the product to obtain the gypsum crystal transformation excitant.
Further, the mass ratio of the maleic anhydride to the triethanolamine is 0.02-0.04: 0.015-0.03.
Further, the penetrating agent is sodium carbonate.
Further, the mass ratio of the maleic anhydride to the starch is 0.02-0.04: 1, and the mass ratio of the triethanolamine to the starch is 0.015-0.03: 1.
Further, the starch is corn starch, potato starch, tapioca starch or wheat starch.
Further, the concentrated sulfuric acid concentration is 98%.
Further, the catalyst is p-toluenesulfonic acid.
Further, the starch acidolysis reaction is carried out at 20-60 ℃, and the heating reaction time is 1-2 hours.
Furthermore, the addition amount of the penetrating agent aqueous solution is 5-10% of the dry weight of the starch.
The invention also relates to a gypsum salt crystal transformation excitant prepared by the preparation method of the gypsum salt crystal transformation excitant.
The method for transforming the salt gypsum into the crystal by adopting the salt gypsum crystal transformation excitant comprises the following steps
a, adding water into salt gypsum to prepare slurry with the mass fraction of 15-40%, and placing the slurry into a reaction tank;
b, adding a gypsum salt crystal transformation activator into the reaction tank to perform crystal transformation reaction to obtain alpha-type hemihydrate gypsum;
and c, performing solid-liquid separation on the alpha-type semi-hydrated gypsum slurry after crystallization is completed, washing and drying the solid obtained by the solid-liquid separation to obtain pure alpha-type semi-hydrated gypsum crystals, wherein the washing is performed by using a saturated calcium sulfate hot water solution at the temperature of more than 90 ℃, and the drying temperature is 120-170 ℃.
Furthermore, the mixing amount of the crystal transformation activator of the salt gypsum is 0.1-1% of the weight of the salt gypsum.
The beneficial effects produced by the invention comprise: the invention develops crystal transformation technology by researching and preparing the novel salt gypsum crystal transformation excitant, and can ensure that the salt gypsum is directly transformed into the alpha-type high-strength gypsum through hydrothermal transformation in one step. When the semi-dry method is adopted, due to the fact that the maleic anhydride is properly excessive, the self-reaction can be catalyzed, the excessive maleic anhydride continues to form a graft with starch, the maleic anhydride is the gypsum salt gypsum crystal transformation activator, the crystal transformation efficiency is further improved, and waste materials are avoided due to the self-catalysis effect. And the starch has the characteristics of environmental protection, convenient material taking, low price and simple and convenient treatment. The alpha-hemihydrate gypsum is directly obtained by a one-step method, so that redundant steps are saved, the energy consumption is reduced, and the flow is simplified.
The salt gypsum is treated by using the special-effect salt gypsum crystal transformation activator with strong salt adaptability and high tolerance, so that the crystal transformation mother liquor can be recycled for multiple times. The salt concentration of the crystal transformation mother liquor is gradually increased due to salt accumulation during circulation and application, the salt tolerance of a common crystal transformation agent is low, the crystal transformation efficiency is remarkably reduced due to the salt concentration increase during circulation and application, and repeated circulation and application of the crystal transformation mother liquor are difficult to realize, so that the waste of the crystal transformation agent and the increase of the discharge amount of wastewater are caused.
The product alpha-high-strength semi-hydrated gypsum has small length-diameter ratio, coarse particle size and regular crystal form, is favorable for reducing the salt inclusion and reducing the salt content in the product, and can effectively reduce the residual rate of the salt by washing and filtering through a hot saturated gypsum solution. Because the salt has an erosion effect on the steel bars in the reinforced concrete, the corrosion of the steel bars can be accelerated. And the negative influence on the engineering durability is reduced when the gypsum product is cooperatively used in a steel-concrete structure.
The main characteristics are as follows:
(1) the prepared crystal transformation agent has the advantages of salt tolerance, high efficiency and low cost. The starch is low in cost, a special three-dimensional comb-shaped molecular structure is formed after grafting, the activity of maleic acid and triethanolamine is improved, hydroxyl rich in the starch synergistically promotes the crystal transformation effect of the maleic acid and the triethanolamine through the calcium ion complexing effect, the composite synergy is realized, the tolerance of a crystal transformation agent to gypsum containing salt is improved, and meanwhile, the using amount of the maleic acid and the triethanolamine is effectively reduced.
(2) The method can reduce a large amount of salt gypsum waste residues, save a large amount of land and reduce the problem of environmental pollution caused by the salt gypsum waste residues. Is beneficial to realizing the resource utilization and high-value utilization of the salt gypsum by-product under the condition of high salt content.
(3) The crystal transformation agent prepared by the invention is mainly applied to crystal transformation of the salt gypsum waste residue to prepare the alpha-type high-strength building gypsum, can adapt to 25% of high salt content, can be recycled during production, reduces wastewater discharge and reduces production cost.
(4) The crystal transformation agent can realize direct hydrothermal crystal transformation of salt gypsum into alpha-type high-strength gypsum by one-step method, the method is simple and convenient, the flow is shortened, the energy consumption is reduced, and the crystal transformation efficiency is improved.
(5) The alpha-type high-strength building gypsum prepared by the method has high strength and wide application range, and is beneficial to improving the quality of the gypsum building material and expanding the application field of the gypsum building material. The byproduct gypsum is used as a raw material, so that the production cost is greatly reduced, and the method has obvious economic benefit and competitive advantage. The alpha-type high-strength semi-hydrated gypsum prepared by the hydrothermal crystal transformation method has the advantages of high purity, coarse particle size, regular crystal form, low salt content, small water demand and high strength, and is beneficial to reducing chloride corrosion to reinforcing steel bars in a reinforced concrete structure.
Drawings
FIG. 1 blank set of crystal morphologies;
FIG. 2 Crystal morphology of example 2;
FIG. 3 Crystal morphology of example 3;
FIG. 4 crystal morphology of example 5;
FIG. 5 is an infrared spectrum of a crystal modifier.
Detailed Description
The present invention is explained in further detail below with reference to the drawings and the specific examples, but it should be understood that the scope of the present invention is not limited to the specific examples.
Example 1
Adding 75g of water into 50g of industrial-grade common corn starch to prepare starch milk, adding 2g of 98% concentrated sulfuric acid, heating in a water bath to 50 ℃, stopping heating after 2 hours, cooling to room temperature without neutralization, retaining residual sulfuric acid, performing vacuum filtration, washing, drying to obtain acidolysis starch, and storing at low temperature.
Adding 2.5g of maleic anhydride and 1.5g of triethanolamine into a four-mouth bottle, adding 0.1g of p-toluenesulfonic acid, slowly heating to 80 ℃, reacting for 6 hours, and cooling to obtain a maleic anhydride triethanolamine ester and maleic anhydride mixture.
Dissolving 0.2g of sodium carbonate in 5g of water, adding acid hydrolysis starch, uniformly stirring, heating to 60 ℃, keeping the temperature constant for 0.5h, adding a mixture of maleic anhydride triethanolamine ester and maleic anhydride, fully mixing, uniformly stirring, synthesizing by a semi-dry method, placing in an oven at 80 ℃ for reacting for 3h, cooling to room temperature, drying and grinding to obtain the gypsum crystal transformation activator.
Adding water into salt gypsum under normal pressure to prepare slurry of which the concentration is 40%, feeding the slurry into a pressure-resistant kettle, adding a salt gypsum crystal transformation activator of which the concentration is 1% of the mass of the salt gypsum, sealing the pressure-resistant kettle, heating the slurry to 140 ℃ for crystal transformation reaction, and allowing the transformation reaction time to be 8 hours; and (3) performing solid-liquid separation on the alpha-type semi-hydrated gypsum slurry after crystallization, washing the alpha-type semi-hydrated gypsum slurry by using a saturated calcium sulfate hot water solution at 90 ℃, drying the obtained pure alpha-type semi-hydrated gypsum crystal at 130 ℃, and grinding the dried alpha-type semi-hydrated gypsum crystal according to the application fineness to obtain pure alpha-type semi-hydrated gypsum powder.
Example 2
Adding 75g of water into 40g of industrial-grade common corn starch to prepare starch milk, adding 1g of 98% concentrated sulfuric acid, heating in a water bath to 45 ℃, stopping heating after 1.5h, cooling to room temperature without neutralization, retaining residual sulfuric acid, performing vacuum filtration, washing, drying to obtain acidolysis starch, and storing at low temperature. Adding 2g of maleic anhydride and 1.7g of triethanolamine into a four-mouth bottle, adding 0.1g of p-toluenesulfonic acid, slowly heating to 82 ℃, reacting for 5 hours, and cooling to obtain a maleic anhydride triethanolamine ester and maleic anhydride mixture. Dissolving 0.2g of sodium carbonate in 7g of water, adding acid hydrolysis starch, uniformly stirring, heating to 65 ℃, keeping the temperature constant for 0.5h, adding a mixture of maleic anhydride triethanolamine ester and maleic anhydride, fully mixing, uniformly stirring, synthesizing by a semi-dry method, placing in an oven at 80 ℃ for reacting for 2.5h, cooling to room temperature, drying and grinding to obtain the gypsum salted crystal transformation activator.
Adding water into gypsum to prepare 30% slurry under normal pressure, feeding the slurry into a pressure-resistant kettle, adding 0.4% of a gypsum salt crystal transformation activator, sealing the pressure-resistant kettle, heating the slurry to 145 ℃ for crystal transformation reaction, wherein the transformation reaction time is 8 hours; and (3) performing solid-liquid separation on the alpha-type semi-hydrated gypsum slurry after crystallization, washing the alpha-type semi-hydrated gypsum slurry by using a saturated calcium sulfate hot water solution at 90 ℃, drying the obtained pure alpha-type semi-hydrated gypsum crystal at 130 ℃, and grinding the dried alpha-type semi-hydrated gypsum crystal according to the application fineness to obtain pure alpha-type semi-hydrated gypsum powder.
Example 3
Adding 70g of water into 45g of industrial-grade common corn starch to prepare starch milk, adding 1.5g of 98% concentrated sulfuric acid, heating in a water bath to 50 ℃, stopping heating after 2 hours, cooling to room temperature without neutralization, retaining residual sulfuric acid, performing vacuum filtration, washing, drying to obtain acidolysis starch, and storing at low temperature. Adding 2.5g of maleic anhydride and 1.5g of triethanolamine into a four-mouth bottle, adding 0.1g of p-toluenesulfonic acid, slowly heating to 80 ℃, reacting for 6 hours, and cooling to obtain a maleic anhydride triethanolamine ester and maleic anhydride mixture. Dissolving 0.2g of sodium carbonate in 5g of water, adding acid hydrolysis starch, uniformly stirring, heating to 70 ℃, keeping the temperature constant for 0.5h, adding a mixture of maleic anhydride triethanolamine ester and maleic anhydride, fully mixing, uniformly stirring, synthesizing by a semi-dry method, placing in an oven at 80 ℃ for reacting for 3h, cooling to room temperature, drying and grinding to obtain the gypsum crystal transformation activator.
Adding water into gypsum to prepare 25% slurry under normal pressure, feeding the slurry into a pressure-resistant kettle, adding 0.5% of a gypsum salt crystal transformation activator, sealing the pressure-resistant kettle, heating the slurry to 140 ℃ for crystal transformation reaction, wherein the transformation reaction time is 8 hours; and (3) performing solid-liquid separation on the alpha-type semi-hydrated gypsum slurry after crystallization, washing the alpha-type semi-hydrated gypsum slurry by using a saturated calcium sulfate hot water solution at 90 ℃, drying the obtained pure alpha-type semi-hydrated gypsum crystal at 130 ℃, and grinding the dried alpha-type semi-hydrated gypsum crystal according to the application fineness to obtain pure alpha-type semi-hydrated gypsum powder.
Example 4
50g of industrial-grade common corn starch is added with 75g of water to prepare starch milk, 2g of 98% concentrated sulfuric acid is added, and then the starch milk is heated to 55 ℃ in a water bath and is 2 ℃. Stopping heating after 5h, cooling to room temperature without neutralization, retaining residual sulfuric acid, performing vacuum filtration, washing, drying to obtain acid hydrolyzed starch, and storing at low temperature. Adding 2.5g of maleic anhydride and 2g of triethanolamine into a four-mouth bottle, adding 0.1g of p-toluenesulfonic acid, slowly heating to 80 ℃, reacting for 6 hours, and cooling to obtain a maleic anhydride triethanolamine ester and maleic anhydride mixture. Dissolving 0.2g of sodium carbonate in 8g of water, adding acid hydrolysis starch, uniformly stirring, heating to 60 ℃, keeping the temperature constant for 1h, adding a mixture of maleic anhydride triethanolamine ester and maleic anhydride, fully mixing, uniformly stirring, synthesizing by a semi-dry method, placing in an oven at 80 ℃ for reaction for 3h, cooling to room temperature, drying, and grinding to obtain the gypsum salicornia crystal transformation activator.
Adding water into gypsum to prepare 15% slurry under normal pressure, feeding the slurry into a pressure-resistant kettle, adding 0.1% of a gypsum salt crystal transformation activator, sealing the pressure-resistant kettle, heating the slurry to 140 ℃ for crystal transformation reaction, wherein the transformation reaction time is 5 hours; and (3) performing solid-liquid separation on the alpha-type semi-hydrated gypsum slurry after crystallization, washing the alpha-type semi-hydrated gypsum slurry by using a saturated calcium sulfate hot water solution at the temperature of 95 ℃, drying the obtained pure alpha-type semi-hydrated gypsum crystals at the temperature of 130 ℃, and grinding the dried crystals according to the application fineness to obtain pure alpha-type semi-hydrated gypsum powder.
Example 5
55g of industrial-grade common corn starch is added with 75g of water to prepare starch milk, 2g of 98% concentrated sulfuric acid is added, then the starch milk is heated to 50 ℃ in a water bath, the heating is stopped after 2 hours, the temperature is reduced to room temperature without neutralization, residual sulfuric acid is reserved, vacuum filtration, washing and drying are adopted, and the acidolysis starch can be obtained and stored at low temperature. Adding 2.5g of maleic anhydride and 2.2g of triethanolamine into a four-mouth bottle, adding 0.1g of p-toluenesulfonic acid, slowly heating to 80 ℃, reacting for 6 hours, and cooling to obtain a maleic anhydride triethanolamine ester and maleic anhydride mixture. Dissolving 0.1g of sodium carbonate in 5g of water, adding acid hydrolysis starch, uniformly stirring, heating to 60 ℃, keeping the temperature constant for 0.5h, adding a mixture of maleic anhydride triethanolamine ester and maleic anhydride, fully mixing, uniformly stirring, synthesizing by a semi-dry method, placing in an oven at 80 ℃ for reacting for 3h, cooling to room temperature, drying and grinding to obtain the gypsum crystal transformation activator.
Adding water into gypsum to prepare 30% slurry under normal pressure, feeding the slurry into a pressure-resistant kettle, adding 0.5% of a gypsum salt crystal transformation activator, sealing the pressure-resistant kettle, heating the slurry to 140 ℃ for crystal transformation reaction, wherein the transformation reaction time is 6 hours; and (3) performing solid-liquid separation on the alpha-type semi-hydrated gypsum slurry after crystallization, washing the alpha-type semi-hydrated gypsum slurry by using a saturated calcium sulfate hot water solution at the temperature of 93 ℃, drying the obtained pure alpha-type semi-hydrated gypsum crystals at the temperature of 130 ℃, and grinding the dried crystals according to the application fineness to obtain pure alpha-type semi-hydrated gypsum powder.
Example 6
Adding 80g of water into 50g of industrial-grade common corn starch to prepare starch milk, adding 2g of 98% concentrated sulfuric acid, heating in a water bath to 50 ℃, stopping heating after 2 hours, cooling to room temperature without neutralization, retaining residual sulfuric acid, performing vacuum filtration, washing, drying to obtain acidolysis starch, and storing at low temperature. Adding 2.5g of maleic anhydride and 1.5g of triethanolamine into a four-mouth bottle, adding 0.1g of p-toluenesulfonic acid, slowly heating to 85 ℃, reacting for 5 hours, and cooling to obtain a maleic anhydride triethanolamine ester and maleic anhydride mixture. Dissolving 0.2g of sodium carbonate in 5g of water, adding acid hydrolysis starch, uniformly stirring, heating to 60 ℃, keeping the temperature constant for 0.5h, adding a mixture of maleic anhydride triethanolamine ester and maleic anhydride, fully mixing, uniformly stirring, synthesizing by a semi-dry method, placing in an oven at 80 ℃ for reacting for 3h, cooling to room temperature, drying and grinding to obtain the gypsum crystal transformation activator.
Adding water into gypsum to prepare 35% slurry under normal pressure, adding into a pressure-resistant kettle, adding 0.5% of a gypsum salt crystal transformation activator, sealing the pressure-resistant kettle, heating the slurry to 142 ℃ for crystal transformation reaction, wherein the transformation reaction time is 8 h; and (3) performing solid-liquid separation on the alpha-type semi-hydrated gypsum slurry after crystallization, washing the alpha-type semi-hydrated gypsum slurry by using a saturated calcium sulfate hot water solution at 85 ℃, drying the obtained pure alpha-type semi-hydrated gypsum crystal at 130 ℃, and grinding the dried alpha-type semi-hydrated gypsum crystal according to application fineness to obtain pure alpha-type semi-hydrated gypsum powder.
The gypsum crystal transformation excitant is particularly suitable for the crystal transformation treatment of the gypsum containing salt with the sodium chloride content of 0-15%.
Performance testing
As can be seen from figure 1, the gypsum crystal transformation excitant without salt has poor crystallinity, is loose, fine and irregular, has a flaky shape, has a small amount of sheet crystal form and is mainly beta-type hemihydrate gypsum. The alpha-type hemihydrate gypsum in each of the figures 2, 3 and 4 has complete, thick and dense crystals, small length-diameter ratio, regular crystal form and significantly larger specific surface area than that in figure 1.
TABLE 1 hemihydrate Gypsum Performance test
| Group of | Blank space | Example 1 | Example 2 | Example 3 | Example 4 | Example 5 | Example 6 |
| Water consumption for standard consistency | 48% | 35% | 36% | 32% | 30% | 37% | 40% |
| Flexural strength/MPa | 2 | 11.2 | 11.7 | 12.5 | 11.3 | 12.8 | 12.0 |
| Compressive strength/ |
8 | 35.2 | 42.3 | 39.4 | 41.2 | 38.5 | 40.3 |
The flexural strength comprises 2h wet flexural strength and 40 ℃ dry flexural strength. The 2h wet bending strength refers to the strength of the gypsum powder measured on a bending resistance instrument after 2h from the time of putting the gypsum powder into water; the breaking strength at 40 ℃ is the breaking strength tested after the sample is dried to constant weight in an electrothermal blowing dry oven at 40 +/-4 ℃. The wet bending strength of the beta gypsum powder is generally more than 2.7Mpa, and the dry bending strength is generally more than 6 Mpa; the wet breaking strength of the alpha gypsum powder is generally more than 4MPa, and the dry breaking strength is generally more than 7 MPa.
In the ceramic industry, the flexural strength of gypsum powder is generally detected, and the compressive strength is not generally detected. The 2h wet compression strength of the gypsum powder is generally more than 6MPa, and the dry compression strength is more than 12 MPa.
The flexural strength detection method comprises the following steps:
the mass of the gypsum powder and water used for manufacturing 3 gypsum test strips with the size of 40 multiplied by 60 mm is calculated (according to the standard consistency of the gypsum powder or the proportion of the gypsum water in large-scale production), and the gypsum powder and the water are respectively weighed. Pouring water into 2000ml container, spreading Gypsum powder into water uniformly in 30s, standing for 30s, rapidly stirring for 1min, immediately pouring gypsum slurry into mold, lifting one end of the mold by hand for about 10mm, dropping, and vibrating for 5 times to remove air bubbles. When the initial setting is reached, the overflowed pulp is scraped by a scraper, and the mould is removed after the final setting.
The detection method of the compressive strength comprises the following steps:
the half-section sample after the flexural strength test is used for preparing a test block of 40 mm × 40 mm.
It is found from Table 1 that the crystal transformation activator for salt gypsum can reduce the water consumption for standard consistency and improve the compressive strength.
The infrared spectrum is shown in FIG. 5. As can be seen from FIG. 5, the wave number is 3420 cm-1The strong absorption peak is a-OH stretching vibration peak in starch, and is 2920cm-1Corresponding to characteristic peak of C-H, 1160cm-1、1060cm-1、1010m-1 series peaks are C-C, C-O stretching vibration peak and C-OH bending vibration characteristic peak in starch, and fingerprint area is 550cm-1、575cm-1The series of peaks are absorption peaks of the starch skeleton. 1730cm-1The characteristic absorption peak is caused by symmetric and antisymmetric stretching vibration of C = O bond on maleic anhydride ring, 1640cm-1Vibration absorption peak of C = C of maleic anhydride, 1410cm-1In the form of triethanolamine CH2Bending vibration absorption peaks, indicating that maleic anhydride and triethanolamine have been successfully grafted onto the molecular chains of the starch.
The above description is only a preferred embodiment of the present invention, and the present invention is not limited to the content of the embodiment. It will be apparent to those skilled in the art that various changes and modifications can be made within the technical scope of the present invention, and any changes and modifications made are within the protective scope of the present invention.
Claims (8)
1. A preparation method of a salt gypsum crystal transformation excitant is characterized by comprising the following steps: grafting acid-hydrolyzed starch to maleic anhydride triethanolamine ester; the method specifically comprises the following steps:
s01 acid hydrolysis of starch;
s02, preparing a mixture of maleic anhydride triethanolamine ester and maleic anhydride;
s03, grafting the starch subjected to acidolysis to maleic anhydride triethanolamine ester by adopting a semidry method to prepare a gypsum salt crystal transformation activator;
the step S03 specifically includes:
a, preparing an aqueous solution of a penetrant, and adding acidolyzed starch into the aqueous solution of the penetrant to obtain a first mixed solution, wherein the addition amount of the aqueous solution of the penetrant is 5-10% of the dry weight of the starch;
b, adding a mixture of maleic anhydride triethanolamine ester and maleic anhydride into the mixed solution I, and uniformly mixing to obtain a mixture II;
and c, putting the mixture II into an oven at the temperature of 70-90 ℃, reacting for 2-4 h, and drying and grinding the product to obtain the gypsum crystal transformation excitant.
2. The method for producing the salt gypsum crystal transformation stimulant according to claim 1, wherein: the acidolysis starch comprises the following specific processes:
a, adding water into starch to prepare starch milk with the mass content of starch being 40-50%;
b, adding concentrated sulfuric acid into the starch milk and reacting, wherein the mass of the concentrated sulfuric acid is 1-5% of the mass of the starch, the reaction temperature is 20-60 ℃, and the reaction time is 1-2 hours;
and c, after the reaction is finished, carrying out vacuum filtration, washing and drying on the reaction product, and then storing.
3. The method for producing the salt gypsum crystal transformation stimulant according to claim 1, wherein: the preparation process of the mixture of maleic anhydride triethanolamine ester and maleic anhydride comprises the following steps: and adding triethanolamine and excessive maleic anhydride into a container, adding a catalyst for catalyzing the reaction of the maleic anhydride and the triethanolamine, and carrying out catalytic reaction for 5-6 h at the reaction temperature of 75-80 ℃ to obtain a maleic anhydride triethanolamine ester and maleic anhydride mixture.
4. The method for producing the salt gypsum crystal transformation stimulant according to claim 3, wherein: the mass ratio of the maleic anhydride to the triethanolamine is 0.02-0.04: 0.015-0.03.
5. The method for producing the salt gypsum crystal transformation stimulant according to claim 1, wherein: the penetrant is sodium carbonate.
6. A salt gypsum crystal transformation stimulant prepared by the preparation method of the salt gypsum crystal transformation stimulant according to any one of claims 1 to 5.
7. A method for crystallizing salt gypsum using the salt gypsum crystal transformation stimulant of claim 6, wherein: comprises the following steps
a, adding water into salt gypsum to prepare slurry with the mass fraction of 15-40%, and placing the slurry into a reaction tank;
b, adding a gypsum salt crystal transformation activator into the reaction tank to perform crystal transformation reaction to obtain alpha-type hemihydrate gypsum;
and c, performing solid-liquid separation on the alpha-type semi-hydrated gypsum slurry after crystallization is completed, washing and drying the solid obtained by the solid-liquid separation to obtain pure alpha-type semi-hydrated gypsum crystals, wherein the washing is performed by using a saturated calcium sulfate solution, and the drying temperature is 120-170 ℃.
8. The method for crystal transformation of salt gypsum according to claim 7, wherein: the dosage of the crystal transformation activator of the salt gypsum is 0.1-1% of the weight of the salt gypsum.
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