Method for rapidly hydrating anhydrous salt gypsum into dihydrate gypsum

Abstract

The invention discloses a method for rapidly hydrating anhydrous salt gypsum into dihydrate gypsum, which comprises the following steps: (1) mother liquor preparation: dissolving inorganic salt and a surfactant in water to prepare a mother liquor; (2) feeding and crystal transformation: adding the pretreated anhydrous salt gypsum into the mother liquor, mixing to form turbid liquid, and carrying out hydration crystal transformation reaction at normal temperature; and (3) product collection: carrying out solid-liquid separation on the suspension after the crystal transformation reaction, and washing and drying the solid phase to obtain the dihydrate gypsum. The invention provides a method for rapidly hydrating anhydrous salt gypsum into dihydrate gypsum. The anhydrous salt gypsum is rapidly hydrated into the dihydrate gypsum in an aqueous solution system of a compound inorganic salt and a surfactant.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of anhydrous gypsum hydration, in particular to a method for preparing dihydrate gypsum by hydrating anhydrous salt gypsum. TECHNICAL BACKGROUND

[0002] Anhydrous salt gypsum is mainly derived from by-product salt gypsum in the salt industry, and its main component is anhydrous calcium sulfate. If these industrial by-product gypsums are not utilized, they will occupy a large amount of land and cause environmental pollution. Converting anhydrous salt gypsum into dihydrate gypsum provides an effective way for the resource utilization of industrial by-product gypsum, reduces solid waste emissions, and realizes the recycling of resources.

[0003] Anhydrous salt gypsum has low hydration activity and is difficult to react with water in a natural state. It needs to be activated by grinding, calcination (>600℃), chemical activation, etc. The process is complex and has high energy consumption. The hardened body is faced with the bottleneck of slow hardening speed and long hydration time (several days or even longer), which affects the construction efficiency. In addition, the toughness of the hardened body is insufficient, and the brittle hardened body needs to be matched with reinforcing materials such as fibers to improve it, which limits the application scenarios. Dihydrate gypsum can be dehydrated into high-activity building gypsum powder at low temperature (110-180℃), and the hydration and setting speed is fast, and the early strength is high, which is widely used in gypsum board, plastering gypsum, blocks and molds, etc. It is flexible and convenient to use, and is an ideal choice for green and energy-saving building materials. Therefore, converting anhydrous salt gypsum into dihydrate gypsum through hydration technology can improve its performance, expand its application range, and increase the added value of the product.

[0004] Anhydrous salt gypsum is difficult to dissolve in water itself, and hydration needs to be carried out under the condition of excitation. When in contact with water, the surface of anhydrous gypsum slowly dissolves in water to form a saturated solution of calcium sulfate. In the solution, Ca 2+ Combining with SO4 2- water molecules, dihydrate gypsum crystals are generated by crystallization. Alkaline environment or addition of sulfate, lime and other activators can promote the dissolution of anhydrous gypsum, accelerate ion migration and hydration reaction. Physical grinding reduces the particle size and increases the specific surface area, which improves the dissolution rate, so that dihydrate gypsum crystals are crystallized and grown on the surface of anhydrous gypsum particles or in the solution, forming an interwoven structure to realize hardening. This process needs to overcome the limitation of low hydration activity of anhydrous gypsum, and the reaction is promoted by external conditions.

[0005] Invention patent CN 119059750 A discloses a process for the rapid hydration of anhydrous salt gypsum. This patent first grinds anhydrous salt gypsum into powder for later use. Then, the powdered anhydrous salt gypsum, dihydrate gypsum seed crystals, a hydration promoter, a composite surfactant composed of modified lignin-based surfactant and tristyrene-based phenol polyoxyethylene ether phosphate monoester, a water-reducing agent, and deionized water are mixed and stirred at 15-25°C for 23-25 ​​hours to obtain a hydration slurry. After reaching the hydration endpoint, anhydrous ethanol is added to the hydration slurry. Following filtration, washing, and drying to constant weight, dihydrate gypsum is finally obtained. This invention uses calcined alum as a hydration promoter, ensuring the activation and increased fluidity, and has the advantages of low cost and high hydration rate. However, the reaction time is relatively long, which may affect production efficiency and increase time costs in large-scale industrial production. The use of a variety of raw materials increases the difficulty and complexity of production operations. Deviations in the proportions can affect the hydration rate and product quality. Invention patent CN 110128045 A discloses an activator and rapid hydration method for type II anhydrous gypsum. The activator used in this patent includes: an active activator, gypsum dihydrate seed crystals, and an aqueous solution. The active activator includes one or more of potassium aluminum sulfate dodecahydrate, sodium bisulfate, potassium dichromate, sodium oxalate, and calcined alum. The rapid hydration method first grinds the anhydrite, then adds the anhydrite, active activator, gypsum dihydrate seed crystals, and aqueous solution according to the formula and stirs them. After reaching the set hydration endpoint, the hydration product is terminated with anhydrous ethanol, and the content of water of crystallization is measured to calculate the corresponding hydration rate. This invention belongs to the field of building materials, and its rapid hydration method can achieve rapid hydration of gypsum while being energy-saving and environmentally friendly. However, as the amount of activator increases, the strength of gypsum dihydrate weakens, which not only leads to a decline in product quality but also reduces the hydration rate. This problem has not yet been effectively solved.

[0006] This invention employs a method for rapidly activating anhydrous gypsum to prepare dihydrate gypsum by adding inorganic salt compound surfactants at room temperature and pressure. The hydration rate reaches 90% within 24 hours. The method is simple to operate, consumes little energy, and has a high conversion rate, which helps to realize the high-value-added resource utilization of anhydrous gypsum. Summary of the Invention

[0007] This invention provides a method for rapidly hydrating anhydrous gypsum into dihydrate gypsum. By compounding inorganic salts and surfactant activators, anhydrous gypsum is converted into dihydrate gypsum at room temperature, realizing high-value-added resource utilization of solid waste.

[0008] The specific technical solution is as follows:

[0009] (1) Preparation of mother liquor: Dissolve inorganic salts and surfactants in water to prepare a reaction mother liquor;

[0010] (2) Feeding and crystallization: The pretreated anhydrous salt gypsum is added to the reaction mother liquor and mixed to form a suspension. The hydration and crystallization reaction is carried out at room temperature.

[0011] (3) Product collection: The suspension after the crystallization reaction is separated into solid and liquid, and dried to obtain gypsum dihydrate.

[0012] The key to the rapid hydration method proposed in this invention lies in using anhydrous gypsum from industrial solid waste as a raw material. By combining inorganic salts and surfactants as activators, the solution reaches a supersaturated state more quickly, promoting the nucleation of dihydrate gypsum and achieving rapid conversion from anhydrous gypsum to dihydrate gypsum. Inorganic salts dissolve in water and ionize into various ions, increasing the ionic strength of the solution. Through the salt effect, this reduces the activity product of CaSO4, causing a positive shift in the dissolution equilibrium (CaSO4 ⇌ Ca...). 2+ +SO4 2- ), accelerate Ca 2+ and SO4 2- The release of these substances enhances the driving force of the hydration reaction of anhydrous gypsum. The cations of surfactants CTAB, TTAB, and DTAB adsorb onto the negatively charged regions (such as SO42-) on the surface of CaSO4 crystals through electrostatic attraction. 2- The exposed sites, with long-chain alkyl groups facing the solution, form a surface adsorption layer. This adsorption layer reduces the solid-liquid interfacial tension, promotes the penetration of H2O molecules into the CaSO4 crystal surface, accelerates dissolution, and thus promotes the hydration reaction. Furthermore, this invention conducts the reaction at room temperature, resulting in mild reaction conditions, reduced energy consumption, and strong environmental friendliness and economic efficiency.

[0013] In step (1), the surfactant is one or more of hexadecyltrimethylammonium bromide (CTAB), tetradecyltrimethylammonium bromide (TTAB), and dodecyltrimethylammonium bromide (DTAB).

[0014] Further, in step (1), the concentration of the surfactant is 4.0 × 10⁻⁶. -4 ~ 2.0×10 -3 mol / L.

[0015] Further, the inorganic salt mentioned in step (1) is one or more of NaCl, NH4Cl, Na2SO4, (NH4)2SO4, and K2SO4, with a concentration of 0.10 ~ 1.0 mol / L.

[0016] In step (2), the anhydrous gypsum refers to a byproduct of salt production at the Pingdingshan Saltworks. The process of hydrating anhydrous gypsum into dihydrate gypsum is a dissolution-crystallization process. Anhydrous gypsum with different particle sizes has different surface characteristics. Small-particle-size anhydrous gypsum raw materials can provide more nucleation sites, promoting the hydration process.

[0017] Furthermore, the anhydrous salt gypsum is in powder or fine granule form with a particle size of 2 to 50 μm. In step (2), the amount of anhydrous gypsum added is the solid content in the suspension. Increasing the solid content can increase the nucleation sites of dihydrate gypsum and improve the hydration rate; however, excessive solid content will cause the dihydrate gypsum to not develop sufficiently and affect the quality.

[0018] Furthermore, the mass percentage of anhydrous gypsum in the suspension is 10-20 wt%.

[0019] In step (3), the product collection includes washing and drying; washing is done with anhydrous ethanol, and drying is performed at a temperature of 45-60°C.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] (1) The present invention adopts relatively mild reaction conditions, is simple to operate and easy to control, which is conducive to reducing costs and saving energy consumption.

[0022] (2) This invention effectively promotes the hydration process of anhydrous gypsum by controlling the concentration ratio of inorganic salts and surfactants, thereby improving the conversion rate and obtaining a product of higher quality.

[0023] (3) The present invention uses anhydrous salt gypsum as raw material to prepare dihydrate gypsum, which not only solves the problem of anhydrous salt gypsum occupying land resources and polluting and damaging the ecological environment, but also realizes the high-value-added resource utilization of anhydrous salt gypsum. Attached Figure Description

[0024] Figure 1 This is a process flow diagram of the present invention for preparing dihydrate gypsum using anhydrous salt gypsum at room temperature.

[0025] Figure 2 The image shown is a scanning electron microscope image of the gypsum dihydrate prepared in Example 1.

[0026] Figure 3 The hydration rate curve of anhydrous salt gypsum in Example 1 is shown.

[0027] Figure 4 The image shows the XRD pattern of the hydration product from Example 1. Detailed Implementation

[0028] Example 1 First, anhydrous salt gypsum was calcined at 150℃ to obtain thermally activated gypsum for later use. Sodium sulfate, ammonium sulfate, and CTAB were added to deionized water to obtain a mother liquor, with concentrations controlled at 0.5 mol / L, 0.2 mol / L, and 4.0 × 10⁻⁶, respectively. -4 mol / L. Thermally activated anhydrous gypsum was added to the mother liquor, controlling the solid content to be 10 wt%. The reaction was carried out at room temperature and pressure with a stirring rate of 500 rpm for 24 h. After the conversion was complete, the slurry was separated into solid and liquid components. After washing with anhydrous ethanol, the solid was dried at 60 ℃ for 2 h to obtain the dihydrate gypsum product.

[0029] Example 2 First, anhydrous salt gypsum was calcined at 150℃ to obtain thermally activated gypsum for later use. Sodium sulfate, ammonium sulfate, and CTAB were added to deionized water to obtain mother liquor, with concentrations controlled at 0.5 mol / L, 0.2 mol / L, and 7.0 × 10⁻⁶, respectively. -4 mol / L. Thermally activated anhydrous gypsum was added to the mother liquor, controlling the solid content to be 10 wt%. The reaction was carried out at room temperature and pressure with a stirring rate of 500 rpm for 24 h. After the conversion was complete, the slurry was separated into solid and liquid components. After washing with anhydrous ethanol, the solid was dried at 60 ℃ for 2 h to obtain the dihydrate gypsum product.

[0030] Example 3 First, anhydrous salt gypsum was calcined at 150℃ to obtain thermally activated gypsum for later use. Sodium sulfate, ammonium sulfate, and CTAB were added to deionized water to obtain a mother liquor, with concentrations controlled at 0.5 mol / L, 0.2 mol / L, and 1.0 × 10⁻⁶ mol / L, respectively. -3 mol / L. Thermally activated anhydrous gypsum was added to the mother liquor, controlling the solid content to be 10 wt%. The reaction was carried out at room temperature and pressure with a stirring rate of 500 rpm for 24 h. After the conversion was complete, the slurry was separated into solid and liquid components. After washing with anhydrous ethanol, the solid was dried at 60 ℃ for 2 h to obtain the dihydrate gypsum product.

[0031] Example 4 First, anhydrous salt gypsum was calcined at 150℃ to obtain thermally activated gypsum for later use. Sodium sulfate, ammonium sulfate, and CTAB were added to deionized water to obtain a mother liquor, with concentrations controlled at 0.5 mol / L, 0.2 mol / L, and 2.0 × 10⁻⁶, respectively. -3mol / L. Thermally activated anhydrous gypsum was added to the mother liquor, controlling the solid content to be 10 wt%. The reaction was carried out at room temperature and pressure with a stirring rate of 500 rpm for 24 h. After the conversion was complete, the slurry was separated into solid and liquid components. After washing with anhydrous ethanol, the solid was dried at 60 ℃ for 2 h to obtain the dihydrate gypsum product.

[0032] Example 5 First, anhydrous salt gypsum was calcined at 150℃ to obtain thermally activated gypsum for later use. Sodium sulfate, ammonium sulfate, and CTAB were added to deionized water to obtain a mother liquor, with concentrations controlled at 0.5 mol / L, 0.2 mol / L, and 3.0 × 10⁻⁶, respectively. -3 mol / L. Thermally activated anhydrous gypsum was added to the mother liquor, controlling the solid content to be 10 wt%. The reaction was carried out at room temperature and pressure with a stirring rate of 500 rpm for 24 h. After the conversion was complete, the slurry was separated into solid and liquid components. After washing with anhydrous ethanol, the solid was dried at 60 ℃ for 2 h to obtain the dihydrate gypsum product.

[0033] Example 6 First, anhydrous salt gypsum was calcined at 150℃ to obtain thermally activated gypsum for later use. Sodium sulfate, ammonium sulfate, and CTAB were added to deionized water to obtain mother liquor, with concentrations controlled at 1.0 mol / L, 0.4 mol / L, and 8.0 × 10⁻⁶, respectively. -4 mol / L. Thermally activated anhydrous gypsum was added to the mother liquor, controlling the solid content to be 20 wt%. The reaction was carried out at room temperature and pressure with a stirring rate of 500 rpm for 24 h. After the conversion was complete, the slurry was separated into solid and liquid components. After washing with anhydrous ethanol, the solid was dried at 60 ℃ for 2 h to obtain the dihydrate gypsum product.

[0034] Example 7 First, anhydrous salt gypsum was calcined at 150℃ to obtain thermally activated gypsum for later use. Sodium chloride, ammonium chloride, and CTAB were added to deionized water to obtain mother liquor, with concentrations controlled at 0.5 mol / L, 0.2 mol / L, and 4.0 × 10⁻⁶, respectively. -4 mol / L. Thermally activated anhydrous gypsum was added to the mother liquor, controlling the solid content to be 10 wt%. The reaction was carried out at room temperature and pressure with a stirring rate of 500 rpm for 24 h. After the conversion was complete, the slurry was separated into solid and liquid components. After washing with anhydrous ethanol, the solid was dried at 60 ℃ for 2 h to obtain the dihydrate gypsum product.

[0035] Example 8 First, anhydrous salt gypsum was calcined at 150℃ to obtain thermally activated gypsum for later use. Potassium sulfate, ammonium sulfate, and CTAB were added to deionized water to obtain mother liquor, with concentrations controlled at 0.1 mol / L, 0.2 mol / L, and 4.0 × 10⁻⁶, respectively. -4 mol / L. Thermally activated anhydrous gypsum was added to the mother liquor, controlling the solid content to be 10 wt%. The reaction was carried out at room temperature and pressure with a stirring rate of 500 rpm for 24 h. After the conversion was complete, the slurry was separated into solid and liquid components. After washing with anhydrous ethanol, the solid was dried at 60 ℃ for 2 h to obtain the dihydrate gypsum product.

[0036] Example 9 First, anhydrous salt gypsum was calcined at 150℃ to obtain thermally activated gypsum for later use. Sodium sulfate, ammonium sulfate, and TTAB were added to deionized water to obtain mother liquor, with concentrations controlled at 0.5 mol / L, 0.2 mol / L, and 4.0 × 10⁻⁶ mol / L, respectively. -4 mol / L. Thermally activated anhydrous gypsum was added to the mother liquor, controlling the solid content to be 10 wt%. The reaction was carried out at room temperature and pressure with a stirring rate of 500 rpm for 24 h. After the conversion was complete, the slurry was separated into solid and liquid components. After washing with anhydrous ethanol, the solid was dried at 60 ℃ for 2 h to obtain the dihydrate gypsum product.

[0037] Example 10 First, anhydrous salt gypsum was calcined at 150℃ to obtain thermally activated gypsum for later use. Sodium sulfate, ammonium sulfate, and DTAB were added to deionized water to obtain a mother liquor, with concentrations controlled at 0.5 mol / L, 0.2 mol / L, and 4.0 × 10⁻⁶, respectively. -4 mol / L. Thermally activated anhydrous gypsum was added to the mother liquor, controlling the solid content to be 10 wt%. The reaction was carried out at room temperature and pressure with a stirring rate of 500 rpm for 24 h. After the conversion was complete, the slurry was separated into solid and liquid components. After washing with anhydrous ethanol, the solid was dried at 60 ℃ for 2 h to obtain the dihydrate gypsum product.

[0038] Example 10 First, anhydrous salt gypsum was calcined at 100℃ to obtain thermally activated gypsum for later use. Sodium sulfate, ammonium sulfate (CTAB), and TTAB were added to deionized water to obtain a mother liquor, with concentrations controlled at 0.5 mol / L, 0.2 mol / L, and 2.0 × 10⁻⁶ mol / L, respectively. -4 mol / L and 2.0×10 -4mol / L. Thermally activated anhydrous gypsum was added to the mother liquor, controlling the solid content to be 10 wt%. The reaction was carried out at room temperature and pressure with a stirring rate of 500 rpm for 24 h. After the conversion was complete, the slurry was separated into solid and liquid components. After washing with anhydrous ethanol, the solid was dried at 60 ℃ for 2 h to obtain the dihydrate gypsum product.

[0039] Example 10 First, anhydrous salt gypsum was calcined at 300℃ to obtain thermally activated gypsum for later use. Sodium sulfate, ammonium sulfate (TTAB), and DTAB were added to deionized water to obtain a mother liquor, with concentrations controlled at 0.5 mol / L, 0.2 mol / L, and 2.0 × 10⁻⁶, respectively. -4 mol / L and 2.0×10 -4 mol / L. Thermally activated anhydrous gypsum was added to the mother liquor, controlling the solid content to be 10 wt%. The reaction was carried out at room temperature and pressure with a stirring rate of 500 rpm for 24 h. After the conversion was complete, the slurry was separated into solid and liquid components. After washing with anhydrous ethanol, the solid was dried at 60 ℃ for 2 h to obtain the dihydrate gypsum product.

Claims

1. A method for rapidly hydrating anhydrous gypsum into dihydrate gypsum, characterized in that, The steps are as follows: (1) Preparation of mother liquor: Dissolve inorganic salts and surfactants in water to prepare a reaction mother liquor; (2) Feeding and crystallization: The pretreated anhydrous salt gypsum is added to the reaction mother liquor and mixed to form a suspension. The hydration and crystallization reaction is carried out at room temperature. (3) Product collection: The suspension after the crystallization reaction is separated into solid and liquid, and dried to obtain gypsum dihydrate.

2. The method according to claim 1, characterized in that, In step (1), the inorganic salt is one or more of NaCl, NH4Cl, Na2SO4, (NH4)2SO4, and K2SO4.

3. The method according to claim 1, characterized in that, In step (1), the concentration of the inorganic salt is 0.1 ~ 1.0 mol / L.

4. The method according to claim 1, characterized in that, In step (1), the surfactant is one or more of hexadecyltrimethylammonium bromide (CTAB), tetradecyltrimethylammonium bromide (TTAB), and dodecyltrimethylammonium bromide (DTAB).

5. The method according to claim 1, characterized in that, In step (1), the concentration of the surfactant is 4.0 × 10⁻⁶. -4 ~ 3.0×10 -3 mol / L.

6. The method according to claim 1, characterized in that, In step (2), the anhydrous salt gypsum is thermally activated gypsum obtained by calcining at 100~300℃ for 2 hours, with a gypsum content of 92.33% and the main impurity being SiO2.

7. The method according to claim 1, characterized in that, In step (2), the mass percentage of anhydrous salt gypsum in the suspension is 10 ~ 20 wt%.

8. The method according to claim 1, characterized in that, In step (2), the crystallization reaction time is 10 to 24 hours.

9. The method according to claim 1, characterized in that, In step (3), the solid phase component of the solid-liquid separation is dried at 45-60℃ to obtain gypsum dihydrate.

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