Preparation method of micron-sized II-type anhydrous gypsum

Abstract

The invention discloses a preparation method of micron-sized II-type anhydrous gypsum. The preparation method comprises the following steps: firstly, uniformly mixing a natural gypsum raw material or a purified industrial byproduct gypsum raw material, a crystal form control agent and a crystal transformation acid solution, then carrying out high-speed shearing and stirring in a reaction kettle, and filtering, washing and drying slurry after the crystal transformation reaction is finished, the mass fraction of the natural gypsum raw material or the purified industrial byproduct gypsum raw material, the mass fraction of the crystal form control agent and the mass fraction of the crystal transformation acid solution are 10%-20%, 0.5%-3% and 77%-89.5% respectively. According to the method, mutual contact and collision among particles are intensified through the high-speed shearing effect, meanwhile, the crystal form control agent inhibits growth of crystals in the C-axis direction, the average particle size of the obtained II-type anhydrite is more than ten micrometers, and the II-type anhydrite has the advantages of being high in whiteness and low in crystal water content and is an ideal filler used in the polymer field. Compared with a traditional calcination method, the method provided by the invention has the advantages that high-temperature calcination and grinding are not needed, the production energy consumption and cost are greatly reduced, and high-value utilization of the industrial byproduct gypsum is realized.

Description

Technical Field

[0001] This invention relates to the field of industrial solid waste resource utilization technology, specifically to a method for preparing micron-sized type II anhydrous gypsum. Background Technology

[0002] Industrial by-product gypsum refers to by-products or waste generated during industrial production processes through chemical reactions. Its main component is calcium sulfate containing zero to two molecules of water of crystallization. Also known as chemical gypsum, its chemical composition and physical properties are similar to natural gypsum. It mainly includes phosphogypsum, desulfurization gypsum, fluorogypsum, titanium gypsum, and citric acid gypsum, with annual emissions exceeding 200 million tons and cumulative stockpiles exceeding 1 billion tons. Desulfurization gypsum mainly comes from coal-fired power plants, with annual emissions comparable to phosphogypsum. Due to its low impurity content, its comprehensive utilization rate reaches approximately 80%. Titanium gypsum has annual emissions of around 10 million tons, with a comprehensive utilization rate of about 40%. Fluorogypsum has annual emissions of around 1 million tons, with a comprehensive utilization rate exceeding 80%. Citric acid gypsum has annual emissions of around 1.5 million tons, with a comprehensive utilization rate of less than 50%. The comprehensive utilization rate and level of industrial by-product gypsum in my country are low. Large quantities of unused industrial by-product gypsum occupy land resources and negatively impact the surrounding environment.

[0003] Currently, the resource utilization of industrial by-product gypsum mainly involves three aspects: First, it is directly used as a cement retarder, such as desulfurized gypsum and phosphogypsum; second, it is calcined into building gypsum powder, which is then used to produce plastering gypsum, plastering mortar, self-leveling mortar, and various gypsum products (paper-faced / paperless gypsum board, gypsum blocks, GRG moldings, etc.); third, it is used to prepare non-calcined gypsum hydraulic composite cementitious materials, which in turn lead to non-calcined gypsum-based mortars and blocks. In addition, industrial by-product gypsum, after harmless treatment, is also used as a soil conditioner. Due to the current sluggish construction market, the utilization rate and added value of industrial by-product gypsum in building materials are continuously decreasing. Coupled with the strict supervision of industrial by-product gypsum by agricultural and rural departments, it is urgent to explore new ways to utilize industrial by-product gypsum resources for high-value purposes, transforming it into high-value-added products.

[0004] Type II anhydrous gypsum, also known as hard gypsum, comes in two forms: one found in natural hard gypsum mines, and the other prepared by calcining and dehydrating dihydrate gypsum. Natural hard gypsum is primarily composed of Type II anhydrous gypsum, characterized by its dense structure, slow dissolution, and low hydration activity. Calcined Type II anhydrous gypsum, obtained by calcining and dehydrating dihydrate gypsum, exhibits higher whiteness, with impurities largely removed, a dense structure, and uniform particle size distribution. Both types of Type II anhydrous gypsum possess characteristics such as dense structure, stable performance, and low hydration, making them excellent substitutes for heavy calcium carbonate and talc as polymer fillers. Furthermore, they have applications in construction, environmental protection, agriculture, and medicine, demonstrating high economic value. Type II anhydrous gypsum is typically prepared using a calcination method at around 700℃. Under calcination conditions, the water of crystallization in the dihydrate gypsum rapidly evaporates through the crystal surface, without altering the original microstructure of the dihydrate gypsum. The resulting Type II anhydrous gypsum typically exhibits a rhomboid microstructure. The calcined product still needs to be ultra-finely ground before it can be used as a filler, resulting in high overall production energy consumption and costs. When preparing type II anhydrous gypsum using the atmospheric pressure acidification method, the dihydrate gypsum first dissolves Ca... 2+ With SO4 2- When the concentration of these ions reaches the supersaturation of anhydrous gypsum, anhydrous gypsum crystal nuclei will form. As the dihydrate gypsum continues to dissolve, the anhydrous gypsum crystals grow, which is the dissolution-recrystallization process. The resulting Type II anhydrous gypsum usually has a flaky, needle-like, or long fibrous microstructure. The overall particle size is relatively coarse, and post-processing processes such as grinding are required to meet the requirements of polymer fillers.

[0005] This invention utilizes a crystal form control agent to inhibit the growth of type II anhydrous gypsum crystals along the C-axis, while simultaneously intensifying the interparticle contact and collision through high-speed shearing, thereby preparing type II anhydrous gypsum with an average particle size of tens of micrometers. It also features high whiteness and low water of crystallization content, making it an ideal filler for the polymer field. This significantly reduces production energy consumption and costs, and realizes the high-value utilization of industrial by-product gypsum. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing micron-sized type II anhydrous gypsum. This method intensifies the contact and collision between particles through high-speed shearing, while a crystal form control agent inhibits crystal growth along the C-axis. The resulting type II anhydrous gypsum has an average particle size of tens of micrometers and also features high whiteness and low water of crystallization content, making it an ideal filler for the polymer field. Compared with the traditional calcination method, the method provided by this invention eliminates the need for high-temperature calcination and grinding, significantly reducing production energy consumption and costs, and realizing the high-value utilization of industrial by-product gypsum.

[0007] To achieve the above objectives, this invention provides a method for preparing micron-sized type II anhydrous gypsum. Natural gypsum raw material or purified industrial by-product gypsum raw material, crystal form control agent, and crystallization acid solution are uniformly mixed, and then subjected to high-speed shearing and stirring in a reaction vessel. After the crystallization reaction is completed, the slurry is filtered, washed, and dried to obtain the final product. The mass fractions of the natural gypsum raw material or purified industrial by-product gypsum raw material, crystal form control agent, and crystallization acid solution are 10%~20%, 0.5%~3%, and 77%~89.5%, respectively.

[0008] As a preferred embodiment, the natural gypsum raw material or the purified industrial by-product gypsum raw material has a whiteness of 60% or above, a grade of 80% or above, and an attached water content of 1% or below.

[0009] As a preferred embodiment, the natural gypsum raw material or the purified industrial by-product gypsum raw material is dried at 40℃~80℃ to constant weight to ensure that the attached water is removed while the crystal water does not escape.

[0010] As a preferred embodiment, the crystal form control agent is selected from any one or more of hydroxypropyl methylcellulose phthalate, maleic acid, sodium polyphosphate, and hydroxypropyl distarch phosphate.

[0011] The transcrystallization acid solution is hydrochloric acid-glycine buffer, hydrochloric acid-citric acid buffer, phthalic acid-hydrochloric acid buffer, or pyromellitic acid-hydrochloric acid buffer; The hydrochloric acid-glycine buffer solution is prepared in a 1:1 molar ratio; the hydrochloric acid-citric acid buffer solution is prepared in a 1:1 molar ratio; the phthalic acid-hydrochloric acid buffer solution is prepared in a 1:1 molar ratio; and the pyromellitic acid-hydrochloric acid buffer solution is prepared in a 1:1 molar ratio.

[0012] The mass concentration of the transcrystallization acid solution is 25% to 50%.

[0013] As a preferred embodiment, the high-speed shear-transformation reaction is carried out at a temperature of 85°C to 100°C and for a reaction time of 1 hour to 5 hours.

[0014] As a preferred embodiment, the high-speed shear stirring rate is between 1000 r / min and 3000 r / min.

[0015] As a preferred embodiment, the slurry is filtered and then washed at least twice before being placed in an oven at 40°C to 60°C for drying. The filtrate is returned to the crystallization reaction for recycling, and the wash water is returned to the crystallization acid solution for recycling.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) This invention intensifies the contact and collision between particles through high-speed shearing, while the crystal form control agent inhibits the growth of crystals in the C-axis direction. The resulting type II anhydrous gypsum has an average particle size of more than ten micrometers and also has the characteristics of high whiteness and low crystal water content. It is an ideal filler for the polymer field and realizes the high-value utilization of industrial by-product gypsum.

[0017] 2) Compared with the traditional calcination method, the method provided by this invention does not require high-temperature calcination and grinding, which greatly reduces the energy consumption and cost of producing type II anhydrous gypsum and reduces the environmental pollution caused by the stockpiling of industrial by-product gypsum, thus having good social and economic benefits. Detailed Implementation

[0018] The following embodiments further illustrate the technical solution of the present invention, but are not intended to limit the scope of protection of the present invention.

[0019] Example 1 475g of purified phosphogypsum raw material was dried to constant weight in a 50℃ oven (whiteness of phosphogypsum raw material was 64.8%, grade was 88.6%, and attached water was 0.12%). Then, it was uniformly mixed with 25g of hydroxypropyl methylcellulose phthalate (a crystal form control agent) and 2000g of 30% hydrochloric acid-glycine buffer solution in a reactor. The crystallization reaction temperature was controlled at 90℃, the reaction time at 4 hours, and the high-speed shear stirring rate at 1500 r / min. After the reaction, the slurry was filtered and washed three times. The filtrate was returned to the crystallization reaction for recycling, and the wash water was returned to the crystallization acid solution for recycling. After washing, the Type II anhydrous gypsum was dried in a 50℃ oven to constant weight, and its whiteness, water of crystallization content and particle size were tested. The test results were: whiteness of 95.3%, water of crystallization content of 0.18%, and average D90 particle size of 11.6µm. It is a relatively ideal alternative filler for the polymer field.

[0020] Example 2 250g of purified citric acid gypsum raw material was dried to constant weight in a 50℃ oven (citric acid gypsum raw material whiteness 88.5%, grade 92.1%, and attached water 0.13%). Then, it was uniformly mixed with 50g of hydroxypropyl distarch phosphate (a crystal form control agent) and 2200g of 35% phthalic acid-hydrochloric acid buffer in a reactor. The crystallization reaction temperature was controlled at 100℃, the reaction time at 3 hours, and the high-speed shear stirring rate at 2000 r / min. After the reaction, the slurry was filtered and washed three times. The filtrate was returned to the crystallization reaction for recycling, and the wash water was returned to the crystallization acid solution for recycling. After washing, the Type II anhydrous gypsum was dried in a 50℃ oven to constant weight, and its whiteness, water of crystallization content and particle size were tested. The test results were: whiteness of 94.7%, water of crystallization content of 0.23%, and average D90 particle size of 10.2µm. It is a relatively ideal alternative filler for the polymer field.

[0021] Example 3 500g of natural gypsum raw material was dried to constant weight in a 50℃ oven (whiteness of natural gypsum raw material was 90.1%, grade was 93.8%, and attached water content was 0.09%). Then, it was uniformly mixed with 75g of sodium polyphosphate (a crystal form control agent) and 1925g of 40% hydrochloric acid-citric acid buffer solution in a reactor. The crystallization reaction temperature was controlled at 95℃, the reaction time at 5 hours, and the high-speed shear stirring rate at 2500 r / min. After the reaction, the slurry was filtered and washed three times. The filtrate was returned to the crystallization reaction for recycling, and the wash water was returned to the crystallization acid solution for recycling. After washing, the type II anhydrous gypsum was dried to constant weight in a 50℃ oven, and its whiteness, water of crystallization content, and particle size were tested. The results showed a whiteness of 96.6%, a water of crystallization content of 0.28%, and an average D90 particle size of 11.4µm, making it a relatively ideal alternative filler for polymer applications.

[0022] Comparative Example 1 475g of purified phosphogypsum raw material was dried to constant weight in a 50℃ oven (whiteness of phosphogypsum raw material was 64.8%, grade was 88.6%, and adsorbed water was 0.12%). Then, it was uniformly mixed with 2000g of 30% sulfuric acid solution in a reactor. The crystallization reaction temperature was controlled at 90℃, the reaction time at 4 hours, and the high-speed shear stirring rate at 1500 r / min. After the reaction, the slurry was filtered and washed three times. The filtrate was returned to the crystallization reaction for recycling, and the wash water was returned to the crystallization acid solution for recycling. After washing, the Type II anhydrous gypsum was dried in a 50℃ oven to constant weight, and its whiteness, water of crystallization content and particle size were tested. The test results were: whiteness 79.5%, water of crystallization content 0.51%, and average D90 particle size 33.6µm. It can be seen that the particle size of the Type II anhydrous gypsum prepared in the absence of crystal form control agent is relatively coarse. Microscopic observation shows that the overall particle crystal form is fibrous and the aspect ratio is large.

[0023] Comparative Example 2 475g of purified phosphogypsum raw material was dried to constant weight in a 50℃ oven (whiteness of phosphogypsum raw material was 64.8%, grade was 88.6%, and attached water content was 0.12%). Then, it was uniformly mixed in a reactor with a mixture of 25g of crystal form control agent citric acid and hexadecyltrimethylammonium bromide, and 2000g of 30% sulfuric acid solution. The crystallization reaction temperature was controlled at 90℃, the reaction time at 4h, and the high-speed shear stirring rate at 1500r / min. After the reaction, the slurry was filtered and washed three times. The filtrate was returned to the crystallization reaction for recycling, and the wash water was returned to the crystallization acid solution for recycling. After washing, the type II anhydrous gypsum was dried to constant weight in a 50℃ oven, and its whiteness, water of crystallization content, and particle size were tested. The results were: whiteness 79.3%, water of crystallization content 0.42%, and average D90 particle size 18.6µm.

[0024] Comparative Example 3 475g of purified phosphogypsum raw material was dried to constant weight in a 50℃ oven (whiteness of phosphogypsum raw material was 64.8%, grade was 88.6%, and attached water was 0.12%). Then, it was uniformly mixed with 25g of hydroxypropyl methylcellulose phthalate (a crystal form control agent) and 2000g of 30% sulfuric acid solution in a reactor. The crystallization reaction temperature was controlled at 90℃, the reaction time at 4 hours, and the high-speed shear stirring rate at 1500 r / min. After the reaction, the slurry was filtered and washed three times. The filtrate was returned to the crystallization reaction for recycling, and the wash water was returned to the crystallization acid solution for recycling. After washing, the Type II anhydrous gypsum was dried in a 50℃ oven to constant weight, and its whiteness, water of crystallization content and particle size were tested. The test results were: whiteness of 90.3%, water of crystallization content of 0.3%, and average D90 particle size of 22.4µm. It is a relatively ideal alternative filler for the polymer field.

Claims

1. A method for preparing micron-sized type II anhydrous gypsum, characterized in that: Natural gypsum raw materials or purified industrial by-product gypsum raw materials, crystal form control agents and crystallization acid solutions are uniformly mixed, and then subjected to high-speed shearing and stirring in a reaction vessel. After the crystallization reaction is completed, the slurry is filtered, washed and dried to obtain the final product.

2. The method for preparing micron-sized type II anhydrous gypsum as described in claim 1, characterized in that: The mass fractions of the natural gypsum raw material or purified industrial by-product gypsum raw material, crystal form control agent, and transcrystalline acid solution are 10%~20%, 0.5%~3%, and 77%~89.5%, respectively.

3. The method for preparing micron-sized type II anhydrous gypsum as described in claim 2, characterized in that: The natural gypsum raw material or the purified industrial by-product gypsum raw material has a whiteness of 60% or above, a grade of 80% or above, and an attached water content of 1% or below.

4. The method for preparing micron-sized type II anhydrous gypsum as described in claim 1, characterized in that: The natural gypsum raw material or the purified industrial by-product gypsum raw material is dried at 40℃~80℃ to constant weight to ensure that the attached water is removed while the crystal water does not escape.

5. The method for preparing micron-sized type II anhydrous gypsum as described in claim 1, characterized in that: The crystal form control agent is selected from any one or more of hydroxypropyl methylcellulose phthalate, maleic acid, sodium polyphosphate, and hydroxypropyl distarch phosphate.

6. The method for preparing micron-sized type II anhydrous gypsum as described in claim 1, characterized in that: The transcrystallization acid solution is hydrochloric acid-glycine buffer, hydrochloric acid-citric acid buffer, phthalic acid-hydrochloric acid buffer, or pyromellitic acid-hydrochloric acid buffer.

7. The method for preparing micron-sized type II anhydrous gypsum as described in claim 6, characterized in that: The mass concentration of the acid solution for crystallization is between 25% and 50%.

8. The method for preparing micron-sized type II anhydrous gypsum as described in claim 1, characterized in that: The high-speed shear-transformation reaction is carried out at a temperature of 85℃~100℃ and for a reaction time of 1h~5h.

9. The method for preparing micron-sized type II anhydrous gypsum as described in claim 1, characterized in that: The high-speed shear stirring rate is between 1000 r / min and 3000 r / min.

10. The method for preparing micron-sized type II anhydrous gypsum as described in claim 1, characterized in that: The slurry is filtered and then washed at least twice before being dried in an oven at 40°C to 60°C. The filtrate is returned to the crystallization reaction for recycling, and the wash water is returned to the crystallization acid solution for recycling.