Preparation method of calcium sulfate whisker

Abstract

The invention provides a preparation method of calcium sulfate whiskers. The preparation method comprises the following steps: S1, raw material pretreatment: selecting desulfurized gypsum or phosphogypsum as a raw material; the desulfurized gypsum is subjected to screening to remove large-particle impurities, ball-milling to refine particles and pickling to remove calcium sulfite and fly ash in sequence, so that the content of dihydrate gypsum in the pretreated desulfurized gypsum is greater than or equal to 95%, the desulfurized gypsum does not contain calcium sulfite and chloride ions, and the particle size distribution is uniform; according to the method, efficient resource utilization of industrial byproduct gypsum and precise regulation and control of directional growth of whiskers are deeply fused, specific impurities in the byproduct gypsum are removed through a targeted pretreatment process, and the solubility difference of dihydrate gypsum and semi-hydrate gypsum in a hydrothermal environment is used as growth driving force; the method has the advantages that the low-grade industrial solid waste is directly converted into the high-quality calcium sulfate crystal whiskers under the assistance of the guidance of the crystal modifier on the oriented growth of crystal nucleuses, and the process not only solves the environmental protection problem of byproduct gypsum stockpiling, but also breaks through the dependence of the traditional preparation method on high-purity raw materials.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of calcium sulfate whisker preparation, in particular to a preparation method of calcium sulfate whisker. BACKGROUND

[0002] The calcium sulfate whisker is a fibrous single crystal of calcium sulfate, which can be prepared by calcining natural gypsum or chemical synthesis, and has the structural characteristics of high order of atomic arrangement and large length-diameter ratio. The core performance is outstanding, and the calcium sulfate whisker has the characteristics of high strength, high elastic modulus, high temperature resistance, corrosion resistance, good insulation, excellent compatibility with plastic, rubber, cement and other matrix materials, and easy dispersion. The calcium sulfate whisker is widely used in industry, and is commonly used in the fields of composite material reinforcement (such as improving the strength of plastic parts and improving the toughness of cement products), friction material (wear-resistant components of brake pads and clutch plates), filter material (high-efficiency filter medium) and papermaking filler, and is an ideal inorganic reinforcing material for replacing part of metals and glass fibers due to the easy availability of raw materials, low cost and environmental friendliness.

[0003] At present, the calcium sulfate whisker preparation technology (such as the normal pressure acidification method) has the following core defects, which are fully verified in the patent CN105133003B "Production method of alpha hemihydrate calcium sulfate whisker from wet-process phosphoric acid by-product": (1) Dual limitation of raw material conversion rate and whisker performance, and limited conversion rate of phosphogypsum: The patent embodiment shows that the fluorine ions (F - ) in the phosphogypsum combine with calcium ions to form calcium fluoride precipitate, directly inhibiting the nucleation and growth of crystals, so that the conversion rate of the phosphogypsum is only about 68%. In addition, phosphoric acid (H3PO4) reacts with calcium ions to form calcium dihydrogen phosphate (Ca(H2PO4)2), further reducing the utilization rate of raw materials, and the final conversion rate is less than 68%.

[0004] (2) The length-diameter ratio is seriously insufficient: The length-diameter ratio of the whisker prepared by the normal pressure acidification method is only 10-20, which is far lower than the international standard requirement of 50-80. The powder network research points out that the crystal growth along the C axis is blocked in the acid medium, and the lateral growth is dominant, resulting in rough surface of the whisker and high breakage rate of up to 30%; (3) The impurity residues significantly affect the purity: The content of phosphorus pentoxide (P2O5) in the whisker reaches 0.05%, and an additional impurity removal process is required to meet the building material industry standard. When the fluorine ion exceeds 0.3%, the whisker has a rough structure, and the content of hemihydrate gypsum phase further decreases. SUMMARY

[0005] (I) Technical problems solved In view of the deficiencies of the prior art, the application provides a preparation method of calcium sulfate whiskers, which solves the problems of limited conversion rate, serious lack of length-diameter ratio and significant impurity residue of calcium sulfate whiskers prepared by the prior art.

[0006] (II) Technical solutions To achieve the above object, the application is implemented by the following technical solutions: a preparation method of calcium sulfate whiskers, comprising the following steps: S1, raw material pretreatment: Desulfurization gypsum or phosphogypsum is selected as the raw material; for the desulfurization gypsum, large-particle impurities are removed by screening, the particles are refined by ball milling, and calcium sulfite and fly ash are removed by acid washing, so that the content of dihydrate gypsum in the pretreated desulfurization gypsum is ≥95%, and the pretreated desulfurization gypsum does not contain calcium sulfite and chloride ions, and the particle size distribution is uniform; For the phosphogypsum, at least 5 times of water washing is performed to remove undecomposed phosphate ore, organic matter, phosphoric acid and fluorine, so that the content of dihydrate gypsum in the pretreated phosphogypsum is ≥95%, and the pretreated phosphogypsum does not contain phosphoric acid and fluorine, and the whiteness meets the preparation requirements of calcium sulfate whiskers; S2, slurry preparation: The pretreated gypsum in S1 is mixed with water, and the slurry concentration is controlled to make the solution system be in a suitable supersaturation degree, so that a uniform slurry is obtained; S3, adding a crystal mediation agent: The crystal mediation agent is added to the slurry in S2, the crystal mediation agent is a reagent that can control the directional growth of calcium oxide and sulfur dioxide on the crystal nucleus, and the amount is adjusted according to the type to promote the concentrated burst nucleation of the crystal nucleus and guide the growth of calcium sulfate whiskers, and does not change the hemihydrate gypsum phase composition of the calcium sulfate whiskers; S4, hydrothermal reaction: The slurry after adding the crystal mediation agent is placed in a high-temperature and high-pressure reaction kettle, and the reaction temperature is controlled to be 130-140 DEG C; The reaction pressure is controlled to be the saturated steam pressure corresponding to the temperature; The stirring rate is controlled to be 50-150 r / min; The reaction time is controlled to be 2-4 h; The solution pH is controlled to be 6-8; During the reaction process, the dissolution of dihydrate gypsum and the growth of hemihydrate calcium sulfate whiskers coexist, and the solubility difference between the two is used as the driving force for the growth of calcium sulfate whiskers, until the crystallization is completed; S5, subsequent treatment: After the reaction is completed, the product is dried and dehydrated, the drying temperature is 200-600 DEG C, and a stabilizing agent can be optionally added in stages to obtain calcium sulfate whiskers.

[0007] Preferably, in S2, the liquid-solid mass ratio of the slurry is 5-10:1, so as to avoid the influence of too thick or too thin slurry on the growth of calcium sulfate whiskers.

[0008] Preferably, in the S3, the crystal agent is an agent capable of regulating the directional arrangement of calcium oxide and sulfur dioxide, and the addition amount is 0.5%-2% of the mass of gypsum.

[0009] Preferably, in the S4, the preset low speed is 50-150 r / min to prevent the calcium sulfate whisker from breaking.

[0010] Preferably, in the S4, the reaction time is 2-4 h to avoid secondary dissolution or incomplete growth of the calcium sulfate whisker.

[0011] Preferably, in the S5, the staged addition of the stabilizer is specifically: adding the first portion of the stabilizer during the preparation of the calcium sulfate whisker, and adding the second portion of the stabilizer after the reaction is completed, and the total amount of the two portions of the stabilizer is reduced by 10%-30% compared with single-stage addition.

[0012] Preferably, in the S5, the staged addition of the stabilizer is specifically: adding the first portion of the stabilizer during the preparation of the calcium sulfate whisker, and adding the second portion of the stabilizer after the reaction is completed, and the total amount of the two portions of the stabilizer is reduced by 10%-30% compared with single-stage addition.

[0013] (Three) beneficial effects The application provides a preparation method of calcium sulfate whisker. The application has the following beneficial effects: 1. The application deeply integrates the efficient resource utilization of industrial by-product gypsum and the precise regulation of whisker directional growth. The specific impurities in the by-product gypsum are removed through targeted pretreatment process, the solubility difference between dihydrate gypsum and hemihydrate gypsum under hydrothermal environment is used as a growth driving force, and the crystal nucleus directional growth is guided by the crystal agent. The direct conversion from low-grade industrial solid waste to high-quality calcium sulfate whisker is realized. This process not only solves the environmental protection problem of by-product gypsum storage, but also breaks through the dependence of traditional preparation methods on high-purity raw materials.

[0014] 2. The application realizes the controllable adjustment of the performance of calcium sulfate whisker through the synergistic optimization of multi-dimensional process parameters. The product has uniform crystal morphology and strong structural stability, and can be adjusted in performance according to the application scene requirements, breaking through the bottleneck of single product performance and limited application of traditional methods. Specific embodiments

[0015] The technical solutions in the embodiments of the application will be described below. Obviously, the described embodiments are only part of the embodiments of the application, not all. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the application.

[0016] Embodiment: The embodiment of the present application provides a preparation method of calcium sulfate whiskers, comprising the following steps: S1, raw material pretreatment: Desulfurization gypsum or phosphogypsum is selected as the raw material; for the desulfurization gypsum, large particle impurities are removed by screening, particles are refined by ball milling, and calcium sulfite and fly ash are removed by acid washing, so that the content of dihydrate gypsum in the pretreated desulfurization gypsum is greater than or equal to 95%, and the dihydrate gypsum does not contain calcium sulfite and chloride ions, and the particle size distribution is uniform; For the phosphogypsum, at least 5 times of water washing is performed to remove undecomposed phosphate ore, organic matter, phosphoric acid and fluorine, so that the content of dihydrate gypsum in the pretreated phosphogypsum is greater than or equal to 95%, and the dihydrate gypsum does not contain phosphoric acid and fluorine, and the whiteness meets the preparation requirements of calcium sulfate whiskers; S2, slurry preparation: The pretreated gypsum in S1 is mixed with water, and the slurry concentration is controlled to make the solution system in a suitable supersaturation degree, so that a uniform slurry is obtained; S3, adding a crystal mediation agent: The crystal mediation agent is added to the slurry in S2, the crystal mediation agent is a reagent capable of adjusting the directional growth of calcium oxide and sulfur dioxide on the crystal nucleus, and the amount is adjusted according to the type to promote the concentrated burst nucleation of the crystal nucleus and guide the growth of calcium sulfate whiskers, and does not change the hemihydrate gypsum phase composition of the calcium sulfate whiskers; S4, hydrothermal reaction: The slurry after adding the crystal mediation agent is placed in a high-temperature and high-pressure reaction kettle, and the reaction temperature is controlled at 130-140 DEG C; The reaction pressure is controlled at the saturated steam pressure corresponding to the temperature; The stirring rate is controlled at 50-150 r / min; The reaction time is controlled at 2-4 h; The solution pH is controlled at 6-8; During the reaction process, the dissolution of dihydrate gypsum and the growth of hemihydrate calcium sulfate whiskers coexist, and the solubility difference between the two is used as the driving force for the growth of calcium sulfate whiskers until the crystallization is completed; S5, subsequent treatment: After the reaction is completed, the product is dried and dehydrated, the drying temperature is 200-600 DEG C, and a stabilizing agent is optionally added in stages to obtain calcium sulfate whiskers.

[0017] In S2, the liquid-solid mass ratio of the slurry is 5-10:1, so as to avoid the influence of the slurry concentration on the growth of calcium sulfate whiskers.

[0018] In S3, the crystal mediation agent is a reagent capable of adjusting the directional arrangement of calcium oxide and sulfur dioxide, and the addition amount is 0.5%-2% of the mass of the gypsum.

[0019] In S4, the preset low speed is 50-150 r / min, so as to prevent the fracture of the calcium sulfate whiskers.

[0020] In S4, the reaction time is 2-4 h to avoid secondary dissolution or incomplete growth of calcium sulfate whiskers.

[0021] In S5, the stabilizer is added in stages: the first stabilizer is added during the preparation of the calcium sulfate whiskers, and the second stabilizer is added after the reaction is completed. The total amount of the two stabilizers is reduced by 10%-30% compared with the single-stage addition.

[0022] In S5, the stabilizer is added in stages: the first portion of the stabilizer is added during the preparation of the calcium sulfate whiskers, and the second portion of the stabilizer is added after the reaction is completed. The total amount of the two stabilizers is reduced by 10%-30% compared to single-stage addition.

[0023] Comparative Example: According to the conventional process of existing technology: Acid preparation: Prepare 4% hydrochloric acid solution; Reaction: The pretreated gypsum was mixed with hydrochloric acid at a liquid-solid ratio of 10:1 and placed in a constant temperature stirred reactor with a controlled temperature of 98°C, a stirring rate of 200 r / min, and a crystallization time of 4 h. Subsequent processing: natural drying, no stabilizer added.

[0024] Experimental example: The calcium sulfate whiskers prepared by the above two methods (one group each of desulfurized gypsum raw material group and phosphogypsum raw material group, a total of four groups of samples) were tested from the following three dimensions: (1) Aspect ratio and morphology comparison experiment: The whisker micromorphology was observed using a polarizing microscope. The length and diameter of 100 whiskers were counted, the average aspect ratio was calculated, and the crystal uniformity (whether there was breakage or agglomeration) was observed. (2) Conversion rate comparison experiment: Weigh the mass of the product after drying and calculate "product mass / raw material mass × 100%" to reflect the raw material conversion efficiency; (3) Purity test: X-ray diffraction (XRD) was used to analyze the content of hemihydrate gypsum phase in the whiskers and verify the residual impurities; (4) Composite material reinforcement test: The two types of whiskers were mixed into polypropylene (PP) at a ratio of 10%, and the tensile strength and flexural strength of the composite materials were tested using a universal material testing machine. The specific experimental data are shown in Table 1 below: Table 1

[0025] In summary, the calcium sulfate whiskers prepared by the present invention are significantly superior to the existing technology in terms of aspect ratio, conversion rate, purity and reinforcement, and have better comprehensive performance.

[0026] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely exemplary of the principles and application of the present application. Numerous modifications and adaptions can be effected without departing from the spirit and scope of the present application, which is not limited to the exact construction and arrangement described. It is intended, therefore, to cover all modifications and adaptions that fall within the scope of the claims and their equivalents.

Claims

1. A method for preparing calcium sulfate whiskers, characterized in that, The following steps are involved: S1. Raw material pretreatment: Select desulfurized gypsum or phosphogypsum as raw material; For desulfurization gypsum, screening is used to remove large particles of impurities, ball milling is used to refine the particles, and acid washing is used to remove calcium sulfite and fly ash. After pretreatment, the content of dihydrate gypsum in the desulfurization gypsum is ≥95%, and it does not contain calcium sulfite and chloride ions, and the particle size distribution is uniform. The phosphogypsum is washed at least five times to remove undecomposed phosphate rock, organic matter, phosphoric acid and fluorine, so that the dihydrate gypsum content in the pretreated phosphogypsum is ≥95%, and does not contain phosphoric acid and fluorine, and the whiteness meets the requirements for the preparation of calcium sulfate whiskers; S2. Slurry preparation: The gypsum pretreated in S1 is mixed with water, and the slurry concentration is controlled so that the solution system is at an appropriate supersaturation to obtain a uniform slurry; S3. Adding a crystallizing agent: Adding a crystallization agent to the slurry in S2, the crystallization agent is a reagent that can regulate the directional growth of calcium oxide and sulfur dioxide on the crystal nucleus. The amount of the crystallization agent is adjusted according to the type to promote the concentrated nucleation of the crystal nucleus and guide the growth of calcium sulfate whiskers without changing the hemihydrate gypsum phase composition of the calcium sulfate whiskers; S4. Hydrothermal reaction: Place the slurry after adding the crystallization agent in a high-temperature and high-pressure reactor, and control the reaction temperature to 130-140°C; Control the reaction pressure to the saturated vapor pressure at the corresponding temperature; Control the stirring rate to 50-150r / min; Control reaction time is 2-4h; Control the solution pH at 6-8; During the reaction, the dissolution of dihydrate gypsum and the growth of hemihydrate calcium sulfate whiskers coexist, and the solubility difference between the two is used as the driving force for the growth of calcium sulfate whiskers until the crystallization is completed. S5. Subsequent processing: After the reaction is completed, the product is dried and dehydrated at a drying temperature of 200-600° C., and a stabilizer is optionally added in stages to obtain calcium sulfate whiskers.

2. the preparation method of a kind of calcium sulfate whisker according to claim 1, is characterized in that: In the S2, the liquid-to-solid mass ratio of the slurry is 5-10:1 to avoid the slurry being too concentrated or too diluted to affect the growth of calcium sulfate whiskers.

3. the preparation method of a kind of calcium sulfate whisker according to claim 1, is characterized in that: In the above-mentioned S3, the crystallizing agent is a reagent that can regulate the directional arrangement of calcium oxide and sulfur dioxide, and its addition amount is 0.5%-2% of the mass of gypsum.

4. the preparation method of a kind of calcium sulfate whisker according to claim 1, is characterized in that: In the step S4, the low speed is preset to 50-150 r / min to prevent the calcium sulfate whiskers from breaking.

5. the preparation method of a kind of calcium sulfate whisker according to claim 1, is characterized in that: In S4, the reaction time is 2-4 hours to avoid secondary dissolution or incomplete growth of the calcium sulfate whiskers.

6. the preparation method of a kind of calcium sulfate whisker according to claim 1, is characterized in that: In S5, the stabilizer is added in stages: the first stabilizer is added during the preparation of the calcium sulfate whiskers, and the second stabilizer is added after the reaction is completed. The total amount of the two stabilizers is reduced by 10%-30% compared with the single-stage addition.

7. a preparation method of calcium sulfate whisker according to claim 1, is characterized in that: In S5, the stabilizer is added in stages: the first stabilizer is added during the preparation of the calcium sulfate whiskers, and the second stabilizer is added after the reaction is completed. The total amount of the two stabilizers is reduced by 10%-30% compared with the single-stage addition.

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