A method for efficiently extracting calcium sulfate whiskers from semi-dry desulfurization ash

Abstract

The present invention discloses a method for efficiently extracting calcium sulfate whiskers from semi-dry desulfurized ash, belonging to the technical field of industrial solid waste resource utilization. The method comprises the following steps: (1) Pretreatment: screening out impurity particles larger than 5 mm; (2) Using a ball milling device combined with zirconia / aluminum oxide balls for grinding to exfoliate calcium sulfate whiskers; (3) Adding a fatty acid or sulfonate collector and selectively separating calcium sulfate whiskers from calcium hydroxide by flotation; (4) Washing with deionized water and drying at low temperature to obtain calcium sulfate whiskers with a purity ≥ 95% and an aspect ratio greater than 15, and recovering a highly active desulfurizer with a specific surface area ≥ 50 m 2 / g and a Ca(OH)2 content ≥ 90 wt%. Through the synergistic effect of physical desorption and flotation separation, the present invention solves the problems of acidic wastewater pollution, strong equipment dependence and high energy consumption in the prior art, and there is no secondary pollution, realizing the high-value utilization and resource recycling of desulfurized ash.

Description

Technical Field

[0001] The present invention relates to the technical field of resource utilization of industrial waste, and particularly relates to a method for efficiently extracting calcium sulfate whiskers from semi-dry desulfurization ash. Background Art

[0002] Semi-dry desulfurization ash is the main by-product of industrial flue gas semi-dry desulfurization. Its composition is complex and unstable, usually containing free calcium oxide, calcium sulfite, calcium carbonate, calcium sulfate, calcium hydroxide and other substances. Due to the easy decomposition or mutual reaction of these components, it is extremely challenging to efficiently extract high-purity calcium sulfate whiskers from desulfurization ash. Although preparing calcium sulfate whiskers from semi-dry desulfurization ash has significant economic and environmental value, the existing technologies generally have defects such as low extraction efficiency, high cost, complex process and poor environmental protection, which are specifically reflected in the following mainstream methods:

[0003] (1) Direct acidolysis method (chemical method)

[0004] This method uses a strong acid (such as sulfuric acid) solution to mix with semi-dry desulfurization ash and stirs and reacts at 50 - 70 °C, so that the calcium-based components (calcium oxide, calcium hydroxide) react with the acid to form calcium sulfate precipitate (such as CN108707292A). This method has a relatively direct reaction, but a large amount of acidic waste liquid will be generated during the reaction, which needs to be neutralized additionally, increasing the cost (such as a wastewater treatment system needs to be equipped in CN108707292A), and the strong acid environment seriously corrodes the reaction equipment, with high maintenance costs. In addition, the high-temperature acidic environment also poses a threat to the safety of operators.

[0005] (2) Hydrothermal synthesis method (high-pressure method)

[0006] This method reacts semi-dry desulfurization ash with water in a high-temperature and high-pressure environment. For example, the desulfurization ash and water are mixed in a ratio of 1:5 - 1:10, placed in a high-pressure reaction kettle, and reacted at 120 - 200 °C and 1 - 3 MPa for 4 - 8 hours to generate calcium sulfate whiskers (such as JP2020158176A). This method can prepare calcium sulfate products with specific morphologies and properties, but it has a strong dependence on equipment and requires a professional high-pressure reaction kettle, with high equipment investment (such as JP2020158176A mentions that the equipment cost accounts for more than 60% of the total investment); the operating conditions are also relatively harsh, carried out in a high-temperature and high-pressure environment, requiring strict safety specifications, and it is difficult to promote industrially; at the same time, long-term high-pressure operation leads to significant energy consumption.

[0007] (3) Calcination-leaching method (high-temperature method)

[0008] This method first conducts high-temperature calcination on semi-dry desulfurized ash, and then uses a solvent to leach the calcined product. For example, the desulfurized ash is calcined at 800 - 1000 °C for 2 - 4 hours, and calcium sulfite is oxidized to calcium sulfate, and then purified by hot water leaching (US20190185758A1). This method can obtain calcium sulfate products with relatively high purity, but the calcination process releases sulfur-containing waste gas, resulting in secondary pollution. Desulfurization equipment needs to be equipped (such as the waste gas treatment cost accounts for 15% of the total cost in US20190185758A1), and the high-temperature calcination has huge energy consumption and poor economy.

[0009] (4) Salting-out method (physical and chemical method)

[0010] This method adds salts such as calcium chloride to the aqueous solution of semi-dry desulfurized ash, and uses the salt effect to reduce the solubility of calcium sulfate and precipitate it (CN110117163A). This method is relatively simple to operate, but the addition of salts may introduce new impurities, and the salt residues need to be washed multiple times (such as more than 3 purification steps in CN110117163A), the separation efficiency is low, the crystals are easy to entrap impurities, and the product purity is insufficient; moreover, the consumption of salts and purification steps increase the overall cost.

[0011] Generally speaking, the existing technologies mainly have the following bottlenecks:

[0012] (1) Component complexity: Multiple components coexist in the desulfurized ash (such as free CaO is easy to hydrate and release heat), resulting in poor process stability;

[0013] (2) Insufficient environmental protection: Problems such as chemical method wastewater, high-temperature method waste gas, and salting-out method impurities are prominent;

[0014] (3) Low economic efficiency: The proportion of equipment investment and energy consumption cost is too high (such as high-pressure equipment accounts for 60%, and calcination energy consumption accounts for 40%);

[0015] (4) Product performance limitations: The whiskers obtained by the existing technologies have low purity (<90%) and small aspect ratio (<10), which are difficult to meet the requirements of high-end applications.

[0016] Therefore, developing a process for extracting calcium sulfate whiskers from semi-dry desulfurized ash with "low cost, high purity, and environmental protection" has important scientific significance and broad application prospects. Through technological innovation and process optimization, improving the extraction efficiency and purity will open up new ways for the resource utilization of semi-dry desulfurized ash, promote the development of circular economy, and at the same time reduce environmental pollution and resource waste, achieving the dual goals of effective utilization of industrial waste and environmental protection. Summary of the Invention

[0017] In view of the above problems, the present invention provides a method for efficiently extracting calcium sulfate whiskers from semi-dry desulfurized ash. Through the combination of "physical desorption + flotation separation", chemical reagents and high-pressure / high-temperature equipment are abandoned. By using ball milling to exfoliate the whiskers, flotation for selective separation, and low-temperature drying for refining, the extraction efficiency and environmental friendliness are significantly optimized (for example, the purity in Example 1 reaches 96% and the recycling rate of calcium hydroxide is 85%). This technological breakthrough not only solves the core defects of existing methods but also provides an industrially feasible path for the resource utilization of desulfurized ash.

[0018] The technical solution adopted by the present invention is as follows:

[0019] A method for efficiently extracting calcium sulfate whiskers from semi-dry desulfurized ash, comprising the following steps:

[0020] S1. Pretreatment: Screening out impurity particles with a particle size greater than 5 mm in the semi-dry desulfurized ash; before starting the whisker desorption process, performing pretreatment on the semi-dry desulfurized ash to remove impurity particles with a particle size greater than 5 mm. This measure can effectively reduce the wear of equipment during subsequent ball milling, and at the same time improve the ball milling efficiency and product quality.

[0021] S2. Whisker desorption: Placing the pretreated material in a ball milling device, controlling the ball milling speed at 120 - 200 revolutions per minute, the grinding duration at 1.5 - 3 hours, and the ball-to-material mass ratio at 3:1 - 5:1, so that the calcium sulfate whiskers are detached from the surface of the desulfurized ash;

[0022] S3. Component separation: Mixing the material ground in step S2 with water to form a suspension, adding 0.3% - 0.8% of a fatty acid or sulfonate collector based on the mass of the material, and separating calcium sulfate whiskers and calcium hydroxide by flotation;

[0023] S4. Product refinement: Washing and drying the calcium sulfate whiskers with deionized water, and recovering calcium sulfate whiskers with a purity ≥ 95% and calcium hydroxide with a desulfurization efficiency ≥ 80%.

[0024] Furthermore, in step S1, the screening is carried out using a sieve, preferably a stainless steel sieve with a pore size of 5 mm. <\

[0025] Further, in step S2, zirconia balls or alumina balls are used as grinding media. Grinding media such as zirconia balls or alumina balls have high strength and chemical stability. During the ball milling process, they can withstand large impact forces and are not easily worn, ensuring the consistency and continuity of the ball milling effect. With the precise control of the ball milling device, such as the running speed (120 - 200 revolutions per minute), the grinding duration (1.5 - 3 hours), and the mass ratio of grinding media to materials (3:1 - 5:1), physical interactions occur sufficiently during the grinding process of semi-dry desulfurized ash. Under these precisely controlled conditions, the semi-dry desulfurized ash particles continuously collide and rub against each other and with the grinding media, enabling the calcium sulfate whiskers attached to the surface of the semi-dry desulfurized ash to be effectively detached.

[0026] Further, in step S3, the liquid-solid mass ratio of the ground material to water is 5:1 - 10:1.

[0027] Further, in step S3, the fatty acid collectors include fatty acid collectors and modified fatty acid collectors. Fatty acid collectors such as oleic acid, linolenic acid, sodium oleate, etc., modified fatty acid collectors such as sulfonated oleic acid, octyl hydroxamic acid, benzohydroxamic acid, etc., and sulfonate collectors such as sodium dodecyl sulfonate, sodium p-methoxybenzenesulfonate, sodium dodecylbenzenesulfonate, etc.

[0028] Further, in step S3, the dosage of the collector is preferably 0.4% - 0.6% of the material mass. An appropriate dosage of the collector can selectively adsorb well on the surface of the calcium sulfate whiskers, changing their surface wettability and converting them from hydrophilic to hydrophobic. Due to its own chemical structure and properties, the surface of calcium hydroxide is not easily strongly adsorbed by the separation reagent and remains hydrophilic. Air is introduced into the suspension system to generate a large number of tiny bubbles. The hydrophobic calcium sulfate whiskers quickly attach to the bubbles and rise to the liquid surface with the bubbles, gathering to form a foam layer, while the hydrophilic calcium hydroxide remains in the suspension. By scraping the foam layer, the effective separation of calcium sulfate whiskers and calcium hydroxide is achieved.

[0029] Further, in step S3, during the flotation process, the stirring speed is controlled at 150 - 300 revolutions per minute to ensure the uniform dispersion of bubbles in the suspension and the full suspension of the materials, thereby improving the flotation effect and separation efficiency.

[0030] Further, in step S4, the drying temperature is 100-120°C. Purification is achieved by washing with deionized water multiple times to thoroughly remove the flotation agents, impurities, and other substances that may affect its performance remaining on the surface of the calcium sulfate whiskers. Drying is carried out by low-temperature drying, and the temperature is strictly controlled within 100-120°C. This temperature range can not only ensure the full evaporation of water in the calcium sulfate whiskers but also avoid changes in its crystal structure or damage to its performance due to excessive temperature. For the recovered calcium hydroxide, due to its high activity, it can be directly used as a desulfurization agent in the desulfurization process.

[0031] Further, in step S4, the purity of the dried calcium sulfate whiskers is not less than 95%, and the aspect ratio of the calcium sulfate whiskers ranges from 10 to 50.

[0032] The beneficial effects of the present invention are as follows:

[0033] (1) High efficiency: The whisker desorption rate ≥ 80%, and the purity ≥ 95%;

[0034] (2) Low cost: No strong acid / high-pressure equipment is required, and the energy consumption is significantly reduced;

[0035] (3) Environmental protection: There is no acidic wastewater, and calcium hydroxide can be recycled. Description of the Drawings

[0036] Figure 1 It is the SEM image of the semi-dry desulfurized ash raw material in Example 1, Figure 1 indicating that the surface of the calcium hydroxide substrate particles in the semi-dry desulfurized ash is coated with calcium sulfate whiskers. The calcium sulfate whiskers show a network structure, and a small amount of irregular blocky impurity particles can be seen, corresponding to the 7.34% impurity content in the raw material.

[0037] Figure 2 It is the SEM image of the calcium hydroxide obtained in Example 1, Figure 2 showing that there are a large number of fresh fracture surfaces on the surface of the separated calcium hydroxide particles (the roughness is significantly increased), indicating that the calcium sulfate whiskers have detached from the substrate during the ball milling process. The calcium hydroxide after whisker desorption exposes more active sites.

[0038] Figure 3 It is the SEM image of the calcium sulfate whisker calcium hydroxide obtained in Example 1, Figure 3 showing that the calcium sulfate whiskers have a uniform needle-like structure, with a diameter of 0.3-0.8 μm, a length of 20-50 μm, an aspect ratio > 15, a smooth surface without attachments, and a whisker purity of 96.57%, meeting the industrial application standards. Detailed Embodiments

[0039] To facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings of the specification and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments. Example 1

[0040] Raw material preparation: 100 kg of semi-dry desulfurized ash was collected from a certain thermal power plant. Through scanning electron microscope analysis (as shown in its SEM diagram), it was found that calcium sulfate whiskers covered the surface of calcium hydroxide base particles in the semi-dry desulfurized ash, and the calcium sulfate whiskers densely coated the surface of calcium hydroxide particles in a network structure. The composition of the semi-dry desulfurized ash was accurately detected by chemical analysis methods. The results showed that the calcium sulfate content was 49.93 wt%, the calcium hydroxide content was 42.73 wt%, and the content of other impurities was 7.34%. At the same time, the physical properties such as the particle size distribution of the semi-dry desulfurized ash were also measured, and its average particle size was 8.901 μm. Figure 1

[0041] Pretreatment: A stainless steel sieve with a pore size of 5 mm was selected to screen the semi-dry desulfurized ash. During the screening process, through the mechanical vibration of the vibrating screen, the semi-dry desulfurized ash moved evenly on the sieve, and large particle impurities were effectively intercepted above the sieve. After about 30 minutes of screening operation, the impurity particles with a particle size greater than 5 mm were removed, and 98 kg of pretreated semi-dry desulfurized ash was obtained. The particle size of the pretreated semi-dry desulfurized ash was detected again, and it was found that the removal of large particle impurities made the particle size of the semi-dry desulfurized ash more uniform, providing better raw material conditions for subsequent ball milling.

[0042] Whisker desorption (ball milling): The pretreated semi-dry desulfurized ash was put into a ball milling device. Zirconia balls were selected as the grinding medium, the ball-to-material mass ratio was 3:1, the rotation speed was 150 revolutions per minute, and the grinding duration was 2 hours. During the ball milling process, a temperature sensor was used to monitor the temperature in the ball milling tank in real time to ensure that the temperature was maintained within an appropriate range to avoid affecting the whisker desorption effect or changing the material properties due to too high temperature.

[0043] Component separation (flotation): The ball-milled material was added to a flotation cell. Deionized water was slowly added at a liquid-to-solid mass ratio of 5:1, and at the same time, the stirring device was turned on and stirred at a speed of 150 revolutions per minute to make the material fully disperse to form a uniform suspension. Then, oleic acid was added as a collector, and the dosage was 0.5% of the material mass. After adding the reagent, the stirring speed was increased to 200 revolutions per minute and stirred continuously for 60 minutes to ensure that the reagent was fully in contact with the material and played a role. Then, air was introduced into the bottom of the flotation cell through an air compressor to generate a large number of tiny bubbles. During the flotation process, the formation of the foam layer and the flotation effect were observed every 15 minutes. After 120 minutes of flotation, the foam layer was scraped off by a foam scraping machine to obtain the preliminarily separated calcium sulfate whiskers.

[0044] Product refinement: Place the obtained calcium sulfate whiskers in a cleaning tank and wash them 3 times with deionized water. During each washing, stir at a speed of 200 revolutions per minute for 30 minutes, and then perform solid-liquid separation through a filtration device to ensure that residual flotation reagents, impurities, etc. are fully removed. The washed calcium sulfate whiskers are placed in an oven and dried at a temperature of 110 °C for 8 hours. During the drying process, use the humidity sensor in the oven to monitor the humidity change to ensure the stability of the drying environment. For the separated calcium hydroxide, Figure 2 As can be seen from the SEM image shown in, a large number of fresh fracture surfaces are exposed on the surface of the separated calcium hydroxide, indicating that the calcium sulfate whiskers have detached from the surface of the semi-dry desulfurized ash, realizing the recovery of calcium hydroxide. Perform BET testing and content analysis on the recovered calcium hydroxide, and find that its specific surface area (static BET) is 53 m 2 / g, and the Ca(OH)2 content is 90.58 wt%, meeting the requirements for a highly active desulfurization agent and can be directly recycled.

[0045] For the dried calcium sulfate whiskers, perform particle size classification using a laser particle size analyzer. The results show that approximately 90% of the products meet the target particle size range. For the non-conforming products, reintroduce them into the ball mill for secondary ball milling. During secondary ball milling, the rotation speed is controlled at 160 revolutions per minute, and the ball milling duration is 0.7 hours. After secondary ball milling, repeat the steps of flotation separation, purification, and drying. Finally, obtain 48 kg of calcium sulfate whisker products with a purity of 96.57%, whose aspect ratio is greater than 15, and its SEM image is as shown in Figure 3 shown. Example 2

[0046] Raw material preparation: Collect 150 kg of semi-dry desulfurized ash from a certain steel plant. Through professional component analysis in a laboratory, the calcium sulfate content in this semi-dry desulfurized ash is 48.22 wt%, the calcium hydroxide content is 46.48 wt%, and the content of other impurities is 5.3 wt%.

[0047] Pretreatment: Use the same material and pore size sieve as in Example 1 to screen the semi-dry desulfurized ash. During the screening process, in order to improve the screening efficiency, adjust the amplitude and frequency of the vibrating screen. After about 30 minutes of screening operation, 147 kg of semi-dry desulfurized ash is obtained after removing impurity particles.

[0048] Whisker desorption: Put the semi-dry desulfurized ash into a ball mill device, select alumina balls as the grinding medium, and the mass ratio of balls to materials is 4:1. Through the intelligent control panel of the ball mill device, set the running speed of the ball mill device to 180 revolutions per minute and the grinding duration to 2.5 hours. During the ball milling process, regularly check the running status of the ball mill device to ensure the stable operation of the equipment. Use SEM to observe and perform quantitative analysis in combination with image analysis software, and it is found that about 90% of the calcium sulfate whiskers have detached from the surface of the semi-dry desulfurized ash.

[0049] Component separation: Put the ball-milled material into a flotation cell, slowly add deionized water at a liquid-solid mass ratio of 10:1, and at the same time turn on the stirring device and stir at a speed of 120 revolutions per minute to make a suspension. Then add sulfated modified oleic acid as a collector (the molar ratio of oleic acid to sulfuric acid is 1:0.3), and the dosage is 0.6% of the mass of the ball-milled material. After adding the reagent, increase the stirring speed to 250 revolutions per minute and stir for 60 minutes to make the reagent evenly dispersed and fully interact with the material. Then, pass air into the flotation cell through an air distributor for flotation, and the flotation time is 20 minutes. During the flotation process, carefully observe the characteristics of the foam layer such as color and thickness to judge the flotation effect. Collect the foam layer to obtain the preliminarily separated calcium sulfate whiskers. Conduct a preliminary purity test on the collected foam layer to provide a reference for the subsequent refining process.

[0050] Product refinement: Wash the calcium sulfate whiskers 4 times. Each time during washing, use different combinations of stirring speed and washing time to achieve the best washing effect. After washing, perform solid-liquid separation through a vacuum filtration device to minimize moisture residue. Then put the calcium sulfate whiskers into an oven and dry them at a temperature of 105 °C for 8 hours. During the drying process, adjust the ventilation system of the oven to ensure the uniformity of the drying environment. Directly recycle the separated calcium hydroxide. Conduct particle size classification on the dried calcium sulfate whiskers, and about 88% of the products meet the target particle size range. Process the non-conforming products again. The rotational speed of the secondary ball mill is 170 revolutions per minute, and the ball milling duration is 0.8 hours. After secondary ball milling, repeat the steps of flotation separation, purification, and drying. Finally, obtain 70.26 kg of calcium sulfate whisker products with a purity of 95.5%, and the aspect ratio is between 12 and 45. Example 3

[0051] Raw materials: Desulfurized ash from a chemical plant (calcium sulfate 58.71 wt%, calcium hydroxide 36.28 wt%, other impurity content is 5.01%);

[0052] Pretreatment: Remove impurities with a 5 mm stainless steel sieve mesh;

[0053] Ball milling: The mass ratio of balls to materials is 5:1, the rotational speed is 200 revolutions per minute, and the duration is 1.5 hours;

[0054] Flotation: Using 0.5% sodium dodecylbenzenesulfonate as collector, stirring speed 300 rpm;

[0055] Fine grinding: Drying at 100 °C for 10 hours, calcium sulfate purity 95%. Example 4

[0056] Raw materials: Desulfurized ash from a cement plant (calcium sulfate 54.46 wt%, calcium hydroxide 41.25 wt%, other impurity content 4.29%);

[0057] Pretreatment: Removing impurities with a 5 mm stainless steel sieve;

[0058] Ball milling: Ball-to-material mass ratio 3.5:1, rotation speed 130 rpm, duration 2.8 hours;

[0059] Flotation: Using a compound of oleic acid and sodium dodecylbenzenesulfonate (SDBS) with a mass ratio of 3:1 as collector, total addition amount maintained at 0.5%, stirring speed 180 rpm;

[0060] Fine grinding: Drying at 120 °C for 6 hours, calcium sulfate purity 97.5%. Example 5

[0061] Raw materials: Desulfurized ash from a waste incineration plant (calcium sulfate 61.63 wt%, calcium hydroxide 35.58 wt%, other impurity content 2.79%);

[0062] Pretreatment: Removing impurities with a 5 mm stainless steel sieve;

[0063] Ball milling: Ball-to-material mass ratio 4.5:1, rotation speed 170 rpm, duration 2.2 hours;

[0064] Flotation: Using a compound of oleic acid and sodium dodecylbenzenesulfonate (SDBS) with a mass ratio of 1:3 as collector, total addition amount maintained at 0.5%, stirring speed 220 rpm;

[0065] Fine grinding: Drying at 115 °C for 7 hours, calcium sulfate purity 96.5%. [[ID=4...]]

[0066] Comparative Example 1

[0067] This comparative example was implemented using the traditional acid hydrolysis method disclosed in CN108707292A, and the comparison items and results are shown in Table 1.

[0068] Table 1 Comparison items and results of Comparative Example 1 and Example 1

[0069] [[ID=...]]

Claims

1. A method for efficiently extracting calcium sulfate whiskers from semi-dry desulfurized ash, characterized in that, It includes the following steps: S1. Pretreatment: Screening out impurity particles with a particle size greater than 5 mm in the semi-dry desulfurized ash; S2. Whisker desorption: Placing the pretreated material in a ball milling device, controlling the ball milling speed at 120 - 200 revolutions per minute, the grinding duration at 1.5 - 3 hours, and the ball-to-material mass ratio at 3:1 - 5:1, so that the calcium sulfate whiskers are detached from the surface of the desulfurized ash; S3. Component separation: Mixing the material ground in step S2 with water to form a suspension, with the liquid-solid mass ratio of the ground material to water being 5:1 - 10:1, adding a fatty acid or sulfonate collector accounting for 0.4% - 0.6% of the material mass. The fatty acid collector includes a fatty acid collector and a modified fatty acid collector, and separating calcium sulfate whiskers from calcium hydroxide by flotation; S4. Product fine grinding: Washing the calcium sulfate whiskers with deionized water and drying them to recover calcium sulfate whiskers with a purity ≥ 95% and calcium hydroxide with a desulfurization efficiency ≥ 80%; 2. The method for efficiently extracting calcium sulfate whiskers from semi-dry desulfurized ash according to claim 1, characterized in that, In step S1, the screening is carried out using a sieve.

3. The method for efficiently extracting calcium sulfate whiskers from semi-dry desulfurized ash according to claim 1, characterized in that, In step S2, zirconia balls or alumina balls are used as the grinding medium.

4. The method for efficiently extracting calcium sulfate whiskers from semi-dry desulfurization ash according to claim 1, characterized in that In step S3, during the flotation process, the stirring speed is controlled at 150 - 300 revolutions per minute.

5. The method for efficiently extracting calcium sulfate whiskers from semi-dry desulfurized ash according to claim 1, characterized in that, In step S3, the calcium hydroxide is directly reused as a desulfurizer, and the desulfurization efficiency is not lower than 80% of the original desulfurizer.

6. The method for efficiently extracting calcium sulfate whiskers from semi-dry desulfurized ash according to claim 1, characterized in that In step S4, the drying temperature is 100 - 120 °C.

7. The method for efficiently extracting calcium sulfate whiskers from semi-dry desulfurized ash according to claim 1, characterized in that, In step S4, the purity of the dried calcium sulfate whiskers is not lower than 95%, and the aspect ratio range of the calcium sulfate whiskers is between 10 - 50.

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