Calcium fluoride whisker recovery method

Abstract

The invention relates to the technical field of inorganic reinforced materials, and discloses a calcium fluoride whisker recovery method which comprises the following steps: S1, mixing pretreated calcium fluoride whiskers with a compound functional treatment liquid for reaction to obtain slurry; the composite functional treating fluid comprises the following raw material components: 5%-12% of a stripping agent, 0.5%-2.5% of a structure protecting agent, 0.1%-0.8% of a surfactant, 1%-3% of an oxidizing agent and the balance of water, s2, carrying out solid-liquid separation on the slurry to obtain a solid product; and S3, the solid product is washed, floated and dried, and the recycled calcium fluoride whiskers are obtained. According to the recycling method, the original structure of the calcium fluoride whiskers can be protected to the maximum extent while the high-purity calcium fluoride whiskers are recycled, the average length-diameter ratio of the recycled calcium fluoride whiskers is larger than or equal to 76, compared with the length-diameter ratio of original whiskers in raw materials, the retention rate exceeds 89%, and the purity and performance are remarkably improved.

Description

Technical Field

[0001] This application relates to the technical field of inorganic reinforcing materials, and in particular to a method for recovering calcium fluoride whiskers. Background Technology

[0002] Calcium fluoride (CaF2) whiskers, as a high-performance inorganic reinforcing material, are widely used in polymer composites, friction materials, precision ceramics and other fields due to their good heat resistance, wear resistance, corrosion resistance and electrical insulation, in order to significantly improve the mechanical properties and dimensional stability of the matrix material.

[0003] The performance of calcium fluoride whiskers, especially their reinforcing properties in composite materials, is highly dependent on the integrity of their morphology, with the aspect ratio being the core indicator. Calcium fluoride whiskers with a high aspect ratio exhibit superior reinforcing effects, require lower addition amounts, and retain performance better compared to ordinary or low aspect ratio whiskers. Therefore, the ability to retain the original aspect ratio of calcium fluoride whiskers to the greatest extent possible is crucial in evaluating the quality of recycling methods and the value of the product.

[0004] However, due to the inherent mechanical fragility of calcium fluoride whiskers, their sensitivity to harsh chemical environments, the complex problem of impurity stripping, and the serious secondary agglomeration issue, existing calcium fluoride whisker recycling technologies have the following problems: efficient recycling processes often involve damage to the structure of the calcium fluoride whisker itself. As a result, high purity is obtained at the expense of the high aspect ratio of the calcium fluoride whiskers, so the recycled calcium fluoride whiskers can only be used as ordinary fillers and cannot enter high-value-added application fields.

[0005] Therefore, developing a recovery method that can recover high-purity calcium fluoride whiskers while maximally protecting the original structure of the calcium fluoride whiskers has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] In order to develop a recovery method that can maximize the protection of the original structure of calcium fluoride whiskers while recovering high-purity calcium fluoride whiskers, this invention provides a calcium fluoride whisker recovery method.

[0007] The present invention provides a method for recovering calcium fluoride whiskers, which adopts the following technical solution: A method for recovering calcium fluoride whiskers includes the following steps: S1. Pretreated calcium fluoride whiskers are mixed with composite functional treatment liquid and reacted to obtain slurry; The composite functional treatment liquid, by mass percentage, comprises the following raw material components: 5%-12% stripping agent, 0.5%-2.5% structure protectant, 0.1%-0.8% surfactant, and 1%-3% oxidant, with the balance being water; S2. Separate the slurry from its solid and liquid components to obtain a solid product; S3. The solid product is washed, floated and dried to obtain recovered calcium fluoride whiskers.

[0008] Optionally, in step S1, the stripping agent is selected from one or more of citric acid, gluconic acid, and tartaric acid.

[0009] Optionally, in step S1, the structural protective agent is sodium hexametaphosphate or sodium tripolyphosphate.

[0010] Optionally, in step S1, the surfactant is an alkylphenol polyoxyethylene ether or a fatty alcohol polyoxyethylene ether.

[0011] Optionally, in step S1, the mass-to-volume ratio of the pretreated calcium fluoride whiskers to the composite functional treatment liquid is 1:(6-8) kg / L.

[0012] Optionally, in step S1, the temperature of the mixing reaction is 50-65℃, and the time of the mixing reaction is 90-150 min.

[0013] Optionally, in step S1, the pretreated calcium fluoride whiskers include the following processing steps: After crushing the calcium fluoride whisker raw material, air separation is performed to obtain pretreated calcium fluoride whiskers.

[0014] Optionally, in step S3, the washing is a three-stage countercurrent washing, and the temperature of the washing water is 60-70℃.

[0015] Optionally, in step S3, the frother used in the flotation is methyl isobutyl methanol.

[0016] Optionally, in step S3, the drying is freeze-drying and vacuum drying in sequence. The freeze-drying temperature is (-30)-(-40)℃ and the freeze-drying time is 4-6h. The vacuum degree of the vacuum drying is <10Pa and the vacuum drying time is 20-24h.

[0017] In summary, the present invention has at least one of the following beneficial technical effects: This invention reacts pretreated calcium fluoride whiskers with a composite functional treatment liquid to form a dynamic protective film on the surface of the calcium fluoride whiskers, effectively preventing damage to the original structure of the whiskers. By adding a flotation step after the washing step, a large number of difficult-to-remove hydrophobic impurities present in the calcium fluoride whisker raw material are effectively removed, while reducing secondary damage to the whiskers. Results from the examples show that the recovered calcium fluoride whiskers have an average aspect ratio ≥76, a retention rate exceeding 89% compared to the aspect ratio of the original whiskers in the raw material, and a purity significantly improved to over 99.65%. Furthermore, the agglomeration index is 0.15-0.22, and the impact strength in PP composites is 7.8-8.5 kJ / m². 2 It has excellent performance. Detailed Implementation

[0018] The following detailed description of the calcium fluoride whisker recovery method provided by the present invention, in conjunction with specific embodiments, is provided. It should be understood that the following detailed embodiments are merely for the purpose of helping those skilled in the art to understand the present invention, and are not intended to limit the invention. Any equivalent changes or modifications made by those skilled in the art based on the essence of the present invention should be covered within the scope of protection of the present invention.

[0019] Unless otherwise specified, the materials and equipment used in the various embodiments of the present invention are all commercially available products in the art.

[0020] This invention provides a method for recovering calcium fluoride whiskers, comprising the following steps: S1. Pretreated calcium fluoride whiskers are mixed with composite functional treatment liquid and reacted to obtain slurry; S2. Separate the slurry from its solid and liquid components to obtain a solid product; S3. The solid product is washed, floated and dried to obtain recovered calcium fluoride whiskers.

[0021] In step S1, the pretreated calcium fluoride whiskers include the following processing steps: After crushing the calcium fluoride whisker raw material, air separation was performed to obtain pretreated calcium fluoride whiskers; The above crushing is preferably carried out in a jaw crusher, and the particle size of the crushed calcium fluoride whiskers is preferably ≤10mm; The above-mentioned airflow separation is preferably carried out in an airflow separator, and the airflow velocity for airflow separation is preferably 8-12 m / s; light organic matter and dust can be separated through airflow separation.

[0022] By sequentially crushing and air-separating the calcium fluoride whisker raw material, the primary damage to the calcium fluoride whiskers can be effectively reduced.

[0023] In step S1, the composite functional treatment liquid comprises, by mass percentage, the following raw material components: 5%-12% stripping agent, 0.5%-2.5% structure protectant, 0.1%-0.8% surfactant and 1%-3% oxidant, balance being water; Preferably, the composite functional treatment liquid comprises, by mass percentage, the following raw material components: 8%-10% stripping agent, 1.0%-2.0% structure protectant, 0.3%-0.5% surfactant and 1.5%-2.5% oxidant, balance being water; More preferably, the composite functional treatment liquid comprises, by mass percentage, the following raw material components: 10% stripping agent, 1.5% structural protectant, 0.5% surfactant and 2.0% oxidant, balance water; The stripping agent is preferably selected from one or more of citric acid, gluconic acid, and tartaric acid; in this invention, the stripping agent can provide an acidic environment to dissolve acid-soluble impurities such as calcium carbonate and metal oxides contained in the pretreated calcium fluoride whiskers; the carboxyl groups in the stripping agent can react with dissolved metal ions (such as Fe) 3+ Al 3+ This forms a stable water-soluble complex, preventing it from hydrolyzing and depositing again and contaminating the whisker surface; The structure protectant is preferably sodium hexametaphosphate or sodium tripolyphosphate. In this invention, the anions in the structure protectant can preferentially and strongly adsorb onto the surface of calcium fluoride whiskers to form a dense steric hindrance protective film, which physically isolates the acid solution from direct contact with the calcium fluoride whiskers, greatly slows down surface etching, and disperses the calcium fluoride whiskers from each other through strong electrostatic repulsion, thus preventing the calcium fluoride whiskers from being worn and broken during subsequent processes. The surfactant is preferably alkylphenol polyoxyethylene ether or fatty alcohol polyoxyethylene ether. In this invention, the surfactant can significantly reduce the surface tension of the composite functional treatment liquid, allowing it to quickly penetrate into the micro-gaps of the calcium fluoride whisker raw material, wet and coat the impurities such as ultrafine silicates and carbon particles that are physically attached. The hydrophobic chain of the surfactant inserts into the impurity particles, and the hydrophilic chain extends into the aqueous phase. Through the encapsulation mechanism, the impurities are peeled off from the surface of the whiskers, and the steric hindrance makes them stably suspended in the liquid, preventing re-attachment. The preferred oxidant is hydrogen peroxide, and the mass concentration of the oxidant is 30%. In this invention, the oxidant can decompose organic pollutants (such as oil and graphite) and destroy the surface structure of some silicate minerals, making them loose and easy to peel off. Under weakly acidic conditions, the oxidation effect of the oxidant is mild and controllable. The water mentioned above is preferably deionized water.

[0024] The oxidant, structure protectant, and surfactant produce a synergistic effect: the surfactant delivers the oxidant to the surface of the organic impurity to improve the oxidation efficiency; the structure protectant ensures that the oxidation reaction is limited to the impurity, while the calcium fluoride whiskers are protected.

[0025] In step S1, the mixing ratio of the pretreated calcium fluoride whiskers to the composite functional treatment solution is calculated by mass-volume ratio as follows: pretreated calcium fluoride whiskers: composite functional treatment solution = 1: (6-8) kg / L.

[0026] In step S1, the mixing reaction of the pretreated calcium fluoride whiskers and the composite functional treatment solution is carried out in a reaction vessel. The preferred temperature for the mixing reaction is 50-65°C, and the preferred reaction time is 90-150 min. In this invention, the above reaction conditions ensure that impurities are fully reacted and stripped away.

[0027] In step S1, the mixing reaction of the pretreated calcium fluoride whiskers and the composite functional treatment solution is preferably carried out under stirring conditions, with the stirring speed preferably being 150-300 rpm. In this invention, the above stirring speed can avoid mechanical shearing and breaking of the calcium fluoride whiskers.

[0028] In step S2, the solid-liquid separation is preferably sieving, and the mesh size of the sieve used for sieving is preferably 325 mesh.

[0029] In step S3, the washing is preferably a three-stage countercurrent washing, and the temperature of the water used for the three-stage countercurrent washing is preferably 60-70℃; the present invention preferably washes the solid product until the pH of the effluent is neutral (pH 6-7) and the conductivity is <100μS / cm.

[0030] In step S3, the flotation is preferably carried out in a microbubble flotation machine, and the flotation agent is preferably methyl isobutyl methanol.

[0031] This invention generates microbubbles through flotation to remove trace amounts of hydrophobic impurities, while the hydrophilic calcium fluoride whiskers are discharged from the bottom of the tank as the product.

[0032] In step S3, the product obtained after flotation is dehydrated, preferably in a centrifugal dewatering machine or a belt vacuum filter; preferably, the product obtained after flotation is dehydrated to a moisture content of 20%-25%. When the dehydration is carried out in a centrifugal dehydrator, the rotation speed of the centrifugal dehydrator is preferably 800-1200 rpm; When the water removal is carried out in a belt vacuum filter, the vacuum degree of the belt vacuum filter is preferably (-0.04)-(-0.06) MPa.

[0033] In step S3, the drying process consists of freeze drying and vacuum drying. The freeze drying temperature is preferably (-30) - (-40)℃, and the freeze drying time is preferably 4-6h. The vacuum degree of the vacuum drying is preferably <10Pa, and the vacuum drying time is preferably 20-24h.

[0034] This invention completely eliminates the capillary force caused by the surface tension of water through freeze drying, thereby fundamentally avoiding the hard agglomeration of nano-sized calcium fluoride whiskers and obtaining a fluffy, highly dispersible ultrafine powder.

[0035] Performance testing Unless otherwise specified, the experimental methods and testing equipment used in this invention are conventional methods in the art. In the embodiments of this invention, the methods used for performance testing are as follows: 1. Average length-to-diameter ratio The scanning electron microscope (SEM) was used for observation and statistical methods. The specific steps are as follows: Sample preparation: Disperse a small amount of sample in anhydrous ethanol, sonicate for 5-10 minutes, take a drop of suspension and drop it onto a silicon wafer or conductive adhesive, dry and then spray with gold.

[0036] Image acquisition: At an appropriate magnification (usually 5000-20000 times), at least 5 different fields of view are randomly selected for photography to ensure that the total number of whiskers counted is ≥100 to guarantee statistical significance.

[0037] Measurement and Calculation: Use image analysis software (such as Image J, Nano Measurer) to measure the length (L) and diameter (D) of each complete and independent whisker, calculate its aspect ratio (L / D), and finally calculate the arithmetic mean of all aspect ratio measurements, which is the "average aspect ratio of the product whisker".

[0038] 2. Average length-to-diameter ratio retention rate Determination of the aspect ratio of native whiskers in raw materials: A small amount of relatively pure whiskers are separated from the raw materials without any chemical treatment by physical grinding and air separation. The aspect ratio of at least 50 whiskers is measured according to the above-mentioned method for measuring the "average aspect ratio". The average aspect ratio is taken as the "aspect ratio of native whiskers in raw materials". Calculation formula: Average aspect ratio retention rate = (Average aspect ratio of product whiskers / Aspect ratio of primary whiskers in raw materials) × 100%.

[0039] 3. CaF2 content: The content was determined according to GB / T 30903-2014 "Determination of impurity elements in inorganic chemical products by inductively coupled plasma mass spectrometry (ICP-MS)".

[0040] 4. Agglomeration index: The D50 value is measured by a laser particle size analyzer and compared with the theoretical size of the single crystal. The particle size test follows GB / T19077-2024 "Particle size distribution by laser diffraction".

[0041] 5. The impact strength test procedure for PP composite materials is as follows: Preparation of composite materials: Calcium fluoride whiskers and polypropylene resin were premixed in a high-speed mixer at a mass fraction of 10%, and then melt-blended and granulated using a twin-screw extruder at an extrusion temperature range of 180-200℃ to obtain granules; Use an injection molding machine to inject the granules into standard impact test specimens (e.g., 80mm×10mm×4mm), with an injection temperature range of 190-210℃.

[0042] Notch preparation: A standard type A notch (notch depth 2mm, root radius 0.25mm) is made on a standard impact specimen using a notch preparation machine to obtain a notched specimen.

[0043] Impact test: The notched specimen is conditioned in a standard laboratory environment (23±2℃, 50±10% RH) for at least 16 hours. Using a simply supported beam impact testing machine, the span is adjusted according to the remaining thickness of the specimen (usually 62mm). The pendulum is released to impact the back of the notched specimen, and the energy absorbed by the fracture impact is recorded.

[0044] Calculation results: Notched impact strength (kJ / m) 2 = Impact absorbed energy (J) / Remaining cross-sectional area of ​​the spline at the notch (m²) 2 (), take the average value.

[0045] Example 1 The waste residue raw material containing calcium fluoride whiskers mainly consists of: 75% CaF2, 15% CaCO3, 5% SiO2, trace metal oxides and organic impurities.

[0046] A method for recovering calcium fluoride whiskers includes the following steps: S1. The waste residue containing calcium fluoride whiskers is crushed to a particle size of about 8mm in a jaw crusher, and then light impurities are removed by air separation in an air classifier with a wind speed of 10m / s to obtain pretreated calcium fluoride whiskers. S2. Add 86 kg of deionized water to the reactor, and add 10 kg of citric acid, 1.5 kg of sodium hexametaphosphate, 0.5 kg of alkylphenol polyoxyethylene ether and 2 kg of hydrogen peroxide (mass concentration of 30%) in sequence while stirring. Stir until homogeneous to obtain the composite functional treatment solution. S3. Add the pretreated calcium fluoride whiskers and the composite functional treatment solution to the reaction vessel according to the ratio of 1 kg to 7 L. Mix them and react at 60 °C and 250 rpm for 120 min to obtain a slurry. S4. The slurry is sieved through a 325-mesh sieve to obtain a solid product; S5. The solid product is sent to a three-stage countercurrent washing system and washed with 65°C hot water until the effluent is neutral and the conductivity is <100μS / cm. S6. After washing, the slurry is fed into a microbubble flotation machine for flotation. Add 40g of methyl isobutyl methanol frother per ton of slurry, scrape off the scum, and collect the product from the bottom of the tank. S7. Use a centrifuge to remove water from the collected bottom product at 1000 rpm until the moisture content is about 22%. S8. Place the dehydrated wet material at -35℃ for 5 hours, and then vacuum dry it at a vacuum degree <10Pa for 22 hours to obtain the final product - white, fluffy recycled calcium fluoride whisker powder.

[0047] Examples 2-5 The difference between Examples 2-5 and Example 1 is that the content of each component in the composite functional treatment solution in step S2 is different. The specific dosage (kg) is shown in Table 1 below: Table 1. Dosage of each raw material component in the composite functional treatment liquid in Examples 2-5

[0048] The recovered calcium fluoride whisker powders obtained in Examples 1-5 were subjected to performance tests, and the results are shown in Table 2 below: Table 2 Performance test results of recovered calcium fluoride whisker powder in Examples 1-5

[0049] Analysis of the data in the table above shows that the calcium fluoride whiskers recovered using the above method have an average aspect ratio of 76-82, an average aspect ratio retention rate of 89%-96%, a CaF2 content of 99.65%-99.82%, an agglomeration index of 0.15-0.22, and an impact strength of 7.8-8.5 kJ / m² in PP composites. 2 This indicates that the recycling method causes minimal damage to the calcium fluoride whiskers, largely preserving their original structure. Furthermore, the recycled whiskers exhibit extremely low impurity content, good toughness, and high performance, making them suitable for future applications in high-value-added fields.

[0050] Furthermore, when the composite functional treatment liquid comprises 8%-10% stripping agent, 1.0%-2.0% structural protectant, 0.3%-0.5% surfactant, and 1.5%-2.5% oxidant, with the balance being water, the recovered calcium fluoride whiskers have an average aspect ratio of 80-82, an average aspect ratio retention rate of 94%-96%, a CaF2 content of 99.75-99.82%, an agglomeration index of 0.15-0.18, and an impact strength of 8.2-8.5 kJ / m² in PP composite materials. 2 It has better performance.

[0051] In particular, when processed using the recycling method of Example 1, the obtained calcium fluoride whiskers had an average aspect ratio of 82, an average aspect ratio retention rate of 96%, a CaF2 content of 99.82%, an agglomeration index of 0.15, and an impact strength of 8.5 kJ / m² in PP composites. 2 This method achieves maximum protection of the original structure of calcium fluoride whiskers, resulting in calcium fluoride whiskers with excellent properties.

[0052] Example 6 The difference between this embodiment and Embodiment 1 is that the mixing ratio of the pretreated calcium fluoride whiskers and the composite functional treatment solution in step S3 is 1 kg: 6 L.

[0053] Example 7 The difference between this embodiment and Embodiment 1 is that the mixing ratio of the pretreated calcium fluoride whiskers and the composite functional treatment solution in step S3 is 1 kg: 8 L.

[0054] The recovered calcium fluoride whisker powder obtained in Examples 6-7 was subjected to performance tests, and the results were compared with those in Example 1. The results are shown in Table 3 below: Table 3 Performance test results of recovered calcium fluoride whisker powder in Examples 1 and 6-7

[0055] Analysis of the data in the table above shows that when the mixing ratio of pretreated calcium fluoride whiskers to composite functional treatment liquid is within the range of 1:(6-8) kg / L, the calcium fluoride whiskers obtained by the above recovery method all have good performance.

[0056] Example 8 The waste residue raw material containing calcium fluoride whiskers mainly consists of: 75% CaF2, 15% CaCO3, 5% SiO2, trace metal oxides and organic impurities.

[0057] A method for recovering calcium fluoride whiskers includes the following steps: S1. The waste residue containing calcium fluoride whiskers is crushed to a particle size of about 8mm in a jaw crusher, and then light impurities are removed by air separation in an air classifier with a wind speed of 8m / s to obtain pretreated calcium fluoride whiskers. S2. Add 86 kg of deionized water to the reactor, and add 10 kg of tartaric acid, 1.5 kg of sodium tripolyphosphate, 0.5 kg of alkylphenol polyoxyethylene ether and 2 kg of hydrogen peroxide (mass concentration of 30%) in sequence while stirring. Stir until homogeneous to obtain the composite functional treatment solution. S3. Add the pretreated calcium fluoride whiskers and the composite functional treatment solution to the reaction vessel according to the ratio of 1 kg to 6 L. Mix them and react at 50 °C and 150 rpm for 150 min to obtain a slurry. S4. The slurry is sieved through a 325-mesh sieve to obtain a solid product; S5. Send the solid product into a three-stage countercurrent washing system and wash it with 60°C hot water until the effluent is neutral and the conductivity is <100μS / cm. S6. After washing, the slurry is fed into a microbubble flotation machine for flotation. Add 40g of methyl isobutyl methanol frother per ton of slurry, scrape off the scum, and collect the product from the bottom of the tank. S7. Use a centrifuge to remove water from the collected bottom product at 800 rpm until the moisture content is about 25%. S8. Place the dehydrated wet material at -30℃ for 6 hours, and then vacuum dry it at a vacuum degree <10Pa for 20 hours to obtain the final product - white, fluffy recycled calcium fluoride whisker powder.

[0058] Example 9 The waste residue raw material containing calcium fluoride whiskers mainly consists of: 75% CaF2, 15% CaCO3, 5% SiO2, trace metal oxides and organic impurities.

[0059] A method for recovering calcium fluoride whiskers includes the following steps: S1. The waste residue containing calcium fluoride whiskers is crushed to a particle size of about 8mm in a jaw crusher, and then light impurities are removed by air separation in an air classifier with a wind speed of 12m / s to obtain pretreated calcium fluoride whiskers. S2. Add 86 kg of deionized water to the reactor, and add 10 kg of citric acid, 1.5 kg of sodium hexametaphosphate, 0.5 kg of fatty alcohol polyoxyethylene ether and 2 kg of hydrogen peroxide (mass concentration of 30%) in sequence while stirring. Stir until homogeneous to obtain the composite functional treatment solution. S3. According to the ratio of pretreated calcium fluoride whiskers to composite functional treatment solution = 1kg: 8L, add the pretreated calcium fluoride whiskers and composite functional treatment solution into the reaction vessel and mix. React at 65℃ and 300rpm for 90min to obtain slurry. S4. The slurry is sieved through a 325-mesh sieve to obtain a solid product; S5. Send the solid product into a three-stage countercurrent washing system and wash it with 70°C hot water until the effluent is neutral and the conductivity is <100μS / cm. S6. After washing, the slurry is fed into a microbubble flotation machine for flotation. Add 40g of methyl isobutyl methanol frother per ton of slurry, scrape off the scum, and collect the product from the bottom of the tank. S7. Use a centrifuge to remove water from the collected bottom product at 1200 rpm until the moisture content is about 20%. S8. Place the dehydrated wet material at -40℃ for 4 hours, and then vacuum dry it at a vacuum degree <10Pa for 24 hours to obtain the final product - white, fluffy recycled calcium fluoride whisker powder.

[0060] The recovered calcium fluoride whisker powders obtained in Examples 8-9 were subjected to performance tests, and the results were compared with those in Example 1. The results are shown in Table 4 below: Table 4 Performance test results of recovered calcium fluoride whisker powder in Examples 1 and 8-9

[0061] Analysis of the data in the table above shows that the calcium fluoride whiskers obtained by the recovery methods in Examples 1 and 8-9 all have good performance.

[0062] Comparative Example 1 The waste residue containing calcium fluoride whiskers mainly consists of: 75% CaF2, 15% CaCO3, 5% SiO2, trace metal oxides and organic impurities.

[0063] A method for recovering calcium fluoride whiskers includes the following steps: S1. The waste residue containing calcium fluoride whiskers is crushed to about 8mm in a jaw crusher, and then light impurities are removed by air separation in an air classifier with a wind speed of 10m / s to obtain pretreated calcium fluoride whiskers. S2. According to the ratio of pretreated calcium fluoride whiskers to hydrochloric acid solution (10wt%) = 1kg: 7L, add the pretreated calcium fluoride whiskers and hydrochloric acid solution (10wt%) into the reaction vessel and mix. React at 70℃ and 250rpm for 120min to obtain a slurry. S3. Filter the slurry and collect the solid product; S4. Wash the solid product with plenty of water until it is neutral; S5. The washed wet material is sent into a 110℃ hot air circulating oven to dry to constant weight, and the recovered calcium fluoride whisker powder is obtained.

[0064] The recovered calcium fluoride whisker powder obtained in Comparative Example 1 was subjected to performance testing, and the results were compared with those of Example 1. The results are shown in Table 5 below: Table 5 Performance test results of recovered calcium fluoride whisker powder in Example 1 and Comparative Example 1

[0065] Analysis of the data in the table above shows that, compared with the commonly used recycling method of Comparative Example 1, the average aspect ratio of the calcium fluoride whisker powder obtained by Example 1 was increased by 82.2%, the retention rate was increased by 81.1% compared with the aspect ratio of the original whiskers in the raw material, and the agglomeration index and impact strength were significantly improved.

[0066] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for recovering calcium fluoride whiskers, comprising the following steps: S1. Pretreated calcium fluoride whiskers are mixed with composite functional treatment liquid and reacted to obtain slurry; The composite functional treatment liquid, by mass percentage, comprises the following raw material components: 5%-12% stripping agent, 0.5%-2.5% structure protectant, 0.1%-0.8% surfactant, and 1%-3% oxidant, with the balance being water; S2. Separate the slurry from its solid and liquid components to obtain a solid product; S3. The solid product is washed, floated and dried to obtain recovered calcium fluoride whiskers.

2. The method for recovering calcium fluoride whiskers as described in claim 1, characterized in that, In step S1, the stripping agent is selected from one or more of citric acid, gluconic acid, and tartaric acid.

3. The method for recovering calcium fluoride whiskers as described in claim 1, characterized in that, In step S1, the structural protective agent is sodium hexametaphosphate or sodium tripolyphosphate.

4. The method for recovering calcium fluoride whiskers as described in claim 1, characterized in that, In step S1, the surfactant is an alkylphenol polyoxyethylene ether or a fatty alcohol polyoxyethylene ether.

5. The method for recovering calcium fluoride whiskers as described in claim 1, characterized in that, In step S1, the mass-to-volume ratio of the pretreated calcium fluoride whiskers to the composite functional treatment liquid is 1:(6-8) kg / L.

6. The method for recovering calcium fluoride whiskers as described in claim 1, characterized in that, In step S1, the temperature of the mixing reaction is 50-65℃, and the time of the mixing reaction is 90-150 min.

7. The method for recovering calcium fluoride whiskers as described in claim 1, characterized in that, In step S1, the pretreated calcium fluoride whiskers include the following processing steps: After crushing the calcium fluoride whisker raw material, air separation is performed to obtain pretreated calcium fluoride whiskers.

8. The method for recovering calcium fluoride whiskers as described in claim 1, characterized in that, In step S3, the washing is a three-stage countercurrent washing, and the temperature of the washing water is 60-70℃.

9. The method for recovering calcium fluoride whiskers as described in claim 1, characterized in that, In step S3, the frother used in the flotation is methyl isobutyl methanol.

10. The method for recovering calcium fluoride whiskers as described in claim 1, characterized in that, In step S3, the drying process consists of freeze drying and vacuum drying. The freeze drying temperature is (-30) to (-40) °C, and the freeze drying time is 4-6 h. The vacuum degree of the vacuum drying is <10 Pa, and the vacuum drying time is 20-24 h.

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