Method for preparing high-oil-absorption and high-reinforcement white carbon black by using fluorine-containing silicon slag

Abstract

The invention belongs to the field of chemical production, and discloses a method for preparing high-oil-absorption and high-reinforcement white carbon black by using fluorine-containing silicon slag, which comprises the following steps: adding liquid-containing fluorine-containing silicon slag into a hot aluminum hydroxide solution to react until the liquid-containing fluorine-containing silicon slag is clear, and adding water to dilute to obtain a solution A; heating the solution A, adding dilute sulphuric acid in stages to neutralize to a target pH value, stirring, filtering, and carrying out countercurrent washing on the silica gel with pure water until the conductivity of washing water reaches the standard; adding an organic azeotropic solvent into the desalted silica gel, heating and preserving heat, and evaporating out part of the solvent to obtain a white carbon black primary product; and calcining the primary product at 500-800 DEG C, and crushing to obtain the target white carbon black. According to the invention, high-value utilization of the fluorine-containing silicon slag is realized, and the problems of poor reinforcing effect, low oil absorption value and insufficient activity of a traditional process product are solved.

Description

Technical Field

[0001] This invention relates to the field of technology, and in particular to a method for preparing highly oil-absorbing and highly reinforcing silica from fluorinated silica slag. Background Technology

[0002] In industrial processes such as phosphate fertilizer production and hydrogen fluoride preparation, fluorine-containing waste gases (such as SiF4 and HF) generate large amounts of fluorinated silica slag after being absorbed by water. Its main components are amorphous silica (SiO2) and fluorosilicic acid (H2SiF6). Due to its high fluorine content (typically 5%–20%), low activity, and environmental toxicity, this type of silica slag cannot be directly used as industrial filler. Long-term storage can easily lead to fluoride ion leakage and pollution of soil and water bodies. With increasingly stringent environmental regulations, how to achieve high-value utilization of fluorinated silica slag has become an industry challenge.

[0003] Traditional technologies for treating fluorinated silica slag mainly include the following categories:

[0004] Wet chemical treatment:

[0005] For example, patent CN103663474B proposes using an alkaline solution (such as NaOH) to react with fluorinated silicon slag at 40-80℃ to convert fluorine into soluble fluoride salts, followed by countercurrent washing to obtain silica. However, this method has high wastewater treatment costs and results in products with low specific surface area and oil absorption value.

[0006] For example, patent CN118724000A uses ammonia to decompose fluorosilicic acid, combined with grinding with ammonium halide pore-forming agent and vacuum heating, to increase the surface area to 240~270 m² / g, but the loss of ammonia volatilization and the problem of pore-forming agent recovery increase the complexity of the process.

[0007] High-temperature calcination method:

[0008] For example, patent CN110156030A uses calcination at 800~1700℃ to remove fluorine, which can reduce the fluorine content to below 0.1%, but the energy consumption is extremely high, and the high temperature can easily cause SiO2 to crystallize, reducing its reinforcing performance.

[0009] Composite process:

[0010] For example, patent CN118479487A describes the use of low-temperature deacidification and dehydration, and magnetic Fe3O4@SiO2 nanoparticles for adsorption and defluorination to prepare silica with a specific surface area of ​​358 m² / g. However, the preparation and recycling of magnetic materials are complicated.

[0011] Traditional processing methods mainly focus on fluorosilicone separation and increasing the specific surface area of ​​silica; however, as a rubber reinforcing agent, improving its mechanical properties is more important. Summary of the Invention

[0012] This invention mainly provides a method for preparing high oil absorption value and high reinforcing silica using fluorinated silica slag, which enables fluorinated silica slag to overcome the problems of poor reinforcing effect, low oil absorption value and insufficient activity caused by traditional processing technology.

[0013] The technical implementation scheme of the present invention is as follows:

[0014] This invention overcomes the difficulty of removing fluoride from the silica lattice through direct wet alkaline dissolution, further improving the purity of silica. High-speed stirring and dilute acid neutralization generate ultrafine silica gel. Without traditional aging processes, countercurrent washing yields sulfate and fluoride salt solutions as curing agent mother liquors. An organic azeotropic solvent is added to the desalted silica gel to fill the porous structure of the dehydrated silica. The resulting primary silica is then calcined at 500–800°C to remove surface hydroxyl groups and expose the internal loose porous structure. After pulverization, a silica product with high oil absorption and high reinforcing properties is obtained. The specific steps are as follows:

[0015] A method for preparing highly oil-absorbing and highly reinforcing silica from fluorinated silica slag includes the following steps:

[0016] S1. Dissolution and dilution: Add the liquid fluorine-containing silicon slag into the hot aluminum hydroxide solution and stir until the solution is clear. Dilute with pure water to the preset density to obtain solution A.

[0017] S2, Neutralization and Washing: Heat the A solution obtained in step S1 to the preset temperature, add dilute sulfuric acid in stages under high speed stirring to neutralize to the target pH value, stir for a preset time after neutralization, filter to obtain silica gel and liquid containing fluoride and sulfate, and wash the silica gel with pure water countercurrent until the conductivity of the wash water is lower than the preset value.

[0018] S3, Azeotropic Dehydration: Add an organic azeotropic solvent to the desalted silica gel after washing in S2, stir and mix evenly, then heat to the first preset temperature and keep it at the preset temperature for a preset time, then heat up to evaporate the preset proportion of azeotropic solvent to obtain a primary product of silica with solid flowability.

[0019] S4. Calcination and pulverization: The primary silica product obtained in S3 is placed in a muffle furnace and calcined at 500-800℃ for a preset time. After calcination, it is pulverized to obtain silica products with high oil absorption value and high reinforcing properties.

[0020] Optionally, in step S1, the temperature of the hot sodium hydroxide solution is 90°C and the mass concentration is 30%–50%; the mass ratio of the liquid-containing fluorosilicone slag to 96% caustic soda flakes is 10:1.5–1.6; the stirring reaction time is 1–2 hours; in step S1, the fluorosilicone slag is first filtered through a plate and frame filter press before being added to the sodium hydroxide solution.

[0021] Optionally, the water content of the liquid fluorine-containing silicon slag in step S1 is 65% to 68% under the test conditions of 105°C; the density of solution A after dilution with pure water is 1.1 to 1.3 g / cm³. The purpose of this method is that the hot concentrated alkali accelerates the reaction rate, and the excess alkali ensures the dissolution of silicon and fluorine while avoiding the high viscosity of the solution that would cause subsequent silicon gel polymerization.

[0022] Optionally, the preset temperature in step S2 is 40°C; dilute sulfuric acid with a mass concentration of 10% to 20% is added under high-speed stirring for neutralization, and the dropping rate of dilute sulfuric acid is 1% / min of the volume of liquid A.

[0023] Optionally, the phased neutralization described in step S2 is as follows: in the first stage, the pH value is adjusted to 10.5, the addition of acid is stopped and the mixture is allowed to stand for 30 minutes, and then in the second stage, dilute sulfuric acid is added to adjust the pH value to 6.5-7.5; after neutralization is completed, stirring is continued for 30 minutes.

[0024] Optionally, in step S2, the silica gel is washed countercurrently with pure water until the conductivity of the wash water is below 100 μs / cm; the filtered liquid containing fluoride and sulfate is directly used to prepare cement curing agent masterbatch; the silica gel generated at 40℃ is fine, and acid is added slowly to prevent local over-concentration; a large amount of silica gel appears at around pH 10.5, and stopping the addition of acid is beneficial for its uniform dispersion; a silica gel with a conductivity below 100 is required to obtain high-purity silica; the liquid mainly consists of sodium fluoride, sodium sulfate, fluoride ions, sodium ions, and sulfate ions, all of which are beneficial for cement curing and strength improvement, and can be directly used to prepare cement curing agent masterbatch.

[0025] Optionally, the volume of the organic azeotropic solvent added in step S3 is 1 to 2 times the water content of the silica gel; after stirring and mixing evenly, the temperature is first raised to 60°C and kept at that temperature for 1 hour, and then the temperature is raised to evaporate 85% of the azeotropic solvent; the organic solvent filling of the silica gel can ensure that the silica gel is dehydrated to produce silica while ensuring that the precipitated silica can be supported by the organic solvent to prevent the internal structure from collapsing, which greatly increases its activity.

[0026] Optionally, the organic azeotropic solvent is a compound with a molecular dynamic diameter ≥ 0.55 nm and a polarity index ≤ 4.0; selected from one or more of ethanol, n-propanol, xylene, n-butanol, and tert-butanol, preferably xylene, n-butanol, or n-propanol; the distilled azeotropic solvent is dehydrated by molecular sieve and reused.

[0027] In this process, high-temperature calcination is the key step in imparting high oil absorption value and high reinforcing properties to silica. Its core mechanism and process control requirements are as follows:

[0028] Under calcination temperatures of 500–800°C, the organic azeotropic solvent filling the interior of the precipitated silica can be fully burned off, thereby exposing the original loose porous structure inside the silica. This porous structure is the core basis for improving the oil absorption value of the product and can significantly enhance its wetting and dispersion capabilities in application systems (such as rubber, coatings, etc.).

[0029] Simultaneously, this temperature range effectively removes the hydroxyl groups on the surface of silica. Appropriate removal of surface hydroxyl groups reduces the tendency for silica particles to agglomerate, improving its dispersion compatibility in polymer materials such as rubber, thereby enhancing its reinforcing effect. The calcination temperature must be strictly controlled to not exceed 800℃. If the temperature is too high, it will cause amorphous silica to undergo a crystalline transformation. Crystalline silica will lose its loose, porous structure and high activity, significantly reducing its reinforcing properties.

[0030] To ensure stable and satisfactory calcination results, the calcination process must meet the following two key requirements:

[0031] 1. The surface hydroxyl density of calcined silica needs to be reduced to 0.5-1.5 OH / nm², which can be determined by thermogravimetric-mass spectrometry (TGA-MS).

[0032] 2. The X-ray diffraction (XRD) pattern of the calcined product shows no characteristic crystalline peaks in the range of 2θ = 15° to 30°, proving that it maintains an amorphous structure. Based on the above requirements, the calcination temperature is determined to be 500–800℃, and the calcination time is 1 hour.

[0033] The present invention has the following advantages:

[0034] 1. This invention features a short process route and simple operation. It enables the low-activity silica from defluorinated fluorinated silica slag to meet the standards for rubber-reinforcing silica, particularly in terms of high oil absorption and strong mechanical properties. Ordinary fluorinated silica slag (DBP) has an oil absorption value of 200 cm³ / kg, a rubber tensile strength of 6.2 MPa, and a tensile stress of 3.8 MPa. After treatment with this invention, the oil absorption value, rubber tensile strength, and tensile stress of the silica are increased by 100%, 300%, and 137%, respectively. Furthermore, the fluoride salts generated after defluorination can be used as mother liquor in the production of cement curing agents, without generating additional wastewater. This method not only yields high-performance silica but also provides a good outlet for the rational utilization of fluorine resources, overcoming the difficulties brought about by traditional treatment processes while reducing enterprise costs and environmental pressure. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, a further detailed description will be provided below in conjunction with this invention. It is hereby declared that the directional terms such as up, down, left, right, front, back, inside, and outside appearing or about to appear in this text are only based on this invention and are not intended to specifically limit this invention.

[0036] Example 1:

[0037] First, 1 kg of fluorinated silicon slag was added to a 512 g sodium hydroxide (30%) solution at 90 °C and stirred for 2 h. After the solution became clear, 2 L of pure water was added to dilute the liquid to a density of 1.1 g / cm3, thus obtaining solution A.

[0038] Next, the obtained solution A was heated to 40℃, and 20% dilute sulfuric acid was added at a rate of 30 ml / min under high-speed stirring at 500 rpm for neutralization; the pH was adjusted to 10.5 in the first stage, and after stopping the addition of acid for 30 minutes, the pH was adjusted to 6.5-7.5 by adding dilute acid in the second stage, and the mixture was stirred for 30 minutes after neutralization was completed; the silica gel and fluoride and sulfate liquids were separated by filtration; the silica gel was washed with pure water countercurrently until the conductivity of the wash water was lower than 100 μs / cm, at which point the silica gel contained 85% water;

[0039] Next, in the above steps, add 1.5L of xylene to the washed silica gel, stir and mix evenly, first heat to 60℃ and maintain for 1 hour, then increase the temperature to distill off 2.6L of the azeotropic liquid and stop; at this time, the obtained precipitated silica has solid fluidity;

[0040] Finally, the initial silica product is calcined in a muffle furnace at 600℃ for 1 hour, and then pulverized to obtain the silica product.

[0041] The test results are as follows:

[0042] <![CDATA[DBP oil absorption value (cm 3 / kg)]]> Tensile strength (MPa) 300% constant tensile stress (MPa) Total silicon content (%) 364 24.5 7.2 99.5

[0043] Example 2:

[0044] First, 1 kg of fluorinated silicon slag was added to a 307 g sodium hydroxide (50%) solution at 90 °C and stirred for 50 min. After the solution became clear, 2 L of pure water was added to dilute the liquid to a density of 1.1 g / cm3 to obtain solution A.

[0045] Next, the obtained solution A was heated to 40℃, and 10% dilute sulfuric acid was added at a rate of 30 ml / min under high-speed stirring at 500 rpm for neutralization; the pH was adjusted to 10.5 in the first stage, and after stopping the addition of acid for 30 minutes, the pH was adjusted to 6.5-7.5 by adding dilute acid in the second stage, and the mixture was stirred for 30 minutes after neutralization was completed; the silica gel and fluoride and sulfate liquids were separated by filtration; the silica gel was washed with pure water countercurrently until the conductivity of the wash water was lower than 100 μs / cm, at which point the silica gel contained 90% water.

[0046] Next, add 4.5L of n-butanol to the washed silica gel, stir and mix evenly, first heat to 60℃ and maintain for 1 hour, then increase the temperature to distill off 6L of the azeotropic liquid and stop. At this point, the obtained fumed silica has solid fluidity.

[0047] Finally, the initial silica product is calcined in a muffle furnace at 800℃ for 1 hour, and then pulverized to obtain the silica product.

[0048] The test results are as follows:

[0049] <![CDATA[DBP oil absorption value (cm 3 / kg)]]> Tensile strength (MPa) 300% constant tensile stress (MPa) Total silicon content (%) 412 25.3 8.1 99.5

[0050] Example 3:

[0051] First, 1 kg of fluorinated silicon slag was added to a 384 g sodium hydroxide (40%) solution at 90 °C and stirred for 1.5 h. After the solution became clear, 2 L of pure water was added to dilute the solution to a density of 1.1 g / cm3, thus obtaining solution A.

[0052] Next, the obtained solution A was heated to 40℃, and 15% dilute sulfuric acid was added at a rate of 30 ml / min under high-speed stirring at 500 rpm for neutralization; the pH was adjusted to 10.5 in the first stage, and after stopping the addition of acid for 30 minutes, the pH was adjusted to 6.5-7.5 by adding dilute acid in the second stage, and the mixture was stirred for 30 minutes after neutralization was completed; the silica gel and fluoride and sulfate liquids were separated by filtration; the silica gel was washed with pure water countercurrently until the conductivity of the wash water was lower than 100 μs / cm, at which point the silica gel contained 88% water.

[0053] Next, add 2.6L of n-propanol to the washed silica gel, stir and mix evenly, first heat to 60℃ and maintain for 1 hour, then increase the temperature to distill off 4.25L of the azeotropic liquid and stop; at this point, the obtained precipitated silica has solid fluidity;

[0054] Finally, the initial silica product is calcined in a muffle furnace at 700℃ for 1 hour, and then pulverized to obtain the silica product.

[0055] The test results are as follows:

[0056] <![CDATA[DBP oil absorption value (cm 3 / kg)]]> Tensile strength (MPa) 300% constant tensile stress (MPa) Total silicon content (%) 378 23.5 7.8 99.5

[0057] Scientific verification of the calcination temperature range:

[0058] The same precipitated silica was calcined at 400℃, 600℃, 800℃, and 900℃ for 1 h, respectively. The following were determined: surface hydroxyl density (TGA-MS method, the hydroxyl group corresponding to the weight loss peak at 100-300℃); crystallinity (XRD semi-quantitative method, based on the area ratio of the characteristic peak of cristobalite at 2θ=22°).

[0059] Temperature (°C) Hydroxyl group density (OH / nm²) Crystallinity (%) Rubber tensile strength (MPa) 400 3.8 0 18.2 600 1.2 0 24.5 800 0.7 ＜1 25.3 900 0.5 15 19.1

[0060] Performance data of curing agent made from by-product fluoride brine (based on cement):

[0061] Mother liquor dosage 3-day compressive strength (MPa) 28-day compressive strength (MPa) 0% 21.6MPa 46.7MPa 3% 24.5MPa 48.2MPa 6% 28.1MPa 53.6MPa 9% 26.8MPa 50.1MPa

[0062] Through experimental comparison of the above embodiments, the oil absorption value and reinforcing performance of Embodiment 2 are superior to those of other embodiments.

[0063] The embodiments of the present invention have been described in detail, but the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for preparing highly oil-absorbing and highly reinforcing silica using fluorinated silica slag, characterized in that, Includes the following steps: S1. Dissolution and dilution: Add the liquid fluorine-containing silicon slag into the hot aluminum hydroxide solution and stir until the solution is clear. Dilute with pure water to the preset density to obtain solution A. S2, Neutralization and Washing: Heat the A solution obtained in step S1 to the preset temperature, add dilute sulfuric acid in stages under high speed stirring to neutralize to the target pH value, stir for a preset time after neutralization, filter to obtain silica gel and liquid containing fluoride and sulfate, and wash the silica gel with pure water countercurrent until the conductivity of the wash water is lower than the preset value. S3, Azeotropic Dehydration: Add an organic azeotropic solvent to the desalted silica gel washed in step S2, stir and mix evenly, then heat to the first preset temperature and keep it at the preset temperature for a preset time, then heat up to evaporate the preset proportion of azeotropic solvent to obtain a primary product of silica with solid flowability. S4. Calcination and pulverization: Place the precipitated silica obtained in step S3 into a muffle furnace and calcine it at 500-800℃ for a preset time. After calcination, pulverize it to obtain a precipitated silica product with high oil absorption value and high reinforcing properties.

2. The method for preparing high oil absorption and high reinforcing silica using fluorinated silica slag according to claim 1, characterized in that, The temperature of the hot sodium hydroxide solution in step 1 is 90°C, and the mass concentration is 30%–50%; the mass ratio of the liquid-containing fluorine-silica slag to 96% caustic soda flakes is 10:1.5–1.6; and the stirring reaction time is 1–2 hours.

3. A method for preparing highly oil-absorbing and highly reinforcing silica using fluorinated silica slag according to claim 2, characterized in that, The water content of the liquid-containing fluorine-silica slag in step S1 is 65% to 68% under the test condition of 105℃; the density of solution A after dilution with pure water is 1.1 to 1.3 g / cm³.

4. A method for preparing high oil absorption and high reinforcing silica using fluorinated silica slag according to claim 1, characterized in that, S2 The preset temperature mentioned in the steps is 40℃; under high-speed stirring, dilute sulfuric acid with a mass concentration of 10% to 20% is added for neutralization, and the dropping rate of dilute sulfuric acid is 1% / min of the volume of liquid A.

5. A method for preparing highly oil-absorbing and highly reinforcing silica using fluorinated silica slag according to claim 4, characterized in that, The phased neutralization described in step S2 is as follows: In the first stage, adjust the pH value to 10.5, stop adding acid and let it stand for 30 minutes, then proceed to the second stage by adding dilute sulfuric acid to adjust the pH value to 6.5-7.5; after neutralization is completed, continue stirring for 30 minutes.

6. A method for preparing high oil absorption and high reinforcing silica using fluorinated silica slag according to claim 5, characterized in that, S2 In the process, the silica gel is washed with pure water in a countercurrent manner until the conductivity of the wash water is lower than 100 μs / cm; the filtered liquid containing fluoride and sulfate is directly used to prepare cement curing agent masterbatch.

7. A method for preparing highly oil-absorbing and highly reinforcing silica using fluorinated silica slag according to claim 1, characterized in that, The volume of the organic azeotropic solvent added in step S3 is 1 to 2 times the water content of the silicone gel; after stirring and mixing evenly, the temperature is first raised to 60°C and kept at that temperature for 1 hour, and then the temperature is raised to evaporate 85% of the azeotropic solvent.

8. A method for preparing highly oil-absorbing and highly reinforcing silica using fluorinated silica slag according to claim 7, characterized in that, The organic azeotropic solvent is a compound with a molecular dynamic diameter ≥ 0.55 nm and a polarity index ≤ 4.0; it is selected from one or more of ethanol, n-propanol, xylene, n-butanol, and tert-butanol, preferably xylene, n-butanol, or n-propanol; the distilled azeotropic solvent is dehydrated by molecular sieve and reused.