Method for efficiently separating and purifying aluminum fluoride silicon slag and preparing white carbon black

Abstract

The invention belongs to the technical field of chemical product preparation, and particularly relates to a method for efficiently separating and purifying aluminum fluoride silicon slag and preparing white carbon black. Dropwise adding the ammonium fluoride solution into the aluminum fluoride silicon slag solution, then heating and stirring, then adding melamine and formaldehyde as dispersing agents, filtering after the reaction is finished, and filtering by adopting a carbon fiber membrane to obtain a filter cake which is high-purity aluminum fluoride and a filtrate which is an ammonium fluosilicate solution for later use; then slowly dripping the ammonium fluosilicate solution into the ammonia water solution, and maintaining the pH value of the reaction solution at 9.3-9.4; and after the reaction is finished, carrying out solid-liquid separation and drying to obtain the white carbon black. When the white carbon black is prepared, ammonia water is selected as a base solution, the white carbon black is ensured to be separated out under an alkaline condition, the purity of the prepared white carbon black is 99% or above, the specific surface area is larger than 300 m / g, the oil absorption value exceeds 250 mL / 100 g, and the fluorine ion concentration is lower than 50 ppm. The silicon slag used in the invention is derived from solid waste of aluminum fluoride prepared from fluosilicic acid, the cost is low, and the whole process is environment-friendly and is suitable for industrial-scale production and application.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical product preparation, and particularly relates to a method for separating and purifying aluminum fluoride silicon slag to prepare white carbon black. Background Art

[0002] Aluminum fluoride silicon slag is a solid waste generated during the production of aluminum fluoride from fluorosilicic acid. Its main components are SiO2, AlF3, Al(OH)3, H2SiF6, and HF. Due to its complex composition and high concentration of fluoride ions, it is classified as hazardous waste. Direct discharge or storage can release large amounts of toxic fluorine-containing gases, or, after prolonged exposure to rain, contaminate soil and groundwater, causing secondary environmental pollution. Currently, most companies mix fluorosilicone slag with slurry and then pump it into phosphogypsum storage yards for disposal. However, this method wastes resources and contaminates the phosphogypsum.

[0003] A great deal of work has been done on the effective utilization of aluminum fluoride silicate slag. Patent CN102674367A reports that aluminum fluoride silicate slag and ammonium fluoride are dissolved at 90-108°C, filtered, and ammonia water is added to the filtrate to produce silica. However, this process can only effectively utilize part of the silicon source, and AlF3 is not effectively recovered. Patent CN103663474B reports that alkali is mixed with aluminum fluoride silicate slag at 40-80°C to prepare a mixed aqueous solution, and fluoride salt and silica are obtained through solid-liquid separation. However, this process cannot effectively remove impurities such as aluminum fluoride encapsulated in silicate, resulting in low silica purity. Patent CN110156030A reports that aluminum fluoride silicate slag is placed in a calcining kiln, heated at 800-1700°C for 1-10 hours, then cooled and pulverized, ultimately producing a low-fluorine, low-water silica product, but its specific surface area is not high. In summary, the separation, purification, and reuse of aluminum fluoride silicon slag face challenges such as high investment costs, poor separation efficiency, suboptimal product quality, and complex processes, which limit its industrial application. Therefore, how to scientifically and effectively separate, purify, and reuse aluminum fluoride silicon slag with low purity, large particle size, small specific surface area, and high fluorine content has become a key technical challenge that companies urgently need to solve. Summary of the Invention To solve the above problems, the present invention provides a method for separating, purifying aluminum fluorosilicate slag and preparing precipitated silica, which can efficiently separate and purify aluminum fluorosilicate slag and obtain precipitated silica with a high specific surface area and high-purity aluminum fluoride. The fluoride ions in the fluorosilicate slag form ammonium fluoride solution that can be recycled. The iron ions brought about by equipment corrosion during the production of aluminum fluoride are removed through filtration by a carbon fiber membrane. Eventually, fluorine, silicon, and aluminum in the silicon slag are effectively recycled. The precipitated silica with a high specific surface area prepared by the present invention plays an important role in many fields. It can be used as a key reinforcing agent for rubber, with a usage ratio as high as 70%, and can make the paint form a paint film with good matting effect, enhancing the overall texture of the paint. In addition, precipitated silica is also widely used in many fields such as electronic packaging materials and daily necessities, with broad application potential. The technical solution of the present invention is as follows: A method for preparing precipitated silica with a high specific surface area from fluorosilicic acid, the method comprising the following steps: S1, Take a certain amount of aluminum fluorosilicate slag in a reaction vessel, add water and a cosolvent with a feeding pump and stir, then dropwise add the previously prepared ammonium fluoride solution with a peristaltic pump. Pass in nitrogen, heat and stir for 2 h, filter, the filter cake is aluminum fluoride, and the filtrate is ammonium fluorosilicate solution. The ammonium fluorosilicate solution is filtered through a carbon fiber membrane to remove iron ions in the solution, and then melamine and formaldehyde are added and stirred for standby.

[0004] S2, Take a certain amount of ammonia water with a certain concentration and add it to a reaction vessel equipped with a stirring paddle, a peristaltic pump, and a reflux condenser.

[0005] S3, While stirring, slowly add a certain proportion of ammonia water and the ammonium fluorosilicate solution in step 1 with a pump, and age after dropping.

[0006] S4, Transfer the reaction solution to a belt filter with a pump, cool and crystallize the filtrate, and then filter and dry to obtain ammonium fluoride finished product.

[0007] S5, Adjust the pH of the filter cake and then make it into a slurry, filter, wash the filter cake with pure water, and place the filter cake in a dryer to dry to obtain precipitated silica finished product.

[0008] The present invention provides a method for separating, purifying aluminum fluoride silicate slag and preparing white carbon black. The key step is that in an ammonium fluoride solution, the aluminum fluoride silicate slag is effectively dissolved to form ammonium fluorosilicate, and aluminum fluoride is separated out. Specifically, in this process, a certain amount of aluminum fluoride silicate slag is first added to a reaction kettle and stirred, then a cosolvent and an ammonium fluoride solution are added dropwise, nitrogen is introduced and stirred, and then filtration is carried out. The filtrate is an ammonium fluorosilicate solution, and the filter cake is high-purity aluminum fluoride. During this preparation process, the addition of the cosolvent is mainly to promote the dissolution on the surface of the aluminum fluoride silicate slag, so that the silicon in the aluminum fluoride silicate slag dissolves in the ammonium fluoride solution faster. The strategy of adding the ammonium fluoride solution dropwise solves two problems. First, when a large amount of ammonium fluoride reacts with aluminum fluoride silicate slag at 140 °C, a large amount of ammonia gas will be rapidly released, resulting in the alkalization of the solution. In an alkaline environment, ammonium fluorosilicate reacts with the released ammonia gas to form white carbon black again. These newly formed white carbon blacks are easily mixed with the unreacted aluminum fluoride silicate slag, so that aluminum fluoride cannot be effectively separated and purified, resulting in incomplete recovery of silicon resources and poor purity of the recovered aluminum fluoride. By adding the ammonium fluoride solution dropwise, the reaction process can be finely controlled, and the release amount of ammonia gas can be controlled. A small amount of ammonia gas generated in the reaction quickly escapes from the system under heating conditions. By adding external nitrogen to change the dissolution amount of ammonia gas in the reaction and adjusting the pH of the reaction system, the whole reaction system is maintained in a weakly acidic state to ensure that the aluminum fluoride silicate slag can be fully dissolved. Another problem is that at high temperatures, a large amount of ammonium fluoride reacts quickly with aluminum fluoride silicate slag to generate SiF4. The SiO2 generated by the reaction of SiF4 with water easily clogs the pipeline. By using the method of adding the ammonium fluoride solution dropwise, the reaction rate can be effectively slowed down, and the release amount of SiF4 can be reduced, thus avoiding the occurrence of the above problems. This method is stirred for 2 h under the condition of 130-150 °C, and the silicon in the aluminum fluoride silicate slag is completely dissolved in the ammonium fluoride solution to form ammonium fluorosilicate, and the purity of the insoluble aluminum fluoride is the highest. The filtrate after filtration is an ammonium fluorosilicate solution. In this solution, there are iron ions introduced due to equipment corrosion during the production of aluminum fluoride, making the whole solution show a red color, which affects the quality of the subsequent white carbon black. In order to effectively remove iron ions, carbon fiber membrane is used to adsorb them, effectively reducing the iron ion content in the filtrate.

[0009] The ammonium fluorosilicate solution after filtration is weakly acidic. Melamine and formaldehyde added under acidic conditions will polymerize to form polymer chains. During the subsequent generation of white carbon black, the precipitated white carbon black adheres to the polymer chains, making the generated white carbon black have good dispersibility.

[0010] In the process of preparing silica white, ammonium fluorosilicate solution and ammonia water are simultaneously dropped into an initial solution containing ammonia water, and stirred to obtain a uniform mixed material. Then, through aging and solid-liquid separation, a silica white product with a high specific surface area is obtained. Experimental data analysis shows that the pH value of the reaction solution has a significant impact on the quality of silica white. In the reaction stage, it is necessary to ensure that the pH of the reaction system is maintained between 9.3 and 9.4. Under alkaline conditions, ammonium fluorosilicate is added to the reaction system, and the following reaction occurs: (NH4)2SiF6 + 4NH3·H2O → 6NH4F + SiO2·nH2O Under the action of high-speed stirring of the mixed material, silica white precipitates with extremely fine particle size and is quickly dispersed. Since the feeding process of ammonium fluorosilicate is carried out under alkaline conditions, the added ammonium fluorosilicate can quickly generate silica white, avoiding its attachment on the surface of the already generated silica white, thereby reducing the specific surface area of silica white.

[0011] To ensure the precipitation of silica white under alkaline conditions, preferably, in step 2, ammonia water needs to be added to the bottom of the kettle with a pump first, and the ammonium fluorosilicate is dropped into the bottoming liquid.

[0012] Preferably, the composition of the aluminum fluoride silicate slag in step 1 is: SiO2 45% - 49%, H2O 30% - 35%, AlF3 6% - 10%, Al(OH)3 2% - 3%, H2SiF6 1% - 2%, HF 0.5% - 1%, Fe 0.02 - 0.03%.

[0013] Preferably, the cosolvent added in step 1 accelerates the dissolution of the aluminum fluoride silicate slag. The cosolvent includes fluorosilicic acid or ammonium hydrogen fluoride or others, and the addition amount of the cosolvent is 4 - 7% of the aluminum fluoride silicate slag.

[0014] Preferably, during the preparation process of step 1, nitrogen is introduced to adjust the dissolution amount of the generated ammonia gas, and ensure that the pH of the reaction system is maintained between 6.0 and 6.5.

[0015] Preferably, to ensure that the aluminum fluoride silicate slag can react quickly and fully, the reaction temperature in step 1 is 130 - 150°C, the stirring speed is 100 - 300 rpm, stirring is carried out for 1.5 - 2.5 h, the equivalent of ammonium fluoride is 1.2 - 1.5 times the effective silicon equivalent of the aluminum fluoride silicate slag, the recovery rate of aluminum fluoride is above 95%, and the purity is above 99%. Ammonium fluoride is added by the way of dropping with a peristaltic pump. After dropping, stir, filter and wash. The filtrate is ammonium fluorosilicate solution, and the filter cake is high-purity aluminum fluoride.

[0016] Preferably, in step 1, formaldehyde accounting for 0.1 - 0.3% of the total mass of the reaction solution and melamine accounting for 0.1 - 0.3% of the total mass of the reaction solution are respectively added under the condition of 25 - 35°C. The two condense under acidic conditions to form urea - formaldehyde resin as a dispersant.

[0017] Preferably, in step 1, the ammonium fluoride solution is added to the reaction system by means of peristaltic pump dropping, and the concentration of ammonium fluoride is 30 - 40%.

[0018] Preferably, in step 1, ammonium fluorosilicate needs to be filtered to remove iron ions in the solution at 50 - 70°C by using a wound activated carbon fiber felt with a pore size distribution of micropores (<2nm) in a five - layer stacking manner.

[0019] Preferably, in step 2, the pH of the reaction solution is maintained at 9.3 - 9.4 throughout the reaction process.

[0020] Preferably, in step 3, the aging time after the reaction ends is 6.0 - 8.0 h; the condition for cooling and crystallization of the filtrate after filtration in step 4 is 25°C; the pH of the filter cake obtained in step 4 is adjusted to 6.8 - 7.3 and then slurried, filtered, and the filter cake is washed with pure water, and the filter cake is placed in a dryer and dried at 110 - 130°C to obtain the finished product of white carbon black. The beneficial effects of the present invention are as follows: The present invention provides a method capable of efficiently separating and purifying aluminum fluorosilicate slag to obtain white carbon black with a high specific surface area and high - purity aluminum fluoride. The fluoride ions in the fluorosilicate slag form ammonium fluoride solution that can be recycled, and finally, fluorine, silicon, and aluminum in the slag are effectively recycled. The purity of the aluminum fluoride filter cake separated in the first step of the present invention reaches more than 99%, and the recovery rate reaches more than 95%. The ammonium fluoride filtrate generated during the formation of white carbon black can be recycled, and the silicon recovery rate in the slag reaches more than 95%. Fluorine, silicon, and aluminum in the slag are effectively recycled. When preparing white carbon black, ammonia water is selected as the bottom liquid to ensure the precipitation of white carbon black under alkaline conditions. The purity of the prepared white carbon black is more than 99%, the specific surface area is greater than 300 m² / g, the oil absorption value exceeds 250 mL / 100g, and the fluoride ion concentration is lower than 50 ppm. The silicon slag used in the present invention is derived from the solid waste of preparing aluminum fluoride from fluorosilicic acid, with low cost, and the whole process is environmentally friendly, suitable for industrial - scale production applications. Description of the Drawings

[0021] Figure 1 It is a schematic flow chart of separating, purifying aluminum fluorosilicate slag and preparing white carbon black in Example 1 of the present invention.

[0022] Figure 2 It is a SEM diagram of white carbon black prepared in Table 7 of Example 1 of the present invention showing the influence of adding dispersant (a is Comparative Example 7 - 1 and b is Example 1). Detailed implementation mode

[0023] The following will combine specific embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. The described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the protection scope of the present invention.

[0024] Example 1 S1 Place the aluminum fluorosilicate slag in a reaction vessel, then add water twice the mass of the aluminum fluorosilicate slag and 5% ammonium bifluoride. Pass nitrogen to purge and ensure that the pH of the reaction system is 6.1. At 140 °C and with stirring, slowly add dropwise a 25% ammonium fluoride solution with an equivalent concentration of 1.2. After the addition is complete, continue stirring for 2 h, filter, wash the filter cake and place it in an oven at 120 °C for drying for 3 h to obtain high-purity aluminum fluoride. The filtrate is ammonium fluorosilicate solution, which is filtered through a carbon fiber membrane (using a spiral activated carbon fiber felt with a pore size distribution of micropores of 1 nm, stacked in five layers), and formaldehyde (the addition amount is 0.2% of the total mass of the reaction solution) and melamine (the addition amount is 0.2% of the total mass of the reaction solution) are added and stirred for standby.

[0025] S2 Add a certain amount of 28% ammonia water to a reaction vessel equipped with stirring, a peristaltic pump and a reflux condenser tube. The addition of ammonia water controls the pH to 9.3 - 9.4. S3 Under the conditions of a stirring speed of 600 rpm and a temperature of 30 °C, within 0.5 h, simultaneously pump in the above-obtained filtrate (i.e., ammonium fluorosilicate solution) and ammonia water, and control the pH value of the reaction system to be 9.3 - 9.4. After the reaction ends, continue stirring for 7 h for aging.

[0026] S4 Transfer the reaction solution to a belt filter by pump, cool and crystallize the filtrate, and then filter and dry to obtain ammonium fluoride finished product; S5 Adjust the pH value of the filter cake to 7 with hydrofluoric acid, filter, re-slurry the filter cake and wash it with pure water, and then place it in a dryer at 120 °C for drying for 3 h to obtain white carbon black finished product.

[0027] The recovery rate of aluminum fluoride recovered in this example is greater than 97.5%, the purity is 99.5%, the specific surface area is 359 m 2 / g, and the oil absorption value is 283 mL / 100g.

[0028] Comparative example 1 The preparation method of the precipitated silica in this comparative example is only different from that of the precipitated silica in Example 1 in that, in the first-step S1 reaction process of the preparation method of the precipitated silica in this comparative example, the feeding method is to add ammonium fluoride and aluminum fluorosilicate slag simultaneously. After the reaction ends, the AlF3 content in the AlF3 filter cake and the precipitated silica yield in step S4 of the reaction are compared, and the results are shown in Table 1.

[0029] Table 1. Influence of ammonium fluoride feeding method on the separation and purification of aluminum fluorosilicate slag

[0030] According to Comparative Example 1, in the preparation of precipitated silica from aluminum fluorosilicate slag, the feeding method of raw materials will affect the dissolution status of fluorosilicate slag. A large amount of ammonia gas generated by simultaneous feeding will cause the silicon in the aluminum fluorosilicate slag to be difficult to dissolve completely, and the slow dropping method can make it dissolve fully.

[0031] Comparative Example 2 The preparation method of the precipitated silica in this comparative example is only different from that of the precipitated silica in Example 1 in that, in the first-step reaction process of the preparation method of the precipitated silica in this comparative example, the filtrate after ammonium fluoride and aluminum fluoride are dissolved is not filtered through a carbon fiber membrane to remove the iron ions introduced in the raw materials. The carbon fiber membrane is used to adsorb and compare the iron ion content in the filtrate and the undiluted original solution, as well as the whiteness of the precipitated silica prepared therefrom, and the results are shown in Table 2.

[0032] Table 2. Filtrate treatment method and whiteness of precipitated silica

[0033] According to Comparative Example 2, in the preparation of precipitated silica from aluminum fluorosilicate slag, the adsorption of ammonium fluorosilicate solution through a carbon fiber membrane can greatly reduce the iron ion content in the filtrate, thereby improving the whiteness of the subsequent precipitated silica product.

[0034] Comparative Example 3 The preparation method of the precipitated silica in this comparative example is only different from that of the precipitated silica in Example 1 in that, in the first-step reaction process of the preparation method of the precipitated silica in this comparative example, a cosolvent is added. The dissolution status of aluminum fluorosilicate slag at the same time is compared, and the results are shown in Table 3.

[0035] Table 3. Cosolvent and dissolution status of aluminum fluorosilicate slag

[0036] According to Comparative Example 3, in the process of preparing precipitated silica from aluminum fluorosilicate slag, the addition of a cosolvent can accelerate the dissolution of aluminum fluorosilicate slag. The cosolvent can quickly dissolve the surface layer of aluminum fluorosilicate slag and accelerate the dissolution of aluminum fluorosilicate slag in ammonium fluoride solution. Among them, the effect of the cosolvent ammonium bifluoride is more likely to promote the dissolution of aluminum fluorosilicate slag than fluorosilicic acid.

[0037] Comparative Example 4 The silica preparation method of this comparative example differs from the silica preparation method of Example 1 only in that nitrogen is introduced during the first reaction step, thereby varying the amount of dissolved ammonia in the reaction solution to adjust the pH of the reaction and promote the dissolution of the aluminum fluoride silicon slag. Table 4 shows a comparison of the dissolution of the aluminum fluoride silicon slag over the same time period.

[0038] Table 4. Nitrogen purge and dissolution of aluminum fluoride silicon slag

[0039] According to Comparative Example 4, the introduction of nitrogen during the preparation of silica from aluminum fluoride slag can accelerate the dissolution of the aluminum fluoride slag. The introduction of nitrogen during the dissolution of the aluminum fluoride slag can regulate the amount of ammonia dissolved, preventing ammonia from dissolving in the solution and causing silica precipitation, thereby prolonging the reaction time.

[0040] Comparative Example 5 The preparation method of the white carbon black in this comparative example is different from the preparation method of the white carbon black in Example 1 only in that the reaction time at 140° C. is 1.0-3.0 h. The results are shown in Table 5.

[0041] Table 5. Effect of reaction time on separation and purification of aluminum fluoride silicon slag

[0042] According to Comparative Example 5, in the process of preparing white carbon black from aluminum fluoride silicon slag, different reaction times have different effects on the recovery of silicon resources in aluminum fluoride. At 140°C, the reaction time of 2h has the best effect, the most complete reaction and the lowest energy consumption.

[0043] Comparative Example 6 The preparation method of the white carbon black in this comparative example is different from the preparation method of the white carbon black in Example 1 only in that the reaction solution in step S3 is maintained at different pH values during the preparation of the white carbon black in this comparative example. The results are shown in Table 6.

[0044] Table 6. Effect of pH value of reaction solution on preparation of white carbon black

[0045] According to Comparative Example 6, in the process of preparing white carbon black from aluminum fluoride silicon slag, the pH of the reaction base liquid is crucial. After precise screening of the pH of the ammonia base liquid, it was found that the various indicators of the prepared white carbon black were best when the pH was maintained at 9.3~9.4.

[0046] Comparative Example 7 The preparation method of the silica in this comparative example is only different from that of the silica in Example 1 in that formaldehyde and melamine are added as dispersants in step S1 during the preparation process of the silica in this comparative example. After the experiment, the performance values of the silica products are shown in Table 7.

[0047] Table 7. Performance values of silica

[0048] According to Comparative Example 7, during the preparation of silica, in order to improve the quality of the prepared silica, when formaldehyde and melamine are added as dispersants, the quality of the silica is the best, and both the specific surface area and the oil absorption value have been greatly improved. In order to observe the microscopic morphology of the prepared silica, SEM tests were carried out on the silica prepared in Example 1 and Comparative Example 7-1, as Figure 2 . The results show that the morphology of the silica prepared using formaldehyde and melamine as dispersants is uniform.

[0049] Comparative Example 8 The preparation method of the silica in this comparative example is only different from that of the silica in Example 1 in that the initial pH of the reaction is controlled by whether ammonia water is added as a base in S2 during the preparation process of the silica in this comparative example. After the experiment, the performance values of the silica products are shown in Table 8.

[0050] Table 8. Performance values of silica

[0051] According to Comparative Example 8, during the preparation of silica, adding ammonia water as a base provides an alkaline environment for the reaction of silica. By comparing adding ammonia water as a base and not adding ammonia water as a base, it is found that adding ammonia water as a base can improve the quality of the generated silica.

[0052] In summary, through the optimization of various aspects such as the feeding method, post-treatment method, preparation temperature, preparation pH, and dispersant used in the preparation process of preparing silica from aluminum fluoride silicate slag, the prepared silica has lower preparation cost, higher specific surface area, oil absorption value, purity and other indicators compared with the original preparation process, and has a larger application market.

Claims

1. A method for efficient separation, purification of aluminum fluorosilicate slag and preparation of silica white, comprising the following steps: S1. Take aluminum fluorosilicate slag in a reaction vessel, add water and a cosolvent, stir, then dropwise add ammonium fluoride solution, then introduce nitrogen, heat and stir, filter, the filter cake is aluminum fluoride, and the filtrate is ammonium fluorosilicate solution. The ammonium fluorosilicate solution is further filtered through a carbon fiber membrane to remove iron ions in the solution, and then add melamine and formaldehyde and stir for standby; S2. Take ammonia water and add it to a reaction vessel equipped with a stirring paddle, a peristaltic pump, and a reflux condenser; S3. Under stirring conditions, simultaneously pump in ammonia water and the ammonium fluorosilicate solution obtained in step 1, and age after dropping; S4. Transfer the reaction solution to a belt filter by pump, cool and crystallize the filtrate, and then filter and dry to obtain ammonium fluoride finished product; S5. Adjust the pH of the filter cake obtained by filtration on the belt filter, then make it into a slurry, filter, wash the filter cake with pure water, and place the filter cake in a dryer and dry it to obtain silica white finished product.

2. The method for highly efficient separation, purification of aluminum fluorosilicate slag and preparation of white carbon black according to claim 1, characterized in that: The composition of the aluminum fluorosilicate slag in step 1 is: SiO2 45% - 49%, H2O 30% - 35%, AlF3 6% - 10%, Al(OH)3 2% - 3%, H2SiF6 1% - 2%, HF 0.5% - 1%, Fe 0.02 - 0.03%.

3. The method for preparing precipitated silica with high specific surface area from aluminum fluorosilicate slag according to claim 1, characterized in that: The cosolvent added in step 1, the cosolvent includes fluorosilicic acid or ammonium bifluoride or others, and the addition amount of the cosolvent is 4 - 7% of the aluminum fluorosilicate slag.

4. The method for preparing white carbon black with high specific surface area from aluminum fluoride-silicon slag according to claim 1, characterized in that: During the preparation process of step 1, introducing nitrogen ensures that the pH of the reaction system is maintained at 6.0 - 6.

5.

5. The method for highly efficient separation, purification of aluminum fluorosilicate slag and preparation of white carbon black according to claim 1, characterized in that: In step 1, the reaction temperature is 130 - 150 °C, the stirring speed is 100 - 300 rpm, stir for 1.5 - 2.5 h, the equivalent of ammonium fluoride is 1.2 - 1.5 times the effective silicon equivalent of the aluminum fluorosilicate slag, the recovery rate of aluminum fluoride is above 95%, and the purity is above 99%.

6. The method for highly efficient separation, purification of aluminum fluorosilicate slag and preparation of white carbon black according to claim 1, characterized in that: In step 1, under the condition of 25 - 35 °C, add 0.1 - 0.3% of formaldehyde based on the total mass of the reaction solution and 0.1 - 0.3% of melamine based on the total mass of the reaction solution respectively.

7. The method for efficient separation, purification of aluminum fluorosilicate slag and preparation of precipitated silica according to claim 1, characterized in that: In step 1, the ammonium fluoride solution is added to the reaction system by the way of dropwise addition with a peristaltic pump, and the concentration of the ammonium fluoride solution is 30 - 40%.

8. The method for highly efficient separation, purification of aluminum fluoride-silicon slag and preparation of white carbon black according to claim 1, characterized in that: In step 1, ammonium fluorosilicate needs to be filtered through a wound activated carbon fiber felt with a pore size distribution of micropores <2 nm at 50 - 70 °C to remove iron ions in the solution by the way of five - layer superposition.

9. The method for efficient separation, purification of aluminum fluorosilicate slag and preparation of white carbon black according to claim 1, characterized in that: In step 2, during the whole reaction process, ensure that the pH of the reaction solution is maintained at 9.3 - 9.

4.

10. The method for efficient separation, purification of aluminum fluoride-silicate slag and preparation of white carbon black according to claim 1, characterized in that: In step 3, the concentration of ammonia water is 15 - 25%, and the aging time after the reaction ends is 6.0 - 8.0 h; the condition for cooling and crystallizing the filtrate after filtration in step 4 is 20 - 28 °C; the filter cake obtained by filtration in step 4 is adjusted to a pH of 6.8 - 7.3, then made into a slurry, filtered, washed with pure water, and placed in a dryer and dried at 110 - 130 °C to obtain silica white finished product.

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