A method for preparing white carbon black from fluorine-containing silicon slag

Abstract

The present application relates to the field of resource recovery technology, and in particular to a method for preparing white carbon black from fluorine-containing silicon slag. The present application provides a method for preparing white carbon black from fluorine-containing silicon slag, which comprises the following steps: drying the fluorine-containing silicon slag to obtain crude silicon slag; mixing the crude silicon slag with an alkaline solution and reacting it, and performing solid-liquid separation to obtain a first solution; adding benzenesulfonic acid to the first solution for reaction, performing solid-liquid separation on the reactants to obtain a colloid, and washing and drying the colloid to obtain white carbon black. The preparation method of the present application can improve the recovery rate of silicon in the fluorine-containing silicon slag through the steps of drying, alkaline solution leaching, and reaction with benzenesulfonic acid, and the prepared white carbon black has high purity, low fluorine content, and high specific surface area, and can also reduce production costs.

Description

Technical Field

[0001] The present application relates to the field of resource recovery technology, and in particular to a method for preparing white carbon black from fluorine-containing silicon slag. Background Art

[0002] The production of anhydrous hydrogen fluoride using fluorosilicic acid is gaining increasing attention. However, this process generates a large amount of fluorine-containing silicon slag. When anhydrous hydrogen fluoride is produced by decomposing H2SiF6 with sulfuric acid, 0.625 tons of fluorine-containing silicon slag are generated for every ton of anhydrous hydrogen fluoride produced. Fluorine-containing silicon slag is also produced during the production of phosphate fertilizers and fluoride salts. This fluorine-containing silicon slag is a highly acidic and toxic industrial waste, potentially polluting the environment and threatening human health. However, it has not yet been effectively treated and is primarily disposed of in piles, resulting in significant resource waste.

[0003] Fluorine-containing silicon slag contains a high SiO2 content, which can be recycled to produce white carbon black. The main method for producing white carbon black in the prior art is the acid method, which involves reacting the fluorine-containing silicon slag with a strong alkaline solution to produce a sodium silicate solution. This sodium silicate solution is then reacted with an acid to produce white carbon black. Acidifiers commonly used include sulfuric acid, hydrochloric acid, and carbonic acid. While these acidifiers effectively promote the hydrolysis and precipitation of sodium silicate, they also have several disadvantages. For example, sulfuric acid is highly corrosive, reacts violently, and is difficult to control; hydrochloric acid is highly volatile and corrosive, reacts rapidly, and particle size and morphology are difficult to control; and carbonic acid reacts slowly, resulting in prolonged reaction times, poor precipitation, and incomplete precipitation. Furthermore, the use of these common acids as acidifiers produces sodium salts as byproducts with low value. Furthermore, conventional recovery methods tend to cause white carbon black to agglomerate, resulting in a small specific surface area. This makes the resulting white carbon black product difficult to meet the requirements of certain applications (such as rubber and coatings), significantly limiting the application range of the recovered white carbon black. Therefore, there is an urgent need to develop a method for preparing white carbon black from fluorine-containing silicon slag to achieve the recycling of fluorine-containing silicon slag and obtain high-quality white carbon black while reducing production costs. Summary of the Invention

[0004] The purpose of this application is to provide a method for preparing silica from fluorine-containing silicon slag, thereby improving the recovery rate of silicon. The prepared silica has high purity, low fluorine content, and high specific surface area, while also reducing production costs. The specific technical solution is as follows:

[0005] A first aspect of the present application provides a method for preparing white carbon black from fluorine-containing silicon slag, comprising the following steps:

[0006] (1) Drying the fluorine-containing silicon slag to obtain crude silicon slag;

[0007] (2) mixing and reacting the crude silicon slag with an alkaline solution, and performing solid-liquid separation to obtain a first solution;

[0008] (3) adding benzenesulfonic acid to the first solution to react and obtain a reactant, performing solid-liquid separation on the reactant to obtain a colloid, and washing and drying the colloid to obtain white carbon black.

[0009] In some embodiments of the present application, in step (3), benzenesulfonic acid is added to the first solution at a temperature of 30°C to 50°C until the pH of the solution is 1-3, and the solution is aged after heating to obtain the colloid.

[0010] In some embodiments of the present application, the aging temperature is 80° C. to 110° C., and the aging time is 1 h to 4 h.

[0011] In some embodiments of the present application, in step (3), the benzenesulfonic acid is a benzenesulfonic acid aqueous solution, the mass fraction of the benzenesulfonic acid aqueous solution is 4.9%~19.6%, and the benzenesulfonic acid aqueous solution is added to the first solution by dropwise addition. When the pH of the solution is ≤7, the dropwise addition rate of the benzenesulfonic acid aqueous solution is 1mL / (200mL·min)~2mL / (200mL·min), and the dropwise addition is stopped until the pH of the solution is 1~3.

[0012] In some embodiments of the present application, in step (1), the temperature of the drying treatment is 60° C. to 180° C., and the time of the drying treatment is 4 h to 12 h.

[0013] In some embodiments of the present application, in step (1), the drying treatment is divided into a first drying stage and a second drying stage, the temperature of the first drying stage is T1, 60°C ≤ T1 ≤ 120°C, and the time of the first drying stage is t1, 2h ≤ t1 ≤ 4h; the temperature of the second drying stage is T2, 120°C < T2 ≤ 180°C, and the time of the second drying stage is t2, 2h ≤ t2 ≤ 8h.

[0014] In some embodiments of the present application, in step (2), the alkaline solution is selected from at least one of a sodium hydroxide solution or a potassium hydroxide solution; the concentration of the alkaline solution is 140 g / L to 250 g / L, and the alkaline solution is mixed with the crude silicon slag at a liquid-to-solid ratio of 8 mL / g to 13 mL / g.

[0015] In some embodiments of the present application, in step (2), the alkaline solution is selected from a sodium hydroxide solution, the concentration of the sodium hydroxide solution is 180 g / L to 200 g / L, and the sodium hydroxide solution is mixed with the crude silicon slag at a liquid-to-solid ratio of 8 mL / g to 13 mL / g.

[0016] In some embodiments of the present application, in step (2), the reaction temperature is 65°C to 105°C, and the reaction time is 0.5h to 4h.

[0017] In some embodiments of the present application, in step (2), the reaction is carried out under ultrasonic conditions, and the ultrasonic frequency is 20 kHz to 40 kHz.

[0018] In some embodiments of the present application, in step (3), the drying temperature is 100°C to 150°C.

[0019] Beneficial effects of this application:

[0020] This application provides a method for preparing silica from fluorine-containing silicon slag, comprising the following steps: drying the fluorine-containing silicon slag to produce crude silicon slag; mixing the crude silicon slag with an alkaline solution and reacting the mixture, followed by solid-liquid separation to produce a first solution; adding benzenesulfonic acid to the first solution to react and produce a reactant; subjecting the reactant to solid-liquid separation to produce a colloid; and washing and drying the colloid to produce silica. The preparation method of this application, through the steps of drying, alkaline leaching with an alkaline solution, and reaction with benzenesulfonic acid, can improve the recovery rate of silicon from the fluorine-containing silicon slag. The prepared silica has high purity, low fluorine content, and high specific surface area, while also reducing production costs.

[0021] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. DETAILED DESCRIPTION

[0022] The technical solutions in this application are described clearly and completely below. Obviously, the embodiments described are only some of the embodiments of this application, not all of them. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0023] A first aspect of the present application provides a method for preparing white carbon black from fluorine-containing silicon slag, comprising the following steps:

[0024] (1) Drying the fluorine-containing silicon slag to obtain crude silicon slag;

[0025] (2) mixing and reacting the crude silicon slag with an alkaline solution, and performing solid-liquid separation to obtain a first solution;

[0026] (3) adding benzenesulfonic acid to the first solution to react and obtain a reactant, performing solid-liquid separation on the reactant to obtain a colloid, and washing and drying the colloid to obtain white carbon black.

[0027] The fluorine in fluorine-containing silicon slag exists mainly in the form of free fluorine and lattice fluorine. Among them, free fluorine is mainly fluorosilicic acid attached to the surface of silicon dioxide, and lattice fluorine is the fluorine in the solution that occupies the position of oxygen when silicon dioxide crystallizes. Fluorine exists in the form of crystal defects in silicon dioxide. If it is simply dried, washed with water, etc., only the free fluorine attached to the surface of silicon dioxide can be removed, and the lattice fluorine cannot be removed. The study found that first drying the fluorine-containing silicon slag can effectively remove the free fluorine on the surface of the fluorine-containing silicon slag and the moisture in the fluorine-containing silicon slag, which is beneficial to reduce the amount of subsequent alkaline solution. Then the obtained crude silicon slag is mixed with the alkaline solution. The silicon dioxide in the crude silicon slag reacts with the alkaline solution to form silicate, which causes the lattice fluorine to be leached and converted into free fluorine. The leached free fluorine can be removed through subsequent processing steps, which is beneficial to reduce the fluorine content in the white carbon black product and improve the purity of white carbon black.

[0028] More importantly, in step (3), the present application uses benzenesulfonic acid as an acidifying agent. On the one hand, benzenesulfonic acid can promote the hydrolysis of silicate to generate white carbon black, and the hydrolysis reaction between benzenesulfonic acid and silicate is relatively mild, which can reduce the situation of local reaction overheating, and is conducive to regulating the particle size of white carbon black and increasing the specific surface area of white carbon black. On the other hand, in the early stage of the acidification reaction, benzenesulfonic acid first reacts with the remaining alkaline solution in the first solution, and the sodium benzenesulfonate or potassium benzenesulfonate generated by the reaction can act as a surfactant and participate in the acidification reaction stage. Sodium benzenesulfonate or potassium benzenesulfonate is adsorbed on the surface of white carbon black to form a protective film to prevent particle agglomeration, thereby improving the dispersibility of white carbon black in the solution, which is conducive to preparing a white carbon black product with uniform particle size, good dispersibility and large specific surface area. That is, the present application uses benzenesulfonic acid as an acidifying agent, which not only plays an acidifying role on sodium silicate or potassium silicate, but also the generated sodium benzenesulfonate or potassium benzenesulfonate has the function of a surfactant, and the specific surface area of white carbon black can be effectively increased without adding additional surfactants. In addition, compared with commonly used surfactants, such as hexadecyltrimethylammonium bromide, sodium benzenesulfonate or potassium benzenesulfonate is easier to remove from the surface of silica during the washing process to obtain high-purity silica. In addition, sodium benzenesulfonate or potassium benzenesulfonate, as a by-product after the reaction, has good biodegradability, has less impact on the environment, and has a high recycling value.

[0029] The preparation method of the present application can improve the recovery rate of silicon in fluorine-containing silicon slag through the steps of drying treatment, alkaline solution leaching, and acidification reaction with benzenesulfonic acid, and the prepared white carbon black has high purity, low fluorine content and high specific surface area, and can also reduce production costs.

[0030] In step (2) of the present application, the crude silicon slag may contain HF, H2SiF6, etc. in addition to SiO2. For example, when the alkaline solution is selected from sodium hydroxide solution, the reaction between the crude silicon slag and the sodium hydroxide solution is as follows:

[0031] .

[0032] Furthermore, in step (3) of the present application, benzenesulfonic acid is added to the first solution, and the reaction that occurs is as follows:

[0033] .

[0034] In some embodiments of the present application, in step (3), benzenesulfonic acid is added to the first solution at a temperature of 30°C to 50°C until the solution pH is 1 to 3, and then the solution is aged after heating to obtain the colloid. For example, the temperature when adding benzenesulfonic acid to the first solution can be 30°C, 32°C, 35°C, 38°C, 40°C, 42°C, 45°C, 48°C, 50°C, or a range consisting of any two values therein; the solution pH is adjusted to 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, or a range consisting of any two values therein. Preheating the first solution to a temperature of 30°C to 50°C is beneficial to accelerating the acidification reaction process, and the resulting silicate colloid (SiO2·H2O) is not easy to agglomerate. At the same time, controlling the pH to 1-3 can also reduce the agglomeration of silicate colloid, further increase the specific surface area, and help further increase the specific surface area of the final white carbon black product, and facilitate the hydrolysis of silicate in the solution into silicate colloid (SiO2·H2O).

[0035] In some embodiments of the present application, the aging temperature is 80°C to 110°C, and the aging time is 1h to 4h. For example, the aging temperature can be 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, or a range consisting of any two values therein; the aging time can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, or a range consisting of any two values therein. The aging process can be carried out under stirring. The present application does not specifically limit the stirring speed, as long as the purpose of the present application can be achieved. For example, the stirring speed is 200rpm to 800rpm. By regulating the aging temperature and time within the scope of the present application, it is beneficial to improve the dispersibility of the silica colloid, reduce agglomeration, and thus help increase the specific surface area of white carbon black.

[0036] In some embodiments of the present application, in step (3), the benzenesulfonic acid is an aqueous solution of benzenesulfonic acid, the mass fraction of the aqueous solution of benzenesulfonic acid is 4.9% to 19.6%, and the aqueous solution of benzenesulfonic acid is added to the first solution by dropwise addition. When the pH of the solution is ≤7, the dropwise addition rate of the aqueous solution of benzenesulfonic acid is 1mL / (200mL·min) to 2mL / (200mL·min), and the dropwise addition is stopped until the pH of the solution is 1 to 3. For example, the mass fraction of the aqueous solution of benzenesulfonic acid can be 4.9%, 5%, 8%, 10%, 12%, 15%, 18%, 19.6%, or a range consisting of any two of these values. In the present application, the dropwise addition rate of the aqueous solution of benzenesulfonic acid is 1mL / (200mL·min) to 2mL / (200mL·min) means that 1mL to 2mL of the aqueous solution of benzenesulfonic acid is added dropwise to every 200mL of the first solution per minute. For example, when the first solution is 400 mL, then according to this dropwise addition rate, 2 mL to 4 mL of the benzenesulfonic acid aqueous solution will be added thereto per minute; when the first solution is 100 mL, then 0.5 mL to 1 mL of the benzenesulfonic acid aqueous solution will be added thereto per minute. When the solution pH is ≤ 7, the benzenesulfonic acid aqueous solution dropwise addition rate can be 1 mL / (200 mL·min), 1.2 mL / (200 mL·min), 1.5 mL / (200 mL·min), 1.8 mL / (200 mL·min), 2 mL / (200 mL·min), or a range consisting of any two values therein; the benzenesulfonic acid aqueous solution is added dropwise to the first solution until the solution pH is 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, or a range consisting of any two values therein. When the solution pH is greater than 7, the present application does not particularly limit the rate at which the benzenesulfonic acid aqueous solution is added to the first solution, as long as the objectives of the present application are achieved. For example, the benzenesulfonic acid aqueous solution addition rate can be 5 mL / (200 mL·min) to 10 mL / (200 mL·min). By selecting benzenesulfonic acid within the scope of the present application and regulating the benzenesulfonic acid aqueous solution addition rate within the scope of the present application, the dispersion of the silica colloid is improved, agglomeration is reduced, and the specific surface area of the white carbon black is increased.

[0037] In the present application, after the first solution in step (3) undergoes an acidification reaction with benzenesulfonic acid, the reactants are subjected to solid-liquid separation to obtain a colloid and a filtrate, wherein the main component of the filtrate is sodium benzenesulfonate or potassium benzenesulfonate, which has a high recycling value.

[0038] In some embodiments of the present application, in step (1), the temperature of the drying treatment is 60°C to 180°C, and the time of the drying treatment is 4h to 12h. For example, the temperature of the drying treatment can be 60°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, or a range consisting of any two of these values; the time of the drying treatment can be 4h, 5h, 8h, 10h, 12h, or a range consisting of any two of these values. By regulating the temperature and time of the drying treatment within the scope of the present application, it is beneficial to remove the free fluorine on the surface of the fluorine-containing silicon slag and the moisture in the fluorine-containing silicon slag, which is beneficial to reducing the amount of subsequent alkaline solution and reducing costs. At the same time, it is also beneficial to reduce the fluorine content in the solution in the subsequent treatment steps, which is beneficial to the recycling of the by-product solution.

[0039] In some embodiments of the present application, in step (1), the drying treatment is divided into a first drying stage and a second drying stage, the temperature of the first drying stage is T1, 60°C ≤ T1 ≤ 120°C, and the time of the first drying stage is t1, 2h ≤ t1 ≤ 4h; the temperature of the second drying stage is T2, 120°C < T2 ≤ 180°C, and the time of the second drying stage is t2, 2h ≤ t2 ≤ 8h. For example, T1 can be 60°C, 80°C, 90°C, 100°C, 110°C, 120°C, or a range consisting of any two of these values; t1 can be 2h, 2.5h, 3h, 3.5h, 4h, or a range consisting of any two of these values; T2 can be 121°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, or a range consisting of any two of these values; t2 can be 2h, 3h, 4h, 5h, 6h, 7h, 8h, or a range consisting of any two of these values. By dividing the drying process into a first drying stage and a second drying stage, the first drying stage mainly removes free fluorine on the surface of the fluorine-containing silicon slag, and the second stage mainly removes moisture in the fluorine-containing silicon slag. By using a staged drying process, efficient removal of free fluorine and moisture in the fluorine-containing silicon slag can be achieved, and energy consumption and costs can be further reduced.

[0040] In some embodiments of the present application, in step (2), the alkaline solution is selected from at least one of a sodium hydroxide solution or a potassium hydroxide solution; the concentration of the alkaline solution is 140 g / L to 250 g / L, and the alkaline solution is mixed with the crude silicon slag at a liquid-to-solid ratio of 8 mL / g to 13 mL / g. For example, the concentration of the alkaline solution can be 140 g / L, 150 g / L, 160 g / L, 170 g / L, 180 g / L, 190 g / L, 200 g / L, 210 g / L, 220 g / L, 230 g / L, 240 g / L, 250 g / L, or a range consisting of any two of the values therein; the liquid-to-solid ratio of the alkaline solution to the crude silicon slag can be 8 mL / g, 9 mL / g, 10 mL / g, 11 mL / g, 12 mL / g, 13 mL / g, or a range consisting of any two of the values therein. Selecting an alkaline solution within the scope of this application facilitates the conversion of silicon dioxide in the crude silicon slag into silicate, and leaches the lattice fluorine in the crude silicon slag, converting it into free fluorine. Subsequent processing steps can then remove the leached free fluorine, thereby reducing the fluorine content in the silica product and improving the purity of the silica. In this application, the concentration of the alkaline solution refers to the mass of solute contained per liter of the alkaline solution.

[0041] In some embodiments of the present application, in step (2), the alkaline solution is selected from a sodium hydroxide solution, the concentration of the sodium hydroxide solution is 180 g / L to 200 g / L, and the sodium hydroxide solution is mixed with the crude silicon slag at a liquid-to-solid ratio of 8 mL / g to 13 mL / g. For example, the concentration of the sodium hydroxide solution can be 180 g / L, 190 g / L, 200 g / L, or a range consisting of any two values therein; the liquid-to-solid ratio of the sodium hydroxide solution to the crude silicon slag can be 8 mL / g, 9 mL / g, 10 mL / g, 11 mL / g, 12 mL / g, 13 mL / g, or a range consisting of any two values therein. By regulating the concentration of the sodium hydroxide solution and the liquid-solid ratio of the sodium hydroxide solution to the crude silicon slag within the scope of the present application, it is beneficial to convert the silicon dioxide in the crude silicon slag into sodium silicate, and to leach the lattice fluorine in the crude silicon slag and convert it into free fluorine. The leached free fluorine can then be removed through subsequent processing steps, which is beneficial to reducing the fluorine content in the white carbon black product and improving the purity of the white carbon black.

[0042] In some embodiments of the present application, in step (2), the reaction temperature is 65°C to 105°C, and the reaction time is 0.5h to 4h. For example, the reaction temperature can be 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, or a range consisting of any two values therein; the reaction time can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, or a range consisting of any two values therein. The reaction between silicon dioxide in the fluorine-containing silicon slag and sodium hydroxide is an endothermic reaction. By regulating the reaction temperature and time within the scope of the present application, it is beneficial to further promote the reaction between silicon dioxide in the fluorine-containing silicon slag and sodium hydroxide, and the silicon in the fluorine-containing silicon slag can be effectively leached and converted into sodium silicate.

[0043] In some embodiments of the present application, in step (2), the reaction is carried out under ultrasonic conditions, and the ultrasonic frequency is 20kHz~40kHz. For example, the ultrasonic frequency can be 20kHz, 25kHz, 30kHz, 35kHz, 40kHz or a range consisting of any two of these values. By applying ultrasonic waves during the reaction of fluorine-containing silicon slag and sodium hydroxide, and regulating the frequency of ultrasonic waves within the scope of the present application, it is beneficial to destroy the agglomerated structure of fluorine-containing silicon slag particles, accelerate the penetration of sodium hydroxide solution in fluorine-containing silicon slag, promote the reaction of silicon dioxide in fluorine-containing silicon slag and sodium hydroxide, and improve the conversion rate of silicon; at the same time, it promotes the leaching of lattice fluorine and converts it into free fluorine, which is beneficial to improve its defluorination effect.

[0044] In the present application, the colloid obtained in step (3) is washed to remove sodium benzenesulfonate and fluoride ions contained in the colloid. The present application does not particularly limit the washing conditions, as long as the purpose of the present application can be achieved. In some embodiments of the present application, the colloid is mixed and stirred with ultrapure water in a mass ratio of 1: (2 to 5) for 30 minutes to 100 minutes to perform solid-liquid separation. In some embodiments of the present application, ultrasound can be applied during the washing process. In some embodiments of the present application, the number of washings can be 2 to 6 times.

[0045] In some embodiments of the present application, in step (3), the drying temperature is 100°C to 150°C. For example, the drying temperature can be 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, or a range consisting of any two of these values. By regulating the drying temperature in step (3) within the range of the present application, it is advantageous to remove moisture from the silica.

[0046] Example

[0047] The following examples and comparative examples are provided to further illustrate the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are by weight. All raw materials in the examples and comparative examples of the present application are commercially available.

[0048] Test methods and equipment:

[0049] Testing of white carbon black purity and fluorine element mass percentage

[0050] The silica prepared in each of the examples and comparative examples of this application was tested by X-ray fluorescence spectrometry to determine the mass percentage of silicon dioxide and the mass percentage of fluorine in the silica. The mass percentage of silicon dioxide in the silica represents the purity of the silica.

[0051] Silicon recovery test

[0052] The crude silicon slag was sampled and tested by X-ray fluorescence spectrometer. The mass percentage of silicon element in the crude silicon slag was W1, the mass of the crude silicon slag was M1, and the mass of silicon in the crude silicon slag was calculated to be W1×M1; the white carbon black obtained in each embodiment and comparative example was tested by X-ray fluorescence spectrometer. The mass percentage of silicon element in the white carbon black was W2, the mass of the white carbon black was M2, and the mass of silicon in the white carbon black was calculated to be W2×M2; the silicon recovery rate was calculated to be [(W2×M2) / (W1×M1)]×100%.

[0053] Test of specific surface area of white carbon black

[0054] The specific surface area of silica was measured using a surface area analyzer using the nitrogen adsorption method. The specific test was conducted in accordance with the national standard GB / T 19587-2017, "Determination of the Specific Surface Area of Solid Substances by the BET Method for Gas Adsorption."

[0055] Example 1

[0056] The fluorine-containing silicon slag used in this application is a by-product of the process of producing hydrogen fluoride from fluorosilicic acid. The fluorine-containing silicon slag is sampled and tested by thermogravimetric analysis and X-ray fluorescence spectrometer. The main components of the fluorine-containing silicon slag are: the mass percentage of H2O is 60.59%, the mass percentage of SiO2 is 28.48%, and the mass percentage of F element is 10.61%.

[0057] (1) 200 g of fluorine-containing silicon slag was dried in an oven at 80°C for 2 h and then at 160°C for 7 h to obtain crude silicon slag. The mass percentage of H2O in the crude silicon slag was 0.76%, and the water removal rate was 98.74%. The mass percentage of F in the crude silicon slag was 4.03%, and the fluorine removal rate was 62.02%.

[0058] (2) The crude silicon slag obtained above was poured into a PFA (soluble polytetrafluoroethylene) reaction flask. A 190 g / L sodium hydroxide solution was then added to the flask, with a liquid-to-solid ratio of 10 mL / g. The reaction was stirred at 95°C for 1 hour while applying ultrasonic waves at a frequency of 40 kHz and a stirring rate of 500 rpm. The mixture was then filtered to obtain a first solution.

[0059] (3) The first solution prepared above was placed in a PFA reaction bottle, which was placed in an oil bath and heated to 40°C. After the temperature in the reaction bottle reached 40°C, a 9.8% mass fraction of benzenesulfonic acid aqueous solution was added dropwise to the first solution. When the pH of the solution was greater than 7, the dropwise addition rate of the benzenesulfonic acid aqueous solution was 8 mL / (200 mL·min). When the pH of the solution was less than or equal to 7, the dropwise addition rate of the benzenesulfonic acid aqueous solution was adjusted to 1 mL / (200 mL·min). When the pH of the solution reached 2, the addition of the benzenesulfonic acid aqueous solution was stopped. The solution was then heated to 80°C and aged under stirring at a speed of 300 rpm for 2 h. The solution was then filtered to obtain a colloid. The colloid was ultrasonically washed with water three times and then dried at 120°C to obtain white carbon black.

[0060] Example 2

[0061] The process was the same as in Example 1 except that the addition of benzenesulfonic acid was stopped when the final pH of the solution was adjusted to 1 in step (3).

[0062] Example 3

[0063] The process was the same as in Example 1 except that the addition of benzenesulfonic acid was stopped when the final pH of the solution was adjusted to 3 in step (3).

[0064] Example 4

[0065] The process was the same as in Example 1 except that the addition of benzenesulfonic acid was stopped when the final pH of the solution was adjusted to 5 in step (3).

[0066] Example 5

[0067] The process was the same as in Example 1 except that in step (3), when the pH of the solution was ≤ 7, the dropping rate of the benzenesulfonic acid aqueous solution was adjusted to 2 mL / (200 mL·min).

[0068] Example 6

[0069] The process was the same as in Example 1 except that in step (3), when the pH of the solution was ≤ 7, the dropping rate of the benzenesulfonic acid aqueous solution was adjusted to 4 mL / (200 mL·min).

[0070] Example 7

[0071] The process was the same as in Example 1 except that the oil bath was heated to 30°C in step (3) and 9.8% benzenesulfonic acid aqueous solution was added dropwise after the temperature in the reaction flask reached 30°C.

[0072] Example 8

[0073] The process was the same as in Example 1 except that the oil bath was heated to 50°C in step (3) and 9.8% benzenesulfonic acid aqueous solution was added dropwise after the temperature in the reaction flask reached 50°C.

[0074] Example 9

[0075] The process was the same as in Example 1 except that in step (3), the oil bath was not heated and 9.8% benzenesulfonic acid aqueous solution was added dropwise at 20°C.

[0076] Example 10

[0077] The process was the same as in Example 1 except that in step (3), the aging temperature was adjusted to 110° C. and the aging time was 1 h.

[0078] Example 11

[0079] The process is the same as in Example 1 except that in step (3), the aging temperature is adjusted to 70° C. and the aging time is 2 h.

[0080] Example 12

[0081] The reaction was the same as in Example 1 except that in step (2), the reaction was stirred at 95° C. for 1 h without ultrasonic wave application.

[0082] Example 13

[0083] The same procedures as in Example 1 were followed except that the drying treatment in step (1) was directly performed at 60°C for 9 hours without a staged drying process. The mass percentage of H2O in the crude silicon slag obtained was 47.48%, and the water removal rate was 21.64%. The mass percentage of F element in the crude silicon slag was 6.12%, and the fluorine removal rate was 42.32%.

[0084] Example 14

[0085] The same procedures as in Example 1 were followed except that the drying treatment in step (1) was directly carried out at 180°C for 9 hours without a staged drying process. The mass percentage of H2O in the crude silicon slag obtained was 0.74%, and the water removal rate was 98.78%. The mass percentage of F element in the crude silicon slag was 3.99%, and the fluorine removal rate was 62.39%.

[0086] Example 15

[0087] Except that the concentration of sodium hydroxide in step (2) was adjusted to 140 g / L, the rest was the same as in Example 1.

[0088] Example 16

[0089] Except that the concentration of sodium hydroxide in step (2) was adjusted to 250 g / L, the rest was the same as in Example 1.

[0090] Example 17

[0091] The same procedures as in Example 1 were followed except that the alkaline solution in step (2) was replaced by a mixed alkaline solution of sodium hydroxide and potassium hydroxide, and the concentration of the alkaline solution was 190 g / L, wherein the concentration of sodium hydroxide in the alkaline solution was 80 g / L and the concentration of potassium hydroxide in the alkaline solution was 110 g / L.

[0092] Comparative Example 1

[0093] Except that benzenesulfonic acid is replaced by a sulfuric acid solution with a mass fraction of 9.8% in step (3), the rest is the same as Example 1.

[0094] The purity, mass percentage of fluorine element, specific surface area and silicon recovery rate of the white carbon black prepared in each embodiment and comparative example are shown in Table 1.

[0095] Table 1

[0096]

[0097] As can be seen from Examples 1 to 17 and Comparative Example 1, the silica obtained using the preparation method of the present application has high purity, low fluorine content, and a high specific surface area, as well as a high silicon recovery rate. However, Comparative Example 1, which uses sulfuric acid instead of benzenesulfonic acid as the acidifying agent, yields a lower specific surface area for the silica. This indicates that the use of benzenesulfonic acid as the acidifying agent in the preparation method of the present application not only acidifies the sodium silicate, but also allows the resulting sodium benzenesulfonate to function as a surfactant, effectively increasing the specific surface area of the silica without the need for the addition of additional surfactants.

[0098] In step (3), the pH value of the solution adjusted by adding benzenesulfonic acid will affect the specific surface area of silica and the recovery rate of silicon. It can be seen from Examples 1 to 4 that when the pH of the solution adjusted by adding benzenesulfonic acid is in the range of 1 to 3, it is beneficial to further improve the specific surface area of silica and the recovery rate of silicon. The obtained silica has higher purity, lower fluorine content and higher specific surface area, and the recovery rate of silicon is also higher.

[0099] In step (3), when the pH value of the solution is ≤7, the droplet acceleration rate of the benzenesulfonic acid aqueous solution will affect the specific surface area of the silica. It can be seen from Examples 1, 5 and 6 that by regulating the droplet acceleration rate of the benzenesulfonic acid aqueous solution within the range of 1 mL / (200 mL·min) to 2 mL / (200 mL·min), it is beneficial to further increase the specific surface area of the silica. The obtained silica has higher purity, lower fluorine content and higher specific surface area, and the recovery rate of silicon is also higher.

[0100] In step (3), the temperature when the benzenesulfonic acid solution is added to the first solution will affect the specific surface area of the silica. It can be seen from Examples 1 and 7 to 9 that by regulating the temperature when adding benzenesulfonic acid to the first solution within the range of 30°C to 50°C, the specific surface area of the silica can be further increased. The obtained silica has a higher purity, a lower fluorine content, a higher specific surface area, and a higher silicon recovery rate.

[0101] In step (3), the aging temperature and aging time will affect the specific surface area of white carbon black. It can be seen from Examples 1, 10 and 11 that by regulating the aging temperature within the range of 80°C to 110°C and the aging time within the range of 1h to 4h, it is beneficial to further increase the specific surface area of white carbon black. The obtained white carbon black has higher purity, lower fluorine content and higher specific surface area, and the silicon recovery rate is also higher.

[0102] In step (2), the reaction conditions after adding the alkaline solution affect the fluorine leaching rate and the silicon recovery rate. As can be seen from Examples 1 and 12, applying ultrasound during the reaction process of step (2) is beneficial to the fluorine leaching and can improve the silicon recovery rate. The resulting silica has a higher purity, a lower fluorine content, and a higher specific surface area, and the silicon recovery rate is also higher.

[0103] In step (2), the concentration of the alkaline solution affects the fluorine leaching rate and the silicon recovery rate. As can be seen from Examples 1 and 15 to 17, by adjusting the concentration of the alkaline solution within the range of 140 g / L to 250 g / L, the silicon recovery rate is improved. The obtained silica has a higher purity, a lower fluorine content, and a higher specific surface area, and the silicon recovery rate is also higher.

[0104] In step (1), the drying process affects the water content and fluorine content in the crude silicon slag. It can be seen from Examples 1, 13 and 14 that by dividing the drying process into two stages, efficient removal of free fluorine and moisture in the fluorine-containing silicon slag can be achieved, which is also beneficial to further reduce energy consumption and reduce costs.

[0105] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for preparing white carbon black from fluorine-containing silicon slag, characterized in that: The following steps are involved: (1) Drying the fluorine-containing silicon slag to obtain crude silicon slag; (2) mixing and reacting the crude silicon slag with an alkaline solution, and performing solid-liquid separation to obtain a first solution; (3) adding benzenesulfonic acid to the first solution to react and obtain a reactant, performing solid-liquid separation on the reactant to obtain a colloid, and washing and drying the colloid to obtain white carbon black; In the step (3), benzenesulfonic acid is added to the first solution at a temperature of 30°C to 50°C until the pH of the solution is 1-3, and then the solution is aged after heating to obtain the colloid, wherein the aging temperature is 80°C to 110°C and the aging time is 1h to 4h; In the step (3), the benzenesulfonic acid is a benzenesulfonic acid aqueous solution, and the benzenesulfonic acid aqueous solution is added to the first solution by dropwise addition. When the pH value of the solution is ≤7, the dropwise addition rate of the benzenesulfonic acid aqueous solution is 1mL / (200mL·min)~2mL / (200mL·min), and 1mL / (200mL·min)~2mL / (200mL·min) means that 1mL~2mL of the benzenesulfonic acid aqueous solution is added dropwise to every 200mL of the first solution per minute until the pH value of the solution is 1~3, and then the dropwise addition is stopped.

2. The method according to claim 1, characterized in that In the step (3), the mass fraction of the benzenesulfonic acid aqueous solution is 4.9% to 19.6%.

3. The method according to any one of claims 1 to 2, characterized in that In the step (1), the temperature of the drying treatment is 60° C. to 180° C., and the time of the drying treatment is 4 h to 12 h.

4. The method according to claim 3, characterized in that In step (1), the drying process is divided into a first drying stage and a second drying stage, wherein the temperature of the first drying stage is T1, 60°C ≤ T1 ≤ 120°C, and the time of the first drying stage is t1, 2h ≤ t1 ≤ 4h; the temperature of the second drying stage is T2, 120°C < T2 ≤ 180°C, and the time of the second drying stage is t2, 2h ≤ t2 ≤ 8h.

5. The method according to any one of claims 1 to 2, characterized in that In step (2), the alkaline solution is selected from at least one of a sodium hydroxide solution and a potassium hydroxide solution; The concentration of the alkaline solution is 140 g / L to 250 g / L, and the alkaline solution is mixed with the crude silicon slag at a liquid-to-solid ratio of 8 mL / g to 13 mL / g.

6. The method according to any one of claims 1 to 2, characterized in that In the step (2), the alkaline solution is selected from a sodium hydroxide solution, the concentration of the sodium hydroxide solution is 180 g / L to 200 g / L, and the sodium hydroxide solution is mixed with the crude silicon slag at a liquid-to-solid ratio of 8 mL / g to 13 mL / g.

7. The method according to any one of claims 1 to 2, characterized in that In the step (2), the reaction temperature is 65°C to 105°C, and the reaction time is 0.5h to 4h.

8. The method according to any one of claims 1 to 2, characterized in that In the step (2), the reaction is carried out under ultrasonic conditions, and the ultrasonic frequency is 20kHz~40kHz.

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