Method for preparing white carbon black from hydrogen fluoride by-product fluorosilicon slag

Abstract

The invention relates to a preparation method of white carbon black, and belongs to the technical field of chemical product preparation. The method for preparing the white carbon black with the high specific surface area from the fluorine-silicon slag comprises the following steps: carrying out ball-milling reaction on the hydrogen fluoride silicon slag and ammonium fluoride to obtain ammonium fluosilicate; ammonium fluosilicate is slowly added into ammonia water, and the pH value of the reaction liquid is always controlled to be 9.0-9.5; and after reaction, performing solid-liquid separation to obtain a white carbon black finished product. A ball milling mode is adopted, a reaction system can maintain weak acidity, silicon dioxide is prevented from being separated out, and then the fluorine-silicon slag is efficiently converted into ammonium fluosilicate. The purity of the obtained white carbon black is 99% or above, the yield is 95% or above, the F <-> concentration is smaller than 50 ppm, and the specific surface area of the white carbon black is gt; 300 m < 2 > / g, and the oil absorption value is gt; the yield of ammonium fluoride is more than 95% when the volume is 250mL / 100g. The raw material used for preparation is solid waste generated in the process of preparing hydrogen fluoride from fluosilicic acid, and the process is simple, environmentally friendly and suitable for industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical product preparation, and particularly relates to a method for preparing white carbon black from fluorosilicate slag by-produced from hydrogen fluoride. Background Art

[0002] Anhydrous hydrogen fluoride is a widely used chemical product, which is widely used in many fields such as the preparation of fluorine salts, fluorohaloalkanes, fluorine refrigerants, etching glass, impregnating wood, etc. All along, the mainstream production method of anhydrous hydrogen fluoride is the fluorite method. However, due to the non-renewable and low reserves of fluorite, its mining and utilization are restricted. Using fluosilicic acid, a by-product in the production process of phosphate fertilizer, to produce hydrogen fluoride has become an environmentally friendly and economical process route. The main production process is as follows: Dilute fluosilicic acid in the phosphoric acid production system is concentrated and then reacts with concentrated sulfuric acid to generate hydrogen fluoride and silicon tetrafluoride. A large amount of fluorosilicate slag mainly composed of SiO2 will be generated during this process. However, due to its low specific surface area, poor dispersibility, and high fluorine content, it cannot be directly used as a product. Usually, it is stacked as solid waste, which causes environmental pollution and waste of resources. How to make good use of the fluorosilicon resources in the fluorosilicate slag is an urgent problem to be solved.

[0003] Chinese Patent CN 102491370A discloses a method in which fluorosilicate slag is dissolved in ammonium fluoride solution, and ammonia gas is introduced into the obtained ammonium fluorosilicate solution after cooling, and white carbon black is precipitated out, and the white carbon black solid and ammonium fluoride solution are obtained by filtration and washing. Chinese Patent CN 105271254A discloses a method in which anhydrous hydrogen fluoride silicon slag reacts with ammonium fluoride solution to produce ammonium fluorosilicate and ammonia gas, and then the obtained ammonium fluorosilicate solution reacts with ammonia water to obtain white carbon black. Chinese Patent CN102674367B discloses a method in which anhydrous hydrogen fluoride silicon slag is heated and dissolved in ammonium fluoride solution under negative pressure, and the undissolved SiO2 impurities are removed by hot filtration to obtain ammonium fluorosilicate. However, the above methods generally have the problem that the silicon slag cannot be completely dissolved. The reason is that ammonium fluoride and fluorosilicate slag will undergo the following reversible reaction:

[0004] During the reaction between ammonium fluoride and fluorosilicate slag, a large amount of ammonia gas will be rapidly released. The ammonia gas dissolves in the solution, making the solution alkaline. Under alkaline conditions, ammonium fluorosilicate in the solution will react with the released ammonia gas to generate white carbon black. The newly generated white carbon black is mixed with the unreacted fluorosilicate slag, thereby making it impossible to effectively separate and utilize the silicon in the fluorosilicate slag. At the same time, if the subsequent preparation of white carbon black is carried out directly without filtration after the above reaction, the newly generated white carbon black adheres to the surface of the undissolved white carbon black, and the particles agglomerate with each other, thereby reducing the specific surface area of the white carbon black. Based on this, there is an urgent need for a method that can efficiently dissolve hydrogen fluoride silicon slag to prepare white carbon black with a high specific surface area. Summary of the Invention

[0005] To solve the above problems, the present invention provides a method for preparing precipitated silica from by-product fluorosilicate slag of hydrogen fluoride. The technical solution of the present invention is as follows: A method for preparing precipitated silica from by-product fluorosilicate slag of hydrogen fluoride, the method comprising the following steps: S1 Take a certain amount of by-product fluorosilicate slag of hydrogen fluoride and ammonium fluoride in a ball mill reactor, add polyvinyl alcohol as a dispersant, and perform a ball milling reaction under high temperature conditions to obtain ammonium fluorosilicate, and configure it into an ammonium fluorosilicate solution; S2 Take formaldehyde and add it to a reaction kettle equipped with stirring, a peristaltic pump and a condenser; while stirring, simultaneously pump the ammonium fluorosilicate solution and ammonia water in step 1, and after the feeding is completed, age to obtain a reaction solution; S3 Filter the reaction solution, cool and crystallize the filtrate, and dry it after filtration to obtain ammonium fluoride for recycling; S4 Adjust the pH of the filter cake and then slurry it, filter it, wash the filter cake with pure water, and place the filter cake in a dryer to dry to obtain the finished product of precipitated silica.

[0006] The composition of the fluorosilicate slag is: SiO2 43% - 48%, H2O 40% - 50%, H2SiF6 2% - 5%, H2SO4 0.5% - 2%, HF 1% - 3%. In the method for preparing precipitated silica of the present invention, ammonium fluorosilicate is first prepared by mixing and ball milling reaction of fluorosilicate slag and ammonium fluoride under high temperature conditions, and then precipitated silica and ammonium fluoride products are obtained through ammoniation. During this preparation process, the reaction system is in a solid phase, and the generated ammonia gas will immediately overflow from the reaction system and be carried out by nitrogen or clean air, so that the reaction system can maintain a weak acidity and silica will not precipitate, thereby ensuring the efficient conversion of fluorosilicate slag into ammonium fluorosilicate.

[0007] To ensure the efficient conversion of fluorosilicate slag, preferably, the ball milling reaction in step S1 is carried out in an environment filled with clean air or nitrogen, the equivalent of ammonium fluoride is 1.0 - 1.5 times the effective silicon equivalent of fluorosilicate slag, the ball-to-material ratio is (60 - 100):1, the ball milling speed is 300 - 500 rpm, the ball milling time is 2 - 6 h, and the ball milling temperature is 100 - 150 °C. After the reaction is completed, cool the solid powder to room temperature to obtain ammonium fluorosilicate. Configure the ammonium fluorosilicate into a solution with a concentration of 8 - 15%.

[0008] Preferably, the gas generated in the reaction system of step 1 can be directly introduced into water by externally purging air to obtain ammonia water, which can be recycled for the next ammoniation.

[0009] To ensure the precipitation of precipitated silica under alkaline conditions, preferably, ammonia water needs to be added first to the bottom of the reaction kettle in step 2, and the initial pH is controlled between 9.0 - 9.5, preferably 9.0 - 9.3.

[0010] Preferably, in step 2, the concentration of ammonia water is 25%, the feeding time is controlled within 0.5 - 2.0 h, and the pH of the reaction system is always maintained between 9.0 - 9.5.

[0011] The polyvinyl alcohol added in step 1 is a dispersant during the ball milling process, ensuring that the materials in the ball milling process are evenly dispersed without forming aggregates, enabling the complete reaction of fluosilicate slag and ammonium fluoride, effectively dispersing the materials in the ball milling process, and obtaining particles with uniform particle size. The added amount is 5 - 10% of the amount of precipitated silica produced.

[0012] The formaldehyde added in step 2 condenses with polyvinyl alcohol to form polyvinyl formal. In the ammoniation step, polyvinyl formal serves as a skeleton structure, and the precipitated silica adheres to its surface, which can effectively play a dispersing role and improve the quality of the prepared silica. The added amount of formaldehyde is 5 - 10% of the amount of precipitated silica produced.

[0013] In step 2, the feeding method is to pump ammonia water and ammonium fluorosilicate simultaneously, the feeding time is 0.5 - 2.0 h, the stirring speed is 600 - 800 rpm, and the aging time of the reaction solution after the reaction is 6.0 - 8.0 h. To obtain excellent properties of the prepared silica product, preferably, in step 4, the pH of the filter cake is adjusted to 6.8 - 7.3 with hydrofluoric acid, and the drying temperature of the silica after re - slurrying and filtration is 120 °C.

[0014] The beneficial effects of the present invention are as follows: The prepared silica has good performance values, and the by - product ammonium fluoride can be recycled. The raw materials used in the preparation are solid waste generated during the preparation of hydrogen fluoride from fluosilicic acid. The process is simple and environmentally friendly, and is suitable for industrial production. Brief Description of the Drawings

[0015] Figure 1 It is a schematic process flow diagram for preparing silica from fluosilicate slag, which is a by - product of hydrogen fluoride in Example 1 of the present invention. Detailed Description of the Embodiments

[0016] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the specific embodiments of the present invention. The described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the protection scope of the present invention.

[0017] Example 1 S1 Put hydrogen fluoride silicate slag, 1.2 equivalents (effective silicon equivalent of fluorosilicate slag), ammonium fluoride, and 3.5% of the mass of the silicate slag of polyvinyl alcohol into a stainless steel ball mill tank and ball mill for 4 h at a rotation speed of 500 rpm. The ball-to-material ratio is 80:1, and the reaction temperature is 140 °C. The ammonia gas generated in the reaction system is introduced into water to obtain ammonia water through externally blown air. After the reaction, the solid powder is cooled to room temperature to obtain ammonium fluorosilicate. Prepare a 10% solution of ammonium fluorosilicate for standby.

[0018] S2 Add a certain amount of water and formaldehyde (3.5% of the mass of the silicate slag) to a reaction kettle equipped with stirring, a peristaltic pump, and a condenser. Under the conditions of a stirring speed of about 700 rpm and a temperature of about 30 °C, simultaneously and slowly pump in ammonia water (25%) and the prepared ammonium fluorosilicate solution. The feeding time is controlled within 0.5 h, and the pH of the reaction solution is controlled at 9.0 - 9.3 and the pH at the end point of the reaction is 9.0 - 9.3. After the reaction is completed, stir and age for 7 h.

[0019] S3 Filter the reaction solution, and after the filtrate is cooled and crystallized, filter and dry to obtain the finished product of ammonium fluoride.

[0020] S4 Adjust the pH of the filter cake to 7 with hydrofluoric acid and re-slurry, filter, wash the filter cake three times with pure water, and place the filter cake in a dryer at 120 °C and dry for 3 h to obtain the finished product of white carbon black.

[0021] The purity of the white carbon black obtained in this example is 99.5%, the yield is 99.3%, the specific surface area of the white carbon black is 361 m 2 / g, the oil absorption value is 275 mL / 100 g, the F - concentration is 41 ppm, and the yield of ammonium fluoride is 96%. Example 2 The difference between the preparation method of the white carbon black in this example and the preparation method of the white carbon black in Example 1 is only that the equivalent of ammonium fluoride in step S1 of the preparation process of the white carbon black in this example is 1.0 - 1.5. After the experiment, the performance values of the white carbon black product are measured as shown in Table 1.

[0022] Table 1 Influence of ammonium fluoride equivalent on the performance values of white carbon black

[0023] As can be seen from Table 1, the detection results of the performance values of the obtained white carbon black show that when the equivalent of ammonium fluoride is 1.2 eq, the hydrogen fluoride silicate slag can be fully dissolved, and a white carbon black product with a high oil absorption value and a high specific surface area can be prepared.

[0024] Example 3 The preparation method of the silica in this example is only different from that of the silica in Example 1 in that the ball milling reaction time in the preparation process of the silica in this example is 2 - 6h. After the experiment, the performance values of the silica products are shown in Table 2.

[0025] Table 2 Influence of Ball Milling Reaction Time on Performance Values of Silica

[0026] As can be seen from Table 2, the test results of the performance values of the obtained silica show that when the ball milling reaction time is 4.0h, the silicon fluoride slag can be fully dissolved, and a silica product with a high oil absorption value and a high specific surface area can be prepared.

[0027] Example 4 The preparation method of the silica in this example is only different from that of the silica in Example 1 in that the ball milling reaction temperature in the preparation process of the silica in this example is 100 - 150°C. After the experiment, the performance values of the silica products are shown in Table 3: Table 3 Influence of Ball Milling Reaction Temperature on Performance Values of Silica

[0028] As can be seen from Table 3, the test results of the performance values of the obtained silica show that when the ball milling reaction temperature is 140°C, the silicon fluoride slag can be fully dissolved, and a silica product with a high oil absorption value and a high specific surface area can be prepared.

[0029] Example 5 The preparation method of the silica in this example is only different from that of the silica in Example 1 in that the ball - to - material ratio in the preparation process of the silica in this example is 60 - 100:1. After the experiment, the performance values of the silica products are shown in Table 4: Table 4 Influence of Ball - to - Material Ratio on Performance Values of Silica

[0030] As can be seen from Table 4, the test results of the performance values of the obtained silica show that when the ball - to - material ratio of the ball milling reaction is 80:1, the silicon fluoride slag can be fully dissolved, and a silica product with a high oil absorption value and a high specific surface area can be prepared.

[0031] Example 6 The preparation method of the silica in this example is only different from that of the silica in Example 1 in that the dispersant in the ammoniation step in the preparation process of the silica in this example is the combined use of polyvinyl alcohol and formaldehyde. After the experiment, the performance values of the silica products are shown in Table 5.

[0032] Table 5 Influence of Dispersant on Performance Values of Silica

[0033] As can be seen from Table 5, the test results of the performance values of the obtained silica show that, compared with adding only formaldehyde and polyvinyl alcohol and without a dispersing machine, when polyvinyl alcohol and formaldehyde are used in combination as a dispersant, the dispersing effect is the best, and the generated silica can be rapidly dispersed to avoid agglomeration.

[0034] In summary, during the preparation of silica from the by-product fluorosilicate slag of hydrogen fluoride, when the amount of ammonium fluoride used is 1.2 equivalents, the ball milling reaction temperature is 140 °C, the ball milling ball-to-material ratio is 80:1, the ball milling reaction time is 4.0 h, and the dispersant used is a combination of polyvinyl alcohol and formaldehyde, the fluorosilicate slag of hydrogen fluoride can be fully dissolved to prepare a silica product with high performance values.

Claims

1. A method for preparing white carbon black from fluorosilicate slag as a by-product of hydrogen fluoride, characterized in that, The method includes the following steps: S1: Take a certain amount of by-product fluorosilicate slag of hydrogen fluoride and ammonium fluoride in a ball mill reactor, add polyvinyl alcohol, and carry out a mixed ball milling reaction under high temperature conditions to prepare ammonium fluorosilicate, and configure it into an ammonium fluorosilicate solution; S2: Take formaldehyde and add it to a reaction kettle equipped with stirring, a peristaltic pump and a condenser; while stirring, pump in the ammonium fluorosilicate solution and ammonia water in step 1 at the same time. After the feeding is completed, the reaction solution is obtained through aging; S3: Filter the reaction solution, cool and crystallize the filtrate, and dry it after filtration to obtain the finished product of ammonium fluoride; S4: Adjust the pH of the filter cake and then reslurry it, filter it, wash the filter cake with pure water, and place the filter cake in a dryer to dry to obtain the finished product of white carbon black.

2. The method for preparing precipitated silica from fluorosilicate slag as a by-product of hydrogen fluoride, as described in claim 1, is characterized in that The composition of the fluorosilicate slag is: SiO2 43% - 48%, H2O 40% - 50%, H2SiF6 2% - 5%, H2SO4 0.5% - 2%, HF 1% - 3%.

3. The method for preparing white carbon black from fluorosilicic slag as a by-product of hydrogen fluoride according to claim 1, characterized in that, In step S1, the ball milling reaction is carried out in an environment filled with clean air or nitrogen, and the equivalent amount of ammonium fluoride is 1.0 - 1.5 times the effective silicon equivalent of the fluorosilicate slag.

4. The method for preparing white carbon black from fluorosilicate slag, a by-product of hydrogen fluoride, as claimed in claim 3, wherein In step S1, the ball-to-material ratio is (60 - 100):1, the ball milling speed is 300 - 500 rpm, the ball milling time is 2 - 6 h, and the ball milling temperature is 100 - 150 °C.

5. The method for preparing precipitated silica from fluorosilicic slag as a by-product of hydrogen fluoride, as claimed in claim 1, wherein In step S2, add a certain amount of ammonia water as a base in the reaction kettle to keep the pH of the reaction system always at 9.0 - 9.5, preferably 9.0 - 9.

3.

6. The method for preparing white carbon black from fluorosilicate slag as a by-product of hydrogen fluoride according to claim 5, characterized in that, In step S2, the pH of the reaction system is always kept at 9.0 - 9.

3.

7. The method for preparing white carbon black from by-product fluorosilicate slag of hydrogen fluoride as claimed in claim 1, characterized in that, The amount of polyvinyl alcohol added in step 1 is 5 - 10% of the amount of white carbon black generated.

8. The method for preparing precipitated silica from fluorosilicic slag, a by-product of hydrogen fluoride, as described in claim 1, is characterized in that, The amount of formaldehyde added in step S2 is 5 - 10% of the amount of white carbon black generated.

9. The method for preparing white carbon black from fluorosilicate slag as a by-product of hydrogen fluoride according to claim 1, characterized in that, In step S2, the feeding method is to pump in ammonia water and ammonium fluorosilicate solution at the same time, the feeding time is 0.5 - 2.0 h, the stirring speed is 600 - 800 rpm, and the aging time of the reaction solution after the reaction is 6.0 - 8.0 h.

10. The method for preparing white carbon black from fluorosilicate slag as a by-product of hydrogen fluoride according to claim 1, characterized in that, In step S4, the pH during the reslurrying of the filter cake is 6.8 - 7.3.

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