Method for preparing white carbon black from fluorine-containing silicon slag

Abstract

The application relates to a method for preparing white carbon black from fluorine-containing silicon slag, and belongs to the technical field of waste recycling. The method for preparing white carbon black from fluorine-containing silicon slag comprises the following steps: mixing and reacting silicon slag and ammonia water, then filtering and drying to obtain anhydrous silicon slag, mixing and grinding the anhydrous silicon slag with a pore-forming agent, heating treatment, and cooling to obtain white carbon black with high specific surface area. In the application, alkaline ammonia water is used to react with the fluorine-containing silicon slag, so that fluorosilicate is decomposed into silicon dioxide and fluoride ions, and the fluoride ions are removed with the solution by filtration; and the silicon slag only needs to be ground and crushed to increase the specific surface area, so that the method is simple and easy to implement; further, the silicon dioxide particles are pore-formed by heating sublimation to increase the specific surface area, and white carbon black with high specific surface area is obtained; the whole preparation process is short in time, high in efficiency, low in wastewater, and easy to be industrialized.

Description

Technical Field

[0001] This invention belongs to the field of recycling technology, specifically relating to a method for preparing silica from fluorinated silica slag. Background Technology

[0002] The phosphate fertilizer industry produces a large amount of fluorosilicic acid as a byproduct. While the production of anhydrous hydrogen fluoride from fluorosilicic acid recovers most of the fluorine, it also produces fluorine-containing silica slag. This silica slag has poor activity and contains fluorine, making it unsuitable as a filler in rubber or other fields. Furthermore, its fluorine content causes environmental pollution when stored. This silica slag contains approximately 8% fluorosilicic acid and 30% moisture. Extensive research has been conducted on how to effectively utilize this silica slag.

[0003] Patent application CN105271254A discloses a method for preparing precipitated silica from waste silica slag. First, the waste silica slag containing silica is chemically reacted with ammonium fluoride to produce ammonium fluorosilicate and ammonia. Then, the resulting ammonium fluorosilicate is chemically reacted with ammonia water to produce silica and ammonium fluoride. Finally, the resulting silica is aged, washed, and dried to obtain precipitated silica. This method converts all the silica slag into ammonium fluorosilicate, resulting in a slow, time-consuming reaction and poor economic efficiency.

[0004] Patent CN103663474B discloses a method for preparing precipitated silica from fluorinated silica slag, comprising: adding fluorinated silica slag and a metered alkaline solution to a reaction vessel equipped with a stirrer and a heating device according to a ratio; heating the mixture to 40-80°C under thorough stirring and maintaining the reaction for 20-50 minutes to ensure complete reaction of the fluorosilicic acid in the fluorinated silica slag, thereby obtaining a mixed solution of silica and fluoride salts; separating the obtained silica and fluoride salt liquid-solid mixture by filtration or centrifugation while hot or cooled to ≤50°C, thereby obtaining a silica wet cake and a fluoride salt filtrate; subjecting the obtained silica wet cake to 4-6 countercurrent washings, combining the first washing solution and the fluoride salt filtrate to obtain a fluoride salt solution for other uses, and placing the second to sixth washing solutions into the first to fifth washing solution storage tanks for use in the next first to fifth washings; and drying the silica wet filter cake to obtain the precipitated silica product. The silica product obtained by this method has a relatively small specific surface area, generally between 160-180 μm². 2 / g, and the highest it ever reached was 205m. 2 / g, which does not meet the standard for high-quality silica. Summary of the Invention

[0005] To overcome the above shortcomings, this application provides a method for utilizing fluorinated silicon slag, specifically as follows:

[0006] The silica slag is mixed with ammonia water and reacted, then filtered and dried to obtain anhydrous silica slag, which is then mixed with a pore-forming agent, ground, heated, and cooled to obtain high specific surface area silica.

[0007] The reaction of silicon slag and ammonia is controlled at a final pH of 8-9 and a temperature of 45-60℃. The fluorosilicic acid in the silicon slag reacts with ammonia in the following order to produce silicon dioxide and ammonium fluoride.

[0008] H2SiF6+2NH4OH→(NH4)2SiF6+2H2O

[0009] (NH4)2SiF6+4NH4OH→SiO2+6NH4F+2H2O

[0010] The ammonia concentration is not particularly limited, but in order to reduce wastewater production, the ammonia concentration should be as high as possible.

[0011] The filtration is preferably pressure filtration to minimize the moisture content in the filter cake. The purpose of drying is to remove water completely and prevent the reaction of ammonium fluoride with silicon dioxide to form ammonium fluorosilicate in the presence of water in the subsequent process.

[0012] The pore-forming agent is ammonium halide, selected from at least one of ammonium fluoride, ammonium chloride, and ammonium iodide, and is used in an amount of 5-10% of the weight of the silica slag. The pore-forming agent and anhydrous silica slag are thoroughly mixed under grinding conditions, and at the same time, the micron-sized silica particles are pulverized into nano-sized particles, increasing the specific surface area.

[0013] The heat treatment causes the ammonium halide to sublimate, and the ammonium halide gas escapes from the silica particles, creating pores inside and on the surface of the particles, thus increasing the specific surface area. The preferred heat treatment temperature is 100-120℃, and the time is 10-30 min. More preferably, the system is evacuated during the heat treatment to -30 to -90 kPa; this negative pressure condition accelerates the sublimation rate of the ammonium halide.

[0014] Furthermore, the collected sublimated ammonium halide gas can be cooled and condensed and then reused as a pore-forming agent, thus recycling the pore-forming agent and further reducing production costs.

[0015] The beneficial effects of this invention are as follows:

[0016] (1) This application uses alkaline ammonia water to react with fluorinated silicon slag, so that fluorosilicate ions are decomposed into silicon dioxide and fluoride ions, and the fluoride ions are removed by filtration with the solution; (2) This application does not require dissolving the silicon slag, but only grinding and crushing the silicon slag to achieve the purpose of increasing the specific surface area, which is simple and easy to implement; (3) The silicon dioxide particles are further pore-forming by heating and sublimation to increase the specific surface area, and high specific surface area silica is obtained; (4) The entire preparation process is short, efficient, and produces little wastewater, making it easy to industrialize. Detailed Implementation

[0017] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. The fluorinated silicon slag used was purchased from a hydrogen fluoride plant, and its composition and parameters are listed below:

[0018] <![CDATA[SiO2]]> <![CDATA[H2SiF6]]> <![CDATA[H2O]]> other D50 Specific surface area pH 58.60％ 8.40％ 31.50％ 1.50％ 9.7μm <![CDATA[12.1m 2 / g]]> 2.9

[0019] The technical solution of the present invention will be further described in detail below with reference to specific embodiments.

[0020] Example 1

[0021] A method for utilizing fluorinated silicon slag:

[0022] 500g of fluorinated silica slag was mixed with 28% ammonia solution and reacted at 50℃ for 60min. The pH at the end of the reaction was 8.9. The mixture was then filtered using a filter press, and the resulting filter cake was dried at 100℃ for 2h to obtain anhydrous silica slag. This anhydrous silica slag was then mixed with 35g of ammonium chloride and ground for 40min. The mixture was then heated at 110℃ under vacuum (-60kPa) for 120min, and cooled to obtain 308g of high specific surface area silica with a specific surface area of ​​244.8m². 2 / g, fluorine content 0.06%.

[0023] Example 2

[0024] A method for utilizing fluorinated silicon slag:

[0025] 600g of fluorinated silica slag was mixed with 18% ammonia solution and reacted at 60℃ for 40min. The pH at the end of the reaction was 8.5. The mixture was then filtered using a filter press, and the resulting filter cake was dried at 100℃ for 2h to obtain anhydrous silica slag. This anhydrous silica slag was then mixed with 25g of ammonium fluoride and ground for 60min. The mixture was then heated at 105℃ under vacuum (-80kPa) for 100min, and cooled to obtain 370g of high specific surface area silica with a specific surface area of ​​226.1m². 2 / g, fluorine content 0.08%.

[0026] Example 3

[0027] A method for utilizing fluorinated silicon slag:

[0028] 800g of fluorinated silica slag was mixed with 25% ammonia solution and reacted at 45℃ for 80min. The pH at the end of the reaction was 8.0. The mixture was then filtered using a filter press, and the resulting filter cake was dried at 100℃ for 2h to obtain anhydrous silica slag. This anhydrous silica slag was then mixed with 80g of ammonium iodide and ground for 120min. The mixture was then heated at 120℃ under vacuum (-90kPa) for 80min, and cooled to obtain 490g of high specific surface area silica with a specific surface area of ​​268.9m². 2 / g, fluorine content 0.07%.

[0029] Example 4

[0030] A method for utilizing fluorinated silicon slag:

[0031] 500g of fluorinated silica slag was mixed with 28% ammonia solution and reacted at 50℃ for 60min. The pH at the end of the reaction was 8.9. The mixture was then filtered using a filter press, and the resulting filter cake was dried at 100℃ for 2h to obtain anhydrous silica slag. This anhydrous silica slag was then mixed with 35g of ammonium chloride and ground for 40min. The mixture was then heated at 110℃ for 300min and cooled to obtain 307g of high specific surface area silica with a specific surface area of ​​230.2m². 2 / g, fluorine content 0.06%.

[0032] Comparative Example

[0033] A method for utilizing fluorinated silicon slag:

[0034] 500g of fluorinated silica slag was mixed with 28% ammonia solution and reacted at 50℃ for 60min. The pH at the end of the reaction was 8.9. The mixture was then filtered using a filter press. The resulting filter cake was dried at 100℃ for 2h to obtain anhydrous silica slag. This anhydrous silica slag was then ground directly for 40min without using a pore-forming agent and heated under vacuum at -60kPa for 120min. After cooling, 306g of high specific surface area silica with a specific surface area of ​​203.4m² was obtained. 2 / g, fluorine content 0.06%.

[0035] Compared with Example 1, the comparative example did not use a pore-forming agent, and the specific surface area of ​​the resulting silica decreased by 16.9%.

Claims

1. A method for preparing silica from fluorinated silica slag, characterized in that, The silica slag is mixed with ammonia water and reacted, then filtered and dried to obtain anhydrous silica slag, which is then mixed with a pore-forming agent, ground, heated, and cooled to obtain high specific surface area silica. The pore-forming agent is ammonium halide, and the amount of pore-forming agent used is 5-10% of the weight of silicon slag; the heat treatment is performed by evacuating to -30 to -90 kPa.

2. The method according to claim 1, characterized in that, The reaction of silica slag and ammonia was controlled at the final pH of 8-9 and the temperature of 45-60℃.

3. The method according to claim 1, characterized in that, The ammonium halide is selected from at least one of ammonium fluoride, ammonium chloride, and ammonium iodide.

4. The method according to claim 1, characterized in that, The grinding time is 0.3-3 hours.

5. The method according to claim 4, characterized in that, The grinding time is 30-150 minutes.

6. The method according to claim 1, characterized in that, The heat treatment is performed at a temperature of 100-120℃ for a time of 60-300 minutes.