Fluorine-containing silicon slag recycling process

Abstract

The invention relates to the technical field of industrial solid waste resource utilization, and particularly discloses a fluorine-containing silicon slag recycling process which comprises five steps of fluorine-containing silicon slag raw material pretreatment, acid leaching fluorine extraction, ammonium fluosilicate preparation, nanometer silica gel purification and wastewater recycling. Fluorine in the fluorine-containing silicon slag is converted into ammonium fluosilicate solid to be recycled, fluorine in the fluorine-containing silicon slag is converted into sodium silicate to be manufactured into nano silica gel to be recycled, only feeding reaction is needed in the whole process, then filtering is conducted, the technological process is simple, and the treatment efficiency of the fluorine-containing silicon slag is improved. 0.3 ton of ammonium fluosilicate (the market price is 8000 yuan / ton) and 0.2 ton of nano silica gel (the market price is 15000 yuan / ton) can be produced from each ton of fluorine-containing silicon slag, and huge economic value can be brought to factories.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial solid waste resource utilization, and in particular to a process for recycling and reusing fluorine-containing silicon slag. Background Art

[0002] Fluorosilicon slag is a hazardous solid waste produced in the process of producing anhydrous hydrogen fluoride from fluorosilicic acid, a by-product of phosphorus chemical industry. Its main components are fluoride (such as NaF, CaF2) and silicon dioxide (SiO2), and it also contains a small amount of heavy metal impurities.

[0003] In order to effectively recycle the fluorine in fluorine-containing silicon slag and avoid environmental pollution caused by its landfill or solidification, a Chinese invention patent with the publication number "CN115869950B" discloses a method for preparing a Fenton-like catalyst from fluorine-containing silicon slag and producing a fluorine salt as a by-product. This method includes three steps: Step 1, dispersing the fluorine-containing silicon slag with water, then adding a transition metal and dissolving it to obtain a mixed system; Step 2, adjusting the pH of the mixed system to alkaline, followed by reaction, and filtering and separating after the reaction to obtain a solid Fenton-like catalyst; Step 3, recovering the fluorine salt from the separated liquid. This method uses fluorine-containing silicon slag as raw material, and by adding a transition metal to react under closed conditions to prepare a Fenton-like catalyst while separating and extracting fluorine. The prepared Fenton-like catalyst has a large specific surface area, high catalytic activity, and low preparation cost. It can also simultaneously recover the fluorine resources in the fluorine-containing silicon slag, achieving its high-value utilization. Among them, the recovery method of fluoride salt in step 3 is evaporation crystallization. The process of evaporation crystallization requires the reconstruction of crystallization equipment, which has high procurement costs. The crystallization process requires thermal energy, resulting in high investment costs for fluorine recovery, thereby reducing the economic value of fluorine-containing silicon slag recovery to the factory. Summary of the Invention

[0004] The purpose of the present invention is to provide a fluorine-containing silicon slag recovery and reuse process to solve the problems of complex process and high investment cost of fluorine recovery in existing fluorine-containing silicon slag recovery methods.

[0005] In order to solve the above problems, the technical solutions provided are as follows: A process for recycling and reusing fluorine-containing silicon slag comprises the following steps: S1: Raw material pretreatment, crushing the fluorine-containing silicon slag to a particle size of less than 100 mesh, and using a combined magnetic separation-flotation process to remove metal impurities such as iron and aluminum; S2: Acid leaching to extract fluorine: add 15%-20% sulfuric acid solution at a liquid-to-solid ratio of 5:1, stir and react at 60-80°C for 2-3 hours, and separate the solid and liquid to obtain fluorine-containing acid leaching solution and silicon slag filter cake; S3: Preparation of ammonium fluorosilicate: adding ammonia water to the fluorine-containing acid leaching solution to adjust the pH to 3-4, controlling the reaction temperature at 40-50°C to generate ammonium fluorosilicate precipitate; S4: Nano-silica gel purification: the silicon slag filter cake is mixed with a sodium hydroxide solution having a mass concentration of 5%, and an alkaline dissolution reaction is carried out at 100-120°C for 1.5-2 hours to generate a sodium silicate solution; sulfuric acid is added to adjust the pH to 9-10, and the mixture is aged for 12-18 hours, then filtered and washed to obtain nano-silica gel; S5: Wastewater recycling: process wastewater is neutralized with lime and adsorbed with activated carbon, and then returned to the acid leaching process for recycling.

[0006] The beneficial effects of the above technical solution are: 1. Compared with the existing method of recovering fluorine resources from fluorine-containing silicon slag by evaporation and crystallization, this technical solution converts the fluorine in the fluorine-containing silicon slag into ammonium fluorosilicate precipitate through acid leaching and fluorine extraction process. The ammonium fluorosilicate precipitate can be directly filtered for recovery, and the silicon in the fluorine-containing silicon slag is converted into sodium silicate solution. The sodium silicate solution is filtered to produce nano-silica gel for recovery after pH adjustment and chemical treatment. The entire process of recovering fluorine and silicon in the fluorine-containing silicon slag only requires adding materials for reaction, and then filtering to extract ammonium fluorosilicate. The process is simple, improves the treatment efficiency of fluorinated silicon slag, does not require the construction of a crystallization device and does not require a heat source, and saves investment costs; 2. Each ton of fluorine-containing silicon slag can produce 0.3 tons of ammonium fluorosilicate (market price 8,000 yuan / ton) and 0.2 tons of nano silica gel (market price 15,000 yuan / ton), which can bring huge economic value to the factory; 3. The wastewater generated in the process is recycled and the wastewater recycling rate is 100%, which reduces resource waste and saves cost investment.

[0007] Preferred Solution 1: As a further optimization of the basic solution, the magnetic separation process in step S1 adopts a wet permanent magnetic drum magnetic separator with a magnetic field strength of 0.8-1.2T, a flotation reagent of a composite reagent of sodium oleate and sodium lauryl sulfate (mass ratio 1:0.5), and a flotation time of 8-12 minutes.

[0008] Preferred solution 2: As a further optimization of preferred solution 1, step S2 is to use a ceramic membrane with a pore size of 0.1 μm for solid-liquid separation.

[0009] Preferred Option 3: As a further optimization of Preferred Option 2, the ammonia concentration in step S3 is 10%-15%, the addition rate is controlled at 0.5-1.0 L / min, the pH value at the reaction endpoint is monitored in real time by an online pH meter and automatically adjusted, and the precipitate is separated by a centrifuge at a speed of 3000 rpm and then dried using a vacuum belt dryer at a temperature below 80°C.

[0010] Preferred solution four: As a further optimization of preferred solution three, the aging process in step S4 is carried out in an ultrasonic field with a frequency of 40 kHz.

[0011] Preferred solution five: As a further optimization of preferred solution four, the process wastewater in step S5 is neutralized with lime to a pH of 7-8, and then circulated through an activated carbon adsorption column and a resin exchange column for more than five times. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Schematic diagram of the process flow of an embodiment of the present invention. DETAILED DESCRIPTION

[0013] The following is further described in detail through specific implementation methods: The embodiment is basically as shown in the attached Figure 1 As shown: Example 1 A process for recycling and reusing fluorine-containing silicon slag comprises the following steps: S1: Raw material pretreatment: using fluorine-containing silicon slag with a F content of 25wt% and a SiO2 content of 60wt% as raw material, 100g of the fluorine-containing silicon slag was crushed to a particle size of 100 mesh, and a magnetic separation-flotation combined process was used to remove metal impurities such as iron and aluminum. The magnetic separation process used a wet permanent magnetic drum magnetic separator with a magnetic field strength of 0.8-1.2T. The flotation reagent used was a composite reagent of sodium oleate and sodium lauryl sulfate with a mass ratio of 1:0.5. The flotation time was 8-12 minutes, and a fluorine-silicon mixture with a purity greater than 95% was obtained; S2: Acid leaching to extract fluorine: add a 15% sulfuric acid solution to the fluorine-silicon mixture at a liquid-solid ratio of 5:1, and stir the reaction at 80°C for 3 hours to convert fluorides (NaF and CaF2) into soluble fluorosilicic acid (H2SiF6). A ceramic membrane with a pore size of 0.1μm is used for solid-liquid separation to obtain a fluorine-containing acid leaching solution and a silicon slag filter cake. The reaction equation is as follows: 2 NaF + H 2 SO 4→ Na 2 SO 4+2 HF ↑ 6 HF + SiO 2→ H 2 SiF 6+2 H 2 O S3: Preparation of ammonium fluorosilicate: 10% ammonia water was added dropwise to the fluorine-containing acid leaching solution to adjust the pH to 3-4. The addition rate was controlled at 0.5-1.0 L / min. The pH value at the reaction endpoint was monitored in real time by an online pH meter and automatically adjusted. The reaction temperature was controlled at 40-50°C to generate ammonium fluorosilicate precipitate. The precipitate was separated by a centrifuge at a speed of 3000 rpm and dried in a vacuum belt dryer at a temperature below 80°C to obtain 43.53 g of ammonium fluorosilicate product. The fluorine recovery rate was 92.6%. The reaction equation is shown below: H 2 SiF 6+4 NH 3⋅ H 2 O →( NH 4)2 SiF 6+6 H 2 O S4: Nano-silica gel purification: The silicon slag filter cake is mixed with a sodium hydroxide solution having a mass concentration of 5%, and an alkaline dissolution reaction is carried out at 100-120°C for 1.5 hours to generate a sodium silicate solution. Sulfuric acid is added to adjust the pH to between 9-10. The solution is aged for 18 hours, filtered, and washed to obtain nano-silica gel. The aging process is carried out in an ultrasonic field with a frequency of 40kHz. The reaction equation is as follows: SiO2+2NaOH→Na2SiO3+H2O S5: Wastewater recycling: After the process wastewater is neutralized with lime to a pH between 7 and 8, it passes through the activated carbon adsorption column and the resin exchange column for 5 cycles, and then returns to the acid leaching process for recycling.

[0014] Example 2 The difference between Example 2 and Example 1 is that a sulfuric acid solution with a mass concentration of 18% is used in the process of acid leaching fluorine in step S2; finally, 38.51 g of ammonium fluorosilicate product is obtained, and the fluorine recovery rate is 81.95%.

[0015] Example 3 The difference between Example 3 and Example 1 is that a sulfuric acid solution with a mass concentration of 20% is used in the process of acid leaching fluorine in step S2; finally, 32.84 g of ammonium fluorosilicate product is obtained, and the fluorine recovery rate is 69.88%.

[0016] The quality data of the finished ammonium fluorosilicate obtained in Examples 1-3 show that Example 1 has the largest amount of ammonium fluorosilicate, so a sulfuric acid solution with a concentration of 15% and a fluorine-silicon mixture are used to achieve the highest fluorine recovery rate in the fluorine-containing silicon slag, with a fluorine recovery rate of 92.6%. The sulfuric acid concentration used in Example 1 is lower than that in Examples 2 and 3. The low-concentration sulfuric acid environment is conducive to the stable existence of fluorosilicic acid, reducing its tendency to further decompose into SiF4 gas, thereby retaining more fluorine in the liquid phase. Although the low-concentration sulfuric acid has a slow reaction rate, it will preferentially react with the target fluorine compound, reducing excessive corrosion or side reactions, so that most of the fluorine in the fluorine-containing silicon slag can be converted into ammonium fluorosilicate for recovery, thereby improving the recovery rate of fluorine in the fluorine-containing silicon slag. Selling ammonium fluorosilicate can bring huge economic benefits to the factory.

[0017] The above is only an embodiment of the present invention, and the common knowledge such as the specific structure and characteristics of the scheme is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A process for recycling fluorine-containing silicon slag, characterized in that: The following steps are involved: S1: Raw material pretreatment, crushing the fluorine-containing silicon slag to a particle size of less than 100 mesh, and using a combined magnetic separation-flotation process to remove metal impurities such as iron and aluminum; S2: Acid leaching to extract fluorine: add 15%-20% sulfuric acid solution at a liquid-to-solid ratio of 5:1, stir and react at 60-80°C for 2-3 hours, and separate the solid and liquid to obtain fluorine-containing acid leaching solution and silicon slag filter cake; S3: Preparation of ammonium fluorosilicate: adding ammonia water to the fluorine-containing acid leaching solution to adjust the pH to 3-4, controlling the reaction temperature at 40-50°C to generate ammonium fluorosilicate precipitate; S4: Nano-silica gel purification: the silicon slag filter cake is mixed with a sodium hydroxide solution having a mass concentration of 5%, and an alkaline dissolution reaction is carried out at 100-120°C for 1.5-2 hours to generate a sodium silicate solution; sulfuric acid is added to adjust the pH to 9-10, and the mixture is aged for 12-18 hours, then filtered and washed to obtain nano-silica gel; S5: Wastewater recycling: process wastewater is neutralized with lime and adsorbed with activated carbon, and then returned to the acid leaching process for recycling.

2. A fluorine-containing silicon slag recovery and reuse process according to claim 1, characterized in that: The magnetic separation process in step S1 adopts a wet permanent magnetic drum magnetic separator with a magnetic field strength of 0.8-1.2 T, a flotation reagent of a composite reagent of sodium oleate and sodium lauryl sulfate in a mass ratio of 1:0.5, and a flotation time of 8-12 minutes.

3. The process for recycling fluorine-containing silicon slag according to claim 1, characterized in that: The step S2 is to use a ceramic membrane with a pore size of 0.1 μm to perform solid-liquid separation.

4. The process for recycling fluorine-containing silicon slag according to claim 1, wherein: In step S3, the concentration of the aqueous ammonia is 10%-15%, the addition rate is controlled at 0.5-1.0 L / min, the pH value at the reaction endpoint is monitored in real time by an online pH meter and automatically adjusted, and the precipitate is separated by a centrifuge at a speed of 3000 rpm and then dried using a vacuum belt dryer at a temperature below 80°C.

5. The process for recycling fluorine-containing silicon slag according to claim 1, characterized in that: The aging process in step S4 is performed in an ultrasonic field with a frequency of 40 kHz.

6. The process for recycling fluorine-containing silicon slag according to claim 1, characterized in that: The process wastewater in step S5 is neutralized with lime to a pH of 7-8, and then circulated through an activated carbon adsorption column and a resin exchange column for more than 5 times.

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