System for recycling fluorine in silica gel and operation method

Abstract

A method for recycling fluorine in silica gel comprises the following steps that 1, silica gel is subjected to ball milling pretreatment, a small amount of circulating water is supplemented during ore grinding, and ground slurry is obtained; 2, the grinding slurry enters a plate-and-frame filter press to be subjected to filter pressing, filtrate enters a concentration section secondary fluorine absorption circulating tank and serves as washing water of a concentrated fluorine absorption tower, SiF4 gas escaped in the concentration process of dilute phosphoric acid is absorbed, and a fluosilicic acid product is generated; and 3, mixing the filtered silica gel with returned acid, repulping, simultaneously introducing a stabilizer into a repulping tank, entering an acidolysis reaction tank after repulping is completed, adjusting the molar ratio of fluorine to active silicon in the reaction tank, carrying out chemical reaction on the silica gel in the reaction tank to further release silicon tetrafluoride, and generating a fluosilicic acid product by the silicon tetrafluoride and water. The method is highly matched with an existing production device, free fluorine and lattice fluorine in silica gel are recycled step by step, the process is simple, and industrial application is easy.

Description

Technical Field

[0001] The invention relates to the field of fluorine recovery in silica gel, and in particular to a system for recovering fluorine in silica gel and an operating method. Background Art

[0002] Phosphate ore is rich in fluorine resources. During the production of wet phosphoric acid, part of the fluorine will be recovered in the form of fluorosilicic acid to produce anhydrous hydrogen fluoride. During the production of anhydrous hydrogen fluoride from fluorosilicic acid, a large amount of fluorine-containing silica gel that is difficult to digest and utilize will be produced. Its main component is silicon dioxide, but the fluorine content is relatively high, usually between 3-15%. Therefore, fluorine-containing silica gel is a hazardous solid waste, which is difficult to handle and has high costs. Large-scale storage of fluorine-containing silica gel causes waste of resources and environmental pollution. According to the production principle of anhydrous hydrogen fluoride, most of the fluorine in fluorine-containing silica gel exists in the form of fluorosilicic acid. Except for a small part attached to the surface of silica gel, most of it is wrapped by SiO2. How to efficiently open the package and economically separate and recover fluorine is the key to achieving high-value utilization of fluorine-containing silica slag.

[0003] Patent CN111392748A uses sodium carbonate low-temperature washing and caustic soda high-temperature leaching to jointly treat fluorine-containing silicon slag. This method uses sodium carbonate washing to remove surface fluorosilicic acid, and uses caustic soda high-temperature leaching to allow SiO2 and encapsulated fluorine to enter the solution at the same time, and separate sodium silicate and sodium fluoride in the mixed solution. The process is relatively long and does not achieve the purpose of efficient recovery. Patent CN103663474B uses alkaline solution at 40-80°C to treat fluorine-containing silicon slag by leaching. If caustic soda is used for treatment, both fluorine and silicon will enter the solution and need to be further separated. If carbonate solution is used for treatment, the thermodynamic reaction conditions are not met and the encapsulated fluorine is difficult to separate. Patent CN110156030A defluorinates by placing fluorine-containing silicon slag into a calcining kiln and heating it to 800-1700°C, and keeping it warm for 1-10 hours. This method can obtain low-fluorine and low-water white carbon black with a particle size of no more than 9μm. During the insulation process, water or water vapor needs to be sprayed, which is acidic, has high requirements for equipment, and consumes a lot of energy. The above processes all have the characteristics of complex processes and difficulty in separating and recovering fluorine, making it difficult to efficiently recycle fluorine resources in silica gel. Summary of the invention

[0004] The invention solves the problem of fluorine recovery of fluorine-containing silica gel in the process of producing anhydrous hydrogen fluoride from fluorosilicic acid and solves the problem that lattice fluorine in the fluorine-containing silica gel cannot be fully released into the liquid phase.

[0005] In order to solve the above problems, the present invention is achieved through the following technical solutions: A system for recovering fluorine in silica gel comprises a silica gel storage tank, wherein the outlet of the silica gel storage tank is connected to a ball mill feed inlet, the ball mill discharge port is connected to a filter press, the filtrate outlet of the filter press is connected to a fluorine absorption circulation tank, and the fluorine absorption circulation tank discharge port is connected to a fluorosilicic acid storage tank; the filter cake outlet of the filter press is connected to a re-slurry tank, the re-slurry tank inlet is also connected to an acid return tank and a stabilizer tank, the re-slurry tank outlet is connected to a reaction tank, the reaction tank gas outlet is connected to the fluorine absorption circulation tank, the reaction tank feed inlet is also connected to a phosphate ore tank, the reaction tank solid outlet is connected to a dilute phosphoric acid tank, the dilute phosphoric acid tank discharge port is connected to a dilute phosphoric acid evaporator inlet, and the dilute phosphoric acid evaporator gas outlet is connected to the inlet of the fluorine absorption circulation tank.

[0006] The fluorine absorption circulation tank is provided with an exhaust pipe; the exhaust pipe is connected to the atmosphere.

[0007] The bottom notch of the reaction tank is connected to the gypsum storage tank.

[0008] Preferably, the liquid phase outlet of the dilute phosphoric acid evaporator is connected to the concentrated phosphoric acid tank.

[0009] Preferably, the reslurry tank is equipped with a stirring device, and the reaction tank is equipped with a heating device, a stirring device and a filtering device.

[0010] The operating method of the system for recovering fluorine from silica gel comprises the following steps: S1, adding water to fluorinated silica gel and ball-milling to obtain a slurry, and filtering the slurry to obtain a filtrate and filtered silica gel; S2, after evenly stirring the returned acid, stabilizer and the filtered silica gel in step S1, adding phosphate rock, heating and stirring to obtain gypsum and silicon tetrafluoride gas; S3, the SiF4-containing gas in the reaction tank and the dilute phosphoric acid evaporator is countercurrently introduced into the filtrate in step S1 to obtain finished fluorosilicic acid.

[0011] In the slurry of step S1, the mass ratio of fluorinated silica gel to water is 2-4:1, and the content of silica gel particle size -200 mesh in the slurry is ≥90%.

[0012] The filter pressing pressure in step S1 is 0.3-0.5 MPa.

[0013] In the step S2, the mass ratio of returned acid: filtered silica gel: phosphate rock is 4-8:1:200-500.

[0014] In step S3, the heating temperature is 90° C.-93° C., and the stirring time is 1-3 h.

[0015] In the step S3, the mass ratio of SiF4-containing gas to filtrate is 1:10-20.

[0016] In the step S2, the stabilizer is sodium polyacrylate, and the mass ratio of sodium polyacrylate to filtered silica gel is 1:5000-8000.

[0017] Preferably, in step S1, the SiO2 content in the fluorine-containing silica gel is 45%, the H2SiF6 content is 5%, and the water content is 50%.

[0018] Preferably, in step S2, the P2O5 content in the returned acid is 39%, the MgO content is 1.35%, the F content is 0.55%, and the remainder is water.

[0019] Preferably, in step S2, the P2O5 content in the phosphate rock is 29.5%, the F content is 1.5%, and the remainder is gypsum.

[0020] The main chemical reactions in step S2: 4HF+SiO2=SiF4↑+2H2O; 2H2SiF6+SiO2=3SiF4↑+2H2O; The main chemical reaction in step S3: 3SiF4+(n+2)H2O=2H2SiF6+SiO2*nH2O; Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention can utilize the existing wet-process phosphoric acid production process to recover free fluorine and lattice fluorine in fluorine-containing silica gel, thereby realizing the recovery and utilization of fluorine resources in wastes. The economic benefits are obvious, the recovery process is simple, and it is easy to implement industrially, and has great application advantages.

[0021] 2. The present invention solves the difficult problems of difficult recovery of fluorine resources and high treatment costs in solid waste fluorine-containing silica gel. The present invention relies on the existing equipment for wet-process phosphoric acid production, and adopts multiple stages of different measures to recover free fluorine and lattice fluorine in fluorine-containing silica gel. First, ball milling pretreatment can cause a certain degree of physical damage to the structure of the fluorine-containing silica gel, release all free fluorine, and the free fluorine dissolved in the liquid phase is finally converted into finished fluorosilicic acid through the fluorine absorption system. The silica gel after filter pressing enters the reaction system, and a chemical reaction occurs under strong acid and high temperature conditions to destroy the microstructure of the silica gel, and its lattice fluorine is released. The stabilizer can make the generated silicon tetrafluoride gas escape from the liquid phase continuously and stably, so that hydrogen fluoride or fluorosilicic acid and silica gel continue to react in the direction of generating silicon tetrafluoride, greatly improving the yield of silicon tetrafluoride gas. After the above treatment, the free fluorine and lattice fluorine in the fluorine-containing silica gel are effectively recovered, and finally the fluorine-free silica gel enters the gypsum storage tank for external transportation.

[0022] 3. The present invention utilizes the equipment in the original wet-process phosphoric acid production system and adjusts the connection relationship, connection sequence and feeding method between the equipment to recover the water-soluble fluorine and lattice fluorine in the fluorine-containing silica gel. No additional modification or purchase of new equipment is required, which saves costs and has obvious economic benefits. Fluorine-free silica gel can be mass-produced. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 Schematic diagram of the system for recovering fluorine from silica gel according to the present invention; Figure numerals: silica gel storage tank 1, ball mill 2, filter press 3, fluorine absorption circulation tank 4, dilute phosphoric acid evaporator 5, concentrated phosphoric acid tank 501, acid return tank 6, re-slurry tank 7, stabilizer tank 701, reaction tank 8, dilute phosphoric acid tank 801, phosphate rock tank 9, gypsum storage tank 10, fluorosilicic acid storage tank 11. DETAILED DESCRIPTION

[0024] like Figure 1 The connection relationship of the device in the present invention is as follows: a system for recovering fluorine in silica gel, comprising a silica gel storage tank 1, the outlet of the silica gel storage tank 1 is connected to the feed inlet of the ball mill 2, the discharge port of the ball mill 2 is connected to the filter press 3, the filtrate outlet of the filter press 3 is connected to the fluorine absorption circulation tank 4, and the discharge port of the fluorine absorption circulation tank 4 is connected to the fluorosilicic acid storage tank 11; the filter cake outlet of the filter press 3 is connected to the re-slurry tank 7, the inlet of the re-slurry tank 7 is also connected to the acid return tank 6 and the stabilizer tank 701, the outlet of the re-slurry tank 7 is connected to the reaction tank 8, the gas outlet of the reaction tank 8 is connected to the fluorine absorption circulation tank 4, the feed inlet of the reaction tank 8 is also connected to the phosphate ore tank 9, the solid outlet of the reaction tank 8 is connected to the dilute phosphoric acid tank 801, the discharge port of the dilute phosphoric acid tank 801 is connected to the inlet of the dilute phosphoric acid evaporator 5, and the gas outlet of the dilute phosphoric acid evaporator 5 is connected to the inlet of the fluorine absorption circulation tank 4. The fluorine absorption circulation tank 4 is provided with an exhaust pipe; the exhaust pipe is connected to the atmosphere. The bottom notch of the reaction tank 8 is connected to the gypsum storage tank 10.

[0025] Preferably, the liquid phase outlet of the dilute phosphoric acid evaporator 5 is connected to the concentrated phosphoric acid tank 501. Preferably, the reslurry tank 7 is equipped with a stirring device, and the reaction tank 8 is equipped with a heater, a stirring device and a filter.

[0026] A method for operating a system for recovering fluorine from silica gel comprises the following steps: S1, adding water to fluorinated silica gel and ball-milling to obtain a slurry, and filtering the slurry to obtain a filtrate and filtered silica gel; S2, after mixing the returned acid, stabilizer and the filtered silica gel in step S1 evenly, adding phosphate rock, heating and stirring to obtain gypsum and SiF4-containing gas; S3, the gas containing SiF4 in the reaction tank and the dilute phosphoric acid evaporator is countercurrently fed into the filtrate in step S1 to obtain the finished fluorosilicic acid. Part of SiF4 is entrained in the dilute phosphoric acid in the dilute phosphoric acid tank and then fed into the dilute phosphoric acid evaporator to evaporate and precipitate silicon tetrafluoride.

[0027] The material composition and mass fraction in the present invention are as follows: fluorine-containing silica gel: silicon dioxide content is 45%, fluosilicic acid H2SiF6 content is 5%, and water content is 50%. The P2O5 content in the return acid is 39%, the MgO content is 1.35%, the F content is 0.55% (the total fluorine content in hydrofluoric acid and fluosilicic acid in the return acid), and the balance is water. The P2O5 content in the phosphate rock is 29.5%, the F content is 1.5%, and the balance is gypsum.

[0028] Example 1 Experimental group: see Figure 1 , add 1000 kg of fluorine-containing silica gel to the silica gel storage tank, and pre-treat the slurry by ball milling with water according to the mass ratio of fluorine-containing silica gel to water of 4:1, grind to the mass of silica gel particle size -200 mesh accounts for 95%, and then filter through a plate and frame filter press at 0.5 MPa to obtain 650 kg of filtrate and 600 kg of filtered silica gel. The filtrate enters the fluorine absorption circulation tank, and the water in the filtrate is used to absorb SiF4 in the gas, and the fluorosilicic acid (H2SiF6) dissolved in the water in the filtrate is recovered to the fluorosilicic acid storage tank; Filtrate from filter press 3: 650 kg of filtrate contains 610 kg of water and 40 kg of fluorosilicic acid; Filter silica gel of filter press 3: 600 kg of filter silica gel contains 140 kg of water, 450 kg of SiO2 and 10 kg of fluorosilicic acid; In the fluorine absorption circulation tank, the mass ratio of SiF4-containing gas: filtrate = 1:15; the mass ratio of return acid: filter silica gel: phosphate rock = 4:1:300; the mass ratio of sodium polyacrylate: filter silica gel = 1:5000; The stirring rate of the reslurry tank 7 is 200 rpm, and the stirring time is 1 hour. The heating temperature of the reaction tank 8 is 90°C, and the reaction time is 3 hours. The evaporation temperature of the dilute phosphoric acid evaporator is set to 83°C.

[0029] At this time, the fluorosilicic acid output in the fluorosilicic acid storage tank is 2530 kg.

[0030] Since the returned acid in the returned acid tank and the phosphate ore in the phosphate ore tank also contain fluorine, the present invention also recovers the fluorine in these materials. In order to quantify the yield of fluorine in the fluorine-containing silica gel, a control group needs to be set up. The system is operated by fluorine-free silica gel to measure the fluorine recovery in the returned acid and phosphate ore, and the fluorosilicic acid production in the fluorosilicic acid storage tank. The steps are as follows: Control group: In order to measure the fluorine recovery rate in fluorine-containing silica gel, 610 kg of water was introduced into the fluorine absorption circulation tank 4, and fluorine-free silica gel was added to the re-slurry tank 7. The fluorine-free silica gel has the same properties as the filtered silica gel obtained by treating the fluorine-containing silica gel, except that it does not contain fluorosilicic acid. The filtered fluorine-free silica gel was added to the re-slurry tank. The water content in the filtered fluorine-free silica gel was also 140 kg, and the mass of SiO2 was also 450 kg. The addition amount of other materials, steps, and reaction conditions were the same as the operating steps in the above-mentioned experimental group. At this time, the output of fluorosilicic acid in the fluorosilicic acid storage tank was 2482.5 kg.

[0031] The results of the fluorosilicic acid production in the experimental group and the control group show that the fluorosilicic acid production increased by 47.5 kg, and the fluorine recovery rate in the fluorine-containing silica gel was 95%.

[0032] Example 2 Experimental group: fluorinated silica gel was ground with water until the silica gel particle size was -200 mesh accounting for 90%, and other conditions were exactly the same as those of the experimental group in Example 1; The 648 kg filtrate contained 610 kg of water and 38 kg of fluorosilicic acid; The mass of water in the 602 kg filtered silica gel is 140 kg, the mass of SiO2 is 450 kg, and the mass of fluorosilicic acid is 12 kg; Finally, the yield of fluorosilicic acid was 2536 kg.

[0033] Control group: referring to the mass of water in the filtrate of the experimental group in Example 2, 610 kg of water of the same mass as the filtrate was added to the fluorine absorption circulation tank 4; Referring to the mass of water and SiO2 in the filtered silica gel of the experimental group in Example 2, 140 kg of water and 450 kg of SiO2 of filtered fluorine-free silica gel were added to the reslurry tank, and the addition amount of other materials, steps, and reaction conditions were the same as those of the experimental group in the above Example 2.

[0034] At this time, the output of fluorosilicic acid in the fluorosilicic acid storage tank is 2490 kg.

[0035] The results of the fluorosilicic acid production in the experimental group and the control group show that the fluorosilicic acid production increased by 46 kg and the fluorine recovery rate in the fluorine-containing silica gel was 92%.

[0036] Example 3 Experimental group: compared with the experimental group in Example 1, the difference is that the temperature of the reaction tank is 93°C, and other conditions are the same; Finally, the yield of fluorosilicic acid was 2665 kg.

[0037] Control group: compared with the control group in Example 1, the difference is that the temperature of the reaction tank is 93°C, and other conditions are the same.

[0038] At this time, the output of fluorosilicic acid was 2617 kg.

[0039] The results of the fluorosilicic acid production in the experimental group and the control group show that the fluorosilicic acid production increased by 48 kg and the fluorine recovery rate in the fluorine-containing silica gel was 96%.

[0040] Example 4 Experimental group: Compared with the experimental group in Example 1, the difference is that, in terms of mass ratio, the ratio of reflux acid: filtered silica gel: phosphate rock is 4:1:400; other conditions are exactly the same as those of the experimental group in Example 1; Finally, the yield of fluorosilicic acid was 2598 kg.

[0041] Control group: compared with the control group in Example 1, the difference is that, by mass ratio, the ratio of reflux acid: filtered silica gel: phosphate rock is 4:1:400; other conditions are exactly the same as those of the control group in Example 1; At this time, the output of fluorosilicic acid was 2549 kg.

[0042] The results of fluorosilicic acid production in the experimental group and the control group show that the fluorosilicic acid production increased by 49 kg and the fluorine recovery rate in fluorine-containing silica gel was 98%.

[0043] Example 5 Experimental group: Compared with the experimental group in Example 1, the difference is that, in terms of mass ratio, the ratio of reflux acid: filtered silica gel: phosphate rock is 4:1:200; other conditions are exactly the same as those of the experimental group in Example 1; Finally, the yield of fluorosilicic acid was 2496 kg.

[0044] Control group: compared with the control group in Example 1, the difference is that, by mass ratio, the ratio of reflux acid: filtered silica gel: phosphate rock is 4:1:200; other conditions are exactly the same as those of the control group in Example 1; At this time, the output of fluorosilicic acid in the fluorosilicic acid storage tank was 2451 kg.

[0045] The results of the fluorosilicic acid production in the experimental group and the control group show that the fluorosilicic acid production increased by 45 kg and the fluorine recovery rate in silica gel was 90%.

[0046] Comparative Example 1 Experimental group: Compared with Example 1, the silica gel was not subjected to ball milling pretreatment, and the slurry was directly prepared with water according to the mass ratio of fluorinated silica gel to water of 4:1. At this time, the 600 kg filtrate contains 572 kg of water and 28 kg of fluorosilicic acid. The mass of water in 650 kg of filtered silica gel is 178 kg, the mass of SiO2 is 450 kg, and the mass of fluorosilicic acid is 22 kg. Finally, the yield of fluorosilicic acid is 2512 kg.

[0047] Control group: referring to the mass of water in the filtrate of the experimental group, add 588 kg of water of the same mass to the fluorine absorption circulation tank 4; Referring to the mass of water and SiO2 in the filtered silica gel in the reference experimental group, the water content in the filtered fluorine-free silica gel added to the re-slurry tank was also 178 kg, and the mass of SiO2 was also 450 kg. The addition amount of other materials, steps, and reaction conditions were the same as those of the experimental group in Example 6. At this time, the output of fluorosilicic acid in the fluorosilicic acid storage tank was 2488 kg.

[0048] The results of the fluorosilicic acid production in the experimental group and the control group show that the fluorosilicic acid production increased by 24 kg and the fluorine recovery rate in silica gel was 48%.

[0049] Comparative Example 2 Experimental group: compared with the experimental group of Example 1, the difference is that sodium polyacrylate is not added, and other conditions are exactly the same as the experimental group of Example 1; finally, the yield of fluorosilicic acid is 2492 kg.

[0050] Control group: compared with the control group of Example 1, the difference is that sodium polyacrylate is not added, and other conditions are exactly the same as the control group of Example 1. At this time, the yield of fluorosilicic acid in the fluorosilicic acid storage tank is 2459 kg.

[0051] The results of fluorosilicic acid production in the experimental group and the control group show that the fluorosilicic acid production increased by 33 kg and the fluorine recovery rate in silica gel was 66%.

Claims

1. A system for recovering fluorine from silica gel, comprising a silica gel storage tank (1), characterized in that: The outlet of the silica gel storage tank (1) is connected to the inlet of the ball mill (2), the outlet of the ball mill (2) is connected to the filter press (3), the filtrate outlet of the filter press (3) is connected to the fluorine absorption circulation tank (4), and the outlet of the fluorine absorption circulation tank (4) is connected to the fluorosilicic acid storage tank (11); the filter cake outlet of the filter press (3) is connected to the reslurry tank (7), the inlet of the reslurry tank (7) is also connected to the acid return tank (6) and the stabilizer tank (701), the outlet of the reslurry tank (7) is connected to the reaction tank (8), the gas outlet of the reaction tank (8) is connected to the fluorine absorption circulation tank (4), the inlet of the reaction tank (8) is also connected to the phosphate ore tank (9), the solid outlet of the reaction tank (8) is connected to the dilute phosphoric acid tank (801), the outlet of the dilute phosphoric acid tank (801) is connected to the inlet of the dilute phosphoric acid evaporator (5), and the gas outlet of the dilute phosphoric acid evaporator (5) is connected to the inlet of the fluorine absorption circulation tank (4).

2. A system for recovering fluorine from silica gel according to claim 1, characterized in that: The fluorine absorption circulation tank (4) is provided with an exhaust pipe; the exhaust pipe is connected to the atmosphere.

3. A system for recovering fluorine from silica gel according to claim 1, characterized in that: The bottom notch of the reaction tank (8) is connected to the gypsum storage tank (10).

4. The operating method of a system for recovering fluorine from silica gel according to any one of claims 1 to 3, characterized in that: The steps include: S1, adding water to fluorinated silica gel and ball-milling to obtain a slurry, and filtering the slurry to obtain a filtrate and filtered silica gel; S2, after mixing the returned acid, stabilizer and the filtered silica gel in step S1 evenly, adding phosphate rock, heating and stirring to obtain gypsum and SiF4-containing gas; S3, the SiF4-containing gas in the reaction tank and the dilute phosphoric acid evaporator is countercurrently introduced into the filtrate in step S1 to obtain finished fluorosilicic acid.

5. The operating method of a system for recovering fluorine from silica gel according to claim 4, characterized in that: In the slurry of step S1, the mass ratio of fluorinated silica gel to water is 2-4:1, and the content of silica gel particle size -200 mesh in the slurry is ≥90%.

6. The method for operating a system for recovering fluorine from silica gel according to claim 4, characterized in that: The filter pressing pressure in step S1 is 0.3-0.5 MPa.

7. The method for operating a system for recovering fluorine from silica gel according to claim 4, characterized in that: In the step S2, the mass ratio of returned acid: filtered silica gel: phosphate rock is 4-8:1:200-500.

8. The method for operating a system for recovering fluorine from silica gel according to claim 4, characterized in that: In step S3, the heating temperature is 90° C.-93° C., and the stirring time is 1-3 hours.

9. The method for operating a system for recovering fluorine from silica gel according to claim 4, characterized in that: In the step S3, the mass ratio of SiF4-containing gas to filtrate is 1:10-20.

10. The method for operating a system for recovering fluorine from silica gel according to claim 4, characterized in that: In the step S2, the stabilizer is sodium polyacrylate, and the mass ratio of sodium polyacrylate to filtered silica gel is 1:5000-8000.

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