Recovery method of glass etching waste liquid

Abstract

The invention relates to a recovery method of glass etching waste liquid. The method comprises the following steps: (1) crystallizing and desiliconizing; (2) crystallizing to synthesize magnesium fluoride; (3) calcining magnesium fluoride at high temperature; (4) removing fluorine; and (5) crystallizing ammonium sulfate. The method aims at the glass etching waste liquid with high content of fluosilicate and sulfate, white carbon black with low water content and high purity can be prepared, magnesium fluoride and ammonium sulfate products with good filtering performance and high purity can be obtained, and the method is simple and efficient in process, low in energy consumption, environmentally friendly, high in recovery rate and suitable for industrial application.

Description

Technical Field

[0001] This invention relates to the field of waste liquid recycling, and in particular to a method for recycling glass etching waste liquid. Background Technology

[0002] Glass etching mainly involves reacting hydrofluoric acid (HF)-based mixed acids (such as HF-H2SO4 or NH4HF2-(NH4)2SO4 systems) with silicon dioxide (SiO2) in the glass to generate soluble fluorosilicic acid (H2SiF6) or ammonium fluorosilicate ((NH4)2SiF6), as follows:

[0003] 6HF + SiO2 = H2SiF6 + 2H2O or

[0004] 4NH4HF2+SiO2=(NH4)2SiF6+2NH4F+2H2O.

[0005] For HF-H2SO4 etching solutions, as etching progresses, the HF concentration decreases while the H2SiF6 concentration gradually increases to 10%–15%, leading to increased etching solution viscosity, reduced etching efficiency, and the formation of waste liquid. A typical waste liquid composition is: 3%–10% HF, 10%–15% H2SiF6, and 5%–10% H2SO4. For NH4HF2-(NH4)2SO4 etching solutions, as etching progresses, the free HF concentration decreases, resulting in a lower etching rate and the formation of waste liquid. A typical waste liquid composition is: 5%–8% NH4HF2, 2%–3% NH4F, 0.5–2% (NH4)2SiF6, and 5%–10% (NH4)2SO4.

[0006] The glass etching waste liquid contains high concentrations of fluoride ions (F-), fluorosilicate ions (SiF62-), and sulfate (SO4-). 2- Substances such as acidity or ammonia nitrogen, when directly discharged, will pollute water bodies and soil. Traditional treatment methods mainly employ lime neutralization, supplemented by a certain amount of soluble calcium salts (such as calcium chloride), to neutralize F-, SiF62-, and SO42- in the waste liquid. 2- When these substances are converted into insoluble calcium fluoride, calcium fluorosilicate, and calcium sulfate, a large amount of mixed hazardous sludge is generated and landfilled, which not only wastes valuable landfill capacity but also results in serious resource waste.

[0007] To address this issue, some research has been conducted on the resource recovery of fluoride-containing wastewater. For example, patents CN102745837A and CN109626646A respectively use alkali metal inorganic salts and alkali metal organic salts to remove fluorosilicic acid from glass thinning etching wastewater. The remaining liquid is then replenished with fresh acid and reused on the original production line. The former also uses alkaline conversion of the obtained fluorosilicates to obtain silica gel and metal fluorides for separate utilization. However, the online reuse technology used in these two documents cannot completely remove alkali metals or organic compounds such as sodium and potassium. The fresh etching solution used on the production line of the waste-generating unit generally does not contain these impurities, and most companies dare not risk reuse, making this type of technology difficult to apply in practice. For BOE wastewater, patent CN119750828A aims to recover hydrofluoric acid and ammonium sulfate products, and patent CN112158858A aims to recover ammonium bifluoride products. The technical route targeting hydrofluoric acid and ammonium bifluoride products requires extremely high corrosion resistance of equipment and is costly. Patent CN119263335A aims to recover ammonia and calcium fluoride products. The technical route targeting calcium fluoride products requires the lowest possible sulfate content in the waste liquid. Patent CN116395701A aims to recover sodium fluorosilicate, cryolite, and ammonium salt products. However, the co-precipitation of aluminum ammonium sulfate (NH4Al(SO4)2·12H2O) leads to excessive sulfate content in the cryolite products, making a system with lower sulfate content more suitable. Patent CN118754172A involves first adjusting the pH of the BOE waste liquid to 6-7 with magnesium hydroxide, then adding magnesium sulfate solution to precipitate magnesium fluoride. Magnesium fluoride obtained using this method is extremely difficult to filter.

[0008] In summary, current technologies for recycling glass etching waste liquid generally have limitations such as high requirements for the impurity composition of the etching waste liquid, unsuitability for fluorine-containing waste liquids with high fluorosilicate and sulfate content, high requirements for equipment corrosion resistance, or extremely difficult-to-filter products, making industrial application difficult. Summary of the Invention

[0009] Based on this, the purpose of this invention is to provide a method for recycling glass etching waste liquid, especially for glass etching waste liquid with high fluorosilicate and sulfate content. It can prepare white carbon black with low water content and high purity, and at the same time, it can also obtain magnesium fluoride and ammonium sulfate products with good filtration performance and high purity. The process is simple and efficient, with low energy consumption, environmental friendliness and high recovery rate, and is suitable for industrial application.

[0010] The technical solution of the present invention is as follows:

[0011] A method for recycling glass etching waste liquid, comprising the following steps:

[0012] (1) Crystallization and desiliconization: 6-10% ammonia solution and glass etching waste liquid are added to the control crystallizer at the same time. The pH of the reaction solution is adjusted to alkaline. After the reaction, sedimentation is carried out. The supernatant is used as desiliconization waste liquid. The mud is filtered to obtain wet silica. After washing and drying, silica product is obtained.

[0013] (2) Crystallization synthesis of magnesium fluoride: Desiliconization waste liquid and 15-25% magnesium sulfate solution are added to a crystallization reactor at the same time, heated and stirred at 60-90℃; the crystallization reactor includes a stirring device and a partition; a crystallization space is formed inside the partition, and a settling space is formed between the partition and the reactor wall; after the reaction liquid reacts and crystallizes in the crystallization space, it flows to the settling space for settling, and the supernatant after settling enters the supernatant tank through the overflow port. After the sludge after settling is filtered, magnesium fluoride is obtained.

[0014] (3) High-temperature calcination of magnesium fluoride: The magnesium fluoride obtained by filtration in step (2) is calcined at a high temperature of 500-700℃ to obtain high-purity magnesium fluoride;

[0015] (4) Defluorination: In the supernatant tank described in step (2), aluminum sulfate solution is added, and the pH is adjusted to 6-7.5 with 6-10% ammonia water. After the reaction, solid-liquid separation is performed.

[0016] (5) Crystallized ammonium sulfate: The liquid obtained in step (4) enters the evaporation tank, concentrated sulfuric acid is added, the pH is adjusted to 2-4, and evaporation and crystallization are carried out to obtain ammonium sulfate.

[0017] In some embodiments, in step (1), the pH of the reaction solution is adjusted to 8 to 9.5.

[0018] In some embodiments, in step (1), a 6-10% ammonia solution and glass etching waste liquid are simultaneously added to a controlled crystallizer. The controlled crystallizer is set to continuous feeding and continuous discharging, and the residence time of the reaction liquid in the controlled crystallizer is made to exceed 1 hour by controlling the feeding rate.

[0019] In some embodiments, in step (1), the reaction liquid after the reaction is completed enters the settling tank through the overflow port of the control crystallizer for settling, and the supernatant of the settling tank is desiliconization waste liquid, which flows into the desiliconization waste liquid pool.

[0020] In some embodiments, in step (1), the slurry obtained from sedimentation is pumped into the first vacuum turning filter tank for filtration and washing. The filtrate obtained from filtration is incorporated into the desiliconization waste liquid tank, while the washing liquid is returned to the front end for diluting ammonia water. The silicon slag obtained from washing is wet silica, which is dried to obtain silica product.

[0021] In some embodiments, in step (1), the moisture content of the wet silica is less than 30%.

[0022] In some embodiments, in step (2), the desiliconization waste liquid and 15-25% magnesium sulfate solution are simultaneously added to the crystallization reactor from the feed port at the top of the crystallization reactor. There is a valve at the bottom of the crystallization reactor. Every 8 to 12 hours, part of the slurry is discharged by opening the valve at the bottom of the enhanced crystallization reactor. The discharged slurry enters the second vacuum turning filter tank for filtration, and the filtrate is incorporated into the supernatant tank.

[0023] In some embodiments, in step (2), the heating is performed by introducing steam. The steam pipe extends from the top of the reactor into the reactor and is made of polytetrafluoroethylene. If the reaction temperature exceeds 90°C, the steam valve is closed to stop heating; if the reaction temperature is below 60°C, the steam valve is opened to introduce steam for heating.

[0024] In some embodiments, in step (2), the discharged slurry enters a vacuum filtration tank for filtration and washing, the filtrate is incorporated into the supernatant tank, and the washing liquid is returned to the front end for dissolving magnesium sulfate. A portion of the magnesium fluoride obtained in this step will co-precipitate with ammonium fluoride, forming magnesium ammonium fluoride (NH4MgF3) precipitate.

[0025] In some embodiments, the calcination time in step (3) is 2 to 3 hours.

[0026] In some embodiments, in step (3), the calcined high-temperature magnesium fluoride is fed back to the furnace head via a screw conveyor and a scraper conveyor. 40-60% of the calcined magnesium fluoride is returned as return material and fed into the premixer of the calcining furnace via a return material speed-regulating star feeder. The magnesium fluoride obtained from the filtration in step (2) is first fed into the premixer of the rotary calcining furnace via a belt conveyor and a star feeder to mix with the high-temperature return material. After pre-drying, it is then fed into the rotary calcining furnace for high-temperature calcination. The remaining magnesium fluoride is cooled to obtain high-purity magnesium fluoride product.

[0027] In some of these embodiments, in step (3), the rotary kiln can be heated by electricity or gas.

[0028] In some embodiments, in step (3), the dust generated by calcination (mainly composed of ammonium fluoride) is discharged after being removed by cyclone dust removal and bag dust removal, and the dust is dissolved in fluorine-containing waste liquid for recycling.

[0029] In some embodiments, in step (4), the amount of aluminum sulfate used is 100 to 200 times the fluorine content in the supernatant, and the concentration of the aluminum sulfate solution is 10 to 20%. The supernatant tank is a sloping plate sedimentation tank structure. The supernatant, aluminum sulfate and ammonia water enter the intermediate water channel through the inlet and then enter the sloping plate zone. The sludge settles to the sludge hopper at the bottom, and the supernatant enters the evaporation raw liquid tank through the outlet at the top of the sloping plate zone.

[0030] In some embodiments, in step (5), the evaporation rate of the evaporation crystallization is controlled at 60-80%, and then pumped into a thickener to be cooled to 35-45°C. The solid and liquid are separated to obtain ammonium sulfate product, and the resulting liquid is returned to the supernatant pool.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) For glass etching waste liquid with high fluorosilicate and sulfate content, the present invention controls the ammonia concentration to 6-10%, controls the pH value of the reaction solution to 8-9.5, and controls the ammonia solution to be added to the glass etching waste liquid simultaneously and continuously fed and discharged, thereby continuously forming the optimal environment for the generation and growth of silica crystals. The prepared wet silica has a water content of less than 30%, a purity of more than 98%, high processing efficiency, and high desiliconization rate of waste liquid. It overcomes the defects of existing technologies such as high silica water content (70-80%), difficult washing, high impurity content of silica products, and low processing efficiency.

[0033] (2) This invention controls the concentration of a suitable magnesium sulfate solution to 15-25%, the reaction temperature to 60-90℃, and controls the simultaneous addition of desilication waste liquid and 15-25% magnesium sulfate solution with continuous feeding and discharge. Under these conditions, magnesium fluoride seed crystals with good crystal form are continuously formed in situ in the crystallization reactor. Furthermore, by setting up crystallization space and sedimentation space, the magnesium fluoride seed crystals have a suitable environment to grow slowly, and finally magnesium fluoride with low water content, good filtration performance and high purity is obtained, overcoming the defects of magnesium fluoride prepared by the prior art which is extremely difficult to filter and has low purity.

[0034] In addition, step (3) of the present invention, combined with the process of high-temperature material return, can not only achieve the pre-drying of wet-based magnesium fluoride sludge cake, but also reduce the calcination time, thereby significantly reducing energy consumption while ensuring that the magnesium fluoride product meets the standards.

[0035] (3) By optimizing the defluorination and evaporation crystallization process of the supernatant, the present invention further recovers ammonium sulfate products, which efficiently recovers the components in the etching waste liquid and greatly avoids resource waste.

[0036] In summary, this invention addresses glass etching waste liquid with high fluorosilicate and sulfate content, continuously producing high-purity silica with low water content, high-quality magnesium fluoride with excellent filtration performance and high purity, and ammonium sulfate products. Through precise and efficient coordination of each step, the main components of the glass etching waste liquid are fully recovered and utilized, yielding a variety of high-quality products with great potential for industrial application. Furthermore, this technology can achieve continuous automated operation. Detailed Implementation

[0037] To facilitate understanding of the present invention, a more complete description will be given below with reference to embodiments, of which preferred embodiments are provided. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided so that a thorough and complete understanding of the disclosure of the present invention will be achieved.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. % as used herein, unless otherwise specified, refers to a percentage by mass.

[0039] The present invention will be further described in detail below with reference to specific embodiments.

[0040] The glass etching waste liquid in the following examples is obtained by mixing waste liquids generated from two typical glass etching processes in a 1:1 ratio. The typical composition of the glass frosting etching waste liquid is: 6.53% NH4HF2, 2.54% NH4F, 1.34% (NH4)2SiF6 and 7.28% (NH4)2SO4, and the typical composition of the glass thinning etching waste liquid is: 4.55% HF, 12.38% H2SiF6 and 8.33% H2SO4.

[0041] Example 1

[0042] A method for recycling glass etching waste liquid, comprising the following steps:

[0043] (1) Continuous controlled crystallization desilication: Ammonia water is diluted to a concentration of 6-10% and pumped into the controlled crystallizer together with glass etching waste liquid. The pH value of the reaction solution is controlled at 8-9.5. The controlled crystallizer is set to continuous feeding and continuous discharge. By controlling the feeding speed, the residence time of the reaction solution in the controlled crystallizer is made to exceed 1 hour. The reaction solution enters the settling tank through the overflow port of the controlled crystallizer for settling. The supernatant of the settling tank flows into the desilication waste liquid pool. The slurry obtained from settling is pumped into the first vacuum turning filter tank for filtration and washing. The filtrate obtained from filtration is incorporated into the desilication waste liquid pool. The washing liquid is returned to the front end for diluting ammonia water. The silicon slag obtained from washing is dried to obtain the white carbon black product.

[0044] (2) Continuous enhanced crystallization synthesis of magnesium fluoride: Desiliconized waste liquid from the desiliconized waste liquid pool and 20% magnesium sulfate solution are simultaneously pumped into the enhanced crystallization reactor from the feed port at the top of the enhanced crystallization reactor, and steam is introduced for heating. The steam pipe extends into the reactor from the top of the reactor and is made of polytetrafluoroethylene. The crystallization reaction temperature is controlled at 60-90℃ by a thermometer. If the reaction temperature exceeds 90℃, the steam valve is automatically closed and heating is stopped. If the reaction temperature is below 60℃, the steam valve is automatically opened to introduce steam for heating. The enhanced crystallization reactor includes a stirring device and a partition; it is divided into a crystallization space and a settling space, separated by a partition (PP board). The crystallization space is formed inside the partition, and the settling space is formed outside the partition and the reactor wall. After the reaction liquid reacts and crystallizes in the crystallization space, it flows to the settling space for settling. The supernatant in the settling space enters the supernatant tank through the overflow port. The magnesium fluoride slurry obtained from settling is partially discharged every 8-12 hours by opening the solenoid valve at the bottom of the enhanced crystallization reactor. The discharged slurry enters the second vacuum turning filter tank for filtration and washing. The filtrate is combined with the supernatant tank, and the washing liquid is returned to the front end for dissolving magnesium sulfate. In this step, some ammonium fluoride will co-precipitate with the magnesium fluoride to form magnesium ammonium fluoride (NH4MgF3) precipitate.

[0045] (3) High-temperature calcination of magnesium fluoride: The washed magnesium fluoride sludge cake is fed into the premixer of the rotary calcining furnace via a belt conveyor and a star feeder. In the premixer, it is mixed with high-temperature return material. After pre-drying the wet sludge cake, it is sent to the rotary calcining furnace. The rotary calcining furnace can be heated electrically or by gas, with a calcination temperature of 500–700℃ and a calcination time of 2–3 hours. The calcined high-temperature magnesium fluoride product is conveyed back to the furnace head via a screw conveyor and a scraper conveyor. 40–60% of this is returned material and fed into the premixer of the calcining furnace via a variable-speed star feeder. The remaining magnesium fluoride is cooled to obtain high-purity magnesium fluoride product. The dust generated during calcination (mainly composed of ammonium fluoride) is discharged after being collected by cyclone dust collectors and bag filters. The dust is dissolved in fluorine-containing waste liquid for recycling.

[0046] (4) Deep defluorination: The supernatant tank contains 100-200 mg / L of fluoride. Deep defluorination is carried out by adding aluminum sulfate with a fluoride content of about 100-200 times. The aluminum sulfate is prepared into a 10-20% concentration solution and added to the supernatant tank through a metering pump. 6-10% ammonia water is added to adjust the pH of the reaction solution to 6-7.5. The supernatant tank is a sloping plate sedimentation tank. The supernatant, aluminum sulfate and ammonia water enter the middle channel through the inlet and then enter the sloping plate zone. The sludge settles to the sludge hopper at the bottom, and the supernatant enters the evaporation raw liquid tank through the outlet at the top of the sloping plate zone. The sludge in the sludge hopper is periodically pumped into a filter press for filtration. The sludge cake obtained is entrusted to a qualified unit for disposal, and the filtrate flows into the evaporation raw liquid tank.

[0047] (5) Evaporation and crystallization of ammonium sulfate: Add concentrated sulfuric acid to the evaporation stock solution tank, adjust the pH value to 2-4, and then pump it into a single evaporation kettle for evaporation and crystallization. The evaporation rate is controlled at 60-80%. Then pump it into a thickener and cool it to about 40°C. The ammonium sulfate product is obtained by centrifugation. The mother liquor is returned to the supernatant tank for subsequent operations.

[0048] Example 2

[0049] A method for recycling glass etching waste liquid differs from Example 1 in that step (1) is as follows:

[0050] (1) Continuous controlled crystallization desilication: Ammonia water is diluted to a concentration of 15-20% and pumped into the controlled crystallizer together with glass etching waste liquid. The pH value of the reaction solution is controlled at 8-9.5. The controlled crystallizer is set to continuous feeding and continuous discharge. By controlling the feeding rate, the residence time of the reaction solution in the reactor is made to exceed 1 hour. The reaction solution enters the settling tank through the overflow port of the controlled crystallizer for settling. The supernatant of the settling tank flows into the desilication waste liquid pool. The sludge obtained from settling is pumped into the vacuum turning filter tank for filtration and washing. The filtrate obtained from filtration is incorporated into the desilication waste liquid pool. The washing liquid is returned to the front end for diluting ammonia water. The silicon slag obtained from washing is dried to obtain the white carbon black product.

[0051] Example 3

[0052] A method for recycling glass etching waste liquid differs from Example 1 in that step (1) is as follows:

[0053] (1) Continuous controlled crystallization desilication: Ammonia water is diluted to a concentration of 6-10% and pumped into the controlled crystallizer together with glass etching waste liquid. The pH value of the reaction solution is controlled at 6-7.5. The controlled crystallizer is set to continuous feeding and continuous discharge. By controlling the feeding rate, the residence time of the reaction solution in the reactor is made to exceed 1 hour. The reaction solution enters the settling tank through the overflow port of the controlled crystallizer for settling. The supernatant of the settling tank flows into the desilication waste liquid pool. The sludge obtained from settling is pumped into the vacuum turning filter tank for filtration and washing. The filtrate obtained from filtration is incorporated into the desilication waste liquid pool. The washing liquid is returned to the front end for diluting ammonia water. The silicon slag obtained from washing is dried to obtain the white carbon black product.

[0054] Example 4

[0055] A method for recycling glass etching waste liquid differs from Example 1 in that step (2) is as follows:

[0056] (2) Continuous enhanced crystallization synthesis of magnesium fluoride: Desiliconized waste liquid from the desiliconized waste liquid pool and 20% magnesium sulfate solution are simultaneously pumped into the enhanced crystallization reactor from the feed port at the top of the enhanced crystallization reactor, and steam is introduced for heating. The steam pipe extends into the reactor from the top of the reactor and is made of polytetrafluoroethylene. The crystallization reaction temperature is controlled at 45-55℃ by a thermometer. If the reaction temperature exceeds 55℃, the steam valve is closed and heating is stopped. If the reaction temperature is below 45℃, the steam valve is opened to introduce steam for heating. The enhanced crystallization reactor includes a stirring device and a partition; it is divided into a crystallization space and a settling space, separated by a partition (PP board). The crystallization space is formed inside the partition, and the settling space is formed outside the partition and the reactor wall. After the reaction liquid reacts and crystallizes in the crystallization space, it flows to the settling space for settling. The supernatant in the settling space enters the supernatant tank through an overflow port. The magnesium fluoride slurry obtained from settling is partially discharged every 8-12 hours by opening a solenoid valve at the bottom of the enhanced crystallization reactor. The discharged slurry enters a second vacuum turning filter tank for filtration and washing. The filtrate is added to the supernatant tank, and the washing liquid is returned to the front end for dissolving magnesium sulfate. In this step, some ammonium fluoride will co-precipitate with the magnesium fluoride to form magnesium ammonium fluoride (NH4MgF3) precipitate.

[0057] Example 5 (using a batch reactor)

[0058] A method for recycling glass etching waste liquid differs from Example 1 in that step (2) is as follows:

[0059] (2) Synthesis of magnesium fluoride: A certain amount of desiliconization waste liquid from the desiliconization waste liquid tank is pumped into a PE-lined steel reactor, and then 20% magnesium sulfate solution is added until the fluoride content of the filtrate stabilizes at 100-200 mg / L. The reaction is stirred for 1-2 hours. Steam is introduced for heating while adding magnesium sulfate solution. The steam pipe extends into the reactor from the top (the amount of desiliconization waste liquid added must submerge the steam pipe outlet). The material is polytetrafluoroethylene. The crystallization reaction temperature is controlled at 60-90℃ by an interlocking thermometer. If the reaction temperature exceeds 90℃, the steam valve is closed and heating is stopped. If the reaction temperature is below 60℃, the steam valve is opened to introduce steam for heating. After the reaction is completed, the mixture is allowed to settle for 1-2 hours. The slurry in the reactor is pumped into a vacuum turning filter tank for filtration and washing. The filtrate enters the supernatant tank, and the washing liquid is returned to the front end for dissolving magnesium sulfate. Some of the magnesium fluoride obtained in this step will co-precipitate with the magnesium fluoride to form magnesium ammonium fluoride (NH4MgF3) precipitate.

[0060] The moisture content of the wet silica prepared in Examples 1-5, the impurity content of the dried silica, and the silicon content of the silicon-containing wastewater were determined. At the same time, the moisture content and purity of magnesium fluoride were tested. The results are shown in Table 1.

[0061] Table 1

[0062]

[0063] This invention addresses glass etching waste liquid with high fluorosilicate and sulfate content, enabling the continuous production of precipitated silica with low water content and high purity, magnesium fluoride with excellent filtration performance and high purity, and ammonium sulfate products. Through precise and efficient coordination of each step, the main components of the glass etching waste liquid are fully recovered and utilized, resulting in a variety of high-quality products. Furthermore, this technology can achieve continuous automated operation, demonstrating excellent social benefits and promising prospects for industrial application.

[0064] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0065] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for recycling glass etching waste liquid, wherein, Includes the following steps: (1) Crystallization and desiliconization: 6-10% ammonia solution and glass etching waste liquid are added to the control crystallizer at the same time. The pH of the reaction solution is adjusted to alkaline. After the reaction, sedimentation is carried out. The supernatant is used as desiliconization waste liquid. The mud is filtered to obtain wet silica. After washing and drying, silica product is obtained. (2) Crystallization synthesis of magnesium fluoride: Desiliconization waste liquid and 15-25% magnesium sulfate solution are added to a crystallization reactor at the same time, heated and stirred at 60-90℃; the crystallization reactor includes a stirring device and a partition; a crystallization space is formed inside the partition, and a settling space is formed between the partition and the reactor wall; after the reaction liquid reacts and crystallizes in the crystallization space, it flows to the settling space for settling, and the supernatant after settling enters the supernatant tank through the overflow port. After the sludge after settling is filtered, magnesium fluoride is obtained. (3) High-temperature calcination of magnesium fluoride: The magnesium fluoride obtained by filtration in step (2) is calcined at a high temperature of 500-700℃ to obtain high-purity magnesium fluoride; (4) Defluorination: In the supernatant tank described in step (2), aluminum sulfate solution is added, and the pH is adjusted to 6-7.5 with 6-10% ammonia water. After the reaction, solid-liquid separation is performed. (5) Crystallized ammonium sulfate: The liquid obtained in step (4) enters the evaporation tank, concentrated sulfuric acid is added, the pH is adjusted to 2-4, and evaporation and crystallization are carried out to obtain ammonium sulfate.

2. The recycling method according to claim 1, wherein, In step (1), the pH of the reaction solution is adjusted to 8 to 9.

5.

3. The recycling method according to claim 1, wherein, In step (1), 6-10% ammonia solution and glass etching waste liquid are added to the controlled crystallizer at the same time. The controlled crystallizer is set to continuous feeding and continuous discharging. By controlling the feeding speed, the residence time of the reaction liquid in the controlled crystallizer is made to exceed 1 hour.

4. The recycling method according to claim 1, wherein, In step (1), the reaction liquid after the reaction is completed enters the settling tank through the overflow port of the control crystallizer for settling. The supernatant of the settling tank is desiliconization waste liquid, which flows into the desiliconization waste liquid pool.

5. The recycling method according to claim 1, wherein, In step (1), the moisture content of the wet silica is less than 30%.

6. The recycling method according to any one of claims 1-5, wherein, In step (2), the desiliconization waste liquid and 15-25% magnesium sulfate solution are simultaneously added to the crystallization reactor from the feed port at the top of the crystallization reactor. The crystallization reactor is set to continuous feeding and continuous discharging. There is a valve at the bottom of the crystallization reactor. Every 8 to 12 hours, part of the slurry is discharged by opening the valve at the bottom of the enhanced crystallization reactor. The discharged slurry enters the vacuum turning filter tank for filtration, and the filtrate is added to the supernatant tank.

7. The recycling method according to any one of claims 1-5, wherein, In step (2), the supernatant tank is equipped with an online fluoride ion meter. When the fluoride content of the supernatant is higher than 200 mg / L, a feedback signal is generated to increase the feed rate of the magnesium sulfate solution at the front end or decrease the feed rate of the desiliconization waste liquid. If the fluoride content of the supernatant measured by the online fluoride ion meter is lower than 100 mg / L, a feedback signal is generated to increase the feed rate of the desiliconization waste liquid at the front end or decrease the feed rate of the magnesium sulfate solution.

8. The recycling method according to any one of claims 1-5, wherein, In step (3), the calcination time is 2-3 hours. The calcined high-temperature magnesium fluoride is conveyed by a screw conveyor and then sent back to the furnace head by a scraper conveyor. 40-60% of it is used as return material and is fed into the premixer of the calcining furnace through a variable speed star feeder. The magnesium fluoride obtained from the filtration in step (2) is first fed into the premixer of the rotary calcining furnace by a belt conveyor and a star feeder to mix with the high-temperature return material. After pre-drying, it is sent into the rotary calcining furnace for high-temperature calcination. The remaining magnesium fluoride is cooled to obtain high-purity magnesium fluoride product.

9. The recycling method according to any one of claims 1-5, wherein, In step (4), the amount of aluminum sulfate used is 100 to 200 times the fluorine content in the supernatant, and the concentration of the aluminum sulfate solution is 10 to 20%. The supernatant tank is a sloping plate sedimentation tank. The supernatant, aluminum sulfate and ammonia water enter the middle water channel through the inlet and then enter the sloping plate zone. The sludge settles to the sludge hopper at the bottom, and the supernatant enters the evaporation raw liquid tank through the outlet at the top of the sloping plate zone.

10. The recycling method according to any one of claims 1-5, wherein, In step (5), the evaporation rate of the evaporation crystallization is controlled at 60-80%, and then pumped into a thickener to be cooled to 35-45°C. The solid and liquid are separated to obtain ammonium sulfate product, and the resulting liquid is returned to the supernatant pool.

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