A resource treatment method for BOE waste liquid

Abstract

The present invention relates to the technical field of water treatment, more specifically, it relates to a kind of resource treatment method of BOE waste liquid, and its technical scheme key points are, comprise the following steps: S1, sodium salt solution is added to BOE waste liquid to react, obtain sodium fluorosilicate and the first waste liquid;S2, aluminum salt solution is added to the first waste liquid, and pH is adjusted to 4-7, and cryolite and the second waste liquid are obtained;S3, defluorinating agent and heavy capture agent are added to the second waste liquid, and the first waste residue and the third waste liquid are obtained;S4, pH of the third waste liquid is adjusted to 2-4, evaporation crystallization is carried out, and evaporation condensation water and concentrated liquid are obtained;S5, the concentrated liquid is pumped into cooling crystallization tank and cooled, centrifuged, and ammonium salt and final mother liquor are obtained;S6, the third waste liquid and the final mother liquor are returned to the S1 and the S2 for circulation. The present invention can realize the resource recovery of components in BOE waste liquid, and has the advantages of obtaining high-value sodium fluorosilicate, cryolite and agricultural grade ammonium salt products.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, and more particularly to a method for resource-based treatment of BOE waste liquid. Background Art

[0002] The direct reaction between hydrofluoric acid and silicon dioxide is highly reactive, making defective products more likely to occur during pattern etching of silicon wafers (chips) in the semiconductor industry. BOE (buffered oxide etch) is a buffered oxide etchant, a mixture of HF and NH4F. It is typically prepared by adding a 40wt% NH4F solution to a 49wt% hydrofluoric acid solution and reacting at room temperature. The concentration ratio can be adjusted according to the desired etching rate. The NH4F in the etchant acts as a buffer. During the reaction between silicon dioxide and the HF in the etchant to produce H2SiF6, NH4F continuously ionizes to replenish the fluoride ions required for the reaction, thereby achieving a stable etching rate and achieving pattern etching stability.

[0003] The etching principle of BOE is as follows:

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

[0005] When the etching effect of the etching solution deteriorates, it is discharged as waste liquid. The main components of BOE waste liquid are a mixture of 3-10% (wt) ammonium fluorosilicate, 10-20% (wt) ammonium fluoride, and a small amount of unreacted hydrofluoric acid (about 0.5% (wt)). It also contains small amounts of other components, such as 300-50,000 mg / L of sulfate, 500-20,000 mg / L of chloride ions, and 50-100 mg / L of heavy metals (Pb).

[0006] Patent number CN 114132953 A discloses a system and method for producing high-purity calcium fluoride from BOE wastewater. This method involves reacting calcium salts with fluorides and fluorosilicates in the BOE wastewater, followed by high-temperature calcination to produce a calcium fluoride product with a purity exceeding 97%. While this method can recycle the main components of the BOE wastewater, it requires a high-temperature calcination process, resulting in high energy consumption and low product value.

[0007] Patent number CN 112158858 A discloses a method for producing ammonium bifluoride from BOE wastewater. This method involves first removing fluorosilicates and sulfates from the wastewater using barium hydroxide, then adding anhydrous hydrogen fluoride to convert the ammonium fluoride into ammonium bifluoride. The ammonium bifluoride product is then evaporated and crystallized in a triple-effect evaporator at a temperature of 70-120°C and a pressure of -0.03 to -0.06 MPa. This method severely corrodes the triple-effect evaporator, hindering the long-term use of the equipment.

[0008] Patent number CN 114105097 A discloses a method and apparatus for producing hydrogen fluoride using electrodialysis of BOE waste liquid. Specifically, the BOE waste liquid is first reacted with ammonia to produce an ammonium fluoride solution, which is then decomposed through bipolar membrane electrodialysis to produce a dilute hydrofluoric acid solution and dilute ammonia water. The dilute ammonia water is stripped to remove ammonia gas, part of which is returned to the front end to react with the BOE waste liquid. The dilute hydrofluoric acid solution is then concentrated by distillation and then mixed with concentrated sulfuric acid to evaporate hydrogen fluoride gas. This method does not consider the presence of fluorosilicic acid in the BOE waste liquid, and membrane blockage may occur during the bipolar membrane electrodialysis process. The dilute hydrofluoric acid solution also poses a serious corrosion risk to the evaporator equipment during evaporation and concentration.

[0009] The harmless treatment method for BOE wastewater is generally to neutralize it with lime or slaked lime, generating calcium fluoride and ammonia. Disposal units with the necessary facilities will recycle the ammonia, while the calcium fluoride is disposed of in landfills. This disposal method not only wastes a significant amount of valuable resources but also suffers from problems such as slow calcium fluoride filtration, incomplete fluoride ion removal (residual fluoride levels as high as 50-500 mg / L), severe fugitive ammonia emissions during treatment, and high sludge landfill costs. Summary of the Invention

[0010] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a resource-based treatment method for BOE waste liquid, which can not only realize the resource recovery of the main components of the waste liquid, such as fluorosilicate, fluoride, ammonia nitrogen, sulfate or chloride, but also has good treatment effect. There is basically no unorganized emission of ammonia during the treatment process. At the same time, fluoride ions are completely removed (the residual fluoride content can be stably reduced to below 3 mg / L), which can greatly reduce the corrosion of fluoride ions on the evaporator.

[0011] The above technical objectives of the present invention are achieved through the following technical solutions: a method for resource-based treatment of BOE waste liquid, comprising the following steps:

[0012] S1, dissolving sodium salt to obtain a sodium salt solution, adding the sodium salt solution to the BOE waste liquid, reacting for 30 minutes, and then filtering to obtain sodium fluorosilicate and the first waste liquid;

[0013] S2, dissolving aluminum salt to obtain an aluminum salt solution, adding the aluminum salt solution to the first waste liquid, and adjusting the pH of the first waste liquid to 4-7 with a first pH adjuster, reacting for 1-2 hours, and then filtering to obtain cryolite and a second waste liquid;

[0014] S3, adding a defluorinating agent and a heavy capture agent to the second waste liquid, reacting for 30 minutes and then filtering to obtain a first waste residue and a third waste liquid, and disposing the first waste residue into a landfill;

[0015] S4, adding a second pH regulator to the third waste liquid to adjust the pH of the third waste liquid to 2-4, evaporating and crystallizing to obtain evaporated condensed water and concentrated liquid, and biochemically treating the evaporated condensed water to meet the standards before discharging;

[0016] S5, pumping the concentrated solution into a cooling crystallization tank and cooling it to 40° C., and then centrifuging to obtain ammonium salt and final mother liquor;

[0017] S6. Returning the third waste liquor and the final mother liquor to S1 and S2 for circulation to prepare the sodium salt solution and the aluminum salt solution.

[0018] In one embodiment, the sodium salt comprises one or more of sodium chloride, sodium sulfate, sodium carbonate and sodium bicarbonate, and the amount of the sodium salt added (calculated as sodium) is calculated based on the sodium required to completely remove the fluorosilicate and fluoride in the BOE waste liquid and precipitate sodium fluorosilicate and sodium hexafluoroaluminate, and the excess coefficient is 1-1.2 times.

[0019] In one embodiment, the aluminum salt includes one or more of aluminum chloride, aluminum sulfate and sodium aluminate, and the amount of the aluminum salt added (calculated as aluminum) is calculated based on the aluminum required to completely remove fluoride in the first waste liquid and precipitate sodium hexafluoroaluminate, and the excess coefficient is 1-1.2 times.

[0020] In one embodiment, the first pH adjuster includes one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, ammonia, ammonium bicarbonate and ammonium carbonate.

[0021] In one embodiment, the steps S1 and S2 further include washing and drying the sodium fluorosilicate and the cryolite, respectively.

[0022] In one embodiment, the defluoridating agent includes one or more of aluminum chloride, polyaluminum chloride, aluminum sulfate, hydroxyapatite, magnesium chloride and magnesium sulfate.

[0023] In one embodiment, the second pH adjuster is hydrochloric acid or sulfuric acid.

[0024] The above-mentioned method for resource recovery of BOE waste liquid has the following beneficial effects:

[0025] First, the present invention can fully realize the resource utilization of the main components in BOE waste liquid, produce sodium fluorosilicate, cryolite and agricultural ammonium salt products with purity that meets relevant national standards, and realize high-value utilization of resources;

[0026] Secondly, in the present invention, by adding an excess of sodium salt in S1, not only can the fluorosilicate in the waste liquid be precipitated more completely, thereby increasing the yield of sodium fluorosilicate, but the excess sodium ions can also be used to prepare the cryolite product in S2;

[0027] Third, in the present invention, S1 and S2 can significantly reduce the moisture content of the two products by controlling the crystallization process, improve the filtration efficiency, and reduce the subsequent drying cost of the products;

[0028] Fourthly, in the present invention, the defluoridating agent removes fluoride ions from the wastewater in the form of a complex salt precipitate with lower solubility, and the fluoride content can be stably reduced to below 3 mg / L, significantly reducing the corrosion of the subsequent evaporator by fluoride ions. It can also simultaneously remove heavy metal ions from the wastewater, preventing the heavy metal ions from entering the subsequent ammonium salt product and affecting its quality.

[0029] Fifth, in the present invention, all reactions are carried out at a pH value less than or equal to 7, and there is basically no unorganized emission of ammonia during the treatment process, which is friendly to the environment and the physical and mental health of the operators. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a flow chart of the steps of the present invention;

[0031] Figure 2 It is a schematic flow diagram of the present invention. DETAILED DESCRIPTION

[0032] The present invention is described in further detail below in conjunction with the examples. It should be noted that the following examples are intended to facilitate understanding of the present invention and are not intended to limit the present invention in any way. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as those of ordinary skill in the art to which the present invention belongs. In the event of a conflict, the definitions in this specification shall prevail.

[0033] As used herein, the term "prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0034] The conjunction "consisting of" excludes any unspecified element, step, or component. If used in a claim, this phrase renders the claim closed, excluding materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim, rather than immediately following the subject matter, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0035] When amount, concentration or other value or parameter is represented with range, preferred range or the range that a series of upper preferred value and lower preferred value limit are expressed, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value and any range lower limit or preferred value, no matter whether this range is disclosed separately.For example, when disclosing scope "1 to 5", described scope should be interpreted as including scope "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5" etc.When numerical range is described in this article, unless otherwise stated, otherwise this scope is intended to include its end value and all integers and fractions within this range.

[0036] See Figure 1 A method for recycling BOE waste liquid comprises the following steps:

[0037] S1. Dissolve the sodium salt to obtain a sodium salt solution, add the sodium salt solution to the BOE waste liquid, react for 30 minutes, and then filter to obtain sodium fluorosilicate and the first waste liquid.

[0038] The sodium salt solution is used to react with the fluorosilicate in the BOE waste liquid to obtain sodium fluorosilicate and to prepare cryolite in the subsequent steps. The sodium salt solution required to completely precipitate the fluorosilicate and fluoride to obtain sodium fluorosilicate and sodium hexafluoroaluminate is added to the BOE waste liquid. The specific calculation process of the required amount of sodium salt solution is as follows: First, determine the fluorosilicate content in the BOE waste liquid, and calculate the amount of fluorosilicate substance n 氟硅酸盐 , press n 钠 :n 氟硅酸盐 =2-2.4:1 ratio to calculate the mass m1 of the sodium salt solution required; then measure the fluoride content in the waste liquid after complete removal of fluorosilicate, and calculate the amount of fluoride substance n 氟化物 , press n 钠 :n 氟化物 = 0.5-0.6:1 ratio to calculate the mass m2 of the sodium salt solution required; the sum of the masses of m1 and m2 is the total mass of the sodium salt solution required to be added in this step.

[0039] S2. Dissolve the aluminum salt to obtain an aluminum salt solution, add the aluminum salt solution to the first waste liquid, and adjust the pH of the first waste liquid to 4-7 with a first pH adjuster. After reacting for 1-2 hours, filter to obtain cryolite and the second waste liquid.

[0040] In actual operation, the aluminum salt solution required for complete precipitation of sodium hexafluoroaluminate is added to the first waste liquid. The specific calculation process of the required aluminum salt solution is as follows: Determine the fluoride content in the first waste liquid and calculate the amount of fluoride substance n 氟化物 , then press n 铝 :n 氟化物 =1.0-1.2:6 ratio to calculate the mass of the aluminum salt solution required, which is the mass of the aluminum salt solution required to be added in this step.

[0041] S3, adding a defluorinating agent and a heavy capture agent to the second waste liquid, reacting for 30 minutes and then filtering to obtain a first waste residue and a third waste liquid, and disposing the first waste residue into a landfill;

[0042] The amount of defluoridation agent and heavy metal capture agent added to the second waste liquid can be calculated according to the following scheme. The specific amount can be adjusted according to the removal effect: the mass concentration (mg / L) of the remaining fluoride ions and heavy metals (in terms of Pb) in the second waste liquid is measured, and multiplied by the treatment volume to calculate the mass m of fluoride ions and heavy metals (in terms of Pb). 氟离子 and m 重金属 , then follow m 除氟剂 :m 氟离子 =2-10:1,m 重捕剂 :m 重金属 = Add defluorinating agent and heavy capture agent in a ratio of 10-20:1.

[0043] S4, adding a second pH regulator to the third waste liquid to adjust the pH of the third waste liquid to 2-4, evaporating and crystallizing to obtain evaporated condensed water and concentrated liquid, and biochemically treating the evaporated condensed water to meet the standards before discharging;

[0044] S5. The concentrated solution is pumped into a cooling crystallization tank and cooled to 40° C., and then centrifuged to obtain ammonium salt and final mother liquor;

[0045] In the present invention, the obtained ammonium salt is ammonium chloride or ammonium sulfate, and the ammonium salt is packaged and sold or packaged and sold after drying.

[0046] S6, returning the third waste liquid and the final mother liquor to S1 and S2 for recycling and dissolving the sodium salt solution and the aluminum salt solution;

[0047] After the mother liquor has circulated too many times, it needs to be opened for treatment.

[0048] Specifically, sodium salts include one or more of sodium chloride, sodium sulfate, sodium carbonate and sodium bicarbonate;

[0049] In actual operation, sodium chloride or sodium sulfate is mainly used, and sodium carbonate and sodium bicarbonate are used to control the pH value of the reaction within a limited range. Sodium salts are generally added in the form of solutions, but can also be added in the form of solids.

[0050] Specifically, the aluminum salt includes one or more of aluminum chloride, aluminum sulfate, and sodium metaaluminate;

[0051] In actual operation, aluminum chloride or aluminum sulfate is mainly used, and sodium aluminate is used to control the pH value of the reaction system within a limited range; and in order to obtain cryolite products with low water content, aluminum salt needs to be added in the form of a solution.

[0052] Specifically, the first pH regulator includes one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, ammonia water, ammonium bicarbonate and ammonium carbonate; the pH of the first waste liquid is adjusted to 4-7, preferably 5.0-6.5 by the first pH regulator.

[0053] Specifically, S1 and S2 also include drying the sodium fluorosilicate and cryolite, or washing and drying them respectively; the dried sodium fluorosilicate and cryolite are packaged and sold.

[0054] Specifically, the defluoridating agent includes one or more of aluminum chloride, polyaluminum chloride, aluminum sulfate, hydroxyapatite, magnesium chloride, and magnesium sulfate.

[0055] Specifically, the heavy metal scavenger is one or more of xanthate esters, dithiocarbamate derivatives (DTCs), trisodium trimercaptotriazine (TMTs), sodium trithiocarbonate (STCs) and other novel organic sulfur heavy metal scavengers.

[0056] Specifically, the second pH adjuster is hydrochloric acid or sulfuric acid.

[0057] Specifically, the ammonium salt product is one of ammonium chloride or ammonium sulfate. If it is ammonium chloride, the agent used in the above steps is selected to be an agent that does not contain sulfate. If it is ammonium sulfate, the agent used in the above steps is selected to be an agent that does not contain chloride.

[0058] Specifically, the ammonium salt product can be packaged and sold directly or packaged and sold after being dried.

[0059] The resource recovery method for BOE waste liquid comprises adding a sodium salt solution to the BOE waste liquid to fully precipitate the fluorosilicate in the waste liquid to obtain a sodium fluorosilicate product, and the excess sodium can be further utilized in the subsequent preparation of a cryolite product. An aluminum salt solution is added proportionally to the filtrate after the fluorosilicate is removed, and the pH is adjusted to 4-7. After sufficient reaction, 80-90% of the fluoride ions in the filtrate can be recovered as a cryolite product. A defluoridating agent and a heavy metal capture agent are added to the remaining wastewater to stably reduce the fluoride ion level to below 3 mg / L, and the heavy metal (Pb) content is below the detection limit. This not only significantly reduces the corrosion of the subsequent evaporator by fluoride ions, but also allows evaporation and crystallization to obtain an ammonium salt product with a low heavy metal content. After a series of reactions and impurity removal in the above steps, the evaporated liquid is mainly composed of a high-purity ammonium salt. To reduce the ammonia nitrogen content in the evaporated condensed water and avoid impacting the biochemical system, the pH of the evaporated liquid is adjusted to 2-4 by adding acid. Subsequently, a high-purity ammonium salt product is obtained through evaporation concentration, cooling crystallization, and centrifugal separation.

[0060] The present invention can determine whether to primarily produce ammonium chloride or ammonium sulfate, depending on the level of impurities such as sulfate or chloride in the BOE wastewater. This fully utilizes the main components of the BOE wastewater as resources, producing sodium fluorosilicate, cryolite, and agricultural ammonium salt products that meet relevant national standards, thus achieving high-value resource utilization. Furthermore, all reactions in the present invention are carried out at a pH of less than or equal to 7, and there is virtually no fugitive ammonia emission during the process, which is environmentally friendly and friendly to the physical and mental health of operators.

[0061] The following is a specific embodiment:

[0062] It should be noted that in the following examples, the tests of various indicators of sodium fluorosilicate products are determined according to the method specified in "GB / T 23936-2018 Industrial Sodium Fluorosilicate", the tests of various indicators of cryolite products are determined according to the method specified in "GB / T 4291-2017 Cryolite", and the tests of various indicators of ammonium salt products (ammonium sulfate or ammonium chloride) are determined according to the methods specified in "GB / T 535-2020 Fertilizer Grade Ammonium Sulfate" and "GB / T 2946-2018 Ammonium Chloride".

[0063] Example 1

[0064] The main components of the BOE waste liquid in this example are ammonium fluorosilicate 3.58% (wt), ammonium fluoride 18.36% (wt), hydrofluoric acid 0.48% (wt), sulfate 46300 mg / L, chloride 529 mg / L, heavy metals (Pb) 70 mg / L, density 1.18 g / cm -3 The specific processing methods are as follows:

[0065] (1) Weighing 570 g of sodium sulfate decahydrate, dissolving it in 1400 g of water, and adding it to 1 L of BOE waste liquid at a feed rate of 50 mg / L. After the addition is completed, react for 30 minutes, and filter to obtain sodium fluorosilicate and a first waste liquid;

[0066] (2) Weigh 340 g of aluminum sulfate 18hydrate, dissolve it in 800 g of water, and add it to the first waste liquid at a feed rate of 40 mg / L. After the addition is completed, solid sodium hydroxide is added to adjust the pH value of the waste liquid to 6.5, react for 2 h, and filter to obtain cryolite and the second waste liquid;

[0067] (3) The fluorine content of the second waste liquid was determined to be 322 mg / L, and the heavy metal content (in terms of Pb) was 45 mg / L. 9 g of a defluorinating agent and 2.7 g of a heavy metal trapping agent were added, and the mixture was reacted for 30 min and then filtered to obtain the first waste residue and the third waste liquid;

[0068] (4) adding sulfuric acid to the third waste liquid to adjust the pH of the third waste liquid to 4, evaporating and crystallizing to obtain evaporated condensed water and concentrated liquid;

[0069] (5) cooling the concentrated solution to room temperature and filtering to obtain ammonium sulfate and a final mother liquor;

[0070] (6) The third waste liquor and the final mother liquor are returned to the front end for preparing sodium sulfate solution and aluminum sulfate solution.

[0071] In this embodiment, the purity of the sodium fluorosilicate product after drying can reach 99.2%, the free acid content (calculated as HCl) is 0.05%, the drying loss is 0.08%, the chloride content is 0.02%, the water-insoluble matter content is 0.11%, the sulfate content is 0.24%, the iron content and the phosphorus pentoxide content are both below the detection limit, and the heavy metal (calculated as Pb) is 0.0001%. The contents of each index meet the requirements of Type I superior products of "GB / T 23936-2018 Industrial Sodium Fluorosilicate"; after washing and drying, the cryolite product has a fluorine content of 52.3%, an aluminum content of 12.2%, a sodium content of 33.6%, a silicon dioxide content of 0.15%, iron oxide, calcium oxide, and phosphorus pentoxide contents are all below the detection limit, the sulfate content is 0.52%, the wet water content is 0.12%, and the ignition loss is 1.3%. The contents of each index meet the requirements of "GB / T 4291-2017 Cryolite》CH-1 brand requirements; after drying, the ammonium sulfate product has a nitrogen content of 20.8%, a sulfur content of 24.5%, a free acid (H2SO4) content of 0.001%, a moisture content of 0.13%, a water-insoluble matter content of 0.22%, a chloride ion content of 0.05%, a fluorine content of 12 mg / kg, and the total amount of thiocyanate ions and polycyclic aromatic hydrocarbons are all below the detection limit. The mercury content is 0.02 mg / kg, the arsenic content is 0.05 mg / kg, the cadmium content is 0.11 mg / kg, the lead content is 1.5 mg / kg, and the chromium content is 2.6 mg / kg. The contents of each indicator meet the index requirements of Type I products of "GB / T 535-2020 Fertilizer Grade Ammonium Sulfate"; in addition, the fluorine content in the third waste liquid is 1.5 mg / L, which greatly reduces the corrosion of fluoride ions on subsequent evaporators.

[0072] Example 2

[0073] The main components of the BOE waste liquid in this example are ammonium fluorosilicate 3.58% (wt), ammonium fluoride 18.36% (wt), hydrofluoric acid 0.48% (wt), sulfate 46300 mg / L, chloride 529 mg / L, heavy metals (Pb) 70 mg / L, density 1.18 g / cm -3 The specific processing methods are as follows:

[0074] (1) Weigh 627 g of sodium sulfate decahydrate, dissolve it in 1500 g of water, and add it to 1 L of BOE waste liquid at a feed rate of 50 mg / L. After the addition is completed, react for 30 minutes and filter to obtain sodium fluorosilicate and a first waste liquid;

[0075] (2) Weigh 375 g of aluminum sulfate 18hydrate, dissolve it in 1000 g of water, and add it to the first waste liquid at a feed rate of 40 mg / L. After the addition is completed, add solid ammonium bicarbonate, adjust the pH value of the waste liquid to 4.5, react for 2 h, and filter to obtain cryolite and the second waste liquid;

[0076] (3) The fluorine content of the second waste liquid was determined to be 1189 mg / L, and the heavy metal content (in terms of Pb) was 66 mg / L. 20.8 g of a defluorinating agent and 3.5 g of a heavy metal trapping agent were added, and the mixture was reacted for 30 min and then filtered to obtain the first waste residue and the third waste liquid;

[0077] (4) adding sulfuric acid to the third waste liquid to adjust the pH of the third waste liquid to 3, evaporating and crystallizing to obtain evaporated condensed water and concentrated liquid;

[0078] (5) cooling the concentrated solution to room temperature and filtering to obtain ammonium sulfate and a final mother liquor;

[0079] (6) The third waste liquor and the final mother liquor are returned to the front end for preparing sodium sulfate solution and aluminum sulfate solution.

[0080] In this embodiment, the purity of the sodium fluorosilicate product after drying can reach 98.7%, the free acid content (calculated as HCl) is 0.08%, the drying loss is 0.1%, the chloride content is 0.02%, the water-insoluble matter content is 0.18%, the sulfate content is 0.27%, the iron content and the phosphorus pentoxide content are both below the detection limit, and the heavy metal (calculated as Pb) is 0.0002%. The contents of each index meet the requirements of Type I first-class products of "GB / T 23936-2018 Industrial Sodium Fluorosilicate"; after washing and drying, the cryolite product has a fluorine content of 53.2%, an aluminum content of 13.1%, a sodium content of 32.3%, a silicon dioxide content of 0.18%, iron oxide, calcium oxide, and phosphorus pentoxide contents are all below the detection limit, the sulfate content is 0.38%, the wet water content is 0.13%, and the ignition loss is 1.6%. The contents of each index meet the requirements of "GB / T 4291-2017 Cryolite》CM-0 brand requirements; after drying, the ammonium sulfate product has a nitrogen content of 20.6%, a sulfur content of 25.2%, a free acid (H2SO4) content of 0.01%, a moisture content of 0.12%, a water-insoluble matter content of 0.18%, a chloride ion content of 0.04%, a fluorine content of 23 mg / kg, and the total amount of thiocyanate ions and polycyclic aromatic hydrocarbons are all below the detection limit. The mercury content is 0.02 mg / kg, the arsenic content is 0.04 mg / kg, the cadmium content is 0.13 mg / kg, the lead content is 0.8 mg / kg, and the chromium content is 1.9 mg / kg. The contents of each indicator meet the index requirements of Type I products of "GB / T 535-2020 Fertilizer Grade Ammonium Sulfate"; in addition, the fluorine content in the third waste liquid is 2.3 mg / L, which greatly reduces the corrosion of fluoride ions on subsequent evaporators.

[0081] Example 3

[0082] The main components of the BOE waste liquid in this example are 9.66% (wt) ammonium fluorosilicate, 10.28% (wt) ammonium fluoride, 0.52% (wt) hydrofluoric acid, 368 mg / L sulfate, 17400 mg / L chloride, 95 mg / L heavy metals (Pb), and a density of 1.15 g / cm -3 The specific processing methods are as follows:

[0083] (1) Weighing 210 g of sodium chloride, dissolving it in 600 g of water, and adding it to 1 L of BOE waste liquid at a feed rate of 30 mg / L. After the addition is completed, react for 30 minutes, and filter to obtain sodium fluorosilicate and the first waste liquid;

[0084] (2) Weigh 170 g of aluminum chloride hexahydrate, dissolve it in 400 g of water, and add it to the first waste liquid at a feed rate of 20 mg / L. After the addition is completed, add ammonia water to adjust the pH value of the waste liquid to 7.0, react for 2 h, and filter to obtain cryolite and the second waste liquid;

[0085] (3) The fluorine content of the second waste liquid was determined to be 155 mg / L, and the heavy metal content (in terms of Pb) was 38 mg / L. 1.0 g of a defluorinating agent and 0.8 g of a heavy metal trapping agent were added, and the mixture was reacted for 30 min and then filtered to obtain the first waste residue and the third waste liquid;

[0086] (4) adding hydrochloric acid to the third waste liquid to adjust the pH of the third waste liquid to 2, evaporating and crystallizing to obtain evaporated condensed water and concentrated liquid;

[0087] (5) cooling the concentrated solution to room temperature and filtering to obtain ammonium chloride and a final mother liquor;

[0088] (6) The third waste liquor and the final mother liquor are returned to the front end for preparing sodium chloride solution and aluminum chloride solution.

[0089] In this embodiment, the purity of the sodium fluorosilicate product after drying can reach 98.6%, the free acid content (calculated as HCl) is 0.08%, the drying loss is 0.23%, the chloride content is 0.18%, the water-insoluble matter content is 0.25%, the sulfate content is 0.01%, the iron content and the phosphorus pentoxide content are both below the detection limit, and the heavy metal (calculated as Pb) is 0.0002%. The contents of each index meet the requirements of Type I first-class products of "GB / T 23936-2018 Industrial Sodium Fluorosilicate"; after washing and drying, the cryolite product has a fluorine content of 53.1%, an aluminum content of 13.5%, a sodium content of 32.7%, a silicon dioxide content of 0.13%, iron oxide, calcium oxide, and phosphorus pentoxide contents are all below the detection limit, the sulfate content is 0.01%, the wet water content is 0.11%, and the ignition loss is 2.2%. The contents of each index meet the requirements of "GB / T The ammonium chloride product has a nitrogen content of 23.7%, a water content of 8.2%, a sodium content of 1.4%, an arsenic content of 0.000002%, a cadmium content of 0.000015%, a lead content of 0.00013%, a chromium content of 0.00016%, and a mercury content of 0.000001%. All indicators meet the requirements of qualified products in GB / T 2946-2018 Ammonium Chloride. In addition, the fluorine content in the third waste liquid is 0.56 mg / L, which greatly reduces the corrosion of fluoride ions on subsequent evaporators.

[0090] Example 4

[0091] The main components of the BOE waste liquid in this example are 9.66% (wt) ammonium fluorosilicate, 10.28% (wt) ammonium fluoride, 0.52% (wt) hydrofluoric acid, 368 mg / L sulfate, 17400 mg / L chloride, 95 mg / L heavy metals (Pb), and a density of 1.15 g / cm -3 The specific processing methods are as follows:

[0092] (1) Weigh 192 g of sodium chloride, dissolve it in 600 g of water, and add it to 1 L of BOE waste liquid at a feed rate of 30 mg / L. After the addition is completed, react for 30 minutes and filter to obtain sodium fluorosilicate and the first waste liquid;

[0093] (2) Weigh 155 g of aluminum chloride hexahydrate, dissolve it in 400 g of water, and add it to the first waste liquid at a feed rate of 20 mg / L. After the addition is completed, add sodium carbonate solid, adjust the pH value of the waste liquid to 4.0, react for 2 h, and filter to obtain cryolite and the second waste liquid;

[0094] (3) The fluorine content of the second waste liquid was determined to be 2350 mg / L, and the heavy metal content (in terms of Pb) was 86 mg / L. 45 g of a defluorinating agent and 3.0 g of a heavy metal trapping agent were added, and the mixture was reacted for 30 min and then filtered to obtain the first waste residue and the third waste liquid;

[0095] (4) adding hydrochloric acid to the third waste liquid to adjust the pH of the third waste liquid to 3.5, evaporating and crystallizing to obtain evaporated condensed water and concentrated liquid;

[0096] (5) cooling the concentrated solution to room temperature and filtering to obtain ammonium chloride and a final mother liquor;

[0097] (6) The third waste liquid and the final mother liquor are returned to the front end for preparing sodium chloride solution and aluminum chloride solution.

[0098] In this embodiment, the purity of the sodium fluorosilicate product after drying can reach 98.8%, the free acid content (calculated as HCl) is 0.06%, the drying loss is 0.19%, the chloride content is 0.16%, the water-insoluble matter content is 0.21%, the sulfate content is 0.01%, the iron content and the phosphorus pentoxide content are both below the detection limit, and the heavy metal (calculated as Pb) is 0.0003%. The contents of each index meet the requirements of Type I first-class products of "GB / T 23936-2018 Industrial Sodium Fluorosilicate"; after washing and drying, the cryolite product has a fluorine content of 52.2%, an aluminum content of 12.3%, a sodium content of 33.3%, a silicon dioxide content of 0.16%, iron oxide, calcium oxide, and phosphorus pentoxide contents are all below the detection limit, the sulfate content is 0.013%, the wet water content is 0.12%, and the ignition loss is 1.1%. The contents of each index meet the requirements of "GB / T The ammonium chloride product has a nitrogen content of 23.8%, a water content of 7.8%, a sodium content of 1.2%, an arsenic content of 0.000003%, a cadmium content of 0.00002%, a lead content of 0.00018%, a chromium content of 0.00019%, and a mercury content of 0.000002%. All indicators meet the requirements of qualified products in GB / T 2946-2018 Ammonium Chloride. In addition, the fluorine content in the third waste liquid is 1.22 mg / L, which greatly reduces the corrosion of fluoride ions on subsequent evaporators.

[0099] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for recycling BOE waste liquid, characterized in that: The following steps are involved: S1, dissolving sodium salt to obtain a sodium salt solution, adding the sodium salt solution to the BOE waste liquid, reacting for 30 minutes, and then filtering to obtain sodium fluorosilicate and the first waste liquid; S2, dissolving aluminum salt to obtain an aluminum salt solution, adding the aluminum salt solution to the first waste liquid, and adjusting the pH of the first waste liquid to 4-7 with a first pH adjuster, reacting for 1-2 hours, and then filtering to obtain cryolite and a second waste liquid; S3, adding a defluorinating agent and a heavy capture agent to the second waste liquid, reacting for 30 minutes and then filtering to obtain a first waste residue and a third waste liquid, and disposing the first waste residue into a landfill; S4, adding a second pH regulator to the third waste liquid to adjust the pH of the third waste liquid to 2-4, evaporating and crystallizing to obtain evaporated condensed water and concentrated liquid, and biochemically treating the evaporated condensed water to meet the standards before discharging; S5, pumping the concentrated solution into a cooling crystallization tank and cooling it to 40° C., and then centrifuging to obtain ammonium salt and final mother liquor; S6, returning the third waste liquid and the final mother liquor to S1 and S2 for circulation, and being used for preparing the sodium salt solution and the aluminum salt solution; Wherein, the defluoridating agent includes one or more of aluminum chloride, polyaluminum chloride, aluminum sulfate, hydroxyapatite, magnesium chloride and magnesium sulfate; The second pH adjuster is hydrochloric acid or sulfuric acid.

2. The method for recycling BOE waste liquid according to claim 1, wherein: The sodium salt includes one or more of sodium chloride, sodium sulfate, sodium carbonate and sodium bicarbonate, and the amount of the sodium salt added (calculated as sodium) is calculated based on the sodium required to completely remove the fluorosilicate and fluoride in the BOE waste liquid and precipitate sodium fluorosilicate and sodium hexafluoroaluminate, with an excess coefficient of 1-1.2 times.

3. The resource recovery treatment method for BOE waste liquid according to claim 1, characterized in that: The aluminum salt includes one or more of aluminum chloride, aluminum sulfate and sodium metaaluminate, and the amount of the aluminum salt added (calculated as aluminum) is calculated based on the aluminum required to completely remove fluoride in the first waste liquid and precipitate sodium hexafluoroaluminate, with an excess coefficient of 1-1.2 times.

4. The method for recycling BOE waste liquid according to claim 1, wherein: The first pH adjuster includes one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, ammonia water, ammonium bicarbonate and ammonium carbonate.

5. The resource recovery treatment method for BOE waste liquid according to claim 1, characterized in that: The S1 and S2 further include washing and drying the sodium fluorosilicate and the cryolite respectively.

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