Method for high-value utilization of sodium aluminum fluorochlorate in secondary aluminum ash wet pretreatment solution

Abstract

The invention provides a method for high-value utilization of sodium aluminum fluorochlorate in a secondary aluminum ash wet pretreatment solution, and relates to the field of secondary aluminum ash resourceful treatment. The method specifically comprises the following steps: adding secondary aluminum ash into an aqueous solution, carrying out controllable reaction, carrying out wet pretreatment on the secondary aluminum ash, and filtering slurry, so as to obtain a solution containing fluorine, chlorine, aluminum and sodium ions besides high-aluminum slag; adding an additive into the solution, carrying out controllable precipitation and enhanced crystallization, precipitating coarse and well-crystallized sodium hexafluoroaluminate (cryolite), and carrying out solid-liquid separation to obtain cryolite; and performing membrane concentration on the filtrate to obtain a high-concentration sodium chloride solution, and performing concentration or evaporative crystallization on the high-concentration sodium chloride solution to obtain a sodium chloride solid which can be used as a caustic soda industrial raw material. According to the method, sodium, aluminum, fluorine, chlorine and other elements in the secondary aluminum ash wet pretreatment liquid are efficiently, safely and comprehensively utilized, solution circulation is achieved, the negative effects of fluorine and chlorine on subsequent aluminum oxide production and aluminum oxide-based material preparation are reduced, and safe and full-quantitative utilization of the secondary aluminum ash is promoted.

Description

Technical Field

[0001] The present invention relates to the field of resource treatment of secondary aluminum ash, and particularly to a method for highly valorizing sodium, aluminum, fluoride, and chloride in a wet pretreatment solution of secondary aluminum ash. Background Art

[0002] Secondary aluminum ash is a hazardous solid waste with complex components generated in the processes of aluminum electrolysis, aluminum processing, and aluminum recycling. Its main components include valuable substances such as aluminum oxide and metallic aluminum, and at the same time, it also contains harmful components such as aluminum nitride, fluorides, and chlorides. With the rapid development of the aluminum industry, the amount of secondary aluminum ash has increased significantly, and the problems of safe disposal and comprehensive utilization of secondary aluminum ash have become increasingly prominent, which has become one of the important factors hindering the sustainable development of the aluminum industry.

[0003] At present, wet pretreatment of secondary aluminum ash for denitrification and desalination is a commonly used method in China. However, the pretreatment solution contains elements such as sodium, aluminum, fluoride, and chloride, with large differences and fluctuations in the concentrations of each element, making it difficult to be economically and highly valorized. Among them, fluoride is a toxic element, while sodium and chloride are low-valence elements, and aluminum is a common element, so safe and highly valorized utilization is even more difficult. For the problem of removing fluoride ions from industrial wastewater, chemical precipitation, coagulation precipitation, and adsorption methods are commonly used in industrial applications. In actual production, calcium salts (such as calcium oxide, calcium hydroxide, and calcium chloride) are mainly used for chemical precipitation to remove fluoride, generating insoluble calcium fluoride precipitate, thereby realizing the separation and removal of fluoride ions from the wastewater. Patent CN202111428343 proposes a method for recycling fluoride in fluoride-containing wastewater based on calcium fluoride-induced precipitation. Calcium chloride is added according to the molar ratio n(Ca 2 + / F-) = 1.0, and then the coagulant aid polyacrylamide (PAM) is added. This method can reduce the fluoride ion concentration in the effluent to below 10 mg / L, the moisture content of the sludge to below 50%, and the calcium fluoride content to above 80%. However, in actual production, the fluoride concentration in the solution after defluorination is high, making it difficult to meet the discharge requirements. Patent CN202310459043 discloses a method for treating fluoride-containing wastewater based on the combination of natural mineral-induced precipitation and multi-stage adsorption. Soluble calcium salts and lanthanum salts are added as precipitants, and fluorite and calcite are introduced as induced crystal nuclei. The filtrate passes through a first adsorption column filled with calcite and a second adsorption column filled with a porous adsorbent in sequence, and finally the fluoride content of the treated solution is lower than 7 mg / L. This method requires precise control of multiple parameters, and the process is complex. In short, when only calcium salts are added, the dosage needs to be 3 - 4 times the theoretical value, the precipitation is difficult to filter, the defluorinated solution is difficult to meet the national standard requirements (the defluorination rate is less than 99%), the impure calcium fluoride is difficult to be further resourcefully utilized, the cost of safe landfill is high, and the secondary environmental risk is large. To meet the discharge requirements, it is usually necessary to combine with precipitation and adsorption methods and perform multi-stage treatment to achieve the purpose of deep defluorination, and the process is complex.

[0004] In the reports on the treatment of wastewater containing chloride salts, Patent CN202311438273 discloses a method for reducing chloride ions in lithium sulfate-containing wastewater at low cost. By adding a copper sulfate solution to the wastewater and controlling the Cu:Cl molar ratio, and reacting with a reducing agent to generate cuprous chloride slag for dechlorination. This method effectively reduces the chloride ion concentration, but the cost is high. Patent CN201611243285 proposes an electrochemical reactor and a method for electrocatalytic removal of chloride ions. By designing a special electrochemical reactor to efficiently treat high-concentration chloride ions in wastewater, the anode of the reactor is composed of a refractory metal mesh basket and Ru-Ti-AC catalytic material filled therein. After reacting for 0.1 - 2 h, efficient degradation of chloride ions can be achieved. The preparation process of the catalytic material in this method is complex and the cost is relatively high.

[0005] In addition, in the synchronous treatment of wastewater containing fluorochloride salts, Patent CN202310190459 discloses a method for synergistic defluorination and dechlorination of acidic fluorine- and chlorine-rich wastewater in the photovoltaic industry. The concentrated acid wastewater is pumped into the reaction tank, and NaOH and NaAlO 2 are added to generate cryolite precipitate. After solid-liquid separation, dehydration and drying, cryolite products are obtained. The supernatant is mixed with concentrated alkali, dilute acid, and dilute alkali wastewater, and an iron- and manganese-doped sludge carbon material electrode is used to optimize the dechlorination effect. After further deep defluorination, the effluent is ensured to meet the standards for fluoride ions and chloride ions before being discharged. The fluoride ion content in the effluent of this method can be reduced to 1 - 2 mg / L, and the chloride ion content is less than 200 mg / L, meeting the national discharge standards. At the same time, cryolite products are recovered. However, the preparation process of the iron- and manganese-doped sludge carbon material electrode is complex and the cost is high. Patent CN113930624A discloses a method for removing fluorine and chlorine during the first-stage active controllable dissolution process of secondary aluminum ash, but this method adds additives such as water glass or kaolin, and seeds are used to prepare coarse-grained fluorinated salts for the defluorination process of fluorine- and chlorine-containing waste liquid. Chlorine cannot be reused, and the defluorination rate is between 40 - 70%.

[0006] Since the pH > 7, the composition is complex, the composition fluctuates greatly, and there are few valuable elements in the solution after wet pretreatment of secondary aluminum ash. Therefore, there are few reports on the treatment methods for high-concentration fluorine-, chlorine-, aluminum-, and sodium-containing waste liquid obtained from wet pretreatment of secondary aluminum ash. And due to different systems, the above-reported treatment methods for fluorine-, chlorine-, aluminum-, and sodium-containing waste liquid are not applicable to the high-value utilization of fluorine, chlorine, aluminum, and sodium elements in the wet pretreatment solution of secondary aluminum ash. Summary of the Invention

[0007] The present invention provides a method for high-value utilization of sodium fluoroaluminate chloride in the wet pretreatment solution of secondary aluminum ash, aiming to solve the above problems existing in the background technology.

[0008] To achieve the above object, an embodiment of the present invention provides a method for highly valuing the utilization of sodium fluorochloroaluminate in the wet pretreatment liquid of secondary aluminum ash, which specifically includes: adding secondary aluminum ash into an aqueous solution, carrying out a controllable reaction, wet-preprocessing the secondary aluminum ash, filtering the slurry, and in addition to obtaining high-aluminum slag, obtaining a solution containing sodium, fluorine, chlorine and aluminum ions; adding an additive to this solution, carrying out controllable precipitation, strengthening crystallization, and precipitating sodium hexafluoroaluminate (cryolite, Na 3 AlF 6 ) which is better than coarser crystallization. After solid-liquid separation, cryolite is obtained; the filtrate is concentrated by a membrane method to obtain a high-concentration sodium chloride solution, and the high-concentration sodium chloride solution is further concentrated or evaporated to crystallize to obtain sodium chloride solid, which can be used as a raw material for the caustic soda industry. The present invention comprehensively utilizes elements such as sodium, aluminum, fluorine and chlorine in the wet pretreatment liquid of secondary aluminum ash efficiently and safely, realizes solution recycling, reduces the negative impacts of fluorine and chlorine on subsequent alumina production and the preparation of alumina-based materials, and promotes the safe and total utilization of secondary aluminum ash.

[0009] An embodiment of the present invention provides a method for highly valuing the utilization of sodium fluorochloroaluminate in the wet pretreatment liquid of secondary aluminum ash, including the following steps:

[0010] S1: Add secondary aluminum ash into an aqueous solution for a controllable reaction and fluorochloro leaching (pretreatment), and after the reaction, the slurry is subjected to solid-liquid separation to obtain high-aluminum slag and a solution containing aluminum, sodium, fluorine and chlorine ions;

[0011] S2: Add an additive and cryolite seeds into the solution containing aluminum, sodium, fluorine and chlorine ions, and then add acid to adjust the pH for precipitation reaction, and obtain cryolite and filtrate through vacuum filtration; the purpose of the controllable precipitation process is to strengthen the agglomeration of fine particles and promote the growth of high-purity cryolite;

[0012] S3: Concentrate the filtrate in step S2 by a membrane method to obtain a high-concentration sodium chloride solution, concentrate or evaporate and crystallize the high-concentration sodium chloride solution to precipitate sodium chloride, and use it for the caustic soda industry.

[0013] Preferably, in step S1, in the controllable reaction process: the total amount of secondary aluminum ash is less than 300 g / L, and the amount added each time is less than 30 g / L; or, using the previous pretreatment liquid as the solution, continue to add secondary aluminum ash, and the controllable reaction is two-stage or three-stage reverse wet pretreatment. When performing the latter-stage or the latter two-stage wet pretreatment, the total amount of secondary aluminum ash is less than 200 g / L, and the amount added each time is less than 30 g / L.

[0014] Preferably, in step S1, the aqueous solution is an aqueous solution containing 0-10 g / L of sodium hydroxide, and the temperature of the aqueous solution is lower than 80 °C.

[0015] Preferably, in step S1, the reaction temperature is less than 80 °C, and the reaction time is less than 180 min; after the reaction, the temperature is raised to 95-100 °C, and stirring is continued for 0-5 h.

[0016] Preferably, in step S2, the additive includes at least one of sodium fluoride and hydrofluoric acid, and the dosage of the additive is such that the molar ratio of fluorine to aluminum in the sodium fluoroaluminate chloride solution is 6:1; the addition amount of the seed crystal is based on the mass ratio of the fluorine content of the seed crystal to the fluorine in the solution being 0 to 6:1.

[0017] Preferably, in step S2, hydrochloric acid or a mixed solution of hydrochloric acid and hydrofluoric acid is added to adjust the pH value to 5 to 9. The addition rate of hydrochloric acid increases with the increase in the cryolite solid content (seed crystal and newly precipitated cryolite) in the solution; the reaction temperature is 10 to 50 °C; the stirring speed is less than 100 r / min, and more preferably 50 r / min.

[0018] Preferably, in step S2, the aging time during the cryolite precipitation process is 0 to 10 h, the cryolite is coarse-grained, and the median diameter d50 > 4 μm; the defluorination rate of the filtrate is greater than 99%, and the concentrations of fluorine and aluminum ions in the filtrate after defluorination are both less than 20 mg / L, and the sodium chloride concentration is less than or equal to 20 g / L.

[0019] Preferably, in step S3, the membrane concentration process includes: controlling the membrane stack voltage to be less than 25 V, the volume ratio of the chlorine-containing salt waste liquid in the concentrated water tank to the desalted liquid tank to be 1:2 to 1:3, and the influent flow rate to be less than 300 L / h. Through one-stage electrodialysis, the chlorine-containing salt wastewater in the concentrated water tank is concentrated to a salt concentration of more than 60 g / L, and the chlorine-containing salt wastewater in the desalted liquid tank is desalinated to less than 800 mg / L; it also includes:

[0020] Performing secondary electrodialysis on the concentrated chlorine-containing salt wastewater to obtain a high-concentration sodium chloride solution, controlling the membrane stack voltage to be less than 25 V, the volume ratio of the chlorine-containing salt wastewater in the concentrated water tank to the desalted liquid tank to be 1:2 - 1:3, and the influent flow rate to be less than 300 L / h. The secondary electrodialysis concentrates the chlorine-containing salt wastewater in the concentrated water tank to a salt concentration of more than 110 g / L.

[0021] Preferably, all the washing liquids and separated water generated in steps S1 to S3 are recycled and not discharged externally.

[0022] This invention combines the research results of the inventors on the safe and high-value utilization of the sodium fluoroaluminate chloride waste liquid in the wet pretreatment of secondary aluminum ash, and specifically discovers:

[0023] (1) By controlling the addition amount of secondary aluminum ash, reaction temperature, and stirring rate, a controllable reaction wet pretreatment of secondary aluminum ash is achieved, ensuring the stable and safe escape of harmful gases and a high fluorine and chlorine leaching rate; adopting two-stage or three-stage reverse wet pretreatment can significantly increase the concentration of sodium fluoroaluminate chloride in the pretreatment liquid.

[0024] (2) After the controllable reaction of secondary aluminum ash, the slurry is further heated to 90 - 100 °C and stirred for a period of time, which can further increase the leaching rate of fluorine and chlorine.

[0025] (3) Cryolite with good crystallization and coarse particle size has a low solubility, which can improve the defluorination rate; the aging of the cryolite slurry can reduce the amount of nanoparticles, reduce the liquid adhering amount of cryolite, reduce the washing water amount, and at the same time, promote filtration.

[0026] (4) The agglomeration rate should match the amount of crystal seeds and the newly precipitated cryolite. The newly precipitated cryolite has high reactivity, can bond fine particles, promote the agglomeration of fine particles, inhibit the large production of dispersed nano-cryolite, and realize the controllable precipitation of cryolite;

[0027] (5) After the cryolite slurry is aged, the particle size increases. As the aging time prolongs, the particle size increases greatly ( Figure 4 ).

[0028] (6) Ensuring the fluorine-aluminum ratio of the solution and matching the addition rate of hydrochloric acid are the keys to precipitating pure cryolite;

[0029] (7) The defluorination rate is greater than 99%, and the fluorine concentration in the solution after defluorination is less than 20 mg / L; this ensures the safe operation of the equipment in the membrane method for concentrating sodium chloride solution.

[0030] The above-mentioned solutions of the present invention have the following beneficial effects:

[0031] (1) Safe and effective removal of harmful elements such as fluorine and chlorine in secondary aluminum ash: Using wet pretreatment of secondary aluminum ash can safely and effectively remove 100% of chlorine and 50% of fluorine in secondary aluminum ash, obtain high-aluminum slag with low fluorine and no chlorine, and significantly reduce the negative impact of fluorine and chlorine on the subsequent resource utilization of high-aluminum slag;

[0032] (2) High-value synchronous utilization of fluorine, aluminum, and sodium: The controllable precipitation of cryolite adopted in the present invention realizes the efficient synchronous utilization of fluorine, aluminum, and sodium elements in the waste liquid, and prepares cryolite products with high added value, and the product purity is greater than 98%.

[0033] (3) Low-cost resource utilization of sodium chloride: Using the combined technology of electrodialysis concentration-evaporation crystallization can more effectively improve the crystallization efficiency of sodium chloride compared with multi-effect evaporation for concentrating sodium chloride-containing wastewater, reduce investment, and lower production costs. At the same time, the concentrated sodium chloride solution can be directly used in the caustic soda industry, and sodium chloride is utilized with a short process and low cost.

[0034] (4) No wastewater discharge: High-value utilization of fluorine and chlorine-containing waste liquid, and all washing liquid and desalting liquid are recycled, without discharging fluorine-containing wastewater, and there is no secondary environmental risk.

[0035] (5) Easy to industrialize and promote the safe comprehensive utilization of secondary aluminum ash: The process is relatively simple and the investment is small. Especially combined with the existing sintering method for using secondary aluminum ash or strong acid (alkali) for using secondary aluminum ash, it can significantly reduce the fluorine and chlorine content in the materials of subsequent processes, reduce environmental risks, and will greatly promote the safe comprehensive utilization of secondary aluminum ash. Description of the Drawings

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0037] Figure 1 is a process flow diagram of a method for highly utilizing sodium fluorochloroaluminate in the wet pretreatment liquid of secondary aluminum ash according to an embodiment of the present invention;

[0038] Figure 2 is the XRD pattern of cryolite prepared according to an embodiment of the present invention;

[0039] Figure 3 is the SEM image of cryolite prepared according to an embodiment of the present invention;

[0040] Figure 4 is the particle size diagram of cryolite prepared according to an embodiment of the present invention. Detailed Embodiments

[0041] To make the technical problems, technical solutions, and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the drawings and specific embodiments.

[0042] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0043] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through the market or prepared by existing methods.

[0044] The "seed crystal" mentioned in this article is an active cryolite seed crystal or a recycled cryolite seed crystal prepared from laboratory analytical pure sodium hexafluoroaluminate as the raw material.

[0045] In view of the existing problems, the present invention provides a method for highly utilizing sodium fluorochloroaluminate in the wet pretreatment liquid of secondary aluminum ash. The process flow schematic diagram is as Figure 1 shown.

[0046] Example 1

[0047] This example provides a method for highly utilizing sodium fluorochloroaluminate in the wet pretreatment liquid of secondary aluminum ash.

[0048] The method of this example includes the following steps:

[0049] (1) Wet process controllable reaction for impurity removal: Divide 100 g of secondary aluminum ash into four equal parts and add them to 1 L of a NaOH solution with a concentration of 7 g / L at 40 °C. At a reaction temperature of 80 °C and a stirring speed of 300 revolutions per minute (rpm), carry out the reactions of aluminum nitride and aluminum and the leaching (pretreatment) of fluorine and chlorine. When the reaction time is 80 min, a secondary aluminum ash slurry is obtained; continue to heat up to 95 °C and keep it warm for 4 h. After solid-liquid separation, a high-aluminum slag and a waste liquid containing sodium fluoroaluminate (pretreatment liquid) are obtained. The high-aluminum slag is used for Bayer process digestion. The composition of the waste liquid containing fluorine and chlorine is: F-: 3.014 g / L, Cl - : 3.327 g / L, Al 3+ : 1.058 g / L, Na + : 5.80 g / L, pH 12.45.

[0050] (2) Controllable precipitation of cryolite for fluorine removal: Add 3.21 g of sodium fluoride to 1 L of the waste liquid containing fluorine and chlorine to adjust the molar ratio of fluorine to aluminum to 6:1. Add seeds according to the ratio of the fluorine content of the seeds to the fluorine mass in the solution of 0.5:1. Then place it in a water bath at 25 °C. At a stirring speed of 20 r / min, slowly drop a mixed solution of 4 mol / L HCl and 10% HF into the waste liquid containing fluorine and chlorine at a rate of 0.5 mL / min until the pH value of the waste liquid reaches 7; the slurry is aged at 25 °C for 5 h; after vacuum filtration, a filter cake and defluorinated chlorine-containing wastewater are obtained. The filter cake is dried to obtain cryolite ( Figure 2 ), and the cryolite has good original crystal crystallization after agglomeration ( Figure 3 ) and relatively coarse particle size; the measured residual fluorine and aluminum ion concentrations in the defluorinated chlorine-containing wastewater are 13.46 mg / L and 11.63 mg / L respectively, and the utilization rates of fluorine and aluminum are 99.55% and 98.90% respectively.

[0051] (3) Electrodialysis-evaporation to precipitate chlorides: Carry out electrodialysis concentration on the defluorinated chlorine-containing salt wastewater at room temperature. At a membrane stack voltage of 25 V, a volume ratio of sodium chloride solution in the concentrated water tank to the desalted liquid tank of 1:2, and an inlet flow rate of 300 L / h, after one-stage electrodialysis, the sodium chloride solution in the concentrated water tank can be enriched to a sodium chloride concentration of 59.81 g / L, and the sodium chloride solution in the desalted liquid tank is desalinated to 790 mg / L. Set the same parameters and carry out secondary electrodialysis on the sodium chloride solution concentrated by one-stage electrodialysis. The secondary electrodialysis concentrates the sodium chloride solution in the concentrated water tank to a salt concentration of 112.98 g / L. Then heat and evaporate the high-concentration sodium chloride solution to above 400 g / L, cool it to 25 °C and crystallize to obtain solid sodium chloride, which can be used as a raw material for the caustic soda industry or as a chemical raw material after drying.

[0052] Example 2

[0053] This example provides a method for highly valuing the utilization of sodium fluoroaluminate in the wet pretreatment liquid of secondary aluminum ash.

[0054] The method of this embodiment includes the following steps:

[0055] (1) Wet process controllable reaction for impurity removal: Divide 100 g of secondary aluminum ash into five equal parts, and add them to 1 L of NaOH solution with a concentration of 3 g / L at 25°C respectively. At a reaction temperature of 75°C and a stirring speed of 300 rpm, carry out the reactions of aluminum nitride and aluminum and the leaching of fluorine and chlorine. When the reaction time is 60 min, obtain a secondary aluminum ash slurry, and through solid-liquid separation, obtain high-aluminum slag and fluorine- and chlorine-containing waste liquid; the high-aluminum slag is used for Bayer process digestion, and the composition of the fluorine- and chlorine-containing waste liquid is: F - : 3.028 g / L, Cl - : 3.316 g / L, Al 3+ : 1.055 g / L, Na + : 5.808 g / L, pH 11.07.

[0056] (2) Controllable precipitation of cryolite for fluorine removal: Add 3 g of sodium fluoride and 2.2 mL of 40% hydrofluoric acid to 1 L of the fluorine- and chlorine-containing waste liquid to maintain a fluorine-aluminum molar ratio of 6:1. Add seeds according to a ratio of 1:1 of the fluorine content of the seeds and the fluorine mass in the solution, and then place it in a water bath at a temperature of 35°C with a stirring speed of 50 rpm. Drop 2 mol / L HCl into the fluorine- and chlorine-containing waste liquid at a rate of 1 mL / min relatively quickly until the pH value of the waste liquid reaches 7; the cryolite slurry is further aged for 5 h with a stirring speed of 10 rpm. After vacuum filtration, obtain a filter cake and fluorine-removed chlorine-containing wastewater. The filter cake is dried to obtain cryolite. The measured remaining fluorine and aluminum ion concentrations in the fluorine-removed chlorine-containing wastewater are 9.15 mg / L and 10.22 mg / L respectively, and the utilization rates of fluorine and aluminum are 99.70% and 99.03% respectively. The particle size d50 of the cryolite is 4.27 μm, with good crystallization and easy filtration.

[0057] (3) Electrodialysis-evaporation for precipitation of chlorides: Carry out electrodialysis concentration on the fluorine- and chlorine-containing salt wastewater at room temperature. At a membrane stack voltage of 20 V, a volume ratio of sodium chloride solution in the concentrated water tank to the desalinated liquid tank of 1:3, and an influent flow rate of 200 L / h, after one-time electrodialysis, the sodium chloride solution in the concentrated water tank can be enriched to a sodium chloride concentration of 69.35 g / L, and the sodium chloride solution in the desalinated liquid tank is desalinated to 337 mg / L. Set the same parameters and carry out secondary electrodialysis on the sodium chloride solution concentrated by one-time electrodialysis. The secondary electrodialysis concentrates the sodium chloride solution in the concentrated water tank to a salt concentration of 120.14 g / L, and directly sends the high-concentration sodium chloride solution to the caustic soda industry.

[0058] Example 3

[0059] This embodiment provides a method for highly utilizing fluorine, chlorine, aluminum, and sodium in the wet pretreatment liquid of secondary aluminum ash.

[0060] The method of this embodiment includes the following steps:

[0061] (1) Wet process controllable reaction for impurity removal: Divide 200 g of secondary aluminum ash into 8 equal parts, and add them to 1 L of NaOH solution with a concentration of 9 g / L at 25 °C. At a reaction temperature of 50 °C and a stirring speed of 300 rpm, carry out the reactions of aluminum nitride and aluminum and the leaching of fluorine and chlorine. When the reaction time is 120 min, a secondary aluminum ash slurry is obtained; heat the slurry to 98 °C and stir for 2 h, then carry out solid-liquid separation to obtain high-aluminum slag and fluorine- and chlorine-containing waste liquid. The high-aluminum slag is used for the production of alumina by the sintering method. The composition of the fluorine- and chlorine-containing waste liquid is: F-: 3.072 g / L, Cl - : 6.631 g / L, Al 3+ : 1.085 g / L, Na + : 8.05 g / L, pH 13.09.

[0062] (2) Controllable precipitation of cryolite for defluorination: Add 3.34 g of sodium fluoride to 1 L of fluorine- and chlorine-containing waste liquid to adjust the molar ratio of fluorine to aluminum to 6:1, with a seed crystal concentration of 0 g / L. Then place it in a water bath at 50 °C and slowly add 2 mol / L HCl dropwise at a rate of 0.2 mL / min under a stirring speed of 50 r / min until the pH value of the fluorine- and chlorine-containing waste liquid reaches 6; ripen the slurry at 50 °C for 10 h; carry out vacuum filtration to obtain a filter cake and defluorinated chlorine-containing wastewater. The filter cake is dried to obtain cryolite. The remaining fluorine and aluminum ion concentrations in the defluorinated chlorine-containing wastewater are measured to be 11.05 mg / L and 11.42 mg / L respectively. The utilization rates of fluorine and aluminum in the wastewater are 99.64% and 98.95% respectively. The particle size d50 of the cryolite is 7.27 μm, with good crystallization and easy filtration.

[0063] (3) Electrodialysis-evaporation for precipitation of chloride salts: Carry out electrodialysis concentration on the defluorinated chlorine-containing salt waste liquid at room temperature. At a membrane stack voltage of 20 V, a volume ratio of sodium chloride solution in the concentrated water tank to the desalted liquid tank of 1:3, and an influent flow rate of 250 L / h, after one-time electrodialysis, the sodium chloride solution in the concentrated water tank can be enriched to a sodium chloride concentration of 65.88 g / L, and the sodium chloride solution in the desalted liquid tank is desalinated to 455 mg / L. Set the same parameters and carry out secondary electrodialysis on the sodium chloride solution concentrated by one-time electrodialysis. The secondary electrodialysis concentrates the sodium chloride solution in the concentrated water tank to a salt concentration of 115.88 g / L, and then evaporate the high-concentration sodium chloride solution to more than 400 g / L, cool it to 15 °C and crystallize to obtain solid sodium chloride, which can be used as a raw material for the caustic soda industry after drying.

[0064] Example 4

[0065] This example provides a method for the high-value utilization of fluorine, chlorine, aluminum, and sodium in the wet pretreatment liquid of secondary aluminum ash.

[0066] The method of this example includes the following steps:

[0067] (1) Wet process controllable reaction for impurity removal: Divide 200 g of secondary aluminum ash into 10 equal parts and add them to water at 30 °C respectively. At a reaction temperature of 55 °C and a stirring speed of 300 rpm, carry out the reactions of aluminum nitride and aluminum and the leaching of fluorine and chlorine for 150 min; after the reaction, raise the temperature to 95 °C and continue stirring for 60 min. The obtained secondary aluminum ash slurry is subjected to solid-liquid separation to obtain high-aluminum slag and fluorine- and chlorine-containing waste liquid. Under the same leaching conditions, then add 200 g / L of secondary aluminum ash to this fluorine- and chlorine-containing waste liquid at 20 g / L for countercurrent two-stage leaching. The high-aluminum slag is used for preparing ceramics, and the composition of the high-concentration fluorine- and chlorine-containing waste liquid is: F - : 5.322 g / L, Cl-: 12.661 g / L, Al 3+ : 1.605 g / L, Na + 14.645 g / L, pH 10.2.

[0068] (2) Controllable precipitation of cryolite for defluorination: Add sodium fluoride and hydrofluoric acid to 1 L of fluorine- and chlorine-containing waste liquid to adjust the fluorine-aluminum molar ratio to 6:1. Add seeds according to the ratio of the fluorine content of the seeds to the fluorine mass in the solution of 4:1. Then place it in a water bath at 20 °C and, at a stirring speed of 50 r / min, quickly drip 3 mol / L HCl at 4 mL / min until the pH value of the fluorine- and chlorine-containing waste liquid reaches 8. The cryolite slurry is aged for 10 h at a stirring speed of 10 r / min. After vacuum filtration, filter cakes and defluorinated chlorine-containing wastewater are obtained. The filter cakes are dried to obtain cryolite. The measured remaining fluorine and aluminum ion concentrations in the defluorinated chlorine-containing wastewater are 17.35 mg / L and 12.14 mg / L respectively. The utilization rates of fluorine and aluminum in the waste liquid are 99.67% and 99.24% respectively. The particle size d50 of the cryolite is 8.72 μm, with good crystallization and easy filtration.

[0069] (3) Electrodialysis-evaporation for precipitation of chloride salts: Concentrate the defluorinated chlorine-containing salt wastewater by electrodialysis at room temperature. At a membrane stack voltage of 15 V, a volume ratio of sodium chloride solution in the concentrated water tank to the desalted liquid tank of 1:3, and an inlet flow rate of 150 L / h, after one-stage electrodialysis, the sodium chloride solution in the concentrated water tank can be enriched to a sodium chloride concentration of 75.18 g / L, and the sodium chloride solution in the desalted liquid tank is desalinated to 795 mg / L. Set the same parameters and carry out secondary electrodialysis on the sodium chloride solution concentrated by one-stage electrodialysis. The secondary electrodialysis concentrates the sodium chloride solution in the concentrated water tank to a salt concentration of 137.67 g / L. Then evaporate the high-concentration sodium chloride solution, cool it to 15 °C for crystallization to obtain solid sodium chloride, which can be used as a raw material for the caustic soda industry after drying.

[0070] The above is the preferred implementation mode of the present invention. It should be pointed out that for those of ordinary skill in the art in this technical field, without departing from the principle described in the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for high-value utilization of sodium fluorochloroaluminate in secondary aluminum ash wet pretreatment liquid, characterized in that: The steps include: S1: adding secondary aluminum ash into aqueous solution for controlled reaction and fluorine and chlorine leaching pretreatment, and the slurry after the reaction is subjected to solid-liquid separation to obtain high-aluminum slag and a solution containing aluminum, sodium, fluorine and chloride ions; S2: adding additives and cryolite seed crystals to the solution containing aluminum, sodium, fluorine and chloride ions, adding acid to adjust the pH to perform a precipitation reaction, and obtaining cryolite and a filtrate by vacuum filtration; S3: The filtrate of step S2 is concentrated by membrane method to obtain a high-concentration sodium chloride solution, and the high-concentration sodium chloride solution is concentrated or evaporated and crystallized to precipitate sodium chloride, which is used in the caustic soda industry.

2. The method for high-value utilization of sodium fluorochloroaluminate in secondary aluminum ash wet pretreatment liquid according to claim 1, characterized in that: In step S1, the controllable reaction process is: the total amount of secondary aluminum ash is less than 300g / L, and the amount added each time is less than 30g / L; or, the controllable reaction is a two-stage or three-stage reverse wet pretreatment, with the pretreatment liquid in the first stage as the solution, and secondary aluminum ash is added to continue the pretreatment, and the total amount of secondary aluminum ash in the second stage or the second two stages of wet pretreatment is less than 200g / L, and the amount added each time is less than 30g / L.

3. The method for high-value utilization of sodium fluorochloroaluminate in secondary aluminum ash wet pretreatment liquid according to claim 1, characterized in that: In step S1, the aqueous solution is an aqueous solution containing sodium hydroxide at a concentration of 0 to 10 g / L, and the temperature of the aqueous solution is lower than 80°C.

4. The method for high-value utilization of sodium chlorofluoroaluminate in secondary aluminum ash wet pretreatment liquid according to claim 1, characterized in that: In step S1, the reaction temperature is less than 80° C. and the reaction time is less than 180 min. After the reaction, the temperature is raised to 90-100° C. and stirring is continued for 0-5 h.

5. The method for high-value utilization of sodium chlorofluoroaluminate in secondary aluminum ash wet pretreatment liquid according to claim 1, characterized in that: In step S2, the additive includes at least one of sodium fluoride and hydrofluoric acid, and the amount of the additive is to satisfy the fluorine-aluminum molar ratio of 6:1 in the fluorine-containing sodium chloroaluminum solution; the amount of seed crystal added is 0 to 6:1 according to the mass ratio of fluorine content in the seed crystal to fluorine in the solution.

6. The method for high-value utilization of sodium chlorofluoroaluminate in secondary aluminum ash wet pretreatment liquid according to claim 1, characterized in that: Step S2, adding hydrochloric acid or a mixture of hydrochloric acid and hydrofluoric acid to adjust the pH value to 5-9, the rate of adding hydrochloric acid increases with the increase of the total cryolite solid content of the solution; the reaction temperature is 10-50° C.; the stirring speed is less than 50 r / min.

7. The method for high-value utilization of sodium fluorochloroaluminate in secondary aluminum ash wet pretreatment liquid according to claim 1, characterized in that: In step S2, the slurry is matured for 0 to 10 hours after cryolite is precipitated, the cryolite is coarse particles with a median diameter d50>4μm; the fluorine removal rate of the filtrate is greater than 99%, and the fluorine and aluminum ion concentrations in the filtrate after fluorine removal are both less than 20mg / L, and the sodium chloride concentration is less than or equal to 20g / L.

8. The method for high-value utilization of sodium chlorofluoroaluminate in secondary aluminum ash wet pretreatment liquid according to claim 1, characterized in that: In step S3, the membrane concentration process includes: controlling the membrane stack voltage to be less than 25V, the volume ratio of the chlorine-containing wastewater in the concentrate tank to the desalination liquid tank to be 1:2-1:3, and the water inlet flow rate to be less than 300L / h, and concentrating the chlorine-containing wastewater in the concentrate tank to a salt concentration of more than 60g / L by a primary electrodialysis, and desalinating the chlorine-containing wastewater in the desalination liquid tank to less than 800mg / L; and also includes: The concentrated chloride-containing wastewater is subjected to secondary electrodialysis to obtain a high-concentration sodium chloride solution. The membrane stack voltage is controlled to be less than 25V, the volume ratio of the chloride-containing wastewater in the concentrate tank and the desalination liquid tank is 1:2-1:3, and the inlet flow rate is less than 300L / h. The secondary electrodialysis concentrates the chloride-containing wastewater in the concentrate tank to a salt concentration of more than 110g / L.

9. The method for high-value utilization of sodium fluorochloroaluminate in secondary aluminum ash wet pretreatment liquid according to claim 1, characterized in that: The washing liquid and separated water produced in steps S1 to S3 are all circulated and not discharged.

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