Method for recovering fluorine, aluminum and carbon from cathode carbon

Abstract

The invention discloses a method for recovering fluorine, aluminum and carbon from cathode carbon. The method comprises the following steps: (1) mixing cathode carbon with process water, carrying out primary pulpifying leaching on the obtained slurry, and carrying out liquid-solid separation to obtain primary leaching liquid and primary leaching residues; (2) carbon powder is recycled from the primary leaching residues, and carbon powder and tailings are obtained; 3) mixing the tailings with an alkali solution, carrying out secondary slurrying leaching on the slurry, and carrying out solid-liquid separation to obtain a secondary leaching solution and secondary leaching residues; (4) acid is added into the secondary immersion liquid for a neutralization reaction, solid-liquid separation is conducted, and regenerated cryolite and neutralized filtrate are obtained; 5) crystallizing the neutralized filtrate to obtain sodium salt and crystallization mother liquor; and carrying out salting-out on the primary immersion liquid by adopting a salting-out agent to obtain sodium fluoride, wherein the salting-out agent at least partially comprises the sodium salt obtained in the step 5). According to the method disclosed by the invention, carbon, aluminum and fluorine resources in the cathode carbon block can be recycled, the process is clean and pollution-free, the medicament can be regenerated and recycled, and the cost is low.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical metallurgy and relates to a method for recovering fluorine, aluminum and carbon from cathode carbon. Background Art

[0002] China is a major aluminum industry country. In 2022, my country's electrolytic aluminum production will be about 40 million tons, ranking first in the world. At present, the domestic aluminum electrolysis industry adopts the cryolite-alumina molten salt electrolysis method, with cryolite as the electrolyte, alumina as the solute dissolved in the molten cryolite, and carbon body as the anode and cathode of the electrolysis. Direct current is passed at 950-970℃ for electrolysis to obtain aluminum products. The cathode carbon block is used as the lining material at the bottom of the electrolytic cell. During the electrolysis process, it will be eroded by the electrolyte, resulting in some cracks that cause the electrolyte to flow into the cathode cell, resulting in increased energy consumption during the electrolysis process. Therefore, the general aluminum electrolysis cathode will be replaced after 3-5 years of use. The scrapped cathode is called a waste cathode. Studies have shown that about 30 to 50 kilograms of waste cathode materials are discharged for every ton of electrolytic aluminum produced.

[0003] Because the waste cathode is scrapped due to the electrolyte infiltration in the electrolytic cell cathode, the main components of the waste cathode are carbon and electrolyte, specifically C, NaF, Na3AlF6, Al2O3 and CaF2. The fluoride and cyanide contained in the waste cathode are highly toxic substances and are included in the list of Class I hazardous wastes by the state, and it is expressly prohibited to discard them at will. At present, most of the waste cathodes in my country are disassembled from the electrolytic cells and are mostly disposed of by open-air stacking or landfill. This will not only lead to the occupation of a large amount of precious land resources, but also the waste cathode contains highly toxic substances that are soluble in water, which will infiltrate into the soil and groundwater with rainwater, causing damage to the ecological environment, and will cause waste of resources such as carbon, fluorine and aluminum.

[0004] In order to achieve sustainable development and resource recycling of my country's electrolytic aluminum industry, there are currently many methods for extracting and recovering carbon and fluorine resources from cathode carbon blocks, and some of these methods have been put into industrial application.

[0005] Regarding the recovery of carbon and fluorine resources in cathode carbon blocks, CN114572981A discloses a method for treating waste cathodes by microwave heating in a water vapor atmosphere, using high-temperature water vapor to dissolve the fluoride salt in the waste cathode to achieve the purpose of separating carbon. CN117139322A discloses a method for high-value treatment of waste cathode carbon blocks, firstly, the waste cathode carbon blocks are pulverized by electrolysis, then carbon powder and electrolyte slurry are obtained by flotation separation, and finally the electrolyte slurry is evaporated and calcined to obtain the electrolyte product. CN111233019A discloses an environmentally friendly treatment method for waste cathodes and aluminum ash of aluminum electrolytic cells, wherein the aluminum ash is alkali-melted and roasted to obtain a sodium aluminate solution, and the waste cathode is floated to recover refined carbon powder and cryolite, and finally the flotation liquid enriched with sodium fluoride is mixed with the sodium aluminate solution to obtain high molecular weight cryolite.

[0006] However, the current method of recovering carbon, fluorine and cryolite resources from cathode carbon blocks still has problems such as high dosage of reagents, low utilization rate and high cost.

[0007] In summary, it is urgent to develop a new method for recovering fluorine, aluminum and carbon from cathode carbon blocks with low cost, recyclable reagents and clean process, so as to achieve efficient extraction and recovery of fluorine, aluminum and carbon. Summary of the invention

[0008] In view of the problems existing in the prior art, the object of the present invention is to provide a method for recovering fluorine from cathode carbon. The method of the present invention obtains a sodium fluoride leaching solution (also known as a primary leaching solution) by water leaching, and the sodium fluoride leaching solution is converted into a sodium fluoride product by adding a sodium salt (such as sodium nitrate) to react; the method can realize the recovery of fluorine resources in the cathode carbon block, and the leaching residue (also known as the primary leaching residue) first separates high-purity carbon powder, and then alkali leaches to obtain a leaching solution containing fluorine, aluminum, and sodium, and neutralizes to obtain a high-purity regenerated cryolite product, and the neutralized filtrate can be recovered by a simple crystallization step to obtain a sodium salt product, which can be recycled as a sodium fluoride salting-out agent, and the neutralized filtrate and the crystallization mother liquor can be distilled to obtain reusable sodium salt and distilled condensed water. At the same time, the cyanide-breaking agent can effectively decompose toxic cyanide. The method of the present invention has the advantages of clean and pollution-free process, recyclable reagents and low cost, and has broad application prospects.

[0009] To achieve this object, the present invention adopts the following technical solutions:

[0010] The present invention provides a method for recovering fluorine, aluminum and carbon from cathode carbon, the method comprising the following steps:

[0011] (1) mixing cathode carbon with process water, subjecting the obtained slurry to primary slurry leaching, and then separating liquid from solid to obtain a primary leaching liquid and a primary leaching residue;

[0012] (2) recovering carbon powder from the primary leaching residue of step (1) to obtain carbon powder and tailings;

[0013] (3) mixing the tailings from step (2) with an alkaline solution, subjecting the obtained slurry to secondary slurry leaching, and then separating the solid and liquid to obtain a secondary leaching solution and a secondary leaching residue;

[0014] (4) adding acid to the secondary leaching solution of step (3) to carry out a neutralization reaction, and performing solid-liquid separation to obtain regenerated cryolite and a neutralization filtrate;

[0015] (5) crystallizing the neutralization filtrate of step (4) to obtain a sodium salt and a crystallization mother liquor;

[0016] The primary leaching solution of step (1) is subjected to salting-out by a salting-out agent to obtain sodium fluoride, wherein the salting-out agent at least partially comprises the sodium salt obtained in step (5).

[0017] In the method of the present invention, firstly, the cathode carbon is leached with process water as the leaching liquid, and the easily soluble sodium fluoride is leached to obtain the sodium fluoride leaching solution (i.e., the primary leaching solution), and the sodium fluoride can be obtained by salting out the solution; then, the carbon powder in the leached residue is recovered; and the tailings after the carbon powder is separated are leached again under the condition of the coexistence of an alkaline solution and a cyanide-breaking agent, which can realize the decomposition of components such as cryolite and alumina in the cathode carbon on the one hand, and on the other hand, the alkaline environment can effectively prevent the volatilization of the cyanide-generated gas, and the chemical oxidation of the cyanide-breaking agent can also effectively decompose the cyanide; then, cryolite with higher purity is obtained in the process of neutralization reaction; sodium salt and crystallization mother liquor are obtained after the neutralization filtrate is crystallized, and the sodium salt part can be used for salting out of the sodium fluoride solution.

[0018] The method of the invention can realize the recovery of fluorine, aluminum and carbon resources in cathode carbon, the recovery rate of sodium fluoride obtained by salting out after water leaching is high, the purity of the obtained sodium fluoride product is high, the purity of the cryolite product obtained by neutralization reaction after alkali leaching is high, and the sodium salt obtained after crystallization of the neutralization filtrate can be used for salting out of the sodium fluoride solution, thus realizing renewable circulation, the process is pollution-free, and has broad application prospects.

[0019] In the method of the present invention, the process water can be pure water, deionized water, or distilled water, which is not specifically limited in the present invention and can be selected by those skilled in the art according to their needs.

[0020] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0021] Preferably, the cathode carbon is a cathode carbon block, and before the primary slurry leaching in step (1), the cathode carbon block is first crushed and ground to obtain cathode carbon block powder.

[0022] Preferably, the particle size of the cathode carbon block powder is not greater than 150 μm, for example 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 140 μm or 150 μm, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] Preferably, during the one-time slurry leaching process in step (1), the solid-liquid mass volume ratio is 1g:(2-10)mL, for example 1g:2mL, 1g:2.5mL, 1g:3mL, 1g:3.5mL, 1g:4mL, 1g:5mL, 1g:6.25mL, 1g:6.5mL, 1g:6.97mL, 1g:7mL, 1g:7.5mL, 1g:8mL, 1g:8.12mL, 1g:8.5mL, 1g:8.75mL, 1g:9mL or 1g:10mL, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable, preferably 1g:(4-6)mL.

[0024] Preferably, the temperature of the primary slurry leaching in step (1) is 20-100°C, for example, 20°C, 30°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0025] Preferably, the time for the primary slurry leaching in step (1) is 0.5 to 5 h, for example, 0.5 h, 1 h, 1.25 h, 1.5 h, 1.75 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h or 5 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0026] In the present invention, a higher sodium fluoride recovery rate can be obtained by controlling the solid-liquid mass volume ratio, temperature and time in the primary slurry leaching process.

[0027] As a preferred technical solution of the method of the present invention, the method for recovering carbon powder in step (2) is a flotation method, which comprises: adding process water, a collector, a foaming agent and a dispersant to the primary leaching residue of step (1) to obtain a flotation pulp, performing flotation, liquid-solid separation, and obtaining a carbon concentrate, tailings and a flotation mother liquor, wherein the carbon concentrate is the carbon powder.

[0028] Optionally, the flotation mother liquor is returned to step (2) to continue flotation.

[0029] The carbon is recovered by flotation, which has the advantages of high flotation carbon recovery rate and high purity of the obtained carbon powder product.

[0030] Preferably, the collector comprises one or a combination of at least two of kerosene, light diesel, diethyl phthalate, dewaxed kerosene or natural gas condensate. Typical but non-limiting examples of the combination include: a combination of kerosene and light diesel, a combination of kerosene and diethyl phthalate, a combination of kerosene and dewaxed kerosene, a combination of kerosene and natural gas condensate, a combination of light diesel and diethyl phthalate, a combination of light diesel and dewaxed kerosene, a combination of diethyl phthalate and dewaxed kerosene, a combination of diethyl phthalate and natural gas condensate, a combination of dewaxed kerosene and natural gas condensate, a combination of kerosene, light diesel and diethyl phthalate, a combination of kerosene, light diesel and dewaxed kerosene, a combination of kerosene, light diesel, dewaxed kerosene and natural gas condensate, and the like.

[0031] Preferably, the amount of the collector added is 150 g to 1000 g / t of primary leaching residue, which means that for each ton (t) of primary leaching residue, the amount of the collector used is 50 g to 600 g. Exemplarily, the amount of the collector added is 150 g / t, 180 g / t, 200 g / t, 301 g / t, 487 g / t, 564 g / t, 695 g / t, 726 g / t, 800 g / t, 950 g / t or 1000 g / t, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] Preferably, the foaming agent comprises one or a combination of at least two of sec-butyl alcohol, sec-octanol or pine oil. Typical but non-limiting examples of the combination include: a combination of sec-butyl alcohol and sec-octanol, a combination of sec-butyl alcohol and pine oil, a combination of sec-octanol and pine oil, a combination of sec-butyl alcohol, sec-octanol and pine oil, and the like.

[0033] Preferably, the amount of the foaming agent added is 50g-500g / t of primary leaching residue, which means that for each ton (t) of primary leaching residue, the amount of the foaming agent used is 50g-600g. Exemplarily, the amount of the foaming agent added is 50g / t, 80g / t, 95g / t, 112g / t, 174g / t, 237g / t, 266g / t, 300g / t, 420g / t, 470g / t or 500g / t, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0034] Preferably, the dispersant comprises one or a combination of at least two of water glass, modified starch, carboxymethyl cellulose or sodium hexametaphosphate. Typical but non-limiting examples of the combination include: a combination of water glass and modified starch, a combination of water glass and carboxymethyl cellulose, a combination of water glass and sodium hexametaphosphate, a combination of modified starch and carboxymethyl cellulose, a combination of modified starch and sodium hexametaphosphate, a combination of carboxymethyl cellulose and sodium hexametaphosphate, a combination of water glass, modified starch and carboxymethyl cellulose, a combination of water glass, modified starch and sodium hexametaphosphate, a combination of modified starch, carboxymethyl cellulose and sodium hexametaphosphate, a combination of water glass, modified starch, carboxymethyl cellulose and sodium hexametaphosphate, and the like.

[0035] Preferably, the amount of the dispersant added is 50 g to 600 g / t of primary leaching residue, which means that for each ton (t) of primary leaching residue, the amount of the dispersant used is 50 g to 600 g. Exemplarily, the amount of the dispersant added is 50 g / t, 80 g / t, 95 g / t, 112 g / t, 266 g / t, 384 g / t, 413 g / t, 500 g / t, 520 g / t, 570 g / t or 600 g / t, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] Preferably, the mass concentration of the flotation slurry is 15-30%, for example 15%, 16%, 16.5%, 17%, 17.25%, 17.70%, 18%, 19%, 20%, 25% or 30%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] Preferably, the flotation process parameters are: a rotation speed of 800 to 2000 r / min, such as 800 r / min, 900 r / min, 950 r / min, 1000 r / min, 1040 r / min, 1100 r / min, 1200 r / min, 1300 r / min, 1400 r / min, 1500 r / min or 2000 r / min, etc., but are not limited to the listed values, and other values ​​not listed in the numerical range are also applicable; an inflation volume of 0.15 to 0.25 m 3 / h, for example 0.15m 3 / h, 0.16m 3 / h, 0.165m 3 / h, 0.17m 3 / h, 0.173m 3 / h, 0.176m 3 / h, 0.179m 3 / h、0.18m 3 / h, 0.19m 3 / h、0.20m 3 / h or 0.25m 3 / h, etc., but are not limited to the listed values, and other values ​​not listed within the numerical range are equally applicable; the scraper speed is 5-10r / min, for example 5r / min, 5.5r / min, 6r / min, 6.2r / min, 6.4r / min, 6.75r / min, 7r / min, 8r / min, 9r / min or 10r / min, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are equally applicable.

[0038] For example, the speed is 800r / min, 900r / min, 950r / min, 1000r / min, 1040r / min, 1100r / min, 1200r / min, 1300r / min, 1400r / min, 1500r / min or 2000r / min, etc., but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] Preferably, the flotation method includes roughing, scavenging and cleaning.

[0040] In the present invention, roughing is the preliminary flotation of the original flotation pulp to separate the concentrate and tailings; scavenging is the re-floatation of the tailings of the previous level, and concentrating is the further flotation of the concentrate of the previous level.

[0041] Preferably, the number of rough selections is 1 to 3 times, for example, 1 time, 2 times or 3 times; the number of sweep selections is 1 to 5 times, for example, 1 time, 2 times, 3 times, 4 times or 5 times; the number of fine selections is 2 to 5 times, for example, 2 times, 3 times, 4 times or 5 times.

[0042] Preferably, the middle residues from the first scavenging and the last cleaning are returned to the first cleaning for re-floatation, and the middle residues from the second to the last roughing, the second to the last scavenging and the first to the second to last cleaning are returned to the first roughing for re-floatation.

[0043] As a preferred technical solution of the method of the present invention, the alkaline solution in step (3) is a sodium hydroxide aqueous solution prepared by process water and sodium hydroxide.

[0044] Preferably, in the secondary slurry leaching process of step (3), the solid-liquid mass volume ratio is 1g:(5-30)mL, for example 1g:5mL, 1g:6mL, 1g:6.5mL, 1g:7mL, 1g:7.7mL, 1g:8mL, 1g:9mL, 1g:10mL, 1g:11mL, 1g:12mL, 1g:13mL, 1g:14mL, 1g:15mL, 1g:20mL, 1g:22mL, 1g:24mL, 1g:25.5mL, 1g:28mL or 1g:30mL, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable, preferably 1g:(8-25)mL, more preferably 1g:(10-20)mL.

[0045] Preferably, the molar ratio of aluminum in the secondary slurry to the alkali in the alkaline solution in step (3) is 1:(4-8), for example 1:4, 1:4.25, 1:4.5, 1:5, 1:5.5, 1:5.75, 1:6, 1:6.5, 1:7, 1:7.5 or 1:8, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0046] Preferably, the temperature of the secondary slurry leaching in step (3) is 60-250°C, for example, 60°C, 70°C, 80°C, 90°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 215°C, 230°C, 245°C or 250°C, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable, preferably 80-200°C, more preferably 100-150°C;

[0047] Preferably, the time for the secondary slurry leaching in step (3) is 0.5 to 5 h, for example, 0.5 h, 0.75 h, 1 h, 1.5 h, 1.75 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h or 5 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0048] In the secondary slurry leaching process of the present invention, by regulating one or more of the appropriate solid-liquid mass volume ratio, the molar ratio of aluminum to alkali, the leaching temperature and time, the components such as cryolite and alumina in the cathode carbon can be decomposed into sodium aluminate and sodium fluoride. By utilizing the difference in the physical and chemical properties of sodium fluoride, sodium aluminate and impurities, the sodium aluminate and sodium fluoride can be introduced into the secondary leaching solution, while the harmless impurities are retained in the secondary leaching residue.

[0049] As a preferred technical solution of the method of the present invention, in the mixing step of step (3), the tailings, the cyanide-breaking agent and the alkaline solution are mixed.

[0050] Preferably, the cyanide-breaking agent comprises one or a combination of at least two of peroxide, hypochlorous acid, hypochlorite, perchloric acid, perchlorate, persulfuric acid, persulfate, oxygen, ozone and chlorine. Typical but non-limiting examples of the combination include: a combination of peroxide and ozone, a combination of hypochlorous acid, hypochlorite, persulfuric acid and persulfate, a combination of hypochlorous acid, hypochlorite, perchloric acid, perchlorate, persulfuric acid and persulfate, a combination of peroxide, perchloric acid, perchlorate, persulfuric acid, persulfate and chlorine, a combination of hypochlorous acid, hypochlorite, perchloric acid, perchlorate, persulfuric acid, persulfate and oxygen, a combination of hypochlorous acid, hypochlorite, perchloric acid, perchlorate, persulfuric acid, persulfate, oxygen and ozone, a combination of hypochlorous acid, hypochlorite, perchloric acid, perchlorate, persulfuric acid, persulfate, oxygen, ozone and chlorine, a combination of peroxide, hypochlorous acid, hypochlorite, perchloric acid, perchlorate, persulfuric acid, persulfate, oxygen, ozone and chlorine, and the like.

[0051] Preferably, if the cyanide-breaking agent is liquid or solid, the amount of the cyanide-breaking agent liquid / solid added is 0.2-0.6 mg / L, for example, 0.2 mg / L, 0.3 mg / L, 0.4 mg / L, 0.5 mg / L or 0.6 mg / L, more preferably 0.3-0.5 mg / L.

[0052] Preferably, if the cyanide-breaking agent is a gas, the gas introduction rate of the cyanide-breaking agent is 0.5m 3 / L~1.0m 3 / L, for example, it can be 0.5m 3 / L, 0.6m 3 / L, 0.7m 3 / L, 0.8m 3 / L, 0.9m 3 / L or 1m 3 / L, etc.

[0053] As an example and not as a limitation of the present invention, peroxides may be, for example, sodium peroxide, potassium peroxide or calcium peroxide; hypochlorites may be, for example, sodium hypochlorite, calcium hypochlorite or potassium hypochlorite; perchlorates may be, for example, sodium perchlorate or potassium perchlorate; and persulfates may be, for example, sodium persulfate or ammonium persulfate.

[0054] As a preferred technical solution of the method of the present invention, in step (4), acid is added to adjust and control the pH of the soaking liquid until the neutralization reaction is completed.

[0055] Preferably, the acid is nitric acid.

[0056] Preferably, the pH is 4-12, for example 4, 4.5, 5, 5.2, 5.6, 6, 6.8, 7, 7.5, 8, 9, 10, 11 or 12, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable. Preferably, pH is 6-10, and more preferably pH is 7-9.

[0057] At a suitable pH, sodium aluminate and sodium fluoride are conducive to the recombination to generate regenerated cryolite, resulting in a higher recovery rate and high purity cryolite.

[0058] Preferably, the time of the neutralization reaction in step (4) is 0.25 to 2 hours, such as 0.25 hours, 0.3 hours, 0.5 hours, 0.75 hours, 1 hours, 1.2 hours, 1.25 hours, 1.3 hours, 1.5 hours, 1.75 hours or 2 hours, but it is not limited to the listed values, and other unlisted values ​​in the numerical range are also applicable. As a preferred technical solution of the method of the present invention, the crystallization method in step (5) is cooling crystallization, and the temperature of the cooling crystallization is preferably 20 to 40°C, such as 20°C, 22.5°C, 24.5°C, 26°C, 28°C, 30°C, 33°C, 36°C, 37.7°C, 39°C or 40°C, but it is not limited to the listed values, and other unlisted values ​​in the numerical range are also applicable.

[0059] Preferably, in step (5), the neutralization filtrate is evaporated to obtain steam condensate and evaporation concentrate, and the evaporation concentrate is crystallized.

[0060] Preferably, the steam condensate is reused as process water.

[0061] Preferably, the evaporation is reduced-pressure evaporation, and the evaporation temperature is 80-95°C, for example, 80°C, 80.5°C, 82.5°C, 85°C, 87°C, 88°C, 90°C, 91.5°C, 92.5°C or 95°C, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0062] As a preferred technical solution of the method of the present invention, the step of using a salting-out agent to salt out the primary leaching solution of step (1) to obtain sodium fluoride comprises: adding the salting-out agent to the primary leaching solution, and after the salting-out reaction, performing solid-liquid separation to obtain sodium fluoride and a salting-out mother liquor.

[0063] Preferably, the salting-out mother liquor is evaporated to obtain steam condensed water and evaporation concentrated liquid. The evaporation concentrated liquid is cooled and crystallized to achieve the regeneration of sodium salt (such as sodium nitrate), which can be reused in the crystallization reaction of sodium fluoride solution; the steam condensed water can be reused as process water, for example, the process water can be reused in the steps of primary slurry leaching, alkaline solution preparation or flotation.

[0064] In the present invention, after sodium fluoride is obtained by crystallization, the differences in solubility, azeotropic point, etc. between the salting-out mother liquor and the sodium salt (such as sodium nitrate) in the system can be used to recover the sodium salt by precise temperature-controlled distillation, so that the sodium salt can be regenerated and reused in the crystallization reaction of the sodium fluoride solution. The solution after the sodium salt is recovered can be reused in the secondary slurry leaching process.

[0065] Preferably, the volume mass ratio of the primary immersion solution to the salting-out agent is 1 mL:(0.4-1.2) g, for example, 1 g:0.4 mL, 1 g:0.5 mL, 1 g:0.65 mL, 1 g:7 mL, 1 g:0.75 mL, 1 g:0.8 mL, 1 g:0.9 mL, 1 g:0.96 mL, 1 g:1.0 mL, 1 g:1.14 mL or 1 g:1.2 mL, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are equally applicable.

[0066] Preferably, the temperature of the salting-out reaction is 25-60°C, for example, 25°C, 27.5°C, 30°C, 32.5°C, 35°C, 40°C, 47.5°C, 52°C, 57°C or 60°C, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0067] Preferably, the salting-out reaction time is 0.25 to 2 h, for example, 0.25 h, 0.3 h, 0.5 h, 0.75 h, 1 h, 1.2 h, 1.25 h, 1.3 h, 1.5 h, 1.75 h or 2 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0068] In the present invention, the differences in solubility and crystallization properties of sodium fluoride in a mixture of water and sodium salt (such as sodium nitrate) in an immersion solution are studied and utilized, and the reagent ratio, reaction temperature and reaction time are adjusted to promote the precipitation and crystallization reaction of sodium fluoride, thereby obtaining a sodium fluoride product with a higher recovery rate and purity.

[0069] As a preferred technical solution of the method of the present invention, the crystallization mother liquor obtained in step (5) is recycled to the secondary slurry leaching step in step (3).

[0070] Optionally, the solids such as the leached residue, regenerated cryolite and sodium fluoride in the present invention can be washed with water. Exemplarily, pure water is used for washing, and the washing liquid is combined with the filtrate. The washing liquid refers to the liquid obtained by eluting the product filtered out during the filtration process, and the filtrate refers to the liquid obtained by filtering the slurry during the filtration process. The combination of the two can maintain the water balance of the system, and the washing liquid is used to supplement the liquid taken away by the filtrate.

[0071] Optionally, the method of the present invention further comprises drying the cryolite, carbon powder and sodium salt (such as sodium nitrate, sodium fluoride).

[0072] As a preferred technical solution of the method of the present invention, the method comprises the following steps:

[0073] S1. Crush and grind the cathode carbon block to obtain cathode carbon block powder with a particle size of no more than 150 μm, and perform a slurry leaching on the cathode carbon block powder and process water at a solid-liquid mass volume ratio of 1 g: (2-10) mL. The temperature of the slurry leaching is 20-100 ° C. The time of the slurry leaching is 0.5-5 h. After the slurry leaching is completed, liquid-solid separation is performed to obtain a primary leaching liquid and a primary leaching residue;

[0074] S2. Sodium nitrate is added to the first leaching solution of step S1 at a volume-mass ratio of 1 mL: (0.4-1.2) g, and the mixture is reacted at 25-60° C. for 0.25-2 h, and liquid-solid separation is performed to obtain sodium fluoride and a salting-out mother liquor;

[0075] S3: adding process water, dispersant, foaming agent and collector to the primary leaching residue of step S1 to obtain flotation pulp, flotating the flotation pulp, wherein the flotation includes 1 to 3 roughing, 1 to 5 scavenging and 2 to 5 cleaning, liquid-solid separation, and obtaining carbon concentrate, tailings and flotation mother liquor, wherein the carbon concentrate is the carbon powder, and the flotation mother liquor is recycled to step S3;

[0076] The mass concentration of the flotation pulp is 15-30%, the rotation speed is 800-2000 r / min, the aeration volume is 0.15-0.25 m3 / h, the scraper speed is 5-10 r / min, the addition amount of the dispersant is 50g-600g / t of the primary leaching residue, the addition amount of the collector is 150g-1000g / t of the primary leaching residue, and the addition amount of the foaming agent is 50g-500g / t of the primary leaching residue;

[0077] S4: adding a cyanide-breaking agent and a sodium hydroxide aqueous solution to the tailings of step S3 at a solid-liquid mass volume ratio of 1 g: (5-30) mL for secondary slurry leaching, the temperature of the secondary slurry leaching is 60-250° C., and the time of the secondary slurry leaching is 0.5-5 h, wherein the molar ratio of aluminum in the slurry to sodium hydroxide is 1: (4-8), the cyanide-breaking agent is one or a combination of at least two of peroxide, hypochlorous acid, hypochlorite, perchloric acid, perchlorate, persulfate, persulfate, oxygen, ozone and chlorine, liquid-solid separation is performed to obtain a secondary leaching solution and a secondary leaching residue;

[0078] S5: adding nitric acid to the secondary leaching solution of step S4 to adjust the pH to 4-12 for a neutralization reaction of 0.25-2h, and separating the liquid and solid to obtain regenerated cryolite and a neutralization filtrate;

[0079] S6: evaporate the salting-out mother liquor of step S2 and the neutralization filtrate of step S5 under reduced pressure at 80-95° C. to obtain steam condensate and evaporation concentrate, and the steam condensate is reused as process water;

[0080] In step S7, the evaporated concentrated liquid of step S6 is cooled and crystallized at 20-40° C., and the liquid-solid separation is performed to obtain sodium nitrate and a crystallization mother liquor. The sodium nitrate is partially recycled to step S2, and the crystallization mother liquor is recycled to secondary slurry leaching.

[0081] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0082] Compared with the prior art, the present invention has the following beneficial effects:

[0083] (1) The method of the present invention obtains a sodium fluoride leaching solution by water leaching, and the sodium fluoride leaching solution is converted into a sodium fluoride product by adding a sodium salt reaction; the method can realize the recovery of fluorine resources in the cathode carbon block, and the leaching slag is first separated into high-purity carbon powder, and then alkali leaching is performed to obtain a leaching solution containing fluorine, aluminum, and sodium, and neutralization is performed to obtain a high-purity regenerated cryolite product, and the neutralization filtrate can be recovered through a simple crystallization step to obtain a sodium salt product, which can be recycled as a sodium fluoride salting-out agent, and the neutralization filtrate and the crystallization mother liquor can be distilled to obtain reusable sodium salt and distilled condensed water. At the same time, the cyanide-breaking agent can effectively decompose toxic cyanide. The method of the present invention has the advantages of clean and pollution-free process, recyclable reagents, and low cost, and has broad application prospects.

[0084] (2) The present invention can realize the recovery of carbon, fluorine and aluminum resources in the cathode carbon block, and the purity of carbon powder, cryolite and sodium fluoride products is greater than 85%, 98% and 99% respectively. By optimizing the process parameters in the method of the present invention, the recovery rate of carbon can be greater than 80%, the recovery rate of fluorine can be greater than 90%, and the recovery rate of aluminum can be greater than 90%. BRIEF DESCRIPTION OF THE DRAWINGS

[0085] Figure 1 This is a process flow chart of the method for recovering fluorine, aluminum and carbon from cathode carbon blocks provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0086] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0087] The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0088] Example 1

[0089] In order to better illustrate the present invention and facilitate understanding of the technical solution of the present invention, the present invention is further described in detail below. However, the following embodiments are only simple examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0090] The specific embodiment of the present invention provides a method for recovering fluorine, aluminum and carbon from a cathode carbon block, the method comprising the following steps:

[0091] (1) The cathode carbon block is subjected to a slurry leaching with process water, and liquid-solid separation is performed to obtain a primary leaching liquid and a primary leaching residue;

[0092] (2) adding sodium nitrate to the primary leaching solution of step (1) for salting out, and separating the liquid from the solid to obtain sodium fluoride and a salting out mother liquor;

[0093] (3) adding process water, a dispersant, a foaming agent and a collector to the primary leaching residue of step (1) for flotation and liquid-solid separation to obtain carbon concentrate, tailings and flotation mother liquor, and the flotation mother liquor is recycled to step (3);

[0094] (4) adding a cyanide-breaking agent and a sodium hydroxide aqueous solution to the tailings of step (3) for secondary slurry leaching, and liquid-solid separation to obtain a secondary leaching solution and a secondary leaching residue;

[0095] (5) adding nitric acid to the secondary leaching solution of step (4) for neutralization, and performing liquid-solid separation to obtain regenerated cryolite and a neutralization filtrate;

[0096] (6) evaporating the salting-out mother liquor of step (2) and the neutralization filtrate of step (5) to obtain steam condensate and evaporation concentrate, and reusing the steam condensate as process water;

[0097] (7) cooling and crystallizing the evaporated concentrated liquid of step (6), separating the liquid from the solid, and obtaining sodium nitrate and a crystallization mother liquor. The sodium nitrate is partially recycled to step (2), and the crystallization mother liquor is recycled to secondary slurry leaching.

[0098] The following are typical but non-limiting embodiments of the present invention:

[0099] Example 1

[0100] The present embodiment provides a method for recovering fluorine, aluminum and carbon from a cathode carbon block, wherein the main components and contents of the cathode carbon block are: Al 4.74wt%, F 11.37wt%, Na 4.90wt%, K 0.49wt%, Ca2.10wt%, Mg0.09wt%, Si 3.40wt%, C 46.37wt%, CN - 0.30wt%.

[0101] The process flow chart of the method is as follows Figure 1 As shown, the following steps are included:

[0102] (1) crushing and grinding the cathode carbon block to obtain a cathode carbon block powder with a particle size of no more than 118 μm, and subjecting the cathode carbon block powder to a slurry leaching with process water at a solid-liquid mass volume ratio of 1 g:5 mL, the temperature of the slurry leaching is 50° C., the time of the slurry leaching is 3 h, and liquid-solid separation is performed to obtain a primary leaching liquid and a primary leaching residue;

[0103] (2) adding sodium nitrate to the first leaching solution of step (1) at a volume-mass ratio of 1 mL:1.2 g, reacting at 45° C. for 2 h, and performing liquid-solid separation to obtain sodium fluoride and a salting-out mother liquor;

[0104] (3) adding process water, dispersant (sodium hexametaphosphate), foaming agent (pine oil) and collector (kerosene) to the primary leaching residue of step (1) to obtain flotation pulp, and flotating the flotation pulp, wherein the flotation pulp is subjected to 1 roughing selection, 3 scavenging selections and 3 concentrating selections, wherein the mass concentration of the flotation pulp is 30%, the rotation speed is 2000r / min, and the aeration volume is 0.25m 3 / h, the scraper speed is 10r / min, the added amount of dispersant is 600g / t of primary leaching residue, the added amount of collector is 1000g / t of primary leaching residue, the added amount of foaming agent is 500g / t of primary leaching residue, liquid-solid separation is performed to obtain carbon concentrate, tailings and flotation mother liquor, and the flotation mother liquor is reused in step (3);

[0105] (4) adding hydrogen peroxide and sodium hydroxide aqueous solution to the tailings of step (3) for secondary slurry leaching, the solid-liquid mass volume ratio is 1g:10mL, the temperature of the secondary slurry leaching is 150°C, the time of the secondary slurry leaching is 3h, wherein the molar ratio of aluminum to sodium hydroxide in the slurry is 1:6, the amount of hydrogen peroxide added is 0.5mg / L, and liquid-solid separation is performed to obtain secondary leaching solution and secondary leaching residue;

[0106] (5) adding nitric acid to the secondary leaching solution of step (4) to adjust the pH to 9 and carry out neutralization reaction for 1 hour, and then separating the liquid and solid to obtain regenerated cryolite and neutralization filtrate.

[0107] (6) The salting-out mother liquor of step (2) and the neutralization filtrate of step (5) are evaporated under reduced pressure at 90° C. to obtain steam condensate and evaporation concentrate, and the steam condensate is reused as process water.

[0108] (7) The evaporated concentrated liquid of step (6) is cooled and crystallized at 27° C., and the liquid-solid separation is performed to obtain sodium nitrate and a crystallization mother liquor. The sodium nitrate is partially recycled to step (2), and the crystallization mother liquor is recycled to secondary slurry leaching.

[0109] Example 2

[0110] This embodiment provides a method for recovering fluorine, aluminum and carbon from a cathode carbon block. The main components and contents of the cathode carbon block are the same as those in Example 1.

[0111] The method comprises the following steps:

[0112] (1) crushing and grinding the cathode carbon block to obtain a cathode carbon block powder with a particle size of no more than 118 μm, and subjecting the cathode carbon block powder to a slurry leaching with process water at a solid-liquid mass volume ratio of 1 g:3 mL, the temperature of the slurry leaching is 100° C., the time of the slurry leaching is 4 h, and liquid-solid separation is performed to obtain a primary leaching liquid and a primary leaching residue;

[0113] (2) adding sodium nitrate to the first leaching solution of step (1) at a volume-mass ratio of 1 mL:0.4 g, reacting at 25° C. for 0.5 h, and performing liquid-solid separation to obtain sodium fluoride and a salting-out mother liquor;

[0114] (3) adding process water, dispersant (water glass), foaming agent (sec-butyl alcohol) and collector (light diesel oil) to the primary leaching residue of step (1) to obtain flotation pulp, and flotating the flotation pulp, wherein the flotation pulp is subjected to flotation, and the flotation includes 1 roughing selection, 4 scavenging selections and 2 cleaning selections, wherein the mass concentration of the flotation pulp is 20%, the rotation speed is 1000 r / min, and the aeration volume is 0.20 m 3 / h, the scraper speed is 6r / min, the added amount of dispersant is 200g / t of primary leaching residue, the added amount of collector is 300g / t of primary leaching residue, the added amount of foaming agent is 150g / t of primary leaching residue, liquid-solid separation is performed to obtain carbon concentrate, tailings and flotation mother liquor, and the flotation mother liquor is reused in step (3);

[0115] (4) adding hypochlorous acid and sodium hydroxide aqueous solution to the tailings of step (3) for secondary slurry leaching, the solid-liquid mass volume ratio is 1g:20mL, the temperature of the secondary slurry leaching is 100°C, the time of the secondary slurry leaching is 1h, wherein the molar ratio of aluminum to sodium hydroxide in the slurry is 1:8, the amount of hypochlorous acid added is 0.3mg / L, and liquid-solid separation is performed to obtain a secondary leaching solution and a secondary leaching residue;

[0116] (5) adding nitric acid to the secondary leaching solution of step (4) to adjust the pH to 6 for neutralization, reacting for 2 hours, and performing liquid-solid separation to obtain regenerated cryolite and a neutralization filtrate.

[0117] (6) The salting-out mother liquor of step (2) and the neutralization filtrate of step (5) are evaporated under reduced pressure at 80° C. to obtain steam condensate and evaporation concentrate, and the steam condensate is reused as process water.

[0118] (7) The evaporated concentrated liquid of step (6) is cooled and crystallized at 24° C., and the liquid-solid separation is performed to obtain sodium nitrate and a crystallization mother liquor. The sodium nitrate is partially recycled to step (2), and the crystallization mother liquor is recycled to secondary slurry leaching.

[0119] Example 3

[0120] This embodiment provides a method for recovering fluorine, aluminum and carbon from a cathode carbon block. The main components and contents of the cathode carbon block are the same as those in Example 1.

[0121] The method comprises the following steps:

[0122] (1) crushing and grinding the cathode carbon block to obtain a cathode carbon block powder with a particle size of no more than 118 μm, and subjecting the cathode carbon block powder to a slurry leaching with process water at a solid-liquid mass volume ratio of 1 g:10 mL, the temperature of the slurry leaching is 20° C., the time of the slurry leaching is 1 h, and liquid-solid separation is performed to obtain a primary leaching liquid and a primary leaching residue;

[0123] (2) adding sodium nitrate to the first leaching solution of step (1) at a volume-mass ratio of 1 mL:0.5 g, reacting at 30° C. for 1 h, and performing liquid-solid separation to obtain sodium fluoride and a salting-out mother liquor;

[0124] (3) adding process water, dispersant (modified starch), foaming agent (octanol) and collector (natural gas condensate) to the leached residue of step (1) to obtain flotation pulp, and flotating the flotation pulp, wherein the flotation pulp is subjected to flotation, and the flotation includes 2 roughing selections, 2 scavenging selections and 4 concentrating selections, wherein the mass concentration of the flotation pulp is 15%, the rotation speed is 800 r / min, and the aeration volume is 0.15 m 3 / h, the scraper speed is 5.5r / min, the addition amount of dispersant is 50g / t of primary leaching residue, the addition amount of collector is 150g / t of primary leaching residue, the addition amount of foaming agent is 50g / t of primary leaching residue, liquid-solid separation is performed to obtain carbon concentrate, tailings and flotation mother liquor, and the flotation mother liquor is reused in step (3);

[0125] (4) adding perchloric acid and sodium hydroxide aqueous solution to the tailings of step (3) for secondary slurry leaching, the solid-liquid mass volume ratio is 1g:5mL, the temperature of the secondary slurry leaching is 250°C, the time of the secondary slurry leaching is 5h, wherein the molar ratio of aluminum to sodium hydroxide in the slurry is 1:4, the amount of perchloric acid added is 0.4mg / L, and liquid-solid separation is performed to obtain secondary leaching solution and secondary leaching residue;

[0126] (5) adding nitric acid to the secondary leaching solution of step (4) to adjust the pH to 12 for neutralization, reacting for 0.5 h, and performing liquid-solid separation to obtain regenerated cryolite and a neutralization filtrate.

[0127] (6) The salting-out mother liquor of step (2) and the neutralization filtrate of step (5) are evaporated under reduced pressure at 95° C. to obtain steam condensate and evaporation concentrate, and the steam condensate is reused as process water.

[0128] (7) The evaporated concentrated liquid of step (6) is cooled and crystallized at 22° C., and the liquid-solid separation is performed to obtain sodium nitrate and a crystallization mother liquor. The sodium nitrate is partially recycled to step (2), and the crystallization mother liquor is recycled to secondary slurry leaching.

[0129] Example 4

[0130] This embodiment provides a method for recovering fluorine, aluminum and carbon from a cathode carbon block, wherein the main components and contents of the cathode carbon block are: Al 5.10wt%, F 13.41wt%, Na 5.82wt%, K 0.88wt%, Ca1.89wt%, Mg0.13wt%, Si 2.17wt%, C 41.29wt%, CN - 0.10wt%.

[0131] The method comprises the following steps:

[0132] (1) crushing and grinding the cathode carbon block to obtain cathode carbon block powder with a particle size of no more than 150 μm, and subjecting the cathode carbon block powder to a slurry leaching with process water at a solid-liquid mass volume ratio of 1 g:8 mL, the slurry leaching temperature is 40° C., the slurry leaching time is 0.5 h, and liquid-solid separation is performed to obtain a primary leaching solution and a primary leaching residue;

[0133] (2) adding sodium nitrate to the first leaching solution of step (1) at a volume-mass ratio of 1 mL:1 g, reacting at 35° C. for 1.5 h, and performing liquid-solid separation to obtain sodium fluoride and a salting-out mother liquor;

[0134] (3) adding process water, dispersant (carboxymethyl cellulose), foaming agent (sec-butyl alcohol), foaming agent (pine oil) and collector (dewaxed kerosene) to the leached residue of step (1) to obtain flotation pulp, and flotating the flotation pulp, wherein the flotation pulp is subjected to three roughing selections, one scavenging selection and three cleaning selections, wherein the mass concentration of the flotation pulp is 25%, the rotation speed is 1700 r / min, and the aeration volume is 0.21 m 3 / h, the scraper speed is 8.5r / min, the added amount of dispersant is 400g / t of primary leaching residue, the added amount of collector is 600g / t of primary leaching residue, the added amount of foaming agent is 340g / t of primary leaching residue, liquid-solid separation is performed to obtain carbon concentrate, tailings and flotation mother liquor, and the flotation mother liquor is reused in step (3);

[0135] (4) The tailings of step (3) were subjected to secondary slurry leaching by adding ozone and sodium hydroxide aqueous solution, the solid-liquid mass volume ratio was 1 g:25 mL, the temperature of the secondary slurry leaching was 225 ° C, the time of the secondary slurry leaching was 2 h, wherein the molar ratio of aluminum to sodium hydroxide in the slurry was 1:5, and the ozone introduction amount was 0.8 m 3 / L, liquid-solid separation, to obtain secondary leaching liquid and secondary leaching residue;

[0136] (5) adding nitric acid to the secondary leaching solution of step (4) to adjust the pH to 4 for neutralization, reacting for 1 hour, and performing liquid-solid separation to obtain regenerated cryolite and a neutralization filtrate.

[0137] (6) The salting-out mother liquor of step (2) and the neutralization filtrate of step (5) are evaporated under reduced pressure at 90° C. to obtain steam condensate and evaporation concentrate, and the steam condensate is reused as process water.

[0138] (7) The evaporated concentrated liquid of step (6) is cooled and crystallized at 30° C., and the liquid-solid separation is performed to obtain sodium nitrate and a crystallization mother liquor. The sodium nitrate is partially recycled to step (2), and the crystallization mother liquor is recycled to secondary slurry leaching.

[0139] Example 5

[0140] This embodiment provides a method for recovering fluorine, aluminum and carbon from a cathode carbon block. The main components and contents of the cathode carbon block are the same as those in Example 4.

[0141] The method comprises the following steps:

[0142] (1) crushing and grinding the cathode carbon block to obtain cathode carbon block powder with a particle size of no more than 150 μm, and subjecting the cathode carbon block powder to a slurry leaching with process water at a solid-liquid mass volume ratio of 1 g:6 mL, the slurry leaching temperature is 80° C., the slurry leaching time is 5 h, and liquid-solid separation is performed to obtain a primary leaching liquid and a primary leaching residue;

[0143] (2) adding sodium nitrate to the first leaching solution of step (1) at a volume-mass ratio of 1 mL:0.8 g, reacting at 40° C. for 0.25 h, and performing liquid-solid separation to obtain sodium fluoride and a salting-out mother liquor;

[0144] (3) adding process water, a dispersant (a mixture of water glass and modified starch in a mass ratio of 2:3), a foaming agent (pine oil) and a collector (diethyl phthalate) to the leached residue of step (1) to obtain a flotation pulp, and flotating the flotation pulp, wherein the flotation pulp is subjected to 1 roughing selection, 4 scavenging selections and 5 concentrating selections, wherein the mass concentration of the flotation pulp is 22%, the rotation speed is 1500 r / min, and the aeration volume is 0.18 m 3 / h, the scraper speed is 7r / min, the added amount of dispersant is 300g / t of primary leaching residue, the added amount of collector is 400g / t of primary leaching residue, the added amount of foaming agent is 175g / t of primary leaching residue, liquid-solid separation is performed to obtain carbon concentrate, tailings and flotation mother liquor, and the flotation mother liquor is reused in step (3);

[0145] (4) The tailings of step (3) were subjected to secondary pulp leaching by adding chlorine gas and sodium hydroxide aqueous solution, the solid-liquid mass volume ratio was 1 g:15 mL, the temperature of the secondary pulp leaching was 200 ° C, the time of the secondary pulp leaching was 4 h, wherein the molar ratio of aluminum to sodium hydroxide in the slurry was 1:7, the amount of chlorine gas introduced was 0.5 m 3 / L, liquid-solid separation, to obtain secondary leaching liquid and secondary leaching residue;

[0146] (5) The secondary leaching solution of step (4) was neutralized by adding nitric acid to adjust the pH to 2, reacting for 1.5 hours, and liquid-solid separation to obtain regenerated cryolite and neutralization filtrate.

[0147] (6) The salting-out mother liquor of step (2) and the neutralization filtrate of step (5) are evaporated under reduced pressure at 95° C. to obtain steam condensate and evaporation concentrate, and the steam condensate is reused as process water.

[0148] (7) The evaporated concentrated liquid of step (6) is cooled and crystallized at 20° C., and the liquid-solid separation is performed to obtain sodium nitrate and a crystallization mother liquor. The sodium nitrate is partially recycled to step (2), and the crystallization mother liquor is recycled to secondary slurry leaching.

[0149] Example 6

[0150] This embodiment provides a method for recovering fluorine, aluminum and carbon from a cathode carbon block. The main components and contents of the cathode carbon block are the same as those in Example 4.

[0151] The method comprises the following steps:

[0152] (1) The cathode carbon block is crushed and ground to obtain a cathode carbon block powder with a particle size of no more than 150 μm, and the cathode carbon block powder is subjected to a slurry leaching with process water at a solid-liquid mass volume ratio of 1 g:4 mL, the temperature of the slurry leaching is 95° C., the time of the slurry leaching is 2.5 h, and liquid-solid separation is performed to obtain a primary leaching liquid and a primary leaching residue;

[0153] (2) adding sodium nitrate to the first leaching solution of step (1) at a volume-mass ratio of 1 mL:0.6 g, reacting at 60° C. for 1.25 h, and performing liquid-solid separation to obtain sodium fluoride and a salting-out mother liquor;

[0154] (3) adding process water, dispersant (sodium hexametaphosphate), foaming agent (sec-butyl alcohol), and collector (a mixture of light diesel and dewaxed kerosene in a mass ratio of 1:1) to the primary leaching residue of step (1) to obtain flotation pulp, and flotating the flotation pulp, wherein the flotation includes 3 roughing selections, 2 scavenging selections, and 1 concentrating selection, wherein the mass concentration of the pulp is 18%, the rotation speed is 1200 r / min, and the aeration volume is 0.17 m 3 / h, the scraper speed is 6.5r / min, the added amount of dispersant is 120g / t of primary leaching residue, the added amount of collector is 240g / t of primary leaching residue, the added amount of foaming agent is 100g / t of primary leaching residue, liquid-solid separation is performed to obtain carbon concentrate, tailings and flotation mother liquor, and the flotation mother liquor is reused in step (3);

[0155] (4) The tailings of step (3) were subjected to secondary slurry leaching by adding oxygen and sodium hydroxide aqueous solution, the solid-liquid mass volume ratio was 1 g:18 mL, the temperature of the secondary slurry leaching was 180 ° C, the time of the secondary slurry leaching was 3.25 h, wherein the molar ratio of aluminum to sodium hydroxide in the slurry was 1:5.5, and the oxygen introduction amount was 0.9 m 3 / L, liquid-solid separation, to obtain secondary leaching liquid and secondary leaching residue;

[0156] (5) adding nitric acid to the secondary leaching solution of step (4) to adjust the pH to 5 and conduct a neutralization reaction for 0.5 h, and then separate the liquid and solid to obtain regenerated cryolite and a neutralization filtrate.

[0157] (6) The salting-out mother liquor of step (2) and the neutralization filtrate of step (5) are evaporated under reduced pressure at 85° C. to obtain steam condensate and evaporation concentrate, and the steam condensate is reused as process water.

[0158] (7) The evaporated concentrated liquid of step (6) is cooled and crystallized at 32° C., and the liquid-solid separation is performed to obtain sodium nitrate and a crystallization mother liquor. The sodium nitrate is partially recycled to step (2), and the crystallization mother liquor is recycled to secondary slurry leaching.

[0159] Example 7

[0160] The present embodiment provides a method for recovering fluorine, aluminum and carbon from a cathode carbon block, wherein the main components and contents of the cathode carbon block are: Al 3.89wt%, F 12.66wt%, Na 4.47wt%, K 1.32wt%, Ca0.74wt%, Mg0.07wt%, Si 1.65wt%, C 43.60wt%, CN - 0.05wt%.

[0161] The method comprises the following steps:

[0162] (1) crushing and grinding the cathode carbon block to obtain a cathode carbon block powder with a particle size of no more than 75 μm, and subjecting the cathode carbon block powder to a slurry leaching with process water at a solid-liquid mass volume ratio of 1 g:2 mL, the slurry leaching temperature is 75° C., the slurry leaching time is 2 h, and liquid-solid separation is performed to obtain a primary leaching liquid and a primary leaching residue;

[0163] (2) adding sodium nitrate to the first leaching solution of step (1) at a volume-mass ratio of 1 mL:0.7 g, reacting at 55° C. for 0.75 h, and performing liquid-solid separation to obtain sodium fluoride and a salting-out mother liquor;

[0164] (3) adding process water, a dispersant (a mixture of modified starch and carboxymethyl cellulose in a mass ratio of 3:5), a foaming agent (a mixture of octanol and pine oil in a mass ratio of 1:2), and a collector (a mixture of natural gas condensate and kerosene in a mass ratio of 4:5) to the leached residue of step (1) to obtain a flotation pulp, and flotating the flotation pulp, wherein the flotation pulp is subjected to one roughing selection, two scavenging selections, and three cleaning selections, wherein the mass concentration of the flotation pulp is 27%, the rotation speed is 1800 r / min, and the aeration volume is 0.22 m 3 / h, the scraper speed is 9r / min, the added amount of dispersant is 520g / t of primary leaching residue, the added amount of collector is 700g / t of primary leaching residue, the added amount of foaming agent is 400g / t of primary leaching residue, liquid-solid separation is performed to obtain carbon concentrate, tailings and flotation mother liquor, and the flotation mother liquor is reused in step (3);

[0165] (4) adding sodium persulfate and sodium hydroxide aqueous solution to the tailings of step (3) for secondary slurry leaching, the solid-liquid mass volume ratio is 1g:27mL, the temperature of the secondary slurry leaching is 60°C, the time of the secondary slurry leaching is 0.5h, wherein the molar ratio of aluminum to sodium hydroxide in the slurry is 1:4.5, the amount of sodium persulfate added is 0.6mg / L, and liquid-solid separation is performed to obtain secondary leaching solution and secondary leaching residue;

[0166] (5) adding nitric acid to the secondary leaching solution of step (4) to adjust the pH to 7 for neutralization, reacting for 2 hours, and performing liquid-solid separation to obtain regenerated cryolite and a neutralization filtrate.

[0167] (6) The salting-out mother liquor of step (2) and the neutralization filtrate of step (5) are evaporated under reduced pressure at 88° C. to obtain steam condensate and evaporation concentrate, and the steam condensate is reused as process water.

[0168] (7) The evaporated concentrated liquid of step (6) is cooled and crystallized at 36° C., and the liquid-solid separation is performed to obtain sodium nitrate and a crystallization mother liquor. The sodium nitrate is partially recycled to step (2), and the crystallization mother liquor is recycled to secondary slurry leaching.

[0169] Example 8

[0170] This embodiment provides a method for recovering fluorine, aluminum and carbon from a cathode carbon block. The main components and contents of the cathode carbon block are the same as those in Example 4.

[0171] The method comprises the following steps:

[0172] (1) The cathode carbon block is crushed and ground to obtain a cathode carbon block powder with a particle size of no more than 75 μm, and the cathode carbon block powder is subjected to a slurry leaching with process water at a solid-liquid mass volume ratio of 1 g:5.5 mL, the slurry leaching temperature is 35° C., the slurry leaching time is 1.5 h, and liquid-solid separation is performed to obtain a primary leaching liquid and a primary leaching residue;

[0173] (2) adding sodium nitrate to the first leaching solution of step (1) at a volume-mass ratio of 1 mL:1.1 g, reacting at 50° C. for 1.75 h, and performing liquid-solid separation to obtain sodium fluoride and a salting-out mother liquor;

[0174] (3) adding process water, dispersant (modified starch), foaming agent (a mixture of pine oil and sec-butyl alcohol in a mass ratio of 3:2), and collector (a mixture of kerosene, diethyl phthalate and dewaxed kerosene in a mass ratio of 3:5:2) to the leached residue of step (1) to obtain flotation pulp, and flotation of the flotation pulp is performed, wherein the flotation pulp has a mass concentration of 16%, a rotation speed of 900 r / min, and an aeration volume of 0.16 m 3 / h, the scraper speed is 5.2r / min, the amount of dispersant added is 80g / t of primary leaching residue, the amount of collector added is 200g / t of primary leaching residue, the amount of foaming agent added is 80g / t of primary leaching residue, liquid-solid separation is performed to obtain carbon concentrate, tailings and flotation mother liquor, and the flotation mother liquor is reused in step (3);

[0175] (4) adding hypochlorous acid, sodium hypochlorite and sodium hydroxide aqueous solution to the tailings of step (3) for secondary slurry leaching, the solid-liquid mass volume ratio is 1g:16mL, the temperature of the secondary slurry leaching is 120°C, the time of the secondary slurry leaching is 1.8h, wherein the molar ratio of aluminum to sodium hydroxide in the slurry is 1:6.8, the addition amount of hypochlorous acid and sodium hypochlorite is 0.2mg / L, and liquid-solid separation is performed to obtain secondary leaching liquid and secondary leaching residue;

[0176] (5) The secondary leaching solution of step (4) was neutralized by adding nitric acid to adjust the pH to 10, reacting for 1.25 hours, and liquid-solid separation to obtain regenerated cryolite and a neutralization filtrate.

[0177] (6) The salting-out mother liquor of step (2) and the neutralization filtrate of step (5) are evaporated under reduced pressure at 92° C. to obtain steam condensate and evaporation concentrate, and the steam condensate is reused as process water.

[0178] (7) The evaporated concentrated liquid of step (6) is cooled and crystallized at 25° C., and the liquid-solid separation is performed to obtain sodium nitrate and a crystallization mother liquor. The sodium nitrate is partially recycled to step (2), and the crystallization mother liquor is recycled to secondary slurry leaching.

[0179] Example 9

[0180] This embodiment provides a method for recovering fluorine, aluminum and carbon from a cathode carbon block. The main components and contents of the cathode carbon block are the same as those in Example 4.

[0181] The method comprises the following steps:

[0182] (1) The cathode carbon block is crushed and ground to obtain a cathode carbon block powder with a particle size of no more than 75 μm, and the cathode carbon block powder is subjected to a slurry leaching with process water at a solid-liquid mass volume ratio of 1 g:8.5 mL, the slurry leaching temperature is 64° C., the slurry leaching time is 3.5 h, and liquid-solid separation is performed to obtain a primary leaching liquid and a primary leaching residue;

[0183] (2) adding sodium nitrate to the first leaching solution of step (1) at a volume-mass ratio of 1 mL:0.9 g, reacting at 38° C. for 1.5 h, and performing liquid-solid separation to obtain sodium fluoride and a salting-out mother liquor;

[0184] (3) adding process water, dispersant (a mixture of water glass, modified starch and carboxymethyl cellulose in a mass ratio of 1:2:3), foaming agent (a mixture of sec-butyl alcohol and sec-octanol in a mass ratio of 1:1), and collector (a mixture of diethyl phthalate, dewaxed kerosene and light diesel in a mass ratio of 3:4:1) to the leached residue of step (1) for flotation, wherein the flotation slurry has a mass concentration of 24%, a rotation speed of 1620 r / min, and an aeration volume of 0.19 m 3 / h, the scraper speed is 7.5r / min, the added amount of dispersant is 360g / t of primary leaching residue, the added amount of collector is 500g / t of primary leaching residue, the added amount of foaming agent is 280g / t of primary leaching residue, liquid-solid separation is performed to obtain carbon concentrate, tailings and flotation mother liquor, and the flotation mother liquor is reused in step (3);

[0185] (4) The tailings of step (3) were subjected to secondary slurry leaching by adding oxygen, sodium perchlorate and sodium hydroxide aqueous solution, the solid-liquid mass volume ratio was 1 g:30 mL, the temperature of the secondary slurry leaching was 240 ° C, the time of the secondary slurry leaching was 2.4 h, wherein the molar ratio of aluminum to sodium hydroxide in the slurry was 1:7.2, the oxygen introduction amount was 0.85 m 3 / L, liquid-solid separation, to obtain secondary leaching liquid and secondary leaching residue;

[0186] (5) adding nitric acid to the secondary leaching solution of step (4) to adjust the pH to 8 for neutralization, reacting for 3 hours, and performing liquid-solid separation to obtain regenerated cryolite and a neutralization filtrate;

[0187] (6) evaporating the salting-out mother liquor of step (2) and the neutralization filtrate of step (5) under reduced pressure at 94° C. to obtain steam condensate and evaporation concentrate, and reusing the steam condensate as process water;

[0188] (7) The evaporated concentrated liquid of step (6) is cooled and crystallized at 40° C., and the liquid-solid separation is performed to obtain sodium nitrate and a crystallization mother liquor. The sodium nitrate is partially recycled to step (2), and the crystallization mother liquor is recycled to secondary slurry leaching.

[0189] Example 10

[0190] This embodiment provides a method for recovering fluorine, aluminum and carbon from a cathode carbon block. The raw materials and method are referred to those of Embodiment 1, with the only difference being that the pH in step (5) is 6.

[0191] Embodiment 11

[0192] This embodiment provides a method for recovering fluorine, aluminum and carbon from a cathode carbon block. The raw materials and method are referred to those of Embodiment 1, with the only difference being that the pH in step (5) is 10.

[0193] Comparative Example 1

[0194] This comparative example provides a method for recovering fluorine, aluminum and carbon from a cathode carbon block. The raw materials and method are referred to those of Example 1, with the only difference being that sodium nitrate is added in step (2) at a volume-to-mass ratio of 1:0.2.

[0195] The comparative example was analyzed and tested, and the recovery rate of fluorine was low.

[0196] Comparative Example 2

[0197] This comparative example provides a method for recovering fluorine, aluminum and carbon from a cathode carbon block. The raw materials and method are referred to those of Example 1, with the only difference being that the molar ratio of aluminum to sodium hydroxide in the slurry in step (4) is 1:3.

[0198] The comparative example was analyzed and tested and the recovery rate of aluminum was low.

[0199] The carbon, aluminum and fluorine contents in the liquid and solid phases of Examples 1-11 and Comparative Examples 1-2 were measured, and the recovery rates of carbon, aluminum and fluorine, and the purity of carbon, cryolite and sodium fluoride products were calculated. The test results are shown in Table 1.

[0200] Table 1

[0201]

[0202]

[0203] From the above embodiments and comparative examples, it can be seen that the method of the present invention uses water to extract the soluble fluoride salt in the cathode carbon block, and then uses sodium nitrate to salt it out, and the product purity of sodium fluoride can reach more than 99%; the present invention uses flotation to extract carbon from the cathode carbon block, and the recovery rate can reach more than 80%, and the product purity can reach more than 85%; the present invention uses a strong alkali to completely dissolve the cryolite, alumina and other components in the cathode carbon block, and then uses nitric acid to adjust the pH to generate regenerated cryolite, and the recovery rate of fluorine and aluminum can reach more than 90%, and the purity of the obtained cryolite product can reach more than 98%. The sodium nitrate added by the salting out of the method of the present invention can be recycled and reused, with low production cost, clean process and no pollution, and has broad application prospects.

[0204] At the same time, by comparing Example 1 with Examples 10-11, it can be seen that if the pH adjusted during the neutralization process is too high or too low, the aluminum recovery rate will be reduced and the quality of the generated cryolite will be reduced.

[0205] By comparing Example 1 with Comparative Example 1, it can be seen that if the amount of the salt precipitation agent sodium nitrate is too small, the recovery rate of fluorine will be reduced.

[0206] By comparing Example 1 with Comparative Example 2, it can be seen that if the amount of alkali used is too small, the recovery rate of aluminum will be reduced.

[0207] The applicant declares that the present invention illustrates the detailed method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed method, that is, it does not mean that the present invention must rely on the above-mentioned detailed method to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for recovering fluorine, aluminum and carbon from cathode carbon, characterized in that: The method comprises the following steps: (1) mixing cathode carbon with process water, subjecting the obtained slurry to primary slurry leaching, and then separating liquid from solid to obtain a primary leaching liquid and a primary leaching residue; (2) recovering carbon powder from the primary leaching residue of step (1) to obtain carbon powder and tailings; (3) mixing the tailings from step (2) with an alkaline solution, subjecting the obtained slurry to secondary slurry leaching, and then separating the solid and liquid to obtain a secondary leaching solution and a secondary leaching residue; (4) adding acid to the secondary leaching solution of step (3) to carry out a neutralization reaction, and performing solid-liquid separation to obtain regenerated cryolite and a neutralization filtrate; (5) crystallizing the neutralization filtrate of step (4) to obtain a sodium salt and a crystallization mother liquor; The primary leaching solution of step (1) is subjected to salting-out by a salting-out agent to obtain sodium fluoride, wherein the salting-out agent at least partially comprises the sodium salt obtained in step (5).

2. The method for recovering fluorine, aluminum and carbon from cathode carbon according to claim 1, characterized in that: The cathode carbon is a cathode carbon block. Before the primary slurry leaching in step (1), the cathode carbon block is first crushed and ground to obtain cathode carbon block powder; Preferably, the particle size of the cathode carbon block powder is not greater than 150 μm; Preferably, during the first slurry leaching process in step (1), the solid-liquid mass volume ratio is 1 g: (2-10) mL, preferably 1 g: (4-6) mL; Preferably, the temperature of the first slurry leaching in step (1) is 20 to 100° C. Preferably, the time for the first slurry leaching in step (1) is 0.5 to 5 hours.

3. The method for recovering fluorine, aluminum and carbon from cathode carbon according to claim 1 or 2, characterized in that: The method for recovering carbon powder in step (2) is a flotation method, which comprises: adding process water, a collector, a foaming agent and a dispersant to the primary leaching residue of step (1) to obtain a flotation pulp, performing flotation, liquid-solid separation, and obtaining a carbon concentrate, tailings and a flotation mother liquor, wherein the carbon concentrate is the carbon powder; Preferably, the collector comprises one or a combination of at least two of kerosene, light diesel, diethyl phthalate, dewaxed kerosene or natural gas condensate; Preferably, the addition amount of the collector is 150 g to 1000 g / t of primary leaching residue; Preferably, the foaming agent comprises one or a combination of at least two of sec-butyl alcohol, sec-octanol or pine oil; Preferably, the amount of the foaming agent added is 50 g to 500 g / t of primary leaching residue; Preferably, the dispersant comprises one or a combination of at least two of water glass, modified starch, carboxymethyl cellulose or sodium hexametaphosphate; Preferably, the amount of the dispersant added is 50 g to 600 g / t of primary leaching residue; Preferably, the mass concentration of the flotation pulp is 15-30%; Preferably, the flotation process parameters are: rotation speed of 800-2000 r / min, aeration volume of 0.15-0.25 m 3 / h, scraper speed is 5~10r / min; Preferably, the flotation method includes roughing, scavenging and cleaning; Preferably, the number of rough selection is 1 to 3 times, the number of sweep selection is 1 to 5 times, and the number of fine selection is 2 to 5 times; Preferably, the middle residues from the first scavenging and the last cleaning are returned to the first cleaning for re-floatation, and the middle residues from the second to the last roughing, the second to the last scavenging and the first to the second to last cleaning are returned to the first roughing for re-floatation.

4. The method for recovering fluorine, aluminum and carbon from cathode carbon according to any one of claims 1 to 3, characterized in that: The alkaline solution in step (3) is a sodium hydroxide aqueous solution prepared by process water and sodium hydroxide; Preferably, during the secondary slurry leaching process in step (3), the solid-liquid mass volume ratio is 1 g: (5-30) mL, preferably 1 g: (8-25) mL, and more preferably 1 g: (10-20) mL; Preferably, the molar ratio of the aluminum in the secondary slurry to the alkali in the alkali solution in step (3) is 1:(4-8); Preferably, the temperature of the secondary slurry leaching in step (3) is 60 to 250° C., preferably 80 to 200° C., more preferably 100 to 150° C.; Preferably, the time for the secondary slurry leaching in step (3) is 0.5 to 5 hours.

5. The method for recovering fluorine, aluminum and carbon from cathode carbon according to any one of claims 1 to 4, characterized in that: In the mixing step of step (3), the tailings, the cyanide-breaking agent and the alkaline solution are mixed; Preferably, the cyanide-destroying agent comprises one or a combination of at least two of peroxide, hypochlorous acid, hypochlorite, perchloric acid, perchlorate, persulfuric acid, persulfate, oxygen, ozone and chlorine; Preferably, if the cyanide-breaking agent is a liquid or solid, the amount of the cyanide-breaking agent liquid / solid agent added is 0.2 to 0.6 mg / L, more preferably 0.3 to 0.5 mg / L; Preferably, if the cyanide-breaking agent is a gas, the gas introduction rate of the cyanide-breaking agent is 0.5m 3 / L~1.0m 3 / L.

6. The method for recovering fluorine, aluminum and carbon from cathode carbon according to any one of claims 1 to 4, characterized in that: In step (4), acid is added to adjust and control the pH of the immersion solution until the neutralization reaction is complete; Preferably, the pH is 4 to 12, preferably pH is 6 to 10, more preferably pH is 7 to 9; Preferably, the neutralization reaction time in step (4) is 0.25 to 2 hours.

7. The method for recovering fluorine, aluminum and carbon from cathode carbon according to any one of claims 1 to 6, characterized in that: The crystallization method of step (5) is cooling crystallization, and the temperature of cooling crystallization is preferably 20-40° C.; Preferably, in step (5), the neutralized filtrate is evaporated to obtain steam condensate and evaporation concentrate, and the evaporation concentrate is crystallized; Preferably, the steam condensate is reused as process water; Preferably, the evaporation is reduced-pressure evaporation, and the evaporation temperature is 80-95°C.

8. The method for recovering fluorine, aluminum and carbon from cathode carbon according to any one of claims 1 to 7, characterized in that: The step of using a salting-out agent to salt out the primary leaching solution of step (1) to obtain sodium fluoride comprises: adding the salting-out agent to the primary leaching solution, and after the salting-out reaction, performing solid-liquid separation to obtain sodium fluoride and a salting-out mother solution; Preferably, the volume mass ratio of the primary immersion liquid to the salting-out agent is 1 mL: (0.4-1.2) g; Preferably, the temperature of the salting-out reaction is 25 to 60°C; Preferably, the salting-out reaction time is 0.25 to 2 hours.

9. The method for recovering fluorine, aluminum and carbon from cathode carbon according to any one of claims 1 to 8, characterized in that: The crystallization mother liquor obtained in step (5) is recycled to the secondary slurry leaching step in step (3).

10. The method for recovering fluorine, aluminum and carbon from cathode carbon according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: S1. Crush and grind the cathode carbon block to obtain cathode carbon block powder with a particle size of no more than 150 μm, and perform a slurry leaching on the cathode carbon block powder and process water at a solid-liquid mass volume ratio of 1 g: (2-10) mL. The temperature of the slurry leaching is 20-100 ° C. The time of the slurry leaching is 0.5-5 h. After the slurry leaching is completed, liquid-solid separation is performed to obtain a primary leaching liquid and a primary leaching residue; S2. Sodium nitrate is added to the first leaching solution of step S1 at a volume-mass ratio of 1 mL: (0.4-1.2) g, and the mixture is reacted at 25-60° C. for 0.25-2 h, and liquid-solid separation is performed to obtain sodium fluoride and a salting-out mother liquor; S3: adding process water, dispersant, foaming agent and collector to the primary leaching residue of step S1 to obtain flotation pulp, flotating the flotation pulp, wherein the flotation includes 1 to 3 roughing, 1 to 5 scavenging and 2 to 5 cleaning, liquid-solid separation, and obtaining carbon concentrate, tailings and flotation mother liquor, wherein the carbon concentrate is the carbon powder, and the flotation mother liquor is recycled to step S3; The mass concentration of the flotation pulp is 15-30%, the rotation speed is 800-2000r / min, and the aeration volume is 0.15-0.25m 3 / h, the scraper speed is 5-10r / min, the addition amount of dispersant is 50g-600g / t of primary leaching residue, the addition amount of collector is 150g-1000g / t of primary leaching residue, and the addition amount of foaming agent is 50g-500g / t of primary leaching residue; S4: adding a cyanide-breaking agent and a sodium hydroxide aqueous solution to the tailings of step S3 at a solid-liquid mass volume ratio of 1 g: (5-30) mL for secondary slurry leaching, the temperature of the secondary slurry leaching is 60-250° C., and the time of the secondary slurry leaching is 0.5-5 h, wherein the molar ratio of aluminum in the slurry to sodium hydroxide is 1: (4-8), the cyanide-breaking agent is one or a combination of at least two of peroxide, hypochlorous acid, hypochlorite, perchloric acid, perchlorate, persulfate, persulfate, oxygen, ozone and chlorine, liquid-solid separation is performed to obtain a secondary leaching solution and a secondary leaching residue; S5: adding nitric acid to the secondary leaching solution of step S4 to adjust the pH to 4-12 for neutralization reaction for 0.25-2h, and separating the liquid and solid to obtain regenerated cryolite and neutralization filtrate; S6: evaporate the salting-out mother liquor of step S2 and the neutralization filtrate of step S5 under reduced pressure at 80-95° C. to obtain steam condensed water and evaporation concentrate, and the steam condensed water is reused as process water; In step S7, the evaporated concentrated liquid of step S6 is cooled and crystallized at 20-40° C., and the liquid-solid separation is performed to obtain sodium nitrate and a crystallization mother liquor. The sodium nitrate is partially recycled to step S2, and the crystallization mother liquor is recycled to secondary slurry leaching.

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