A method for recovering lithium, sodium, fluorocarbon and aluminum from cryolite-containing solid waste in an aluminum electrolysis plant

Abstract

The invention discloses a method for recovering lithium sodium carbon fluoride aluminum from cryolite solid waste in an electrolytic aluminum plant, which comprises the following steps: S1: pretreatment; S2: leaching reaction; S3: primary solid-liquid separation; S4: leachate treatment; S5: leachate residue treatment. Advantages: (1) alkaline calcium is mixed with waste cryolite for alkaline leaching, and cyanide in the alkaline leachate is treated by high-temperature hydrolysis, so no hydrogen cyanide and hydrogen fluoride gas are generated, thereby improving safety; (2) inexpensive alkaline calcium such as carbide slag and calcium hydroxide is used as an auxiliary material for alkaline leaching recovery of cryolite solid waste produced in an electrolytic aluminum plant, thereby reducing the use of acid and greatly reducing the recovery cost; (3) by using this system, effective components such as sodium, aluminum, carbon, lithium, and fluorine in cryolite solid waste can be recovered and utilized, and the separated calcium fluoride component has a high content and can be sold as fluorite powder, thereby greatly reducing the solid waste stockpile and improving economic benefits.

Description

Technical Field

[0001] The invention relates to the technical field of solid waste treatment in aluminum electrolysis plants, and in particular to a method for recovering lithium, sodium, carbon, fluorine and aluminum from cryolite-containing solid waste in aluminum electrolysis plants. Background Art

[0002] The cryolite-containing solid wastes produced by aluminum electrolysis plants mainly include overhaul slag, cathode carbon blocks, anode carbon blocks, shell surface blocks, and electrolytes. 3 AlF 6 and Na 4 Fe(CN) 6 The other is refractory bricks, cathode carbon blocks, anode carbon blocks except the main component Na 3 AlF 6 、Na 2 LiF 6 and Na 3 Fe(CN) 6 The outside is carbon powder, and the main component of the shell is Na 3 AlF 6 and metallic aluminum, the electrolyte is mainly composed of Na 3 AlF 6 and Na 2 LiF 6 .

[0003] At present, the main treatment process for solid waste produced by aluminum electrolytic plants is to use sulfuric acid or hydrochloric acid for acid leaching to extract lithium salts. The sodium ions are replaced with low-priced sodium chloride or sodium sulfate, while carbon and fluorine cannot be recovered and are treated as secondary solid waste. In addition, cathode carbon blocks, anode carbon blocks and overhaul slag contain fluorine and cyanide, which will produce highly toxic gas hydrogen cyanide and highly corrosive gas hydrogen fluoride during acid leaching, posing extremely high safety risks. Summary of the invention

[0004] The object of the present invention is to provide a method for recovering lithium sodium carbon fluoride aluminum from cryolite-containing solid waste in an aluminum electrolytic plant.

[0005] The present invention is implemented by the following technical scheme: A method for recovering lithium sodium fluorocarbon aluminum from solid waste containing cryolite in an aluminum electrolysis plant, comprising the following steps:

[0006] S1: Preprocessing

[0007] The solid waste blocks containing cryolite from the electrolysis plant are mixed and crushed to remove the elemental aluminum and elemental iron therein, and then finely ground into powder with a size less than 200 meshes, and then the powder is floated to float out carbon powder to obtain the powder to be processed;

[0008] S2: Leaching reaction

[0009] The powder to be treated obtained in S1 is mixed with alkaline calcium and water at a solid-liquid ratio of 1:2-6 to prepare a slurry, wherein the weight ratio of alkaline calcium to the powder to be treated is 1.1-1.5, and a leaching slurry is obtained after the reaction;

[0010] S3: Primary solid-liquid separation

[0011] The leached slurry obtained in S2 is subjected to a solid-liquid separation to obtain leached residue and leached liquid;

[0012] S4: Leachate treatment

[0013] The leachate obtained in S3 is treated to obtain crude lithium carbonate and heavy soda ash;

[0014] S5: Leaching residue treatment

[0015] The leached residue obtained from S3 is treated to obtain calcium chloride solution, sodium carbonate solution, aluminum hydroxide and high-grade calcium fluoride.

[0016] Furthermore, the temperature of the S2 leaching reaction is 30-95°C, and the reaction time is 30-180min.

[0017] Furthermore, the alkaline calcium in S2 is carbide slag or calcium hydroxide.

[0018] Furthermore, the S4 specifically includes the following processing steps:

[0019] S4-1: firstly introducing carbon dioxide into the leachate to obtain a first mixed slurry; then performing solid-liquid separation on the first mixed slurry to separate crude lithium carbonate and obtain a first sodium carbonate solution;

[0020] S4-2: Evaporating and concentrating the first sodium carbonate solution obtained in S4-1 once, so that lithium carbonate slightly dissolved in the first sodium carbonate solution is precipitated due to supersaturation, and separating the precipitated lithium carbonate to obtain a second sodium carbonate solution;

[0021] S4-3: hydrolyzing the second sodium carbonate solution obtained in S4-2 at high temperature to convert the sodium cyanide in the second sodium carbonate solution into sodium formate, and then cooling the solution to obtain a third sodium carbonate solution;

[0022] S4-4: After filtering and removing impurities from the third sodium carbonate solution obtained in S4-3, an alkaline extractant is added to extract the remaining lithium in the third sodium carbonate solution to obtain a fourth sodium carbonate solution;

[0023] S4-5: subjecting the fourth sodium carbonate solution obtained in S4-4 to secondary evaporation and crystallization to separate the saturated sodium carbonate mother liquor to obtain a high-solid sodium carbonate monohydrate slurry;

[0024] S4-6: heating and stirring the sodium carbonate monohydrate slurry obtained in S4-5 to remove crystal water to obtain a second mixed slurry; performing solid-liquid separation on the second mixed slurry to separate a saturated sodium carbonate solution to obtain a sodium carbonate solid;

[0025] S4-7: Dry the sodium carbonate solid obtained in S4-6 to obtain heavy soda ash.

[0026] Furthermore, in S4-1, carbon dioxide is introduced at a pressure of 0.2-2.0 MPa, the reaction temperature is controlled to be 25-105°C, the reaction time is 30-300 min, and the pH of the first mixed slurry is controlled to be 9-13.8.

[0027] Further, in S4-3, the second sodium carbonate solution obtained in S4-2 is heated to 160-180°C and reacted at a pressure of 0.6-0.8 MPa for 30-150 min to convert the sodium cyanide in the second sodium carbonate solution into sodium formate, and then cooled to 30-45°C to obtain a third sodium carbonate solution.

[0028] Further, in S4-6, the sodium carbonate monohydrate slurry obtained in S4-5 is heated to 110-130° C. and stirred at a pressure of 0.2-1.2 MPa for 30-120 min to obtain a second mixed slurry.

[0029] Further, in S4-5, when the potassium content in the separated saturated sodium carbonate mother liquor is lower than 100 g / L, it is subjected to secondary evaporation crystallization together with the fourth sodium carbonate solution; in S4-6, when the potassium content in the separated saturated sodium carbonate mother liquor is lower than 100 g / L, it is sent back to S4-5 and subjected to secondary evaporation crystallization together with the fourth sodium carbonate solution.

[0030] Furthermore, S5 specifically includes the following processing steps:

[0031] S5-1: mixing the leached residue and the calcium chloride solution to prepare a low-grade calcium fluoride slurry with a solid-liquid ratio of 1:3-5;

[0032] S5-2: Add hydrochloric acid to the low-grade calcium fluoride slurry obtained in S5-1, adjust the pH to 1-4, the reaction temperature to 80-110° C., and the reaction time to 30-300 min to obtain a first mixed slurry;

[0033] S5-3: performing a solid-liquid separation on the first mixed slurry obtained in S5-2 to separate the calcium chloride solution and obtain medium-grade calcium fluoride containing aluminum hydroxide;

[0034] S5-4: adding water and sodium hydroxide to the medium-grade calcium fluoride obtained in S5-3 to prepare a medium-grade calcium fluoride slurry with a solid-liquid ratio of 1:1-6, wherein the amount of sodium hydroxide added is 1.1-1.5 times the molar amount of aluminum hydroxide, the reaction temperature is 30-110°C, the reaction time is 30-300 min, and a second mixed slurry is obtained after the reaction;

[0035] S5-5: The second mixed slurry obtained in S5-4 is subjected to secondary solid-liquid separation, and the solid phase obtained by separation is a high-grade calcium fluoride product.

[0036] S5-6: First, carbon dioxide is introduced into the solution separated in S5-5 to react to obtain a third mixed slurry, and then the third mixed slurry is subjected to three solid-liquid separations to obtain a solid phase of aluminum hydroxide and a liquid phase of sodium carbonate solution.

[0037] Furthermore, in S5-3, the first solid-liquid separation is carried out in the first filter-washing integrated machine, and the washing water discharged from the first filter-washing integrated machine is sent back to S5-1 for pulping: in S5-5, the second solid-liquid separation is carried out in the second filter-washing integrated machine, and the washing water discharged from the second filter-washing integrated machine is sent back to S5-4 for preparing medium-grade calcium fluoride slurry.

[0038] The advantages of the present invention are as follows: (1) alkaline calcium is mixed with waste cryolite for alkaline leaching, and high-temperature hydrolysis is used to remove cyanide in the solution, and no hydrogen cyanide and hydrogen fluoride gas are generated, thereby improving safety; (2) inexpensive alkaline calcium such as carbide slag and calcium hydroxide are used as auxiliary materials for alkaline leaching recovery of cryolite-containing solid waste produced by electrolytic aluminum plants, thereby reducing the use of acid and greatly reducing the recovery cost; (3) using this system, effective components such as sodium, aluminum, carbon, lithium, and fluorine in cryolite-containing solid waste can be recovered and utilized, and the separated calcium fluoride component has a high content and can be sold as fluorite powder, thereby greatly reducing the solid waste stockpile and improving economic benefits. DETAILED DESCRIPTION

[0039] Example 1: A method for recovering lithium sodium fluorocarbon aluminum from cryolite-containing solid waste in an aluminum electrolysis plant, comprising the following steps:

[0040] S1: Preprocessing

[0041] The solid waste blocks containing cryolite from the electrolysis plant are mixed and crushed to remove the elemental aluminum and elemental iron therein, and then finely ground into powder with a mesh size less than 180, and then the powder is floated to float out carbon powder to obtain the powder to be processed; the floated carbon powder can be recycled;

[0042] S2: Leaching reaction

[0043] The powder to be treated obtained in S1 is added with calcium hydroxide and water in a solid-liquid ratio of 1:2 to prepare a slurry, wherein the weight ratio of alkaline calcium to the powder to be treated is 1.1, and a leaching slurry is obtained after the reaction; the leaching reaction temperature is 30°C and the reaction time is 180 minutes. The reaction process is as follows:

[0044] 2Na 3 AlF 6 +7Ca(OH) 2 =6NaOH + 6CaF 2 ↓+CaAl 2 (OH) 8 ↓

[0045] 2Li 3 AlF 6 +7Ca(OH) 2 =6LiOH + 6CaF 2 ↓ +CaAl 2 (OH) 8 ↓

[0046] 2LiF+Ca(OH) 2 =LiOH+CaF 2 ↓

[0047] Na 3 Fe(CN) 6 +3NaOH=6NaCN +Fe(OH) 3 ↓

[0048] Na 3 AlF 6 + 2Ca(OH) 2 =2NaF↓+NaAlO 2 +2CaF 2 ↓+2H 2 O

[0049] 2KF+ Ca(OH) 2 =2KOH+ CaF 2 ↓

[0050] S3: Primary solid-liquid separation

[0051] The leached slurry obtained from S2 is subjected to a solid-liquid separation to obtain leaching residue and leaching liquid; the leaching residue mainly includes NaF, CaF 2、 CaAl 2 (OH) 8 and Fe(OH) 3 The leaching solution mainly includes NaOH, LiOH, NaAlO 2 and NaCN;

[0052] S4: Leachate treatment

[0053] The leachate obtained in S3 is treated to obtain crude lithium carbonate and heavy soda ash; S4 specifically includes the following treatment process:

[0054] S4-1: First, introduce carbon dioxide into the leaching solution. Specifically, introduce carbon dioxide at a pressure of 0.2 MPa, control the reaction temperature to be 25° C., the reaction time to be 300 min, and control the pH of the first mixed slurry to be 9;

[0055] The reaction equation is as follows:

[0056] CO 2 + 2NaOH = Na 2 CO 3 + H 2 O

[0057] CO 2 + 2LiOH = Li 2 CO 3 ↓ + H 2 O

[0058] 2NaAlO 2 + CO 2 + 3H 2 O = 2Al(OH) 3 ↓ + Na 2 CO 3

[0059] 2KOH + CO 2 = K 2 CO 3 + H 2 O

[0060] After the reaction, a first mixed slurry containing lithium carbonate, sodium carbonate and aluminum hydroxide is obtained; then the first mixed slurry is subjected to solid-liquid separation to separate crude lithium carbonate and obtain a first sodium carbonate solution;

[0061] S4-2: Evaporating and concentrating the first sodium carbonate solution obtained in S4-1 once, thereby increasing the concentration of the first sodium carbonate solution and causing lithium carbonate slightly soluble in the first sodium carbonate solution to precipitate due to supersaturation, and separating the precipitated lithium carbonate to obtain a second sodium carbonate solution;

[0062] S4-3: The second sodium carbonate solution obtained in S4-2 is heated to 160°C and reacted at a pressure of 0.6 MPa for 150 min to convert the sodium cyanide in the second sodium carbonate solution into sodium formate. The reaction equation is as follows:

[0063] NaCN + 2H 2O = HCOONa + NH 3 ↑

[0064] Then the temperature was cooled to 30° C. to obtain a third sodium carbonate solution.

[0065] S4-4: After filtering and removing impurities from the third sodium carbonate solution obtained in S4-3, an alkaline extractant (HBL121 or 3938H) is added to extract the remaining lithium in the third sodium carbonate solution to obtain a fourth sodium carbonate solution;

[0066] S4-5: subjecting the fourth sodium carbonate solution obtained in S4-4 to secondary evaporation and crystallization to separate the saturated sodium carbonate mother liquor to obtain a high-solid sodium carbonate monohydrate slurry;

[0067] S4-6: heating the sodium carbonate monohydrate slurry obtained in S4-5 to 110° C. and stirring for 120 min at a pressure of 0.2 MPa to obtain a second mixed slurry; performing solid-liquid separation on the second mixed slurry to separate a saturated sodium carbonate solution to obtain a sodium carbonate solid;

[0068] S4-7: Dry the sodium carbonate solid obtained in S4-6 to obtain heavy soda ash.

[0069] In S4-5, when the potassium content in the separated saturated sodium carbonate mother liquor is lower than 100 g / L, it is subjected to secondary evaporation crystallization together with the fourth sodium carbonate solution; in S4-6, when the potassium content in the separated saturated sodium carbonate mother liquor is lower than 100 g / L, it is sent back to S4-5 for secondary evaporation crystallization together with the fourth sodium carbonate solution.

[0070] S5: Leaching residue treatment

[0071] The leached residue obtained from S3 is treated to obtain calcium chloride solution, sodium carbonate solution, aluminum hydroxide and high-grade calcium fluoride.

[0072] S5 specifically includes the following processing steps:

[0073] S5-1: mixing the leached residue and the calcium chloride solution to prepare a low-grade calcium fluoride slurry with a solid-liquid ratio of 1:3;

[0074] S5-2: Add hydrochloric acid to the low-grade calcium fluoride slurry obtained in S5-1, adjust the pH to 1, the reaction temperature to 80°C, the reaction time to 300 min, and obtain a first mixed slurry; the reaction process is as follows:

[0075] CaAl 2 (OH) 8 +2HCl=2Al(OH) 3 ↓+CaCl 2 +2H 2 O

[0076] CaCl 2 +2NaF=2NaCl+CaF 2 ↓

[0077] Fe(OH) 3 +3HCl=FeCl 3 +3H 2 O

[0078] Al(OH) 3 +3HCl = AlCl 3 +3H 2 O

[0079] S5-3: performing a solid-liquid separation on the first mixed slurry obtained in S5-2 to separate the calcium chloride solution and obtain medium-grade calcium fluoride containing aluminum hydroxide;

[0080] S5-4: Add water and sodium hydroxide to the medium-grade calcium fluoride obtained in S5-3 to prepare a medium-grade calcium fluoride slurry with a solid-liquid ratio of 1:1, the amount of sodium hydroxide added is 1.1 times the molar amount of aluminum hydroxide, the reaction temperature is 30°C, the reaction time is 300 min, and a second mixed slurry is obtained; the reaction equation is:

[0081] Al(OH) 3 +NaOH =NaAlO 2 +2H 2 O

[0082] S5-5: The second mixed slurry obtained in S5-4 is subjected to secondary solid-liquid separation, and the solid phase obtained by separation is a high-grade calcium fluoride product.

[0083] S5-6: Carbon dioxide is first introduced into the solution separated from S5-5 to react to obtain a third mixed slurry, and the reaction equation is:

[0084] 2NaAlO 2 + CO 2 +3H 2 O=Na 2 CO 3 +2Al(OH) 3 ↓

[0085] 2NaOH + CO 2 = Na 2 CO 3 + H 2 O

[0086] The third mixed slurry is then subjected to three solid-liquid separations, and the obtained solid phase is aluminum hydroxide, and the obtained liquid phase is a sodium carbonate solution.

[0087] In S5-3, the primary solid-liquid separation is carried out in the first integrated filter-washer, and the washing water discharged from the first integrated filter-washer is sent back to S5-1 for pulping: in S5-5, the secondary solid-liquid separation is carried out in the second integrated filter-washer, and the washing water discharged from the second integrated filter-washer is sent back to S5-4 for preparing medium-grade calcium fluoride slurry.

[0088] Example 2: A method for recovering lithium sodium fluorocarbon aluminum from cryolite-containing solid waste in an aluminum electrolysis plant, comprising the following steps:

[0089] S1: Preprocessing

[0090] The solid waste blocks containing cryolite from the electrolysis plant are mixed and crushed to remove the elemental aluminum and elemental iron therein, and then finely ground into powder with a mesh size less than 150, and then the powder is floated to float out carbon powder to obtain the powder to be treated;

[0091] S2: Leaching reaction

[0092] The powder to be treated obtained in S1 is mixed with calcium hydroxide and water at a solid-liquid ratio of 1:6 to prepare a slurry, wherein the weight ratio of alkaline calcium to the powder to be treated is 1.5, and a leaching slurry is obtained after the reaction; the leaching reaction temperature is 95°C and the reaction time is 30 minutes. The reaction process is as follows:

[0093] 2Na 3 AlF 6 +7Ca(OH) 2 =6NaOH + 6CaF 2 ↓+CaAl 2 (OH) 8 ↓

[0094] 2Li 3 AlF 6 +7Ca(OH) 2 =6LiOH + 6CaF 2 ↓ +CaAl 2 (OH) 8 ↓

[0095] 2LiF+Ca(OH) 2 =LiOH+CaF 2 ↓

[0096] Na 3 Fe(CN) 6 +3NaOH=6NaCN +Fe(OH) 3 ↓

[0097] Na 3 AlF 6 + 2Ca(OH) 2 =2NaF↓+NaAlO2 +2CaF 2 ↓+2H 2 O

[0098] 2KF+ Ca(OH) 2 =2KOH+ CaF 2 ↓

[0099] S3: Primary solid-liquid separation

[0100] The leached slurry obtained in S2 is subjected to a solid-liquid separation to obtain leached residue and leached liquid;

[0101] The leaching residue mainly includes NaF, CaF 2、 CaAl 2 (OH) 8 and Fe(OH) 3 The leaching solution mainly includes NaOH, LiOH, NaAlO 2 and NaCN;

[0102] S4: Leachate treatment

[0103] The leachate obtained in S3 is treated to obtain crude lithium carbonate and heavy soda ash; S4 specifically includes the following treatment process:

[0104] S4-1: First, introduce carbon dioxide into the leaching solution. Specifically, introduce carbon dioxide at a pressure of 2.0 MPa, control the reaction temperature to be 105° C., the reaction time to be 30 min, and control the pH of the first mixed slurry to be 13.8;

[0105] The reaction equation is as follows:

[0106] CO 2 + 2NaOH = Na 2 CO 3 + H 2 O

[0107] CO 2 + 2LiOH = Li 2 CO 3 ↓ + H 2 O

[0108] 2NaAlO 2 + CO 2 + 3H 2 O = 2Al(OH) 3 ↓ + Na 2 CO 3

[0109] 2KOH + CO 2 = K 2 CO3 + H 2 O

[0110] After the reaction, a first mixed slurry containing lithium carbonate, sodium carbonate and aluminum hydroxide is obtained; then the first mixed slurry is subjected to solid-liquid separation to separate crude lithium carbonate and obtain a first sodium carbonate solution;

[0111] S4-2: Evaporating and concentrating the first sodium carbonate solution obtained in S4-1 once, thereby increasing the concentration of the first sodium carbonate solution and causing lithium carbonate slightly soluble in the first sodium carbonate solution to precipitate due to supersaturation, and separating the precipitated lithium carbonate to obtain a second sodium carbonate solution;

[0112] S4-3: The second sodium carbonate solution obtained in S2 is heated to 180°C and reacted at a pressure of 0.8 MPa for 30 minutes to convert the sodium cyanide in the second sodium carbonate solution into sodium formate. The reaction equation is as follows:

[0113] NaCN + 2H 2 O = HCOONa + NH 3 ↑

[0114] Then the temperature was cooled to 45° C. to obtain a third sodium carbonate solution.

[0115] S4-4: After filtering and removing impurities from the third sodium carbonate solution obtained in S4-3, an alkaline extractant (HBL121) is added to extract the remaining lithium in the third sodium carbonate solution to obtain a fourth sodium carbonate solution;

[0116] S4-5: subjecting the fourth sodium carbonate solution obtained in S4-4 to secondary evaporation and crystallization to separate the saturated sodium carbonate mother liquor to obtain a high-solid sodium carbonate monohydrate slurry;

[0117] S4-6: heating the sodium carbonate monohydrate slurry obtained in S4-5 to 130° C. and stirring for 30 min at a pressure of 1.2 MPa to obtain a second mixed slurry; performing solid-liquid separation on the second mixed slurry to separate a saturated sodium carbonate solution to obtain a sodium carbonate solid;

[0118] S4-7: Dry the sodium carbonate solid obtained in S4-6 to obtain heavy soda ash.

[0119] In S4-5, when the potassium content in the separated saturated sodium carbonate mother liquor is lower than 100 g / L, it is subjected to secondary evaporation crystallization together with the fourth sodium carbonate solution; in S4-6, when the potassium content in the separated saturated sodium carbonate mother liquor is lower than 100 g / L, it is sent back to S4-5 for secondary evaporation crystallization together with the fourth sodium carbonate solution.

[0120] S5: Leaching residue treatment

[0121] The leached residue obtained from S3 is treated to obtain calcium chloride solution, sodium carbonate solution, aluminum hydroxide and high-grade calcium fluoride.

[0122] S5 specifically includes the following processing steps:

[0123] S5-1: mixing the leached residue and the calcium chloride solution to prepare a low-grade calcium fluoride slurry with a solid-liquid ratio of 1:5;

[0124] S5-2: Add hydrochloric acid to the low-grade calcium fluoride slurry obtained in S5-1, adjust the pH to 4, the reaction temperature to 110°C, the reaction time to 30 minutes, and obtain the first mixed slurry; the reaction process is as follows:

[0125] CaAl 2 (OH) 8 +2HCl=2Al(OH) 3 ↓+CaCl 2 +2H 2 O

[0126] CaCl 2 +2NaF=2NaCl+CaF 2 ↓

[0127] Fe(OH) 3 +3HCl=FeCl 3 +3H 2 O

[0128] Al(OH) 3 +3HCl = AlCl 3 +3H 2 O

[0129] S5-3: performing a solid-liquid separation on the first mixed slurry obtained in S5-2 to separate the calcium chloride solution and obtain medium-grade calcium fluoride containing aluminum hydroxide;

[0130] S5-4: Add water and sodium hydroxide to the medium-grade calcium fluoride obtained in S5-3 to prepare a medium-grade calcium fluoride slurry with a solid-liquid ratio of 1:6, the amount of sodium hydroxide added is 1.5 times the molar amount of aluminum hydroxide, the reaction temperature is 110°C, the reaction time is 30 minutes, and a second mixed slurry is obtained; the reaction equation is:

[0131] Al(OH) 3 +NaOH =NaAlO 2 +2H 2 O

[0132] S5-5: The second mixed slurry obtained in S5-4 is subjected to secondary solid-liquid separation, and the solid phase obtained by separation is a high-grade calcium fluoride product.

[0133] S5-6: Carbon dioxide is first introduced into the solution separated from S5-5 to react to obtain a third mixed slurry, and the reaction equation is:

[0134] 2NaAlO 2 + CO 2 +3H 2 O=Na 2 CO 3 +2Al(OH) 3 ↓

[0135] 2NaOH + CO 2 = Na 2 CO 3 + H 2 O

[0136] The third mixed slurry is then subjected to three solid-liquid separations, and the obtained solid phase is aluminum hydroxide, and the obtained liquid phase is a sodium carbonate solution.

[0137] In S5-3, the primary solid-liquid separation is carried out in the first integrated filter-washer, and the washing water discharged from the first integrated filter-washer is sent back to S5-1 for pulping: in S5-5, the secondary solid-liquid separation is carried out in the second integrated filter-washer, and the washing water discharged from the second integrated filter-washer is sent back to S5-4 for preparing medium-grade calcium fluoride slurry.

[0138] Example 3: A method for recovering lithium sodium fluorocarbon aluminum from cryolite-containing solid waste in an aluminum electrolysis plant, comprising the following steps:

[0139] S1: Preprocessing

[0140] The solid waste blocks containing cryolite from the electrolysis plant are mixed and crushed to remove the elemental aluminum and elemental iron therein, and then finely ground into powder with a size less than 200 meshes, and then the powder is floated to float out carbon powder to obtain the powder to be processed;

[0141] S2: Leaching reaction

[0142] The powder to be treated obtained in S1 is added with carbide slag and water in a solid-liquid ratio of 1:2 to prepare a slurry, wherein the weight ratio of alkaline calcium to the powder to be treated is 1.3, and a leaching slurry is obtained after the reaction; the leaching reaction temperature is 65°C and the reaction time is 100 minutes. The reaction process is as follows:

[0143] 2Na 3 AlF 6 +7Ca(OH) 2 =6NaOH + 6CaF 2 ↓+CaAl 2 (OH) 8 ↓

[0144] 2Li3 AlF 6 +7Ca(OH) 2 =6LiOH + 6CaF 2 ↓ +CaAl 2 (OH) 8 ↓

[0145] 2LiF+Ca(OH) 2 =LiOH+CaF 2 ↓

[0146] Na 3 Fe(CN) 6 +3NaOH=6NaCN +Fe(OH) 3 ↓

[0147] Na 3 AlF 6 + 2Ca(OH) 2 =2NaF↓+NaAlO 2 +2CaF 2 ↓+2H 2 O

[0148] 2KF+ Ca(OH) 2 =2KOH+ CaF 2 ↓

[0149] S3: Primary solid-liquid separation

[0150] The leached slurry obtained in S2 is subjected to a solid-liquid separation to obtain leached residue and leached liquid;

[0151] The leaching residue mainly includes NaF, CaF 2、 CaAl 2 (OH) 8 and Fe(OH) 3 The leaching solution mainly includes NaOH, LiOH, NaAlO 2 and NaCN;

[0152] S4: Leachate treatment

[0153] The leachate obtained in S3 is treated to obtain crude lithium carbonate and heavy soda ash; S4 specifically includes the following treatment process:

[0154] S4-1: First, introduce carbon dioxide into the leaching solution. Specifically, introduce carbon dioxide at a pressure of 1 MPa, control the reaction temperature to 50° C., the reaction time to 150 min, and control the pH of the first mixed slurry to 12;

[0155] The reaction equation is as follows:

[0156] CO2 + 2NaOH = Na 2 CO 3 + H 2 O

[0157] CO 2 + 2LiOH = Li 2 CO 3 ↓ + H 2 O

[0158] 2NaAlO 2 + CO 2 + 3H 2 O = 2Al(OH) 3 ↓ + Na 2 CO 3

[0159] 2KOH + CO 2 = K 2 CO 3 + H 2 O

[0160] After the reaction, a first mixed slurry containing lithium carbonate, sodium carbonate and aluminum hydroxide is obtained; then the first mixed slurry is subjected to solid-liquid separation to separate crude lithium carbonate and obtain a first sodium carbonate solution;

[0161] S4-2: Evaporating and concentrating the first sodium carbonate solution obtained in S4-1 once, thereby increasing the concentration of the first sodium carbonate solution and causing lithium carbonate slightly soluble in the first sodium carbonate solution to precipitate due to supersaturation, and separating the precipitated lithium carbonate to obtain a second sodium carbonate solution;

[0162] S4-3: The second sodium carbonate solution obtained in S2 is heated to 170°C and reacted at a pressure of 0.7 MPa for 100 min to convert the sodium cyanide in the second sodium carbonate solution into sodium formate. The reaction equation is as follows:

[0163] NaCN + 2H 2 O = HCOONa + NH 3 ↑

[0164] Then the temperature was cooled to 40° C. to obtain a third sodium carbonate solution.

[0165] S4-4: After filtering and removing impurities from the third sodium carbonate solution obtained in S4-3, an alkaline extractant (3938H) is added to extract the remaining lithium in the third sodium carbonate solution to obtain a fourth sodium carbonate solution;

[0166] S4-5: subjecting the fourth sodium carbonate solution obtained in S4-4 to secondary evaporation and crystallization to separate the saturated sodium carbonate mother liquor to obtain a high-solid sodium carbonate monohydrate slurry;

[0167] S4-6: heating the sodium carbonate monohydrate slurry obtained in S4-5 to 120° C. and stirring for 80 min at a pressure of 0.8 MPa to obtain a second mixed slurry; performing solid-liquid separation on the second mixed slurry to separate a saturated sodium carbonate solution to obtain sodium carbonate solid;

[0168] S4-7: Dry the sodium carbonate solid obtained in S4-6 to obtain heavy soda ash.

[0169] In S4-5, when the potassium content in the separated saturated sodium carbonate mother liquor is lower than 100 g / L, it is subjected to secondary evaporation crystallization together with the fourth sodium carbonate solution; in S4-6, when the potassium content in the separated saturated sodium carbonate mother liquor is lower than 100 g / L, it is sent back to S4-5 for secondary evaporation crystallization together with the fourth sodium carbonate solution.

[0170] S5: Leaching residue treatment

[0171] The leached residue obtained from S3 is treated to obtain calcium chloride solution, sodium carbonate solution, aluminum hydroxide and high-grade calcium fluoride.

[0172] S5 specifically includes the following processing steps:

[0173] S5-1: mixing the leached residue and the calcium chloride solution to prepare a low-grade calcium fluoride slurry with a solid-liquid ratio of 1:4;

[0174] S5-2: Add hydrochloric acid to the low-grade calcium fluoride slurry obtained in S5-1, adjust the pH to 2, the reaction temperature to 100° C., the reaction time to 150 min, and obtain a first mixed slurry; the reaction process is as follows:

[0175] CaAl 2 (OH) 8 +2HCl=2Al(OH) 3 ↓+CaCl 2 +2H 2 O

[0176] CaCl 2 +2NaF=2NaCl+CaF 2 ↓

[0177] Fe(OH) 3 +3HCl=FeCl 3 +3H 2 O

[0178] Al(OH) 3 +3HCl = AlCl3 +3H 2 O

[0179] S5-3: performing a solid-liquid separation on the first mixed slurry obtained in S5-2 to separate the calcium chloride solution and obtain medium-grade calcium fluoride containing aluminum hydroxide;

[0180] S5-4: Add water and sodium hydroxide to the medium-grade calcium fluoride obtained in S5-3 to prepare a medium-grade calcium fluoride slurry with a solid-liquid ratio of 1:4, the amount of sodium hydroxide added is 1.3 times the molar amount of aluminum hydroxide, the reaction temperature is 70°C, the reaction time is 150 minutes, and a second mixed slurry is obtained; the reaction equation is:

[0181] Al(OH) 3 +NaOH =NaAlO 2 +2H 2 O

[0182] S5-5: The second mixed slurry obtained in S5-4 is subjected to secondary solid-liquid separation, and the solid phase obtained by separation is a high-grade calcium fluoride product.

[0183] S5-6: Carbon dioxide is first introduced into the solution separated from S5-5 to react to obtain a third mixed slurry, and the reaction equation is:

[0184] 2NaAlO 2 + CO 2 +3H 2 O=Na 2 CO 3 +2Al(OH) 3 ↓

[0185] 2NaOH+CO 2 = Na 2 CO 3 +H 2 O

[0186] The third mixed slurry is then subjected to three solid-liquid separations, and the obtained solid phase is aluminum hydroxide, and the obtained liquid phase is a sodium carbonate solution.

[0187] In S5-3, the primary solid-liquid separation is carried out in the first integrated filter-washer, and the washing water discharged from the first integrated filter-washer is sent back to S5-1 for pulping: in S5-5, the secondary solid-liquid separation is carried out in the second integrated filter-washer, and the washing water discharged from the second integrated filter-washer is sent back to S5-4 for preparing medium-grade calcium fluoride slurry.

[0188] The invention adopts cheap alkaline calcium as an auxiliary material to carry out alkaline leaching recovery of solid waste produced by an electrolytic aluminum plant, reduces the use of acid, and greatly reduces the recovery cost; the leachate can be treated to obtain crude lithium carbonate and heavy soda ash, the crude lithium carbonate can be further treated to be recovered as lithium carbonate, and the heavy soda ash can be directly sold as a product; the leachate residue can be treated to obtain calcium chloride solution, sodium carbonate solution, aluminum hydroxide and high-grade calcium fluoride, wherein the aluminum hydroxide and the high-grade calcium fluoride can be directly sold as products, and the calcium chloride solution and the sodium carbonate solution can be further treated to be recovered as calcium chloride and sodium carbonate respectively; and detoxification treatment is carried out in the process of treating the leachate, no hydrogen cyanide and hydrogen fluoride gas are generated, and safety is improved. In summary, the aluminum, sodium, lithium, fluorine and carbon in the cryolite-containing solid waste can be recovered respectively through this method, and the heavy soda ash and high-content calcium fluoride produced can increase the profit; and the alkaline calcium used for leaching is finally recovered as calcium chloride. The entire treatment method uses cheap alkaline calcium leaching, which reduces the use of acid and reduces the treatment cost, while the final output of solid waste is less, so that all effective components in the cryolite-containing solid waste are recovered, effectively increasing the overall profit, having good industrial feasibility, and being suitable for popularization and application.

[0189] Finally, it should be noted that the solid-liquid ratio described in the present invention refers to the weight ratio of the solid phase to the liquid phase; the above embodiments are only used to illustrate the technical solution of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solution deviate from the scope of the technical solution of the embodiments of the present invention.

Claims

1. A method for recovering lithium sodium fluorocarbon aluminum from cryolite-containing solid waste in an aluminum electrolysis plant, characterized in that: It includes the following steps: S1: Preprocessing The solid waste blocks containing cryolite from the electrolysis plant are mixed and crushed to remove the elemental aluminum and elemental iron therein, and then finely ground into powder with a size less than 200 meshes, and then the powder is floated to float out carbon powder to obtain the powder to be processed; S2: Leaching reaction The powder to be treated obtained in S1 is mixed with alkaline calcium and water at a solid-liquid ratio of 1:2-6 to prepare a slurry, wherein the weight ratio of alkaline calcium to the powder to be treated is 1.1-1.5, and a leaching slurry is obtained after the reaction; S3: Primary solid-liquid separation The leached slurry obtained in S2 is subjected to a solid-liquid separation to obtain leached residue and leached liquid; S4: Leachate treatment The leachate obtained in S3 is treated to obtain crude lithium carbonate and heavy soda ash; S5: Leaching residue treatment The leached residue obtained in S3 is treated to obtain calcium chloride solution, sodium carbonate solution, aluminum hydroxide and high-grade calcium fluoride; The alkaline calcium in S2 is carbide slag or calcium hydroxide; The S4 specifically includes the following processing steps: S4-1: firstly introducing carbon dioxide into the leachate to obtain a first mixed slurry; then performing solid-liquid separation on the first mixed slurry to separate crude lithium carbonate and obtain a first sodium carbonate solution; S4-2: Evaporating and concentrating the first sodium carbonate solution obtained in S4-1 once, so that lithium carbonate slightly dissolved in the first sodium carbonate solution is precipitated due to supersaturation, and separating the precipitated lithium carbonate to obtain a second sodium carbonate solution; S4-3: hydrolyzing the second sodium carbonate solution obtained in S4-2 at high temperature to convert the sodium cyanide in the second sodium carbonate solution into sodium formate, and then cooling the solution to obtain a third sodium carbonate solution; S4-4: After filtering and removing impurities from the third sodium carbonate solution obtained in S4-3, an alkaline extractant is added to extract the remaining lithium in the third sodium carbonate solution to obtain a fourth sodium carbonate solution; S4-5: subjecting the fourth sodium carbonate solution obtained in S4-4 to secondary evaporation and crystallization to separate the saturated sodium carbonate mother liquor to obtain a high-solid sodium carbonate monohydrate slurry; S4-6: heating and stirring the sodium carbonate monohydrate slurry obtained in S4-5 to remove crystal water to obtain a second mixed slurry; performing solid-liquid separation on the second mixed slurry to separate a saturated sodium carbonate solution to obtain a sodium carbonate solid; S4-7: Dry the sodium carbonate solid obtained in S4-6 to obtain heavy soda ash.

2. The method for recovering lithium sodium fluorocarbon aluminum from cryolite-containing solid waste in an aluminum electrolysis plant according to claim 1, characterized in that: The temperature of S2 leaching reaction is 30-95℃, and the reaction time is 30-180min.

3. The method for recovering lithium sodium fluorocarbon aluminum from cryolite-containing solid waste in an aluminum electrolysis plant according to claim 1, characterized in that: In S4-1, carbon dioxide is introduced at a pressure of 0.2-2.0 MPa, the reaction temperature is controlled to be 25-105°C, the reaction time is 30-300 min, and the pH of the first mixed slurry is controlled to be 9-13.

8.

4. The method for recovering lithium sodium fluorocarbon aluminum from cryolite-containing solid waste in an aluminum electrolysis plant according to claim 1, characterized in that: In S4-3, the second sodium carbonate solution obtained in S4-2 is heated to 160-180°C and reacted at a pressure of 0.6-0.8 MPa for 30-150 min to convert the sodium cyanide in the second sodium carbonate solution into sodium formate, and then cooled to 30-45°C to obtain a third sodium carbonate solution.

5. The method for recovering lithium sodium fluorocarbon aluminum from cryolite-containing solid waste in an aluminum electrolysis plant according to claim 1, characterized in that: In S4-6, the sodium carbonate monohydrate slurry obtained in S4-5 is heated to 110-130° C. and stirred at a pressure of 0.2-1.2 MPa for 30-120 min to obtain a second mixed slurry.

6. The method for recovering lithium sodium fluorocarbon aluminum from cryolite-containing solid waste in an aluminum electrolysis plant according to claim 1, characterized in that: In S4-5, when the potassium content in the separated saturated sodium carbonate mother liquor is lower than 100 g / L, it is subjected to secondary evaporation crystallization together with the fourth sodium carbonate solution; in S4-6, when the potassium content in the separated saturated sodium carbonate mother liquor is lower than 100 g / L, it is sent back to S4-5 for secondary evaporation crystallization together with the fourth sodium carbonate solution.

7. The method for recovering lithium sodium fluorocarbon aluminum from cryolite-containing solid waste in an aluminum electrolysis plant according to claim 1, characterized in that: S5 specifically includes the following processing steps: S5-1: mixing the leached residue and the calcium chloride solution to prepare a low-grade calcium fluoride slurry with a solid-liquid ratio of 1:3-5; S5-2: Add hydrochloric acid to the low-grade calcium fluoride slurry obtained in S5-1, adjust the pH to 1-4, the reaction temperature to 80-110° C., and the reaction time to 30-300 min to obtain a first mixed slurry; S5-3: performing a solid-liquid separation on the first mixed slurry obtained in S5-2 to separate the calcium chloride solution and obtain medium-grade calcium fluoride containing aluminum hydroxide; S5-4: adding water and sodium hydroxide to the medium-grade calcium fluoride obtained in S5-3 to prepare a medium-grade calcium fluoride slurry with a solid-liquid ratio of 1:1-6, wherein the amount of sodium hydroxide added is 1.1-1.5 times the molar amount of aluminum hydroxide, the reaction temperature is 30-110°C, the reaction time is 30-300 min, and a second mixed slurry is obtained after the reaction; S5-5: performing secondary solid-liquid separation on the second mixed slurry obtained in S5-4, and the solid phase obtained by separation is a high-grade calcium fluoride product; S5-6: First, carbon dioxide is introduced into the solution separated in S5-5 to react to obtain a third mixed slurry, and then the third mixed slurry is subjected to three solid-liquid separations to obtain a solid phase of aluminum hydroxide and a liquid phase of sodium carbonate solution.

8. The method for recovering lithium sodium fluorocarbon aluminum from cryolite-containing solid waste in an aluminum electrolysis plant according to claim 7, characterized in that: In S5-3, the primary solid-liquid separation is carried out in the first integrated filter-washer, and the washing water discharged from the first integrated filter-washer is sent back to S5-1 for pulping: in S5-5, the secondary solid-liquid separation is carried out in the second integrated filter-washer, and the washing water discharged from the second integrated filter-washer is sent back to S5-4 for preparing medium-grade calcium fluoride slurry.