A method for recovering alkaline leaching solution from solid waste containing cryolite in an aluminum electrolysis plant

Abstract

The present invention discloses a method for treating alkaline leaching solution for recovering cryolite-containing solid waste from an electrolytic aluminum plant, which comprises the following steps: S1: reaction; S2: primary evaporation and concentration; S3: detoxification; S4: alkaline extraction; S5: secondary evaporation and crystallization. Advantages: The alkaline leaching solution is first subjected to a carbon dioxide carbonation reaction and filtered to separate the crude lithium carbonate containing aluminum fluoride, and then the separated filtrate is evaporated and concentrated once to further precipitate lithium carbonate; the concentrated solution is subjected to high-temperature hydrolysis and detoxification, so that sodium cyanide can be converted into sodium formate without the need for acid detoxification, thereby avoiding the generation of highly toxic hydrogen cyanide gas and improving safety; then alkaline extraction is used to separate the lithium in the sodium carbonate solution in the form of lithium salt, thereby improving the purity of the sodium carbonate solution. Furthermore, the sodium carbonate solution is subjected to evaporation, crystallization, separation and drying to obtain a heavy sodium carbonate product, which can improve economic benefits.

Description

Technical Field

[0001] The invention relates to the technical field of cryolite-containing solid waste recovery in aluminum electrolysis plants, and in particular to an alkaline leaching solution treatment method for recovering cryolite-containing solid waste in aluminum electrolysis plants. Background Art

[0002] The cryolite-containing solid waste produced by the electrolytic aluminum plant mainly includes five categories: overhaul slag, cathode carbon block, anode carbon block, shell surface block, and electrolyte. Among them, the overhaul slag is refractory bricks except for the main components Na3AlF6 and Na3Fe(CN)6. The cathode carbon block and anode carbon block are carbon powder except for the main components Na3AlF6, Na2LiAlF6 and Na3Fe(CN)6. The main components of shell surface block are Na3AlF6 and metallic aluminum, and the main components of electrolyte are Na3AlF6 and Na2LiAlF6. At present, an alkaline calcium leaching process has been developed. First, the above-mentioned cryolite-containing solid waste is pre-treated through crushing, screening, flotation and other processes to remove the elemental aluminum and carbon powder, and obtain lithium-containing waste cryolite powder; then the lithium-containing waste cryolite powder is mixed with alkaline calcium (carbide slag, calcium hydroxide) solution for leaching, and the reaction equation is as follows:

[0003] 2Na3AlF6+7Ca(OH)2=6NaOH + 6CaF2↓+CaAl2(OH)8↓

[0004] 2Li3AlF6+7Ca(OH)2=6LiOH + 6CaF2↓ +CaAl2(OH)8↓

[0005] 2LiF+Ca(OH)2=LiOH+CaF2↓

[0006] Na3Fe(CN)6+3NaOH=6NaCN +Fe(OH)3↓

[0007] Na3AlF6+ 2Ca(OH)2=2NaF↓+NaAlO2+2CaF2↓+2H2O

[0008] 2KF+ Ca(OH)2=2KOH+ CaF2↓

[0009] After solid-liquid separation, NaF, CaF 2、 In view of the alkaline leaching residue mainly composed of CaAl2(OH)8 and Fe(OH)3, and the alkaline leaching solution mainly composed of KOH, NaOH, LiOH, NaAlO2 and NaCN, a method for recovering alkaline leaching solution from cryolite-containing solid waste in electrolytic aluminum plants is proposed to achieve the separation of sodium and lithium. Summary of the invention

[0010] The object of the present invention is to provide a method for recovering alkaline leaching solution from solid waste containing cryolite in an aluminum electrolytic plant.

[0011] The present invention is implemented by the following technical scheme: a method for recovering alkaline leaching solution from solid waste containing cryolite in an electrolytic aluminum plant, comprising the following steps:

[0012] S1: Reaction

[0013] First, carbon dioxide is introduced into the alkaline leaching solution to obtain a first mixed slurry; then the first mixed slurry is subjected to solid-liquid separation to separate crude lithium carbonate solids to obtain a first sodium carbonate solution;

[0014] S2: One-time evaporation concentration

[0015] The first sodium carbonate solution obtained in S1 is evaporated and concentrated once, and while the concentration of the sodium carbonate solution is increased, lithium carbonate slightly soluble in the first sodium carbonate solution is supersaturated and precipitated to obtain a second sodium carbonate solution;

[0016] S3: Detoxification

[0017] The second sodium carbonate solution obtained in S2 is subjected to high temperature hydrolysis to convert the sodium cyanide in the second sodium carbonate solution into sodium formate, and then cooled to obtain a third sodium carbonate solution;

[0018] S4: Alkaline extraction

[0019] adding an alkaline extractant to the third sodium carbonate solution obtained in S3 to extract the remaining lithium in the third sodium carbonate solution to obtain a fourth sodium carbonate solution;

[0020] S5: Secondary evaporation crystallization

[0021] The fourth sodium carbonate solution obtained in S4 is subjected to secondary evaporation and crystallization to separate the saturated sodium carbonate mother liquor to obtain a high-solid sodium carbonate monohydrate slurry.

[0022] Further, it also includes S6: removing crystal water, S7: drying; specifically:

[0023] S6 de-crystallization water

[0024] The sodium carbonate monohydrate slurry obtained in S5 is heated and stirred to remove crystal water to obtain a second mixed slurry; the second mixed slurry is subjected to solid-liquid separation to separate a saturated sodium carbonate solution to obtain a sodium carbonate solid;

[0025] S7: Dry

[0026] The sodium carbonate solid obtained in S6 is dried to obtain heavy soda ash.

[0027] Furthermore, in S1, 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.

[0028] Further, in S3, the second sodium carbonate solution obtained in S2 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.

[0029] Further, in S6, the sodium carbonate monohydrate slurry obtained in S5 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.

[0030] Furthermore, in S5, when the potassium content in the separated saturated sodium carbonate mother liquor is lower than 100 g / L, secondary evaporation crystallization is performed together with the fourth sodium carbonate solution.

[0031] Furthermore, in S6, when the potassium content in the separated saturated sodium carbonate mother liquor is lower than 100 g / L, it is sent back to S5 for secondary evaporation and crystallization together with the fourth sodium carbonate solution.

[0032] Furthermore, in S4, the third sodium carbonate solution obtained in S3 is first filtered to remove impurities and then subjected to alkaline extraction.

[0033] The advantages of the present invention are as follows: the alkaline leaching solution is first subjected to carbonization reaction of carbon dioxide and filtered to separate the crude lithium carbonate containing aluminum fluoride, and then the separated filtrate is evaporated and concentrated to further precipitate lithium carbonate; the concentrated solution is subjected to high-temperature hydrolysis and detoxification, so that sodium cyanide can be converted into sodium formate without the need for acid detoxification, thus avoiding the generation of highly toxic hydrogen cyanide gas and improving safety; then alkaline extraction is used to separate the lithium in the sodium carbonate solution in the form of lithium salt, further removing impurities and improving the purity of the sodium carbonate solution. Furthermore, the sodium carbonate solution can be subjected to evaporation, crystallization, separation and drying to obtain a heavy sodium carbonate product, which can improve economic benefits, and the recovery of sodium as heavy soda ash is more valuable than the recovery as sodium chloride or sodium sulfate, and safer than the recovery as sodium nitrate. DETAILED DESCRIPTION

[0034] Using the same batch of alkaline leaching solution as raw material, the following examples were carried out respectively:

[0035] Example 1: A method for recovering alkaline leaching solution from solid waste containing cryolite in an aluminum electrolysis plant, comprising the following steps:

[0036] S1: Reaction

[0037] First, carbon dioxide is introduced into the alkaline leaching solution. Specifically, carbon dioxide is introduced at 0.20 MPa, the reaction temperature is controlled to be 25° C., the reaction time is 300 min, and the pH of the first mixed slurry is controlled to be 9. The reaction equation is as follows:

[0038] CO2 + 2NaOH = Na2CO3 + H2O

[0039] CO2 + 2LiOH = Li2CO3↓ + H2O

[0040] 2NaAlO2+ CO2+ 3H2O = 2Al(OH)3↓ + Na2CO3

[0041] 2KOH + CO2 = K2CO3 + H2O

[0042] 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 the crude lithium carbonate solid containing aluminum hydroxide to obtain a first sodium carbonate solution;

[0043] S2: One-time evaporation concentration

[0044] The first sodium carbonate solution obtained in S1 is evaporated and concentrated once, and while increasing the sodium carbonate solution, lithium carbonate slightly soluble in the first sodium carbonate solution is supersaturated and precipitated to obtain a second sodium carbonate solution;

[0045] S3: Detoxification

[0046] The second sodium carbonate solution obtained in S2 is subjected to high temperature hydrolysis to convert the sodium cyanide in the second sodium carbonate solution into sodium formate, and then cooled to obtain a third sodium carbonate solution;

[0047] Specifically, the second sodium carbonate solution obtained in S2 is heated to 160°C and reacted at a pressure of 0.6 MPa for 150 minutes to convert the sodium cyanide in the second sodium carbonate solution into sodium formate, and then cooled to 30°C to obtain a third sodium carbonate solution. The reaction equation is as follows:

[0048] NaCN + 2H2O = HCOONa + NH3↑

[0049] S4: Alkaline extraction

[0050] The third sodium carbonate solution obtained in S3 is first filtered and impurities are removed, and then an alkaline extractant (HBL121 or 3938H) is added to the filtered and impurity-removed third sodium carbonate solution to extract the remaining lithium in the third sodium carbonate solution to obtain a fourth sodium carbonate solution;

[0051] S5: Secondary evaporation crystallization

[0052] The fourth sodium carbonate solution obtained in S4 is subjected to secondary evaporation and crystallization to separate the saturated sodium carbonate mother liquor to obtain a high-solid sodium carbonate monohydrate slurry;

[0053] In S5, when the potassium content in the separated saturated sodium carbonate mother liquor is lower than 100 g / L, secondary evaporation crystallization is performed together with the fourth sodium carbonate solution;

[0054] S6 de-crystallization water

[0055] The sodium carbonate monohydrate slurry obtained in S5 is heated and stirred to remove crystal water to obtain a second mixed slurry containing sodium carbonate solid and a saturated sodium carbonate solution; specifically, the sodium carbonate monohydrate slurry obtained in S5 is heated to 110° C. and stirred at a pressure of 0.2 MPa for 120 min to obtain a second mixed slurry;

[0056] The second mixed slurry is subjected to solid-liquid separation to separate the saturated sodium carbonate solution and obtain sodium carbonate solid;

[0057] In S6, when the potassium content in the separated saturated sodium carbonate mother liquor is lower than 100 g / L, it is sent back to S5 for secondary evaporation and crystallization together with the fourth sodium carbonate solution.

[0058] S7: Dry

[0059] The sodium carbonate solid obtained in S6 is dried to obtain heavy soda ash.

[0060] Example 2: A method for recovering alkaline leaching solution from solid waste containing cryolite in an aluminum electrolysis plant, comprising the following steps:

[0061] S1: Reaction

[0062] First, carbon dioxide is introduced into the alkaline leaching solution. Specifically, carbon dioxide is introduced under a pressure of 2.0 MPa, the reaction temperature is controlled to be 105° C., the reaction time is 30 min, and the pH of the first mixed slurry is controlled to be 13.8. The reaction equation is as follows:

[0063] CO2 + 2NaOH = Na2CO3 + H2O

[0064] CO2 + 2LiOH = Li2CO3↓ + H2O

[0065] 2NaAlO2+ CO2+ 3H2O = 2Al(OH)3↓ + Na2CO3

[0066] 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 the crude lithium carbonate solid containing aluminum hydroxide to obtain a first sodium carbonate solution;

[0067] S2: One-time evaporation concentration

[0068] The first sodium carbonate solution obtained in S1 is evaporated and concentrated once, and while the concentration of the sodium carbonate solution is increased, lithium carbonate slightly soluble in the first sodium carbonate solution is supersaturated and precipitated to obtain a second sodium carbonate solution;

[0069] S3: Detoxification

[0070] The second sodium carbonate solution obtained in S2 is subjected to high temperature hydrolysis to convert the sodium cyanide in the second sodium carbonate solution into sodium formate, and then cooled to obtain a third sodium carbonate solution;

[0071] Specifically, 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, and then cooled to 45°C to obtain a third sodium carbonate solution. The reaction equation is as follows:

[0072] NaCN + 2H2O = HCOONa + NH3↑

[0073] S4: Alkaline extraction

[0074] Adding an alkaline extractant (HBL121 or 3938H) to the third sodium carbonate solution obtained in S3 to extract the remaining lithium salt in the third sodium carbonate solution to obtain a fourth sodium carbonate solution;

[0075] S5: Secondary evaporation crystallization

[0076] The fourth sodium carbonate solution obtained in S4 is subjected to secondary evaporation and crystallization to separate the saturated sodium carbonate mother liquor to obtain a high-solid sodium carbonate monohydrate slurry;

[0077] In S5, when the potassium content in the separated saturated sodium carbonate mother liquor is lower than 100 g / L, secondary evaporation crystallization is performed together with the fourth sodium carbonate solution;

[0078] S6 de-crystallization water

[0079] The sodium carbonate monohydrate slurry obtained in S5 is heated and stirred to remove crystal water to obtain a second mixed slurry containing sodium carbonate solid and a saturated sodium carbonate solution; specifically, the sodium carbonate monohydrate slurry obtained in S5 is heated to 130° C. and stirred at a pressure of 1.2 MPa for 30 min to obtain a second mixed slurry;

[0080] The second mixed slurry is subjected to solid-liquid separation to separate the saturated sodium carbonate solution and obtain sodium carbonate solid;

[0081] In S6, when the potassium content in the separated saturated sodium carbonate mother liquor is lower than 100 g / L, it is sent back to S5 for secondary evaporation and crystallization together with the fourth sodium carbonate solution.

[0082] S7: Dry

[0083] The sodium carbonate solid obtained in S6 is dried to obtain heavy soda ash.

[0084] Example 3: A method for recovering alkaline leaching solution from solid waste containing cryolite in an aluminum electrolysis plant, comprising the following steps:

[0085] S1: Reaction

[0086] First, carbon dioxide is introduced into the alkaline leaching solution. Specifically, carbon dioxide is introduced under a pressure of 1 MPa, the reaction temperature is controlled to be 55° C., the reaction time is 150 min, and the pH of the first mixed slurry is controlled to be 12. The reaction equation is as follows:

[0087] CO2 + 2NaOH = Na2CO3 + H2O

[0088] CO2 + 2LiOH = Li2CO3↓ + H2O

[0089] 2NaAlO2+ CO2+ 3H2O = 2Al(OH)3↓ + Na2CO3

[0090] 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 the crude lithium carbonate solid containing aluminum hydroxide to obtain a first sodium carbonate solution;

[0091] S2: One-time evaporation concentration

[0092] The first sodium carbonate solution obtained in S1 is evaporated and concentrated once, and while the concentration of the sodium carbonate solution is increased, lithium carbonate slightly soluble in the first sodium carbonate solution is supersaturated and precipitated to obtain a second sodium carbonate solution;

[0093] S3: Detoxification

[0094] The second sodium carbonate solution obtained in S2 is subjected to high temperature hydrolysis to convert the sodium cyanide in the second sodium carbonate solution into sodium formate, and then cooled to obtain a third sodium carbonate solution;

[0095] Specifically, the second sodium carbonate solution obtained in S2 is heated to 170°C and reacted at a pressure of 0.7 MPa for 100 minutes to convert the sodium cyanide in the second sodium carbonate solution into sodium formate, and then cooled to 40°C to obtain a third sodium carbonate solution. The reaction equation is as follows:

[0096] NaCN + 2H2O = HCOONa + NH3↑

[0097] S4: Alkaline extraction

[0098] Adding an alkaline extractant (HBL121 or 3938H) to the third sodium carbonate solution obtained in S3 to extract the remaining lithium in the third sodium carbonate solution to obtain a fourth sodium carbonate solution;

[0099] S5: Secondary evaporation crystallization

[0100] The fourth sodium carbonate solution obtained in S4 is subjected to secondary evaporation and crystallization to separate the saturated sodium carbonate mother liquor to obtain a high-solid sodium carbonate monohydrate slurry;

[0101] In S5, when the potassium content in the separated saturated sodium carbonate mother liquor is lower than 100 g / L, secondary evaporation crystallization is performed together with the fourth sodium carbonate solution;

[0102] S6 de-crystallization water

[0103] The sodium carbonate monohydrate slurry obtained in S5 is heated and stirred to remove crystal water to obtain a second mixed slurry containing sodium carbonate solid and a saturated sodium carbonate solution; specifically, the sodium carbonate monohydrate slurry obtained in S5 is heated to 120° C. and stirred at a pressure of 0.8 MPa for 90 minutes to obtain a second mixed slurry;

[0104] The second mixed slurry is subjected to solid-liquid separation to separate the saturated sodium carbonate solution and obtain sodium carbonate solid;

[0105] In S6, when the potassium content in the separated saturated sodium carbonate mother liquor is lower than 100 g / L, it is sent back to S5 for secondary evaporation and crystallization together with the fourth sodium carbonate solution.

[0106] S7: Dry

[0107] The sodium carbonate solid obtained in S6 is dried to obtain heavy soda ash.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions 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 with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for recovering alkaline leaching solution from solid waste containing cryolite in an aluminum electrolytic plant, characterized in that: It includes the following steps: S1: Reaction First, carbon dioxide is introduced into the alkaline leaching solution to obtain a first mixed slurry; then the first mixed slurry is subjected to solid-liquid separation to separate crude lithium carbonate solids to obtain a first sodium carbonate solution; S2: One-time evaporation concentration The first sodium carbonate solution obtained in S1 is evaporated and concentrated once, and while the concentration of the sodium carbonate solution is increased, lithium carbonate slightly soluble in the first sodium carbonate solution is supersaturated and precipitated to obtain a second sodium carbonate solution; S3: Detoxification The second sodium carbonate solution obtained in S2 is subjected to high temperature hydrolysis to convert the sodium cyanide in the second sodium carbonate solution into sodium formate, and then cooled to obtain a third sodium carbonate solution; S4: Alkaline extraction adding an alkaline extractant to the third sodium carbonate solution obtained in S3 to extract the remaining lithium in the third sodium carbonate solution to obtain a fourth sodium carbonate solution; S5: Secondary evaporation crystallization The fourth sodium carbonate solution obtained in S4 is subjected to secondary evaporation and crystallization to separate the saturated sodium carbonate mother liquor to obtain sodium carbonate monohydrate slurry; S6 de-crystallization water The sodium carbonate monohydrate slurry obtained in S5 is heated and stirred to remove crystal water to obtain a second mixed slurry; the second mixed slurry is subjected to solid-liquid separation to separate a saturated sodium carbonate solution to obtain a sodium carbonate solid; S7: Dry The sodium carbonate solid obtained in S6 is dried to obtain heavy soda ash; In S1, 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; In S3, the second sodium carbonate solution obtained in S2 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.

2. The method for recovering alkaline leaching solution from solid waste containing cryolite from an aluminum electrolytic plant according to claim 1, characterized in that: In S6, the sodium carbonate monohydrate slurry obtained in S5 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.

3. The method for recovering alkaline leaching solution from solid waste containing cryolite from an aluminum electrolytic plant according to claim 1, characterized in that: In S5, when the potassium content in the separated saturated sodium carbonate mother liquor is lower than 100 g / L, secondary evaporation crystallization is performed together with the fourth sodium carbonate solution.

4. The method for recovering alkaline leaching solution from solid waste containing cryolite from an aluminum electrolytic plant according to claim 1, characterized in that: In S6, when the potassium content in the separated saturated sodium carbonate mother liquor is lower than 100 g / L, it is sent back to S5 for secondary evaporation and crystallization together with the fourth sodium carbonate solution.

5. The method for recovering alkaline leaching solution from cryolite-containing solid waste in an aluminum electrolysis plant according to claim 1, characterized in that: In S4, the third sodium carbonate solution obtained in S3 is first filtered to remove impurities and then subjected to alkaline extraction.