A method for increasing the main content of aluminum-containing calcium fluoride

Abstract

The invention discloses a method for increasing the main content of aluminum-containing calcium fluoride, which comprises the following steps: S1: primary pulping; S2: leaching calcium chloride; S3: primary solid-liquid separation; S4: secondary pulping; S5: secondary solid-liquid separation. Advantages: After the alkali leaching residue is pulped, hydrochloric acid is added to leach the excess calcium ions in the calcium fluoride and convert them into calcium chloride solution, and the aluminum ions are converted into aluminum hydroxide; after a solid-liquid separation, the calcium chloride solution and the medium-grade calcium fluoride containing aluminum hydroxide are separated, and sodium hydroxide is added to the separated medium-grade calcium fluoride after pulping to convert the aluminum hydroxide into sodium metaaluminate, and then a secondary solid-liquid separation is performed to obtain high-grade calcium fluoride. The excess calcium and aluminum in the alkali leaching residue are removed through the above-mentioned treatment, the main content of calcium fluoride is increased, and thus the economic benefits of calcium fluoride are increased.

Description

Technical Field

[0001] The invention relates to the technical field of solid waste recovery in aluminum electrolysis plants, and in particular to a method for increasing the main content of aluminum-containing calcium fluoride. Background Art

[0002] Valuable metal resources such as Li, Na, and K in solid wastes such as electrolytes, carbon slag, and overhaul slag from aluminum smelters are mainly composed of Na3AlF6 and Na2LiAlF6 cryolite. An alkaline leaching process has been developed. After the solid wastes are crushed to a certain particle size, alkaline calcium is used for leaching at 70-80°C. The reaction equation for leaching with calcium hydroxide 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] Na4Fe(CN)6+3NaOH=6NaCN +Fe(OH)3↓

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

[0008] 2KF+ Ca(OH)2=2KOH+ CaF2↓

[0009] The mixed slurry after the reaction in the leaching tank is sent to solid-liquid separation to obtain NaF, CaF 2、 The alkaline leaching residue is mainly composed of CaAl2(OH)8 and Fe(OH)3, and the alkaline leaching solution is mainly composed of NaOH, LiOH, NaAlO2 and NaCN; the presence of NaF, CaAl2(OH)8 and Fe(OH)3 affects the main content of calcium fluoride, reduces the product grade, and calcium cannot be effectively utilized, resulting in low economic benefits. Summary of the invention

[0010] The object of the present invention is to provide a method for increasing the main content of aluminum-containing calcium fluoride.

[0011] The present invention is implemented by the following technical scheme: a method for increasing the main content of aluminum-containing calcium fluoride, comprising the following steps:

[0012] S1: One-step pulping

[0013] The solid waste of the aluminum smelter is mixed with the alkaline leaching residue after alkaline calcium leaching and separation and a calcium chloride solution to prepare a low-grade calcium fluoride slurry;

[0014] S2: Leaching calcium chloride

[0015] Add hydrochloric acid to the low-grade calcium fluoride slurry obtained in S1, 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;

[0016] S3: Primary solid-liquid separation

[0017] The first mixed slurry obtained in S2 is subjected to a solid-liquid separation to separate the calcium chloride solution and obtain medium-grade calcium fluoride containing aluminum hydroxide;

[0018] S4: Secondary pulping

[0019] The medium-grade calcium fluoride obtained in S3 is added with water and sodium hydroxide to obtain a medium-grade calcium fluoride slurry, 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 30-300min, and the second mixed slurry is obtained.

[0020] S5: Secondary solid-liquid separation

[0021] The second mixed slurry obtained in S4 is subjected to secondary solid-liquid separation, and the separated solid phase is a high-grade calcium fluoride product.

[0022] Furthermore, the solid-liquid ratio of the low-grade calcium fluoride slurry in S1 is 1:3-5.

[0023] Furthermore, the solid-liquid ratio of the medium-grade calcium fluoride slurry in S4 is 1:1-6.

[0024] Furthermore, carbon dioxide is first introduced into the solution separated in S5 to react to obtain a third mixed slurry, and then the third mixed slurry is subjected to three solid-liquid separations, and the obtained solid phase is an aluminum hydroxide product, and the obtained liquid phase is a sodium carbonate solution.

[0025] Furthermore, the solid-liquid separation in S3 is carried out in the first integrated filter-washer, and the washing water discharged from the first integrated filter-washer is sent back to S1 for pulping.

[0026] Furthermore, the secondary solid-liquid separation in S5 is carried out in the second integrated filter-washer, and the washing water discharged from the second integrated filter-washer is sent back to S4 for preparing medium-grade calcium fluoride slurry.

[0027] The advantages of the present invention are as follows: after the alkali leaching residue is pulped, hydrochloric acid is added to leach the excess calcium ions in the calcium fluoride and convert them into a calcium chloride solution, and the aluminum ions are converted into aluminum hydroxide; after a solid-liquid separation, the calcium chloride solution and the medium-grade calcium fluoride containing aluminum hydroxide are separated, and after the separated medium-grade calcium fluoride is pulped, sodium hydroxide is added to convert the aluminum hydroxide into sodium metaaluminate, and then a secondary solid-liquid separation is performed to obtain high-grade calcium fluoride. The excess calcium and aluminum in the alkali leaching residue are removed through the above-mentioned treatment, the main content of calcium fluoride is increased, and the economic benefits of calcium fluoride are increased. At the same time, the separated calcium chloride solution can be further processed to obtain a calcium chloride product, and the aluminum hydroxide can be directly used as a by-product to further increase the benefits. DETAILED DESCRIPTION

[0028] Using 1 t of alkaline leaching residue obtained by leaching calcium hydroxide from the same batch of solid waste from the electrolytic aluminum plant as raw material (the main content of calcium fluoride in the alkaline leaching residue is 58.4%, which is lower than the minimum standard specified in the ferrous metallurgical industry standard - YB / T5217-2019 - fluorite ore powder FF-70), the following examples are carried out respectively:

[0029] Example 1: A method for increasing the main content of aluminum-containing calcium fluoride, comprising the following steps:

[0030] S1: One-step pulping

[0031] The solid waste of the aluminum smelter is mixed with the alkaline leaching residue after alkaline calcium leaching and separation and a calcium chloride solution to prepare a low-grade calcium fluoride slurry with a solid-liquid ratio of 1:3;

[0032] S2: Leaching calcium chloride

[0033] Hydrochloric acid is added to the low-grade calcium fluoride slurry obtained in S1, the pH is adjusted to 1, the reaction temperature is 80°C, and the reaction time is 300 min, so that the calcium ions in the alkaline leaching residue are leached into the solution in the form of calcium chloride to obtain a first mixed slurry. The reaction equation is as follows:

[0034] CaAl2(OH)8+2HCl=2Al(OH)3↓+CaCl2+2H2O

[0035] CaCl2+2NaF=2NaCl+CaF2↓

[0036] Fe(OH)3+3HCl=FeCl3+3H2O

[0037] Al(OH)3+3HCl= AlCl3+3H2O

[0038] S3: Primary solid-liquid separation

[0039] The first mixed slurry obtained in S2 is subjected to a solid-liquid separation to separate the calcium chloride solution containing aluminum chloride and ferric chloride, thereby obtaining medium-grade calcium fluoride containing aluminum hydroxide;

[0040] The first solid-liquid separation in S3 is carried out in the first integrated filter-washer, and the washing water discharged from the first integrated filter-washer is sent back to S1 for pulping.

[0041] S4: Secondary pulping

[0042] The medium-grade calcium fluoride separated from S3 was added with water and sodium hydroxide to prepare a medium-grade calcium fluoride slurry with a solid-liquid ratio of 1:1. The reaction temperature was 30°C and the reaction time was 300 min to obtain a second mixed slurry. The reaction equation is:

[0043] Al(OH)3+NaOH=NaAlO2+2H2O

[0044] The amount of sodium hydroxide added is 1.1 times the molar amount of aluminum hydroxide;

[0045] S5: Secondary solid-liquid separation

[0046] The second mixed slurry obtained in S4 is subjected to secondary solid-liquid separation, and the solid phase obtained by the secondary separation is a high-grade calcium fluoride product, and the separated liquid is a mixed solution of sodium hydroxide and sodium aluminate.

[0047] Carbon dioxide is first introduced into the mixed solution obtained by separation in S5 to obtain a third mixed slurry, and the reaction equation is:

[0048] 2NaAlO2+ CO2+3H2O=Na2CO3+2Al(OH)3↓

[0049] 2NaOH + CO2 = Na2CO3 + H2O

[0050] The third mixed slurry is then subjected to three solid-liquid separations, and the obtained solid phase is an aluminum hydroxide product, and the obtained liquid phase is a sodium carbonate solution.

[0051] The secondary solid-liquid separation in S5 is carried out in the second integrated filter-washer, and the washing water discharged from the second integrated filter-washer is sent back to S4 for preparing medium-grade calcium fluoride slurry.

[0052] Example 2: A method for increasing the main content of aluminum-containing calcium fluoride, comprising the following steps:

[0053] S1: One-step pulping

[0054] The solid waste of the aluminum smelter is mixed with the alkaline leaching residue after alkaline calcium leaching and separation and a calcium chloride solution to prepare a low-grade calcium fluoride slurry with a solid-liquid ratio of 1:4;

[0055] S2: Leaching calcium chloride

[0056] Hydrochloric acid is added to the low-grade calcium fluoride slurry obtained in S1, and the pH is adjusted to 2.5, the reaction temperature is 95°C, and the reaction time is 150 min, so that the calcium ions in the alkaline leaching residue are leached into the solution in the form of calcium chloride to obtain a first mixed slurry. The reaction equation is as follows:

[0057] CaAl2(OH)8+2HCl=2Al(OH)3↓+CaCl2+2H2O

[0058] CaCl2+2NaF=2NaCl+CaF2↓

[0059] Fe(OH)3+3HCl=FeCl3+3H2O

[0060] Al(OH)3+3HCl= AlCl3+3H2O

[0061] S3: Primary solid-liquid separation

[0062] The first mixed slurry obtained in S2 is subjected to a solid-liquid separation to separate the calcium chloride solution containing aluminum chloride and ferric chloride, thereby obtaining medium-grade calcium fluoride containing aluminum hydroxide;

[0063] The first solid-liquid separation in S3 is carried out in the first integrated filter-washer, and the washing water discharged from the first integrated filter-washer is sent back to S1 for pulping.

[0064] S4: Secondary pulping

[0065] The medium-grade calcium fluoride separated from S3 was added with water and sodium hydroxide to prepare a medium-grade calcium fluoride slurry with a solid-liquid ratio of 1:4. The reaction temperature was 60°C and the reaction time was 150 min to obtain a second mixed slurry. The reaction equation is:

[0066] Al(OH)3+NaOH=NaAlO2+2H2O

[0067] The amount of sodium hydroxide added is 1.3 times the molar amount of aluminum hydroxide;

[0068] S5: Secondary solid-liquid separation

[0069] The second mixed slurry obtained in S4 is subjected to secondary solid-liquid separation, and the solid phase obtained by the secondary separation is a high-grade calcium fluoride product, and the separated liquid is a mixed solution of sodium hydroxide and sodium aluminate.

[0070] Carbon dioxide is first introduced into the mixed solution obtained by separation in S5 to obtain a third mixed slurry, and the reaction equation is:

[0071] 2NaAlO2+ CO2+3H2O=Na2CO3+2Al(OH)3↓

[0072] 2NaOH + CO2 = Na2CO3 + H2O

[0073] The third mixed slurry is then subjected to three solid-liquid separations, and the obtained solid phase is an aluminum hydroxide product, and the obtained liquid phase is a sodium carbonate solution.

[0074] The secondary solid-liquid separation in S5 is carried out in the second integrated filter-washer, and the washing water discharged from the second integrated filter-washer is sent back to S4 for preparing medium-grade calcium fluoride slurry.

[0075] Embodiment 3: A method for increasing the main content of aluminum-containing calcium fluoride, comprising the following steps:

[0076] S1: One-step pulping

[0077] The solid waste of the aluminum smelter is mixed with the alkaline leaching residue after alkaline calcium leaching and separation and a calcium chloride solution to prepare a low-grade calcium fluoride slurry with a solid-liquid ratio of 1:5;

[0078] S2: Leaching calcium chloride

[0079] Add hydrochloric acid to the low-grade calcium fluoride slurry obtained in S1, adjust the pH to 4, the reaction temperature to 110°C, and the reaction time to 30 minutes, so that the calcium ions in the alkaline leaching residue are leached into the solution in the form of calcium chloride to obtain a first mixed slurry. The reaction equation is as follows:

[0080] CaAl2(OH)8+2HCl=2Al(OH)3↓+CaCl2+2H2O

[0081] CaCl2+2NaF=2NaCl+CaF2↓

[0082] Fe(OH)3+3HCl=FeCl3+3H2O

[0083] Al(OH)3+3HCl= AlCl3+3H2O

[0084] S3: Primary solid-liquid separation

[0085] The mixed slurry obtained in S2 is subjected to a solid-liquid separation to separate the calcium chloride solution containing aluminum chloride and ferric chloride, thereby obtaining medium-grade calcium fluoride containing aluminum hydroxide;

[0086] The first solid-liquid separation in S3 is carried out in the first integrated filter-washer, and the washing water discharged from the first integrated filter-washer is sent back to S1 for pulping.

[0087] S4: Secondary pulping

[0088] The medium-grade calcium fluoride separated from S3 is added with water and sodium hydroxide to prepare a medium-grade calcium fluoride slurry with a solid-liquid ratio of 1:6, and then sodium hydroxide solution is added. The reaction temperature is 110°C and the reaction time is 30 minutes to obtain a second mixed slurry. The reaction equation is:

[0089] Al(OH)3+NaOH=NaAlO2+2H2O

[0090] The amount of sodium hydroxide added is 1.5 times the molar amount of aluminum hydroxide;

[0091] S5: Secondary solid-liquid separation

[0092] The second mixed slurry obtained in S4 is subjected to secondary solid-liquid separation, and the solid phase obtained by the secondary separation is a high-grade calcium fluoride product, and the separated liquid is a mixed solution of sodium hydroxide and sodium aluminate.

[0093] Carbon dioxide is first introduced into the mixed solution obtained by separation in S5 to obtain a third mixed slurry, and the reaction equation is:

[0094] 2NaAlO2+ CO2+3H2O=Na2CO3+2Al(OH)3↓

[0095] 2NaOH + CO2 = Na2CO3 + H2O

[0096] The third mixed slurry is then subjected to three solid-liquid separations, and the obtained solid phase is an aluminum hydroxide product, and the obtained liquid phase is a sodium carbonate solution.

[0097] The secondary solid-liquid separation in S5 is carried out in the second integrated filter-washer, and the washing water discharged from the second integrated filter-washer is sent back to S4 for preparing medium-grade calcium fluoride slurry.

[0098] The concentration of the calcium chloride solution obtained in Examples 1 to 3, the weight of aluminum hydroxide and the main content of high-grade calcium fluoride were tested, and the test results are shown in the following table:

[0099]

[0100] As shown in the table above, by treating the alkaline leaching residue according to the method of the present invention, the main content of calcium fluoride obtained is above 94%, reaching the fluorite ore powder FF-90 and above grades specified in the ferrous metallurgical industry standard-YB / T5217-2019; and a calcium chloride solution with a concentration of more than 24% and an aluminum hydroxide product of more than 35 kg can be obtained.

[0101] Taking Example 3 as an example, according to the calculation of high-grade calcium fluoride 1,300 yuan / ton, aluminum hydroxide 1,850 yuan / ton, and calcium chloride 750 yuan / ton, processing 1 ton of alkaline leaching slag can increase the added value of the slag by 1,203.97 yuan.

[0102] 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 increasing the main content of aluminum-containing calcium fluoride, characterized in that: It includes the following steps: S1: One-step pulping The solid waste of the aluminum smelter is mixed with the alkaline leaching residue after alkaline calcium leaching and separation and a calcium chloride solution to prepare a low-grade calcium fluoride slurry; S2: Leaching calcium chloride Add hydrochloric acid to the low-grade calcium fluoride slurry obtained in S1, 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; S3: Primary solid-liquid separation The first mixed slurry obtained in S2 is subjected to a solid-liquid separation to separate the calcium chloride solution and obtain medium-grade calcium fluoride containing aluminum hydroxide; S4: Secondary pulping The medium-grade calcium fluoride obtained in S3 is added with water and sodium hydroxide to obtain a medium-grade calcium fluoride slurry, 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 30-300min, and the second mixed slurry is obtained. S5: Secondary solid-liquid separation The second mixed slurry obtained in S4 is subjected to secondary solid-liquid separation, and the separated solid phase is a high-grade calcium fluoride product.

2. A method for increasing the main content of aluminum-containing calcium fluoride according to claim 1, characterized in that: The solid-to-liquid ratio of low-grade calcium fluoride slurry S1 is 1:3-5.

3. A method for increasing the main content of aluminum-containing calcium fluoride according to claim 1, characterized in that: The solid-to-liquid ratio of the medium-grade calcium fluoride slurry in S4 is 1:1-6.

4. A method for increasing the main content of aluminum-containing calcium fluoride according to claim 1, characterized in that: Carbon dioxide is first introduced into the solution separated in S5 to react to obtain a third mixed slurry, and then the third mixed slurry is subjected to three solid-liquid separations, the obtained solid phase is an aluminum hydroxide product, and the obtained liquid phase is a sodium carbonate solution.

5. A method for increasing the main content of aluminum-containing calcium fluoride according to claim 1, characterized in that: The first solid-liquid separation in S3 is carried out in the first integrated filter-washer, and the washing water discharged from the first integrated filter-washer is sent back to S1 for pulping.

6. A method for increasing the main content of aluminum-containing calcium fluoride according to claim 1, characterized in that: The secondary solid-liquid separation in S5 is carried out in the second integrated filter-washer, and the washing water discharged from the second integrated filter-washer is sent back to S4 for preparing medium-grade calcium fluoride slurry.

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