Technical method for recycling lithium from electrolytic aluminum lithium-containing waste cathode carbon block

Abstract

The invention relates to a technical method for recovering lithium from an electrolytic aluminum lithium-containing waste cathode carbon block. The preparation method comprises the following steps: firstly, grinding carbon blocks into powder, wherein the fineness is more than 200 meshes; the preparation method comprises the following steps: stirring and mixing powdered carbon and ammonium persulfate {(NH4) 2S2O8} in proportion by a dry method to obtain a precursor, feeding the precursor into a kiln, carrying out anaerobic calcination at 300-500 DEG C for 3-8 hours to obtain calcined clinker, spraying and absorbing tail gas by adopting dilute sulfuric acid, and treating absorption liquid by adopting lime. The clinker is stirred and leached with clear water, the ratio of water to materials is (1-3): 1, a lithium sulfate solution and carbon powder are obtained after filtering separation, and the carbon powder can be used as fuel after being washed and dried. The lithium concentration of the filtrate is 3g / L-8 g / L, lithium precipitation is carried out by adopting trisodium phosphate to obtain a lithium phosphate crude product, and the comprehensive yield of lithium is greater than 90%.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical power source material preparation, and relates to a technical method for recovering lithium from lithium-containing waste cathode carbon blocks from electrolytic aluminum and its application. Background Art

[0002] In aluminum electrolysis production, in order to improve the properties of the electrolyte, improve current efficiency and reduce energy consumption, in addition to adding aluminum fluoride or cryolite to the electrolyte, some fluoride or chloride salts are also added to the electrolyte. One of the commonly used additives is lithium fluoride. Lithium fluoride salts are currently used in the aluminum electrolysis industry to good effect. They can effectively reduce the electrolyte initial crystallization temperature and reduce fluorine emissions, which promotes energy conservation and consumption reduction in aluminum electrolysis enterprises.

[0003] The destination of lithium fluoride in the process is mainly in overhaul slag, electrolyte and carbon block. China's electrolytic aluminum produces 6.8 million tons of overhaul slag, 700,000 tons of electrolyte and 1 million tons of carbon block each year, with a lithium content of 0.5% to 2.5%. With the development of lithium batteries, the price of metallic lithium has increased nearly 10 times. Therefore, the extraction of metallic lithium from electrolytic aluminum waste slag has great commercial value.

[0004] The present invention grinds waste cathode carbon blocks into powder and mixes them with ammonium persulfate for calcination. The oxidizing and acidic properties of ammonium persulfate are used to convert cyanide and lithium fluoride in the carbon powder into lithium sulfate, carbon dioxide and hydrogen fluoride. The tail gas is treated by a unique device. Lithium sulfate is leached out by water, and then solid-liquid separation is performed to obtain carbon powder, which is then used as fuel after drying. Lithium sulfate is then used to recover lithium phosphate by precipitation, and the lithium recovery rate reaches more than 95%. Table 1 is a table of the main chemical components of waste cathode carbon blocks from electrolytic aluminum. Table 1 Main chemical composition of waste cathode carbon blocks from electrolytic aluminum Summary of the invention

[0005] The present invention grinds waste cathode carbon blocks into powder and mixes them with ammonium persulfate for calcination, converting cyanide and lithium fluoride in carbon powder into lithium sulfate, carbon dioxide and hydrogen fluoride. The calcined clinker is leached with water, and solid-liquid separation is performed to obtain carbon powder and lithium sulfate solution. The carbon powder is dried and used as fuel, and the lithium sulfate is then used to recover lithium phosphate by precipitation.

[0006] 1. First, grind the carbon block into powder with a fineness of >200 mesh, and then dry-mix it with ammonium sulfate powder to obtain a precursor;

[0007] 2. The precursor is sent into a kiln and calcined at 300℃~500℃ for 3-8h to obtain calcined clinker, and the tail gas is sprayed and absorbed by dilute sulfuric acid;

[0008] 3. Stir and leach the clinker with clean water at a temperature of 40°C to 60°C, a water-to-material ratio of (1-3):1, and a leaching time of 0.5h to 1h. After filtration and separation, lithium sulfate solution and carbon powder filter cake are obtained;

[0009] 4. Dry the filter cake to obtain a carbon powder product; the filtrate lithium concentration is 3g / L to 8g / L, and lithium is precipitated using trisodium phosphate to obtain a crude lithium phosphate product;

[0010] 5. The technical method for recovering lithium from waste cathode carbon blocks containing lithium from aluminum electrolysis according to claim 1, characterized in that the carbon blocks are waste cathodes from aluminum electrolysis plants, the powder grinding fineness is greater than 200 mesh, and the lithium content is 0.5% to 2.5%;

[0011] 6. The technical method for recovering lithium from waste cathode carbon blocks containing lithium from aluminum electrolysis according to claim 1, characterized in that the ammonium persulfate is an industrial grade product, the main content is greater than 98%, the powder fineness is greater than 40 mesh, and the amount used is 0.1 to 0.5 times that of carbon powder;

[0012] 7. The technical method for recovering lithium from lithium-containing waste cathode carbon blocks from aluminum electrolysis according to claim 1, characterized in that the trisodium phosphate is industrial grade with a purity of 98%;

[0013] 8. The technical method for recovering lithium from waste cathode carbon blocks containing lithium from aluminum electrolysis according to claim 1, characterized in that the main content of crude lithium phosphate is greater than 90%;

[0014] 9. The technical method for recovering lithium from waste cathode carbon blocks containing lithium from aluminum electrolysis according to claim 1, characterized in that the lithium phosphate precipitation temperature is 90°C to 95°C, and the endpoint synthesis pH is 9 to 12;

[0015] The method of the present invention has the following advantages:

[0016] 1. Turn waste into treasure and recycle resources;

[0017] 2. Short process flow, low cost and high recovery rate;

[0018] 3. The impurities of the recovered crude lithium phosphate, except sodium, are all less than 200ppm, and the purity is relatively high;

[0019] 3. Small amount of wastewater, low energy consumption, can reduce the harm of cyanide and fluoride to the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a process flow chart for recovering lithium from lithium-containing waste cathode carbon blocks from aluminum electrolysis to prepare lithium phosphate. DETAILED DESCRIPTION

[0021] The present invention is further described below in conjunction with the examples, which are merely further supplements and explanations of the present invention, rather than limitations of the invention.

[0022] Example 1

[0023] Grind the carbon block into powder, weigh 100kg of carbon powder, the lithium content is 1.26%; weigh 35kg of ammonium persulfate, stir and mix thoroughly to obtain the precursor. Send it into the kiln and calcine at 300℃ for 3h and 500℃ for 2h to obtain calcined clinker. Weigh 100kg of calcined product, add 200kg of water and stir to leach, the leaching temperature is 60℃, and the leaching time is 1h. Filter and wash to obtain carbon powder filter cake and lithium sulfate solution. After testing, the lithium content in the carbon powder is less than 0.05%; the mother liquor pH is 8, the lithium concentration is 5g / L, and the fluorine content is less than 0.01%. Add 25kg of trisodium phosphate to the filtrate to precipitate lithium to obtain crude lithium phosphate, the mother liquor lithium content is 0.01%, the lithium content of lithium phosphate is 15.8%, and the comprehensive lithium yield is 91%.

[0024] Example 2

[0025] Grind the carbon block into powder, weigh 100kg of carbon powder, the lithium content is 1.26%; weigh 40kg of ammonium persulfate, stir and mix thoroughly to obtain the precursor. Send it into the kiln and calcine at 350℃ for 2h and 450℃ for 3h to obtain calcined clinker. Weigh 100kg of calcined product, add 300kg of water and stir to leach, the leaching temperature is 60℃, and the leaching time is 1h. Filter and wash to obtain carbon powder filter cake and lithium sulfate solution. After testing, the lithium content in the carbon powder is less than 0.05%; the mother liquor pH is 8, the lithium concentration is 3.5g / L, and the fluorine content is less than 0.008%. Add 28kg of trisodium phosphate to the filtrate to precipitate lithium to obtain crude lithium phosphate, the mother liquor lithium content is 0.01%, the lithium content of lithium phosphate is 15.4%, and the comprehensive lithium yield is 92%.

[0026] Comparative Example

[0027] Weigh 100kg of carbon powder, add 50% sulfuric acid, stir and dissolve at 100℃ for 5h, absorb the tail gas fluorine with dilute sulfuric acid, filter and obtain lithium with a resolution of 92%, add sodium hydroxide to the filtrate to adjust the pH to 8, filter and remove impurities, there is some lithium fluoride in the precipitate, use trisodium phosphate to precipitate lithium to obtain lithium phosphate, the lithium content of lithium phosphate is 12.5%, and the impurities are relatively high.

Claims

1. A technical method for recovering lithium from lithium-containing waste cathode carbon blocks from aluminum electrolysis, characterized in that: The preparation method comprises the following steps: (1) First, the carbon block is ground into powder with a fineness of more than 200 mesh, and then the powder is mixed with ammonium persulfate in a dry method according to a proportion to obtain a precursor; (2) The precursor is sent into a kiln for oxygen-free calcination at 300°C to 500°C for 3h to 8h to obtain calcined clinker. The tail gas is mainly ammonia, hydrogen fluoride, sulfur dioxide and carbon dioxide, which is treated by spraying and absorbing with dilute sulfuric acid; (3) The clinker is stirred and leached with clean water at a leaching temperature of 40°C to 60°C, a water-to-material ratio of (1 to 3):1, and a leaching time of 0.5 to 1 h. After filtration and separation, a lithium sulfate solution and a carbon powder filter cake are obtained; (4) The filter cake is dried to obtain a carbon powder product; the lithium concentration of the filtrate is 3g / L~8g / L, and lithium is precipitated using trisodium phosphate to obtain a crude lithium phosphate product.

2. The technical method for recovering lithium from waste cathode carbon blocks containing lithium from aluminum electrolysis according to claim 1, characterized in that The carbon block is a discarded cathode from an aluminum electrolytic plant, the powder grinding fineness is greater than 200 meshes, and the lithium content is 0.5% to 2.5%.

3. The technical method for recovering lithium from waste cathode carbon blocks containing lithium from aluminum electrolysis according to claim 1, characterized in that The ammonium persulfate is an industrial-grade product, with a main content of more than 98%, a powder fineness of more than 40 mesh, and a dosage of 0.1 to 0.5 times that of carbon powder.

4. The technical method for recovering lithium from waste cathode carbon blocks containing lithium from aluminum electrolysis according to claim 1, characterized in that The trisodium phosphate is of industrial grade with a purity of 98%.

5. The technical method for recovering lithium from waste cathode carbon blocks containing lithium from aluminum electrolysis according to claim 1, characterized in that The main content of crude lithium phosphate is >90%.

6. The technical method for recovering lithium from waste cathode carbon blocks containing lithium from aluminum electrolysis according to claim 1, characterized in that The lithium phosphate precipitation temperature is 90℃~95℃, and the end point synthesis pH is 9~12.

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