A method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum

Abstract

The present invention relates to the field of lithium carbonate preparation, and specifically relates to a method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum, which includes the following steps: mixing and crushing the waste cathode carbon blocks of electrolytic aluminum with ammonium sulfate, flash roasting, and leaching to obtain a lithium-rich solution and leaching residue; purifying the lithium-rich solution and obtaining lithium carbonate after lithium precipitation. The present invention utilizes flash roasting to enable the raw material reactants to have the ability to be suspended, greatly shortening the roasting time, improving the roasting efficiency, and having low energy consumption. At the same time, ammonium sulfate is selected as the raw material for reacting with the cathode carbon blocks, which can greatly fix the fluoride ions in the cathode carbon blocks, avoiding the formation of lithium fluoride due to the presence of fluoride ions and affecting the recovery rate and purity of lithium carbonate.

Description

Technical Field

[0001] The present invention relates to the field of lithium carbonate preparation, and particularly relates to a method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum. Background Art

[0002] As a high-value resource, lithium element is involved in many fields such as high-energy batteries, pharmaceutical glass, nuclear power generation, and surface modification of non-metallic minerals. The existing preparation of lithium carbonate mainly adopts two types of technologies: lithium extraction from ores and lithium extraction from brines. The lithium extraction from ores technology is mature, with high recovery rate and simple process, but it has disadvantages such as high energy consumption, large material flow rate, and high cost. The lithium extraction from salt lake brines technology is greatly restricted by resource endowment and technical level. Therefore, using waste resources to extract lithium element to prepare lithium carbonate has become an important way to alleviate the scarcity of lithium element at the present stage.

[0003] The electrolytic aluminum cell adopts the cryolite-aluminum oxide molten salt electrolysis method, with carbon materials as the anode and cathode respectively. After a long time of operation, the carbon at the anode and cathode is severely damaged by the erosion of the electrolyte solution and becomes solid waste. Among them, the cathode carbon block is rich in a large number of valuable elements including C, Na3AlF6, NaF, CaF2, Al2O3, MgF2, and LiF, especially the recovery of lithium element is more important. At present, the main method for extracting lithium element from the cathode carbon block is to react the cathode carbon block with concentrated sulfuric acid at high temperature. The reaction steps are complex, and a large amount of additives need to be added additionally during the lithium precipitation process, resulting in low purity of lithium carbonate. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects of long reaction time and low purity of the prepared lithium carbonate in the prior art for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum, so as to provide a method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum.

[0005] For this purpose, the present invention provides a method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum, including mixing and crushing the waste cathode carbon blocks of electrolytic aluminum with ammonium sulfate, flash roasting, and leaching to obtain a lithium-rich solution and leaching residue; removing impurities from the lithium-rich solution and obtaining lithium carbonate after lithium precipitation.

[0006] During the flash roasting, the roasting temperature is 280 - 650 °C, the roasting time is 3 - 9 s, and the negative pressure is 10 - 80 KPa.

[0007] Optionally, during the flash roasting, the roasting temperature is 380 - 613 °C.

[0008] The flash roasting uses air as the carrier gas, and the gas flow rate of the carrier gas is 50 - 200 L / kg based on the weight of the mixture of waste cathode carbon blocks of electrolytic aluminum and ammonium sulfate.

[0009] The mass ratio of the ammonium sulfate to the waste cathode carbon block of electrolytic aluminum is 0.3 - 0.6.

[0010] The leaching step includes crushing the mixture after flash roasting, mixing it with water, stirring, and filtering to obtain a lithium-rich solution and leaching residues. Among them, the liquid-solid ratio of the crushed roasted mixture to the leaching agent is 1 - 5 mL / g, the leaching temperature is 40 - 80 °C, the leaching time is 10 - 60 min, and the stirring rate is 150 - 450 r / min. The impurity removal step includes injecting fluoride into the lithium-rich solution to obtain a first filtrate, and injecting aluminum salt into the first filtrate to obtain a second filtrate.

[0011] Adjust the pH of the lithium-rich solution to 3.5 - 4.5, then inject fluoride and stir for reaction for 1 - 3 h to obtain a first filtrate. Among them, the total molar number of calcium ions and magnesium ions in the first filtrate is in a molar ratio of 1:(2.2 - 2.4) to the fluoride ions in the fluoride, the reaction temperature is 20 - 40 °C, and the stirring rate is 150 - 300 r / min.

[0012] According to the molar ratio of aluminum ions to fluoride ions of 1:(3 - 6), after injecting aluminum salt into the first filtrate, adjust the pH of the first filtrate to 4.5 - 6 with an alkali solution, stir and react for 0.5 - 3 h to obtain a second filtrate. Among them, the reaction temperature is 40 - 60 °C, the stirring rate is 100 - 300 r / min, and the alkali solution is at least one of sodium hydroxide, potassium hydroxide, and lithium hydroxide.

[0013] The aluminum ions and the aluminum salt are at least one of aluminum sulfate, aluminum nitrate, and aluminum chloride; and / or, the fluoride is at least one of sodium fluoride, potassium fluoride, and lithium fluoride.

[0014] The lithium precipitation step includes concentrating the second filtrate, adding sodium carbonate, stirring, and filtering to obtain lithium carbonate. Among them, the molar ratio of lithium ions to sodium carbonate is 2:(1.1 - 1.2), the stirring temperature is 80 - 100 °C, the stirring time is 0.5 - 2 h, and the stirring rate is 150 - 300 r / min.

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

[0016] 1. The method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum provided by the present invention involves mixing and crushing the waste cathode carbon blocks of electrolytic aluminum with ammonium sulfate, followed by flash roasting and leaching to obtain a lithium-rich solution and leaching residue; the lithium-rich solution is purified and then lithium carbonate is obtained after lithium precipitation. In the flash roasting furnace of the present invention, hot gas enters the furnace from the bottom through a nozzle, and the mixture of waste cathode carbon blocks of electrolytic aluminum and ammonium sulfate directly contacts the hot gas flow above the nozzle. Small particles are immediately entrained by the hot gas flow and react, while large particles fall towards the nozzle and are entrained and react again when encountering the high-speed gas flow at the nozzle until the roasting is completed. Flash roasting enables the raw material reactants to have the ability to suspend, greatly reducing the roasting time, improving the roasting efficiency, and having low energy consumption. When the mixture of cathode carbon blocks and ammonium sulfate contacts the hot gas flow, ammonium sulfate reacts with the fluoride in the cathode carbon blocks to generate ammonia, hydrogen fluoride, and soluble sulfates, quickly fixing the fluorine element in the cathode carbon blocks through flash roasting, avoiding the influence of the presence of fluorine element on the leaching purity of lithium element in the cathode carbon blocks, and achieving the purpose of improving the purity of lithium carbonate.

[0017] 2. The method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum provided by the present invention limits the temperature, roasting time, and negative pressure of flash roasting. The roasting temperature is controlled within the range of 280 - 650 °C to ensure that during flash roasting, ammonium sulfate reacts with the fluoride in the cathode carbon blocks to generate ammonia, hydrogen fluoride, etc., and ammonium sulfate is used to fix the fluorine element. At the same time, when the negative pressure is limited to 10 - 80 KPa, it is ensured that the mixture of ammonium sulfate and cathode carbon blocks can be suspended in the furnace cavity of the flash furnace for 3 - 9 s, promoting the full reaction between ammonium sulfate and cathode carbon blocks while avoiding the high-temperature decomposition of excessive ammonium sulfate, which affects the effect of ammonium sulfate in fixing fluoride ions in the leaching reaction. Therefore, using ammonium sulfate as the raw material reacting with the cathode carbon blocks can greatly fix the fluoride ions in the cathode carbon blocks, avoiding the formation of lithium fluoride due to the presence of fluoride ions, which affects the recovery rate and purity of lithium carbonate.

[0018] 3. The method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum provided by the present invention limits the mass ratio of waste cathode carbon blocks of electrolytic aluminum to ammonium sulfate. Excessive ammonium sulfate is mixed with the cathode carbon blocks. During the flash roasting of the cathode carbon blocks and ammonium sulfate, ammonium sulfate reacts with the fluoride in the cathode carbon blocks to generate ammonia, hydrogen fluoride, and soluble sulfates. The excessive ammonium sulfate does not react but decomposes to form ammonium bisulfate. During the water leaching process after flash roasting, the sulfate ions of ammonium bisulfate react with the hydrogen ions ionized from water to form sulfuric acid, and the sulfuric acid reacts with the fluoride in the solution to form soluble sulfates. The gaseous substances such as hydrogen fluoride and ammonia generated during the preparation process are absorbed by an alkali solution such as sodium hydroxide to form fluorides and ammonium salts, realizing the recovery of fluorides, avoiding the formation of lithium fluoride due to the presence of fluoride ions, which affects the recovery rate and purity of lithium carbonate. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0020] Figure 1 It is the process flow chart of the method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum in Example 1 of the present invention. Specific embodiments

[0021] The following embodiments are provided to better further understand the present invention. It is not limited to the best embodiment, and does not limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior art features falls within the protection scope of the present invention.

[0022] For those not specifying specific experimental steps or conditions in the embodiments, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For the reagents or instruments not indicating the manufacturer, they are all conventional reagent products that can be obtained through commercial purchase. Among them, metal ion detection adopts the ICP - OES method, and F ion detection adopts the fluoride ion selective electrode method.

[0023] Example 1

[0024] Please refer to Figure 1 the process flow chart shown. This embodiment provides a method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum. The specific steps and parameters are as follows:

[0025] Take 100 g of waste cathode carbon blocks of electrolytic aluminum and 60 g of ammonium sulfate, mix and grind them to a particle size less than 200 mesh. Take 100 g of the ground mixture and spray it into a flash furnace at 380 °C with an air carrier gas volume of 5 L and roast for 6 s. The negative pressure of the flash furnace is 60 KPa;

[0026] Take 50 g of the mixture after flash roasting, mix it with 250 ml of water, and stir and leach it at 80 °C and 250 r / min for 30 min to obtain a lithium - rich solution and a first filter residue. The main component of the first filter residue is carbon powder;

[0027] Perform impurity removal on the lithium - rich solution. The impurity removal steps include using ICP to detect the Ca 2+ concentration and Mg 2 + concentration in the lithium - precipitation solution, and according to (Ca 2+ +Mg 2+ ):F- The molar ratio is 1:2.4. Sodium fluoride is injected into the lithium precipitation solution, and the pH of the lithium precipitation solution added with sodium fluoride is adjusted to 4.5 using a NaOH solution. At 25 °C, it is stirred at a rate of 150 r / min for 1 h to obtain a first filtrate and a second filter residue. The second filter residue is a calcium-magnesium mixture; the F in the first filtrate is detected by ICP - concentration. According to the molar ratio of Al 3+ :F - adjusted to 1:6, aluminum sulfate is injected into the first filtrate, and the pH of the first filtrate added with aluminum sulfate is adjusted to 5 using NaOH, heated to 60 °C, and the reaction solution is stirred at a rate of 300 r / min for 30 min to obtain a second filtrate and a third filter residue. The third filter residue is cryolite;

[0028] Lithium precipitation. The second filtrate is concentrated to 1 / 6 of the original volume, and the Li in the concentrated solution is detected by ICP + concentration. According to the molar ratio of Li + to saturated sodium carbonate of 2:1.1, saturated sodium carbonate is injected into the concentrated solution, and it is stirred at a rate of 200 r / min at 80 °C for 30 min to obtain a third filtrate and a fourth filter residue. The third filtrate is the lithium precipitation mother liquor. The lithium precipitation mother liquor is neutralized, evaporated and crystallized to obtain sulfate, and there is no wastewater discharge. The fourth filter residue is lithium carbonate.

[0029] Example 2

[0030] This example provides a method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum. The specific steps and parameters are as follows:

[0031] Take 100 g of waste cathode carbon blocks of electrolytic aluminum and 40 g of ammonium sulfate, mix and grind them to a particle size less than 200 mesh. Take 100 g of the ground mixture and spray it into a flash furnace at 613 °C with an air carrier gas volume of 10 L for roasting for 3 s. The negative pressure of the flash furnace is 30 KPa;

[0032] Take 50 g of the mixture after flash roasting, mix it with 100 ml of water, and stir and leach it at 40 °C and 450 r / min for 60 min to obtain a lithium-rich solution and a first filter residue. The main component of the first filter residue is carbon powder;

[0033] Impurity removal is carried out on the lithium-rich solution. The impurity removal steps include detecting the Ca 2+ concentration and Mg 2 + concentration in the lithium precipitation solution by ICP. According to (Ca 2+ +Mg 2+ ):F -The molar ratio is 1:2.2. Lithium fluoride is injected into the lithium precipitation solution. The pH of the lithium precipitation solution added with sodium fluoride is adjusted to 3.5 using a NaOH solution, heated to 40 °C, and stirred at a rate of 300 r / min for 3 h to obtain a first filtrate and a second filter residue. The second filter residue is a calcium-magnesium mixture; the first filtrate is detected by ICP, and the F - concentration, according to Al 3+ :F - The molar ratio is adjusted to 1:3. Aluminum chloride is injected into the first filtrate. The pH of the first filtrate added with aluminum sulfate is adjusted to 5.5 using NaOH, heated to 50 °C, and the reaction solution is stirred at a rate of 100 r / min for 1 h to obtain a second filtrate and a third filter residue. The third filter residue is cryolite;

[0034] Lithium precipitation. The second filtrate is concentrated to 1 / 6 of the original volume. The Li + concentration of the concentrated solution is detected by ICP. According to the molar ratio of Li + to saturated sodium carbonate of 2:1.2, saturated sodium carbonate is injected into the concentrated solution and stirred at a rate of 150 r / min at 100 °C for 2 h to obtain a third filtrate and a fourth filter residue. The third filtrate is the lithium precipitation mother liquor, which is neutralized, evaporated, and crystallized to obtain sulfate, and there is no waste water discharge. The fourth filter residue is lithium carbonate.

[0035] Example 3

[0036] This example provides a method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum. The specific steps and parameters are as follows:

[0037] Take 100 g of waste cathode carbon blocks of electrolytic aluminum and 50 g of ammonium sulfate, mix and grind them to a particle size less than 200 mesh. Take 100 g of the ground mixture and spray it into a flash furnace at 350 °C with an air carrier gas volume of 20 L and roast for 9 s. The negative pressure of the flash furnace is 80 KPa;

[0038] Take 100 g of the flash-roasted mixture, mix it with 100 ml of water, and stir and leach it at 60 °C and 150 r / min for 30 min to obtain a lithium-rich solution and a first filter residue. The main component of the first filter residue is carbon powder;

[0039] Impurity removal is carried out on the lithium-rich solution. The impurity removal steps include detecting the Ca 2+ concentration and Mg 2 + concentration of the lithium precipitation solution by ICP. According to (Ca 2+ +Mg 2+ ):F -The molar ratio is 1:2.4. Potassium fluoride is injected into the lithium precipitation solution, and the pH of the lithium precipitation solution added with potassium fluoride is adjusted to 4 using LiOH solution. The system temperature is maintained at 20 °C, and it is stirred at a rate of 200 r / min for 2 h to obtain a first filtrate and a second filter residue. The second filter residue is a calcium-magnesium mixture; the first filtrate is obtained by ICP detection, F - concentration, according to Al 3+ :F - The molar ratio is adjusted to 1:5. Aluminum nitrate is injected into the first filtrate, and the pH of the first filtrate added with aluminum sulfate is adjusted to 4.5 using LiOH. The temperature of the reaction system is heated to 50 °C, and the reaction solution is stirred at a rate of 350 r / min for 3 h to obtain a second filtrate and a third filter residue. The third filter residue is cryolite;

[0040] For lithium precipitation, the second filtrate is concentrated to 1 / 6 of the original volume, and the Li + concentration of the concentrated solution is obtained by ICP detection. According to Li + and the molar ratio of saturated sodium carbonate is 2:1.1. Saturated sodium carbonate is injected into the concentrated solution, and it is stirred at a rate of 250 r / min at 90 °C for 2 h to obtain a third filtrate and a fourth filter residue. The third filtrate is the lithium precipitation mother liquor, which is neutralized, evaporated, and crystallized to obtain sulfate, and there is no wastewater discharge. The fourth filter residue is lithium carbonate.

[0041] Example 4

[0042] This example provides a method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum. The specific steps and parameters are as follows:

[0043] 100 g of waste cathode carbon blocks of electrolytic aluminum and 50 g of ammonium sulfate are mixed and ground to a particle size less than 200 mesh. 100 g of the ground mixture is sprayed into a flash furnace at 300 °C with an air carrier gas volume of 12 L and roasted for 4 s. The negative pressure of the flash furnace is 40 KPa;

[0044] 50 g of the mixture after flash roasting is mixed with 20 ml of solution and stirred for 40 min at 70 °C and 200 r / min for leaching to obtain a lithium-rich solution and a first filter residue. The main component of the first filter residue is carbon powder;

[0045] For impurity removal of the lithium-rich solution, the impurity removal steps include obtaining the Ca 2+ concentration and Mg 2 + concentration of the lithium precipitation solution by ICP detection. According to (Ca 2+ +Mg 2+ ):F -The molar ratio is 1:2.3. Sodium fluoride is injected into the lithium precipitation solution, and the pH of the lithium precipitation solution added with sodium fluoride is adjusted to 4.5 using a KOH solution. At 35°C, it is stirred at a rate of 200 r / min for 2.5 h to obtain a first filtrate and a second filter residue. The second filter residue is a calcium-magnesium mixture; the first filtrate is obtained by ICP detection. According to the molar ratio of Al 3+ :F - The molar ratio is adjusted to 1:6. Aluminum sulfate is injected into the first filtrate, and the pH of the first filtrate added with aluminum sulfate is adjusted to 6 using KOH. It is heated to 40°C and the reaction solution is stirred at a rate of 200 r / min for 2 h to obtain a second filtrate and a third filter residue. The third filter residue is cryolite;

[0046] Lithium precipitation: The second filtrate is concentrated to 1 / 6 of the original volume. The Li + concentration of the concentrated solution is obtained by ICP detection. According to the molar ratio of Li + to saturated sodium carbonate of 2:1.2, saturated sodium carbonate is injected into the concentrated solution and stirred at a rate of 300 r / min at 80°C for 1 h to obtain a third filtrate and a fourth filter residue. The third filtrate is the lithium precipitation mother liquor, which is neutralized, evaporated and crystallized to obtain sulfate, and there is no wastewater discharge. The fourth filter residue is lithium carbonate.

[0047] Example 5

[0048] This example provides a method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum. The specific steps and parameters are as follows:

[0049] 100 g of waste cathode carbon blocks of electrolytic aluminum and 50 g of ammonium sulfate are mixed and ground to a particle size less than 200 mesh. 100 g of the ground mixture is sprayed into a flash furnace at 500°C with an air carrier gas volume of 18 L and roasted for 3 s. The negative pressure of the flash furnace is 30 KPa;

[0050] 50 g of the mixture after flash roasting is mixed with 300 ml of an acid solution and stirred and leached at 80°C and 400 r / min for 30 min to obtain a lithium-rich solution and a first filter residue. The main component of the first filter residue is carbon powder;

[0051] The lithium-rich solution is purified. The purification steps include detecting the Ca 2+ concentration and Mg 2 + concentration of the lithium precipitation solution by ICP detection. According to (Ca 2+ +Mg 2- ):F +The molar ratio is 1:2.4. Sodium fluoride is injected into the lithium precipitation solution, and the pH of the lithium precipitation solution added with sodium fluoride is adjusted to 3.5 using NaOH solution. At 20 °C, it is stirred at a rate of 150 r / min for 1.5 h to obtain a first filtrate and a second filter residue. The second filter residue is a calcium-magnesium mixture; the first filtrate is obtained by ICP detection. According to Al 3+ :F - The molar ratio is adjusted to 1:4. Aluminum sulfate is injected into the first filtrate, and the pH of the first filtrate added with aluminum sulfate is adjusted to 4.5 using NaOH. The system temperature is heated to 60 °C, and the reaction solution is stirred at a rate of 300 r / min for 2.5 h to obtain a second filtrate and a third filter residue. The third filter residue is cryolite;

[0052] Lithium precipitation: The second filtrate is concentrated to 1 / 6 of the original volume. The Li + concentration of the concentrated solution is obtained by ICP detection. According to Li + The molar ratio to saturated sodium carbonate is 2:1.1. Saturated sodium carbonate is injected into the concentrated solution, and it is stirred at a rate of 200 r / min at 80 °C for 1.5 h to obtain a third filtrate and a fourth filter residue. The third filtrate is the lithium precipitation mother liquor, which is neutralized and evaporated to crystallize to obtain sulfates, and there is no wastewater discharge. The fourth filter residue is lithium carbonate.

[0053] Example 6

[0054] This example provides a method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum. The specific steps and parameters are as follows:

[0055] Take 100 g of waste cathode carbon blocks of electrolytic aluminum and 60 g of ammonium sulfate, mix and grind them to a particle size less than 200 mesh. Take 100 g of the ground mixture and spray it into a flash furnace at 280 °C with an air carrier gas volume of 5 L and roast for 6 s. The negative pressure of the flash furnace is 60 KPa;

[0056] Take 50 g of the mixture after flash roasting, mix it with 250 ml of water, and stir and leach it at 80 °C and 250 r / min for 30 min to obtain a lithium-rich solution and a first filter residue. The main component of the first filter residue is carbon powder;

[0057] The steps of impurity removal and lithium precipitation for the lithium-rich solution are the same as those in Example 1.

[0058] Example 7

[0059] This example provides a method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum. The specific steps and parameters are as follows:

[0060] Take 100 g of waste cathode carbon blocks of electrolytic aluminum and 60 g of ammonium sulfate, mix and grind them to a particle size less than 200 mesh. Take 100 g of the ground mixture and spray it into a flash furnace at 650 °C with an air carrier gas volume of 5 L and roast for 6 s. The negative pressure of the flash furnace is 60 KPa;

[0061] Take 50 g of the mixture after flash roasting, mix it with 250 ml of water, stir and leach for 30 min under the conditions of 80°C and 250 r / min to obtain a lithium-rich solution and a first filter residue, and the main component of the first filter residue is carbon powder;

[0062] The steps of impurity removal and lithium precipitation for the lithium-rich solution are the same as those in Example 1.

[0063] Example 8

[0064] This example provides a method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum, and the specific steps and parameters are as follows:

[0065] Take 100 g of waste cathode carbon blocks of electrolytic aluminum and 30 g of ammonium sulfate, mix and grind them to a particle size less than 200 mesh. Take 100 g of the ground mixture, spray it into a flash furnace at 380°C with an air carrier gas volume of 5 L and roast for 6 s, and the negative pressure of the flash furnace is 60 KPa;

[0066] Take 50 g of the mixture after flash roasting, mix it with 250 ml of water, stir and leach for 30 min under the conditions of 80°C and 250 r / min to obtain a lithium-rich solution and a first filter residue, and the main component of the first filter residue is carbon powder;

[0067] The steps of impurity removal and lithium precipitation for the lithium-rich solution are the same as those in Example 1.

[0068] Example 9

[0069] This example provides a method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum, and the specific steps and parameters are as follows:

[0070] Take 100 g of waste cathode carbon blocks of electrolytic aluminum and 60 g of ammonium sulfate, mix and grind them to a particle size less than 200 mesh. Take 100 g of the ground mixture, spray it into a flash furnace at 380°C with an air carrier gas volume of 5 L and roast for 3 s, and the negative pressure of the flash furnace is 10 KPa;

[0071] Take 50 g of the mixture after flash roasting, mix it with 250 ml of water, stir and leach for 30 min under the conditions of 80°C and 250 r / min to obtain a lithium-rich solution and a first filter residue, and the main component of the first filter residue is carbon powder;

[0072] The steps of impurity removal and lithium precipitation for the lithium-rich solution are the same as those in Example 1.

[0073] Comparative Example

[0074] This comparative example provides a method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum, and the specific steps and parameters are as follows:

[0075] Take 100 g of waste cathode carbon blocks from electrolytic aluminum and 60 g of potassium sulfate, mix them evenly, and grind them to a particle size of less than 200 mesh. Take 100 g of the ground mixture and spray it into a flash furnace at 350 °C with an air carrier gas volume of 5 L and roast for 6 s. The negative pressure of the flash furnace is 60 KPa;

[0076] Take 50 g of the mixture after flash roasting, mix it with 250 ml of water, and stir and leach it at 80 °C and 250 r / min for 30 min to obtain a lithium-rich solution and a first filter residue. The main component of the first filter residue is carbon powder;

[0077] Detect the recovery rate of lithium in the lithium-rich solution. The detection result shows that the recovery rate of lithium is 5.75%, and the recovery rate of lithium is too low to be meaningful for lithium carbonate preparation.

[0078] Experimental example

[0079] Detect the purity of lithium carbonate and the recovery rate of lithium in the lithium carbonate prepared in Examples 1-9. The purity of lithium carbonate and the recovery rate of lithium in the solution are detected by ICP-OES. The detection results are shown in Table 1.

[0080] Table 1. Detection results of the purity of lithium carbonate and the recovery rate of lithium in the lithium carbonate prepared in Examples 1-9

[0081] Purity of lithium carbonate Recovery rate of lithium Example 1 98.21％ 85.36％ Example 2 98.78％ 87.12％ Example 3 98.26％ 88.45％ Example 4 97.35 64.76％ Example 5 98.73％ 83.46％ Example 6 84.52％ 36.52％ Example 7 89.25％ 54.24％ Example 8 80.11％ 23.47％ Example 9 85.36％ 48.35％

[0082] According to the purity of lithium carbonate, the recovery rate of lithium in the lithium carbonate prepared in Examples 1-9, and the recovery rate of lithium in the comparative example, it can be seen that compared with the detection results of the comparative example and Example 1, the recovery rate of lithium in the comparative example decreased by 79.61%, which proves that the reaction of ammonium sulfate with cathode carbon blocks in the present invention has a significant improvement in the recovery rate of lithium. And due to the too low recovery rate of lithium in the comparative example, it does not meet the requirements for preparing lithium carbonate. Comparing the detection results of Examples 1-5 with those of Examples 6 and 7, the recovery rate of lithium in Examples 1-5 is higher. It can be seen that the flash roasting temperature performs better in the range of 380-613 °C. A higher temperature will cause over-roasting of ammonium sulfate, and there is no excessive ammonium sulfate to generate ammonium bisulfate in the leaching reaction. A lower temperature will cause insufficient reaction between ammonium sulfate and cathode carbon blocks. Therefore, both higher or lower temperatures will cause a decrease in the lithium recovery rate, and thus a decrease in the purity of lithium carbonate. Comparing the detection results of Examples 1-5 with those of Example 8, the recovery rate of lithium prepared in Example 8 is lower. The reason for this result is that while the constant ammonium sulfate reacts with the waste cathode carbon blocks of electrolytic aluminum, the ammonium sulfate decomposes and there is no ammonium sulfate remaining, so ammonium bisulfate cannot be decomposed and generated in the leaching reaction. Therefore, during the water leaching process, ammonium bisulfate does not react with H ionized by water +Sulfuric acid is generated by the reaction, and thus there is no reaction between sulfuric acid and fluoride, resulting in a low lithium recovery rate. In addition, fluoride reacts with ammonium sulfate, and the amount of the reactant ammonium sulfate is insufficient, leading to a relatively low lithium recovery rate. Comparing the test results of Examples 1-5 with those of Example 9, it can be seen that the lithium recovery rate in the preparation method of Example 9 is poor. It can be known that a relatively good performance is shown when the negative pressure in the flash furnace during flash roasting is 20-80 KPa. A negative pressure lower than 20 KPa will result in a shorter suspension time of ammonium sulfate and cathode carbon blocks in the furnace, and the reaction between ammonium sulfate and cathode carbon blocks is insufficient, leading to a decrease in the lithium recovery rate.

[0083] Obviously, the above examples are only for illustration and are not intended to limit the implementation methods. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. And the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum, characterized in that, It includes the following steps: Mix and crush the waste cathode carbon blocks of electrolytic aluminum with ammonium sulfate, conduct flash roasting, and leach to obtain a lithium-rich solution and leaching residues. During the flash roasting, the roasting temperature is 380 - 613 °C, the roasting time is 3 - 9 s. The flash roasting uses air as the carrier gas, and the carrier gas is introduced into the flash roasting furnace by spraying. The gas volume of the carrier gas is 50 - 200 L / kg based on the weight of the mixture of waste cathode carbon blocks of electrolytic aluminum and ammonium sulfate, and the negative pressure is 20 - 80 KPa. The mass ratio of ammonium sulfate to the waste cathode carbon blocks of electrolytic aluminum is 0.5 - 0.6; Purify the lithium-rich solution and obtain lithium carbonate after lithium precipitation.

2. The method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum according to claim 1, characterized in that, The steps of the purification include injecting fluoride into the lithium-rich solution to obtain a first filtrate, and injecting aluminum salt into the first filtrate to obtain a second filtrate.

3. The method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum according to claim 2, characterized in that, Adjust the pH of the lithium-rich solution to 3.5 - 4.5, then inject fluoride and stir for reaction for 1 - 3 h to obtain a first filtrate. Among them, the total molar ratio of calcium ions and magnesium ions in the first filtrate to the fluoride ions in the fluoride is 1:(2.2 - 2.4), and the reaction temperature is 20 - 40 °C.

4. The method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum according to claim 3, characterized in that, According to the molar ratio of aluminum ions to fluoride ions of 1:(3 - 6), after injecting aluminum salt into the first filtrate, adjust the pH of the first filtrate to 4.5 - 6, and stir for reaction for 0.5 - 3 h to obtain a second filtrate. Among them, the reaction temperature is 40 - 60 °C.

5. The method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum according to claim 4, characterized in that, The aluminum ions and the aluminum salt are at least one of aluminum sulfate, aluminum nitrate, and aluminum chloride; and / or, the fluoride is at least one of sodium fluoride, potassium fluoride, and lithium fluoride.

6. The method for preparing lithium carbonate from waste cathode carbon blocks of electrolytic aluminum according to claim 5, characterized in that, The steps of lithium precipitation include concentrating the second filtrate, adding sodium carbonate, stirring, and filtering to obtain lithium carbonate. Among them, the molar ratio of lithium ions to sodium carbonate is 2:(1.1 - 1.2), the stirring temperature is 80 - 100 °C, and the stirring time is 0.5 - 2 h.

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