Method for preparing lithium phosphate from aluminum electrolysis overhaul slag and carbon slag

Abstract

This invention relates to the field of lithium phosphate technology and discloses a method for preparing lithium phosphate from aluminum electrolytic overhaul slag and carbon slag, comprising the following steps: S1 Take aluminum electrolytic overhaul slag and carbon slag separately, perform pretreatment, and mix the treated aluminum electrolytic overhaul slag and carbon slag to obtain a mixture; S2 Prepare a slurry of the mixture, and perform alkali leaching and cyanide removal treatment in sequence, followed by solid-liquid separation to obtain a mixed alkali leaching solution and a mixed alkali leaching residue; S3 Take the mixed alkali leaching residue, wash it, and perform acid leaching treatment, followed by solid-liquid separation to obtain a mixed acid leaching solution and a mixed acid leaching residue; S4 Mix the above mixed alkali leaching solution and mixed acid leaching solution, perform neutralization and precipitation, perform solid-liquid separation, take the supernatant, remove impurities, and obtain a purified lithium sulfate solution; S5 Add trisodium phosphate to the purified lithium sulfate solution, heat and react to obtain lithium phosphate. This method can achieve efficient recovery and utilization of lithium from aluminum electrolytic overhaul slag and carbon slag with low lithium content, and is simple and convenient to operate, highly controllable, and has low processing costs.

Description

Technical Field

[0001] This invention relates to the field of lithium phosphate technology, and more specifically, to a method for preparing lithium phosphate from aluminum electrolysis overhaul slag and carbon slag. Background Technology

[0002] Electrolytic aluminum overhaul slag is a type of solid waste generated during the electrolytic aluminum production process. In aluminum electrolysis, bauxite undergoes high-temperature smelting and electrolytic reactions to obtain aluminum metal. During the maintenance, repair, or electrolyte replacement of the electrolytic cells, a large amount of solid waste, known as electrolytic aluminum overhaul slag, is generated. Electrolytic aluminum overhaul slag often contains incompletely electrolyzed aluminum and other chemical components. Therefore, after treatment and extraction, it can be recycled. Furthermore, the aluminum electrolysis byproducts in the slag must undergo appropriate treatment to minimize their environmental impact and harm.

[0003] Based on the above, it can be seen that electrolytic aluminum overhaul slag is an unavoidable byproduct of electrolytic aluminum production. Therefore, it is crucial to find a more efficient way to handle and utilize electrolytic aluminum overhaul slag. Currently, after purification and other treatments, the remaining residues from aluminum electrolytic overhaul slag and carbon slag are mainly disposed of through pyrometallurgical treatment or landfill, resulting in significant losses of elements such as fluorine, aluminum, and lithium. This leads to resource waste and environmental pollution, and has long been a problem hindering industrialized electrolytic aluminum production technology.

[0004] Therefore, in order to recycle and utilize the slag from the overhaul of electrolytic aluminum to a greater extent and to expand the reuse of the slag more efficiently and feasiblely, it is urgent to find a treatment measure that can reduce the waste of waste resources and control the emission of harmful substances that pollute the environment. Summary of the Invention

[0005] The present application aims to solve the technical problems of:

[0006] During aluminum electrolysis, lithium oxide or other added lithium salts in alumina react with AlF3 or Na3AlF6 in the molten electrolyte at high temperatures to generate lithium fluoride. With the periodic addition of lithium-rich alumina or other lithium salts, lithium oxide continuously enters the electrolyte, causing lithium element electrolyte to permeate into the cathode lining, refractory materials, or carbon slag, resulting in problems such as low resource utilization efficiency.

[0007] The technical scheme adopted by the present application is:

[0008] This invention provides a method for preparing lithium phosphate from aluminum electrolysis overhaul slag and carbon slag, comprising the following steps:

[0009] S1 Take electrolytic aluminum overhaul slag and carbon slag separately, perform pretreatment, and mix the treated electrolytic aluminum overhaul slag and carbon slag to obtain a mixture.

[0010] S2 The mixture is slurried and then subjected to alkali leaching and cyanide removal treatment in sequence, followed by solid-liquid separation to obtain alkali leaching solution and alkali leaching residue of the mixture.

[0011] S3 Take the mixed alkaline leaching residue, wash it, perform acid leaching treatment, and separate the solid and liquid to obtain mixed acid leaching solution and mixed acid leaching residue;

[0012] S4 Mix the alkaline leaching solution from step S2 with the acidic leaching solution from step S3, neutralize and precipitate, separate the solid and liquid, take the supernatant, remove impurities, and obtain lithium sulfate purified solution.

[0013] S5. Add trisodium phosphate to the lithium sulfate purification solution and heat to react, thereby obtaining the lithium phosphate.

[0014] Preferably, in step S1, during the pretreatment, both the electrolytic aluminum overhaul slag and the carbon slag are ground to 100-325 mesh.

[0015] Preferably, in step S1, the electrolytic aluminum overhaul slag and carbon slag are mixed at a mass ratio of 10:1-2.

[0016] Preferably, in step S2, during the alkaline leaching treatment, an alkaline solution is added to the mixture, mixed, and the solid-liquid ratio is controlled at 1:4-6, with a pH value of 12-14.

[0017] Preferably, the alkaline leaching treatment is carried out at a temperature of 100-160℃, a pressure of 0.1-0.5MPa, and a time of 3-5h.

[0018] Preferably, in step S3, the washing of the mixed alkaline leaching residue includes the following steps: placing the alkaline leaching residue in water, controlling the solid-liquid ratio to be 1:2-5, washing, and then separating the solid and liquid. The separated filtrate is used for mixing the mixed material in step S2, and the separated filter residue is used as the mixed alkaline leaching residue for acid leaching.

[0019] Preferably, in step S3, acid solution is added to the washed alkaline leaching residue, mixed, and the solid-liquid ratio is controlled at 1:5-10, the pH value is 2-3, and hydrogen peroxide is added for acid leaching treatment.

[0020] Preferably, the acid leaching treatment is carried out at a temperature of 85°C or higher for 3-5 hours.

[0021] Preferably, in step S4, the pH value of the mixed slurry is controlled to be 4.5-5.0, and the molar mass ratio of fluorine to aluminum in the slurry is 1.6-1.65:1.

[0022] Preferably, the lithium concentration in the lithium sulfate purification solution is 1-4 g / L.

[0023] The beneficial effects of the present application are reflected in:

[0024] The present invention provides a method for preparing lithium phosphate from aluminum electrolysis overhaul slag and carbon slag. This method enables the harmless treatment of low-lithium-content aluminum electrolysis overhaul slag and carbon slag, and allows for the efficient recovery and utilization of lithium. It also reduces the processing costs of aluminum electrolysis overhaul slag and carbon slag. The method is simple and convenient to operate, has high controllability, low processing costs, and significant economic benefits. It can be widely applied to industrialized aluminum electrolysis recycling and reuse production. Attached Figure Description

[0025] Figure 1 This is a process flow diagram for preparing lithium phosphate from aluminum electrolysis overhaul slag and carbon slag in Example 1. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0027] During aluminum electrolysis, lithium oxide or other added lithium salts in alumina react with AlF3 or Na3AlF6 in the molten electrolyte at high temperatures to generate lithium fluoride. With the periodic addition of lithium-rich alumina or other lithium salts, lithium oxide continuously enters the electrolyte, causing lithium-ion electrolyte to permeate into the cathode lining, refractory materials, or carbon slag, resulting in low resource utilization. Based on this, the present invention provides a method for preparing lithium phosphate from aluminum electrolysis overhaul slag and carbon slag, comprising the following steps:

[0028] (1) The slag from the overhaul of electrolytic aluminum is manually sorted to initially separate steel bars and aluminum blocks, and then subjected to multi-stage crushing, grinding, and magnetic separation to remove iron; the carbon slag is taken and ground.

[0029] The grinding particle size of both the electrolytic aluminum overhaul slag and carbon powder is 100-325 mesh, which is beneficial for improving the leaching rate of valuable elements such as fluorine and lithium in the mixture, effectively controlling production costs, and achieving a greater degree of lithium leaching and recycling. Specifically, if the overhaul slag particle size is too large, it will reduce the leaching rate of valuable elements such as fluorine and lithium in the overhaul slag; if the overhaul slag particle size is too small, it will cause the ball mill equipment to be overloaded, increasing production losses and costs.

[0030] The treated electrolytic aluminum overhaul slag and carbon slag were mixed at a mass ratio of 10:1-2 and stirred evenly to obtain a mixture. Mixing within this ratio range effectively adjusts the fluorine to aluminum ratio in the mixture, which is beneficial for the synthesis of the aluminum fluoride precursor Al₂F₃ in the leaching solution. 3.24 (OH) 2.76 ·H2O.

[0031] After iron removal and mixing, the amount of iron entering the system can be reduced, and the ratio of fluorine to aluminum in the mixture of overhaul slag and carbon slag can be adjusted, which is beneficial to the subsequent leaching effect of the mixture, thereby increasing the leaching rate of lithium in the mixture.

[0032] (2) The mixture is slurryed and then subjected to alkali leaching and cyanide removal treatment in sequence. After solid-liquid separation, the mixture alkali leaching solution and mixture alkali leaching residue are obtained.

[0033] The alkaline leaching conditions are as follows: solid-liquid ratio of 1:4-6, pH value of 12-14, temperature of 100-160℃, pressure of 0.1-0.5MPa, and leaching time of 3-5h.

[0034] Specifically, if the solid-liquid ratio of the mixture during alkali leaching is too high, it will affect the leaching rate of valuable elements such as fluorine and lithium in the mixture, and increase the viscosity of the slurry, causing blockages in pumping pipelines, etc. If the solid-liquid ratio of the mixture during alkali leaching is too low, it will result in a large consumption of alkali solution, increase production costs, and consequently aggravate the environmental impact.

[0035] Alkaline leaching treatment can use alkaline solutions such as sodium hydroxide solution, and the pH value should be controlled at 12-14. This is because if the concentration of the alkaline solution is too low, it will affect the leaching rate of valuable elements such as fluorine and lithium in the mixture. If the concentration of the alkaline solution is too high, it will increase the requirements for equipment corrosion prevention and increase production costs.

[0036] Cyanide removal can be achieved by adding cyanide-removing agents, such as hydrogen peroxide, which, after a reaction, can reduce the cyanide content.

[0037] (3) Wash the alkaline leaching residue of the mixture, recover the soluble sodium hydroxide, sodium fluoride and other substances remaining in the alkaline leaching residue of the mixture, separate the solid and liquid, and the filtrate after washing can be used for the mixing of the previous step, while the filter residue is subjected to the next step of acid leaching treatment.

[0038] The solid-liquid ratio during washing is 1:2-5, and experiments have shown that washing with a solid-liquid ratio of 1:2, followed by washing with 300ml of water... 2 Backwashing of plate and frame filter presses can achieve a recovery rate of 80-90% for sodium hydroxide and sodium fluoride.

[0039] The washed alkaline leaching residue is then subjected to acid leaching treatment to dissolve elements such as fluorine, aluminum, and lithium in the residue. After solid-liquid separation, the acid leaching solution and the acid leaching residue are obtained.

[0040] The main chemical reactions involved in the acid leaching process are as follows:

[0041] 2LiF+H2SO4→Li2SO4+2HF↑ (1);

[0042] Li2O + H2O → 2LiOH (2);

[0043] 2LiOH+H2SO4=Li2SO4+H2O (3);

[0044] Li2C2+2H2O=2LiOH+C2H2(4);

[0045] 2LiOH+H2SO4=Li2SO4+H2O (5);

[0046] The acid leaching conditions are as follows: solid-liquid ratio of 1:5-10, temperature above 85℃, addition of sulfuric acid to a pH of 2-3, and addition of 3-5‰ hydrogen peroxide by volume of the slurry. The acid leaching time is 3-5 hours. Under these conditions, the fluorine leaching rate can reach over 90%, the aluminum leaching rate over 80%, and the lithium leaching rate over 95%. The addition of hydrogen peroxide oxidizes the dissolved ferrous ions in the slurry to ferric ions, which then react with sodium sulfate in the slurry to form sodium ferric sulfate [NaFe3(SO4)2(OH)6]. n The reaction principle for reducing the iron content in the mixed acid leaching solution is as follows:

[0047] 3Fe2(SO4)3+12H2O+Na2SO4= Na2Fe6(SO4)4(OH) 12 ↓+6H2SO4(6).

[0048] (4) Mix the above-mentioned alkaline leaching solution and acidic leaching solution for neutralization and precipitation. The neutralization reaction conditions are: reaction temperature 60-80℃, pH value 4.5-5.0, molar mass ratio of fluorine to aluminum in the slurry 1.6-1.65:1, and reaction time 3-5h. After solid-liquid separation, take the supernatant.

[0049] In the above reaction process, if the pH value is too low, the neutralization and precipitation reaction will be insufficient; if the pH value is too high, cryolite phase will be generated, affecting the purity of aluminum fluoride and alumina products.

[0050] After neutralization and precipitation, fluoride ions and aluminum ions can react at a mass ratio of 1.62:1 under the above conditions to form the fluorine-aluminum precursor Al2F. 3.24 (OH) 2.76 H2O can be used to utilize valuable elements such as fluorine and aluminum in aluminum electrolysis overhaul slag and carbon slag. The reaction principle is as follows:

[0051] 0.76Al 3+ +3.24AlF2++2H + +7.52NaOH→2Al2F 3.24 (OH) 2.76 H₂O↓ + 7.52Na + (7).

[0052] The supernatant was subjected to iron removal, silicon removal, calcium removal, and magnesium removal in sequence. The impurity removal conditions were as follows: first, hydrogen peroxide with a volume fraction of 3-5‰ was added to the neutralized liquid, then lime was added to adjust the pH value to 8±0.2, and the reaction was carried out for 1-2 hours. Solid-liquid separation was performed, and sodium hydroxide was added to the clear liquid obtained after separation to adjust the pH value to 10.5-11.5. The reaction was carried out for 1-2 hours, and solid-liquid separation was performed again. The filtrate was taken and the pH value was adjusted to 7-8.

[0053] The neutralized liquid still contains unreacted fluorine, aluminum, and impurities such as iron, silicon, calcium, and magnesium. Therefore, hydrogen peroxide is added to the supernatant to oxidize the ferrous ions to ferric ions. The pH value is then adjusted with lime, and impurities such as fluorine, aluminum, iron, and silicon are removed through solid-liquid separation. Adding sodium hydroxide and reacting with it, followed by solid-liquid separation, removes impurities such as calcium and magnesium from the neutralized liquid. Finally, the pH value is adjusted to obtain a mixed purified liquid containing lithium sulfate and sodium sulfate.

[0054] Then, after concentration by reverse osmosis membrane filtration, the system membrane pressure is 7-8 MPa, and the volume ratio of fresh water to concentrated water is about 4:6, which can increase the lithium concentration in the purified solution by about 1.5-2 times. Then, it is placed at 0-3℃ for freeze crystallization, which can remove a large amount of sodium sulfate Na2SO4·10H2O, and further increase the lithium concentration in the purified solution by about 1.2-1.3 times, to obtain lithium sulfate purified solution, and the lithium ion concentration in the lithium sulfate purified solution is as high as 1g / L or more.

[0055] The alkaline leaching solution is mixed with the acidic leaching solution for neutralization and precipitation, and the fluorine and aluminum elements in the leaching solution are recovered and utilized. After removing impurities from the obtained supernatant, it is concentrated by reverse osmosis membrane filtration and frozen crystallization to remove sodium sulfate, which can effectively increase the lithium ion concentration in the purified solution and reduce the sodium sulfate concentration.

[0056] (5) Add trisodium phosphate to the lithium sulfate purification solution with a lithium concentration of about 1-4 g / L according to the stoichiometric ratio of the reaction. The amount of trisodium phosphate added can be controlled at 1-1.2 times the stoichiometric ratio so that the reaction can be fully carried out in the actual operation. Place it at 80-90℃ for 1-2 hours. After solid-liquid separation and washing, lithium phosphate with a purity of up to 98-99.5% is obtained, with a yield of about 90% or more.

[0057] The reaction principle described above is as follows:

[0058] 3Li2SO4+2Na3PO4=2Li3PO4↓+3Na2SO4 (8).

[0059] In the above reaction process, trisodium phosphate can be added directly as solid Na3PO4·12H2O, or it can be added in solution after the solid Na3PO4·12H2O has been dissolved into a solution. Furthermore, Na3PO4·12H2O can be prepared from the phosphate recovered during the process of preparing lithium carbonate from lithium phosphate, so as to realize the recycling of trisodium phosphate and improve the comprehensive utilization level of resources.

[0060] This invention, through the above-described processing steps, enables the harmless treatment of electrolytic aluminum overhaul slag and carbon slag with low lithium content, and the efficient recovery and utilization of lithium. The operation is simple and convenient, the process is highly controllable, the processing cost is low, and the economic benefits are significant. It can be widely promoted in industrialized electrolytic aluminum recycling and reuse production.

[0061] Example 1

[0062] Step 1: Take electrolytic aluminum overhaul slag and carbon slag separately. Measurements show that the lithium content in the electrolytic aluminum overhaul slag is 0.31%, and the lithium content in the carbon slag is 0.29%. After crushing, impurity removal, and grinding, ball mill the electrolytic aluminum overhaul slag and carbon slag to a particle size of 200±50 mesh. Mix the above electrolytic aluminum overhaul slag and carbon slag evenly at a mass ratio of 10:1 to obtain a mixture.

[0063] Step 2: The mixture is slurried using a sodium hydroxide solution with a pH of 12, and the solid-liquid ratio of the mixture is controlled to be 1:6. Then, it is pressurized to 0.3 MPa, heated to 120°C, and alkali-leached for 3 hours. After alkali leaching, the temperature and pressure are reduced, hydrogen peroxide is added, and the mixture is mixed to remove cyanide. The mixture is then filtered and separated using a plate and frame filter press to obtain the alkali leaching solution and the alkali leaching residue of the mixture.

[0064] Step 3: Wash the mixed alkaline leaching residue on a plate and frame filter press. The mass ratio of washing liquid to mixed alkaline leaching residue is 2:1. Add 98% sulfuric acid solution to the washed mixed alkaline leaching residue, control the solid-liquid ratio at 1:5, the pH value at 2.0, and the temperature at 85℃. Acid leaching is carried out for 2 hours. Then, add 3‰ of the total volume of slurry of hydrogen peroxide and continue acid leaching for 1 hour. After acid leaching, separate the mixed acid leaching liquid and mixed acid leaching residue using a plate and frame filter press. The mixed acid leaching residue is then treated to obtain harmless carbon material.

[0065] Step 4: Take the mixed acid leaching solution and add it to the mixed alkaline leaching solution obtained in Step 2 until the pH value is 4.5. React at 60℃ for 3 hours. Filter using a plate and frame filter press to obtain the fluoroaluminum precursor and the neutralized solution. Take the neutralized solution, add 3‰ hydrogen peroxide, and then add lime to adjust the pH value to 8. React for 1 hour, then separate the solid and liquid, take the filtrate, add sodium hydroxide solution to adjust the pH value to 10.5, react for 2 hours, then separate the solid and liquid again, and add 98% sulfuric acid solution to the filtrate until the pH value is 8 to obtain the lithium sulfate purified solution.

[0066] Step 5: The lithium sulfate purified solution is filtered and concentrated through a reverse osmosis membrane filtration system at a membrane pressure of 7.5 MPa, resulting in a water-to-concentrate ratio of approximately 2:3. The concentrated solution is then frozen at 0°C to crystallize and remove sodium sulfate, yielding a pre-concentrated purified solution with a lithium concentration of 3.6 g / L. 1.2 times the stoichiometric amount of trisodium phosphate is added to the pre-concentrated purified solution, and the mixture is heated to 90°C and reacted for 1 hour. The solution is then filtered and separated using a plate and frame filter press. The washing solution is then washed on the plate and frame filter press at a mass ratio of 4:1 to lithium phosphate to obtain the lithium phosphate product.

[0067] The purity of the lithium phosphate product was determined to be 98.7%, and the yield of lithium phosphate (actual amount of lithium phosphate produced / theoretical amount of lithium phosphate produced × 100%) was 92.4%.

[0068] Example 2

[0069] Step 1: Take electrolytic aluminum overhaul slag and carbon slag separately. Measurements show that the lithium content in the electrolytic aluminum overhaul slag is 0.35%, and the lithium content in the carbon slag is 0.33%. After crushing, impurity removal, and grinding, ball mill the electrolytic aluminum overhaul slag and carbon slag to a particle size of 200±30 mesh. Mix the above electrolytic aluminum overhaul slag and carbon slag evenly at a mass ratio of 10:1 to obtain a mixture.

[0070] Step 2: The mixture is slurried using a sodium hydroxide solution with a pH of 12.2, and the solid-liquid ratio of the mixture is controlled at 1:5. Then, it is pressurized to 0.5 MPa, heated to 155℃, and alkali-leached for 2.2 hours. After alkali leaching, the temperature and pressure are reduced, hydrogen peroxide is added, and the mixture is mixed to remove cyanide. The mixture is then filtered and separated using a plate and frame filter press to obtain the mixed alkali leaching solution and the mixed alkali leaching residue.

[0071] Step 3: Wash the mixed alkaline leaching residue on a plate and frame filter press. The mass ratio of washing liquid to mixed alkaline leaching residue is 2:1. Add 98% sulfuric acid solution to the washed mixed alkaline leaching residue, control the solid-liquid ratio at 1:5, the pH value at 2.0, and the temperature at 85℃. Acid leaching is carried out for 2 hours. Then, add 3‰ of the total volume of slurry of hydrogen peroxide and continue acid leaching for 1 hour. After acid leaching, separate the mixed acid leaching liquid and mixed acid leaching residue using a plate and frame filter press. The mixed acid leaching residue is then treated to obtain harmless carbon material.

[0072] Step 4: Take the mixed acid leaching solution and add it to the mixed alkaline leaching solution obtained in Step 2 until the pH value is 4.5. React at 60℃ for 3 hours. Filter using a plate and frame filter press to obtain the fluoroaluminum precursor and the neutralized solution. Take the neutralized solution, add 3‰ hydrogen peroxide, and then add lime to adjust the pH value to 8. React for 1 hour, then separate the solid and liquid, take the filtrate, add sodium hydroxide solution to adjust the pH value to 10.5, react for 2 hours, then separate the solid and liquid again, and add 98% sulfuric acid solution to the filtrate until the pH value is 8 to obtain the lithium sulfate purified solution.

[0073] Step 5: The lithium sulfate purified solution is filtered and concentrated through a reverse osmosis membrane filtration system at a membrane pressure of 7.5 MPa, resulting in a water-to-concentrate ratio of approximately 2:3. The concentrated solution is then frozen at 0°C to crystallize and remove sodium sulfate, yielding a pre-concentrated purified solution with a lithium concentration of 3.7 g / L. 1.2 times the stoichiometric amount of trisodium phosphate is added to the pre-concentrated purified solution, and the mixture is heated to 90°C and reacted for 1 hour. The solution is then filtered and separated using a plate and frame filter press. The washing solution is then washed on the plate and frame filter press at a mass ratio of 4:1 to obtain the lithium phosphate product.

[0074] The purity of the lithium phosphate product was determined to be 98.8%, and the yield of lithium phosphate (actual amount of lithium phosphate produced / theoretical amount of lithium phosphate produced × 100%) was 91.7%.

[0075] Example 3

[0076] Step 1: Take electrolytic aluminum overhaul slag and carbon slag separately. Measurements show that the lithium content in the electrolytic aluminum overhaul slag is 0.32%, and the lithium content in the carbon slag is 0.37%. After crushing, impurity removal, and grinding, ball mill the electrolytic aluminum overhaul slag and carbon slag to a particle size of 200±50 mesh. Mix the above electrolytic aluminum overhaul slag and carbon slag evenly at a mass ratio of 10:1 to obtain a mixture.

[0077] Step 2: The mixture is slurried using a sodium hydroxide solution with a pH of 12, and the solid-liquid ratio of the mixture is controlled to be 1:6. Then, it is pressurized to 0.3 MPa, heated to 120°C, and alkali-leached for 3 hours. After alkali leaching, the temperature and pressure are reduced, hydrogen peroxide is added, and the mixture is mixed to remove cyanide. The mixture is then filtered and separated using a plate and frame filter press to obtain the alkali leaching solution and the alkali leaching residue of the mixture.

[0078] Step 3: Wash the mixed alkaline leaching residue on a plate and frame filter press. The mass ratio of washing liquid to mixed alkaline leaching residue is 3.4:1. Add 98% sulfuric acid solution to the washed mixed alkaline leaching residue, control the solid-liquid ratio at 1:8, pH value at 2.1, temperature at 90℃, and acid leaching for 2.8h. Then add 5‰ hydrogen peroxide of the total slurry volume and continue acid leaching for 1.2h. After acid leaching, separate the mixed acid leaching liquid and mixed acid leaching residue using a plate and frame filter press. The mixed acid leaching residue is then treated to obtain harmless carbon material.

[0079] Step 4: Take the mixed acid leaching solution and add it to the mixed alkaline leaching solution obtained in Step 2 until the pH value is 4.5. React at 60℃ for 3 hours. Filter using a plate and frame filter press to obtain the fluoroaluminum precursor and the neutralized solution. Take the neutralized solution, add 3‰ hydrogen peroxide, and then add lime to adjust the pH value to 8. React for 1 hour, then separate the solid and liquid, take the filtrate, add sodium hydroxide solution to adjust the pH value to 10.5, react for 2 hours, then separate the solid and liquid again, and add 98% sulfuric acid solution to the filtrate until the pH value is 8 to obtain the lithium sulfate purified solution.

[0080] Step 5: The lithium sulfate purified solution is filtered and concentrated through a reverse osmosis membrane filtration system at a membrane pressure of 7.5 MPa, resulting in a water-to-concentrate ratio of approximately 2:3. The concentrated solution is then frozen at 0°C to crystallize and remove sodium sulfate, yielding a pre-concentrated purified solution with a lithium concentration of 3.7 g / L. 1.2 times the stoichiometric amount of trisodium phosphate is added to the pre-concentrated purified solution, and the mixture is heated to 90°C and reacted for 1 hour. The solution is then filtered and separated using a plate and frame filter press. The washing solution is then washed on the plate and frame filter press at a mass ratio of 4:1 to obtain the lithium phosphate product.

[0081] The purity of the lithium phosphate product was determined to be 99.0%, and the yield of lithium phosphate (actual amount of lithium phosphate produced / theoretical amount of lithium phosphate produced × 100%) was 92.7%.

[0082] Example 4

[0083] Step 1: Take electrolytic aluminum overhaul slag and carbon slag separately. Measurements show that the lithium content in the electrolytic aluminum overhaul slag is 0.45%, and the lithium content in the carbon slag is 0.34%. After crushing, impurity removal, and grinding, ball mill the electrolytic aluminum overhaul slag and carbon slag to a particle size of 180±50 mesh. Mix the above electrolytic aluminum overhaul slag and carbon slag evenly at a mass ratio of 10:1 to obtain a mixture.

[0084] Step 2: The mixture is slurried using a sodium hydroxide solution with a pH of 12, and the solid-liquid ratio of the mixture is controlled to be 1:6. Then, it is pressurized to 0.3 MPa, heated to 120°C, and alkali-leached for 3 hours. After alkali leaching, the temperature and pressure are reduced, hydrogen peroxide is added, and the mixture is mixed to remove cyanide. The mixture is then filtered and separated using a plate and frame filter press to obtain the alkali leaching solution and the alkali leaching residue of the mixture.

[0085] Step 3: Wash the mixed alkaline leaching residue on a plate and frame filter press. The mass ratio of washing liquid to mixed alkaline leaching residue is 2:1. Add 98% sulfuric acid solution to the washed mixed alkaline leaching residue, control the solid-liquid ratio at 1:5, the pH value at 2.0, and the temperature at 85℃. Acid leaching is carried out for 2 hours. Then, add 3‰ of the total volume of slurry of hydrogen peroxide and continue acid leaching for 1 hour. After acid leaching, separate the mixed acid leaching liquid and mixed acid leaching residue using a plate and frame filter press. The mixed acid leaching residue is then treated to obtain harmless carbon material.

[0086] Step 4: Take the mixed acid leaching solution and add it to the mixed alkaline leaching solution obtained in Step 2 until the pH value is 4.8. React at 70℃ for 2.8 hours. Filter using a plate and frame filter press to obtain the fluoroaluminum precursor and the neutralized solution. Take the neutralized solution, add 5‰ hydrogen peroxide, and then add lime to adjust the pH value to 8. React for 1.5 hours. After solid-liquid separation, take the filtrate, add sodium hydroxide solution to adjust the pH value to 11.2, react for 1.5 hours, and then perform solid-liquid separation again. Add 98% sulfuric acid solution to the filtrate until the pH value is 7.9 to obtain the lithium sulfate purified solution.

[0087] Step 5: The lithium sulfate purified solution is filtered and concentrated through a reverse osmosis membrane filtration system at a membrane pressure of 7.5 MPa, resulting in a water-to-concentrate ratio of approximately 2:3. The concentrated solution is then frozen at 0°C to crystallize and remove sodium sulfate, yielding a pre-concentrated purified solution with a lithium concentration of 3.9 g / L. 1.2 times the stoichiometric amount of trisodium phosphate is added to the pre-concentrated purified solution, and the mixture is heated to 90°C and reacted for 1 hour. The solution is then filtered and separated using a plate and frame filter press. The washing solution is then washed on the plate and frame filter press at a mass ratio of 4:1 to obtain the lithium phosphate product.

[0088] The purity of the lithium phosphate product was determined to be 98.8%, and the yield of lithium phosphate (actual amount of lithium phosphate produced / theoretical amount of lithium phosphate produced × 100%) was 94.1%.

[0089] Example 5

[0090] Step 1: Take electrolytic aluminum overhaul slag and carbon slag separately. Measurements show that the lithium content in the electrolytic aluminum overhaul slag is 0.39%, and the lithium content in the carbon slag is 0.41%. After crushing, impurity removal, and grinding, ball mill the electrolytic aluminum overhaul slag and carbon slag to a particle size of 200±50 mesh. Mix the above electrolytic aluminum overhaul slag and carbon slag evenly at a mass ratio of 10:1 to obtain a mixture.

[0091] Step 2: The mixture is slurried using a sodium hydroxide solution with a pH of 12, and the solid-liquid ratio of the mixture is controlled to be 1:6. Then, it is pressurized to 0.3 MPa, heated to 120°C, and alkali-leached for 3 hours. After alkali leaching, the temperature and pressure are reduced, hydrogen peroxide is added, and the mixture is mixed to remove cyanide. The mixture is then filtered and separated using a plate and frame filter press to obtain the alkali leaching solution and the alkali leaching residue of the mixture.

[0092] Step 3: Wash the mixed alkaline leaching residue on a plate and frame filter press. The mass ratio of washing liquid to mixed alkaline leaching residue is 2:1. Add 98% sulfuric acid solution to the washed mixed alkaline leaching residue, control the solid-liquid ratio at 1:5, the pH value at 2.0, and the temperature at 85℃. Acid leaching is carried out for 2 hours. Then, add 3‰ of the total volume of slurry of hydrogen peroxide and continue acid leaching for 1 hour. After acid leaching, separate the mixed acid leaching liquid and mixed acid leaching residue using a plate and frame filter press. The mixed acid leaching residue is then treated to obtain harmless carbon material.

[0093] Step 4: Take the mixed acid leaching solution and add it to the mixed alkaline leaching solution obtained in Step 2 until the pH value is 4.5. React at 60℃ for 3 hours. Filter using a plate and frame filter press to obtain the fluoroaluminum precursor and the neutralized solution. Take the neutralized solution, add 3‰ hydrogen peroxide, and then add lime to adjust the pH value to 8. React for 1 hour, then separate the solid and liquid, take the filtrate, add sodium hydroxide solution to adjust the pH value to 10.5, react for 2 hours, then separate the solid and liquid again, and add 98% sulfuric acid solution to the filtrate until the pH value is 8 to obtain the lithium sulfate purified solution.

[0094] Step 5: The lithium sulfate purified solution is filtered and concentrated through a reverse osmosis membrane filtration system at a membrane pressure of 8MPa, resulting in a water-to-concentrate ratio of approximately 2:3. The concentrated solution is then frozen at 2℃ to crystallize and remove sodium sulfate, yielding a pre-concentrated purified solution with a lithium concentration of 4.1 g / L. 1.2 times the stoichiometric amount of trisodium phosphate is added to the pre-concentrated purified solution, and the mixture is heated to 85℃ and reacted for 1.65 h. The solution is then filtered and separated using a plate and frame filter press. The washing solution is then washed on the plate and frame filter press at a mass ratio of 5:1 to lithium phosphate to obtain the lithium phosphate product.

[0095] The purity of the lithium phosphate product was determined to be 99.2%, and the yield of lithium phosphate (actual amount of lithium phosphate produced / theoretical amount of lithium phosphate produced × 100%) was 94.5%.

[0096] Example 6

[0097] Step 1: Take electrolytic aluminum overhaul slag and carbon slag separately. Measurements show that the lithium content in the electrolytic aluminum overhaul slag is 0.31%, and the lithium content in the carbon slag is 0.29%. After crushing, impurity removal, and grinding, ball mill the electrolytic aluminum overhaul slag and carbon slag to a particle size of 200±50 mesh. Mix the above electrolytic aluminum overhaul slag and carbon slag evenly at a mass ratio of 10:1 to obtain a mixture.

[0098] Step 2: Use 30g / L sodium hydroxide solution to prepare the mixture into a slurry, controlling the solid-liquid ratio of the mixture to be 1:4. Then pressurize to 0.5MPa, heat to 160℃, and alkali leaching for 2 hours. After alkali leaching, cool and depressurize, add hydrogen peroxide, mix well to remove cyanide, and filter and separate using a plate and frame filter press to obtain the mixed alkali leaching solution and the mixed alkali leaching residue.

[0099] Step 3: Wash the mixed alkaline leaching residue on a plate and frame filter press. The mass ratio of washing liquid to mixed alkaline leaching residue is 5:1. Add 98% sulfuric acid solution to the washed mixed alkaline leaching residue, control the solid-liquid ratio at 1:10, the pH value at 2.5, and the temperature at 90℃. Acid leaching is carried out for 3 hours. Then, add 5‰ hydrogen peroxide of the total volume of slurry and continue acid leaching for 1 hour. After acid leaching, separate the mixed acid leaching liquid and mixed acid leaching residue using a plate and frame filter press. The mixed acid leaching residue is then treated to obtain harmless carbon material.

[0100] Step 4: Take the mixed acid leaching solution and add it to the mixed alkaline leaching solution obtained in Step 2 until the pH value is 5. React at 70℃ for 3 hours. Filter using a plate and frame filter press to obtain the fluoroaluminum precursor and the neutralized solution. Take the neutralized solution, add 5‰ hydrogen peroxide, and then add lime to adjust the pH value to 8. React for 2 hours, then perform solid-liquid separation. Take the filtrate, add sodium hydroxide solution to adjust the pH value to 11.5, react for 1 hour, then perform solid-liquid separation again. Add 98% sulfuric acid solution to the filtrate until the pH value is 7 to obtain the lithium sulfate purified solution.

[0101] Step 5: The lithium sulfate purified solution is filtered and concentrated through a reverse osmosis membrane filtration system at a membrane pressure of 7.5 MPa, resulting in a water-to-concentrate ratio of approximately 2:3. The concentrated solution is then frozen at 3°C ​​to crystallize and remove sodium sulfate, yielding a pre-concentrated purified solution with a lithium concentration of 3.2 g / L. 1.2 times the stoichiometric amount of trisodium phosphate is added to the pre-concentrated purified solution, and the mixture is heated to 80°C and reacted for 2 hours. The solution is then filtered and separated using a plate and frame filter press. The washing solution is then washed on the plate and frame filter press at a mass ratio of 5:1 to lithium phosphate to obtain the lithium phosphate product.

[0102] The purity of the lithium phosphate product was determined to be 99.2%, and the yield of lithium phosphate (actual amount of lithium phosphate produced / theoretical amount of lithium phosphate produced × 100%) was 91.5%.

[0103] Using the preparation methods in Examples 1 to 6, lithium phosphate products with a purity of over 98% can be obtained, and the yield of lithium phosphate is over 90%. It can be seen that the method for preparing lithium phosphate using aluminum electrolysis overhaul slag and carbon slag provided by the present invention can prepare high-purity lithium phosphate from overhaul slag and carbon slag with low lithium content, realize more complete and efficient resource utilization of lithium element, and alleviate the problem of low resource utilization of by-products generated in aluminum electrolysis.

[0104] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing lithium phosphate from aluminum electrolysis overhaul slag and carbon slag, characterized in that, Includes the following steps: S1 Take electrolytic aluminum overhaul slag and carbon slag separately, perform pretreatment, and mix the treated electrolytic aluminum overhaul slag and carbon slag to obtain a mixture. S2 The mixture is slurried and then subjected to alkali leaching and cyanide removal treatment in sequence, followed by solid-liquid separation to obtain alkali leaching solution and alkali leaching residue of the mixture. S3 Take the mixed alkaline leaching residue, wash it, perform acid leaching treatment, and separate the solid and liquid to obtain mixed acid leaching solution and mixed acid leaching residue; S4 Mix the alkaline leaching solution from step S2 with the acidic leaching solution from step S3, neutralize and precipitate, separate the solid and liquid, take the supernatant, remove impurities, and obtain lithium sulfate purified solution. S5. Add trisodium phosphate to the lithium sulfate purification solution and heat to react, thereby obtaining the lithium phosphate.

2. The method for preparing lithium phosphate from aluminum electrolysis overhaul slag and carbon slag according to claim 1, characterized in that, In step S1, during the pretreatment, both the electrolytic aluminum overhaul slag and the carbon slag are ground to 100-325 mesh.

3. The method for preparing lithium phosphate from aluminum electrolysis overhaul slag and carbon slag according to claim 1, characterized in that, In step S1, the electrolytic aluminum overhaul slag and carbon slag are mixed at a mass ratio of 10:1-2.

4. The method for preparing lithium phosphate from aluminum electrolysis overhaul slag and carbon slag according to claim 1, characterized in that, In step S2, during the alkali leaching treatment, alkali solution is added to the mixture, mixed, and the solid-liquid ratio is controlled at 1:4-6, with a pH value of 12-14.

5. The method for preparing lithium phosphate from aluminum electrolysis overhaul slag and carbon slag according to claim 4, characterized in that, The alkaline leaching treatment is carried out at a temperature of 100-160℃, a pressure of 0.1-0.5MPa, and a time of 3-5h.

6. The method for preparing lithium phosphate from aluminum electrolysis overhaul slag and carbon slag according to claim 1, characterized in that, In step S3, the washing of the mixed alkaline leaching residue includes the following steps: The alkali leaching residue is placed in water, and the solid-liquid ratio is controlled at 1:2-5. After washing, the solid and liquid are separated. The separated filtrate is used for slurry preparation in step S2, and the separated filter residue is used as the alkali leaching residue of the acid leaching mixture.

7. The method for preparing lithium phosphate from aluminum electrolysis overhaul slag and carbon slag according to claim 1, characterized in that, In step S3, acid solution is added to the washed alkaline leaching residue, mixed, and the solid-liquid ratio is controlled at 1:5-10, the pH value is 2-3, and hydrogen peroxide is added for acid leaching treatment.

8. The method for preparing lithium phosphate from aluminum electrolysis overhaul slag and carbon slag according to claim 7, characterized in that, The acid leaching treatment is carried out at a temperature above 85℃ for 3-5 hours.

9. The method for preparing lithium phosphate from aluminum electrolysis overhaul slag and carbon slag according to any one of claims 1 to 8, characterized in that, In step S4, the pH value of the mixed slurry is controlled to be 4.5-5.0, and the molar mass ratio of fluorine to aluminum in the slurry is 1.6-1.65:

1.

10. The method for preparing lithium phosphate from aluminum electrolysis overhaul slag and carbon slag according to claim 9, characterized in that, The lithium concentration in the lithium sulfate purification solution is 1-4 g / L.

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