Method for recycling mixed waste residues in lithium carbonate production process

Abstract

The application discloses a method for recycling mixed waste residues in a lithium carbonate production process and belongs to the technical field of nonferrous metallurgy. The method realizes efficient separation of silicon-aluminum residues and calcium salt residues through high-temperature direct filtration and step-by-step neutralization and precipitation, improves the resource utilization value of the waste residues, reduces the entrainment loss of lithium in the waste residues, has the advantages of simple process, good filtration performance and high resource recovery rate, and can be widely applied to a lithium extraction process of spodumene or lepidolite.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metal metallurgy technology, specifically relating to a method for recovering mixed waste residue from the lithium carbonate production process. Background Technology

[0002] With the rapid development of the new energy vehicle industry, the market demand for lithium carbonate, as a core raw material for lithium-ion batteries, continues to rise. Currently, the mainstream process for extracting lithium carbonate from lithium ores (such as spodumene and lepidolite) is the sulfuric acid process. The sulfuric acid process involves roasting lithium ore with sulfuric acid, and then leaching, purifying, and precipitating the clinker to obtain lithium carbonate products. In this process, the traditional process usually uses a single neutralization and filtration method to treat the acid leaching slurry. That is, lime milk or limestone is added to the acid leaching slurry once to neutralize it to a neutral pH, causing aluminum, iron, and calcium impurity ions in the solution to precipitate together, resulting in a large amount of complex mixed waste residue. This mixed waste residue mainly contains silicon-aluminum components (SiO2, Al2O3) and calcium salt components (CaSO4), as well as a small amount of residual lithium and other metal impurities. This method has the following drawbacks: the mixed waste residue has a complex composition, with silicon and aluminum components mixed with calcium salt components, making it difficult to utilize them separately, resulting in low added value of the waste residue, which can usually only be used as raw material for low-end building materials or stockpiled; the mixed residue contains 0.5% to 1.5% residual lithium, which is difficult to recover mixed in with the waste residue, resulting in a waste of lithium resources; during the one-time neutralization process, a large amount of Al(OH)3 and Fe(OH)3 colloids are easily generated, which encapsulate lithium ions and make filtration difficult, affecting production efficiency.

[0003] To address the aforementioned issues, some researchers have attempted to separate valuable components from waste residue using a stepwise precipitation method. For example, CN117867280A discloses a method for recovering nickel, cobalt, and lithium from iron-aluminum waste, achieving iron-aluminum separation through roasting, selective leaching, and pH adjustment separation steps. CN114702048A discloses a lithium slag solid waste resource recovery process, which precipitates iron, aluminum, and heavy metal components separately by adjusting the pH value stepwise. However, the above methods are mainly aimed at the recovery of waste batteries or specific lithium slags and cannot effectively solve the problem of deep dissociation between mixed waste residues generated during the sulfuric acid process for lithium carbonate production. Aluminum ions easily generate Al(OH)3 colloids during pH adjustment, which not only adsorb and entrain residual lithium and clog filter channels but also interfere with the selective separation of silicon, aluminum, and calcium. Summary of the Invention

[0004] To address the technical problems of mixed waste residue, low resource utilization, and difficulty in lithium recovery in existing lithium carbonate production processes, this invention provides a method for recovering mixed waste residue from lithium carbonate production.

[0005] This invention effectively separates silicon-aluminum slag from calcium salt slag through high-temperature direct filtration and stepwise neutralization and precipitation, solving the problem of mixed waste residue components that are difficult to separate and utilize in traditional processes.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows.

[0007] The first objective of this invention is to provide a method for recycling mixed waste residue from the lithium carbonate production process, comprising the following steps: The unneutralized acidic slurry after the leaching process in the sulfuric acid process for lithium carbonate production is subjected to a first filtration separation at 60℃~90℃ to obtain silicon-aluminum slag containing silicon-aluminum components and the first filtrate.

[0008] The first filtrate is neutralized and precipitated in steps. The method of step-by-step neutralization and precipitation is as follows: adjust the pH of the first filtrate to 3-4, separate the iron and aluminum slag precipitate, mix the separated solution with a Ca-containing precipitant so that the solution forms calcium sulfate precipitate at pH 4-6, and then perform a second solid-liquid separation to obtain gypsum slag containing calcium sulfate and lithium-containing purified solution.

[0009] In a preferred embodiment, the temperature for the first filtration separation is 75°C to 90°C.

[0010] In a preferred embodiment, the pH of the acidic slurry is <3, and further, the pH of the acidic slurry is 1 to 2.

[0011] In a preferred embodiment, the Ca-containing precipitant is lime milk or limestone powder.

[0012] Limestone powder is preferred because its neutralization reaction is mild, which can prevent excessively high local pH values ​​from causing co-precipitation of colloids such as aluminum hydroxide and ensure the purity of the gypsum slag.

[0013] In a preferred embodiment, the limestone powder has a fineness of 180 mesh to 220 mesh.

[0014] In a preferred embodiment, the pH of the first filtrate is adjusted using a neutralizing agent, which is a sodium hydroxide solution.

[0015] As a preferred embodiment, the conditions for the stepwise neutralization and precipitation are: the temperature for neutralization and precipitation is 40℃~60℃, and the precipitation time is 30 minutes~90 minutes.

[0016] In a preferred embodiment, the acidic slurry is prepared by calcining spodumene / lepidolite at 1000℃~1100℃ for 30 minutes, then grinding it to below 200 mesh to obtain spodumene fine powder; mixing sulfuric acid with spodumene fine powder and calcining at 250℃ for 30 minutes to obtain acidified clinker; and leaching the acidified clinker in water at 60℃~80℃ for 0.5 hours~1 hour.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The method for recycling mixed waste residue from lithium carbonate production provided by this invention effectively separates silicon-aluminum slag and calcium salt slag through high-temperature direct filtration and stepwise neutralization precipitation. This solves the problem of mixed waste residue components and difficulty in separate utilization in traditional processes. The separated silicon-aluminum slag (first filter residue) has a SiO2+Al2O3 content of over 80%, and the gypsum slag (second filter residue) has a CaSO4 content of over 85%, laying the foundation for subsequent high-value utilization and achieving efficient component separation. At the same time, the process is greatly simplified, eliminating the need for separate precipitation treatment of aluminum and the step of using expensive alkali sources (such as sodium hydroxide). Lime milk or limestone powder is used directly for calcium precipitation, significantly reducing raw material costs, shortening the process flow, and simplifying operation.

[0018] Furthermore, the lithium recovery rate is improved. The lithium-containing filtrate obtained in the first separation step does not contain silica-alumina slag, avoiding lithium loss caused by the coating of lithium by silica-alumina slag. In the second step of calcium precipitation, due to the absence of aluminum colloid interference, the gypsum slag crystallizes well and is not prone to encapsulating lithium, which can effectively reduce the entrainment loss of lithium in the waste residue. The total lithium recovery rate can reach over 97%. The filtration performance is significantly improved. The high-temperature filtration in the first step avoids the formation of aluminum colloid at low temperatures and the filtration speed is fast. In the second step of calcium precipitation, the pH is controlled in the neutral to slightly acidic range, and the calcium sulfate crystallizes well, making solid-liquid separation easy. Compared with the traditional one-time neutralization process, the total filtration time can be shortened by more than 30%. The resource utilization value of the waste residue is enhanced. The high-purity silica-alumina slag (containing active Al2O3) obtained can be used as a high-quality cement admixture or concrete admixture. The high-purity gypsum slag can be used as a cement retarder to replace natural gypsum or to produce gypsum board building materials, realizing the high-value utilization of waste residue. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the process flow for the method of recovering mixed waste residue in the lithium carbonate production process according to the present invention. Detailed Implementation

[0020] To enable those skilled in the art to better understand and implement the technical solutions of this invention, the invention will be further described below with reference to specific embodiments and accompanying drawings. Unless otherwise specified, all reagents used in this invention are commercially available, and all methods used are conventional techniques in the art.

[0021] The sulfuric acid process involves roasting lithium ore with sulfuric acid, followed by leaching, purification, and precipitation to produce lithium carbonate. This process generates a large amount of acid leaching waste. Traditional methods typically treat the leaching solution with a single neutralization and filtration process. This involves adding lime slurry or limestone to the leaching solution to neutralize it to a neutral pH, causing aluminum, iron, and calcium impurities to precipitate together, forming a complex mixed waste. This mixed waste mainly contains silicon-aluminum components (SiO2, Al2O3) and calcium salt components (CaSO4), as well as small amounts of residual lithium and other metallic impurities. This method has the following drawbacks: the mixed waste has a complex composition, with silicon-aluminum components mixed with calcium salt components, making it difficult to separate and utilize, resulting in low added value. It is typically only used as a low-end building material raw material or for stockpiling. The mixed waste contains 0.5%–1.5% residual lithium, which is difficult to recover, leading to a waste of lithium resources. Furthermore, the single neutralization process easily generates large amounts of Al(OH)3 and Fe(OH)3 colloids, which encapsulate lithium ions and cause filtration difficulties, affecting production efficiency. To address the aforementioned problems, this invention provides a method for recovering mixed waste residue from the lithium carbonate production process.

[0022] The technical solution of the present invention will be analyzed in detail below.

[0023] This invention provides a method for recycling mixed waste residue from the lithium carbonate production process, comprising the following steps: The unneutralized acidic slurry after the leaching process in the sulfuric acid process for lithium carbonate production is subjected to a first filtration separation at 60℃~90℃ to obtain silicon-aluminum slag containing silicon-aluminum components and the first filtrate.

[0024] The first filtrate is neutralized and precipitated in steps. The method of step-by-step neutralization and precipitation is as follows: adjust the pH of the first filtrate to 3-4, separate the iron and aluminum slag precipitate, mix the separated solution with a Ca-containing precipitant so that the solution forms calcium sulfate precipitate at pH 4-6, and then perform a second solid-liquid separation to obtain gypsum slag containing calcium sulfate and lithium-containing purified solution.

[0025] In the above technical solution, this invention effectively separates silica-alumina slag and calcium salt slag through high-temperature direct filtration and stepwise neutralization precipitation, solving the problem of mixed waste residue components and difficulty in separate utilization in traditional processes. The separated silica-alumina slag has a SiO2+Al2O3 content of over 80%, and the gypsum slag has a CaSO4 content of over 85%, laying the foundation for subsequent high-value utilization and achieving efficient separation of components. At the same time, the process is greatly simplified, eliminating the need for separate precipitation treatment of aluminum and the step of using expensive alkali sources (such as sodium hydroxide). Lime milk or limestone powder can be used directly for calcium precipitation, significantly reducing raw material costs, shortening the process flow, and simplifying operation.

[0026] The technical solution of the present invention will be further illustrated below through the following embodiments and comparative examples.

[0027] Example 1 A method for recycling mixed waste residue from lithium carbonate production processes includes the following steps: The unneutralized acidic slurry from the sulfuric acid leaching process of a lithium extraction production line of a certain spodumene (Li2O: 8%, Al2O3: 27%, SiO2: 65%; actual Li2O content: approximately 0.8%–1.3% in raw ore and 5.5%–7.0% in concentrate; typical impurities: Na2O, K2O, FeO, CaO, MgO, MnO, Cr, Rb, Cs) was used as the treatment object. The acidic slurry temperature was approximately 80℃, and its main components included suspended silica-alumina slag, lithium sulfate, aluminum sulfate, calcium sulfate, and small amounts of iron and magnesium ions.

[0028] Acidic slurry preparation method: Spodumene is placed in a rotary kiln and roasted at 1050℃ for 30 minutes. The roasted spodumene powder is then ground to below 200 mesh using a lithium ore grinding mill to obtain spodumene powder. Sulfuric acid (purity 95%) is added at 140% of the theoretical amount and mixed with the spodumene powder for roasting at approximately 250℃ for approximately 30 minutes to obtain acidified clinker. The acidified clinker is then stirred and leached in hot water at 70℃ (solid-liquid ratio 1.5:1) for approximately 1 hour to obtain an acidic slurry with a pH of 1 (the theoretical amount of sulfuric acid is calculated based on the reaction equation: β-Li2O·Al2O3·4SiO2+H2SO4→Li2SO4+H2O·Al2O3·4SiO2).

[0029] S1, High-Temperature Filtration: Acidic slurry at 80℃ is directly fed into a plate and frame filter press for the first solid-liquid separation. During the filtration process, the slurry temperature is maintained at no less than 75℃, resulting in the separation of silicon-aluminum slag containing silicon and aluminum components and the first filtrate. Testing revealed that the first filter residue (dry weight) contained 69.1% SiO2, 25.7% Al2O3, and ≤0.15% residual lithium.

[0030] S2, Neutralization and Calcium Precipitation: The first filtrate is transferred to a neutralization reactor and kept at 50°C. A 10% sodium hydroxide solution is added to adjust the pH to 3.5, and iron-aluminum slag is obtained through precipitation (which can be returned to the leaching process). Then, limestone powder is added to control the pH within the range of 5.0±0.2, and the mixture is stirred for 60 minutes. After the reaction is complete, a second solid-liquid separation is performed to obtain gypsum slag containing calcium sulfate (second filter residue) and a lithium-containing purified solution (second filtrate). Testing shows that the second filter residue contains 98.5% CaSO4·2H2O, and the residual lithium content is less than 0.1%; the second filtrate has a lithium concentration of 4.2 g / L, and the aluminum and calcium ion contents are both less than 0.1 g / L.

[0031] S3, Subsequent processing: After the second filtrate is thoroughly purified, sodium carbonate solution is added to precipitate and lithium carbonate product is obtained with a purity of 99.5%.

[0032] Example 2 A method for recycling mixed waste residue from lithium carbonate production processes includes the following steps: This embodiment focuses on the unneutralized acidic slurry produced after the sulfuric acid leaching process in a lithium extraction production line of a certain lepidolite (theoretical composition: Li2O: 1%~6%, Al2O3: 27%, SiO2: 54%, K2O: 10%; actual Li2O content: 0.3%~0.6% in raw ore, 3.5%~4.5% in concentrate; typical impurities: K, Al, Si, Rb, Cs, F, Fe, Ca, Mg, Mn, etc.). Because the raw material contains fluorine, the fluoride ion concentration in the acid leaching solution is high, which easily generates fluorine-containing waste residue in traditional processes.

[0033] Preparation method of acidic slurry: Lithium mica is calcined in a rotary kiln at 1050℃ for 30 minutes. The calcined lithium mica is then ground to below 200 mesh using a grinding mill to obtain lithium mica powder. Sulfuric acid (95% purity) is added at 140% of the theoretical amount and mixed with the lithium mica powder for calcination at approximately 250℃ for about 30 minutes to obtain acidified clinker. The acidified clinker is then leached in hot water at 70℃ (solid-liquid ratio 1.5:1) with stirring for about 1 hour to obtain the acidic slurry. According to the reaction equation: K(Li,Al)3(Si,Al)4O 10 (F,OH)2+H2SO4→Li2SO4+(K,Al)2(SO4)3+ other salts, calculate the theoretical amount of sulfuric acid needed.

[0034] S1, High-temperature filtration: The acidic slurry at 85℃ is centrifuged and filtered to obtain silicon-aluminum slag containing silicon and aluminum components and the first filtrate. Some residual lithium can be recovered from the silicon-aluminum slag after washing with water.

[0035] S2, Neutralization and Calcium Precipitation: The first filtrate is transferred to a neutralization vessel and kept at 55°C. A 10% sodium hydroxide solution is added to adjust the pH to 3.5, and iron-aluminum slag is obtained through precipitation (which can be returned to the leaching process). Then, lime slurry is added to adjust the pH to 5.5, and precipitation is allowed for 60 minutes. Filtration yields gypsum slag containing calcium sulfate (second filter residue) and a lithium-containing purified solution (second filtrate). Testing shows that the dry CaSO4 content in the second filter residue is 92.7%, and the fluorine content is less than 0.1%, meeting the requirements for cement retarder use.

[0036] S3, Subsequent processing: After the second filtrate is thoroughly purified, sodium carbonate solution is added to precipitate and lithium carbonate product is obtained.

[0037] To further illustrate the technical effects of the present invention, a comparative example is also provided, as follows.

[0038] Comparative Example 1 The acidic slurry, treated using the same traditional one-step neutralization process as in Example 1, was neutralized to pH 7.0 by directly adding lime slurry and filtering to obtain a mixed waste residue. Testing revealed that the mixed waste residue contained 45.6% SiO2+Al2O3, 32.8% CaSO4, and 0.8% residual lithium. The mixed residue had a complex composition, making it difficult to utilize at high value, and the filtration time was approximately 40% longer than in Example 1.

[0039] Performance comparison: The main technical indicators of Examples 1-2 and Comparative Example 1 were compared, and the results are shown in Table 1.

[0040] Table 1 Comparison of Technical Effects As shown in Table 1, the method for recycling mixed waste residue provided by the present invention significantly improves the separation purity and lithium recovery rate of the waste residue compared with the method of Comparative Example 1, while also improving the filtration performance.

[0041] It should be noted that when numerical ranges are involved in this invention, it should be understood that the two endpoints of each numerical range, as well as any value between the two endpoints, can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described in this invention to avoid redundancy. Although preferred embodiments of this invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments, and all such changes and modifications fall within the scope of this invention.

[0042] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. If these modifications and variations fall within the scope of equivalents of this invention, then this invention also intends to include these modifications and variations.

Claims

1. A method for recovering mixed waste residue from the lithium carbonate production process, characterized in that, Includes the following steps: The unneutralized acidic slurry after the leaching process in the sulfuric acid process for lithium carbonate production is subjected to a first filtration separation at 60℃~90℃ to obtain silicon-aluminum slag containing silicon-aluminum components and the first filtrate. The first filtrate is neutralized and precipitated in steps. The method of step-by-step neutralization and precipitation is as follows: adjust the pH of the first filtrate to 3-4, separate the iron and aluminum slag precipitate, mix the separated solution with a Ca-containing precipitant so that the solution forms calcium sulfate precipitate at pH 4-6, and then perform a second solid-liquid separation to obtain gypsum slag containing calcium sulfate and lithium-containing purified solution.

2. The method for recovering mixed waste residue from the lithium carbonate production process according to claim 1, characterized in that, The temperature for the first filtration separation is 75℃~90℃.

3. The method for recovering mixed waste residue from the lithium carbonate production process according to claim 1, characterized in that, The acidic slurry has a pH < 3, and further, the acidic slurry has a pH of 1 to 2.

4. The method for recovering mixed waste residue from the lithium carbonate production process according to claim 1, characterized in that, The Ca-containing precipitant is lime milk or limestone powder.

5. The method for recovering mixed waste residue from the lithium carbonate production process according to claim 4, characterized in that, The limestone powder has a fineness of 180 mesh to 220 mesh.

6. The method for recovering mixed waste residue from the lithium carbonate production process according to claim 1, characterized in that, The pH of the first filtrate is adjusted by using a neutralizing agent, which is a sodium hydroxide solution.

7. The method for recovering mixed waste residue from the lithium carbonate production process according to claim 1, characterized in that, The conditions for the stepwise neutralization and precipitation are as follows: the temperature for neutralization and precipitation is 40℃~60℃, and the precipitation time is 30 minutes~90 minutes.

8. The method for recovering mixed waste residue from the lithium carbonate production process according to claim 1, characterized in that, The acidic slurry is obtained by calcining spodumene / lepidolite at 1000℃~1100℃ for 30 minutes and then grinding it to below 200 mesh to obtain spodumene fine powder; mixing sulfuric acid with spodumene fine powder and calcining at 250℃ for 30 minutes to obtain acidified clinker; and leaching the acidified clinker in water at 60℃~80℃ for 0.5 hours~1 hour.

Images