A method for recovering lithium from lithium-rich alkaline waste liquid based on the thermal reduction of carbide.

Abstract

This invention provides a method for recovering lithium from lithium-rich alkaline waste liquid based on a carbonization thermal reduction method, belonging to the field of lithium material recovery technology. The method includes: heating the lithium-rich alkaline waste liquid and then introducing CO2 for a carbonization reaction; after solid-liquid separation, crude carbon solid and carbonized waste liquid are obtained; the carbonized waste liquid is concentrated and the carbonization reaction is repeated to collect the crude carbon solid; the two crude carbons are combined, washed, dried, and ground to obtain lithium carbonate; lithium carbonate is generated by microwave vacuum calcination with calcium oxide; lithium oxide is then ball-milled with a reducing agent at high energy to obtain a nano-scale mixed powder; under vacuum conditions, the mixed powder is first microwave-heated to 700-850℃ for a first reduction roasting to remove Mg vapor; then microwave-heated to 1100-1350℃ for a second reduction roasting to collect Li vapor; and after cooling, high-purity metallic lithium is obtained. This invention uses a combined process of two-stage carbonization + thermal decomposition carbonization + two-stage reduction roasting to efficiently solve the problem of secondary utilization of lithium resources in waste liquid and obtain high-quality metallic lithium.

Description

Technical Field

[0001] This invention belongs to the field of lithium material recycling technology, and specifically relates to a method for recovering lithium from lithium-rich alkaline waste liquid based on the thermal reduction method of carbide. Background Technology

[0002] Lithium, renowned as an "energy metal" due to its high specific capacity and strong electron-gathering ability, has seen a surge in demand due to the global new energy revolution, particularly the rapid development of electric vehicles and energy storage markets. However, the immaturity of traditional lithium mining and extraction methods generates lithium-rich alkaline wastewater. This wastewater contains large amounts of lithium, as well as other heavy metal ions and organic matter; direct discharge without effective treatment will cause serious harm to the environment and ecosystems. Furthermore, the lack of utilization of the lithium resources in this wastewater represents a significant waste. Therefore, exploring methods for the secondary utilization of lithium resources in lithium-rich wastewater has become an urgent problem to be solved.

[0003] Currently, lithium extraction technologies for lithium-rich wastewater exhibit diverse characteristics, but a widely accepted unified treatment solution has yet to be established. Mainstream technologies encompass various methods, including extraction, precipitation, membrane separation, biological treatment, high-salt biochemical technology, and electrolysis. Specifically, extraction methods, due to their numerous systems and the need for drastically different extractants for lithium-rich wastewater with varying impurity content, coupled with their high cost and complex synthesis pathways, limit their application potential in large-scale industrial production. While precipitation methods are simple to operate and have relatively low technical barriers, they generate large amounts of waste residue, causing secondary pollution and failing to meet the demands for efficient treatment due to limited treatment effectiveness. Membrane separation, on the other hand, offers advantages such as convenient operation, ease of automation, significantly reduced labor costs, and effective removal of dissolved solids and organic matter. However, there is a scarcity of domestically developed companies capable of independently preparing membrane materials, making reliance on imports not only costly but also susceptible to contamination, requiring frequent replacements. Therefore, this method is primarily limited to laboratory research or small-scale preparation. As for other processes such as biological treatment, high-salt biochemical technology, and electrolysis, they also face insufficient technological maturity or other similar problems. Summary of the Invention In view of this, the present invention provides a method for recovering lithium from lithium-rich alkaline waste liquid based on the thermal reduction method of carbide, aiming to solve at least one of the technical problems in the background art.

[0004] This invention is implemented as follows: A method for recovering lithium from lithium-rich alkaline waste liquid based on the thermal reduction of carbide method, the method comprising the following steps: After heating, the lithium-rich alkaline waste liquid is introduced with CO2 to carry out a carbonization reaction. After solid-liquid separation, crude carbon solid and carbonized waste liquid are obtained. The carbonized waste liquid is concentrated 3 to 5 times and the above carbonization reaction is repeated to collect the crude carbon solid. The crude carbon solids obtained from the two carbonization reactions were combined, washed with water to remove impurities, and then dried and ground to obtain lithium carbonate powder. Lithium carbonate powder and calcium oxide are microwave-calcined in vacuum to thermally decompose and decarbonize to produce lithium oxide. Lithium oxide and a reducing agent were ball-milled at high energy to obtain a nanoscale mixed powder; Under vacuum conditions, the mixed powder is first microwave-heated to 700℃~850℃ for a first reduction roasting to remove Mg impurities in vapor form; then microwave-heated to 1100℃~1350℃ for a second reduction roasting to collect Li in vapor form, and after cooling, high-purity lithium metal is obtained. In the carbonization reaction, the flow rate of CO2 is adjusted according to the pH value of the reaction solution; the reducing agent is a mixed metal powder of aluminum, silicon, and iron.

[0005] Furthermore, the carbonization reaction is specifically operated as follows: The reaction solution was heated to 70℃~90℃, and CO2 was introduced into the bottom of the solution at a flow rate of 0.5 L / min~1.5 L / min, while magnetic stirring was performed at a speed of 150 rpm~250 rpm. The pH value of the reaction solution is monitored in real time. When the pH is greater than 11, the flow rate is adjusted to 0.1 L / min to 0.3 L / min, and the magnetic stirring speed is increased to 300 rpm to 400 rpm. When the pH of the reaction solution reaches 9.5~10.5, the CO2 flow is stopped, and the carbonization reaction terminates.

[0006] Furthermore, the lithium carbonate powder and calcium oxide are subjected to microwave vacuum calcination in a vacuum reduction vessel. The molar ratio of lithium carbonate to calcium oxide is 1:0.9~1.5, the pressure inside the vacuum reduction vessel is no more than 30 Pa, the calcination temperature is 1000℃~1200℃, and the time is 3h~5h. During the reaction, a rotary vane vacuum pump is used to remove the generated gas.

[0007] Furthermore, according to the molar ratio, the reducing agent contains aluminum:silicon:iron = 1:1.5~2:0.2~0.6.

[0008] Furthermore, the reducing agent is in excess by 30% to 50%.

[0009] Furthermore, the high-energy ball mill is operated at a speed of 300 rpm to 400 rpm for 2 hours.

[0010] Furthermore, the reduction calcination time is 2h to 3h.

[0011] Furthermore, the secondary reduction calcination time is 3h~5h.

[0012] Furthermore, during the primary reduction calcination and the secondary reduction calcination, the pressure inside the reaction vessel is controlled below 30 Pa.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention uses a combination process of two-stage carbonization + thermal decomposition carbonization + two-stage reduction roasting to efficiently solve the problem of secondary utilization of lithium resources in waste liquid, overcome the technical defects in the prior art, and produce high-quality metallic lithium.

[0014] 2. The high-purity metallic lithium obtained by this invention has a higher market value than lithium carbonate and lithium hydroxide obtained by other processing methods, thereby effectively improving the overall profit of the entire production process.

[0015] 3. This invention uses two-stage carbonization for waste liquid pretreatment, which maximizes the recovery of lithium in the waste liquid and reduces lithium loss.

[0016] 4. This invention uses thermal decomposition to decarbonize, which efficiently removes carbonate ions generated by the carbonation reaction.

[0017] 5. This invention employs a two-stage reduction roasting process, which efficiently removes stubborn magnesium impurities.

[0018] 6. This invention, through a multi-step reduction heating process and the replacement of traditional electric heating with microwave heating, not only ensures stable and efficient waste liquid treatment and high product purity, but also significantly improves the heating speed, achieves efficient energy utilization, and further reduces energy and time costs.

[0019] 7. The process conditions of this invention can generally be easily achieved using existing common equipment in various lithium plants, without the need to add new production lines. Furthermore, the carbon dioxide used for carbonization can be recycled, thereby greatly saving the expensive costs incurred by introducing new equipment and materials. Attached Figure Description Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] like Figure 1As shown, the method for recovering lithium from lithium-rich alkaline waste liquid based on the thermal reduction method of carbide includes steps S1 to S3.

[0022] S1, two-stage carbonization reaction Primary carbonization: Take lithium-rich alkaline waste liquid (mainly composed of LiOH, Li + The content is above 12g / L, including Na, K, Ca, and CO3. 2- SO4 2- Si, Mg, Cl - The waste liquid (containing high or near-saturated impurity ions) is placed in a reaction vessel. The waste liquid is heated to 70℃~90℃, and CO2 is introduced into the bottom of the solution. The gas flow rate is controlled within the range of 0.5 L / min~1.5 L / min using a flow meter, and the magnetic stirring speed is 200 rpm. Simultaneously, the pH value of the solution is monitored in real time. When the pH exceeds 11, the gas flow rate is controlled at 0.1 L / min~0.3 L / min, and the magnetic stirring speed is 400 rpm. The carbonization endpoint is reached when the pH is within the range of 10.5~9.5. The solution is then centrifuged and dried at 1000 rpm~3000 rpm for 2 min~5 min. The residue is filtered to obtain crude carbon (lithium carbonate with many impurities) and the carbonized waste liquid. Secondary carbonization: The carbonized waste liquid is evaporated and concentrated 3 to 5 times. The concentrated waste liquid is then carbonized again using the same method and reaction parameters as primary carbonization. After centrifugation and filtration, secondary crude carbon and low-lithium waste liquid are obtained (at this point, Li...). + Content <0.5g / L). The crude carbon obtained from primary and secondary carbonization is mixed and added to deionized water at a liquid-to-solid ratio of 3-5:1. The mixture is then washed with water for 30 minutes at a magnetic stirring speed of 200 rpm (to remove soluble impurities such as Na, K, and SO42-). 2- Cl - After washing, the product is centrifuged and filtered, and the filter residue is dried in an oven at 150 °C for 3 h. After it is completely dried, the filter residue is taken out and ground until there are no obvious large particles. The main component of the product is lithium carbonate. The reason for adjusting the CO2 flow rate based on the pH of the carbonization reaction solution is that when the pH of the waste liquid drops to around 11, the pH drops extremely rapidly after CO2 is introduced, decreasing by 1 within tens of seconds or even a few seconds. If a smaller flow rate is not adjusted, the solution pH is very likely to exceed the carbonization endpoint, and some lithium carbonate will be converted into soluble lithium bicarbonate, significantly reducing the lithium recovery rate in the waste liquid.

[0023] The purpose of carbonization is to precipitate lithium ions in the solution through lithium carbonate precipitation. Concentration and secondary carbonization are for further and thorough precipitation and separation of lithium from the liquid. Water washing can remove soluble impurities from the solid precipitate.

[0024] S2, thermal decomposition and carbonization reaction The product from step S1 and a certain amount of high-purity calcium oxide (content greater than or equal to 99.9%, molar ratio of lithium to calcium oxide 1:0.9~1.5) are placed in a vacuum reduction vessel. The pressure inside the reduction vessel is evacuated to below 30 Pa using a rotary vane vacuum pump. The powder is then heated using a microwave device, with the temperature controlled at 1000℃~1200℃ for 3h~5h. During calcination, impurity gases such as CO2 and CO (mainly CO2) released from the decomposition in the reduction vessel are continuously removed using a rotary vane vacuum pump. The waste gas obtained in this step can be recycled and reused as a gaseous feedstock for the carbonization reaction in step S1.

[0025] This step heats and decomposes lithium carbonate into lithium oxide to prevent lithium metal from containing lithium carbonate impurities if oxidation is completed in one step. The role of calcium oxide is to effectively promote the decomposition of lithium carbonate, allowing it to decompose at a lower temperature, thereby reducing energy consumption and ensuring complete decomposition of lithium carbonate.

[0026] S3, Two-stage reduction calcination reaction After the product from the thermal decomposition and decarburization reaction in step S2 is cooled in the furnace, the heated solid is removed and aluminum, silicon, and iron metal powders are added as reducing agents. The molar ratio of the three metals is aluminum:silicon:iron = 1:1.5~2:0.2~0.6, with a total excess of 30%~50% reducing agent. This mixture, along with agate balls, is placed in a ball mill jar and ball-milled at 300 rpm~400 rpm for 2 hours to obtain a mixed powder. The excess reducing agent refers to an excess relative to the theoretical molar amount, which is calculated based on the reaction formula between the reducing agent and lithium oxide. Si(s)+2Li2O(s)→SiO2(s)+4Li(g); 2Al(s)+3Li2O(s)→Al2O3(s)+6Li(g); 3Fe(s)+4Li2O(s)→Fe3O4(s)+8Li(g); The mixed powder is then placed in a vacuum reduction vessel for a second reduction calcination reaction. The pressure inside the reduction vessel is evacuated to below 30 Pa using a rotary vane vacuum pump, and microwave heating is turned on to 700℃~850℃. During this process, the reduced and vaporized Mg impurity gas in the reduction vessel is continuously removed by the rotary vane vacuum pump. The magnesium vapor is collected in a double-layer condenser container in an inert gas environment (argon, helium, and neon can be selected) at the same temperature. The interlayer exchanges heat with the inner layer magnesium vapor through circulating water to cool the impurity Mg into a metallic state and collect it. This process is maintained for 2 to 3 hours. After the first reduction roasting reaction is completed, a second reduction roasting reaction is carried out by microwave heating. The temperature of the mixed powder is increased to 1100℃~1350℃. During this period, the reduced and vaporized Li vapor in the reduction tank is continuously removed by a rotary vane vacuum pump. Similar to step five, the Li vapor is collected in another double-layer condenser. The roasting and reduction time is 3 hours to 5 hours. Finally, after complete cooling, metallic lithium is obtained.

[0027] The principle of the two-stage reduction roasting reaction is as follows: In the reduction roasting, the aluminum, silicon and iron of the reducing agent are oxidized into oxides, and lithium oxide is reduced to low-boiling-point metallic lithium and vaporized; taking advantage of the different vaporization temperatures of metallic magnesium and metallic lithium, reduction roasting is carried out in steps at different temperatures to remove magnesium impurities first; then the temperature is raised to the vaporization temperature of lithium, and lithium vapor is generated and collected to form metallic lithium with fewer impurities and higher purity.

[0028] This invention efficiently solves the problem of secondary utilization of lithium resources in waste liquid and improves upon the shortcomings of existing processes. It also effectively addresses the problems of current processes, such as: membrane separation, which is extremely costly and reliant on imported products; extraction, which is complex, has high costs for extractant development and preparation, and poor applicability to different waste liquids; and precipitation, which has poor treatment effects, low recovery value of treated products, and generates large amounts of waste residue causing secondary pollution.

[0029] Example 1 A method for recovering lithium from lithium-rich alkaline waste liquid based on the thermal reduction of carbide method includes steps S1 to S3: S1, two-stage carbonization reaction One liter of lithium-rich alkaline waste liquid was placed in a beaker and heated to 70°C. CO2 was then introduced into the bottom of the solution for primary carbonization. The gas flow rate was controlled at 0.5 L / min using a flow meter, and the magnetic stirring speed was 200 rpm. Simultaneously, the pH value of the solution was monitored in real time. When the pH exceeded 11, the gas flow rate was controlled at 0.1 L / min, and the magnetic stirring speed was 400 rpm. The carbonization endpoint was reached when the pH was within the range of 9.5. The solution was then centrifuged at 1000 rpm for 2 minutes to dry the waste liquid. The resulting crude carbon and carbonized waste liquid were then filtered. The carbonized waste liquid was evaporated and concentrated three times. A secondary carbonization reaction and centrifugation were then performed on the concentrated liquid using the same methods and experimental parameters as the primary carbonization reaction. The resulting crude carbon and low-lithium waste liquid were then filtered to obtain secondary crude carbon and low-lithium waste liquid. The crude carbon obtained after the two-stage carbonization reaction was mixed and deionized water was added at a liquid-to-solid ratio of 3:1. The mixture was then washed with water for 30 minutes at a magnetic stirring speed of 200 rpm. After washing, the mixture was centrifuged and filtered, and the filter residue was dried in an oven at 150 °C for 3 hours. After complete drying, the filter residue was removed and ground until there were no obvious large particles.

[0030] S2, thermal decomposition and carbonization reaction The product obtained from S1 and a certain amount of high-purity calcium oxide (the molar ratio of lithium to calcium oxide is 1:0.9) were placed in a vacuum reduction vessel. The pressure inside the reduction vessel was evacuated to below 30 Pa using a rotary vane vacuum pump. The powder was heated using a microwave device, and the temperature was controlled at 1000℃ for 5 hours. During the calcination, impurity gases such as CO2 and CO decomposed in the reduction vessel were continuously removed using a rotary vane vacuum pump.

[0031] S3, Two-stage reduction calcination reaction After cooling in the furnace, the heated solid was removed, and aluminum, silicon, and iron metal powders were added as reducing agents (the molar ratio of the three metals was aluminum:silicon:iron = 1:1.5:0.2, and the total reducing agent was in excess of 30%). The powder was placed in a ball mill jar along with agate balls and ball milled at 300 rpm for 2 hours to obtain a mixed powder. The mixed powder was then placed in a vacuum reduction jar, and the pressure inside the reduction jar was evacuated to below 30 Pa using a rotary vane vacuum pump. Microwave heating was then turned on to 700°C. During this time, the reduced and vaporized Mg impurity gas in the reduction jar was continuously evacuated using a rotary vane vacuum pump. The magnesium vapor was collected in a double-layer condenser container in a helium environment at the same temperature. The jacket was cooled to a metallic state by heat exchange between circulating water and the inner magnesium vapor, and the mixture was collected. This process was maintained for 3 hours. The mixed powder was heated again by microwave to increase the temperature to 1100℃. During this time, the reduced and vaporized Li vapor in the reduction tank was continuously removed by a rotary vane vacuum pump. The powder was then transferred to another double-layer condenser for collection under the same inert gas and temperature conditions. The calcination and reduction time was 5 hours. Finally, after complete cooling, metallic lithium was obtained.

[0032] Example 2 A method for recovering lithium from lithium-rich alkaline waste liquid based on the thermal reduction of carbide method includes steps S1 to S3: S1, two-stage carbonization reaction One liter of lithium-rich alkaline waste liquid was placed in a beaker and heated to 80°C. CO2 was then introduced into the bottom of the solution for primary carbonization. The gas flow rate was controlled at 1 L / min using a flow meter, and the magnetic stirring speed was 200 rpm. The pH value of the solution was monitored in real time. When the pH exceeded 11, the gas flow rate was controlled at 0.2 L / min, and the magnetic stirring speed was 400 rpm. Carbonization ended at pH 10. The solution was then centrifuged at 2000 rpm for 3 minutes to dry, and the crude carbon and carbonized waste liquid were obtained by filtration. The carbonized waste liquid was then evaporated and concentrated four times. A secondary carbonization reaction and centrifugation were performed on the concentrated liquid using the same method and experimental parameters as the primary carbonization reaction. The resulting crude carbon and low-lithium waste liquid were obtained by filtration. The crude carbon obtained after the two-stage carbonization reaction was mixed and deionized water was added at a liquid-to-solid ratio of 4:1. The mixture was then washed with water at a magnetic stirring speed of 200 rpm for 30 minutes. After washing, the mixture was centrifuged and filtered, and the filter residue was dried in an oven at 150 °C for 3 hours. After complete drying, the filter residue was removed and ground until there were no obvious large particles.

[0033] S2, thermal decomposition and carbonization reaction The product obtained from S1 and a certain amount of high-purity calcium oxide (the molar ratio of lithium to calcium oxide is 1:1.2) were placed in a vacuum reduction vessel. The pressure inside the reduction vessel was evacuated to below 30 Pa using a rotary vane vacuum pump. The powder was heated by a microwave device, and the temperature was controlled at 1100℃ for 4 hours. During the calcination, CO2, CO and other impurity gases decomposed in the reduction vessel were continuously removed by the rotary vane vacuum pump.

[0034] S3, Two-stage reduction calcination reaction After furnace cooling, the heated solid was removed, and aluminum, silicon, and iron metal powders were added as reducing agents (the molar ratio of the three metals was aluminum:silicon:iron = 1:1.7:0.4, with a total reducing agent excess of 40%). These powders, along with agate balls, were placed in a ball mill jar and ball-milled at 350 rpm for 2 hours to obtain a mixed powder. The mixed powder was then placed in a vacuum reduction jar, and the pressure inside the jar was evacuated to below 30 Pa using a rotary vane vacuum pump. Microwave heating was then initiated to 800°C. During this process, the reduced and vaporized Mg impurity gas in the reduction jar was continuously removed using the rotary vane vacuum pump. The magnesium vapor was collected in a double-layered condenser under argon atmosphere at the same temperature. The jacket layer was cooled to a metallic state by heat exchange between circulating water and the inner magnesium vapor, which was then collected. This process was maintained for 2.5 hours. The mixed powder was then heated by microwave to increase the temperature to 1200℃. During this time, the reduced and vaporized Li vapor in the reduction vessel was continuously removed by a rotary vane vacuum pump. The powder was then transferred to another double-layer condenser for collection under the same inert gas and temperature conditions. The calcination and reduction time was 4 hours. Finally, after complete cooling, metallic lithium was obtained.

[0035] Example 3 A method for recovering lithium from lithium-rich alkaline waste liquid based on the thermal reduction of carbide method includes steps S1 to S3: S1, two-stage carbonization reaction One liter of lithium-rich alkaline waste liquid was placed in a beaker and heated to 90°C. CO2 was then introduced into the bottom of the solution for primary carbonization. The gas flow rate was controlled at 1.5 L / min using a flow meter, and the magnetic stirring speed was 200 rpm. Simultaneously, the pH value of the solution was monitored in real time. When the pH exceeded 11, the gas flow rate was controlled at 0.3 L / min, and the magnetic stirring speed was 400 rpm. The carbonization endpoint was reached at pH 10.5. The solution was then centrifuged at 3000 rpm for 5 minutes to dry the waste liquid. The resulting crude carbon and carbonized waste liquid were filtered. The carbonized waste liquid was then evaporated and concentrated five times. A secondary carbonization reaction and centrifugation were performed on the concentrated liquid using the same method and experimental parameters as the primary carbonization reaction. The resulting crude carbon and low-lithium waste liquid were filtered to obtain secondary crude carbon and low-lithium waste liquid. The crude carbon obtained after the two-stage carbonization reaction was mixed and deionized water was added at a liquid-to-solid ratio of 5:1. The mixture was washed with water for 30 minutes at a magnetic stirring speed of 200 rpm to remove soluble impurities. After washing, the mixture was centrifuged and filtered, and the filter residue was dried in an oven at 150 °C for 3 hours. After complete drying, the filter residue was taken out and ground until there were no obvious large particles.

[0036] S2, thermal decomposition and carbonization reaction The dried crude carbon and a certain amount of high-purity calcium oxide (the molar ratio of lithium to calcium oxide is 1:1.5) are placed in a vacuum reduction vessel. The pressure inside the reduction vessel is evacuated to below 30 Pa using a rotary vane vacuum pump. The powder is heated by a microwave device, and the temperature is controlled at 1200℃ for 5 hours. During the calcination, the CO2, CO and other impurity gases decomposed in the reduction vessel are continuously removed by the rotary vane vacuum pump.

[0037] S3, Two-stage reduction calcination reaction After furnace cooling, the heated solid was removed, and aluminum, silicon, and iron metal powders were added as reducing agents (the molar ratio of the three metals was aluminum:silicon:iron = 1:2:0.6, with a total reducing agent excess of 50%). These powders, along with agate balls, were placed in a ball mill jar and ball-milled at 400 rpm for 2 hours to obtain a mixed powder. The mixed powder was then placed in a vacuum reduction jar, and the pressure inside the jar was evacuated to below 30 Pa using a rotary vane vacuum pump. Microwave heating was then initiated to 850°C. During this process, the reduced and vaporized Mg impurity gas in the reduction jar was continuously removed using the rotary vane vacuum pump. The magnesium vapor was collected in a double-layered condenser under argon atmosphere at the same temperature. The jacket layer was cooled to a metallic state by heat exchange between circulating water and the inner magnesium vapor, and the collected Mg impurities were maintained for 2 hours. The mixed powder was then heated by microwave to increase the temperature to 1350°C. During this time, the reduced and vaporized Li vapor in the reduction vessel was continuously removed by a rotary vane vacuum pump. The powder was then transferred to another double-layer condenser under the same inert gas and temperature conditions for collection. The calcination and reduction time was 3 hours. Finally, after complete cooling, metallic lithium was obtained.

[0038] Comparative Example 1 This comparative example is based on the method of recovering lithium from lithium-rich alkaline waste liquid by the carbide thermal reduction method. The only difference between this method and Example 2 is that step S3 uses a first-stage reduction roasting reaction. Specifically, a second-stage reduction roasting reaction is carried out directly without a low-temperature first-stage reduction roasting. The other steps and reaction conditions are the same as in Example 2.

[0039] Comparative Example 2 The method for recovering lithium from lithium-rich alkaline waste liquid in this comparative example differs from Example 2 only in that step S2 is omitted and the thermal decarbonization step is not performed. The other steps and reaction conditions are the same as in Example 2.

[0040] Comparative Example 3 This comparative example is based on the method of recovering lithium from lithium-rich alkaline waste liquid by the carbonization thermal reduction method. The only difference between this method and Example 2 is that step S1 uses a first-stage carbonization reaction. Specifically, after the first-stage carbonization is completed, the waste liquid after carbonization is not evaporated and concentrated, and the filter residue from the second centrifugation is not collected. Only the crude carbon after the first carbonization is collected and washed, centrifuged, dried, and ground. Other steps and reaction conditions are the same as in Example 2.

[0041] The products obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were analyzed according to GB / T20931-2007 "Chemical Analysis Methods for Lithium" (Li, Mg, Si, Na, K, Ca, Cl). - (etc.) and ion chromatography (CO3) 2- SO4 2- The components were measured and analyzed, and the results are shown in Table 1.

[0042] Table 1

[0043] Note: "-" in Table 1 indicates that no detection was performed.

[0044] As shown in Table 1, the purity of lithium metal obtained in Examples 1 to 3 of this invention is all above 99.95%, and the purity of Na, K, Ca, Si, Mg, and Cl is also high. - All impurities are below the requirements for Li-2 product composition in the national standard GB / T4369-2015.

[0045] A comparison of the data from Comparative Example 1 and Example 2 shows that, due to the direct high-temperature reduction roasting of Comparative Example 1, a large amount of magnesium impurities were still present in the product, which significantly reduced the purity of metallic lithium.

[0046] A comparison of the data from Comparative Example 2 and Example 2 shows that, because Comparative Example 2 omitted the thermal decarbonation step of lithium carbonate and calcium oxide and directly carried out reduction roasting, the product still contained a large amount of lithium carbonate, which significantly reduced the purity of metallic lithium.

[0047] A comparison of the data from Comparative Example 3 and Example 2 shows that the lithium purity is not significantly different between the two. This is because Comparative Example 3 omits the secondary carbonization reaction step, which has little impact on purity, but there is lithium loss because a certain amount of lithium remains in the waste liquid after the first carbonization. The lithium content in the waste liquid after the completion of the S1 carbonization reaction in Examples 1 to 3 and Comparative Examples 1 to 3 is measured, and the results are shown in Table 2.

[0048] Table 2

[0049] As can be seen from Table 2, Examples 1 to 3, Comparative Example 1 and Comparative Example 2 all adopted a two-stage carbonization reaction, and the lithium content in their waste liquid was less than 0.47 g / L. However, the lithium content in the waste liquid of Comparative Example 3, which adopted a one-stage carbonization reaction, increased significantly, reaching 2.76 g / L.

[0050] The reduction rate of lithium in step S3 of Examples 1 to 3 and Comparative Examples 1 to 3 was calculated as follows: Reduction rate = (mass of S3 product × lithium purity) / (mass of initial waste lithium liquid - mass of waste lithium liquid after S1) × 100%; the results are shown in Table 3.

[0051] Table 3

[0052] As can be seen from Table 3, Examples 1 to 3, Comparative Example 1 and Comparative Example 3 all adopted a two-stage reduction calcination reaction, and their reduction rates were all above 99.5%. However, Comparative Example 2, which only adopted a one-stage reduction calcination reaction, had a significantly reduced reduction rate of only 96.88%.

[0053] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for recovering lithium from lithium-rich alkaline waste liquid based on the thermal reduction of carbide, characterized in that, The method includes the following steps: After heating, the lithium-rich alkaline waste liquid is introduced with CO2 to carry out a carbonization reaction. After solid-liquid separation, crude carbon solid and carbonized waste liquid are obtained. The carbonized waste liquid is concentrated 3 to 5 times and the above carbonization reaction is repeated to collect the crude carbon solid. The crude carbon solids obtained from the two carbonization reactions were combined, washed with water to remove impurities, and then dried and ground to obtain lithium carbonate powder. Lithium carbonate powder and calcium oxide are microwave-calcined in vacuum to thermally decompose and decarbonize to produce lithium oxide. Lithium oxide and a reducing agent were ball-milled at high energy to obtain a nano-sized mixed powder; Under vacuum conditions, the mixed powder is first microwave heated to 700℃~850℃ for a single reduction calcination to remove Mg impurities in vapor form. The lithium was then microwaved to 1100℃~1350℃ for a second reduction roasting, and the vapor form of Li was collected. After cooling, high-purity metallic lithium was obtained. In the carbonization reaction, the flow rate of CO2 is adjusted according to the pH value of the reaction solution; the reducing agent is a mixed metal powder of aluminum, silicon, and iron.

2. The method for recovering lithium from lithium-rich alkaline waste liquid based on the thermal reduction method of carbide according to claim 1, characterized in that, The carbonization reaction is specifically operated as follows: The reaction solution was heated to 70℃~90℃, and CO2 was introduced into the bottom of the solution at a flow rate of 0.5 L / min~1.5 L / min, while magnetic stirring was performed at a speed of 150 rpm~250 rpm. The pH value of the reaction solution is monitored in real time. When the pH is greater than 11, the flow rate is adjusted to 0.1 L / min to 0.3 L / min, and the magnetic stirring speed is increased to 300 rpm to 400 rpm. When the pH of the reaction solution reaches 9.5~10.5, the CO2 flow is stopped, and the carbonization reaction terminates.

3. The method for recovering lithium from lithium-rich alkaline waste liquid based on the thermal reduction method of carbide according to claim 1, characterized in that, The lithium carbonate powder and calcium oxide are subjected to microwave vacuum calcination in a vacuum reduction vessel. The molar ratio of lithium carbonate to calcium oxide is 1:0.9~1.5, and the pressure inside the vacuum reduction vessel does not exceed 30 Pa. The calcination temperature is 1000℃~1200℃, and the time is 3h~5h. During the reaction, a rotary vane vacuum pump is used to remove the generated gas.

4. The method for recovering lithium from lithium-rich alkaline wastewater based on the thermal reduction method according to claim 1, characterized in that, According to the molar ratio, the reducing agent contains aluminum:silicon:iron = 1:1.5~2:0.2~0.

6.

5. The method for recovering lithium from lithium-rich alkaline waste liquid based on the thermal reduction method according to claim 4, characterized in that, The reducing agent is in excess by 30% to 50%.

6. The method for recovering lithium from lithium-rich alkaline waste liquid based on the thermal reduction method of carbide according to claim 1, characterized in that, The high-energy ball mill operates at a speed of 300 rpm to 400 rpm for 2 hours.

7. The method for recovering lithium from lithium-rich alkaline waste liquid based on the thermal reduction method according to claim 1, characterized in that, The reduction calcination time is 2h~3h.

8. The method for recovering lithium from lithium-rich alkaline waste liquid based on the thermal reduction method according to claim 1 or 7, characterized in that, The secondary reduction calcination time is 3h~5h.

9. The method for recovering lithium from lithium-rich alkaline wastewater based on the thermal reduction method of carbide according to claim 1, characterized in that, During the primary and secondary reduction roasting processes, the pressure inside the reaction vessel is controlled below 30 Pa.

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