Method for recovering lithium in lithium carbonate lithium precipitation mother liquor

Abstract

The invention provides a method for recovering lithium in lithium carbonate lithium precipitation mother liquor, which comprises the following steps: (1) mixing lithium iron phosphate leaching residues with the lithium carbonate lithium precipitation mother liquor to obtain a mixed material; and (2) heating the mixed material, introducing a reducing agent solution to carry out lithium extraction reaction, and carrying out post-treatment to obtain lithium extraction post-liquid and lithium extraction post-slag. The method is easy to operate, lithium in the lithium carbonate lithium precipitation mother liquor is recycled through the lithium iron phosphate leaching residues, consumption and cost of auxiliary materials can be reduced, and the recovery rate of lithium can be increased.

Description

Technical Field

[0001] The present invention belongs to the technical field of resource recovery and relates to a method for recovering lithium from the mother liquor of lithium carbonate precipitation. Background Art

[0002] Due to its characteristics such as high energy density and strong cycle stability, lithium-ion batteries have been widely used in new energy vehicles, laptop computers, and other portable devices. As the most common lithium precursor for producing the positive electrode of lithium-ion batteries, lithium carbonate is often prepared by the process of precipitation synthesis of sodium carbonate and lithium sulfate. Since lithium carbonate has a certain solubility in water (20 °C, 1.33 g / 100 g water), there are inevitably unutilized lithium (about 2.5 g / L) and carbonate (about 18 g / L) in the mother liquor of lithium precipitation generated during the synthesis of lithium carbonate using lithium sulfate solution and sodium carbonate solution or the "carbonization - pyrolysis" synthesis process of crude lithium carbonate. To improve the recovery rate of lithium, the current industry's disposal methods for the mother liquor of lithium precipitation include decarbonization - evaporation concentration, phosphate precipitation method, recycling to the front-end process, etc. As an auxiliary material for lithium carbonate synthesis, the chloride ions introduced by sodium carbonate (impurity ions in the sodium carbonate raw material) are enriched in the system. Therefore, when the chloride in the mother liquor of lithium precipitation is enriched to a certain concentration, it needs to be removed from the system (the corresponding mother liquor of lithium precipitation is called the open-circuit mother liquor of lithium precipitation) to avoid the rapid corrosion of equipment in the system by halogen ions.

[0003] CN104925837A discloses a method for recovering lithium salts from the mother liquor of lithium carbonate precipitation for battery grade. First, phosphoric acid is used to adjust the pH and decarbonize the mother liquor of lithium precipitation, and then sodium hydroxide is used for secondary pH adjustment to convert the lithium in the mother liquor into lithium phosphate precipitation; then, the lithium phosphate is slurried with water or washing liquid and dissolved with hydrochloric acid or nitric acid to obtain an acidified slurry of lithium phosphate; finally, calcium salt is used to transform and precipitate phosphorus, and solid-liquid separation is carried out to obtain calcium phosphate and a lithium-containing solution. This process requires the use of phosphoric acid and sodium hydroxide with relatively high costs for pH adjustment, and the lithium recovery rate is not high. Similarly, some manufacturers directly use the phosphate precipitation method to recover lithium from the mother liquor of lithium precipitation, and the lithium phosphate slag is recycled to the front-end process for de-lithiation, but its disadvantages of large phosphate consumption and high auxiliary material costs limit its application.

[0004] CN107201452A discloses an electrochemical method for extracting lithium from a lithium-containing solution based on lithium battery electrode materials. Utilizing the property of reversible deintercalation / insertion of lithium in lithium battery materials under the action of electric potential, under the condition of constant voltage reaction, the LiMn2O4 electrode and the Li 1-x Mn2O4 electrode are respectively placed in the recovery liquid and the extraction liquid isolated by an anion exchange membrane, and the two reactions of deintercalation and insertion of lithium are combined and carried out simultaneously to achieve the enrichment and extraction of lithium ions. However, this method has high equipment costs and relatively complex operations.

[0005] The above-mentioned lithium extraction method has large consumption of auxiliary materials, high cost and complex operation, which limits its practical application. Therefore, there is a need to develop a simple, efficient, green and economical method for recovering lithium from the lithium precipitation mother liquor. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for recovering lithium from the lithium precipitation mother liquor of lithium carbonate. The method of the present invention is simple to operate, and uses the leaching residue of lithium iron phosphate to recover lithium from the lithium precipitation mother liquor of lithium carbonate, which can not only reduce the consumption and cost of auxiliary materials, but also improve the recovery rate of lithium.

[0007] To achieve the purpose of this invention, the following technical solutions are adopted:

[0008] In the first aspect, the present invention provides a method for recovering lithium from the lithium precipitation mother liquor of lithium carbonate, and the recovery method includes the following steps:

[0009] (1) Mix the leaching residue of lithium iron phosphate with the lithium precipitation mother liquor of lithium carbonate to obtain a mixed material;

[0010] (2) After heating the mixed material, introduce a reducing agent solution to carry out the lithium extraction reaction, and obtain the lithium extraction post-liquid and the lithium extraction post-residue through post-treatment.

[0011] The recovery method of the present invention uses the leaching residue of lithium iron phosphate as a carrier, introduces a reducing agent to extract lithium from the lithium precipitation mother liquor of lithium carbonate, and can simultaneously utilize the leaching residue of lithium iron phosphate (the leaching residue generated during the recycling of waste lithium iron phosphate batteries) and the lithium precipitation mother liquor of lithium carbonate, achieving the purpose of treating waste with waste.

[0012] The chemical reaction principle involved in the lithium extraction reaction of the present invention is as follows:

[0013] 2FePO4 + 2Li + + R + CO3 2- = 2LiFePO4 + RO + CO2↑, where R is a reducing agent, LiFePO4 is a reduction product, and RO is an oxidation product.

[0014] The method of the present invention for synergistically extracting lithium using the leaching residue of lithium iron phosphate and a reducing agent can not only be applied to the lithium precipitation mother liquor of lithium carbonate (including the primary lithium precipitation mother liquor and the secondary lithium precipitation mother liquor), but also to the lithium carbonate carbonization-pyrolysis mother liquor (i.e., the remaining liquid phase part after pyrolysis in the carbonization-pyrolysis process of lithium carbonate), the lithium carbonate washing water (i.e., the washing liquid obtained after washing the solid lithium carbonate after lithium carbonate precipitation, filtration or centrifugal separation), etc. in lithium-containing solution systems.

[0015] Preferably, the leaching residue of lithium iron phosphate in step (1) includes the leaching residue of lithium iron phosphate battery powder and / or the leaching residue of lithium iron phosphate electrode sheet powder.

[0016] Preferably, the lithium carbonate mother liquor in step (1) includes the primary lithium carbonate mother liquor and / or the open - circuit lithium carbonate mother liquor, preferably the open - circuit lithium carbonate mother liquor.

[0017] The primary lithium carbonate mother liquor in the present invention is the mother liquor after the reaction of the lithium sulfate solution after impurity removal and the sodium carbonate solution. The open - circuit lithium carbonate mother liquor is the mother liquor after the decarbonation and evaporation concentration of the primary lithium precipitation mother liquor and then the reaction with the sodium carbonate solution.

[0018] In the present invention, the lithium ions in the lithium carbonate mother liquor are selectively extracted by means of redox reaction. Compared with the traditional phosphate precipitation method, it avoids the disadvantage of high solubility of lithium phosphate in the high - salt system and can effectively improve the lithium recovery rate.

[0019] Preferably, the pH of the lithium carbonate mother liquor in step (1) is 10 - 12, for example: 10, 10.5, 11, 11.5 or 12, etc.

[0020] Preferably, the pH of the mixed material in step (1) is 8 - 9, for example: 8, 8.2, 8.5, 8.8 or 9, etc. It is not limited to the listed values, and other unlisted values within this range are also applicable.

[0021] The lithium carbonate mother liquor in the present invention can naturally provide carbonate ions to buffer the pH during the reaction process without the need to additionally introduce an alkali solution to adjust the pH, reducing the consumption of auxiliary materials and simplifying the process operation.

[0022] Preferably, the molar ratio of iron element in the lithium iron phosphate leaching residue to lithium element in the lithium carbonate mother liquor in step (1) is (1.3 - 1.8):1, for example: 1.3:1, 1.4:1, 1.5:1, 1.6:1 or 1.8:1, etc. It is not limited to the listed values, and other unlisted values within this range are also applicable.

[0023] Preferably, the lithium iron phosphate leaching residue is the leaching residue of lithium iron phosphate battery powder, and the molar ratio of iron element in the lithium iron phosphate leaching residue to lithium element in the lithium carbonate mother liquor is (1.7 - 1.8):1, for example: 1.7:1, 1.72:1, 1.75:1, 1.78:1 or 1.8:1, etc. It is not limited to the listed values, and other unlisted values within this range are also applicable.

[0024] Preferably, the lithium iron phosphate leaching residue is the leaching residue of lithium iron phosphate electrode powder, and the molar ratio of iron element in the lithium iron phosphate leaching residue to lithium element in the lithium carbonate mother liquor is (1.3 - 1.5):1, for example: 1.3:1, 1.35:1, 1.4:1, 1.45:1 or 1.5:1, etc. It is not limited to the listed values, and other unlisted values within this range are also applicable.

[0025] Preferably, stirring is performed during the mixing process in step (1).

[0026] Preferably, the stirring speed is 600 rpm to 800 rpm, for example, 600 rpm, 650 rpm, 700 rpm, 750 rpm or 800 rpm, etc., and is not limited to the listed values. Other values not listed within the numerical range are also applicable.

[0027] Preferably, the heating temperature in step (2) is 80°C to 85°C, for example, 80°C, 81°C, 82°C, 83°C, 84°C or 85°C, etc., and is not limited to the listed values. Other values not listed within this numerical range are also applicable.

[0028] Preferably, the solute of the reducing agent solution in step (2) includes any one of sodium sulfite, potassium sulfite, sodium thiosulfate or sodium sulfide, or a combination of at least two thereof, preferably sodium sulfite and / or potassium sulfite.

[0029] The choice of reducing agent in the present invention significantly impacts recovery efficiency. Compared to sodium sulfite, sodium thiosulfate is significantly less effective at lithium extraction under the same conditions due to its relatively weak reducing properties. Furthermore, sodium sulfite's oxidation product is harmless sodium sulfate, while sodium thiosulfate readily produces byproducts such as elemental sulfur, which is detrimental to subsequent processes.

[0030] Taking sulfite as an example, the chemical reaction equation involved in the lithium extraction reaction of the present invention is as follows:

[0031] 2FePO4+2Li + +SO3 2- +CO3 2- =2LiFePO4+SO4 2- +CO2↑.

[0032] Preferably, the mass percentage concentration of the reducing agent solution in step (2) is 15% to 26%, for example: 15%, 18%, 20%, 22% or 26%, etc., and is not limited to the listed values. Other values not listed within this numerical range are also applicable.

[0033] In order to reduce water expansion, the present invention needs to select a reducing agent solution with a relatively high concentration, and the concentration of the reducing agent solution is close to its saturated solubility.

[0034] Preferably, the molar ratio of the solute in the reducing agent solution described in step (2) to the lithium in the lithium precipitation mother liquor of lithium carbonate is (0.4 - 0.6):1. For example: 0.4:1, 0.45:1, 0.5:1, 0.55:1 or 0.6:1, etc. It is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0035] Preferably, during the lithium extraction reaction in step (2), the flow rate of the reducing agent solution is 1 mL / min - 4 mL / min. For example: 1 mL / min, 1.5 mL / min, 2 mL / min, 2.5 mL / min, 3 mL / min or 4 mL / min, etc. It is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0036] Preferably, the time of the lithium extraction reaction in step (2) is 120 min - 150 min. For example: 120 min, 125 min, 130 min, 140 min or 150 min, etc. It is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0037] Preferably, stirring is carried out during the lithium extraction reaction in step (2).

[0038] Preferably, the stirring speed is 600 rpm - 800 rpm. For example: 600 rpm, 650 rpm, 700 rpm, 750 rpm or 800 rpm, etc. It is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0039] Preferably, the post-treatment in step (2) includes solid-liquid separation.

[0040] Preferably, the methods of solid-liquid separation include filtration and / or centrifugal separation.

[0041] The lithium extraction residue obtained by solid-liquid separation in the present invention at least includes lithium iron phosphate (and iron phosphate), and the lithium extraction residue can be returned to the front-end leaching process (that is, combined with waste lithium iron phosphate for lithium ion leaching).

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] (1) The method provided by the present invention is simple to operate. Using the lithium extraction residue of lithium iron phosphate to recover lithium in the lithium precipitation mother liquor of lithium carbonate can not only reduce the consumption and cost of auxiliary materials, but also improve the lithium recovery rate.

[0044] (2) The present invention uses the leaching residue of lithium iron phosphate as the lithium extraction carrier, and conducts redox reaction for lithium extraction using a reducing agent. By adjusting conditions such as the excess coefficient of the leaching residue, reaction temperature, and the addition rate of the reducing agent, the recovery rate of metallic lithium in the mother liquor for lithium precipitation can reach over 98%. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a process flow diagram of the method for recovering lithium in the mother liquor for lithium carbonate precipitation provided in Embodiment 1 of the present invention.

[0046] Figure 2 It is an XRD pattern of the residue after lithium extraction obtained in Embodiment 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047] The technical solution of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0048] In the lithium iron phosphate leaching residue used in the embodiments of the present invention, the percentage content of iron element is 18% - 28%, and the percentage content of lithium ion is 0.01% - 0.1%.

[0049] Embodiment 1

[0050] This embodiment provides a method for recovering lithium in the mother liquor for lithium carbonate precipitation. The process flow diagram of the recovery method is as Figure 1 shown, and the recovery method includes the following steps:

[0051] (1) Weigh the leaching residue of lithium iron phosphate electrode powder, and add it to a reaction kettle containing 1.5 L of open - circuit mother liquor for lithium carbonate precipitation at a stirring rate of 600 rpm to obtain a mixed material. Among them, the lithium concentration in the mother liquor for lithium precipitation is 3 g / L, the pH is 11, and the CO3 2- concentration is 16.6 g / L; the pH of the mixed material is 8.5, and the molar amount of iron element in the leaching residue of lithium iron phosphate electrode powder is 1.5 times the molar amount of lithium in the mother liquor for lithium precipitation (Fe:Li = 1.5);

[0052] (2) Heat the reaction kettle to 85°C, and pump a sodium sulfite solution with a mass concentration of 17% into the mother liquor for lithium precipitation in the reaction kettle at a flow rate of 1.4 mL / min using a peristaltic pump. The amount of substance of sodium sulfite is 0.5 times the amount of substance of lithium in the mother liquor for lithium precipitation. Carry out lithium extraction by continuously reacting for 150 min at a stirring rate of 600 rpm. Filter the slurry after the lithium extraction reaction to obtain the solution after lithium extraction and the residue after lithium extraction respectively. The solution after lithium extraction is discharged as wastewater.

[0053] The XRD pattern of the residue after lithium extraction is as Figure 2As shown. It can be seen from the figure that the main phase in the slag after lithium extraction of the present invention is lithium iron phosphate.

[0054] Example 2

[0055] This example provides a method for recovering lithium from the lithium carbonate precipitation mother liquor. The recovery method includes the following steps:

[0056] (1) Weigh the leaching residue of lithium iron phosphate electrode powder and add it to a reaction kettle containing 3.5 L of open-circuit lithium carbonate precipitation mother liquor at a stirring rate of 600 rpm to obtain a mixed material. Among them, the lithium concentration in the precipitation mother liquor is 3.4 g / L, the pH is 10, and the CO3 2- concentration is 17.9 g / L; the pH of the mixed material is 9, and the molar amount of iron element in the leaching residue of lithium iron phosphate electrode powder is 1.3 times that of lithium in the precipitation mother liquor (Fe:Li = 1.3);

[0057] (2) Heat the reaction kettle to 85 °C, and pump a sodium sulfite solution with a mass concentration of 22% into the precipitation mother liquor in the reaction kettle at a flow rate of 3.3 mL / min using a peristaltic pump. The amount of substance of sodium sulfite is 0.5 times that of lithium in the precipitation mother liquor. Carry out lithium extraction by continuously reacting for 150 min at a stirring rate of 800 rpm. Filter the slurry after the lithium extraction reaction to obtain the lithium-extracted solution and the lithium-extracted residue respectively. The lithium-extracted solution is discharged as wastewater.

[0058] Example 3

[0059] This example provides a method for recovering lithium from the lithium carbonate precipitation mother liquor. The recovery method includes the following steps:

[0060] (1) Weigh the leaching residue of lithium iron phosphate battery powder and add it to a reaction kettle containing 1.5 L of open-circuit lithium carbonate precipitation mother liquor at a stirring rate of 600 rpm to obtain a mixed material. Among them, the lithium concentration in the precipitation mother liquor is 3 g / L, the pH is 12, and the CO3 2- concentration is 16.6 g / L; the pH of the mixed material is 8.5, and the molar amount of iron element in the leaching residue of lithium iron phosphate battery powder is 1.8 times that of lithium in the precipitation mother liquor (Fe:Li = 1.8);

[0061] (2) Heat the reaction kettle to 85 °C, and pump a sodium sulfite solution with a mass concentration of 17% into the precipitation mother liquor in the reaction kettle at a flow rate of 1.3 mL / min using a peristaltic pump. The amount of substance of sodium sulfite is 0.5 times that of lithium in the precipitation mother liquor. Carry out lithium extraction by continuously reacting for 150 min at a stirring rate of 800 rpm. Filter the slurry after the lithium extraction reaction to obtain the lithium-extracted solution and the lithium-extracted residue respectively. The lithium-extracted solution is discharged as wastewater.

[0062] Example 4

[0063] This embodiment provides a method for recovering lithium from the lithium precipitation mother liquor of lithium carbonate, and the recovery method includes the following steps:

[0064] (1) Weigh the leaching residue of lithium iron phosphate electrode powder. At a stirring rate of 600 rpm, add it to a reaction kettle containing 1.5 L of the primary lithium precipitation mother liquor of lithium carbonate to obtain a mixed material. Among them, the lithium concentration in the lithium precipitation mother liquor is 2.4 g / L, the pH is 11, and the CO3 2- concentration is 13.9 g / L; the pH of the mixed material is 8.5, and the molar amount of iron element in the leaching residue of lithium iron phosphate electrode powder is 1.5 times that of lithium in the lithium precipitation mother liquor (Fe:Li = 1.5);

[0065] (2) Heat the reaction kettle to 85 °C, and use a peristaltic pump to pump the sodium sulfite solution with a mass concentration of 17% into the lithium precipitation mother liquor in the reaction kettle at a flow rate of 1.3 mL / min. The amount of substance of sodium sulfite is 0.5 times that of lithium in the lithium precipitation mother liquor. Carry out lithium extraction by continuously reacting for 150 min at a stirring rate of 800 rpm. Filter the slurry after the lithium extraction reaction to obtain the lithium extraction post-liquid and the lithium extraction post-residue respectively. The lithium extraction post-liquid is discharged as wastewater.

[0066] Example 5

[0067] The difference between this embodiment and Example 3 is only that the molar amount of iron element in the leaching residue of lithium iron phosphate battery powder is 1.6 times that of lithium in the lithium precipitation mother liquor (Fe:Li = 1.6), and other conditions and parameters are exactly the same as those in Example 3.

[0068] Example 6

[0069] The difference between this embodiment and Example 1 is only that the flow rate of the sodium sulfite solution is 0.5 mL / min, and other conditions and parameters are exactly the same as those in Example 1.

[0070] Example 7

[0071] The difference between this embodiment and Example 1 is only that the flow rate of the sodium sulfite solution is 5 mL / min, and other conditions and parameters are exactly the same as those in Example 1.

[0072] Example 8

[0073] The difference between this embodiment and Example 1 is only that the reaction kettle is heated to 75 °C, and other conditions and parameters are exactly the same as those in Example 1.

[0074] Example 9

[0075] The difference between this embodiment and Example 1 is only that the reaction kettle is heated to 90 °C, and other conditions and parameters are exactly the same as those in Example 1.

[0076] Example 10

[0077] The difference between this example and Example 1 is only that the sodium sulfite solution is replaced with the sodium thiosulfate solution, and other conditions and parameters are exactly the same as those in Example 1.

[0078] Comparative Example 1

[0079] The difference between this comparative example and Example 1 is only that sodium sulfite is directly added to the mixed materials, and other conditions and parameters are exactly the same as those in Example 1.

[0080] Performance test:

[0081] The lithium concentration in the lithium-extracted solution, the lithium concentration in the lithium carbonate precipitation mother liquor, and the lithium content percentage in the lithium-extracted residue obtained from the examples and comparative examples are tested by atomic absorption spectrometry, and the lithium extraction rate is calculated. Among them, the lithium extraction rate (%) = 1 - (the volume of the lithium-extracted solution × the lithium concentration in the lithium-extracted solution) / (the volume of the lithium carbonate precipitation mother liquor × the lithium concentration in the lithium carbonate precipitation mother liquor)) × 100%. The test results are shown in Table 1:

[0082] Table 1

[0083]

[0084]

[0085] It can be seen from Table 1 that from Examples 1-10, it can be obtained that the present invention uses the lithium iron phosphate leaching residue as the lithium extraction carrier, and uses reducing agents such as sodium sulfite to carry out redox reactions for lithium extraction. By adjusting conditions such as the excess coefficient of the leaching residue, that is, the molar ratio of iron elements in the lithium iron phosphate leaching residue to the molar ratio of lithium elements in the lithium carbonate precipitation mother liquor, the reaction temperature, and the addition rate of the reducing agent, metal lithium in the lithium precipitation mother liquor can be effectively recovered to obtain a lithium-rich lithium extraction residue. Among them, the lithium extraction effect of the lithium iron phosphate electrode powder leaching residue is better than that of the lithium iron phosphate battery powder leaching residue (there are differences in the proportion of iron phosphate). The lithium concentration in the lithium-extracted solution obtained by the recovery method provided by the present invention can reach within 0.40 g / L, the lithium content percentage in the lithium-extracted residue can reach more than 1.47% (the lithium content percentage in the lithium-extracted residue of the battery-grade lithium iron phosphate can reach 0.81%), and the lithium extraction rate can reach more than 85.3% (up to more than 99% at most).

[0086] By comparison of Example 3 and Example 5, it can be seen that in the method for recovering lithium from lithium carbonate mother liquor of the present invention, the amount of lithium iron phosphate leaching residue added will affect the recovery effect, and the amount of the lithium iron phosphate leaching residue added needs to be adjusted according to its type. The lithium iron phosphate leaching residue is lithium iron phosphate battery powder leaching residue, and the molar ratio of the iron element in the lithium iron phosphate leaching residue to the lithium element in the lithium carbonate mother liquor is controlled at (1.7-1.8): 1, and the recovery effect is better. If it is too low, the effective iron phosphate component in the leaching residue is insufficient, resulting in poor lithium extraction effect. If it is too high, it causes waste.

[0087] A comparison of Example 1 and Examples 6-7 shows that the flow rate of the sodium sulfite solution affects the recovery effect. If the flow rate of the sodium sulfite solution is too fast, localized reactions will occur, and the local pH will drop rapidly, thus affecting the lithium extraction effect. If the flow rate of the sodium sulfite solution is too slow, the lithium extraction rate will not increase significantly and the feeding time will be too long. Taking all factors into consideration, it is recommended to control the flow rate of the sodium sulfite solution between 1 mL / min and 4 mL / min for better recovery effect.

[0088] By comparing Example 1 with Examples 8-9, it can be seen that the heating temperature of the lithium extraction reaction affects the reaction rate and thus affects the recovery effect. When the heating temperature is controlled at 80°C to 85°C, the recovery effect is better. If the heating temperature is too high, the energy consumption is large and the decomposition rate of sodium sulfite is accelerated, which is not conducive to the lithium extraction reaction. If the heating temperature is too low, the reaction rate is slow, which is not conducive to improving the lithium recovery rate.

[0089] A comparison of Examples 1 and 10 shows that the choice of reducing agent in the present invention significantly affects the recovery efficiency. Compared with sodium sulfite, the lithium extraction efficiency of sodium thiosulfate as a reducing agent is significantly worse under the same conditions. This is due to the relatively weak reducing properties of sodium thiosulfate. In addition, the oxidation product of sodium sulfite is harmless sodium sulfate, while sodium thiosulfate easily produces byproducts such as elemental sulfur, which is detrimental to subsequent processes.

[0090] By comparing Example 1 and Comparative Example 1, it can be seen that the slow addition of the reducing agent solution in the present invention is conducive to stable reaction and better lithium extraction effect; while the direct addition of the reducing agent solid will cause local overacidity, and the sodium sulfite is easily decomposed to produce sulfur dioxide that escapes and thus affects the lithium extraction effect.

[0091] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for recovering lithium from the mother liquor of lithium carbonate precipitation, characterized in that, The recovery method includes the following steps: (1) Mix the lithium iron phosphate leaching residue with the lithium carbonate lithium precipitation mother liquor to obtain a mixed material; (2) After heating the mixed material, introduce a reducing agent solution to carry out the lithium extraction reaction, and obtain the post-lithium extraction solution and the post-lithium extraction residue through post-treatment.

2. The recovery method according to claim 1, wherein The lithium iron phosphate leaching residue described in step (1) includes the lithium iron phosphate battery powder leaching residue and / or the lithium iron phosphate electrode powder leaching residue; Preferably, the lithium carbonate lithium precipitation mother liquor described in step (1) includes the primary lithium carbonate lithium precipitation mother liquor and / or the open-circuit lithium carbonate lithium precipitation mother liquor, preferably the open-circuit lithium carbonate lithium precipitation mother liquor; Preferably, the pH of the lithium carbonate lithium precipitation mother liquor described in step (1) is 10-12.

3. The recycling method according to claim 1 or 2, characterized in that, The molar ratio of iron element in the lithium iron phosphate leaching residue to lithium element in the lithium carbonate lithium precipitation mother liquor in step (1) is (1.3-1.8):1; Preferably, the lithium iron phosphate leaching residue is the lithium iron phosphate battery powder leaching residue, and the molar ratio of iron element in the lithium iron phosphate leaching residue to lithium element in the lithium carbonate lithium precipitation mother liquor is (1.7-1.8):1; Preferably, the lithium iron phosphate leaching residue is the lithium iron phosphate electrode powder leaching residue, and the molar ratio of iron element in the lithium iron phosphate leaching residue to lithium element in the lithium carbonate lithium precipitation mother liquor is (1.3-1.5):1; Preferably, stirring is carried out during the mixing process in step (1); Preferably, the stirring speed is 600 rpm - 800 rpm.

4. The recovery method according to any one of claims 1 to 3, characterized in that, The pH of the mixed material described in step (1) is 8-9.

5. The recovery method according to any one of claims 1-4, characterized in that, The heating temperature in step (2) is 80°C - 85°C.

6. The recovery method according to any one of claims 1-5, characterized in that, The solute of the reducing agent solution described in step (2) includes any one or a combination of at least two of sodium sulfite, potassium sulfite, sodium thiosulfate or sodium sulfide, preferably sodium sulfite and / or potassium sulfite; Preferably, the mass percentage concentration of the reducing agent solution described in step (2) is 15% - 26%.

7. The recovery method according to any one of claims 1-6, characterized in that, The molar ratio of the solute in the reducing agent solution to lithium in the lithium carbonate lithium precipitation mother liquor in step (2) is (0.4-0.6):

1.

8. The recovery method according to any one of claims 1 to 7, characterized in that, During the lithium extraction reaction in step (2), the flow rate of the reducing agent solution is 1 mL / min - 4 mL / min; Preferably, the lithium extraction reaction time in step (2) is 120 min - 150 min.

9. The recovery method according to any one of claims 1-8, characterized in that, Stirring is carried out during the lithium extraction reaction in step (2); Preferably, the stirring speed is 600 rpm - 800 rpm.

10. The recovery method according to any one of claims 1-9, characterized in that, The post-treatment in step (2) includes solid-liquid separation; Preferably, the solid-liquid separation method includes filtration and / or centrifugal separation.

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