Method for realizing selective recovery of cobalt and efficient leaching of lithium in lithium cobalt oxide in one step by using natural eutectic solvent

Abstract

The invention discloses a method for realizing selective recovery of cobalt and efficient leaching of lithium in lithium cobalt oxide in one step by using a natural eutectic solvent, and relates to the field of lithium battery metal recovery. A natural DES system based on amino acid is used for leaching the lithium cobalt oxide positive electrode material, the provided natural DES system can completely dissolve lithium cobalt oxide under the mild leaching condition, selective separation of lithium and cobalt in the liquid phase and the solid phase is achieved, and the advantages of being small in toxicity and high in safety are achieved. Comprising the following steps: preparation of a natural eutectic solvent, leaching of a lithium cobalt oxide positive electrode material, and recovery of valuable metals. According to the method, green, safe and mild reaction conditions are created for recycling valuable metal in the lithium cobalt oxide positive electrode material, use of a large number of precipitants in the recycling process is avoided, the metal recycling process is simplified, recycling energy consumption and cost are saved, and the method has good application prospects.

Description

Technical Field

[0001] The invention relates to the field of waste lithium-ion battery recovery and low eutectic solvents, and in particular to a method for realizing selective recovery of cobalt from lithium cobalt oxide and efficient leaching of lithium using a natural low eutectic solvent in one step. Background Art

[0002] With the rapid development of new energy industries such as grid energy storage, electric vehicles and electronic equipment, scarce lithium, cobalt and nickel have become key elements in the transition to clean energy. The ever-expanding application areas of lithium batteries and their limited service life have led to the rapid accumulation of a large number of retired batteries, and the world is gradually ushering in a peak in the retirement of waste lithium-ion batteries. Fluorine-containing substances, heavy metals, electrolytes and various organic auxiliary materials make waste lithium batteries a complex hazardous pollutant. Among them, waste active positive electrode materials account for 40% of the total lithium battery waste. It is worth noting that although the lattice structure of waste positive electrode materials is destroyed, the content of precious metals they contain is much higher than the grade of some natural ores. Therefore, the recycling of waste lithium battery positive electrodes is crucial to stabilizing the supply chain of precious metals such as lithium, cobalt and nickel and promoting the efficient and intensive use of natural resources, and has multiple economic, environmental and social benefits.

[0003] At present, the common waste positive electrode recycling processes include pyrometallurgy, hydrometallurgy and direct regeneration. Hydrometallurgy has become the current mainstream technical route due to its high metal recovery rate and product purity, but the use of a large number of harmful chemical reagents and the complex and delicate separation and purification process are key technical issues that need to be overcome in wet recycling. In recent years, deep eutectic solvents (DES) have shown great potential in the recycling of waste lithium battery positive electrodes due to their low vapor pressure, high chemical stability, no need for additional reducing agents and biodegradable properties. In particular, the DES system with acid-coordination and acid-reduction properties can easily transform high-priced precious metals in waste positive electrode materials into low-priced states, promoting the efficient leaching and recovery of valuable metals such as lithium (Li), cobalt (Co), manganese (Mn), and nickel (Ni).

[0004] However, most DES solvents almost dissolve the precious metals in the waste cathode materials and disperse them in the leachate at the same time. Therefore, it is necessary to add additional precipitants to recover the valuable metals in the leachate in steps. The addition of precipitants will affect the solution environment of DES, thereby limiting the recycling of DES. In addition, the current DES systems generally have disadvantages such as high viscosity, slow reaction rate, and high reaction temperature. Although the new DES system based on alcohol substances overcomes the disadvantages of high viscosity and slow mass transfer, the occurrence of esterification side reactions still limits the leaching process. In addition, although DES based on guanidines and amides have good solubility for waste lithium battery cathodes, their significant disadvantage is that some compounds in the original components and final products still have potential genotoxicity.

[0005] In summary, constructing a DES system that can selectively recover valuable metals from natural ingredients such as sugars, polyols, and amino acids will have better recycling economy and environmental compatibility. Summary of the invention

[0006] In view of the above problems, the present invention proposes a method for realizing selective recovery of cobalt from lithium cobalt oxide and efficient leaching of lithium in one step using a natural low eutectic solvent, and utilizes a natural DES system based on amino acids to leach lithium cobalt oxide positive electrode materials. The provided natural DES system can completely dissolve lithium cobalt oxide under relatively mild leaching conditions, and realize selective separation of lithium and cobalt in liquid and solid phases, and also has the advantages of low toxicity and high safety.

[0007] The technical solution of the present invention is: comprising the following steps:

[0008] Step S1: mixing an amino acid as a hydrogen bond acceptor and an organic acid as a hydrogen bond donor in a molar ratio of 1:16 to 1:40, stirring at 60° C. until the mixture becomes colorless and transparent, and adding a diluent having a content of 0 to 40 wt % to reduce the viscosity, thereby preparing a natural deep eutectic solvent;

[0009] Step S2, mixing the lithium cobalt oxide positive electrode material with the natural deep eutectic solvent in step S1 at a solid-liquid ratio of 14.29 to 47.62 g / L, stirring for 3 to 8 hours at a leaching temperature of 60 to 110° C., so that the metal in the lithium cobalt oxide is leached to form a new solid-liquid mixed system;

[0010] Step S3, separating the solid-liquid mixture after leaching in step A2 to obtain a lithium-containing leaching solution and a pink leaching residue;

[0011] Step S4: The pink leached residue in step A3 is washed with anhydrous ethanol, dried, ground, and then air-roasted at 600° C. for 5 h to form black Co3O4 powder.

[0012] Furthermore, in step S1, the amino acid, organic acid and diluent are cysteine, lactic acid and deionized water respectively.

[0013] Preferably, the content of deionized water in step S1 is 5 wt %.

[0014] Preferably, the molar ratio of cysteine ​​to lactic acid in step S1 is 1:24.

[0015] Preferably, the stirring time in step S2 is 8 hours.

[0016] Preferably, the solid-to-liquid ratio in step S2 is 33.33 g / L.

[0017] Preferably, the leaching temperature in step S2 is 100°C.

[0018] The invention includes the preparation of a natural low eutectic solvent, the leaching of a lithium cobalt oxide positive electrode material, and the recovery of valuable metals. The low eutectic solvent synthesized from natural metabolites amino acids and organic acids can completely dissolve lithium cobalt oxide under mild conditions. After the solvent system composed of L-cysteine, lactic acid and a small amount of water dissolves the lithium cobalt oxide positive electrode material, a black lithium-containing leachate and a pink cobalt precipitate can be directly obtained by solid-liquid separation. The precipitate can be converted into Co3O4 after aerobic roasting.

[0019] The beneficial effects of the present invention are:

[0020] 1. The present invention uses natural metabolites amino acids and organic acids as monomer components to prepare a green, safe and efficient natural low eutectic solvent, and dissolves lithium cobalt oxide positive electrode powder at different monomer molar ratios, so that cobalt and lithium can be converted into solid and liquid phases respectively during the leaching process, directly realizing one-step recovery of cobalt and complete leaching of lithium.

[0021] 2. Compared with the H2SO4-H2O2 leaching combination commonly used in industry, the natural DES leaching scheme proposed in the present invention adopts green, safe and inexpensive cysteine ​​and lactic acid as monomer components, which can completely dissolve lithium cobalt oxide under mild conditions, effectively avoiding the corrosiveness, health risks and safety hazards brought by strong acids and strong oxidants. The leaching and recovery process is simple, less toxic and highly safe.

[0022] 3. The green, safe and efficient natural DES leaching scheme proposed in the present invention will further shorten the recovery process of positive electrode materials, avoid the use of large amounts of precipitants and cumbersome separation and purification steps, and reduce pollution and energy consumption in the recovery process of valuable metals.

[0023] 4. The present invention creates green, safe and mild reaction conditions for the recovery of valuable metals in lithium cobalt oxide positive electrode materials. It does not require additional reducing agents, high temperature and high pressure and other harsh reaction conditions. The process is simple and easy, which improves the efficiency and safety of resource recovery and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Flow chart of leaching lithium cobalt oxide cathode material for natural DES;

[0025] Figure 2 The black lithium-containing leaching solution and the pink cobalt-containing leaching residue after the lithium cobalt oxide is dissolved in Example 1 when the water content of DES is 30wt% (a), and the pink leaching residue after washing, drying and grinding (b);

[0026] Figure 3 This is the XRD diagram of the roasted product of the leached slag obtained when the moisture content of DES is 30wt% in Example 1. DETAILED DESCRIPTION

[0027] In order to clearly illustrate the technical features of this patent, this patent is elaborated in detail below through a specific implementation method and in combination with its accompanying drawings.

[0028] Embodiment 1:

[0029] This embodiment provides a method for realizing selective recovery of cobalt and efficient leaching of lithium from lithium cobalt oxide positive electrode materials in one step using a natural deep eutectic solvent, comprising the following steps:

[0030] S1. Preparation of natural DES: 1 g of cysteine ​​and lactic acid were mixed (molar ratio of 1:32), and stirred at 60°C for 30 min-1 h until the solution became clear and transparent. Then, deionized water of different contents (0-40 wt%) was added to the system, and the mixture was stirred at 60°C for 5-10 min to form a transparent solution, thereby preparing natural DES;

[0031] S2. Dissolution of lithium cobalt oxide: lithium cobalt oxide and natural DES were mixed at a solid-liquid ratio of 23.81:1 (g / L), and stirred at 80° C. for 6 h until the lithium cobalt oxide was completely dissolved to obtain a new solid-liquid mixed system;

[0032] S3, leaching effect analysis: the solid-liquid mixture is filtered to obtain a black leachate and a pink leachate residue, respectively, the concentrations of lithium and cobalt in the leachate are detected by ICP-OES, the pink leachate residue is washed with anhydrous ethanol, and the dry pink powder is collected after drying and grinding;

[0033] S4. Metal recovery: The pink powder was placed in a muffle furnace and calcined at 600° C. for 5 h to obtain a black solid product, and the black product was subjected to XRD analysis.

[0034] After leaching, the DES solvent changed from colorless and transparent to a dark black solution, and the black lithium cobalt oxide powder was completely dissolved and transformed into a pink precipitate.

[0035] Furthermore, the calculation formula for the leaching rate of metal elements in lithium cobalt oxide positive electrode materials is:

[0036]

[0037] Where η i represents the leaching rate (i represents Li or Co), C i (mg / L) represents the concentration of metal ions, V(L) represents the volume of the leaching solution, m i (mg) and w i They represent the mass proportion of lithium cobalt oxide and metal respectively.

[0038] Furthermore, the calculation formula of the separation coefficient ε of lithium and cobalt in the leaching solution is:

[0039]

[0040] The results (Table 1) show that when the content of deionized water in step S1 is 5wt%, the leaching effect is the best, the leaching rate of lithium can reach 99%, the leaching rate of cobalt is 19%, and the separation ratio of Li and Co reaches 5.179. The XRD test results show that the black product obtained by calcining the pink solid is Co3O4.

[0041] Table 1 Leaching efficiency and separation coefficient of metal elements in the leachate at different water contents.

[0042] Water content, wt% <![CDATA[η Li ]]> <![CDATA[η Co ]]> ε 0 89.99 18.05 4.987 5 99.73 19.26 5.179 10 99.55 24.53 4.059 20 101.52 35.20 2.884 40 102.21 89.23 1.146

[0043] Example 2

[0044] The difference between this embodiment and embodiment 1 is that in step S1, cysteine ​​and lactic acid are mixed in different molar ratios (1:16-1:32), and 5wt% of deionized water is added to form a series of DES, and other conditions remain unchanged, and the leaching effect of natural DES with different molar ratios on lithium cobalt oxide positive electrode materials is investigated. The results are shown in Table 2. When the molar ratio is 1:24, the leaching effect is the best, the leaching rate of lithium can reach 97%, and the leaching rate of cobalt is 19%.

[0045] Table 2 Leaching efficiency and separation coefficient of metal elements in leachate at different molar ratios

[0046]

[0047]

[0048] Example 3

[0049] The difference between this embodiment and embodiment 1 is that in step S1, cysteine ​​and lactic acid are mixed at a molar ratio of 1:24, and 5wt% of deionized water is added to prepare DES, and the stirring time in step S2 is set to 3-8h, and other conditions remain unchanged, and the effect of different leaching times on the leaching of natural DES into lithium cobalt oxide positive electrode materials is investigated. The results are shown in Table 3. When the leaching time is 8h, the leaching effect is the best, the leaching rate of lithium can reach 100%, the leaching rate of cobalt is 18%, and the separation ratio of Li and Co reaches 5.388.

[0050] Table 3 Leaching efficiency and separation coefficient of metal elements in the leaching solution at different leaching times

[0051] Leaching time <![CDATA[η Li ]]> <![CDATA[η Co ]]> ε 3 86.96 17.86 4.869 4 99.06 24.91 3.976 5 96.26 21.59 4.459 6 98.56 19.79 4.981 7 99.51 19.93 4.992 8 100.36 18.63 5.388

[0052] Example 4

[0053] The difference between this embodiment and embodiment 1 is that in step S1, cysteine ​​and lactic acid are mixed at a molar ratio of 1:24, and 5 wt% of deionized water is added to prepare DES, and the lithium cobalt oxide and natural DES in step S2 are leached at 80°C for 8 hours at a solid-liquid ratio of 14.286 to 47.619:1 (g / L), and other conditions remain unchanged. The effect of different solid-liquid ratios on the leaching of lithium cobalt oxide positive electrode materials by natural DES is investigated, and the results are shown in Table 4. When the solid-liquid ratio is 33.33 g / L, the leaching effect is the best, the leaching rate of lithium can reach 99%, the leaching rate of cobalt is 14%, and the separation ratio of Li and Co reaches 6.914.

[0054] Table 4 Leaching efficiency and separation coefficient of metal elements in the leachate at different solid-liquid ratios

[0055]

[0056]

[0057] Example 5

[0058] The difference between this embodiment and embodiment 1 is that in step S1, cysteine ​​and lactic acid are mixed at a molar ratio of 1:24, and 5 wt% of deionized water is added to prepare DES, and the lithium cobalt oxide and natural DES in step S2 are leached at 60-110°C for 8 hours at a solid-liquid ratio of 33.333 g / L, and other conditions remain unchanged, and the effect of different leaching temperatures on the leaching of lithium cobalt oxide positive electrode materials by natural DES is investigated, and the results are shown in Table 5. When the leaching temperature is 100°C, the leaching effect is the best, the leaching rate of lithium can reach 101%, the leaching rate of cobalt is 12%, and the separation ratio of Li and Co reaches 8.017.

[0059] Table 5 Leaching efficiency and separation coefficient of metal elements in the leachate at different leaching temperatures

[0060] Leaching temperature℃ <![CDATA[η Li ]]> <![CDATA[η Co ]]> ε 60 60.55 15.34 3.948 70 87.47 16.67 5.248 80 91.99 14.86 6.191 90 105.18 13.78 7.634 100 101.72 12.69 8.017 110 96.58 10.48 9.217

[0061] There are many specific implementation ways of the present invention. The above is only the preferred implementation mode of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements can be made without departing from the principle of the present invention. These improvements should also be regarded as the protection scope of the present invention.

Claims

1. A method for realizing selective recovery of cobalt from lithium cobalt oxide and efficient leaching of lithium using a natural deep eutectic solvent in one step, characterized in that: The following steps are involved: Step S1: mixing an amino acid as a hydrogen bond acceptor and an organic acid as a hydrogen bond donor in a molar ratio of 1:16 to 1:40, stirring at 60° C. until the mixture becomes colorless and transparent, and adding a diluent having a content of 0 to 40 wt % to reduce the viscosity, thereby preparing a natural deep eutectic solvent; Step S2, mixing the lithium cobalt oxide positive electrode material with the natural deep eutectic solvent in step S1 at a solid-liquid ratio of 14.29 to 47.62 g / L, stirring for 3 to 8 hours at a leaching temperature of 60 to 110° C., so that the metal in the lithium cobalt oxide is leached to form a new solid-liquid mixed system; Step S3, separating the solid-liquid mixture after leaching in step A2 to obtain a lithium-containing leaching solution and a pink leaching residue; Step S4: The pink leached residue in step A3 is washed with anhydrous ethanol, dried, ground, and then air-roasted at 600° C. for 5 h to form black Co3O4 powder.

2. The method for realizing selective recovery of cobalt from lithium cobalt oxide and efficient leaching of lithium using a natural deep eutectic solvent in one step according to claim 1, characterized in that: In step S1, the amino acid, organic acid and diluent are cysteine, lactic acid and deionized water respectively.

3. The method for realizing selective recovery of cobalt from lithium cobalt oxide and efficient leaching of lithium using a natural deep eutectic solvent in one step according to claim 2, characterized in that: The content of deionized water in step S1 is 5 wt %.

4. The method for realizing selective recovery of cobalt from lithium cobalt oxide and efficient leaching of lithium using a natural deep eutectic solvent in one step according to claim 2, characterized in that: The molar ratio of cysteine ​​to lactic acid in step S1 is 1:

24.

5. The method for realizing selective recovery of cobalt from lithium cobalt oxide and efficient leaching of lithium using a natural deep eutectic solvent in one step according to claim 2, characterized in that: The stirring time in step S2 is 8 h.

6. The method for realizing selective recovery of cobalt from lithium cobalt oxide and efficient leaching of lithium using a natural deep eutectic solvent in one step according to claim 2, characterized in that: The solid-liquid ratio in step S2 is 33.33 g / L.

7. The method for realizing selective recovery of cobalt from lithium cobalt oxide and efficient leaching of lithium using a natural deep eutectic solvent in one step according to claim 2, characterized in that: The leaching temperature in step S2 is 100°C.

Images