A gradient washing method of cobalt carbonate

Abstract

The application provides a gradient washing method of cobalt carbonate, which comprises the following steps: first washing cobalt carbonate by using a washing liquid with a temperature of T1 at a flow rate of v1; then continuing to wash by using a washing liquid with a temperature of T2 at a flow rate of v2, and performing solid-liquid separation after the second washing to obtain washed cobalt carbonate; wherein T2 is less than T1, and v2 is greater than v1. The gradient washing method of cobalt carbonate can not only significantly reduce water consumption and energy consumption in the washing process, realize efficient and uniform removal of impurities, but also can simultaneously maintain the sphericity and surface state of cobalt carbonate particles by the cooperation of high-temperature low-flow and low-temperature high-flow washing.

Description

Technical Field

[0001] This invention belongs to the field of cobalt carbonate preparation technology, and relates to a gradient washing method for cobalt carbonate. Background Technology

[0002] Cobalt carbonate (CoCO3) is a key precursor for the preparation of lithium cobalt oxide, a high-performance cathode material for lithium-ion batteries. Industrially, it is typically synthesized via liquid-phase precipitation using soluble cobalt salts (such as cobalt chloride and cobalt sulfate) and precipitants (such as ammonium bicarbonate). However, this process inevitably introduces a large amount of anionic impurities, such as chloride ions (Cl...). - ) or sulfate ions (SO4) 2- If these impurities remain in the precursor, they will cause a series of problems in the subsequent high-temperature calcination process, such as Cl... - It may corrode equipment and produce toxic gases, SO4. 2- Difficult to completely decompose, residual sulfur will degrade the electrochemical performance of the final cathode material, accelerate battery capacity decay, and pose safety hazards. Therefore, washing is a crucial impurity removal process in the preparation of cobalt carbonate.

[0003] Currently, the commonly used cobalt carbonate washing process in industrial production is "constant temperature, constant volume, and intermittent washing." The specific operation typically involves placing the cobalt carbonate slurry in a centrifuge and, at a fixed speed, using a constant temperature and a fixed volume of washing liquid for multiple cycles of "water intake-washing-separation." This traditional process has the following inherent drawbacks:

[0004] High water and energy consumption: To ensure that the concentration of impurities is reduced to below the standard, a large amount of washing water is often required for repeated dilution, resulting in high water treatment costs. If heated washing is used, maintaining a constant temperature throughout the process leads to high heat energy consumption.

[0005] The washing effect is uneven, and there is a "weakest link effect": because the filter cake forms a radial density gradient under the centrifugal force field, the constant temperature and constant amount of washing water cannot penetrate the entire filter cake evenly, resulting in excessive local impurity residue and uneven overall product quality.

[0006] Balancing impurity removal and morphology protection is challenging: the washing process involves not only physical impurity removal but also complex physicochemical changes. Enhancement measures taken to improve impurity removal efficiency often negatively impact the morphology of cobalt carbonate particles, such as increasing temperature, extending washing time, and increasing rotation speed. For example, excessively high temperatures or washing times can exacerbate the dissolution-recrystallization process on the particle surface, inducing particle segregation; excessively high centrifuge speeds may produce fine powder. These morphological degradations directly reduce the tap density and processing performance of the precursor, and are inherited by the final product, impairing the battery's energy density and cycle life.

[0007] Therefore, developing a washing method that can achieve deep impurity removal, high efficiency and energy saving, and maintain the morphology of cobalt carbonate particles has become an urgent need to improve the quality of lithium-ion battery cathode material precursors and production economic benefits. Summary of the Invention

[0008] The purpose of this invention is to provide a gradient washing method for cobalt carbonate. This gradient washing method for cobalt carbonate, through the combination of high temperature and low flow rate and low temperature and high flow rate washing, can not only significantly reduce water and energy consumption in the washing process and achieve efficient and uniform removal of impurities, but also maintain the sphericity and surface condition of cobalt carbonate particles.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] This invention provides a gradient washing method for cobalt carbonate, the method comprising the following steps:

[0011] First, cobalt carbonate is washed with a washing solution at temperature T1 and a flow rate of v1.

[0012] Then, a second washing is performed using a washing solution at temperature T2 and a flow rate of v2. After the second washing is completed, solid-liquid separation is performed to obtain washed cobalt carbonate.

[0013] T2 < T1, and v2 > v1.

[0014] In the gradient washing method described in this invention, high-temperature, low-flow-rate washing is performed first, followed by low-temperature, high-flow-rate washing. The high temperature significantly reduces the viscosity of the wash water, thereby significantly increasing the viscosity of impurity ions (Cl). - SO4 2- The diffusion coefficient of the particle is high, which enables efficient desorption and rapid diffusion of impurities on the particle surface and in shallow pores at a relatively small washing flow rate. On this basis, a large amount of low-temperature washing water is used for rapid rinsing and dilution. The low temperature helps to inhibit the dissolution and recrystallization activity on the particle surface and avoid morphological deterioration. The large flow rate ensures that the high concentration of impurities washed out in the first stage is quickly carried away from the system, achieving uniform washing and allowing the washing liquid to fully penetrate cobalt carbonate.

[0015] Preferably, both the washing solution at temperature T1 and the washing solution at temperature T2 are deionized water.

[0016] Preferably, T2≤T1-30℃ (meaning T2≤T1 minus 30℃) can be, for example, T1-30℃, T1-35℃, T1-40℃ or T1-45℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0017] The temperature difference between the washing liquid temperature T1 in the first stage and the washing liquid temperature T2 in the second stage of this invention is more than 30°C, which can promote the efficient desorption and rapid diffusion of impurities at high temperatures, and further prevent the particle morphology from being destroyed at low temperatures.

[0018] Preferably, T1 is 50℃~80℃, for example, it can be 50℃, 60℃, 70℃ or 80℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] Preferably, T2 is 20℃~50℃, for example, it can be 20℃, 30℃, 40℃ or 50℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 20℃~50℃.

[0020] Preferably, v2 ≥ (1.2~2)×v1 (meaning v2 ≥ 1.2 to 2 times v1), for example, can be 1.2×v1, 1.4×v1, 1.6×v1, 1.8×v1 or 2×v1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] The washing flow rate v1 in the first stage of this invention is relatively smaller than the washing flow rate v2 in the second stage, in order to meet the principle that the first stage penetrates and replaces most of the free pore liquid in cobalt carbonate and forms a strong mass transfer driving force for surface adsorbed impurities.

[0022] Preferably, v1 is 50L / min to 100L / min, for example, it can be 50L / min, 60L / min, 70L / min, 80L / min, 90L / min or 100L / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] Preferably, the amount of washing liquid at temperature T2 is V2', the amount of washing liquid at temperature T1 is V1', and V2' > V1'.

[0024] The amount of washing liquid used in the first stage of this invention is less than that used in the second stage. That is, by optimizing the combination of high temperature and low usage and low temperature and high usage, compared with traditional constant temperature washing, energy consumption is saved while achieving the same impurity index. At the same time, due to the improved mass transfer efficiency, the total water consumption is reduced, thereby reducing production costs and environmental burden.

[0025] Preferably, V2'≥(2~6)×V1' (meaning V2'≥2 to 6 times V1') can be, for example, 2×V1', 3×V1', 4×V1', 5×V1' or 6×V1', but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] Preferably, the mass of the cobalt carbonate is m, and V1' = K1 × m (where V1' and m correspond in unit, i.e., when V1' is in L, m is in kg, and when V1' is in mL, m is in g), and K1 is 1.2 to 3.0, for example, it can be 1.2, 1.5, 2.0, 2.5 or 3.0, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] Preferably, the method for preparing cobalt carbonate includes the following steps:

[0028] The cobalt source solution and ammonium bicarbonate solution are passed into the base liquid to carry out a precipitation reaction, thereby obtaining the cobalt carbonate.

[0029] Preferably, the cobalt source solution includes cobalt ions and doped metal ions, wherein the doped metal ions include any one or a combination of at least two of Mg ions, Al ions, Ti ions, Ni ions or Mn ions.

[0030] Preferably, the cobalt source in the cobalt source solution includes cobalt chloride and / or cobalt sulfate.

[0031] Preferably, in the cobalt carbonate, based on the molar amount of cobalt ions, the doping amount of the doped metal ions is 1000ppm to 15000ppm, for example, it can be 1000ppm, 5000ppm, 10000ppm or 15000ppm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, during the precipitation reaction, the reaction is carried out at a temperature of t1 until 1 / 2 to 3 / 4 of the target particle size is reached, for example, 1 / 2, 3 / 5, 2 / 3, 5 / 7, or 3 / 4. Specifically, 1 / 2 to 3 / 4 of the target particle size is 2 to 14 μm, for example, 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, or 14 μm. Then, the reaction is carried out at a temperature of t2 until the target particle size is reached, where the particle size D50 is 3-21 μm, for example, 3 μm, 6 μm, 9 μm, 12 μm, 15 μm, 18 μm, or 21 μm, wherein t2 > t1.

[0033] In this invention, the temperature is increased in the later stage of the precipitation reaction for preparing cobalt carbonate, resulting in strong crystallinity on the particle surface. This change in surface state enhances the mechanical strength of the particles and reduces the liquid bridging force and van der Waals force between particles, making them less prone to segregation under the fluid shearing action of subsequent gradient washing, thus improving their washability.

[0034] Preferably, t2 is 45℃~50℃, for example, it can be 45℃, 46℃, 47℃, 48℃, 49℃ or 50℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] Preferably, t1 is 35℃~40℃, for example, it can be 35℃, 36℃, 37℃, 38℃, 39℃ or 40℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] Preferably, the pH of the precipitation reaction is 7 to 8, for example, 7, 7.2, 7.4, 7.6, 7.8 or 8, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, the base liquid comprises an ammonium bicarbonate solution.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The present invention utilizes high temperature to significantly reduce the viscosity of the washing water and significantly improve the diffusion coefficient of impurity ions. Under relatively small washing flow rate, it achieves efficient desorption and rapid diffusion of impurities on the particle surface and in shallow pores. On this basis, a large amount of low temperature washing water is used for rapid rinsing and dilution. Low temperature helps to inhibit the dissolution and recrystallization activity on the particle surface and avoid morphological deterioration. Large flow rate ensures that the high concentration of impurities washed out in the first stage is quickly carried away from the system, achieving uniform washing and allowing the washing liquid to fully penetrate cobalt carbonate.

[0040] (2) By combining high temperature and low usage with low temperature and high usage, this invention saves energy consumption compared to traditional constant temperature washing, while achieving the same impurity index. At the same time, due to the improved mass transfer efficiency, the total water consumption is reduced, thus reducing production costs and environmental burden.

[0041] (3) This invention achieves deep removal of impurities and excellent preservation of particle morphology by using a gradient washing process of high temperature and low quantity deep impurity removal + low temperature and high quantity shape preservation and homogenization, combined with specially made washable cobalt carbonate, and significantly reduces energy consumption and water consumption, which is conducive to improving the overall performance of precursor and final battery materials. Detailed Implementation

[0042] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0043] Example 1

[0044] This embodiment provides a gradient washing method for cobalt carbonate, the gradient washing method comprising the following steps:

[0045] (1) A cobalt source solution was prepared using cobalt sulfate and aluminum sulfate as raw materials. An ammonium bicarbonate solution was used as a precipitant. The cobalt source solution and the ammonium bicarbonate solution were passed into the bottom liquid (ammonium bicarbonate solution). The precipitation reaction was carried out at 37°C until the particle size D50 was 14 μm. The precipitation reaction was carried out at 45°C until the particle size D50 was 18.5 μm. The pH of the precipitation reaction was controlled at 7.5. An aluminum-doped cobalt carbonate slurry was prepared. The doping amount of the doped metal ions was 4000 ppm, based on the molar amount of cobalt ions.

[0046] (2) Start the centrifuge to the set speed, and pass the aluminum-doped cobalt carbonate slurry (dry basis m=50kg) described in step (1) into the centrifuge to separate the mother liquor and form a cobalt carbonate filter cake;

[0047] First stage washing: Deionized water at 75℃ (T1) is used to wash the cobalt carbonate filter cake at a flow rate of 50 L / min (v1), with a total water consumption of V1' = 0.1 m³. 3 (K1=2).

[0048] Second stage washing: Use deionized water at a temperature of 40℃ (T2, T2 = T1 - 35℃) and continue washing at a flow rate of 100L / min (v2, v2 = 2 × v1). The total water consumption is V2' = 0.4m³. 3 (V2'=4×V1');

[0049] After washing, centrifugation was performed to obtain cobalt carbonate filter cake.

[0050] Example 2

[0051] This embodiment provides a gradient washing method for cobalt carbonate, the gradient washing method comprising the following steps:

[0052] (1) A cobalt source solution was prepared using cobalt sulfate and aluminum sulfate as raw materials. An ammonium bicarbonate solution was used as a precipitant. The cobalt source solution and the ammonium bicarbonate solution were passed into the bottom liquid (ammonium bicarbonate solution). The precipitation reaction was carried out at 40°C until the particle size D50 was 15 μm. The precipitation reaction was carried out at 50°C until the particle size D50 was 20 μm. The pH of the precipitation reaction was controlled at 7.2. An aluminum-doped cobalt carbonate slurry was prepared. The doping amount of the doped metal ions was 1000 ppm, based on the molar amount of cobalt ions.

[0053] (2) Start the centrifuge to the set speed, and pass the aluminum-doped cobalt carbonate slurry (dry basis m=50kg) described in step (1) into the centrifuge to separate the mother liquor and form a cobalt carbonate filter cake;

[0054] First stage washing: Deionized water at 50℃ (T1) is used to wash the cobalt carbonate filter cake at a flow rate of 80 L / min (v1), with a total water consumption of V1' = 0.15 m³. 3 (K1=3).

[0055] Second stage washing: Use deionized water at a temperature of 20℃ (T2, T2 = T1 - 30℃) and continue washing at a flow rate of 160L / min (v2, v2 = 2 × v1). The total water consumption is V2' = 0.3m³. 3 (V2'=2×V1');

[0056] After washing, centrifugation was performed to obtain cobalt carbonate filter cake.

[0057] Example 3

[0058] This embodiment provides a gradient washing method for cobalt carbonate, the gradient washing method comprising the following steps:

[0059] (1) A cobalt source solution was prepared using cobalt sulfate and aluminum sulfate as raw materials. An ammonium bicarbonate solution was used as a precipitant. The cobalt source solution and the ammonium bicarbonate solution were passed into the bottom liquid (ammonium bicarbonate solution). The precipitation reaction was carried out at 35°C until the particle size D50 was 13 μm. The precipitation reaction was carried out at 45°C until the particle size D50 was 16 μm. The pH of the precipitation reaction was controlled at 8. An aluminum-doped cobalt carbonate slurry was prepared. The doping amount of the doped metal ions was 15000 ppm, based on the molar amount of cobalt ions.

[0060] (2) Start the centrifuge to the set speed, and pass the aluminum-doped cobalt carbonate slurry (dry basis m=50kg) described in step (1) into the centrifuge to separate the mother liquor and form a cobalt carbonate filter cake;

[0061] First stage washing: Deionized water at 80℃ (T1) is used to wash the cobalt carbonate filter cake at a flow rate of 50 L / min (v1), with a total water consumption of V1' = 0.06 m³. 3 (K1=1.2).

[0062] Second stage washing: Use deionized water at a temperature of 30℃ (T2, T2 = T1 - 50℃) and continue washing at a flow rate of 60L / min (v2, v2 = 1.2 × v1). The total water consumption is V2' = 0.36m³. 3 (V2'=6×V1');

[0063] After washing, centrifugation was performed to obtain cobalt carbonate filter cake.

[0064] Example 4

[0065] This embodiment provides a gradient washing method for cobalt carbonate. Except for T1 being 45°C and T2 being T1-5°C, the gradient washing method is the same as in Embodiment 1.

[0066] Example 5

[0067] This embodiment provides a gradient washing method for cobalt carbonate. The gradient washing method is the same as that in Example 1, except that T2 is 60°C and T2 = T1 - 15°C.

[0068] Example 6

[0069] This embodiment provides a gradient washing method for cobalt carbonate. The gradient washing method is the same as that in Embodiment 1, except that v2 is 120 L / min and v2 = 2.4 × v1.

[0070] Example 7

[0071] This embodiment provides a gradient washing method for cobalt carbonate. The gradient washing method is the same as that in Embodiment 1, except that v2 is 55 L / min and v2 = 1.1 × v1.

[0072] Comparative Example 1

[0073] This comparative example provides a method for washing cobalt carbonate, the method comprising the following steps:

[0074] The same aluminum-doped cobalt carbonate slurry as in Example 1 was passed into a centrifuge to separate the mother liquor, forming a cobalt carbonate filter cake. The filter cake was washed and separated using deionized water at 30°C at a fixed flow rate of 150 L / min each time, and this washing was repeated twice. The water volume for each wash was 0.5 m³. 3 The total water consumption is 1m³ 3 After washing, centrifugation is performed to obtain cobalt carbonate filter cake.

[0075] Comparative Example 2

[0076] This comparative example provides a method for washing cobalt carbonate, the method comprising the following steps:

[0077] The same aluminum-doped cobalt carbonate slurry as in Example 1 was passed into a centrifuge to separate the mother liquor, forming a cobalt carbonate filter cake. The filter cake was washed and separated using deionized water at 90°C at a fixed flow rate of 50 L / min each time, and this washing was repeated twice. The water volume for each wash was 0.1 m³. 3 The total water consumption is 0.2m³. 3 After washing, centrifugation is performed to obtain cobalt carbonate filter cake.

[0078] The chlorine content, sulfur content, and morphological segregation of the cobalt carbonate filter cakes obtained in the above examples and comparative examples are shown in Table 1:

[0079] Table 1

[0080]

[0081] As can be seen from Table 1 above:

[0082] As can be seen from Examples 1-3 and Comparative Examples 1-2, the gradient washing method of the present invention not only has excellent impurity removal effect compared with the traditional washing method, but also does not cause significant segregation of particle morphology. At the same time, the total water consumption is reduced, thus lowering production costs. As can be seen from Examples 1 and Examples 4-5, if the washing temperature in the first stage is too low, or the washing temperature in the second stage is too high, and the temperature difference between the two stages is too small, the synergistic effect of high temperature and low flow rate and low temperature and high flow rate will decrease, affecting the final washing effect. Similarly, as can be seen from Examples 1 and Examples 6-7, if the flow rate of the second stage washing is too low or too high, the gradient washing effect of high temperature and low flow rate and low temperature and high flow rate will decrease.

[0083] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A gradient washing method for cobalt carbonate, characterized in that, The gradient washing method for cobalt carbonate includes the following steps: First, cobalt carbonate is washed with a washing solution at temperature T1 and a flow rate of v1. Then, a second washing is performed using a washing solution at temperature T2 and a flow rate of v2. After the second washing is completed, solid-liquid separation is performed to obtain washed cobalt carbonate. T2 < T1, and v2 > v1.

2. The gradient washing method for cobalt carbonate according to claim 1, characterized in that, The temperature T2 ≤ T1 - 30℃.

3. The gradient washing method for cobalt carbonate according to claim 1 or 2, characterized in that, The temperature T1 is 50℃~80℃; Preferably, T2 is 20℃~50℃.

4. The gradient washing method for cobalt carbonate according to claim 1 or 2, characterized in that, The v2 ≥ (1.2~2) × v1; Preferably, v1 is 50L / min to 100L / min.

5. The gradient washing method for cobalt carbonate according to claim 1 or 2, characterized in that, The amount of washing liquid used at temperature T2 is V2', the amount of washing liquid used at temperature T1 is V1', and V2' > V1'.

6. The gradient washing method for cobalt carbonate according to claim 5, characterized in that, The V2'≥(2~6)×V1'; Preferably, the mass of the cobalt carbonate is m, and V1' = K1 × m, where K1 is 1.2 to 3.

0.

7. The gradient washing method for cobalt carbonate according to claim 1 or 2, characterized in that, The method for preparing cobalt carbonate includes the following steps: The cobalt source solution and ammonium bicarbonate solution are passed into the base liquid to carry out a precipitation reaction, thereby obtaining the cobalt carbonate.

8. The gradient washing method for cobalt carbonate according to claim 7, characterized in that, The cobalt source solution includes cobalt ions and doped metal ions, wherein the doped metal ions include any one or a combination of at least two of Mg ions, Al ions, Ti ions, Ni ions or Mn ions; Preferably, in the cobalt carbonate, the doping amount of the doped metal ions is 1000ppm to 15000ppm, based on the molar amount of cobalt ions.

9. The gradient washing method for cobalt carbonate according to claim 7 or 8, characterized in that, During the precipitation reaction, the particles are reacted at a temperature of t1 until they reach 1 / 2 to 3 / 4 of the target particle size, and then reacted at a temperature of t2 until they reach the target particle size, wherein t2 > t1; Preferably, t2 is 45℃~50℃; Preferably, t1 is 35℃~40℃.

10. The gradient washing method for cobalt carbonate according to claim 7 or 8, characterized in that, The pH of the precipitation reaction is 7-8; Preferably, the base liquid comprises an ammonium bicarbonate solution.

Images