A continuous crystallization method for lithium carbonate

Abstract

The present invention discloses a method for continuous crystallization of lithium carbonate. The Na2CO3 solution and the LiCl solution enter a DTB crystallizer for crystallization. In the DTB crystallizer, the diameter of the draft tube is 44 - 55 mm, and the diameter of the baffle bucket is 70 - 95 mm; the distance from the bottom of the draft tube to the bottom of the baffle bucket is 20 - 60 cm; the distance between the lowest end of the stirring paddle and the lowest end of the DTB crystallizer is 50 - 65 mm; the LiCl solution and the Na2CO3 solution are respectively fed into the DTB crystallizer at a feeding rate of 3.0 - 10.0 ml / min and 9.0 - 30.0 ml / min, the discharging rate of the DTB crystallizer is 10.0 - 30.0 mL / min, and the rotation speed of the stirring paddle is 400 - 600 rpm. By using the method of the present invention, the particle size of lithium carbonate can meet the set requirements, and the production efficiency and purity can be improved.

Description

Technical Field

[0001] The present invention relates to the field of chemical technology, and particularly to a method for continuous crystallization of lithium carbonate. Background Art

[0002] Lithium carbonate is an important basic raw material in the new energy industry. For the technology of preparing lithium carbonate from salt lake brine, most of the salt lake brine is subjected to different separation and extraction processes to obtain a lithium-rich solution containing impurities, and then sodium carbonate is added to the solution to precipitate lithium carbonate. At present, most of the lithium carbonate produced by enterprises is industrial grade. Due to small particle size, large specific surface area, serious agglomeration, mother liquor entrainment and peritectic structure, etc., the purity of lithium carbonate products and specific impurities do not meet the requirements of the lithium battery industry. Due to the lack of systematic regulation of the control of key operating conditions in its process production, the particle size of the product is less than 25 μm, the particles are easy to agglomerate, and the purity is lower than 98%. As a result, the particle size, purity and batches of the product are all unstable and do not meet the set requirements. Moreover, there are the following problems: high production cost, high energy consumption, large investment in human resources, and no timely feedback and solution to the problems occurring in the production process.

[0003] The present invention aims to optimize the process of continuous production of lithium carbonate, provides theoretical guidance and technical support for the process of producing lithium carbonate from salt lake brine, and has potential economic value. Summary of the Invention

[0004] The object of the present invention is to provide a method for continuous crystallization of lithium carbonate aiming at the problems that the particle size and purity do not meet the set requirements in the continuous crystallization process of lithium carbonate in the prior art.

[0005] The technical solution adopted to achieve the object of the present invention is as follows:

[0006] A method for continuous crystallization of lithium carbonate, in which a Na 2 CO 3 solution and a LiCl solution enter a DTB crystallizer for crystallization. In the DTB crystallizer, the diameter of the draft tube is 44 - 55 mm, and the diameter of the baffle bucket is 70 - 95 mm; the distance from the bottom of the draft tube to the bottom of the baffle bucket is 20 - 60 cm; the distance between the lowest end of the stirring paddle and the lowest end of the DTB crystallizer is 50 - 65 mm;

[0007] The LiCl solution and the Na 2 CO 3 solution are respectively fed into the DTB crystallizer at a feeding rate of 3.0 - 10.0 ml / min and 9.0 - 30.0 ml / min, the discharging rate of the DTB crystallizer is 10.0 - 30.0 mL / min, and the rotation speed of the stirring paddle is 400 - 600 rpm.

[0008] In the above technical solution, the blade angle of the stirring paddle is 40-50°.

[0009] In the above technical solution, the flow velocity of the fluid in the draft tube is 0.6-6 m / s.

[0010] In the above technical solution, the Na 2 CO 3 solution is transported into the crystallizer under the action of the first peristaltic pump, and the LiCl solution stored in the second storage tank is transported into the crystallizer under the action of the second peristaltic pump. A thermal jacket is provided on the outer wall of the crystallizer, and the thermal jacket is connected to a constant temperature water bath. A stirring paddle is coaxially arranged in the crystallizer, and the stirring paddle is coaxially located inside the draft tube. A baffle tube is also provided outside the draft tube. The draft tube is fixed inside the baffle tube through a connecting rod. The bottom of the draft tube is lower than the bottom of the baffle tube, and the top of the draft tube is higher than the top of the baffle tube. A water outlet nozzle is opened at the bottom of the crystallizer, and a Li 2 CO 3 crystal storage device is provided directly below the water outlet nozzle.

[0011] In the above technical solution, the solid content rate of lithium carbonate particles in the draft tube is 50-80%, the solid content rate of lithium carbonate particles on the surface layer of the draft tube is 8-15%, the solid content rate of lithium carbonate particles in the baffle barrel is 25-40%, the solid content rate of lithium carbonate particles in the settling zone is 2.0-13%, and the underflow solid content rate is 9-16%.

[0012] In the above technical solution, the residence time of lithium carbonate particles in the DTB crystallizer is 0.2-10 S.

[0013] In the above technical solution, the distance between the blade of the stirring paddle and the lower edge of the draft tube is 0-5 cm.

[0014] In the above technical solution, the mass percentage of Li + in the LiCl solution is 2.9-4.5%, and the mass percentage of Cl - is 17.6-27.3%.

[0015] In the above technical solution, the mass percentage of Na 2 CO 3 in the solution is 9.6-19.6%, and the mass percentage of CO + is 12.5-25.5%. 3 2- The mass percentage of is 12.5-25.5%.

[0016] In the above technical solution, the system temperature of the crystallization process is 75-85 °C.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] 1. The present invention compares and optimizes multiple parameters that affect the concentration distribution and particle size distribution of lithium carbonate particles in the crystallizer, and finds that the feeding and discharging rates, the rotation speed and relative position of the control stirring paddle are the most sensitive factors. Therefore, the above-mentioned several parameters are organically adjusted and an effective control range is established to obtain the law of effectively controlling the concentration distribution of lithium carbonate particles in the crystallizer, achieving the goal of meeting the set requirements for the particle size of lithium carbonate and improving production efficiency and purity.

[0019] 2. The present invention organically controls the feeding, discharging and rotation speed in the continuous crystallization process of lithium carbonate, mainly using the solid content in the crystallizer as the measurement standard; the present invention treats the distribution of lithium carbonate particles in the crystallizer as an uneven distribution, that is: the solid content distribution is controlled in regions in the crystallizer; by controlling the operating parameters in the crystallization process, the lithium purity of the optimized continuous crystallization process of lithium carbonate is increased from less than 98.0% to 99.5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Shown is a schematic structural diagram of a continuous lithium carbonate crystallization system.

[0021] Figure 2 Is a schematic structural diagram of the crystallizer.

[0022] Figure 3 Is a dimensional structure diagram of the crystallizer.

[0023] In the figure: 1 - crystallizer, 2 - first storage tank, 3 - first peristaltic pump, 4 - constant temperature water bath, 5 - thermometer, 6 - stirring paddle, 7 - Li 2 CO 3 crystal storage device, 8 - second storage tank, 9 - second peristaltic pump, 10 - water outlet nozzle, 11 - thermal jacket, 12 - draft tube, 13 - connecting rod, 14 - baffle tube, 15 - outer cylinder. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] The following further describes the present invention in detail with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0025] Example 1

[0026] As Figures 1-3 shown, the continuous lithium carbonate crystallization system of the present invention includes a crystallizer 1, the crystallizer 1 is a DTB crystallizer, the material of the outer cylinder 15 of the crystallizer 1 is glass, and Na stored in the first storage tank 2 2 CO 3Under the action of the first peristaltic pump 3, the solution is transported into the crystallizer 1. The LiCl solution stored in the second storage tank 8 is transported into the crystallizer 1 under the action of the second peristaltic pump 9. The outer wall of the crystallizer 1 is provided with a thermal jacket 11, and the thermal jacket 11 is communicated with a constant temperature water bath 4. A stirring paddle 6 is coaxially arranged in the crystallizer 1, and the stirring paddle 6 is coaxially located inside a draft tube 12. A baffle tube 14 is further arranged outside the draft tube 12. The draft tube 12 is fixed inside the baffle tube 14 through a connecting rod 16. The bottom of the draft tube 12 is lower than the bottom of the baffle tube 14, and the top of the draft tube 12 is higher than the top of the baffle tube 14. A water outlet nozzle 10 is opened at the bottom of the crystallizer 1, and a Li 2 CO 3 crystal storage device 7 is arranged directly below the water outlet nozzle 10. A thermometer 5 is further arranged in the crystallizer 1 to monitor the material temperature.

[0027] Optimizing its structure, the diameter of the draft tube 12 is 44 - 55 mm, and the diameter of the baffle tube 14 is 70 - 95 mm; the distance between the bottom of the draft tube 12 and the bottom of the baffle tube 14 is 20 - 60 cm; the structure and installation height of the stirring paddle 6: the optimal angle of the blade is 40 - 50°, and the optimal installation height is 50 - 65 mm (this position is measured from the vertex of the triangular cone of the crystallizer, that is, the distance between the lowest end of the crystallizer 1 and the lowest end of the stirring paddle 6). The distance between the blade of the stirring paddle and the lower edge of the draft tube 12 is 0 - 5 mm.

[0028] Furthermore, the inner diameter of the crystallizer 1 is 150 mm, the height is 190 mm, the height of the bottom conical part of the crystallizer 1 is 72.5 mm, the diameter of the draft tube 12 is 55 mm, the height of the draft tube 12 is 132 mm, the distance between the bottommost part of the draft tube 12 and the bottommost part of the outer cylinder 15 is 35 mm, the diameter of the baffle tube 14 is 75 mm, the height of the baffle tube 14 is 112 mm, and the diameter of the water outlet nozzle 10 is 15 mm.

[0029] Example 2

[0030] Continuous lithium carbonate crystallization operation is carried out in the crystallizer 1 with fixed parameters in Example 1.

[0031] A continuous lithium carbonate crystallization method includes the following steps:

[0032] Step 1, take the brine rich in lithium from the salt lake, solution A after deep impurity removal, add it into a DTB crystallizer, and add a soda ash solution B into it to prepare a lithium carbonate product. The chemical compositions of solution A and B are:

[0033] A: Li + : 2.9%, Cl - : 17.6%;

[0034] B: Na+ : 9.6%, CO 3 2- : 12.5%.

[0035] Reaction crystallization system temperature range: 80 °C.

[0036] Step 2, conduct experiments and comparisons on the feed rate, discharge rate, stirring paddle speed, and relative position, and find that they are the most sensitive to the lithium carbonate reaction crystallization process. Control the following parameters for continuous production: the feed rate of solution A is 3.0 mL / min, the feed rate of solution B is 9.0 mL / min, and the discharge rate of the water outlet 10 is 10.0 mL / min.

[0037] Solid content of lithium carbonate particles in the draft tube 12: 80%, solid content of lithium carbonate particles on the surface layer of the draft tube 12: 15%, solid content of lithium carbonate particles in the baffle bucket: 40%, solid content of lithium carbonate particles in the settling zone: 13%, bottom flow solid content: 12%. The above values are measured values and are controlled by the feed rate.

[0038] The residence time of the particles is 7S, and the discharge rate is controlled by the residence time.

[0039] The flow rate of the fluid in the draft tube 12 in the crystallizer is 0.6 m / s. This flow rate is controlled by the speed of the stirring paddle.

[0040] The distance between the stirring paddle blade and the lower edge of the draft tube 12 is 3 cm.

[0041] In this embodiment, the particle size of lithium carbonate is controllable under steady-state conditions. The particle size of the lithium carbonate product: D[4,3]: 70 μm; purity ≥ 99.5%.

[0042] Example 3

[0043] Carry out continuous production according to the method of Example 2. The parameters different from those in Example 2 are:[[]]

[0044] The chemical compositions of solutions A and B are: A: Li + : 4.5%, Cl - : 27.3%; B: Na + : 19.6%, CO 3 2- : 25.5%.

[0045] Reaction crystallization system temperature range: 75 °C.

[0046] Feed rate: Solution A is 10.0 ml / min, solution B is 30.0 ml / min.

[0047] Discharge rate: 30.0 m / g.

[0048] Solid content rate of lithium carbonate particles in the draft tube 12: 50%; solid content rate of lithium carbonate particles on the surface layer of the draft tube 12: 8%; solid content rate of lithium carbonate particles in the baffle bucket: 25%; solid content rate of lithium carbonate particles in the settling zone: 2.0%; solid content rate of the underflow: 9%.

[0049] Residence time of the particles: 0.2S.

[0050] Flow velocity of the fluid in the draft tube 12 in the crystallizer: 4.8m / s.

[0051] Distance between the blade of the stirring paddle and the lower edge of the draft tube 12: 5cm.

[0052] In this embodiment, the particle size of lithium carbonate is controllable under steady-state conditions. Particle size of the lithium carbonate product: D[4,3]: 110μm; purity ≥ 99.5%.

[0053] Example 4

[0054] Continuous production is carried out according to the method of Example 2. The parameters different from those in Example 2 are as follows:

[0055] Chemical compositions of solutions A and B are: A: Li + : 4.0%, Cl - : 20.1%; B: Na + : 12.7%, CO 3 2- : 16.6%.

[0056] Temperature range of the reaction crystallization system: 82°C.

[0057] Feeding rate: Solution A is 7.5ml / min, solution B is 18.9ml / min,

[0058] Discharging rate: 28m / g.

[0059] Solid content rate of lithium carbonate particles in the draft tube 12: 61%; solid content rate of lithium carbonate particles on the surface layer of the draft tube 12: 12%; solid content rate of lithium carbonate particles in the baffle bucket: 31%; solid content rate of lithium carbonate particles in the settling zone: 11%; solid content rate of the underflow: 16%.

[0060] Residence time of the particles: 10S.

[0061] Flow velocity of the fluid in the draft tube 12 in the crystallizer: 6.0m / s.

[0062] Distance between the blade of the stirring paddle and the lower edge of the draft tube 12: 0cm.

[0063] In this embodiment, the particle size of lithium carbonate is controllable under steady-state conditions. Particle size of the lithium carbonate product: D[4,3]: 98μm; purity ≥ 99.5%.

[0064] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A continuous crystallization method for lithium carbonate, characterized in that, Na 2 CO 3 The Na 2 CO 3 solution and the LiCl solution enter the DTB crystallizer for crystallization. In the DTB crystallizer, the diameter of the draft tube is 44 - 55 mm, the diameter of the baffle bucket is 70 - 95 mm; the distance between the bottom of the draft tube and the bottom of the baffle bucket is 20 - 60 cm; the distance between the lowest end of the stirring paddle and the lowest end of the DTB crystallizer is 50 - 65 mm; LiCl solution and Na 2 CO 3 The solutions are fed into the DTB crystallizer at feeding rates of 3.0 - 10.0 ml / min and 9.0 - 30.0 ml / min respectively. The discharging rate of the DTB crystallizer is 10.0 - 30.0 mL / min. The rotational speed of the stirring paddle is 400 - 600 rpm; the blade angle of the stirring paddle is 40 - 50°; the flow rate of the fluid in the draft tube is 0.6 - 6 m / s; the solid content rate of lithium carbonate particles in the draft tube is 50 - 80%, the solid content rate of lithium carbonate particles on the surface layer of the draft tube is 8 - 15%, the solid content rate of lithium carbonate particles in the baffle bucket is 25 - 40%, the solid content rate of lithium carbonate particles in the settling zone is 2.0 - 13%, and the bottom flow solid content rate is 9 - 16%; Na stored in the first storage tank 2 CO 3 The solution is transported into the crystallizer under the action of the first peristaltic pump. The LiCl solution stored in the second storage tank is transported into the crystallizer under the action of the second peristaltic pump. A thermal jacket is provided on the outer wall of the crystallizer, and the thermal jacket is communicated with a constant temperature water bath. A stirring paddle is coaxially arranged in the crystallizer, and the stirring paddle is coaxially located inside the draft tube. A baffle tube is also provided outside the draft tube. The draft tube is fixed in the baffle tube through a connecting rod. The bottom of the draft tube is lower than the bottom of the baffle tube, and the top of the draft tube is higher than the top of the baffle tube. A water outlet nozzle is opened at the bottom of the crystallizer, and a Na 2 CO 3 crystal storage device is provided directly below the water outlet nozzle.

2. The continuous crystallization method for lithium carbonate according to claim 1, characterized in that, the residence time of lithium carbonate particles in the DTB crystallizer is 0.2 - 10S.

3. The continuous crystallization method for lithium carbonate according to claim 1, characterized in that, the distance between the blade of the stirring paddle and the lower edge of the draft tube is 0 - 5 cm.

4. The continuous crystallization method for lithium carbonate according to claim 1, characterized in that, Li in LiCl solution + has a mass percentage of 2.9 - 4.5%, and Cl - has a mass percentage of 17.6 - 27.3%.

5. The continuous crystallization method for lithium carbonate according to claim 1, characterized in that, Na 2 CO 3 The mass percentage of Na + in the solution is 9.6 to 19.6%, and the mass percentage of CO 3 2- is 12.5 to 25.5%.

6. The continuous crystallization method for lithium carbonate according to claim 1, characterized in that, the system temperature of the crystallization process is 75 - 85°C.

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