Production process of cryolite

Abstract

The invention relates to an ice crystal production process, which comprises the following steps: pulp dissolving: conveying dilute hydrofluoric acid into a dissolving kettle, and adding single cryolite into the dissolving kettle for pulp dissolving; crystallization: adding the slurry in the dissolving kettle and caustic soda into a guide cylinder in a crystallization kettle in proportion, adjusting the pH value, and controlling the reaction endpoint; the slurry and caustic soda are fully mixed under the action of the stirrer and are conveyed upwards to flow out of the guide cylinder, and the slurry at the bottom of the kettle body enters the guide cylinder for continuous circulation; and filtering: enabling the slurry flowing out of the crystallization kettle to enter a filter, enabling the filtered ointment-shaped cryolite to enter a dryer, enabling filtrate to enter a dissolving kettle, and drying the ointment-shaped cryolite to obtain the finished cryolite. According to the invention, the mixing uniformity and cooling uniformity of the slurry and caustic soda are improved, local oversaturation of the solution is avoided, and the apparent density of cryolite can be improved. The inner wall of the guide cylinder of the crystallization kettle is provided with a plurality of round recesses which are similar to a water cube structure, so that the heat exchange coefficient is greatly increased.

Description

Technical Field

[0001] The invention belongs to the technical field of cryolite production, and in particular relates to a production process of cryolite. Background Art

[0002] The inorganic silane method is one of the commonly used methods for producing polycrystalline. However, every ton of polycrystalline silicon produced will produce at least 4.5 tons of cryolite with a high impurity content. Its main components are sodium tetrafluoroaluminate (NaAlF4), aluminum, silicon-containing compounds, etc. Because of its complex composition and difficulty in handling, many companies adopt the method of stacking or burying for treatment, which not only causes environmental pollution but also wastes resources.

[0003] Cryolite (Na3AlF6) can dissolve alumina and is an important flux in the cryolite-alumina molten salt electrolysis method. It can be obtained by crystallizing and drying cryolite with hydrofluoric acid and caustic soda, which not only solves the pollution problem but also utilizes resources. However, in the original crystallization process, since the reaction is completed in an instant, the solution is partially oversaturated, and a large number of fine crystals are generated, which makes subsequent processing difficult, energy consumption is high, and the packaging volume is large, which is difficult to meet the needs of some production companies (for example, some customers require the loose density of cryolite to reach 0.8g / cm 3 However, the bulk density of the cryolite product produced by the above process can only reach 0.6g / cm 3 ). Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a production process of cryolite.

[0005] The technical solution of a cryolite production process of the present invention is:

[0006] A cryolite production process, wherein the equipment used in the production process comprises a dissolving kettle, a crystallization kettle, a filter and a dryer, wherein the crystallization kettle comprises a kettle body, wherein an agitator and a guide tube coaxially arranged outside the agitator are arranged in the kettle body, wherein the agitator comprises a stirring shaft, a spiral blade and a stirring paddle, wherein the spiral blade is arranged on the stirring shaft located in the guide tube, wherein the stirring paddle is located at the lower end of the stirring shaft, wherein the kettle body is provided with a caustic soda inlet pipe and a slurry inlet pipe, wherein the lower ends of the caustic soda inlet pipes and the slurry inlet pipes are respectively extended into the middle of the guide tube, wherein a cooling annular cavity is arranged in the cylinder wall of the guide tube, wherein the kettle body is provided with a cooling liquid inlet pipe and a cooling liquid outlet pipe connected with the cooling annular cavity;

[0007] The production process includes the following steps:

[0008] Slurry dissolution: dilute hydrofluoric acid is transported into the dissolution kettle, and cryolite is added into the dissolution kettle for slurry dissolution;

[0009] Crystallization: Add the slurry and caustic soda in the dissolving kettle into the guide tube in the crystallization kettle in proportion, adjust the pH value, and control the reaction end point; in this process, the slurry and caustic soda are fully mixed under the action of the agitator and transported upward and out of the guide tube, and the slurry at the bottom of the kettle enters the guide tube and circulates continuously;

[0010] Filtration: The slurry flowing out of the crystallization kettle enters the filter, the filtered paste-like cryolite enters the dryer, and the filtrate enters the dissolution kettle. After the paste-like cryolite is dried, the finished cryolite is obtained.

[0011] As a further improvement of the above technical solution, a plurality of hollow heat exchange columns are provided on the inner wall of the kettle body, the heat exchange columns are connected to the cooling ring cavity, and a plurality of cooling liquid tanks corresponding to the heat exchange columns are provided in the cooling ring cavity. A piston plate is installed on the guide seal in the cooling liquid tank, the piston plate and the cooling liquid tank form a sealed cavity, and the sealed cavity is connected with the interior of the heat exchange column through a connecting pipe, the cooling liquid tank is provided with a liquid outlet one-way valve for letting liquid flow from the sealed cavity into the connecting pipe, the cooling liquid tank is provided with a liquid inlet one-way valve for letting liquid flow into the sealed cavity, a push rod is inserted in the guide of the heat exchange column, the end of the push rod passes through the cooling liquid tank and enters the cooling ring cavity, the push rod is fixedly connected to the piston plate, and a return spring is mounted on the push rod located in the sealed cavity, the two ends of the return spring are respectively fixedly connected to the piston plate and the cooling liquid tank, and a flow channel connecting the cooling ring cavity and the interior of the heat exchange column is provided in the push rod.

[0012] As a further improvement of the above technical solution, the heat exchange column is arranged tilted downward, and the angle between the axis of the heat exchange column and the horizontal line is 45° to 60°. A push plate is provided at one end of the heat exchange column located inside the guide tube, and the push plate is vertically fixedly connected to the heat exchange column.

[0013] As a further improvement of the above technical solution, a plurality of recesses are provided on the inner wall of the guide tube, the number of the recesses is equal to the number of heat exchange columns, a plurality of the heat exchange columns are fixedly connected in the recesses in a one-to-one correspondence, a plurality of the recesses are arranged in multiple circles, the recesses in each circle are evenly spaced in the axial direction of the guide tube, and the recesses in each circle are evenly spaced in the axial direction of the guide tube.

[0014] As a further improvement to the above technical solution, the bottom of the kettle body is a conical structure, a discharge pipe is provided at the bottom center of the kettle body, a discharge valve is provided on the discharge pipe, and the guide tube is fixedly connected to the kettle body by a fixing rod.

[0015] As a further improvement to the above technical solution, in the crystallization process, the stirring speed of the agitator is 75-80r / min, and the cooling rate in the crystallization kettle is controlled to be 10-15℃ / h.

[0016] As a further improvement to the above technical solution, at least one of the dissolving kettle, the crystallizing kettle, the filter and the dryer is used in parallel in two or more ways.

[0017] The present invention provides a cryolite production process, which has the following beneficial effects compared with the prior art:

[0018] In the crystallization process of the cryolite production process of the present invention, slurry and caustic soda are added to the crystallization kettle in proportion. In order to achieve the required bulk density of cryolite after crystallization, the structure of the crystallization kettle is specially designed. By setting a guide tube, a cooling annular cavity is designed in the guide tube, and the slurry and caustic soda enter the middle position of the guide tube. The agitator mixes the slurry and caustic soda evenly and transports the slurry upward. The slurry flows out from the upper side of the guide tube, and the slurry at the bottom is transported to the guide tube by the agitator. This is repeated, thereby improving the uniformity of mixing the slurry and caustic soda. The cooling annular cavity in the guide tube cools the slurry. In this process, the slurry moving upward pushes the push rod to move inside the heat exchange column through the push plate, and the push rod drives the piston plate to move. The piston plate compresses the reset spring, and the piston plate presses the cooling liquid in the sealing cavity into the connecting pipe. The cooling liquid in the connecting pipe enters the heat exchange column, and the heat exchange column contacts the slurry and caustic soda to further cool them. The coolant in the heat exchange column flows downward under the action of gravity, and its temperature rises after heat exchange with the slurry and caustic soda. The coolant that enters the heat exchange column later pushes the coolant that has been heated up after heat exchange at the bottom into the flow channel, enters the cooling ring cavity through the flow channel, and is circulated out. When the slurry and caustic soda are separated from the push plate, the piston plate moves under the action of the reset spring, and the piston plate sucks the coolant in the cooling ring cavity into the sealed cavity through the liquid inlet one-way valve. When the slurry and caustic soda push the push plate to move, the next cycle is started. The crystallization kettle improves the mixing uniformity and cooling uniformity of the slurry and caustic soda, avoids local oversaturation of the solution, and helps to improve the looseness of the cryolite. The inner wall of the guide tube of the crystallization kettle is provided with several rounded depressions, which are shaped like a water cube structure, greatly increasing the heat transfer coefficient, and the liquid generates rotational shear when flowing through the surface, achieving a self-cleaning effect. The surface is not easy to scale, which greatly extends the scale cleaning cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The cryolite production process flow chart of the present invention;

[0020] Figure 2 It is a structural schematic diagram of a crystallization kettle in the production process of cryolite of the present invention;

[0021] Figure 3 yes Figure 2 The enlarged view of point A in the middle;

[0022] In the figure: 1. kettle body; 2. flange; 3. blind flange; 4. slurry inlet pipe; 5. caustic soda inlet pipe; 6. discharge pipe; 7. discharge valve; 8. support leg; 9. motor fixing seat; 10. drive motor; 11. guide tube; 12. fixing rod; 13. cooling ring cavity; 14. stirring shaft; 15. spiral blade; 16. stirring paddle; 17. coolant inlet pipe; 18. coolant outlet pipe; 19. heat exchange column; 20. push rod; 21. push plate; 22. coolant tank; 23. piston plate; 24. sealing cavity; 25. flow channel; 26. depression; 27. connecting pipe; 28. liquid outlet check valve; 29. ​​liquid inlet check valve; 30. reset spring. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments.

[0024] The specific embodiment of the cryolite production process of the present invention, the equipment used in the process includes a dissolving kettle, a crystallization kettle, a filter and a dryer, the dissolving kettle has a hydrofluoric acid inlet and a single crystal cryolite inlet, the dissolving kettle has a discharge port connected to the slurry inlet on the synthesis kettle through a pipeline, and the dissolving kettle has a caustic soda inlet. The discharge port of the crystallization kettle is connected to the feed port of the filter through a pipeline, the solid discharge port on the filter is connected to the dryer through a pipeline, and the filtrate outlet on the filter is connected to the reflux port on the dissolving kettle through a pipeline.

[0025] The crystallization kettle comprises a kettle body 1, which comprises a cylindrical section and a conical section integrally connected to the lower end of the cylindrical section. A flange 2 is welded on the outer wall of the upper end of the cylindrical section, and a blind flange 3 is fixedly connected to the upper end of the flange 2 through a bolt assembly. A plurality of support legs 8 are fixedly connected to the outer wall of the conical section. An agitator and a guide tube 11 coaxially arranged outside the agitator are arranged in the kettle body 1. The agitator comprises an agitator shaft 14, a spiral blade 15 and a stirring paddle 16. The upper end of the agitator shaft 14 is rotatably mounted on the blind flange 3 through a bearing. The upper end of the blind flange 3 is fixedly connected to a motor fixing seat 9 coaxial with the guide tube 11. The upper end of the motor fixing seat 9 is fixedly connected to a driving motor 10. The upper end of the agitator shaft 14 extends into the motor fixing seat 9. The upper end of the agitator shaft 14 is fixedly connected to the output shaft of the driving motor 10 through a coupling. The spiral blade 15 is arranged on the agitator shaft 14 located in the guide tube 11, and the stirring paddle 16 is located at the lower end of the agitator shaft 14. The caustic soda inlet of the kettle body 1 is sealed and fixedly connected with a caustic soda inlet pipe 5, and the lower end of the caustic soda inlet pipe 5 extends into the middle position of the guide tube 11. The slurry inlet of the kettle body 1 is sealed and fixedly connected with a slurry inlet pipe 4, and the lower end of the slurry inlet pipe 4 extends into the middle position of the guide tube 11. A cooling annular cavity 13 is provided in the wall of the guide tube 11, and a coolant inlet pipe 17 and a coolant outlet pipe 18 connected with the cooling annular cavity 13 are provided on the kettle body 1.

[0026] A plurality of hollow heat exchange columns 19 are arranged on the inner wall of the kettle body 1, and the heat exchange columns 19 are connected to the cooling ring cavity 13. A plurality of cooling liquid tanks 22 corresponding to the heat exchange columns 19 are arranged in the cooling ring cavity 13. A piston plate 23 is installed in the guide seal of the cooling liquid tank 22. The piston plate 23 and the cooling liquid tank 22 form a sealed cavity 24. The sealed cavity 24 is connected to the inside of the heat exchange column 19 through a connecting pipe 27. A liquid outlet check valve 28 is arranged on the cooling liquid tank 22 for liquid to flow from the sealed cavity 24 into the connecting pipe 27. The coolant tank 22 is provided with a liquid inlet check valve 29 for letting liquid into the sealed cavity 24. A push rod 20 is inserted into the guide in the heat exchange column 19. The end of the push rod 20 passes through the coolant tank 22 and enters the cooling ring cavity 13. The push rod 20 is fixedly connected to the piston plate 23. A return spring 30 is mounted on the push rod 20 located in the sealed cavity 24. The two ends of the return spring 30 are respectively fixedly connected to the piston plate 23 and the coolant tank 22. A flow channel 25 connecting the cooling ring cavity 13 and the inside of the heat exchange column 19 is provided in the push rod 20. The heat exchange column 19 is arranged tilted downward, and the angle between the axis of the heat exchange column 19 and the horizontal line is 45°. A push plate 21 is provided at one end of the heat exchange column 19 located inside the guide tube 11. The push plate 21 is vertically fixedly connected to the heat exchange column 19. In other embodiments, the angle between the axis of the heat exchange column 19 and the horizontal line can be any angle between 45° and 60°.

[0027] A plurality of recesses 26 are provided on the inner wall of the guide tube 11, and the number of recesses 26 is equal to the number of heat exchange columns 19. A plurality of heat exchange columns 19 are fixedly connected in the recesses 26 in a one-to-one correspondence. A plurality of recesses 26 are arranged in multiple circles, and each circle of recesses 26 is evenly spaced in the axial direction of the guide tube 11. Each circle of recesses 26 is evenly spaced in the axial direction of the guide tube 11. The bottom of the kettle body 1 is a conical structure, and a discharge pipe 6 is provided at the center of the bottom of the kettle body 1, and a discharge valve 7 is provided on the discharge pipe 6. The guide tube 11 is fixedly connected to the kettle body 1 through a fixing rod 12.

[0028] The production process of cryolite of the present invention comprises the following steps:

[0029] Slurry dissolution: dilute hydrofluoric acid is transported into the dissolution kettle, and cryolite is added into the dissolution kettle for slurry dissolution;

[0030] Crystallization: Add the slurry and caustic soda in the dissolving kettle into the guide tube 11 in the crystallization kettle in proportion, adjust the pH value, and control the reaction end point; in this process, the slurry and caustic soda are fully mixed under the action of the agitator and transported upward and flow out of the guide tube 11, and the slurry at the bottom of the kettle body 1 enters the guide tube 11 and circulates continuously;

[0031] Filtration: The slurry flowing out of the crystallization kettle enters the filter, the filtered paste-like cryolite enters the dryer, and the filtrate enters the dissolution kettle. After the paste-like cryolite is dried, the finished cryolite is obtained.

[0032] In the crystallization process of the cryolite production process of the present invention, slurry and caustic soda are added to the crystallization kettle in proportion. In order to achieve the required bulk density of cryolite after crystallization, the structure of the crystallization kettle is specially designed. By setting a guide tube 11, a cooling annular cavity 13 is designed in the guide tube 11, and the slurry and caustic soda enter the middle position of the guide tube 11. The agitator mixes the slurry and caustic soda evenly and transports the slurry upward. The slurry flows out from the upper side of the guide tube 11, and the slurry at the bottom is transported to the guide tube 11 by the agitator. This is repeated to improve the uniformity of mixing the slurry and caustic soda. The cooling annular cavity 13 in the guide tube 11 cools the slurry. During this process, the slurry moving upward pushes the push rod 20 to move inside the heat exchange column 19 through the push plate 21, and the push rod 20 drives the piston plate 23 to move. The piston plate 23 compresses the return spring 30, and the piston plate 23 injects the cooling liquid in the sealing cavity 24 into the connecting pipe 27. The cooling liquid in the connecting pipe 27 enters the heat exchange column 19, and the heat exchange column 19 contacts the slurry and caustic soda to further cool them. The cooling liquid in the heat exchange column 19 flows downward under the action of gravity, and the temperature rises after heat exchange with the slurry and caustic soda. The cooling liquid that enters the heat exchange column 19 later injects the cooling liquid that has been heated up at the bottom after heat exchange into the flow channel 25, enters the cooling ring cavity 13 through the flow channel 25, and is circulated out. When the slurry and caustic soda leave the push plate 21, the piston plate 23 moves under the action of the return spring 30, and the piston plate 23 sucks the cooling liquid in the cooling ring cavity 13 into the sealing cavity 24 through the liquid inlet check valve. When the slurry and caustic soda push the push plate 21 to move, the next cycle is started. The crystallization kettle improves the mixing uniformity of the slurry and caustic soda and the uniformity of cooling, avoids local oversaturation of the solution, and helps to improve the looseness of the cryolite. The inner wall of the guide tube 11 of the crystallization kettle is provided with a number of rounded depressions 26, which are shaped like a water cube structure, greatly increasing the heat transfer coefficient, and the liquid generates rotational shear when flowing through the surface, achieving a self-cleaning effect, and the surface is not easy to scale, which greatly extends the scale cleaning cycle.

[0033] In the crystallization kettle, the slurry is cooled by the guide tube 11 under stirring conditions to cause crystallization; the cooling rate is set to be constant at 10°C / h, and the stirring rates are set to 55, 65, 75, 85, and 95r / min respectively. The bulk density of the obtained product is listed in the following table:

[0034]

[0035] According to the experimental results in the above table, as the stirring rate increases, the bulk density also increases continuously. However, when the stirring rate increases to above 75r / min, the average particle size increases slowly. After comprehensively considering the equipment operation and cost control, it is believed that when the cooling rate is 10℃ / h, the stirring rate is most appropriately controlled at 75r / min.

[0036] In the crystallization kettle, the slurry is cooled by the guide tube 11 under stirring conditions to cause crystallization; the stirring rate is set to 75r / min, and the cooling rate is set to 6, 8, 10, 12, and 14°C / h respectively. The bulk density of the obtained product is listed in the following table:

[0037]

[0038]

[0039] According to the experimental results in the above table, when the stirring rate is constant at 75r / min, the cooling rate is continuously increased, and the loose density of the crystal is continuously improved. When the cooling rate is adjusted from 6℃ / h to 8℃ / h, the loose density increases fastest. When the cooling rate is above 10℃ / h, the growth rate gradually slows down. After comprehensive consideration, the following conclusion is drawn: when the stirring rate is 75r / min, it is most appropriate to control the cooling rate at 10℃ / h.

[0040] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A production process of cryolite, characterized in that: The equipment used in the production process includes a dissolving kettle, a crystallization kettle, a filter and a dryer. The crystallization kettle includes a kettle body, a stirrer and a guide tube coaxially arranged outside the stirrer are provided in the kettle body, the stirrer includes a stirring shaft, a spiral blade and a stirring paddle, the spiral blade is arranged on the stirring shaft located in the guide tube, the stirring paddle is located at the lower end of the stirring shaft, the kettle body is provided with a caustic soda inlet pipe and a slurry inlet pipe, the lower ends of which extend into the middle position of the guide tube respectively, a cooling ring cavity is provided in the cylinder wall of the guide tube, and the kettle body is provided with a coolant inlet pipe and a coolant outlet pipe communicated with the cooling ring cavity; The production process includes the following steps: Slurry dissolution: dilute hydrofluoric acid is transported into the dissolution kettle, and cryolite is added into the dissolution kettle for slurry dissolution; Crystallization: Add the slurry and caustic soda in the dissolving kettle into the guide tube in the crystallization kettle in proportion, adjust the pH value, and control the reaction end point; in this process, the slurry and caustic soda are fully mixed under the action of the agitator and transported upward and out of the guide tube, and the slurry at the bottom of the kettle enters the guide tube and circulates continuously; Filtration: The slurry flowing out of the crystallization kettle enters the filter, the filtered paste-like cryolite enters the dryer, and the filtrate enters the dissolution kettle. After the paste-like cryolite is dried, the finished cryolite is obtained.

2. The production process of cryolite according to claim 1, characterized in that: A plurality of hollow heat exchange columns are provided on the inner wall of the kettle body, and the heat exchange columns are connected to the cooling ring cavity. The cooling ring cavity is provided with a plurality of cooling liquid tanks corresponding to the heat exchange columns one by one. A piston plate is installed on the guide seal in the cooling liquid tank, and the piston plate and the cooling liquid tank form a sealed cavity. The sealed cavity is connected with the interior of the heat exchange column through a connecting pipe. The cooling liquid tank is provided with a liquid outlet one-way valve for letting liquid flow from the sealed cavity into the connecting pipe, and the cooling liquid tank is provided with a liquid inlet one-way valve for letting liquid flow into the sealed cavity. A push rod is inserted in the guide of the heat exchange column, and the end of the push rod passes through the cooling liquid tank and enters the cooling ring cavity. The push rod is fixedly connected to the piston plate, and a return spring is mounted on the push rod located in the sealed cavity. The two ends of the return spring are respectively fixedly connected to the piston plate and the cooling liquid tank, and a flow channel connecting the cooling ring cavity and the interior of the heat exchange column is provided in the push rod.

3. The production process of cryolite according to claim 2, characterized in that: The heat exchange column is arranged obliquely downward, and the angle between the axis of the heat exchange column and the horizontal line is 45° to 60°. A push plate is provided at one end of the heat exchange column located inside the guide tube, and the push plate is vertically fixedly connected to the heat exchange column.

4. The production process of cryolite according to claim 3, characterized in that: A plurality of recesses are provided on the inner wall of the guide tube, the number of the recesses is equal to the number of the heat exchange columns, the plurality of heat exchange columns are fixedly connected in the recesses in a one-to-one correspondence, the plurality of recesses are arranged in multiple circles, the recesses in each circle are evenly spaced in the axial direction of the guide tube, and the recesses in each circle are evenly spaced in the axial direction of the guide tube.

5. The production process of cryolite according to claim 1, characterized in that: The bottom of the kettle body is in a conical structure. A discharge pipe is provided at the center of the bottom of the kettle body. A discharge valve is provided on the discharge pipe. The guide tube is fixedly connected to the kettle body via a fixing rod.

6. The production process of cryolite according to claim 1, characterized in that: In the crystallization process, the stirring speed of the agitator is 75-80r / min, and the cooling rate in the crystallization kettle is controlled to be 10-15℃ / h.

7. The production process of cryolite according to claim 1, characterized in that: At least one of the dissolving kettle, the crystallizing kettle, the filter and the dryer is used in parallel in two or more ways.

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