Sodium-potassium separation method for potassium-containing sodium carbonate solution

Abstract

The invention discloses a sodium-potassium separation method for a potassium-containing sodium carbonate solution, which is characterized by comprising the following steps: S1, concentration, S2, primary solid-liquid separation, S3, freezing crystallization, S4, secondary solid-liquid separation, S5, reaction and S6, tertiary solid-liquid separation. The method has the advantages that sodium carbonate monohydrate is separated out in a concentration mode, and sodium carbonate decahydrate is separated from centrifugal mother liquor in a freezing crystallization mode according to the characteristic that potassium carbonate and sodium carbonate are different in solubility at the same temperature; afterwards, according to the principle that the solubility of potassium bicarbonate is far lower than that of potassium carbonate at low temperature, carbon dioxide is introduced into the low-sodium and high-potassium sodium carbonate solution separated out through freezing crystallization under the pressure condition, so that potassium carbonate is converted into potassium bicarbonate, potassium precipitation without sodium precipitation is achieved, and finally a potassium bicarbonate product is obtained.

Description

Technical field:

[0001] The invention relates to a sodium-potassium separation system of a carbonate system, in particular to a sodium-potassium separation method of a potassium-containing sodium carbonate solution. Background technology:

[0002] The solid waste produced by aluminum electrolysis plants mainly includes five categories: overhaul slag, cathode carbon blocks, anode carbon blocks, shell blocks, and electrolytes. 3 AlF 6 The other is refractory bricks, cathode carbon blocks, anode carbon blocks except the main component Na 3 AlF 6 The outside is carbon powder, and the main component of the shell is Na 3 AlF 6 and aluminum, the electrolyte is mainly composed of Na 3 AlF 6 . It can be seen that the solid waste produced by the electrolysis plant contains a large amount of cryolite, which has a high utilization value. However, the existing electrolysis plant solid waste recovery is mainly to recover the lithium element, and there is no effective recovery of aluminum, fluorine and sodium, resulting in serious waste of resources. At present, our company has developed a process for alkaline calcium leaching to recover cryolite-containing solid waste from electrolysis plants. The process mainly uses alkaline calcium to leach the solid waste, and sodium, potassium and lithium are leached into the alkaline leaching solution, while aluminum and fluorine remain in the alkaline leaching residue. The alkaline leaching solution and the alkaline leaching residue are then treated and the effective components are recovered. Among them, the alkaline leaching solution is mainly separated into sodium carbonate mother liquor and crude lithium carbonate through carbonization reaction and MVR evaporation and concentration. The sodium carbonate mother liquor continues to undergo MVR evaporation and crystallization and is then centrifuged to obtain sodium carbonate monohydrate. The centrifuged mother liquor contains potassium ions, and the potassium-sodium ratio is 1:20, that is, when the sodium ions in the sodium carbonate solution are 100g / l, the potassium ions reach 5g / l. The solution is already a carbonate system, and the potassium salt produced when recovering sodium carbonate is only potassium carbonate or potassium bicarbonate; common sodium-potassium salt separation systems are all strongly acidic hydrochloric acid solutions, that is, strong acid is added to sodium-potassium salt to form a chloride system, sulfate hydrochloric acid system or nitrate system, etc., and then separation is carried out. The separated sodium and potassium salts have low purity and need to be recrystallized, which is costly, complex process, and low efficiency. Summary of the invention:

[0003] The object of the present invention is to provide a method for separating sodium and potassium from a potassium-containing sodium carbonate solution with low cost and high product purity.

[0004] The present invention is implemented by the following technical scheme: a method for separating sodium and potassium from a potassium-containing sodium carbonate solution, characterized in that it comprises the following steps:

[0005] S1 Concentrate

[0006] The potassium-containing sodium carbonate original solution is concentrated to sodium saturation to crystallize sodium carbonate monohydrate, thereby obtaining a first crystal slurry containing sodium carbonate monohydrate;

[0007] When the concentration of sodium carbonate reaches 31.3%, a saturated sodium carbonate solution is formed, and further concentration will produce sodium carbonate monohydrate; while at 105°C, the saturated concentration of potassium carbonate is above 43%. When the solution is concentrated to a K content of about 100g / l, sodium carbonate generates a large amount of sodium carbonate monohydrate crystals, achieving the separation of sodium and potassium;

[0008] Specifically, the concentration is carried out by MVR evaporation concentration, the concentration temperature is 90-105° C., and the pressure is -0.09 MPa-normal pressure.

[0009] S2 primary solid-liquid separation

[0010] The first crystal slurry obtained in S1 is subjected to a solid-liquid separation to separate the sodium carbonate monohydrate solid and obtain a high-sodium and high-potassium potassium carbonate solution;

[0011] S3 Frozen Crystallization

[0012] The high sodium and high potassium potassium carbonate solution obtained in S2 is frozen until sodium carbonate decahydrate is crystallized to obtain a second crystal slurry containing sodium carbonate decahydrate;

[0013] S4 Secondary solid-liquid separation

[0014] The second crystal slurry obtained in S3 is subjected to a secondary solid-liquid separation to separate sodium carbonate decahydrate solid and a low-sodium high-potassium potassium carbonate solution;

[0015] S5 reaction

[0016] Passing carbon dioxide into the low-sodium high-potassium potassium carbonate solution obtained in S4 to convert the potassium carbonate into potassium bicarbonate, thereby obtaining a third crystal slurry of potassium bicarbonate crystals and a hydrogenation mother liquor containing sodium carbonate;

[0017] S6 three-stage solid-liquid separation

[0018] The third crystal slurry obtained in S5 is subjected to three solid-liquid separations to separate the hydrogenation mother liquor containing sodium carbonate to obtain a potassium bicarbonate product.

[0019] Furthermore, the sodium carbonate decahydrate solid separated in step S4 is sent back to step S1 to be concentrated together with the potassium-containing sodium carbonate original solution.

[0020] Furthermore, the sodium carbonate decahydrate solid separated in step S4 is heated and melted into liquid before being sent back to step S1.

[0021] Furthermore, the hydrogenated mother liquor containing sodium carbonate separated in step S6 is sent back to step S3 for freeze crystallization.

[0022] Furthermore, the hydrogenated mother liquor containing sodium carbonate separated in step S6 is first concentrated until the potassium ion content is 80-120 g / L before being sent back to step S3 for freeze crystallization.

[0023] Furthermore, the freezing temperature of step S3 is 0-10°C and the time is 30-150min. Since the solubility of potassium carbonate at a low temperature of 0°C is 51.53%, and the solubility of sodium carbonate in water at 10°C is only 11.11%, potassium carbonate does not crystallize during cooling crystallization, and sodium carbonate crystallizes into decahydrate. One sodium carbonate with a molecular weight of 106 takes away 180 parts of water to achieve sodium-potassium separation.

[0024] Furthermore, when the carbon dioxide is introduced into the S5, the carbon dioxide pressure is maintained at 0-0.4 MPa, and the S5 is reacted at a temperature of 5-10° C. for 90-120 min. Based on the principle that the solubility of potassium bicarbonate at low temperature is much lower than that of potassium carbonate, carbon dioxide is introduced under pressure to generate potassium bicarbonate, thereby achieving potassium precipitation without sodium precipitation, and finally obtaining a potassium bicarbonate product.

[0025] The advantages of the present invention are as follows: sodium carbonate monohydrate is first separated by concentration, and then sodium carbonate decahydrate is separated by freezing crystallization of the centrifuged mother liquor by utilizing the different solubility characteristics of potassium carbonate and sodium carbonate at the same temperature; thereafter, the low sodium and high potassium sodium carbonate solution separated by freezing crystallization is introduced with carbon dioxide under pressure conditions by utilizing the principle that the solubility of potassium bicarbonate at low temperature is much lower than that of potassium carbonate, so that potassium carbonate is converted into potassium bicarbonate without sodium precipitation, and finally a potassium bicarbonate product is obtained. The carbonate-type sodium potassium salt in the entire separation process does not need to be transformed into a strong acid-type sodium potassium salt, and can be separated, thereby reducing the risk of introducing impurities and salts, and the product purity is high; and the separated sodium carbonate and potassium bicarbonate do not need to be repeatedly crystallized, and the process is simple, the cost is low, and the efficiency is high. Description of the drawings:

[0026] Figure 1 This is a schematic diagram of the structure of the sodium-potassium separation system for potassium-containing sodium carbonate solution.

[0027] MVR evaporator 1, first centrifuge 2, refrigerator 3, second centrifuge 4, carbonizer 5, third centrifuge 6, potassium bicarbonate discharge pipe 7, heating stirring tank 8, concentrator 9, sodium carbonate discharge pipe 10. Specific implementation method:

[0028] In the description of the present invention, it should be noted that, if the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, if the terms "first", "second", "third" appear, they are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0029] Embodiment 1: Sodium-potassium separation method of potassium-containing sodium carbonate solution, which comprises the following steps:

[0030] S1 Concentrate

[0031] The potassium-containing sodium carbonate original solution is concentrated to sodium saturation to crystallize sodium carbonate monohydrate, thereby obtaining a first crystal slurry containing sodium carbonate monohydrate; specifically, the concentration is carried out by MVR evaporation concentration, and the concentration temperature is 90° C. and the pressure is -0.09 MPa.

[0032] S2 primary solid-liquid separation

[0033] The first crystal slurry obtained in S1 is subjected to a solid-liquid separation to separate the sodium carbonate monohydrate solid and obtain a high-sodium and high-potassium potassium carbonate solution; the water content of the sodium carbonate monohydrate crystals after centrifugal separation is less than 1%, and the proportion of K ions brought in by free water in the crystal weight is less than 0.1%, which is beneficial to the increase of the main content of sodium carbonate.

[0034] S3 Frozen Crystallization

[0035] The high sodium and high potassium potassium carbonate solution obtained in S2 is frozen until sodium carbonate decahydrate is crystallized to obtain a second crystal slurry containing sodium carbonate decahydrate; the freezing temperature of the frozen crystallization is 0° C. and the time is 30 min.

[0036] S4 Secondary solid-liquid separation

[0037] The second crystal slurry obtained in S3 is subjected to a secondary solid-liquid separation to separate the sodium carbonate decahydrate solid and obtain a low-sodium high-potassium potassium carbonate solution;

[0038] The sodium carbonate decahydrate solid separated in step S4 is first heated and melted into liquid, and then sent back to step S1 for concentration together with the original potassium-containing sodium carbonate solution.

[0039] S5 reaction

[0040] Passing carbon dioxide into the low-sodium, high-potassium potassium carbonate solution obtained in S4, maintaining the carbon dioxide pressure at 0 MPa, reacting at a temperature of 5° C. for 90 min to convert potassium carbonate into potassium bicarbonate, and obtaining a third crystal slurry of potassium bicarbonate crystals and a hydrogenation mother liquor containing sodium carbonate;

[0041] S6 three-stage solid-liquid separation

[0042] The third crystal slurry obtained in S5 is subjected to three solid-liquid separations to separate the hydrogenation mother liquor containing sodium carbonate and obtain potassium bicarbonate solid.

[0043] The hydrogenation mother liquor containing sodium carbonate separated in step S6 is first concentrated until the potassium ion content is 80 g / L, and then sent back to step S3 for freeze crystallization.

[0044] Embodiment 2: Sodium-potassium separation method of potassium-containing sodium carbonate solution, which comprises the following steps:

[0045] S1 Concentrate

[0046] The potassium-containing sodium carbonate original solution is concentrated to sodium saturation to crystallize sodium carbonate monohydrate, thereby obtaining a first crystal slurry containing sodium carbonate monohydrate; specifically, the concentration is carried out by MVR evaporation concentration, the concentration temperature is 105° C., and the pressure is normal pressure.

[0047] S2 primary solid-liquid separation

[0048] The first crystal slurry obtained in S1 is subjected to a solid-liquid separation to separate the sodium carbonate monohydrate solid and obtain a high-sodium and high-potassium potassium carbonate solution; the water content of the sodium carbonate monohydrate crystals after centrifugal separation is less than 1%, and the proportion of K ions brought in by free water in the crystal weight is less than 0.1%, which is beneficial to the increase of the main content of sodium carbonate.

[0049] S3 Frozen Crystallization

[0050] The high sodium and high potassium potassium carbonate solution obtained in S2 is frozen until sodium carbonate decahydrate is crystallized to obtain a second crystal slurry containing sodium carbonate decahydrate; the freezing temperature of the freeze crystallization is 10° C. and the time is 150 min.

[0051] S4 Secondary solid-liquid separation

[0052] The second crystal slurry obtained in S3 is subjected to a secondary solid-liquid separation to separate the sodium carbonate decahydrate solid and obtain a low-sodium high-potassium potassium carbonate solution;

[0053] The sodium carbonate decahydrate solid separated in step S4 is first heated and melted into liquid, and then sent back to step S1 for concentration together with the original potassium-containing sodium carbonate solution.

[0054] S5 reaction

[0055] Passing carbon dioxide into the low-sodium, high-potassium potassium carbonate solution obtained in S4, maintaining the carbon dioxide pressure at 0.4 MPa, reacting at a temperature of 10° C. for 120 min to convert potassium carbonate into potassium bicarbonate, and obtaining a third crystal slurry of potassium bicarbonate crystals and a hydrogenation mother liquor containing sodium carbonate;

[0056] S6 three-stage solid-liquid separation

[0057] The third crystal slurry obtained in S5 is subjected to three solid-liquid separations to separate the hydrogenation mother liquor containing sodium carbonate to obtain a potassium bicarbonate solid product.

[0058] The hydrogenation mother liquor containing sodium carbonate separated in step S6 is first concentrated until the potassium ion content is 120 g / L, and then sent back to step S3 for freeze crystallization.

[0059] Embodiment 3: Sodium-potassium separation method of potassium-containing sodium carbonate solution, which comprises the following steps:

[0060] S1 Concentrate

[0061] The potassium-containing sodium carbonate original solution is concentrated to sodium saturation to crystallize sodium carbonate monohydrate, thereby obtaining a first crystal slurry containing sodium carbonate monohydrate; specifically, the concentration is carried out by MVR evaporation concentration, and the concentration temperature is 100° C. and the pressure is -0.05 MPa.

[0062] S2 primary solid-liquid separation

[0063] The first crystal slurry obtained in S1 is subjected to a solid-liquid separation to separate the sodium carbonate monohydrate solid and obtain a high-sodium and high-potassium potassium carbonate solution; the water content of the sodium carbonate monohydrate crystals after centrifugal separation is less than 1%, and the proportion of K ions brought in by free water in the crystal weight is less than 0.1%, which is beneficial to the increase of the main content of sodium carbonate.

[0064] S3 Frozen Crystallization

[0065] The high sodium and high potassium potassium carbonate solution obtained in S2 is frozen until sodium carbonate decahydrate is crystallized to obtain a second crystal slurry containing sodium carbonate decahydrate; the freezing temperature of the frozen crystallization is 5° C. and the time is 100 min.

[0066] S4 Secondary solid-liquid separation

[0067] The second crystal slurry obtained in S3 is subjected to a secondary solid-liquid separation to separate the sodium carbonate decahydrate solid and obtain a low-sodium high-potassium potassium carbonate solution;

[0068] The sodium carbonate decahydrate solid separated in step S4 is first heated and melted into liquid, and then sent back to step S1 for concentration together with the original potassium-containing sodium carbonate solution.

[0069] S5 reaction

[0070] Passing carbon dioxide into the low-sodium high-potassium potassium carbonate solution obtained in S4, maintaining the carbon dioxide pressure at 0.2 MPa, reacting at a temperature of 7° C. for 100 min to convert potassium carbonate into potassium bicarbonate, and obtaining a third crystal slurry of potassium bicarbonate crystals and a hydrogenation mother liquor containing sodium carbonate;

[0071] S6 three-stage solid-liquid separation

[0072] The third crystal slurry obtained in S5 is subjected to three solid-liquid separations to separate the hydrogenation mother liquor containing sodium carbonate to obtain a potassium bicarbonate product.

[0073] The hydrogenation mother liquor containing sodium carbonate separated in step S6 is first concentrated until the potassium ion content is 100 g / L, and then sent back to step S3 for freeze crystallization.

[0074] Example 4: Examples 1 to 3 use Figure 1 The sodium-potassium separation system of the potassium-containing sodium carbonate solution shown in the figure is carried out, which includes an MVR evaporator 1, a first centrifuge 2, a refrigerator 3, a second centrifuge 4, a carbonizer 5 and a third centrifuge 6, the feed pipe is connected to the inlet of the MVR evaporator 1, the outlet of the MVR evaporator 1 is connected to the inlet of the first centrifuge 2, and the solid phase outlet of the first centrifuge 2 is connected to a sodium carbonate discharge pipe 10; the liquid phase outlet of the first centrifuge 2 is connected to the inlet of the refrigerator 3, the outlet of the refrigerator 3 is connected to the inlet of the second centrifuge 4, and the solid phase outlet of the second centrifuge 4 is connected to the inlet of the MVR evaporator 1. A heating stirring tank 8 is arranged between the solid phase outlet of the second centrifuge 4 and the inlet of the MVR evaporator 1, the solid phase outlet of the second centrifuge 4 is connected to the inlet of the heating stirring tank 8, and the outlet of the heating stirring tank 8 is connected to the inlet of the MVR evaporator 1.

[0075] The liquid phase outlet of the second centrifuge 4 is connected to the inlet of the carbonizer 5 , the outlet of the carbonizer 5 is connected to the inlet of the third centrifuge 6 , and the solid phase outlet of the third centrifuge 6 is connected to a potassium bicarbonate discharge pipe 7 .

[0076] The liquid phase outlet of the third centrifuge 6 is connected to the inlet of the refrigerator 3. A concentrator 9 is arranged between the liquid phase outlet of the third centrifuge 6 and the inlet of the refrigerator 3, and the liquid phase outlet of the third centrifuge 6 is connected to the inlet of the concentrator 9, and the outlet of the concentrator 9 is connected to the inlet of the refrigerator 3.

[0077] The separation process is as follows:

[0078] S1 Concentrate

[0079] The potassium-containing sodium carbonate raw solution is concentrated in the MVR evaporator 1 to sodium saturation to crystallize sodium carbonate monohydrate, the concentration temperature is 90-105° C., and the pressure is -0.09 MPa-normal pressure, to obtain a first crystal slurry containing sodium carbonate monohydrate;

[0080] S2 primary solid-liquid separation

[0081] The first crystal slurry obtained in S1 is sent to the first centrifuge 2 for solid-liquid separation, and the sodium carbonate monohydrate solid is separated to obtain a high-sodium and high-potassium potassium carbonate solution;

[0082] S3 Frozen Crystallization

[0083] The high sodium and high potassium potassium carbonate solution obtained in S2 is frozen in a freezer 3 until sodium carbonate decahydrate is crystallized to obtain a second crystal slurry containing sodium carbonate decahydrate; the freezing temperature of the frozen crystallization is 0-10° C., and the time is 30-150 min.

[0084] S4 Secondary solid-liquid separation

[0085] The second crystal slurry obtained in S3 is subjected to a second solid-liquid separation in a second centrifuge 4 to separate the sodium carbonate decahydrate solid and obtain a low-sodium high-potassium potassium carbonate solution;

[0086] The sodium carbonate decahydrate solid separated in step S4 is sent back to step S1 to be concentrated together with the potassium-containing sodium carbonate original solution. The sodium carbonate decahydrate solid separated in step S4 is first sent to the heating stirring tank 8 to be heated and melted into liquid before being sent back to step S1.

[0087] S5 reaction

[0088] The low-sodium and high-potassium potassium carbonate solution obtained in S4 is sent to a carbonizer 5, and carbon dioxide is introduced to convert the potassium carbonate into potassium bicarbonate, thereby obtaining a third crystal slurry of potassium bicarbonate crystals and a hydrogenation mother liquor containing sodium carbonate;

[0089] S6 three-stage solid-liquid separation

[0090] The third crystal slurry obtained in S5 is sent to the third centrifuge 6 for solid-liquid separation, and the separated hydrogenated mother liquor containing sodium carbonate is sent to the concentrator 9 for concentration and then sent back to the refrigerator 3 for circulation treatment; the separated potassium bicarbonate product is discharged through the potassium bicarbonate discharge pipe 7.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for separating sodium and potassium from a potassium-containing sodium carbonate solution, characterized in that: It includes the following steps: S1 Concentrate The potassium-containing sodium carbonate original solution is concentrated to sodium saturation to crystallize sodium carbonate monohydrate, thereby obtaining a first crystal slurry containing sodium carbonate monohydrate; S2 primary solid-liquid separation The first crystal slurry obtained in S1 is subjected to a solid-liquid separation to separate the sodium carbonate monohydrate solid and obtain a high-sodium and high-potassium potassium carbonate solution; S3 Frozen Crystallization The high sodium and high potassium potassium carbonate solution obtained in S2 is frozen until sodium carbonate decahydrate is crystallized to obtain a second crystal slurry containing sodium carbonate decahydrate; S4 Secondary solid-liquid separation The second crystal slurry obtained in S3 is subjected to a secondary solid-liquid separation to separate the sodium carbonate decahydrate solid and obtain a low-sodium high-potassium potassium carbonate solution; S5 reaction Passing carbon dioxide into the low-sodium high-potassium potassium carbonate solution obtained in S4 to convert the potassium carbonate into potassium bicarbonate, thereby obtaining a third crystal slurry of potassium bicarbonate crystals and a hydrogenation mother liquor containing sodium carbonate; S6 three-stage solid-liquid separation The third crystal slurry obtained in S5 is subjected to three solid-liquid separations to separate the hydrogenation mother liquor containing sodium carbonate to obtain a potassium bicarbonate product.

2. The method for separating sodium and potassium from potassium-containing sodium carbonate solution according to claim 1, wherein: The sodium carbonate decahydrate solid separated in step S4 is sent back to step S1 to be concentrated together with the potassium-containing sodium carbonate original solution.

3. The method for separating sodium and potassium from potassium-containing sodium carbonate solution according to claim 2, wherein: The sodium carbonate decahydrate solid separated in step S4 is heated and melted into liquid before being sent back to step S1.

4. The method for separating sodium and potassium from potassium-containing sodium carbonate solution according to claim 1, wherein: The hydrogenated mother liquor containing sodium carbonate separated in step S6 is sent back to step S3 for freeze crystallization.

5. The method for separating sodium and potassium from potassium-containing sodium carbonate solution according to claim 4, characterized in that: The hydrogenated mother liquor containing sodium carbonate separated in step S6 is first concentrated until the potassium ion content is 80-120 g / L before being sent back to step S3 for freeze crystallization.

6. The method for separating sodium and potassium from potassium-containing sodium carbonate solution according to claim 1, characterized in that: The freezing temperature of the freezing crystallization in step S3 is 0-10° C. and the time is 30-150 min.

7. The method for separating sodium and potassium from potassium-containing sodium carbonate solution according to claim 1, characterized in that: When the carbon dioxide is introduced into the S5, the carbon dioxide pressure is maintained at 0-0.4 MPa, and the S5 is reacted at a temperature of 5-10° C. for 90-120 minutes.

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