Method for separating sodium and potassium from mixed sulfate containing sodium and potassium

Abstract

The invention relates to a method for separating sodium and potassium from mixed sulfate containing sodium and potassium, which comprises the following steps: mixing the mixed sulfate containing sodium and potassium, a calcium-containing compound and water, dissolving and reacting to obtain potassium-removed mother liquor and double salt precipitate; performing first crystallization on the potassium-removed mother liquor to obtain a sodium sulfate product; mixing the double salt precipitate with water for elution treatment to obtain a potassium sulfate solution; performing secondary crystallization on the potassium sulfate solution to obtain a potassium sulfate product; according to the method, efficient separation of sodium and potassium in the mixed sulfate containing sodium and potassium is achieved, the purity of the obtained sodium sulfate product is preferably as high as 99.0% or above, the potassium content in potassium sulfate is preferably as high as 54.2 wt% or above based on the mass content of potassium oxide, the whole technological process is short, potassium chloride does not need to be added, the separation cost is low, waste gas, waste liquid and solid waste are not generated, and the method is suitable for industrial production. And green resource utilization of the mixed sulfate containing sodium and potassium is realized.

Description

Technical Field

[0001] The invention relates to the technical field of chemical separation, and in particular to a method for separating sodium and potassium in a mixed sulfate containing sodium and potassium. Background Art

[0002] Potassium salt is the most important raw material for agricultural production. It can make crop stems grow strong, promote flowering and fruiting, and enhance drought resistance, cold resistance, disease and pest resistance. Common potassium salts such as potassium sulfate and potassium chloride have always been expensive. However, the preparation of potassium chloride in potassium products is relatively simple and can be directly extracted from sylvite, carnallite or seawater, but the preparation of potassium sulfate is obtained by converting potassium chloride, such as the Mannheim process and double decomposition process. The processing cost per ton of potassium sulfate is high, and the by-products hydrochloric acid and sodium chloride are difficult to absorb in the market. In addition, the prices of potassium chloride and potassium sulfate are comparable, resulting in low profits or even losses for potassium sulfate. In addition, potassium sulfate and most sulfates will form complex salts with low solubility, especially potassium sulfate formed with sodium sulfate is the most common and difficult to separate.

[0003] The existing method for separating potassium sulfate and sodium sulfate mixed salt and the method for preparing potassium sulfate have the problems of long separation process, low product purity, large system circulation volume, difficult operation and high energy consumption. For example, CN118529749A discloses a high-value conversion process and system for potassium sulfate and sodium sulfate mixed salt resource, which first dissolves all potassium sulfate in the potassium sulfate and sodium sulfate mixed salt with a saturated sodium sulfate solution, cools and crystallizes the potassium sulfate, and then adds water to the potassium sulfate and sodium sulfate mixed salt solid after the potassium sulfate is dissolved to fully dissolve the sodium sulfate and prepare sodium bicarbonate and ammonium sulfate; however, by comparing the phase diagram of the water-salt system of sodium sulfate and potassium sulfate at high temperature and low temperature, the process cools and crystallizes the sodium sulfate and potassium sulfate mixed salt, resulting in a relatively low purity of potassium sulfate, and the remaining sodium sulfate will carry potassium sulfate, which then enters the subsequent product, affecting the purity of the subsequent product.

[0004] CN118125473A discloses a method for preparing high-purity potassium sulfate from lithium precipitation mother liquor, wherein the potassium sulfate separated from the lithium precipitation mother liquor is reacted with potassium chloride to prepare potassium sulfate and sodium chloride by a double decomposition reaction method; however, the overall system circulation volume of the method is large, the control of parameters at each node is relatively strict, the operation is difficult, the volume is easily increased, and the sodium chloride product value is low, resulting in poor overall economic benefits.

[0005] CN116768240A discloses a process for recovering potassium sulfate from a mixed salt solution of potassium sulfate and sodium sulfate. The process first recovers glauberite from the mixed salt solution of sodium sulfate and potassium sulfate, washes the glauberite with water at low temperature to obtain potassium sulfate, flashes the washing liquid to separate part of the glauberite, and evaporates the flash mother liquor to obtain sodium sulfate. The whole process of this method is relatively complicated, and the requirements for process indicators are relatively high, especially the flash crystallization of glauberite and the evaporation crystallization of sodium sulfate. The system circulation volume is relatively large, and continuous heating and cooling are required, which has high energy consumption.

[0006] In view of this, how to provide a method for efficiently separating sodium and potassium from a mixed sulfate containing sodium and potassium to obtain high-purity sodium sulfate and potassium sulfate products is a technical problem that urgently needs to be solved in the current field. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a method for separating sodium and potassium in a mixed sulfate containing sodium and potassium, which overcomes the difficulties of long sodium sulfate and potassium sulfate separation process, low product purity, large system circulation volume, difficult operation and high energy consumption, and realizes efficient separation of sodium and potassium in a mixed sulfate containing sodium and potassium, successfully obtains high-quality sodium sulfate and potassium sulfate products, and the whole process does not generate waste gas, waste liquid and solid waste, and has both economic and environmental benefits.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] The present invention provides a method for separating sodium and potassium in a mixed sulfate containing sodium and potassium, and the separation method comprises the following steps:

[0010] (1) mixing a mixed sulfate containing sodium and potassium, a calcium-containing compound and water, dissolving and reacting to obtain a depotassium-removed mother liquor and a double salt precipitate; the depotassium-removed mother liquor is subjected to a first crystallization to obtain a sodium sulfate product;

[0011] (2) mixing the double salt precipitate of step (1) with water for elution to obtain a potassium sulfate solution; and subjecting the potassium sulfate solution to a second crystallization to obtain a potassium sulfate product.

[0012] The separation method of the present invention utilizes the influence of a calcium-containing compound as a crystallization inducer on the crystallization process of potassium sulfate and the difference in solubility and crystallization behavior between potassium sulfate and sodium sulfate, thereby realizing the efficient separation of sodium and potassium in a mixed sulfate containing sodium and potassium, wherein the calcium-containing compound reacts with potassium sulfate in a solution to generate a low-solubility complex salt precipitate, thereby changing the concentration and solubility balance of each component in the solution, inducing potassium sulfate to crystallize and precipitate preferentially, and inhibiting the crystallization of sodium sulfate, thereby realizing the separation of potassium sulfate and sodium sulfate; in addition, the calcium-containing compound can also serve as a heterogeneous nucleation center in the solution, and can also promote the crystallization process of potassium sulfate.

[0013] Preferably, the mass ratio of sodium sulfate to potassium sulfate in the sodium-potassium mixed sulfate in step (1) is (0.1-6):1, for example, it can be 0.1:1, 0.25:1, 0.5:1, 0.0.75:1, 1:1, 1.25:1, 1.5:1, 1.75:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1 or 6:1, etc.

[0014] Preferably, the calcium-containing compound in step (1) comprises any one of calcium sulfate, calcium oxide or calcium hydroxide, or a combination of at least two thereof, wherein typical but non-limiting combinations include a combination of calcium sulfate and calcium oxide, a combination of calcium sulfate and calcium hydroxide, or a combination of calcium oxide and calcium hydroxide, etc.

[0015] The present invention does not impose any restriction on the amount of water added in step (1), as long as the sodium-potassium mixed sulfate is completely dissolved.

[0016] Preferably, the molar ratio of potassium in the sodium-potassium mixed sulfate to the calcium-containing compound in step (1) is 1:(0.5-1.5), for example, it can be 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.2, 1:1.4 or 1:1.5, etc., preferably 1:(0.6-0.9).

[0017] The present invention further preferably has a molar ratio of potassium to the calcium-containing compound in the sodium-potassium mixed sulfate of 1:(0.6-0.9), which is conducive to the efficient separation of sodium and potassium in the sodium-potassium mixed sulfate; if the molar ratio of potassium to the calcium-containing compound in the sodium-potassium mixed sulfate is too high, that is, the amount of calcium-containing oxide added is too small, part of the potassium sulfate will not enter the double salt precipitation, resulting in potassium sulfate still existing in the depotassium mother liquor, and the purity of the sodium sulfate product is reduced; if the molar ratio of potassium to the calcium-containing compound in the sodium-potassium mixed sulfate is too low, that is, the amount of calcium-containing oxide added is too large, the separation effect cannot be significantly improved, but the separation cost is increased.

[0018] Preferably, the reaction temperature in step (1) is 0-40°C, for example, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C or 40°C, etc., preferably 10-40°C.

[0019] The present invention further preferably adopts the reaction temperature of step (1) to be 10-40° C., which is conducive to the formation of double salt precipitation, thereby facilitating the separation of sodium and potassium in the mixed sulfate containing sodium and potassium. If the reaction temperature of step (1) is too high, the double salt precipitation will be too small or unable to form, thereby failing to achieve the separation effect. If the reaction temperature of step (1) is too low, it will lead to problems such as increased operating energy consumption and large equipment investment.

[0020] Preferably, the reaction time of step (1) is 0.2h, 0.5h, 0.8h, 1h, 1.2h, 1.5h, 1.8h or 2h, etc.

[0021] Preferably, the double salt precipitate in step (1) comprises K2SO4·CaSO4·2H2O.

[0022] Preferably, the depotassium-removed mother liquor in step (1) further comprises adjusting the pH before the first crystallization.

[0023] Preferably, the pH adjustment comprises adjusting the pH of the depotassium mother liquor to 6-8 with sulfuric acid, for example, 6, 6.2, 6.5, 6.8, 7, 7.2, 7.5, 7.8 or 8.

[0024] Preferably, the mass volume ratio of the double salt precipitate to water in step (2) is 1:(10-20) g / L, for example, it can be 1:10 g / L, 1:12 g / L, 1:15 g / L, 1:18 g / L or 1:20 g / L, etc., preferably 1:(15-18) g / L.

[0025] Preferably, the temperature of the elution treatment is 60-100°C, for example, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C, etc.; preferably, 70-90°C.

[0026] The present invention further preferably adopts the mass volume ratio of the double salt precipitate to water in step (2) to be 1:(15-18) g / L, and the temperature of the elution treatment to be 60-100° C., which is beneficial to improving the quality of the potassium sulfate product; if the mass volume ratio of the double salt precipitate to water is too low and the elution temperature is too low, the double salt precipitate will not be fully decomposed, thereby causing the quality of potassium sulfate to decrease; if the mass volume ratio of the double salt precipitate to water is too high and the elution temperature is too high, the quality of the potassium sulfate product will not be significantly improved, but the separation energy consumption will be increased.

[0027] Preferably, the elution treatment time in step (2) is 0.2 to 2 h, preferably 0.2 h, 0.5 h, 0.8 h, 1 h, 1.2 h, 1.5 h, 1.8 h or 2 h, etc.

[0028] Preferably, the first crystallization in step (1) and the second crystallization in step (2) each independently include evaporative crystallization or cooling crystallization.

[0029] Preferably, the first crystallization in step (1) also produces a crystallization mother liquor, and the crystallization mother liquor is returned to the mixing step in step (1) to continue the reaction.

[0030] Preferably, when the first crystallization in step (1) is evaporation crystallization, the temperature of the first crystallization is 70-100°C, for example, it can be 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C.

[0031] Preferably, when the second crystallization in step (2) is evaporative crystallization, the temperature of the second crystallization is 70-100°C, for example, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C.

[0032] Preferably, calcium sulfate is obtained after the elution treatment in step (2), and the calcium sulfate is returned to step (1) for repeated utilization.

[0033] That is, the calcium-containing compound of the present invention acts as a crystallization inducer to promote the efficient separation of sodium and potassium in the mixed sulfate containing sodium and potassium, and can be returned to the system for reuse, that is, it has regeneration, thereby reducing the separation cost.

[0034] As a further preferred technical solution of the present invention, according to Figure 1 The separation method comprises the following steps:

[0035] (1) mixing a sodium-potassium mixed sulfate, a calcium-containing compound and water, dissolving the mixture and reacting at 0-40° C. for 0.2-2 h, and obtaining a depotassium mother liquor and a double salt precipitate through solid-liquid separation; adjusting the pH of the depotassium mother liquor to 6-8 with sulfuric acid, and then subjecting the depotassium mother liquor to a first crystallization at 70-100° C. to obtain a sodium sulfate product and a crystallization mother liquor; and returning the crystallization mother liquor to the mixing step of step (1) to continue the reaction;

[0036] The mass ratio of sodium sulfate to potassium sulfate in the sodium-potassium mixed sulfate is (0.1-6):1; the calcium-containing compound includes any one or a combination of at least two of calcium sulfate, calcium oxide or calcium hydroxide; the molar ratio of potassium in the sodium-potassium mixed sulfate to the calcium-containing compound is 1:(0.5-1.5);

[0037] (2) mixing the double salt precipitate and water in step (1) at a mass volume ratio of 1:(10-20) g / L, and performing elution treatment at 60-100° C. for 0.2-2 h, and obtaining potassium sulfate solution and calcium sulfate through solid-liquid separation; the potassium sulfate solution is subjected to a second crystallization at 70-100° C. to obtain a potassium sulfate product; and the calcium sulfate is returned to step (1) for repeated use.

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

[0039] (1) The method for separating sodium and potassium from a sodium-potassium mixed sulfate provided by the present invention uses a calcium-containing compound as a crystallization inducer. At low temperature, the calcium-containing compound reacts with potassium sulfate in a sodium-potassium mixed sulfate solution to generate a low-solubility decomposable double salt precipitate, thereby inducing potassium sulfate to crystallize preferentially and inhibiting the crystallization of sodium sulfate. The double salt precipitate is then eluted at high temperature to obtain potassium sulfate, thereby achieving efficient separation of potassium sulfate and sodium sulfate, and the crystallization inducer can be regenerated and reused.

[0040] (2) The method for separating sodium and potassium from a sodium-potassium mixed sulfate provided by the present invention further optimizes the process parameters such as the amount of calcium-containing compound added, the reaction temperature and the elution temperature to further obtain a sodium sulfate product with a purity of preferably more than 99.0%, and a potassium sulfate product with a potassium content of preferably up to 54.2 wt% (based on the mass content of potassium oxide), thereby realizing the resource utilization of the sodium-potassium mixed sulfate. The entire process is short, no potassium chloride needs to be added, no waste gas, waste liquid and solid waste are generated, and the cost is low and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 The present invention provides a process flow chart of a method for separating sodium and potassium from a sodium-potassium mixed sulfate. DETAILED DESCRIPTION

[0042] The technical solution of the present invention is further described below by specific implementation methods. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0043] 1. Implementation

[0044] Example 1

[0045] This embodiment provides a method for separating sodium and potassium in a mixed sulfate containing sodium and potassium, and the separation method comprises the following steps:

[0046] (1) Mixing a mixed sulfate containing sodium and potassium, calcium sulfate and water, dissolving the mixture and reacting at 20° C. for 1 hour, filtering to obtain a depotassium-removed mother liquor and potassium gypsum (K2SO4·CaSO4·2H2O); adjusting the pH of the depotassium-removed mother liquor to 7 with sulfuric acid, and then subjecting the depotassium-removed mother liquor to a first crystallization (evaporative crystallization) at 100° C. to obtain a sodium sulfate product and a crystallization mother liquor; and returning the crystallization mother liquor to the mixing step of step (1) to continue reacting;

[0047] The mass ratio of sodium sulfate to potassium sulfate in the sodium-potassium mixed sulfate is 1.5:1; the molar ratio of potassium to calcium sulfate in the sodium-potassium mixed sulfate is 1:0.7;

[0048] (2) mixing the potassium gypsum and water in step (1) at a mass volume ratio of 1:18 g / L, and performing an elution treatment at 90° C. for 1 h, and obtaining a potassium sulfate solution and calcium sulfate by filtration; the potassium sulfate solution is subjected to a second crystallization (evaporative crystallization) at 100° C. to obtain a potassium sulfate product; and the calcium sulfate is returned to step (1) for repeated use.

[0049] Example 2

[0050] This embodiment provides a method for separating sodium and potassium in a mixed sulfate containing sodium and potassium, and the separation method comprises the following steps:

[0051] (1) Mixing a sodium-potassium mixed sulfate, calcium sulfate, calcium oxide and water, dissolving the mixture and reacting at 10° C. for 1.5 h, filtering to obtain a depotassium-removed mother liquor and potassium gypsum (K2SO4·CaSO4·2H2O); adjusting the pH of the depotassium-removed mother liquor to 6 with sulfuric acid, and then subjecting the depotassium-removed mother liquor to a first crystallization (evaporative crystallization) at 90° C. to obtain a sodium sulfate product and a crystallization mother liquor; and returning the crystallization mother liquor to the mixing step of step (1) to continue reacting;

[0052] The mass ratio of sodium sulfate to potassium sulfate in the sodium-potassium mixed sulfate is 1:1; the molar ratio of potassium in the sodium-potassium mixed sulfate to the sum of the contents of calcium sulfate and calcium oxide is 1:0.9; the molar ratio of calcium sulfate to calcium oxide is 1:1;

[0053] (2) mixing the potassium gypsum and water in step (1) at a mass volume ratio of 1:15 g / L, and performing an elution treatment at 80° C. for 0.5 h, and obtaining a potassium sulfate solution and calcium sulfate by filtration; the potassium sulfate solution is subjected to a second crystallization (evaporative crystallization) at 90° C. to obtain a potassium sulfate product; and the calcium sulfate is returned to step (1) for repeated use.

[0054] Example 3

[0055] This embodiment provides a method for separating sodium and potassium in a mixed sulfate containing sodium and potassium, and the separation method comprises the following steps:

[0056] (1) Mixing a sodium-potassium mixed sulfate, calcium sulfate, calcium hydroxide and water, dissolving the mixture and reacting at 40° C. for 0.2 h, filtering to obtain a depotassium-removed mother liquor and potassium gypsum (K2SO4·CaSO4·2H2O); adjusting the pH of the depotassium-removed mother liquor to 6 with sulfuric acid, and then subjecting the depotassium-removed mother liquor to a first crystallization (evaporative crystallization) at 80° C. to obtain a sodium sulfate product and a crystallization mother liquor; and returning the crystallization mother liquor to the mixing step of step (1) to continue reacting;

[0057] The mass ratio of sodium sulfate to potassium sulfate in the sodium-potassium mixed sulfate is 2.3:1; the molar ratio of potassium in the sodium-potassium mixed sulfate to the sum of the contents of calcium sulfate and calcium hydroxide is 1:0.6; the molar ratio of calcium sulfate to calcium hydroxide is 1:1;

[0058] (2) mixing the potassium gypsum and water in step (1) at a mass volume ratio of 1:20 g / L, and performing an elution treatment at 70° C. for 1.5 h, and obtaining a potassium sulfate solution and calcium sulfate by filtration; subjecting the potassium sulfate solution to a second crystallization (evaporative crystallization) at 70° C. to obtain a potassium sulfate product; and returning the calcium sulfate to step (1) for repeated use.

[0059] Example 4

[0060] This embodiment provides a method for separating sodium and potassium from a mixed sulfate containing sodium and potassium. The separation method is the same as that of Embodiment 1 except that the reaction temperature in step (1) is 5° C.

[0061] Example 5

[0062] This embodiment provides a method for separating sodium and potassium from a sodium-potassium mixed sulfate. The separation method is the same as that of Embodiment 1 except that the reaction temperature in step (1) is 50°C.

[0063] Example 6

[0064] This embodiment provides a method for separating sodium and potassium in a sodium-potassium mixed sulfate. The separation method is the same as that of Embodiment 1 except that the molar ratio of potassium to calcium sulfate in the sodium-potassium mixed sulfate in step (1) is 1:0.5.

[0065] Example 7

[0066] This embodiment provides a method for separating sodium and potassium in a sodium-potassium mixed sulfate. The separation method is the same as that of Embodiment 1 except that the molar ratio of potassium to calcium sulfate in the sodium-potassium mixed sulfate in step (1) is 1:1.5.

[0067] Example 8

[0068] This embodiment provides a method for separating sodium and potassium from a mixed sulfate containing sodium and potassium. The separation method is the same as that of Embodiment 1 except that the temperature of the elution treatment in step (2) is 60°C.

[0069] Example 9

[0070] This embodiment provides a method for separating sodium and potassium from a mixed sulfate containing sodium and potassium. The separation method is the same as that of Embodiment 1 except that the temperature of the elution treatment in step (2) is 100°C.

[0071] Example 10

[0072] This embodiment provides a method for separating sodium and potassium in a sodium-potassium mixed sulfate. The separation method is the same as that of Embodiment 1 except that the mass volume ratio of potassium gypsum to water in step (2) is 1:12 g / L.

[0073] Embodiment 11

[0074] This embodiment provides a method for separating sodium and potassium in a sodium-potassium mixed sulfate. The separation method is the same as that of Embodiment 1 except that the mass volume ratio of potassium gypsum to water in step (2) is 1:20 g / L.

[0075] 2. Comparison

[0076] Comparative Example 1

[0077] This comparative example provides a method for separating sodium and potassium in a mixed sulfate containing sodium and potassium. The separation method is the same as Example 1 except that the calcium sulfate described in Example 1 is replaced by iron sulfate.

[0078] In this comparative example, since ferrous sulfate and potassium sulfate react to form yellow jarovanadium precipitate and sulfuric acid is generated at the same time, sulfuric acid needs to be added to adjust the pH of the solution to maintain acidic conditions in order to maintain the reaction, so as to ensure that the reaction proceeds in the direction of generating yellow jarovanadium, thereby achieving the separation of potassium sulfate, and subsequently, alkali needs to be added to separate ferrous sulfate and sodium sulfate. Therefore, this comparative example only replaces calcium sulfate with ferrous sulfate on the basis of Example 1, and does not add acid or alkali to adjust the pH, and cannot achieve efficient separation of sodium and potassium in sodium-potassium mixed sulfate.

[0079] Comparative Example 2

[0080] This comparative example provides a method for separating sodium and potassium in a mixed sulfate containing sodium and potassium, and the separation is performed using the process and system disclosed in CN118529749A.

[0081] Since the mixed salt of sodium sulfate and potassium sulfate is precipitated by cooling crystallization in this comparative example, and potassium sulfate is also entrained in the remaining sodium sulfate, the purity of the sodium sulfate and potassium sulfate products is relatively low, and the separation process of this method is long, the equipment is complex, and the energy consumption is high.

[0082] 3. Test and its results

[0083] The purity of the sodium sulfate product obtained by the separation method provided in the above embodiment and comparative example and the potassium content (measured in terms of the mass content of potassium oxide) in the potassium sulfate product were tested, and the results are shown in Table 1;

[0084] Table 1

[0085]

[0086] From the data in Table 1, we can see that:

[0087] (1) It can be seen from Examples 1 to 3 that the method for separating sodium and potassium from a sodium-potassium mixed sulfate provided by the present invention achieves efficient separation of potassium sulfate and sodium sulfate, and obtains high-quality sodium sulfate and potassium sulfate products. The purity of sodium sulfate is as high as 99.0% or more, and the potassium content in potassium sulfate is as high as 54.2 wt % or more (based on the mass content of potassium oxide). At the same time, the crystallization inducing agent used is low in price and reusable. No waste gas, waste liquid and solid waste are generated in the entire separation process, thereby realizing the green resource utilization of the sodium-potassium mixed sulfate.

[0088] (2) Combining Example 1 with Example 4 and Example 5, it can be seen that the reaction temperature of step (1) in Example 4 is low, resulting in a purity of 98.4% of the sodium sulfate product after separation, and a potassium content of 53.3wt% in potassium sulfate (based on the mass content of potassium oxide); the reaction temperature of step (1) in Example 5 is high, resulting in a purity of 94.1% of the sodium sulfate product after separation, and a potassium content of 53.0wt% in potassium sulfate (based on the mass content of potassium oxide); thus, the present invention further preferably sets the reaction temperature of step (1) to 10-40°C, thereby further improving the separation effect of sodium and potassium in the sodium-potassium mixed sulfate.

[0089] (3) Combining Example 1 with Example 6 and Example 7, it can be seen that the molar ratio of potassium to calcium sulfate in the sodium-potassium mixed sulfate described in Example 6 is relatively high, that is, the amount of calcium sulfate added is relatively small, resulting in a purity of 95.6% for the sodium sulfate product after separation, and a potassium content in potassium sulfate (calculated as the mass content of potassium oxide) of 53.8wt%; the molar ratio of potassium to calcium sulfate in the sodium-potassium mixed sulfate described in Example 7 is relatively low, that is, the amount of calcium sulfate added is relatively large, resulting in a purity of 98.5% for the sodium sulfate product after separation, and a potassium content in potassium sulfate (calculated as the mass content of potassium oxide) of 53.4wt%; this shows that the present invention further preferably has a molar ratio of potassium to the calcium-containing compound in the sodium-potassium mixed sulfate described in step (1) of 1:(0.6-0.9), which further improves the separation effect, thereby improving the quality of the obtained potassium sulfate and sodium sulfate products.

[0090] (4) Combining Example 1 with Examples 8 to 11, it can be seen that the temperature of the elution treatment in Example 8 is too low, resulting in a potassium content of 50.1 wt% in the obtained potassium sulfate (based on the mass content of potassium oxide); the temperature of the elution treatment in Example 9 is too high, and the quality of the potassium sulfate product is not significantly improved; the mass volume ratio of potassium gypsum to water in Example 10 is too low, resulting in a potassium content of 50.2 wt% in the obtained potassium sulfate (based on the mass content of potassium oxide); the mass volume ratio of potassium gypsum to water in Example 11 is too high, and the quality of the potassium sulfate product is not significantly improved; thus, it is shown that the present invention further preferably sets the temperature of the elution treatment in step (2) to 70-90°C, and further preferably sets the mass volume ratio of the double salt precipitate to water in step (2) to 1:(15-18) g / L, which further improves the quality of the separated potassium sulfate product while ensuring low energy consumption.

[0091] (5) It can be seen from the combination of Example 1, Comparative Examples 1 and Comparative Examples 2 that, since ferric sulfate is used as a crystallization inducer in Comparative Example 1, when it is used as an inducer, acid needs to be added to adjust the pH in the depotassium process to induce potassium sulfate crystallization, and alkali needs to be added in the elution process to obtain the sodium sulfate product, that is, the separation process requires the consumption of a large amount of acid and alkali, and the crystallization inducer is difficult to regenerate, and acid still needs to be consumed; since the cooling crystallization of Comparative Example 2 precipitates a mixed salt of sodium sulfate and potassium sulfate, and potassium sulfate is also entrained in the remaining sodium sulfate, the purity of the sodium sulfate and potassium sulfate products is relatively low, and the separation process of this method is long, the equipment is complex, and the energy consumption is high.

[0092] In summary, the present invention adopts a calcium-containing compound as a crystallization inducer to induce potassium sulfate to crystallize preferentially and inhibit the crystallization of sodium sulfate, thereby realizing the separation of potassium sulfate and sodium sulfate; and by further controlling the amount of calcium-containing compound added, the potassium removal temperature, the elution temperature and other parameters, high-quality sodium sulfate and potassium sulfate products are successfully obtained, wherein the sodium sulfate product meets the requirements of Class II qualified products in GB / T 6009-2014 industrial anhydrous sodium sulfate, and the potassium sulfate product meets the requirements of powder crystalline superior products in GB / T20406-2017 agricultural potassium sulfate; potassium chloride does not need to be added in the whole process, no waste liquid, waste gas and solid waste are generated, and the calcium-containing compound can be regenerated and reused as a crystallization inducer.

[0093] The applicant declares that the above is only a specific implementation mode 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 thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A method for separating sodium and potassium from a mixed sulfate containing sodium and potassium, characterized in that: The separation method comprises the following steps: (1) mixing a mixed sulfate containing sodium and potassium, a calcium-containing compound and water, dissolving and reacting to obtain a depotassium-removed mother liquor and a double salt precipitate; the depotassium-removed mother liquor is subjected to a first crystallization to obtain a sodium sulfate product; (2) mixing the double salt precipitate of step (1) with water for elution to obtain a potassium sulfate solution; The potassium sulfate solution is subjected to a second crystallization to obtain a potassium sulfate product.

2. The separation method according to claim 1, characterized in that The mass ratio of sodium sulfate to potassium sulfate in the sodium-potassium mixed sulfate in step (1) is (0.1-6):

1.

3. The separation method according to claim 1, characterized in that The calcium-containing compound in step (1) includes any one of calcium sulfate, calcium oxide or calcium hydroxide, or a combination of at least two of them.

4. The separation method according to claim 1, characterized in that The molar ratio of potassium in the sodium-potassium mixed sulfate to the calcium-containing compound in step (1) is 1:(0.5-1.5).

5. The separation method according to claim 1, characterized in that The reaction temperature in step (1) is 0 to 40°C; Preferably, the reaction time in step (1) is 0.2 to 2 hours.

6. The separation method according to claim 1, characterized in that The double salt precipitate in step (1) includes K2SO4·CaSO4·2H2O.

7. The separation method according to claim 1, characterized in that The depotassium-removed mother liquor in step (1) further comprises adjusting the pH before the first crystallization; Preferably, the pH adjustment comprises adjusting the pH of the depotassium mother liquor to 6-8 using sulfuric acid.

8. The separation method according to claim 1, characterized in that The mass volume ratio of the double salt precipitate to water in step (2) is 1:(10-20) g / L; Preferably, the temperature of the elution treatment in step (2) is 60 to 100°C; Preferably, the elution treatment time in step (2) is 0.2 to 2 hours.

9. The separation method according to claim 1, characterized in that The first crystallization in step (1) and the second crystallization in step (2) each independently include evaporative crystallization or cooling crystallization.

10. The separation method according to claim 1, characterized in that Calcium sulfate is also obtained after the elution treatment in step (2), and the calcium sulfate is returned to step (1) for repeated utilization.

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