Method for preparing potassium chloride and magnesium chloride from carnallite

Abstract

The invention relates to a method for preparing potassium chloride and magnesium chloride from carnallite. The method comprises the following steps: (1) putting anhydrous carnallite into a melting electric furnace, and heating to a molten state; (2) pouring the molten anhydrous carnallite into an electrolytic bath, increasing the temperature in the electrolytic bath, starting an external voltage, and starting electrolysis; and (3) respectively collecting products in the cathode space and the anode space for testing, when the purity of the products KCl and MgCl2 is greater than or equal to 90%, turning off the external voltage, and respectively taking out the products KCl and MgCl2 from the cathode space and the anode space. According to the method, molten anhydrous carnallite is electrolyzed, so that adverse effects of migration of H < + > and OH <-> in a solution on the electrolysis process are avoided, and the decomposition degree of the carnallite is low; by controlling the electrolysis temperature, the power consumption and the cathode current density, the decomposition degree of carnallite is effectively improved, meanwhile, the yield and purity of potassium chloride and magnesium chloride are remarkably improved, the yield of potassium chloride and magnesium chloride is larger than or equal to 80%, and the purity of potassium chloride and magnesium chloride is larger than or equal to 90%.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of potassium chloride and magnesium chloride, and in particular to a method for preparing potassium chloride and magnesium chloride from carnallite. Background Art

[0002] Carnallite is one of the common potassium salt minerals, with the main component of KCl·MgCl2·6H2O. It is a very good raw material for preparing potassium chloride and magnesium chloride. In 1988, Лебедев Ο.Α. et al. reported a method for preparing potassium chloride and magnesium chloride by vacuum decomposing molten carnallite at 800°C. The decomposition degree of carnallite under this method is low and the product purity is not high. At the same time, this method involves a phase change from liquid to gas, which will cause a lot of energy loss. Patent CN97103513.X discloses a process for producing potassium chloride from carnallite. The potassium chloride produced by this method has a coarse particle size and is easy to dry. The purity of the product is not limited by the quality of the original ore, but the magnesium chloride (MgCl2·6H2O) obtained by this method is difficult to dehydrate. When heated to above 160°C, MgCl2·6H2O is thermally decomposed: MgCl2·6H2O→Mg(OH)Cl+HCl↑+5H2O, and the MgCl2 yield is low. The Handbook of Industrial Membranes published in 2006 proposed a method for electrolyzing carnallite solution to produce potassium chloride and magnesium chloride. This method not only involves the migration of potassium, magnesium cations and chloride anions, but also involves the migration of H + and OH - The migration of H on the electrode leads to a lower degree of decomposition of carnallite. + and OH - The discharge leads to the appearance of new complexes in the electrolyte, which affects the electrolysis process. Therefore, it is of great significance to design and develop a method for preparing potassium chloride and magnesium chloride with high yield. Summary of the invention

[0003] In view of the problem of low yield of potassium chloride and magnesium chloride prepared from carnallite in the above-mentioned prior art, the present invention provides a method for preparing potassium chloride and magnesium chloride from carnallite, by controlling the power consumption, temperature and cathode current density of the electrolysis process, improving the decomposition degree of molten anhydrous carnallite, thereby improving the yield and purity of the product potassium chloride and magnesium chloride.

[0004] To achieve the above object, the technical solution of the present invention is as follows:

[0005] A method for preparing potassium chloride and magnesium chloride from carnallite comprises the following steps:

[0006] (1) placing anhydrous carnallite in a melting electric furnace and heating it to a molten state;

[0007] (2) pouring molten anhydrous carnallites into an electrolytic cell, wherein a porous ceramic diaphragm is provided in the electrolytic cell to divide the electrolytic cell into a cathode space and an anode space, wherein a notch is provided at the top of the porous ceramic diaphragm and a valve is provided at the bottom; raising the temperature in the electrolytic cell, opening the valve at the bottom of the porous ceramic diaphragm so that the molten anhydrous carnallites in the anode space and the cathode space of the electrolytic cell are level, turning on an external voltage, and starting electrolysis; during the electrolysis process, the cation K in the molten anhydrous carnallites + Move toward the metal cathode, the anion Cl - and MgCl3 - Move toward the graphite anode, so that KCl is deposited in the cathode space and MgCl2 is deposited in the anode space;

[0008] (3) Collecting the products of the cathode space and the anode space for testing respectively, when the purity of KCl and MgCl2 is ≥90%, turning off the applied voltage, and taking out the products KCl and MgCl2 from the cathode space and the anode space respectively;

[0009] (4) Pour the next batch of molten anhydrous carnallite into the electrolytic cell and repeat steps (1) to (3).

[0010] Furthermore, the cathode space generates KCl, and the anode space generates Cl2 and MgCl2.

[0011] Furthermore, the Cl2 enters the cathode space through the gap in the upper part of the porous ceramic diaphragm.

[0012] Furthermore, the Cl2 is ionized at the molten carnallite-metal cathode-chlorine three-phase interface and re-enters the molten electrolyte.

[0013] Furthermore, in step (2), the temperature in the electrolytic cell is 770-850°C.

[0014] Furthermore, the applied voltage in step (2) is 5-7V.

[0015] Furthermore, the power consumption of electrolyzing the molten anhydrous carnallite in step (2) is 1-10A·h / kg.

[0016] Furthermore, in the electrolysis process of step (2), the cathode current density is 0.1-1A / cm 2 .

[0017] The reaction mechanism involved in the present invention is as follows:

[0018] During electrolysis, the ions in the molten anhydrous carnallite move in a directional manner under the action of an applied voltage, among which the cation K + Moving toward the cathode, the anion Cl - and MgCl3- Moving toward the anode, KCl is generated in the cathode space, Cl2 and MgCl2 are generated in the anode space, and Cl2 enters the cathode space through the gap in the porous ceramic diaphragm, is ionized at the three-phase interface of molten carnallite-metal cathode-chlorine gas, and re-enters the molten electrolyte.

[0019] In the present invention, the electrolysis temperature of anhydrous carnallite is 770-850° C. The melting point of KCl is 770° C. When the temperature of molten carnallite is lower than 770° C., KCl deposited in the cathode space will be transformed into a solid state, resulting in a sharp decrease in the conductivity of the electrolyte, thereby terminating the electrolysis process; when the temperature of molten carnallite is higher than 850° C., the carnallite begins to decompose, its material composition changes, and the porous ceramic diaphragm is destroyed, and the ions in the cathode space and the anode space diffuse strongly, resulting in a decrease in product yield.

[0020] The power consumption of the electrolysis of molten anhydrous carnallite in the present invention is 1-10A·h / kg. If the power consumption is less than 1A·h / kg, the electrolysis reaction of the molten carnallite cannot be fully carried out, and the amount of product generated is relatively small; if the power consumption is greater than 10A·h / kg, the reaction may be out of control or a side reaction may occur, resulting in a decrease in the purity of the product.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention provides a method for preparing potassium chloride and magnesium chloride from carnallite, wherein the H + and OH - The migration of carbon monoxide has an adverse effect on the electrolysis process, resulting in a low degree of decomposition of carnallites. By controlling the electrolysis temperature, power consumption and cathode current density, the decomposition degree of carnallites is effectively improved, and at the same time, the yield and purity of potassium chloride and magnesium chloride are significantly improved, with the yield of potassium chloride and magnesium chloride being ≥80% and the purity being ≥90%. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The embodiments of the present invention are further described below with reference to the accompanying drawings, in which:

[0024] Figure 1 A schematic diagram of the electrolysis process of molten anhydrous carnallite is shown;

[0025] Figure 2 The relationship between the electrolysis product yield and the electrolysis temperature under different power consumption is shown;

[0026] Figure 3 The relationship between the purity of electrolysis products and the electrolysis temperature under different power consumption is shown;

[0027] Figure symbols: 1-electrolytic cell, 2-porous ceramic diaphragm, 3-anode space, 4-cathode space, 5-graphite anode, 6-metal cathode, 7-valve. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] A method for preparing potassium chloride and magnesium chloride from carnallite comprises the following steps:

[0030] (1) placing anhydrous carnallite in a melting electric furnace and heating it to a molten state;

[0031] (2) pouring molten anhydrous carnallites into an electrolytic cell, wherein a porous ceramic diaphragm is provided in the electrolytic cell to divide the electrolytic cell into a cathode space and an anode space, wherein a notch is provided at the top of the porous ceramic diaphragm and a valve is provided at the bottom; raising the temperature in the electrolytic cell, opening the valve at the bottom of the porous ceramic diaphragm so that the molten anhydrous carnallites in the anode space and the cathode space of the electrolytic cell are level, turning on an external voltage, and starting electrolysis; during the electrolysis process, the cation K in the molten anhydrous carnallites + Move toward the metal cathode, the anion Cl - and MgCl3 - Move toward the graphite anode, so that KCl is deposited in the cathode space and MgCl2 is deposited in the anode space;

[0032] (3) Collecting the products of the cathode space and the anode space for testing respectively, when the purity of KCl and MgCl2 is ≥90%, turning off the applied voltage, and taking out the products KCl and MgCl2 from the cathode space and the anode space respectively;

[0033] (4) Pour the next batch of molten anhydrous carnallite into the electrolytic cell and repeat steps (1) to (3).

[0034] The reaction mechanism of the present invention is shown in the attached Figure 1 The porous ceramic diaphragm 2 divides the electrolytic cell 1 into the anode space 3 and the cathode space 4. The molten anhydrous carnallite is poured into the electrolytic cell 1. The valve 7 is opened to make the molten anhydrous carnallite in the anode space 3 and the cathode space 4 level. The external voltage is turned on to start electrolysis. During the electrolysis process, the cation K + Move toward the metal cathode 6, the anion Cl - and MgCl3 -It moves toward the graphite anode 5, KCl is generated in the cathode space 4, Cl2 and MgCl2 are generated in the anode space 5, and Cl2 enters the cathode space 4 through the gap in the upper part of the porous ceramic diaphragm 2, is ionized at the molten carnallite-metal cathode-chlorine three-phase interface and re-enters the molten electrolyte.

[0035] Example 1: Effect of electrolysis process parameters on product yield

[0036] Place anhydrous carnallites in a melting electric furnace and heat them to a molten state. Pour the molten anhydrous carnallites into an electrolytic cell, raise the temperature in the electrolytic cell, open the valve of the electrolytic cell, make the molten anhydrous carnallites in the anode space and cathode space of the electrolytic cell level, turn on the applied voltage, and start electrolysis. After the electrolysis is completed, take out the products KCl and MgCl2 from the cathode space and anode space respectively, weigh the products, obtain the actual product mass, and calculate the product yield according to the formula. The test results are shown in the attached figure. Figure 2 And as shown in Table 1.

[0037]

[0038] Pour the carnallite solution into the electrolytic cell, increase the temperature in the electrolytic cell, open the valve of the electrolytic cell, make the carnallite solution in the anode space and cathode space of the electrolytic cell level, turn on the external voltage, and start electrolysis; after the electrolysis is completed, take out the products KCl and MgCl2 from the cathode space and anode space respectively, weigh the product mass, and calculate the product yield according to the formula. The test results are shown in Table 1.

[0039] Table 1 Product yield of carnallite electrolysis under different process parameters (%)

[0040]

[0041]

[0042] From the attached Figure 2 As shown in Table 1, when the electrolysis temperature is 770-850℃, the power consumption is 1-10A·h / kg, and the cathode current density is 0.1-1A / cm 2 When the production of potassium chloride and magnesium chloride is high, the product yields are both above 80%.

[0043] Example 2: Effect of electrolysis process parameters on product purity

[0044] Place anhydrous carnallite in a melting electric furnace and heat it to a molten state, pour the molten anhydrous carnallite into the electrolytic cell, increase the temperature in the electrolytic cell, open the valve of the electrolytic cell, make the molten anhydrous carnallite in the anode space and the cathode space of the electrolytic cell level, turn on the external voltage, and start electrolysis; after the electrolysis is completed, take out the products KCl and MgCl2 from the cathode space and the anode space respectively, test the product purity, and the test results are shown in the attached Figure 3 And as shown in Table 2.

[0045] The carnallite solution was poured into the electrolytic cell, the temperature in the electrolytic cell was increased, the valve of the electrolytic cell was opened, so that the carnallite solution in the anode space and the cathode space of the electrolytic cell was level, the external voltage was turned on, and electrolysis began; after the electrolysis was completed, the products KCl and MgCl2 were taken out from the cathode space and the anode space respectively, and the purity of the products was tested. The test results are shown in Table 2.

[0046] Table 2 Product purity of carnallite electrolysis under different process parameters (%)

[0047]

[0048]

[0049] From the attached Figure 3 As shown in Table 2, when the electrolysis temperature is 770-850℃, the power consumption is 1-12A·h / kg, and the cathode current density is 0.1-1A / cm 2 When the potassium chloride and magnesium chloride are prepared, the purity is relatively high, and the purity of the products reaches more than 90%.

[0050] The present invention provides a method for preparing potassium chloride and magnesium chloride from carnallite, wherein the H + and OH - The migration of carbon monoxide has an adverse effect on the electrolysis process, resulting in a low degree of decomposition of carnallites. By controlling the electrolysis temperature, power consumption and cathode current density, the decomposition degree of carnallites is effectively improved, and at the same time, the yield and purity of potassium chloride and magnesium chloride are significantly improved, with the yield of potassium chloride and magnesium chloride being ≥80% and the purity being ≥90%.

[0051] Some exemplary embodiments of the present invention are described above. It can be understood that the above embodiments are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention. The features in these embodiments can be recombined in a suitable manner, and the scheme obtained thereby is still within the protection scope required by the present invention. Based on the above embodiments, all other embodiments obtained by those skilled in the art without making creative work, that is, all modifications, equivalent substitutions and improvements made within the spirit and principles of this application, fall within the protection scope required by the present invention.

Claims

1. A method for preparing potassium chloride and magnesium chloride from carnallite, characterized in that: The following steps are involved: (1) placing anhydrous carnallite in a melting electric furnace and heating it to a molten state; (2) pouring molten anhydrous carnallites into an electrolytic cell, wherein a porous ceramic diaphragm is provided in the electrolytic cell to divide the electrolytic cell into a cathode space and an anode space, wherein a notch is provided at the top of the porous ceramic diaphragm and a valve is provided at the bottom; raising the temperature in the electrolytic cell, opening the valve at the bottom of the porous ceramic diaphragm so that the molten anhydrous carnallites in the anode space and the cathode space of the electrolytic cell are level, turning on an external voltage, and starting electrolysis; during the electrolysis process, the cation K in the molten anhydrous carnallites + Move toward the metal cathode, the anion Cl - and MgCl3 - Move toward the graphite anode, so that KCl is deposited in the cathode space and MgCl2 is deposited in the anode space; (3) Collecting the products of the cathode space and the anode space for testing respectively, when the purity of KCl and MgCl2 is ≥90%, turning off the applied voltage, and taking out the products KCl and MgCl2 from the cathode space and the anode space respectively; (4) Pour the next batch of molten anhydrous carnallite into the electrolytic cell and repeat steps (1) to (3).

2. A method for preparing potassium chloride and magnesium chloride from carnallite according to claim 1, characterized in that: The cathode space generates KCl, and the anode space generates Cl2 and MgCl2.

3. A method for preparing potassium chloride and magnesium chloride from carnallite according to claim 2, characterized in that: The Cl2 enters the cathode space through the gap in the upper part of the porous ceramic diaphragm.

4. A method for preparing potassium chloride and magnesium chloride from carnallite according to claim 3, characterized in that: The Cl2 is ionized at the molten carnallite-metal cathode-chlorine gas three-phase interface and re-enters the molten electrolyte.

5. A method for preparing potassium chloride and magnesium chloride from carnallite according to claim 1, characterized in that: In step (2), the temperature in the electrolytic cell is 770-850°C.

6. A method for preparing potassium chloride and magnesium chloride from carnallite according to claim 1, characterized in that: The applied voltage in step (2) is 5-7V.

7. A method for preparing potassium chloride and magnesium chloride from carnallite according to claim 1, characterized in that: The power consumption of electrolyzing the molten anhydrous carnallite in step (2) is 1-10A·h / kg.

8. A method for preparing potassium chloride and magnesium chloride from carnallite according to claim 1, characterized in that: The cathode current density during the electrolysis process of step (2) is 0.1-1A / cm 2 .

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