Process for the production of potassium chloride from carnallite

Abstract

The application relates to a method for producing potassium chloride from halite, which comprises a primary screening step (S1), in which large-particle materials are removed from halite ore slurry through screening to obtain underflow slurry; a primary flotation step (S2), in which the underflow slurry is concentrated and then subjected to primary flotation to obtain low-sodium halite slurry; a dehalogenation filter cake preparation step (S3), in which the low-sodium halite slurry is concentrated and then subjected to dehalogenation to obtain dehalogenation filter cake; a decomposition and crystallization step (S4), in which the dehalogenation filter cake is subjected to decomposition and crystallization to obtain crystallization slurry; a secondary screening step (S5), in which the crystallization slurry is screened through a second screening device to obtain second undersize; a secondary flotation step (S6), in which the second undersize is concentrated and then subjected to secondary flotation to obtain coarse potassium ore slurry; and a potassium chloride preparation step (S7), in which the coarse potassium ore slurry is subjected to solid-liquid separation, washing and drying to obtain potassium chloride products. The application can remove large-size sodium chloride particles, reduce the amount of fresh water used for washing potassium chloride, and improve the product grade and yield of potassium chloride.

Description

Technical Field

[0001] This invention relates to the field of potassium chloride production technology, and more particularly to a method for producing potassium chloride using carnallite. Background Technology

[0002] Salt lake brines are rich in minerals such as sodium, potassium, lithium, and magnesium. Carnallite, obtained by drying salt lake brines, is the main raw material for producing potassium chloride, magnesium chloride, and lithium carbonate. The main processes for producing potassium chloride from carnallite ore include reverse flotation, direct flotation, and thermal crystallization.

[0003] Among them, the direct flotation method involves decomposing carnallite ore with water, adding potassium chloride flotation reagent to scrape off the potassium chloride in the form of foam, and then washing, separating, and drying to obtain potassium chloride. This method is simple but has a low yield. The thermal fusion crystallization method utilizes the different solubilities of sodium chloride and potassium chloride at different temperatures to remove sodium chloride and produce potassium chloride. This method produces potassium chloride with high purity, but it consumes a lot of energy and has high costs.

[0004] Reverse flotation has a relatively high yield of potassium chloride and is a commonly used production process. It involves adding sodium chloride flotation reagent to the slurry, causing sodium chloride to float to the surface with the foam and be scraped off, while carnallite remains in the slurry. After dehalogenation, low-sodium carnallite is obtained. The low-sodium carnallite enters the crystallizer for decomposition and crystallization, and then is filtered and washed to obtain potassium chloride product.

[0005] However, when the brine from the salt lake is spread out for drying, sodium chloride particles will precipitate. Sodium chloride enters the production system with the slurry. When producing chlorine through reverse flotation, sodium chloride particles larger than 0.47 mm will settle in the flotation cell due to their large weight and enter the subsequent production system with the slurry. This ultimately leads to a decrease in the grade of potassium chloride product. Moreover, when washing potassium chloride in subsequent processes, the amount of fresh water used for washing needs to be increased, which affects the potassium yield.

[0006] The purpose of this invention is to solve the problems of low grade and low yield of potassium chloride products in existing potassium chloride production processes. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a method for producing potassium chloride from carnallite, comprising: a primary screening step S1, in which carnallite slurry is screened through a first screening device 1 to remove large particles, yielding an underflow slurry; a primary flotation step S2, in which the underflow slurry is concentrated and then added to a first flotation device 3 for primary flotation to obtain a low-sodium carnallite slurry; and a dehalogenation filter cake preparation step S3, in which the low-sodium carnallite slurry is concentrated and then dehalogenated to obtain a dehalogenation filter cake.

[0008] In the decomposition and crystallization step S4, the dehalogenated filter cake and fresh water are added to crystallizer 6 for decomposition and crystallization to obtain a crystallized slurry. In the secondary screening step S5, the crystallized slurry is added to a second screening device 7 for screening to obtain a second oversize and a second undersize. The sieve aperture of the second screening device 7 is 0.7–0.9 mm. In the secondary flotation step S6, the undersize is concentrated and added to a second flotation device 9 for secondary flotation to obtain secondary flotation froth and crude potassium ore slurry. The medium density of the crude potassium ore slurry is 1.265–1.275 g / cm³. 3 In step S7 of potassium chloride preparation, the crude potassium ore slurry is separated into solid and liquid phases, washed, and dried to obtain the potassium chloride product.

[0009] This invention precisely controls the medium density of the crude potassium ore slurry, ensuring that the buoyancy and adhesion of the slurry to sodium chloride particles in the second flotation unit 9 are within an appropriate range. This allows sodium chloride particles larger than 0.47 mm to float to the surface with the secondary flotation froth and be scraped off, preventing large-diameter sodium chloride particles from entering subsequent production processes. This improves the grade of the potassium chloride product, reduces the amount of fresh water used in potassium chloride washing, and increases the yield of potassium chloride. It solves the problem in existing processes where large sodium chloride particles cannot be removed by flotation, resulting in low potassium chloride product grade and low yield.

[0010] Preferably, the aperture of the screen in the first screening device 1 is 2.1 to 2.3 cm. This can remove large-diameter carnallite particles and impurities from the carnallite slurry, preventing blockage of production equipment and pipelines.

[0011] Preferably, the medium density of the low-sodium carnallite slurry is 1.280–1.310 g / cm³. 3 .

[0012] Preferably, the time for one flotation is 12 to 20 minutes.

[0013] Preferably, the aperture of the sieve in the second screening device 7 is 0.8 mm.

[0014] Preferably, the aperture of the sieve holes in the first screening device 1 is 2.3 cm.

[0015] Preferably, the secondary flotation time is 8 to 12 minutes.

[0016] Preferably, in the secondary screening step S5, the material over the second sieve is crushed and returned to the crystallizer 6 for further decomposition and crystallization. The material over the second sieve contains some potassium chloride; returning it to the crystallizer 6 after crushing and further decomposition and crystallization can improve the yield of potassium chloride.

[0017] Preferably, in the secondary flotation step S6, the secondary flotation foam is returned to the first flotation device 3 to continue flotation.

[0018] The process of this invention is simple and easy to control, improves the product quality of potassium chloride, reduces the amount of fresh water used in potassium chloride washing, and achieves a potassium chloride yield of over 65%, thus reducing potassium resource waste. Attached Figure Description

[0019] Figure 1 A schematic diagram of a system for producing potassium chloride from carnallite;

[0020] Figure 2 A schematic diagram of the process for producing potassium chloride from carnallite.

[0021] In the figure, 1. First screening device, 2. First thickener, 3. First flotation device, 4. Second thickener, 5. Dehalogenation device, 6. Crystallizer, 7. Second screening device, 8. Third thickener, 9. Second flotation device, 10. Centrifuge, 11. Washing and stirring tank, 12. Dryer, 13. Crusher. Detailed Implementation

[0022] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0023] like Figure 1 As shown, the system for producing potassium chloride from carnallite includes a first screening device 1, a first thickener 2, a first flotation device 3, a second thickener 4, a dehalogenation device 5, a crystallizer 6, a second screening device 7, a third thickener 8, a second flotation device 9, a centrifuge 10, a washing and stirring tank 11, and a dryer 12 connected in sequence, as well as a crusher 13 connected to the second screening device 7 and the crystallizer 6.

[0024] Carnallite is obtained by cold decomposition, filtration and solid-liquid separation of carnallite ore. Carnallite slurry is obtained by slurry preparation of carnallite.

[0025] The carnallite slurry is fed into the first screening device 1 for screening to obtain a first oversize and a first undersize. The first oversize consists of large-diameter carnallite particles and solid impurities, while the first undersize is the underflow slurry containing small carnallite particles. The aperture of the screen in the first screening device 1 is 2.2–2.4 cm, with the most preferred aperture being 2.3 cm.

[0026] The carnallite slurry is screened by the first screening device 1 to remove large-diameter carnallite particles and impurities, preventing them from clogging downstream equipment and pipelines.

[0027] The underflow slurry is added to the first thickener 2 for concentration. The concentrated underflow is then added to the first flotation unit 3, where sodium chloride flotation reagent is added for primary flotation. Flotation lasts 12–20 minutes, yielding primary flotation froth containing sodium chloride and underflow slurry containing carnallite, i.e., low-sodium carnallite slurry. The medium density of the low-sodium carnallite slurry is 1.280–1.310 g / cm³. 3 .

[0028] The sodium chloride particles in the primary flotation froth have a diameter of less than 0.47 mm. The primary flotation froth is discharged into the tailings pond for sodium chloride production.

[0029] The low-sodium carnallite slurry is added to the second thickener 4 for concentration, and the underflow after concentration is added to the dehalogenation unit 5 for dehalogenation to obtain dehalogenated filter cake.

[0030] The dehalogenated filter cake and an appropriate amount of fresh water are added to crystallizer 6. At room temperature, the mixture is stirred to decompose and crystallize. The underflow discharged after decomposition and crystallization is the crystallized slurry.

[0031] During decomposition and crystallization, low-sodium carnallite gradually dissolves into magnesium chloride and potassium chloride. Since the solubility of magnesium chloride at room temperature is much greater than that of potassium chloride and sodium chloride, potassium chloride crystallizes out to form potassium chloride particles, while magnesium chloride dissolves in the liquid phase.

[0032] The sodium chloride particles trapped in the dehalogenated filter cake do not dissolve, and the solid phase of the crystallized slurry contains potassium chloride particles and sodium chloride particles.

[0033] Table 1. Solubility of co-saturated solutions of KCl, NaCl, and MgCl2

[0034]

[0035] Table 1 shows that, under conditions of 10–15℃, in a co-saturated solution of KCl, NaCl, and MgCl2, the solubility of MgCl2 is 31.6–34.6 g, which is much greater than the solubility of NaCl and KCl. Since carnallite is an asymmetrical double salt, it can completely decompose upon the addition of water. After decomposition, all MgCl2 enters the liquid phase, a small amount of KCl and NaCl enter the liquid phase, and the remaining KCl and NaCl exist in the solid phase. The KCl undergoes a process of dissolution followed by crystallization.

[0036] The crystallized slurry is added to the second screening device 7 for screening to obtain the second oversize and the second undersize. The second oversize includes large-diameter sodium chloride particles and undecomposed low-sodium carnallite particles. After being crushed by the crusher 13, the second oversize is returned to the crystallizer 6 for further decomposition and crystallization to improve the yield of potassium chloride.

[0037] The aperture of the sieve in the second screening device 7 is 0.7-0.9 mm, and the preferred aperture is 0.8 mm.

[0038] Large particles larger than 0.8 mm are mainly large sodium chloride particles and undecomposed carnallite. The content of potassium chloride particles larger than 0.8 mm is relatively small. Moreover, sodium chloride particles larger than 0.8 mm are heavy and difficult to float. If the concentration of crude potassium ore pulp is further increased, although the buoyancy of sodium chloride particles will increase, the viscosity of the pulp will be too large, making it difficult for sodium chloride particles to float with the foam.

[0039] The material under the second screening is concentrated by the third thickener 8 and then added to the second flotation unit 9. Sodium chloride flotation reagent is added for secondary flotation, which takes 8 to 12 minutes to obtain secondary flotation froth and crude potassium ore slurry.

[0040] The secondary flotation foam is returned to the first flotation unit 3 for further flotation. The secondary flotation foam contains small amounts of potassium chloride and sodium flotation reagents; returning it to the primary flotation unit increases the potassium chloride recovery rate and improves the utilization rate of the sodium flotation reagent.

[0041] The crude potassium ore slurry has a medium density of 1.265–1.275 g / cm³. 3 During the secondary flotation, fresh water is added to the flotation machine to control the concentration of the crude potassium ore pulp. This allows the pulp in the second flotation unit 9 to generate suitable viscosity and buoyancy for the sodium chloride particles, enabling sodium chloride particles larger than 0.47 mm to rise to the surface of the pulp with the secondary flotation froth and be scraped off. This prevents large-diameter sodium chloride particles from entering subsequent production processes, improves the grade of potassium chloride product, reduces the amount of fresh water used in potassium chloride washing, and increases the yield of potassium chloride.

[0042] The crude potassium ore slurry is sequentially subjected to solid-liquid separation by centrifuge 10, washing by washing and stirring tank 11, and drying by dryer 12 to obtain potassium chloride product.

[0043] like Figure 2 As shown, the method for producing potassium chloride from carnallite includes a primary screening step S1, in which the carnallite slurry is screened through a first screening device 1 to remove large particles and obtain underflow slurry.

[0044] In the first flotation step S2, the underflow slurry is concentrated in the first thickener 2 and then added to the first flotation device 3 for a first flotation. The flotation lasts for 12 to 20 minutes to obtain a low-sodium carnallite slurry.

[0045] The aperture of the sieve in the first screening device 1 is 2.1–2.3 cm, with the optimal aperture being 2.3 cm. The medium density of the low-sodium carnallite slurry is 1.280–1.310 g / cm³. 3 .

[0046] In step S3, the low-sodium carnallite slurry is concentrated by the second thickener 4 and then added to the dehalogenation device for dehalogenation to obtain the dehalogenation filter cake.

[0047] In the decomposition and crystallization step S4, the dehalogenated filter cake and fresh water are added to the crystallizer 6 for decomposition and crystallization. The underflow discharged after decomposition and crystallization is the crystallization slurry.

[0048] In the secondary screening step S5, the crystallized slurry is added to the second screening device 7 for screening to obtain the second oversize and the second undersize. The second oversize is crushed and returned to the crystallizer 6 for further decomposition and crystallization. The aperture of the screen in the second screening device 7 is 0.7-0.9 mm, and the most preferred aperture is 0.8 mm.

[0049] In the secondary flotation step S6, the material undersized from the second screen is concentrated by the third thickener 8 and then added to the second flotation unit 9 for secondary flotation. Flotation lasts for 8–12 minutes, yielding secondary flotation froth and crude potassium ore pulp. The secondary flotation froth is returned to the first flotation unit 3 for further flotation. The crude potassium ore pulp has a medium density of 1.265–1.275 g / cm³. 3 .

[0050] In potassium chloride preparation step S7, the crude potassium ore slurry is subjected to solid-liquid separation by centrifuge 10, washed in washing and stirring tank 11, and dried in dryer to obtain potassium chloride product.

[0051] The following examples illustrate this.

[0052] Carnallite contains 17.09% potassium chloride, 23.96% magnesium chloride, 29.34% sodium chloride, and 29.61% other substances.

[0053] Example 1

[0054] 1500g of carnallite was mixed to obtain carnallite slurry. The carnallite slurry was then sieved using a first screening device 1 (sieve aperture 2.3cm) to remove large particles, yielding underflow slurry. After concentration, the underflow slurry was added to a first flotation device 3 for one flotation cycle of 15 minutes to obtain a low-sodium carnallite slurry (medium density 1.3g / cm³). 3 Low-sodium carnallite slurry is concentrated and dehalogenated to obtain a dehalogenated filter cake. The dehalogenated filter cake and fresh water are added to crystallizer 6 for decomposition and crystallization to obtain a crystallized slurry. The crystallized slurry is added to a second screening device 7 (sieve aperture 0.8 mm) for screening to obtain a second oversize and a second undersize. The second oversize is crushed and returned to crystallizer 6 for further decomposition and crystallization. The second undersize is concentrated and added to a second flotation device 9 for secondary flotation for 10 minutes to obtain secondary flotation froth and crude potassium slurry (medium density 1.265 g / cm³). 3The froth from the secondary flotation is returned to the first flotation unit 3 for further flotation. After solid-liquid separation, washing, and drying, the crude potassium ore slurry yields potassium chloride product.

[0055] Example 2

[0056] 1500g of carnallite was mixed to obtain carnallite slurry. The carnallite slurry was then sieved using a first screening device 1 (sieve aperture 2.3cm) to remove large particles, yielding underflow slurry. After concentration, the underflow slurry was added to a first flotation device 3 for one flotation cycle of 15 minutes to obtain a low-sodium carnallite slurry (medium density 1.3g / cm³). 3 The low-sodium carnallite slurry is concentrated and then dehalogenated to obtain a dehalogenated filter cake. The dehalogenated filter cake and fresh water are added to crystallizer 6 for decomposition and crystallization to obtain a crystallized slurry. The crystallized slurry is then added to a second screening device 7 (0.7 mm aperture) for sieving, yielding a second oversize and a second undersize. The second oversize is crushed and returned to crystallizer 6 for further decomposition and crystallization. The second undersize is concentrated and added to a second flotation device 9 for secondary flotation for 12 minutes, yielding secondary flotation froth and crude potassium slurry (medium density 1.270 g / cm³). 3 The froth from the secondary flotation is returned to the first flotation unit 3 for further flotation. After solid-liquid separation, washing, and drying, the crude potassium ore slurry yields potassium chloride product.

[0057] Example 3

[0058] 1500g of carnallite was mixed to obtain carnallite slurry. The carnallite slurry was then sieved using the first screening device 1 (sieve aperture 2.3cm) to remove large particles, yielding underflow slurry. After concentration, the underflow slurry was added to the first flotation device 3 for a single flotation process of 15 minutes, yielding a low-sodium carnallite slurry (medium density 1.95g / cm³). 3 The low-sodium carnallite slurry is concentrated and then dehalogenated to obtain a dehalogenated filter cake. The dehalogenated filter cake and fresh water are added to crystallizer 6 for decomposition and crystallization to obtain a crystallized slurry. The crystallized slurry is then added to a second screening device 7 (sieve aperture 0.9 mm) for sieving, yielding a second oversize and a second undersize. The second oversize is crushed and returned to crystallizer 6 for further decomposition and crystallization. The second undersize is concentrated and then added to a second flotation device 9 for secondary flotation for 12 minutes, yielding secondary flotation froth and crude potassium ore slurry (medium density 1.275 g / cm³). 3 The froth from the secondary flotation is returned to the first flotation unit 3 for further flotation. After solid-liquid separation, washing, and drying, the crude potassium ore slurry yields potassium chloride product.

[0059] Example 4

[0060] 1500g of carnallite was mixed to obtain carnallite slurry. The carnallite slurry was then sieved using a first screening device 1 (sieve aperture 2.2cm) to remove large particles, yielding underflow slurry. After concentration, the underflow slurry was added to a first flotation device 3 for one flotation cycle of 20 minutes, yielding a low-sodium carnallite slurry (medium density 1.290g / cm³). 3 Low-sodium carnallite slurry is concentrated and dehalogenated to obtain a dehalogenated filter cake. The dehalogenated filter cake and fresh water are added to crystallizer 6 for decomposition and crystallization to obtain a crystallized slurry. The crystallized slurry is added to a second screening device 7 (sieve aperture 1.0 mm) for screening to obtain a second oversize and a second undersize. The second oversize is crushed and returned to crystallizer 6 for further decomposition and crystallization. The second undersize is concentrated and added to a second flotation device 9 for secondary flotation for 8 minutes to obtain secondary flotation froth and crude potassium slurry (medium density 1.270 g / cm³). 3 The froth from the secondary flotation is returned to the first flotation unit 3 for further flotation. After solid-liquid separation, washing, and drying, the crude potassium ore slurry yields potassium chloride product.

[0061] Example 5

[0062] The difference between this embodiment and Embodiment 1 is that the density of the crude potassium slurry is set to 1.250 g / cm³. 3 Under the same conditions as in Example 1, 1500g of carnallite was used to prepare potassium chloride product.

[0063] Example 6

[0064] The difference between this embodiment and Embodiment 2 is that the density of the crude potassium slurry is set to 1.280 g / cm³. 3 Under the same conditions as in Example 1, 1500g of carnallite was used to prepare potassium chloride product.

[0065] Example 7

[0066] Potassium chloride was produced from 1500g of carnallite using the existing reverse flotation process.

[0067] The potassium chloride products obtained in Examples 1 to 7 were tested, and the test results are shown in Table 2.

[0068] Table 2 shows the calculation results of potassium chloride product composition and recovery rate in Examples 1-7.

[0069]

[0070] As can be seen from Examples 1 to 3, the potassium chloride product produced by the method of the present invention has a product grade of over 95% and a yield of over 65%, which is a significant improvement compared to the potassium chloride produced by the prior art reverse flotation process (Example 7).

[0071] A comparison of Examples 1-3 and 4-6 shows that when potassium chloride is produced using the method of this invention, the pore size of the second screening device is 0.7-0.9 mm, and the medium density of the crude potassium slurry is 1.265-1.275 g / cm³. 3 At that time, the potassium chloride product had the highest grade and a relatively high yield.

[0072] This invention precisely controls the medium density of the crude potassium ore slurry, ensuring that the buoyancy and adhesion of the slurry to sodium chloride particles in the second flotation unit are within an appropriate range. This allows sodium chloride particles larger than 0.47 mm to float with the froth and be scraped off, preventing large-diameter sodium chloride from entering subsequent production processes. This improves the grade of the potassium chloride product, reduces the amount of fresh water used in potassium chloride washing, and increases the yield of potassium chloride. It solves the problem in existing processes where large sodium chloride particles cannot be removed by flotation, resulting in low-grade and low-yield potassium chloride products. This invention features a simple and easily controllable process, improves the grade of potassium chloride products, reduces the amount of fresh water used in potassium chloride washing, achieves a potassium chloride yield of over 65%, and reduces potassium resource waste.

[0073] It should be noted that the above embodiments are illustrative of the present invention and not restrictive of the present invention, and that those skilled in the art can devise alternative embodiments without departing from the scope of the appended claims.

Claims

1. A method for producing potassium chloride from carnallite, characterized in that, include, In the first screening step (S1), the carnallite slurry is screened through the first screening device (1) to remove large particles and obtain the underflow slurry. In the first flotation step (S2), the underflow slurry is concentrated and then added to the first flotation device (3) for a first flotation to obtain a low-sodium carnallite slurry. In the dehalogenation filter cake preparation step (S3), the low-sodium carnallite slurry is concentrated and then dehalogenated to obtain a dehalogenation filter cake. In the decomposition and crystallization step (S4), the dehalogenated filter cake and fresh water are added to the crystallizer (6) for decomposition and crystallization to obtain crystallized slurry; In the secondary screening step (S5), the crystallized slurry is added to the second screening device (7) for screening to obtain the second oversize and the second undersize. The aperture of the sieve in the second screening device (7) is 0.7 to 0.9 mm; In the secondary flotation step (S6), the undersize material from the second screen is concentrated and then added to the second flotation device (9) for secondary flotation to obtain secondary flotation froth and crude potassium ore slurry. The crude potassium slurry has a medium density of 1.265–1.275 g / cm³. 3 ; Potassium chloride preparation step (S7): The crude potassium slurry is subjected to solid-liquid separation, washing, and drying to obtain potassium chloride product.

2. The method for producing potassium chloride from carnallite according to claim 1, characterized in that, The aperture of the sieve of the first screening device (1) is 2.1 to 2.3 cm.

3. The method for producing potassium chloride from carnallite according to claim 2, characterized in that, The medium density of the low-sodium carnallite slurry is 1.280–1.310 g / cm³. 3 .

4. The method for producing potassium chloride from carnallite according to claim 3, characterized in that, The time for one flotation is 12 to 20 minutes.

5. The method for producing potassium chloride from carnallite according to claim 4, characterized in that, The aperture of the sieve of the second screening device (7) is 0.8 mm.

6. The method for producing potassium chloride from carnallite according to claim 5, characterized in that, The aperture of the sieve hole of the first screening device (1) is 2.3 cm.

7. The method for producing potassium chloride from carnallite according to claim 6, characterized in that, The secondary flotation time is 8 to 12 minutes.

8. The method for producing potassium chloride from carnallite according to claim 7, characterized in that, In the secondary screening step (S5), the material on the second sieve is crushed and returned to the crystallizer (6) for further decomposition and crystallization.

9. The method for producing potassium chloride from carnallite according to any one of claims 1 to 8, characterized in that, In the secondary flotation step (S6), the secondary flotation foam is returned to the first flotation device (7) to continue flotation.

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