A production process for producing potassium chloride from carnallite containing potash rocks.

Abstract

A production process for producing potassium chloride from carnallite ore containing potassium rock includes: crushing the raw ore; adding water (TDS / mg / L < 45000), potassium-containing mother liquor, and blending mother liquor for crystallization; performing a primary screening of the crystallization underflow, with the oversize S1 sent to the secondary crystallization stage and the undersize slurry undergoing primary thickening; conveying the primary thickened underflow to a flotation conditioning tank; adding water (TDS / mg / L < 45000), flotation mother liquor, and blending mother liquor to the secondary crystallization stage; performing a secondary screening of the secondary crystallization underflow, with the oversize S2 sent to grinding and the undersize slurry undergoing secondary thickening; conveying the secondary thickened underflow to a flotation conditioning tank; conveying the ground discharge to a flotation conditioning tank; obtaining concentrate K1 and tailings T1 through flotation; washing the concentrate K1 with fresh water and conditioning mother liquor, followed by solid-liquid separation to obtain the potassium chloride product. This invention features a simple process and high product yield.

Description

Technical Field

[0001] This invention relates to the field of potassium chloride preparation methods, and particularly to a production process for producing potassium chloride from carnallite ore containing potassium rock. Background Technology

[0002] Currently, carnallite ore is generally processed into agricultural potassium chloride fertilizer using decomposition-direct flotation or decomposition-crystallization-direct flotation processes. Water is added at the front end of the process (i.e., the decomposition or decomposition-crystallization step) to decompose the carnallite before flotation, as disclosed in CN107739037A, CN 102963912A, and CN 204079502U. Another method involves adding the water required for carnallite decomposition to the rear end of the process for washing crude potassium and tailings; for example, CN112551553B discloses a high-recovery production process for extracting potassium chloride from carnallite ore.

[0003] The disadvantages of adding water at the front end of the process to decompose carnallite are that the amount of water added is difficult to control. Insufficient water increases the concentration and viscosity of the MgCl2 in the decomposition solution, slows down the decomposition rate, and increases the entrainment rate of flotation foam impurities, leading to a significant decrease in the crude potassium grade (the crude potassium grade in Qinghai's Qarhan Salt Lake is generally between 58% and 70%), and the potassium chloride grade in the flotation tailings is between 3% and 5.7%, resulting in a low potassium chloride yield. Adding water at the back end of the process also presents problems of numerous water usage points and large water volumes. For example, CN112551553B adds water for washing after primary crystallization and after flotation to wash the tailings slurry and crude potassium, still resulting in numerous water usage points and low precision control. Furthermore, this process requires carnallite ore to be crushed to ≤8mm, which requires high particle size control, high-end equipment, and high costs. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a potassium chloride production process that is low in cost and high in yield.

[0006] Technical solution

[0007] To achieve the above objectives, embodiments of the present invention provide a production process for producing potassium chloride from carnallite containing potassium rock, comprising:

[0008] The collected primary carnallite ore was crushed to ≤15mm;

[0009] Add water (TDS / mg / L < 45000), potassium-containing mother liquor, and blending mother liquor for crystallization. The amount of water added is 17-30% of the mass of the crushed ore with a particle size ≤ 15mm. The amount of potassium-containing mother liquor added is 20%-28% of the mass of the crushed ore with a particle size ≤ 15mm. Control the overflow of the first-stage crystallization at 8%-12%. The amount of blending mother liquor added is used to control the mass concentration of the bottom flow of the first-stage crystallization at 25%-40%.

[0010] The underflow of the first crystallization stage is screened once to obtain the oversize material S1 and the undersize slurry. The oversize material S1 is sent to the second crystallizer for processing, and the undersize slurry is thickened in one stage.

[0011] A section of thickened underflow is transported to the flotation conditioning tank, part of the thickened overflow is returned to the crystallization section as a blending mother liquor, and the excess thickened overflow is evaporated.

[0012] Add water, flotation mother liquor, and blending mother liquor with a TDS / mg / L < 45000 to the two-stage crystallization operation. The amount of water added to the two-stage operation is 1.5% to 5.0% of the mass of the crushed ore with a particle size ≤ 15mm. The amount of flotation mother liquor added is 50% to 65% of the mass of the crushed ore with a particle size ≤ 15mm. The amount of blending mother liquor added is 65% to 75% of the mass of the crushed ore with a particle size ≤ 15mm.

[0013] The underflow from the second-stage crystallization is subjected to secondary screening to obtain oversize material S2 and undersize slurry. Oversize material S2 is sent to the grinding operation, and undersize slurry is subjected to secondary thickening. The supernatant from the secondary thickening is returned to the secondary crystallizer as blending mother liquor.

[0014] The second-stage thickened underflow is transported to the flotation conditioning tank, part of the second-stage thickened overflow is returned to the second-stage crystallization as the blending mother liquor, and the excess second-stage thickened overflow is transported to the grinding operation.

[0015] During the grinding operation, the oversize material S2 is controlled to have a slurry concentration of 50% to 65% through a two-stage thickening overflow, and the discharged material after grinding is transported to the flotation slurry conditioning tank.

[0016] Add flotation agent to obtain flotation concentrate and flotation tailings. Filter the flotation concentrate and flotation tailings separately to obtain concentrate filter cake K1 and tailings filter cake T1. The filtrate is returned to the second-stage crystallization operation as a blending mother liquor or returned to the flotation slurry conditioning tank for slurry conditioning.

[0017] After the concentrate filter cake K1 is mixed and washed with water and washing mother liquor, potassium chloride product is obtained by solid-liquid separation. Part of the separated filtrate is returned to the mixing and washing operation of the concentrate filter cake K1 for mixing, and the excess filtrate is returned to the flotation operation.

[0018] In one embodiment, the particle size of both the primary and secondary screening is 0.6 mm to 1 mm.

[0019] In one embodiment, the potassium-containing mother liquor is a brine with a KCl mass content of 6.00-13.0%, and the blending mother liquor has a KCl mass content of 2.0-6.5%, a MgCl2 mass content of 21.3-26.6%, and a NaCl mass content of 2.0-3.0%.

[0020] In one embodiment, the mass concentration of the dense underflow is 40% to 55%.

[0021] In one embodiment, the mass concentration of the underflow in the two-stage crystallization process is 25% to 33%.

[0022] In one embodiment, the mass concentration of the slurry in the flotation slurry conditioning tank is controlled to be 26% to 33% by adjusting the opening and closing degree of the thickener underflow valve.

[0023] In one embodiment, the flotation agent is a three-in-one flotation agent composed of octadecylamine, hydrochloric acid, and a frother.

[0024] In one embodiment, the flotation agent is in the form of oil and wax, and is prepared into a 2% (by mass) solution using water at 85°C.

[0025] In one embodiment, the amount of flotation agent added is 130 g / t raw ore to 200 g / t raw ore.

[0026] In one embodiment, the potassium-containing mother liquor is a two-stage crystallization overflow mother liquor.

[0027] (III) Beneficial Effects

[0028] The beneficial effects of this invention are as follows: In this invention, the collected primary carnallite ore containing potassium rock (potassium rock content 1-8%) is crushed to ≤15mm. Compared with the prior art, which first crushes the raw ore to a finer particle size, such as below 8mm, this application only requires crushing to 15mm. This not only saves equipment costs but also alleviates the problem of salt blockage in the crushing equipment. The coarser particle size can slow down the decomposition of carnallite, control a large number of potassium chloride crystal nuclei, create conditions for potassium chloride crystallization, and achieve the purpose of controlled crystallization rate. The amount of crystallization water added in the first stage is 17-30% of the mass of the crushed ore with a particle size ≤15mm. In the prior art, due to the multiple points of water addition and the difficulty in controlling the water usage in the equipment, the mother liquor is unsaturated, resulting in low system yield. In this application, the main water addition point is in the first stage of crystallization, and the subsequent water addition is very small and is not discharged after addition, but directly recycled. This effectively controls the amount of water used, and the discharged mother liquor is saturated or supersaturated, which can reduce the scale of evaporation, reduce potassium discharge, and improve the recovery rate. A two-stage crystallization process is employed. In the second stage, refined potassium mother liquor and a small amount of water are added to fully decompose incompletely decomposed carnallite, improving the yield. After two-stage crystallization, carnallite is fully decomposed, and the oversize material from the second-stage screening is almost entirely potassium rock. This potassium rock can be recovered after grinding, increasing the yield by at least 3%. Furthermore, because some water may be introduced during flotation or filtration, leading to unsaturated mother liquor, the mother liquor generated during flotation is not discharged but recycled within the system, reducing potassium emissions and further improving the recovery rate.

[0029] In summary, this application addresses the problem of low system yield caused by only one stage of crystallizer overflow in the discharged mother liquor, which is in a saturated or supersaturated state. This solves the problem of traditional tailings filtrate discharge, where some water enters the mother liquor due to the use of horizontal belt filters, leading to unsaturated mother liquor, partial potassium dissolution, and low system yield. By employing two-stage crystallization and grinding, the system yield is further improved. This application can achieve a potassium chloride system yield of over 81.95%, a potassium chloride grade of ≥95%, and a tailings KCl grade controlled below 1.0%. Compared to existing technologies with a potassium chloride yield of 55% and tailings KCl of 6.5%, the yield and grade are significantly improved. Furthermore, this application has lower costs, a simpler process, and is suitable for industrial production. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of a production process for producing potassium chloride from carnallite containing potassium rock, according to one embodiment. Detailed Implementation

[0031] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below through specific embodiments.

[0032] Please see Figure 1This invention provides a production process for producing potassium chloride from carnallite containing potassium rock, comprising the following steps:

[0033] S1. Crush the collected primary carnallite ore to ≤15mm.

[0034] The collected primary carnallite ore containing potassium rock (potassium rock content 1-8%) is crushed to ≤15mm. Compared with the existing technology, which first crushes the raw ore to a finer particle size, such as below 8mm, this application only needs to crush it to 15mm. This not only saves equipment costs, but also alleviates the problem of salt blockage in the crushing equipment. The coarser particle size can slow down the decomposition of carnallite, control a large number of potassium chloride crystal nuclei, create conditions for potassium chloride crystallization, and achieve the purpose of controlling the crystallization rate.

[0035] S2. Add water, potassium-containing mother liquor, and blending mother liquor with a TDS / mg / L < 45000 to crystallize. The amount of water added is 17-30% of the mass of the crushed ore with a particle size ≤ 15mm. The amount of potassium-containing mother liquor added is 20%-28% of the mass of the ore. Control the overflow of the first-stage crystallization at 8%-12%. The amount of blending mother liquor added is used to control the underflow concentration of the first-stage crystallization at 25%-40%.

[0036] Specifically, in one embodiment, the potassium-containing mother liquor is a brine with a KCl mass content of 6.00-13.0%, and the blending mother liquor has a KCl mass content of 2.0-6.5%, a MgCl2 mass content of 21.3-26.6%, and a NaCl mass content of 2.0-3.0%.

[0037] Preferably, the overflow mother liquor from the second-stage crystallization process can be used as a potassium-containing mother liquor. Preferably, the liquid obtained from flotation filtration can be used as a blending mother liquor. Using the solutions generated in the process as corresponding functional liquids can save costs and improve efficiency.

[0038] In the first stage of crystallization, the amount of water added is 17-30% of the mass of the crushed ore with a particle size ≤15mm. Existing technologies suffer from unsaturated mother liquor and low system yield due to multiple water addition points and difficulty in controlling water usage. This application controls the main water addition point to be in the first stage of crystallization, with subsequent water additions being minimal and not discharged, but directly recycled. This effectively controls water usage, ensuring that the discharged mother liquor is saturated or supersaturated. This reduces the scale of evaporation, decreases potassium emissions, and improves the recovery rate.

[0039] S3. The underflow of the first crystallization stage is screened once to obtain the oversize material S1 and the undersize slurry. The oversize material S1 is sent to the second crystallizer for processing, and the undersize slurry is thickened in one stage.

[0040] Specifically, in one embodiment, the particle size of a single screening is 0.6 mm to 1 mm.

[0041] S4. A section of thickened underflow is transported to the flotation conditioning tank, part of the thickened overflow is returned to the crystallization section as the blending mother liquor, and the excess thickened overflow is evaporated.

[0042] The additional thick overflow is the only discharge point in this application. Due to the design of the added liquid volume and the crushing of the raw ore particle size, the discharged mother liquor is saturated or supersaturated, which can reduce the scale of evaporation, reduce the amount of potassium discharged, and improve the recovery rate.

[0043] Specifically, in one embodiment, the mass concentration of a dense underflow is 40% to 55%.

[0044] S5. Add water, flotation mother liquor, and blending mother liquor with a TDS / mg / L < 45000 to the two-stage crystallization operation. The amount of water added in the two-stage operation is 1.5% to 5.0% of the mass of the crushed ore with a particle size ≤ 15mm. The amount of flotation mother liquor added is 50% to 65% of the mass of the crushed ore with a particle size ≤ 15mm. The amount of blending mother liquor added is 65% to 75% of the mass of the crushed ore with a particle size ≤ 15mm.

[0045] Adding potassium mother liquor and a small amount of water to the second-stage crystallization process can fully decompose the incompletely decomposed carnallite, thereby increasing the yield. After the second-stage crystallization, the carnallite can be fully decomposed, and the oversize material in the second-stage screening is almost entirely potassium rock. The potassium rock can be recovered after grinding, which can increase the yield by at least 3%.

[0046] S6. The underflow of the second-stage crystallization is subjected to secondary screening to obtain the oversize material S2 and the undersize slurry. The oversize material S2 is sent to the grinding operation, and the undersize slurry is subjected to secondary thickening. The supernatant of the secondary thickening is returned to the secondary crystallizer as the blending mother liquor.

[0047] The particle size for secondary screening is 0.6 mm to 1 mm.

[0048] S7. The second-stage thickened underflow is transported to the flotation slurry conditioning tank. Part of the second-stage thickened overflow is returned to the second-stage crystallization as the blending mother liquor, and the excess second-stage thickened overflow is transported to the grinding operation.

[0049] In one embodiment, the mass concentration of the underflow in the two-stage crystallization process is 25% to 33%.

[0050] S8. During the grinding operation, the oversize material S2 is controlled by two-stage thickening overflow to adjust the slurry concentration to 50% to 65%, and after grinding, the discharged material is transported to the flotation slurry tank.

[0051] After two-stage crystallization and decomposition, the material on the screen is coarse-grained potash rock ore (which cannot be decomposed in the crystallization and decomposition process). By grinding it to a suitable particle size, the potash rock can be separated by flotation, thereby improving the product yield.

[0052] S9. Add flotation agent to obtain flotation concentrate and flotation tailings. Filter the flotation concentrate and flotation tailings respectively to obtain concentrate filter cake K1 and tailings filter cake T1. The filtrate is returned to the second-stage crystallization operation as blending mother liquor or returned to the flotation slurry conditioning tank for slurry conditioning.

[0053] Specifically, in one embodiment, the mass concentration of the slurry in the flotation preparation tank is controlled to be 26%–33% by adjusting the opening and closing of the thickener underflow valve. The flotation agent is a three-in-one flotation agent composed of octadecylamine, hydrochloric acid, and a frother. In one embodiment, the flotation agent is in an oil-wax form, and is prepared as a 2% (by mass) solution using water at 85°C. In one embodiment, the amount of flotation agent added is 130 g / t to 200 g / t of raw ore.

[0054] During flotation or filtration operations, some water may be mixed in, causing the mother liquor to become unsaturated. The mother liquor produced during flotation is not discharged but recycled in the system, reducing potassium emissions and improving recovery rate.

[0055] S10. After the concentrate filter cake K1 is mixed and washed with water and washing mother liquor, potassium chloride product is obtained by solid-liquid separation. Part of the separated filtrate is returned to the mixing and washing operation of the concentrate filter cake K1 for mixing, and the excess filtrate is returned to the flotation operation.

[0056] The present invention will be further described below with reference to embodiments. The raw material used in the implementation of the present invention is a primary carnallite deposit from an underground potash mine in Africa.

[0057] Components of primary carnallite in Examples 1-3

[0058]

[0059] Example 1

[0060] Carnallite deposits containing potassium-bearing rocks were collected from an underground primary source in Laos and crushed to -15mm.

[0061] A belt conveyor was used to transport crushed carnallite ore with a particle size ≤15mm (the raw ore mass referred to in this article refers to the mass of crushed carnallite ore with a particle size ≤15mm) to a primary crystallizer for crystallization. Simultaneously, water with a TDS / mg / L <45000, potassium-containing mother liquor (derived from the overflow L2 mother liquor of the secondary crystallizer), and a blending mother liquor (from the primary thickening overflow) were added to the primary crystallizer. The water content was 30% of the raw ore mass, L2 was 20% of the raw ore mass, and the amount added to the primary thickening overflow was 40% of the raw ore mass. The mixture circulated in the primary crystallizer for approximately 2 hours. The overflow height in the crystallizer was controlled to maintain an overflow rate of 12%. The slurry circulated in the crystallizer for 2 hours. The blending mother liquor was the saturated mother liquor point E of potassium carnallite, carnallite, and potassium chloride at 25℃.

[0062] The underflow from the first crystallization stage is fed to a screening machine, where the particle size is 0.6 mm, yielding oversize (S1) and undersize slurry. Oversize (S1) is then sent to the second-stage crystallization process, while the undersize slurry undergoes first-stage thickening. The underflow concentration of the first-stage thickener is controlled at 45%. The first-stage underflow is then fed to a flotation mixing tank, and the first-stage thickening overflow is stored in a storage tank. A portion of the first-stage thickening overflow is sent to the first-stage crystallization stage as blending mother liquor, while excess mother liquor is sent to a mother liquor evaporation unit for evaporation.

[0063] The oversize material S1 from the first-stage screening is conveyed to the second-stage crystallizer. Water and flotation mother liquor are added to the second-stage crystallizer as the driving force for the second-stage decomposition. Simultaneously, the subsequent second-stage thickening overflow is added as a blending mother liquor. The amount of water added in the second stage is 1.5% of the raw ore mass, and the amount of flotation mother liquor added is 58% of the raw ore mass. The amount of blending mother liquor added is 72.5% of the raw ore mass, and the underflow concentration in the second-stage crystallizer is controlled at 25%.

[0064] The underflow from the second-stage crystallization process is fed to a screening machine, where the particle size is 0.6 mm, yielding oversize (S2) and undersize slurry. The oversize (S2) is sent to the grinding operation, while the undersize slurry undergoes second-stage thickening. The underflow concentration of the second-stage thickener is controlled at 45%. The underflow is then fed to the flotation conditioning tank, and the overflow from the second-stage thickener is stored in a storage tank. A portion of the overflow goes to the second-stage crystallization process as blending mother liquor, while the remaining mother liquor is sent to the grinding operation.

[0065] The S2 material oversize is added to the secondary thickening overflow to adjust its concentration to 50%. The grinding time is controlled at 6 minutes, and the mill discharge is conveyed to the flotation mixing tank.

[0066] The slurry in the flotation conditioning tank is prepared with mother liquor from the flotation mother liquor tank to a mass concentration of 26%. Flotation reagents are added at a rate of 130 g / t of raw ore. The flotation operation adopts a one-roughing, two-cleaning, one-scavenging operation with middlings returned in sequence to obtain flotation concentrate and flotation tailings. The flotation concentrate and flotation tailings are filtered separately to obtain concentrate filter cake K1 and tailings filter cake T1. The filtrate is stored in the flotation mother liquor storage tank and used for secondary crystallization conditioning of mother liquor or flotation slurry.

[0067] After adding water and washing mother liquor to filter cake K1 for slurry preparation, the mixture is stirred and washed for 40 minutes. The resulting slurry is then subjected to solid-liquid separation. The solid phase is wet potassium chloride, which is dried to obtain potassium chloride product with a potassium chloride content of 96% and a recovery rate of approximately 82%. The mother liquor obtained after separation is partially returned to the concentrate filter cake K1 washing operation for slurry preparation, while the excess mother liquor is returned to the roughing operation.

[0068] Example 2

[0069] The primary carnallite deposit in Laos was collected and crushed to -15mm.

[0070] The crushed carnallite is transported to a primary crystallizer using a belt conveyor. Simultaneously, water (TDS / mg / L < 45000), secondary crystallization overflow (L2 mother liquor), and primary thickening overflow are added to the primary crystallizer. The water addition is 17% of the original ore mass, L2 is 28% of the original ore mass, and the primary thickening overflow is 25% of the original ore mass. The mixture circulates within the primary crystallizer for approximately 2 hours. The overflow height is controlled to maintain a primary crystallizer overflow rate of 8%. The slurry circulates within the crystallizer for 2 hours. The theoretically, the blending mother liquor is the saturated mother liquor point E of potassium carnallite, carnallite, and potassium chloride at 25℃.

[0071] The underflow from the first crystallization stage is fed to a screening machine, where the particle size is 0.8 mm, yielding oversize (S1) and undersize slurry. Oversize (S1) is then sent to the second-stage crystallization process, while the undersize slurry undergoes first-stage thickening. The underflow concentration of the first-stage thickener is controlled at 45%. The first-stage underflow is then fed to a flotation mixing tank, and the first-stage thickening overflow is stored in a storage tank. A portion of the first-stage thickening overflow is sent to the first-stage crystallization stage as blending mother liquor, while excess mother liquor is sent to a mother liquor evaporation unit for evaporation.

[0072] The oversize material S1 from the first-stage screening is conveyed to the second-stage crystallizer. Water and flotation mother liquor are added to the second-stage crystallizer as the driving force for the second-stage decomposition. Simultaneously, the subsequent second-stage thickening overflow is added as a blending mother liquor. The amount of water added in the second stage is 5.0% of the raw ore mass, and the amount of flotation mother liquor added is 65% of the raw ore mass. The amount of blending mother liquor added is 75% of the raw ore mass, and the underflow concentration in the second-stage crystallizer is controlled at 33%.

[0073] The underflow from the second-stage crystallization process is fed to a screening machine, where the particle size is 0.8 mm, yielding oversize (S2) and undersize slurry. The oversize (S2) is sent to the grinding operation, while the undersize slurry undergoes second-stage thickening. The underflow concentration of the second-stage thickener is controlled at 45%. The underflow is then fed to the flotation mixing tank, and the overflow from the second-stage thickener is stored in a storage tank. A portion of the overflow goes to the second-stage crystallization process as blending mother liquor, while the remaining mother liquor is used in the grinding operation.

[0074] Grinding operation: The S2 material on the screen is added to the second stage thickening overflow to adjust its concentration to 50%. The grinding time is controlled at 6 minutes. The mill discharge is then conveyed to the flotation mixing tank.

[0075] The slurry in the flotation conditioning tank is prepared to a concentration of 26% using mother liquor from the flotation mother liquor tank. Flotation reagents are added at a rate of 165 g / t of raw ore. The flotation operation adopts a one-roughing, two-cleaning, one-scavenging operation with middlings returned in sequence to obtain flotation concentrate and flotation tailings. The flotation concentrate and flotation tailings are filtered separately to obtain filter cakes, namely concentrate filter cake K1 and tailings filter cake T1. The filtrate is stored in the flotation mother liquor storage tank and used for secondary crystallization conditioning of mother liquor or flotation slurry.

[0076] After adding water and washing mother liquor to concentrate filter cake K1 for slurry preparation, the mixture is stirred and washed for 40 minutes. The resulting slurry undergoes solid-liquid separation, with the solid phase being wet potassium chloride. After drying, potassium chloride product is obtained with a potassium chloride content of 96% and a recovery rate of approximately 82%. The mother liquor obtained after separation is partially returned to the concentrate filter cake K1 washing operation for slurry preparation, while the excess mother liquor is returned to the roughing operation.

[0077] Example 3

[0078] Carnallite from a primary underground carnallite deposit in Laos was crushed to -15mm.

[0079] The crushed carnallite was transported to a first-stage crystallizer using a belt conveyor. Simultaneously, water (TDS / mg / L < 45000), second-stage crystallization overflow L2 mother liquor, and first-stage thickening overflow were added to the first-stage crystallizer. The water content was 17.25% of the raw ore mass, L2 was 25.52% of the raw ore mass, and the first-stage thickening overflow was 35% of the raw ore mass. The mixture circulated within the first-stage crystallizer for approximately 2 hours. The overflow height within the crystallizer was controlled to maintain an overflow rate of 10.05%. The slurry circulated within the crystallizer for 2 hours. The theoretically, the blending mother liquor was the E-point mother liquor, representing the saturation point of potassium carnallite, carnallite, and potassium chloride at 25°C.

[0080] The underflow from the first crystallization stage is fed to a screening machine, where the particle size is 1.0 mm, yielding oversize (S1) and undersize slurry. Oversize (S1) is then sent to the second-stage crystallization process, while the undersize slurry undergoes first-stage thickening. The underflow concentration of the first-stage thickener is controlled at 45%. The first-stage underflow is then fed to a flotation mixing tank, and the first-stage thickening overflow is stored in a storage tank. A portion of the first-stage thickening overflow is sent to the first-stage crystallization stage as blending mother liquor, while excess mother liquor is sent to a mother liquor evaporation unit.

[0081] The oversize material S1 from the first-stage screening is conveyed to the second-stage crystallizer. Water and flotation mother liquor are added to the second-stage crystallizer as the driving force for the second-stage decomposition. Simultaneously, the subsequent second-stage thickening overflow is added as a blending mother liquor. The amount of water added in the second stage is 2.5% of the raw ore mass, and the amount of flotation mother liquor added is 50% of the raw ore mass. The amount of blending mother liquor added is 65% of the raw ore mass, and the underflow concentration in the second-stage crystallizer is controlled at 25%.

[0082] The underflow from the second-stage crystallization process is fed to a screening machine, where the particle size is 0.6 mm, yielding oversize (S2) and undersize slurry. The oversize (S2) is sent to the grinding operation, while the undersize slurry undergoes second-stage thickening. The underflow concentration of the second-stage thickener is controlled at 45%. The underflow is then fed to the flotation conditioning tank, and the overflow from the second-stage thickener is stored in a storage tank. A portion of the overflow goes to the second-stage crystallization process as blending mother liquor, while the remaining mother liquor is sent to the grinding operation.

[0083] The S2 material oversize is added to the secondary thickening overflow to adjust its concentration to 50%. The grinding time is controlled at 6 minutes, and the mill discharge is conveyed to the flotation mixing tank.

[0084] The slurry in the flotation conditioning tank is prepared to a concentration of 26% using mother liquor from the flotation mother liquor tank. Flotation reagents are added at a rate of 180 g / t of raw ore. The flotation operation adopts a one-roughing, two-cleaning, one-scavenging operation with middlings returned in sequence to obtain flotation concentrate and flotation tailings. The flotation concentrate and flotation tailings are filtered separately to obtain concentrate filter cake K1 and tailings filter cake T1. The filtrate is stored in the flotation mother liquor storage tank and used for secondary crystallization conditioning of mother liquor or flotation slurry.

[0085] After adding water and washing mother liquor to concentrate filter cake K1 for slurry preparation, the mixture is stirred and washed for 40 minutes. The resulting slurry undergoes solid-liquid separation, with the solid phase being wet potassium chloride. After drying, potassium chloride product is obtained with a potassium chloride content of 96% and a recovery rate of approximately 82%. The mother liquor obtained after separation is partially returned to the concentrate filter cake K1 washing operation for slurry preparation, while the excess mother liquor is returned to the roughing operation.

[0086] As can be seen from the specific embodiments, in this invention, the collected primary carnallite ore containing potassium rock (potassium rock content 1-8%) is crushed to ≤15mm. Compared with the prior art, which first crushes the raw ore to a finer particle size, such as below 8mm, this application only needs to crush it to 15mm. This not only saves equipment costs but also alleviates the problem of salt blockage in the crushing equipment. The coarser particle size can slow down the decomposition of carnallite, control a large number of potassium chloride crystal nuclei, create conditions for potassium chloride crystallization, and achieve the purpose of controlling the crystallization rate. The amount of crystallization water added in the first stage is 17-30% of the mass of the crushed ore with a particle size ≤15mm. The prior art has multiple decomposition water addition points and difficulty in controlling the water usage in the equipment, resulting in unsaturated mother liquor and low system yield. In this application, the main water addition point is in the first crystallization stage, and the subsequent water addition is very small and is not discharged after addition, but directly recycled. This effectively controls the amount of water used, and the discharged mother liquor is saturated or supersaturated. This reduces the scale of evaporation, reduces potassium discharge, and improves the recovery rate. A two-stage crystallization process is employed. In the second stage, refined potassium mother liquor and a small amount of water are added, allowing for the complete decomposition of insufficiently decomposed carnallite, thus increasing the yield. After two-stage crystallization, the carnallite is fully decomposed, and the oversize material from the second-stage screening is almost entirely potassium rock. This potassium rock can be recovered after grinding, increasing the yield by at least 3%. Furthermore, because some water may be introduced during flotation or filtration, leading to unsaturated mother liquor, the mother liquor generated during flotation is not discharged but recycled within the system, reducing potassium emissions and further improving the recovery rate.

[0087] In summary, this application achieves a single-stage crystallizer overflow in the discharged mother liquor, which is in a saturated or supersaturated state. This solves the problem in traditional processes where, due to the use of horizontal belt filters for tailings filtrate discharge, some water enters the mother liquor, leading to unsaturated mother liquor, partial potassium dissolution, and low system yield. By employing two-stage crystallization and grinding, the system yield is further improved. This application can achieve a potassium chloride system yield of over 81.95%, a potassium chloride grade of 95%, and a tailings KCl grade controlled below 1.0%. Compared to existing technologies with a potassium chloride yield of 55% and tailings KCl of 6.5%, the yield and grade are significantly improved. Furthermore, this application has lower costs, a simpler process, and is suitable for industrial production.

[0088] In the description of this specification, the terms "one embodiment," "some embodiments," "embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0089] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make modifications, alterations, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A production process for producing potassium chloride from carnallite containing potassium rock, characterized in that, include: The collected primary carnallite ore was crushed to ≤15mm; Add water (TDS / mg / L < 45000), potassium-containing mother liquor, and blending mother liquor for crystallization. The amount of water added is 17-30% of the mass of the crushed ore with a particle size ≤ 15mm. The amount of potassium-containing mother liquor added is 20%-28% of the mass of the crushed ore with a particle size ≤ 15mm. Control the overflow of the first-stage crystallization at 8%-12%. The amount of blending mother liquor added is used to control the mass concentration of the bottom flow of the first-stage crystallization at 25%-40%. The underflow of the first crystallization stage is screened once to obtain the oversize material S1 and the undersize slurry. The oversize material S1 is sent to the second crystallizer for processing, and the undersize slurry is thickened in one stage. A section of thickened underflow is transported to the flotation conditioning tank, part of the thickened overflow is returned to the crystallization section as a blending mother liquor, and the excess thickened overflow is evaporated. Add water, flotation mother liquor, and blending mother liquor with a TDS / mg / L < 45000 to the two-stage crystallization operation. The amount of water added to the two-stage operation is 1.5% to 5.0% of the mass of the crushed ore with a particle size ≤ 15mm. The amount of flotation mother liquor added is 50% to 65% of the mass of the crushed ore with a particle size ≤ 15mm. The amount of blending mother liquor added is 65% to 75% of the mass of the crushed ore with a particle size ≤ 15mm. The underflow from the second-stage crystallization is subjected to secondary screening to obtain oversize material S2 and undersize slurry. Oversize material S2 is sent to the grinding operation, and undersize slurry is subjected to secondary thickening. The supernatant from the secondary thickening is returned to the secondary crystallizer as blending mother liquor. The second-stage thickened underflow is transported to the flotation conditioning tank, part of the second-stage thickened overflow is returned to the second-stage crystallization as the blending mother liquor, and the excess second-stage thickened overflow is transported to the grinding operation. During the grinding operation, the oversize material S2 is controlled to have a slurry concentration of 50% to 65% through a two-stage thickening overflow, and the discharged material after grinding is transported to the flotation slurry conditioning tank. Flotation is carried out with flotation reagent to obtain flotation concentrate K1 and flotation tailings T1. After flotation concentrate K1 is mixed and washed with water and washing mother liquor, solid-liquid separation is carried out to obtain potassium chloride product. Part of the separated filtrate is returned to the mixing and washing operation of concentrate filter cake K1 for mixing and washing, and the excess filtrate is returned to the flotation operation.

2. The production process for producing potassium chloride from carnallite containing potassium rock according to claim 1, characterized in that, The particle size for both the primary and secondary screening is 0.6 mm to 1 mm.

3. The production process for producing potassium chloride from carnallite containing potassium rock according to claim 1, characterized in that, The potassium-containing mother liquor is brine with a KCl mass content of 6.0–13.0%, and the blending mother liquor has a KCl mass content of 2.0–6.5%, a MgCl2 mass content of 21.3–26.6%, and a NaCl mass content of 2.0–3.0%.

4. The production process for producing potassium chloride from carnallite containing potassium rock according to claim 1, characterized in that, The mass concentration of the dense underflow section is 40%–55%.

5. The production process for producing potassium chloride from carnallite containing potassium rock according to claim 1, characterized in that, The mass concentration of the undercurrent in the second-stage crystallization stage is 25%–33%.

6. The production process for producing potassium chloride from carnallite containing potassium rock according to claim 1, characterized in that, The mass concentration of the slurry in the flotation slurry conditioning tank is controlled to be 26%–33% by adjusting the opening and closing of the underflow valve of the thickener.

7. The production process for producing potassium chloride from carnallite containing potassium rock according to claim 1, characterized in that, The flotation agent is a three-in-one flotation agent composed of octadecylamine, hydrochloric acid and a frother.

8. The production process for producing potassium chloride from carnallite containing potassium rock according to claim 7, characterized in that, The flotation agent is in the form of oil and wax. When using it, the flotation agent is prepared into a 2% (by mass) solution with water at 85°C.

9. The production process for producing potassium chloride from carnallite containing potassium rock according to claim 7, characterized in that, The amount of flotation agent added is 130g / t raw ore to 200g / t raw ore.

10. The production process for producing potassium chloride from carnallite containing potassium rock according to claim 1, characterized in that, The overflow mother liquor from the second-stage crystallization process is used as a potassium-containing mother liquor.

Images