Process for preparing potassium chloride by using potassium mixed salt

Abstract

The invention relates to a process for preparing potassium chloride by using potassium mixed salt. The process comprises the following steps: (1) crushing and screening; (2) ore grinding and grading; (3) concentrating the slurry; (4) decomposing and crystallizing; (5) size mixing before flotation; (6) flotation; (7) filtering crude potassium; (8) washing crude potassium; (9) filtering refined potassium; and (10) drying the wet product to obtain a final potassium chloride finished product. By the adoption of the method, the defect that when the sylvinite content in the raw materials is high, due to the fact that sylvinite dissociation is insufficient, the one-time potassium recovery rate of the simple cold decomposition-flotation-washing process is low can be remarkably improved, and the overall potassium yield of the production process is effectively increased; and meanwhile, raw material over-grinding can be effectively reduced, flotation reagent consumption can be reduced, energy consumption for ore grinding and drying can be reduced, the treatment efficiency of solid-liquid separation equipment and other equipment can be improved, the product granularity can be effectively improved, and high application and popularization value is achieved.

Description

Technical Field

[0001] The present invention relates to a production process of potassium chloride fertilizer, and particularly to a process for preparing potassium chloride by using a potassium mixed salt mined from a mixture of solid carnallite and sylvinite as a raw material. Background Art

[0002] Potassium fertilizer is one of the three major types of chemical fertilizers used in agricultural production. Potassium deficiency in the soil will seriously affect the metabolism of plants, increase the risks of diseases, pests and lodging, inhibit plant growth and lead to yield reduction, especially for leguminous and tuber crops, where the yield will be severely affected.

[0004] There are significant differences between the production processes of potassium chloride using carnallite as a raw material and those using sylvinite as a raw material. Currently, the "cold decomposition - flotation - washing" process is mainly used to produce potassium chloride from carnallite raw materials. That is, carnallite is first crushed and then fed into the decomposition and crystallization operation to complete decomposition and crystallization. Subsequently, granular sodium chloride and potassium chloride are fed into the flotation operation for sodium - potassium separation. Since the flotation concentrate will entrain fine - grained sodium chloride, the crude potassium product needs to be further washed to obtain the refined potassium product, and then fed into the drying operation to obtain the qualified potassium chloride finished product. When preparing potassium chloride from sylvinite as a raw material, it needs to be crushed and then ground to a suitable particle size to dissociate sodium chloride and potassium chloride, and then the flotation operation is carried out for sodium - potassium separation. Similarly, the crude potassium product needs to be further washed to obtain the refined potassium product, and then fed into the drying operation to obtain the qualified potassium chloride finished product.

[0005] In the late stage of the formation of the primary carnallite ore in some areas, part of the carnallite rock is transformed into potassium - rich sylvinite rock (secondary sylvinite) under the action of continental water leaching during the post - sedimentary transformation stage. It is very difficult to accurately obtain the ore body boundary and quality distribution of this part of sylvinite rock before the start of mining engineering. If the reserves of this part of sylvinite rock are limited, during the design of shaft engineering and production mining, it is usually not considered to separately excavate and transport the sylvinite rock, but the sylvinite and carnallite are mined together and sent to the processing plant as raw materials for preparing potassium chloride. In addition, during the entire life cycle of the mine, in order to recover the investment as soon as possible in the early production stage, the first - mining area is usually set in the area of the sylvinite ore body with a higher potassium content, and almost all the raw materials used in the early production stage are sylvinite. Then, as the mining range changes, the sylvinite ore body is gradually mined out, resulting in a gradual decrease in the content of sylvinite and a gradual increase in the content of carnallite in the raw materials. In the middle and late stages of production, the raw materials may all be carnallite. Although the fluctuations in the raw material grade can be smoothed through production exploration, mining design, excavation planning, storage regulation, etc., the raw material grade cannot be kept constant. That is to say, the impact of the change in raw material properties on the production process will still exist for a long time.

[0006] During the mining process of underground primary carnallite ore, the mining product obtained by mixing sylvinite and carnallite is called potassium mixed salt. Currently, the "cold decomposition - flotation - washing" simple process is generally used to prepare potassium chloride from such potassium mixed salt raw materials. When the content of sylvinite is low (the ratio of sylvinite to carnallite is less than 20%), this process can partially recover the potassium in sylvinite; when the content of sylvinite in the raw material is high, because the sylvinite cannot be effectively monomer-dissociated after crushing operation and decomposition (crystallization) operation and is directly fed into the subsequent flotation operation, the undissociated particles cannot be captured by bubbles and float up to become foam products but remain in the tailings, resulting in a high potassium content in the tailings (the potassium chloride content ≥ 3.5%), reducing the potassium recovery rate of the overall process, causing resource waste and affecting economic benefits.

[0007] To solve this problem, one technical idea is to improve the decomposition and crystallization device. For example: 1) CN105597362A discloses a mechanical crystallizer for potassium salt industry, which effectively improves the mass concentration of circulating slurry and the processing capacity of the crystallizer, increases the particle size of the crystalline product, and reduces the raw material entrainment rate in the crystalline product by setting a bowl-shaped baffle at the lower part of the inner cylinder; 2) CN110229024B discloses a decomposition and crystallization device for potassium salt industry, which reduces the raw material entrainment in the product by introducing a liquid distribution device and a diversion cone in the middle and lower parts of the crystallizer and introducing a local upflow inside the crystallizer; 3) CN111643924B discloses a circulating fluidized bed decomposition and crystallization device and a decomposition and crystallization method, which form a fluidized bed layer stratified by density at the bottom of the crystallizer by changing the liquid supplementing method of the crystallizer and change the discharging method, making the raw material entrainment rate in the final crystal slurry product lower and the average particle size of the product particles larger; the above technologies solve the problem of raw material entrainment in the decomposition and crystallization products to a certain extent and improve the decomposition and crystallization effect; another technical idea is to separate sylvinite and carnallite by pretreatment and treat them separately. For example: 4) CN118385026A discloses a pretreatment method for mixed mined potassium salt raw materials, which pretreats the raw materials through a heavy medium separation device; 5) CN112007750A discloses a separation method for carnallite-type ores, which uses a gravity separation operation for pretreatment to improve the quality of carnallite raw materials, but the added gravity separation scheme will make the process complex and significantly increase the investment in plant and equipment, and it has not been industrially applied yet; 6) CN103708504B discloses a method for preparing potassium chloride from mixed potassium salt ore, which first decomposes and crystallizes all the raw materials, classifies the slurry after decomposition and crystallization, grinds and floats the coarse particles, and separately floats the fine particles. This technology feeds all the raw materials into the decomposition and crystallization, resulting in an increase in the selection of crystallization equipment and an increase in the investment in plant and equipment due to the use of two independent flotation systems. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a process for preparing potassium chloride using potassium mixed salts. This process can effectively recover potassium from sylvinite, with a relatively high potassium recovery rate in the overall production process and a relatively low potassium content in the tailings.

[0009] The present invention aims to overcome the defects of the current "cold decomposition - flotation - washing" simple process, which has insufficient adaptability in the production process when solid - mined carnallite and sylvinite are co - mined, resulting in a high potassium content in the tailings, ineffective recovery of potassium from sylvinite, and a relatively low potassium recovery rate in the overall production process.

[0010] The process for preparing potassium chloride using potassium mixed salts according to the present invention includes the following steps:

[0011] (1) Crushing and screening: Crush and screen the potassium mixed salts, and take the fine particles under the sieve.

[0012] (2) Grinding and classification: Feed the fine particles under the sieve obtained in step (1) into a screening machine for classification. The coarse particles on the sieve and the coarse particles after classification from step (11) are fed into a mill for grinding operations. After grinding, the material is returned to the screening machine for classification. The coarse particles on the sieve are returned to grinding, and the fine particles under the sieve are fed into step (3).

[0013] (3) Slurry concentration: Feed the fine particles under the sieve after classification in step (2) into a thickener for concentration. The overflow clear liquid obtained enters the mother liquor circulation system, and the underflow slurry is fed into step (4).

[0014] (4) Decomposition and crystallization: Feed the underflow slurry after concentration in step (3) into a decomposition device, add an appropriate amount of fresh water and a part of the refined potassium mother liquor from step (9) for decomposition operations. The decomposed slurry is fed into step (5).

[0015] (5) Slurry adjustment before flotation: Add a foaming agent and a collector to the slurry obtained in step (4) and stir evenly, and then feed it into step (6).

[0016] (6) Flotation: Feed the slurry obtained in step (5) into a flotation device for flotation. The tailing slurry obtained is fed into step (11), and the concentrate foam obtained is fed into step (7).

[0017] (7) Coarse potassium filtration: Feed the concentrate foam obtained in step (6) into a filtration device for filtration. The filter cake obtained is the coarse potassium (coarse potassium chloride), which is fed into step (8), and the filtrate enters the mother liquor circulation system to become the circulating mother liquor.

[0018] (8) Coarse potassium washing: Feed the coarse potassium obtained in step (7) or the concentrate foam obtained in step (6) into a washing tank, add the refined potassium mother liquor and fresh water from step (9) for re - slurrying and washing. The obtained slurry is fed into step (9).

[0019] (9) Filtration of refined potassium: Feed the slurry obtained in step (8) into a filtration device for filtration. The filtrate obtained is the refined potassium mother liquor. Part of it is fed into step (8), and the rest is fed into step (4) or step (6) according to the ratio of carnallite and sylvite in the raw material. The filter cake, i.e., the wet refined potassium product, is fed into step (10);

[0020] (10) Drying of wet product: Feed the wet refined potassium product obtained in step (9) into a drying device for drying. The product obtained is the final potassium chloride finished product.

[0021] (11) Tailings classification: Feed the tailings slurry obtained in step (6) into a classification device for classification, recover the coarse-grained materials therein, and feed the fine-grained materials after classification into step (12). The coarse-grained materials after classification are returned to the mill in step (2) for grinding again;

[0022] ((12) Tailings thickening and filtration: Feed the fine-grained materials after classification in step (11) into a thickener for thickening. The overflow clear liquid after thickening enters the mother liquor circulation system, and the underflow slurry is fed into a filtration device for filtration. The filtrate obtained enters the mother liquor circulation system and becomes the circulating mother liquor. The filter cake, i.e., the solid tailings, is fed into step (13);

[0023] (13) Tailings filling: Transport the solid tailings obtained in step (12) to the underground goaf for filling.

[0024] Furthermore, in step (1), the crusher used for the crushing operation is at least one of a column crusher, a cage crusher, a hammer crusher, and a roll crusher, preferably a cage crusher. The solid raw material potassium mixed salt lifted from underground mining is crushed and then fed into a screening machine for classification. The coarse-grained materials on the screen are returned to the crusher. The fine-grained materials under the screen are fed into step (2).

[0025] Furthermore, in step (1), the classification particle size for the screening and classification operation is 5 - 20 mm, preferably 10 mm.

[0026] Furthermore, in step (2), the equipment used for the classification operation is at least one of a linear vibrating screen, a circular vibrating screen, a banana screen, a relaxation screen, a hydrocyclone, and a heavy medium classification device, preferably a linear vibrating screen.

[0027] Furthermore, in step (2), the classification particle size is 0.5 mm - 2 mm, preferably 1 mm.

[0028] Furthermore, in step (2), the following operation can also be carried out: The fine-grained materials under the screen obtained in step (1) can also be fed into the mill. The slurry after grinding is then fed into a screening machine for classification. The coarse-grained materials on the screen are returned to the mill, and the fine-grained materials under the screen are fed into the subsequent thickening operation.

[0029] Further, in step (2), the following operations can also be performed: Feed the fine screened particles obtained in step (1) into a screening machine for classification. The coarse screened particles and the coarse particles after classification from step (7) are fed into a mill for grinding together. The slurry after grinding is fed into step (3).

[0030] Further, the theoretical value of the water addition in step (4) is determined by referring to the Na + , K + , Mg 2+ / / Cl - -H2O quaternary water-salt system phase diagram to obtain the water volume at which all carnallite in the raw material is just completely decomposed. The actual addition amount is 105% - 130% of the theoretical calculated value, and the decomposition time is 30 min - 60 min. The actual addition amount of water is the sum of the fresh water and the water in the refined potassium mother liquor.

[0031] Further, step (4) can be determined according to the proportion of sylvite in the raw material. When the ratio of the mass of sylvite in the raw material / (the mass of sylvite + the mass of carnallite) is not less than 80%, the underflow slurry from step (3) can be directly fed into step (5).

[0032] Further, in step (5), the foaming agent is No. 2 oil, and its addition amount is 15 - 60 g / ton of raw ore. The collector is octadecylamine, and its addition amount is 50 - 120 g / ton of raw ore.

[0033] Further, in step (6), the flotation operation process is adjusted and determined according to the properties of the raw material, and is preferably the process of "one roughing, one scavenging, and two cleanings".

[0034] Further, in step (8), the concentrated ore foam obtained in step (6) can also be directly fed into step (8) for washing of the crude potassium without passing through step (7) for filtration of the crude potassium.

[0035] Further, in step (8), the theoretical value of the water addition is determined by referring to the Na + , K + , Mg 2+ / / Cl - -H2O quaternary water-salt system phase diagram to obtain the water volume at which all sodium chloride in the slurry to be washed is just dissolved. The actual addition amount is 110% - 120% of the theoretical value, and the washing time is 30 min - 60 min. The actual addition amount of water is the sum of the fresh water and the water in the refined potassium mother liquor.

[0036] Further, in step (11), the classification equipment used for the tailings classification operation is one of a straight vibrating screen, a circular vibrating screen, a banana screen, a relaxation screen, and a hydrocyclone, and is preferably a straight vibrating screen.

[0037] Further, the classification particle size in step (11) is 0.4 mm to 0.8 mm, preferably 0.5 mm.

[0038] Further, in step (12), the equipment used for the tailings thickening operation is one or a combination of a thickener and a hydrocyclone, preferably a thickener.

[0039] Further, the equipment used for the tailings filtration operation in step (12) is one of a belt vacuum filter, a disc vacuum filter, a rotary table (disc) vacuum filter, and a plate and frame filter press, preferably a belt vacuum filter.

[0040] Further, in step (12), the fine-grained material after classification from step (11) may also be directly fed into the filtration equipment for filtration without passing through the tailings thickening operation.

[0041] Compared with the prior art, the process for preparing potassium chloride using potassium mixed salt in the present invention has good applicability to raw materials, can be used for the co-mining of carnallite and sylvite, and potassium mixed salt formed by mixing carnallite and sylvite in different proportions can be used as the raw material to prepare potassium chloride, and the production process is flexible. By adopting the present invention, using potassium mixed salt as the raw material to prepare potassium chloride can significantly improve the shortcoming of the low primary potassium recovery rate in the simple process of "cold decomposition - flotation - washing" due to insufficient dissociation of sylvite when the sylvite content in the raw material is relatively high, effectively improve the overall potassium recovery rate of the production process, and at the same time can effectively reduce over-grinding of raw materials, reduce the consumption of flotation reagents, reduce the energy consumption of grinding and drying, improve the treatment efficiency of equipment such as solid-liquid separation, and can also effectively improve the product particle size, having high application and promotion value. Specific Embodiments

[0042] The following further describes the present invention in detail with specific embodiments.

[0043] Unless otherwise specified, the percentages in the present invention are all weight percentages.

[0044] Example 1

[0045] In the raw material potassium mixed salt of this example, the KCl content is 30.81%, the NaCl content is 65.58%, the MgCl2 content is 1.03%, the insoluble matter content is 1.42%, and the ratio of carnallite to sylvite is 1:10 (calculated based on the removal of halite in the raw material), that is, the raw material is mainly sylvite.

[0046] The process for preparing potassium chloride using potassium mixed salt in this example includes the following steps:

[0047] (1) Crushing and screening: The solid raw material potassium mixed salt lifted from underground mining is crushed and screened, and the fine-grained material under the sieve is taken, and the particle size of the treated material ≤ 10 mm;

[0048] (2) Grinding and classification: Feed the materials obtained from crushing and screening in step (1) into a linear vibrating screen for wet pre-screening. The oversize materials (+0.8 mm) are fed into a rod mill. After grinding, the materials are returned to the linear vibrating screen for classification. The oversize coarse-grained materials (+0.8 mm) after classification are returned to grinding, and the undersize fine-grained materials (-0.8 mm) are fed into slurry thickening.

[0049] (3) Slurry thickening: Pump the undersize fine-grained materials from grinding and classification in step (2) to a thickener for thickening. The overflow clear liquid obtained enters the mother liquor recycling system, and the underflow slurry is controlled at a concentration of 40% and fed into decomposition and crystallization.

[0050] (4) Decomposition and crystallization: Feed the underflow slurry after thickening in step (3) into a decomposition tank and add an appropriate amount of fresh water. The addition amount of fresh water is 110% of the theoretical decomposition water amount corresponding to the carnallite amount in the raw materials, and the decomposition time is 40 min.

[0051] (5) Slurry adjustment before flotation: Feed the slurry after decomposition and crystallization into a slurry adjustment and stirring tank, and add No. 2 oil (20 g / ton of raw ore) as a foaming agent and octadecylamine (100 g / ton of raw ore) as a collector, and stir evenly.

[0052] (6) Flotation: Feed the slurry after slurry adjustment into a flotation device for separation. It is a flotation process of one roughing, two scavengings, and two cleanings. The tailing slurry obtained is fed into step (11), and the concentrate foam obtained is fed into step (7).

[0053] (7) Coarse potassium washing: Feed the concentrate foam obtained from flotation in step (6) into a re-slurrying and washing tank, and add the refined potassium mother liquor from step (8) and fresh water for washing. The addition amount of water is 120% of the theoretical dissolution water amount corresponding to sodium chloride in the coarse potassium, and the washing time is 30 min.

[0054] (8) Refined potassium filtration: Feed the slurry obtained in step (7) into a belt filter for dehalogenation. The filter cake material obtained by filtration is the wet refined potassium product. Part of the mother liquor obtained by filtration is returned to the re-slurrying and washing tank, and part enters the mother liquor recycling system and goes to the flotation operation.

[0055] (9) Wet product drying: Feed the wet refined potassium product into a rotary dryer for drying, and the product obtained is the final potassium chloride finished product.

[0056] (10) Tailings classification: Feed the tailing slurry obtained from flotation in step (6) into a linear vibrating screen for classification. The classification particle size is 0.5 mm. The oversize coarse-grained materials are returned to the grinding and classification operation for re-grinding, and the undersize fine-grained materials are fed into a tailings thickener for thickening.

[0057] (11) Tailings thickening and filtration: The underflow slurry of the tailings thickener is pumped to a belt filter for filtration at a concentration of 40%. The filtered cake material is transported to the underground goaf for filling, and the mother liquor obtained from filtration enters the mother liquor circulation system.

[0058] In Example 1, the KCl content in the final potassium chloride product obtained is 95.21%, that is, the K2O content ≥ 60%. The KCl content in the tailings obtained is 2.0%, and the overall potassium recovery rate is 86.5%.

[0059] Example 2

[0060] In this example, the raw material contains 16.11% KCl, 38.95% NaCl, 20.58% MgCl2, and 1.05% insoluble matter. The raw material is mixed with halite and a small amount of insoluble matter such as gypsum and clay, and there is no sylvite.

[0061] The process for preparing potassium chloride from potassium mixed salt in this example includes the following steps:

[0062] (1) Crushing and screening: The solid raw material lifted from underground mining is crushed and screened, and the particle size of the processed material ≤ 15 mm;

[0063] (2) Grinding and classification: The material after crushing and screening is fed into a circular vibrating screen for wet pre-screening. The oversize material (+2 mm) is fed into a rod mill. The material after grinding is returned to the circular vibrating screen for classification. The oversize coarse particle material (+2 mm) after classification is returned to grinding, and the undersize fine particle material (-2 mm) is fed into slurry thickening;

[0064] (3) Slurry thickening: The undersize fine particle material after grinding and classification is pumped into a thickener for thickening; the overflow clear liquid obtained enters the mother liquor circulation system, and the underflow slurry obtained is controlled at a concentration of 40% and fed into decomposition and crystallization;

[0065] (4) Decomposition and crystallization: The thickened underflow slurry is fed into a decomposition tank, and fresh water and the refined potassium mother liquor from step (9) are added. The added water volume in the fresh water and the refined potassium mother liquor is 120% of the theoretical decomposition water volume corresponding to the carnallite amount in the raw material, and the decomposition time is 45 min;

[0066] (5) Slurry adjustment before flotation: The slurry after decomposition and crystallization is fed into a slurry adjustment and stirring tank, and the circulating mother liquor is added to adjust to a concentration of about 25%. Foaming agent No. 2 oil (25 g / ton of raw ore) and collector octadecylamine (120 g / ton of raw ore) are added and stirred evenly;

[0067] (6) Flotation: The slurry after slurry adjustment is fed into a flotation device for separation, which is a flotation process of one roughing, one scavenging, and two cleanings; the obtained tailings slurry is fed into step (11), and the obtained concentrate foam is fed into step (7);

[0068] (7) Coarse potassium filtration: Feed the concentrate foam obtained from flotation in step (6) into a belt filter for filtration. The mother liquor obtained from filtration enters the mother liquor recycling system, and the solid phase obtained from filtration is the coarse potassium product;

[0069] (8) Coarse potassium washing: Feed the coarse potassium obtained in step (7) into a repulping and washing tank, and add the mother liquor of refined potassium from step (9) and fresh water for washing. The addition amount of water is 110% of the theoretically dissolved water amount corresponding to sodium chloride in the coarse potassium, and the washing time is 40 min;

[0070] (9) Refined potassium filtration: Feed the slurry obtained in step (8) into a belt filter for dehalogenation. The filter cake material obtained from filtration is the wet refined potassium product. Part of the mother liquor obtained from filtration is returned to the repulping and washing tank, and part enters the mother liquor recycling system and goes to the decomposition operation;

[0071] (10) Drying of wet product: Feed the wet refined potassium product obtained in step (9) into a rotary dryer for drying, and the obtained product is the final potassium chloride finished product.

[0072] (11) Tailings thickening and filtration: Control the concentration of the tailings slurry obtained in step (6) at 40% and pump it to a belt filter for filtration. The filter cake material obtained from filtration is transported to the underground goaf for filling, and the mother liquor obtained from filtration enters the mother liquor recycling system;

[0073] In Example 2, the KCl content in the finally obtained potassium chloride finished product is 95.12%, that is, the K2O content ≥ 60%. The KCl content in the obtained tailings is 1.7%, and the overall potassium recovery rate is 74.6%.

Claims

1. A process for preparing potassium chloride using potassium mixed salts, characterized in that, It includes the following steps: (1) Crushing and screening: Crush and screen the potassium mixed salt, and take the fine particles under the screen; (2) Grinding and classification: Feed the fine particles under the screen obtained in step (1) into a screening machine for classification. The coarse particles on the screen and the coarse particles after classification from step (11) are fed into a mill for grinding operations together. After grinding, the material is returned to the screening machine for classification. The coarse particles on the screen are returned to grinding, and the fine particles under the screen are fed into step (3); (3) Slurry concentration: Send the fine particles under the screen after classification in step (2) to a thickener for concentration. The overflow clear liquid obtained enters the mother liquor circulation system, and the underflow slurry is fed into step (4); (4) Decomposition and crystallization: Feed the underflow slurry after concentration in step (3) into a decomposition device, add an appropriate amount of fresh water and part of the refined potassium mother liquor from step (9) for decomposition operations. The decomposed slurry is fed into step (5); (5) Slurry adjustment before flotation: Add a foaming agent and a collector to the slurry obtained in step (4) and stir evenly, and then feed it into step (6); (6) Flotation: Feed the slurry obtained in step (5) into a flotation device for flotation. The tailing slurry obtained is fed into step (11), and the concentrate foam obtained is fed into step (7); (7) Coarse potassium filtration: Feed the concentrate foam obtained in step (6) into a filtration device for filtration. The filter cake obtained is the coarse potassium (coarse potassium chloride) and is fed into step (8), and the filtrate obtained enters the mother liquor circulation system and becomes the circulating mother liquor; (8) Coarse potassium washing: Feed the coarse potassium obtained in step (7) or the concentrate foam obtained in step (6) into a washing tank, add the refined potassium mother liquor and fresh water from step (9) for re-slurry washing. The slurry obtained is fed into step (9); (9) Refined potassium filtration: Feed the slurry obtained in step (8) into a filtration device for filtration. The filtrate obtained is the refined potassium mother liquor. Part of it is fed into step (8), and the rest is fed into step (4) or step (6) according to the ratio of carnallite and sylvite in the raw material. The filter cake obtained is the wet refined potassium product and is fed into step (10); (10) Drying of wet product: Feed the wet refined potassium product obtained in step (9) into a drying device for drying, and the product obtained is the final potassium chloride finished product.

2. The process for preparing potassium chloride using potassium mixed salts according to claim 1, characterized in that, It also includes the following steps: (11) Tailings classification: Feed the tailing slurry obtained in step (6) into a classification device for classification, recover the coarse particles therein. The fine particles after classification are fed into step (12), and the coarse particles after classification are returned to the mill in step (2) for grinding again; (12) Tailings concentration and filtration: Feed the fine particles after classification in step (11) into a thickener for concentration. The overflow clear liquid after concentration enters the mother liquor circulation system, and the underflow slurry is fed into a filtration device for filtration. The filtrate obtained enters the mother liquor circulation system and becomes the circulating mother liquor, and the filter cake is the solid tailings and is fed into step (13); (13) Tailings filling: Transport the solid tailings obtained in step (12) to the underground goaf for filling.

3. The process for preparing potassium chloride by using potassium mixed salt according to claim 1 or 2, characterized in that, In step (1), the crusher used for crushing operations is at least one of a column crusher, a cage crusher, a hammer crusher, and a roll crusher; And / or, in step (1), the classification particle size for screening and classification operations is 5 - 20 mm.

4. The process for preparing potassium chloride by using potassium mixed salt according to claim 1 or 2, characterized in that, In step (2), the equipment used for the classification operation is at least one of a straight vibrating screen, a circular vibrating screen, a banana screen, a relaxation screen, a hydrocyclone, and a heavy medium classification device; And / or, in step (2), the classification particle size is 0.5 mm to 2 mm; And / or, in step (2), the following operations are performed: The fine particle material obtained from the screen underflow in step (1) can also be fed into a mill, and the slurry after grinding is then fed into a screening machine for classification. The coarse particle material on the screen is returned to the mill, and the fine particle material under the screen is fed into the subsequent thickening operation.

5. The process for preparing potassium chloride by using potassium mixed salt according to claim 1 or 2, characterized in that, In step (2), the following operations are performed: The fine particle material obtained from the screen underflow in step (1) is fed into a screening machine for classification. The coarse particle material on the screen and the coarse particle material after classification in step (7) are fed into a mill together for grinding, and the slurry after grinding is fed into step (3).

6. The process for preparing potassium chloride using potassium mixed salt according to claim 1 or 2, characterized in that, The theoretical value of the water addition in step (4) is based on the phase diagram of the quaternary water-salt system of Na + , K + , Mg 2+ / / Cl - -H2O to obtain the amount of water when all the carnallite in the raw materials is just completely decomposed. The actual addition amount is 105% - 130% of the theoretical calculated value, and the decomposition time is 30 min - 60 min; And / or, step (4) can be determined according to the proportion of sylvite in the raw material. When the ratio of the mass of sylvite / (the mass of sylvite + the mass of carnallite) in the raw material is not less than 80%, the underflow slurry from step (3) is directly fed into step (5); And / or, in step (5), the foaming agent is No. 2 oil, and its addition amount is 15 to 60 grams per ton of raw ore; And / or, in step (5), the collector is octadecylamine, and its addition amount is 50 to 120 grams per ton of raw ore. In step (5), in step (6), the flotation operation process is a "one roughing, one scavenging, and two cleaning" process.

7. The process for preparing potassium chloride by using potassium mixed salt according to claim 1 or 2, characterized in that, In step (8), the concentrate foam obtained in step (6) is directly fed into the crude potassium washing in step (8) without passing through the crude potassium filtration in step (7).

8. The process for preparing potassium chloride using potassium mixed salts according to claim 1 or 2, characterized in that, In step (8), the theoretical value of the water addition is based on the Na + , K + , Mg 2+ / / Cl - -H2O quaternary water-salt system phase diagram to obtain the amount of water when all sodium chloride in the slurry to be washed is just dissolved. The actual addition amount is 110% - 120% of the theoretical value, and the washing time is 30 min - 60 min.

9. The process for preparing potassium chloride by using potassium mixed salt according to claim 1 or 2, characterized in that, In step (11), the classification equipment used for the tailings classification operation is one of a straight vibrating screen, a circular vibrating screen, a banana screen, a relaxation screen, and a hydrocyclone. In step (5), in step (11), the classification particle size of the classification operation is 0.4 mm to 0.8 mm.

10. The process for preparing potassium chloride using potassium mixed salts according to claim 1 or 2, characterized in that, In step (12), the equipment used for the tailings thickening operation is one or a combination of a thickener and a hydrocyclone; And / or, in step (12), the equipment used for the tailings filtration operation is one of a belt vacuum filter, a disc vacuum filter, a rotary table vacuum filter, and a plate and frame filter press; And / or, in step (12), the fine particle material after classification from step (11) is directly fed into a filtration equipment for filtration without passing through the tailings thickening operation.