阅读说明：本技术 一种氯化钾精制工艺及生产系统 (Potassium chloride refining process and production system ) 是由 冯冬娅 张强 方静 颜学伦 雷婷 李春霖 于 2021-09-26 设计创作，主要内容包括：本发明公开了一种氯化钾精制工艺及生产系统,所述精制工艺包括如下内容：将高钠氯化钾与水混合得到氯化钾晶浆,并在晶浆中加入精制剂,离心得到用于高品质氢氧化钾生产的98％以上的低钠氯化钾,输送至盐水工段作为生产原料,同时形成的沉淀物随着原盐在盐水工段形成盐泥后,可用作复合缓释肥的原料。离心母液在多次循环洗涤后经蒸发浓缩、冷结晶得到纯度较高的氯化钾,一段结晶母液液经二次蒸发热结晶析出的氯化钠可用于饲料添加剂的原料,母液经冷结晶再一次析出纯度较高的氯化钾,得到的氯化钾经干燥后可制备食品级氯化钾,二段结晶母液送至锅炉房可用于树脂再生。本发明工艺流程及设备简单,具有较好的综合经济效益,易于实现工业化生产。(The invention discloses a potassium chloride refining process and a production system, wherein the refining process comprises the following contents: mixing high-sodium potassium chloride with water to obtain potassium chloride crystal slurry, adding a refining agent into the crystal slurry, centrifuging to obtain over 98 percent of low-sodium potassium chloride for producing high-quality potassium hydroxide, conveying the low-sodium potassium chloride to a salt water working section as a production raw material, and forming a precipitate which is used as a raw material of the composite slow-release fertilizer after the precipitate forms salt mud in the salt water working section along with original salt. The centrifugal mother liquor is subjected to repeated circulating washing, evaporation concentration and cold crystallization to obtain potassium chloride with high purity, sodium chloride separated out by the first-stage crystallization mother liquor through secondary evaporation heat crystallization can be used as a raw material of a feed additive, potassium chloride with high purity is separated out again by the mother liquor through cold crystallization, the obtained potassium chloride can be used for preparing food-grade potassium chloride after drying, and the second-stage crystallization mother liquor is sent to a boiler room and can be used for resin regeneration. The method has simple process flow and equipment, has better comprehensive economic benefit and is easy to realize industrial production.)

1. The potassium chloride refining process is characterized by comprising the following steps of: (1) mixing high-sodium potassium chloride raw salt and water according to a solid-to-liquid ratio of 1-3: 1 to obtain crystal slurry, mixing the crystal slurry with a refining agent, washing for 0.5-3 h, and centrifuging to obtain low-sodium potassium chloride and high-potassium mother liquor.

2. The potassium chloride refining process of claim 1, wherein KCl in the high-sodium potassium chloride raw salt is not more than 95 percent, and NaCl is not less than 3 percent;

the solid-liquid ratio of the high-sodium potassium chloride raw salt to the water is 2: 1.

3. The potassium chloride refining process of claim 1, wherein the refining agent is a calcium magnesium refining agent; further, the calcium and magnesium refining agent is selected from one or more of phosphoric acid, potassium phosphate salt and potassium carbonate salt;

the dosage of the refining agent is 0.1-0.5% of the high-sodium potassium chloride raw salt, and further 0.2%.

4. The potassium chloride refining process according to claim 1, wherein the pH value of the mixture and the refining agent during washing is 10-12, and the washing time is 0.5-1.5 h.

5. The potassium chloride refining process according to any one of claims 1 to 4, further comprising:

(2) recycling the high-potassium mother liquor in the step (1), mixing with high-sodium potassium chloride, water and a refining agent, and washing to obtain food-grade potassium chloride and high-potassium mother liquor;

(3) adjusting the pH value of the mother liquor obtained in the step (2) to 6-7, performing first-stage evaporation concentration in an evaporation crystallization kettle, and centrifuging to obtain food-grade low-sodium potassium chloride and high-sodium mother liquor;

(4) returning the high-sodium mother liquor obtained in the step (3) to an evaporation crystallization kettle for second-stage evaporation concentration, filtering to obtain feed additive sodium chloride and high-potassium mother liquor, and centrifuging the cooled high-potassium mother liquor to obtain food-grade low-sodium potassium chloride and high-sodium mother liquor;

and (3) circularly washing in the step (2) until the content of sodium chloride in potassium chloride reaches 0.1-1%.

6. The utility model provides a refined production system of potassium chloride, its characterized in that, includes refined cauldron (1), first centrifuge (2), evaporation crystallization cauldron (4), and has at least one first liquid feeding pipe (6) on refined cauldron (1), is connected with mother liquor backflow pipeline (7) between first centrifuge (2) liquid outlet and refined cauldron (1), still is connected with mother liquor pipeline (13) between first centrifuge (2) liquid outlet and evaporation crystallization cauldron (4).

7. The production system according to claim 6, wherein the first filling pipe (6) is further provided with a first cut-off valve (8) and a first flow meter (9), and the first flow meter (9) is in linkage connection with the first cut-off valve (8);

refined cauldron (1) still is equipped with first inlet pipe (10) that are used for sending into the PH regulator, still installs first ooff valve (11) on first inlet pipe (10), and still is equipped with on refined cauldron (1) at first online PH meter (12), first online PH meter (12) and first ooff valve (11) linkage are connected.

8. The production system according to claim 6 or 7, wherein a second shut-off valve (14) and a second flow meter (15) are further mounted on the mother liquor conveying pipeline (13), and the second flow meter (15) is in linkage connection with the second shut-off valve (14);

the evaporation crystallization kettle (4) is also provided with a second feeding pipe (16) for feeding a PH regulator, a second switch valve (17) is further installed on the second feeding pipe (16), a second on-line PH meter (18) is further arranged on the evaporation crystallization kettle (4), and the second on-line PH meter (18) is in linkage connection with the second switch valve (17);

the evaporative crystallization kettle (4) is further provided with an online thermometer (19), the outer wall of the evaporative crystallization kettle (4) is further provided with a jacket (20), the jacket (20) is connected with a cooling water conveying pipe (21), a temperature switch valve (22) is installed on the cooling water conveying pipe (21), and the online thermometer (19) is in linkage connection with the temperature switch valve (22).

9. The production system according to claim 8, wherein a steam input pipe (23) is further connected to the jacket (20);

the evaporation crystallization kettle (4) is also provided with a steam output pipeline (24), the output end of the steam output pipeline (24) is sequentially connected with a condenser (25) and a condensed water tank (26), the condenser (25) is also connected with a vacuum pump (27) for emptying non-condensable gas, and the condensed water tank (26) is connected with the refining kettle (1);

still install level gauge (28) on condensate tank (26), and install control valve (29) on steam input pipe (23), and level gauge (28) and control valve (29) linkage are connected.

10. The production system according to claim 6, wherein a mother liquor storage tank (3) is further installed between the liquid outlet of the first centrifuge (2) and the evaporative crystallization kettle (4), and a mother liquor reflux pipeline (7) is connected between the refining kettle (1) and the mother liquor storage tank (3);

the evaporation crystallization kettles (4) are multiple, the outlets of the evaporation crystallization kettles (4) are all provided with a second centrifugal machine (5), and the liquid outlet of the second centrifugal machine (5) at the outlet section of the last evaporation crystallization kettle (4) is connected with the next evaporation crystallization kettle (4).

Technical Field

The invention belongs to the technical field of chlor-alkali industry, and particularly relates to a potassium chloride refining process and a potassium chloride refining production system.

Background

The main raw material for producing potassium hydroxide products in the chlor-alkali industry is potassium chloride, and due to different production processes and production areas, the content of impurities such as sodium, calcium, magnesium, total nitrogen, sulfate and the like in the potassium chloride raw salt has large difference. At present, calcium, magnesium, total nitrogen and sulfate can be removed in a saline water working section by a mode of increasing pH and adding a refining agent for sedimentation, but sodium in potassium chloride cannot be removed by simple refining, and high-quality potassium hydroxide with high requirement on sodium content can be caused when the sodium chloride content exceeds 1%, such as the quality of reagent-grade and electronic-grade products.

At present, the separation of potassium chloride and sodium chloride is difficult, and a forward-reverse flotation method, an extraction method and an organic solvent salting-out method in the industry are mainly applied to the crude extraction of potassium chloride, but the methods can cause the content of organic matters in the potassium chloride to be overhigh, thereby influencing the electrolysis. The hot-melting cold crystallization method can improve the purity of the potassium chloride to more than 98 percent, but can generate a large amount of mother liquor, and is not suitable for being widely popularized in the refining of the potassium chloride required by the production of high-quality potassium hydroxide except that enterprises around salt lakes can adopt the process.

The patent CN108862329B discloses a recovery method for preparing salt-containing mother liquor of edible-grade potassium chloride, which comprises the steps of dissolving industrial potassium chloride with the purity of 97-98%, evaporating, crystallizing, centrifugally separating, drying to obtain a refined edible-grade potassium chloride product, adding a refining agent into the mother liquor separated by the centrifugal machine, and returning the mother liquor as a circulating liquid to an evaporation system to prepare low-sodium salt, wherein the content of the potassium chloride obtained by the method is low.

Patent CN 112624156 a discloses a process for producing high-purity green low-sodium salt from sodium chloride solution and low-grade potassium chloride solution, which comprises the following steps: the method is mainly characterized in that sodium chloride solution and potassium chloride solution formed by adding water into low-grade potassium chloride are used as raw materials, sodium hydroxide or lime and soda ash are added for double decomposition reaction, calcium and magnesium impurities are removed to obtain refined raw material liquid, and the refined raw material liquid is evaporated to obtain a high-purity low-sodium salt product.

Therefore, there is a need to develop a potassium chloride purification process that can remove sodium from potassium chloride to obtain high-purity potassium chloride and maximize the utilization of the byproduct mother liquor generated during the purification process.

Disclosure of Invention

The invention aims to provide a potassium chloride refining process and a potassium chloride refining production system of food-grade potassium chloride raw materials and feed additive raw materials with high added values, and improve the resource utilization rate in the potassium chloride refining process.

In the prior art, a refining agent is added into a potassium chloride solution or the refining agent is added during the recovery of mother liquor, but the prepared potassium chloride product has low content or low purity and cannot meet the production requirement. In the production process, the inventor finds that the potassium chloride product index can be improved by controlling the dissolution ratio of potassium chloride and water, but the content of potassium chloride is still low, sodium chloride, calcium and magnesium ions contained in the potassium chloride cannot be effectively removed, and after a large amount of literature research, the inventor cannot find the reason of the problem and an effective method for solving the problem.

After long-term exploration, the inventor unexpectedly finds that potassium chloride crystal slurry is added with a refining agent to remove calcium and magnesium ions and then is subjected to evaporation concentration, the obtained potassium chloride can be used as a raw material of high-quality potassium hydroxide, the reason is probably that the refining agent is combined with a filter cake layer formed by potassium chloride, the filtering effect of calcium and magnesium precipitates can be improved, and the generated calcium and magnesium precipitates have longer aging time than a salt water stage and larger particles and are probably more favorable for subsequent precipitation.

In order to achieve the purpose, the invention adopts the following scheme:

provides a potassium chloride refining process, which comprises the following steps: (1) mixing high-sodium potassium chloride raw salt and water according to a solid-to-liquid ratio of 1-3: 1 to obtain crystal slurry, mixing the crystal slurry with a refining agent, washing for 0.5-3 h, and centrifuging to obtain low-sodium potassium chloride and high-potassium mother liquor.

The low-sodium potassium chloride produced by the method can be used as a raw material for producing high-quality potassium hydroxide, and meanwhile, the precipitate formed in the refining process can be used as a raw material of a compound slow-release fertilizer after forming salt mud in a saline water working section along with original salt.

The invention can obtain qualified industrial potassium chloride for producing potassium hydroxide by a washing mode, reduces the purchasing demand of enterprises on high-grade potassium chloride and reduces the production cost.

Furthermore, KCl in the high-sodium potassium chloride raw salt is less than or equal to 95 percent, and NaCl is more than or equal to 3 percent;

the solid-liquid ratio of the high-sodium potassium chloride raw salt to the water is 2: 1.

The solid-liquid ratio refers to the mass ratio.

Further, the refining agent is a calcium-magnesium refining agent; the calcium and magnesium refining agent is selected from one or more of phosphoric acid, potassium phosphate salt and potassium carbonate salt;

the dosage of the refining agent is 0.1-0.5% of the high-sodium potassium chloride raw salt, and further 0.2%.

Further, the pH value of the mixture and the refining agent during washing is 10-12, and the washing time is 0.5-1.5 h.

Because a large amount of mother liquor is generated in the refining process, in order to utilize the mother liquor, the inventor makes a series of attempts and comparisons, and finally finds that the mother liquor is used for washing high-sodium potassium chloride raw salt, parameters such as washing times, solid-to-liquid ratio, pH value, concentration times and the like are controlled, the obtained potassium chloride can be used as a food-grade potassium chloride raw material after evaporation concentration and crystallization, the sodium chloride generated in the concentration and crystallization process can also be used as a feed additive, the economic benefit is greatly improved, and the final mother liquor can also be used as resin for continuous utilization.

Further, the potassium chloride refining process further comprises the following steps:

(2) recycling the high-potassium mother liquor in the step (1), mixing with high-sodium potassium chloride, water and a refining agent, and washing to obtain food-grade potassium chloride and high-potassium mother liquor;

(3) adjusting the pH value of the mother liquor obtained in the step (2) to 6-7, performing first-stage evaporation concentration in an evaporation crystallization kettle, and centrifuging to obtain food-grade low-sodium potassium chloride and high-sodium mother liquor;

(4) and (4) returning the high-sodium mother liquor obtained in the step (3) to an evaporation crystallization kettle for two-stage evaporation concentration, filtering to obtain feed additive sodium chloride and high-potassium mother liquor, and centrifuging the cooled high-potassium mother liquor to obtain food-grade low-sodium potassium chloride and high-sodium mother liquor.

The mother liquor obtained by centrifugation can obtain potassium chloride with high purity of more than 99 percent after repeated circulating washing through evaporation concentration and cold crystallization, sodium chloride separated out by the first-stage crystallization mother liquor in (3) through secondary evaporation heat crystallization can be used as a raw material of a feed additive, potassium chloride with high purity of more than 99 percent can be separated out by the mother liquor through cold crystallization, the potassium chloride obtained by the two-stage evaporation and cold crystallization can be dried to prepare food-grade potassium chloride, and the mother liquor generated by the second-stage crystallization can be sent to a boiler room for resin regeneration.

The invention controls the evaporation amount in the kettle by collecting the amount of the evaporated condensate water, the evaporated steam is condensed by the condenser to obtain the condensate water, namely the amount of the condensate water is equal to the evaporation amount, and the evaporated condensate liquid returns to the refining kettle to be used as the washing liquid.

Further, the sodium chloride in the potassium chloride obtained in the step (2) is washed in a circulating manner until the content of the sodium chloride in the potassium chloride is 0.1-1%.

The invention also provides a potassium chloride refining production system which comprises a refining kettle (1), a first centrifugal machine (2) and an evaporative crystallization kettle (4), wherein the refining kettle (1) is provided with at least one first liquid adding pipe (6), a mother liquid backflow pipeline (7) is connected between a liquid outlet of the first centrifugal machine (2) and the refining kettle (1), and a mother liquid conveying pipeline (13) is also connected between the liquid outlet of the first centrifugal machine (2) and the evaporative crystallization kettle (4).

Furthermore, a first cut-off valve (8) and a first flow meter (9) are further mounted on the first liquid adding pipe (6), and the first flow meter (9) is in linkage connection with the first cut-off valve (8);

refined cauldron (1) still is equipped with first inlet pipe (10) that are used for sending into the PH regulator, still installs first ooff valve (11) on first inlet pipe (10), and still is equipped with on refined cauldron (1) at first online PH meter (12), first online PH meter (12) and first ooff valve (11) linkage are connected.

Furthermore, a second shut-off valve (14) and a second flow meter (15) are further mounted on the mother liquid conveying pipeline (13), and the second flow meter (15) is in linkage connection with the second shut-off valve (14);

the evaporation crystallization kettle (4) is also provided with a second feeding pipe (16) for feeding a PH regulator, a second switch valve (17) is further installed on the second feeding pipe (16), a second on-line PH meter (18) is further arranged on the evaporation crystallization kettle (4), and the second on-line PH meter (18) is in linkage connection with the second switch valve (17);

the evaporative crystallization kettle (4) is further provided with an online thermometer (19), the outer wall of the evaporative crystallization kettle (4) is further provided with a jacket (20), the jacket (20) is connected with a cooling water conveying pipe (21), a temperature switch valve (22) is installed on the cooling water conveying pipe (21), and the online thermometer (19) is in linkage connection with the temperature switch valve (22).

Further, a steam input pipe (23) is connected to the jacket (20);

the evaporation crystallization kettle (4) is also provided with a steam output pipeline (24), the output end of the steam output pipeline (24) is sequentially connected with a condenser (25) and a condensed water tank (26), the condenser (25) is also connected with a vacuum pump (27) for emptying non-condensable gas, and the condensed water tank (26) is connected with the refining kettle (1);

still install level gauge (28) on condensate tank (26), and install control valve (29) on steam input pipe (23), and level gauge (28) and control valve (29) linkage are connected.

Further, a mother liquor storage tank (3) is also arranged between the liquid outlet of the first centrifuge (2) and the evaporation crystallization kettle (4), and a mother liquor reflux pipeline (7) is connected between the refining kettle (1) and the mother liquor storage tank (3);

the evaporation crystallization kettles (4) are multiple, the outlets of the evaporation crystallization kettles (4) are all provided with a second centrifugal machine (5), and the liquid outlet of the second centrifugal machine (5) at the outlet section of the last evaporation crystallization kettle (4) is connected with the next evaporation crystallization kettle (4).

According to the invention, the evaporation crystallization kettle is connected with the liquid outlet of the first centrifugal machine, so that the evaporation crystallization kettle evaporates and crystallizes the mother liquor centrifuged by the first centrifugal machine, high-purity potassium chloride and sodium chloride can be obtained, and a product with a high added value can be obtained for enterprises.

The invention has the following beneficial effects:

(1) the raw materials used by the invention do not influence the potassium hydroxide production system.

(2) According to the invention, high-purity potassium chloride and sodium chloride can be obtained through evaporation and crystallization operations, and products and by-products (mother liquor) generated in the whole refining process can be used as raw materials of other working sections, so that various products with high added values, such as high-quality potassium hydroxide raw materials, food-grade potassium chloride raw materials and feed-grade additive raw materials, can be obtained for enterprises.

(3) The refining process disclosed by the invention generates less waste liquid, waste water and waste gas, does not generate a new waste disposal problem, saves energy, reduces emission and can generate additional benefits.

(4) According to the invention, the refining kettle is directly connected with the first centrifuge, the potassium chloride crystal slurry is obtained after the high-sodium potassium chloride and the pure water are mixed in the refining kettle, the refining agent is added into the potassium chloride crystal slurry, and the high-quality low-sodium potassium chloride is obtained through the first centrifuge, so that the obtained high-quality low-sodium potassium chloride can not influence a potassium hydroxide production system; meanwhile, mother liquor generated after the first centrifugal machine is centrifuged returns to the refining kettle through a mother liquor backflow pipeline, so that the mother liquor generated in the production process is greatly reduced, the purchasing demand of enterprises on high-grade potassium chloride is greatly reduced, the production cost is reduced, and the method is suitable for all enterprises and is suitable for wide popularization.

(5) The invention has the advantages of simple process, low investment, convenient maintenance and operation, good comprehensive economic benefit and easy realization of industrial production.

Drawings

FIG. 1 is a system block diagram of a potassium chloride production system provided by the present invention;

FIG. 2 is a schematic diagram of the structure of the refining vessel in FIG. 1;

FIG. 3 is a schematic view of the structure of the evaporative crystallization kettle of FIG. 1.

Reference numbers and corresponding part names in the drawings:

1. a refining kettle, 2, a first centrifuge, 3, a mother liquid storage tank, 4, an evaporative crystallization kettle, 5, a second centrifuge, 6, a first liquid adding pipe, 7, a mother liquid return pipeline, 8, a first cut-off valve, 9, a first flowmeter, 10, a first feeding pipe, 11, a first switch valve, 12, a first on-line PH meter, 13, a mother liquid conveying pipeline, 14, a second cut-off valve, 15, a second flowmeter, 16, a second feeding pipe, 17, a second switch valve, 18, a second on-line PH meter, 19, an on-line thermometer, 20, a jacket, 21, a cooling water conveying pipe, 22, a temperature switch valve, 23, a steam input pipe, 24, a steam output pipeline, 25, a condenser, 26, a condensate water tank, 27, a vacuum pump, 28, a liquid level meter, 29, a control valve, 30, a circulating water inlet, 31, a circulating water outlet, 32, a steam inlet, 33, a steam outlet, 34, a circulating water outlet, a condensate tank, a pump, Medium inlet, 35, medium outlet.

Detailed Description

The technical solutions of the present invention are described clearly and completely below, and it is obvious that the described embodiments are some, not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

As shown in fig. 1 and fig. 2, the potassium chloride preparation system provided by the present invention includes a refining kettle 1 and a first centrifuge 2, wherein the refining kettle 1 is provided with at least one first liquid adding pipe 6, the plurality of first liquid adding pipes 6 are respectively used for adding pure water, a refining agent, etc. into the refining kettle 1, and the first centrifuge 2 is used for centrifuging a product refined in the refining kettle 1; simultaneously, be connected with mother liquor backflow pipeline 7 between 2 liquid outlets of first centrifuge and the refined cauldron 1, the one end of mother liquor backflow pipeline 7 is connected with the liquid outlet of first centrifuge 2 promptly, and the other end and the refined cauldron 1 of mother liquor backflow pipeline 7 are connected, make the mother liquor that produces through 2 centrifugation of first centrifuge in the refined cauldron 1 is sent into from new through mother liquor backflow pipeline 7.

In the preparation process of the potassium chloride, firstly, high-sodium potassium chloride and pure water are fed into a refining kettle 1 through a first liquid feeding pipe 6 according to a certain solid-liquid ratio and are fully stirred after being mixed to obtain potassium chloride crystal slurry, a refining agent is added into the refining kettle 1 through the first liquid feeding pipe 6, the potassium chloride crystal slurry and the refining agent are stirred and mixed and are fed into a first centrifugal machine 2, the mixture is filtered and centrifuged by the first centrifugal machine 2 to obtain over 98 percent low-sodium potassium chloride for producing high-quality potassium hydroxide, the low-sodium potassium chloride is fed into a brine workshop section to be used as a production raw material, and at the moment, a precipitate formed by calcium and magnesium in the low-sodium potassium chloride is used as a raw material of a composite slow release fertilizer after forming salt mud in the brine workshop section along with original salt; meanwhile, mother liquor filtered and centrifuged by the first centrifuge 2 is newly sent into the refining kettle 1 for recycling through a mother liquor backflow pipeline 7, pure water and high-sodium potassium chloride are supplemented according to the same solid-to-liquid ratio, a refining agent with the same proportion is added into the refining kettle 1 to wash the next batch of high-sodium potassium chloride, and when the content of sodium chloride in the potassium chloride recycled to be washed reaches 0.1-1%, the mother liquor finishes the recycling washing.

In some embodiments, the first liquid adding pipe 6 and the mother liquid backflow pipeline 7 are both provided with a first cut-off valve 8 and a first flow meter 9, the first flow meter 9 can monitor the flow of the material in the first liquid adding pipe 6 and the flow of the mother liquid in the mother liquid backflow pipeline 7 in real time, the first cut-off valve 8 is used for controlling the disconnection and the communication of the first liquid adding pipe 6 and the mother liquid backflow pipeline 7, when the first flow meter 9 monitors that the amount passing through the first liquid adding pipe 6 or the mother liquid backflow pipeline 7 reaches a preset value, the first flow meter 9 sends a control signal to the first cut-off valve 8, the first cut-off valve 8 acts after receiving the control signal to disconnect the first liquid adding pipe 6 or the mother liquid backflow pipeline 7, so that the amount of the mother liquid newly reflowing into the refining kettle 1 or pure water, high-sodium potassium chloride and refining agent added into the mother liquid is precisely controlled, and the amounts of high-sodium potassium chloride, high-sodium chloride, potassium chloride and refining agent are precisely controlled, The amount of the refining agent is strictly controlled, so that the quality of the low-sodium potassium chloride and high-potassium mother liquor is ensured.

In some embodiments, the refining kettle 1 is further provided with a first feeding pipe 10, the first feeding pipe 10 is mainly used for adding a PH regulator into the refining kettle 1, and the PH regulator may be 30% potassium hydroxide, but the PH regulator is not limited to 30% potassium hydroxide, the first feeding pipe 10 is further provided with a first switch valve 11, the first switch valve 11 is used for controlling the disconnection and connection of the first feeding pipe 10, the refining kettle 1 is further provided with a first online PH meter 12 for detecting the PH value in the refining kettle 1, the PH value in the refining kettle 1 is detected in real time by the first online PH meter 12, when the PH value in the refining kettle 1 reaches a preset value, the first online PH meter 12 sends a control signal to the first switch valve 11, the first switch valve 11 acts upon receiving the control signal to disconnect the first feeding pipe 10, so that the amount of the PH regulator fed into the refining kettle 1 through the first feeding pipe 10 is precisely controlled, the adjustment precision of the potassium chloride crystal slurry is higher, the potassium chloride crystal slurry is fully refined after the refining agent is added subsequently, and the quality of the low-sodium potassium chloride and the high-potassium mother liquor is ensured.

In some embodiments, as shown in fig. 3, the potassium chloride preparation system further includes an evaporation crystallization kettle 4, the evaporation crystallization kettle 4 is configured to evaporate a potassium chloride mother liquor with a sodium chloride content of 0.1-1% obtained by filtering and centrifuging through a first centrifuge 2, a mother liquor conveying pipeline 13 is mainly disposed on the evaporation crystallization kettle 4, an inlet end of the mother liquor conveying pipeline 13 is connected to a liquid outlet of the first centrifuge 2, so that when the potassium chloride mother liquor with a sodium chloride content of 0.1-1% is obtained by filtering and centrifuging through the first centrifuge 2, the mother liquor is directly conveyed into the evaporation crystallization kettle 4 through the mother liquor conveying pipeline 13, and the mother liquor is evaporated in the evaporation crystallization kettle 4 to obtain a potassium chloride crystal slurry, so that the potassium chloride mother liquor with a sodium chloride content of 0.1-1% is further processed.

In some embodiments, a second cut-off valve 14 and a second flow meter 15 are further installed on the mother liquid conveying pipeline 13, the second flow meter 15 can monitor the flow rate of the mother liquid in the mother liquid conveying pipeline 13 in real time, the first cut-off valve 8 is used for controlling the disconnection and the connection of the mother liquid conveying pipeline 13, the second flow meter 15 is in linkage connection with the second cut-off valve 14, when the second flow meter 15 monitors that the mother liquid amount passing through the mother liquid conveying pipeline 13 reaches a preset value, the second flow meter 15 sends a control signal to the second cut-off valve 14, and the second cut-off valve 14 acts after receiving the control signal to disconnect the mother liquid conveying pipeline 13, so that the mother liquid amount sent into the evaporative crystallization kettle 4 is precisely controlled, the mother liquid amount is strictly controlled, and the potassium chloride mother liquid with the sodium chloride content of 0.1-1% is processed more precisely.

In some embodiments, the evaporation crystallization kettle 4 is further provided with a second feeding pipe 16, the second feeding pipe 16 is mainly used for adding a PH regulator into the refining kettle 1, and the PH regulator may be industrial hydrochloric acid, but the PH regulator is not limited to industrial hydrochloric acid, and the second feeding pipe 16 is further provided with a second switch valve 17, the second switch valve 17 is used for controlling the disconnection and connection of the second feeding pipe 16, the evaporation crystallization kettle 4 is further provided with a second on-line PH meter 18, the second on-line PH meter 18 is used for detecting the PH value in the evaporation crystallization kettle 4, the PH value in the evaporation crystallization kettle 4 is detected in real time by the second on-line PH meter 18, when the PH value in the evaporation crystallization kettle 4 reaches a preset value, the second on-line PH meter 18 sends a control signal to the second switch valve 17, the second switch valve 17 is actuated after receiving the control signal to disconnect the second feeding pipe 16, therefore, the amount of the PH regulator fed into the evaporative crystallization kettle 4 through the second feeding pipe 16 is accurately controlled, the adjustment precision of the potassium chloride crystal slurry is higher, the potassium chloride crystal slurry is fully refined after the refining agent is added subsequently, and the quality of the low-sodium potassium chloride and the high-potassium mother liquor is ensured.

In some embodiments, the evaporative crystallization kettle 4 is further provided with an online thermometer 19, the online thermometer 19 detects the temperature in the evaporative crystallization kettle 4 in real time, the outer wall of the evaporative crystallization kettle 4 is further provided with a jacket 20, circulating cooling water can be introduced into the jacket 20, that is, the jacket 20 is provided with a circulating water inlet 30 and a circulating water outlet 31, the circulating water inlet 30 is located at the lower end of the jacket 20, and the circulating water outlet 31 is located at the upper end of the jacket 20; meanwhile, a cooling water delivery pipe 21 is further installed on the jacket 20, the cooling water delivery pipe 21 is used for delivering circulating cooling water into the jacket 20, the outlet end of the cooling delivery pipe 21 is connected with a circulating water inlet 30, a circulating water outlet 31 can be directly connected with a pipeline for delivering the circulating cooling water in the jacket 20, a temperature switch valve 22 is further installed on the cooling water delivery pipe 21, the temperature switch valve 22 is a switch valve controlled according to the temperature in the evaporative crystallization kettle 4, the temperature switch valve 22 is used for controlling the disconnection and the connection of the cooling water delivery pipe 21, and the online thermometer 19 is in linkage connection with the temperature switch valve 22. When the evaporative crystallization kettle 4 needs to be cooled after mother liquor is evaporated, opening the temperature switch valve 22, feeding circulating cooling water into the jacket 20 through the cooling water conveying pipe 21, and performing heat exchange between the circulating cooling water entering the jacket 20 and the evaporative crystallization kettle 4, so that the interior of the evaporative crystallization kettle 4 is cooled, and the mother liquor entering the evaporative crystallization kettle 4 is concentrated to obtain potassium chloride crystal slurry; meanwhile, when the circulating cooling water exchanges heat with the inside of the evaporative crystallization kettle 4, the online thermometer 19 detects the temperature inside the evaporative crystallization kettle 4 in real time, when the online thermometer 19 detects that the temperature inside the evaporative crystallization kettle 4 reaches a preset value, the online thermometer 19 sends a control signal to the temperature switch valve 22, the temperature switch valve 22 acts after receiving the control signal, so that the cooling water conveying pipe 21 is disconnected, the temperature inside the evaporative crystallization kettle 4 is accurately controlled, and the quality of the potassium chloride crystal slurry is higher.

In some embodiments, the jacket 20 further has a steam inlet 32 and a steam outlet 33, the jacket 20 is further connected with a steam input pipe 23, an outlet end of the steam input pipe 23 is connected with the steam inlet 32, the steam input pipe 23 is mainly used for feeding high-temperature steam into the jacket 20, the high-temperature steam entering the jacket 20 exchanges heat with the evaporative crystallization kettle 4 to gradually raise the temperature in the evaporative crystallization kettle 4, so that the mother liquor entering the evaporative crystallization kettle 4 is concentrated and evaporated, after the heat exchange of the hot steam in the jacket 20 is completed, the low-temperature steam is directly discharged through the steam outlet 33, and at this time, the steam discharged from the steam outlet 33 can be sent to the next process through a pipe connected to the steam outlet 33. Because the temperature rise in the evaporation crystallization kettle 4 and the temperature reduction in the evaporation crystallization kettle 4 can not be carried out simultaneously, the jacket 20 at the position can be used for introducing high-temperature steam to heat the evaporation crystallization kettle 4 and also can be introduced with circulating cooling water to cool the evaporation crystallization kettle 4.

In some embodiments, the evaporative crystallization kettle 4 is further provided with a steam output pipeline 24, the steam output pipeline is mainly used for sending out steam generated when the mother liquor is concentrated and evaporated in the evaporative crystallization kettle 4, and the output end of the steam output pipeline 24 is sequentially connected with a condenser 25 and a condensed water tank 26, the condenser 25 is a shell and tube condenser, the condenser 25 is provided with a medium inlet 34 and a medium outlet 35 for feeding condensing medium, the medium inlet 34 can be used for connecting pipelines for inputting the medium into the condenser 25, the medium outlet 25 can be used for connecting pipelines for sending the medium after heat exchange out of the condenser 25, namely, the condenser 25 is used for condensing the steam sent out by the evaporation crystallization kettle 4 to ensure that the steam sent out by the evaporation crystallization kettle 4 forms a liquid state, and the condensate water tank 26 is used for storing the condensate condensed by the condenser 25; meanwhile, the condensate water tank 26 is connected with the refining kettle 1, so that the condensate stored in the condensate water tank 26 can be sent into the refining kettle 1 again to be used as washing liquid, and the condensate can be recycled.

In some embodiments, a liquid level meter 28 is further installed on the condensed water tank 26, the liquid level meter 28 is used for detecting the liquid level of the condensed liquid in the condensed water tank 26, a control valve 29 is installed on the steam input pipe 23, the control valve 29 is used for controlling the steam input pipe 23 to be disconnected and connected, and the liquid level meter 28 and the control valve 29 are connected in an interlocking manner. When the evaporation crystallization kettle 4 is normally concentrating and evaporating the mother liquid, the control valve 29 is opened to enable the steam input pipe 23 to be in an open state, and the mother liquid is concentrated and evaporated in the evaporation crystallization kettle 4; when the liquid level in the condensed water tank 26 exceeds the preset value, the liquid level meter 28 sends a control signal to the control valve 29, and the control valve 29 acts after receiving the control signal to disconnect the steam input pipe 23, so that the mother liquid in the evaporation crystallization kettle 4 stops concentration and evaporation, and the mother liquid is more conveniently controlled in the whole concentration and evaporation process.

In some embodiments, a vacuum pump 27 is further connected to the condenser 25, and the vacuum pump 27 is used for discharging the non-condensable gas in the condenser 25.

In some embodiments, a mother liquor storage tank 3 is further installed between the liquid outlet of the first centrifuge 2 and the evaporation crystallization kettle 4, so that the high potassium mother liquor generated after filtration, filtration and centrifugation by the first centrifuge 2 can be stored through the mother liquor storage tank 3, at this time, a mother liquor backflow pipeline 7 is connected between the refining kettle 1 and the mother liquor storage tank 3, so that the high potassium mother liquor stored in the mother liquor storage tank 3 is sent into the refining kettle 1 through the mother liquor backflow pipeline 7.

In some embodiments, a plurality of evaporation crystallization kettles 4 are provided, the outlets of the plurality of evaporation crystallization kettles 4 are all provided with a second centrifuge 5, the second centrifuge 5 is used for filtering and centrifuging again potassium chloride crystal slurry generated by concentration and evaporation in the evaporation crystallization kettle 4, and the high sodium mother liquor centrifuged by the second centrifuge 5 at the outlet section of the previous evaporation crystallization kettle 4 is sent to the next evaporation crystallization kettle 4 and is continuously concentrated and evaporated in the next evaporation crystallization kettle 4, so that sodium chloride is continuously separated out from the next evaporation crystallization kettle 4, and the obtained sodium chloride crystal slurry is sent to the second centrifuge 5 at the output end of the evaporation crystallization kettle 4 for centrifuging again, and finally low sodium potassium chloride and high sodium mother liquor are obtained.

When potassium chloride needs to be prepared, a certain amount of high-sodium potassium chloride raw salt (KCl is less than or equal to 95 percent and NaCl is more than or equal to 3 percent) and pure water are added into a refining kettle 1 through a first liquid adding pipe 6, the solid-liquid ratio of the high-sodium potassium chloride raw salt to the pure water is controlled to be 2:1, the sodium potassium chloride raw salt and the pure water are stirred in the refining kettle 1 to obtain potassium chloride crystal slurry, a refining agent with the mass of 0.2 percent of the sodium potassium chloride raw salt is added into the refining kettle 1 through the first liquid adding pipe 6 after stirring, 30 percent KOH is added into the refining kettle 1 through a first feeding pipe 10 to adjust the pH value of the potassium chloride crystal slurry to 10-12, the potassium chloride crystal slurry is sent into a first centrifuge 2 after stirring for 0.5-1.5 h at normal temperature, low-sodium potassium chloride and high-potassium mother liquor are obtained after centrifugation through the first centrifuge 2, at the moment, the low-sodium potassium chloride can be sent to brine as a raw material for producing potassium hydroxide, and the high-potassium mother liquor enters a mother liquor storage tank 3, then returns to the refining kettle 1 from the beginning through a mother liquor backflow pipeline 7 for recycling, high-sodium potassium chloride raw salt and pure water are supplemented according to the solid-to-liquid ratio of the high-sodium potassium chloride raw salt to the pure water, after potassium chloride crystal slurry is obtained, a refining agent with the same ratio is added according to the solid-to-liquid ratio of the high-sodium potassium chloride raw salt to the pure water to wash the next batch of added high-sodium potassium chloride, the steps are circulated, when the content of sodium chloride in the potassium chloride centrifuged by the first centrifuge 2 reaches 0.1-1%, the high-potassium mother liquor finishes circulating washing, and the high-potassium mother liquor in the mother liquor storage tank 3 is conveyed to the evaporative crystallization kettle 4 through a mother liquor conveying pipe.

After the high-potassium mother liquor is sent into an evaporative crystallization kettle 4, industrial hydrochloric acid is added into the evaporative crystallization kettle 4 through a second feeding pipe 16 to adjust the pH value to 6-7, high-temperature steam is sent into a jacket 20 through a steam input pipe 23 and heats the interior of the evaporative crystallization kettle 4, the high-potassium mother liquor is concentrated and evaporated in the evaporative crystallization kettle 4, steam generated in the concentration and evaporation process is sent into a condenser 25 through a steam output pipe 24 to be condensed, condensed liquid is sent into a condensed water tank 26 and finally sent into a refining kettle 1 to be used as washing liquid, concentrated potassium chloride crystal slurry is cooled in the evaporative crystallization kettle 4 and is centrifuged by a second centrifuge 5 to obtain low-sodium potassium chloride and high-sodium mother liquor, and at the moment, the low-sodium potassium chloride can be used as a food-grade potassium chloride raw material.

And (3) the high-sodium mother liquor is sent into the next evaporation crystallization kettle 4 to be continuously concentrated and evaporated, the concentration and evaporation mode is the same as that in the previous evaporation crystallization kettle 4, the concentrated potassium chloride crystal slurry is cooled in the evaporation crystallization kettle 4, and after the potassium chloride crystal slurry is centrifuged by a second centrifuge 5, low-sodium potassium chloride and high-sodium mother liquor are obtained, wherein at the moment, the low-sodium potassium chloride can be used as a food-grade potassium chloride raw material.

Example 2

(1) Adding a certain amount of high-sodium potassium chloride raw salt (KCl is less than or equal to 95 percent, NaCl is more than or equal to 3 percent) and pure water into a refining kettle, controlling the solid-to-liquid ratio to be 2:1, starting stirring, adding refining agent phosphoric acid with the mass of 0.2 percent of the raw salt, adjusting the pH value of crystal mush to 10-12 by using 30 percent KOH, stirring at normal temperature for 0.5-1.5 h, centrifuging the potassium chloride crystal mush by using a centrifuge to obtain low-sodium potassium chloride and high-potassium mother liquor, sending the low-sodium potassium chloride to a salt water working section as a raw material for producing potassium hydroxide, returning the high-potassium mother liquor to the refining kettle for recycling, washing the next batch of high-sodium potassium chloride according to the same solid-to-liquid ratio and adding the refining agent with the same proportion, circulating until the sodium chloride content in the washed potassium chloride reaches 0.1-1 percent, and sending the mother liquor to a section of an evaporator concentrator after the recycling.

(2) Adjusting the pH of the washing mother liquor to 6-7 by using industrial hydrochloric acid, evaporating in an evaporation crystallization kettle, controlling the evaporation amount in the kettle by collecting the amount of evaporated condensate water, wherein the amount of the condensate water is equal to the evaporation amount, returning the evaporated condensate liquid to a refining kettle to be used as a washing liquid, cooling the concentrated potassium chloride crystal slurry in the kettle, and centrifuging by using a centrifuge to obtain low-sodium potassium chloride and high-sodium mother liquor.

(3) And returning the high-sodium mother liquor to the evaporation crystallization kettle for evaporation, controlling the evaporation amount according to the same control method, returning the evaporated condensate to the refining kettle to be used as a washing liquid, filtering sodium chloride precipitated in the concentration process while the condensate is hot after concentration, cooling the filtered high-potassium mother liquor in the crystallization kettle, centrifuging by a centrifugal machine to obtain low-sodium potassium chloride and high-sodium mother liquor, and sending the high-sodium mother liquor to a boiler room for use.

Example 3

(1) Adding a certain amount of high-sodium potassium chloride raw salt (KCl is less than or equal to 95 percent, NaCl is more than or equal to 3 percent) into a refining kettle, producing water, controlling the solid-liquid ratio to be 2:1, starting stirring, adding a refining agent potassium phosphate salt accounting for 0.3 percent of the mass of the raw salt, adjusting the pH value of a crystal slurry to be 11, stirring for 1h, centrifuging the potassium chloride crystal slurry by a centrifugal machine to obtain low-sodium potassium chloride and high-potassium mother liquor, sending the low-sodium potassium chloride to a salt water working section as a raw material for producing potassium hydroxide, returning the high-potassium mother liquor to the refining kettle for recycling, washing the next batch of high-sodium potassium chloride according to the same solid-liquid ratio and adding the refining agent in the same proportion, recycling until the sodium chloride content in the washed potassium chloride reaches 0.1-1 percent, finishing recycling the mother liquor, and sending to a section of an evaporation concentrator.

(2) Adjusting the pH of the washing mother liquor to 6-7 by using industrial hydrochloric acid, evaporating in an evaporation crystallization kettle, controlling the evaporation amount in the kettle by collecting the amount of evaporated condensate water to enable the amount of the condensate water to be equal to the evaporation amount in the kettle, returning the evaporated condensate liquid to a refining kettle to be used as a washing liquid, cooling and crystallizing concentrated potassium chloride crystal slurry in the kettle, and centrifuging by using a centrifuge to obtain low-sodium potassium chloride and high-sodium mother liquor.

(3) And returning the high-sodium mother liquor to the evaporation crystallization kettle for evaporation, controlling the evaporation amount according to the same control method, returning the evaporated condensate to the refining kettle to be used as a washing liquid, filtering sodium chloride precipitated in the concentration process while the condensate is hot after concentration, cooling and crystallizing the filtered high-potassium mother liquor in the crystallization kettle, centrifuging the high-potassium mother liquor by a centrifuge to obtain low-sodium potassium chloride and high-sodium mother liquor, and sending the high-sodium mother liquor to a boiler room for use.

Comparative example 1

In comparison with example 2, a lower pH was used for the washing

(1) Adding a certain amount of high-sodium potassium chloride raw salt (KCl is less than or equal to 95 percent, NaCl is more than or equal to 3 percent) into a refining kettle, producing water, controlling the solid-liquid ratio to be 2:1, adding refining agent phosphoric acid accounting for 0.2 percent of the mass of the raw salt after stirring, adjusting the pH value of crystal slurry to be 9, stirring for 0.5-1.5 h, centrifuging the potassium chloride crystal slurry by a centrifugal machine to obtain low-sodium potassium chloride and high-potassium mother liquor, sending the low-sodium potassium chloride to a salt water working section as a raw material for producing potassium hydroxide, returning the high-potassium mother liquor to the refining kettle for recycling, washing the next batch of high-sodium potassium chloride by adding the refining agent in the same proportion according to the same solid-liquid ratio, circulating until the content of sodium chloride in the washed potassium chloride reaches 0.1-1 percent, finishing the recycling of the mother liquor, and sending the mother liquor to an evaporation concentrator.

(2) Adjusting the pH of the washing mother liquor to 6-7 by using industrial hydrochloric acid, evaporating in an evaporation crystallization kettle, controlling the evaporation amount in the kettle by collecting the amount of evaporated condensate water, returning the evaporated condensate liquid to a refining kettle to be used as washing liquid, cooling and crystallizing the concentrated potassium chloride crystal slurry in the kettle, and centrifuging by using a centrifuge to obtain low-sodium potassium chloride and high-sodium mother liquor.

(3) And returning the high-sodium mother liquor to the evaporation crystallization kettle for evaporation, controlling the evaporation amount according to the same control method, returning the evaporated condensate to the refining kettle to be used as a washing liquid, filtering sodium chloride precipitated in the concentration process while the condensate is hot after concentration, cooling and crystallizing the filtered high-potassium mother liquor in the crystallization kettle, centrifuging the high-potassium mother liquor by a centrifuge to obtain low-sodium potassium chloride and high-sodium mother liquor, and sending the high-sodium mother liquor to a boiler room for use.

Comparative example 2

Shorter wash times than in example 2

(1) Adding a certain amount of high-sodium potassium chloride raw salt (KCl is less than or equal to 95 percent, NaCl is more than or equal to 3 percent) into a refining kettle, producing water, controlling the solid-liquid ratio to be 2:1, adding refining agent phosphoric acid accounting for 0.2 percent of the mass of the raw salt after stirring, adjusting the pH value of crystal mush to 10-12, stirring for 0.25h, centrifuging the potassium chloride crystal mush by a centrifugal machine to obtain low-sodium potassium chloride and high-potassium mother liquor, sending the low-sodium potassium chloride to a brine working section as a raw material for producing potassium hydroxide, returning the high-potassium mother liquor to the refining kettle for recycling, washing the next batch of high-sodium potassium chloride according to the same solid-liquid ratio and adding the refining agent with the same proportion, recycling until the sodium chloride content in the washed potassium chloride reaches 0.1-1 percent, finishing the recycling of the mother liquor, and sending the washed potassium chloride to an evaporation concentrator.

(2) Adjusting the pH of the washing mother liquor to 6-7 by using industrial hydrochloric acid, evaporating in an evaporation crystallization kettle, controlling the evaporation amount in the kettle by collecting the amount of evaporated condensate water, returning the evaporated condensate liquid to a refining kettle to be used as washing liquid, cooling and crystallizing the concentrated potassium chloride crystal slurry in the kettle, and centrifuging by using a centrifuge to obtain low-sodium potassium chloride and high-sodium mother liquor.

(3) And returning the high-sodium mother liquor to the evaporation crystallization kettle for evaporation, controlling the evaporation amount according to the same control method, returning the evaporated condensate to the refining kettle to be used as a washing liquid, filtering sodium chloride precipitated in the concentration process while the condensate is hot after concentration, cooling and crystallizing the filtered high-potassium mother liquor in the crystallization kettle, centrifuging the high-potassium mother liquor by a centrifuge to obtain low-sodium potassium chloride and high-sodium mother liquor, and sending the high-sodium mother liquor to a boiler room for use.

Comparative example 3

Higher solid-to-liquid ratio than in example 2

(1) Adding a certain amount of high-sodium potassium chloride raw salt (KCl is less than or equal to 95 percent, NaCl is more than or equal to 3 percent) into a refining kettle, producing water, controlling the solid-liquid ratio to be 3:1, adding refining agent phosphoric acid accounting for 0.2 percent of the mass of the raw salt after stirring, adjusting the pH value of crystal mush to 10-12, stirring for 0.5-1.5 h, centrifuging the potassium chloride crystal mush by a centrifugal machine to obtain low-sodium potassium chloride and high-potassium mother liquor, sending the low-sodium potassium chloride to a salt water working section as a raw material for producing potassium hydroxide, returning the high-potassium mother liquor to the refining kettle for recycling, washing the next batch of high-sodium potassium chloride by adding the refining agent with the same ratio according to the same solid-liquid ratio and the same proportion, circulating until the content of sodium chloride in the washed potassium chloride reaches 0.1-1 percent, and finishing the cyclic washing of the mother liquor, and sending the mother liquor to an evaporation concentrator.

(2) Adjusting the pH of the washing mother liquor to 6-7 by using industrial hydrochloric acid, evaporating in an evaporation crystallization kettle, controlling the evaporation amount in the kettle by collecting the amount of evaporated condensate water, returning the evaporated condensate liquid to a refining kettle to be used as washing liquid, cooling and crystallizing the concentrated potassium chloride crystal slurry in the kettle, and centrifuging by using a centrifuge to obtain low-sodium potassium chloride and high-sodium mother liquor.

(3) And returning the high-sodium mother liquor to the evaporation crystallization kettle for evaporation, controlling the evaporation amount according to the same control method, returning the evaporated condensate to the refining kettle to be used as a washing liquid, filtering sodium chloride precipitated in the concentration process while the condensate is hot after concentration, cooling and crystallizing the filtered high-potassium mother liquor in the crystallization kettle, centrifuging the high-potassium mother liquor by a centrifuge to obtain low-sodium potassium chloride and high-sodium mother liquor, and sending the high-sodium mother liquor to a boiler room for use.

Comparative example 4

Compared with example 2, a refining agent is added during the recovery of the mother liquor.

(1) Adding a certain amount of high-sodium potassium chloride raw salt (KCl is less than or equal to 95 percent, NaCl is more than or equal to 3 percent) and pure water into a refining kettle, controlling the solid-liquid ratio to be 2:1, adjusting the pH value of crystal mush to 10-12 by using 30 percent KOH, stirring for 0.5-1.5 h at normal temperature, centrifuging the potassium chloride crystal mush by using a centrifugal machine to obtain low-sodium potassium chloride and high-potassium mother liquor, sending the low-sodium potassium chloride to a salt water working section to be used as a raw material for producing potassium hydroxide, returning the high-potassium mother liquor to the refining kettle for recycling, adding refining agent phosphoric acid with the mass of 0.2 percent of the raw salt according to the same solid-liquid ratio, washing the next batch of high-sodium potassium chloride, recycling to the washed potassium chloride with the sodium chloride content of 0.1-1 percent, finishing the recycling of the mother liquor, and sending the mother liquor to a section of an evaporation concentrator.

(2) Adjusting the pH of the washing mother liquor to 6-7 by using industrial hydrochloric acid, evaporating in an evaporation crystallization kettle, controlling the evaporation amount in the kettle by collecting the amount of evaporated condensate water, returning the evaporated condensate liquid to a refining kettle to be used as washing liquid, cooling the concentrated potassium chloride crystal slurry in the kettle, and centrifuging by using a centrifuge to obtain low-sodium potassium chloride and high-sodium mother liquor.

(3) And returning the high-sodium mother liquor to the evaporation crystallization kettle for evaporation, controlling the evaporation amount according to the same control method, returning the evaporated condensate to the refining kettle to be used as a washing liquid, filtering sodium chloride precipitated in the concentration process while the condensate is hot after concentration, cooling the filtered high-potassium mother liquor in the crystallization kettle, centrifuging by a centrifugal machine to obtain low-sodium potassium chloride and high-sodium mother liquor, and sending the high-sodium mother liquor to a boiler room for use.

The indexes of potassium chloride products in each stage of examples 2 and 3 and comparative examples 1 to 4 are shown in tables 1 to 6.

TABLE 1 index of potassium chloride product at each stage of example 1

TABLE 2 Potassium chloride product index at each stage of example 2

TABLE 3 index for potassium chloride product at each stage of comparative example 1

TABLE 4 index for potassium chloride product at each stage of comparative example 2

TABLE 5 Potassium chloride product index at each stage of comparative example 3

TABLE 6 index of potassium chloride product at each stage of comparative example 4

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.