A method for recycling potassium resources in potassium nitrate mother liquor

Abstract

The present invention relates to a high-salt wastewater resource utilization technology, particularly to the resource utilization of potassium nitrate mother liquor, and specifically to a method for recycling potassium resources in the potassium nitrate mother liquor. The method comprises brine adjustment, first-stage cooling, second-stage cooling, solid-liquid separation, decomposition and washing, and evaporation and concentration. A decomposition liquid produced by the decomposition and washing is mixed with a concentrated liquid produced by evaporation and concentration to adjust the MgCl2 content in the system. The brine-adjusted system is cooled in two stages, followed by solid-liquid separation to obtain a crystalline solid and a crystalline mother liquor. The crystalline solid is added to the potassium nitrate mother liquor and stirred thoroughly, followed by solid-liquid separation to obtain potassium chloride solid and a decomposition liquid. The potassium chloride solid is reused as a production raw material. The crystalline mother liquor is evaporated and concentrated, and a portion of the concentrated liquid and the decomposition liquid are recycled by mixing brine. The remaining concentrated liquid is cooled to room temperature to obtain MgCl2·6H2O solid. The present invention recycles potassium chloride in the by-product mother liquor without adding additional steam and water.

Description

Technical Field

[0001] The invention relates to a high-salt wastewater resource utilization technology, in particular to resource utilization of potassium nitrate mother liquor, and specifically to a method for recycling potassium resources in potassium nitrate mother liquor. Background Art

[0002] Potassium nitrate is an important inorganic chemical product and a high-quality, chloride-free, nitrogen-potassium binary compound fertilizer. In agriculture, potassium nitrate possesses ideal chemical and physical properties and favorable environmental qualities. It is primarily used in tobacco, flowers, citrus fruits, and other chloride-sensitive cash crops to increase yield and improve crop quality. Industrially, potassium nitrate is widely used in ceramics, precision instrument glass, touch screen glass, optical glass, gunpowder, fireworks, as well as in the food and pharmaceutical industries. Furthermore, utilizing high-temperature nitrate molten salts for power generation is a new application area.

[0003] Relying on the co-production of nitric acid from coal chemical industry, the magnesium nitrate and potassium chloride double decomposition process for producing potassium nitrate has become a key technology for potassium nitrate production in my country due to its simple process flow, low investment, low energy consumption, high primary conversion rate, safe operation, and convenient operation. The low-temperature potassium nitrate mother liquor produced by this process is often evaporated and concentrated to produce MgCl2·6H2O, which is sold cheaply as magnesium fertilizer or building decoration material. However, due to the small amount of potassium chloride and magnesium nitrate in the potassium nitrate mother liquor, the MgCl2·6H2O product is of low quality and cannot meet the quality requirements of magnesium chloride products. This also results in a significant waste of potassium resources in the potassium nitrate mother liquor. Therefore, how to recycle the potassium resources in the potassium nitrate mother liquor and improve the quality of the byproduct MgCl2·6H2O is a technical bottleneck that urgently needs to be addressed in this field. Summary of the Invention

[0004] In response to the above-mentioned technical problems existing in the prior art, the present invention provides a method for recycling potassium resources in potassium nitrate mother liquor. Specifically, based on brine addition and cooling crystallization, a high-efficiency and energy-saving potassium resource recycling technology is developed. Without adding additional steam and water (combined with the existing mother liquor evaporation treatment process), potassium chloride in the by-product mother liquor is recycled and utilized, while also improving the quality of the by-product MgCl2·6H2O. The development and application of this technology can effectively reduce the production costs of enterprises, improve economic benefits, conform to the concept of circular economy, and have good prospects for industry promotion.

[0005] In order to achieve the above technical effects, the present invention discloses a method for recycling potassium resources in potassium nitrate mother liquor, wherein the mass components of the potassium nitrate mother liquor include: 15.00%≤MgCl2≤22.00%, KCl≥2.00%, Mg(NO3)2≤5.00%, NaCl≤5.00%, and the remainder is water; the temperature of the potassium nitrate mother liquor is 5-15°C; and the recycling method comprises the following steps:

[0006] S1. Preparation of initial raw materials - crystallization mother liquor, decomposition liquid and concentrated liquid;

[0007] S2, brine adjustment: the decomposition liquid produced by decomposition and washing is mixed with part of the concentrated liquid produced by evaporation and concentration, and the brine is added to adjust the MgCl2 content of the system;

[0008] S3, first stage cooling: the crystallization mother liquor is used as the cooling medium to exchange heat with the brine adjustment system;

[0009] S4, second stage cooling: using potassium nitrate mother liquor as cooling medium to exchange heat with the brine adjustment system after the first stage cooling;

[0010] S5, solid-liquid separation: After the second stage cooling and brine adjustment system in S4 is insulated and settled, solid-liquid separation is performed to obtain crystallized solid and crystallization mother liquor. The crystallization mother liquor is used as the cooling medium again to participate in the first stage cooling of S3;

[0011] S6, decomposition and washing: adding crystalline solid to the potassium nitrate mother liquor after heat exchange in S4 and stirring thoroughly, and then separating the solid and liquid to obtain potassium chloride solid and decomposition liquid, and the potassium chloride solid is reused as a production raw material;

[0012] S7, evaporation and concentration: After the crystallization mother liquor after heat exchange in S3 is evaporated and concentrated, a part of the concentrated liquid is mixed with the decomposition liquid and brine for recycling, and the remaining concentrated liquid is cooled to room temperature to obtain MgCl2·6H2O solid.

[0013] As a preferred technical solution, the step of preparing the crystallization mother liquor in S1 is as follows: under continuous stirring, magnesium chloride hexahydrate is added to the potassium nitrate mother liquor, and the mass fraction of magnesium chloride in the system is adjusted to 30-35%, and the above system is heated to 90-100° C., at which time the magnesium chloride hexahydrate is completely dissolved, and then cooled to 30-40° C., kept warm and settled for 0.5-1 hour, and solid-liquid separation is performed to obtain a crystalline solid and a crystallization mother liquor.

[0014] As a preferred technical solution, the steps of preparing the decomposition liquid in S1 are as follows: adding a crystalline solid to the potassium nitrate mother liquor under continuous stirring, with a mass ratio of the crystalline solid to the potassium nitrate mother liquor of 1:2.0-6.0, heating to 30-40°C, washing for 0.5-3.0h, and solid-liquid separation to obtain potassium chloride solid and decomposition liquid.

[0015] As a preferred technical solution, the step of preparing the concentrated solution in S1 is as follows: a portion of the prepared crystallization mother liquor is reserved for standby use, and the remaining crystallization mother liquor is evaporated and concentrated to a temperature of 125-135° C. to obtain a concentrated solution.

[0016] As a preferred technical solution, the brine adjustment in S2 is to mix the decomposition liquid with part of the concentrated liquid, and the mass fraction of magnesium chloride in the brine adjustment system is 30-35%.

[0017] As a preferred technical solution, the cooling stage in S3 utilizes the crystallization mother liquor as a cooling medium to exchange heat with the brine adjustment system in S2.

[0018] As a preferred technical solution, the second stage cooling in S4 uses 5-15°C potassium nitrate mother liquor as a cooling medium to exchange heat with the system after the first stage cooling, and the terminal temperature of the second stage cooling is 30-40°C.

[0019] As a preferred technical solution, the solid-liquid separation in S5 is to keep the S4 second-stage cooling and brine adjustment system at 30-40°C and let it settle for 0.5-1h, and then separate the solid and liquid to obtain a crystallization mother liquor and a crystallized solid; the crystallization mother liquor obtained by the solid-liquid separation is used as a cooling medium again to participate in the first-stage cooling of S3.

[0020] As a preferred technical solution, the decomposition washing in S6 is to add crystalline solid to the potassium nitrate mother liquor after the second stage cooling and heat exchange, the mass ratio of crystalline solid to potassium nitrate mother liquor is 1:2.0~6.0, the washing temperature is 30~40℃, the washing time is 0.5~3h, and then the solid-liquid separation is carried out to obtain potassium chloride solid and decomposition liquid, and the decomposition liquid is returned to the brine adjustment process in S2 for recycling.

[0021] As a preferred technical solution, the evaporation concentration in S7 is to evaporate and concentrate the crystallization mother liquor after a cooling and heat exchange process to a system temperature of 125-135°C, and a part of the concentrated liquid is returned to the brine adjustment process in S2 for recycling, and the remaining concentrated liquid is cooled to room temperature to obtain MgCl2·6H2O solid.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] Based on the existing mother liquor evaporation treatment process, the technical steps of the present invention include: brine adjustment, first-stage cooling, second-stage cooling, solid-liquid separation, decomposition and washing, and evaporation and concentration. The decomposition liquid produced by the decomposition and washing is mixed with the concentrated liquid produced by the evaporation and concentration to adjust the MgCl2 content of the system. After the brine-adjusted system is cooled in two stages, the solid-liquid separation is performed to obtain a crystalline solid and a crystalline mother liquor. The crystalline solid is added to the potassium nitrate mother liquor and stirred thoroughly. After solid-liquid separation, potassium chloride solid and decomposition liquid are obtained. The potassium chloride solid is reused as a production raw material. After the crystalline mother liquor is evaporated and concentrated, a part of the concentrated liquid and the decomposition liquid are mixed with brine for recycling. The remaining concentrated liquid is cooled to room temperature to obtain MgCl2·6H2O solid.

[0024] The present invention achieves efficient extraction of potassium resources from potassium nitrate mother liquor without requiring additional steam or water. Potassium chloride recovery rates exceeding 80% and purity exceeding 90% meet requirements for reuse as a production raw material. The process of the present invention reduces production costs, offers a stable process, and reduces technical risk, making it suitable for industrial production. According to incomplete statistics, the national production capacity of potassium nitrate by double decomposition of magnesium nitrate and potassium chloride is approximately 270,000 tons / year, with approximately 650,000 tons / year of mother liquor as a byproduct. Using the present process, approximately 16,000 tons of potassium chloride can be recovered from this production, resulting in significant economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0026] The following is combined with Figure 1 The present invention is further described:

[0027] The invention provides a method for recycling potassium resources in potassium nitrate mother liquor. The mass components of the potassium nitrate mother liquor include: 20.79% of MgCl2, 2.55% of KCl, 3.49% of Mg(NO3)2, 2.69% of NaCl, and the remainder is water; the temperature of the potassium nitrate mother liquor is 10°C.

[0028] Example a: Preparation of crystallization mother liquor, decomposition liquid and concentrated liquid;

[0029] S1a, preparing a crystallization mother liquor: under continuous stirring, add 4.74 kg of magnesium chloride hexahydrate to 4 kg of potassium nitrate mother liquor, adjust the mass fraction of magnesium chloride in the system to 35%, heat the above system to 90 ° C, at which time the magnesium chloride hexahydrate is completely dissolved, and then cool to 30 ° C, keep warm and settle for 0.5 h, and separate the solid-liquid to obtain 0.40 kg of crystalline solid and 8.34 kg of crystallization mother liquor.

[0030] S2a. Preparation of decomposition liquid: Add the above crystalline solid to 1.54 kg of potassium nitrate mother liquor under continuous stirring, raise the temperature to 35° C., wash for 2 h, and separate the solid and liquid to obtain 0.04 kg of potassium chloride solid and 1.90 kg of decomposition liquid.

[0031] S3a, preparing concentrated solution: evaporating and concentrating half of the crystallization mother liquor in S1a, i.e. 4.17 kg, to a temperature of 135°C to obtain 3.12 kg of 135°C concentrated solution, and the remaining 4.17 kg of 30°C crystallization mother liquor for standby use.

[0032] Example b:

[0033] The following cycle experiment was carried out using 1.90 kg of the 35°C decomposition liquid obtained in Example a, 3.12 kg of the 135°C concentrated liquid, 4.17 kg of the remaining 30°C crystallization mother liquor, and 10°C potassium nitrate mother liquor as the initial raw materials:

[0034] S1b, brine adjustment;

[0035] Mix 1.17 kg of the decomposition liquid at 35°C with 0.67 kg of the concentrated liquid at 135°C, and adjust the magnesium chloride mass fraction of the system to 32% by adding brine. At this time, the temperature of the brine system is 65°C.

[0036] S2b, first stage cooling

[0037] 1.65 kg of crystallization mother liquor at 30°C was used as a cooling medium to exchange heat with the brine adjustment system S1b. After the heat exchange, the temperature of the crystallization mother liquor was 52°C and the temperature of the brine adjustment system was 44°C.

[0038] S3b, Second stage cooling

[0039] 1.0 kg of potassium nitrate mother liquor at 10°C is used as a cooling medium to exchange heat with the brine adjustment system after cooling in the first stage of S2b. After the heat exchange, the temperature of the potassium nitrate mother liquor is 35°C, and the temperature of the brine adjustment system is 30°C.

[0040] S4b, solid-liquid separation

[0041] The S3b second stage cooling and brine adjustment system was kept at 30°C for 1 hour, and then solid-liquid separation was performed to obtain 1.65 kg of 30°C crystallization mother liquor and 0.19 kg of crystalline solid. The 30°C crystallization mother liquor obtained by solid-liquid separation was used as the cooling medium to participate in the S2b first stage cooling.

[0042] S5b, decomposition washing

[0043] Under sufficient stirring, the crystalline solid of S4b was added to 1.0 kg of 35°C potassium nitrate mother liquor after the second stage cooling and heat exchange of S3b, and washed at 35°C for 1 hour. Then, solid-liquid separation was performed to obtain 0.024 kg of potassium chloride solid and 1.17 kg of 35°C decomposition liquid. The purity of potassium chloride solid was 90.14%, and the recovery rate was 85%. The 35°C decomposition liquid was returned to S1b for recycling;

[0044] S6b, evaporation concentration

[0045] The crystallization mother liquor of S2b after a cooling and heat exchange is evaporated and concentrated to a system temperature of 135°C. A portion of the concentrated liquid at 135°C, 0.67 kg, is returned to S1b for recycling, and the remaining concentrated liquid at 135°C, 0.44 kg, is cooled to room temperature to obtain MgCl2·6H2O solid.

[0046] This method enables efficient and energy-efficient recycling of potassium resources from potassium nitrate mother liquor. The extracted potassium chloride can achieve a purity exceeding 90% and a recovery rate exceeding 80%, meeting the requirements for reuse as a production raw material. The process of the present invention reduces production costs for enterprises, is stable, and has low technical risks, making it suitable for industrial production. According to incomplete statistics, the national production capacity of potassium nitrate by the double decomposition method of magnesium nitrate and potassium chloride is approximately 270,000 tons / year, with approximately 650,000 tons / year of by-product mother liquor. Using the process of the present invention, approximately 16,000 tons of potassium chloride can be recovered from this, resulting in significant economic benefits.

[0047] Utilizing the technical solution described in the present invention, or those skilled in the art designing similar technical solutions inspired by the technical solution of the present invention to achieve the above technical effects, all fall within the scope of protection of the present invention.

Claims

1. A method for recycling potassium resources in potassium nitrate mother liquor, characterized in that: The mass composition of the potassium nitrate mother liquor includes: 15.00%≤MgCl2≤22.00%, KCl≥2.00%, Mg(NO3)2≤5.00%, NaCl≤5.00%, and the remainder is water; the temperature of the potassium nitrate mother liquor is 5~15°C; and the recycling method comprises the following steps: S1: Preparation of initial raw materials - crystallization mother liquor, decomposition liquid and concentrated liquid; The steps of preparing a crystallization mother liquor are as follows: adding magnesium chloride hexahydrate to a potassium nitrate mother liquor under continuous stirring to adjust the mass fraction of magnesium chloride in the system to 30-35%, heating the system to 90-100°C until the magnesium chloride hexahydrate is completely dissolved, then cooling the system to 30-40°C, keeping the temperature and allowing the solution to settle for 0.5-1 hour, and performing solid-liquid separation to obtain a crystalline solid and a crystallization mother liquor; The steps of preparing the decomposition liquid are as follows: adding a crystalline solid to a potassium nitrate mother liquor under continuous stirring, with a mass ratio of the crystalline solid to the potassium nitrate mother liquor of 1:2.0-6.0, heating the mixture to 30-40°C, washing the mixture for 0.5-3.0 hours, and performing solid-liquid separation to obtain potassium chloride solid and a decomposition liquid; The steps of preparing the concentrated solution are as follows: a portion of the prepared crystallization mother liquor is reserved for standby use, and the remaining crystallization mother liquor is evaporated and concentrated to a temperature of 125-135° C. to obtain a concentrated solution; S2, brine adjustment: the decomposition liquid produced by decomposition and washing is mixed with part of the concentrated liquid produced by evaporation and concentration, and the brine is added to adjust the MgCl2 content of the system; S3, first stage cooling: crystallization mother liquor is used as cooling medium to exchange heat with brine adjustment system; S4, second stage cooling: potassium nitrate mother liquor is used as cooling medium to exchange heat with brine adjustment system after first stage cooling; S5, solid-liquid separation: After the second stage cooling and brine adjustment system in S4 is insulated and settled, solid-liquid separation is performed to obtain crystallized solid and crystallization mother liquor. The crystallization mother liquor is used as the cooling medium again to participate in the first stage cooling of S3; S6, decomposition and washing: adding crystalline solid to the potassium nitrate mother liquor after heat exchange in S4 and stirring thoroughly, and performing solid-liquid separation to obtain potassium chloride solid with a purity of ≥90% and decomposition liquid, and the potassium chloride solid is reused as a production raw material; S7, evaporation and concentration: After the crystallization mother liquor after heat exchange in S3 is evaporated and concentrated, a portion of the concentrated liquid is mixed with the decomposition liquid and brine for recycling, and the remaining concentrated liquid is cooled to room temperature to obtain MgCl2·6H2O solid.

2. the recycling method of potassium resource in the potassium nitrate mother liquor as claimed in claim 1, is characterized in that, The brine adjustment in S2 is to mix the decomposition liquid with the concentrated liquid, and the mass fraction of magnesium chloride in the brine adjustment system is 30~35%.

3. The method for recycling potassium resources in the potassium nitrate mother liquor as claimed in claim 1, wherein The first stage of cooling in S3 utilizes the crystallization mother liquor as the cooling medium to exchange heat with the brine adjustment system in S2.

4. The method for recycling potassium resources in the potassium nitrate mother liquor as claimed in claim 1, wherein The second stage cooling in S4 uses 5~15℃ potassium nitrate mother liquor as cooling medium to exchange heat with the system after the first stage cooling, and the terminal temperature of the second stage cooling is 30~40℃.

5. The method for recycling potassium resources in the potassium nitrate mother liquor as claimed in claim 1, wherein The solid-liquid separation in S5 is to keep the S4 second-stage cooling and brine adjustment system at 30~40℃ and let it settle for 0.5~1h, and then separate the solid and liquid to obtain crystallization mother liquor and crystallization solid; the crystallization mother liquor obtained by solid-liquid separation is used as a cooling medium to participate in the first-stage cooling of S3.

6. The method for recycling potassium resources in the potassium nitrate mother liquor as claimed in claim 1, wherein: The decomposition and washing in S6 is to add crystalline solid to the potassium nitrate mother liquor after the second stage cooling and heat exchange. The mass ratio of crystalline solid to potassium nitrate mother liquor is 1:2.0~6.0, the washing temperature is 30~40 ℃, and the washing time is 0.5~3 h. Then the solid-liquid separation is carried out to obtain potassium chloride solid and decomposition liquid. The decomposition liquid is returned to the brine adjustment process in S2 for recycling.

7. The method for recycling potassium resources in the potassium nitrate mother liquor as claimed in claim 1, wherein: The evaporation concentration in S7 is to evaporate and concentrate the crystallization mother liquor after a cooling and heat exchange process to a system temperature of 125~135℃. A part of the concentrated liquid is returned to the brine adjustment process in S2 for recycling, and the remaining concentrated liquid is cooled to room temperature to obtain MgCl2·6H2O solid.

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