Method for simultaneously preparing magnesium chloride and potassium nitrate

Abstract

The invention belongs to the technical field of chemical production, and particularly relates to a method for simultaneously preparing magnesium chloride and potassium nitrate, which comprises the following steps: mixing nitric acid, magnesium oxide, potassium chloride and water, dissolving, cooling for crystallization, and carrying out solid-liquid separation to obtain a first mother solution and a first potassium nitrate crystal; concentrating the first mother liquor until the specific gravity is 1.31-1.38, cooling, crystallizing, and carrying out solid-liquid separation to obtain second mother liquor and carnallite; concentrating the second mother liquor until the specific gravity is 1.4-1.47, cooling and crystallizing until the temperature is 25-35 DEG C and the solid-liquid ratio is 65-70%, and carrying out solid-liquid separation to obtain third mother liquor and magnesium chloride crystals; and S3, dissolving the carnallite obtained in the step S2 by using a third mother solution, performing cooling crystallization, and performing solid-liquid separation to obtain a second potassium nitrate crystal and a fourth mother solution. According to the method, the magnesium chloride crystal with high purity can be obtained while the potassium nitrate crystal is prepared, the prepared magnesium chloride does not have a caking phenomenon, meanwhile, the use amount of raw materials can be reduced, and cost reduction and efficiency improvement are realized.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical production, and particularly relates to a method for simultaneously preparing magnesium chloride and potassium nitrate. Background Art

[0002] In the prior art, potassium nitrate is prepared from potassium chloride, magnesium oxide, and nitric acid as raw materials, or directly from potassium chloride and magnesium nitrate as raw materials. When potassium nitrate is prepared, a large amount of magnesium nitrate hexahydrate is produced as a by-product, and the quality of the produced magnesium nitrate hexahydrate is even higher than that of potassium nitrate. However, during the crystallization of potassium nitrate, some potassium nitrate that has not been precipitated will enter the finished magnesium chloride product, which results in a low purity of magnesium chloride and easily causes agglomeration of the magnesium chloride product, which greatly affects the use and sales of the by-product magnesium nitrate hexahydrate. Summary of the invention

[0003] Therefore, the object of the present invention is to provide a method for simultaneously preparing magnesium chloride and potassium nitrate, which can simultaneously prepare high-purity magnesium chloride and potassium nitrate products, the prepared magnesium chloride will not agglomerate, and at the same time can reduce the amount of raw materials used, thereby achieving cost reduction and efficiency improvement.

[0004] To this end, the present invention provides the following technical solutions.

[0005] The present invention provides a method for simultaneously preparing magnesium chloride and potassium nitrate, comprising the following steps:

[0006] S1: mixing nitric acid, magnesium oxide, potassium chloride and water, dissolving, cooling and crystallizing, and performing solid-liquid separation to obtain a first mother liquor and a first potassium nitrate crystal;

[0007] S2: concentrating the first mother liquor to a specific gravity of 1.34 to 1.38, cooling and crystallizing, and performing solid-liquid separation to obtain a second mother liquor and carnallite;

[0008] S3: concentrating the second mother liquor to a specific gravity of 1.4 to 1.47, cooling and crystallizing to 25 to 35° C., with a solid-liquid ratio of 65% to 70%, and performing solid-liquid separation to obtain a third mother liquor and magnesium chloride crystals;

[0009] S4: using the third mother liquor to dissolve the carnallite obtained in step S2, cooling and crystallizing, and separating the solid and the liquid to obtain the second potassium nitrate crystals and the fourth mother liquor.

[0010] Optionally, the method further includes returning the fourth mother liquor to step S1 to participate in cooling crystallization; the fourth mother liquor has the same composition as the first mother liquor.

[0011] Optionally, in step S2, the cooling crystallization step is cooling crystallization to 25-35° C., with a solid-liquid ratio of 15%-30%.

[0012] Optionally, in the step S1, the cooling crystallization step is cooling crystallization to -5 to -15°C, with a solid content of 28% to 35%; optionally, in the step S1, the cooling crystallization is carried out in three stages, the first stage of cooling crystallization is cooling crystallization to 40 to 60°C, with a solid content of 10% to 14%, the second stage of cooling crystallization is cooling crystallization to 10 to 30°C, with a solid content of 15% to 25%; the third stage of crystallization is cooling crystallization to -5 to -15°C, with a solid content of 28% to 35%; further optionally, in the step S1, the first mother liquor is used to cool the second stage of cooling crystallization.

[0013] Optionally, in step S1, the dissolving step is performed at 100-120°C.

[0014] Optionally, in step S1, after the dissolution step and before the cooling crystallization step, a solid-liquid separation step is also included to separate insoluble impurities; optionally, a step of washing the insoluble impurities is also included to obtain washing water and the washed insoluble impurities; further optionally, the washing water is returned to step S1 to participate in the dissolution step.

[0015] Optionally, in the step S4, the cooling crystallization is cooling crystallization to -15 to -8°C; optionally, in the step S4, the cooling crystallization is carried out in two stages, the first stage of cooling crystallization is cooling crystallization to 28 to 22°C for 5 to 6 hours, and the second stage of cooling crystallization is cooling crystallization to -15 to -8°C for 5 to 6 hours; further optionally, in the step S4, the first mother liquor is used to cool the first stage of cooling crystallization.

[0016] Optionally, in step S2, the concentration includes evaporation concentration; optionally, the temperature of the evaporation concentration is 70-80°C.

[0017] Optionally, in step S3, the concentration includes evaporation concentration; optionally, the temperature of the evaporation concentration is 80-90°C.

[0018] Optionally, in step S2, the first mother liquor is concentrated to a specific gravity of 1.34 to 1.35.

[0019] Optionally, in step S3, the second mother liquor is concentrated to a specific gravity of 1.43 to 1.44.

[0020] Optionally, the method further includes the steps of recrystallizing the first potassium nitrate crystals and the second potassium nitrate crystals, and separating the solid from the liquid to obtain third potassium nitrate crystals and a fifth mother liquor; optionally, returning the fifth mother liquor to the step S4 to dissolve the carnallite obtained in the step S2.

[0021] Optionally, the recrystallization step includes dissolving the first potassium nitrate crystals and the second potassium nitrate crystals with deionized water at 90-110°C, cooling and crystallizing to 0--10°C, with a solid content of 50%; optionally, the recrystallization includes two stages of cooling crystallization, the first stage of cooling crystallization is cooling crystallization to 20-30°C, and the second stage of cooling crystallization is cooling crystallization to 0--10°C, with a solid content of 50%.

[0022] Optionally, a thickening step is included before solid-liquid separation; optionally, thickening equipment is used for thickening; further optionally, the thickening equipment includes a thickener.

[0023] Optionally, the solid-liquid separation includes any one of centrifugation and filtration; optionally, the solid-liquid separation is centrifugation.

[0024] Optionally, the mass ratio of magnesium oxide, nitric acid, potassium chloride and water is 1:3-3.5:3.5-4:4.5-5; optionally, the mass ratio of magnesium oxide, nitric acid, potassium chloride and water is 1:3.2:3.8:4.8; before cooling crystallization in step S1, the molar ratio of chloride ions to magnesium ions is maintained at approximately 2:1.

[0025] Optionally, the mass concentration of the nitric acid is 40% to 60%; optionally, the mass concentration of the nitric acid is 50%.

[0026] Optionally, in step S1, the pH value of the solution is adjusted to 5 to 5.5 before cooling and crystallization.

[0027] The method for preparing magnesium chloride and potassium nitrate at the same time provided by the present invention also includes 1 to 10 raw material reaction tanks connected in series so as to fully react the raw materials. During the reaction, as nitric acid is continuously consumed, the pH of the solution gradually increases. After nitric acid, magnesium oxide, potassium chloride and water are mixed and dissolved, a filter press step is also included to remove insoluble impurities, and the water used to wash the insoluble impurities is returned to the system to dissolve the raw materials for use, thereby avoiding the waste of the effective components mixed therein.

[0028] The beneficial effects of the present invention are:

[0029] The method for preparing magnesium chloride and potassium nitrate at the same time provided by the present invention comprises the following steps: S1: mixing nitric acid, magnesium oxide, potassium chloride and water, dissolving, cooling crystallization, solid-liquid separation, and obtaining a first mother liquor and a first potassium nitrate crystal; S2: concentrating the first mother liquor to a specific gravity of 1.31-1.38, cooling crystallization, solid-liquid separation, and obtaining a second mother liquor and carnallite; S3: concentrating the second mother liquor to a specific gravity of 1.4-1.47, cooling crystallization to 25-35°C, a solid-liquid ratio of 65%-70%, solid-liquid separation, and obtaining a third mother liquor and magnesium chloride crystals; S4: using the third mother liquor to dissolve the carnallite obtained in step S2, cooling crystallization, solid-liquid separation, and obtaining a second potassium nitrate crystal and a fourth mother liquor. The preparation method can obtain high-purity magnesium chloride crystals while preparing potassium nitrate crystals, and the prepared magnesium chloride will not agglomerate, and at the same time can reduce the amount of raw materials used, thereby achieving cost reduction and efficiency improvement. The carnallite obtained in step S2 is dissolved by the third mother liquor, and potassium nitrate crystals are separated, thereby achieving full utilization of raw materials. Among them, the third mother liquor obtained at the same time as the crystallization of magnesium chloride crystals is used to dissolve carnallite to further recover potassium nitrate crystals, rather than returning a large amount of it to the second mother liquor to participate in the crystallization of magnesium chloride again, and the second mother liquor will not be diluted; maintaining the concentration of the second mother liquor also helps to improve the purity of the obtained magnesium chloride.

[0030] The method for simultaneously preparing magnesium chloride and potassium nitrate provided by the present invention further comprises the step of returning the fourth mother liquor to step S1 to participate in cooling and crystallization, so that in the entire process, only potassium nitrate and magnesium chloride are produced without generating other wastes, the raw materials are fully utilized, and energy conservation and environmental protection are achieved.

[0031] The method for preparing magnesium chloride and potassium nitrate at the same time provided by the present invention also includes the steps of recrystallizing the first potassium nitrate crystal and the second potassium nitrate crystal, and performing solid-liquid separation to obtain the third potassium nitrate crystal and the fifth mother liquor; optionally, the fifth mother liquor is returned to the step S4 to dissolve the carnallite obtained in the step S2. When potassium nitrate is purified by recrystallization, the corresponding fifth mother liquor can also be used in the entire process cycle, further realizing the purification of potassium nitrate without the generation of waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 The figure is a schematic diagram of the process flow of the method for simultaneously preparing magnesium chloride and potassium nitrate in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0035] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0036] Example 1

[0037] This embodiment provides a method for simultaneously preparing magnesium chloride and potassium nitrate. The specific process flow diagram is as follows Figure 1 As shown, the following steps are included:

[0038] (1) Mix magnesium oxide, nitric acid (50 wt%), potassium chloride and water in a mass ratio of 1:3.2:3.8:4.8, fully dissolve at 110°C, and separate by filter press to obtain insoluble impurities and filter press solution. Wash the insoluble impurities, and return the washing water to participate in the dissolution. The filter press solution has a pH of 5-5.5, first cools and crystallizes to 50°C and a solid content of 13%, then continues to cool and crystallize to 20°C and a solid content of 20%, and finally cools and crystallizes to -10°C and a solid content of 31%. After thickening in a thickener, centrifuge solid-liquid separation is performed to obtain the first mother liquor and the first potassium nitrate crystals. The first mother liquor is returned to help cool and crystallize to 20°C.

[0039] (2) The first mother liquor is evaporated and concentrated at 78° C. to a specific gravity of 1.34, cooled and crystallized to 35° C. and a solid-liquid ratio of 17%, thickened in a thickener, and then centrifuged to separate the solid and liquid to obtain a second mother liquor and carnallite.

[0040] (3) The second mother liquor is evaporated and concentrated at 88° C. to a specific gravity of 1.43, cooled and crystallized to 35° C. and a solid-liquid ratio of 65%, thickened in a thickener, and then centrifuged to separate the solid and liquid to obtain a third mother liquor and magnesium chloride crystals 1.

[0041] (4) The third mother liquor is used to dissolve carnallite, and the solution is first cooled and crystallized for 5 hours to 25° C. This cooling is achieved by heat exchange with the first mother liquor, and then cooled and crystallized for 6 hours to -10° C. After thickening in a thickener, the solid-liquid separation is performed by a centrifuge to obtain the second potassium nitrate crystals and the fourth mother liquor, and the fourth mother liquor is returned to step (1) to participate in cooling and crystallization.

[0042] (5) Recrystallizing the first potassium nitrate crystals and the second potassium nitrate crystals, dissolving the first potassium nitrate crystals and the second potassium nitrate crystals in deionized water at 100° C., cooling and crystallizing to 25° C., and then cooling and crystallizing to -5° C., with a solid content of 50%. After thickening in a thickener, centrifuge solid-liquid separation is performed to obtain third potassium nitrate crystals and a fifth mother liquor, and the fifth mother liquor is returned to step (4) to dissolve carnallite.

[0043] The method consumes 790 kg of potassium chloride per ton of potassium nitrate, the purity of the obtained magnesium chloride crystals is 98.5%, and the purity of the third potassium nitrate crystals is 99.9%; and the potassium recovery rate in the carnallite can reach 80%.

[0044] Comparative Example 1

[0045] This comparative example provides a method for simultaneously preparing magnesium chloride and potassium nitrate, which specifically comprises the following steps:

[0046] (1) Mix magnesium oxide, nitric acid (50 wt%), potassium chloride and water in a mass ratio of 1:3.2:3.8:4.8, fully dissolve at 110°C, and separate by filter press to obtain insoluble impurities and filter press solution. Wash the insoluble impurities, and return the washing water to participate in the dissolution. The filter press solution is first cooled and crystallized to 50°C and a solid content of 13%, and then cooled and crystallized to 20°C and a solid content of 20%, and finally cooled and crystallized to -10°C and a solid content of 31%. After thickening in a thickener, the first mother liquor and the first potassium nitrate crystal are separated by a centrifuge. The first mother liquor is returned to help cool the crystallization to 20°C.

[0047] (2) The first mother liquor is evaporated and concentrated at 78° C. to a specific gravity of 1.34, cooled and crystallized to 35° C. and a solid-liquid ratio of 17%, thickened in a thickener, and then centrifuged to separate the solid and liquid to obtain a second mother liquor and carnallite.

[0048] (3) The second mother liquor is evaporated and concentrated at 88° C. to a specific gravity of 1.36, cooled and crystallized to 35° C. and a solid-liquid ratio of 65%, thickened in a thickener, and then centrifuged to separate the solid and liquid to obtain a third mother liquor and magnesium chloride crystals.

[0049] The method consumes 830 kg of potassium chloride per ton of potassium nitrate, and the purity of the obtained magnesium chloride crystals is 98%.

[0050] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the protection scope of the invention.

Claims

1. A method for simultaneously preparing magnesium chloride and potassium nitrate, characterized in that: The steps include: S1: mixing nitric acid, magnesium oxide, potassium chloride and water, dissolving, cooling and crystallizing, and performing solid-liquid separation to obtain a first mother liquor and a first potassium nitrate crystal; S2: concentrating the first mother liquor to a specific gravity of 1.34 to 1.38, cooling and crystallizing, and performing solid-liquid separation to obtain a second mother liquor and carnallite; S3: concentrating the second mother liquor to a specific gravity of 1.4 to 1.47, cooling and crystallizing to 25 to 35° C., with a solid-liquid ratio of 65% to 70%, and performing solid-liquid separation to obtain a third mother liquor and magnesium chloride crystals; S4: using the third mother liquor to dissolve the carnallite obtained in step S2, cooling and crystallizing, and separating the solid and the liquid to obtain the second potassium nitrate crystals and the fourth mother liquor.

2. The method for simultaneously preparing magnesium chloride and potassium nitrate according to claim 1, characterized in that: The fourth mother liquor is also returned to step S1 to participate in cooling crystallization; And / or, in step S2, the cooling crystallization step is cooling crystallization to 25-35° C., with a solid-liquid ratio of 15%-30%.

3. The method for simultaneously preparing magnesium chloride and potassium nitrate according to claim 1 or 2, characterized in that, In the step S1, the step of cooling crystallization is cooling crystallization to -5 to -15°C, with a solid content of 28% to 35%; optionally, in the step S1, the cooling crystallization is carried out in three stages, the first stage of cooling crystallization is cooling crystallization to 40 to 60°C, with a solid content of 10% to 14%, the second stage of cooling crystallization is cooling crystallization to 10 to 30°C, with a solid content of 15% to 25%; the third stage of crystallization is cooling crystallization to -5 to -15°C, with a solid content of 28% to 35%; further optionally, in the step S1, the first mother liquor is used to cool the second stage of cooling crystallization; And / or, in step S1, the dissolving step is performed at 100-120°C; And / or, in the step S1, after the dissolution step and before the cooling crystallization step, a solid-liquid separation step is also included to separate insoluble impurities; optionally, a step of washing the insoluble impurities is also included to obtain washing water and the washed insoluble impurities; further optionally, the washing water is returned to the step S1 to participate in the dissolution step.

4. The method for simultaneously preparing magnesium chloride and potassium nitrate according to any one of claims 1 to 3, characterized in that: In the step S4, the cooling crystallization is cooling crystallization to -15 to -8°C; optionally, in the step S4, the cooling crystallization is carried out in two stages, the first stage of cooling crystallization is cooling crystallization to 28 to 22°C for 5 to 6 hours, and the second stage of cooling crystallization is cooling crystallization to -15 to -8°C for 5 to 6 hours; further optionally, in the step S4, the first mother liquor is used to cool the first stage of cooling crystallization.

5. The method for simultaneously preparing magnesium chloride and potassium nitrate according to any one of claims 1 to 4, characterized in that: In the step S2, the concentration includes evaporation concentration; optionally, the temperature of the evaporation concentration is 70-80° C.; And / or, in step S3, the concentration includes evaporation concentration; optionally, the temperature of the evaporation concentration is 80-90°C.

6. The method for simultaneously preparing magnesium chloride and potassium nitrate according to any one of claims 1 to 5, characterized in that: In the step S2, the first mother liquor is concentrated to a specific gravity of 1.34 to 1.35; And / or, in step S3, the second mother liquor is concentrated to a specific gravity of 1.43 to 1.

44.

7. The method for simultaneously preparing magnesium chloride and potassium nitrate according to any one of claims 2 to 6, characterized in that: The method further includes the steps of recrystallizing the first potassium nitrate crystals and the second potassium nitrate crystals, and performing solid-liquid separation to obtain third potassium nitrate crystals and a fifth mother liquor; optionally, returning the fifth mother liquor to the step S4 to dissolve the carnallite obtained in the step S2.

8. The method for simultaneously preparing magnesium chloride and potassium nitrate according to claim 7, characterized in that: The recrystallization step includes dissolving the first potassium nitrate crystals and the second potassium nitrate crystals with deionized water at 90-110°C, cooling and crystallizing to 0--10°C, with a solid content of 50%; optionally, the recrystallization includes two stages of cooling crystallization, the first stage of cooling crystallization is cooling crystallization to 20-30°C, and the second stage of cooling crystallization is cooling crystallization to 0--10°C, with a solid content of 50%.

9. The method for simultaneously preparing magnesium chloride and potassium nitrate according to any one of claims 1 to 7, characterized in that: A thickening step is included before solid-liquid separation; optionally, thickening is performed using a thickening device; further optionally, the thickening device includes a thickener; And / or, the solid-liquid separation includes any one of centrifugation and filtration; optionally, the solid-liquid separation is centrifugation.

10. The method for simultaneously preparing magnesium chloride and potassium nitrate according to any one of claims 1 to 9, characterized in that: The mass ratio of magnesium oxide, nitric acid, potassium chloride and water is 1:3-3.5:3.5-4:4.5-5; optionally, the mass ratio of magnesium oxide, nitric acid, potassium chloride and water is 1:3.2:3.8:4.8; And / or, the mass concentration of the nitric acid is 40% to 60%; optionally, the mass concentration of the nitric acid is 50%; And / or, in step S1, the pH value of the solution is adjusted to 5 to 5.5 before cooling and crystallization.

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