CN112875728B - Preparation method of high-purity potassium nitrate and high-purity potassium nitrate - Google Patents
Preparation method of high-purity potassium nitrate and high-purity potassium nitrate Download PDFInfo
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Abstract
The application relates to a preparation method of high-purity potassium nitrate and the high-purity potassium nitrate, which relate to the field of preparation of chemical raw materials and comprise the following steps: s1, preparing a potassium nitrate supersaturated solution: mixing and dissolving solid potassium nitrate and water in a mass ratio of 2:1, heating to 95 ℃, and filtering to obtain a potassium nitrate saturated solution; s2, cooling and crystallizing: cooling the potassium nitrate saturated solution obtained in the step S1 for 30min by using water at the temperature of 85-88 ℃, adding seed crystals, and stirring all the time in the process to obtain a potassium nitrate supersaturated solution for crystallization; s3, multiple grading cooling: and (3) carrying out grading cooling on the potassium nitrate supersaturated solution obtained in the step S2 for multiple times by using cooling water with gradually reduced temperature, stirring the potassium nitrate supersaturated solution all the time in the process until the temperature of the potassium nitrate solution is 20 ℃, and blow-drying the potassium nitrate crystals to obtain the high-purity potassium nitrate. The method has the effects of higher purity of the prepared potassium nitrate, better granularity, better flowability and higher looseness due to difficult caking.
Description
Technical Field
The application relates to the field of chemical raw material preparation, in particular to a preparation method of high-purity potassium nitrate and the high-purity potassium nitrate.
Background
Potassium nitrate is an important material used in the food industry as a color former, a color fixative, an antimicrobial agent, a preservative, etc., and high-purity potassium nitrate is used in the ceramic industry for manufacturing enamel chemicals, as well as a glass clarifier for manufacturing automobile lamp glass bulb, optical glass kinescope glass bulb, etc., in addition to being used as a food additive. The high-purity potassium nitrate also has wide application in the pharmaceutical industry, and the pharmaceutical-grade potassium nitrate is a raw material medicine, such as ophthalmic medicine and the like.
Potassium nitrate is deliquescent and easy to agglomerate, and the moisture absorption and agglomeration phenomena are more serious in the presence of a small amount of chloride ions. The common granular or powdery potassium nitrate has a caking phenomenon, so that the potassium nitrate generally has poor looseness and fluidity. Meanwhile, potassium nitrate is a strong oxidant, and can cause combustion and explosion when contacting with organic matters, so that the potassium nitrate is not suitable for strong crushing operation. The application of potassium nitrate is seriously affected due to the characteristics that potassium nitrate is easy to absorb moisture and agglomerate and is not suitable for strong crushing.
At present, in order to prevent potassium nitrate from caking, many chemical production enterprises add an anticaking agent such as magnesium stearate or sodium alkyl sulfonate as a main surfactant into the product, but the anticaking agent is equivalent to artificially introducing impurities, so that the quality of the product is greatly influenced, and the application of potassium nitrate in high-end fields cannot be met. In addition, the potassium nitrate is made into granulated potassium nitrate in a common mode, namely, the potassium nitrate in a round granular shape is pressed through a die after being melted at a high temperature, but the problems of fluidity and looseness are only solved, the high purity of the potassium nitrate cannot be guaranteed, and impurities are often introduced in the operation process.
In view of the above-mentioned related technologies, the inventors consider that potassium nitrate on the market at present has the defects of easy caking, poor fluidity, poor looseness and low purity, and how to balance the fluidity, the looseness and the high purity of potassium nitrate is a problem to be solved urgently.
Disclosure of Invention
In order to solve the problems of easy caking, poor fluidity, poor looseness and low purity of potassium nitrate, the application provides a preparation method of high-purity potassium nitrate and the high-purity potassium nitrate.
The preparation method of the high-purity potassium nitrate provided by the application adopts the following technical scheme:
a preparation method of high-purity potassium nitrate comprises the following steps:
s1, preparing a potassium nitrate supersaturated solution: mixing and dissolving solid potassium nitrate and water in a mass ratio of 2:1, heating to 95 ℃, and filtering to obtain a potassium nitrate saturated solution;
s2, cooling and crystallizing: cooling the potassium nitrate saturated solution obtained in the step S1 for 30min by using water at the temperature of 85-88 ℃, adding seed crystals, and stirring all the time in the process to obtain a potassium nitrate supersaturated solution for crystallization;
s3, multiple grading cooling: cooling the potassium nitrate supersaturated solution obtained in the step S2 for multiple times by cooling water with gradually decreasing temperature, stirring the potassium nitrate supersaturated solution all the time in the process until the temperature of the potassium nitrate solution is 20 ℃, and drying the potassium nitrate crystals to obtain high-purity potassium nitrate;
the technical indexes of the high-purity potassium nitrate are as follows: the purity is higher than 97.0%, the granularity is 0.3-3.5mm, the water content is not more than 0.45%, the looseness of a 7-30 mesh sieve is more than 60%, and the shape of the crystal is an elliptical sphere crystal.
By adopting the technical scheme, in the step S1, the low-purity and easily-caked solid potassium nitrate is mixed with water and heated to prepare a potassium nitrate saturated solution with the temperature of 95 ℃, so that the potassium nitrate is crystallized and purified. In the step S2, the temperature of the saturated potassium nitrate solution at 95 ℃ is reduced for 30min through water at 85-88 ℃, seed crystals are added, the supersaturated potassium nitrate solution generated by new crystal nuclei is formed through stirring, and the supersaturation degree of the supersaturated potassium nitrate solution is gradually reduced along with the formation and growth of the new crystal nuclei until the supersaturated potassium nitrate solution approaches to the state of a saturated solution.
And S3, cooling the supersaturated potassium nitrate solution which is in a saturated state to increase the supersaturation degree of the supersaturated potassium nitrate solution again, and cooling the potassium nitrate solution in a plurality of times in a grading manner in the whole S3 step to keep the supersaturated potassium nitrate solution in a 'saturated-supersaturated-saturated- … …' circulating state all the time, so that new crystal nuclei are continuously precipitated and the previously formed crystal nuclei grow up, and finally the number, granularity, purity, fluidity, looseness and the like of the precipitated potassium nitrate crystals meet the application requirements of high-end fields.
In the cooling crystallization process of the step S3, when the solution tends to be in a saturated state at the end stage of each stage of cooling, the number and the size of crystals are kept relatively stable, the solution is in a dynamic balance, and the stirring at the stage can carry out surface grinding on the crystals without basically changing the number and the particle size of the crystals, so that the crystals are finally changed into elliptical sphere crystals with smooth surfaces, and the flowability and the looseness of the crystals are finally improved. According to experimental data, the potassium nitrate finally prepared by adopting the fractional cooling crystallization mode in the step S3 has the excellent quality of higher purity, better granularity, better fluidity and better looseness.
Preferably, in the step S3, when the cooling water cools the supersaturated potassium nitrate solution a plurality of times, the cooling water has a temperature gradient of 3 to 10 ℃ per time.
By adopting the technical scheme, experimental data show that the temperature reduction gradient of the cooling water is beneficial to improving the granularity of potassium nitrate crystals and improving the fluidity of potassium nitrate when the temperature reduction gradient is 3-10 ℃.
Preferably, in the step S3, the temperatures of the cooling water in the respective stages are 88 ℃, 85 ℃, 82 ℃, 79 ℃, 75 ℃, 71 ℃, 66 ℃, 61 ℃, 56 ℃, 50 ℃, 44 ℃, 37 ℃, 30 ℃ and 20 ℃ in sequence.
By adopting the technical scheme, the experimental data show that when the temperatures of all stages of the cooling water are 88 ℃, 85 ℃, 82 ℃, 79 ℃, 75 ℃, 71 ℃, 66 ℃, 61 ℃, 56 ℃, 50 ℃, 44 ℃, 37 ℃, 30 ℃ and 20 ℃ in sequence, the granularity of the precipitated potassium nitrate crystals is more uniform and the yield is higher.
Preferably, in the step S3, the temperature reduction time of each stage of the cooling water is 30-60 min.
Through adopting above-mentioned technical scheme, every grade of cooling time of cooling water is in 30-60min, can make the cooling water in this time will be in the supersaturated potassium nitrate solution that saturated potassium nitrate solution cooled down to be close with cooling water temperature to realize good crystallization and crystal nucleus growth, improve the yield of high-purity potassium nitrate.
Preferably, in the step S3, the cooling time of the cooling water at 88 ℃, 85 ℃, 82 ℃, 79 ℃, 75 ℃, 71 ℃, 66 ℃, 61 ℃, 56 ℃, 50 ℃, 44 ℃, 37 ℃ and 30 ℃ is 30min, and the cooling time of the cooling water at 20 ℃ is 60 min.
By adopting the technical scheme, according to the supersaturation-supersolubility curve of potassium nitrate, the maximum supersaturation temperature (supercooling temperature) delta T of the potassium nitrate solution is known along with the reduction of the temperature of the potassium nitrate solutionmaxThe temperature is decreased slightly to reach the supersaturation degree needed by nucleation in the high temperature area, and the temperature is decreased more greatly to form new crystal nucleus in the low temperature area, and the growth speed of the crystal nucleus is slower. Therefore, the cooling amplitude of the cooling water is gradually increased, the cooling time of the last low-temperature stage is also prolonged to 60min, the potassium nitrate in the solution can be more fully separated out, and the yield is improved.
Preferably, in the step S2 and the step S3, the stirring speed of the supersaturated potassium nitrate solution is 10 to 40 r/min.
By adopting the technical scheme, the stirring speed has great influence on the quantity and size of crystallization, the stirring speed is too high, the nucleation quantity is too large, crystal nuclei are not easy to grow, and the crystals are separated out to be powdery and are easy to absorb moisture to form blocks; the stirring speed is too slow, nucleation is not easy to occur, the crystal nucleus growth speed is slow, and the yield and the production efficiency are reduced.
The application provides a high-purity potassium nitrate adopts following technical scheme:
high-purity potassium nitrate, wherein the purity of the high-purity potassium nitrate is higher than 99.0%.
Preferably, the high-purity potassium nitrate is an oval spherical crystal with the particle size of 0.5-3 mm.
Preferably, the water content of the high-purity potassium nitrate is not more than 0.36%.
Preferably, the high purity potassium nitrate has a looseness of greater than 70% with a 7-30 mesh sieve.
By adopting the technical scheme, the elliptic spherical potassium nitrate crystal with the granularity of 0.5-3mm, the purity higher than 90 percent and the looseness larger than 70 percent of a 7-30 mesh sieve has better granularity, higher purity, better fluidity and looseness, is more difficult to absorb moisture and agglomerate, has higher quality, and meets the application requirement of the high-end field of potassium nitrate.
In summary, the present application includes at least one of the following beneficial technical effects:
1. according to the method, a potassium nitrate saturated solution at 95 ℃ is prepared firstly, then the temperature is reduced to enable the potassium nitrate saturated solution to become a supersaturated solution, and then the potassium nitrate solution is subjected to multiple grading temperature reduction to enable the potassium nitrate solution to repeat a cycle of 'saturation-supersaturation-saturation- … …', so that new crystal nuclei are continuously precipitated and the previously formed crystal nuclei grow up, and finally the number, granularity, purity, fluidity, looseness and the like of the precipitated potassium nitrate crystals meet the application requirements of high-end fields;
2. the crystallization is carried out by adopting a multi-step cooling mode, the cooling amplitude is gradually increased and the stirring speed is suitable, so that the crystallization yield of the potassium nitrate solution is higher, the granularity is better, the surface of the potassium nitrate crystal can be polished, the crystal is changed into an elliptical spherical crystal with a smooth surface, and the fluidity and the looseness of the crystal are finally improved.
Detailed Description
The present application will be described in further detail with reference to specific examples.
Example 1
S1, preparing a potassium nitrate supersaturated solution: mixing and dissolving solid potassium nitrate and water in a mass ratio of 2:1, heating to 95 ℃, and carrying out pressure filtration while the mixture is hot to obtain a potassium nitrate saturated solution;
s2, cooling and crystallizing: cooling the potassium nitrate saturated solution obtained in the step S1 by using water at 85 ℃ for 30min, adding seed crystals, and stirring at the speed of 60r/min all the time to obtain a potassium nitrate supersaturated solution for crystallization;
s3, multiple grading cooling: cooling the potassium nitrate supersaturated solution obtained in the step S2 for multiple times by using cooling water with gradually reduced temperature, wherein the potassium nitrate supersaturated solution is stirred at the speed of 60r/min all the time in the process;
the initial temperature of the cooling water is 85 ℃, the temperature reduction amplitude of each time is 15 ℃, the temperature reduction time of each time is 60min, the temperature of the potassium nitrate solution is 20 ℃, and the potassium nitrate crystals are filtered and dried to obtain the high-purity potassium nitrate.
The present embodiment also provides a high purity potassium nitrate prepared by the above method, and the technical indexes of the obtained high purity potassium nitrate are as follows: the purity is 98.4%, the granularity is 0.3-0.8mm, the water content is 0.43%, the looseness of a 24-mesh sieve is 68%, the purification yield is 80.1%, and the shape is an elliptical spherical crystal.
Example 2:
a method for preparing high purity potassium nitrate, which is different from example 1 in that the stirring speed of the potassium nitrate solution in the S2 step and the S3 step is 40 r/min.
The present embodiment also provides a high purity potassium nitrate prepared by the above method, and the technical indexes of the obtained high purity potassium nitrate are as follows: the purity is 99.2%, the granularity is 0.4-0.9mm, the water content is 0.35%, the looseness of a 20-mesh sieve is 72%, the purification yield is 80.22%, and the shape is an elliptical spherical crystal.
Example 3:
a preparation method of high-purity potassium nitrate comprises the following steps:
s1, preparing a potassium nitrate supersaturated solution: mixing and dissolving solid potassium nitrate and water in a mass ratio of 2:1, heating to 95 ℃, and carrying out pressure filtration while the mixture is hot to obtain a potassium nitrate saturated solution;
s2, cooling and crystallizing: cooling the potassium nitrate saturated solution obtained in the step S1 by using water at 88 ℃ for 30min, adding seed crystals, and stirring at the speed of 40r/min all the time in the process to obtain a potassium nitrate supersaturated solution for crystallization;
s3, multiple grading cooling: cooling the potassium nitrate supersaturated solution obtained in the step S2 for multiple times by using cooling water with gradually reduced temperature, wherein the potassium nitrate supersaturated solution is stirred at the speed of 40r/min all the time in the process;
the initial temperature of the cooling water is 88 ℃, the temperature reduction amplitude of each time is 10 ℃, the temperature reduction time of each time is 40min, the temperature of the potassium nitrate solution is 20 ℃, and the potassium nitrate crystals are filtered and dried to obtain the high-purity potassium nitrate.
The present embodiment also provides a high purity potassium nitrate prepared by the above method, and the technical indexes of the obtained high purity potassium nitrate are as follows: the purity is 99.3%, the granularity is 0.5-1.2mm, the water content is 0.3%, the looseness of a 12-mesh sieve is 87%, the purification yield is 80.35%, and the shape is an elliptical spherical crystal.
Example 4:
a preparation method of high-purity potassium nitrate comprises the following steps:
s1, preparing a potassium nitrate supersaturated solution: mixing and dissolving solid potassium nitrate and water in a mass ratio of 2:1, heating to 95 ℃, and carrying out pressure filtration while the mixture is hot to obtain a potassium nitrate saturated solution;
s2, cooling and crystallizing: cooling the potassium nitrate saturated solution obtained in the step S1 by using water at 85 ℃ for 30min, adding seed crystals, and stirring at the speed of 20r/min all the time to obtain a potassium nitrate supersaturated solution for crystallization;
s3, multiple grading cooling: cooling the potassium nitrate supersaturated solution obtained in the step S2 for multiple times by using cooling water with gradually reduced temperature, wherein the potassium nitrate supersaturated solution is stirred at the speed of 20r/min all the time in the process;
the initial temperature of the cooling water is 85 ℃, the temperature reduction range of each time is 5 ℃, the temperature reduction time of each time is 30min, the temperature of the potassium nitrate solution is 20 ℃, and the potassium nitrate crystals are filtered and dried to obtain the high-purity potassium nitrate.
The present embodiment also provides a high purity potassium nitrate prepared by the above method, and the technical indexes of the obtained high purity potassium nitrate are as follows: the purity is 99.4%, the granularity is 0.5-1.5mm, the water content is 0.26%, the looseness to a 10-mesh sieve is 90%, the purification yield is 80.5%, and the shape is an elliptical spherical crystal.
Example 5:
the present example differs from example 4 in that the initial temperature of the cooling water in the step S3 is 88 ℃, the temperature reduction range is 3 ℃ each time, and the temperature reduction time is 30min each time.
The present embodiment also provides a high purity potassium nitrate prepared by the above method, and the technical indexes of the obtained high purity potassium nitrate are as follows: the purity was 99.8%, the particle size was 0.5 to 2mm, the water content was 0.16%, the degree of looseness to an 8-mesh sieve was 93%, the purification yield was 80.82%, and the shape was an ellipsoidal crystal.
Example 6:
a preparation method of high-purity potassium nitrate comprises the following steps:
s1, preparing a potassium nitrate supersaturated solution: mixing and dissolving solid potassium nitrate and water in a mass ratio of 2:1, heating to 95 ℃, and carrying out pressure filtration while the mixture is hot to obtain a potassium nitrate saturated solution;
s2, cooling and crystallizing: cooling the potassium nitrate saturated solution obtained in the step S1 by using water at 88 ℃ for 30min, adding seed crystals, and stirring at the speed of 40r/min all the time in the process to obtain a potassium nitrate supersaturated solution for crystallization;
s3, multiple grading cooling: cooling the potassium nitrate supersaturated solution obtained in the step S2 for multiple times by using cooling water with gradually reduced temperature, wherein the potassium nitrate supersaturated solution is stirred at the speed of 40r/min all the time in the process;
the initial temperature of the cooling water is 88 ℃, 85 ℃, 82 ℃, 79 ℃, 75 ℃, 71 ℃, 66 ℃, 61 ℃, 56 ℃, 50 ℃, 44 ℃, 37 ℃, 30 ℃ and 20 ℃ at all stages in sequence, the cooling time of each stage is 30min, the temperature of the potassium nitrate solution is 20 ℃, and the potassium nitrate crystals are filtered and dried to obtain the high-purity potassium nitrate.
The present embodiment also provides a high purity potassium nitrate prepared by the above method, and the technical indexes of the obtained high purity potassium nitrate are as follows: the purity is 99.6%, the granularity is 0.5-3mm, the water content is 0.17%, the looseness to a 7-mesh sieve is 94%, the purification yield is 81.2%, and the shape is an elliptical spherical crystal.
Example 7:
this example is different from example 5 in that in step S3, the cooling water was cooled at 88 ℃, 85 ℃, 82 ℃, 79 ℃, 75 ℃, 71 ℃, 66 ℃, 61 ℃, 56 ℃, 50 ℃, 44 ℃, 37 ℃ and 30 ℃ for 30min, and the cooling water was cooled at 20 ℃ for 60 min.
The present embodiment also provides a high purity potassium nitrate prepared by the above method, and the technical indexes of the obtained high purity potassium nitrate are as follows: the purity is 99.7%, the granularity is 0.5-3mm, the water content is 0.18%, the looseness to a 7-mesh sieve is 95%, the purification yield is 81.45%, and the shape is an elliptical spherical crystal.
Example 8:
the present example differs from example 6 in that a supersaturated potassium nitrate solution was constantly stirred at a stirring rate of 30r/min during the multiple classification cooling in step S3.
The present embodiment also provides a high purity potassium nitrate prepared by the above method, and the technical indexes of the obtained high purity potassium nitrate are as follows: the purity is 99.6%, the granularity is 0.5-3mm, the water content is 0.16%, the looseness to a 7-mesh sieve is 94%, the purification yield is 81.5%, and the shape is an elliptical spherical crystal.
Example 9:
this example is different from example 7 in that the stirring speeds of the supersaturated potassium nitrate solution and the saturated potassium nitrate solution were 20r/min in both the step S2 and the step S3.
The present embodiment also provides a high purity potassium nitrate prepared by the above method, and the technical indexes of the obtained high purity potassium nitrate are as follows: the purity is 99.7%, the granularity is 0.5-3mm, the water content is 0.12%, the looseness of a 7-mesh sieve is 95%, the purification yield is 82.5%, and the shape is an elliptical spherical crystal.
Example 10:
this example is different from example 7 in that the stirring speeds of the supersaturated potassium nitrate solution and the saturated potassium nitrate solution were 10r/min in both the step S2 and the step S3.
The present embodiment also provides a high purity potassium nitrate prepared by the above method, and the technical indexes of the obtained high purity potassium nitrate are as follows: the purity is 99.9%, the granularity is 0.5-3mm, the water content is 0.06%, the looseness of a 7-mesh sieve is 96%, the purification yield is 83.1%, and the shape is an elliptical spherical crystal.
Comparative example 1:
the difference between the comparative example and the example 1 is that in the step of S3, cooling water with the temperature of 20 ℃ is always adopted for cooling and crystallizing until the temperature of the potassium nitrate solution is 20 ℃.
Comparative example 2:
this comparative example is different from example 1 in that the potassium nitrate supersaturated solution was not stirred in the S3 step.
And (3) product performance testing:
the potassium nitrate crystals obtained in examples 1 to 10 and comparative examples 1 to 2 were subjected to product performance tests and appearance records, and the results are shown in table 1.
(1) The purity test method of potassium nitrate is as follows:
specification and preparation of a chromatographic exchange column: length 0.3m, inner diameter 10mm, filler: 10G strong acid type cation exchange resin, which is covered and protected by carbon dioxide-free water, and liquid with the thickness of 1cm is always maintained above the resin.
100ml of dilute hydrochloric acid solution was passed through the column at a rate of 5ml/min, the column was rinsed with carbon dioxide-free water until neutral (the neutral blue test paper turned blue), a 0.200g sample of potassium nitrate was dissolved in 2ml of carbon dioxide-free water in a beaker and transferred to a water storage bottle, the solution was passed through the column at a flow rate of about 3ml/min and the eluate was collected, the beaker was rinsed with 10ml of carbon dioxide-free water and passed through the column at the same rate before the liquid ran dry, and then the column was rinsed with 200ml of carbon dioxide-free water until neutral (the neutral blue test paper turned blue).
Finally titrating the total washing solution by using a sodium hydroxide solution with the concentration of 0.1mol/L, judging an end point by using 1ml of phenolphthalein indicator solution, wherein 1ml of the sodium hydroxide solution with the concentration of 0.1mol/L is equivalent to 10.11mg of KNO3Converting the sodium hydroxide amount into KNO3And the purity was calculated.
(2) The method for testing the moisture content of the potassium nitrate comprises the following steps:
precisely weighed potassium nitrate crystal1.0g, placing the mixture in a weighing bottle which is dried to constant weight, drying the mixture to constant weight at 105 ℃, and calculating according to the following formula: water (loss on drying) ((m))1-m2)/(m1-m0) X is 100%; in the formula, m0-weight of the weighing bottle, m1-weighing the total weight of the bottle and the potassium nitrate sample before drying; m is2Weigh the bottle and potassium nitrate sample together after drying.
(3) The method for measuring the looseness of the potassium nitrate comprises the following steps:
selecting a screen (7-30 meshes) with proper mesh number according to different potassium nitrate crystal particle size ranges, sieving 100% of potassium nitrate crystals, packaging the sieved potassium nitrate according to the specification of 1 kg/bag, pressing a weight of 5kg on the packaging bag, and naturally standing for 3 months;
after three months, the test potassium nitrate samples (whole bags) were allowed to free-fall from a height of 1m onto a rigid flat surface, and the samples in the bags were then poured into a sieve (same size sieve sieved 3 months before) and sieved. The potassium nitrate looseness (w) is expressed by mass percent and calculated according to the following formula: w ═ m (m-m)1) M.times.100%; in the formula: m-sample mass in bag before sieving, m1The mass of sample remaining on the sieve after sieving.
(4) The fluidity of the potassium nitrate crystal was measured as follows:
80g of potassium nitrate crystals are placed in a funnel fixed on the central point of a circular culture dish (the radius r is 5cm), the potassium nitrate crystals flow out of the funnel until the potassium nitrate crystals are accumulated to overflow from the upper edge of the culture dish, the height h from the top point of the steep stack of the cone to the upper edge of the culture dish is measured, the repose angle is the included angle alpha between the bottom surface of the cone and the inclined edge of the cone, and the rest angle cote alpha is the r/h value, namely the fluidity of the potassium nitrate crystals is defined. The angle of repose cotangent value is an index of fluidity, and the larger the cotangent value is, the better the fluidity is.
TABLE 1 Performance test and appearance record Table
The principle of the embodiment of the application is as follows: according to the method, a potassium nitrate saturated solution at 95 ℃ is prepared firstly, then the temperature is reduced to change the potassium nitrate saturated solution into a supersaturated solution, and then the potassium nitrate solution is subjected to multiple grading temperature reduction to repeat a cycle of 'saturation-supersaturation-saturation- … …', so that new crystal nuclei are continuously precipitated and the previously formed crystal nuclei grow up; and meanwhile, a multi-step cooling mode is adopted for crystallization, the cooling amplitude is gradually increased and is matched with a proper stirring speed, the surface of the potassium nitrate crystal is polished, the crystal is changed into an elliptical spherical crystal with a smooth surface, the fluidity and the looseness of the crystal are improved, and finally the number, the granularity, the purity, the fluidity, the looseness and the like of the precipitated potassium nitrate crystal meet the application requirements of high-end fields.
The above embodiments are preferred embodiments of the present application, and the protection scope of the present application is not limited by the above embodiments, so: all equivalent changes made according to the structure, shape and principle of the present application shall be covered by the protection scope of the present application.
Claims (1)
1. The preparation method of the high-purity potassium nitrate is characterized by comprising the following steps of:
s1, preparing a potassium nitrate supersaturated solution: mixing and dissolving solid potassium nitrate and water in a mass ratio of 2:1, heating to 95 ℃, and filtering to obtain a potassium nitrate saturated solution;
s2, cooling and crystallizing: cooling the potassium nitrate saturated solution obtained in the step S1 for 30min by using water at 85 ℃, adding seed crystals, and stirring all the time in the process, wherein the stirring speed of the potassium nitrate supersaturated solution is 20r/min, so as to obtain a potassium nitrate supersaturated solution for crystallization;
s3, multiple grading cooling: cooling the potassium nitrate supersaturated solution obtained in the step S2 for multiple times by cooling water with gradually decreasing temperature, wherein when the cooling water is used for cooling the potassium nitrate supersaturated solution for multiple times, the temperature of each stage of cooling water is 88 ℃, 85 ℃, 82 ℃, 79 ℃, 75 ℃, 71 ℃, 66 ℃, 61 ℃, 56 ℃, 50 ℃, 44 ℃, 37 ℃, 30 ℃ and 20 ℃ in sequence, the cooling time of each stage of cooling water is 30min, and the cooling time of the cooling water at 20 ℃ is 60min, the process is always carried out on the potassium nitrate supersaturated solution, the stirring speed of the potassium nitrate supersaturated solution is 20r/min, and the potassium nitrate crystals are dried until the temperature of the potassium nitrate solution is 20 ℃, so that the high-purity potassium nitrate is obtained;
the technical indexes of the high-purity potassium nitrate are as follows: the purity was 99.7%, the particle size was 0.5 to 3.0mm, the water content was 0.12%, the degree of looseness with a 7-mesh sieve was 95%, the fluidity cot α was 2.2, the shape was an ellipsoidal crystal, and the purification rate was 82.5%.
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