Synthetic method: Potassium hydroxide or potassium carbonate is used to neutralize nitric acid, and potassium nitrate is obtained by evaporative crystallization; or potassium hydroxide or potassium carbonate solution is used to absorb tail gas in nitric acid production and processed to obtain potassium nitrate. 
Solvent extraction method: At 5~10°C, potassium chloride is dissolved in 60%~70% nitric acid and extracted with organic solvent to separate potassium nitrate and hydrochloric acid. 
Metathesis: Sodium nitrate and potassium chloride are metathesized to give potassium nitrate and sodium chloride. They can be separated using their solubility at different temperatures. This method is widely used in industry and is the main production method of industrial potassium nitrate. First dissolve the sodium nitrate in hot water, gradually add potassium chloride under the mixing ratio of sodium nitrate: potassium chloride=100:85, and concentrate by evaporation. When the temperature is 119°C, sodium chloride crystallizes out. The solution and the crystals are subjected to hot filtration to obtain a large amount of sodium chloride crystals. The mother liquor after separating the sodium chloride is slowly cooled, and potassium nitrate is crystallized. After filtering, washing and drying, the crude product (purity≥85%) can be obtained, and pure product and high purity product can be obtained through recrystallization. 
Ion exchange method: The ammonium nitrate solution and the potassium chloride solution pass through the cation exchange resin bed, respectively. Potassium nitrate and ammonium chloride can be produced separately. This method is widely used in industry and is one of the main production methods of industrial potassium nitrate.
Nitrate preparation method: Potassium nitrate commonly known as fire nitrate or soil nitrate. It is an important raw material and compound fertilizer for black powder. Preparation of potassium nitrate can use nitrate and ash as raw materials. After the organic matter in the soil is corrupted, nitric acid is generated by the action of nitrous acid bacteria and nitric acid bacteria. Nitrate combines with potassium, sodium, and magnesium ions in the soil to form nitrates. Nitrate in the nitrates is like this. Nitrates are generally found in toilets, pigs, bullpen houses, old courtyard walls, cliffs, caves, and floors that are not easily washed by rain. Nitrate is wet, not easy to dry, slightly purple after sun exposure. Good nitrifies on sparkling charcoal.
The main principle of extracting potassium nitrate from nitrates is to use potassium ions in grass ash to replace sodium ions in nitrates to generate potassium nitrate. In addition, the carbonate ions and sulfate ions in the plant ash combine with the calcium and magnesium ions in the nitrifying soil to form insoluble salts and precipitate, thereby removing impurities such as calcium and magnesium. The main reaction is
Nitrate itself also contains potassium nitrate. Finally, the difference in the solubility of various salts is used to control the temperature and concentration, so that potassium nitrate crystallizes out of the mixture.