GB712724A - Improvements in or relating to a process for preparing potassium nitrate - Google Patents

Abstract

In a cyclic process for the production of potassium nitrate by the reaction of nitric acid on potassium chloride, the reactants are added to a residual solution from previous operations, potassium nitrate formed is crystallized and removed so as to leave a mother liquor having a concentration of hydrogen ions at least equal to the sum of the concentration of potassium and chlorine ions therein and at most 1.3 times as great as the concentration of chlorine ions therein, and the mother liquor is distilled under reduced pressure to remove hydrochloric acid therefrom to leave a residual solution for subsequent operations. If impurities are introduced with the reactants, a portion of the reaction liquid may be removed after potassium nitrate separation and the loss of reactants compensated. The final temperature of crystallization of the potassium nitrate is preferably above -20 DEG C. and desirably between -10 and +10 DEG C., a saturated solution of potassium chloride remaining after separation of the nitrate. The distillation, preferably with rectification, may be carried out at below 75 DEG C. at pressures below 100 mm. of mercury to avoid the formation of nitrosyl chloride and chlorine, and is preferably effected in two columns, the first having bottom and top temperatures of 52 and 45 DEG C. and the second, 60 and 55 DEG C. The distillation is preferably carried out to such an extent that potassium chloride does not crystalline out. The reaction of potassium chloride and nitric acid may be effected under such conditions that the potassium nitrate crystallizes out on undissolved potassium chloride but this is not preferred and a temperature of 75 DEG C. for this reaction is therefore not exceeded and 50 DEG C. is preferred.