GB1077073A - Manufacture of potassium nitrate - Google Patents

Abstract

Potassium nitrate is produced by heating a mixture of potassium chloride and phosphoric acid at a temperature of 200-700 DEG C. until the evolution of gaseous HCl ceases, adding to the resulting solution an aqueous solution of nitric acid eo as to produce a potassium nitrate solution from which crystals may be obtained by cooling the solution preferably to ambient or 0 DEG C. Either a great excess, i.e. 50 to 100% by weight or an approximately stoichiometric amount of phosphoric acid may be used when reaction temperature is 200-400 DEG C. or 400 DEG to 700 DEG C. respectively. In the first case, potassium dihydrogen phosphate and in the second potassium metaphosphate is produced in the reaction solution. The amount of nitric acid used is preferably in the proportion of 1 to 1.1 mole of nitric acid to each mole of either potassium dihydrogen phosphate or potassium metaphosphate in the solution. The mother liquor obtained from the crystallization may be heated, preferably at 150-250 DEG C., when nitric acid distils over and may be utilized in the process and the distillation residue contains potassium dihydrogen phosphate and phosphoric acid which may be used in the first step of the process. The process may also be used for preparing potassium nitrate based fertilizers, by neutralizing a slurry of potassium nitrate and the mother liquor with ammonia. An alternative fertilizer product may be obtained by treating rock-phosphate with the acid mother liquor obtained after crystallization of the KNO3. To produce fertilizer compositions more economically, part of the original nitric acid used to attack the KCl may be replaced with NH4NO3.