A method for preparing
potassium nitrate and
ammonium chloride employing double
decomposition reaction comprises the following steps: dissolving
ammonium nitrate and
potassium chloride in water according to a defined ratio at 110 DEG C, continuously adding
potassium chloride and water, heating while stirring to ensure that
potassium nitrate is in
supersaturation state, after stopping heating, cooling the solution in a
vacuum cooling crystallizer to 36-40 DEG C to separate
potassium nitrate crystal, placing the
potassium nitrate crystal in a centrifugal
machine with a filter cloth lining to obtain coarse potassium
nitrate, then washing the potassium nitrate with cold water,
drying to obtain the finished potassium nitrate; in addition, adding
ammonium nitrate in mother solution I and cleaning solution to adjust solution concentration so that
ammonium chloride can reach
supersaturation state, using a vacuum concentration device to perform negative pressure
evaporation, separating and precipitating
ammonium chloride by centrifuging and obtaining a
solid ammonium chloride product, wherein, when dissolving
ammonium nitrate and potassium chloride, the ratio of ammonium
ion to
chlorine ion is 1:2 and when using the centrifugal
machine to obtain the coarse potassium nitrate, the separated mother solution is another mother solution I sharing the same saturation point of potassium nitrate and ammonium chloride. The solution of feed liquid circular reaction overcomes the defects of the prior art that the price of potassium nitrate used in reaction is high, the resource of potassium nitrate is in short supply and the cost of devices used in
ion-exchange method is high, thus being applicable to the production of potassium nitrate.