The invention discloses a method for preparing
potassium chloride from
potassium mixed salt. The method comprises the steps that the
potassium mixed salt is dissolved in water,
solid-liquid separation is carried out, and a potassium mixed
salt solution is obtained; a first-section
nanofiltration step is carried out, wherein a
nanofiltration membrane
system is adopted for carrying out first-section
nanofiltration treatment on the potassium mixed
salt solution, first-section concentrated water and first-section
produced water are obtained, the nanofiltration
system comprises a first nanofiltration membrane
assembly, a first concentrated water box and a first
produced water box, and the first concentrated water box and the first
produced water box are connected to the first nanofiltration membrane
assembly; the first-section concentrated water is stored in the first concentrated water box, and the first-section produced water is stored in the first produced water box; the first-section produced water is subjected to evaporative
crystallization, and
sylvinite ore is obtained; the
sylvinite ore is subjected to flash melting
crystallization, and potassium
chloride is obtained. The novel method is used for producing potassium
chloride from the potassium mixed salt and has the advantages of being simple in process, high in product purity, large in particle and high in yield.