The invention discloses a method for preparing
raw material phosphoric acid for
monopotassium phosphate by multi-stage synergistic purification of wet-process
phosphoric acid, and relates to the technical field of wet-process
phosphoric acid purification. The method specifically comprises the following steps: firstly, adding part of SiO2 into dilute phosphoric acid, and pumping the dilute phosphoric acid into a defluorination
tower for stripping and defluorination; adding the rest SiO2, pumping into a flash chamber, and carrying out vacuum concentration and defluorination; pumping into a desulfurization reaction tank, adding phosphoric ore pulp according to a
calcium-
sulfur ratio, clarifying the
slurry in a thickener after reaction, and filtering the upper overflow
clear liquid to obtain desulfurized phosphoric acid; adding
sodium sulfide, reacting at normal temperature, heating, continuously reacting, and carrying out
solid-liquid separation to obtain dehydrophosphoric acid; and enabling the de-heavy phosphoric acid to sequentially pass through three
activated carbon fiber filtering devices which are connected in series, so as to obtain the
raw material phosphoric acid which can be directly used for producing the
monopotassium phosphate after being purified. A gradient purification
system is constructed through concentration defluorination, phosphoric ore pulp desulfurization,
sodium sulfide heavy component removal and
activated carbon fiber decoloration in a multi-stage process cooperation mode, and step-by-step efficient removal of
fluorine,
sulfur, heavy
metal and
pigment in wet-process phosphoric acid is achieved.