The invention discloses a preparation method of superfine active
hydromagnesite flame-retardant filler. The preparation method comprises the steps that
hydromagnesite powder and an inorganic dispersant are added into water to prepare
powder slurry with the
mass concentration of 35%-55%; the
powder slurry is fed into a horizontal sand mill for
superfine grinding, and meanwhile a
silane coupling agent is added for first-time
surface modification according to the
mass ratio 1,000:(3-10) of the
hydromagnesite powder to the
silane coupling agent; after
grinding size distribution reaches the conditions that d50 is equal to 1
micrometer to 3 micrometers and d97 is equal to 3 micrometers to 10 micrometers, press filter
dewatering is conducted; filter cakes are fed into a
beehive mill to be dried and depolymerized, a modifying agent is added according to the
mass ratio 1,000:(5-15) of the hydromagnesite powder to the modifying agent, and after second-time
surface modification is conducted at the temperature of 110 DEG C to 180 DEG C, the superfine active hydromagnesite
flame-retardant filler is obtained. According to the preparation method, wet surface organic modification is conducted while
superfine grinding is conducted through the horizontal sand mill, dry surface organic modification is conducted while depolymerizing and
drying are conducted through the
beehive mill, and therefore the superfine active hydromagnesite
flame-retardant filler which is fine in size distribution and full in surface organic modification can be prepared.