Ammonium Paratungstate Producing Ammonium Metatungstate

A process for preparing ammonium metatungstate using ammonium paratungstate as raw material comprising:
(A) leaching wet ammonium paratungstate with nitric acid to obtain a dilute solution of ammonium metatungstate;
(B) concentrating the dilute solution of ammonium metatungstate to be a concentrated solution of ammonium metatungstate;
(C) spray-drying the concentrated solution of ammonium metatungstate to obtain powder of ammonium metatungstate.

A.The leaching of wet ammonium paratungstate: Pure water is added to a reactor and preheated to boiling; wet ammonium paratungstate [5(NH4)2O12WO35H2O] is added slowly to the pure water at a speed of 150 to 200 Kg/h while stirring; when adding the wet ammonium paratungstate, a 1:3 dilute nitric acid (HNO3) is added slowly to control the solution at pH 3 to 5; the above process is stopped when the WO3 content of the solution reaches 150 g/l; After boiling and being stirred for half an hour, the materials are allowed to pass through a suction filter for natural filtration, in order to produce a dilute solution of ammonium metatungstate.

B.The conversion of dilute solution of ammonium metatungstate to concentrated solution of ammonium metatungstate: the dilute solution of ammonium metatungstate from step A is standing aged for 4 hours, followed by a primarily natural filtration to obtain a filtrate 1; the above filtrate 1 is pumped into a reactor in multiple times for heating to concentrate it, each time the filtrate 1 is pumped, a dilute ammonia water (NH3H2O) of 1:5 is used to adjust the solution at pH 3 to 4; when the density of the solution reaches 2, the pumping of the filtrate 1 is stopped, following 1 hour of cooling, the materials are allowed to pass through a suction filter for a secondarily natural filtration to obtain a filtrate 2; the above filtrate 2 is pumped into a settling tank, standing aged for 8 hours, then the materials are allowed to pass through a suction filter for a tertiarily natural filtration to obtain a concentrated solution of ammonium metatungstate.

C.The spray-drying of the concentrated solution of ammonium metatungstate: The concentrated solution of ammonium metatungstate from step B is dried into a powdery product of ammonium metatungstate by the use of homemade advanced high-speed centrifugal spray-drying equipment or a spray atomizing dryer. The conditions for spray-drying are controlled at: inlet air temperature 220 to 280° C., outlet air temperature 110 to 160° C., and feeding speed 300 to 400 kg/h.