Thermal decomposition mechanism of ammonium phosphotungstate hydrate in air atmosphere

Abstract

Production of W from scheelite mineral (CaWO4) by hydrometallurgical processes has grown up in the last decade. CaWO4 dissolves in HCl solutions containing H3PO4 as chelating agent and forms phosphotungstic acid (H-3(PW12O40), PhTA). Ammonium phoshpotungstate hydrate ((NH4)(3)[PW12O40NH2O, APhT) can be precipitated by addition of NH4Cl to solutions containing PhTA and WO3 can be produced by the thermal decomposition of APhT. W powder can be obtained by H-2 reduction of WO3.