Dissolving behavior of ammonium paratungstate in (NH4)2CO3-NH3？H2O-H2O system
(School of Metallurgy and Environment, Central South University, Changsha 410083, China)
Abstract: The effects of temperature, ammonia concentration and ammonium carbonate concentration on the dissolving behavior of ammonium paratungstate were studied in (NH4)2CO3-NH3？H2O-H2O system. The results show that rising temperature, prolonging duration, increasing ammonia concentration and decreasing ammonium carbonate concentration favor dissolving of ammonium paratungstate at temperature below 90 °C, while the WO3 concentration decreases after a certain time at temperature above 100 °C. Furthermore, the undissolved tungsten exists in the form of either APT·4H2O below 90 °C or pyrochlore-type tungsten trioxide above 100 °C. In dissolving process, the ammonium paratungstate dissolves into paratungstate ions followed by partially converting to tungstate ion, resulting in the coexistence of the both ions. This study may provide a new idea to exploit a novel technique for manufacturing ammonium paratungstate and pyrochlore-type tungsten trioxide.
Key words: ammonium paratungstate; dissolving behavior; ammonium carbonate; ammonia; pyrochlore -type tungsten trioxide