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