Synergistic Coupling of Thermal Decomposition–Ammonia Dissolution and Segmented Crystallization for High-Purity Ammonium Paratungstate

To address the escalating demand for ultra-high-purity tungsten in advanced applications such as semiconductor targets and nuclear-grade shielding, this study synergistically coupled the processes of thermal decomposition, ammonia dissolution, and segmented evaporation crystallization. The optimal parameters for the thermal decomposition and ammonia dissolution stages were subsequently identified through systematic optimization. By independently regulating the nucleation and crystal growth processes during the crystallization of ammonium paratungstate (APT), the limitation of traditional methods, which require multiple crystallization cycles to achieve high purity, is effectively overcome. Experimental results demonstrated that under optimized conditions—thermal decomposition at ~280 °C and ammonia dissolution at 90 °C—high-purity APT (4N5 grade, total impurities < 50 ppm) was achieved in a single crystallization cycle. Furthermore, under segmented crystallization conditions (nucleation at 80 °C with a stirring speed of 1.26 m/s and growth at 90 °C with a stirring speed of 1.09 m/s), the product exhibited an average particle size of 34.43 μm and a direct recovery efficiency of 73.1%. By suppressing burst nucleation and reducing impurity adsorption, this process provides a critical technological pathway for large-scale production of ultra-high-purity tungsten materials.