SI process is a thermochemical process producing hydrogen by decomposing water while recycling sulfur and iodine. Various technologies have been developed to improve the efficiency on Section III of SI process, where iodine is separated and recycled. EED(electro-electrodialysis) could increase the efficiency of Section III without additional chemical compounds but a substantial amount of I2 from a process stream is loaded on EED. In order to reduce the load, a crystallization technology prior to EED is considered as an I2 removal process. In this work, I2 particle sinking behavior was modeled to secure basic data for designing an I2 crystallizer applied to I2-saturated HIx solutions. The composition of HIx solution was determined by thermodynamic UVa model and correlation equations and pure properties were used to evaluate the solution properties. A multiphysics computational tool was utilized to calculate particle sinking velocity changes with respect to I2 particle radius and temperature. The terminal velocity of an I2 particle was estimated around 0.5 m/s under considered radius (1.0 to 2.5 mm) and temperature (10 to 50 ℃) ranges and it was analyzed that the velocity is more dependent on the solution density than the solution viscosity.