Kinetics of Dechlorination of Molten Chloride Salt Using Protonated Ultrastable Y Zeolite

Abstract

Investigation of the kinetics of the ion exchange between protonated ultrastable Y-type (USHY) and surrogate electrorefiner (ER) waste salt was performed to optimize the dechlorination process. The kinetics of the ion exchange reaction was investigated by measuring the amount of unreacted Cl. In theory, the kinetics of the ion exchange reaction in porous media will be limited by diffusion- or reaction-controlled mechanisms. Therefore, second order kinetics and diffusion-limited rate models have been derived and compared to experimental data to elucidate the rate-limiting step and develop a predictive model for the apparent rate of reaction. Ion exchange experiments were performed with varying zeolite particle sizes (up to 600 μm) at 625 °C. The experiments were performed with both unfluidized and continuously fluidized zeolite particles in static and rotating tube furnaces. It was concluded that the process is limited by reaction kinetics inside the zeolite crystals, and a second order kinetic model best fits the experimental data. Given that the zeolite is not stable at higher temperatures, further increase in the extent of dechlorination for a given batch reaction time requires an increase of the zeolite-to-salt ratio, which has the undesirable effect of increasing the volume of generated waste per amount of salt.