Design of a carousel process for cesium removal using crystalline silicotitanate

A three‐column carousel process based on a pelletized form of CST powder was designed to remove radioactive 137Cs+ from SRS nuclear wastes. A multicomponent ion‐exchange equilibrium model was used to generate cesium loading data, which were fit to the Langmuir equation to obtain effective single‐component cesium isotherm parameters for representative wastes. Mass‐transfer parameters were estimated by analyzing breakthrough curves for two simulated wastes. Simulations based on a pore‐diffusion rate model were performed to determine the lengths of the mass‐transfer zone for different feed compositions and linear velocities. The length of a single segment in the carousel process was the constant‐pattern mass‐transfer zone to ensure consistent high column utilization during startup and cyclic steady state. Analysis of the dimensionless groups in the mass balance equations revealed that the mass‐transfer zone length is proportional to the particle Peclet number. The proportionality constant is a function of the waste composition and the Cs+ concentration in the waste. A higher distribution coefficient and isotherm nonlinearity result in a smaller proportionality constant. With this analysis designs can be easily adjusted for variations in isotherms, feed concentration, particle size, linear velocity, and intraparticle diffusivity.