Complex adsorption modeling for nuclear energy applications

Abstract

Adsorption is a complex physio-chemical process by which molecules are attached to surfaces of solid particles. The type of adsorption that occurs may often depend on the media the phenomenon is occurring in, making the design of models for various adsorption systems an arduous task. Regardless of the media, however, the basic mechanisms of the adsorption process are the same. Therefore, a plausible approach to the development of adsorption models in different systems would be to design a generalized mathematical framework with all the necessary methods built in that will be used as a platform to develop system specific adsorption models. In this work, the investigation and development of such a structure will be discussed and a host of system specific adsorption models that have been developed on top of that framework will be detailed. The specific problems of interest are all related to nuclear energy and specifically the availability of uranium in the Nuclear Fuel Cycle via recycling spent uranium fuel rods and capturing new raw uranium from seawater. In recycling spent uranium, the reprocessing procedure produces numerous gas pollutants that must be removed from the off-gases before emission to the atmosphere. To facilitate the design of that capture system, adsorption models have been developed to predict isothermal equilibria of complex gas mixtures and to quantify the rates of adsorption for various adsorbent materials. For recovering uranium from seawater, two different models were produced: (i) a predictive, multi-ligand adsorption model to incorporate effects of pH, ionic strength, and competing metals and (ii) an analytical model for quantifying the impact of current velocity on the mass transfer limitations of braided fiber adsorbents. The culmination of these adsorption models will provide tools for scientists and engineers to better understand adsorption phenomena in the applications of interest and subsequently design the necessary capture systems at both the front and back ends of the Nuclear Fuel Cycle.