A boundary-layer model of a parallel-plate electrochemical reactor for the destruction of nitrates and nitrites in alkaline waste solutions

Electrochemical processes appear to be attractive for treating low level nuclear wastes. The development of a simple divided electrochemical-cell model operating in a batch mode, used for the reduction of nitrates and nitrites from nuclear wastes, is presented. This model, based on a boundary-layer approach, is simple and yet encompasses the key features of a previously developed distributed-parameter model that includes diffusion, migration, and convection as the flux components. Because it dramatically reduces computation time, this boundary-layer model is well suited for use in a complex interactive flowsheet model and for optimization studies. The boundary-layer model is sued to predict partial current densities, reservoir concentrations, and off-gas compositions as a function of time. Good agreement between simulated and experimental data (i.e., nitrate and nitrite concentrations and off-gas compositions) is observed over the course of a batch run. In addition, a comparison with a rigorous distributed-parameter model is made to illustrate the accuracy and robustness of this model. The results of selected case studies are shown, and a preliminary batch optimization is carried out to show how the model can be used to maximize the destruction of nitrates and nitrites