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 lev el nuclear wastes. The development of a simple divided electrochemical -cell model operating in a batch mode, used for the reduction of nitra tes and nitrites from nuclear wastes, is presented. This model, based on a boundary-layer approach, is simple and yet encompasses the key fe atures of a previously developed distributed-parameter model that incl udes diffusion, migration, and convection as the flux components. Beca use it dramatically reduces computation time, this boundary-layer mode l is well suited for use in a complex interactive flowsheet model and for optimization studies. The boundary-layer model is used to predict partial current densities, reservoir concentrations, and off-gas compo sitions as a function of time.,Good agreement between simulated and ex perimental 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 i llustrate the accuracy and robustness of this model. The results of se lected case studies are shown, and a preliminary batch optimization is carried out to show how the model can be used to maximize the destruc tion of nitrates and nitrites.