| This research deals with characterizing a novel electrochemical reactor for the removal of toxic metals from dilute waste streams, slurries, and rinse waters. This reactor is a hybrid between an expanded moving packed bed and an entrained/fluidized bed, which we call a Circulating Particulate Bed Electrode (CPBE).; The CPBE cell has a number of features representing the positive features of both the fixed bed cell and the fluidized bed cell, which make it suitable for treating solutions of low metal ion concentrations. These include high mass transfer rates, an enhanced surface area, uniform particle utilization and a capability for treating slurries and three phase mixtures. All particles have equal probability of growing and dissolving. The particle and fluid dynamics of the CPBE cell enhance fluid-particle mass transfer rates. These dynamics also tend to level temperature distribution and effectively mix various fluid and gas phases together. So CPBE is particularly well suited for many electrochemical applications as exemplified by the organic electrosynthesis, metal recovery and pollution treatments for metal containing effluents.; The mass transfer coefficient and the current efficiency for the removal of copper ions from dilute solutions were measured under various operating conditions. The efficiency of the CPBE in batch recovery experiments is found to be a function of cell current density, cell tilt angle, and electrolyte pH. Experiments demonstrate that the CPBE can treat a waste containing copper metal ions down to less than 0.1 ppm. A mathematical model for the batch depletion of copper ions has been used to estimate the overall mass transfer coefficient, which was found to be within the range of 2.0-5.0 10{dollar}sp{lcub}-3{rcub}{dollar} cm/sec.; A quantitative understanding of the hydrodynamics of the circulating particulate bed is needed for design and scale-up of an efficient device in order to optimize its performance. To understand the influence of the cell design and operating parameters on cell performance, an experimental hydrodynamic studies of the CPBE was pursued to predict basic bed characteristics, such as the particle descending layer velocity and solution distributions. These hydrodynamic characteristics will serve as a basis for the prediction of the electrochemical performance and scale-up of the CPBE cell.; The distribution of potential in a particulate bed electrode is of great importance in most applications especially for scale-up. A theoretical model for potential distribution within the CPBE has been developed. This model allows one to predict the potential drop and current distribution as a function of basic bed characteristics. More importantly, the model can be used to predict maximum potential drop as a function of average superficial flow rate, particle size and density, fluid properties, cell tilt angle and cell geometry. These characteristics will be important for predicting the performance of this electrochemical reactor and scale-up.; In carrying out a plating reaction, we found that most of the particles inside the CPBE grow uniformly, which means that all the particles enter the active zone inside the cell. Also, it was observed that no deposition takes place on the current feeder, an important advantage of the CPBE. (Abstract shortened by UMI.)... |
