High speed electrodeposition using fluidised beds

The relevant literature, relating to electrochemical cells, mass transfer, fluidised beds and mass transfer in fluidised beds, has been reviewed. Extensive experimental data for the cathodic reduction of copper fron acid CuSO4 electrolytes, in fluidised beds of copper powder, demonstrated the effectiveness of the cell at removing copper from the electrolytes. For a given bed weight the cell only acted efficiently below 25% bed expansion. Above this the operation of the cell changed to that of acting as a turbulent promoter for the feeder electrode. Two modes of cell operation were investigated. The electrolyte flow was either parallel or perpendicular to current flow. Of the two, electrolyte flow perpendicular to current flow was more effective overall, as it was more amenable to scale-up of the cell. When electrolyte flow and current flow were parallel particles in the bed had to be within a radius of one centimetre for the cell to act efficiently Potential. gradients within the bed caused many problems and prevented limiting currents from being observed because of secondary reactions increasing the total current from the bed. Preferential polarization. of the bed during potentiodynamic sweeps of the cathode caused reactions-to occur at low 'apparent' overvoltages. This was more noticeable in concentrated electrolytes or when larger beds were used