Electrochemical removal of lead ions from flowing electrolytes using packed bed electrodes

Packed bed electrodes, made of stacked screens, have been used as cathodes for the removal of lead ions from flowing alkaline electrolytes. We consider the coulombic efficiency ξ = i Pb / ( i Pb + i H ) , where i Pb and i H are, respectively, the lead deposition and hydrogen evolution currents, and the collection efficiency given by ψ = i L ( exp . ) / nF ν c o , where i L ( exp . ) is the geometric limiting current for lead deposition, ν is the electrolyte flow rate, and c o is the feed concentration of lead ions. Two regions are defined in the current‐ potential relations, depending on whether hydrogen evolution does, or does not, contribute to the measured current, corresponding to ξ less than, or equal to, 100%, respectively. The geometric limiting current, i L ( exp . ) , increases with increase of ν, electrode thickness ( L ), or specific surface area ( S ), and with decrease of the viscosity of the electrolyte (μ). The collection efficiency (ψ) increases as ν or μ decreases and L and/or S increases. Operating the cell at higher flow rates increases the overall coulombic efficiency, over a broader range of cell currents. It also increases the geometric limiting current although it decreases the collection efficiency. © 1999 The Electrochemical Society. All rights reserved.