62    ELECTROCHEMICAL ABSTRACTION OF
CADMIUM FROM DILUTE AQUEOUS SOLUTIONS
USING THE ROTATING CATHODE CELL
A. I. Sheikh, Research Assistant
G. K. Anderson, Senior Lecturer
Solid & Hazardous Waste Research Unit (SHWRU)
L. M. Evison, Senior Lecturer
Environmental Engineering Group.
Department of Civil Engineering,
University of Newcastle Upon Tyne,
Newcastle Upon Tyne, NE1 7RU, England
F. S. Holland, Consultant Chemist
Electrochemical Techniques Limited (ETL)
Stockport, Cheshire, England
INTRODUCTION
An EC-funded multidisciplinary consortium has successfully developed a new approach for
the removal and recovery of aqueous cadmium, at low concentrations, from industrial effluents
and other metal contaminated wastewaters. Biosorption, elution and electrolysis processes generate clean water and high quality metal for recycling and reuse. The electrochemical deposition of
cadmium results in the production of metallic cadmium powder and a cadmium-depleted electrolyte for reuse as an eluant for cadmium-loaded biomass in the previous elution stage. This has
been achieved using a Rotating Cathode Cell (RC Cell) which is a pilot-scale continuous flow
cell, operating at very high mass transport rates, recovering the metal automatically outside the
cell. The development of the process entailed conditioning the electrolyte with buffering and
complexing agents. Batch and steady-state controlled potentiostatic electrolysis were shown to
be conducive to fine powder production with selective electrolytes.
The introduction of ever more stringent wastewater disposal guidelines is emphasizing the fact
that improved processes for the recovery of cadmium and other hazardous metals from dilute solutions are required more and more urgently. Ion-exchange, solvent extraction, or precipitation
processes are suitable for reducing the residual cadmium content of solutions down to very low
final concentrations, but pose the risk of further producing a sludge hazard with alkaline precipitation. None of these processes are suitable for the recovery of cadmium as a metal from dilute
solutions, and there is no doubt that it would be more economically and environmentally sound if
metallic cadmium could be recovered from a waste stream.
Electrochemical technology can contribute elegantly in many ways to a better relationship
with the environment. The use of the electron as a reaction reagent ensures that the contaminants, which are often heavy metals, can be efficiently concentrated into a volume-reduced form
amenable to subsequent disposal or recovery operations. This is achieved without the need to introduce chemical reagents which themselves add to the total volume of secondary waste generated. Electrochemical methods are also suitable for automation because of their simplicity and
high sensitivity.
Numerous laboratory cell designs have been suggested for the removal of metals via cathodic
deposition but relatively few of these have reached pilot- or full-scale. The Rotating Cathode
Cell (RC Cell) is one of the most successful geometries and may be classified as a moving, two-
51st Purdue Industrial Waste Conference Proceedings, 1996, Ann Arbor Press, Inc.. Chelsea. Michigan 48118.
Printed in U.S.A.
613