The Chemelec Cell
is an electrochemical reactor which achieves
the recovery of metals from electroplating effluent by electrodeposition
at concentrations too low to be considered for conventional
electrolysis. The combination of a mesh-type configuration of
electrodes together with the use of a non-conducting (inert) fluidised
bed electrolyte engenders a sufficiently high rate of mass transport
in the cell for efficient deposition to be carried out at metal ion
concentrations below 1.0 gl-1.
Two approaches have been made to the investigation of the system.
First, experiments have been conducted using a laboratory scale
Chemelec Cell in which the electrodeposition of nickel from
Watts electrolytes has been carried out under a wide range of conditions
of electrode potential, pH and metal ion concentration. Relatively
long-term experiments have been attempted in which the cell is operated
under conditions of constant electrode potential, temperature, pH and
fluidisation and the fall of nickel ion concentration plotted as a
function of time. Measurement of the charge passed (also as a
function of time) has allowed access to the cathode current efficiency.
Polarisation data, comprising two regions of electrode potential in
which the current density varies semi-logarithmically with a large
apparent Tafel slope (570 mV/dec.) separated by a region of some
300-500 mV in which the current density is almost independent of
potential, have been obtained under these diffe rent conditions. An
interpretation of these somewhat unusual characteristits has been
Secondly, more fundamental studies concerning the electrode
kinetics of cadmium in various electrolytes have been carried out.
The techniques of faradaic impedance, linear sweep voltammetry and
the rotating disc have been applied and the results of these experiments
interpreted. The presence of a hydroxide film on the electrode has
been demonstrated and this obscures the true kinetics.
Finally, the observed electrode kinetics and the experimental
results obtained from the operation of the Chemelec Cell
and critically discussed.
Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.