Chemistry Reference
In-Depth Information
Fig. 19.17
Recovery of copper and
lead by successive deposition.
[46,47], processing of nickel cadmium and alkaline
batteries [48] and recovery of metals from used
catalysts [49].
separation of ionic species in which a potential field
is used to enhance the normal operation of standard
ion exchange. In this enhanced ion-exchange opera-
tion, an ion-exchange material is attached to an
electrode structure (typically platinised titanium)
[51] using a suitable binder (see Fig. 19.18). The
adsorption and elution properties are controlled by
the external applied potential.
Suggested applications are in the removal of toxic
metal ions, precious metals, nitrates and corrosive
anions and in the deionisation of water. The tech-
nique has been demonstrated in the removal of chlo-
ride and sulfate in the presence of borate/boric acid
and for the removal of Co from feeds, from concen-
trations of 100 ppb to undetectable levels. The feasi-
bility of removing Mo and V polyanions arising from
the treatment of hydrodesulfurisation waste catalysts
and slags from oil-fired boilers has been examined
[52].
Combined electrodeposition and ion-exchange systems
The integration of electrochemical recovery and ion-
exchange systems to treat the various metal pollu-
tants at point of source or end of pipe is a potentially
useful method. With the use of chelating ion-
exchange resins, e.g. iminodiacetate, an even greater
potential for metal ion separation is possible because
these resins are particularly selective for metals such
as Cu, Ni and Zn. The combined use of electrodepo-
sition and ion exchange can give the appropriate
levelling control in individual metal finishing and
plating applications [50]. Each metal recovered gen-
erally will require a separate electrowinner because
of requirements of different bath conditions (pH,
temperature) and varying removal rates. For several
metals electrodeposition becomes impractical below
certain concentrations, and thus the cell effluent
electrolyte can be recycled back to the ion-exchange
system.
6.5 Electrochemical membrane processes
Electrochemical membrane separations have appli-
cations in the areas of effluent treatment and recy-
cling [2,53]. Electrodialysis is a process in which
electrolyte solutions are either concentrated or
diluted (or deionised). Over the years the process has
been the dominant technique for the desalination of
brackish water. Electrodialysis has many applications
for the removal or recovery of ionic species and gen-
6.4 Electrochemical ion exchange
Electrochemical ion-exchange systems have been
developed by the Atomic Energy Authority, Harwell,
UK, in which an electrochemical potential is applied
to the ion exchanger. The process is a method of
