Chemistry Reference
In-Depth Information
(a)
(b)
Fig. 19.14
Examples of electro-organic
synthesis using a consumable anode.
(c)
tions, can be utilised to recover and recycle the metal
ions back to the electrodeposition.
Under the general umbrella of electrochemical
technologies for waste minimisation, there are three
broad categories of processes: direct electrochemi-
cal, indirect electrochemical and electrochemically
driven separations. The scope of electrochemistry in
waste minimisation is outlined in Table 19.5. The
processes are varied and are used for:
• Removal of acid gases such as SO
2
, HCl, NO
x
and
H
2
S from process and combustion gas
• Purification of water using with Cl
2
, OCl
-
, OH
-
and
O
3
• Recycling of constituents in plating operations and
reagents for oxidation and reduction reactions, e.g.
Cr(VI) and Ce(IV) ions
• Separation processes for solid/liquid and liquid/
liquid dispersions
• Recovery and recycling of valuable components
from wastewaters, e.g. metal ions such as Ni, Cu,
Pb, Hg, etc.
• Separation and recycling of salts via electrochemi-
cal membrane processes
• Treatment of process waters containing cyanide,
chromium species, phenols, PCBs etc.
6.1 Recovery and recycling of metal ions
Electrodeposition functions typically in aqueous
solution, but not exclusively. Processing of solid
'waste' material to recover metal by electrodeposi-
tion frequently will involve a dissolution step of a
metal or metal salt. The removal and recycling of dis-
