Page 253 - Materials Chemistry, Second Edition

234 Life Cycle Assessment of Wastewater Treatment

The ion exchange technique can remove trace particle contamination from water
and process streams and give a result of the desired quality. Ion exchangers are widely
used in investigative science, hydrometallurgy, anti-infection agents, cleaning, and
the separation of radioisotopes and find extensive application in water treatment and
contamination control (Cavaco et al., 2007; Inglezakis et al., 2002). The list of metals
that are recovered and filtered on a mechanical scale by particle exchange methods
includes uranium, thorium, rare earth elements (REEs), gold, silver, chromium, cop-
per, zinc, nickel, cobalt, and tungsten (Luca et al., 2009).
In some of these cases, the size of operations is moderately small, for example, in
the rare earth elements or noble metals, yet estimates of recovered metals are high.
The ion exchange process is especially suitable for cleaning metal particles with high
value and low charge. It can also be used as a procedure for the large-scale recovery
of metals from waste streams, for example, cadmium and mercury, chromium, or
copper and zinc. The use of ion exchange methods in hydrometallurgy is high and
constantly evolving. It is related basically to the advances in new specific chelating
ion exchangers containing complexing ligands.
The drawback of this strategy is that it cannot deal with concentrated metal sys-
tems, as the lattice is easily fouled by organics and different solids in the wastewater.
Also, particle exchange is non-selective and is exceptionally sensitive to the pH of
the system.
Issues commonly encountered with ion exchange treatment include:

• Metallic fouling (from Fe, Mn, Cu, etc.) of the particle exchange medium.
• Fouling because of oil, residues, dirt, colloidal silica, natural materials, and
organisms. The decision to undertake an authorized cleaning procedure can
re-establish a great part of the lost efficiency.
• The proximity of free acid diminishes the efficiency of the operation.
• Fairly high operational costs exist.

11.5.3 aDsorpTion
Adsorption has developed as a compelling, conservative, and ecofriendly treat-
ment strategy (Barakat, 2011; Zamboulis et al., 2011). It is a procedure suffi-
ciently powerful to satisfy water reuse commitment and high effluent standards
in industry. Adsorption is fundamentally a mass transfer process by which a sub-
stance is exchanged from the fluid stage to the surface of a strong adsorbent and
winds up noticeably bound by physical as well as chemical interactions (Babel
and Kurniawan, 2003). It is a segment procedure in which couple of parts of the
fluid stage are migrated to the surface of the strong adsorbents. All adsorption
techniques are dependent on strong fluid balance and on mass exchange rates.
The adsorption system can be batch, semi-batch, or continuous. The adsorption
process offers adaptability in outline and operation and much of the time, will
create good-quality treated effluent. Moreover, in light of the fact that adsorp-
tion is now and again reversible, adsorbents can be recovered by an appropriate
desorption process. On the molecular level, adsorption takes place for the most