Environmental Engineering Reference
In-Depth Information
Disposal/
recycling
Raw material
Production
Use
FIGURE 18.3
Product life cycle.
18.2.2.1 Raw Materials
There are two methods for nano-iron production, chemical and physical. In the case of the
chemical method, the iron-based compounds have been employed to produce nanopar-
ticles in liquid media. Then, the nanoparticles can be separated from the liquid phase via
a centrifugal process or drying methods, or also can be used in nanocolloidal form. In
the chemical process, there is no complicated equipment and only control of the process
is vital. The chemicals used in this process, as raw materials, are not toxic and are not of
any concern regarding environmental health and safety (EHS) issues. In the case of physi-
cal methods, the bulk iron is to be converted into the nanoparticulates through a physical
phenomenon like electrical explosion of wires (EEW). In both cases, the raw materials are
available and cheap.
18.2.2.2 Production
As mentioned before, there are two methods for nZVI particle production, chemical and
physical. In the chemical method through a reduction reaction process, Fe
2+
and Fe
3+
are
reduced into nanosize Fe
0
(zerovalent iron) particulates. The nZVI is highly active and can
react easily with oxygen and consequently explode. This high reaction capability makes
the nZVI very effective for removing contaminants from water.
In the physical process, an up-down approach is taken. In fact, the iron bulk material is
converting into the nano-iron particles through a physical phenomenon. For instance, EEW
can be applied for this purpose. In this method, through applying a high voltage and current,
an explosion will occur in a narrow wire. Then, the wire is converted into the metals cluster,
containing a few atoms and after agglomeration the clusters create spherical nanoparticles.
As an example in developing countries, in Iran, PNF Co. has been applying this technol-
ogy to supply both nanoparticles and also nanofabrication devices. The EHS issues should
be considered through the whole process of nanopowder production and storage.
18.2.2.3 Use
The nZVI is to be injected into the ground and to be diffused simultaneously far away
from the injection point. This process does not need any complicated devices and equip-
ment. As a result, in the affected zone, the extracted groundwater would be clean without
any contaminants. To inject the nZVI, a sludge form of iron nanocolloid is needed.
18.2.2.4 Disposal/Recycling
The injected iron nanoparticles are to stay underground and can be oxidized into iron
oxide particles. Nanoparticles could be extracted with treated groundwater, which can be
gathered via a magnetic technique.
