156
6.5 Effect of Nanoparticles on Heavy Metal Recovery
Membrane technologies provide superior advantages such as zero sludge production, environmentally friendly, high separation efficiency, and easy scalability.
Nanofiltration and reverse osmosis membranes for the removal of heavy metal cations have been attracted more attention. Size repellent and Donnan charge repulsion
are the main mechanisms responsible for the separation. Successful treatments of
these membranes in wastewater have been reported. For example, 98% rejection of
cadmium cations has been accomplished with an asymmetric polyethersulfone
membrane (Saljoughi and Mousavi 2012). However, concentrated retentate solutions in these systems include complex chemicals depending on the source of the
wastewater; hence, further treatments are generally required. In addition, they need
high working pressures but yet have low permeate volume. On the other hand,
adsorption provides a simple, easy, and efficient separation process especially when
the size of the adsorbent is at nanoscale. However, instability of nano-sized particles, excessive pressure drop in flow-through systems, and tedious posttreatment for
recovery of nanoparticles reduce their wide range of applications. Combination of
superior adsorption properties of nanoparticles with polymeric membranes that
offer dual functionality of adsorbing and filtrating toxic metals simultaneously has
opened a new era in the removal of heavy metals. This type of membrane configuration has been practically used in the gas phase operations since 1970 by utilizing the
sorption characteristics of the adsorbent which alters the selectivity of the gas mixtures (Zornoza et al. 2011). Their performances in wastewater applications, however, started to be explored after the pioneered work of Ladhe et al. (2009). In their
study, polysulfone or cellulose acetate polymer matrix, to the aim of capturing silver
ion (Ag
+
) from aqueous solution, was incorporated with the functionalized silica
particles using 3-mercaptopropyltrimethoxy silane to introduce free thiol groups.
The performance of the composite membrane against silver ion capacity was studied as a function of particle size, specific surface area, and porous/nonporous morphology of the silica particles. The authors demonstrated the composite membrane
has a high capacity at low operational pressures to capture aqueous phase Ag
+
selectively and also remarked that the concept of composite membrane is a promising
platform in the process of heavy metal capture. Current advances in the development of membrane adsorbers for removal of heavy metals in the aqueous environment have been extensively studied by Nasir et al. (2019a, b).
Zeolite nanoparticles are an important class of adsorbent with their well-defined
porous structures and cation exchange property that comes from the charge deficiency between Si
4+
and Al
3+
in the framework. Nano-sized zeolite provides more
active sites, high specific surface area, and rapid response, hence increasing the
efficiency of the sorption processes. In addition, zeolite nanoparticles offer high
selectivity and stability at harsh conditions (wide pH and temperature range), easy
regeneration, and multiple reuses preserving almost all initial sorption capacity
Yurekli (2019). Yurekli (2016) studied the effect of zeolite nanoparticle loading on
the Pb
2+
and Ni
2+
removal capability of the polysulfone membrane adsorbers under
different initial metal concentrations using dead-end stirred cell. Accordingly,
Y. Yurekli
6.5 Effect of Nanoparticles on Heavy Metal Recovery
Membrane technologies provide superior advantages such as zero sludge production, environmentally friendly, high separation efficiency, and easy scalability.
Nanofiltration and reverse osmosis membranes for the removal of heavy metal cations have been attracted more attention. Size repellent and Donnan charge repulsion
are the main mechanisms responsible for the separation. Successful treatments of
these membranes in wastewater have been reported. For example, 98% rejection of
cadmium cations has been accomplished with an asymmetric polyethersulfone
membrane (Saljoughi and Mousavi 2012). However, concentrated retentate solutions in these systems include complex chemicals depending on the source of the
wastewater; hence, further treatments are generally required. In addition, they need
high working pressures but yet have low permeate volume. On the other hand,
adsorption provides a simple, easy, and efficient separation process especially when
the size of the adsorbent is at nanoscale. However, instability of nano-sized particles, excessive pressure drop in flow-through systems, and tedious posttreatment for
recovery of nanoparticles reduce their wide range of applications. Combination of
superior adsorption properties of nanoparticles with polymeric membranes that
offer dual functionality of adsorbing and filtrating toxic metals simultaneously has
opened a new era in the removal of heavy metals. This type of membrane configuration has been practically used in the gas phase operations since 1970 by utilizing the
sorption characteristics of the adsorbent which alters the selectivity of the gas mixtures (Zornoza et al. 2011). Their performances in wastewater applications, however, started to be explored after the pioneered work of Ladhe et al. (2009). In their
study, polysulfone or cellulose acetate polymer matrix, to the aim of capturing silver
ion (Ag
+
) from aqueous solution, was incorporated with the functionalized silica
particles using 3-mercaptopropyltrimethoxy silane to introduce free thiol groups.
The performance of the composite membrane against silver ion capacity was studied as a function of particle size, specific surface area, and porous/nonporous morphology of the silica particles. The authors demonstrated the composite membrane
has a high capacity at low operational pressures to capture aqueous phase Ag
+
selectively and also remarked that the concept of composite membrane is a promising
platform in the process of heavy metal capture. Current advances in the development of membrane adsorbers for removal of heavy metals in the aqueous environment have been extensively studied by Nasir et al. (2019a, b).
Zeolite nanoparticles are an important class of adsorbent with their well-defined
porous structures and cation exchange property that comes from the charge deficiency between Si
4+
and Al
3+
in the framework. Nano-sized zeolite provides more
active sites, high specific surface area, and rapid response, hence increasing the
efficiency of the sorption processes. In addition, zeolite nanoparticles offer high
selectivity and stability at harsh conditions (wide pH and temperature range), easy
regeneration, and multiple reuses preserving almost all initial sorption capacity
Yurekli (2019). Yurekli (2016) studied the effect of zeolite nanoparticle loading on
the Pb
2+
and Ni
2+
removal capability of the polysulfone membrane adsorbers under
different initial metal concentrations using dead-end stirred cell. Accordingly,
Y. Yurekli