Nanoscale Porous Materials for Water Treatment: Advances and Challenges - Nanotechnologies for Water Environment Applications - page 317

The use of zeolitic materials for environmental applications, such as water
treatment, has emerged significant attention, due to their excellent physico-chemical
properties, e.g., selective sorption capacity, non toxic nature, availability and low cost.
Table 11.3 shows some of the recent development in zeolite containing adsorbents for
water treatment. NaP1 zeolites (Na 6 Al 6 Si 10 O 32 ·12H 2 O) has a high density of Na ion
exchange sites. This is evaluated as ion exchange media for the removal of heavy metals
from acid mine wastewaters (Moreno et al., 2001). The successful use of synthetic
NaP1 zeolites to remove Cr(III), Ni(Iijima), Zn(II), Cu(Iijima) and Cd(II) from metal
electroplating wastewaters has also been reported (Alvarez-Ayuso et al., 2003).
Lead and cadmium removal from aqueous solution by batch ion exchange with a
solid NaY zeolite has been studied under competitive and non-competitive conditions.
The extent of heavy metal (HM) removal is found to be independent of the nature of the
anion, and equilibrium exchange isotherms are presented for NaY treatment of lead,
cadmium, nitrate and chloride solutions. An increase in the solution phase HM
concentration lowers the affinity of the zeolite for the on-going HM ion, but lead was
preferred to the indigenous sodium ion over the entire range of the ratios of the initial
metal concentration to zeolite weight that were studied. Lead removal was much greater
than that of cadmium under identical experimental conditions and NaY exchange
efficiency is shown to increase in the order of: Ni 2+ < Cu 2+ < Cd 2+ < Pb 2+ . Treatment of
the lead/cadmium solutions resulted in a greater depletion (by a factor of 2) of the lead
component (Ahmed et al., 1998).
The removal of Fe, Pb, Cd, and Zn from synthetic mine waters by a natural
zeolite was also reported. The emphasis was given to the zeolite's behavior toward a few
cations in competition with each other. Pb was removed efficiently from neutral and
acidic solutions, whereas the uptake of Zn and Cd decreased with low pH and high iron
concentrations. With increasing Ca concentrations in solution, elimination of Zn and Cd
became poorer while removal of Pb remained virtually unchanged. The zeolite was
stable in acidic solutions; disintegration was only observed below pH 2.0. Adding more
zeolites further diminished Pb concentrations but did not have an effect on Zn and Cd
concentrations in solution. During re-acidification of the solution, remobilization of Pb
was weaker in the presence than in the absence of zeolite. No substantial differences
were observed for Fe, Cd, and Zn immobilization. The immobilization of the metals
during pH increase and the subsequent remobilization caused by re-acidification can be
well described by a geochemical equilibrium speciation model that accounts for metal
complexation at hydrous ferric oxides, for ion exchange on the zeolite surfaces, as well
as for dissolution and precipitation processes (Wingenfelder et al., 2005).
Zeolite has been found to retain methyl teart-butyl ether (MTBE), chloroform
and trichloroethylene (TCE) from water, with an efficiency 8-12 times higher than