Environmental Engineering Reference
In-Depth Information
(a)
(b)
Zn
2+
Al
O
Si
1 µm
FIGURE 30.1
(See color insert.)
Representation of a Zn-clinoptilolite unit cell without water molecules (a) and clinoptilolite
crystals with tabular and lath morphology (b).
Many drugs based on zinc compounds for different therapeutic treatments are described
in pharmacopoeia but their effectiveness depends on their capacity to release Zn
2+
from
the compound used as active ingredient. A zeolite may act as a controlled releaser of Zn
2+
ions; however, two issues must be addressed: (i) the toxicity of the zeolite and (ii) the abil-
ity of the zeolite to release the amount of Zn
2+
required after its incorporation to the drug
without creating a health hazard.
Our early results in the formulation of the antidiarrheal drug Enterex [6], based on puri-
ied natural clinoptilolite NZ, answered the toxicological
incognita
about the zeolitic raw
material. Still, the new material Zn
2+
-NZ, named ZZ [7], was submitted to toxicological
testing.
The second issue required an extensive ion-exchange study of Zn
2+
in this zeolite
considering
1. The introduction of zinc in clinoptilolite by the exchange of the natural extra-
framework cations (Ca
2+
, K
+
, Mg
2+
, and Na
+
) invokes a rather dificult reaction
because the selectivity of clinoptilolite for Zn
2+
is lower with respect to the selec-
tivity for its natural cations. Then, the chemical equilibrium of the exchange reac-
tions must be shifted toward the introduction of Zn
2+
in zeolite.
2. The controlled release of Zn
2+
from the clinoptilolite should also take place through
ion exchange of the ions present in drinking water or biological media at room
or human body temperature (37°C), respectively. The inal zinc content in water
or biological media must be lower than the toxic level. The recommended zinc
content for drinking water is 5 ppm because of taste (palatability), while in other
biological media it depends on the human organ or animal species.
ZZ was irst certiied as a water puriier by the Registro Sanitario of Cuba in 1999, after
several years of study [8]. Thirteen years later, other studies have been completed that
show the microbicidal properties of the product and its value as a basic element of the
water puriication systems.
ZZ is a carrier that releases zinc into water in a slow and calibrated manner, within
the limits recommended by the WHO. Zinc, which acts like a microbicide on the patho-
genic microorganisms, is also a fundamental element for human and animal life. Various
