Environmental Engineering Reference
In-Depth Information
quartz + feldspar + montmorillonite + iron oxides (15%). The unit cell parameters of clino-
ptilolite were not modiied because the Zn
2+
ions exchanged mainly with the Ca
2+
ions
from their cation position.
30.3.2 Chemical Studies
The chemical analysis of NZ and ZZ, described in Table 30.3, showed that zinc exchanges
calcium at large (1.70%) in clinoptilolite even when the selectivity of this zeolite is lower for
zinc ions. Sodium was the second cation exchanged in NZ by Zn
2+
; however, the quantity
(0.3%) is lower as compared with calcium. The ion exchange of potassium and magnesium
was very small (0.1%). The hydrothermal conditions established for the ion-exchange reac-
tion increased the zinc incorporation to the clinoptilolite structure.
Figure 30.5 shows the performance of the different cations in the ion-exchange process
when ZZ was placed in a column as part of a 10.7-cm-long bed of 2.5 cm in diameter,
and drinking water was moved through at a low rate of 15 mL/min. An increase in the
sodium content of water was observed because calcium ions exchanged the sodium ions
of the clinoptilolite not previously removed by the zinc ions during the ZZ production.
Magnesium and potassium content in the drinking water did not change, thus conirming
that calcium ions only remove zinc and sodium cations [15]. These results also indicate that
the counter exchange of Zn
2+
ions was not totally veriied at room temperature, saving zinc
ions for further exchange.
To establish the best relation between drinking water volume and the ZZ mass, a simple
experiment was conducted. Different drinking water volumes were exposed to a ZZ mass
but without stirring. The time of exposure was 1, 2, 3, and 4 h, and the ratio of water vol-
ume with the ZZ mass was established from 1:1 to 10:1. The zinc content in the water was
TABLE 30.3
Chemical Composition of ZZ as Compared with NZ and Cuban Standard NC 625:2008
Elements
NZ (%)
ZZ (%)
NC 625 (%)
SiO
2
65.00
65.12
64.00-66.00
Al
2
O
3
10.96
11.01
10.00-12.00
Fe
2
O
3
1.70
1.70
1.5-2.20
FeO
0.47
0.45
0.20-0.5
MgO
0.40
0.36
0.30-0.90
CaO
4.27
2.57
2.50-6.00
Na
2
O
1.10
0.87
1.00-2.00
K
2
O
1.30
1.28
1.00-2.00
P
2
O
5
0.05
0.05
0.05-0.07
H
2
O
12.00
11.00
10.00-14.00
Zn
-
1.7
-
Toxic Elements
F
1 ppm
1 ppm
<10 ppm
Pb
2 ppm
2 ppm
<10 ppm
As
0.1 ppm
0.1 ppm
<3 ppm
Cd
0.5 ppm
0.5 ppm
<2 ppm
Hg
0.2 ppm
0.2 ppm
<5 ppm
