Theoretical And Experimental Studies
THEORETICAL aND EXPERIMENTAL STUDIES
OF WASTEWAtER treatment with Zeolite Inorganic Ion Exchange
I. Dedenko1, I. Samodumova1, F. Bobonich2, P. Jaremov2,
O. Shvets2, G. Telbiz2, V. Il’in2
1Scientific-Research Center “Sorption” Kyiv, Ukraine,
Tereshchenkivska 17V, 01004, Kyiv, Ukraine
2Institute of Physical Chemistry, Nat. Acad. Sci. of Ukraine,
03028, Prospekt Nauky 31, Kyiv, Ukraine
Summary
Theoretical and experimental approach for choice of the selecting zeolite sorbents for treatment of difficult waste streams such as removal of trace toxic elements from industrial wastewater (e.g. Chernobyl disaster region) on the base of Eiseman theory has been studied.
Introduction
Efficient clearing of the water solutions from toxic elements can be realized with use the abilities of sorbents (e.g. zeolites). In accordance with chemical thermodynamics, free Gibbs energy of ion-exchange reactions (accordingly its equilibrium constant Кр) is defined the equation:
ΔGo = (ΔGгМе1 - ΔGгМе2) - (ΔGсМе1 - ΔGсМе2)
where ΔGгМе1and ΔGгМе2- free Gibbs hydration ion-energy of the exchange cations, ΔGсМе1 - ΔGсМе2 - free Gibbs energy of the solvation for ion exchange cations are situated in cavities of zeolite. Sherry, on base of the ion-exchange zeolite properties has installed that observed of ranks of the selectivity of ion exchange for alkaline and alkaline earth metals comply with predicted by G. Eiseman, (Biophys.J.-1962, N2.-p.259). Moreover, zeolite with big porosity and high correlation of atoms Si/Al in framework are characterized ranks of selectivity, which must exist for ion-exchanger with weak field - Cs>Rb>K>Na>Li. Thick low-silica zeolites, with strong field, on the contrary, are characterized rank of selectivity- Li>Na>K>Rb>Cs. Since porosity of zeolites is defined of the density of their framework without water and cation dk, for estimation of power of field of zeolites in [4] there was offered to use
instead of hypothetical efficient radius of the anionic center, theoretical exchange capacity units of zeolite volume, which is defined the values of density of framework qo and Si/Al ratio.
qo = 16.6dk/((Si/Al)+1)
Within the limits of such approach was shown (F.Bobonich, Teor. Eksp. Khim. 1991,27,p.619), that on measure of increase to exchange capacity of zeolite qo rank of selectivity of exchange alkaline cation are transformed exactly in accordance with their change on measure of reinforcement of electrostatic field of ion-exchanger. For clarification of possibility of goal-directed selection of zeolites, for sorption (e.g. Сu2+), on the base of the values their exchange capacity is organized the analysis literary data about sorption of variable cations on the different zeolites and explored sorption of various cation in steady-state conditions from solutions as model for industrial wastewater.
Experimental
The granulated NaA and NaX with exchange capacity E =4,4 mg-eq/g and 3,8 mg-eq/g, natural mordenite (Voditsa, Ukraine) (МV, Е=1,7 mg-eq/g), natural mordenite/clinoptilolite from (Lipcha, Ukraine, mordenite/clinoptilolite ratio 3:1, E=1,9 mg-eq/g and natural clinoptilolite from Sokirnitsa, Ukraine (Kl, E=1,7 mg-eq/g) was used. The factors of distribution Kd calculate in the manner of relations of contents fixed cation in unit of mass of zeolite to their contents in 1 ml solution after sorption an e.g. cuprum cations. Results of analysis ion-exchange balances Na-forms of zeolites confirm the suggestion about change of the selective sorption of the cations at variation of the exchange capacity. The amounts of cation in solutions were determined by atomic absorption and Xray-fluorescent spectroscopy.
Result and Discussion
As can be seen from data in Tables 1, on measure of the increase relationship zeolites to Cu2+ increases, (the reduction of positive value of free
Table 1. Theoretical exchange capacity and free Gibbs energy of ion-exchange reaction
Zeolite
Si/Al ratio
dk,г/см3
qo,mg-eq cm3
ΔGo,kJ/g-eq.
Mordenite
5.0
1.70
4.5
+7.6
Erionite
3.5
1.51
5.6
+4.1
Clinoptilolite
4.0
1.71
5.7
+3.6
NaY
2.56
1.27
5.9
+1.05
NaX
1.26
1.27
9.3
-2.05
NaA
1.0
1.27
10.5
Gibbs energy of ion exchange reactions). We will note that ion-exchanger with weak electrostatic field (low value qo) show selectivity not to cuprum cations, but to a sodium cation (positive value ΔGo) while NaX with strong electrostatic field – (qo=9,3mg-eq/g) selective absorbs cuprum cations (negative value ΔGo). From observed in Table 1 correlations, possible to expect the high affinity to cuprum cations for NaA.
When the granules NaA was powder (particles 0,50-0,25 mm and less), in consequence of increase the external surface of the particles and improvements of conditions of mass exchange a degree of extraction Cu2+ increases practically in 3 times (Table 2). The reduction of solid and liquid phases ratio (S/L) from 1:20000 up to 1:10000 for this sorbent with size of granules 1-2 mm practically does not affect on the degrees of extraction Cu2+ from solution. The sorption Cu2+ depends also from change рН solutions, in consequence of the hydrolysis of absorbents. In case of NaA and NaX, рН of solution greatly increase with the result that in fluid phase was formed colloidal cuprum hydroxide that, naturally, because of the weak solubility of the Cu (OH)2, prevents sorption of Cu2+, at reduction (S/L), particularly.
Table 2. Ion-exchange sorption of Cu2+ by zeolites: CCu=9.70 and 6.04 (2, 4) mg/l; S/L=1:1000
№
Zeolite
Size, mm
рН* equilibrium solution
Absorption of Cu2+, mg-eq/g
Absorption degree, %
Kd
1
NaA granule
1-2
6,50
0.104
34,5
520
2
NaA powdered
0,25-0,5
8,48
0.190
100
6040000
3
NaA (powder)
-
9,38
0.289
99,0
96000
4
NaХ powdered
0,25-0,5
8,41
0.190
100
6040000
5
Mordenite (MV)
1-2
5,71
0.092
30,0
430
6
Mordenite МLP)
1-2
5,63
0,076
24,8
330
7
Clinoptilolite (S)
1-2
5,68
0,079
26,1
350
*) рН of source solution Cu(NO3)2 - 5,39 (СCu=6.04 мg/l), 5.50 (СCu= 9,7 мg/l)
The received data for the synthetic and natural zeolites are corresponded, with term of the Eiseman theory, with absorption data for cuprum and other toxic cations by zeolites, as well as carbon sorbents.
Acknowlegment
The work was financially supported by the Ukrainian Scientific- Technical Center under grant № 1437.
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