| dc.description.abstract-en | A sodium montmorillonite from Ivančice
(Czech Republic) was treated with solutions containing
various molar concentrations of Zn and Cd for the purpose
of determining ion exchange equilibria. The sorption
isotherms for Zn and Cd exhibit a rather similar shape,
which depends on pH; the maxima for Zn and Cd sorbed
on Na-montmorillonite are very close to each other (e.g.,
0.419 mmol/1 g and 0.440 mmol/1 g, respectively, for
pH=5). It is a characteristic of both elements that a high
level of sorption is reached at low concentration in solution.
The leachability of Zn and Cd in deionized water
from fully saturated montmorillonites is very similar,
but a different results were observed for Na leached from
fully saturated Na-montmorillonite. The total amount of
leached Na was 21.7% (after four consecutive leaching
runs). However, only 2.1% and 1.6% were found for Cd
and Zn, respectively. Different quantities of Cd and Zn
exchanged in Na-montmorillonite influence significantly
the shape and position of maximum of the 001 XRD profile.
Experimental XRD profiles of montmorillonites, fully
saturated with Na, Cd and Zn, corrected for instrumental
and physical factors exhibit maxima at 12.59, 14.86,
and 14.77 Å, respectively. When the d001 spacing is determined
from a corrected profile, it varies systematically
with the percentage of exchanged Zn and Cd and the relationships
seem to be linear for both elements. For montmorillonites,
not fully saturated with one element, the
peak shift and peak broadening, characteristic for mixed
layered structures with random layer sequences, has been
observed. | en |