Doktorska disertacija - Prirodno

Bearing in mind that the characteristics of each material depends on its chemical composition
and structure, a detailed characterization of the composite microstructure and
micromorphology was carried out, as well as thir chemical composition was acquired by EDS
method. Besides the usual peaks related to the chemical composition of the aluminosilicate
matrix, there are additional peaks of iron and copper on the EDS diagrams, which confirms
that the alloying and microalloying of aluminosilicate matrix was performed, resulting in
essentially changed initial electrochemical properties. Differences in peak intensities of
present alloying and microalloying additions, combined with XRD analysis, indicate that the
composite samples are composed of individual phases, which differ in quantity. Taking into
account the chemical and electrochemical processes on the surface of the composite, during
its interaction with synthetic water containing sulfide ions, the model of the interactions
which in detail presents all the stages of this process was created. As already mentioned, the
composite has a distinct electrochemical activity, which causes mass exchange between the
composite and water. The basic mechanism of sulphide removal from synthetic water is its
oxidation to elemental, colloidal sulfur, which then gets "captured" and retained in the porous
structure of the composite. Additionally, chemical bonding of sulfur to Fe 2+ centers occurrs
on the composite surface. Moreover, it is certain that the surplus of elemental iron dissolves
when ceramic comes in contact with sulfide aqueous solutions, owing to the negative
reversible potential of iron, causing the reduction of H 2S to HS - ions. This activity continues
until complete oxidation of alloying iron. Simple procedure of iron(III) hydroxide and
magnesium hydroxide layering on the bentonite matrix, during obtaining KPM3 composite,
leads to significant changes in structure and texture of montmorillonite, which is the most
common ingredient of bentonite. During the synthesis, partial delamination of
montmorillonite and the formation of less ordered structures resembling a house of cards
occurrs. Thermal treatment leads to dehydration of surface and interlayer area which increase
the specific surface area and microporosity compared to the starting bentonite. Langmuir
adsorption isotherm model fits the experimental results better than Freundlich and Dubinin-
Radushkevich models. The composite effectively removes ionic and colloidal forms of Pb(II),
with the highest removal efficiency in the pH region 5-10. The explanation lies in the fact that
a decrease in pH values below 5 causes protonation of the surface, i.e. there is a competitive
process bitween adsorption of protons and Pb(II) ions. Increase in pH leads to the formation
of colloidal forms of Pb(II), which are more or less binded to the surface of the composite
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depending on the colloidal micelle charge. At pH 12, soluble form of lead Pb(OH) 3 was
removed very well. The main mechanism of Pb (II) removal was ion exchange, but the
formation of the outer- and inner-sphere surface complexes is also possible. With increasing
ionic force of solution, the percentage removal of lead is reduced because the surfaces charge
on the composite sheltered by Na + ions. Having in mind the results obtained we can conclude
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