Electrokinetic potential of bentonite and kaolin particles in the presence of polymer mixtures |
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Authors: | S Barany I Kozakova L Marcinova J Skvarla |
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Institution: | 1.University of Miskolc,Miskolc-Egyetemvaros,Hungary;2.Technical University of Kosice,Kosice,Slovakia |
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Abstract: | In order to elucidate the mechanisms of flocculation by polymer mixtures, the effect of adsorption of non-ionic poly(ethylene
oxide) — PEO, two samples of strongly (SNF FO 4800) and medium charged (SNF FO 4350) cationic and two samples of medium (SNF
AN 935) and weakly charged (SNF AN 905) anionic polyelectrolytes (PE) as well as their binary mixtures on the electrokinetic
potential of bentonite and kaolin particles has been studied. It is shown that in the presence of PEO-anionic/cationic polymer
mixture, the electrokinetic potential of particles is determined by the adsorption of the polyelectrolyte; neither cationic
nor anionic segments can be displaced by the non-ionic polymer. In mixtures of cationic and anionic polyelectrolytes, the
ζ-potential of particles is determined by the adsorbed amount of anionic polymer independently of the charge density of PE
and way of addition of the mixture components to the suspension, i.e. (1) first adding the cationic polymer, then the anionic
one, or (2) first adding the anionic polymer then the cationic one, or (3) adding an increasing amount of pre-prepared 1:
1 mixture. The highest absolute ζ-potential values are observed for pH 7.5 when the surface of bentonite or kaolin particles
is “purely” negatively charged and the anionic PE layer is most extended because of few contacts to the surface. With decreasing
the pH, the (negative) ζ-potential of particles decreases due to appearance of a small amount of positive charges on the surface
that bond an increasing amount of negative segments and results in shrinking of the adsorbed layer of the anionic PE. It is
shown also that the electrokinetic potential of particles in anionic and cationic PE mixtures at all studied pH (4, 5, and
7.5) depends on the spatial distribution of negatively charged segments near the surface. The regularities observed are explained
by formation of long loops and tails of anionic segments on the surface because of the small number of contacts to the surface;
the cationic polyelectrolyte forms on the surface a thin layer with a big number of contacts and which is hidden behind the
more extended anionic polymer layer. |
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