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Empirical and mechanistic evaluation of sodium exchange isotherms on natural mineral and organic adsorbents and organically functionalized nanoparticles
Ranjbar, F. & Jalali, M.
Abstract
This study was conducted to evaluate the efficiency of low-cost adsorbents including bentonite, kaolinite and zeolite saturated with calcium and potassium,
potato and wheat residues, and three metal oxide
nanoparticles functionalized with an acidic extract of
potato residues in improving the quality of sodic waters.
The optimization of factors such as pH, contact time, and
adsorbent dosage was investigated using a solution containing sodium, calcium, magnesium, and potassium. The
optimal pH and contact time were 7.0 and 24 h, respectively. The optimal dosage for using functionalized
nanoparticles was 0.1 g and for using other adsorbents was
1.0 g. The sodium exchange isotherms were conducted in
binary sodium–calcium and sodium–potassium and quaternary sodium–calcium–magnesium–potassium systems.
Zeolite saturated with potassium was the most effective
adsorbent in removing sodium from aqueous solutions with
an average removal efficiency of 69.2 and 66.5 % in binary
and quaternary systems, respectively. Freundlich and
Langmuir equations fitted well to experimental data in both
binary and quaternary systems. Cation selectivity coefficients calculated based on the Gaines–Thomas convention
varied with changing pH and adsorbent dosage. Graphical
and statistical evaluations confirmed that the mechanistic
cation exchange model using average Gaines–Thomas
selectivity coefficients in geochemical PHREEQC program
was able to successfully simulate the sodium exchange on
different adsorbents in both systems. The Gaines–Thomas
selectivity coefficient values greater than unity and as a
consequence, the negative values of the Gibbs free energy
change of adsorption indicated that sodium exchange
reactions in the presence of different adsorbents used is this
study were exergonic and spontaneous.
Keywords
Sodium exchange isotherm; Functionalized nanoparticles; PHREEQC; Sodic waters; Mechanistic simulation; Agricultural residues
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