Proton Adsorption Selectivity of Zeolites in Aqueous Media: Effect of Si/Al Ratio of Zeolites

Abstract

In addition to their well-known uses as catalysts, zeolites are utilized to adsorb and remove various cations from aqueous system. The adsorption of the cations is ascribed to the negative charge of zeolites derived from isomorphous substitution of Si by Al. The amount of Na+ adsorption on 4A, X, Y, Na-P1 and mordenite type zeolites were determined in aqueous media, in a two-cation (Na+ and H+) system. Although each zeolite has a constant amount of negative charge, the amount of Na+ adsorption of each zeolite decreased drastically at low pH-pNa values, where pH-pNa is equal to log{(Na+)/(H+)}. By using the plot of the amount of Na+ adsorption versus pH-pNa, an index of the H+ selectivity, which is similar to the pKa of acids, of each zeolite was estimated, and the index tended to increase with decreasing Si/Al ratio of zeolites. These indicate that zeolites with lower Si/Al and higher negative charge density have higher H+ adsorption selectivity, and in fact, such a zeolite species (4A and X) adsorbed considerable amount of H+ even at weakly alkaline pH region. The adsorption of H+ results in the decrease of cation adsorption ability, and may lead to the dissolution of zeolites in aqueous media.

Cs+and Sr2+adsorption selectivity of zeolites in relation to radioactive decontamination

“…Na-P1 zeolite was hydrothermally synthesized from chemical reagents [35]. The CEC values of the zeolite samples are 5.56 mmol g −1 in Linde-type A, 4.40 mmol g −1 in faujasite X, 4.29 mmol g −1 in Na-P1, 2.40 mmol g −1 in faujasite Y, and 1.76 mmol g −1 in mordenite [36].…”

Kinetic Adsorption Study of Silver Nanoparticles on Natural Zeolite: Experimental and Theoretical Models

“…These minerals present a great porosity and a significant cation-exchange capacity [1,2]. Because of this, natural zeolites offer a wide range of applications, and one of the most notable is the removal of contaminant ions in water and soil [3][4][5]. It is reported that natural zeolites, specifically clinoptilolite, have been used in the removal of Mn, Cu, Ar, Pd, Cd, and Zn [4][5][6].…”

Proton Adsorption Selectivity of Zeolites in Aqueous Media: Effect of Exchangeable Cation Species of Zeolites

“…Now considering faujasite X and faujasite Y, the (pH-pCs)90 value of faujasite X was 3.21, while for faujasite Y, the value was 0.57. These results suggest that faujasite X has a higher H + adsorption selectivity than faujasite Y, possibly due to its lower Si/Al and higher CEC [37].…”

“…This explains why the H + selectivity was different among Li + , Na + , K + , Rb + and Cs + saturated zeolites. Furthermore, the difference in the Si/Al ratio among zeolites resulted in variations in the amount of negative charge or cation exchange capacity (CEC) of mordenite (179 cmol•kg −1 ), Linde-type A (565 cmol•kg −1 ), Na-P1 (429 cmol•kg −1 ), faujasite X (461 cmol•kg −1 ) and faujasite Y (250 cmol•kg −1 ) [37].…”