The Exchange Mechanism of Alkaline and Alkaline-Earth Ions in Zeolite N.

Monireh Khosravi,Vinuthaa Murthy,Ian D R Mackinnon

doi:10.3390/molecules24203652

Monireh Khosravi, Vinuthaa Murthy + Show 1 more

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https://doi.org/10.3390/molecules24203652

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Abstract

Zeolite N is a synthetic zeolite of the EDI framework family from the more than 200 known zeolite types. Previous experimental laboratory and field data show that zeolite N has a high capacity for exchange of ions. Computational modelling and simulation techniques are effective tools that help explain the atomic-scale behaviour of zeolites under different processing conditions and allow comparison with experiment. In this study, the ion exchange behaviour of synthetic zeolite N in an aqueous environment is investigated by molecular dynamics simulations. The exchange mechanism of K+ extra-framework cations with alkaline and alkaline-earth cations NH4+, Li+, Na+, Rb+, Cs+, Mg2+ and Ca2+ is explored in different crystallographic directions inside the zeolite N structure. Moreover, the effect of different framework partial charges on MD simulation results obtained from different DFT calculations are examined. The results show that the diffusion and exchange of cations in zeolite N are affected by shape and size of channels controlling the ion exchange flow as well as the nature of cation, ionic size and charge density.

Highlights

The potassium-rich zeolite K-F(Cl), later renamed zeolite N with the general formulaK12 Al10 Si10 O40 Cl2 .5H2 O, was initially synthesised by Barrer et al in 1953 [1]
We present further details of ion exchange mechanisms for zeolite N based on exchange of monovalent cations inside a zeolite N membrane, as well as the relative performance of
We investigate the relative mobility of ions inside and outside zeolite N membranes by calculating the self-diffusion coefficient (D) of ions from their mean square displacement (MSD) over the simulation time

Summary

Introduction

The potassium-rich zeolite K-F(Cl), later renamed zeolite N with the general formulaK12 Al10 Si10 O40 Cl2 .5H2 O, was initially synthesised by Barrer et al in 1953 [1]. The structure of zeolite N is orthorhombic with space group I222 and lattice parameters a = 9.9041 Å, b = 9.8860 Å and c = 13.0900 Å. The Si/Al ratio of the end-member zeolite N is one and, in general, affords a high ion-exchange capacity. The framework of zeolite N has low tortuosity and the predominant eight membered channel along the c axis provides an unimpeded path for ions to transfer or transport to exchangeable sites inside the cages. The extra-framework potassium cations can be exchanged due to their accessible positions and weak electrostatic bonds to water molecules and framework atoms. These properties make zeolite N an interesting candidate for ion-exchange applications

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