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

Molecules ◽  
2019 ◽  
Vol 24 (20) ◽  
pp. 3652 ◽  
Author(s):  
Monireh Khosravi ◽  
Vinuthaa Murthy ◽  
Ian D R Mackinnon
Keyword(s):  
Ion Exchange ◽  
Alkaline Earth ◽  
Computational Modelling ◽  
High Capacity ◽  
Synthetic Zeolite ◽  
Atomic Scale ◽  
Exchange Mechanism ◽  
Aqueous Environment ◽  
Exchange Flow ◽  
Dynamics Simulations

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.

Crystalline insoluble acid salts of tetravalent metals—XXI ion exchange mechanism of alkaline earth metal

1976 ◽  
Vol 38 (4) ◽  
pp. 843-848 ◽  
Author(s):  
G. Alberti ◽  
R. Bertrami ◽  
M. Casciola ◽  
U. Costantino ◽  
J.P. Gupta
Keyword(s):  
Ion Exchange ◽  
Alkaline Earth ◽  
Earth Metal ◽  
Exchange Mechanism ◽  
Alkaline Earth Metal ◽  
Acid Salts

On the Adsorption of Aspartate Derivatives to Calcite Surfaces in Aqueous Environment

2020 ◽  
Author(s):  
Robert Stepic ◽  
Lara Jurković ◽  
Ksenia Klementyeva ◽  
Marko Ukrainczyk ◽  
Matija Gredičak ◽  
...  
Keyword(s):  
Active Sites ◽  
Realistic Model ◽  
Binding Energies ◽  
Inhibition Mechanism ◽  
Aqueous Environment ◽  
Binding Modes ◽  
Carboxylate Groups ◽  
Dissolved Ions ◽  
Living Organisms ◽  
Dynamics Simulations

In many living organisms, biomolecules interact favorably with various surfaces of calcium carbonate. In this work, we have considered the interactions of aspartate (Asp) derivatives, as models of complex biomolecules, with calcite. Using kinetic growth experiments, we have investigated the inhibition of calcite growth by Asp, Asp2 and Asp3.This entailed the determination of a step-pinning growth regime as well as the evaluation of the adsorption constants and binding free energies for the three species to calcite crystals. These latter values are compared to free energy profiles obtained from fully atomistic molecular dynamics simulations. When using a flat (104) calcite surface in the models, the measured trend of binding energies is poorly reproduced. However, a more realistic model comprised of a surface with an island containing edges and corners, yields binding energies that compare very well with experiments. Surprisingly, we find that most binding modes involve the positively charged, ammonium group. Moreover, while attachment of the negatively charged carboxylate groups is also frequently observed, it is always balanced by the aqueous solvation of an equal or greater number of carboxylates. These effects are observed on all calcite features including edges and corners, the latter being associated with dominant affinities to Asp derivatives. As these features are also precisely the active sites for crystal growth, the experimental and theoretical results point strongly to a growth inhibition mechanism whereby these sites become blocked, preventing further attachment of dissolved ions and halting further growth.

scholarly journals Local structure and distortions of mixed methane-carbon dioxide hydrates

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Bernadette R. Cladek ◽  
S. Michelle Everett ◽  
Marshall T. McDonnell ◽  
Matthew G. Tucker ◽  
David J. Keffer ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Exchange Process ◽  
Carbon Dioxide Sequestration ◽  
Distribution Functions ◽  
Atomic Scale ◽  
Mixed Gas ◽  
Pure Compounds ◽  
Dynamics Simulations ◽  
Pair Distribution Functions ◽  
Methane Carbon

AbstractA vast source of methane is found in gas hydrate deposits, which form naturally dispersed throughout ocean sediments and arctic permafrost. Methane may be obtained from hydrates by exchange with hydrocarbon byproduct carbon dioxide. It is imperative for the development of safe methane extraction and carbon dioxide sequestration to understand how methane and carbon dioxide co-occupy the same hydrate structure. Pair distribution functions (PDFs) provide atomic-scale structural insight into intermolecular interactions in methane and carbon dioxide hydrates. We present experimental neutron PDFs of methane, carbon dioxide and mixed methane-carbon dioxide hydrates at 10 K analyzed with complementing classical molecular dynamics simulations and Reverse Monte Carlo fitting. Mixed hydrate, which forms during the exchange process, is more locally disordered than methane or carbon dioxide hydrates. The behavior of mixed gas species cannot be interpolated from properties of pure compounds, and PDF measurements provide important understanding of how the guest composition impacts overall order in the hydrate structure.

Effectiveness of Calcium Deficiency in Nanosized Hydroxyapatite for Removal of Fe(II), Cu(II), Ni(II) and Cr(VI) Ions from Aqueous Solutions

2019 ◽  
Vol 56 ◽  
pp. 17-27
Author(s):  
Van Dat Doan ◽  
Van Thuan Le ◽  
Hoang Sinh Le ◽  
Dinh Hien Ta ◽  
Hoai Thuong Nguyen
Keyword(s):  
Electron Microscopy ◽  
Ion Exchange ◽  
Aqueous Solutions ◽  
Calcium Deficiency ◽  
Exchange Mechanism ◽  
Precipitation Method ◽  
X Ray ◽  
Transmission Electron ◽  
Bet Method ◽  
Langmuir Isotherm Model

In this work, nanosized calcium deficient hydroxyapatite (nCDHA) was synthesized by the precipitation method, and then utilized as an adsorbent for removal of Fe (II), Cu (II), Ni (II) and Cr (VI) ions from aqueous solutions after characterizing it by various techniques as scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX) and BET method. A possible structure of synthesized nCDHA was proposed. The adsorption study indicated that the adsorption equilibrium is well fitted with Langmuir isotherm model with the maximum adsorption capacities followed the order of Fe (II) > Cu (II) > Ni (II) > Cr (VI) with the values of 137.23, 128.02, 83.19 and 2.92 mg/g, respectively. The ion-exchange mechanism was dominant for the adsorption of metal ions onto nCDHA at initial metal concentrations lower than 0.01 mol/L. Along with the ion-exchange mechanism, there was an additional precipitation occurred on the surface of nCDHA in the case of Fe (II) and Cu (II) at initial concentrations higher than 0.01 mol/L.

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