Modeling of Neptunium(V) Sorption Behavior onto Iron-Containing Minerals

AbstractSorption behaviors of neptunium (V) on naturally-occurring magnetite (Fe3O4) and goethite (α-FeOOH) in 0.1M NaN03 electrolyte solution under aerobic conditions were interpreted using the surface complexation model (SCM). The surface properties of these materials were experimentally investigated by C02-free potentiometric titration, and SCM parameters for the constant capacitance model, such as protonation/deprotonation constants of the surface hydroxyl group, were determined. The number of negatively charged sorption sites of goethite rapidly increased with the increase of the bulk solution pH compared with that of magnetite and this tendency was similar to the pH dependence of neptunium sorption. This implies that the neptunyl cation, NpO2+, plays a dominant role in possible sorption reactions. Assuming that the dominant surface complex is XO-NpO2, modeling by means of SCM was carried out, and the results were found to agree with experimental data.

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THERMODINAMIC PARAMETERS ON THE SORPTION OF PHOSPHATE IONS BY MONTMORILLONITE

Jurnal Sains Dasar ◽

10.21831/jsd.v4i1.8429 ◽

2016 ◽

Vol 4 (1) ◽

Author(s):

Ikhsan Jaslin ◽

Wijayanti Endang ◽

Sunarto Sunarto

Keyword(s):

Active Sites ◽

Surface Complexation ◽

Outer Sphere ◽

Hydroxyl Groups ◽

Process Data ◽

Surface Complexes ◽

Surface Complexation Model ◽

Surface Hydroxyl ◽

Phosphate Ions ◽

Sorbate Concentration

The sorption of phosphate by montmorillonite at 10, 30, and 50 oC were investigated aiming to mainly determine thermodynamic parameters for the formation of surface complexes in the adsorption of phosphate ions by montmorillonite. Data were collected by adsorption edge experiments investigating the effect of pH, adsorption isotherms enabling the effect of sorbate concentration, and acid-base titration calculating protons released or taken up by adsorption process. Data analysis was carried out using surface complexation model to fit the data collected in this study using the parameters obtained from previous study, as well as to calculate the values of ΔH and ΔS. Previous study reported that phosphate ions formed two outer-sphere surface complexes with active sites of montmorillonite through hydrogen bonding. In the first complex, [(XH)0– H2L─]─, the phosphate was held to permanent-charge X─ sites on the tetrahedral siloxane faces, and the second complex, [[(SO─)(SOH)]– – [H2L]─] 2─ was formed through the interaction between the phosphate and variable charge surface hydroxyl groups at the edges of montmorillonite crystals and on the octahedral alumina faces. The values of ΔH for the first and second reactions are 39.756 and 3.765x10-7 kJ mol‒1 respectively. Since both reactions have positive enthalpy values, it can be concluded that the reactions are endothermic. Large energy for the first reaction is needed by X─ sites (permanent negatively charge sites of montmorillonite) to be partially desolvated, on which K+ or other surface cations are replaced by H+ ions in the surface protonated process, and are then ready to interact phosphate ions in the solution. Small values of ΔH for the second reactions indicates that hydrogen bonds formed by phosphate and SOH sites in the second reaction are easily broken out, and the phosphate can easily desorbed from the surface. The values of ΔS for the first and second reactions are 122.523 and 2.393 x10-2 J K‒1 mol‒1, which are greater than -10 kJ mol‒1 and indicates that the surface reactions occurs through dissociative mechanisms.Keywords: montmorillonite, adsorption edge, extended constant capacitance, surface complexation model, enthalpy, reaction mechanisms

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Uranyl Sorption Onto Alumina

MRS Proceedings ◽

10.1557/proc-465-797 ◽

1996 ◽

Vol 465 ◽

Cited By ~ 1

Author(s):

Anna-Maria M. Jacobsson ◽

Robert S. Rundberg

Keyword(s):

Metal Ion ◽

Dissociation Constants ◽

Surface Complexation ◽

Uranyl Complex ◽

Acid Dissociation ◽

Oxide Surface ◽

Acid Dissociation Constants ◽

Surface Complexation Model ◽

Surface Hydroxyl ◽

Free Environment

ABSTRACTThe mechanism for the adsorption of uranyl onto alumina from aqueous solution was studied experimentally and the data were modeled using a triple layer surface complexation model. The experiments were carried out at low uranium concentrations (9×10-11 - 5×10-8M) in a CO2 free environment at varying electrolyte concentrations (0.01 – 1 M) and pH (4.5 – 12). The first and second acid dissociation constants, pKal and pKa2, of the alumina surface were determined from potentiometric titrations to be 7.2 ± 0.6 and 11.2 ± 0.4, respectively. The adsorption of uranium was found to be independent of the electrolyte concentration. We therefore conclude that the uranium binds as an inner sphere complex. The results were modeled using the code FITEQL. Two reactions of uranium with the surface were needed to fit the data, one forming a uranyl complex with a single surface hydroxyl and the other forming a bridged or bidentate complex reacting with two surface hydroxyls of the alumina. There was no evidence from these experiments of site heterogeneity. The constants used for the reactions were based in part on predictions made utilizing the Hard Soft Acid Base, HSAB, theory, relating the surface complexation constants to the hydrolysis of the sorbing metal ion and the acid dissociation constants of the mineral oxide surface.

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Comparison of a Non Electrostatic Surface Complexation Model and Surface Phase Theories for Prediction of Future Sorption Properties.

MRS Proceedings ◽

10.1557/proc-824-cc7.2 ◽

2004 ◽

Vol 824 ◽

Author(s):

Allan T. Emrén ◽

Anna-Maria Jacobsson

Keyword(s):

Aqueous Solution ◽

Chemical Potential ◽

Surface Complexation ◽

Sorption Properties ◽

Phase Method ◽

Detailed Knowledge ◽

Surface Phase ◽

Surface Complexation Model ◽

Advantages And Disadvantages ◽

The One

AbstractIn performance assessments, sorption of radionuclides dissolved in groundwater is mostly handled by the use of fixed Kd values. It has been well known that this approach is unsatisfying. Only during the last few years, however, tools have become available that make it possible to predict the actual Kd value in an aqueous solution that differs from the one in which the sorption properties were measured.One such approach is surface complexation (SC) that gives a detailed knowledge of the sorption properties. In SC, one tries to find what kinds of sorbed species are available on the surface and the thermodynamics for their formation from species in the bulk aqueous solution. Recently, a different approach, surface phase method (SP), has been developed. In SP, a thin layer including the surface is treated as a separate phase. In the bulk aqueous solution, the surface phase is treated as a virtual component, and from the chemical potential of this component, the sorption properties can be found.In the paper, we compare advantages and disadvantages of the two kinds of models. We also investigate the differences in predicted sorption properties of a number of radionuclides (Co, Np, Th and U). Furthermore, we discuss under which circumstances, one approach or the other is preferable.

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A surface complexation model of oil–brine–sandstone interfaces at 100°C: Low salinity waterflooding

Journal of Petroleum Science and Engineering ◽

10.1016/j.petrol.2011.12.020 ◽

2012 ◽

Vol 81 ◽

pp. 171-176 ◽

Cited By ~ 87

Author(s):

Patrick V. Brady ◽

James L. Krumhansl

Keyword(s):

Surface Complexation ◽

Surface Complexation Model ◽

Low Salinity ◽

Low Salinity Waterflooding

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Variable charges of a red soil from different depths: Acid-base buffer capacity and surface complexation model

Applied Clay Science ◽

10.1016/j.clay.2017.08.003 ◽

2018 ◽

Vol 159 ◽

pp. 107-115 ◽

Cited By ~ 10

Author(s):

Ying Wang ◽

Pengfei Cheng ◽

Fangbai Li ◽

Tongxu Liu ◽

Kuan Cheng ◽

...

Keyword(s):

Buffer Capacity ◽

Surface Complexation ◽

Red Soil ◽

Acid Base ◽

Surface Complexation Model ◽

Different Depths

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pH-sensitivity of the ribosomal peptidyl transfer reaction dependent on the identity of the A-site aminoacyl-tRNA

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1012612107 ◽

2010 ◽

Vol 108 (1) ◽

pp. 79-84 ◽

Cited By ~ 90

Author(s):

Magnus Johansson ◽

Ka-Weng Ieong ◽

Stefan Trobro ◽

Peter Strazewski ◽

Johan Åqvist ◽

...

Keyword(s):

Ph Value ◽

Ph Dependence ◽

Peptide Bond ◽

Bulk Solution ◽

Peptide Bond Formation ◽

Transfer Rates ◽

Peptidyl Transfer ◽

A Site ◽

Rate Limiting ◽

Site Binding

We studied the pH-dependence of ribosome catalyzed peptidyl transfer from fMet-tRNAfMet to the aa-tRNAs Phe-tRNAPhe, Ala-tRNAAla, Gly-tRNAGly, Pro-tRNAPro, Asn-tRNAAsn, and Ile-tRNAIle, selected to cover a large range of intrinsic pKa-values for the α-amino group of their amino acids. The peptidyl transfer rates were different at pH 7.5 and displayed different pH-dependence, quantified as the pH-value, , at which the rate was half maximal. The -values were downshifted relative to the intrinsic pKa-value of aa-tRNAs in bulk solution. Gly-tRNAGly had the smallest downshift, while Ile-tRNAIle and Ala-tRNAAla had the largest downshifts. These downshifts correlate strongly with molecular dynamics (MD) estimates of the downshifts in pKa-values of these aa-tRNAs upon A-site binding. Our data show the chemistry of peptide bond formation to be rate limiting for peptidyl transfer at pH 7.5 in the Gly and Pro cases and indicate rate limiting chemistry for all six aa-tRNAs.

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The syntheses of 6-C-alkyl derivatives of methyl α-isomaltoside for a study of the mechanism of hydrolysis by amyloglucosidase

Canadian Journal of Chemistry ◽

10.1139/v01-005 ◽

2001 ◽

Vol 79 (2) ◽

pp. 238-255 ◽

Cited By ~ 4

Author(s):

Ulrike Spohr ◽

Nghia Le ◽

Chang-Chun Ling ◽

Raymond U Lemieux

Keyword(s):

Hydrogen Bonds ◽

Molecular Model ◽

Aromatic Amino Acids ◽

Hydroxyl Group ◽

Bulk Solution ◽

Anomeric Effect ◽

Nmr Studies ◽

Intermolecular Hydrogen Bonds ◽

Model Calculations ◽

Derivatives Of

The epimeric (6aR)- and (6aS)-C-alkyl (methyl, ethyl and isopropyl) derivatives of methyl α-isomaltoside (1) were synthesized in order to examine the effects of introducing alkyl groups of increasing bulk on the rate of catalysis for the hydrolysis of the interunit α-glycosidic bond by the enzyme amyloglucosidase, EC 3.2.1.3, commonly termed glucoamylase (AMG). It was previously established that methyl (6aR)-C-methyl α-isomaltoside is hydrolysed about 2 times faster than methyl α-isomaltoside and about 8 times faster than its S-isomer. The kinetics for the hydrolyses of the ethyl and isopropyl analogs were also recently published. As was expected from molecular model calculations, all the R-epimers are good substrates. A rationale is presented for the catalysis based on conventional mechanistic theories that includes the assistance for the decomposition of the activated complex to products by the presence of a hydrogen bond, which connects the 4a-hydroxyl group to the tryptophane and arginine units. It is proposed that activation of the initially formed complex to the transition state is assisted by the energy released as a result of both of the displacement of perturbed water molecules of hydration at the surfaces of both the polyamphiphilic substrate and the combining site and the establishment of intermolecular hydrogen bonds, i.e., micro-thermodynamics. The dissipation of the heat to the bulk solution is impeded by a shell of aromatic amino acids that surround the combining site. Such shields are known to be located around the combining sites of lectins and carbohydrate specific antibodies and are considered necessary to prevent the disruption of the intermolecular hydrogen bonds, which are of key importance for the stability of the complex. These features together with the exquisite stereoelectronic dispositions of the reacting molecules within the combining site offer a rationalization for the catalysis at ambient temperatures and near neutral pH. The syntheses involved the addition of alkyl Grignard reagents to methyl 6-aldehydo-α-D-glucopyranoside. The addition favoured formation of the S-epimers by over 90%. Useful amounts of the active R-isomers were obtained by epimerization of the chiral centers using conventional methods. Glycosylation of the resulting alcohols under conditions for bromide-ion catalysis, provided methyl (6aS)- and (6aR)-C-alkyl-hepta-O-benzyl-α-isomaltosides. Catalytic hydrogenolysis of the benzyl groups afforded the desired disaccharides. 1H NMR studies established the absolute configurations and provided evidence for conformational preferences.Key words: amyloglucosidase (AMG), exo-anomeric effect, 6-C-alkyl-α-D-glucopyranosides and isomaltosides, mechanism of enzyme catalysis.

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