scholarly journals Adsorption of strontium on manganese oxide (δ-MnO2) at elevated temperatures: experiment and modeling

2019 ◽  
Vol 64 (10) ◽  
pp. 1091-1104
Author(s):  
O. N. Karaseva ◽  
L. I. Ivanova ◽  
L. Z. Lakshtanov
Keyword(s):  
Ionic Strength ◽  
Elevated Temperatures ◽  
Equilibrium Constants ◽  
Surface Complexation ◽  
Outer Sphere ◽  
Acid Base ◽  
Surface Complexes ◽  
Different Temperatures ◽  
Low Ionic Strength ◽  
Outer Sphere Complexes

Strontium adsorption has been studied by the method of acid-base potentiometric titrations at three different temperatures: 25, 50, 75C. The effect of pH, ionic strength, sorbate/sorbent ratio, and temperature on adsorption was investigated. Experimental data were simulated using two various surface complexation models, with two different electrostatic descriptions of the interface: the constant capacitance model (CCM) and the triple-layer model (TLM). Although the both models used are able to account for the acid-base reactions and surface complexation of strontium on birnessite, we consider that the TLM is more applicable for a description of heterophaseous system H+ MnOH Sr2+. Under conditions of low ionic strength and negatively charged surface, Sr2+ ions compete with the electrolyte ions and form outer-sphere complexes along with inner-sphere complexes. Consequently, using the CCM for description of strontium adsorption data could be mathematically satisfactory, but physically senseless. The equilibrium model proposed here consists of the complexes of inner (MnOHSr2+, MnOSr+, MnOSrOH0) and outer types ([MnO Sr2+]+). The corresponding intrinsic equilibrium constants of the formation of these surface complexes were calculated for 25,50, and 75C.

scholarly journals Surface Complexation Modeling in Variable Charge Soils: Charge Characterization by Potentiometric Titration

2015 ◽  
Vol 39 (5) ◽  
pp. 1387-1394 ◽  
Author(s):  
Giuliano Marchi ◽  
Cesar Crispim Vilar ◽  
George O’Connor ◽  
Marx Leandro Naves Silva
Keyword(s):  
Ionic Strength ◽  
Potentiometric Titration ◽  
Equilibrium Constants ◽  
Surface Complexation ◽  
Soil Surface ◽  
Reactive Site ◽  
Surface Complexation Modeling ◽  
Visual Minteq ◽  
Hand Calculation ◽  
Low Ionic Strength

ABSTRACT Intrinsic equilibrium constants of 17 representative Brazilian Oxisols were estimated from potentiometric titration measuring the adsorption of H+ and OH− on amphoteric surfaces in suspensions of varying ionic strength. Equilibrium constants were fitted to two surface complexation models: diffuse layer and constant capacitance. The former was fitted by calculating total site concentration from curve fitting estimates and pH-extrapolation of the intrinsic equilibrium constants to the PZNPC (hand calculation), considering one and two reactive sites, and by the FITEQL software. The latter was fitted only by FITEQL, with one reactive site. Soil chemical and physical properties were correlated to the intrinsic equilibrium constants. Both surface complexation models satisfactorily fit our experimental data, but for results at low ionic strength, optimization did not converge in FITEQL. Data were incorporated in Visual MINTEQ and they provide a modeling system that can predict protonation-dissociation reactions in the soil surface under changing environmental conditions.

Thermodynamic of metal complexation of the macrocyclic antibiotic rifampicin

2001 ◽  
Vol 79 (1) ◽  
pp. 42-49
Author(s):  
I Shehatta ◽  
I Kenawy ◽  
A H Askalany ◽  
Ayman A Hassan
Keyword(s):  
Binding Sites ◽  
Equilibrium Constants ◽  
Ionic Species ◽  
Ligand Field ◽  
Water Medium ◽  
Acid Base ◽  
Distribution Diagram ◽  
Macrocyclic Antibiotic ◽  
Transition Series ◽  
Different Temperatures

The acid-base and complexation equilibria of rifampicin with H+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+, and Pb2+ were studied by means of potentiometry. The stoichiometric equilibrium constants were determined in 50% (v/v) methanol-water medium at different temperatures and constant ionic strength (0.05 M KCl). It was established that rifampicin has two proton-binding sites. The distribution diagram of the corresponding ionic species as a function of pH is given and indicated that rifampicin exists predominantly in the zwitterionic form at pH [Formula: see text] 5. The thermodynamic parameters of protonation and complexation were derived and discussed. The formation of the complexes is spontaneous, more favourable at lower temperatures, entropically unfavourable, and an enthalpy-driven process. The order of the changes in Gibbs energy and enthalpy accompanying the complexation was found to be Mn2+ < Co2+ < Ni2+ < Cu2+ > Pb2+ > Zn2+ > Cd2+ > Hg2+ in accordance with the well-known sequence of Irving and Williams. The transition series contraction energy (Er(Mn-Zn)), and the ligand field stabilization energy (δH) were calculated from the enthalpy changes.Key words: rifampicin, thermodynamics, potentiometry, and complexation.

Honeybee flight muscle phosphoglucose isomerase: matching enzyme capacities to flux requirements at a near-equilibrium reaction

1997 ◽  
Vol 200 (8) ◽  
pp. 1247-1254 ◽  
Author(s):  
J Staples ◽  
R Suarez
Keyword(s):  
Ionic Strength ◽  
Flight Muscle ◽  
Equilibrium Constants ◽  
Muscle Metabolism ◽  
Phosphoglucose Isomerase ◽  
Glycolytic Flux ◽  
Cell Water ◽  
Economical Design ◽  
Equilibrium Reactions ◽  
Low Ionic Strength

In honeybee flight muscle, there are close matches between physiological flux rates and the maximal activities (Vmax; determined using crude homogenates) of key enzymes catalyzing non-equilibrium reactions in carbohydrate oxidation. In contrast, phosphoglucose isomerase (PGI), which catalyzes a reaction believed to be close to equilibrium, occurs at Vmax values greatly in excess of glycolytic flux rates. In this study, we measure the Vmax of flight muscle PGI, the kinetic parameters of the purified enzyme, the apparent equilibrium constants for the reaction and the tissue concentrations of substrate and product. Using the Haldane equation, we estimate that the forward flux capacity (Vf) for PGI required to achieve physiological glycolytic flux rates is between 800 and 1070 units ml-1 cell water, approximately 45&shy;60 % of the empirically measured Vmax of 1770 units ml-1 cell water at optimal pH (8.0) and low ionic strength (no added KCl). When measured at physiological pH (7.0) and ionic strength (120 mmol l-1 KCl) with saturating levels of substrate, PGI activity is 1130 units ml-1 cell water, a value close to the calculated Vf. These results reveal a very close match between predicted and measured PGI flux capacities, and support the concept of an economical design of muscle metabolism in systems working at very high metabolic rates.

Acid−Base Equilibrium Constants for Glycine in NaClO4, KCl, and KBr at 298 K. Dependence on Ionic Strength

1998 ◽  
Vol 43 (5) ◽  
pp. 876-879 ◽  
Author(s):  
P. Alonso ◽  
J. L. Barriada ◽  
P. Rodríguez ◽  
I. Brandariz ◽  
M. E. Sastre de Vicente
Keyword(s):  
Ionic Strength ◽  
Equilibrium Constants ◽  
Acid Base ◽  
Base Equilibrium ◽  
Acid Base Equilibrium ◽  
Dependence On Ionic Strength

Ion association and charge-transfer excitation between N-heterocyclic cations and cyanoiron complexes

1979 ◽  
Vol 57 (16) ◽  
pp. 2079-2084 ◽  
Author(s):  
Henrique E. Toma
Keyword(s):  
Charge Transfer ◽  
Equilibrium Constants ◽  
Ion Association ◽  
Outer Sphere ◽  
Binding Properties ◽  
Donor And Acceptor ◽  
Charge Transfer Excitation ◽  
Optical Charge ◽  
Heterocyclic Cations ◽  
Outer Sphere Complexes

N-Heterocyclic cations form with substituted pentacyanoferrates a series of outer-sphere complexes of general formula Fe(CN)5L//N-Het, suitable for systematic studies in aqueous solution. The equilibrium constants for the association of dipositive cations (e.g. N,N′-dimethyl-4,4-bipyridyl, or paraquat ion) and monopositive cations (e.g. N-methylpyrazinium) with the hexacyanoferrate(II) anion are typically in the range of 30–40 M−1and 10–13 M−1. The optical charge-transfer energies depend on the nature of the N-heterocyclic acceptor, and on the binding properties of the ligand L as they modify the ionization potentials of the Fe(CN)5Ln− complexes. A linear correlation between the optical charge-transfer energies and ΔE0 was found, with a slope (ΔEop/ΔG0) of 1.03 ± 0.03. The results were interpreted on the light of Hush's theory for intervalence transitions, with the aid of the equation Eop = 2(ΔG11* + ΔG22*) + ΔG120, which correlates the optical energy (Eop) for electron-transfer with the intrinsic barriers (ΔG11* + ΔG22*) of the donor and acceptor ions, and the free energy change (ΔG120) for the process.

scholarly journals Adsorption of Strontium onto Synthetic Iron(III) Oxide up to High Ionic Strength Systems

Minerals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1093
Author(s):  
David García ◽  
Johannes Lützenkirchen ◽  
Maximilien Huguenel ◽  
Léa Calmels ◽  
Vladimir Petrov ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Surface Complexation ◽  
Pitzer Model ◽  
Bulk Solution ◽  
Iron Corrosion ◽  
Acid Base ◽  
Model Framework ◽  
Surface Complexes ◽  
X Ray ◽  
Aqueous Species

In this work, the adsorption behavior of Sr onto a synthetic iron(III) oxide (hematite with traces of goethite) has been studied. This solid, which might be considered a representative of Fe3+ solid phases (iron corrosion products), was characterized by X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS), and its specific surface area was determined. Both XRD and XPS data are consistent with a mixed solid containing more than 90% hematite and 10% goethite. The solid was further characterized by fast acid-base titrations at different NaCl concentrations (from 0.1 to 5 M). Subsequently, for each background NaCl concentration used for the acid-base titrations, Sr-uptake experiments were carried out involving two different levels of Sr concentration (1·10−5 and 5·10−5 M, respectively) at constant solid concentration (7.3 g/L) as a function of −log([H+]/M). A Surface Complexation Model (SCM) was fitted to the experimental data, following a coupled Pitzer/surface complexation approach. The Pitzer model was applied to aqueous species. A Basic Stern Model was used for interfacial electrostatics of the system, which includes ion-specific effects via ion-specific pair-formation constants, whereas the Pitzer-approach involves ion-interaction parameters that enter the model through activity coefficients for aqueous species. A simple 1-pK model was applied (generic surface species, denoted as >XOH−1/2). Parameter fitting was carried out using the general parameter estimation software UCODE, coupled to a modified version of FITEQL2. The combined approach describes the full set of data reasonably well and involves two Sr-surface complexes, one of them including chloride. Monodentate and bidentate models were tested and were found to perform equally well. The SCM is particularly able to account for the incomplete uptake of Sr at higher salt levels, supporting the idea that adsorption models conventionally used in salt concentrations below 1 M are applicable to high salt concentrations if the correct activity corrections for the aqueous species are applied. This generates a self-consistent model framework involving a practical approach for semi-mechanistic SCMs. The model framework of coupling conventional electrostatic double layer models for the surface with a Pitzer approach for the bulk solution earlier tested with strongly adsorbing solutes is here shown to be successful for more weakly adsorbing solutes.

scholarly journals THERMODINAMIC PARAMETERS ON THE SORPTION OF PHOSPHATE IONS BY MONTMORILLONITE

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

Adsorption of hexavalent chromium on dunite

2011 ◽  
Vol 63 (4) ◽  
pp. 818-824 ◽  
Author(s):  
Antri Demetriou ◽  
Ioannis Pashalidis
Keyword(s):  
Experimental Data ◽  
Ionic Strength ◽  
Metal Ion ◽  
Outer Sphere ◽  
Atmospheric Conditions ◽  
Adsorption Model ◽  
Wide Ph Range ◽  
Ph Range ◽  
Relative Adsorption ◽  
Outer Sphere Complexes

The paper presents and discusses the effect of various physicochemical parameters (e.g. pH, ionic strength, Cr(VI) initial concentration, amount of the adsorbent, temperature and contact time between metal ion and adsorbent) on the adsorption efficiency of Cr(VI) on dunite in aqueous solutions under atmospheric conditions. Evaluation of the experimental data shows that dunite presents increased affinity for Cr(VI) over a wide pH range and Cr(VI) concentration, and the experimental data are well fitted by the Kd adsorption model. The relative adsorption is pH dependent and decreases slightly (about 10%) with increasing pH, because of changes in the surface charge of the solid. The effect of the ionic strength is significant (particularly at low pH), indicating the predominance of outer-sphere complexes. Moreover, adsorption experiments at various temperatures, two different pH values (pH 3 and pH 8) and three different ionic strengths (0.0, 0.1 and 1.0 M NaClO4), indicate an endothermic but spontaneous entropy-driven processes.

Approaches to modelling uranium(VI) adsorption on natural mineral assemblages

2000 ◽  
Vol 88 (9-11) ◽  
Author(s):  
T.D. Waite ◽  
James A. Davis ◽  
B.R. Fenton ◽  
Timothy E. Payne
Keyword(s):  
Performance Assessment ◽  
Goodness Of Fit ◽  
Surface Complexation ◽  
Acid Base ◽  
Surface Complexes ◽  
Natural Mineral ◽  
Surface Complexation Model ◽  
Surface Sites ◽  
Stepwise Manner ◽  
Mineral Assemblages

Component additivity (CA) and generalised composite (GC) approaches to deriving a suitable surface complexation model for description of U(VI) adsorption to natural mineral assemblages are pursued in this paper with good success. A single, ferrihydrite-like component is found to reasonably describe uranyl uptake to a number of kaolinitic iron-rich natural substrates at pH > 4 in the CA approach with previously published information on nature of surface complexes, acid-base properties of surface sites and electrostatic effects used in the model. The GC approach, in which little pre-knowledge about generic surface sites is assumed, gives even better fits and would appear to be a method of particular strength for application in areas such as performance assessment provided the model is developed in a careful, stepwise manner with simplicity and goodness of fit as the major criteria for acceptance.

scholarly journals Acid-base equilibria of 2,4-diiodo-6-methylphenylcarbamoylmethyl iminodiacetic acid and its labeling with technetium-99m

2006 ◽  
Vol 71 (1) ◽  
pp. 55-65 ◽  
Author(s):  
Jasmina Brboric ◽  
Mirjana Jovanovic ◽  
Gordana Popovic ◽  
Vera Kapetanovic ◽  
Sote Vladimirov
Keyword(s):  
Ionic Strength ◽  
Radiochemical Purity ◽  
Equilibrium Constants ◽  
Iminodiacetic Acid ◽  
Carboxylic Group ◽  
Acid Base ◽  
Acidity Constants ◽  
Technetium 99M ◽  
Ph Range ◽  
Influence Of Ph

The acid-base equilibria of a novel hepatobiliary imaging agent, 2,4-diiodo-6-methylphenylcarbamoylmethyl iminodiacetic acid (DIIODIDA) were studied. The potentiometrically determined acidity constants of the second carboxylic group, amino and amide groups were pK2 = 2.52 ? 0.02; pK3 = 5.86 ? 0.06 and pK4 = 10.9 ? 0.1. The determinations were performed at 25 ?C and an ionic strength of 0.1 mol/dm3 (NaCl). The acidity constants (pK1 = 1.3 ? 0.4) corresponding to the first carboxylic group was determined indirectly, on the basis of equilibrium constants obtained in a heterogeneous system, at 25 ?C and an ionic strength 1 mol/dm3 (HCl, NaCl). DIIODIDA was labeled with technetium-99m, and the influence of pH on the yield of labeling was investigated. It was found that labeling within the pH range from 5.5 to 6.5 provided a radiopharmaceutical of high radiochemical purity (>98 %).

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