Specific adsorption of bromide and iodide ions from N-methyl formamide solutions with constant ionic strength on liquid ga electrode

The differential capacitance curves were measured with an ac bridge in the Ga/[N-MF + 0.1 m M KBr + 0.1 (1 − m) M KClO₄] and Ga/[N-MF + 0.1 m M KI + 0.1 (1 − m) M KClO₄] systems at the following fractions m of surface-active anions: 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, and 1. As compared with other solvents, N-methyl formamide (N-MF) enables one to realize the largest positive charges of Ga electrode, at which it remains ideally polarizable (up to 20 μ/cm²). The data on the specific adsorption of Br⁻ and I⁻ anions in the system can be quantitatively described by the Frumkin’s isotherm; to the first approximation, free energy of halide ion (Hal⁻) adsorption DG_{adsHal ^{- 1}} \Delta G_{adsHal^{ - 1} } is a linear function of electrode charge. It is found that, in contrast to the Hg/N-MF interface, DG_{adsHal ^{- 1}} \Delta G_{adsHal^{ - 1} } at the Ga/N-MF interface varies in the reverse order: Br^t— ∼ I⁻ < Cl⁻. From the measured results, we can conclude that the energy of metal-Hal⁻ interaction increases in series: $\Delta G_{M - Cl^ - } > \Delta G_{M - Br^ - } > \Delta G_{M - I^ - } $\Delta G_{M - Cl^ - } > \Delta G_{M - Br^ - } > \Delta G_{M - I^ - } and the difference (DG_{Ga - Hal1^-} - DG_{Ga - Hal2^-} )(\Delta G_{Ga - Hal_1^ - } - \Delta G_{Ga - Hal_2^ - } ) is larger than the difference between the solvation energies of Hal^- (DG_{S - Hal1^-} - DG_{S - Hal2^-} )Hal^ - (\Delta G_{S - Hal_1^ - } - \Delta G_{S - Hal_2^ - } ).     

Specific adsorption of chloride ions on liquid Ga electrode from N-methylformamide solutions with constant ionic strength

Differential capacitance curves are measured by mans of an ac-bridge in the system Ga/[N-MF + 0.1m M KCl + 0.1(1 − m) M KClO₄] with the surface-active anion taken in the following molar fractions m: 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, and 1. As compared with the other solvents, N-methylformamide (N-MF) makes it possible to realize the highest positive charges of the Ga electrode at which the electrode remains ideally polarizable (up to 20 μC/cm²). The data on the specific adsorption of Cl⁻ ions in the mentioned system can be described qualitatively by the Frumkin isotherm in which the free energy is considered as a linear function of the electrode charge.     

Quantitative aspects of the adsorption of metal ions from aqueous solutions to container surfaces

An attempt is made to quantify the influence of wall-adsorption in trace analysis. The retention of the aqueous phase is defined in terms of three dimensionless parameters: surface capacity/total amount in the solution, concentration of adsorbable species/total concentration, ratio of adsorption parameters. Based on the measurement of the adsorption parameters by radiotracer experiments and the initial conditions the final retention may be calculated. Time dependence may be included.     

Structure of solvated lithium and chloride ions in formamide

Structure of solvated lithium and chloride ions in formamide was investigated by means of X-ray diffraction at 25°C. Lithium ion has, on average, 5.4 formamide molecules as nearest neighbors with an Li⁺-O distance of 224 pm, while chloride ion is coordinated with 4.5 formamide molecules with the Cl^–···N distance of 327 pm. The amino group within a formamide molecule interacts with a chloride ion in the bifurcate manner through two hydrogen atoms.Session lecture, IX International Conference on Non-Aqueous Solutions, Pittsburgh, PA, August 1984.To whom correspondence should be addressed.     

Alkyl dimethyl benzyl ammonium chloride adsorption mechanism on wood

The adsorption of alkyl dimethyl benzyl ammonium chloride (ADBAC) on wood was investigated. The changes in zeta potential curves of wood and ADBAC adsorption with increasing ADBAC concentration were highly correlated and showed two different mechanisms for ADBAC adsorption on wood: ion exchange reaction at low concentration and additional aggregation form of adsorption by hydrophobic interaction at high concentration. ADBAC adsorbed at a low solution concentration had high leaching resistance while ADBAC adsorbed into wood at above the critical micelle concentration (CMC) had low leaching resistance. The CMC decreased with addition of Mea, Cu-Mea, and buffer chemicals. The anion, Cl⁻ of ADBAC was only adsorbed at solution concentrations above the CMC and was easily leached out. The adsorption isotherm of ADBAC on wood before and after leaching was fit to the Langmuir, BET, and Freundlich isotherm models; the BET and Freundlich models fit the adsorption isotherm well before leaching and the Langmuir and the Freundlich models showed better fits to the adsorption isotherm after leaching. The adsorption capacity of ADBAC into wood by cation exchange did not achieve the cation exchange capacity (CEC) of wood.     

Weak specific adsorption of ions

It is shown that the weak specific adsorption of ions not involving the recharging of the electrode surface is characterized by the following unusual features: practical absence of any shift of p.z.c.; a very small discrepancy between the experimental differential capacity curves and similar curves calculated under the assumption that specific adsorption is absent (q₁ = 0); insensitivity of the total surface excess of cations to their distribution between the dense and diffuse layers; practical independence of q₁ of temperature and the bulk concentration of binary electrolyte; practical coincidence of c.t.p. calculated for different concentrations of surface-active supporting electrolyte assuming q₁ = 0. It is also shown on the basis of the experimental data for the system {mc CsCl + (1 ? m)c LiCl} that the main fraction of the effective charge, determined by the mixed electrolyte method of Hurwitz—Parsons, results from the true specific adsorption of Cs⁺ cations at the Hg/H₂O interface and only a small fraction of this charge (?20%) can be associated with different positions of the o.H.p. for Li⁺ and Cs⁺ ions.     

Tracer-diffusion of Co2+ ions in some transition metal chloride solutions

Tracer-diffusion coefficients of Co²⁺ ions have been determined in 1% agar gel containing transition metal chlorides, viz. ZnCl₂, NiCl₂ and MnCl₂ over the concentration range of 10^–6–0.15 M at 25°C using the zone-diffusion technique. The results are compared with calculated values on the basis of Onsager's theory and the deviations are accounted for on the basis of various types of interactions in the ion-gel water system. Further, activation energy for the tracer-diffusion of Co²⁺ ions in the above mentioned electrolytes has been obtained as a function of electrolyte concentration, using measurements in the temperature range of 25–50°C. The trend in activation energy is explained on the basis of the WANG's model.     

Structure of solvated metal ions in nitrate and chloride solutions of erbium(III) and yttrium(III) in dimethyl sulfoxide

X-ray diffraction measurements on 1M yttrium(III) and erbium(III) nitrate and chloride solutions in dimethyl sulfoxide (DMSO) have shown that Er(III) and Y(III) solutions of equal compositions are isostructural. The intensity difference functions can then be used to derive the detailed structure of the coordination sphere around the metal ions. The DMSO molecules are coordinated over oxygen with average M-O-S bond angles of about 130°. Two different conformations, corresponding to different relative orientations of the M-O and O-S bonds, seem to be prevalent. In the nitrate solutions an average of about 1.5 nitrate ions are coordinated as bidentate ligands to each metal ion. In the chloride solutions about 1.3 chloride ions belong to the inner-coordination sphere.On leave from the Department of Inorganic Chemistry, Royal Institute of Technology, S-10044 Stockholm, Sweden     

Preparation of corn stalk-based adsorbents and their specific application in metal ions adsorption

Corn stalk-based adsorbents modified from corn stalk were prepared by Cu(0)-mediated reversible-deactivation radical polymerization (Cu(0)-mediated RDRP). They were applied to remove metal ions and they exhibited good adsorption capacity, especially for Hg(II). Adsorption properties of corn stalk can be enhanced by introducing cyano, amino, amidoxime, and carboxyl groups onto its surface, which results in efficient adsorbents for different metal ions. TGA, SEM, EA, and FTIR analyses were employed to characterize the structures of corn stalk-graft-polyacrylonitrile (CS-g-PAN), corn stalk-graft-polyacrylamide (CS-g-PAM), amidoxime corn stalk-graft-polyacrylonitrile (AO CS-g-PAN) and carboxyl corn stalk-graft-poly(methyl acrylate) (CO CS-g-PMA). The maximum adsorption capacity for Hg(II) was 8.06 mmol g^?1 of AO CS-g-PAN. Kinetics of the Hg(II) adsorption on AO CS-g-PAN was found to follow the pseudo-second-order model and the adsorption isotherms were well fitted with the Freundlich isotherm model.     

Removal of heavy metal ions from aqueous solutions by alkaline-earth metal phosphates

The possibility of utilization of calcium or magnesium phosphates of various composition for heavy and non-ferrous metal extraction from aqueous solutions has been studied. The efficiency of the phosphates in removal of Pb(II), Cr(III) and Fe(III) ions has been shown to decrease in the following sequence: Mg₃(PO₄)₂>MgNH₄PO₄>Ca₃(PO₄)₂>CaHPO₄>Ca₁₀(PO₄)₆(OH)₂ which is inverse to their hydrolytic stability series. It has been established that phosphates of non-apatite structure are capable of binding up to 12 mmol g⁻¹ of the named heavy metals by a chemical interaction. Hydroxyapatite interacts with the polyvalent metal ions via either the above mentioned or ion-exchange mechanism, depending on preparation method used for the apatite and the nature of metal.     

Free energy of adsorption of water and metal ions on the [1014] calcite surface

We calculated the free energy profiles of water and three metal ions (magnesium, calcium, and strontium) adsorbing on the [1014] calcite surface in aqueous solution. The approach uses molecular dynamics with parametrized equations to describe the interatomic forces. The potential model is able to reproduce the interactions between water and the metal ions regardless of whether they are at the mineral surface or in bulk water. The simulations predict that the free energy of adsorption of water is relatively small compared to the enthalpy of adsorption calculated in previous papers. This suggests a large change in entropy associated with the water adsorption on the surface. We also demonstrate that the free energy profile of a metal ion adsorbing on the surface correlates with the solvent density and that the rate of formation of an innersphere complex depends on overcoming a large free energy barrier, which is mainly electrostatic in nature. Furthermore, comparison among the rates of desorption of magnesium, calcium, and strontium from the calcite surface suggests that magnesium has a much lower rate of desorption due to its strong interactions with both water and the surface.     

Anion-exchange separation of metal ions in dimethyl sulphoxide-methanol-hydrochloric acid

The effect of dimethyl sulphoxide on the anion-exchange behaviour of many metals m a methanolic system with hydrochloric acid was explored. Distribution coefficients for 26 elements were determined in a mixed solvent system of dimethyl sulphoxide-methanol-0.6M hydrochloric acid, in which the proportions of dimethyl sulphoxide and methanoi were varied. Lead(II) and silver(I) complexes are soluble in this system. Interesting effects were noted for gold(III), iron(III), molybdenum(VI) and uranium(VI). As a measure of the usefulness of the systems studied, 27 anion-exchange separations of two- to four-component mixtures of metal ions were carried out, each with quantitative results.     

Extraction of metal ions from chloride solution with N,N-dioctylacetamide

N,N-Di-n-octylacetamide (DOAA) was prepared and shown to be an effective extractant for a number of metal ions from aqueous hydrochloric acid solution. Distribution ratios of 35 metal ions were measured for 1M DOAA in chloroform and hydrochloric acid solutions ranging from 0.10 to 9.0M. Extraction of uranium(VI) from solutions of hydrochloric acid and of nitric acid was compared. The effects of different diluents and varying concentrations of DOAA were studied in an attempt to elucidate the extraction mechanisms involved.     

Specific adsorption of azide ions on mercury electrodes from constant ionic strength solutions

The adsorption of azide ions on mercury from aqueous solutions of NaN₃+NaF at constant ionic strength has been studied by measurements of the double layer capacity. Taking into account changes in the structure of the diffuse layer, it was possible to show that the properties of the inner layer are similar to those observed previously in solutions of pure NaN₃, and that the same adsorption isotherm applies to both systems.     

Sorption of zinc complex ions from chloride solutions with ion exchangers

To characterize the reaction of zinc ions with anion exchangers of various types, the equilibrium compositions of all the components of the sorption system (zinc salt, hydrochloric acid, and water) and distribution of associated molecules in the resin phase were considered.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 9, 2004, pp. 1456–1461.Original Russian Text Copyright © 2004 by Skorokhodov, Radionov, Goryaeva.