Ion association and hydration in aqueous solutions of LiCl and Li2SO4 by dielectric spectroscopy

A systematic study of the dielectric relaxation spectra of aqueous solutions of LiCl and Li2SO4 has been made at solute concentrations of 0.05 < or = c/M < or = 1.0 and 2.0, respectively, and over a wide range of frequencies (0.2 < or = nu/GHz < or = 89) at 25 degrees C. The spectra were best described by a superposition of four Debye processes, consisting of the two well-known water relaxations at ca. 8 and 0.5 ps and two ion-pair contributions at ca. 200 and 20 ps, corresponding to the presence of double-solvent-separated (2SIP) and solvent-shared (SIP) ion pairs, respectively. Consistent with spectroscopic studies, no contact ion pairs were detected over the studied concentration range. The overall ion association constants K(o)(A) obtained were in good agreement with literature data for both salts. Detailed analysis of the solvent relaxations indicated that Li+ has a significant second solvation sheath although there were differences between the effective hydration numbers obtained from LiCl and Li2SO4, which might arise from competition for the solvent from the anions.     

Biosorption of copper(II) from aqueous solutions by Spirogyra species

Batch studies were conducted to investigate the kinetics and isotherms of Cu(II) biosorption on the biomass of green alga Spirogyra species. It is observed that the biosorption capacity of the biomass strongly depends on pH and algal dose. The maximum biosorption capacity of 133.3 mg Cu(II)/g of dry weight of biomass was observed at an optimum pH of 5 in 120 min with an algal dose of 20 g/L. Desorption studies were conducted with 133.3 mg/g of Cu(II) loaded biomass using different desorption agents including HCl, EDTA, H2SO4, NaCl, and H2O. The maximum desorption of 95.3% was obtained with HCl in 15 min. The results indicate that with the advantages of high metal biosorption capacity and satisfactory recovery of Cu(II), Spirogyra can be used as an efficient and economic biosorbent material for the removal and recovery of toxic heavy metals from polluted water.     

Ion association studies in aqueous NiSO4 solutions by positron lifetime spectroscopy

Ion association has been studied by positron lifetime spectroscopy in aqueous solutions containing the Ni²⁺ and SO ₄ ^2– ions at 294 K with the double aim of assessing the reliability of the method for quantitative determination of complex formation constants and of probing the validity of various expressions to calculate single-ion activity coefficients at high ionic strength. The existence of two complexes, identified as NiSO₄ and Ni₂SO ₄ ²⁺ , is shown by the data analysis. Considering the formation constant of the former, K_I=(196±10)M^–1, determined in previous works leads to discarding several of the expressions commonly used for activity corrections. Two possible values are retained for K_I, (193±20)M^–1 and (179±20)M^–1, while K_II related to Ni₂SO ₄ ²⁺ is better defined, as (2.57±0.14)M^–1.     

Scandium sulfate complexation in aqueous solution by dielectric relaxation spectroscopy

Ion association in aqueous solutions of scandium sulfate has been investigated at 25 degrees C and at concentrations from 0.01 to 0.8 M by broadband dielectric spectroscopy over the frequency range 0.2 相似文献   

Ion exchange recovery of chromium (VI) and manganese (II) from aqueous solutions

Sorption recovery of toxic ions – chromium (VI) and manganese (II) – from aqueous solutions with different acidity (0.001–0.5 M HCl) was investigated on cation and anion exchangers synthesized with long-chained cross-linking agents (LCA). The initial concentrations of Cr(VI) and Mn(II) were 1 g/L and 5 g/L, respectively. It was shown that the resins with LCA possess high ionic permeability due to the elasticity of polymeric skeleton. High selectivity and good kinetic properties of these sorbents allowed to achieve quantitative (∼100%) recovery and separation of manganese (II) and chromium (VI) in counter-current columns, which results in the complete purification of solutions from toxicants (below the maximum permissible limits), whereas the valuable components (chromium and manganese) can be returned back to industrial process.     

Ion association dynamics in aqueous solutions of sulfate salts as studied by Raman band shape analysis

A new perspective is shown on the interaction between the sulfate ion and its counter cation in aqueous solutions. We propose the dynamic exchange model of ion association instead of the conventional static equilibrium model. The concentration dependence of the Raman band shape of the totally symmetric (a(1)) SO stretch mode of the sulfate ion is investigated systematically for four sulfate ions, MgSO(4), (NH(4))(2)SO(4), K(2)SO(4), and Li(2)SO(4). The concentration dependence of the a(1) Raman band shape in the MgSO(4) system is successfully reproduced by the analysis based on the dynamic exchange model. As a result, quantitative information about the extremely dynamic nature of the ion association has been obtained: the mean time between associations is a few picoseconds and the mean lifetime of association is several hundred femtoseconds.     

Diffusion in aqueous copper sulfate and copper sulfate-sulfuric acid solutions

Diffusion coefficients of copper sulfate-water and copper sulfate-sulfuric acid-water solutions have been determined at 25°C using conductimetric and diaphragm-cell techniques. The ternary diffusion measurements indicate that diffusion of sulfuric acid can produce large counterflows of copper sulfate and vice versa. If diffusion of copper sulfate in aqueous sulfuric acid solutions is treated as a binary process, the measured apparent diffusivities of copper sulfate can be 1 to 8% lower than the salt's true diffusivity. Equations are developed to predict transport coefficients from the concentrations and mobilities of the diffusing species.     

Amino acid hydration in aqueous magnesium and sodium sulfate solutions

We study the partial volumes of amino acids in aqueous magnesium and sodium sulfate solutions, which have a different effect on the structure of water, and calculate the structural parameters of hydrated complexes of NH ₃ ⁺ and COO^? groups: hydration numbers and water volumes inside and outside the hydration shell. The hydration numbers are given as a sum of the contributions of the interactions in the ternary (water-salt-amino acid) and binary (water-salt) systems.     

Simultaneous removal of copper(II), lead(II), zinc(II) and cadmium(II) from aqueous solutions by multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) were used successfully for the removal of heavy metals from aqueous solution. Characterization techniques showed the carbon as nanotubes with an average diameter between 40 and 60 nm and a specific surface area of 61.5 m² g^?1. The effect of carbon nanotubes mass, contact time, metal ions concentration, solution pH, and ionic strength on the adsorption of Cu(II), Pb(II), Cd(II) and Zn(II) by MWCNTs were studied and optimized. The adsorption of the heavy metals from aqueous solution by MWCNTs was studied kinetically using different kinetic models. A pseudo-second order model and the Elovich model were found to be in good agreement with the experimental data. The mechanism of adsorption was studied by the intra-particle diffusion model, and the results showed that intra-particle diffusion was not the slowest of the rate processes that determined the overall order. This model also revealed that the interaction of the metal ions with the MWCNTs surface might have been the most significant rate process. There was a competition among the metal ions for binding of the active sites present on the MWCNTs surface with affinity in the following order: Cu(II) > Zn(II) > Pb(II) > Cd(II).     

Adsorption of copper(II) ions from aqueous solutions on alumina industrial wastes

Equilibrium adsorption of copper(II) ions on red mud (alumina industrial wastes) modified by various methods was studied. The effect exerted by the nature the modifier (NaHSO₄, NaCl + HCl, and H₂SO₄) on the sorption activity of red mud was determined.     

Temperature effects on ion association and hydration in MgSO4 by dielectric spectroscopy.

A detailed investigation of aqueous solutions of magnesium sulfate has been made by dielectric relaxation spectroscopy (DRS) over a wide range of frequencies (0.2 MgSO(4) (0)(aq) is in good agreement with literature data at lower temperatures but is overestimated at higher temperatures due to processing difficulties. Despite the limited precision of the spectra, analysis of the individual steps in the ion-association process is possible for the first time. The 2SIPs are formed with little disturbance to their hydration shells, the (partial) destruction of which appears to occur mostly during the formation of SIPs. Effective hydration numbers derived from the DRS spectra indicate that both Mg(2+) and SO(4) (2-) influence solvent water molecules beyond their first hydration spheres but that MgSO(4)(aq) is less strongly hydrated than the previously studied CuSO(4)(aq).     

Determination of ratios of sulfate to bisulfate ions in aqueous solutions by Raman spectroscopy

Raman spectra are presented for aqueous ammonium bisulfate and zinc sulfate-sulfuric acid solutions over a wide range of concentration and from 20 to 85°C. The heights of the 980 cm ^–1 (primarily SO ₄ ^–2 ) and 1053 cm ^–1 (primarily HSO ₄ ^– ) bands are correlated with the pH of the solutions. The ratio of the species SO ₄ ^–2 and HSO ₄ ^– can be obtained from the ratio of scattering intensities at 980 and 1053 cm ^–1 . The H obtained from plots of the log of the concentration products versus 1/T is –37±5 kJ-mol ^–1 for ammonium bisulfate solutions and –48±4kJ-mol ^–1 for the ZnSO ₄ -H ₂ SO ₄ solutions. This compares to –22 kJ-mol ^–1 for the H of bisulfate ion dissociation as obtained from thermodynamic equilibrium constants.     

Simulation of copper(II) cations sorption on goethite from aqueous solutions of complexons

Effect of complexons of polyaminopolycarboxylic acid series (IDA, NTA, EDTA, and DTPA) and polyphosphonic acid series (HEDP, NTP, and EDTP) on Cu(II) cations sorption on goethite (α-FeOOH) from aqueous solutions has been studied. Obtained results have been considered in the context of complexation reactions in bulk solution and on sorbent surface. It has been found that all complexons (except for EDTA), depending on nature, produce on goethite surface (≡FeOH) triple complexes of type A (surface–metal–complexon) of composition ≡FeOCuLH _i ^1+i?n and ≡FeOCuL(OH) _j ^1?j?n or type B (surface–complexon–metal) of composition ≡FeLH _i Cu^3+i-n and ≡FeLCu(OH) _j ^3?j?n . pH-Ranges for complex existence and stability constants for the surface complexes have been determined. Factors affecting the character of complexon effect (immobilization/remobilization) on the sorbed metal have been analyzed.     

Sorption of radiocobalt(II) from aqueous solutions to Na-attapulgite

The sorption of Co(II) on Na-attapulgite as a function of contact time, solid content, pH, ionic strength, foreign ions, fulvic acid (FA) and temperature under ambient conditions was studied. The kinetic of Co(II) sorption on Na-attapulgite was described well by pseudo-second-order model. The sorption of Co(II) on Na-attapulgite was strongly dependent on pH and ionic strength. The sorption of Co(II) was mainly dominated by outer-sphere surface complexation and/or ion exchange at low pH, whereas inner-sphere surface complexation or surface precipitation was the main sorption mechanism at high pH values. The presence of FA did not affect Co(II) sorption obviously at pH <7, and a negative effect was observed at pH >7. The Langmuir and Freundlich models were used to simulate the sorption data at different temperatures, and the results indicated that the Langmuir model simulated the data better than the Freundlich isotherm model. The thermodynamic parameters (∆G°, ∆S°, ∆H°) calculated from the temperature-dependent sorption isotherms indicated that the sorption of Co(II) on Na-attapulgite was an endothermic and spontaneous process. The results suggest that the attapulgite sample is a suitable material in the preconcentration and solidification of radiocobalt from large volumes of aqueous solutions.     

Adsorption studies of cesium on potassium copper nickel hexacyanoferrate(II) from aqueous solutions

Adsorption of cesium from aqueous solutions on potassium copper nickel hexacyanoferrate(II) (KCNF) has been investigated in batch experiments and optimized as a function of concentration of acids, salts and adsorbate using a radiotracer technique. The results are presented in terms of distribution coefficient, K_d (ml·g^–1). The uptake of cesium obeys a Freundlich adsorption isotherm over the concentration range of 3.7 to 37 mmol·l^–1 with b values of 0.77, 0.68 and 0.56 at temperatures of 293, 313, 333 K, respectively. The Langmuir adsorption isotherm is followed in the concentration range of 15 to 75 mmol·l^–1 in the same temperature range. The values of limiting adsorption concentration (C_m) have been found to be 2.58, 2.44 and 2.32 mmol·g^–1. The heat of adsorption was calculated as 26.43 kJ·mol^–1. The influence of a number of anions and cations on cesium retention has also been studied. Column experiments have been performed and breakthrough have been obtained under different operating conditions. The low cesium capacity of 1.1 mmol·g^–1 has been obtained under dynamic conditions as compared to batch experiments. Desorption of cesium from the column has been achieved (45.4%) by nitric acid solution of 8M concentration at a flow rate of 0.5 ml·min^–1.     

Spectrophotometric study of the equilibria in aqueous copper(II) azide solutions

The reaction between copper (II) and azide has been studied spectrophotometrically at four wavelengths, at 25 degrees , and ionic strength 4.00M (sodium perchlorate). The formation constants beta(2) and beta(3) found are 2.90 +/- 0.08 x 10(4) and 3.02 +/- 0.07 x 10(6) respectively. The results obtained from potentiometric measurements with a solid-state electrode disagree with those calculated from the spectrophotometric data. Causes of the discrepancy are discussed.     

Modeling adsorption of copper (II) onto fly ash and bentonite complex from aqueous solutions

Transportation of copper (II) ions from aqueous solutions to a fly ash and bentonite complex amorphous heterogeneous oxides (AHO: CaO-SiO(2)-Al(2)O(3)-MgO-FeO) system was studied. The particles of the fly ash and bentonite complex AHO system were highly porous and composed of platelike grains. They provide the physical basis for establishing a liquid-solid reaction model applicable to mesoporous solids. The main innovation of this model was in simplifying the powder granules to aggregates of close particles, while the particles act in accordance with the model better. The calculated curves from the models were well in line with the experimental results.     

Investigation of intermolecular interactions in solutions by means of millimeter-wave spectroscopy 5. Positive and negative hydration effects in aqueous solutions of methylureas

A study has been made of the concentration dependence of absorption of radiation at 5 cm^–1 by aqueous solutions of urea and its N-methyl, N,N-dimethyl, N,N'-dimethyl, and tetramethyl derivatives; and their effective hydration numbers have been calculated. The low values obtained for the effective hydration numbers of urea, N-methylurea, and N,N'-dimethylurea are explained by the close mutual approach of the two hydrogen atoms in the trans position relative to the carbonyl group (negative hydration); in the case of the N,N-dimethyl and tetramethyl derivatives, no negative hydration effect is observed. For the tetramethylurea, very definite hydrophobic hydration is observed. On the basis of data obtained on the effective hydration number, an estimate has been made of the relative contents of different conformers of methylurea and N,N'-dimethylurea in solution.For Previous Communication, See [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 321–326, February, 1990.