Mesure de pO2− au moyen d'une electrode a membrane de zircone stabilisee et determination potentiometrique de constantes d'equilibre d'echange de O2− dans le melange equimolaire NaCl-KCl fondu

A galvanic cell with a Ag/AgCl reference electrode and a pO^2? indicating electrode—made of a solid-state membrane in zirconia stabilized by calcia and filled by a mixture of Ni + NiO—has been constituted for working in the molten mixture NaCl-KCl (1:1), from 700 to near 1000°C. The response of the zirconia electrode in the fused salt has been tested by known variations of pO^2?, due to coulometric titrations of free oxide ions, then of hydroxide ions, by means of metallic ions (Ni²⁺, Cu⁺) forming scarcely soluble metallic oxides. The results of measurements were in a good accordance with the variation laws theoretically established, giving the proof that measurements of pO^2?, between about 2 and 12, are possible in the electrolytic and temperature range considered, by means of this system. An alteration of the electrode can arise in media with too low a pO^2? value.Equilibrium constants have been determined: solubility products (K_s) of the oxides NiO and Cu₂O, constant values of the equilibria 2OH^? ? H₂O (g) + O^2? (K₁) and H₂O (g) + 2Cl^? ? O^2? + 2HCl (g) (K₂); as functions of the absolute temperature T/°K and in the molar fraction scale (partial pressure of the gazeous substances in atm):

The solubility product values (at 727°C) for a few metallic oxides have been calculated from the free enthalpy values of formation and experimental values of the activity coefficients of the metallic ions and O^2? dissolved in NaCl-KCl.Limitations to the ability of the membrane electrode for measuring pO^2? have been established by an analysis based on the chemical and electrochemical behaviour of zirconia. A potential-pO^2? diagram shows the area inside which one has to work.     

Electrophoretic studies of mixed ligand complexes in solution—copper(II), nickel(II), cobalt(II), uranyl(II) and thorium(IV)—tartarate—nitrilotriacetate

Paper electrophoresis has been used for the study of the equilibria in mixed ligand complex systems in solution. The method is based on the migration of a spot of a metal ion, with the complexants added in the background electrolyte (0.1 M perchloric acid), at a fixed pH. The concentration of one of the complexants [A] is kept constant, while that of second ligand [L] is varied. A graph of—log [L] against mobility is used to obtain information on the formation of the mixed ligand complex, and to calculate the stability constant. Using this technique, the values of overall stability constant of the complex metal—tartarate—nitrilotriacetate have been found to be 10^12.25, 10^5.98, 10^?3.56, and 10^3.74 for Cu(II), Ni(II), Co(II), UO₂(II) and Th(IV) complexes, respectively at μ = 0.1 and temp. = 40°C.     

Conductometric studies of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) tetrafluoroborates in N,N—dimethylacetamide solutions

Results are reported for the molar conductivities at 25°C of N,N—dimethylacetamide (DMA) solutions of Bu₄NBF₄ and Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) tetrafluoroborates. The limiting molar conductivities of [M(DMA)₆]²⁺ (M  MN, Co, Ni, Cu, Zn) and BF^?₄, as well as association constants for Co(BF₄)₂ in DMA solutions have been calculated. The slight differences between conductometric curves of different metal ions are discussed.     

Studies on electrode kinetics of mixed ligand complexes of Co(II) in dimethyl formamide at dme

Mixed ligand complexes of Co(II) with pyridines and halide and pseudohalide have been synthesised. The reduction of synthesised complexes at dropping mercury electrode in various percentage of dimethyl formamide have been studied. The reduction is diffusion controlled. Slope values indicate the reduction to be irreversible. Kinetic parameters (K_s, K^o_f and α_n) have been calculated by Matsuda and Koutecky's method. K_s value was found to be in order 10^?4 cm. The effect of temperature and various composition of dmf have been investigated. At higher temperature the reduction becomes less irreversible.     

Removal, preconcentration and determination of trace heavy metal ions in water samples by AAS via chemically modified silica gel N-(1-carboxy-6-hydroxy) benzylidenepropylamine ion exchanger

The use of chemically modified silica gel N-(1-carboxy-6-hydroxy) benzylidenepropylamine (SiG-CHBPA), ion exchanger for removal and preconcentration of Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb in natural water samples collected from River Nile, Mediterranean Sea and other locations followed by their consecutive AAS determination was described. The effects on the percentage of recovered metal ions including mass change of ion exchanger, stirring time, pH of sample solutions and eluent concentration were studied. The distribution coefficient K_d, ml g^− 1 and the percentage concentration of the studied metal ions on the ion exchanger at equilibrium, C_M,_eqm ,% (Recovery, %) were studied as a function of experimental parameters. The logarithmic values of the distribution coefficients, log K_d are 3-6.3. The interfering effects of some foreign ions on the removal, preconcentration and determination of the investigated metal ions were described. The metal-chelates formed between the ion exchanger and the studied metal ions were characterized by IR (absorption and reflectance), UV spectrometry, potentiometric titration and thermal analysis (TG and DTG). The reliability of the present method was confirmed by the comparison with a standard solvent extraction method. The present method is simple and rapidly applicable for the determination of the studied metal ions, ng ml^− 1 in different natural water samples.     

Polarographic study of the system containing cadmium(II) and cobalt(II) and TTHA reagent

Polarographic study of the substitution reaction between cadmium(II) complex with Triethylenetetramine-N, N, N′, N″, N?, N?-hexaacetic acid (TTHA = H₆L) and cobalt(II) ion is described. According to the amperometric titration curves and polarograms, the existence of mixed binuclear complex and a new wave (Wave P appears above pH 4.5, ?0.8～?0.9 V. vs sce) involved in the reactions between two different metal ion (Cd(II) and Co(II) and TTHA was presented. The mixed complex [CdLCo]^2? then decomposed forming slowly the complex CdHL^3? and Co²⁺, as expressed by the reactions

and binuclear complexes were formed according to the reactions.

The logarithmic formation constant, K^Cd_CdLCo was calculated to be 8.10 using (1) and the known values of log K^H_CoHL = 8.12, log α_Cd(OAc) = 0.46 and log K′_CdLCo = 4.32 at pH 4.80.

The calculated value verified the proposal of mixed binuclear complex formation is low compared to log K^Cd_CdLNi = 9.2. The mixed complexes of TTHA reagents are stable species compared with binuclear type of EDTA complexes which exist only as reaction intermediates.The electrode reaction of wave P is proposed.

The species: CoL^4? obtained has a strong adsorption on the dropping mercury electrode.     

Mass transfer at horizontal gas-evolving electrodes

The effect of H₂ and O₂ evolution on the mass transfer coefficient of the reduction of K₃Fe(CN)₆ and the oxidation of K₄Fe(CN)₆ at nickel electrodes was studied up to 105 mA/cm². The relation between the rate gas evolution and the mass transfer coefficient was found to be: log K = a + 0·25 log V for a H₂-evolving horizontal electrode and log K = a + 0·4 log V for an O₂-evolving horizontal electrode.Comparison was made between mass transfer coefficients at horizontal and vertical gas-evolving electrodes. Mass transfer coefficients at horizontal electrodes are much higher than at vertical electrodes.     

Elution Behavior of Metal Ions with Mixed Glycine-Nitric Acid Eluents in Dowex 50W-X8 Column: Separation of Th(IV), Ce(IV), Bi(III), Fe(III), and Al(III)

Abstract

Distribution coefficients (K) determined by the batch technique in acidic glycine media using Dowex 50W-X8 cation exchanger (H⁺?form, 100–200 mesh size) revealed that this medium can effectively be employed to separate a number of tetravalent and trivalent metal ions from bivalent metal ions. In fixed glycine (0.40 M) and varying concentration of nitric acid (0.10 to 1.0 M), a number of mixtures containing two or three metal ions were resolved on columns using about 8 g of exchanger. In 0.40 M glycine-1.0 M HNO₃ medium, Th(IV)/Ce(IV) were separated from Al(III)/Fe(III)/Bi(III)/Co(II)/Ni(II)/Cu(II)/Zn(II)/Cd(II)/Hg(II)/Pb(II)/Ag(I) and also Al(III)/Bi(III) from a number of divalent metal ions. In 0.40 M glycine-0.50 M HNO₃ medium, the resolution of following ternary mixtures were also achieved: Th(IV)/Ce(IV)-Al(III)/Bi(III)-Fe(III)/Co(II)/Ni(II)/Cu(II)/Zn(II)/Cd(II)/Hg(II)/Pb(II)/Ag(I). Th(IV)/Al(III)/Fe(III)/Bi(III) were also separated from other divalent metal ions in 1.60 M glycine-0.50 M HNO₃ medium. The values of K, elution characteristics of metal ions, elution curves, and the results of the resolution of a number of mixtures of metal ions along with standard deviations are reported.     

Cinetique electrochimique du couple cobalt(III)—cobalt(II) en milieu acide phosphorique concentre

The electrochemical behaviour of the cobalt(III)—cobalt(II) couple in 96.5% and 85 wt% H₃PO₄ have been studied at a stationary gold electrode by using chronopotentiometry and triangular voltamperometry. The results have shown that the Co(III)—Co(II) system is reversible and the electrode reaction involves a single electron. The Co(II) ions' diffusion coefficient in the two phosphoric acid solutions was determined as 4.3 × 10⁻⁸ cm².s⁻ in 96.5% wt % H₃PO₄ and 1.2 × 10⁻⁷ cm².s⁻¹ in 85 wt % H₃PO₄. The stabillity of the Co(III) ion in 96.5 wt % H₃PO₄ media was also investigated.     

Potentiometric and polarographic studies of cadmium(II) complexes with tetraethylenepentamineheptaacetic acid

Stability constants for cadmium(II) complexes with tetraethylenepentamineheptaacetic acid (TPHA, H₇L) were determined by the pH titration method. In an aqueous solution (μ = 0.1), three complex species, CdH₂L, CdHL and CdL are confirmed. The structure of uninuclear complexes are discussed. The formation constants of the complexes stated above have been calculated as follows (at 25 ± 0.1°C): log K_CdL = 15.35, log K_CdHL = 13.33 and log K_CdH2L = 7.89. The polarographic behaviour of the cadmium(II) in the presence of TPHA was studied over the pH range 3–5. Mechanisms of the electrode processes were elucidated and electrochemical kinetic parameters were evaluated from dependence of the half-wave potentials on the hydrogen ion and TPHA concentration. In the presence of an excess of TPHA, the wave B is assigned to the irreversible reductions of the complex, CdH₂L^3? (pH range 3–4) or CdHL^4? (pH range 4–5). The electrode reaction can be written:

and

Where k_e (the rate constant) = 2.3 × 10^?2 cm s^?1 and k′_e = 1.59 × 10^?4 cm s^?1. The other polarographic methods were also used in the elucidation of the electrode process.     

Extraction of Mn(II) Ions from Sulphate Solution by 1-Phenyl- 3-Methyl-4-Butyryl-Pyrazolone-5: Influence of pH,Sulphate Concentration,and Additional Complexing Agents

The effect of sulphate ions in a buffered medium on the extraction of manganese(II) (Mn(II)) into 1-phenyl-3-methyl-4-butyryl-pyrazolone-5 (HBuP) in chloroform and benzene solutions has been studied. It showed that extraction at lower pH values is more favorable with solvents that have lower dielectric constants. It is also shown that an increase in sulphate ion concentration in the buffered medium leads to a decrease in Mn(II) extraction and a shift of the extraction process to higher pH values. Slight synergism occurred in the distribution of the metal ion into the benzene-butanol phase and data showed that pH_½ was further shifted to lower values on the addition of butanol into either of the organic phases studied. The slope analysis indicated that Mn(BuP)₂ species were extracted during all the extraction processes. The extraction patterns from solutions of mineral acids, salting out, and auxiliary complexing agents were reported. The pH_½, log K_D, and log K_ex of all the extraction systems were determined and used for explaining the various extraction processes observed.     

Adsorption of Cr(III), Ni(II), Zn(II), Co(II) ions onto phenolated wood resin

In this study, phenolated wood resin was used an adsorbent for the removal of Cr(III), Ni(II), Zn(II), Co(II) ions by adsorption from aqueous solution. The adsorption of metal ions from solution was carried at different contact times, concentrations and pHs at room temperature (25°C). For individual metal ion, the amount of metal ions adsorbed per unit weight of phenolated wood resin at equilibrium time increased with increasing concentration and pH. Also, when the amounts of metal ions adsorbed are compared to each other, it was seen that this increase was order of Cr(III) > Ni(II) > Zn(II) > Co(II). This increase was order of Cr(III) > Ni(II) > Co(II) > Zn(II) for commercial phenol–formaldehyde resin. Kinetic studies showed that the adsorption process obeyed the intraparticle diffusion model. It was also determined that adsorption isotherm followed Langmuir and Freundlich models. Adsorption isotherm obtained for commercial phenol–formaldehyde resin was consistent with Freundlich model well. Adsorption capacities from Langmuir isotherm for commercial phenol–formaldehyde resin were higher than those of phenolated wood resin, in the case of individual metal ions. Original adsorption isotherm demonstrated the monolayer coverage of the surface of phenolated wood resin. Adsorption kinetic followed the intraparticle diffusion model. The positive values of ΔG° determined using the equilibrium constants showed that the adsorption was not of spontaneous nature. It was seen that values of distribution coefficient (K_D) decreasing with metal ion concentration in solution at equilibrium (C_e) indicated that the occupation of active surface sites of adsorbent increased with metal ions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2838–2846, 2006     

SOLVENT EXTRACTION OF METALS WITH 4-DINITROBENZOYL-2, 4-DIHYDRO-5-METHYL-2-PHENYL-3H-PYRAZOL-3-ONE (DMPP)

ABSTRACT

The mechanism of the extraction of copper (II), nickel (II), cobalt (II) and thorium (IV) from aqueous buffer media with 4-dinitrobenzoyl1-2, 4-dihydro-5-methyl-2-phenyl-311-pyrazol-3-one (DMPP) in benzene has been investigated. The values of log K^*where K^*refers to the extraction equilibrium Mn⁺+-nHL ? MD_n+ nH⁺are Cu(II)& lpar; + 0.3), Co(II) (?6.65), Ni(II) (?5.04) and Th(IV) ( + 6.1). Solid complexes synthesized have the composition CuL₂· 2H₂O, NiL₂· 2H₂O and ThL₄respectively (L = anion of the ligand). DMPP seems to be superior to the corresponding 4-benzoyland 4-nitrobenzoyl derivatives of 2,4-dihydro-5-methyl-2-phenyl1-3 H-pyrazol1-3-one (MPP) and also better than thenoyltrifluoroacetone, the popularly employed fluorinated β-dike tone in the system investigated.     

Conductometric study of ion—ion and ion-solvent interaction—1. Conductances of lithium acetate in water,methanol and 50, 60 and 70% (W/W) dioxane—water mixtures at 25°C

Conductances of lithium acetate in water, methanol and 50, 60 and 70% (w/w) dioxane—water mixtures were measured. The data was analysed using the Fuoss-Hsia equation in the form of Fernandez—Prini coefficients to find the ion-pair formation constants (K_A) and molar conductances at infinite dilution. The log K_Avs 1/D plot is a straight line passing through the origin in agreement with the Dension—Ramsey theory. The Walden products, solvation numbers and solvodynamic radii were also calculated. The results indicate the formation of solvent separated ion-pairs (SSIP).     

Modification of Malonamide Ion-Exchange/Chelating Resins Using the Fields–Kabatschnik Reaction and Their Application to Metal Ion Removal from Aqueous Solutions

A resin containing 2-aminoethyl-substituted amides of malonic acid was modified in the Fields–Kabatschnik reaction using diethyl phosphite. The resultant ion-exchange/chelating resins have aminomethylphosphonate groups. Modification proceeds almost quantitatively, giving a resin with P=1.97 mmol/g, N=4.20 mmol/g, and water regain of 0.44 g/g. It can be selectively hydrolyzed by treatment with trimethylchlorosilane/potassium bromide in dry acetonitrile. Both acidic and ester forms of the resin were used in the removal of Cu(II), Cd(II), Ni(II), and Zn(II) from their diluted 1×10^–4 N solutions in 0.2 M acetate buffer at pH 3.7 and 5.6. The affinity of the resin in an acid form toward divalent metal cations is high, and at pH 5.6 the log K _d is 7.54, 3.97, 3.41, and 3.98, respectively. The resins are selective and the presence of an excess of sodium ions does not influence the uptake of metal ions. The type of complexes formed between the resins and Cu(II) ions was studied using EPR spectroscopy. The ester form of the resin was used in the removal of tetrachloroaurate anions from hydrochloric acid solution. It has been found that the log K _d is in the range of 3.14–3.94 for the uptake of AuCl^– ₄ from 5.0–0.5 M HCl solutions.     

Electrochemical study on the selective formation of [Pb(cyclodextrin)]surface inclusion complexes at the carbon paste electrode/ClO4 1 M interphase

The formation constants of surface inclusion complexes were determined using a carbon paste electrode, CPE, and cyclic voltammetry for aqueous-based media containing Pb(II) and α, β and γ cyclodextrins. In order to promote the occupation of the molecular cavities in the cyclodextrins, the medium with the support electrolyte contained ClO₄⁻ ions, which have the capacity to modify the hydrophobic properties of such cavities. The results obtained were: Pb(II)-α_CDK = 883.7 ± 13.6 M⁻¹, Pb(II)-β_CDK = 727.5 ± 20.2 M⁻¹, Pb(II)-γ_CDK = 782 ± 10.7 M⁻¹.     

Potential of the Pb,PbSO4/H2SO4 electrode at temperatures up to 240°C

Standard lead—lead sulphate electrode potential was determined over the temperature range 20–240°C from emf measurements of the Pb, PbSO₄H₂SO₄ (0.05M)K₂SO₄KClHCl(0.1M)/AgCl, Ag and Pb, PbSO₄H₂SO₄(m)K₂SO₄H₂SO₄(0.05M)PbSO₄, Pb cells where m = 0.005, 0.01, 0.1 and 0.5 M. To this effect lead—lead sulphate electrode potential was calculated using the temperature relationship of the standard silver—silver chloride electrode potential and activity coefficients of hydrochloric acid determined by Greeley et al. at temperatures up to 260°C. Diffusion potentials occurring at the phase boundaries in the cells under investigation were calculated using the Henderson's equation. Values of the standard lead—lead sulphate electrode potential were determined by extrapolation of the E°′ function to the zero ionic strength which was calculated using the second sulphuric acid dissociation constant determined by Lietzke et al. at temperatures up to 300°C. The standard electrode potential was described in the temperature range 20–240°C by the following relationship: E°_{Pb, PbSO4/SO^2?4}(V) = 0.040-0.00126T. A change in entropy ΔS° of the electrode reaction Pb + SO^2?₄ = PbSO₄ + 2e^? is constant in this temperature range and is ?243 JK^?1 mol^?1 (?1018 cal K^?1 mol^?1).     

Evaluation of sorption behavior of polymethylene-bis(2-hydroxybenzaldehyde) for Cu(II), Ni(II), Fe(III), Co(II) and Cd(II) ions

Poly[5,5??-methylene-bis(2-hydroxybenzaldehyde)1,2-phenylenediimine] resin was prepared and characterized by employing elemental, thermal analysis, FTIR, and UV?Cvisible spectroscopy. The metal uptake behavior of synthesized polymer towards Cu(II), Co(II), Ni(II), Fe(III) and Cd(II) ions was investigated and optimized with respect to pH, shaking speed, and equilibration time. The sorption data of all these metal ions followed Langmuir, Freundlich, and Dubinin?CRadushkevich isotherms. The Freundlich parameters were computed 1/n?=?0.31?±?0.02, 0.3091?±?0.02, 0.3201?±?0.05, 0.368?±?0.04, and 0.23?±?0.01, A?=?3.4?±?0.03, 4.31?±?0.02, 4.683?±?0.01, 5.43?±?0.03, and 2.8?±?0.05?mmol?g^?1 for Cu(II), Co(II), Ni(II), Fe(III), and Cd(II) ions, respectively. The variation of sorption with temperature gives thermodynamic quantity (??H) in the range of 36.72?C53.21?kJ/mol. Using kinetic equations (Morris?CWeber and Lagergren equations), values of intraparticle transport and the first-order rate constant was computed for all the five metals ions. The sorption procedure is utilized to preconcentrate these ions prior to their determination by atomic absorption spectrometer. It was found that the adsorption capacity values for metal-ion intake followed the following order: Cd(II)?>?Co(II)?>?Fe(III)?>?Ni(II)?>?Cu(II).     

Poly(o-aminophenol) film prepared in the presence of sodium dodecyl sulfate: Application for nickel ion dispersion and the electrocatalytic oxidation of methanol and ethylene glycol

Poly(o-aminophenol) (POAP) was formed by successive cyclic voltammetry in monomer solution in the presence of sodium dodecyl sulfate (SDS) on the surface of a carbon paste electrode. The electrochemical behavior of the SDS-POAP carbon paste electrode has been investigated by cyclic voltammetry in 0.5 M HClO₄ and 5 mM K₄[Fe(CN)₆]/0.1 M KCl solutions as the supporting electrolyte and model system, respectively. Ni(II) ions were incorporated into the electrode by immersion of the polymeric modified electrode having amine groups in 0.1 M Ni(II) ion solution. Cyclic voltammetric and chronoamperometric experiments were used for the electrochemical study of this modified electrode. A good redox behavior of the Ni(III)/Ni(II) couple at the surface of electrode can be observed. The electrocatalytic oxidations of methanol and ethylene glycol (EG) at the surface of the Ni/SDS-POAP electrode were studied in a 0.1 M NaOH solution. Compared to bare carbon paste and POAP-modified carbon paste electrodes, the SDS-POAP electrode significantly enhanced the catalytic efficiency of Ni ions for methanol oxidation. Finally, using a chronoamperometric method, the catalytic rate constants (k) for methanol and ethylene glycol were found to be 2.04 × 10⁵ and 1.05 × 10⁷ cm³ mol⁻¹ s⁻¹, respectively.     

Synthese und Eigenschaften neuartiger Alkalimetall-Alkoxo- und -Aroxocobaltate(II)

Synthesis and Properties of Novel Alkali Metal Alkoxo- and Aroxocobaltates(II) . By reaction of CoBr₂ or CoBr₂ · 2THF with 4–5 moles of MOR in THF, M  Li, Na, K, R = iso-propyl (iPr), phenyl (Ph), 2-naphthyl (2-Naph), the following novel alkali metal alkoxo- and aroxocobaltates(II) have been prepared. Li₂Co(OiPr)₄ · LiBr · 3THF ( 1 ), Na₂Co(OiPr)₄ · THF ( 2 ), KCo(OiPr)₃ · THF ( 3 ), Li₂Co(OPh)₄ · 4THF ( 4 ), Na₂Co(OPh)₄ · 5THF ( 5 ), K₂Co(OPh)₄·0,75THF ( 6 ), Li₂Co(O-2-Naph)₄ · 4THF ( 7 ), Na₂Co(O-2-Naph)₄ · 5THF ( 8 ), K₂Co(O-2-Naph)₄ · 2THF ( 9 ), and K₃Co(O-2-Naph)₅ · 2THF ( 10 ). The blue and violet, crystalline and very air-sensitive (i.e. protolytically sensitive) compounds, some with good solubilities in organic solvents, eliminate THF in vacuo at temperatures between 50 and 100°C to yield the corresponding THF-free compounds ( 1a ) to ( 10a ). Electronic spectra (VIS/NIR) and the results of magnetic measurements at 293 K point to preferred (but not exclusive) tetrahedral coordination of cobalt(II).