Ionization equilibria of nickel(II) bromide in acetonitrile solutions

Uv and visible absorption spectra and the molar conductance curve of NiBr₂ in acetonitrile solution have been determined at 25°C. Equilibrium concentrations and formation constants of the consecutive NiBr⁺, NiBr⁰₂, and NiBr^?₃, complexes have been calculated from the spectrophotometric results making use of the isosbestic points found in an auxiliary study of three-component solutions with variable Br^?:Ni(II) mole ratio. The existence of NiBr⁺ in the form of the [NiBrL₅]⁺ pseudooctahedral complex, and that of NiBr^?₃ in the form of the [NiBr₃L]^? pseudotetrahedral complex is inferred, while the nature of NiBr⁰₂ remains unclear.     

Ionization equilibria in solution of nickel(II) chloride in N,N-dimethylformamide

Visible absorption spectra and the molar conductance curve at NiCl₂ dissolved in dimethylformamide (DMF) have been determined at 25°C. Absorption spectra of ternary system Ni(ClO₄)₂ + Et₄NCl + DMF and NiCl₂ + chlorobenzene + DMF have also been determined at 25°C. It has been found that at lower concentrations of NiCl₂ monochloride nickel complex NiCl(DMF)⁺₅ and outer-sphere ion-pair {NiCl(DMF)⁺₅Cl⁻}⁰ coexist in the solution. The presence of pseudotetrahedral complex NiCl₃DMF⁻ and the existence of coordinative disproportionation equilibrium have been established in the more concentrated solutions of NiCl₂. The formation constant of outer-sphere ion-pair equal to (1.33 ± 0.2) × 10² has been derived from the conductometric data. The equilibrium constant of disproportionation reaction equal to (3.89 ± 0.2) × 10² has been determined on the basis of the absorption spectra of NiCl₂ in DMF.     

Ionization equilibria of copper(II) chloride in dimethyl sulphoxide

Visible absorption spectra of the CuCl⁺ and CuCl⁰₂ complexes in dimethyl sulphoxide (DMSO) are derived from an auxiliary study of the Cu(ClO₄)₂ + Et₄NCl mixed solutions of variable chloride concentration. The second step association equilibrium CuCl⁺ + Cl^? ? CuCl⁰₂ is then shown, from the visible absorption spectra, to predominate over a broad concentration range in the solutions of CuCl₂ in DMSO. Accordingly, the second step association constant is derived from the molar conductivity curve of CuCl₂ using the Shedlovsky's method, while the first step association constant is estimated from the conductometric data of the most dilute solutions: K⁰₁ = (16.5 ± 1.5)10⁴, K⁰₂ = (8 ± 0.2)10² at 25°C. The results are compared with those earlier obtained for NiCl₂ and CoCl₂ in DMSO solution, non-conformation of the association constants to the Irving-Williams series being pointed out.     

Ionization equilibria of cobalt (II) chloride in dimethyl sulphoxide

Visible absorption spectra and the molar conductance curve for CoCl₂ in dimethyl sulphoxide (DMSO) have been determined and are analyzed in terms of the nature of ionization equilibria set up in the respective solutions. Auxiliary absorption spectra determinations of the CoCl₂ + Et₄NCl and Co (ClO₄)₂ +Et₄NCl mixed solutions indicate consecutive formation of the CoCl(DMSO)⁺₅, CoCl₃DMSO^t-, and CoCl^2t-₄ complex ions, in addition to the Co(DMSO)²⁺₆ parent cation. Coordinative disproportionation producing the CoCl₃DMSO^t- complex anion is shown to predominate in the more concentrated solution of CoCl₂ in DMSO. Consecutive stability constants of the chloro-complexes of cobalt(II) are derived.     

Ionization equilibria in solutions of cobalt(II) bromide in N,N-dimethylformamide

Visible absorption spectra and the molar conductance curve of CoBr₂ dissolved in N,N-dimethylformamide (DMF) have been determined at 25°C. Absorption spectra of ternary systems Co(ClO₄)₂ + Et₄NBr + DMF and CoBr₂ + chlorobenzene + DMF have also been determined at 25°C. The results indicate the formation of the CoBr(DMF)⁺₅. CoBr₃DMF⁻ complex electrolyte controlling the electrolytic properties of the solution. The stability constants of the individual bromo-complexes of cobalt(II) have been calculated.     

Outer-sphere association of ions in DMSO solutions of nickel(II) salts

The visible absorption spectra and the molar conductance curves of solutions of NiI₂, NiBr₂, Ni(BF₄)₂, Ni(ClO₄)₂ and Ni(CF₃COO)₂ DMSO at 25°C have been determined. The results indicate a weak association which is only of the outer-sphere type, in each case involving the Ni(DMSO)^{2 +}₆ complex. The conductance data are analysed using the Lee-Wheaton conductance equation for unsymmetrical electrolytes. The first-step association constants (K₁) and the limiting ionic conductances, λ₀, for the Ni(DMSO)^{2 +}₆ cation as well as for the BF^?₄ and CF₃COO^? anions are obtained. A linear relation between log K₁ and the reciprocal of the anionic radius is observed. On the basis of this relation, the relative contribution of the outer-sphere association for solutions of NiCl₂ in DMSO is estimated.     

Dissolution of nickel (74%)-copper (4%)-sulphide matte anode in acidic chloride solutions

A comparative study was conducted to assess the performance of 1 N solutions of hydrochloric acid, ferrous chloride and ferric chloride solutions to dissolve the 74% Ni-4% Cu-20% S nickel sulphide matte anodes. The essential variables considered here were: temperature (25° and 75° C), oxygen and controlled potential. The relative aggressiveness as estimated by the potentiokinetic polarization curves and dissolution experiments with open circuit can be arranged in the following sequence: Fe³⁺>Fe²⁺>H⁺. At +400 mV versus SCE, the aggressiveness reversed in the following sequence: H⁺>Fe²⁺>Fe³⁺. The experimental values of dissolution rates with open circuit and at constant potential were higher than those calculated from the dissolution current densities (potentiokinetic polarization curves), and from the amount of charge passed (at +400 mV versus SCE).Attack by intergranular dissolution and pitting was observed throughout these experiments. The formation of -NiS by the reaction Ni₃S₂ Ni²⁺+2-NiS+ 2e was confirmed by X-ray analysis. The above results are interpreted in the light of the possible electrochemical mechanisms.     

Electrodissolution of nickel sulphide concentrates in ferrous chloride solutions

A 3 M ferrous chloride solution of pH 1.5 and operated at 72° C was found suitable to electro-oxidize nickel sulphide concentrates containing the following constituents in wt.%: nickel 20, iron 8, magnesium 10, silicon 8, sulphur 11 and copper 0.83.The percentages of dissolution for 16 A h at current passed (current density 20–120 mAcm^–2 with respect to graphite) were in the ranges: Ni 90–70; Cu 70–50 and Mg 20–15. The changes in mol % of the final (mainly elemental) sulphur to initial sulphide-sulphur were in the range of 50 to 25. On the other hand the mole ratio of initial to final iron decreases, and this relates to the precipitation of hydroxides. Corresponding to these changes, the X-ray diffraction patterns detected the presence of elemental sulphur and hydrated oxides of iron and magnesium. The anolyte pH and electrode potential were followed during the electro-oxidation experiments.Experiments were carried out to establish the feasibility of separating copper from nickel chloride-copper chloride mixtures at 75° C. It was possible to separate copper whose concentration was 5 gl^–1 or above while that of nickel was 75 gl^–1. The cathodic polarization curves for copper, nickel and hydrogen discharge from their individual and binary mixtures were used to predict the conditions required to avoid copper-nickel alloy deposition, and the efficiencies of deposition.     

Influence of tetraalkylammonium cations on the electroreduction of nickel(II) in thiocyanate solutions

Influence of tetrabutyl-, tetrapentyl- and tetraisopentylammonium ions on the reduction of nickel(II) in thiocyanate solutions at the dropping mercury electrode has been investigated. These tetraalkylammonium ions, at their low concentrations, inhibit the reduction of nickel(II). However, at their high concentrations, the strong inhibiting effect disappers with the formation of a new wave corresponding to the reduction of a negatively charged nickel(II) thiocyanate complex, which is stabilized by the formation of ion pair with tetraalkylammonium cation. The variation of the reduction current with tetraalkalylammonium concentration was explained by taking into consideration both the change of the total charge of nickel(II) thocyanate complex involved in the reduction process and the simultaneous adsorption of tetraalkylammonium and thiocyanate ions on the mercury electrode.     

Phase equilibria in quasi-binary poly(α-methylstyrene) solutions

Upper (UCST) and lower (LCST) critical solution temperatures have been measured for poly(α-methyl styrene) in four solvents. The extent of solvent—polymer interaction was found to be reflected in the miscibility range exhibited by these systems. The data could be described by theoretical curves derived using the Patterson—Delmas theory, if an arbitrary selection of the reference temperature was made for each quasi-binary system. Curves showing the relative contributions of the cohesive energy and free volume contribution to the polymer—solvent interaction parameter were also derived from this theory; these illustrated that while the free volume factors predominated at the LCST, the cohesive energy contribution could still play a significant role.     

Selective transport of cobalt (II) from ammoniacal solutions containing cobalt (II) and nickel (II) by emulsion liquid membranes using 8-hydroxyquinoline

The selective transport of cobalt (II) from ammoniacal solutions containing nickel (II) and cobalt (II) by emulsion liquid membranes (ELMs) using 8-hydroxyquinoline (8-HQ) as extractant has been presented. Membrane solution consists of a diluent (kerosene), a surfactant (ECA 4360J), and an extractant (8-HQ). Very dilute sulphuric solution buffered at pH 5.0 has been used as a stripping solution. The ammoniacal feed solution pH was adjusted to 9.0 with hydrochloric acid. The important variables governing the permeation of cobalt (II) have been studied. These variables are membrane composition, pH of the feed solution, cobalt (II) and nickel (II) concentrations of the feed solution, stirring speed, surfactant concentration, extractant concentration, complexing agent concentration and pH of the stripping solution, and phase ratio. After the optimum conditions had been determined, it was possible to selectively transport 95.0% of cobalt (II) from ammoniacal feed solution containing Co²⁺ and Ni²⁺ ions. The separation factors of cobalt (II) with respect to nickel (II), based on initial feed concentration, have experimentally found to be of as high as 31 for equimolar Co(II)–Ni(II) feed solution.     

A modified cellulose adsorbent for the removal of nickel(II) from aqueous solutions

A series of adsorption studies was carried out on a glycidyl methacrylate‐ modified cellulose material functionalised with imidazole (Cellulose‐g‐GMA‐Imidazole) to assess its capacity in the removal of Ni(II) ions from aqueous solution. The study sought to establish the effect of a number of parameters on the removal of Ni(II) from solution by the Cellulose‐g‐GMA‐Imidazole. In particular, the influence of initial metal concentration, contact time, solution temperature and pH were assessed. The studies indicated a Ni(II) uptake on the Cellulose‐g‐GMA‐Imidazole sorbent of approximately 48 mg g^?1 of nickel from aqueous solution. The adsorption process fitted the Langmuir model of adsorption and the binding process was mildly endothermic. The kinetics of the adsorption process indicated that nickel uptake occurred within 400 min and that pseudo‐second order kinetics best describe the overall adsorption process. Nickel(II) adsorption, recovery and re‐adsorption studies indicated that at highly acidic pH values the adsorbent material becomes unstable, but in the range pH 3–6, the adsorbent is stable and shows limited but significant Ni(II) recovery and re‐adsorption capability. Copyright © 2006 Society of Chemical Industry     

Enhanced removal of nickel(II) ions from aqueous solutions by SDS-functionalized graphene oxide

In this paper, a one-pot and easy-to-handle method at room temperature without additional chemicals for the modification of graphene oxide (GO) with surfactant is found. Removal of nickel (II) ions from aqueous solutions by GO and surfactant (sodium dodecyl sulphate) modified graphene oxide (SDS-GO) was studied spectrophotometrically at room temperature as a function of time, initial concentration and pH. Adsorption capacity of the adsorbent was increased dramatically (from 20.19 to 55.16 mg/g found by Langmuir model) due to the functionalization of the surface by SDS. The driving force of the adsorption of Ni(II) ions is electrostatic attraction and Ni(II) ions adsorbed on the GO surface chemically besides ion exchange.     

Adsorption of Hg(II) ions from aqueous chloride solutions using powdered activated carbons

Activated carbons were developed from Casurina equisetifolia leaves, by chemically treating with sulfuric acid (1:1) or zinc chloride (25%), at low (425 °C) and high (825 °C) temperatures. The resulting powdered activated carbons were applied for removing mercuric ions from aqueous solution at different agitation times and mercuric ion concentrations. The equilibrium data fitted well the Langmuir adsorption isotherm. The Langmuir adsorption capacities were 12.3 and 20.3 mg g⁻¹ for low temperature carbons and 43.9 and 38.5 mg g⁻¹ for high temperature carbons impregnated with H₂SO₄ and ZnCl₂, respectively. Studies of the effects of carbon dosage, NaCl concentrations and solution pH values were carried out for the more effective, high temperature carbons. Increasing NaCl concentration resulted in a significant decrease in the adsorption efficiency. Adsorption was high from solutions with low and neutral pH values and lower for solutions with alkaline pH values for the high temperature carbons.     

Polymerization of butadiene in toluene with nickel(II) stearate–diethyl aluminum chloride catalyst. II. Kinetic study

Based on the polymerization data presented in part I of this series, a kinetic mechanism for the polymerization of butadiene in toluene initiated with nickel(II) stearate–diethyl aluminum chloride was proposed. Expressions for the conversion, the degree of polymerization, and the cis content were derived. Those models were then used to correlate the experimental data from which the rate constants were estimated. A quantitative discussion of various aspects of the polymerization is also presented.     

Polymerization of butadiene in toluene with nickel (II) stearate-diethyl aluminum chloride catalyst. I. Catalytic behaviors

The polymerization of butadiene with nickel (II) stearate–Et₂AlCl catalyst has been studied in a batch reactor. The rate of polymerization is first order with respect to monomer and increases with the addition of water. In this system, no appreciable termination reaction has been found and the chain transfer to monomer dictates the molecular weight distribution of the polymer products. Molecular weight increases with conversion and water content. The cis-1,4 content was found to be a function of the extent of polymerization.     

Removal of nickel(II) from aqueous solutions using iminodiacetic acid functionalized polyglycidyl methacrylate grafted-carbon fibers☆

Iminodiacetic acid functionalized polyglycidyl methacrylate grafted-carbon fibers (PGMA-IDA/CFs) were prepared for Ni(II) removal from aqueous solutions. The effects of solution pH value, temperature and adsorption time were investigated. The maximum adsorption capacity of Ni(II) on PGMA-IDA/CFs is 0.923 mmol·L?1 · g?1 at pH 5.2 and 50 °C. Kinetic data indicate that the adsorption process matches the pseudo-second-order model and Elovich kinetic model. Thermodynamic data suggest that the adsorption process is endothermic spontaneous reaction.     

Electrode reactions of nickel(II) at mercury electrodes in aqueous solutions of pyridine at high ionic strengths

At high ionic strength the ion pair (NiPy²⁺₄, nX^?) or complex (NiPy₄X₂), n = 0, 1, 2; X^? = Cl^?, Br^?, SCN^?, N^?₃, F^?, NO^?₃, ClO^?₄; is adsorbed at the surface of mercury electrode. Under specified conditions in chloride, bromide, and thiocyanates solutions the electroreduction is preceded by a crystallization of a complex on the electrode surface. The inductive role of specifically coadsorbed Cl^? ions is discussed.