Characterisation of nickel(II) extraction by 2-hydroxy-5-nonylacetophenone oxime (LIX 84) in a micellar phase

The properties of the nickel(II)/2-hydroxy-5-nonylacetophenone oxime (HNAPO), an active ingredient in LIX 84, extraction system were characterised in a micellar system. The extinction coefficient, λ_max of HNAPO (316 nm) and the Ni²⁺ complex (387 nm) in a neutral micellar system, poly dispersed octa-ethyleneglycol mono-n-dodecyl ether (G₁₂A₈) were determined as 3100 and 3500 M⁻¹ cm⁻¹, respectively. HNAPO was found to have a neutral micellar phase and bulk aqueous phase pK_a of 11.5 and 12.5, respectively. The extraction equilibrium constant, K_ex, was determined to be 10^−8.0, and the deviation from theory observed at high pH can be accounted for by consideration of the competition for nickel(II) ions by hydroxide ions and HNAPO. A micellar phase of octa-ethyleneglycol mono-n-dodecyl ether (C₁₂E₈) was determined to be an appropriate model of the free oil/water interface from the solubilised location of HNAPO. Utilising the interfacial probe, 4-heptadecyl-7-hydroxy coumarin (HHC) allowed the determination of the electrostatic surface potential of mixed micelles of G₁₂A₈ and sodium dodecyl sulphate (SDS) or dodecyl trimethyl ammonium chloride (DTAC). The electrostatic surface potential was a linear function of the number of additional surfactant monomers within the G₁₂A₈ micelle, for the concentration range studied. For G₁₂A₈/DTAC mixed micelles, the surface potential was given by +1.1 mV per DTAC molecule per micelle, and for G₁₂A₈/SDS mixed micelles the relationship was −1.4 mV per SDS molecule per micelle.

Thermodynamics and kinetics of the formation of Al2 O3/ MgAl2O4/MgO in Al-Silica metal matrix composite

The formation of Al₂O₃, MgAl₂O₄, and MgO has been widely studied in different Al base metal matrix composites, but the studies on thermodynamic aspects of the Al₂O₃/ MgAl₂O₄/MgO phase equilibria have been limited to few systems such as Al/Al₂O₃ and Al/SiC. The present study analyzes the Al₂O₃/MgAl₂O₄ and MgAl₂O₄/MgO equilibria with respect to the temperature and the Mg content in Al/SiO2 system using an extended Miedema model. There is a linear and parabolic variation in Mg with respect to the temperature for MgAl₂O₄/MgO and Al₂O₃/MgAl₂O₄ equilibria, respectively, and the influence of Si and Cu in the two equilibria is not appreciable. The experimental verification has been limited to MgAl₂O₄/MgO equilibria due to the high Mg content (≥0.5 wt pct) required for composite processing. The study has been carried out on two varieties of Al/SiO₂ composites, i.e., Al/Silica gel and Al/Micro silica processed by liquid metallurgy route (stir casting route). MgO is found to be more stable compared to MgAl₂O₄ at Mg levels ≥5 and 1 wt pct in Al/Silica gel and Al/Micro silica composites, respectively, at 1073 K. MgO is also found to be more stable at lower Mg content (3 wt pct) in Al/Silica gel composite with decreasing particle size of silica gel from 180 micron to submicron and nanolevels. The MgO to MgAl₂O₄ transformation has taken place through a series of transition phases influenced by the different thermodynamic and kinetic parameters such as holding temperature, Mg concentration in the alloy, holding time, and silica particle size.

Liquid phase adsorption kinetics and equilibrium of toluene by novel modified-diatomite

The adsorption equilibria of toluene from aqueous solutions on natural and modified diatomite were examined at different operation parameters such as pH, contact time, initial toluene concentration was evaluated and optimum experimental conditions were identified. The surface area and morphology of the nanoparticles were characterized by SEM, BET, XRD, FTIR and EDX analysis. It was found that in order to obtain the highest possible removal of toluene, the experiments can be carried out at pH 6, temperature 25°C, an agitation speed of 200 rpm, an initial toluene concentration of 150 mg/L, a centrifugal rate of 4000 rpm, adsorbent dosage = 0.1 g and a process time of 90 min. The results of this work show that the maximum percentage removal of toluene from aqueous solution in the optimum conditions for NONMD was 96.91% (145.36 mg/g). Furthermore, under same conditions, the maximum adsorption of natural diatomite was 71.45% (107.18 mg/g). Both adsorption kinetic and isotherm experiments were carried out. The experimental data showed that the adsorption follows the Langmuir model and Freundlich model on natural and modified diatomite respectively. The kinetics results were found to conform well to pseudo-second order kinetics model with good correlation. Thus, this study demonstrated that the modified diatomite could be used as potential adsorbent for removal of toluene from aqueous solution.