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Adsorption: Journal of the International Adsorption Society (v.13, #2)
Development and optimization of magnetic technologies based processes for removal of some toxic heavy metals by E. H. Borai; E. A. El-Sofany; T. N. Morcos (pp. 95-104).
In the developing countries where the cost is often a decisive factor, extensive studies were undertaken to test the most effective factors on the preparation, optimization and validation of the magnetic particles (or, more accurately, magnetizable particles) for removal of heavy metals from wastewaters. The objective of the proposed work was focused to provide promising solid-phase materials, which, are relatively in expensive and combine high surface capacity with fast efficient treatment. Four various metal oxides including hydrous ferric oxide (HFO), hydrous stannic oxide (HSO) and mixed ferric/stannic oxide (HMO), were prepared by precipitation with ammonia from metal chloride solutions. Two mixed oxides were prepared with different Sn/Fe ratios of 50% and 20%. Optimal conditions for the activation of these particles and the subsequent mixing of various metals oxides are tested together with the utility of the method to get a new composite material with developed chemical characteristics over their individual metal oxides. Factors affecting the sorption behavior of the prepared samples in basic and acid media were elucidated. The magnetic treatment procedure using the mixed oxide (50%) enables the equilibration step to be carried out rapidly mainly due to ferric oxide during the magnetization process and efficiently due to high capacity of the stannic oxide. A key factor in achieving very high uptake percentage is the reduction of non-specific binding of various heavy metals to the solid phase support. This is usually achieved by increasing the ion exchange capability, in addition to their adsorption process.
Keywords: Heavy metals; Magnetic technology; Composite oxide
Can alkane isomers be separated? Adsorption equilibrium and kinetic data for hexane isomers and their binary mixtures on MFI by Alexandre F. P. Ferreira; Marjo C. Mittelmeijer-Hazeleger; Alfred Bliek (pp. 105-114).
In this study we present a global overview of the adsorption behavior of hexane isomers on MFI. With an experimental approach that couples a manometric technique with Near Infrared (NIR) spectroscopy, which has been recently developed, we did address adsorption kinetic properties of n-hexane, 2-methylpentane, 2,2-dimethylbutane and 2,3-dimethylbutane, and their binary mixtures. The adsorption equilibrium properties of the binary mixtures were also assessed using the same technique. Whereas the adsorption isotherms and heats of adsorption for single components have been studied by a manometric technique coupled with a micro calorimeter. The differential heats of adsorption of n-hexane increase slightly with loading, on the other hand the heat of adsorption of branched hexanes exhibits a decrease with loading. The diffusion rates on MFI of n-hexane, 2-methylpentane and 2,3-dimethylbutane are in the same order of magnitude. However, the diffusion rate of 2,2-dimethylbutane is two orders of magnitude lower than rates of the other isomers. In the binary mixtures the components interact and the difference between the diffusion rates of the components decreases. The MFI zeolite presents equilibrium selectivity towards the less branched isomers. In conclusion, a separation process for linear/mono-branched alkanes + double-branched alkanes, has to be based on its equilibrium properties and not based on adsorption kinetics.
Keywords: Zeolites; Alkanes; Isotherms; Differential heat of adsorption
Moisture diffusion into epoxy adhesive: testing and modeling by Mamdouh Al-Harthi; Kevin Loughlin; Ramazan Kahraman (pp. 115-120).
Moisture diffusion into epoxy adhesive is investigated through utilizing complete fluid immersion tests in distilled water. Apparent diffusivity for each specimen is determined by two methods, one using the diffusion data at early times (at low loading) and the other using the data at large times (close to the saturation point). The results of the two methods are quite different, indicating that diffusivity is concentration dependent. The apparent diffusivity values obtained through the method using the early data points are about twice those obtained through the method utilizing the data points at large diffusion times. Variance of diffusivity with concentration is also considered as the third method of analysis to determine the concentration dependency. A good agreement is observed between the resultant Fickian model solved numerically and the experimental data. The latter result appears to indicate a change in the excess volume of mixing during the sorption process.
Keywords: Adhesive; Epoxy; Diffusion; Diffusivity; Distilled water; Concentration; Model; Test
Sorption equilibrium of methanol on new composite sorbents “CaCl2/silica gel” by Yuri I. Aristov; Larissa G. Gordeeva; Yuri D. Pankratiev; Ludmila M. Plyasova; I. V. Bikova; Angelo Freni; Giovanni Restuccia (pp. 121-127).
This paper presents experimental data on methanol sorption on new composite sorbents which consist of mesoporous silica gels and calcium chloride confined to their pores. Sorption isobars and XRD analysis showed the formation of a solid crystalline solvate CaCl2⋅2MeOH at low methanol uptake, while at higher uptake the formation of the CaCl2–methanol solution occurred. The solution confined to the silica pores showed the sorption properties similar to those of the CaCl2–methanol bulk solution. Calorimetric and isosteric analyses showed that the heat of methanol sorption depends on the methanol uptake, ranging from 38±2 kJ/mol for the solution to 81±4 kJ/mol for the solid crystalline phase CaCl2⋅2MeOH. The above mentioned characterizations allowed the evaluation of the methanol sorption and the energy storage capacities, clearly showing that the optimal applications of these new composite sorbents are the methanol removal from gaseous mixtures, heat storage and sorption cooling driven by low temperature heat.
Keywords: Sorption; Methanol; Silica gel; Confined calcium chloride; Heat storage
Adsorption of phenol by oil-palm-shell activated carbons by Aik Chong Lua; Qipeng Jia (pp. 129-137).
Steam activated carbons from oil-palm shells were prepared and used in the adsorption of phenol. The activated carbon had a well-developed mesopore structure which accounted for 45% of the total pore volume. The BET surface area of the activated carbon was 1183 m2/g and a total pore volume of 0.69 cm3/g using N2 adsorption at 77 K. The adsorption capacity of the activated carbon for phenol was 319 mg/g of adsorbent at 298 K. The adsorption isotherms could be described by both the Langmuir-Freundlich and the Langmuir equations. The adsorption kinetics consisted of a rapid initial uptake phase, followed by a slow approach to equilibrium. A new multipore model is proposed that takes into account of a concentration dependent surface diffusion coefficient within the particle. This model is an improvement to the traditional branched pore model. The theoretical concentration versus time curve generated by the proposed model fitted the experimental data for phenol adsorption reasonably well. Phenol adsorption tests were also carried out on a commercial activated carbon known as Calgon OLC Plus 12×30 and the agreement between these adsorption data and the proposed model was equally good.
Keywords: Activated carbon; Oil-palm shell; Phenol adsorption; Kinetic model; Surface diffusion
The effect of burn-off on the adsorption of N2 and Ar on a natural graphite by Kazuhisa Miura; Hiroshi Yanazawa; Kazuyuki Nakai (pp. 139-147).
Adsorption-desorption isotherms of N2 and Ar were measured at 77 K using samples of graphite that were partially burned off at 600 °C in O2 gas saturated with water vapor at 25 °C. The amounts of adsorbed N2 and Ar dropped drastically as the degree of burn-off increased. The isotherms all showed a steep rise, or step, in the amounts of adsorbed N2 and Ar at a relative pressure of around 0.4. Moreover, the hysteresis was much narrower after burn-off than before. These anomalies can be explained by the presence of functional groups on the graphite that produce H2O and CO2 upon decomposition and in terms of pores on the surface of the graphite.
Keywords: Natural graphite; Adsorption; Burn-off; Porosity
Adsorption study of an industrial dye by an organic clay by A. Khenifi; Z. Bouberka; F. Sekrane; M. Kameche; Z. Derriche (pp. 149-158).
In this study, the adsorption of an industrial dye Supranol Yellow 4GL onto Cetyltrimethylammonium-bentonite (CTAB-bentonite) is investigated. The organobentonite is synthesised by exchanging cetyltrimethylammonium cations (CTAB) with inorganic ions on the surface of bentonite. The adsorption of Supranol Yellow 4GL onto organobentonite is found to be maximum when the concentration of CTAB exchanged is 100% according to the cation exchange capacity of the clay (CEC). The modification of organobentonite is examined using XRD and FTIR techniques. The effect of the process parameters such as: contact time, adsorbate concentration, adsorbent dose, pH and temperature are reported. Nearly 1200 seconds of contact time are found to be sufficient for the adsorption to reach equilibrium. The pseudo second order model is used to describe the kinetic data, and the rate constant is therefore evaluated. The dye adsorption to organobentonite is characterized by monolayer isotherm and caused by adsorption with relatively strong uptake. The Langmuir and Freundlich models adsorption are applied to describe the isotherm equilibrium and to determine its constants. The Langmuir and Freundlich models agree well with the experimental data with a adsorption capacity of 0.5 g of dye per g of organobentonite. A better fixation was obtained at acidic pH. The effect of temperature on the adsorption of dye has been also studied and the thermodynamic parameters ΔH, ΔS, ΔG, were determined. Organobentonite is found to be effective for removing Supranol Yellow 4GL dye from wastewater.
Keywords: Adsorption; Supranol Yellow 4GL; Bentonite; CTAB; Langmuir
Competitive adsorption and desorption of a bi-solute mixture: effect of activated carbon type by Özgür Aktaş; Ferhan Çeçen (pp. 159-169).
This study aims to clarify the effects of carbon activation type and physical form on the extent of adsorption capacity and desorption capacity of a bi-solute mixture of phenol and 2-chlorophenol (2-CP). For this purpose, two different PACs; thermally activated Norit SA4 and chemically activated Norit CA1, and their granular countertypes with similar physical characteristics, thermally activated Norit PKDA and chemically activated Norit CAgran, were used. The thermally activated carbons were better adsorbers for phenol and 2-CP compared with chemically activated carbons, but adsorption was more reversible in the latter case. 2-CP was adsorbed preferentially by each type of activated carbon, but adsorption of phenol was strongly suppressed in the presence of 2-CP. The simplified ideal adsorbed solution (SIAS) model underestimated the 2-CP loadings and overestimated the phenol loadings. However, the improved and modified forms of the SIAS model could better predict the competitive adsorption. The type of carbon activation was decisive in the application of these models. For each activated carbon type, phenol was desorbed more readily in the bi-solute case, but desorption of 2-CP was less compared with single-solute. This was attributed to higher energies of 2-CP adsorption.
Keywords: Activated carbon; Activation method; 2-chlorophenol; Competitive adsorption; Desorption; Irreversible adsorption; Phenol; SIAS model