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adsorbate–adsorbent interactions [ 19 ]. They can also permit distinction between the amounts adsorbed into the outer surface and that fixed between macromolecular chains. Analysis of adsorption isotherms by different mathematical models were also developed

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Introduction Adsorption isotherms and differential enthalpies of adsorption at high pressure and temperature are useful in many fields of applications like technological aspects in the petroleum engineering with the problematic

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In describing multi-layer adsorption it is common to use standard isotherms. To establish such isotherms experimental data are required at a wide range of adsorptive pressure. This paper presents the theoretical and experimental analysis of the new t δ-method, which is suitable to predict type II multi-layer adsorption isotherms on the basis of only two adsorption values, measured in the area of mono- and multi-layer saturation and of the surface fractal dimension of the adsorbent.

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The adsorption of phenol and ten substituted phenols on activated carbon was examined. For a comparative study, the substituted phenols were selected after nature, position, and number of functional groups; they, are: o-,m-,p-cresol, o-,m-,p-chlorphenol, m-,p-nitrophenol, resorcine, and methyl-resorcine. p-chloraniline was also studied. The single solute data were statistically fitted on 13 isotherm models: the Freundlich, Langmuir, Freundlich-Langmuir, BET, Dubinin-Raduskevitch, the three parameters empirical equation proposed by Radke and Prausnitz, Redlich-Petersen, Tóth, Myers, as well as generalised, Volmer, virial and sigmoidal isotherms. A computer program was developed to determine the most precise parameter models. The prediction results on the adsorption isotherms are compared by absolute relative percent deviations.

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Water vapour adsorption processes and equilibria on adsorbents with polar surfaces can be well tested with an adsorption method combined with thermal analysis. The first step involves the comparison of isothermal desorption-adsorption curves and thermal curves; in the second step different equilibrium points of the adsorption isotherms are tested by means of thermal analysis.

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The enthalpy of dilution of polyacrylamide 3530s (HPAM) solution, the enthalpy of adsorption of the polymer on sea sand, and the adsorption isotherms, were determined at 298. 15 K. The effect of NaCl on these properties were also determined. From the experimental results and certain assumptions, it was deduced that, for an adsorbedHPAM molecule, a large number of segments are in contact with the surface of the solid, some of them forming hydrogen-bonds, most of them belonging to Van der Waals interactions, which are much weaker than hydrogenbonds, and theHPAM molecules adsorbed on the surface of the solid are spread out.

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Ulva gigantea (Kützing) bliding (UGB) obtained from sea inlet of Izmir-Turkey has been studied as a biosorbent for removal of radioactive metals from water. In this study, unmodified UGB and modified UGB with glutaraldehyde (GUGB) characterized by FTIR spectroscopy were used as biosorbents for removal of U(VI) and Th(IV) ions from aqueous solution. Adsorption experiments performed under batch process with initial pH, contact time, adsorbent mass and temperature as variables. In order to determine the adsorption characteristics, Langmuir, Freundlich and Dubinin-Raduschkevich adsorption isotherms were applied to the adsorption data. Adsorption experiments showed that the adsorption isotherms correlated well with the Freundlich model. The sorption followed pseudo-second-order kinetics. The thermodynamic parameters such as variations of ΔH°, ΔG° and ΔS° were estimated as a function of temperature. The thermodynamics of the adsorption of U(VI) and Th(IV) onto UGB and GUGB indicates that the spontaneous and exothermic nature of the process. The results showed that UGB and GUGB were potential for application in removal of U(VI) and Th(IV) from aqueous solution.

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The influence of initial uranium concentration, solution pH, contact time and adsorbent mass was investigated for removal of uranium from aqueous solutions by pine wood powder and wheat straw using a batch technique. The maximum removal efficiency of uranium achieved at pH 8 and 7 for pine wood powder and wheat straw, respectively. Langmuir and Freundlich adsorption isotherms and three kinetic models of adsorption including; Elovich, Lagergren pseudo-first and Lagergren pseudo-second order were used to describe the adsorption mechanisms. The uranium sorption onto wood and wheat straw powders followed a Freundlich isotherm. The kinetic studies showed that the data fitted very well to the pseudo-second order model in the studied concentration range of uranium for both adsorbents. Uranium desorption from loaded adsorbents also studied using batch techniques as a function of desorptive reagent, desorption time and desorptive reagent concentration. The results of the experiment indicated that the optimum desorption efficiency of uranium for wood powder and wheat straw occurred in 5 min shaking time, using 1.5 M HNO3 and 2 M Na2CO3 solutions, respectively.

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Biosorption of uranyl ions from aqueous solution by Saccharomyces cerevisiae was studied in a batch system. The influence of contact time, initial pH, temperature and initial concentration was investigated. The optimal conditions were found to be 3.5 h of contact time and pH = 4.5. Temperature had no significant effect on adsorption. The uptake of uranyl ions was relatively fast and 85 % of the sorption was completed within 10 min. The experimental data were well fitted with Langmuir isotherm model and pseudo-second order kinetic model. According to this kinetic model, the sorption capacity and the rate constant were 0.455 mmol UO2 2+/g dry biomass and 1.89 g mmol−1 min−1, respectively. The Langmuir isotherm indicated high affinity and capacity of the adsorbent for uranyl biosorption with the maximum loading of 0.477 mmol UO2 2+/g dry weight.

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