The mechanism of extraction of gold by tetradecyldimethylbenzylammonium chloride (TDMBAC)/tri-n-butyl phosphate (TBP)/n-heptane solution from an aqueous alkaline cyanide solution was studied by means of extraction equilibrium, Karl Fischer titration, electrical conductivity, FTIR spectroscopy and dynamic laser scattering (DLS). When the gold concentration is lower than 3 g L À1 and the volume percentage of TBP is less than 10%, the plots of the extraction percentage of gold against the molar ratio of [TDMBA + ] to [Au(CN) 2 À ] and logD-log[TBP] (o) plot indicated that the stoichiometry of the extracted species is a 1 : 1 : 4 complex, TDMBA + : Au(CN) 2 À : TBP. Karl Fischer titration showed that 4 H 2 O molecules participate in the formation of such a species. Electrical conductivity measurements confirmed its ionic character. Fourier self-deconvolution of the O-H stretching bands revealed 4 different kinds of water molecules contained in the organic phase, some of which were bound to TBP via hydrogen bonding. A supramoleculefor the extracted species. Two TBP molecules are bound to [Au(CN) 2 À ] by two H 2 O bridges through hydrogen bonding, forming a [(RO) 3 P=OÁ Á ÁH-O-HÁ Á ÁN= =C-Au-CNÁ Á ÁH-O-HÁ Á ÁO ¼ P(OR) 3 ] À moiety. Two hydrated TBP molecules, (RO) 3 P=OÁ Á ÁH-O-H, surround [TDMBA + ] by ion-dipole interaction.The bulky anion and cation form a lipophilic supramolecule. The possible structure of the supramolecular anion was calculated with an ab initio molecular orbital (MO) method. The DLS study showed that mixing of TDMBAC and Au(CN) 2 À in the aqueous phase led to the formation of micelles. When an organic phase containing TBP was added to this aqueous phase, the complexes transferred into the organic phase and reversed micelles or a microemulsion (W/O) were formed when the gold concentration reached a certain limiting value.
The adsorption of dibenzothiophene (DBT) in hexadecane onto NaY zeolite has been studied by performing equilibrium and kinetic adsorption experiments. The influence of several variables such as contact time, initial concentration of DBT and temperature on the adsorption has been investigated. The results show that the isothermal equilibrium can be represented by the Langmuir equation. The maximum adsorption capacity at different temperatures and the corresponding Langmuir constant (K L ) have been deduced. The thermodynamic parameters ( G 0 , H 0 , S 0 ) for the adsorption of DBT have also been calculated from the temperature dependence of K L using the van't Hoff equation. The value of H 0 , S 0 are found to be −30.3 kJ mol −1 and −33.2 J mol −1 K −1 respectively. The adsorption is spontaneous and exothermic. The kinetics for the adsorption process can be described by either the Langmuir model or a pseudo-second-order model. It is found that the adsorption capacity and the initial rate of adsorption are dependent on contact time, temperature and the initial DBT concentration. The low apparent activation energy (12.4 kJ mol −1 ) indicates that adsorption has a low potential barrier suggesting a mass transfer controlled process. In addition, the competitive adsorption between DBT, naphthalene and quinoline on NaY was also investigated. NomenclatureDBT dibenzothiophene t contact time, min c 0 initial concentration of adsorbate in the solution, mmol L −1 c t the concentration of adsorbate at contact time t, mmol L −1 c e equilibrium concentration of adsorbate in the solution, mmol L −1 c DBT the concentration of DBT, mmol L −1 k 0 temperature independent factor, g mmol −1 min −1 k 2 pseudo-second-order rate constant, g mmol −1 min −1 k ads adsorptive constant, L g −1 min −1 k d desorptive constant, mmol g −1 min −1 K L Langmuir constant, L mmol −1 q e adsorptive amount of adsorbate after equilibrium, mmol g −1 q L a solution of the second-order polynomial expression, mmol g −1 q m adsorptive amount of adsorbate to its maximum, mmol g −1 q t adsorptive amount of adsorbate at time t, mmol g −1 θ dimensionless ratio of coverage of the surface of adsorbent v 0 initial adsorptive rate, mmol g −1 min −1 v ads rate of adsorption, mmol g −1 min −1 v d rate of desorption, mmol g −1 min −1 v t rate of adsorption at time t, mmol g −1 min −1 V the volume of solution, L W the mass of adsorbent, g R 2 regression coefficient E a activation energy of adsorption, kJ mol −1 550 Adsorption (2010) 16: 549-558 R g the universal gas constant, 8.314 J mol −1 K −1 T temperature,°C T K temperature in Kelvin, K G 0 Gibbs free energy, kJ mol −1 H 0 enthalpy, kJ mol −1 S 0 entropy, J mol −1 K −1
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