Sharif Digital Repository

In this study, solvent extraction method has been utilized for separation of molybdenum and vanadium from nitrate solution by utilizing coupling of acid and solvating extractants (D2EHPA and TBP extractants). The outcomes demonstrated that synergistic solvent extraction improves stability of formatted complexes for transfer to the organic phase. The main parameters such as pH value, concentration of extractants, NH4OH concentration as the stripping agent and contact time were optimized at 0.4, 15% (v/v) D2EHPA, 10% (v/v) TBP, 2 M and 30 min, respectively. The maximum separation factor of 24.84 was obtained with a new synergistic mixture of D2EHPA and TBP diluted with kerosene. According to... 

In this study, the mass transfer evaluation of an agitated liquid-liquid system for the extraction of molybdenum and tungsten from aqueous sulfate solution was investigated. It was found from batch experiments for separation of molybdenum from tungsten that the initial aqueous pH, Cyanex272 and D2EHPA concentration, contact time, dispersed phase volume fraction and impeller speed were optimized at 1.3, 0.07 M, 0.29 M, 15 min, 0.09 and 280 rpm, respectively. The results indicate that a suitable composition for stripping is 1.5 M NH4OH and 0.6 M NH4F. Furthermore, a modified correlation based on dimensionless numbers was derived for the prediction of continuous phase mass transfer in the... 

In this study, the mass transfer evaluation of an agitated liquid-liquid system for the extraction of molybdenum and tungsten from aqueous sulfate solution was investigated. It was found from batch experiments for separation of molybdenum from tungsten that the initial aqueous pH, Cyanex272 and D2EHPA concentration, contact time, dispersed phase volume fraction and impeller speed were optimized at 1.3, 0.07 M, 0.29 M, 15 min, 0.09 and 280 rpm, respectively. The results indicate that a suitable composition for stripping is 1.5 M NH4OH and 0.6 M NH4F. Furthermore, a modified correlation based on dimensionless numbers was derived for the prediction of continuous phase mass transfer in the... 

In this study, mass transfer experimental data from the present column with 70 cm active column length and 11.3 cm internal diameter were interpreted for molybdenum extraction with a mixture of D2EHPA and TBP in terms of the axial diffusion model. The influence of extractants concentration and the initial aqueous pH have studied in the bench-scale experiments. The experimental finding demonstrated that the synergistic solvent extraction increases the constancy of the extracted complexes for transfer into the organic phase. The effect of operating parameters, including agitation speed and inlet phase velocities on the overall mass transfer coefficients under the chemical reaction system, is... 

Direct extraction of molybdenum from sulfate solution with synergistic extractants (mixture of D2EHPA and TBP) was studied in the rotation column. The influence of extractant concentration and initial pH of aqueous phase was studied in the bench scale experiments. The outcomes demonstrated that the synergistic solvent extraction enhances the constancy of the extracted complexes for transfer into the organic phase. In the continuous experiments, the effect of different operating parameters such as speed of agitation, inlet solvent flow rate and inlet aqueous flow rate on the holdup, mean drop size, drop size distribution, slip and characteristic velocities and extraction percentage were... 

In the present work, slip velocity has been measured in a 76 mm diameter pulsed disc and doughnut extraction column for four different liquid-liquid systems. The effects of operating variables including pulsation intensity and dispersed and continuous phase flow rates on slip velocity have been investigated. The existence of three different operational regimes, namely mixersettler, transition, and emulsion regimes, was observed when the energy input was changed. Empirical correlations are derived for prediction of the slip velocity in terms of operating variables, physical properties of the liquid systems, and column geometry for different regimes. Good agreement between prediction and... 

Dispersed phase holdup has been measured in a 76 mm diameter pulsed disc and doughnut extraction column for three different liquid-liquid systems. The effects of operational variables such as pulsation intensity and dispersed and continuous phase flow rates on holdup have been investigated and found to be significant. The existence of three different operational regimes, namely mixer-settler, dispersion, and emulsion regimes, was observed when the energy input was changed. The results indicated that the characteristic velocity approach is applicable to this type of extraction column for analysis of holdup in the transition and emulsion regions. Empirical correlations are derived for... 

Lead sulfide quantum dots (PbS QDs) were decorated onto a graphene surface in a semi-core-shell structure using supercritical ethanol. The temperature of ethanol played significant role in controlling size and agglomeration of QDs as well as the extent of reduction of graphene. Average size of the QDs was estimated by transmission electron microscopy to be around 3.96 nm and by quantum models to be about 4.34 nm. PbS QDs prepared at 330 °C were of high purity, and the yield was 99%. Instrumental and chemical analyses demonstrated formation of a strong bond between PbS QDs and graphene, through a Pb-O-C bridge. UV and photoluminescence measurements along with theoretical considerations... 

Reactive extraction development was investigated to extract vanadium ions from sulfate solution in the modified rotating disc column (MRDC). It was found from batch experiments that D2EHPA and TBP concentrations, initial aqueous phase pH, and the concentration of NH4OH as a stripping agent were optimized equal to 0.3 M, 0.36 M, 2, and 1 M, respectively. In the continuous experiments, the effects of rotor speed, aqueous and organic phase flow rates, and mass transfer direction were investigated on the dispersed phase holdup, mass transfer coefficients, and vanadium extraction. The experiment design was based on the response surface design to analyze the dependence of responses with the input... 

In the present work, multistage extraction column performance for reactive separation of molybdenum from the leach aqueous phase by using D2EHPA and TBP in kerosene was investigated by using the axial diffusion model. The variation of volumetric overall mass transfer coefficients based on continuous phases at various operating conditions was obtained. By considering the chemical reaction conditions, the experimental data indicate that the volumetric overall mass transfer coefficients increase with an enhancement in rotor speed and continuous and dispersed phase flow rates. According to the sensitivity analysis, the rotor speed and flow rate of the dispersed phase have more influence on... 

Titanium nitride-carbon nanocomposites are synthesized by the reaction of TiCl4 and NaN3 in supercritical benzene medium that also serves as a carbon source. The as-prepared precursors (SI, SII) are subjected to several heat treatments (SIII-SV). The synthesized nanoparticles are characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The samples are tested as electrocatalyst for oxygen reduction reaction in an alkaline electrolyte. It is shown that the electrocatalytic properties of the synthesized nanoparticles are... 

A novel microspherical adsorbent for the removal of uranium from aqueous solutions was developed by immobilizing of natural bentonite in the polymeric matrix of calcium alginate. Different uptake properties of the prepared microspheres were examined using batch, stirred and column methods. The adsorbent showed high affinity toward uranium ions, especially at pHs above 3. Major uptake mechanisms included ion exchange, chelating of the (UO2)2+ ions to the -OH groups of alginate, and surface complexation with bentonite. Surprisingly, the capacity of microspheres was higher than both its constituents, revealing that a synergetic effect occurs. Adsorption kinetics was controlled by slow chemical... 

Recyclable CuO nanoparticles provide an efficient, economic, and novel method for the synthesis of quinoxaline, benzoxazine, and benzothiazine. This method provides a wide range of substrate applicability, avoids the use of organic solvents, and gives benzoheterocycles in satisfactory yields  

An efficient synthesis of tetrahydrobenzofurans is carried out in one pot through the reaction of 1,3-diketone and phenacyl bromides compound using a heterogeneous basic nano particles copper oxide catalyst. The protocol offers advantages in terms of higher yields, short reaction times, and mild reaction conditions, with reusability of the catalyst. © 2009 Elsevier B.V. All rights reserved  

Carbon-doped zinc oxide/reduced graphene oxide (C-ZnO/rGO) was prepared by a facile one-pot supercritical methanol method. The synthesized C-ZnO/rGO nanocomposite with flower-like ZnO micro-rods (MRs) synergistically inherited all the advantages of carbon doping and rGO heterojunction and exhibited high photocatalytic activity for the photodegradation of methyl orange (MO) under visible light. The x-ray diffraction (XRD) results indicated that in presence of GO, a new carbon-doped phase was formed at the high temperature and pressure of supercritical methanol. The x-ray photoelectron spectroscopy (XPS) at low binding energies demonstrated that the valence band of C-ZnO-rGO is up-shifted by... 

The effects of varying operating conditions on metals removal from aqueous solution using a novel platinum nanopartcles/Zeolite-4A adsorbent are reported in this paper. Characterization of the adsorbent showed successful production of platinum nanopartcles on Zeolite-4A using 3 Wt% platinum. The effects of operation conditions on metals removal using this adsorbent were investigated. The optimal metals adsorption was observed at pH 7, 0.1 g/10 mL dosage and 30 min contact time. Sorption data have been interpreted in terms of Langmuir and Freundlich isotherms  

The current study aimed at application of the plain and supported platinum nanoparticles as a heterogenous catalyst for the reduction of aromatic nitro compounds. Monodispersed platinum nanoparticles were synthesized by reduction of H2PtCl6 by ethanol in the presence of polyvinyl pyrrolidone as a stabilizer, and then were immobilized on four types of zeolites. The obtained catalyst granules were characterized by X-ray diffractometry and transmission electron microscopy. The study then focused on elaboration of the catalytic activity of the nano catalysts under different operational conditions. It was found that reaction is adequately rapid at ambient temperature, and by utilizing a... 

Ultra fine CuO nanoparticles In the range of 2 ± 0.2 nm were synthesized by the supercritical hiydrotliermal method in a batch reactor. Itwas demonstrated that elevating the pH of the Cu2+ precursor solution to around 6 (neutral condition) not only does not lead to excessive agglomeration of the particles, but also reduces particle size and in general promotes their nanoscale characteristics. Prepared nanoparticles were immobilized in the biopolymcric matrix of barium alginate and calcined at different temperatures resulting in micro spherical granules of high porosity and elevated mechanical strength. The fabricated samples were characterized using x-ray diffractometry (XRD), transmission... 

Supercritical water was used for simultaneous fragmentation and reduction of graphene oxide (GO) sheets into water-dispersible graphene quantum dots (GQDs) with tunable sizes. Transmission electron microscopy (TEM) demonstrated that by increasing the temperature above the critical point of water, the average size and thickness of the GQDs were decreased and the size uniformity and production yield were increased. The results of thermal conductivity measurement of GQD nanofluids with different weight fractions indicated that the GQDs prepared at supercritical condition could enhance the thermal conductivity of water by 65% as compared to 35% for the GQDs synthesized at sub-critical... 

Resin in pulp, as the most frequently employed process for extraction of uranium from low-grade ores, encounters difficulties when the pulp contains dense or abrasive minerals, e.g., Saghand ores in central Iran. To overcome these complications, it was suggested to remove solid content of the pulp at first, and inject the clear solution into a cascade of Pachuca reactors, where uranium is adsorbed by an anion exchanger such as Varion-AP. We made two mini pilot cascades, each comprising ten Pachuca reactors, to check both co-current and countercurrent resin in solution processes on the Saghand leach liquor. The countercurrent scheme, having a higher efficiency, was able to adsorb 99% of...