Mohammad Ali Moosavian

MASS TRANSFER COEFFICIENTS IN A HANSON MIXER-SETTLER EXTRACTION COLUMN

The volumetric overall mass transfer coefficients in a pilot plant Hanson mixer-settler extraction column of seven stages have been measured using toluene-acetone-water system. The effects of agitation speed and dispersed and continuous phases flow rates on volumetric overall mass transfer coefficients have been investigated. The results show that the volumetric overall mass transfer coefficient increases with increase in agitation speed and reaches a maximum. After having reached its maximum, it falls with further increase in agitation speed. It was found that the volumetric overall mass transfer coefficient increases with increase in dispersed phase flow rate, while it decreases with increase in continuous phase flow rate. By using interfacial area, the overall mass transfer coefficients for continuous and dispersed phases are determined from volumetric coefficients. An empirical correlation for prediction of the continuous phase overall mass transfer coefficient is proposed in terms of Sherwood and Reynolds numbers. Also the experimental data of the column investigated are compared with data for various extraction columns. Comparison between theoretical models and experimental results for the dispersed phase mass transfer coefficient shows that these models do not have enough accuracy for column design. Using effective diffusivity in the Grober equation results in more accurate prediction of overall mass transfer coefficient. The prediction of overall mass transfer coefficients from the presented equations is in good agreement with experimental results.

Kinetics of gadolinium extraction with D2EHPA and Cyanex301 using single drop column

The extraction kinetics of Gd(III) from the nitric acid medium using bis(2,4,4-trimethylpentyl) dithiophosphinic acid (Cyanex301) and 2-ethylhexyl phosphoric acid (D2EHPA) in kerosene solution were measured by the single drop technique. The influences of hydrogen ion concentration, gadolinium ion concentration, extractant concentration, column height, and nozzle diameter on the extraction rate were investigated. The forward rate equations for the gadolinium extraction with D2EHPA and Cyanex301 were obtained. Based on the experimental results, the forward extraction rate constant was calculated. With the increase of D2EHPA or Cyanex301 concentration, the drop rising diameter and the value of interfacial tension decrease in the studied system, which shows that D2EHPA or Cyanex301 has interfacial activity as a kind of surfactant. Also, the droplet diameter and interfacial tension decrease with the increase of aqueous solution acidity. The experimental results show that the D2EHPA extractant provides faster extraction rate in comparison with Cyanex301 extractant, and it would be useful in industrial continuous extraction process.

Electrospun chitosan/baker’s yeast nanofibre adsorbent: preparation, characterization and application in heavy metal adsorption

In this study, chitosan/baker’s yeast nanofibre was synthesized by electrospinning method and subsequently, the performance of the prepared nanofibre for removal of uranium(VI) and thorium(IV) ions from aqueous solutions was investigated. The prepared adsorbent was characterized by Brunauer–Emmett–Teller (BET), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses. The influences of experimental parameters on the chitosan/baker’s yeast nanofibre such as contact time, pH, temperature and initial concentration were studied in a batch system. The adsorption kinetics was studied by the pseudo-first-order, pseudo-second-order, double-exponential and intra-particle kinetic models. Three isotherm models, namely Langmuir, Freundlich and Dubinin–Radushkevich (D–R) were used for analysis of equilibrium data of heavy metals. The maximum adsorption capacities of U(VI) and Th(IV) were estimated by Langmuir model to be 219 and 131.9 mg g−1 at optimum conditions, respectively. The positive values of the enthalpy changes and negative values of Gibbs free energy changes showed that U(VI) and Th(IV) adsorption process was endothermic and spontaneous. Also, the inhibitory effect of Co(II), Cu(II), Cd(II), Fe(II) and Ni(II) metal ions on U(VI) and Th(IV) adsorption was investigated. The reusability of chitosan/baker’s yeast nanofibre was determined after five adsorption–desorption cycles.

Removal of cadmium and zinc ions from industrial wastewater using nanocomposites of PANI/ZnO and PANI/CoHCF: a comparative study

AbstractPolyaniline (PANI) adsorbents functionalized with zinc oxide nanoparticles (ZnO-NPs) and cobalt hexacyanoferrate (CoHCF) were prepared by chemical precipitation method and they were applied in order to adsorb Cd(II) and Zn(II) from industrial wastewater. First, the adsorbents were characterized by FTIR and XRD analyses for comparison. The adsorption capacity of the polyaniline/CoHCF nanocomposite (PANI/CoHCF/NC) were greater than that of polyaniline/ZnO nanocomposite (PANI/ZnO/NC). PANI/CoHCF/NC was characterized by FTIR, XRD, TEM, SEM, and BET analyses. Experimental parameters affecting Cd(II) and Zn(II) sorption onto the PANI/CoHCF/NC such as pH, adsorbent dosage, contact time, initial concentration of metal ions, and temperature were studied. The kinetic data were analyzed by the pseudo-first-order and pseudo-second-order kinetic models. Consequently, the pseudo-second-order model best described the adsorption of Cd(II) and Zn(II) ions. The equilibrium data was fitted to three isotherm models: ...

Continuous biosorption of U(VI) and Fe(II) using Cystoseira indica biomass packed bed column: Breakthrough curves studies in single, binary and multi-component systems

Ca-pretreated Cystoseira indica algae was used as a biosorbent for the biosorption of U(VI) and Fe(II) ions in single, binary and multi-component systems by using a packed bed column. Experiments were conducted to study the effect of important design parameters such as bed height and flow rate. FTIR and XRF analyses and pH and Ca2+ ion concentration recordings showed that the biosorption of U(VI) and Fe(II) proceeded through ion-exchange mechanism. BDST, Thomas and Modified dose-response models were used for predicting breakthrough curves and for estimations of the parameters necessary for the design of a large-scale packed bed column.

Experimental Study and Numerical Simulation of the Air Gap Membrane Distillation (AGMD) Process

Abstract Some challenges, including inappropriate distribution of currents on the membrane surface, poor hydrodynamics and existing severe temperature polarization (TP) phenomenon in MD modules, impede industrialization of MD process. Computational fluid dynamics (CFD) method was used for numerical simulation of hydrodynamics in air gap membrane distillation modules. One of two simulated modules in this work is a novel developed one in which heat and mass transfer data was compared with available literature data. Moreover, the effect of using baffles in module was investigated. Comparison between the novel module and conventional module indicates higher trans-membrane mass flux and gained output ratio (GOR) coefficient by 7% and 15%, respectively. Moreover, the effects of different operating conditions including feed temperatures and feed flow rates on permeate flux were investigated.

Adsorption of cerium and lanthanum from aqueous solutions by chitosan/polyvinyl alcohol/3-mercaptopropyltrimethoxysilane beads in batch and fixed-bed systems

ABSTRACT Adsorption of La(III) and Ce(III) from aqueous solutions by novel chitosan modified with poly(vinyl alcohol) as a promoter of mechanical and chemical properties and 3-mercaptopropyltrimethoxysilane as a promoter of the functional group was investigated in batch and continuous modes. The FTIR analyses showed that mecapto groups have been successfully added to chitosan/poly(vinyl alcohol). The BET surface area, pore diameter, and pore volume of adsorbents were 1.68 m2 g−1, 2.516 nm, and 0.058 cm3 g−1, respectively. The effects of the operating parameters such as pH, contact time, initial metal ion concentration, adsorbent dosage, and temperature were studied in batch mode operation. Optimum pH was found to be 5. According to the Langmuir model, the maximum adsorption capacities for La(III) and Ce(III) ions were 263.16 and 251.41 mg g−1, respectively. The thermodynamic study showed that the adsorption process of both metal ions was endothermic and spontaneous favored at the higher temperature. In the column study, the effects of the flow rate and initial concentration were investigated. The maximum adsorption capacities based on the Thomas model for La(III) and Ce(III) ions were 460.94 and 374.83 mg g−1 at a flow rate of 4 mL min−1 and an initial metal concentration of 300 mg L−1, respectively.

Optimization and modification of PVDF dual-layer hollow fiber membrane for direct contact membrane distillation; application of response surface methodology and morphology study

RSM methodology was applied to present mathematical models for the fabrication of polyvinylidene fluoride (PVDF) dual-layer hollow fibers in membrane distillation process. The design of experiments was used to investigate three main parameters in terms of polymer concentration in both outer and inner layers and the flow rate of dope solutions by the Box-Behnken method. According to obtained results, the optimization was done to present the proper membrane with desirable properties. The characteristics of the optimized membrane (named HF-O) suggested by the Box-Behnken (at the predicted point) showed that the proposed models are strongly valid. Then, a morphology study was done to modify the fiber by a combination of three types of a structure such as macro-void, sponge-like and sharp finger-like. It also improved the hydrophobicity of outer surface from 87 to 113° and the mean pore size of the inner surface from 108.12 to 560.14 nm. The DCMD flux of modified fiber (named HF-M) enhanced 62% more than HF-O when it was fabricated by considering both of RSM and morphology study results. Finally, HF-M was conducted for long-term desalination process up to 100 hr and showed stable flux and wetting resistance during the test. These stepwise approaches are proposed to easily predict the main properties of PVDF dual-layer hollow fibers by valid models and to effectively modify its structure.

Mass transfer investigation in a horizontal–vertical pulsed packed extraction column

In this study, hydrodynamic parameters and the mass transfer coefficient were investigated in a pilot version of a horizontal–vertical pulsed packed extraction column using a toluene–acetone–water system. The effects of the operational parameters on the volumetric overall mass transfer coefficient and hydrodynamic parameters away from the flooding point were studied, and it was found that the volumetric overall mass transfer coefficient, mean drop size and disperse phase holdup were significantly affected by the pulse intensity. However, the dispersed and continuous phase flow rates have a weaker effect. On the other hand, by increasing the pulse intensity the mean drop size and volumetric overall mass transfer coefficient were reduced and increased, respectively, in both sections of the column, but the disperse phase holdup displayed different behavior in the horizontal and vertical sections. By increasing the pulse intensity, the disperse phase holdup was first reduced and then increased in the horizontal section; however, an incremental trend was observed in the vertical section. The effect of the dispersed phase flow rate was significant for all the investigated parameters, but weaker. For instance, all the investigated parameters were increased by enhancing the dispersed phase flow rate. In contrast, the continuous phase flow rate has sometimes had no significant effect, for example, on the mean drop size in both sections of the column. Finally, two empirical correlations for the prediction of the volumetric overall mass transfer coefficient based on the continuous phase were derived in terms of the Sherwood number, Reynolds number and other dimensionless numbers. Good agreement between predictions and experiments was found for all operating conditions that were investigated.

Investigation of Copper Extraction from Aqueous Sulfate Solution in a Rotating Disc Contactor

The extraction of copper from aqueous sulfate solution with new extractant Cupromex-3302 (active substance is the 5-nonylsalicylaldoxime) using a rotating disc contactor (RDC) was investigated. It was observed from batch experiments that the best results were obtained with the initial aqueous pH and concentration of Cupromex-3302 of 1.9 and 10% (v/v) respectively. In continuous experiments, the first critical rotor speed based on drop breakage probabilities was determined. Then the effects of rotor speed, dispersed and continuous phase flow rates on hydrodynamic parameters such as static hold-up, mean drop sizes and extraction efficiency were studied. The experimental results were compared with the ones obtained by the empirical correlations for prediction of the dispersed phase static hold-up and mean drop sizes in terms of the operating variables and the physical properties. The results of experiments proved the feasibility of operating the solvent extraction of copper from the aqueous solution using rotating disc contactor.