Avijit Bhowal

Studies on transport mechanism of Cr(VI) extraction from an acidic solution using liquid surfactant membranes

Abstract A mathematical model for analysing the extraction of Cr(VI) from aqueous acidic solution by emulsion liquid membrane using Aliquat 336 as extractant and NaOH as stripping agent has been presented. The existing models developed so far do not account for the existence of different forms of Cr(VI) ions in the aqueous phase depending on pH conditions. Accordingly, in the present model, reaction equilibrium has been considered instead of distribution coefficient to represent realistically the transport mechanism for this type of system through liquid surfactant membrane. Unlike other models, liquid–liquid equilibrium of sodium hydroxide-chloride of Aliquat 336 has also been considered. The carrier thus exists in the membrane phase in hydroxide and chloride forms and extraction of hexavalent chromium from the external phase proceeds by the two carriers. The validity of the model has been checked from comparison of the simulated curves and experimental data using chemical reaction equilibrium constant and D eff / R 2 as fitting parameters.

A new model of batch-extraction in emulsion liquid membrane: Simulation of globule-globule interaction and leakage

Abstract The present paper seeks to provide an understanding of the possible effect of interaction between emulsion globules, on batch extraction, utilising emulsion liquid membranes. The conventional reversible model of Bunge and Noble (1984) considers an isolated globule, for explaining type-1, reaction-facilitated transport. Their basic approach has been extended here through Monte Carlo simulation of a system of emulsion globules, interacting via coalescence-redispersion. Collision of such an interacting pair results in internal circulation in membrane phase of globules and causes mixing of solute existing therein. This translates into faster solute penetration inside the globule. Hence, solute depletion rate in the external phase is enhanced, over and above that of a diffusion-limited reaction. In experiments, at high stirring speeds involving extraction of weakly basic amines with a strong internal phase acid ( Baird et al., 1987 ), this trend has been observed during the initial period. A further shortcoming of the reversible model is that it overpredicts the maximum extraction achieved in these experiments, which is corrected by introducing leakage of internal drops during redispersion.

Extraction of dye from aqueous solution in rotating packed bed

The influence of centrifugal acceleration on mass transfer rates in liquid-liquid extraction was investigated experimentally in rotating packed bed (RPB) contactor. The extraction of methyl red using xylene was studied in the equipment. The effect of rotational speed (300-900rpm), flow rate of the aqueous (4.17-20.8×10(-6)m(3)/s), and organic phase (0.83-2.5×10(-6)m(3)/s) on the mass transfer performance was examined. The maximum stage efficiency attained was ∼0.98 at aqueous to organic flow rate ratio of 10. The results suggest that contactor volume required to carry out a given separation can be reduced by an order of magnitude with RPB in comparison to conventional extractors.

A mathematical model for the analysis of extraction data of weak acids/bases in liquid surfactant membranes

An attempt has been made in this paper to overcome the shortcomings of the advancing front model while simplifying the mathematical treatment of mass transfer and reaction occurring in the emulsion globule during extraction by liquid surfactant membranes. This model combines the mathematical simplification achieved in assuming a reaction front in the emulsion globule along with the realistic assumption of reaction equilibrium existing in the internal and external continuous phases. The proposed model predicts satisfactorily the experimental results of the extraction of weak acids and weak bases in a batch separation system as presented in various literatures.

Facilitated transport through liquid surfactant membrane: Analysis of breakage model

A mathematical model for analyzing the experimental data of extraction of weak acid from aqueous solution by liquid surfactant membrane (LSM) using a strong base as internal reagent present in excess in a batch system has been presented. The leakage of internal phase due to membrane breakage is also discussed in the mathematical treatment. The model while considering a reaction front to exist within the emulsion globule assumes reaction equilibrium between the solute and internal reagent in the external continuous phase. The proposed model predicts successfully the experimental results of extraction of a weak acid by a strong base in a batch separation system as presented in the literature. The model is also capable of predicting excellently the experimental pH versus time data in case of the above system.

Bioremediation of Copper-Contaminated Soil by Co-Application of Bioaugmentation and Biostimulation with Organic Nutrient

ABSTRACT This study investigates various factors affecting bioremoval of copper from experimentally contaminated soil by bioaugmentation with a metal-resistant microorganism (B1) accompanied with amendment of an organic matter (mustard oil cake). The initial contamination level reduced by 67% with this joint strategy compared to 13% by application of bioaugmentation. Increasing organic amendment concentration beyond 6 wt% did not significantly improve microbial growth and the extent of bioremediation due to increase of pH. The bioaccessible copper concentration, however, did not change significantly. Controlling pH by one-time application of ferrous sulfate (1 wt%) into the experimental run resulted in enhanced microbial growth. The copper concentration in soil and bioaccessible copper concentration reduced to 55% and 80% of the value obtained without pH control for the same period of incubation. This study suggests the potential of co-application of isolated metal-resistant bacteria (B1) and mustard oil cake amendment in conjunction with pH control for in situ bioremediation of copper-contaminated soil.

Mass Transfer and Immobilized Organic Phase Instability Studies for Cobalt(II)–Nickel(II) Separation by PEHFSD

Pseudo-emulsion-based hollow-fiber strip dispersion (PEHFSD) technique was examined as an alternative to solvent extraction for simultaneous separation and concentration of cobalt(II)–nickel(II) mixture using Cyanex-272 as the extractant. Experiments were carried out by continuous recirculation of the feed and pseudo-emulsion phases through a hollow-fiber module. The separation factor increased rapidly after 60 min of operation. The maximum value after 120 min of operation was ∼128 (pH = 6.5) for the operating conditions studied. The mass transfer resistance from the extraction reaction appeared to be dominant. The results of mathematical modeling of the mass transfer process indicated that higher separation factor and extraction rate can be achieved using PEHFSD in comparison to solvent extraction. Mixing of the stripping and the feed solution was observed at high dispersed phase volume fraction in the pseudo-emulsion and low flow rate of this phase. The maximum value of backtransport flux from the stripping phase due to mixing was estimated to be approximately two orders lower than the initial extraction rates.

Assessment on the decolourization of textile dye (Reactive Yellow) using Pseudomonas sp. immobilized on fly ash: Response surface methodology optimization and toxicity evaluation

This study focuses on the investigation of removal of textile dye (Reactive Yellow) by a combined approach of sorption integrated with biodegradation using low cost adsorbent fly ash immobilized with Pseudomonas sp. To ensure immobilization of bacterial species on treated fly ash, fly ash with immobilized bacterial cells was characterized using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and fluorescence microscopy. Comparative batch studies were carried out using Pseudomonas sp, fly ash and immobilized Pseudomonas sp on flyash and were observed that immobilized Pseudomonas sp on flyash acted as better decolourizing agent. The optimized pH, temperature, and immobilized adsorbent dosage for highest percentage of dye removal were observed to be pH 6, 303 K, 1.2 g/L in all the cases. At optimum condition, the highest percentage of dye removal was found to be 88.51%, 92.62% and 98.72% for sorption (flyash), biodegradation (Pseudomonas sp) and integral approach (Pseudomonas sp on flyash) respectively. Optimization of operating parameters of textile dye decolourization was done by response surface methodology (RSM) using Design Expert 7 software. Phytotoxicity evaluation with Cicer arietinum revealed that seeds exposed to untreated dye effluents showed considerably lower growth, inhibited biochemical, and enzyme parameters with compared to those exposed to treated textile effluents. Thus this immobilized inexpensive technique could be used for removal of synthetic dyes present in textile wastewater.

A MODEL FOR THE PREDICTION OF EXTRACTION CHARACTERISTICS OF STRONG ACIDS/BASES BY LIQUID SURFACTANT MEMBRANE

A model has been developed to predict the extraction characteristics of multicomponent solutes with high dissociation constants by Type-I facilitation employing liquid surfactant membrane in a batch separation system. The conventional reversible model of Bunge and Noble (J. Membr. Sci. 1984, 21, 55) has been extended incorporating charge balance in the aqueous phases of the extraction system and allowing for hydrolysis of salt in the internal droplets. Model predictions for multicomponent systems are found to be in good agreement with the experimental data available in the literature. Extraction profiles simulated for single component systems using this model have been compared with the reversible model given by Bunge and Noble. The flexibility of the present approach in comparison to the reversible model has been illustrated with examples.

Biodegradation of Azo Dye Using the Isolated Novel Bacterial Species: Acinetobacter sp.

Dyes present in water affect the balance of aquatic life as well as human being due to its toxicity. Insufficient sunlight impairs the process of photosynthesis of aquatic plants and phytoplankton, and, thus, they die without having sufficient food. After the death of these plants and animals, the numbers of zooplanktons and other higher organisms present in that aquatic system are automatically reduced. Finally, in this way the aquatic ecosystem loses its balance. The mixing of dye-colored wastewaters into the aquatic ecosystem and, thus, its accumulation in wildlife through food chain can cause many negative ecotoxicological effects and public health hazards.