Efficiency, Kinetics and Mechanism of 4-Nitroaniline Removal from Aqueous Solutions by Emulsion Liquid Membranes Using Type 1 Facilitated Transport.

4-Nitroaniline (4NA) is a common organic pollutant that is released into the environment during the manufacture and processing of a wide variety of industrial products. This article describes the use of an emulsion liquid membrane process to remove 4NA from aqueous solutions using a type 1 facilitated transport mechanism. Optimization of the removal process was carried out by analyzing the efficiency of 4NA removal from the feed phase and the initial apparent feed/membrane fluxes and permeabilities under different experimental conditions. The kinetics of the removal process was analyzed using a simplified mass transfer model involving an empirical mass transfer coefficient calculated from experimental data, assuming that the concentrations of 4NA in the external aqueous phase and in the internal w/o emulsion are uniform. The results show that there is a very good fit between the experimental and model data and that the variation in the values of the overall mass transfer coefficients with the experimental conditions coincides with that of the removal efficiency mentioned above. The transport mechanism was studied by identifying the rate-controlling step of the removal process, using models described for adsorption processes, due to the strong parallelism between the transport mechanisms in adsorption and emulsion liquid membrane processes.

Comparative Study of 4-Aminophenol Removal from Aqueous Solutions by Emulsion Liquid Membranes Using Acid and Basic Type 1 Facilitations: Optimisation and Kinetics.

The molecule 4-aminophenol (4AP) is recognised as a serious environmental pollutant that enters the environment during the manufacture and processing of a variety of industrial processes and through the degradation of some pharmaceutical products. This paper describes a comparative study of 4AP removal from aqueous solutions by emulsion liquid membranes using acid and basic type 1-facilitated transports. The results are explained by analysing the stripping process through both the different relative acid/basic strength of the hydroxyl and amine groups of the 4AP molecule and the hydrogen-bonding capacity with water of the ionisation products generated by the reaction of 4AP with HCl or NaOH. To optimize the 4AP removal process, the influence of different experimental conditions (stripping agent concentration in the product phase, surfactant concentration in the membrane phase, stirring rate, feed phase/emulsion phase volume ratio, product phase/membrane phase volume ratio and emulsification rate and time) were studied. The kinetics of the removal process has been analysed by fitting the experimental results to first order, second order and the Behnajady and Avrami models. The Behnajady model presents an excellent fit, allowing to calculate both the initial removal rate and the maximal removal conversion. Optimal conditions of the removal process obtained through these parameters are in full agreement with those obtained from the experimental study.

Feasibility of Adsorption Kinetic Models to Study Carrier-Mediated Transport of Heavy Metal Ions in Emulsion Liquid Membranes.

Emulsion liquid membranes have been successfully used for the removal of different types of organic and inorganic pollutants by means of carrier-mediated transport mechanisms. However, the models that describe the kinetics and transport of such mechanisms are very complex due to the high number of model parameters. Starting from an analysis of the similarity between the elemental mechanisms of carrier-mediated transport in liquid membranes and of transport in adsorption processes, this paper presents an experimental analysis of the possibility of applying kinetic and mechanistic models developed for adsorption to carrier-mediated transport in emulsion liquid membranes. We study the removal of a target species, in this case, Cu(II), by emulsion liquid membranes containing membrane phase solutions of benzoylacetone (carrier agent), Span 80 (emulsifying agent) and kerosene (diluent), and hydrochloric acid as a stripping agent in the product phase. The experimental results fit the pseudo-second-order adsorption kinetic model, showing good relationships between the experimental and model parameters. Although both Cu(II) diffusion through the feed/membrane interface boundary layer and complex Cu-benzoylacetone diffusion through the membrane phase controls Cu(II) transport, it is the former step that mainly controls the transport process.

Membranes for Water and Wastewater Treatment.

Water is a vital element for life and the environment [...].

Activated Olive Stones as a Low-Cost and Environmentally Friendly Adsorbent for Removing Cephalosporin C from Aqueous Solutions.

In this paper, we describe the removal of cephalosporin C (CPC) from aqueous solutions by adsorption onto activated olive stones (AOS) in a stirred tank. For comparative purposes, several experiments of adsorption onto commercial granular activated carbon were carried out. A quantum study of the different species of cephalosporin C that, depending on the pH, exist in aqueous solution pointed to a favorable mass transfer process during adsorption. Activated olive stones were characterized by SEM, EDX and IR techniques and their pHzc was determined. A 10-3 M HCl cephalosporin C solution has been selected for the adsorption experiments because at the pH of that solution both electrostatic and hydrogen bond interactions are expected to be established between the adsorbate and the adsorbent. The adsorption process is best described by the Freundlich isotherm model and the pseudo-second-order kinetic model, while the adsorption mechanism is mainly controlled by film diffusion. Under the conditions studied, the adsorption process is of a physical nature, endothermic and spontaneous. Comparison of the adsorption results obtained in this paper with those of other authors shows that the efficiency of AOS is 20% of that of activated carbon but 65% higher than that of the XAD-2 adsorbent. Considering its low price, abundance, easy accessibility and eco-compatibility, the use of activated olive stones as adsorbents for the removal of emerging pollutants from aqueous solutions represents an interesting possibility from both the economic and the environmental points of view.

Using Pressure-Driven Membrane Processes to Remove Emerging Pollutants from Aqueous Solutions.

Currently, there is great concern about global water pollution. Wastewater generally contains substances called emerging pollutants, and if the removal of these pollutants is not given sufficient attention, the pollutants can enter into the water cycle and reach the water supply for domestic use, causing adverse effects on the well-being of people. In order to avoid this menace, a multitude of techniques to reduce the high concentration levels of these substances dissolved in water are being researched and developed. One of the most-used techniques for this goal is the physical-chemical separation of contaminants in water through membrane technology. In this study, different membranes were tested with the objective of investigating the removal of three emerging pollutants: caffeine, metformin, and methyl-paraben. Initially, a nanofiltration (NF) membrane was selected, and the influence of pressure was evaluated in the rejection coefficients and permeate fluxes. Next, a screening of three new membranes to remove methyl paraben was completed. The influence of the operating variables, working pressure, and methyl paraben-feed concentration was checked. Finally, the solution-diffusion model was applied to predict the behavior of the different membranes in the removal of methyl paraben. A good correlation between experimental and calculated values of permeate flux and methyl paraben concentration was obtained.

Pertraction of Co(II) through Novel Ultrasound Prepared Supported Liquid Membranes Containing D2EHPA. Optimization and Transport Parameters.

Pertraction of Co(II) through novel supported liquid membranes prepared by ultrasound, using bis-2-ethylhexyl phosphoric acid as carrier, sulfuric acid as stripping agent and a counter-transport mechanism, is studied in this paper. Supported liquid membrane characterization through scanning electron microscopy, energy-dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy shows the impregnation of the microporous polymer support by the membrane phase by the action of ultrasound. The effect on the initial flux of Co(II) of different experimental conditions is analyzed to optimize the transport process. At these optimal experimental conditions (feed phase pH 6, 0.5M sulfuric acid in product phase, carrier concentration 0.65M in membrane phase and stirring speed of 300 rpm in both phases) supported liquid membrane shows great stability. From the relation between the inverse of Co(II) initial permeability and the inverse of the square of carrier concentration in the membrane phase, in the optimized experimental conditions, the transport resistance due to diffusion through both the aqueous feed boundary layer (3.7576×104 s·m-1) and the membrane phase (1.1434×1010 s·m-1), the thickness of the aqueous feed boundary layer (4.0206×10-6 m) and the diffusion coefficient of the Co(II)-carrier in the bulk membrane (4.0490×10-14 m2·s-1) , have been determined.

Removal of Different Dye Solutions: A Comparison Study Using a Polyamide NF Membrane.

The removal of organic dyes in aquatic media is, nowadays, a very pressing environmental problem. These dyes usually come from industries, such as textiles, food, and pharmaceuticals, among others, and their harm is produced by preventing the penetration of solar radiation in the aquatic medium, which leads to a great reduction in the process of photosynthesis, therefore damaging the aquatic ecosystems. The feasibility of implementing a process of nanofiltration in the purification treatment of an aqueous stream with small size dyes has been studied. Six dyes were chosen: Acid Brown-83, Allura Red, Basic Fuchsin, Crystal Violet, Methyl Orange and Sunset Yellow, with similar molecular volume (from 250 to 380 Å). The nanofiltration membrane NF99 was selected. Five of these molecules with different sizes, shapes and charges were employed in order to study the behavior of the membrane for two system characteristic parameters: permeate flux and rejection coefficient. Furthermore, a microscopy study and a behavior analysis of the membrane were carried out after using the largest molecule. Finally, the Spiegler-Kedem-Katchalsky model was applied to simulate the behavior of the membrane on the elimination of this group of dyes.