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.

Sono-assisted adsorption of acid violet 7 and basic violet 10 dyes from aqueous solutions: Evaluation of isotherm and kinetic parameters

In this study, the removal of acid violet 7 (AV7) and basic violet 10 (BV10) synthetic dyes was investigated using fly ash alone, ultrasound (40 kHz) alone, and combined ultrasound/fly ash with various experimental parameters such as fly ash dose, contact time, and initial concentration of dye. The adsorption capacity of the ultrasound/fly ash process increased from 5.10 to 7.43 mg g-1 for AV7, and increased from 5.16 to 7.51 mg g-1 for BV10 compared with using fly ash alone. The sono–assisted adsorption process was successful in improving the dye uptake capacity with cavitation bubbles and acoustic waves, and thus AV7 and BV10 were removed with a shorter contact time and lower fly ash dose. Obtained regeneration and reuse experiment results showed that the fly ash could be reused for four consecutive cycles of the sono–assisted adsorption process, while fly ash could be reused for two consecutive cycles of the adsorption process. The adsorption kinetics for AV7 and BV10 onto fly ash fitted Lagergren’s first–order adsorption kinetic model well. The Langmuir isotherm best described the adsorption with fly ash alone and ultrasound/fly ash process for AV7 and BV10.

The adsorption of Mn(II) by insolubilized humic acid

The eco-friendly and non-toxic natural organic substance, insolubilized humic acid (IHA), was used to remove Mn(II) from aqueous solutions. The adsorption characteristics were studied through a series of static adsorption tests. The results show that conditions such as the dose, the pH of the solution and the initial concentration of Mn(II) all affect removal efficiency, and the optimal pH value was 5.5. The sorption process for Mn(II) on IHA conforms to the pseudo-second-order adsorption kinetic model and intra-particle diffusion is not the only factor affecting the adsorption rate. Both Langmuir and Freundlich models can describe this adsorption behavior, and the experimental maximum adsorption capacity of IHA was 52.87 mg/g under optimal conditions. The thermodynamic analysis of adsorption shows that the adsorption process is a non-spontaneous endothermic physical reaction. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) were used to characterize the samples, it was found that as IHA successfully adsorbed Mn(II), the surface morphology of IHA changed after the adsorption reaction. The adsorption mechanism for Mn(II) on IHA is to provide electron pairs for carboxyl, phenolic hydroxyl and other functional groups to form stable complexes with Mn(II).

Evaluation of Pb (II) Removal from Water Using Sodium Alginate/Hydroxypropyl Cellulose Beads

This study examined the removal of Pb2+ ions from aqueous solution with two different lead concentrations using a hydrogel-forming polymer based on hydroxypropyl cellulose (HPC) and sodium alginate (SA). The feasibility of the adsorption behavior of SA/HPC beads has been investigated with three varying ratios of 50:50, 75:25 and 100:0 under a stir condition. The adsorption experiments were done to determine the effects of contact time, lead concentration and SA-HPC ratio to the adsorption capacity of SA-HPC hydrogel beads. The results showed that the ratio 75:25 showed higher adsorption capacity compared to 100:0 and 50:50. It showcased 47.72 mg/g adsorption capacity and 95.45% adsorption percentage after three hours of contact time. The adsorption kinetic model indicated that the adsorption of Pb2+ ions onto the beads followed a pseudo-second order kinetic equation. This means that the adsorption mechanism shows a chemisorption process and its sole rate-limiting step is intraparticle diffusion.

Removal of Cd(II) from aqueous solution by clay-biochar composite prepared from Alternanthera philoxeroides and bentonite

A novel bentonite-biochar (APB) composite was prepared by incorporating bentonite (BE) with Alternanthera philoxeroides (AP) biochar for the adsorptive removal of Cd(II) from aqueous media. The APB and the pristine biochar (PB) prepared from the AP were produced at 300 °C under a nitrogen environment. The adsorption capabilities of the BE, PB, and APB were tested for the removal of Cd(II) from aqueous solution. The results showed that the pH substantially affected the adsorption of Cd(II) by the PB and APB. The adsorptive capacity of the Cd(II) onto the PB and APB gradually increased as the pH was increased to 6.0, and there was no significant change in adsorption as the pH was further increased to 8.0. The adsorption kinetic data of the PB and APB were fitted to a pseudo-second-order (PSO) adsorption kinetic model and an intraparticle diffusion (ID) model. The Freundlich model matched the experimental data better than the Langmuir model, indicating that the adsorption was heterogeneous. Thermodynamic study revealed that the adsorption was mainly physisorption, and the adsorption process was endothermic and spontaneous, while the orderliness of all adsorption systems decreased. The results demonstrated that the APB was an effective adsorbent for the removal of Cd(II) from aqueous media.

Alkali Lignin from Talahib Grass (Saccharum spontaneum L.) as An Adsorbent for Chromium (III) and Phenolphthalein: Analysis of the Adsorption Kinetics and Mechanism

The study aims to quantitatively assess the capability of lignin extracted from Saccharum spontaneum L. (talahib grass) as an adsorbent of chromium (III) and phenolphthalein in aqueous solution through kinetic methods. Results show that using lignin as an adsorbent, the percentage removal for both chromium (III) and phenolphthalein in aqueous solution are 31.70% and 74.98%, respectively, based on the optimum exposure time of the adsorbent, which is 6.5 hours for chromium (III) and 60 minutes for phenolphthalein. Results from the mechanistic analysis show that a pseudo-second order adsorption kinetic model fits better than a pseudo-first order model for both substrates. Also, among the six selected adsorption isotherm models used in this study, the Flory-Huggins isotherm can best predict the properties of the adsorption process of both phenolphthalein and chromium (III) at equilibrium. Further improvement of the extracted lignin through various physical and chemical modifications may improve its ability to remove the contaminants.