Selective extraction and concentration of chromium(VI) from acidic solutions containing various metal ions through emulsion liquid membranes using Amberlite LA-2

Understanding competitive Cu2+ and Zn2+ adsorption onto functionalized cellulose fiber via experimental and theoretical approach

Amidoxime groups were successfully introduced to develop a novel amidoxime-functionalized cellulose fiber (AO-Cell) for absorptive removal of heavy metal ions in wastewater. The chemical structure, and the competitive adsorption of Cu2+ and Zn2+ by AO-Cell were investigated by experiments study, Density functional theory (DFT) and molecular dynamic (MD) simulation. The results showed the N and O atoms in the amidoxime group can spontaneously interact with Cu2+ and Zn2+ through sharing long pair electrons to generate stable coordination structure, which was the dominant adsorption mechanism. Besides, the enlarged surface area, improved hydrophilicity and dispersion offered by AO-Cell facilitate the adsorption process by increasing the accessibility of absorption sites. As results of these synergetic modification, AO-Cell can remain effective in a wide pH range (1-6) and reach adsorption equilibrium within 60 min. At optimal conditions, the achieved theoretical adsorption capacity is as high as 84.81 mg/g for Cu2+ and 61.46 mg/g for Zn2+ in the solution with multiple ions. The competition between Cu2+ and Zn2+ in occupying the absorption sites arises from the difference in the metallic ion affinity and covalent index with the adsorbent as demonstrated by the MD analysis. Importantly, AO-Cell demonstrated favorable recyclability after up to 10 adsorption-desorption cycles.

Optimization and Prediction of Stability of Emulsified Liquid Membrane (ELM): Artificial Neural Network

In this work, the emulsified liquid membrane (ELM) extraction process was studied as a technique for separating different pollutants from an aqueous solution. The emulsified liquid membrane used consisted of Sorbitan mono-oleate (Span 80) as a surfactant with n-hexane (C6H14) as a diluent; the internal phase used was nitric acid (HNO3). The major constraint in the implementation of the extraction process by an emulsified liquid membrane (ELM) is the stability of the emulsion. However, this study focused first on controlling the stability of the emulsion by optimizing many operational factors, which have a direct impact on the stability of the membrane. Among the important parameters that cause membrane breakage, the surfactant concentration, the emulsification time, and the stirring speed were demonstrated. The optimization results obtained showed that the rupture rate (Tr) decreased until reaching a minimum value of 0.07% at 2% of weight/weight of Span 80 concentration with an emulsification time of 3 min and a stirring speed of 250 rpm. On the other hand, the volume of the inner phase leaking into the outer phase was predicted using an artificial neural network (ANN). The evaluation criteria of the ANN model in terms of statistical coefficient and RMSE error revealed very interesting results and the performance of the model since the statistical coefficients were very high and close to 1 in the four phases (R_training = 0.99724; R_validation = 0.99802; R_test = 0.99852; R_all data = 0.99772), and also, statistical errors of RMSE were minimal (RMSE_training= 0.0378; RMSE_validation = 0.0420; RMSE_test = 0.0509; RMSE_all data = 0.0406).

Recovery of chromium (VI) from hazardous APV wastewater using a novel synergistic extraction system

As a well-known hazardous material, chromium (VI) in industrial wastewater has always attracted extensive attention. Many studies have focused on the recovery of Cr (VI) which is still challenging and received considerable interest. In this study, a novel synergistic extraction system using amide as extractant and Cyanex 272 as synergistic extractant was built to recover chromium (VI) from the APV wastewater. After optimizing the process parameters of extractant concentration, initial pH, extraction temperature, extraction time, extraction phase ratio, ammonia concentration and stripping phase ratio, the final extraction and stripping efficiency reached more than 99% and 98%, respectively. The Cr₂O₃ product with a purity of 99.52 was prepared and the organic phase could be effectively regenerated for recycling. The extraction mechanism of chromium (VI) in the synergistic extraction system was investigated in-depth with slope method, ESI-MS analysis and FT-IR analysis. In addition, molecular electrostatic potentials analysis was used to display visually the formation process of the extract complex. This paper offered a unique approach to guide sustainable chromium (VI) recovery from hazardous wastewater with great industrial and theoretical significance.

Simultaneous extraction and enrichment of reactive dye using green emulsion liquid membrane system

Currently, an extractive green palm oil-based emulsion liquid membrane (ELM) has been used for simultaneous extraction and enrichment of Reactive Red 3BS from simulated synthetic dye wastewater. The ELM consists of two main phases, which are organic liquid membrane (LM) and stripping solution. During the extraction process, the ELM was dispersed into the simulated synthetic dye wastewater containing the Reactive Red 3BS complexes. The organic LM contains tridodecylamine (TDA), Sorbitan Monooleate (Span 80) and palm oil as a carrier, surfactant and diluent, respectively. The sodium bicarbonate (NaHCO₃) was used as stripping solution for the enrichment process. Several important parameters that affected the simultaneous extraction and enrichment of Reactive Red 3BS, such as carrier and stripping agent concentrations, extraction time and treat ratio, were investigated. The results showed that almost 90% of Reactive Red 3BS ions were successfully extracted with 10 times enrichment in the stripping phase at the optimum conditions of 0.2 M TDA, 0.1 M NaHCO₃, 5 min of extraction time and 1:5 of treat ratio. Hence, it can be concluded that palm oil possesses a high potential as green diluent in future technology, especially in ELM process for the removal and recovery of Reactive Red 3BS from synthetic dye wastewater.

The efficient removal of thallium from sintering flue gas desulfurization wastewater in ferrous metallurgy using emulsion liquid membrane

The removal of thallium ions in flue gas desulfurization wastewater from ferrous metallurgic industry was studied by emulsion liquid membrane (ELM) method using 2-ethylhexyl phosphoric acid-2-ethylhexyl ester (P507) as carrier, aviation kerosene (AK) as organic solvent, polyisobutylene succinimide (T154) as surfactant, polyisobutylene (PIB) as additive, and sulfuric acid as internal reagent. Some important influence parameters such as concentrations of carrier, surfactant and stripping agent, agitation speed, extraction time, volume ratios of feed solution to emulsion phase and internal phase to membrane phase, and their effects on the removal efficiency of Tl in the ELM process were investigated and optimized. Under the optimum operating conditions of 2% of carrier, 5% of surfactant, 0.5 M of stripping agent, 350 rpm of agitation speed, 12.5:1 of volume ratio of feed solution to emulsion phase, and 3:1 volume ratio of membrane to internal phase, the maximum extraction efficiency of thallium reached 99.76% within 15-min reaction time. The ICP-MS analysis indicated that the thallium concentration in treated wastewater was below 5 μg/L and could meet the emission standard demand for industrial wastewater enacted by the local government of Hunan province of China. Meanwhile, the extraction of impurity ions calcium and magnesium in the ELM system was investigated. The result showed that an acidic environment would be in favor of the removal of Tl from calcium and magnesium contained in wastewater. Graphical abstract ᅟ.

Ultrasound assisted preparation of water in oil emulsions and their application in arsenic (V) removal from water in an emulsion liquid membrane process

Water in oil emulsions are prepared by using an ultra-sonication device and used in an emulsion liquid membrane process in order to recover arsenic (V) ions from an aqueous medium. The aim of this work is the investigation of the effect of emulsifier concentration and composition, and also sonication time on the emulsion droplet size and the extraction efficiency in order to obtain stable emulsions with small droplets that favor the extraction. Results show that ultrasonic waves reduce internal droplet size which enhances the extraction of arsenic. In addition, internal droplet size is decreased initially and then increased by increasing Span 80 concentration. On the other hand, by increasing Span 80 concentration, extraction amount is increased and then decreased. Furthermore, emulsifier blends provide more stability for the emulsion. Increasing concentration of Tween 20 as a hydrophilic emulsifier up to an optimum concentration decreases internal droplet size and increases extraction amount. By increasing sonication time up to 4 min, the internal droplet size is decreased and the extraction amount is increased. If sonication time is increased further, the internal droplet size is increased and the extraction amount is decreased.

Polyrhodanine modified anodic aluminum oxide membrane for heavy metal ions removal

Polyrhodanine was immobilized onto the inner surface of anodic aluminum oxide (AAO) membrane via vapor deposition polymerization method. The polyrhodanine modified membrane was applied to remove heavy metal ions from aqueous solution because polyrhodanine could be coordinated with specific metal ions. Several parameters such as initial metal concentration, contact time and metal species were evaluated systematically for uptake efficiencies of the fabricated membrane under continuous flow condition. Adsorption isotherms of Hg(II) ion on the AAO-polyrhodanine membrane were analyzed with Langmuir and Freundlich isotherm models. The adsorption rate of Hg(II) ion on the membrane was obeyed by a pseudo-second order equation, indicating the chemical adsorption. The maximum removal capacity of Hg(II) ion onto the fabricated membrane was measured to be 4.2 mmol/g polymer. The AAO-polyrhodanine membrane had also remarkable uptake performance toward Ag(I) and Pb(II) ions. Furthermore, the polyrhodanine modified membrane could be recycled after recovery process. These results demonstrated that the polyrhodanine modified AAO membrane provided potential applications for removing the hazardous heavy metal ions from wastewater.