Selective extraction of Bi(III) from sulfate solutions by a poly(vinyl chloride) based polymer inclusion membrane incorporating bis(2-ethylhexyl)phosphoric acid as the extractant

Polymer Inclusion Membranes (PIMs) for Metal Separation-Toward Environmentally Friendly Production and Applications

Polymer inclusion membranes (PIMs) have been reported to be useful for the selective separation of numerous metal ions, with multiple applications in areas such as analytical chemistry, water quality monitoring, water treatment, and metal recovery. This review aims to update the recent advancements related to PIM technology in metal ion separation, with a particular emphasis on environmentally friendly production and applications. PIMs have many advantages over classical liquid-liquid extraction, such as excellent selectivity, ease of use with simultaneous extraction and back-extraction, stability, and reusability. PIMs typically consist of a base polymer, a carrier, and, if necessary, a plasticizer, and can therefore be tailored to specific analytes and specific matrices. Consequently, numerous studies have been carried out to develop PIMs for specific applications. In analytical chemistry, PIMs have been used mostly for analyte preconcentration, matrix separation, speciation analysis, and sensing. They can be used as passive sampling tools or integrated into automated water monitoring systems. PIMs are also widely studied for the extraction and purification of valuable metals in the frame of the circular economy, as well as for wastewater treatment. Even if they are a greener alternative to classical metal extraction, their production still requires petroleum-based polymers and toxic and volatile solvents. In recent years, there has been a clear trend to replace classical polymers with biodegradable and bio-sourced polymers and to replace the production of PIMs using toxic solvents with those based on green solvents or without solvents. According to the published literature, environmentally friendly PIM-based techniques are a highly recommended area of future research for metal ion separation directed toward a wide range of applications.

A Pyridine Amine Extractant for Separation of La3+ and Ce3+ in HNO3 Solution

The separation of lanthanum and cerium is of great significance for improving the material properties and promoting scientific and technological progress. In this paper, a pyridine amine extractant, (1R,2S)-N1,N2-bis((5-methylpyridin-2-yl)methyl)cyclohexane-1,2-biamine (cis-BMPyMChBA), was designed for the separation of lanthanum and cerium. The aim is to use this extractant to catalyze the oxidation of tri- to tetravalent cerium and to increase the separation efficiency between lanthanum and cerium. The effects of the temperature, diluent, extractant concentration, and pH were evaluated to the extraction and separation performance of lanthanum and cerium. The experimental results demonstrate that cis-BMPyMChBA exhibits high selectivity for cerium, with a separation factor for lanthanum and cerium reaching 122.9. The coordination mechanism between cis-BMPyMChBA and cerium ion was clarified through the combined use of extraction isotherm, Job's curve, spectroscopic methods, and density functional theory (DFT) calculation. It involved the interaction between the secondary amine N atom and the pyridine N atom and the metal ion in which the cerium ion underwent a valence change from trivalent to tetravalent before extraction. This was found to be more conducive to the separation of lanthanum and cerium.

PVDF-HFP-based polymer inclusion membrane functionalized with D2EHPA for the selective extraction of bismuth(III) from sulfate media

This study is the first application of a PVDF-HFP-based polymer inclusion membrane incorporating the poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and di(2-ethylhexyl)phosphoric acid (D2EHPA) as the base polymer and extractant for the extraction of bismuth(III), respectively. It is demonstrated that the PIM comprised of 60 wt% PVDF-HFP and 40 wt% D2EHPA is the most effective in the extraction of bismuth(III) from feed solution containing 20 mg L-1 bismuth(III) and 0.2 mol L-1 sulfate adjusted to pH 1.4. The extracted bismuth(III) ions are back-extracted quantitatively to the receiving solution containing 1 mol L-1 sulfuric acid. The stoichiometry experiments reveal that the Bi: D2EHPA ratio in the bismuth(III) extracted complex is 1:6, and D2EHPA is dimer. Moreover, it is shown that the studied PIM has high selectivity in the extraction of bismuth(III) over other interfering ions such as Mo(VI), Cr(III), Al(III), Fe(III), Ni(II), Zn(II), Cd(II), Co(II), Cu(II), and Mn(II). The interference of Fe(III) is also eliminated by masking with fluoride, leading finally to a nearly pure extraction of bismuth(III).

A Comprehensive Study on the Effect of Plasticizers on the Characteristics of Polymer Inclusion Membranes (PIMs): Exploring Butyl Stearate as a Promising Alternative

This study investigated the influence of various plasticizers commonly used in the manufacture of polymer inclusion membranes (PIMs), such as 2-nitrophenyl octyl ether (NPOE), phthalates, adipates, and sebacates on the mechanical, thermal, and transport properties of membranes. Additionally, butyl stearate (BTS), chosen for its non-toxic nature compared to phthalates and its cost-effectiveness relative to adipates and sebacates, was evaluated as a plasticizer in PIMs for the first time. All plasticizers were incorporated in PIMs made of either cellulose triacetate (CTA) or poly(vinyl chloride) (PVC) as the base polymers and the task-specific ionic liquid trioctylmethylammonium thiosalicylate (TOMATS) as the carrier. The plasticizers were found to significantly affect the characteristics of membrane hydrophilicity, mechanical flexibility, and thermal stability. Transport experiments using Hg(II) as a model target ion revealed that, for CTA-based PIMs, the plasticizer did not significantly affect transport efficiency. However, for PVC-based PIMs, BTS exhibited better efficiency when compared to NPOE. These findings highlight the potential of BTS as an attractive alternative to currently used plasticizers in PVC-based PIM formulations.

The Use of Polymer Inclusion Membranes for the Removal of Metal Ions from Aqueous Solutions-The Latest Achievements and Potential Industrial Applications: A Review

The growing demand for environmentally friendly and economical methods of removing toxic metal ions from polluted waters and for the recovery of valuable noble metal ions from various types of waste, which are often treated as their secondary source, has resulted in increased interest in techniques based on the utilization of polymer inclusion membranes (PIMs). PIMs are characterized by many advantages (e.g., the possibility of simultaneous extraction and back extraction, excellent stability and high reusability), and can be adapted to the properties of the removed target analyte by appropriate selection of carriers, polymers and plasticizers used for their formulation. However, the selectivity and efficiency of the membrane process depends on many factors (e.g., membrane composition, nature of removed metal ions, composition of aqueous feed solution, etc.), and new membranes are systematically designed to improve these parameters. Numerous studies aimed at improving PIM technology may contribute to the wider use of these methods in the future on an industrial scale, e.g., in wastewater treatment. This review describes the latest achievements related to the removal of various metal ions by PIMs over the past 3 years, with particular emphasis on solutions with potential industrial application.