Cd(II) extraction in PEG-based two-phase aqueous systems in the presence of iodide ions. Analysis of PEG-rich solid phases

Abstract

Cd(II) plus iodide species were extracted into PEG-rich phases in the aqueous PEG(1550)-(NH 4 ) 2 SO 4 system at pH 2.05 -7.12. IR spectra show that increasing (NH 4 ) 2 SO 4 solution acidity does not protonate PEG ether oxygen atoms, but decreases water content in the PEG-rich phases. Metallic species' extraction into the PEG predominantly alters how water molecules bind to polymer chains; the changes in their absorption bands depend on pH. Microscopy shows that "fixation" of the extracted metal in the PEG-rich phase occurs by specific interactions which depend on the species. These also determine changes in the polymer chains' conformation.

Extraction of gold(III) from chloride media in aqueous polyethylene glycol-based two-phase system

“…In general, the decreasing of salt stock solution pH determined a decrease of water content from PEG-rich phase [19,21], and thus an enhancement of the metal ion extraction efficiency is obtained. However, because this dependence is not linear, the nature and stability of extracted species have an important role in the extraction process.…”

“…[20][21][22][23]. It has also been shown that gold(I), when it is complexed with cyanide can be quantitatively extracted (>96%) in aqueous PEGbased two-phase system, where Na 2 SO 4 is used as phase-forming inorganic salt [24].…”

Liquid–liquid extraction of metal ions without use of organic solvent

“…Unlike the studies applying ATPS for biomolecule partition, in which a great number of different forming compounds were used [7,8], almost all reports on ATPS metal partitioning show that the biphasic systems are formed only by the polymer poly(ethylene oxide) (PEO) of molar mass 2000 g mol −1 and some inorganic anions (CO 3 2− , SO 4 2− , OH − or PO 4 3− ) [9]. Besides, these limited types of ATPS applied to metal extraction restrict the use of all potential extractants to only water-soluble compounds such as halides, thiocyanates, arsenazo III, alizarin and others, which aqueous two-phase system formed by triblock copolymer and salt and (c) metallic complex or extractant (hydrophobic compounds) preferentially partitioned into the copolymer-enriched phase due to its solubilization in the micelle cores.…”

Separation of Cd and Ni from Ni–Cd batteries by an environmentally safe methodology employing aqueous two-phase systems

“…The influence of pH on the coordination number of the cadmium-iodide complex, and hence on the metal extraction, using an ATPS formed with polyethylene glycol + (NH 4 ) 2 SO 4 + water was reported by Bulgariu and co-workers [22]. According to this study, for pH values lower than 3.10, CdI 4 2− is the preferentially formed species and higher extraction yields are reached.…”

“…Therefore, it is important to devise novel extraction methods which are cleaner and environmentally safer. In view of this, aqueous two-phase systems (ATPS) are introduced as very promising liquid-liquid extraction systems for metal separation, since they are mostly composed of water and other constituents which are neither toxic nor flammable [20][21][22].…”