Solvent Bar Micro-Extraction of Heavy Metals from Natural Water Samples Using 3-Hydroxy-2-Naphthoate-Based Ionic Liquids

Abstract

Developments in the liquid micro-extraction of trace metals from aqueous phases have proven to be limited when extended from pure water to more complex and demanding matrices such as sea water or wastewater treatment effluents. To establish a system that works under such matrices, we successfully tested three task-specific ionic liquids, namely trihexyltetradecyl- phosphonium-, methyltrioctylphosphonium- and methyltrioctylammonium 3-hydroxy-2-naphthoate in two-phase solvent bar micro-extraction (SBME) experiments. We describe the influence of pH, organic additives, time, stirring rate and volume of ionic liquid for multi-elemental micro-extraction of Cu, Ag, Cd and Pb from various synthetic and natural aqueous feed solutions. Highest extraction for all metals was achieved at pH 8.0. Minimal leaching of the ionic liquids into the aqueous phase was demonstrated, with values < 30 mg L−1 DOC in all cases. Sample salinities of up to 60 g L−1 NaCl had a positive effect on the extraction of Cd, possibly due to an efficient extraction mechanism of the present chlorido complexes. In metal-spiked natural feed solutions, the selected SBME setups showed unchanged stability under all conditions tested. We could efficiently (≥85%) extract Cu and Ag from drinking water and achieved high efficacies for Ag and Cd from natural sea water and hypersaline water, respectively. The method presented here proves to be a useful tool for an efficient SBME of heavy metals from natural waters without the need to pretreat or modify the sample.

Heavy Metal Extraction under Environmentally Relevant Conditions Using 3-Hydroxy-2-Naphthoate- Based Ionic Liquids: Extraction Capabilities vs. Acute Algal Toxicity

“…The three ILs utilized in this study have been previously tested for their capability to extract the heavy metals Cu, Ag, Cd and Pb from pure water as well as from several synthetic and natural waters, including drinking water and seawater. High extraction efficacies have been described at mg L −1 levels in liquid-liquid as well as in a solvent bar micro-extraction setup [28,34]. The extraction of Hg had not been tested before.…”

“…Values ranged between a partial dissolution of 0.1%-0.8%, implying a high potential for reusability of the three ILs in liquid-liquid extraction setups. In contrast to the multi-elemental setup of past works [28,34], the single metal experiments in the present study enabled an examination of metal-dependent changes in leaching. This provides insights into the prevalent extraction mechanisms.…”

“…Our results clearly indicate that environmentally favorable conditions in the sample solution after extraction cannot be easily achieved even when using highly hydrophobic ILs. Certainly, the leaching behavior of ILs can be improved in several ways: we demonstrated that immobilizing ILs on solid supports can substantially decrease leaching by up to 88% [34,61], leaving residual IL concentrations in the feed solution at concentrations approximate to the EC 50 values.…”

Radionuclide extraction with different ionic liquids

“…a negligible or only a very low amount of the IL should be dissolved in the aqueous phase after extraction, in order to minimize loss of the IL as well as to avoid water pollution. Aqueous solubility or leaching into the water phase is also known as "bleeding", and different causes might be responsible for this process: solubility of the IL in the aqueous phase (which could be circumvented by using ions with higher hydrophobicity or by immobilization of the IL on an inert carrier [4,5] or in an hollow fiber [6,8]), or ion exchange as extraction mechanism. In the latter case the anion or cation of the IL is substituted by the metal or a metal compound and the leaching is part of the metal extraction mechanism.…”

“…At our institute ILs which can be produced in a straightforward metathesis reaction from cheap precursor molecules were tested for their ability to extract heavy metals such as Ag, Cd, Co, Cu, Hg, Mn, Ni, Pb, Pt and Zn from different water samples as e.g. surface waters or waste waters [3][4][5][6][7][8]. As radionuclides in drinking water is an important issue in radiation protection it was obvious to test some of these ILs (primarily those which had already been used successfully for inactive metal extraction) also for extraction of uranium and thorium [9] and later on also for 226 Ra, 210 210 Po within short times, while the other radionuclides were removed from water to a much lesser extent and often with strong dependence of the pH value.…”