Anja Stojanovic

Ionic Liquids as Extracting Agents for Heavy Metals

The development of applications of ionic liquids in extraction processes stretches back to the mid-1960s when the first studies on ionic liquid- based extractions were published. Since then, the interest of both academics and the industrial community on the development of ionic liquids-based technologies is continuously growing. The main driving force of ionic liquid engineering is to combine their “environmentally friendly” properties (e.g., extremely low vapor pressure) and their unique reactivity and miscibility behavior in order to improve the current “state of the art” technologies. The focus of this review is on the application of ionic liquid in heavy metal extraction processes. The critical aspects of their journey from academic curiosity towards industrial application are highlighted.

Ionic liquids for extraction of metals and metal containing compounds from communal and industrial waste water

In a fundamental study the potential of ionic liquids based on quaternary ammonium- and phosphonium cations and thiol-, thioether-, hydroxyl-, carboxylate- and thiocyanate-functionalized anions has been assessed for future application in advanced sewage treatment. The elimination of the metal(oid)s Ag, As, Cd, Cr, Cu, Hg, Ni, Pb, Pt, Sn, Zn and the cancerostatic platinum compounds cisplatin and carboplatin was screened using a liquid phase micro-extraction set-up. The analytical tool-set consisted of ICP-SFMS and LC-ICP-MS for quantification of metal(oid)s and cancerostatic platinum compounds, respectively. The purity of the ILs was assessed for the investigated metal(oid)s on the base of present EU environmental quality standards and was found to be sufficient for the intended use. In model solutions at environmental relevant concentrations extraction efficiencies≥95% could be obtained for Ag, Cu, Hg and Pt with both phosphonium- and ammonium-based ILs bearing sulphur functionality in the form of thiosalicylate and 2-(methylthiobenzoate) anions, as well as with tricaprylmethylammonium thiocyanate within an extraction time of 120 min. All other metals were extracted to a lower extent (7-79%). In the case of cancerostatic platinum compounds a phosphonium-based IL bearing thiosalicylate functionality showed high extraction efficiency for monoaquacisplatin. For the first time, liquid phase micro extraction with ionic liquids was applied to industrial and communal waste water samples. The concentration of all investigated metal(oid)s could be significantly reduced. The degree of elimination varied with the initial concentration of metals, pH and the amount of suspended particulate matter.

Phosphonium and Ammonium Ionic Liquids with Aromatic Anions: Synthesis, Properties, and Platinum Extraction

Several hydrophobic long-chain quaternary ammonium and phosphonium ionic liquids (ILs) with functionalized aromatic anions were prepared following a metathesis route using tricaprylmethylammonium chloride (Aliquat 336) and trihexyl(tetradecyl)phosphonium chloride (Cyphos IL101) as precursors. The incorporation of aromatic anions bearing hydroxy-, methoxy-, thiol-, and thioether functionalities as well as tetraphenylborate anions resulted in an increased chemical stability of the ILs and an alteration of their physico-chemical properties. Furthermore, aromatic anions significantly decreased the water solubility and water uptake of both ammonium and phosphonium-based ILs. Thiol- and thioether ILs were applied for the extraction of platinum from aqueous phase using liquid phase micro-extraction. Time dependent studies showed a rapid elimination of up to 95% platinum after 30 min. With a leaching of the anion <0.01 wt-% into the aqueous media, the evaluated ILs were found to be suitable as extracting agents for platinum from aqueous solutions.

Uranium extraction from aqueous solutions by ionic liquids.

For determining natural levels of (236)U with its environmental abundance of 10(-16)% rather large sample volumes (approximately 30L) are necessary, therefore the conventional radiochemical uranium analysis (pre-concentration and column chromatography) is very time consuming. To speed up the procedure hydrophobic ionic liquids (ILs) were evaluated as a potential extraction agent for uranium from aqueous solutions. High selectivity and efficiency for uranium compared to calcium and magnesium in natural water was achieved with tricaprylmethylammonium thiosalicylate, [A336][TS]. Uranium was stripped successfully from the investigated ILs with 2M HNO(3).

Analysis of quaternary ammonium and phosphonium ionic liquids by reversed-phase high-performance liquid chromatography with charged aerosol detection and unified calibration.

Several hydrophobic ionic liquids (ILs) based on long-chain aliphatic ammonium- and phosphonium cations and selected aromatic anions were analyzed by reversed-phase high-performance liquid chromatography (RP-HPLC) employing trifluoroacetic acid as ion-pairing additive to the acetonitrile-containing mobile phase and adopting a step-gradient elution mode. The coupling of charged aerosol detection (CAD) for the non-chromophoric aliphatic cations with diode array detection (DAD) for the aromatic anions allowed their simultaneous analysis in a set of new ILs derived from either tricaprylmethylammonium chloride (Aliquat 336) and trihexyltetradecylphosphonium chloride as precursors. Aliquat 336 is a mix of ammonium cations with distinct aliphatic chain lengths. In the course of the studies it turned out that CAD generates an identical detection response for all the distinct aliphatic cations. Due to lack of single component standards of the individual Aliquat 336 cation species, a unified calibration function was established for the quantitative analysis of the quaternary ammonium cations of the ILs. The developed method was validated according to ICH guidelines, which confirmed the validity of the unified calibration. The application of the method revealed molar ratios of cation to anion close to 1 indicating a quantitative exchange of the chloride ions of the precursors by the various aromatic anions in the course of the synthesis of new ILs. Anomalies of CAD observed for the detection of some aromatic anions (thiosalicylate and benzoate) are discussed.

Quaternary Ammonium and Phosphonium Ionic Liquids in Chemical and Environmental Engineering

Quaternary ammonium salts (quats) are an economically advantageous class of industrial compounds. They have surface-active properties, possess anti-microbial activity and are known to be bioactive (Boethling & Lynch, 1992; Juergensen et al., 2000). Contrary, reports regarding low melting tetraalkylphosphonium salts were relatively rare in the literature during the last decades (Bradaric et al., 2003). Although ILs based on quaternary ammonium cations have been known and produced for years, and also numerous phosphonium based ILs have been produced even in ton-scale, these groups of ionic liquids have been more or less “neglected” in the literature comparing to their imidazolium or pyridinium based counterparts. However, during the last decade significant work has been done, pointing out the advantages and broad application spectrum of these types of ionic liquids. Their improved thermal and chemical stability in comparison to e.g. pyridinium and imidazolium based ILs, their unique miscibility behaviour and solvating properties advances their use in specific applications (Rogers et al., 2002; Plechkova & Seddon, 2007; Chowdhury et al., 2007; Wasserscheid & Welton, 2008). Several ILs based on these classes of cations are already commercially available and have been successfully applied as phase-transfer catalysts, solvents, lubricants, gas capture agents, coating materials, or chemical sensors (Bradaric et al., 2003; Weng et al., 2006; Pernak et al., 2006; Yuan et al., 2007; Fraser & MacFarlane, 2009; Werner et al., 2010). Tricaprylylmethylammonium chloride (trade name Aliquat® 336), produced in ton-scale by Henkel, is nowadays widely used as metal extraction agent, phase transfer catalyst, surfactant, or antistatic agent. In contrast, trihexyl(tetradecyl)phosphonium chloride (trade name Cyphos® IL 101) was developed by Cytec Industries as a thermally stable phase transfer catalyst (Bradaric et al., 2003). Due to the relatively simple preparation route, Cyphos® IL 101 is produced in ton-scale and therefore represents a fairly cheap IL. Hence, due to their commercial availability and low prices, both Aliquat® 336 and Cyphos® IL 101 can be used themselves or represent favorable precursors for a series of ionic liquids. The goal of this chapter is to give some insight into the fascinating and fast-growing field of

Application of ionic liquids for the removal of heavy metals from wastewater and activated sludge

This paper presents the results of adsorption studies on the removal of heavy metals (Cr, Cu, Cd, Ni, Pb and Zn) from standard solutions, real wastewater samples and activated sewage sludge using a new technique of liquid-liquid extraction using quaternary ammonium and phosphonium ionic liquids (ILs). Batch sorption experiments were conducted using the ILs [PR4][TS], [PR4][MTBA], [A336][TS] and [A336][MTBA]. Removal of these heavy metals from standard solutions were not effective, however removal of heavy metals from the industrial effluents/wastewater treatment plants were satisfactory, indicating that the removal depends mainly on the composition of the wastewater and cannot be predicted with standard solutions. Removal of heavy metals from activated sludge proved to be more successful than conventional methods such as incineration, acid extraction, thermal treatment, etc. For the heavy metals Cu, Ni and Zn, ≥90% removal was achieved.

Preparation and characterization of immobilized [A336][MTBA] in PVA-alginate gel beads as novel solid-phase extractants for an efficient recovery of Hg (II) from aqueous solutions.

The coarse PVA-alginate matrix gel beads entrapping the micro-droplets of the ionic liquid tricaprylylmethylammonium 2-(methylthio) benzoate ([A336][MTBA]) as novel solid-phase extractants were prepared for the removal of mercury (II) from aqueous media. The ionic liquid [A336][MTBA] immobilized PVA-alginate beads (PVA/IL) have been characterized by FTIR, SEM and TGA. The influence of the uptake conditions was investigated including aqueous pH, PVA/IL dosage, the content of [A336][MTBA] and initial Hg (II) concentration; maximum Hg (II) ion adsorption capacity obtained was 49.89 (± 0.11)mgg(-1) at pH 5.8 with adsorptive removal of approximately 99.98%. The selectivity of the PVA/IL beads towards Hg (II), Pb (II) and Cu (II) ions tested was Hg>Pb>Cu. The rate kinetic study was found to follow second-order and the applicability of Langmuir, Freundlich and Tempkin adsorption isotherm model were tested as well. The results of the study showed that PVA/IL beads could be efficiently used as novel extractants for the removal of divalent mercury from aqueous solutions under comparatively easy operation conditions.

Designing melt flow of poly(isobutylene)-based ionic liquids

A series of novel poly(isobutylene)-based stable ionic liquids (PIB-ILs) with strongly temperature dependent nano- and mesostructures is reported. The molecular design relies on the use of a liquid polymer with an ionic liquid-head-group, introducing liquid properties by both the polymeric chain as well as the ionic liquid (IL) head-group thus enabling terminal flow in a range which cannot be addressed with classical ILs with respect to the design of potential self-healing materials. Modifying both the anchored cation and anion as well as the molecular weight of the attached polymer chain, the nanostructure and the viscoelastic behavior of PIB-ILs can be engineered. Detailed small-angle X-ray scattering (SAXS) investigations as well as rheology studies have been conducted to reveal structure, viscoelastic properties and relaxation behavior of the prepared PIB-ILs. All investigated PIB-ILs exhibited a defined nano- and mesoscale ordering at room temperature, whereas the nature of the anchored cation showed a strong impact on the temperature-dependence of the mesoscale-structure as well as on the flow behavior of PIB-ILs. Exchange of the bromide anion to bis(trifluoromethylsulfonyl)imide led to the loosening of the observed clusters and to lattice disorder–order transitions (LDOT) at lower temperatures, leading also to terminal flow at lower temperatures. Investigated PIB-ILs exhibited short relaxation times and the reestablishment of the nano/mesoscale morphology immediately after cooling at room temperature, which makes them suitable for the engineering of novel self-healing materials.

Evaluation of the Mechanical Properties of Microcapsule-Based Self-Healing Composites

Self-healing materials are beginning to be considered for applications in the field of structural materials. For this reason, in addition to self-healing efficiency, also mechanical properties such as tensile and compressive properties are beginning to become more and more important for this kind of materials. In this paper, three different systems based on epoxy-resins/ethylidene-norbornene (ENB)/Hoveyda-Grubbs 1st-generation (HG1) catalyst are investigated in terms of mechanical properties and healing efficiency. The experimental results show that the mechanical properties of the self-healing systems are mainly determined by the chemical nature of the epoxy matrix. In particular, the replacement of a conventional flexibilizer (Heloxy 71) with a reactive diluent (1,4-butanediol diglycidyl ether) allows obtaining self-healing materials with better mechanical properties and higher thermal stability. An increase in the curing temperature causes an increase in the elastic modulus and a slight reduction of the healing efficiency. These results can constitute the basis to design systems with high regenerative ability and appropriate mechanical performance.