Mechanism of gold (III) extraction using a novel ionic liquid-based aqueous two phase system without additional extractants

Extraction of Gold Based on Ionic Liquid Immobilized in UiO-66: An Efficient and Reusable Way to Avoid IL Loss Caused by Ion Exchange in Solvent Extraction

Ionic liquids (ILs) have received considerable attention as a promising green solvent for extracting metal ions from aqueous solutions. However, the recycling of ILs remains difficult and challenging because of the leaching of ILs, which is caused by the ion exchange extraction mechanism and hydrolysis of ILs in acidic aqueous conditions. In this study, a series of imidazolium-based ILs were confined in a metal-organic framework (MOF) material (UiO-66) to overcome the limitations when used in solvent extraction. The effect of the various anions and cations of the ILs on the adsorption ability of AuCl₄^- was studied, and 1-hexyl-3-methylimidazole tetrafluoroborate ([HMIm]⁺[BF₄]^-@UiO-66) was used for the construction of a stable composite. The adsorption properties and mechanism of [HMIm]⁺[BF₄]^-@UiO-66 for Au(III) adsorption were also studied. The concentrations of tetrafluoroborate ([BF₄]^-) in the aqueous phase after Au(III) adsorption by [HMIm]⁺[BF₄]^-@UiO-66 and liquid-liquid extraction by [HMIm]⁺[BF₄]^- IL were 0.122 mg/L and 18040 mg/L, respectively. The results reveal that Au(III) coordinated with the N-containing functional groups, while [BF₄]^- was effectively confined in UiO-66, instead of undergoing anion exchange in liquid-liquid extraction. Electrostatic interactions and the reduction of Au(III) to Au(0) were also important factors determining the adsorption ability of Au(III). [HMIm]⁺[BF₄]^-@UiO-66 could be easily regenerated and reused for three cycles without any significant drop in the adsorption capacity.

Phase Behavior of Ionic Liquid-Based Aqueous Two-Phase Systems

As an environmentally friendly separation medium, the ionic liquid (IL)-based aqueous two-phase system (ATPS) is attracting long-term attention from a growing number of scientists and engineers. Phase equilibrium data of IL-based ATPSs are an important basis for the design and optimization of chemical reactions and separation processes involving ILs. This article provides the recent significant progress that has been made in the field and highlights the possible directions of future developments. The effects of each component (such as salting-out agents and ILs) on the phase behavior of IL-based ATPSs are summarized and discussed in detail. We mainly focus on the phase behavior of ATPSs by using ILs, expecting to provide meaningful and valuable information that may promote further research and application.

Countercurrent chromatography approach to palladium and platinum separation using aqueous biphasic system

For the first time, widespread aqueous biphasic polymer-salt extraction system was applied for selective separation of Pd(II) and Pt(IV) from chloride technological solutions by countercurrent chromatography using a rotating coiled column (an analog of centrifugal extractor). The principle novelty of the proposed approach is the possibility of multistage extraction process and the needlessness to add any specific reagents for targeted metal binding. The results showed that the use of poly(ethylene glycol)-1500 (PEG-1500) as a stationary phase allows 96-100% of both Pd(II) and Pt(IV) to be recovered from chloride solutions containing copper and nickel. To obtain individual solutions of targeted metals it is enough to change the composition of the salt-rich phase for stripping stage, in particular the salt concentration and pH value. The final purity of the targeted metal fractions obtained after their extraction from model technological solutions is ≥ 99.9%. The components of the aqueous biphasic system are recyclable, non-toxic, available, and widespread in laboratory and technology practice. A scheme of the multistage separation of platinum metals using a rotating coiled column is proposed.

Properties and mechanism for selective adsorption of Au(iii) on an ionic liquid adsorbent by grafting N-methyl imidazole onto chloromethylated polystyrene beads

To recover Au(iii) from an acidic chloride-containing solution efficiently, an ionic liquid absorbent (CMPS-IL) was synthesized by grafting N-methyl imidazole onto chloromethylated polystyrene beads (CMPS). The adsorption capacity, selectivity, and reusability were systematically evaluated by a series of adsorption experiments. The maximum adsorption capacity reached up to 516.5 mg g⁻¹ at 318 K. The adsorbent can selectively recover Au(iii) from binary system solutions with a higher separation factor β_Au/M (10⁴–10⁶). Moreover, the adsorption–desorption cycles (7 cycles) showed that the CMPS-IL maintained a stable adsorption performance and high adsorption efficiency. Finally, the adsorption mechanism of CMPS-IL for Au(iii) was investigated by SEM, TEM, XPS, and FT-IR, then proposed with a combination of electrostatic interactions and d–π interaction between imidazolium and AuCl₄⁻. This study provides an easily-prepared and economical adsorbent for Au(iii) with high selectivity and large adsorption capacity to boost its practical applications.

The synthesis and adsorption properties for Au(iii) of CMPS-IL synthesized by grafting N-methyl imidazole onto chloromethylated polystyrene beads (CMPS).

Evolution of Environmentally Friendly Strategies for Metal Extraction

The demand for the recovery of valuable metals and the need to understand the impact of heavy metals in the environment on human and aquatic life has led to the development of new methods for the extraction, recovery, and analysis of metal ions. With special emphasis on environmentally friendly approaches, efforts have been made to consider strategies that minimize the use of organic solvents, apply micromethodology, limit waste, reduce costs, are safe, and utilize benign or reusable materials. This review discusses recent developments in liquid- and solid-phase extraction techniques. Liquid-based methods include advances in the application of aqueous two- and three-phase systems, liquid membranes, and cloud point extraction. Recent progress in exploiting new sorbent materials for solid-phase extraction (SPE), solid-phase microextraction (SPME), and bulk extractions will also be discussed.

Response Surface Methodology for the Evaluation of Magnetite Partitioning Behavior in Polyethylene Glycol-Based Aqueous Biphasic System

Response surface methodology in the framework of central composite design has successfully applied to polyethylene glycol (PEG)-based aqueous two-phase system in order to evaluate its efficiency in extracting Fe from iron ores with respect to PEG molecular weight, PEG concentration and salt concentration factors. Furthermore, ANOVA and multiple regression analysis have provided a second-order polynomial equation that is highly capable of predicting the experimental results. The PEG molecular weight and weight percent of the salt in the feed had a major and minor effects on the iron ion partition coefficient, respectively.

Extraction and purification of isochlorogenic acid C from Chrysanthemum morifolium using ionic liquid-based ultrasound-assisted extraction and aqueous two-phase system

Ionic liquid-based ultrasonic-assisted extraction (IL-UAE) was developed to extract and separate the isochlorogenic acid C (ICGA) from a cultivar of Chrysanthemum morifolium (Chrysanthemummorifolium Ra Tnat.). The influencing parameters, including IL concentration, liquid-to-solid ratio, and ultrasonic time, were optimized using response surface methodology. Of the ILs studied, 1-butyl-3-methylimidazolium bromide [(Bmim)Br] exhibited the best extraction ability. The optimized conditions included liquid-to-solid ratio of 23.44:1, ultrasonic time of 48.99 min, and IL concentration of 0.65 mol/L. Under the optimal conditions, the extraction yield of ICGA could reach to 4.20 mg/g. An aqueous two-phase system was applied for purification and separation of ICGA. The maximum extraction efficiency of 98.18% was obtained under the conditions of (NH 4)2 SO 4 of 4.5 g, pH of 3.0, and a temperature of 20°C at aqueous solution. Furthermore, the thermodynamic parameters showed that the purification of ICGA from salt-rich phase to IL-rich phase was a spontaneous and exothermic process. The results indicated that the proposed system is simple, rapid, and effective to serve as a viable and sustainable platform for the extraction and purification of ICGA from Chrysanthemum morifolium flowers.

A green separation strategy for neodymium (III) from cobalt (II) and nickel (II) using an ionic liquid-based aqueous two-phase system

It is significant to develop sustainable strategies for the selective separation of rare earth from transition metals from fundamental and practical viewpoint. In this work, an environmentally friendly solvent extraction approach has been developed to selectively separate neodymium (III) from cobalt (II) and nickel (II) by using an ionic liquid-based aqueous two phase system (IL-ATPS). For this purpose, a hydrophilic ionic liquid (IL) tetrabutylphosphonate nitrate ([P₄₄₄₄][NO₃]) was prepared and used for the formation of an ATPS with NaNO₃. Binodal curves of the ATPSs have been determined for the design of extraction process. The extraction parameters such as contact time, aqueous phase pH, content of phase-formation components of NaNO₃ and the ionic liquid have been investigated systematically. It is shown that under optimal conditions, the extraction efficiency of neodymium (III) is as high as 99.7%, and neodymium (III) can be selectively separated from cobalt (II) and nickel (II) with a separation factor of 10³. After extraction, neodymium (III) can be stripped from the IL-rich phase by using dilute aqueous sodium oxalate, and the ILs can be quantitatively recovered and reused in the next extraction process. Since [P₄₄₄₄][NO₃] works as one of the components of the ATPS and the extractant for the neodymium, no organic diluent, extra etractant and fluorinated ILs are used in the separation process. Thus, the strategy described here shows potential in green separation of neodymium from cobalt and nickel by using simple IL-based aqueous two-phase system.

Extraction in cholinium-based magnetic ionic liquid aqueous two-phase system for the determination of berberine hydrochloride in Rhizoma coptidis

A magnetic ionic liquids (MILs)-based aqueous two-phase system (MIL-ATPs) obtained by mixing with a series of inorganic salts, which involves five cholinium MILs with the piperidinyloxy radical anion is reported for the first time. Phase diagrams for the new ATPs were experimentally determined at different temperatures (298.15–318.15 K) and the liquid–liquid equilibrium data for two-phase systems were correlated according to the empirical nonlinear expression. The effects of the types of MILs, temperature and inorganic salts on the binodal curve are discussed in detail. The MIL-ATPs coupled with HPLC-UV analysis was developed in the quantitation of berberine hydrochloride in Rhizoma coptidis. Under optimal conditions, the partition coefficient of berberine hydrochloride was 127.68 with the precision values (RSD%) of 1.40% and 2.83% for intra-day (n = 6) and inter-day (n = 3), respectively. The limit of detection (LOD) and limit of quantification (LOQ) for berberine hydrochloride were 0.023 mg L⁻¹ and 0.077 mg L⁻¹, respectively. The recoveries were obtained in the acceptable range of 97.4–101.2%. Moreover, the content of berberine hydrochloride in the raw material of Rhizoma coptidis was measured as 123.95 mg g⁻¹ with this method. Finally, 99.8% MIL was recovered for cycle application after the removal of berberine hydrochloride by using D101 resin. This study provides a meaningful reference for the application of MIL-ATPs with great prospects.

Five cholinium type organic magnetic ionic liquids have been applied in ionic liquid-based aqueous two-phase systems by mixing with a series of inorganic salts, which is reported to extract berberine in quantitative analysis for the first time.

Behavior, mechanism, and equilibrium studies of rhodium(i) extraction from hydrochloric acid with HMImT

An efficient and low-viscosity extractant (1-hexyl-3-methylimidazole-2-thione) was firstly synthesized and used to extract Rh(i) from multimetal ion solution.

Aqueous two-phase system (ATPS): an overview and advances in its applications

Aqueous two-phase system (ATPS) is a liquid-liquid fractionation technique and has gained an interest because of great potential for the extraction, separation, purification and enrichment of proteins, membranes, viruses, enzymes, nucleic acids and other biomolecules both in industry and academia. Although, the partition behavior involved in the method is complex and difficult to predict. Current research shows that it has also been successfully used in the detection of veterinary drug residues in food, separation of precious metals, sewage treatment and a variety of other purposes. The ATPS is able to give high recovery yield and is easily to scale up. It is also very economic and environment friendly method. The aim of this review is to overview the basics of ATPS, optimization and its applications.

Development of tropine-salt aqueous two-phase systems and removal of hydrophilic ionic liquids from aqueous solution

A novel aqueous two-phase systems (ATPS) composed of a small molecule organic compound tropine and an organic or inorganic salt aqueous solution has been developed for the first time. The phase behavior of tropine-salt ATPS was systemically investigated and the phase equilibrium data were measured in different temperatures and concentrations and correlated by the Merchuk equation with satisfactory results. The detection of the conductivity and particle size proved the formation of micelle in the process of forming tropine-salt ATPS. The separation application of the ATPS was assessed with the removal of hydrophilic benzothiazolium-based ionic liquids (ILs) from aqueous solution. The result showed that ILs were effectively extracted into the top tropine-rich phase. Finally, ILs in the top tropine-rich phase were further separated by the means of adsorption-desorption with DM301 macroporous resin and ethanol. The method of novel tropine-salt ATPS combined with adsorption-desorption is demonstrated a promising alternative thought and approach for the removal or recovery of hydrophilic compounds from aqueous media and also could provide a potential application for bio-separation.