Continuous process for selective metal extraction with an ionic liquid

Synthesis of fatty acid-based ammonium ionic liquids and their application for extraction of Co(II) and Ni(II) metals ions from aqueous solution

Leaching of cobalt and nickel into diverse water streams has become an environmental hazard and is continuously impacting human health through the food chain. Solvent extraction is the most widely accepted for separating these metals, but traditional extractants employed in conjunction with molecular diluents often lack selectivity and caused major environmental hurdles. Therefore, the development of cost-effective, environmentally friendly technologies for recovering these heavy metals has been strongly encouraged in recent years. Herein, two halogens free, low viscous, biocompatible fatty acid-based hydrophobic ionic liquids (ILs), i.e., methytrioctylammonium oleate, methytrioctylammonium linoleate were synthesized, analytically characterized and employed for recovery of cobalt, Co(II) and nickel, Ni(II) from their aqueous solutions. Extraction behaviour of Co(II) and Ni(II) was further evaluated by varying equilibrium time, ILs molar concentration, metal loading, and temperature. Thermodynamic parameters such as enthalpy change and Gibbs free energy change were also studied during extraction process. Slope analysis suggested that the extraction mechanism was an exothermic process that followed ion-transfer from the aqueous phase to the organic phase. Results showed that both fatty acid based-ILs were found to be capable of extracting >99% of Co(II) and Ni(II) from aqueous solutions at 298 K, in 15 min of shaking time using a 1:1 (org: aq.) ratio at low concentrations of 2.5-10 g L^-1. Furthermore, for methyltrioctylammonium oleate IL, Co(II) extraction was selectively preferred over Ni(II) extraction when the metal concentration was increased to above to 10 g L^-1. The stripping results showed that 2 M H₂SO₄, and 2 M HCl successfully stripped out >99% of Co(II) and Ni(II) from the organic phase, respectively compared to HNO₃.

Continuous Counter-Current Ionic Liquid Metathesis in Mixer-Settlers: Efficiency Analysis and Comparison with Batch Operation

Following the initial cation formation, the synthesis of ionic liquids (ILs) often involves an anion-exchange or metathesis reaction. For hydrophobic ILs, this is generally performed through several cross-current contacts of the IL with a fresh salt solution of the desired anion. However, if a large number of contacts is required to attain an adequate conversion, this procedure is not economical because of the large excess of the reagent that is consumed. In this study, the metathesis of an IL, Aliquat 336 or [A336][Cl], to ILs with other anions ([A336][X] with X = HSO4 -, Br-, NO3 -, I-, and SCN-) was studied in a continuous counter-current mixer-settler setup. McCabe-Thiele diagrams were constructed to estimate the required number of stages for quantitative conversion. Significantly higher IL conversions were achieved, combined with reduced reagent consumption and waste production. This improvement in efficiency was most pronounced for anions placed low in the Hofmeister series, for example, HSO4 -, Br-, and NO3 -, which are difficult to exchange. The performance of the counter-current experiments was compared with the conventional multistep cross-current batch process by calculating the reaction mass efficiency (RME) and the environmental factor (E-factor). The RMEs of the cross-current experiments were notably smaller, that is, 38-78% of the values observed for the counter-current experiments. The E-factors of the counter-current experiments were a factor of 2.0-6.8 smaller than those of the cross-current experiments. These sustainability metrics indicate a highly efficient reagent use and a considerable, simultaneous decrease in waste production for the counter-current IL metathesis reactions.

Ionic Liquids as Components of Systems for Metal Extraction

This review addresses research and development on the use of ionic liquids as extractants and diluents in the solvent extraction of metals. Primary attention is given to the efficiency and selectivity of metal extraction from industrial wastewater with ionic liquids composed of various cations and anions. The review covers literature sources published in the period of 2010–2021. The bibliography includes 98 references dedicated to research on the extraction and separation of lanthanides (17 sources), actinides (5 sources), heavy metals (35 sources), noble metals, including the platinum group (16 sources), and some other metals.

Cobalt Recovery from Li-Ion Battery Recycling: A Critical Review

The increasing demand for Li-ion batteries for electric vehicles sheds light upon the Co supply chain. The metal is crucial to the cathode of these batteries, and the leading global producer is the D.R. Congo (70%). For this reason, it is considered critical/strategic due to the risk of interruption of supply in the short and medium term. Due to the increasing consumption for the transportation market, the batteries might be considered a secondary source of Co. The outstanding amount of spent batteries makes them to a core of urban mining warranting special attention. Greener technologies for Co recovery are necessary to achieve sustainable development. As a result of these sourcing challenges, this study is devoted to reviewing the techniques for Co recovery, such as acid leaching (inorganic and organic), separation (solvent extraction, ion exchange resins, and precipitation), and emerging technologies—ionic liquids, deep eutectic solvent, supercritical fluids, nanotechnology, and biohydrometallurgy. A dearth of research in emerging technologies for Co recovery from Li-ion batteries is discussed throughout the manuscript within a broader overview. The study is strictly connected to the Sustainability Development Goals (SDG) number 7, 8, 9, and 12.

An Old Technique with A Promising Future: Recent Advances in the Use of Electrodeposition for Metal Recovery

Although the first published works on electrodeposition dates from more than one century ago (1905), the uses of this technique in the recovery of metals are attracting an increasing interest from the scientific community in the recent years. Moreover, the intense use of metals in electronics and the necessity to assure a second life of these devices in a context of circular economy, have increased the interest of the scientific community on electrodeposition, with almost 3000 works published per year nowadays. In this review, we aim to revise the most relevant and recent publications in the application of electrodeposition for metal recovery. These contributions have been classified into four main groups of approaches: (1) treatment and reuse of wastewater; (2) use of ionic liquids; (3) use of bio-electrochemical processes (microbial fuel cells and microbial electrolysis cells) and (4) integration of electrodeposition with other processes (bioleaching, adsorption, membrane processes, etc.). This would increase the awareness about the importance of the technology and would serve as a starting point for anyone that aims to start working in the field.

Expanding the Electrochemical Window: New Tunable Aryl Alkyl Ionic Liquids (TAAILs) with Dicyanamide Anions

A set of new tunable aryl alkyl ionic liquids (TAAILs) based on the 1-aryl-3-alkyl imidazolium motif has been synthesized, in which the following variables were systematically changed: alkyl chain length, aryl substitution (group and position), and counter ion. TAAILs with dicyanamide (DCA) and bis(trifluoromethylsulfonyl)imide (N(SO₂ CF₃ )₂ , NTf₂ ) anions showed remarkable differences of their physical properties: NTf₂ ionic liquids were found to have high decomposition temperatures and viscosities well below those of the DCA TAAILs. In contrast, the dicyanamide anion increased the electrochemical stability leading to TAAILs with an extremely wide electrochemical window of up to 7.17 V. Additionally, both classes of TAAILs extract transition metals from aqueous solutions: TAAILs with the DCA anion extract both platinum and copper while TAAILs with the NTf₂ anion are selective towards platinum. This demonstrates that minor changes of the molecular structure lead to TAAILs with drastically changed physicochemical properties.

Thioglycolate-based task-specific ionic liquids: Metal extraction abilities vs acute algal toxicity

We studied the extraction behavior of two thioglycolate-based ionic liquids (ILs), for heavy metals from aqueous solutions; substances of interest were methyltrioctylammonium S-hexyl thioglycolate [N₁₈₈₈][C₆SAc] and methyltrioctylphosphonium S-hexyl thioglycolate [P₁₈₈₈][C₆SAc]. Theses ILs previously have shown very good extraction abilities towards cadmium and copper, therefore we investigated time-dependent metal removal experiments with aqueous solutions of cobalt(II), nickel(II) and zinc(II). The highest distribution ratio (R_IL/Water) was determined for zinc (R_IL/Water=2000). Recovery studies for zinc after extraction were performed with different stripping agents showing a successful recycling. Additionally, the two ILs were immobilized on active charcoal, displaying great potential for solid-liquid extraction. Regarding the extraction mechanism, quantum-mechanical calculations were included, which indicate that the metal extraction depends on the stability of the metal-water cluster. Ligands (water as well as ILs) are planar coordinated in nickel complexes but showed a tetrahedral configuration for zinc. As a first estimate of the ecotoxicity of the ILs, in vivo tests toward three freshwater green algae species Tetradesmus obliquus, Desmodesmus armatus and Raphidocelis subcapitata were carried out. The EC₅₀ values (effective concentration after 72 h) confirm high toxicity of all tested ILs to all species, displaying only small differences between the species and EC₅₀ies.

Application of polymer-based membranes containing ionic liquids in membrane separation processes: a critical review

The interest in ionic liquids, particularly in polymerizable ionic liquids, is motivated by their unique properties, such as good thermal stability, negligible vapor pressure, and wide electrochemical window. Due to these features ionic liquids were proposed to be used in the membrane separation technology. The utilization of conventional ionic liquids is, however, limited by their release from the membrane during the given separation process. Therefore, the incorporation of polymerizable ionic liquids may overcome this drawback for the industrial application. This work is a comprehensive overview of the advances of ionic liquid membranes for the separation of various compounds, i.e. gases, organic compounds, and metal ions.

Removal of alkali and transition metal ions from water with hydrophobic deep eutectic solvents

Hydrophobic deep eutectic solvents composed of decanoic acid and lidocaine were used for the removal of metal ions from an aquatic environment.